THE STRUCTURE AND STELLAR CONTENT OF THE OUTER DISKS OF GALAXIES: A NEW VIEW FROM THE Pan-STARRS1 MEDIUM DEEP SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Zheng; Thilker, David A.; Heckman, Timothy M.

2015-02-20

We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (grizy) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis spectral energy distribution fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. We characterize the structure and stellar content of the galaxy disks out to radii of about twice Petrosian r {sub 90}, beyond which the halo light becomes significant. We measure normalized radial profiles for sub-samples ofmore » galaxies in three bins each of stellar mass and concentration. We also fit radial profiles to each galaxy. The majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r {sub 90}. However, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. We find that the mass/light ratio and stellar age radial profiles have a characteristic 'U' shape. There is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the M/L ratio in the outer disk. As we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in M/L both decrease. Our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk.« less

Spot distribution and fast surface evolution on Vega

NASA Astrophysics Data System (ADS)

Petit, P.; Hébrard, E. M.; Böhm, T.; Folsom, C. P.; Lignières, F.

2017-11-01

Spectral signatures of surface spots were recently discovered from high cadence observations of the A star Vega. We aim at constraining the surface distribution of these photospheric inhomogeneities and investigating a possible short-term evolution of the spot pattern. Using data collected over five consecutive nights, we employ the Doppler imaging method to reconstruct three different maps of the stellar surface, from three consecutive subsets of the whole time series. The surface maps display a complex distribution of dark and bright spots, covering most of the visible fraction of the stellar surface. A number of surface features are consistently recovered in all three maps, but other features seem to evolve over the time span of observations, suggesting that fast changes can affect the surface of Vega within a few days at most. The short-term evolution is observed as emergence or disappearance of individual spots, and may also show up as zonal flows, with low- and high-latitude belts rotating faster than intermediate latitudes. It is tempting to relate the surface brightness activity to the complex magnetic field topology previously reconstructed for Vega, although strictly simultaneous brightness and magnetic maps will be necessary to assess this potential link.

The Barnes-Evans color-surface brightness relation: A preliminary theoretical interpretation

NASA Technical Reports Server (NTRS)

Shipman, H. L.

1980-01-01

Model atmosphere calculations are used to assess whether an empirically derived relation between V-R and surface brightness is independent of a variety of stellar paramters, including surface gravity. This relationship is used in a variety of applications, including the determination of the distances of Cepheid variables using a method based on the Beade-Wesselink method. It is concluded that the use of a main sequence relation between V-R color and surface brightness in determining radii of giant stars is subject to systematic errors that are smaller than 10% in the determination of a radius or distance for temperature cooler than 12,000 K. The error in white dwarf radii determined from a main sequence color surface brightness relation is roughly 10%.

The Photometric Properties of a Vast Stellar Substructure in the Outskirts of M33

NASA Astrophysics Data System (ADS)

McConnachie, Alan W.; Ferguson, Annette M. N.; Irwin, Michael J.; Dubinski, John; Widrow, Lawrence M.; Dotter, Aaron; Ibata, Rodrigo; Lewis, Geraint F.

2010-11-01

We have surveyed approximately 40 deg2 surrounding M33 with Canada-France-Hawaii Telescope MegaCam/MegaPrime in the g and i filters out to a maximum projected radius from this galaxy of 50 kpc, as part of the Pan-Andromeda Archaeological Survey (PAndAS). Our observations are deep enough to resolve the top ~4 mag of the red giant branch population in this galaxy. We have previously shown that the disk of M33 is surrounded by a large, irregular, low surface brightness substructure. Here, we quantify the stellar populations and structure of this feature using the PAndAS data. We show that the stellar populations of this feature are consistent with an old population with lang[Fe/H]rang ~ -1.6 dex and an interquartile range in metallicity of ~0.5 dex. We construct a surface brightness map of M33 that traces this feature to μ V ~= 33 mag arcsec-2. At these low surface brightness levels, the structure extends to projected radii of ~40 kpc from the center of M33 in both the northwest and southeast quadrants of the galaxy. Overall, the structure has an "S-shaped" appearance that broadly aligns with the orientation of the H I disk warp. We calculate a lower limit to the integrated luminosity of the structure of -12.7 ± 0.5 mag, comparable to a bright dwarf galaxy such as Fornax or Andromeda II and slightly less than 1% of the total luminosity of M33. Further, we show that there is tentative evidence for a distortion in the distribution of young stars near the edge of the H I disk that occurs at similar azimuth to the warp in H I. The data also hint at a low-level, extended stellar component at larger radius that may be an M33 halo component. We revisit studies of M33 and its stellar populations in light of these new results and discuss possible formation scenarios for the vast stellar structure. Our favored model is that of the tidal disruption of M33 in its orbit around M31.

Hunting Faint Dwarf Galaxies in the Field Using Integrated Light Surveys

NASA Astrophysics Data System (ADS)

Danieli, Shany; van Dokkum, Pieter; Conroy, Charlie

2018-03-01

We discuss the approach of searching the lowest mass dwarf galaxies, ≲ {10}6 {M}ȯ , in the general field, using integrated light surveys. By exploring the limiting surface brightness-spatial resolution (μ eff,lim‑θ) parameter space, we suggest that faint field dwarfs in the Local Volume, between 3 and 10 Mpc, are expected to be detected very effectively and in large numbers using integrated light photometric surveys, complementary to the classical star counts method. We use a sample of dwarf galaxies in the Local Group to construct relations between their photometric and structural parameters, M *–μ eff,V and M *–R eff. We use these relations, along with assumed functional forms for the halo mass function and the stellar mass–halo mass (SMHM) relation, to calculate the lowest detectable stellar masses in the Local Volume and the expected number of galaxies as a function of the limiting surface brightness and spatial resolution. The number of detected galaxies depends mostly on the limiting surface brightness for distances >3 Mpc, while spatial resolution starts to play a role for galaxies at distances >8 Mpc. Surveys with μ eff,lim ∼ 30 mag arcsec‑2 should be able to detect galaxies with stellar masses down to ∼104 M ⊙ in the Local Volume. Depending on the form of the SMHM relation, the expected number of dwarf galaxies with distances between 3 and 10 Mpc is 0.04–0.35 per square degree, assuming a limiting surface brightness of ∼29–30 mag arcsec‑2 and a spatial resolution <4″. We plan to search for a population of low-mass dwarf galaxies in the field by performing a blank wide field photometric survey with the Dragonfly Telephoto Array, an imaging system optimized for the detection of extended ultra low surface brightness structures.

The Andromeda Optical and Infrared Disk Survey

NASA Astrophysics Data System (ADS)

Sick, J.; Courteau, S.; Cuillandre, J.-C.

2014-03-01

The Andromeda Optical and Infrared Disk Survey has mapped M31 in u* g' r' i' JKs wavelengths out to R = 40 kpc using the MegaCam and WIRCam wide-field cameras on the Canada-France-Hawaii Telescope. Our survey is uniquely designed to simultaneously resolve stars while also carefully reproducing the surface brightness of M31, allowing us to study M31's global structure in the context of both resolved stellar populations and spectral energy distributions. We use the Elixir-LSB method to calibrate the optical u* g' r' i' images by building real-time maps of the sky background with sky-target nodding. These maps are stable to μg ≲ 28.5 mag arcsec-2 and reveal warps in the outer M31 disk in surface brightness. The equivalent WIRCam mapping in the near-infrared uses a combination of sky-target nodding and image-to-image sky offset optimization to produce stable surface brightnesses. This study enables a detailed analysis of the systematics of spectral energy distribution fitting with near-infrared bands where asymptotic giant branch stars impose a significant, but ill-constrained, contribution to the near-infrared light of a galaxy. Here we present panchromatic surface brightness maps and initial results from our near-infrared resolved stellar catalog.

Exploring the Surface Brightness Breaks and Star Formation in Disk Galaxies

NASA Astrophysics Data System (ADS)

Malko, Bradley Ann; Hunter, Deidre Ann

2018-06-01

Stellar surface brightness profiles of both spirals and dwarf irregular galaxies often show breaks in which the exponential fall-off abruptly changes slope. Most often the profile is down-bending (Type II) in the outer disk, but sometimes it is up-bending (Type III). Stellar disks extend a long ways beyond the profile breaks, but we do not understand what happens physically at the breaks. To explore this we are examining the star formation activity, as traced with FUV emission, interior to the break compared to that exterior to the break in both dwarf irregulars and spiral galaxies. We present the results for the spiral galaxy NGC 2500 and compare it to the LITTLE THINGS dwarf irregular galaxies.

SDSS IV MaNGA: Deep observations of extra-planar, diffuse ionized gas around late-type galaxies from stacked IFU spectra

NASA Astrophysics Data System (ADS)

Jones, A.; Kauffmann, G.; D'Souza, R.; Bizyaev, D.; Law, D.; Haffner, L.; Bahé, Y.; Andrews, B.; Bershady, M.; Brownstein, J.; Bundy, K.; Cherinka, B.; Diamond-Stanic, A.; Drory, N.; Riffel, R. A.; Sánchez, S. F.; Thomas, D.; Wake, D.; Yan, R.; Zhang, K.

2017-03-01

We have conducted a study of extra-planar diffuse ionized gas using the first year data from the MaNGA IFU survey. We have stacked spectra from 49 edge-on, late-type galaxies as a function of distance from the midplane of the galaxy. With this technique we can detect the bright emission lines Hα, Hβ, [O II]λλ3726, 3729, [O III]λ5007, [N II]λλ6549, 6584, and [S II]λλ6717, 6731 out to about 4 kpc above the midplane. With 16 galaxies we can extend this analysis out to about 9 kpc, I.e. a distance of 2Re, vertically from the midplane. In the halo, the surface brightnesses of the [O II] and Hα emission lines are comparable, unlike in the disk where Hα dominates. When we split the sample by specific star-formation rate, concentration index, and stellar mass, each subsample's emission line surface brightness profiles and ratios differ, indicating that extra-planar gas properties can vary. The emission line surface brightnesses of the gas around high specific star-formation rate galaxies are higher at all distances, and the line ratios are closer to ratios characteristic of H II regions compared with low specific star-formation rate galaxies. The less concentrated and lower stellar mass samples exhibit line ratios that are more like H II regions at larger distances than their more concentrated and higher stellar mass counterparts. The largest difference between different subsamples occurs when the galaxies are split by stellar mass. We additionally infer that gas far from the midplane in more massive galaxies has the highest temperatures and steepest radial temperature gradients based on their [N II]/Hα and [O II]/Hα ratios between the disk and the halo. SDSS IV.

THE PHOTOMETRIC PROPERTIES OF A VAST STELLAR SUBSTRUCTURE IN THE OUTSKIRTS OF M33

DOE Office of Scientific and Technical Information (OSTI.GOV)

McConnachie, Alan W.; Ferguson, Annette M. N.; Irwin, Michael J.

2010-11-10

We have surveyed approximately 40 deg{sup 2} surrounding M33 with Canada-France-Hawaii Telescope MegaCam/MegaPrime in the g and i filters out to a maximum projected radius from this galaxy of 50 kpc, as part of the Pan-Andromeda Archaeological Survey (PAndAS). Our observations are deep enough to resolve the top {approx}4 mag of the red giant branch population in this galaxy. We have previously shown that the disk of M33 is surrounded by a large, irregular, low surface brightness substructure. Here, we quantify the stellar populations and structure of this feature using the PAndAS data. We show that the stellar populations ofmore » this feature are consistent with an old population with ([Fe/H]) {approx} -1.6 dex and an interquartile range in metallicity of {approx}0.5 dex. We construct a surface brightness map of M33 that traces this feature to {mu}{sub V} {approx_equal} 33 mag arcsec{sup -2}. At these low surface brightness levels, the structure extends to projected radii of {approx}40 kpc from the center of M33 in both the northwest and southeast quadrants of the galaxy. Overall, the structure has an 'S-shaped' appearance that broadly aligns with the orientation of the H I disk warp. We calculate a lower limit to the integrated luminosity of the structure of -12.7 {+-} 0.5 mag, comparable to a bright dwarf galaxy such as Fornax or Andromeda II and slightly less than 1% of the total luminosity of M33. Further, we show that there is tentative evidence for a distortion in the distribution of young stars near the edge of the H I disk that occurs at similar azimuth to the warp in H I. The data also hint at a low-level, extended stellar component at larger radius that may be an M33 halo component. We revisit studies of M33 and its stellar populations in light of these new results and discuss possible formation scenarios for the vast stellar structure. Our favored model is that of the tidal disruption of M33 in its orbit around M31.« less

Revealing Stellar Surface Structure Behind Transiting Exoplanets

NASA Astrophysics Data System (ADS)

Dravins, Dainis

2018-04-01

During exoplanet transits, successive stellar surface portions become hidden and differential spectroscopy between various transit phases provide spectra of small surface segments temporarily hidden behind the planet. Line profile changes across the stellar disk offer diagnostics for hydrodynamic modeling, while exoplanet analyses require stellar background spectra to be known along the transit path. Since even giant planets cover only a small fraction of any main-sequence star, very precise observations are required, as well as averaging over numerous spectral lines with similar parameters. Spatially resolved Fe I line profiles across stellar disks have now been retrieved for HD209458 (G0V) and HD189733A (K1V), using data from the UVES and HARPS spectrometers. Free from rotational broadening, spatially resolved profiles are narrower and deeper than in integrated starlight. During transit, the profiles shift towards longer wavelengths, illustrating both stellar rotation at the latitude of transit and the prograde orbital motion of the exoplanets. This method will soon become applicable to more stars, once additional bright exoplanet hosts have been found.

LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

NASA Astrophysics Data System (ADS)

Lin, Ming-Yi; Davies, R. I.; Hicks, E. K. S.; Burtscher, L.; Contursi, A.; Genzel, R.; Koss, M.; Lutz, D.; Maciejewski, W.; Müller-Sánchez, F.; Orban de Xivry, G.; Ricci, C.; Riffel, R.; Riffel, R. A.; Rosario, D.; Schartmann, M.; Schnorr-Müller, A.; Shimizu, T.; Sternberg, A.; Sturm, E.; Storchi-Bergmann, T.; Tacconi, L.; Veilleux, S.

2018-02-01

In a complete sample of local 14-195 keV selected active galactic nuclei (AGNs) and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, eight AGNs and five inactive galaxies. The stellar velocity fields show a disc-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN, but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disc structure, which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.

A study of the H I and optical properties of Low Surface Brightness galaxies: spirals, dwarfs, and irregulars

NASA Astrophysics Data System (ADS)

Honey, M.; van Driel, W.; Das, M.; Martin, J.-M.

2018-06-01

We present a study of the H I and optical properties of nearby (z ≤ 0.1) Low Surface Brightness galaxies (LSBGs). We started with a literature sample of ˜900 LSBGs and divided them into three morphological classes: spirals, irregulars, and dwarfs. Of these, we could use ˜490 LSBGs to study their H I and stellar masses, colours, and colour-magnitude diagrams, and local environment, compare them with normal, High Surface Brightness (HSB) galaxies and determine the differences between the three morphological classes. We found that LSB and HSB galaxies span a similar range in H I and stellar masses, and have a similar M_{H I}/M⋆-M⋆ relationship. Among the LSBGs, as expected, the spirals have the highest average H I and stellar masses, both of about 109.8 M⊙. The LSGBs' (g - r) integrated colour is nearly constant as function of H I mass for all classes. In the colour-magnitude diagram, the spirals are spread over the red and blue regions whereas the irregulars and dwarfs are confined to the blue region. The spirals also exhibit a steeper slope in the M_{H I}/M⋆-M⋆ plane. Within their local environment, we confirmed that LSBGs are more isolated than HSB galaxies, and LSB spirals more isolated than irregulars and dwarfs. Kolmogorov-Smirnov statistical tests on the H I mass, stellar mass, and number of neighbours indicate that the spirals are a statistically different population from the dwarfs and irregulars. This suggests that the spirals may have different formation and H I evolution than the dwarfs and irregulars.

Long-slit Spectroscopy of Edge-on Low Surface Brightness Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Wei; Wu, Hong; Zhu, Yinan

2017-03-10

We present long-slit optical spectra of 12 edge-on low surface brightness galaxies (LSBGs) positioned along their major axes. After performing reddening corrections for the emission-line fluxes measured from the extracted integrated spectra, we measured the gas-phase metallicities of our LSBG sample using both the [N ii]/H α and the R {sub 23} diagnostics. Both sets of oxygen abundances show good agreement with each other, giving a median value of 12 + log(O/H) = 8.26 dex. In the luminosity–metallicity plot, our LSBG sample is consistent with the behavior of normal galaxies. In the mass–metallicity diagram, our LSBG sample has lower metallicitiesmore » for lower stellar mass, similar to normal galaxies. The stellar masses estimated from z -band luminosities are comparable to those of prominent spirals. In a plot of the gas mass fraction versus metallicity, our LSBG sample generally agrees with other samples in the high gas mass fraction space. Additionally, we have studied stellar populations of three LSBGs, which have relatively reliable spectral continua and high signal-to-noise ratios, and qualitatively conclude that they have a potential dearth of stars with ages <1 Gyr instead of being dominated by stellar populations with ages >1 Gyr. Regarding the chemical evolution of our sample, the LSBG data appear to allow for up to 30% metal loss, but we cannot completely rule out the closed-box model. Additionally, we find evidence that our galaxies retain up to about three times as much of their metals compared with dwarfs, consistent with metal retention being related to galaxy mass. In conclusion, our data support the view that LSBGs are probably just normal disk galaxies continuously extending to the low end of surface brightness.« less

The X-ray surface brightness distribution and spectral properties of six early-type galaxies

NASA Technical Reports Server (NTRS)

Trinchieri, G.; Fabbiano, G.; Canizares, C. R.

1986-01-01

Detailed analysis is presented of the Einstein X-ray observations of six early-type galaxies. The results show that effective cooling is probably present in these systems, at least in the innermost regions. Interaction with the surrounding medium has a major effect on the X-ray surface brightness distribution at large radii, at least for galaxies in clusters. The data do not warrant the general assumptions of isothermality and gravitational hydrostatic equilibrium at large radii. Comparison of the X-ray surface brightness profiles with model predictions indicate that 1/r-squared halos with masses of the order of 10 times the stellar masses are required to match the data. The physical model of White and Chevalier (1984) for steady cooling flows in a King law potential with no heavy halo gives a surface brightness distribution that resembles the data if supernovae heating is present.

Color Profile Trends of Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Herrmann, Kimberly A.; LITTLE THINGS Team

2012-01-01

Radial stellar surface brightness profiles of spiral galaxies can be classified into three types: (I) single exponential, (II) truncated: the light falls off with one exponential out to a break radius and then falls off more steeply, and (III) anti-truncated: the light falls off with one exponential out to a break radius and then falls off less steeply. Stellar surface brightness profile breaks are also found in dwarf disk galaxies, but with an additional category: (FI) flat-inside: the light is roughly constant or increasing and then falls off beyond a break. Additionally, Bakos, Trujillo, & Pohlen (2008) showed that for spirals, each profile type has a characteristic color trend with respect to the break location. Furthermore, color trends reveal information about possible stellar population changes at the breaks. Here we show color trends for the four profile types from a large multi-wavelength photometric study of dwarf disk galaxies (the 141 dwarf parent sample of the LITTLE THINGS galaxies). We explore the similarities and differences between spirals and dwarfs and also between different colors. We gratefully acknowledge funding for this research from the National Science Foundation (AST-0707563).

The outskirts of spiral galaxies: touching stellar halos at z˜0 and z˜1

NASA Astrophysics Data System (ADS)

Bakos, J.; Trujillo, I.

Taking advantage of ultra-deep imaging of SDSS Stripe82 and the Hubble Ultra Deep Field by HST, we explore the properties of stellar halos at two relevant epochs of cosmic history. At z˜0 we find that the radial surface brightness profiles of disks have a smooth continuation into the stellar halo that starts to affect the surface brightness profiles at mu r'˜28 {mag arcsec-2}, and at a radial distance of gtrsim 4-10 inner scale-lengths. The light contribution of the stellar halo to the total galaxy light varies from ˜1% to ˜5%, but in case of ongoing mergers, the halo light fraction can be as high as ˜10%. The integrated (g'-r') color of the stellar halo of our galaxies range from ˜0.4 to ˜1.2. By confronting these colors with model predictions, these halos can be attributed to moderately aged and metal-poor populations, however the extreme red colors (˜1) cannot be explained by populations of conventional IMFs. Very red halo colors can be attributed to stellar populations dominated by very low mass stars of low to intermediate metallicity produced by bottom-heavy IMFs. At z˜1 stellar halos appear to be ˜2 magnitudes brighter than their local counterparts, meanwhile they exhibit bluer colors ((g'-r')≲0.3 mag), as well. The stellar populations corresponding to these colors are compatible with having ages ≲1 Gyr. This latter observation strongly suggests the possibility that these halos were formed between z˜1 and z˜2. This result matches very well the theoretical predictions that locate most of the formation of the stellar halos at those early epochs. A pure passive evolutionary scenario, where the stellar populations of our high-z haloes simply fade to match the stellar halo properties found in the local universe, is consistent with our data.

Revealing the Formation Mechanism of Ultra-Diffuse Galaxies

NASA Astrophysics Data System (ADS)

Garmire, Gordon

2017-09-01

Recently a population of large, very low optical surface brightness galaxies, so called ultra-diffuse galaxies (UDGs), were discovered in the outskirts of Coma clusters. Stellar line-of-sight velocity dispersions suggest large dark matter halo masses of 10^12 M_sun with very low baryon fractions ( 1%). The outstanding question waiting to be answered is: How do UDGs form and evolve? One theory is that UDGs are related to bright galaxies, however they are prevented from building a normal stellar population through various violent processes, such as gas stripping. We propose to observe Dragonfly 44, the most massive UDG known, for 100 ks with ACIS-I to test some of the formation theories.

Galaxy Detection in 2MASS: Global Expectations and Results from Several Fields

NASA Technical Reports Server (NTRS)

Chester, T.; Jarrett, T.

1995-01-01

An alogorithm has been developed and used to find galaxies in the 2MASS data. It uses the central surface brightness and measured size to discriminate galaxies from the much larger stellar population.

The Fornax Deep Survey with VST. I. The Extended and Diffuse Stellar Halo of NGC 1399 out to 192 kpc

NASA Astrophysics Data System (ADS)

Iodice, E.; Capaccioli, M.; Grado, A.; Limatola, L.; Spavone, M.; Napolitano, N. R.; Paolillo, M.; Peletier, R. F.; Cantiello, M.; Lisker, T.; Wittmann, C.; Venhola, A.; Hilker, M.; D'Abrusco, R.; Pota, V.; Schipani, P.

2016-03-01

We have started a new, deep multi-imaging survey of the Fornax cluster, dubbed the Fornax Deep Survey (FDS), at the VLT Survey Telescope (VST). In this paper we present the deep photometry inside two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that the core of the Fornax cluster is characterized by a very extended and diffuse envelope surrounding the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (˜192 kpc) from the galaxy center and down to μg ˜ 31 mag arcsec-2 in the g band. The deep photometry allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399 and toward NGC 1387. By analyzing the integrated colors of this feature, we argue that it could be due to the ongoing interaction between the two galaxies, where the outer envelope of NGC 1387 on its east side is stripped away. By fitting the light profile, we found that there exists a physical break radius in the total light distribution at R = 10 arcmin (˜58 kpc) that sets the transition region between the bright central galaxy and the outer exponential halo, and that the stellar halo contributes 60% of the total light of the galaxy (Section 3.5). We discuss the main implications of this work on the build-up of the stellar halo at the center of the Fornax cluster. By comparing with the numerical simulations of the stellar halo formation for the most massive bright cluster galaxies (I.e., 13\\lt {log}{M}200/{M}⊙ \\lt 14), we find that the observed stellar halo mass fraction is consistent with a halo formed through the multiple accretion of progenitors with stellar mass in the range 108-1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through a major merging event. The absence of a significant number of luminous stellar streams and tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early formation epoch. Therefore, different from the Virgo cluster, the extended stellar halo around NGC 1399 is characterized by a more diffuse and well-mixed component, including the intracluster light.

A population of faint low surface brightness galaxies in the Perseus cluster core

NASA Astrophysics Data System (ADS)

Wittmann, Carolin; Lisker, Thorsten; Ambachew Tilahun, Liyualem; Grebel, Eva K.; Conselice, Christopher J.; Penny, Samantha; Janz, Joachim; Gallagher, John S.; Kotulla, Ralf; McCormac, James

2017-09-01

We present the detection of 89 low surface brightness (LSB), and thus low stellar density galaxy candidates in the Perseus cluster core, of the kind named 'ultra-diffuse galaxies', with mean effective V-band surface brightnesses 24.8-27.1 mag arcsec-2, total V-band magnitudes -11.8 to -15.5 mag, and half-light radii 0.7-4.1 kpc. The candidates have been identified in a deep mosaic covering 0.3 deg2, based on wide-field imaging data obtained with the William Herschel Telescope. We find that the LSB galaxy population is depleted in the cluster centre and only very few LSB candidates have half-light radii larger than 3 kpc. This appears consistent with an estimate of their tidal radius, which does not reach beyond the stellar extent even if we assume a high dark matter content (M/L = 100). In fact, three of our candidates seem to be associated with tidal streams, which points to their current disruption. Given that published data on faint LSB candidates in the Coma cluster - with its comparable central density to Perseus - show the same dearth of large objects in the core region, we conclude that these cannot survive the strong tides in the centres of massive clusters.

From 20 cm - 1 micron: Measuring the Gas and Dust in Massive Low Surface Brightness Galaxies

NASA Astrophysics Data System (ADS)

Kearsley, E.; O'Neil, K.

2005-12-01

Archival data from the IRAS, 2MASS, NVSS, and FIRST catalogs, supplemented with new measurements of HI, are used to analyze the relationship between the relative mass of the various components of galaxies (stars, atomic hydrogen, dust, and molecular gas) using a small sample of nearby (z<0.1), massive low surface brightness galaxies. The sample is compared to three sets of published data: a large collection of radio sources from the UGC having a radio continuum intensity >2.5 mJy (Condon, Cotton, & Broderick 2002 AJ 124, 675) ; a smaller sample of low surface brightness galaxies (Galaz, et al 2002 2002 AJ 124, 1360); and a collection of NIR low surface brightness galaxies (Monnier-Ragaigne, et al 2002 Ap&SS 281, 145). Overall, our sample properties are similar to the comparison samples in regard to NIR color, gas, stellar, and dynamic mass ratios, etc. Based off the galaxies' q-value (determined from the FIR/1.4 GHz ratio), it appears likely that at least two of the 28 galaxies studied harbor AGN. Notably, we also find that if we naively assume the ratio of the dust and molecular gas mass relative to the mass of HI is a constant we are unable to predict the observed ratio of stellar mass to HI mass, indicating that the HI mass ratio is a poor indicator of the total baryonic mass in the studied galaxies. HI measurements obtained during this study using the Green Bank Telescope also provide a correction to the velocity of UGC 11068.

Rediscovering the Giant Low Surface Brightness Spiral Galaxy Malin 1

NASA Astrophysics Data System (ADS)

Galaz, Gaspar

2018-01-01

I summarize the latest discoveries regarding this ramarkable diffuse and giant galaxy, the largest single spiral in the universe so far. I describe how the latest discoveries could have been done easily 20 years ago, but an incredible summation of facts and some astronomical sociology, keeped many of them undisclosed. I present the most conspicuous features of the giant spiral arms of Malin 1, including stellar density, colors, stellar populations and some modeling describing their past evolution to the current state. I conclude with pending issues regarding stellar formation in Malin 1, and the efforts to detect its elusive molecular gas.

HST Imaging of the (Almost) Dark ALFALFA Source AGC 229385

NASA Astrophysics Data System (ADS)

Brunker, Samantha; Salzer, John Joseph; McQuinn, Kristen B.; Janowiecki, Steven; Leisman, Luke; Rhode, Katherine L.; Adams, Elizabeth A.; Cannon, John M.; Giovanelli, Riccardo; Haynes, Martha P.

2017-06-01

We present deep HST imaging photometry of the extreme galaxy AGC 229385. This system was first discovered as an HI source in the ALFALFA all-sky HI survey. It was cataloged as an (almost) dark galaxy because it did not exhibit any obvious optical counterpart in the available wide-field survey data (e.g., SDSS). Deep optical imaging with the WIYN 3.5-m telescope revealed an ultra-low surface brightness stellar component located at the center of the HI detection. With a peak central surface brightness of 26.4 mag/sq. arcsec in g and very blue colors (g-r = -0.1), the stellar component to this gas-rich system is quite enigmatic. We have used our HST images to produce a deep CMD of the resolved stellar population present in AGC 229385. We clearly detect a red-giant branch and use it to infer a distance of 5.50 ± 0.23 Mpc. The CMD is dominated by older stars, contrary to expectations given the blue optical colors obtained from our ground-based photometry. Our new distance is substantially lower than earlier estimates, and shows that AGC 229385 is an extreme dwarf galaxy with one of the highest MHI/L ratios known.

Globular clusters in high-redshift dwarf galaxies: a case study from the Local Group

NASA Astrophysics Data System (ADS)

Zick, Tom O.; Weisz, Daniel R.; Boylan-Kolchin, Michael

2018-06-01

We present the reconstructed evolution of rest-frame ultraviolet (UV) luminosities of the most massive Milky Way dwarf spheroidal satellite galaxy, Fornax, and its five globular clusters (GCs) across redshift, based on analysis of the stellar fossil record and stellar population synthesis modelling. We find that (1) Fornax's (proto-)GCs can generate 10-100 times more UV flux than the field population, despite comprising <˜{5} per cent of the stellar mass at the relevant redshifts; (2) due to their respective surface brightnesses, it is more likely that faint, compact sources in the Hubble Frontier Fields (HFFs) are GCs hosted by faint galaxies, than faint galaxies themselves. This may significantly complicate the construction of a galaxy UV luminosity function at z > 3. (3) GC formation can introduce order-of-magnitude errors in abundance matching. We also find that some compact HFF objects are consistent with the reconstructed properties of Fornax's GCs at the same redshifts (e.g. surface brightness, star formation rate), suggesting we may have already detected proto-GCs in the early Universe. Finally, we discuss the prospects for improving the connections between local GCs and proto-GCs detected in the early Universe.

Early type galaxies: Mapping out the two-dimensional space of galaxy star formation histories

NASA Astrophysics Data System (ADS)

Graves, Genevieve J.

Early type galaxies form a multi-parameter family, as evidenced by the two- dimensional (2-D) Fundamental Plane relationship. However, their star formation histories are often treated as a one-dimensional mass sequence. This dissertation presents a systematic study of the relationship between the multi- parameter structural properties of early type galaxies and their star formation histoires. We demonstrate that the stellar populations of early type galaxies span a 2-D space, which means that their star formation histories form a two- parameter family. This 2-D family is then mapped onto several familiar early type galaxy scaling relations, including the color-magnitude relation, the Fundamental Plane, and a cross-section through the Fundamental Plane. We find that the stellar population properties, and therefore the star formation histories of early type galaxies depend most strongly on galaxy velocity dispersion (s), rather than on luminosity ( L ), stellar mass ( M [low *] ), or dynamical mass ( M dyn ). Interestingly, stellar populations are independent of the radius ( R e ) of the galaxies. At fixed s, they show correlated residuals through the thickness of the Fundamental Plane (FP) in the surface-brightness ( I e ) dimension, such that low-surface-brightness galaxies are older, less metal-enriched, and more enhanced in Mg relative to Fe than their counterparts at the same s and R e on the FP midplane. Similarly, high- surface-brightness galaxies are younger, more metal-rich, and less Mg-enhanced than their counterparts on the FP midplane. These differences suggest that the duration of star formation varies through the thickness of the FP. If the dynamical mass-to-light ratios of early type galaxies ( M dyn /L ) were constant for all such galaxies, the FP would be equivalent to the plane predicted by the virial relation. However, the observed FP does not exactly match the virial plane. The FP is tilted from the virial plane, indicating that M dyn /L varies systematically across it. Furthermore the FP relation, although relatively tight, shows more scatter in surface brightness (at fixed s and R e ) than is predicted by observational errors. This finite thickness indicates that M dyn /L also varies at a fixed point on the FP. We observe that the stellar populations of early type galaxies vary through the thickness of the FP. These differences translate into variations in the stellar mass-to-light ratio ( M [low *] /L ) that contribute to both the tilt and the thickness of the FP. However, the mass-to-light variations due to stellar population differences are too small to explain either the tilt of the FP or its thickness. This implies that the tilt and thickness of the FP are driven by systematic variations in either the central dark matter fraction in galaxies or in the IMF with which they form stars. Furthermore, because star formation histories can be mapped onto locations in FP-space, the variations in central dark matter fraction or IMF differences must be correlated with differences in the galaxies' star formation histories.

Ultraviolet Imaging Telescope images of the reflection nebula NGC 7023 - Derivation of ultraviolet scattering properties of dust grains

NASA Technical Reports Server (NTRS)

Witt, Adolf N.; Petersohn, Jens K.; Bohlin, Ralph C.; O'Connell, Robert W.; Roberts, Morton S.; Smith, Andrew M.; Stecher, Theodore P.

1992-01-01

The Ultraviolet Imaging Telescope as part of the Astro-1 mission, was used to obtain high-resolution surface brightness distribution data in six ultraviolet wavelength bands for the bright reflection nebula NGC 7023. From the quantitative comparison of the measured surface brightness gradients ratios of nebular to stellar flux, and detail radial surface brightness profiles with corresponding data from the visible, two major conclusions results: (1) the scattering in the near- and far-ultraviolet in this nebula is more strongly forward-directed than in the visible; (2) the dust albedo in the ultraviolet for wavelengths not less than 140 nm is identical to that in the visible, with the exception of the 220 nm bump in the extinction curve. In the wavelengths region of the bump, the albedo is reduced by 25 to 30 percent in comparison with wavelengths regions both shorter and longer. This lower albedo is expected, if the bump is a pure absorption feature.

The Planetary Nebulae Luminosity Function (PNLF): current perspectives

NASA Astrophysics Data System (ADS)

Méndez, Roberto H.

2017-10-01

This paper starts with a brief historical review about the PNLF and its use as a distance indicator. Then the PNLF distances are compared with Surface Brightness Fluctuations (SBF) distances and Tip of the Red Giant Branch (TRGB) distances. A Monte Carlo method to generate simulated PNLFs is described, leading to the last subject: recent progress in reproducing the expected maximum final mass in old stellar populations, a stellar astrophysics enigma that has been challenging us for quite some time.

Globular clusters as tracers of stellar bimodality in elliptical galaxies: the case of NGC 1399

NASA Astrophysics Data System (ADS)

Forte, Juan C.; Faifer, Favio; Geisler, Doug

2005-02-01

Globular cluster systems (GCSs) frequently show a bimodal distribution of cluster integrated colours. This work explores the arguments to support the idea that the same feature is shared by the diffuse stellar population of the galaxy they are associated with. The particular case of NGC 1399, one of the dominant central galaxies in the Fornax cluster, for which a new B surface brightness profile and (B-RKC) colours are presented, is discussed taking advantage of a recently published wide-field study of its GCS. The results show that the galaxy brightness profile and colour gradient, as well as the behaviour of the cumulative globular cluster specific frequency, are compatible with the presence of two dominant stellar populations, associated with the so-called `blue' and `red' globular cluster families. These globular families are characterized by different intrinsic specific frequencies (defined in terms of each stellar population): Sn= 3.3 +/- 0.3 in the case of the red globulars and Sn= 14.3 +/- 2.5 for the blue ones. We stress that this result does not necessarily conflict with recent works that point out a clear difference between the metallicity distribution of (resolved) halo stars and globulars when comparing their number statistics. The region within 0.5arcmin of the centre shows a deviation from the model profile (in both surface brightness and colour) that may be explained in terms of the presence of a bulge-like high-metallicity component. Otherwise, the model gives an excellent fit up to 12arcmin (or 66.5Kpc) from the centre, the galactocentric limit of our blue brightness profile. The inferred specific frequencies imply that, in terms of their associated stellar populations, the formation of the blue globulars took place with an efficiency about six times higher than that corresponding to their red counterparts. The similarity of the spatial distribution of the blue globulars with that inferred for dark matter, as well as with that of the X-ray-emitting hot gas associated with NGC 1399, is emphasized. The impact of a relatively inconspicuous low-metallicity population, that shares the properties of the blue globulars, as a possible source of chemical enrichment early in the formation history of the galaxy is also briefly discussed.

Modelling dust rings in early-type galaxies through a sequence of radiative transfer simulations and 2D image fitting

NASA Astrophysics Data System (ADS)

Bonfini, P.; González-Martín, O.; Fritz, J.; Bitsakis, T.; Bruzual, G.; Cervantes Sodi, B.

2018-07-01

A large fraction of early-type galaxies (ETGs) hosts prominent dust features, and central dust rings are arguably the most interesting among them. We present here `Lord of the Rings', a new methodology which allows to integrate the extinction by dust rings in a 2D-fittingmodelling of the surface brightness distribution. Our pipeline acts in two steps, first using the surface-fitting software GALFIT to determine the unabsorbed stellar emission, and then adopting the radiative transfer code SKIRT to apply dust extinction. We apply our technique to NGC 4552 and NGC 4494, two nearby ETGs. We show that the extinction by a dust ring can mimic, in a surface brightness profile, a central point source (e.g. an unresolved nuclear stellar cluster or an active galactic nucleus; AGN) superimposed to a `core' (i.e. a central flattening of the stellar light commonly observed in massive ETGs). We discuss how properly accounting for dust features is of paramount importance to derive correct fluxes, especially for low-luminosity AGNs (LLAGNs). We suggest that the geometries of dust features are strictly connected with how relaxed is the gravitational potential, i.e. with the evolutionary stage of the host galaxy. Additionally, we find hints that the dust mass contained in the ring relates to the AGN activity.

Modelling dust rings in early-type galaxies through a sequence of radiative transfer simulations and 2D image fitting

NASA Astrophysics Data System (ADS)

Bonfini, P.; González-Martín, O.; Fritz, J.; Bitsakis, T.; Bruzual, G.; Sodi, B. Cervantes

2018-05-01

A large fraction of early-type galaxies (ETGs) host prominent dust features, and central dust rings are arguably the most interesting among them. We present here `Lord Of The Rings' (LOTR), a new methodology which allows to integrate the extinction by dust rings in a 2D fitting modelling of the surface brightness distribution. Our pipeline acts in two steps, first using the surface fitting software GALFIT to determine the unabsorbed stellar emission, and then adopting the radiative transfer code SKIRT to apply dust extinction. We apply our technique to NGC 4552 and NGC 4494, two nearby ETGs. We show that the extinction by a dust ring can mimic, in a surface brightness profile, a central point source (e.g. an unresolved nuclear stellar cluster or an active galactic nucleus; AGN) superimposed to a `core' (i.e. a central flattening of the stellar light commonly observed in massive ETGs). We discuss how properly accounting for dust features is of paramount importance to derive correct fluxes especially for low luminosity AGNs (LLAGNs). We suggest that the geometries of dust features are strictly connected with how relaxed is the gravitational potential, i.e. with the evolutionary stage of the host galaxy. Additionally, we find hints that the dust mass contained in the ring relates to the AGN activity.

Tracing the stellar component of low surface brightness Milky Way dwarf galaxies to their outskirts. I. Sextans

NASA Astrophysics Data System (ADS)

Cicuéndez, L.; Battaglia, G.; Irwin, M.; Bermejo-Climent, J. R.; McMonigal, B.; Bate, N. F.; Lewis, G. F.; Conn, A. R.; de Boer, T. J. L.; Gallart, C.; Guglielmo, M.; Ibata, R.; McConnachie, A.; Tolstoy, E.; Fernando, N.

2018-01-01

Aims: We present results from deep and very spatially extended CTIO/DECam g and r photometry (reaching out to 2 mag below the oldest main-sequence turn-off and covering 20 deg2) around the Sextans dwarf spheroidal galaxy. We aim to use this dataset to study the structural properties of Sextans overall stellar population and its member stars in different evolutionary phases, as well as to search for possible signs of tidal disturbance from the Milky Way, which would indicate departure from dynamical equilibrium. Methods: We performed the most accurate and quantitative structural analysis to-date of Sextans' stellar components by applying Bayesian Monte Carlo Markov chain methods to the individual stars' positions. Surface density maps are built by statistically decontaminating the sample through a matched filter analysis of the colour-magnitude diagram, and then analysed for departures from axisymmetry. Results: Sextans is found to be significantly less spatially extended and more centrally concentrated than early studies suggested. No statistically significant distortions or signs of tidal disturbances were found down to a surface brightness limit of 31.8 mag/arcsec2 in V-band. We identify an overdensity in the central regions that may correspond to previously reported kinematic substructure(s). In agreement with previous findings, old and metal-poor stars such as Blue Horizontal Branch stars cover a much larger area than stars in other evolutionary phases, and bright Blue Stragglers (BSs) are less spatially extended than faint ones. However, the different spatial distribution of bright and faint BSs appears consistent with the general age and metallicity gradients found in Sextans' stellar component. This is compatible with Sextans BSs having formed by evolution of binaries and not necessarily due to the presence of a central disrupted globular cluster, as suggested in the literature. We provide structural parameters for the various populations analysed and make publicly available the photometric catalogue of point-sources as well as a catalogue of literature spectroscopic measurements with updated membership probabilities. Full Tables 2 and 6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A53

Planetary camera observations of the double nucleus of M31

NASA Technical Reports Server (NTRS)

Lauer, Tod R.; Faber, S. M.; Groth, Edward J.; Shaya, Edward J.; Campbell, Bel; Code, Arthur; Currie, Douglas G.; Baum, William A.; Ewald, S. P.; Hester, J. J.

1993-01-01

HST Planetary Camera images obtained in the V and I band for M31 show its inner nucleus to consist of two components that are separated by 0.49 arcsec. The nuclear component with lower surface brightness closely coincides with the bulge photocenter and is argued to be at the kinematic center of the galaxy. It is surmised that, if dust absorption generates the asymmetric nuclear morphology observed, the dust grain size must either be exceptionally large, or the dust optical depth must be extremely high; the higher surface-brightness and off-center nuclear component may alternatively be a separate stellar system.

Stellar Surface Brightness Profiles of Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Herrmann, K. A.

2014-03-01

Radial stellar surface brightness profiles of spiral galaxies can be classified into three types: (I) single exponential, or the light falls off with one exponential out to a break radius and then falls off (II) more steeply (“truncated”), or (III) less steeply (“anti-truncated”). Why there are three different radial profile types is still a mystery, including why light falls off as an exponential at all. Profile breaks are also found in dwarf disks, but some dwarf Type IIs are flat or increasing (FI) out to a break before falling off. I have been re-examining the multi-wavelength stellar disk profiles of 141 dwarf galaxies, primarily from Hunter & Elmegreen (2004, 2006). Each dwarf has data in up to 11 wavelength bands: FUV and NUV from GALEX, UBVJHK and Hα from ground-based observations, and 3.6 and 4.5μm from Spitzer. Here I highlight some results from a semi-automatic fitting of this data set including: (1) statistics of break locations and other properties as a function of wavelength and profile type, (2) color trends and radial mass distribution as a function of profile type, and (3) the relationship of the break radius to the kinematics and density profiles of atomic hydrogen gas in the 40 dwarfs of the LITTLE THINGS subsample.

Low Metallicities and Old Ages for Three Ultra-diffuse Galaxies in the Coma Cluster

NASA Astrophysics Data System (ADS)

Gu, Meng; Conroy, Charlie; Law, David; van Dokkum, Pieter; Yan, Renbin; Wake, David; Bundy, Kevin; Merritt, Allison; Abraham, Roberto; Zhang, Jielai; Bershady, Matthew; Bizyaev, Dmitry; Brinkmann, Jonathan; Drory, Niv; Grabowski, Kathleen; Masters, Karen; Pan, Kaike; Parejko, John; Weijmans, Anne-Marie; Zhang, Kai

2018-05-01

A large population of ultra-diffuse galaxies (UDGs) was recently discovered in the Coma cluster. Here we present optical spectra of three such UDGs, DF 7, DF 44, and DF 17, which have central surface brightnesses of μ g ≈ 24.4–25.1 mag arcsec‑2. The spectra were acquired as part of an ancillary program within the SDSS-IV MaNGA Survey. We stacked 19 fibers in the central regions from larger integral field units (IFUs) per source. With over 13.5 hr of on-source integration, we achieved a mean signal-to-noise ratio in the optical of 9.5 Å‑1, 7.9 Å‑1, and 5.0 Å‑1, respectively, for DF 7, DF 44, and DF 17. Stellar population models applied to these spectra enable measurements of recession velocities, ages, and metallicities. The recession velocities of DF 7, DF 44, and DF 17 are {6599}-25+40 km s‑1, {6402}-39+41 km s‑1, and {8315}-43+43 km s‑1, spectroscopically confirming that all of them reside in the Coma cluster. The stellar populations of these three galaxies are old and metal-poor, with ages of {7.9}-2.5+3.6 Gyr, {8.9}-3.3+4.3 Gyr, and {9.1}-5.5+3.9 Gyr, and iron abundances of [Fe/H] -{1.0}-0.4+0.3, -{1.3}-0.4+0.4, and -{0.8}-0.5+0.5, respectively. Their stellar masses are (3–6) × 108 M ⊙. The UDGs in our sample are as old or older than galaxies at similar stellar mass or velocity dispersion (only DF 44 has an independently measured dispersion). They all follow the well-established stellar mass–stellar metallicity relation, while DF 44 lies below the velocity dispersion-metallicity relation. These results, combined with the fact that UDGs are unusually large for their stellar masses, suggest that stellar mass plays a more important role in setting stellar population properties for these galaxies than either size or surface brightness.

Deep g'r'i'z' GMOS Imaging of the Dwarf Irregular Galaxy Kar 50

NASA Astrophysics Data System (ADS)

Davidge, T. J.

2002-11-01

Images obtained with the Gemini Multi-Object Spectrograph (GMOS) are used to investigate the stellar content and distance of the dwarf irregular galaxy Kar 50. The brightest object is an H II region, and the bright stellar content is dominated by stars with g'-r'<0. The tips of the main sequence and the red giant branch (RGB) are tentatively identified near r'=24.9 and i'=25.5, respectively. The galaxy has a blue integrated color and no significant color gradient, and we conclude that Kar 50 has experienced a recent galaxy-wide episode of star formation. The distance estimated from the brightest blue stars indicates that Kar 50 is behind the M81 group, and this is consistent with the tentative RGB-tip brightness. Kar 50 has a remarkably flat central surface brightness profile, even at wavelengths approaching 1 μm, although there is no evidence of a bar. In the absence of another large star-forming episode, Kar 50 will evolve into a very low surface brightness galaxy. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council of Canada (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).

Comparing Stellar Populations Across the Hubble Sequence

NASA Astrophysics Data System (ADS)

Loeffler, Shane; Kaleida, Catherine C.; Parkash, Vaishali

2015-01-01

Previous work (Jansen et al., 2000, Taylor et al., 2005) has revealed trends in the optical wavelength radial profiles of galaxies across the Hubble Sequence. Radial profiles offer insight into stellar populations, metallicity, and dust concentrations, aspects which are deeply tied to the individual evolution of a galaxy. The Nearby Field Galaxy Survey (NFGS) provides a sampling of nearby galaxies that spans the range of morphological types, luminosities, and masses. Currently available NFGS data includes optical radial surface profiles and spectra of 196 nearby galaxies. We aim to look for trends in the infrared portion of the spectrum for these galaxies, but find that existing 2MASS data is not sufficiently deep. Herein, we expand the available data for the NGFS galaxy IC1639 deeper into the infrared using new data taken with the Infrared Sideport Imager (ISPI) on the 4-m Blanco Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. Images taken in J, H, and Ks were reduced using standard IRAF and IDL procedures. Photometric calibrations were completed by using the highest quality (AAA) 2MASS stars in the field. Aperture photometry was then performed on the galaxy and radial profiles of surface brightness, J-H color, and H-Ks color were produced. For IC1639, the new ISPI data reveals flat color gradients and surface brightness gradients that decrease with radius. These trends reveal an archetypal elliptical galaxy, with a relatively homogeneous stellar population, stellar density decreasing with radius, and little-to-no obscuration by dust. We have obtained ISPI images for an additional 8 galaxies, and further reduction and analysis of these data will allow for investigation of radial trends in the infrared for galaxies across the Hubble Sequence.

A DEEPER LOOK AT LEO IV: STAR FORMATION HISTORY AND EXTENDED STRUCTURE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sand, David J.; Seth, Anil; Olszewski, Edward W.

We present MMT/Megacam imaging of the Leo IV dwarf galaxy in order to investigate its structure and star formation history, and to search for signs of association with the recently discovered Leo V satellite. Based on parameterized fits, we find that Leo IV is round, with {epsilon} < 0.23 (at the 68% confidence limit) and a half-light radius of r{sub h} {approx_equal} 130 pc. Additionally, we perform a thorough search for extended structures in the plane of the sky and along the line of sight. We derive our surface brightness detection limit by implanting fake structures into our catalog withmore » stellar populations identical to that of Leo IV. We show that we are sensitive to stream-like structures with surface brightness {mu}{sub r} {approx}< 29.6 mag arcsec{sup -2}, and at this limit we find no stellar bridge between Leo IV (out to a radius of {approx}0.5 kpc) and the recently discovered, nearby satellite Leo V. Using the color-magnitude fitting package StarFISH, we determine that Leo IV is consistent with a single age ({approx}14 Gyr), single metallicity ([Fe/H] {approx} -2.3) stellar population, although we cannot rule out a significant spread in these values. We derive a luminosity of M{sub V} = -5.5 {+-} 0.3. Studying both the spatial distribution and frequency of Leo IV's 'blue plume' stars reveals evidence for a young ({approx}2 Gyr) stellar population which makes up {approx}2% of its stellar mass. This sprinkling of star formation, only detectable in this deep study, highlights the need for further imaging of the new Milky Way satellites along with theoretical work on the expected, detailed properties of these possible 'reionization fossils'.« less

A Deeper Look at Leo IV: Star Formation History and Extended Structure

NASA Astrophysics Data System (ADS)

Sand, David J.; Seth, Anil; Olszewski, Edward W.; Willman, Beth; Zaritsky, Dennis; Kallivayalil, Nitya

2010-07-01

We present MMT/Megacam imaging of the Leo IV dwarf galaxy in order to investigate its structure and star formation history, and to search for signs of association with the recently discovered Leo V satellite. Based on parameterized fits, we find that Leo IV is round, with epsilon < 0.23 (at the 68% confidence limit) and a half-light radius of rh ~= 130 pc. Additionally, we perform a thorough search for extended structures in the plane of the sky and along the line of sight. We derive our surface brightness detection limit by implanting fake structures into our catalog with stellar populations identical to that of Leo IV. We show that we are sensitive to stream-like structures with surface brightness μ r <~ 29.6 mag arcsec-2, and at this limit we find no stellar bridge between Leo IV (out to a radius of ~0.5 kpc) and the recently discovered, nearby satellite Leo V. Using the color-magnitude fitting package StarFISH, we determine that Leo IV is consistent with a single age (~14 Gyr), single metallicity ([Fe/H] ~ -2.3) stellar population, although we cannot rule out a significant spread in these values. We derive a luminosity of MV = -5.5 ± 0.3. Studying both the spatial distribution and frequency of Leo IV's "blue plume" stars reveals evidence for a young (~2 Gyr) stellar population which makes up ~2% of its stellar mass. This sprinkling of star formation, only detectable in this deep study, highlights the need for further imaging of the new Milky Way satellites along with theoretical work on the expected, detailed properties of these possible "reionization fossils." Observations reported here were obtained at the MMT observatory, a joint facility of the Smithsonian Institution and the University of Arizona.

New insights on the formation and assembly of M83 from deep near-infrared imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, Kate L.; Van Zee, Liese; Dale, Daniel A.

2014-07-10

We present results from new near-infrared (NIR) imaging from the Spitzer Space Telescope that trace the low surface brightness features of the outer disk and stellar stream in the nearby spiral galaxy, M83. Previous observations have shown that M83 hosts a faint stellar stream to the northwest and a star-forming disk that extends to ∼3 times the optical radius (R{sub 25}). By combining the NIR imaging with archival far-ultraviolet (FUV) and H I imaging, we study the star formation history of the system. The NIR surface brightness profile has a break at ∼5.'8 (equivalent to 8.1 kpc and 0.9 R{submore » 25}) with a shallower slope beyond this radius, which may result from the recent accretion of gas onto the outer disk and subsequent star formation. Additionally, the ratio of FUV to NIR flux increases with increasing radius in several arms throughout the extended star forming disk, indicating an increase in the ratio of the present to past star formation rate with increasing radius. This sort of inside-out disk formation is consistent with observations of gas infall onto the outer disk of M83. Finally, the flux, size, and shape of the stellar stream are measured and the origin of the stream is explored. The stream has a total NIR flux of 11.6 mJy, which implies a stellar mass of 1 × 10{sup 8} M{sub ☉} in an area subtending ∼80°. No FUV emission is detected in the stream at a level greater than the noise, confirming an intermediate-age or old stellar population in the stream.« less

FIRST RESULTS FROM THE DRAGONFLY TELEPHOTO ARRAY: THE APPARENT LACK OF A STELLAR HALO IN THE MASSIVE SPIRAL GALAXY M101

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Dokkum, Pieter G.; Merritt, Allison; Abraham, Roberto

2014-02-20

We use a new telescope concept, the Dragonfly Telephoto Array, to study the low surface brightness outskirts of the spiral galaxy M101. The radial surface brightness profile is measured down to μ {sub g} ∼ 32 mag arcsec{sup –2}, a depth that approaches the sensitivity of star count studies in the Local Group. We convert surface brightness to surface mass density using the radial g – r color profile. The mass density profile shows no significant upturn at large radius and is well-approximated by a simple bulge + disk model out to R = 70 kpc, corresponding to 18 diskmore » scale lengths. Fitting a bulge + disk + halo model we find that the best-fitting halo mass M{sub halo}=1.7{sub −1.7}{sup +3.4}×10{sup 8} M {sub ☉}. The total stellar mass of M101 is M{sub tot,∗}=5.3{sub −1.3}{sup +1.7}×10{sup 10} M {sub ☉}, and we infer that the halo mass fraction f{sub halo}=M{sub halo}/M{sub tot,∗}=0.003{sub −0.003}{sup +0.006}. This mass fraction is lower than that of the Milky Way (f {sub halo} ∼ 0.02) and M31 (f {sub halo} ∼ 0.04). All three galaxies fall below the f {sub halo}-M {sub tot,} {sub *} relation predicted by recent cosmological simulations that trace the light of disrupted satellites, with M101's halo mass a factor of ∼10 below the median expectation. However, the predicted scatter in this relation is large, and more galaxies are needed to better quantify this possible tension with galaxy formation models. Dragonfly is well suited for this project: as integrated-light surface brightness is independent of distance, large numbers of galaxies can be studied in a uniform way.« less

IRAC Imaging of LSB Galaxies

NASA Astrophysics Data System (ADS)

Schombert, James; McGaugh, Stacy; Lelli, Federico

2017-04-01

We propose a program to observe a large sample of Low Surface Brightness (LSB) galaxies. Large galaxy surveys conducted with Spitzer suffer from the unavoidable selection bias against LSB systems (e.g., the S4G survey). Even those programs thathave specifically targeted LSB galaxies have usually been restricted objects of intermediate surface brightness (between 22 and 23 B mag/ []). Our sample is selected to be of a more extreme LSB nature (with central surface brightness fainter than 23 Bmag/[]). Even warm, Spitzer is the ideal instrument to image these low contrast targets in the near infrared: our sample goes a considerable way towards remedying this hole in the Spitzer legacy archive, also increasing coverage in terms of stellar mass, gas mass, and SFR. The sample will be used to address the newly discovered radial acceleration relation (RAR) in disk galaxies. While issues involving the connection between baryons and dark matter have been known since the development of the global baryonic Tully-Fisher (bTF) relation, it is only in the last six months that the particle physics and theoretical communities have recognized and responded to the local coupling between dark and baryonic matter represented by the RAR. This important new correlation is effectively a new natural law for galaxies. Spitzer photometry has been at the forefront of resolving the stellar mass component in galaxies that make-up the RAR and is the primary reason for the discovery of this new kinematic law.

The Next Generation Fornax Survey (NGFS). II. The Central Dwarf Galaxy Population

NASA Astrophysics Data System (ADS)

Eigenthaler, Paul; Puzia, Thomas H.; Taylor, Matthew A.; Ordenes-Briceño, Yasna; Muñoz, Roberto P.; Ribbeck, Karen X.; Alamo-Martínez, Karla A.; Zhang, Hongxin; Ángel, Simón; Capaccioli, Massimo; Côté, Patrick; Ferrarese, Laura; Galaz, Gaspar; Grebel, Eva K.; Hempel, Maren; Hilker, Michael; Lançon, Ariane; Mieske, Steffen; Miller, Bryan; Paolillo, Maurizio; Powalka, Mathieu; Richtler, Tom; Roediger, Joel; Rong, Yu; Sánchez-Janssen, Ruben; Spengler, Chelsea

2018-03-01

We present a photometric study of the dwarf galaxy population in the core region (≲r vir/4) of the Fornax galaxy cluster based on deep u‧g‧i‧ photometry from the Next Generation Fornax Cluster Survey. All imaging data were obtained with the Dark Energy Camera mounted on the 4 m Blanco telescope at the Cerro Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities ‑17 ≲ M g‧ ≲ ‑8 mag, corresponding to typical stellar masses of 9.5≳ {log}{{ \\mathcal M }}\\star /{M}ȯ ≳ 5.5, reaching ∼3 mag deeper in point-source luminosity and ∼4 mag deeper in surface brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that the dwarf galaxy surface-brightness profiles are well represented by single-component Sérsic models with average Sérsic indices of < n{> }u\\prime ,g\\prime ,i\\prime =(0.78{--}0.83)+/- 0.02 and average effective radii of < {r}e{> }u\\prime ,g\\prime ,i\\prime =(0.67{--}0.70)+/- 0.02 {kpc}. Color–magnitude relations indicate a flattening of the galaxy red sequence at faint galaxy luminosities, similar to the one recently discovered in the Virgo cluster. A comparison with population synthesis models and the galaxy mass–metallicity relation reveals that the average faint dwarf galaxy is likely older than ∼5 Gyr. We study galaxy scaling relations between stellar mass, effective radius, and stellar mass surface density over a stellar mass range covering six orders of magnitude. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be identified: (1) dwarf galaxies assemble mass inside the half-mass radius up to {log}{{ \\mathcal M }}\\star ≈ 8.0, (2) isometric mass assembly occurs in the range 8.0 ≲ {log}{{ \\mathcal M }}\\star /{M}ȯ ≲ 10.5, and (3) massive galaxies assemble stellar mass predominantly in their halos at {log}{{ \\mathcal M }}\\star ≈ 10.5 and above.

Surface brightness and color distributions in blue compact dwarf galaxies. I - Haro 2, an extreme example of a star-forming young elliptical galaxy

NASA Technical Reports Server (NTRS)

Loose, Hans-Hermann; Thuan, Trinh X.

1986-01-01

The first results of a large-scale program to study the morphology and structure of blue compact dwarf galaxies from CCD observations are presented. The observations and reduction procedures are described, and surface brightness and color profiles are shown. The results are used to discuss the morphological type of Haro 2 and its stellar populations. It is found that Haro 2 appears to be an extreme example of an elliptical galaxy undergoing intense star formation in its central regions, and that the oldest stars it contains were made only about four million yr ago. The 'missing' mass problem of Haro 2 is also discussed.

Comparative testing of dark matter models with 15 HSB and 15 LSB galaxies

NASA Astrophysics Data System (ADS)

Kun, E.; Keresztes, Z.; Simkó, A.; Szűcs, G.; Gergely, L. Á.

2017-12-01

Context. We assemble a database of 15 high surface brightness (HSB) and 15 low surface brightness (LSB) galaxies, for which surface brightness density and spectroscopic rotation curve data are both available and representative for various morphologies. We use this dataset to test the Navarro-Frenk-White, the Einasto, and the pseudo-isothermal sphere dark matter models. Aims: We investigate the compatibility of the pure baryonic model and baryonic plus one of the three dark matter models with observations on the assembled galaxy database. When a dark matter component improves the fit with the spectroscopic rotational curve, we rank the models according to the goodness of fit to the datasets. Methods: We constructed the spatial luminosity density of the baryonic component based on the surface brightness profile of the galaxies. We estimated the mass-to-light (M/L) ratio of the stellar component through a previously proposed color-mass-to-light ratio relation (CMLR), which yields stellar masses independent of the photometric band. We assumed an axissymetric baryonic mass model with variable axis ratios together with one of the three dark matter models to provide the theoretical rotational velocity curves, and we compared them with the dataset. In a second attempt, we addressed the question whether the dark component could be replaced by a pure baryonic model with fitted M/L ratios, varied over ranges consistent with CMLR relations derived from the available stellar population models. We employed the Akaike information criterion to establish the performance of the best-fit models. Results: For 7 galaxies (2 HSB and 5 LSB), neither model fits the dataset within the 1σ confidence level. For the other 23 cases, one of the models with dark matter explains the rotation curve data best. According to the Akaike information criterion, the pseudo-isothermal sphere emerges as most favored in 14 cases, followed by the Navarro-Frenk-White (6 cases) and the Einasto (3 cases) dark matter models. We find that the pure baryonic model with fitted M/L ratios falls within the 1σ confidence level for 10 HSB and 2 LSB galaxies, at the price of growing the M/Ls on average by a factor of two, but the fits are inferior compared to the best-fitting dark matter model.

GJ 1214: Rotation period, starspots, and uncertainty on the optical slope of the transmission spectrum

NASA Astrophysics Data System (ADS)

Mallonn, M.; Herrero, E.; Juvan, I. G.; Essen, C. von; Rosich, A.; Ribas, I.; Granzer, T.; Alexoudi, X.; Strassmeier, K. G.

2018-06-01

Aims: Brightness inhomogeneities in the stellar photosphere (dark spots or bright regions) affect the measurements of the planetary transmission spectrum. To investigate the star spots of the M dwarf GJ 1214, we conducted a multicolor photometric monitoring from 2012 to 2016. Methods: The time-series photometry was analyzed with the light curve inversion tool StarSim. Using the derived stellar surface properties from the light curve inversion, we modeled the impact of the star spots when unocculted by the transiting planet. We compared the photometric variability of GJ 1214 to published results of mid- to late M dwarfs from the MEarth sample. Results: The measured variability shows a periodicity of 125 ± 5 days, which we interpret as the signature of the stellar rotation period. This value overrules previous suggestions of a significantly shorter stellar rotation period. A light curve inversion of the monitoring data yields an estimation of the flux dimming of a permanent spot filling factor not contributing to the photometric variability, a temperature contrast of the spots of 370 K and persistent active longitudes. The derived surface maps over all five seasons were used to estimate the influence of the star spots on the transmission spectrum of the planet from 400 to 2000 nm. The monitoring data presented here do not support a recent interpretation of a measured transmission spectrum of GJ 1214b as to be caused by bright regions in the stellar photosphere. Instead, we list arguments as to why the effect of dark spots likely dominated over bright regions in the period of our monitoring. Furthermore, our photometry proves an increase in variability over at least four years, indicative for a cyclic activity behavior. The age of GJ 1214 is likely between 6 and 10 Gyr. Conclusions: The long-term photometry allows for a correction of unocculted spots. For an active star such as GJ 1214, there remains a degeneracy between occulted spots and the transit parameters used to build the transmission spectrum. This degeneracy can only be broken by high-precision transit photometry resolving the spot crossing signature in the transit light curve. Based on data obtained with the STELLA robotic telescopes in Tenerife, an AIP facility jointly operated by AIP and IAC.The photometry tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A35

Stellar populations in the bulges of isolated galaxies

NASA Astrophysics Data System (ADS)

Morelli, L.; Parmiggiani, M.; Corsini, E. M.; Costantin, L.; Dalla Bontà, E.; Méndez-Abreu, J.; Pizzella, A.

2016-12-01

We present photometry and long-slit spectroscopy for 12 S0 and spiral galaxies selected from the Catalogue of Isolated Galaxies. The structural parameters of the sample galaxies are derived from the Sloan Digital Sky Survey I-band images by performing a two-dimensional photometric decomposition of the surface brightness distribution. This is assumed to be the sum of the contribution of a Sérsic bulge, an exponential disc, and a Ferrers bar characterized by elliptical and concentric isophotes with constant ellipticity and position angles. The rotation curves and velocity dispersion profiles of the stellar component are measured from the spectra obtained along the major axis of galaxies. The radial profiles of the Hβ, Mg and Fe line-strength indices are derived too. Correlations between the central values of the Mg2 and line-strength indices and the velocity dispersion are found. The mean age, total metallicity and total α/Fe enhancement of the stellar population in the centre and at the radius, where the bulge gives the same contribution to the total surface brightness as the remaining components, are obtained using stellar population models with variable element abundance ratios. We identify intermediate-age bulges with solar metallicity and old bulges with a large spread in metallicity. Most of the sample bulges display supersolar α/Fe enhancement, no gradient in age and negative gradients of metallicity and α/Fe enhancement. These findings support a formation scenario via dissipative collapse where environmental effects are remarkably less important than in the assembly of bulges of galaxies in groups and clusters.

The MESSIER surveyor: unveiling the ultra-low surface brightness universe

NASA Astrophysics Data System (ADS)

Valls-Gabaud, David; MESSIER Collaboration

2017-03-01

The MESSIER surveyor is a small mission designed at exploring the very low surface brightness universe. The satellite will drift-scan the entire sky in 6 filters covering the 200-1000 nm range, reaching unprecedented surface brightness levels of 34 and 37 mag arcsec-2 in the optical and UV, respectively. These levels are required to achieve the two main science goals of the mission: to critically test the ΛCDM paradigm of structure formation through (1) the detection and characterisation of ultra-faint dwarf galaxies, which are predicted to be extremely abundant around normal galaxies, but which remain elusive; and (2) tracing the cosmic web, which feeds dark matter and baryons into galactic haloes, and which may contain the reservoir of missing baryons at low redshifts. A large number of science cases, ranging from stellar mass loss episodes to intracluster light through fluctuations in the cosmological UV-optical background radiation are free by-products of the full-sky maps produced.

A medium-bright quasar sample - New quasar surface densities in the magnitude range from 16.4 to 17.65 for B

NASA Technical Reports Server (NTRS)

Mitchell, K. J.; Warnock, A., III; Usher, P. D.

1984-01-01

A new medium-bright quasar sample (MBQS) is constructed from spectroscopic observations of 140 bright objects selected for varying degrees of blue and ultraviolet excess (B-UVX) in five Palomar 1.2 m Schmidt fields. The MBQS contains 32 quasars with B less than 17.65 mag. The new integral surface densities in the B range from 16.45 to 17.65 mag are approximately 40 percent (or more) higher than expected. The MBQS and its redshift distribution increase the area of the Hubble diagram covered by complete samples of quasars. The general spectroscopic results indicate that the three-color classification process used to catalog the spectroscopic candidates (1) has efficiently separated the intrinsically B-UVX stellar objects from the Population II subdwarfs and (2) has produced samples of B-UVX objects which are more complete than samples selected by (U - B) color alone.

Local stability of galactic discs in modified dynamics

NASA Astrophysics Data System (ADS)

Shenavar, Hossein; Ghafourian, Neda

2018-04-01

The local stability of stellar and fluid discs, under a new modified dynamical model, is surveyed by using WKB approximation. The exact form of the modified Toomre criterion is derived for both types of systems and it is shown that the new model is, in all situations, more locally stable than Newtonian model. In addition, it has been proved that the central surface density of the galaxies plays an important role in the local stability in the sense that low surface brightness (LSB) galaxies are more stable than high surface brightness (HSBs). Furthermore, the growth rate in the new model is found to be lower than the Newtonian one. We found that, according to this model, the local instability is related to the ratio of surface density of the disc to a critical surface density Σcrit. We provide observational evidence to support this result based on star formation rate in HSBs and LSBs.

Experiment requirements document for reflight of the small helium-cooled infrared telescope experiment

NASA Technical Reports Server (NTRS)

1982-01-01

The four astronomical objectives addressed include: the measurement and mapping of extended low surface brightness infrared emission from the galaxy; the measurement of diffuse emission from intergalactic material and/or galaxies and quasi-stellar objects; the measurement of the zodiacal dust emission; and the measurement of a large number of discrete infrared sources.

The catalog of edge-on disk galaxies from SDSS. I. The catalog and the structural parameters of stellar disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bizyaev, D. V.; Kautsch, S. J.; Mosenkov, A. V.

We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS). A visual inspection of the g, r, and i images of about 15,000 galaxies allowed us to split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-on galaxies, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects either show signs of interaction and warps, or nearby bright stars project on it. We added more candidate galaxies from RFGC, EFIGI, RC3, andmore » Galaxy Zoo catalogs found in the SDSS footprints. Our final sample consists of 5747 genuine edge-on galaxies. We estimate the structural parameters of the stellar disks (the stellar disk thickness, radial scale length, and central surface brightness) in the galaxies by analyzing photometric profiles in each of the g, r, and i images. We also perform simplified three-dimensional modeling of the light distribution in the stellar disks of edge-on galaxies from our sample. Our large sample is intended to be used for studying scaling relations in the stellar disks and bulges and for estimating parameters of the thick disks in different types of galaxies via the image stacking. In this paper, we present the sample selection procedure and general description of the sample.« less

A Survey of Stellar Populations in Ultra-Diffuse Galaxies

NASA Astrophysics Data System (ADS)

Romanowsky, Aaron; Laine, Seppo; Pandya, Viraj; Brodie, Jean; Glaccum, Bill; van Dokkum, Pieter; Alabi, Busola; Cohen, Yotam; Danieli, Shany; Abraham, Bob; Martinez-Delgado, David; Greco, Johnny; Greene, Jenny

2018-05-01

Ultra-diffuse galaxies (UDGs) are a recently identified, mysterious class of galaxies with luminosities like dwarfs, but sizes like giants. Quiescent UDGs are found in all environments from cluster to isolated, and intensive study has revealed three very distinctive sub-types: low surface brightness dwarfs, 'failed galaxies', and low-dark-matter UDGs. Following up on our recent, successful Spitzer pilot work to characterize the stellar populations (ages and metallicities) of UDGs, we propose a survey of 25 UDGs with a range of optical properties and environments, in order to understand the formation histories of different the different UDG sub-types.

The very soft X-ray emission of X-ray-faint early-type galaxies

NASA Technical Reports Server (NTRS)

Pellegrini, S.; Fabbiano, G.

1994-01-01

A recent reanaylsis of Einstein data, and new ROSAT observations, have revealed the presence of at least two components in the X-ray spectra of X-ray faint early-type galaxies: a relatively hard component (kT greater than 1.5 keV), and a very soft component (kT approximately 0.2-0.3 keV). In this paper we address the problem of the nature of the very soft component and whether it can be due to a hot interstellar medium (ISM), or is most likely originated by the collective emission of very soft stellar sources. To this purpose, hydrodynamical evolutionary sequences for the secular behavior of gas flows in ellipticals have been performed, varying the Type Ia supernovae rate of explosion, and the dark matter amount and distribution. The results are compared with the observational X-ray data: the average Einstein spectrum for six X-ray faint early-type galaxies (among which are NGC 4365 and NGC 4697), and the spectrum obtained by the ROSAT pointed observation of NGC 4365. The very soft component could be entirely explained with a hot ISM only in galaxies such as NGC 4697, i.e., when the depth of the potential well-on which the average ISM temperature strongly depends-is quite shallow; in NGC 4365 a diffuse hot ISM would have a temperature larger than that of the very soft component, because of the deeper potential well. So, in NGC 4365 the softest contribution to the X-ray emission comes certainly from stellar sources. As stellar soft X-ray emitters, we consider late-type stellar coronae, supersoft sources such as those discovered by ROSAT in the Magellanic Clouds and M31, and RS CVn systems. All these candidates can be substantial contributors to the very soft emission, though none of them, taken separately, plausibly accounts entirely for its properties. We finally present a model for the X-ray emission of NGC 4365, to reproduce in detail the results of the ROSAT pointed observation, including the Position Sensitive Proportional Counter (PSPC) spectrum and radial surface brightness distribution. The present data may suggest that the X-ray surface brightness is more extended than the optical profile. In this case, a straightforward explanation in terms of stellar sources could not be satisfactory. The available data can be better explained with three different contributions: a very soft component of stellar origin, a hard component from X-ray binaries, and an approximately 0.6 keV hot ISM. The latter can explain the extended X-ray surface brightness profile, if the galaxy has a dark-to-luminous mass ratio of 9, with the dark matter very broadly distributed, and a SN Ia explosive rate of approximately 0.6 the Tammann rate.

A Comparison of Young Star Properties with Local Galactic Environment for LEGUS/LITTLE THINGS Dwarf Irregular Galaxies

NASA Astrophysics Data System (ADS)

Hunter, Deidre A.; Adamo, Angela; Elmegreen, Bruce G.; Gallardo, Samavarti; Lee, Janice C.; Cook, David O.; Thilker, David; Kayitesi, Bridget; Kim, Hwihyun; Kahre, Lauren; Ubeda, Leonardo; Bright, Stacey N.; Ryon, Jenna E.; Calzetti, Daniela; Tosi, Monica; Grasha, Kathryn; Messa, Matteo; Fumagalli, Michele; Dale, Daniel A.; Sabbi, Elena; Cignoni, Michele; Smith, Linda J.; Gouliermis, Dimitrios M.; Grebel, Eva K.; Aloisi, Alessandra; Whitmore, Bradley C.; Chandar, Rupali; Johnson, Kelsey E.

2018-07-01

We have explored the role environmental factors play in determining characteristics of young stellar objects in nearby dwarf irregular and blue compact dwarf galaxies. Star clusters are characterized by concentrations, masses, and formation rates; OB associations by mass and mass surface density; O stars by their numbers and near-ultraviolet absolute magnitudes; and H II regions by Hα surface brightnesses. These characteristics are compared to surrounding galactic pressure, stellar mass density, H I surface density, and star formation rate (SFR) surface density. We find no trend of cluster characteristics with environmental properties, implying that larger-scale effects are more important in determining cluster characteristics or that rapid dynamical evolution erases any memory of the initial conditions. On the other hand, the most massive OB associations are found at higher pressure and H I surface density, and there is a trend of higher H II region Hα surface brightness with higher pressure, suggesting that a higher concentration of massive stars and gas is found preferentially in regions of higher pressure. At low pressures we find massive stars but not bound clusters and OB associations. We do not find evidence for an increase of cluster formation efficiency as a function of SFR density. However, there is an increase in the ratio of the number of clusters to the number of O stars with increasing pressure, perhaps reflecting an increase in clustering properties with SFR.

Observing the First Stars in Luminous, Red Galaxies

NASA Technical Reports Server (NTRS)

Heap, Sally; Lindler, Don

2010-01-01

Modern cosmological simulations predict that the first stars are to be found today in luminous, red galaxies. Although observing such stars individually against a background of younger, metal-rich stars is impossible, the first stars should make their presence known by their strong, line-free ultraviolet flux. We have found evidence for a UV-bright stellar population in Sloan spectra of LRG's at z=0.4-0.5. We present arguments for interpreting this UV-bright stellar population as the oldest stars, rather than other types of stellar populations (e.g. young stars or blue straggler stars in the dominant, metal-rich stellar population

An analytic treatment of gravitational microlensing for sources of finite size at large optical depths

NASA Technical Reports Server (NTRS)

Deguchi, Shuji; Watson, William D.

1988-01-01

Statistical methods are developed for gravitational lensing in order to obtain analytic expressions for the average surface brightness that include the effects of microlensing by stellar (or other compact) masses within the lensing galaxy. The primary advance here is in utilizing a Markoff technique to obtain expressions that are valid for sources of finite size when the surface density of mass in the lensing galaxy is large. The finite size of the source is probably the key consideration for the occurrence of microlensing by individual stars. For the intensity from a particular location, the parameter which governs the importance of microlensing is determined. Statistical methods are also formulated to assess the time variation of the surface brightness due to the random motion of the masses that cause the microlensing.

Faint dwarf galaxies in Hickson Compact Group 90*

NASA Astrophysics Data System (ADS)

Ordenes-Briceño, Yasna; Taylor, Matthew A.; Puzia, Thomas H.; Muñoz, Roberto P.; Eigenthaler, Paul; Georgiev, Iskren Y.; Goudfrooij, Paul; Hilker, Michael; Lançon, Ariane; Mamon, Gary; Mieske, Steffen; Miller, Bryan W.; Peng, Eric W.; Sánchez-Janssen, Rubén

2016-12-01

We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with Very Large Telescope/Visible Multi-Object Spectrograph. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range 0.7 ≲ reff/kpc ≲ 1.5 with luminosities of -11.65 ≲ MU ≲ -9.42 and -12.79 ≲ MI ≲ -10.58 mag, corresponding to a colour range of (U - I)0 ≃ 1.1-2.2 mag and surface brightness levels of μU ≃ 28.1 mag arcsec-2 and μI ≃ 27.4 mag arcsec-2. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z⊙ metallicities we obtain stellar masses in the range M*|Z⊙ ≃ 105.7 - 6.3 M⊙ and M_{*}|_{0.02 Z_{⊙} ≃ 10^{6.3-8} M_{⊙}. Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than ˜2 Gyr at any mass/metallicity combination. Altogether, the new LSB dwarf galaxy candidates share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. We find a pair of candidates with ˜2 kpc projected separation, which may represent one of the closest dwarf galaxy pairs found. We also find a nucleated dwarf candidate, with a nucleus size of reff ≃ 46-63 pc and magnitude MU, 0 = -7.42 mag and (U - I)0 = 1.51 mag, which is consistent with a nuclear stellar disc with a stellar mass in the range 104.9 - 6.5 M⊙.

Infrared surface photometry of 3C 65: Stellar evolution and the Tolman signal

NASA Astrophysics Data System (ADS)

Rigler, M. A.; Lilly, S. J.

1994-06-01

We present an analysis of the infrared surface brightness profile of the high-redshift radio galaxy 3C 65 (z = 1.176), which is well fitted by a de Vaucouleurs r1/4 law. A model surface fitting routine yields characteristic photometric parameters comparable to those of low-redshift radio galaxies and brightest cluster members (BCMs) in standard cosmologies. The small displacement of this galaxy from the locus of low-redshift systems on the mur - log(re) plane suggests that little or no luminosity evolution is required in a cosmological model with (Omega0, lambda0 = (1,0), while a modest degree of luminosity evolution, accountable by passive evolution of the stellar population, is implied in models with (0, 0) or (0.1, 0.9). A nonexpanding cosmology is unlikely because it would require 3C 65 to lie at the extreme end of the distribution of properties of local gE galaxies, and the effects of plausible stellar and/or dynamic evolution would make 3C 65 even more extreme by the present epoch.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrmann, Kimberly A.; Hunter, Deidre A.; Elmegreen, Bruce G., E-mail: kah259@psu.edu, E-mail: dah@lowell.edu, E-mail: bge@us.ibm.com

In this second paper of a series, we explore the B  −  V , U  −  B , and FUV−NUV radial color trends from a multi-wavelength sample of 141 dwarf disk galaxies. Like spirals, dwarf galaxies have three types of radial surface brightness profiles: (I) single exponential throughout the observed extent (the minority), (II) down-bending (the majority), and (III) up-bending. We find that the colors of (1) Type I dwarfs generally become redder with increasing radius, unlike spirals which have a blueing trend that flattens beyond ∼1.5 disk scale lengths, (2) Type II dwarfs come in six different “flavors,” one of whichmore » mimics the “U” shape of spirals, and (3) Type III dwarfs have a stretched “S” shape where the central colors are flattish, become steeply redder toward the surface brightness break, then remain roughly constant beyond, which is similar to spiral Type III color profiles, but without the central outward bluing. Faint (−9 >  M{sub B}  > −14) Type II dwarfs tend to have continuously red or “U” shaped colors and steeper color slopes than bright (−14 >  M{sub B}  > −19) Type II dwarfs, which additionally have colors that become bluer or remain constant with increasing radius. Sm dwarfs and BCDs tend to have at least some blue and red radial color trend, respectively. Additionally, we determine stellar surface mass density (Σ) profiles and use them to show that the break in Σ generally remains in Type II dwarfs (unlike Type II spirals) but generally disappears in Type III dwarfs (unlike Type III spirals). Moreover, the break in Σ is strong, intermediate, and weak in faint dwarfs, bright dwarfs, and spirals, respectively, indicating that Σ may straighten with increasing galaxy mass. Finally, the average stellar surface mass density at the surface brightness break is roughly 1−2  M {sub ⊙} pc{sup −2} for Type II dwarfs but higher at 5.9  M {sub ⊙} pc{sup −2} or 27  M {sub ⊙} pc{sup −2} for Type III BCDs and dIms, respectively.« less

Asteroseismology of Red-Giant Stars: Mixed Modes, Differential Rotation, and Eccentric Binaries

NASA Astrophysics Data System (ADS)

Beck, Paul G.

2013-12-01

Astronomers are aware of rotation in stars since Galileo Galilei attributed the movement of sunspots to rotation of the Sun in 1613. In contrast to the Sun, whose surface can be resolved by small telescopes or even the (protected) eye, we detect stars as point sources with no spatial information. Numerous techniques have been developed to derive information about stellar rotation. Unfortunately, most observational data allow only for the surface rotational rate to be inferred. The internal rotational profile, which has a great effect on the stellar structure and evolution, remains hidden below the top layers of the star - the essential is hidden to the eyes. Asteroseismology allows us to "sense" indirectly deep below the stellar surface. Oscillations that propagate through the star provide information about the deep stellar interiors while they also distort the stellar surface in characteristic patterns leading to detectable brightness or velocity variations. Also, certain oscillation modes are sensitive to internal rotation and carry information on how the star is spinning deep inside. Thanks to the unprecedented quality of NASA's space telescope Kepler, numerous detailed observations of stars in various evolutionary stages are available. Such high quality data allow that for many stars, rotation can not only be constrained from surface rotation, but also investigated through seismic studies. The work presented in this thesis focuses on the oscillations and internal rotational gradient of evolved single and binary stars. It is shown that the seismic analysis can reach the cores of oscillating red-giant stars and that these cores are rapidly rotating, while nested in a slowly rotating convective envelope.

The Intriguing Case of the (Almost) Dark Galaxy AGC 229385

NASA Astrophysics Data System (ADS)

Salzer, John

2015-10-01

The ALFALFA blind HI survey has catalogued tens of thousands of HI sources over 7000 square degrees of high Galactic latitude sky. While the vast majority of the sources in ALFALFA have optical counterparts in existing wide-field surveys like SDSS, a class of objects has been identified that have no obvious optical counterparts in existing catalogs. Dubbed almost dark galaxies, these objects represent an extreme in the continuum of galaxy properties, with the highest HI mass-to-optical light ratios ever measured. We propose to use HST to observe AGC 229385, an almost dark object found in deep WIYN imaging to have an ultra-low surface brightness stellar component with extremely blue colors. AGC 229385 falls well off of all galaxy scaling relationships, including the Baryonic Tully-Fisher relation. Ground-based optical and HI data have been able to identify this object as extreme, but are insufficient to constrain the properties of its stellar component or its distance - for this, we need HST. Our science goals are twofold: to better constrain the distance to AGC 229385, and to investigate the stellar population(s) in this mysterious object. The requested observations will not only provide crucial insight into the properties and evolution of this specific system but will also help us understand this important class of ultra low surface brightness, gas-rich galaxies. The proposed observations are designed to be exploratory, yet they promise to pay rich dividends for a modest investment in observing time.

Luminosity and surface brightness distribution of K-band galaxies from the UKIDSS Large Area Survey

NASA Astrophysics Data System (ADS)

Smith, Anthony J.; Loveday, Jon; Cross, Nicholas J. G.

2009-08-01

We present luminosity and surface-brightness distributions of 40111 galaxies with K-band photometry from the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS), Data Release 3 and optical photometry from Data Release 5 of the Sloan Digital Sky Survey (SDSS). Various features and limitations of the new UKIDSS data are examined, such as a problem affecting Petrosian magnitudes of extended sources. Selection limits in K- and r-band magnitude, K-band surface brightness and K-band radius are included explicitly in the 1/Vmax estimate of the space density and luminosity function. The bivariate brightness distribution in K-band absolute magnitude and surface brightness is presented and found to display a clear luminosity-surface brightness correlation that flattens at high luminosity and broadens at low luminosity, consistent with similar analyses at optical wavelengths. Best-fitting Schechter function parameters for the K-band luminosity function are found to be M* - 5 logh = -23.19 +/- 0.04,α = -0.81 +/- 0.04 and φ* = (0.0166 +/- 0.0008)h3Mpc-3, although the Schechter function provides a poor fit to the data at high and low luminosity, while the luminosity density in the K band is found to be j = (6.305 +/- 0.067) × 108LsolarhMpc-3. However, we caution that there are various known sources of incompleteness and uncertainty in our results. Using mass-to-light ratios determined from the optical colours, we estimate the stellar mass function, finding good agreement with previous results. Possible improvements are discussed that could be implemented when extending this analysis to the full LAS.

Homogeneous spectroscopic parameters for bright planet host stars from the northern hemisphere . The impact on stellar and planetary mass

NASA Astrophysics Data System (ADS)

Sousa, S. G.; Santos, N. C.; Mortier, A.; Tsantaki, M.; Adibekyan, V.; Delgado Mena, E.; Israelian, G.; Rojas-Ayala, B.; Neves, V.

2015-04-01

Aims: In this work we derive new precise and homogeneous parameters for 37 stars with planets. For this purpose, we analyze high resolution spectra obtained by the NARVAL spectrograph for a sample composed of bright planet host stars in the northern hemisphere. The new parameters are included in the SWEET-Cat online catalogue. Methods: To ensure that the catalogue is homogeneous, we use our standard spectroscopic analysis procedure, ARES+MOOG, to derive effective temperatures, surface gravities, and metallicities. These spectroscopic stellar parameters are then used as input to compute the stellar mass and radius, which are fundamental for the derivation of the planetary mass and radius. Results: We show that the spectroscopic parameters, masses, and radii are generally in good agreement with the values available in online databases of exoplanets. There are some exceptions, especially for the evolved stars. These are analyzed in detail focusing on the effect of the stellar mass on the derived planetary mass. Conclusions: We conclude that the stellar mass estimations for giant stars should be managed with extreme caution when using them to compute the planetary masses. We report examples within this sample where the differences in planetary mass can be as high as 100% in the most extreme cases. Based on observations obtained at the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées and the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France (Run ID L131N11 - OPTICON_2013A_027).

Apollo-Soyuz pamphlet no. 3: Sun, stars, in between. [experimental design

NASA Technical Reports Server (NTRS)

Page, L. W.; From, T. P.

1977-01-01

The structure of the sun and its surface temperature and brightness are discussed as background for explaining the ASTP joint experiment to photograph the solar corona from Soyuz while the Apollo spacecraft created an artificial eclipse by blocking out the sun. Stellar spectra, stellar evolution, and the Milky Way galaxy are explored in relation to the MA-083 experiment to survey the sky for extreme ultraviolet sources and background radiation. Interstellar gas and the spectrum of helium are discussed in relation to the MA-088 experiment designed to detect interstellar helium entering the solar system and to measure its density and motion.

Stellar Disk Truncations: HI Density and Dynamics

NASA Astrophysics Data System (ADS)

Trujillo, Ignacio; Bakos, Judit

2010-06-01

Using HI Nearby Galaxy Survey (THINGS) 21-cm observations of a sample of nearby (nearly face-on) galaxies we explore whether the stellar disk truncation phenomenon produces any signature either in the HI gas density and/or in the gas dynamics. Recent cosmological simulations suggest that the origin of the break on the surface brightness distribution is produced by the appearance of a warp at the truncation position. This warp should produce a flaring on the gas distribution increasing the velocity dispersion of the HI component beyond the break. We do not find, however, any evidence of this increase in the gas velocity dispersion profile.

The surface brightness of reflection nebulae. Ph.D. Thesis, Dec. 1972

NASA Technical Reports Server (NTRS)

Rush, W. F.

1974-01-01

Hubble's equation relating the maximum apparent angular extent of a reflection nebula to the apparent magnitude of the illuminating star has been reconsidered under a set of less restrictive assumptions. A computational technique is developed which permits the use of fits to observed m, log a values to determine the albedo of the particles composing reflection nebulae, providing only that one assumes a particular phase function. Despite the fact that all orders of scattering, anisotropic phase functions, and illumination by the general stellar field are considered, the albedo which is determined for reflection nebulae by this method appears larger than that for interstellar particles in general. The possibility that the higher surface brightness might be due to a continuous fluorescence mechanism is considered both theoretically and observationally.

Sixteen month decline in the 850 micron continuum brightness of the young stellar object HOPS 358 in NGC 2068

NASA Astrophysics Data System (ADS)

Mairs, Steve; Bell, Graham S.; Johnstone, Doug; Herczeg, Gregory J.; Bower, Geoffrey C.; Aikawa, Yuri; Lee, Jeong-Eun; Chen, Huei-Ru Vivien; Hatchell, Jennifer; Kang, Miju; Contreras Pena, Carlos; Scholz, Alexander; Naylor, Tim

2018-04-01

As part of our young stellar object (YSO) sub-mm monthly monitoring programme, the JCMT Transient Survey (Herczeg et al. 2017 ApJ, 849, 43; Johnstone et al. 2018 ApJ, 854, 31), we have uncovered a steady sixteen-month decline in the 850 micron peak brightness of YSO HOPS 358 (R.A.

Starspots and Activity of the Flare Star GJ 1243

NASA Astrophysics Data System (ADS)

Savanov, I. S.; Dmitrienko, E. S.

2018-04-01

The photometric variability of the uniqueMdwarf flare star GJ 1243 (KIC 9726699) is investigated using the most complete set of observationalmaterial obtained with the Kepler Space Telescope. The analysis is based on 49 487 individual brightness measurements obtained during an interval of 1460 days (nearly four years). The periodicity of the brightness variations with the period P phot = 0.59261 ± 0.00060d is confirmed. The temperature inhomogeneities on the stellar surface reconstructed from the light curve are used to drive maps of these surface-temperature inhomogeneities (of the filling factor f). The resulting maps are used to determine the positions of active regions. Analysis of the surface-temperature maps for GJ 1243 led to the conclusion that the positions of spots on the stellar surface displayed appreciable evolution during the analyzed time interval. The maximum value for the lower limit on the differentialrotation parameter ΔΩ is 0.0022 rad/day. This more accurate estimate of ΔΩ is lower than the values presented earlier by Davenport et al. [1] (0.0058 and 0.0036 rad/day), due to the more accurate account of variations in the positions of the most active longitude in the current study. However, the differentialrotation estimate obtained in [1] using a method based on fitting the evolution of spots using twodimensional Gaussian functions essentially coincides with the new estimate presented here. The fractional area of the total spotted surface S of the star during the observing interval considered varied from 7 to 2%. The amplitude of the brightness variability of the star slowly decreased, varying in the range 1.6-0.5%. Overall, the position of GJ 1243 in spottedness-age, spottedness-rotation period, and spottedness-Rossby number diagrams agrees very well with the general character of the dependences displayed in earlier studies of M dwarfs.

Structural analysis of star-forming blue early-type galaxies. Merger-driven star formation in elliptical galaxies

NASA Astrophysics Data System (ADS)

George, Koshy

2017-02-01

Context. Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L⋆ elliptical galaxies in the local Universe. Aims: We wish to understand the reason for star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. Methods: We carried out structural analysis on SDSS r-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural parameters, analysed the residuals from best-fit to surface brightness distribution, and constructed the galaxy scaling relations. Results: We found that star-forming blue early-type galaxies are bulge-dominated systems with axial ratio >0.5 and surface brightness profiles fitted by Sérsic profiles with index (n) mostly >2. Twenty-three galaxies are found to have n< 2; these could be hosting a disc component. The residual images of the 32 galaxy surface brightness profile fits show structural features indicative of recent interactions. The star-forming blue elliptical galaxies follow the Kormendy relation and show the characteristics of normal elliptical galaxies as far as structural analysis is concerned. There is a general trend for high-luminosity galaxies to display interaction signatures and high star formation rates. Conclusions: The star-forming population of blue early-type galaxies at low redshifts could be normal ellipticals that might have undergone a recent gas-rich minor merger event. The star formation in these galaxies will shut down once the recently acquired fuel is consumed, following which the galaxy will evolve to a normal early-type galaxy.

The distribution of star formation and metals in the low surface brightness galaxy UGC 628

NASA Astrophysics Data System (ADS)

Young, J. E.; Kuzio de Naray, Rachel; Wang, Sharon X.

2015-09-01

We introduce the MUSCEL Programme (MUltiwavelength observations of the Structure, Chemistry and Evolution of LSB galaxies), a project aimed at determining the star-formation histories of low surface brightness galaxies. MUSCEL utilizes ground-based optical spectra and space-based UV and IR photometry to fully constrain the star-formation histories of our targets with the aim of shedding light on the processes that led low surface brightness galaxies down a different evolutionary path from that followed by high surface brightness galaxies, such as our Milky Way. Here we present the spatially resolved optical spectra of UGC 628, observed with the VIRUS-P IFU at the 2.7-m Harlen J. Smith Telescope at the McDonald Observatory, and utilize emission-line diagnostics to determine the rate and distribution of star formation as well as the gas-phase metallicity and metallicity gradient. We find highly clustered star formation throughout UGC 628, excluding the core regions, and a log(O/H) metallicity around -4.2, with more metal-rich regions near the edges of the galactic disc. Based on the emission-line diagnostics alone, the current mode of star formation, slow and concentrated in the outer disc, appears to have dominated for quite some time, although there are clear signs of a much older stellar population formed in a more standard inside-out fashion.

Galaxies in X-ray Selected Clusters and Groups in Dark Energy Survey Data: Stellar Mass Growth of Bright Central Galaxies Since z~1.2

DOE PAGES

Zhang, Y.; Miller, C.; McKay, T.; ...

2016-01-10

Using the science verification data of the Dark Energy Survey for a new sample of 106 X-ray selected clusters and groups, we study the stellar mass growth of bright central galaxies (BCGs) since redshift z ~ 1.2. Compared with the expectation in a semi-analytical model applied to the Millennium Simulation, the observed BCGs become under-massive/under-luminous with decreasing redshift. We incorporate the uncertainties associated with cluster mass, redshift, and BCG stellar mass measurements into analysis of a redshift-dependent BCG-cluster mass relation.

First Characterization of the Neutral ISM in Two Local Volume Dwarf Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bralts-Kelly, Lilly; Bulatek, Alyssa M.; Chinski, Sarah

We present the first H i spectral-line images of the nearby, star-forming dwarf galaxies UGC 11411 and UGC 8245, acquired as part of the “Observing for University Classes” program with the Karl G. Jansky Very Large Array (VLA). These low-resolution images localize the H i gas and reveal the bulk kinematics of each system. Comparing with Hubble Space Telescope ( HST ) broadband and ground-based H α imaging, we find that the ongoing star formation in each galaxy is associated with the highest H i mass surface density regions. UGC 8245 has a much lower current star formation rate thanmore » UGC 11411, which harbors very high surface brightness H α emission in the inner disk and diffuse, lower surface brightness nebular gas that extends well beyond the stellar disk as traced by HST . We measure the dynamical masses of each galaxy and find that the halo of UGC 11411 is more than an order of magnitude more massive than the halo of UGC 8245, even though the H i and stellar masses of the sources are similar. We show that UGC 8245 shares similar physical properties with other well-studied low-mass galaxies, while UGC 11411 is more highly dark matter dominated. Both systems have negative peculiar velocities that are associated with a coherent flow of nearby galaxies at high supergalactic latitude.« less

Precise stellar surface gravities from the time scales of convectively driven brightness variations

PubMed Central

Kallinger, Thomas; Hekker, Saskia; García, Rafael A.; Huber, Daniel; Matthews, Jaymie M.

2016-01-01

A significant part of the intrinsic brightness variations in cool stars of low and intermediate mass arises from surface convection (seen as granulation) and acoustic oscillations (p-mode pulsations). The characteristics of these phenomena are largely determined by the stars’ surface gravity (g). Detailed photometric measurements of either signal can yield an accurate value of g. However, even with ultraprecise photometry from NASA’s Kepler mission, many stars are too faint for current methods or only moderate accuracy can be achieved in a limited range of stellar evolutionary stages. This means that many of the stars in the Kepler sample, including exoplanet hosts, are not sufficiently characterized to fully describe the sample and exoplanet properties. We present a novel way to measure surface gravities with accuracies of about 4%. Our technique exploits the tight relation between g and the characteristic time scale of the combined granulation and p-mode oscillation signal. It is applicable to all stars with a convective envelope, including active stars. It can measure g in stars for which no other analysis is now possible. Because it depends on the time scale (and no other properties) of the signal, our technique is largely independent of the type of measurement (for example, photometry or radial velocity measurements) and the calibration of the instrumentation used. However, the oscillation signal must be temporally resolved; thus, it cannot be applied to dwarf stars observed by Kepler in its long-cadence mode. PMID:26767193

Precise stellar surface gravities from the time scales of convectively driven brightness variations.

PubMed

Kallinger, Thomas; Hekker, Saskia; García, Rafael A; Huber, Daniel; Matthews, Jaymie M

2016-01-01

A significant part of the intrinsic brightness variations in cool stars of low and intermediate mass arises from surface convection (seen as granulation) and acoustic oscillations (p-mode pulsations). The characteristics of these phenomena are largely determined by the stars' surface gravity (g). Detailed photometric measurements of either signal can yield an accurate value of g. However, even with ultraprecise photometry from NASA's Kepler mission, many stars are too faint for current methods or only moderate accuracy can be achieved in a limited range of stellar evolutionary stages. This means that many of the stars in the Kepler sample, including exoplanet hosts, are not sufficiently characterized to fully describe the sample and exoplanet properties. We present a novel way to measure surface gravities with accuracies of about 4%. Our technique exploits the tight relation between g and the characteristic time scale of the combined granulation and p-mode oscillation signal. It is applicable to all stars with a convective envelope, including active stars. It can measure g in stars for which no other analysis is now possible. Because it depends on the time scale (and no other properties) of the signal, our technique is largely independent of the type of measurement (for example, photometry or radial velocity measurements) and the calibration of the instrumentation used. However, the oscillation signal must be temporally resolved; thus, it cannot be applied to dwarf stars observed by Kepler in its long-cadence mode.

Stellar Streams Discovered in the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shipp, N.; et al.

We perform a search for stellar streams around the Milky Way using the first three years of multi-band optical imaging data from the Dark Energy Survey (DES). We use DES data coveringmore » $$\\sim 5000$$ sq. deg. to a depth of $g > 23.5$ with a relative photometric calibration uncertainty of $$< 1 \\%$$. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of $$\\sim 50$$ kpc. We search for stellar streams using a matched-filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of eleven new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extra-tidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, as well as the large- and small-scale distribution of dark matter around the Milky Way.« less

OUTER-DISK POPULATIONS IN NGC 7793: EVIDENCE FOR STELLAR RADIAL MIGRATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radburn-Smith, David J.; Dalcanton, Julianne J.; Roskar, Rok

2012-07-10

We analyzed the radial surface brightness profile of the spiral galaxy NGC 7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image across the disk break. We used the photometry of resolved stars to select distinct populations covering a wide range of stellar ages. We found breaks in the radial profiles of all stellar populations at 280'' ({approx}5.1 kpc). Beyond this disk break, the profiles become steeper for younger populations. This same trend is seen in numerical simulations where the outer disk is formed almost entirely by radial migration. We also found that the older stars ofmore » NGC 7793 extend significantly farther than the underlying H I disk. They are thus unlikely to have formed entirely at their current radii, unless the gas disk was substantially larger in the past. These observations thus provide evidence for substantial stellar radial migration in late-type disks.« less

The HST Frontier Field MACS 1159.5+2223: Flanking Observations for Intracluster Light

NASA Astrophysics Data System (ADS)

Gonzalez, Anthony

2017-08-01

We propose a 6 orbit WFC3/IR imaging program targeting the environs of the HST Frontier Field cluster MACS 1149.5+2223 to obtain a comprehensive view of the intracluster stellar population in a massive galaxy cluster. WFC3/IR enables a vast improvement over ground-based studies in mapping emission from diffuse stellar populations. Our proposed observations are designed to build upon the existing investment in the Frontier Fields to conduct a new, more complete census of the intracluster light (ICL) extending out to 750 kpc. The requested observations are constructed to span the gap between the primary and parallel HFF pointings, detecting ICL to a surface brightness of 29.5 mag per square arcsec in F160W (equivalent to 31.5 mag per square arcsec in V-band). This depth is sufficient to trace the radial ICL profile out to 750 kpc from the BCG. These data will also yield a high-fidelity calibration of the background sky level, enabling two-dimensional mapping of the distribution and color of intracluster light down to 27 mag per square arcsec in F160W. From these maps we will quantify spatial variation in the ratio of the stellar baryons to the ICM, establishing whether the observed low scatter in the global ratio masks underlying smaller scale inhomogeneities due to astrophysical processes in the cluster. The requested observations further serve as a pilot program, enabling future similar analyses with the full ensemble of HFF clusters, and developing techniques that will be required for such low surface brightness programs with upcoming facilities including Euclid and WFIRST.

The origin of ultra diffuse galaxies: stellar feedback and quenching

NASA Astrophysics Data System (ADS)

Chan, T. K.; Kereš, D.; Wetzel, A.; Hopkins, P. F.; Faucher-Giguère, C.-A.; El-Badry, K.; Garrison-Kimmel, S.; Boylan-Kolchin, M.

2018-05-01

We test if the cosmological zoom-in simulations of isolated galaxies from the FIRE project reproduce the properties of ultra diffuse galaxies (UDGs). We show that outflows that dynamically heat galactic stars, together with a passively aging stellar population after imposed quenching, naturally reproduce the observed population of red UDGs, without the need for high spin halos, or dynamical influence from their host cluster. We reproduce the range of surface brightness, radius and absolute magnitude of the observed red UDGs by quenching simulated galaxies at a range of different times. They represent a mostly uniform population of dark matter-dominated dwarf galaxies with M* ˜ 108 M⊙, low metallicity and a broad range of ages; the more massive the UDGs, the older they are. The most massive red UDG in our sample (M* ˜ 3 × 108M⊙) requires quenching at z ˜ 3 when its halo reached Mh ˜ 1011 M⊙. Our simulated UDGs form with normal stellar-to-halo ratios and match the central enclosed masses and the velocity dispersions of the observed UDGs. Enclosed masses remain largely fixed across a broad range of quenching times because the central regions of their dark matter halos complete their growth early. If our simulated dwarfs are not quenched, they evolve into bluer low-surface brightness galaxies with M/L similar to observed field dwarfs. While our simulation sample covers a limited range of formation histories and halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy type around M* ˜ 108 M⊙, both in the field and in clusters.

The origin of ultra diffuse galaxies: stellar feedback and quenching

NASA Astrophysics Data System (ADS)

Chan, T. K.; Kereš, D.; Wetzel, A.; Hopkins, P. F.; Faucher-Giguère, C.-A.; El-Badry, K.; Garrison-Kimmel, S.; Boylan-Kolchin, M.

2018-07-01

We test if the cosmological zoom-in simulations of isolated galaxies from the FIRE project reproduce the properties of ultra diffuse galaxies (UDGs). We show that outflows that dynamically heat galactic stars, together with a passively aging stellar population after imposed quenching, naturally reproduce the observed population of red UDGs, without the need for high spin haloes, or dynamical influence from their host cluster. We reproduce the range of surface brightness, radius, and absolute magnitude of the observed red UDGs by quenching simulated galaxies at a range of different times. They represent a mostly uniform population of dark matter-dominated dwarf galaxies with M* ˜ 108 M⊙, low metallicity, and a broad range of ages; the more massive the UDGs, the older they are. The most massive red UDG in our sample (M* ˜ 3 × 108 M⊙) requires quenching at z ˜ 3 when its halo reached Mh ˜ 1011 M⊙. Our simulated UDGs form with normal stellar-to-halo ratios and match the central enclosed masses and the velocity dispersions of the observed UDGs. Enclosed masses remain largely fixed across a broad range of quenching times because the central regions of their dark matter haloes complete their growth early. If our simulated dwarfs are not quenched, they evolve into bluer low surface brightness galaxies with M/L similar to observed field dwarfs. While our simulation sample covers a limited range of formation histories and halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy type around M* ˜ 108 M⊙, both in the field and in clusters.

The far-ultraviolet emission spectrum of the K2 III star, Arcturus.

NASA Technical Reports Server (NTRS)

Moos, H. W.; Rottman, G. J.

1972-01-01

A moderate-resolution far-ultraviolet spectrum of the K2 IIIp star Arcturus, obtained with a rocket-borne spectrometer, shows chromospheric emission features. Hydrogen L-alpha and O I (1303 A) are clearly identified. The O I (1304 A) stellar surface brightness is as great or greater than that of the sun. Other metal lines, including those of carbon, are weak compared to the O I line.

(Almost) Dark Galaxies in the ALFALFA Survey: Isolated H I-bearing Ultra-diffuse Galaxies

NASA Astrophysics Data System (ADS)

Leisman, Lukas; Haynes, Martha P.; Janowiecki, Steven; Hallenbeck, Gregory; Józsa, Gyula; Giovanelli, Riccardo; Adams, Elizabeth A. K.; Bernal Neira, David; Cannon, John M.; Janesh, William F.; Rhode, Katherine L.; Salzer, John J.

2017-06-01

We present a sample of 115 very low optical surface brightness, highly extended, H I-rich galaxies carefully selected from the ALFALFA survey that have similar optical absolute magnitudes, surface brightnesses, and radii to recently discovered “ultra-diffuse” galaxies (UDGs). However, these systems are bluer and have more irregular morphologies than other UDGs, are isolated, and contain significant reservoirs of H I. We find that while these sources have normal star formation rates for H I-selected galaxies of similar stellar mass, they have very low star formation efficiencies. We further present deep optical and H I-synthesis follow-up imaging of three of these H I-bearing ultra-diffuse sources. We measure H I diameters extending to ˜40 kpc, but note that while all three sources have large H I diameters for their stellar mass, they are consistent with the H I mass-H I radius relation. We further analyze the H I velocity widths and rotation velocities for the unresolved and resolved sources, respectively, and find that the sources appear to inhabit halos of dwarf galaxies. We estimate spin parameters, and suggest that these sources may exist in high spin parameter halos, and as such may be potential H I-rich progenitors to the ultra-diffuse galaxies observed in cluster environments.

The Star-forming Main Sequence of Dwarf Low Surface Brightness Galaxies

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.; Schombert, James M.; Lelli, Federico

2017-12-01

We explore the star-forming properties of late-type, low surface brightness (LSB) galaxies. The star-forming main sequence ({SFR}-{M}* ) of LSB dwarfs has a steep slope, indistinguishable from unity (1.04 ± 0.06). They form a distinct sequence from more massive spirals, which exhibit a shallower slope. The break occurs around {M}* ≈ {10}10 {M}⊙ , and can also be seen in the gas mass—stellar mass plane. The global Kennicutt-Schmidt law ({SFR}-{M}g) has a slope of 1.47 ± 0.11 without the break seen in the main sequence. There is an ample supply of gas in LSB galaxies, which have gas depletion times well in excess of a Hubble time, and often tens of Hubble times. Only ˜ 3 % of this cold gas needs be in the form of molecular gas to sustain the observed star formation. In analogy with the faint, long-lived stars of the lower stellar main sequence, it may be appropriate to consider the main sequence of star-forming galaxies to be defined by thriving dwarfs (with {M}* < {10}10 {M}⊙ ), while massive spirals (with {M}* > {10}10 {M}⊙ ) are weary giants that constitute more of a turn-off population.

Star-forming galaxies in intermediate-redshift clusters: stellar versus dynamical masses of luminous compact blue galaxies

NASA Astrophysics Data System (ADS)

Randriamampandry, S. M.; Crawford, S. M.; Bershady, M. A.; Wirth, G. D.; Cress, C. M.

2017-10-01

We investigate the stellar masses of the class of star-forming objects known as luminous compact blue galaxies (LCBGs) by studying a sample of galaxies in the distant cluster MS 0451.6-0305 at z ≈ 0.54 with ground-based multicolour imaging and spectroscopy. For a sample of 16 spectroscopically confirmed cluster LCBGs (colour B - V < 0.5, surface brightness μB < 21 mag arcsec-2 and magnitude MB < -18.5), we measure stellar masses by fitting spectral energy distribution (SED) models to multiband photometry, and compare with dynamical masses [determined from velocity dispersion in the range 10 < σv(km s- 1) < 80] we previously obtained from their emission-line spectra. We compare two different stellar population models that measure stellar mass in star-bursting galaxies, indicating correlations between the stellar age, extinction and stellar mass derived from the two different SED models. The stellar masses of cluster LCBGs are distributed similarly to those of field LCBGs, but the cluster LCBGs show lower dynamical-to-stellar mass ratios (Mdyn/M⋆ = 2.6) than their field LCBG counterparts (Mdyn/M⋆ = 4.8), echoing trends noted previously in low-redshift dwarf elliptical galaxies. Within this limited sample, the specific star formation rate declines steeply with increasing mass, suggesting that these cluster LCBGs have undergone vigorous star formation.

WHERE ARE THE FOSSILS OF THE FIRST GALAXIES? II. TRUE FOSSILS, GHOST HALOS, AND THE MISSING BRIGHT SATELLITES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bovill, Mia S.; Ricotti, Massimo, E-mail: msbovill@astro.umd.edu

We use a new set of cold dark matter simulations of the local universe to investigate the distribution of fossils of primordial dwarf galaxies within and around the Milky Way. Throughout, we build upon previous results showing agreement between the observed stellar properties of a subset of the ultra-faint dwarfs and our simulated fossils. Here, we show that fossils of the first galaxies have galactocentric distributions and cumulative luminosity functions consistent with observations. In our model, we predict {approx}300 luminous satellites orbiting the Milky Way, 50%-70% of which are well-preserved fossils. Within the Milky Way virial radius, the majority ofmore » these fossils have luminosities L{sub V} < 10{sup 6} L{sub sun}. Despite our multidimensional agreement with observations at low masses and luminosities, the primordial model produces an overabundance of bright dwarf satellites (L{sub V} > 10{sup 4} L{sub sun}) with respect to observations where observations are nearly complete. The 'bright satellite problem' is most evident in the outer parts of the Milky Way. We estimate that, although relatively bright, the primordial stellar populations are very diffuse, producing a population with surface brightnesses below surveys' detection limits, and are easily stripped by tidal forces. Although we cannot yet present unmistakable evidence for the existence of the fossils of first galaxies in the Local Group, the results of our studies suggest observational strategies that may demonstrate their existence: (1) the detection of 'ghost halos' of primordial stars around isolated dwarfs would prove that stars formed in minihalos (M < 10{sup 8} M{sub sun}) before reionization and strongly suggest that at least a fraction of the ultra-faint dwarfs are fossils of the first galaxies; and (2) the existence of a yet unknown population of {approx}150 Milky Way ultra-faints with half-light radii r{sub hl} {approx} 100-1000 pc and luminosities L{sub V} < 10{sup 4} L{sub sun}, detectable by future deep surveys. These undetected dwarfs would have the mass-to-light ratios, stellar velocity dispersions, and metallicities predicted in this work.« less

Are solar brightness variations faculae- or spot-dominated?

NASA Astrophysics Data System (ADS)

Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Yeo, K. L.; Schmutz, W. K.

2016-05-01

Context. Regular spaceborne measurements have revealed that solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims: To understand whether the broader pattern of stellar variations is consistent with the solar paradigm, we assess relative contributions of faculae and spots to solar magnetically-driven brightness variability. We investigate how the solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods: We performed calculations with the SATIRE model, which returns solar brightness with daily cadence from solar disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results: Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Strömgren (b + y)/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year solar variability in the Strömgren (b + y)/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions: The rotational solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about I = 45°. Over the course of the 11-year activity cycle, the solar brightness variability is faculae-dominated shortwards of 1.2 μm independently of the inclination.

Cosmic Chandlery with thermonuclear supernovae

DOE PAGES

Calder, Alan C.; Krueger, Brendan K.; Jackson, A. P.; ...

2017-05-30

Thermonuclear (Type Ia) supernovae are bright stellar explosions, the light curves of which can be calibrated to allow for use as "standard candles" for measuring cosmological distances. Contemporary research investigates how the brightness of an event may be influenced by properties of the progenitor system that follow from properties of the host galaxy such as composition and age. The goals are to better understand systematic effects and to assess the intrinsic scatter in the brightness, thereby reducing uncertainties in cosmological studies. We present the results from ensembles of simulations in the single-degenerate paradigm addressing the influence of age and metallicitymore » on the brightness of an event and compare our results to observed variations of brightness that correlate with properties of the host galaxy. As a result, we also present results from "hybrid" progenitor models that incorporate recent advances in stellar evolution.« less

Modelling Solar and Stellar Brightness Variabilities

NASA Astrophysics Data System (ADS)

Yeo, K. L.; Shapiro, A. I.; Krivova, N. A.; Solanki, S. K.

2016-04-01

Total and spectral solar irradiance, TSI and SSI, have been measured from space since 1978. This is accompanied by the development of models aimed at replicating the observed variability by relating it to solar surface magnetism. Despite significant progress, there remains persisting controversy over the secular change and the wavelength-dependence of the variation with impact on our understanding of the Sun's influence on the Earth's climate. We highlight the recent progress in TSI and SSI modelling with SATIRE. Brightness variations have also been observed for Sun-like stars. Their analysis can profit from knowledge of the solar case and provide additional constraints for solar modelling. We discuss the recent effort to extend SATIRE to Sun-like stars.

Automated detection of very Low Surface Brightness galaxies in the Virgo Cluster

NASA Astrophysics Data System (ADS)

Prole, D. J.; Davies, J. I.; Keenan, O. C.; Davies, L. J. M.

2018-04-01

We report the automatic detection of a new sample of very low surface brightness (LSB) galaxies, likely members of the Virgo cluster. We introduce our new software, DeepScan, that has been designed specifically to detect extended LSB features automatically using the DBSCAN algorithm. We demonstrate the technique by applying it over a 5 degree2 portion of the Next-Generation Virgo Survey (NGVS) data to reveal 53 low surface brightness galaxies that are candidate cluster members based on their sizes and colours. 30 of these sources are new detections despite the region being searched specifically for LSB galaxies previously. Our final sample contains galaxies with 26.0 ≤ ⟨μe⟩ ≤ 28.5 and 19 ≤ mg ≤ 21, making them some of the faintest known in Virgo. The majority of them have colours consistent with the red sequence, and have a mean stellar mass of 106.3 ± 0.5M⊙ assuming cluster membership. After using ProFit to fit Sérsic profiles to our detections, none of the new sources have effective radii larger than 1.5 Kpc and do not meet the criteria for ultra-diffuse galaxy (UDG) classification, so we classify them as ultra-faint dwarfs.

On the fundamental properties of dynamically hot galaxies

NASA Astrophysics Data System (ADS)

Kritsuk, Alexei G.

1997-01-01

A two-component isothermal equilibrium model is applied to reproduce basic structural properties of dynamically hot stellar systems immersed in their massive dark haloes. The origin of the fundamental plane relation for giant ellipticals is naturally explained as a consequence of dynamical equilibrium in the context of the model. The existence of two galactic families displaying different behaviour in the luminosity-surface-brightness diagram is shown to be a result of a smooth transition from dwarfs, dominated by dark matter near the centre, to giants dominated by the luminous stellar component. The comparison of empirical scaling relations with model predictions suggests that probably a unique dissipative process was operating during the violent stage of development of stellar systems in the dark haloes, and the depth of the potential well controlled the observed luminosity of the resulting galaxies. The interpretation also provides some restrictions on the properties of dark haloes implied by the fundamental scaling laws.

Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps

NASA Astrophysics Data System (ADS)

Huang, Po-Chieh; Chen, Wen-Ping; Hu, Chia-Ling; Burkhonov, Otabek; Ehgamberdiev, Shuhrat; Liu, Jinzhong; Naito, Hiroyuki; Pakstiene, Erika; Qvam, Jan Kare Trandem; Rätz, Stefanie; Semkov, Evgeni

2018-04-01

UX Orionis stars are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such an UX Orionis star in the young (∼ 4 Myr) open cluster Trumpler 37 at ∼ 900 pc, showing a prominent infrared access, H-alpha emission, and flare activity. Our multi-color photometric monitoring from 2009 to 2016 showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) cyclic, but not strictly periodical, occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual "blueing" phenomena near the brightness minima, during which the star appeared bluer when dimmer, and (v) a noticeable polarization, from 3 to 9 percent in g', r', and i' -bands. The occultation events may be caused by dust clumps, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. The level of polarization was anti-correlated with the brightness in the bright state, when the dust clump backscattered stellar light. We discussed two potential hypotheses: orbiting dust clumps versus dust clumps along a spiral arm structure.

Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903

NASA Technical Reports Server (NTRS)

Alonso-Herrero, A.; Ryder, S. D.; Knapen, J. H.

1994-01-01

We present high-resolution near-infrared imaging obtained using adaptive optics and HST/NICMOS and ground-based spectroscopy of the hot-spot galaxy NGC 2903. Our near-infrared resolution imaging enables us to resolve the infrared hot spots into individual young stellar clusters or groups of these. The spatial distribution of the stellar clusters is not coincident with that of the bright H II regions, as revealed by the HST/NICMOS Pace image. Overall, the circumnuclear star formation in NGC 2903 shows a ring-like morphology with an approximate diameter of 625 pc. The SF properties of the stellar clusters and H II regions have been studied using the photometric and spectroscopic information in conjunction with evolutionary synthesis models. The population of bright stellar clusters shows a very narrow range of ages, 4 to 7 x 10(exp 6) yr after the peak of star formation, or absolute ages 6.5 to 9.5 x 10(exp 6) yr (for the assumed short-duration Gaussian bursts), and luminosities similar to the clusters found in the Antennae interacting galaxy. This population of young stellar clusters accounts for some 7 - 12% of the total stellar mass in the central 625 pc of NGC 2903. The H II regions in the ring of star formation have luminosities close to that of the super-giant H II region 30 Doradus, they are younger than the stellar clusters, and will probably evolve into bright infrared stellar clusters similar to those observed today. We find that the star formation efficiency in the central regions of NGC 2903 is higher than in normal galaxies, approaching the lower end of infrared luminous galaxies.

Formation of S0 galaxies through mergers. Antitruncated stellar discs resulting from major mergers

NASA Astrophysics Data System (ADS)

Borlaff, Alejandro; Eliche-Moral, M. Carmen; Rodríguez-Pérez, Cristina; Querejeta, Miguel; Tapia, Trinidad; Pérez-González, Pablo G.; Zamorano, Jaime; Gallego, Jesús; Beckman, John

2014-10-01

Context. Lenticular galaxies (S0s) are more likely to host antitruncated (Type III) stellar discs than galaxies of later Hubble types. Major mergers are popularly considered too violent to make these breaks. Aims: We have investigated whether major mergers can result into S0-like remnants with realistic antitruncated stellar discs or not. Methods: We have analysed 67 relaxed S0 and E/S0 remnants resulting from dissipative N-body simulations of major mergers from the GalMer database. We have simulated realistic R-band surface brightness profiles of the remnants to identify those with antitruncated stellar discs. Their inner and outer discs and the breaks have been quantitatively characterized to compare with real data. Results: Nearly 70% of our S0-like remnants are antitruncated, meaning that major mergers that result in S0s have a high probability of producing Type III stellar discs. Our remnants lie on top of the extrapolations of the observational trends (towards brighter magnitudes and higher break radii) in several photometric diagrams, because of the higher luminosities and sizes of the simulations compared to observational samples. In scale-free photometric diagrams, simulations and observations overlap and the remnants reproduce the observational trends, so the physical mechanism after antitruncations is highly scalable. We have found novel photometric scaling relations between the characteristic parameters of the antitruncations in real S0s, which are also reproduced by our simulations. We show that the trends in all the photometric planes can be derived from three basic scaling relations that real and simulated Type III S0s fulfill: hi ∝ RbrkIII, ho ∝ RbrkIII, and μbrkIII ∝ RbrkIII, where hi and ho are the scalelengths of the inner and outer discs, and μbrkIII and RbrkIII are the surface brightness and radius of the breaks. Bars and antitruncations in real S0s are structurally unrelated phenomena according to the studied photometric planes. Conclusions: Major mergers provide a feasible mechanism to form realistic antitruncated S0 galaxies. Table 3 is available in electronic form at http://www.aanda.org

The Tolman Surface Brightness Test for the Reality of the Expansion. III. Hubble Space Telescope Profile and Surface Brightness Data for Early-Type Galaxies in Three High-Redshift Clusters

NASA Astrophysics Data System (ADS)

Lubin, Lori M.; Sandage, Allan

2001-09-01

Photometric data for 34 early-type galaxies in the three high-redshift clusters Cl 1324+3011 (z=0.76), Cl 1604+4304 (z=0.90), and Cl 1604+4321 (z=0.92), observed with the Hubble Space Telescope (HST) and with the Keck 10 m telescopes by Oke, Postman, & Lubin, are analyzed to obtain the photometric parameters of mean surface brightness, magnitudes for the growth curves, and angular radii at various Petrosian η radii. The angular radii at η=1.3 mag for the program galaxies are all larger than 0.24". All the galaxies are well resolved at this angular size using HST, whose point-spread function is 0.05", half-width at half-maximum. The data for each of the program galaxies are listed at η=1.0, 1.3, 1.5, 1.7, and 2.0 mag. They are corrected by color equations and K-terms for the effects of redshift to the rest-frame Cape/Cousins I for Cl 1324+3011 and Cl 1604+4304 and R for Cl 1604+4321. The K-corrections are calculated from synthetic spectral energy distributions derived from evolving stellar population models of Bruzual & Charlot, that have been fitted to the observed broadband (BVRI) AB magnitudes of each program galaxy. The listed photometric data are independent of all cosmological parameters. They are the source data for the Tolman surface brightness test made in Paper IV.

Interaction effects on galaxy pairs with Gemini/GMOS- III: stellar population synthesis

NASA Astrophysics Data System (ADS)

Krabbe, A. C.; Rosa, D. A.; Pastoriza, M. G.; Hägele, G. F.; Cardaci, M. V.; Dors, O. L., Jr.; Winge, C.

2017-05-01

We present an observational study of the impacts of interactions on the stellar population in a sample of galaxy pairs. Long-slit spectra in the wavelength range 3440-7300 Å obtained with the Gemini Multi-Object Spectrograph (GMOS) at Gemini South for 15 galaxies in nine close pairs were used. The spatial distributions of the stellar population contributions were obtained using the stellar population synthesis code starlight. Taking into account the different contributions to the emitted light, we found that most of the galaxies in our sample are dominated by young/intermediate stellar populations. This result differs from the one derived for isolated galaxies, where the old stellar population dominates the disc surface brightness. We interpreted such different behaviour as being due to the effect of gas inflows along the discs of interacting galaxies on the star formation over a time-scale of the order of about 2 Gyr. We also found that, in general, the secondary galaxy of a pair has a higher contribution from the young stellar population than the primary one. We compared the estimated values of stellar and nebular extinction derived from the synthesis method and the Hα/Hβ emission-line ratio, finding that nebular extinctions are systematically higher than stellar ones by about a factor of 2. We did not find any correlation between nebular and stellar metallicities. Neither did we find a correlation between stellar metallicities and ages, while a positive correlation between nebular metallicities and stellar ages was obtained, with older regions being the most metal-rich.

Invited Talk: Photometry of Bright Variable Stars with the BRITE Constellation Nano-Satellites: Opportunities for Amateur Astronomers

NASA Astrophysics Data System (ADS)

Guinan, E. F.

2014-06-01

(Abstract only) The BRIght Target Explorer (BRITE) is a joint Austrian-Canadian-Polish Astronomy mission to carry out high precision photometry of bright (mv < 4 mag.) variable stars. BRITE consists of a "Constellation" of 20 × 20 × 20-cm nano-satellite cubes equipped with wide field (20 × 24 deg.) CCD cameras, control systems, solar panels, onboard computers, and so on. The first two (of up to six) satellites were successfully launched during February 2013. After post-launch commissioning, science operations commenced during October 2013. The primary goals are to carry out continuous multi-color (currently blue and red filters) high-precision millimag (mmag) photometry in particular locations in the sky. Typically these pointings will last for two to four months and secure simultaneous blue/red photometry of bright variable stars within the field. The first science pointing is centered on the Orion region. Since most bright stars are intrinsically luminous, hot O/B stars, giants, and supergiants will be the most common targets. However, some bright eclipsing binaries (such as Algol, b Lyr, e Aur) and a few chromospherically-active RS CVn stars (such as Capella) may be eventually be monitored. The BRITE-Constellation program of high precision, two color photometry of bright stars offers a great opportunity to study a wide range of stellar astrophysical problems. Bright stars offer convenient laboratories to study many current and important problems in stellar astrophysics. These include probing stellar interiors and pulsation in pulsating stars, tests of stellar evolution and structure for Cepheids and other luminous stars. To scientifically enhance the BRITE science returns, the BRITE investigators are very interested in securing contemporaneous ground-based spectroscopy and standardized photometry of target stars. The BRITE Ground Based Observations Team is coordinating ground-based observing efforts for BRITE targets. The team helps coordinate collaborations with amateur and professional astronomer. The ground-based coordinators are: Thomas Eversberg (thomas.eversberg@dlr.de) and, for spectroscopy, Contanze Zwintz (konstanze@ster.kuleuven.be). Detailed information about the BRITE Mission is provided at: www.brite-contellation.at.

Stellar populations in the dwarf elliptical galaxy NGC 185

NASA Technical Reports Server (NTRS)

Lee, Myung G.; Freedman, Wendy L.; Madore, Barry F.

1993-01-01

The study presents BVRI CCD photometry of about 5300 stars in the central area of the dwarf elliptical galaxy NGC 185 in the Local Group. The color-magnitude diagram shows three distinct stellar populations: a dominant RGB population, AGB stars located above the tip of the RGB stars, and a small number of young stars having blue to yellow colors. The foreground reddening is estimated to be 0.19 +/- 0.03 mag using the (B - V) - (V - I) diagram for the bright foreground stars with good photometry. Surface photometry of the central area of NGC 185 is presented; it shows that the colors become rapidly bluer inside R of about 10 arcsec. Structural parameters indicate that the mass-to-luminosity ratio ranges from 3 to 5.

An Ultraviolet and Near-Infrared View of NGC 4214: A Starbursting Core Embedded in a Low Surface Brightness Disk

NASA Astrophysics Data System (ADS)

Fanelli, Michael N.; Waller, William W.; Smith, Denise A.; Freedman, Wendy L.; Madore, Barry; Neff, Susan G.; O'Connell, Robert W.; Roberts, Morton S.; Bohlin, Ralph; Smith, Andrew M.; Stecher, Theodore P.

1997-05-01

During the Astro-2 Spacelab mission in 1995 March, the Ultraviolet Imaging Telescope (UIT) obtained far-UV (λ = 1500 Å) imagery of the nearby Sm/Im galaxy NGC 4214. The UIT images have a spatial resolution of ~3" and a limiting surface brightness, μ1500 > 25 mag arcsec-2, permitting detailed investigation of the intensity and spatial distribution of the young, high-mass stellar component. These data provide the first far-UV imagery covering the full spatial extent of NGC 4214. Comparison with a corresponding I-band image reveals the presence of a starbursting core embedded in an extensive low surface brightness disk. In the far-UV (FUV), NGC 4214 is resolved into several components: a luminous, central knot; an inner region (r <~ 2.5 kpc) with ~15 resolved sources embedded in bright, diffuse emission; and a population of fainter knots extending to the edge of the optically defined disk (r ~ 5 kpc). The FUV light, which traces recent massive star formation, is observed to be more centrally concentrated than the I-band light, which traces the global stellar population. The FUV radial light profile is remarkably well represented by an R1/4 law, providing evidence that the centrally concentrated massive star formation in NGC 4214 is the result of an interaction, possibly a tidal encounter, with a dwarf companion(s). The brightest FUV source produces ~8% of the global FUV luminosity. This unresolved source, corresponding to the Wolf-Rayet knot described by Sargent & Filippenko, is located at the center of the FUV light distribution, giving NGC 4214 an active galactic nucleus-like morphology. Another strong source is present in the I band, located 19" west, 10" north of the central starburst knot, with no FUV counterpart. The I-band source may be the previously unrecognized nucleus of NGC 4214 or an evolved star cluster with an age greater than ~200 Myr. The global star formation rate derived from the total FUV flux is consistent with rates derived using data at other wavelengths and lends support to the scenario of roughly constant star formation during the last few hundred million years at a level significantly enhanced relative to the lifetime averaged star formation rate. The hybrid disk/starburst-irregular morphology evident in NGC 4214 emphasizes the danger of classifying galaxies based on their high surface brightness components at any particular wavelength.

Solo dwarfs I: survey introduction and first results for the Sagittarius dwarf irregular galaxy

NASA Astrophysics Data System (ADS)

Higgs, C. R.; McConnachie, A. W.; Irwin, M.; Bate, N. F.; Lewis, G. F.; Walker, M. G.; Côté, P.; Venn, K.; Battaglia, G.

2016-05-01

We introduce the Solitary Local dwarfs survey (Solo), a wide-field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multiband imaging from Canada-France-Hawaii Telescope/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than MV ≃ -18 situated beyond the nominal virial radius of the Milky Way and M31 (≳300 kpc) are included in this volume-limited sample, for a total of 42 targets. In addition to reviewing the survey goals and strategy, we present results for the Sagittarius dwarf irregular galaxy (Sag DIG), one of the most isolated, low-mass galaxies, located at the edge of the Local Group. We analyse its resolved stellar populations and their spatial distributions. We provide updated estimates of its central surface brightness and integrated luminosity, and trace its surface brightness profile to a level fainter than 30 mag arcsec-2. Sag DIG is well described by a highly elliptical (disc-like) system following a single component Sérsic model. However, a low-level distortion is present at the outer edges of the galaxy that, were Sag DIG not so isolated, would likely be attributed to some kind of previous tidal interaction. Further, we find evidence of an extremely low level, extended distribution of stars beyond ˜5 arcmin (>1.5 kpc) that suggests Sag DIG may be embedded in a very low-density stellar halo. We compare the stellar and H I structures of Sag DIG, and discuss results for this galaxy in relation to other isolated, dwarf irregular galaxies in the Local Group.

VizieR Online Data Catalog: SDSS bulge, disk and total stellar mass estimates (Mendel+, 2014)

NASA Astrophysics Data System (ADS)

Mendel, J. T.; Simard, L.; Palmer, M.; Ellison, S. L.; Patton, D. R.

2014-01-01

We present a catalog of bulge, disk, and total stellar mass estimates for ~660000 galaxies in the Legacy area of the Sloan Digital Sky Survey Data (SDSS) Release 7. These masses are based on a homogeneous catalog of g- and r-band photometry described by Simard et al. (2011, Cat. J/ApJS/196/11), which we extend here with bulge+disk and Sersic profile photometric decompositions in the SDSS u, i, and z bands. We discuss the methodology used to derive stellar masses from these data via fitting to broadband spectral energy distributions (SEDs), and show that the typical statistical uncertainty on total, bulge, and disk stellar mass is ~0.15 dex. Despite relatively small formal uncertainties, we argue that SED modeling assumptions, including the choice of synthesis model, extinction law, initial mass function, and details of stellar evolution likely contribute an additional 60% systematic uncertainty in any mass estimate based on broadband SED fitting. We discuss several approaches for identifying genuine bulge+disk systems based on both their statistical likelihood and an analysis of their one-dimensional surface-brightness profiles, and include these metrics in the catalogs. Estimates of the total, bulge and disk stellar masses for both normal and dust-free models and their uncertainties are made publicly available here. (4 data files).

The mysterious age invariance of the planetary nebula luminosity function bright cut-off

NASA Astrophysics Data System (ADS)

Gesicki, K.; Zijlstra, A. A.; Miller Bertolami, M. M.

2018-05-01

Planetary nebulae mark the end of the active life of 90% of all stars. They trace the transition from a red giant to a degenerate white dwarf. Stellar models1,2 predicted that only stars above approximately twice the solar mass could form a bright nebula. But the ubiquitous presence of bright planetary nebulae in old stellar populations, such as elliptical galaxies, contradicts this: such high-mass stars are not present in old systems. The planetary nebula luminosity function, and especially its bright cut-off, is almost invariant between young spiral galaxies, with high-mass stars, and old elliptical galaxies, with only low-mass stars. Here, we show that new evolutionary tracks of low-mass stars are capable of explaining in a simple manner this decades-old mystery. The agreement between the observed luminosity function and computed stellar evolution validates the latest theoretical modelling. With these models, the planetary nebula luminosity function provides a powerful diagnostic to derive star formation histories of intermediate-age stars. The new models predict that the Sun at the end of its life will also form a planetary nebula, but it will be faint.

Blue diffuse dwarf galaxies: a clearer picture

NASA Astrophysics Data System (ADS)

James, Bethan L.; Koposov, Sergey E.; Stark, Daniel P.; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.; McQuinn, Kristen B. W.

2017-03-01

The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), I.e. galaxies with <1/10 solar metallicity. However, due to the bright emission-line-based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ˜150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43 < 12 + log(O/H) < 8.01), with ˜20 per cent of our sample classified as being XMP galaxies, and find that they are actively forming stars at rates of ˜1-33 × 10-2 M⊙ yr-1 in H II regions randomly embedded in a blue, low-surface-brightness continuum. Stellar masses are calculated from population synthesis models and estimated to be in the range log (M*/M⊙) ≃ 5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.

Stellar mass distribution of S4G disk galaxies and signatures of bar-induced secular evolution

NASA Astrophysics Data System (ADS)

Díaz-García, S.; Salo, H.; Laurikainen, E.

2016-12-01

Context. Models of galaxy formation in a cosmological framework need to be tested against observational constraints, such as the average stellar density profiles (and their dispersion) as a function of fundamental galaxy properties (e.g. the total stellar mass). Simulation models predict that the torques produced by stellar bars efficiently redistribute the stellar and gaseous material inside the disk, pushing it outwards or inwards depending on whether it is beyond or inside the bar corotation resonance radius. Bars themselves are expected to evolve, getting longer and narrower as they trap particles from the disk and slow down their rotation speed. Aims: We use 3.6 μm photometry from the Spitzer Survey of Stellar Structure in Galaxies (S4G) to trace the stellar distribution in nearby disk galaxies (z ≈ 0) with total stellar masses 108.5 ≲ M∗/M⊙ ≲ 1011 and mid-IR Hubble types - 3 ≤ T ≤ 10. We characterize the stellar density profiles (Σ∗), the stellar contribution to the rotation curves (V3.6 μm), and the m = 2 Fourier amplitudes (A2) as a function of M∗ and T. We also describe the typical shapes and strengths of stellar bars in the S4G sample and link their properties to the total stellar mass and morphology of their host galaxy. Methods: For 1154 S4G galaxies with disk inclinations lower than 65°, we perform a Fourier decomposition and rescale their images to a common frame determined by the size in physical units, by their disk scalelength, and for 748 barred galaxies by both the length and orientation of their bars. We stack the resized density profiles and images to obtain statistically representative average stellar disks and bars in bins of M∗ and T. Based on the radial force profiles of individual galaxies we calculate the mean stellar contribution to the circular velocity. We also calculate average A2 profiles, where the radius is normalized to R25.5. Furthermore, we infer the gravitational potentials from the synthetic bars to obtain the tangential-to-radial force ratio (QT) and A2 profiles in the different bins. We also apply ellipse fitting to quantitatively characterize the shape of the bar stacks. Results: For M∗ ≥ 109M⊙, we find a significant difference in the stellar density profiles of barred and non-barred systems: (I) disks in barred galaxies show larger scalelengths (hR) and fainter extrapolated central surface brightnesses (Σ°); (II) the mean surface brightness profiles (Σ∗) of barred and non-barred galaxies intersect each other slightly beyond the mean bar length, most likely at the bar corotation; and (III) the central mass concentration of barred galaxies is higher (by almost a factor 2 when T ≤ 5) than in their non-barred counterparts. The averaged Σ∗ profiles follow an exponential slope down to at least 10 M⊙ pc-2, which is the typical depth beyond which the sample coverage in the radial direction starts to drop. Central mass concentrations in massive systems (≥1010M⊙) are substantially larger than in fainter galaxies, and their prominence scales with T. This segregation also manifests in the inner slope of the mean stellar component of the circular velocity: lenticular (S0) galaxies present the most sharply rising V3.6 μm. Based on the analysis of bar stacks, we show that early- and intermediate-type spirals (0 ≤ T< 5) have intrinsically narrower bars than later types and S0s, whose bars are oval-shaped. We show a clear agreement between galaxy family and quantitative estimates of bar strength. In early- and intermediate-type spirals, A2 is larger within and beyond the typical bar region among barred galaxies than in the non-barred subsample. Strongly barred systems also tend to have larger A2 amplitudes at all radii than their weakly barred counterparts. Conclusions: Using near-IR wavelengths (S4G 3.6 μm), we provide observational constraints that galaxy formation models can be checked against. In particular, we calculate the mean stellar density profiles, and the disk(+bulge) component of the rotation curve (and their dispersion) in bins of M∗ and T. We find evidence for bar-induced secular evolution of disk galaxies in terms of disk spreading and enhanced central mass concentration. We also obtain average bars (2D), and we show that bars hosted by early-type galaxies are more centrally concentrated and have larger density amplitudes than their late-type counterparts. The FITS files of the synthetic images and the tabulated radial profiles of the mean (and dispersion of) stellar mass density, 3.6 μm surface brightness, Fourier amplitudes, gravitational force, and the stellar contribution to the circular velocity are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/596/A84

The Anemic Stellar Halo of M101

NASA Astrophysics Data System (ADS)

Holwerda, Benne

2014-10-01

Models of galaxy formation in a cosmological context predict that massive disk galaxies should have richly-structured extended stellar halos, containing ~10% of a galaxy's stars, originating in large part from the tidal disruption of dwarf galaxies. Observations of a number of nearby disk galaxies have generally agreed with these expectations. Recent new observations in integrated light with a novel array of low scattered-light telephoto lenses have failed to convincingly detect a stellar halo in the nearby massive face-on disk galaxy M101 (van Dokkum et al. 2014). They argue that any halo has to have <0.3% of the mass of the galaxy. This halo would be the least massive of any massive disk galaxy in the local Universe (by factors of several) -- such a halo is not predicted or naturally interpreted by the models, and would present a critical challenge to the picture of ubiquitous stellar halos formed from the debris of disrupting dwarf galaxies.We propose to resolve the stellar populations of this uniquely anemic stellar halo for 6 orbits with HST (ACS and WFC3), allowing us to reach surface brightness limits sufficient to clearly detect and characterize M101's stellar halo if it carries more than 0.1% of M101's mass. With resolved stellar populations, we can use the gradient of stellar populations as a function of radius to separate stellar halo from disk, which is impossible using integrated light observations. The resolved stellar populations will reveal the halo mass to much greater accuracy, measure the halo radial profile, constrain any halo lopsidedness, estimate the halo's stellar metallicity, and permit an analysis of outer disk stellar populations.

Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-03-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c - Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration and virial mass. Although accounting for a NFW dark halo profile can explain rotation curve observations, the implied c - Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L -color correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L - ratios of 51 galaxies (30% of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark halos of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disk galaxies.

Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-07-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c-Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration, and virial mass. Although accounting for a NFW dark halo profile can explain RC observations, the implied c-Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L-colour correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L ratios of 51 galaxies (30 per cent of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark haloes of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disc galaxies.

Andromeda (M31) optical and infrared disk survey. I. Insights in wide-field near-IR surface photometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sick, Jonathan; Courteau, Stéphane; Cuillandre, Jean-Charles

We present wide-field near-infrared J and K{sub s} images of the Andromeda Galaxy (M31) taken with WIRCam at the Canada-France-Hawaii Telescope as part of the Andromeda Optical and Infrared Disk Survey. This data set allows simultaneous observations of resolved stars and near-infrared (NIR) surface brightness across M31's entire bulge and disk (within R = 22 kpc), permitting a direct test of the stellar composition of near-infrared light in a nearby galaxy. Here we develop NIR observation and reduction methods to recover a uniform surface brightness map across the 3° × 1° disk of M31 with 27 WIRCam fields. Two sky-targetmore » nodding strategies are tested, and we find that strictly minimizing sky sampling latency cannot improve background subtraction accuracy to better than 2% of the background level due to spatio-temporal variations in the NIR skyglow. We fully describe our WIRCam reduction pipeline and advocate using flats built from night-sky images over a single night, rather than dome flats that do not capture the WIRCam illumination field. Contamination from scattered light and thermal background in sky flats has a negligible effect on the surface brightness shape compared to the stochastic differences in background shape between sky and galaxy disk fields, which are ∼0.3% of the background level. The most dramatic calibration step is the introduction of scalar sky offsets to each image that optimizes surface brightness continuity. Sky offsets reduce the mean surface brightness difference between observation blocks from 1% to <0.1% of the background level, though the absolute background level remains statistically uncertain to 0.15% of the background level. We present our WIRCam reduction pipeline and performance analysis to give specific recommendations for the improvement of NIR wide-field imaging methods.« less

(Almost) Dark Galaxies in the ALFALFA Survey: Isolated H i-bearing Ultra-diffuse Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leisman, Lukas; Haynes, Martha P.; Giovanelli, Riccardo

2017-06-20

We present a sample of 115 very low optical surface brightness, highly extended, H i-rich galaxies carefully selected from the ALFALFA survey that have similar optical absolute magnitudes, surface brightnesses, and radii to recently discovered “ultra-diffuse” galaxies (UDGs). However, these systems are bluer and have more irregular morphologies than other UDGs, are isolated, and contain significant reservoirs of H i. We find that while these sources have normal star formation rates for H i-selected galaxies of similar stellar mass, they have very low star formation efficiencies. We further present deep optical and H i-synthesis follow-up imaging of three of thesemore » H i-bearing ultra-diffuse sources. We measure H i diameters extending to ∼40 kpc, but note that while all three sources have large H i diameters for their stellar mass, they are consistent with the H i mass–H i radius relation. We further analyze the H i velocity widths and rotation velocities for the unresolved and resolved sources, respectively, and find that the sources appear to inhabit halos of dwarf galaxies. We estimate spin parameters, and suggest that these sources may exist in high spin parameter halos, and as such may be potential H i-rich progenitors to the ultra-diffuse galaxies observed in cluster environments.« less

The dependence of halo mass on galaxy size at fixed stellar mass using weak lensing

NASA Astrophysics Data System (ADS)

Charlton, Paul J. L.; Hudson, Michael J.; Balogh, Michael L.; Khatri, Sumeet

2017-12-01

Stellar mass has been shown to correlate with halo mass, with non-negligible scatter. The stellar mass-size and luminosity-size relationships of galaxies also show significant scatter in galaxy size at fixed stellar mass. It is possible that, at fixed stellar mass and galaxy colour, the halo mass is correlated with galaxy size. Galaxy-galaxy lensing allows us to measure the mean masses of dark matter haloes for stacked samples of galaxies. We extend the analysis of the galaxies in the CFHTLenS catalogue by fitting single Sérsic surface brightness profiles to the lens galaxies in order to recover half-light radius values, allowing us to determine halo masses for lenses according to their size. Comparing our halo masses and sizes to baselines for that stellar mass yields a differential measurement of the halo mass-galaxy size relationship at fixed stellar mass, defined as Mh(M_{*}) ∝ r_{eff}^{η }(M_{*}). We find that, on average, our lens galaxies have an η = 0.42 ± 0.12, i.e. larger galaxies live in more massive dark matter haloes. The η is strongest for high-mass luminous red galaxies. Investigation of this relationship in hydrodynamical simulations suggests that, at a fixed M*, satellite galaxies have a larger η and greater scatter in the Mh and reff relationship compared to central galaxies.

The AU Mic debris ring: density profile and dynamics of the dust

NASA Astrophysics Data System (ADS)

Augereau, Jean-Charles; Beust, Herve

2005-10-01

AU Mic is an M-type star surrounded by a debris disk that is viewed almost perfectly edge-on. This disk shares many common observational properties with the well-known disk orbiting Beta Pictoris but the properties of the AU Mic disk as well as the dynamics of the dust grains have not been studied in detail yet. Using a standard deprojection technique, we derive the surface density profile of the AU Mic disk from near-IR scattered light observations. We show that irrespective of the asymmetry parameter of the phase function, most of the dust emission arises from a ring-like region that extends from 30 to 45 AU. We estimate that the mean collision time-scale at these distances is of the order of a few 10000 years. Therefore, collisional evolution can happen. A striking common feature between AU Mic and Beta Pic is the surface brightness profile. In both cases, the surface brightness falls off as r^{-5} further away than 120 AU in the case of Beta Pic and 35 AU in the case of AU Mic. In the case of Beta Pic, this profile is well explained by the combined effect of collisions and radiation pressure on the smallest dust particules (e.g. Augereau et al. 2001). But this model does not apply to AU Mic because of its low luminosity (thus generating a too low radiation pressure). Conversely, we show that a standard, solar-like stellar wind generates a drag force onto dust particles that behaves much like a radiation pressure. This wind pressure appears stronger than the radiation pressure itself and this effect is considerably enhanced by the recurrent stellar flares of AU Mic. This greatly contributes to populating the extended debris disk of AU Mic and explains the similarity between the Beta Pic and AU Mic brightness profiles.

Starspots

NASA Astrophysics Data System (ADS)

Strassmeier, Klaus G.

2009-09-01

Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere (Biermann in Astronomische Nachrichten 264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots are observable tracers of the yet unknown internal dynamo activity and allow a glimpse into the complex internal stellar magnetic field structure. Starspots also enable the precise measurement of stellar rotation which is among the key ingredients for the expected internal magnetic topology. But whether starspots are just blown-up sunspot analogs, we do not know yet. This article is an attempt to review our current knowledge of starspots. A comparison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image of a young solar-like star (EK Draconis; G1.5V, age 100 Myr, rotation 10 × Ω Sun) and with a mean-field dynamo simulation suggests that starspots can be of significantly different appearance and cannot be explained with a scaling of the solar model, even for a star of same mass and effective temperature. Starspots, their surface location and migration pattern, and their link with the stellar dynamo and its internal energy transport, may have far reaching impact also for our understanding of low-mass stellar evolution and formation. Emphasis is given in this review to their importance as activity tracers in particular in the light of more and more precise exoplanet detections around solar-like, and therefore likely spotted, host stars.

Shadows cast on the transition disk of HD 135344B. Multiwavelength VLT/SPHERE polarimetric differential imaging

NASA Astrophysics Data System (ADS)

Stolker, T.; Dominik, C.; Avenhaus, H.; Min, M.; de Boer, J.; Ginski, C.; Schmid, H. M.; Juhasz, A.; Bazzon, A.; Waters, L. B. F. M.; Garufi, A.; Augereau, J.-C.; Benisty, M.; Boccaletti, A.; Henning, Th.; Langlois, M.; Maire, A.-L.; Ménard, F.; Meyer, M. R.; Pinte, C.; Quanz, S. P.; Thalmann, C.; Beuzit, J.-L.; Carbillet, M.; Costille, A.; Dohlen, K.; Feldt, M.; Gisler, D.; Mouillet, D.; Pavlov, A.; Perret, D.; Petit, C.; Pragt, J.; Rochat, S.; Roelfsema, R.; Salasnich, B.; Soenke, C.; Wildi, F.

2016-11-01

Context. The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter emission which are possibly related to planet formation processes. Aims: We aim to study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface. Methods: We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in the R and I-bands and with IRDIS in the Y and J-bands. The scattered light images and surface brightness profiles are used to study in detail structures in the disk surface and brightness variations. We have constructed a 3D radiative transfer model to support the interpretation of several detected shadow features. Results: The scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. Multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. A positive surface brightness gradient is observed in the stellar irradiation corrected (r2-scaled) images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large (2πa ≳ λ) aggregate dust grains in the disk surface. Part of the non-azimuthal polarization signal in the Uφ image of the J-band observation can be attributed to multiple scattering in the disk. Conclusions: The detected shadow features and their possible variability have the potential to provide insight into the structure of and processes occurring in the innermost disk regions. Possible explanations for the presence of the shadows include a 22° misaligned inner disk, a warped disk region that connects the inner disk with the outer disk, and variable or transient phenomena such as a perturbation of the inner disk or an asymmetric accretion flow. The spiral arms are best explained by one or multiple protoplanets in the exterior of the disk although no gap is detected beyond the spiral arms up to 1.''0. Based on observations collected at the European Southern Observatory, Chile, ESO No. 095.C-0273(A) and 095.C-0273(D).

Galaxy And Mass Assembly (GAMA): detection of low-surface-brightness galaxies from SDSS data

NASA Astrophysics Data System (ADS)

Williams, Richard P.; Baldry, I. K.; Kelvin, L. S.; James, P. A.; Driver, S. P.; Prescott, M.; Brough, S.; Brown, M. J. I.; Davies, L. J. M.; Holwerda, B. W.; Liske, J.; Norberg, P.; Moffett, A. J.; Wright, A. H.

2016-12-01

We report on a search for new low-surface-brightness galaxies (LSBGs) using Sloan Digital Sky Survey (SDSS) data within the Galaxy And Mass Assembly (GAMA) equatorial fields. The search method consisted of masking objects detected with SDSS PHOTO, combining gri images weighted to maximize the expected signal-to-noise ratio, and smoothing the images. The processed images were then run through a detection algorithm that finds all pixels above a set threshold and groups them based on their proximity to one another. The list of detections was cleaned of contaminants such as diffraction spikes and the faint wings of masked objects. From these, selecting potentially the brightest in terms of total flux, a list of 343 LSBGs was produced having been confirmed using VISTA Kilo-degree Infrared Galaxy Survey (VIKING) imaging. The photometry of this sample was refined using the deeper VIKING Z band as the aperture-defining band. Measuring their g - I and J - K colours shows that most are consistent with being at redshifts less than 0.2. The photometry is carried out using an AUTO aperture for each detection giving surface brightnesses of μr ≳ 25 mag arcsec-2 and magnitudes of r > 19.8 mag. None of these galaxies are bright enough to be within the GAMA main survey limit but could be part of future deeper surveys to measure the low-mass end of the galaxy stellar mass function.

The nature of solar brightness variations

NASA Astrophysics Data System (ADS)

Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Yeo, K. L.; Schmutz, W. K.

2017-09-01

Determining the sources of solar brightness variations1,2, often referred to as solar noise3, is important because solar noise limits the detection of solar oscillations3, is one of the drivers of the Earth's climate system4,5 and is a prototype of stellar variability6,7—an important limiting factor for the detection of extrasolar planets. Here, we model the magnetic contribution to solar brightness variability using high-cadence8,9 observations from the Solar Dynamics Observatory (SDO) and the Spectral And Total Irradiance REconstruction (SATIRE)10,11 model. The brightness variations caused by the constantly evolving cellular granulation pattern on the solar surface were computed with the Max Planck Institute for Solar System Research (MPS)/University of Chicago Radiative Magnetohydrodynamics (MURaM)12 code. We found that the surface magnetic field and granulation can together precisely explain solar noise (that is, solar variability excluding oscillations) on timescales from minutes to decades, accounting for all timescales that have so far been resolved or covered by irradiance measurements. We demonstrate that no other sources of variability are required to explain the data. Recent measurements of Sun-like stars by the COnvection ROtation and planetary Transits (CoRoT)13 and Kepler14 missions uncovered brightness variations similar to that of the Sun, but with a much wider variety of patterns15. Our finding that solar brightness variations can be replicated in detail with just two well-known sources will greatly simplify future modelling of existing CoRoT and Kepler as well as anticipated Transiting Exoplanet Survey Satellite16 and PLAnetary Transits and Oscillations of stars (PLATO)17 data.

Stellar populations in the outskirts of M31: the mid-infrared view

NASA Astrophysics Data System (ADS)

Barmby, P.; Ravandi, M. Rafiei

2017-03-01

The mid-infrared provides a unique view of galaxy stellar populations, sensitive to both the integrated light of old, low-mass stars and to individual dusty mass-losing stars. We present results from an extended Spitzer/IRAC survey of M31 with total lengths of 6.6 and 4.4 degrees along the major and minor axes, respectively. The integrated surface brightness profile proves to be surprisingly difficult to trace in the outskirts of the galaxy, but we can also investigate the disk/halo transition via a star count profile, with careful correction for foreground and background contamination. Our point-source catalog allows us to report on mid-infrared properties of individual objects in the outskirts of M31, via cross-correlation with PAndAS, WISE, and other catalogs.

An independent Cepheid distance scale: Current status

NASA Technical Reports Server (NTRS)

Barnes, T. G., III

1980-01-01

An independent distance scale for Cepheid variables is discussed. The apparent magnitude and the visual surface brightness, inferred from an appropriate color index, are used to determine the angular diameter variation of the Cepheid. When combined with the linear displacement curve obtained from the integrated radial velocity curve, the distance and linear radius are determined. The attractiveness of the method is its complete independence of all other stellar distance scales, even though a number of practical difficulties currently exist in implementing the technique.

Roche tomography of cataclysmic variables - VIII. The irradiated and spotted dwarf nova, SS Cygni

NASA Astrophysics Data System (ADS)

Hill, C. A.; Smith, Robert Connon; Hebb, L.; Szkody, P.

2017-12-01

We present the results of our spectroscopic study of the dwarf nova SS Cyg, using Roche tomography to map the stellar surface and derive the system parameters. Given that this technique takes into account the inhomogeneous brightness distribution on the surface of the secondary star, our derived parameters are (in principle) the most robust yet found for this system. Furthermore, our surface maps reveal that the secondary star is highly spotted, with strongly asymmetric irradiation on the inner hemisphere. Moreover, by constructing Doppler tomograms of several Balmer emission lines, we find strong asymmetric emission from the irradiated secondary star, and an asymmetric accretion disc that exhibits spiral structures.

Stellar systems in the direction of the Hickson Compact Group 44. I. Low surface brightness galaxies

NASA Astrophysics Data System (ADS)

Smith Castelli, A. V.; Faifer, F. R.; Escudero, C. G.

2016-11-01

Context. In spite of the numerous studies of low-luminosity galaxies in different environments, there is still no consensus about their formation scenario. In particular, a large number of galaxies displaying extremely low-surface brightnesses have been detected in the last year, and the nature of these objects is under discussion. Aims: In this paper we report the detection of two extended low-surface brightness (LSB) objects (μeffg' ≃ 27 mag) found, in projection, next to NGC 3193 and in the zone of the Hickson Compact Group (HCG) 44, respectively. Methods: We analyzed deep, high-quality, GEMINI-GMOS images with ELLIPSE within IRAF in order to obtain their brightness profiles and structural parameters. We also searched for the presence of globular clusters (GC) in these fields. Results: We have found that, if these LSB galaxies were at the distances of NGC 3193 and HCG 44, they would show sizes and luminosities similar to those of the ultra-diffuse galaxies (UDGs) found in the Coma cluster and other associations. In that case, their sizes would be rather larger than those displayed by the Local Group dwarf spheroidal (dSph) galaxies. We have detected a few unresolved sources in the sky zone occupied by these galaxies showing colors and brightnesses typical of blue globular clusters. Conclusions: From the comparison of the properties of the galaxies presented in this work with those of similar objects reported in the literature, we have found that LSB galaxies display sizes covering a quite extended continous range (reff 0.3-4.5 kpc), in contrast to "normal" early-type galaxies, which show reff 1.0 kpc with a low dispersion. This fact might point to different formation processes for both types of galaxies.

GHOSTS: The Stellar Populations in the Outskirts of Massive Disk Galaxies

NASA Astrophysics Data System (ADS)

De Jong, Roelof; Radburn-Smith, D. J.; Seth, A. C.; GHOSTS Team

2007-12-01

In recent years we have started to appreciate that the outskirts of galaxies contain valuable information about the formation process of galaxies. In hierarchical galaxy formation the stellar halos and thick disks of galaxies are thought to be the result of accretion of minor satellites, predominantly in the earlier assembly phases. The size, metallicity, and amount of substructure in current day halos are therefore directly related to issues like the small scale properties of the primordial power spectrum of density fluctuations and the suppression of star formation in small dark matter halos. I will show highlights from our ongoing HST/ACS/WFPC2 GHOSTS survey of the resolved stellar populations of 14 nearby, massive disk galaxies. I will show that the smaller galaxies (Vrot 100 km/s) have very small halos, but that most massive disk galaxies (Vrot 200 km/s) have very extended stellar envelopes. The luminosity of these envelopes seems to correlate with Hubble type and bulge-to-disk ratio, calling into question whether these are very extended bulge populations or inner halo populations. The amount of substructure varies strongly between galaxies. Finally, I will present the stellar populations of a very low surface brightness stream around M83, showing that it is old and fairly metal rich.

The halo of M 49 and its environment as traced by planetary nebulae populations

NASA Astrophysics Data System (ADS)

Hartke, J.; Arnaboldi, M.; Longobardi, A.; Gerhard, O.; Freeman, K. C.; Okamura, S.; Nakata, F.

2017-07-01

Context. The galaxy M 49 (NGC 4472) is the brightest early-type galaxy in the Virgo Cluster. It is located in subcluster B and has an unusually blue, metal-poor outer halo. Planetary nebulae (PNe) are excellent tracers of diffuse galaxy and intragroup light (IGL). Aims: We aim to present a photometric survey of PNe in the galaxy's extended halo to characterise its PN population, as well as the surrounding IGL of the subcluster B. Methods: PNe were identified based on their bright [OIII]5007 Å emission and absence of a broad-band continuum through automated detection techniques. Results: We identify 738 PNe out to a radius of 155 kpc from M 49's centre from which we define a complete sample of 624 PNe within a limiting magnitude of m5007,lim = 28.8. Comparing the PN number density to the broad-band stellar surface brightness profile, we find a variation of the PN-specific frequency (α-parameter) with radius. The outer halo beyond 60kpc has a 3.2 times higher α-parameter compared to the main galaxy halo (α2.5,innerM 49 = (3.20 ± 0.43) × 10-9 PN L-1⊙,bol), which is likely due to contribution from the surrounding blue IGL. We use the planetary nebulae luminosity function (PNLF) as an indicator of distance and stellar population. Its slope, which correlates empirically with galaxy type, varies within the inner halo. In the eastern quadrant of M 49, the PNLF slope is shallower, indicating an additional localised, bright PN population following an accretion event, likely that of the dwarf irregular galaxy VCC1249. We also determined a distance modulus of μPNLF = 31.29+ 0.07-0.08 for M 49, corresponding to a physical distance of 18.1 ± 0.6 Mpc, which agrees with a recent surface-brightness fluctuations distance. Conclusions: The PN populations in the outer halo of M 49 are consistent with the presence of a main Sérsic galaxy halo with a slight (B - V) colour gradient of 10-4 mag arcsec-1 surrounded by IGL with a very blue colour of (B - V) = 0.25 and a constant surface brightness μV = 28.0 mag arcsec-2. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan under programme S14A-006.

STELLAR ROTATION EFFECTS IN POLARIMETRIC MICROLENSING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sajadian, Sedighe, E-mail: sajadian@ipm.ir

2016-07-10

It is well known that the polarization signal in microlensing events of hot stars is larger than that of main-sequence stars. Most hot stars rotate rapidly around their stellar axes. The stellar rotation creates ellipticity and gravity-darkening effects that break the spherical symmetry of the source's shape and the circular symmetry of the source's surface brightness respectively. Hence, it causes a net polarization signal for the source star. This polarization signal should be considered in polarimetric microlensing of fast rotating stars. For moderately rotating stars, lensing can magnify or even characterize small polarization signals due to the stellar rotation throughmore » polarimetric observations. The gravity-darkening effect due to a rotating source star creates asymmetric perturbations in polarimetric and photometric microlensing curves whose maximum occurs when the lens trajectory crosses the projected position of the rotation pole on the sky plane. The stellar ellipticity creates a time shift (i) in the position of the second peak of the polarimetric curves in transit microlensing events and (ii) in the peak position of the polarimetric curves with respect to the photometric peak position in bypass microlensing events. By measuring this time shift via polarimetric observations of microlensing events, we can evaluate the ellipticity of the projected source surface on the sky plane. Given the characterizations of the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at the Very Large Telescope, the probability of observing this time shift is very small. The more accurate polarimeters of the next generation may well measure these time shifts and evaluate the ellipticity of microlensing source stars.« less

Exploring the Solar System with Stellar Occultations

NASA Technical Reports Server (NTRS)

Elliot, J. L.; Dunham, E. W.

1984-01-01

By recording the light intensity as a function of time when a planet occults a relatively bright star, the thermal structure of the upper atmosphere of the planet can be probed. The main feature of stellar occultation observations is their high spatial resolution, typically several thousand times better than the resolution achievable with ground-based imaging. Five stellar occultations have been observed. The main results of these observations are summarized. Stellar occultations have been observed on Uranus, Mars, Pallas, Neptune and the Jovian Ring.

VLA+WSRT HI Imaging of Two "Almost Dark" Galaxies

NASA Astrophysics Data System (ADS)

Ball, Catie; Singer, Quinton; Cannon, John M.; Leisman, Luke; Haynes, Martha P.; Adams, Elizabeth A.; Bernal Neira, David; Giovanelli, Riccardo; Hallenbeck, Gregory L.; Janesh, William; Janowiecki, Steven; Jozsa, Gyula; Rhode, Katherine L.; Salzer, John Joseph

2017-01-01

We present sensitive HI imaging of the "Almost Dark" galaxies AGC229385 and AGC229101. Selected from the ALFALFA survey, "Almost Dark" galaxies have significant HI reservoirs but lack an obvious stellar counterpart in survey-depth ground-based optical imaging. Deeper ground- and space-based imaging reveals very low surface brightness optical counterparts in both systems. The resulting M_HI/L_B ratios are among the highest ever measured for individual galaxies. Here we combine VLA and WSRT imaging of these two systems, allowing us to preserve surface brightness sensitivity while working at high angular resolution. The resulting maps of HI mass surface density, velocity field, and velocity dispersion are compared to deep optical and ultraviolet imaging. In both systems the highest column density HI gas is clumpy and resolved into multiple components. In the case of AGC229385, the kinematics are inconsistent with a simple rotating disk and may be the result of either an infall episode or an interaction between two HI-rich disks.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College.

Stellar Populations in Elliptical Galaxies

NASA Astrophysics Data System (ADS)

Angeletti, Lucio; Giannone, Pietro

The R1/n law for the radial surface brightness of elliptical galaxies and the "Best Accretion Model" together with the "Concentration Model" have been combined in order to determine the mass and dynamical structure of largely-populated star systems. Families of models depending on four parameters have been used to fit the observed surface radial profiles of some spectro-photometric indices of a sample of eleven galaxies. We present the best agreements of the spectral index Mg2 with observations for three selected galaxies representative of the full sample. For them we have also computed the spatial distributions of the metal abundances, which are essential to achieve a population synthesis.

VizieR Online Data Catalog: FIR data of IR-bright dust-obscured galaxies (DOGs) (Toba+, 2017)

NASA Astrophysics Data System (ADS)

Toba, Y.; Nagao, T.; Wang, W.-H.; Matsuhara, H.; Akiyama, M.; Goto, T.; Koyama, Y.; Ohyama, Y.; Yamamura, I.

2017-11-01

We investigate the star-forming activity of a sample of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme red color in the optical and IR regime, (i-[22])AB>7.0. Combining an IR-bright DOG sample with the flux at 22μm>3.8mJy discovered by Toba & Nagao (2016ApJ...820...46T) with the IRAS faint source catalog version 2 and AKARI far-IR (FIR) all-sky survey bright source catalog version 2, we selected 109 DOGs with FIR data. For a subsample of seven IR-bright DOGs with spectroscopic redshifts (0.07

Far-infrared Properties of Infrared-bright Dust-obscured Galaxies Selected with IRAS and AKARI Far-infrared All-sky Survey

NASA Astrophysics Data System (ADS)

Toba, Yoshiki; Nagao, Tohru; Wang, Wei-Hao; Matsuhara, Hideo; Akiyama, Masayuki; Goto, Tomotsugu; Koyama, Yusei; Ohyama, Youich; Yamamura, Issei

2017-05-01

We investigate the star-forming activity of a sample of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme red color in the optical and IR regime, {(I-[22])}{AB}> 7.0. Combining an IR-bright DOG sample with the flux at 22 μm > 3.8 mJy discovered by Toba & Nagao with the IRAS faint source catalog version 2 and AKARI far-IR (FIR) all-sky survey bright source catalog version 2, we selected 109 DOGs with FIR data. For a subsample of seven IR-bright DOGs with spectroscopic redshifts (0.07< z< 1.0) that were obtained from the literature, we estimated their IR luminosity, star formation rate (SFR), and stellar mass based on the spectral energy distribution fitting. We found that (1) the WISE 22 μm luminosity at the observed frame is a good indicator of IR luminosity for IR-bright DOGs and (2) the contribution of the active galactic nucleus to IR luminosity increases with IR luminosity. By comparing the stellar mass and SFR relation for our DOG sample and the literature, we found that most of the IR-bright DOGs lie significantly above the main sequence of star-forming galaxies at similar redshift, indicating that the majority of IRAS- or AKARI-detected IR-bright DOGs are starburst galaxies.

A New Concept of Coronagraph using Axicon Lenses

NASA Astrophysics Data System (ADS)

Choi, Jae Ho

2017-06-01

High-contrast direct imaging of faint objects nearby bright stellar is essential to investigate planetary systems. The goal of such effort is to find and characterize planets similar to Earth that is a challenging task due to it requires a high angular resolution and high dynamic range detections concurrently. A coronagraph that can be suppressed the bright stellar light or active galactic nuclei during the direct detection of astrophysical activities became one of the essential instruments to image exoplanets. In this presentation, a novel concept of a coronagraph using axicon-lenses is will be presented that is conjunction with a method of noninterferometric quantitative phase imaging for direct imaging of exoplanets. The essential scheme of the axicon-lenses coronagraph is the apodization carried out by excluding evaginated images of the planetary systems by a pair of axicon lens. The laboratory based coronagraph imaging is carried out with the axicon-lenses coronagraph setup which included the axicon lenses optics and phase contrast imaging unit. A simulated stellar and its companion are provided by illuminating light through small holes drilled on a thin metal plate. Those diffracted light at the edge of the holes bears a similarity to the light from the bright stellar. The images are evaginated about the optical axis by passing the first axicon lens. Then the evaginated beams of its external area have cut off by an iris which means the suppressed its central light of the bright stellar light preferentially. A symbolic calculation also is carried out to verify the scheme of the the axicon-lenses coronagraph using the symbolic computation program. The simulation results are shown that the the axicon-lenses coronagraph has feature of ability to achieve the IWA smaller than l/D. The laboratory based coronagraph imaging and simulation results support its potentials in direct imaging for finding exo-planet and various astrophysical activities.

Color Dispersion as an Indicator of Stellar Population Complexity: Insights from the Pixel Color–Magnitude Diagrams of 32 Bright Galaxies in Abell 1139 and Abell 2589

NASA Astrophysics Data System (ADS)

Lee, Joon Hyeop; Pak, Mina; Lee, Hye-Ran; Oh, Sree

2018-04-01

We investigate the properties of bright galaxies of various morphological types in Abell 1139 and Abell 2589, using pixel color–magnitude diagram (pCMD) analysis. The sample contains 32 galaxies brighter than M r = ‑21.3 mag with spectroscopic redshifts, which are deeply imaged in the g and r bands using the MegaCam mounted on the Canada–France–Hawaii Telescope. After masking contaminants with two-step procedures, we examine how the detailed properties in the pCMDs depend on galaxy morphology and infrared color. The mean g ‑ r color as a function of surface brightness (μ r ) in the pCMD of a galaxy shows good performance in distinguishing between early- and late-type galaxies, but it is not perfect because of the similarity between elliptical galaxies and bulge-dominated spiral galaxies. On the other hand, the g ‑ r color dispersion as a function of μ r works better. We find that the best set of parameters for galaxy classification is a combination of the minimum color dispersion at μ r ≤ 21.2 mag arcsec‑2 and the maximum color dispersion at 20.0 ≤ μ r ≤ 21.0 mag arcsec‑2 the latter reflects the complexity of stellar populations at the disk component in a typical spiral galaxy. Finally, the color dispersion measurements of an elliptical galaxy appear to be correlated with the Wide-field Infrared Survey Explorer infrared color ([4.6]–[12]). This indicates that the complexity of stellar populations in an elliptical galaxy is related to its recent star formation activities. From this observational evidence, we infer that gas-rich minor mergers or gas interactions may have usually occurred during the recent growth of massive elliptical galaxies.

The intrinsic three-dimensional shape of galactic bars

NASA Astrophysics Data System (ADS)

Méndez-Abreu, J.; Costantin, L.; Aguerri, J. A. L.; de Lorenzo-Cáceres, A.; Corsini, E. M.

2018-06-01

We present the first statistical study on the intrinsic three-dimensional (3D) shape of a sample of 83 galactic bars extracted from the CALIFA survey. We use the galaXYZ code to derive the bar intrinsic shape with a statistical approach. The method uses only the geometric information (ellipticities and position angles) of bars and discs obtained from a multi-component photometric decomposition of the galaxy surface-brightness distributions. We find that bars are predominantly prolate-triaxial ellipsoids (68%), with a small fraction of oblate-triaxial ellipsoids (32%). The typical flattening (intrinsic C/A semiaxis ratio) of the bars in our sample is 0.34, which matches well the typical intrinsic flattening of stellar discs at these galaxy masses. We demonstrate that, for prolate-triaxial bars, the intrinsic shape of bars depends on the galaxy Hubble type and stellar mass (bars in massive S0 galaxies are thicker and more circular than those in less massive spirals). The bar intrinsic shape correlates with bulge, disc, and bar parameters. In particular with the bulge-to-total (B/T) luminosity ratio, disc g - r color, and central surface brightness of the bar, confirming the tight link between bars and their host galaxies. Combining the probability distributions of the intrinsic shape of bulges and bars in our sample we show that 52% (16%) of bulges are thicker (flatter) than the surrounding bar at 1σ level. We suggest that these percentages might be representative of the fraction of classical and disc-like bulges in our sample, respectively.

KDG218, a nearby ultra-diffuse galaxy

NASA Astrophysics Data System (ADS)

Karachentsev, I. D.; Makarova, L. N.; Sharina, M. E.; Karachentseva, V. E.

2017-10-01

We present properties of the low-surface-brightness galaxy KDG218 observed with the HST/ACS. The galaxy has a half-light (effective) diameter of a e = 47″ and a central surface brightness of SB V (0) = 24.m4/□″. The galaxy remains unresolved with the HST/ACS, which implies its distance of D > 13.1 Mpc and linear effective diameter of A e > 3.0 kpc. We notice that KDG218 is most likely associated with a galaxy group around the massive lenticular NGC4958 galaxy at approximately 22 Mpc, or with the Virgo Southern Extension filament at approximately 16.5 Mpc. At these distances, the galaxy is classified as an ultra-diffuse galaxy (UDG) similar to those found in the Virgo, Fornax, and Coma clusters. We also present a sample of 15 UDG candidates in the Local Volume. These sample galaxies have the following mean parameters: 〈 D〉 = 5.1 Mpc, 〈 A e 〉 = 4.8 kpc, and 〈 SB B ( e)〉 = 27.m4/□″. All the local UDG candidates reside near massive galaxies located in the regions with the mean stellar mass density (within 1 Mpc) about 50 times greater than the average cosmic density. The local fraction of UDGs does not exceed 1.5% of the Local Volume population. We notice that the presented sample of local UDGs is a heterogeneous one containing irregular, transition, and tidal types, as well as objects consisting of an old stellar population.

What Turns Galaxies Off? the Different Morphologies of Star-Forming and Quiescent Galaxies Since z Approximates 2 from CANDELS

NASA Technical Reports Server (NTRS)

Bell, Eric F.; VanDerWel, Arjen; Papovich, Casey; Kocevski, Dale; Lotz, Jennifer; McIntosh, Daniel H.; Kartaltepe, Jeyhan; Faber, S. M.; Ferguson, Harry; Koekemoer, Anton;

DOE Office of Scientific and Technical Information (OSTI.GOV)

Philippov, Alexander A.; Rafikov, Roman R., E-mail: rrr@astro.princeton.edu

The eclipsing binary DI Herculis (DI Her) is known to exhibit anomalously slow apsidal precession below the rate predicted by general relativity. Recent measurements of the Rossiter-McLaughlin effect indicate that stellar spins in DI Her are almost orthogonal to the orbital angular momentum, which explains the anomalous precession in agreement with the earlier theoretical suggestion by Shakura. However, these measurements yield only projections of the spin-orbit angles onto the sky plane, leaving the spin projection onto our line of sight unconstrained. Here we describe a method for determining the full three-dimensional spin orientation of the binary components relying on themore » use of the gravity-darkening effect, which is significant for the rapidly rotating stars in DI Her. Gravity darkening gives rise to a nonuniform brightness distribution over the stellar surface, the pattern of which depends on the stellar spin orientation. Using archival photometric data obtained during multiple eclipses over several decades, we are able to constrain the unknown spin angles in DI Her with this method, finding that the spin axes of both stars lie close to the plane of the sky. Our procedure fully accounts for the precession of stellar spins over the long time span of observations.« less

SOAP: A Tool for the Fast Computation of Photometry and Radial Velocity Induced by Stellar Spots

NASA Astrophysics Data System (ADS)

Boisse, I.; Bonfils, X.; Santos, N. C.; Figueira, P.

2013-04-01

Dark spots and bright plages are present on the surface of dwarf stars from spectral types F to M, even in their low-active phase (like the Sun). Their appearance and disappearance on the stellar photosphere, combined with the stellar rotation, may lead to errors and uncertainties in the characterization of planets both in radial velocity (RV) and photometry. Spot Oscillation and Planet (SOAP) is a tool offered to the community that enables to simulate spots and plages on rotating stars and computes their impact on RV and photometric measurements. This tool will help to understand the challenges related to the knowledge of stellar activity for the next decade: detect telluric planets in the habitable zone of their stars (from G to M dwarfs), understand the activity in the low-mass end of M dwarf (on which future projects, like SPIRou or CARMENES, will focus), limitation to the characterization of the exoplanetary atmosphere (from the ground or with Spitzer, JWST), search for planets around young stars. These can be simulated with SOAP in order to search for indices and corrections to the effect of activity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagen, Lea M. Z.; Hagen, Alex; Seibert, Mark

We provide evidence that UGC 1382, long believed to be a passive elliptical galaxy, is actually a giant low surface brightness (GLSB) galaxy that rivals the archetypical GLSB Malin 1 in size. Like other GLSB galaxies, it has two components: a high surface brightness disk galaxy surrounded by an extended low surface brightness (LSB) disk. For UGC 1382, the central component is a lenticular system with an effective radius of 6 kpc. Beyond this, the LSB disk has an effective radius of ∼38 kpc and an extrapolated central surface brightness of ∼26 mag arcsec{sup 2}. Both components have a combinedmore » stellar mass of ∼8 × 10{sup 10} M {sub ⊙}, and are embedded in a massive (10{sup 10} M {sub ⊙}) low-density (<3 M {sub ⊙} pc{sup 2}) HI disk with a radius of 110 kpc, making this one of the largest isolated disk galaxies known. The system resides in a massive dark matter halo of at least 2 × 10{sup 12} M {sub ⊙}. Although possibly part of a small group, its low-density environment likely plays a role in the formation and retention of the giant LSB and HI disks. We model the spectral energy distributions and find that the LSB disk is likely older than the lenticular component. UGC 1382 has UV–optical colors typical of galaxies transitioning through the green valley. Within the LSB disk are spiral arms forming stars at extremely low efficiencies. The gas depletion timescale of ∼10{sup 11} years suggests that UGC 1382 may be a very-long-term resident of the green valley. We find that the formation and evolution of the LSB disk in UGC 1382 is best explained by the accretion of gas-rich LSB dwarf galaxies.« less

Surface brightness profiles and structural parameters for 53 rich stellar clusters in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Mackey, A. D.; Gilmore, G. F.

2003-01-01

We have compiled a pseudo-snapshot data set of two-colour observations from the Hubble Space Telescope archive for a sample of 53 rich LMC clusters with ages of 106-1010 yr. We present surface brightness profiles for the entire sample, and derive structural parameters for each cluster, including core radii, and luminosity and mass estimates. Because we expect the results presented here to form the basis for several further projects, we describe in detail the data reduction and surface brightness profile construction processes, and compare our results with those of previous ground-based studies. The surface brightness profiles show a large amount of detail, including irregularities in the profiles of young clusters (such as bumps, dips and sharp shoulders), and evidence for both double clusters and post-core-collapse (PCC) clusters. In particular, we find power-law profiles in the inner regions of several candidate PCC clusters, with slopes of approximately -0.7, but showing considerable variation. We estimate that 20 +/- 7 per cent of the old cluster population of the Large Magellanic Cloud (LMC) has entered PCC evolution, a similar fraction to that for the Galactic globular cluster system. In addition, we examine the profile of R136 in detail and show that it is probably not a PCC cluster. We also observe a trend in core radius with age that has been discovered and discussed in several previous publications by different authors. Our diagram has better resolution, however, and appears to show a bifurcation at several hundred Myr. We argue that this observed relationship reflects true physical evolution in LMC clusters, with some experiencing small-scale core expansion owing to mass loss, and others large-scale expansion owing to some unidentified characteristic or physical process.

Life in the Outer Limits: Insight into Hierarchical Merging from the Outermost Structure of the Andromeda Stellar Halo

NASA Astrophysics Data System (ADS)

Beaton, Rachael; Majewski, S. R.; Patterson, R. J.; Guhathakurta, P.; Gilbert, K.; Kalirai, J. S.; Tollerud, E. J.; SPLASH Team

2014-01-01

Owing to their large dynamical timescales, the stellar haloes of Milky Way (MW) sized galaxies represent ideal environments to test modern theories of galaxy formation in the Lambda-CDM paradigm. Only in stellar haloes can the remnants of hierarchical accretion be preserved over long timescales as in-tact dwarf satellites or as tidal debris and can be easily distinguished from the underlying smooth structure. Stellar haloes, however, remain some of the most difficult galactic structures to constrain due to their large angular extent and extremely low surface brightness. Thus, the basic properties of stellar haloes -- the overall stellar distribution, substructure fraction, global kinematics and detailed stellar content -- remained relatively unconstrained. In this thesis, we present several projects designed to understand the current structure and the the formation of the Andromeda (M31) stellar halo, the only stellar halo -- besides our own -- that is within reach of current ground based facilities on the large scale required to constrain the basic properties of stellar haloes. First, we describe a seven season imaging campaign comprising the backbone of the Spectroscopic and Photometric Landscape of the Andromeda Stellar Halo (SPLASH) program. This survey is unique in its application of the Washington + DDO51 filter system to select individual M31 RGB stars without spectroscopic follow up. Second, we use the SPLASH photometric survey to identify sample of halo stars at projected radii of 120 kpc, for which we have obtained spectroscopic follow-up. Third, we add this large radius sample to the existing spectroscopic results from SPLASH, and use this unique sample to explore the stellar kinematics of the halo at large radii with full azimuthal coverage. Lastly, we preview on-going work to constrain the formation of the Andromeda stellar halo, using both in-tact satellites and resolved M31 halo members as tracers of its accretion history.

The PAndAS Field of Streams: Stellar Structures in the Milky Way Halo toward Andromeda and Triangulum

NASA Astrophysics Data System (ADS)

Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael; Collins, Michelle L. M.; Fardal, Mark A.; Irwin, Michael J.; Lewis, Geraint F.; McConnachie, Alan W.; Babul, Arif; Bate, Nicholas F.; Chapman, Scott C.; Conn, Anthony R.; Crnojević, Denija; Ferguson, Annette M. N.; Mackey, A. Dougal; Navarro, Julio F.; Peñarrubia, Jorge; Tanvir, Nial T.; Valls-Gabaud, David

2014-05-01

We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ~5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ~17 kpc. With a surface brightness of Σ V ~ 32-32.5 mag arcsec-2, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s-1 at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.

The PAndAS field of streams: Stellar structures in the milky way halo toward Andromeda and Triangulum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael

We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ∼5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ∼17more » kpc. With a surface brightness of Σ {sub V} ∼ 32-32.5 mag arcsec{sup –2}, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s{sup –1} at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.« less

STELLAR SURFACE MAGNETO-CONVECTION AS A SOURCE OF ASTROPHYSICAL NOISE. I. MULTI-COMPONENT PARAMETERIZATION OF ABSORPTION LINE PROFILES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cegla, H. M.; Shelyag, S.; Watson, C. A.

2013-02-15

We outline our techniques to characterize photospheric granulation as an astrophysical noise source. A four-component parameterization of granulation is developed that can be used to reconstruct stellar line asymmetries and radial velocity shifts due to photospheric convective motions. The four components are made up of absorption line profiles calculated for granules, magnetic intergranular lanes, non-magnetic intergranular lanes, and magnetic bright points at disk center. These components are constructed by averaging Fe I 6302 A magnetically sensitive absorption line profiles output from detailed radiative transport calculations of the solar photosphere. Each of the four categories adopted is based on magnetic fieldmore » and continuum intensity limits determined from examining three-dimensional magnetohydrodynamic simulations with an average magnetic flux of 200 G. Using these four-component line profiles we accurately reconstruct granulation profiles, produced from modeling 12 Multiplication-Sign 12 Mm{sup 2} areas on the solar surface, to within {approx} {+-}20 cm s{sup -1} on a {approx}100 m s{sup -1} granulation signal. We have also successfully reconstructed granulation profiles from a 50 G simulation using the parameterized line profiles from the 200 G average magnetic field simulation. This test demonstrates applicability of the characterization to a range of magnetic stellar activity levels.« less

The reports of thick discs' deaths are greatly exaggerated. Thick discs are NOT artefacts caused by diffuse scattered light

NASA Astrophysics Data System (ADS)

Comerón, S.; Salo, H.; Knapen, J. H.

2018-02-01

Recent studies have made the community aware of the importance of accounting for scattered light when examining low-surface-brightness galaxy features such as thick discs. In our past studies of the thick discs of edge-on galaxies in the Spitzer Survey of Stellar Structure in Galaxies - the S4G - we modelled the point spread function as a Gaussian. In this paper we re-examine our results using a revised point spread function model that accounts for extended wings out to more than 2\\farcm5. We study the 3.6 μm images of 141 edge-on galaxies from the S4G and its early-type galaxy extension. Thus, we more than double the samples examined in our past studies. We decompose the surface-brightness profiles of the galaxies perpendicular to their mid-planes assuming that discs are made of two stellar discs in hydrostatic equilibrium. We decompose the axial surface-brightness profiles of galaxies to model the central mass concentration - described by a Sérsic function - and the disc - described by a broken exponential disc seen edge-on. Our improved treatment fully confirms the ubiquitous occurrence of thick discs. The main difference between our current fits and those presented in our previous papers is that now the scattered light from the thin disc dominates the surface brightness at levels below μ 26 mag arcsec-2. We stress that those extended thin disc tails are not physical, but pure scattered light. This change, however, does not drastically affect any of our previously presented results: 1) Thick discs are nearly ubiquitous. They are not an artefact caused by scattered light as has been suggested elsewhere. 2) Thick discs have masses comparable to those of thin discs in low-mass galaxies - with circular velocities vc< 120 km s-1 - whereas they are typically less massive than the thin discs in high-mass galaxies. 3) Thick discs and central mass concentrations seem to have formed at the same epoch from a common material reservoir. 4) Approximately 50% of the up-bending breaks in face-on galaxies are caused by the superposition of a thin and a thick disc where the scale-length of the latter is the largest. Data of Figs. B.1 and C.1 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A5

The sagittarius tidal stream and the shape of the galactic stellar halo

NASA Astrophysics Data System (ADS)

Newby, Matthew T.

The stellar halo that surrounds our Galaxy contains clues to understanding galaxy formation, cosmology, stellar evolution, and the nature of dark matter. Gravitationally disrupted dwarf galaxies form tidal streams, which roughly trace orbits through the Galactic halo. The Sagittarius (Sgr) dwarf tidal debris is the most dominant of these streams, and its properties place important constraints on the distribution of mass (including dark matter) in the Galaxy. Stars not associated with substructures form the "smooth" component of the stellar halo, the origin of which is still under investigation. Characterizing halo substructures such as the Sgr stream and the smooth halo provides valuable information on the formation history and evolution of our galaxy, and places constraints on cosmological models. This thesis is primarily concerned with characterizing the 3-dimensional stellar densities of the Sgr tidal debris system and the smooth stellar halo, using data from the Sloan Digital Sky Survey (SDSS). F turnoff stars are used to infer distances, as they are relatively bright, numerous, and distributed about a single intrinsic brightness (magnitude). The inherent spread in brightnesses of these stars is overcome through the use of the recently-developed technique of statistical photometric parallax, in which the bulk properties of a stellar population are used to create a probability distribution for a given star's distance. This was used to build a spatial density model for the smooth stellar halo and tidal streams. The free parameters in this model are then fit to SDSS data with a maximum likelihood technique, and the parameters are optimized by advanced computational methods. Several computing platforms are used in this study, including the RPI SUR Bluegene and the Milkyway home volunteer computing project. Fits to the Sgr stream in 18 SDSS data stripes were performed, and a continuous density profile is found for the major Sgr stream. The stellar halo is found to be strongly oblate (flattening parameter q=0.53). A catalog of stars consistent with this density profile is produced as a template for matching future disruption models. The results of this analysis favor a description of the Sgr debris system that includes more than one dwarf galaxy progenitor, with the major streams above and below the Galactic disk being separate substructures. Preliminary results for the minor tidal stream characterizations are presented and discussed. Additionally, a more robust characterization of halo turnoff star brightnesses is performed, and it is found that increasing color errors with distance result in a previously unaccounted for incompleteness in star counts as the SDSS magnitude limit is approached. These corrections are currently in the process of being implemented on MilkyWay home.

Modeling Illumination Conditions on the Moon: Applications to LRO-LAMP

NASA Astrophysics Data System (ADS)

Byron, B. D.; Mazarico, E. M.; Retherford, K. D.; Mandt, K. E.; Greathouse, T.; Gladstone, R.

2017-12-01

LRO-LAMP is a UV spectrograph which uses illumination from Lyman-α sky glow along with UV light from bright stars to image the dark, permanently shadowed regions (PSRs) of the lunar surface. Accurate modeling of this UV illumination is essential to creating albedo maps of the lunar surface, which can shed light on lunar regolith processes and help to constrain the distribution of water ice in polar PSRs. In this study, the variation in reflected intensity received by the LAMP detector was modeled for South Pole crater Amundsen using the illumination program IllumNG. Amundsen was chosen for study due to the PSR in its Northern side and its highly illuminated equator-facing slopes on the Southern wall. The model works by tracing a ray from each LAMP detector pixel along its boresight until the point where it intersects the lunar surface, and calculating the percentage of the total source flux visible above the horizon. In this study, the three main illumination sources used are the Sun, Interplanetary Lyman-α sky glow, and bright UV starlight in the On Band (130-155 nm) and Off Band (155-190 nm) wavelength ranges. The model also has the capability to calculate incident flux received at the surface, as well as intensity reflected from the surface and received by the LAMP detector along each boresight. The study found a noticeable variation in received intensity between six month stretches for the year of 2010. Over the period of January through July, about 6% more IPM Lyman-α flux was reflected from the surface of Amundsen than for July through December. For stellar flux in the On Band, a 13% difference in flux was reflected between the six month periods. In comparing the monthly intensity maps created by the model with LAMP measured monthly brightness maps, similar crater features are apparent. Though the model brightness is generally higher than the LAMP brightness, after accounting for albedo ( 0.05 for the South Pole region) the values are in closer agreement. In the future, inclusion of the model results during pipeline processing could enable better calibration and analysis of LAMP data.

Flattening and surface-brightness of the fast-rotating star δ Persei with the visible VEGA/CHARA interferometer

NASA Astrophysics Data System (ADS)

Challouf, M.; Nardetto, N.; Domiciano de Souza, A.; Mourard, D.; Tallon-Bosc, I.; Aroui, H.; Farrington, C.; Ligi, R.; Meilland, A.; Mouelhi, M.

2017-08-01

Context. Rapid rotation is a common feature for massive stars, with important consequences on their physical structure, flux distribution and evolution. Fast-rotating stars are flattened and show gravity darkening (non-uniform surface intensity distribution). Another important and less studied impact of fast-rotation in early-type stars is its influence on the surface brightness colour relation (hereafter SBCR), which could be used to derive the distance of eclipsing binaries. Aims: The purpose of this paper is to determine the flattening of the fast-rotating B-type star δ Per using visible long-baseline interferometry. A second goal is to evaluate the impact of rotation and gravity darkening on the V - K colour and surface brightness of the star. Methods: The B-type star δ Per was observed with the VEGA/CHARA interferometer, which can measure spatial resolutions down to 0.3 mas and spectral resolving power of 5000 in the visible. We first used a toy model to derive the position angle of the rotation axis of the star in the plane of the sky. Then we used a code of stellar rotation, CHARRON, in order to derive the physical parameters of the star. Finally, by considering two cases, a static reference star and our best model of δ Per, we can quantify the impact of fast rotation on the surface brightness colour relation (SBCR). Results: We find a position angle of 23 ± 6 degrees. The polar axis angular diameter of δ Per is θp = 0.544 ± 0.007 mas, and the derived flatness is r = 1.121 ± 0.013. We derive an inclination angle for the star of I = 85+ 5-20 degrees and a projected rotation velocity Vsini = 175+ 8-11 km s-1 (or 57% of the critical velocity). We find also that the rotation and inclination angle of δ Per keeps the V - K colour unchanged while it decreasing its surface-brightness by about 0.05 mag. Conclusions: Correcting the impact of rotation on the SBCR of early-type stars appears feasible using visible interferometry and dedicated models.

The Surface Density Profile of the Galactic Disk from the Terminal Velocity Curve

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.

2016-01-01

The mass distribution of the Galactic disk is constructed from the terminal velocity curve and the mass discrepancy-acceleration relation. Mass models numerically quantifying the detailed surface density profiles are tabulated. For R0 = 8 kpc, the models have stellar mass 5 < M* < 6 × 1010 {M}⊙ , scale length 2.0 ≤ Rd ≤ 2.9 kpc, LSR circular velocity 222 ≤ Θ0 ≤ 233 {km} {{{s}}}-1, and solar circle stellar surface density 34 ≤ Σd(R0) ≤ 61 {M}⊙ {{pc}}-2. The present interarm location of the solar neighborhood may have a somewhat lower stellar surface density than average for the solar circle. The Milky Way appears to be a normal spiral galaxy that obeys scaling relations like the Tully-Fisher relation, the size-mass relation, and the disk maximality-surface brightness relation. The stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles in the terminal velocity curve correspond to known spiral features (e.g., the Centaurus arm is a ˜50% overdensity). The rotation curve switches between positive and negative over scales of hundreds of parsecs. The rms amplitude {< {| {dV}/{dR}| }2> }1/2≈ 14 {km} {{{s}}}-1 {{kpc}}-1, implying that commonly neglected terms in the Jeans equations may be nonnegligible. The spherically averaged local dark matter density is ρ0,DM ≈ 0.009 {M}⊙ {{pc}}-3 (0.34 {GeV} {{cm}}-3). Adiabatic compression of the dark matter halo may help reconcile the Milky Way with the c-V200 relation expected in ΛCDM while also helping to mitigate the too-big-to-fail problem, but it remains difficult to reconcile the inner bulge/bar-dominated region with a cuspy halo. We note that NGC 3521 is a near twin to the Milky Way, having a similar luminosity, scale length, and rotation curve.

Evidence for a Multiphase ISM in Early Type Galaxies and Elliptical Galaxies with Strong Radio Continuum

NASA Technical Reports Server (NTRS)

Kim, Dong Woo

1997-01-01

We have observed NGC 1316 (Fornax A) with the ROSAT HRI. In this paper, we present the results of these observations and we complement them with the spectral analysis of the archival PSPC data. The spectral properties suggest the presence of a significant component of thermal X-ray emission (greater than 60%), amounting to approx. 10(exp 9) solar mass of hot ISM. Within 3 feet from the nucleus of NGC 1316, the HRI X-ray surface brightness falls as r(exp -2) following the stellar light. In the inner approx. 30 inch., however, the X-ray surface brightness is significantly elongated, contrary to the distribution of stellar light, which is significantly rounder within 10 inch. This again argues for a non-stellar origin of the X-ray emission. This flattened X-ray feature is suggestive of either the disk-like geometry of a rotating cooling flow and/or the presence of extended, elongated dark matter. By comparing the morphology of the X-ray emission with the distribution of optical dust patches, we find that the X-ray emission is significantly reduced at the locations where the dust patches are more pronounced, indicating that at least some of the X-ray photons are absorbed by the cold ISM. We also compare the distribution of the hot and cold ISM with that of the ionized gas, using recently obtained H(sub alpha) CCD data. We find that the ionized gas is distributed roughly along the dust patches and follows the large scale X-ray distribution at r greater than 1 foot from the nucleus. However, there is no one-to-one correspondence between ionized gas and hot gas. Both morphological relations and kinematics suggest different origins for hot and cold ISM. The radio jets in projection appear to pass perpendicularly through the central X-ray ellipsoid. Comparison of thermal and radio pressures suggests that the radio jets are confined by the surrounding hot gaseous medium.

The Extended Halo of Centaurus A: Uncovering Satellites, Streams, and Substructures

NASA Astrophysics Data System (ADS)

Crnojević, D.; Sand, D. J.; Spekkens, K.; Caldwell, N.; Guhathakurta, P.; McLeod, B.; Seth, A.; Simon, J. D.; Strader, J.; Toloba, E.

2016-05-01

We present the widest-field resolved stellar map to date of the closest (D˜ 3.8 Mpc) massive elliptical galaxy NGC 5128 (Centaurus A; Cen A), extending out to a projected galactocentric radius of ˜150 kpc. The data set is part of our ongoing Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) utilizing the Magellan/Megacam imager. We resolve a population of old red giant branch (RGB) stars down to ˜1.5 mag below the tip of the RGB, reaching surface brightness limits as low as {μ }V,0˜ 32 mag arcsec-2. The resulting spatial stellar density map highlights a plethora of previously unknown streams, shells, and satellites, including the first tidally disrupting dwarf around Cen A (CenA-MM-Dw3), which underline its active accretion history. We report 13 previously unknown dwarf satellite candidates, of which 9 are confirmed to be at the distance of Cen A (the remaining 4 are not resolved into stars), with magnitudes in the range {M}V=-7.2 to -13.0, central surface brightness values of {μ }V,0=25.4{--}26.9 mag arcsec-2, and half-light radii of {r}h=0.22{--}2.92 {{kpc}}. These values are in line with Local Group dwarfs but also lie at the faint/diffuse end of their distribution; interestingly, CenA-MM-Dw3 has similar properties to the recently discovered ultradiffuse galaxies in Virgo and Coma. Most of the new dwarfs are fainter than the previously known Cen A satellites. The newly discovered dwarfs and halo substructures are discussed in light of their stellar populations, and they are compared to those discovered by the PAndAS survey of M31. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Colors of Dwarf Ellipticals from GALEX to WISE

NASA Astrophysics Data System (ADS)

Schombert, James M.

2018-02-01

Multicolor photometry is presented for a sample of 60 dwarf ellipticals (dE’s) selected by morphology. The sample uses data from GALEX, SDSS, and WISE to investigate the colors in the NUV, ugri, and W1 (3.4 μm) filters. We confirm the blueward shift in the color–magnitude relation (CMR) for dE’s, compared to the CMR for bright ellipticals, as seen in previous studies. However, we find that the deviation in color across the UV to near-IR for dE’s is a strong signal of a younger age for dE’s, one that indicates decreasing mean age with lower stellar mass. Lower mass dE’s are found to have mean ages of 4 Gyr and mean [Fe/H] values of ‑1.2. Age and metallicity increase tothe most massive dE’s, with mean ages similar to normal ellipticals (12 Gyr) and their lowest metallicities ([Fe/H] = ‑0.3). Deduced initial star formation rates for dE’s, combined with their current metallicities and central stellar densities, suggest a connection between field low surface brightness (LSB) dwarfs and cluster dE’s, where the cluster environment halts star formation for dE’s, triggering a separate evolutionary path.

On the structure of solar and stellar coronae - Loops and loop heat transport

NASA Technical Reports Server (NTRS)

Litwin, Christof; Rosner, Robert

1993-01-01

We discuss the principal constraints on mechanisms for structuring and heating the outer atmospheres - the coronae - of stars. We argue that the essential cause of highly localized heating in the coronae of stars like the sun is the spatially intermittent nature of stellar surface magnetic fields, and that the spatial scale of the resulting coronal structures is related to the spatial structure of the photospheric fields. We show that significant constraints on coronal heating mechanisms derive from the observed variations in coronal emission, and, in addition, show that the observed structuring perpendicular to coronal magnetic fields imposes severe constraints on mechanisms for heat dispersal in the low-beta atmosphere. In particular, we find that most of commonly considered mechanisms for heat dispersal, such as anomalous diffusion due to plasma turbulence or magnetic field line stochasticity, are much too slow to account for the observed rapid heating of coronal loops. The most plausible mechanism appears to be reconnection at the interface between two adjacent coronal flux bundles. Based on a model invoking hyperresistivity, we show that such a mechanism naturally leads to dominance of isolated single bright coronal loops and to bright coronal plasma structures whose spatial scale transverse to the local magnetic field is comparable to observed dimensions of coronal X-ray loops.

Dark Matter Halos with VIRUS-P

NASA Astrophysics Data System (ADS)

Murphy, Jeremy; Gebhardt, K.

2010-05-01

We present new, two-dimensional stellar kinematic data on several of the most massive galaxies in the local universe. These data were taken with the integral field spectrograph, VIRUS-P, and extend to unprecedented radial distances. Once robust stellar kinematics are in hand, we run orbit-based axisymmetric dynamical models in order to constrain the stellar mass-to-light ratio and dark matter halo parameters. We have run a large set of dynamical models on the second rank galaxy in the Virgo cluster, M87, and find clear evidence for a massive dark matter halo. The two-dimensional stellar kinematics for several of our other targets, all first and second rank galaxies, are also presented. Dark matter halos are known to dominate the mass profile of elliptical galaxies somewhere between one to two effective radii, yet due to the low surface brightness at these radial distances, determining stellar dynamics is technologically challenging. To overcome this, constraints on the dark matter halo are often made with planetary nebulae or globular clusters at large radii. However, as results from different groups have returned contradictory results, it remains unclear whether different dynamical tracers always follow the stellar kinematics. Due to VIRUS-P's large field of view and on-sky fiber diameter, we are able to determine stellar kinematics at radial distances that overlap with other dynamical tracers. Understanding what the dynamics of stars, planetary nebula and globular clusters tell us about both the extent of the dark matter halo profile and the formation histories of the largest elliptical galaxies is a primary science driver for this work.

Evaluation of parameters of Black Hole, stellar cluster and dark matter distribution from bright star orbits in the Galactic Center

NASA Astrophysics Data System (ADS)

Zakharov, Alexander

It is well-known that one can evaluate black hole (BH) parameters (including spin) analyz-ing trajectories of stars around BH. A bulk distribution of matter (dark matter (DM)+stellar cluster) inside stellar orbits modifies trajectories of stars, namely, generally there is a apoas-tron shift in direction which opposite to GR one, even now one could put constraints on DM distribution and BH parameters and constraints will more stringent in the future. Therefore, an analyze of bright star trajectories provides a relativistic test in a weak gravitational field approximation, but in the future one can test a strong gravitational field near the BH at the Galactic Center with the same technique due to a rapid progress in observational facilities. References A. Zakharov et al., Phys. Rev. D76, 062001 (2007). A.F. Zakharov et al., Space Sci. Rev. 148, 301313(2009).

Stellar Activity and Outer Atmospheric Structure of Yellow Supergiants from HST STIS and GHRS Spectroscopy

NASA Astrophysics Data System (ADS)

Brown, A.; Ayres, T. R.; Harper, G. M.; Osten, R. A.; Linsky, J. L.; Dupree, A. K.; Jordan, C.

2000-05-01

Yellow supergiants with spectral types F-G show a complex pattern of outer atmospheric structure with stellar wind and activity indicators varying significantly for stars with similar positions in the H-R diagram. The efficiency of the processes driving their stellar winds and heating their atmospheres is critically dependent on the evolutionary position and surface gravity of each star. We present high-resolution ultraviolet HST/STIS and HST/GHRS spectra for a range of intermediate mass F and G supergiants, including Alpha Car (F0 Ib), Beta Cam (G0 Ib), Beta Dra (G2 Ib), and Epsilon Gem (G8 Ib), and compare the atmospheric properties of these stars with lower luminosity giants and bright giants. We provide a systematic overview of the supergiant atmospheric properties dealing particularly with activity levels, the presence of hot ``transition region'' plasma, signatures of wind outflow, and the role of overlying cool absorbing plasma that becomes increasingly prominent for the cooler stars like Epsilon Gem. This work is supported by HST grants for program GO-08280 and by NASA grant NAG5-3226.

Probing the mass assembly of massive nearby galaxies with deep imaging

NASA Astrophysics Data System (ADS)

Duc, P.-A.; Cuillandre, J.-C.; Alatalo, K.; Blitz, L.; Bois, M.; Bournaud, F.; Bureau, M.; Cappellari, M.; Côté, P.; Davies, R. L.; Davis, T. A.; de Zeeuw, P. T.; Emsellem, E.; Ferrarese, L.; Ferriere, E.; Gwyn, S.; Khochfar, S.; Krajnovic, D.; Kuntschner, H.; Lablanche, P.-Y.; McDermid, R. M.; Michel-Dansac, L.; Morganti, R.; Naab, T.; Oosterloo, T.; Sarzi, M.; Scott, N.; Serra, P.; Weijmans, A.; Young, L. M.

2013-07-01

According to a popular scenario supported by numerical models, the mass assembly and growth of massive galaxies, in particular the Early-Type Galaxies (ETGs), is, below a redshift of 1, mainly due to the accretion of multiple gas-poor satellites. In order to get observational evidence of the role played by minor dry mergers, we are obtaining extremely deep optical images of a complete volume limited sample of nearby ETGs. These observations, done with the CFHT as part of the ATLAS3D, NGVS and MATLAS projects, reach a stunning 28.5 - 29 mag.arcsec-2 surface brightness limit in the g' band. They allow us to detect the relics of past collisions such as faint stellar tidal tails as well as the very extended stellar halos which keep the memory of the last episodes of galactic accretion. Images and preliminary results from this on-going survey are presented, in particular a possible correlation between the fine structure index (which parametrizes the amount of tidal perturbation) of the ETGs, their stellar mass, effective radius and gas content.

Influence of stellar multiplicity on planet formation. I. Evidence of suppressed planet formation due to stellar companions within 20 au and validation of four planets from the Kepler multiple planet candidates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei

2014-03-01

The planet occurrence rate for multiple stars is important in two aspects. First, almost half of stellar systems in the solar neighborhood are multiple systems. Second, the comparison of the planet occurrence rate for multiple stars to that for single stars sheds light on the influence of stellar multiplicity on planet formation and evolution. We developed a method of distinguishing planet occurrence rates for single and multiple stars. From a sample of 138 bright (K{sub P} < 13.5) Kepler multi-planet candidate systems, we compared the stellar multiplicity rate of these planet host stars to that of field stars. Using dynamicalmore » stability analyses and archival Doppler measurements, we find that the stellar multiplicity rate of planet host stars is significantly lower than field stars for semimajor axes less than 20 AU, suggesting that planet formation and evolution are suppressed by the presence of a close-in companion star at these separations. The influence of stellar multiplicity at larger separations is uncertain because of search incompleteness due to a limited Doppler observation time baseline and a lack of high-resolution imaging observation. We calculated the planet confidence for the sample of multi-planet candidates and find that the planet confidences for KOI 82.01, KOI 115.01, KOI 282.01, and KOI 1781.02 are higher than 99.7% and thus validate the planetary nature of these four planet candidates. This sample of bright Kepler multi-planet candidates with refined stellar and orbital parameters, planet confidence estimation, and nearby stellar companion identification offers a well-characterized sample for future theoretical and observational study.« less

Near Infrared Maps of Elliptical and so Galaxies Detected by IRAS

NASA Astrophysics Data System (ADS)

Cruz-Gonzalez, L.; Recillas-Cruz, E.; Carrasco, L.

1987-05-01

Lw surface brightness maps at 2.2 and 1.25 µm are presented for an IRAS selected sample composed of 3 elliptical and 7 S0 galaxies. In most cases we have found smooth structures which apparently follow the stellar distribution as inferred from the optical images and that the IR emission is more extended. Elongated structures, reminiscent of "jets", are present in a number of galaxies. These 11jets" do not have optical counterparts in the PoSS. This fact suggests a rather steep spectral index between the visible and infrared wavelengths. Fran data at other wavelengths taken from the literature, we have derived spectral energy distributions from .3 to 100 µm. All objects in our sample show a steep α60-l00 µm -l to -2, while in the near IR the energy distributions are characteristic and hence dominated by the presence of a stellar bulge.

Constraints on Variability of Brightness and Surface Magnetism on Time Scales of Decades to Centuries in the Sun and Sun-Like Stars: A Source of Potential Terrestrial Climate Variability

NASA Technical Reports Server (NTRS)

Baliunas, Sallie L.; Sharber, James (Technical Monitor)

2003-01-01

The following summarizes the most important, results of our research: (1) Conciliation of solar and stellar photometric variability; (2) Demonstration of an inverse correlation between the global temperature of the terrestrial lower troposphere, inferred from the NASA Microwave Sounding Unit (MSU)) radiometers, and the total area of the Sun covered by coronal holes from January 1979 to present (up to May 2000); (3) Identification of a possible climate mechanism amplifying the impact of solar ultraviolet irradiance variations; (4) Exploration of natural variability in an ocean-atmosphere climate model; (5) Presentation of a review of the sun's coronal influence on the terrestrial space environment; (6) Quantification of stellar variability as an influence on the analysis of periodic radial velocities that imply the presence of a planetary companion.

A method for the microlensed flux variance of QSOs

NASA Astrophysics Data System (ADS)

Goodman, Jeremy; Sun, Ai-Lei

2014-06-01

A fast and practical method is described for calculating the microlensed flux variance of an arbitrary source by uncorrelated stars. The required inputs are the mean convergence and shear due to the smoothed potential of the lensing galaxy, the stellar mass function, and the absolute square of the Fourier transform of the surface brightness in the source plane. The mathematical approach follows previous authors but has been generalized, streamlined, and implemented in publicly available code. Examples of its application are given for Dexter and Agol's inhomogeneous-disc models as well as the usual Gaussian sources. Since the quantity calculated is a second moment of the magnification, it is only logarithmically sensitive to the sizes of very compact sources. However, for the inferred sizes of actual quasi-stellar objects (QSOs), it has some discriminatory power and may lend itself to simple statistical tests. At the very least, it should be useful for testing the convergence of microlensing simulations.

X-ray emission from galaxies - The distribution of low-luminosity X-ray sources in the Galactic Centre region

NASA Astrophysics Data System (ADS)

Heard, Victoria; Warwick, Robert

2012-09-01

We report a study of the extended X-ray emission observed in the Galactic Centre (GC) region based on archival XMM-Newton data. The GC diffuse emission can be decomposed into three distinct components: the emission from low-luminosity point sources; the fluorescence of (and reflection from) dense molecular material; and soft (kT ~1 keV), diffuse thermal plasma emission most likely energised by supernova explosions. Here, we examine the emission due to unresolved point sources. We show that this source component accounts for the bulk of the 6.7-keV and 6.9-keV line emission. We fit the surface brightness distribution evident in these lines with an empirical 2-d model, which we then compare with a prediction derived from a 3-d mass model for the old stellar population in the GC region. We find that the X-ray surface brightness declines more rapidly with angular offset from Sgr A* than the mass-model prediction. One interpretation is that the X-ray luminosity per solar mass characterising the GC source population is increasing towards the GC. Alternatively, some refinement of the mass-distribution within the nuclear stellar disc may be required. The unresolved X-ray source population is most likely dominated by magnetic CVs. We use the X-ray observations to set constraints on the number density of such sources in the GC region. Our analysis does not support the premise that the GC is pervaded by very hot (~ 7.5 keV) thermal plasma, which is truly diffuse in nature.

BRITE-Constellation high-precision time-dependent photometry of the early O-type supergiant ζ Puppis unveils the photospheric drivers of its small- and large-scale wind structures

NASA Astrophysics Data System (ADS)

Ramiaramanantsoa, Tahina; Moffat, Anthony F. J.; Harmon, Robert; Ignace, Richard; St-Louis, Nicole; Vanbeveren, Dany; Shenar, Tomer; Pablo, Herbert; Richardson, Noel D.; Howarth, Ian D.; Stevens, Ian R.; Piaulet, Caroline; St-Jean, Lucas; Eversberg, Thomas; Pigulski, Andrzej; Popowicz, Adam; Kuschnig, Rainer; Zocłońska, Elżbieta; Buysschaert, Bram; Handler, Gerald; Weiss, Werner W.; Wade, Gregg A.; Rucinski, Slavek M.; Zwintz, Konstanze; Luckas, Paul; Heathcote, Bernard; Cacella, Paulo; Powles, Jonathan; Locke, Malcolm; Bohlsen, Terry; Chené, André-Nicolas; Miszalski, Brent; Waldron, Wayne L.; Kotze, Marissa M.; Kotze, Enrico J.; Böhm, Torsten

2018-02-01

From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78-d signal previously detected by Coriolis/Solar Mass Ejection Imager, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light-curve inversion algorithm, we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multisite spectroscopic monitoring of the star unveiled cyclical modulation of its He II λ4686 wind emission line with the 1.78-d rotation period, showing signatures of corotating interaction regions that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He II λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability.

THE MOLECULAR GAS DENSITY IN GALAXY CENTERS AND HOW IT CONNECTS TO BULGES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fisher, David B.; Bolatto, Alberto; Drory, Niv

2013-02-20

In this paper we present gas density, star formation rate (SFR), stellar masses, and bulge-disk decompositions for a sample of 60 galaxies. Our sample is the combined sample of the BIMA SONG, CARMA STING, and PdBI NUGA surveys. We study the effect of using CO-to-H{sub 2} conversion factors that depend on the CO surface brightness, and also that of correcting SFRs for diffuse emission from old stellar populations. We estimate that SFRs in bulges are typically lower by 20% when correcting for diffuse emission. Using the surface brightness dependent conversion factor, we find that over half of the galaxies inmore » our sample have {Sigma}{sub mol} > 100 M {sub Sun} pc{sup -2}. Though our sample is not complete in any sense, our results are enough to rule out the assumption that bulges are uniformly gas-poor systems. We find a trend between gas density of bulges and bulge Sersic index; bulges with lower Sersic index have higher gas density. Those bulges with low Sersic index (pseudobulges) have gas fractions that are similar to that of disks. Conversely, the typical molecular gas fraction in classical bulges is more similar to that of an elliptical galaxy. We also find that there is a strong correlation between bulges with the highest gas surface density and the galaxy being barred. However, we also find that classical bulges with low gas surface density can be barred as well. Our results suggest that understanding the connection between the central surface density of gas in disk galaxies and the presence of bars should also take into account the total gas content of the galaxy. Finally, we show that when using the corrected SFRs and gas densities, the correlation between SFR surface density and gas surface density of bulges is similar to that of disks. This implies that at the scale of the bulges the timescale for converting gas into stars is comparable to those results found in disks.« less

The KONA Survey: A Near-IR Perspective of the Circumnuclear Environment of local Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Hicks, Erin K. S.; Mueller Sanchez, Francisco; Malkan, Matthew Arnold

2018-06-01

With the Keck OSIRIS Nearby AGN, KONA, survey we simultaneously probe the stellar, molecular gas, and ionized gas kinematics within the central 400 pc of a sample of 40 local representative AGN. KONA's spatially resolved spectra enable an unprecedented study of the feeding and feedback processes in bona- fide AGN. We present a study the nuclear K-band properties of these local Seyferts, as well as the integrated molecular hydrogen and stellar distribution and kinematic at radii varying from 25 to 200 pc. We find that the luminosities of the unresolved Seyfert 1 sources at 2.1 microns are correlated with the hard X-ray luminosities over 3 orders of magnitude in both K-band and X-ray luminosities, implying that the majority of the emission is non-stellar. No correlation is found between the 2.1 microns luminosity and hard X-ray luminosity for the Seyfert 2 galaxies. The spatial extent and spectral slope of the Seyfert 2 galaxies indicates the presence of nuclear star formation and attenuating material (gas and dust), which is found to be compact in some galaxies and in others extended. A comparison of the circumnuclear stellar and molecular hydrogen properties (flux distribution, surface brightness, and velocity dispersion) in Seyfert 1 and 2 sources will also be presented.

(Almost) Dark Galaxies in the ALFALFA Survey: HI-bearing Ultra-Diffuse Galaxies, and Beyond

NASA Astrophysics Data System (ADS)

Leisman, Luke; Haynes, Martha P.; Giovanelli, Riccardo; ALFALFA Almost Darks Team

2017-01-01

Scaling relations between HI and stars in galaxies suggest strong ties between their atomic gas content and star formation laws. The Arecibo Legacy Fast ALFA (ALFALFA) blind extragalactic HI survey is well positioned to locate very low surface brightness sources that lie off these relations, the most extreme of which may fall below optical detection limits. Thus, the ALFALFA (Almost) Darks Project has been investigating extreme outliers from these relations by studying the ~1% of ALFALFA sources without apparent stellar counterparts in major optical surveys. We have obtained deep HI and optical imaging of 25 of these candidate "dark" sources. We find that most "dark" sources are not extreme "(almost) dark" galaxies. A few are rare OH Megamasers, redshifted into the ALFALFA bandpass, and many are part of large galactic plumes, stretching as far as 600 kpc from their host galaxy. However, a small handful of sources appear to be galaxies with extreme stellar systems. We find multiple systems with HI mass to stellar mass ratios an order of magnitude larger than typical gas rich dwarfs. Further, we find an isolated population of HI-bearing "ultra diffuse" galaxies (UDGs), with stellar masses of dwarfs, but HI and optical radii of L* galaxies. We suggest that these sources may be related to recently reported gas poor, quiescent UDGs.

The Mass-Size Relation of Quenched, Quiescent Galaxies in the WISP Survey

NASA Astrophysics Data System (ADS)

Pahl, Anthony; Scarlata, Claudia; Rutkowski, Michael J.; Zanella, Anita; Bagley, Micaela B.; Colbert, James W.; Baronchelli, Ivano; Henry, Alaina L.; Hathi, Nimish P.; Teplitz, Harry I.; Rafelski, Marc; Dai, Yu Sophia; Malkan, Matthew Arnold; Mehta, Vihang; Beck, Melanie

2016-01-01

The relation between the stellar mass and size, if measured for galaxies of similar types, can be a useful tool for studying galactic evolution. We study the mass-size relation of quenched, quiescent galaxies to determine the effect of star-formation history on the growth of these objects over time. The WFC3 Infrared Spectroscopic Parallels (WISP) survey is a large HST IR grism survey of over 385 fields of ~4 arcmin2 each, and it is ideal for studying the star-formation rate with its broad spectral coverage. Using a subset of these fields with deep IR data and measurements across both filters (28 fields), we perform a color selection and identify 83 quenched galaxies with a median z~1.6. With GALFIT, we measure their effective radius and sersic index on the 2-D surface brightness distribution in the F110W band. We perform fitting of grism spectra of the observed galaxies to derive redshift, stellar mass and age for all galaxies. We combine the size, stellar mass, and stellar age determinations to investigate whether the evolution of the mass-size relation over time is primarily driven by the entrance of newly quenched galaxies or by processes affecting the individual quenched galaxies.

The effect of stellar-mass black holes on the central kinematics of ω Cen: a cautionary tale for IMBH interpretations

NASA Astrophysics Data System (ADS)

Zocchi, Alice; Gieles, Mark; Hénault-Brunet, Vincent

2018-06-01

The search for intermediate-mass black holes (IMBHs) in the centre of globular clusters is often based on the observation of a central cusp in the surface brightness profile and a rise towards the centre in the velocity dispersion profiles. Similar signatures, however, could result from other effects, that need to be taken into account in order to determine the presence (or the absence) of an IMBH in these stellar systems. Following our previous exploration of the role of radial anisotropy in shaping these observational signatures, we analyse here the effects produced by the presence of a population of centrally concentrated stellar-mass black holes. We fit dynamical models to ω Cen data, and we show that models with ˜5% of their mass in black holes (consistent with ˜100% retention fraction after natal kicks) can reproduce the data. When simultaneously considering both radial anisotropy and mass segregation, the best-fit model includes a smaller population of remnants, and a less extreme degree of anisotropy with respect to the models that include only one of these features. These results underline that before conclusions about putative IMBHs can be made, the effects of stellar-mass black holes and radial anisotropy need to be properly accounted for.

SPICA, Stellar Parameters and Images with a Cophased Array: a 6T visible combiner for the CHARA array.

PubMed

Mourard, Denis; Bério, Philippe; Perraut, Karine; Clausse, Jean-Michel; Creevey, Orlagh; Martinod, Marc-Antoine; Meilland, Anthony; Millour, Florentin; Nardetto, Nicolas

2017-05-01

High angular resolution studies of stars in the optical domain have highly progressed in recent years. After the results obtained with the visible instrument Visible spEctroGraph and polArimeter (VEGA) on the Center for High Angular Resolution Astronomy (CHARA) array and the recent developments on adaptive optics and fibered interferometry, we have started the design and study of a new six-telescope visible combiner with single-mode fibers. It is designed as a low spectral resolution instrument for the measurement of the angular diameter of stars to make a major step forward in terms of magnitude and precision with respect to the present situation. For a large sample of bright stars, a medium spectral resolution mode will allow unprecedented spectral imaging of stellar surfaces and environments for higher accuracy on stellar/planetary parameters. To reach the ultimate performance of the instrument in terms of limiting magnitude (Rmag≃8 for diameter measurements and Rmag≃4 to 5 for imaging), Stellar Parameters and Images with a Cophased Array (SPICA) includes the development of a dedicated fringe tracking system in the H band to reach "long" (200 ms to 30 s) exposures of the fringe signal in the visible.

Early science from the Pan-STARRS1 Optical Galaxy Survey (POGS): Maps of stellar mass and star formation rate surface density obtained from distributed-computing pixel-SED fitting

NASA Astrophysics Data System (ADS)

Thilker, David A.; Vinsen, K.; Galaxy Properties Key Project, PS1

2014-01-01

To measure resolved galactic physical properties unbiased by the mask of recent star formation and dust features, we are conducting a citizen-scientist enabled nearby galaxy survey based on the unprecedented optical (g,r,i,z,y) imaging from Pan-STARRS1 (PS1). The PS1 Optical Galaxy Survey (POGS) covers 3π steradians (75% of the sky), about twice the footprint of SDSS. Whenever possible we also incorporate ancillary multi-wavelength image data from the ultraviolet (GALEX) and infrared (WISE, Spitzer) spectral regimes. For each cataloged nearby galaxy with a reliable redshift estimate of z < 0.05 - 0.1 (dependent on donated CPU power), publicly-distributed computing is being harnessed to enable pixel-by-pixel spectral energy distribution (SED) fitting, which in turn provides maps of key physical parameters such as the local stellar mass surface density, crude star formation history, and dust attenuation. With pixel SED fitting output we will then constrain parametric models of galaxy structure in a more meaningful way than ordinarily achieved. In particular, we will fit multi-component (e.g. bulge, bar, disk) galaxy models directly to the distribution of stellar mass rather than surface brightness in a single band, which is often locally biased. We will also compute non-parametric measures of morphology such as concentration, asymmetry using the POGS stellar mass and SFR surface density images. We anticipate studying how galactic substructures evolve by comparing our results with simulations and against more distant imaging surveys, some of which which will also be processed in the POGS pipeline. The reliance of our survey on citizen-scientist volunteers provides a world-wide opportunity for education. We developed an interactive interface which highlights the science being produced by each volunteer’s own CPU cycles. The POGS project has already proven popular amongst the public, attracting about 5000 volunteers with nearly 12,000 participating computers, and is growing rapidly.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mota, D. F.; Salzano, V.; Capozziello, S.

We investigate whether there is any cosmological evidence for a scalar field with a mass and coupling to matter which change accordingly to the properties of the astrophysical system it ''lives in,'' without directly focusing on the underlying mechanism that drives the scalar field scale-dependent-properties. We assume a Yukawa type of coupling between the field and matter and also that the scalar-field mass grows with density, in order to overcome all gravity constraints within the Solar System. We analyze three different gravitational systems assumed as ''cosmological indicators'': supernovae type Ia, low surface brightness spiral galaxies and clusters of galaxies. Resultsmore » show (i) a quite good fit to the rotation curves of low surface brightness galaxies only using visible stellar and gas-mass components is obtained; (ii) a scalar field can fairly well reproduce the matter profile in clusters of galaxies, estimated by x-ray observations and without the need of any additional dark matter; and (iii) there is an intrinsic difficulty in extracting information about the possibility of a scale-dependent massive scalar field (or more generally about a varying gravitational constant) from supernovae type Ia.« less

Testing Modified Newtonian Dynamics with Low Surface Brightness Galaxies: Rotation Curve FITS

NASA Astrophysics Data System (ADS)

de Blok, W. J. G.; McGaugh, S. S.

1998-11-01

We present modified Newtonian dynamics (MOND) fits to 15 rotation curves of low surface brightness (LSB) galaxies. Good fits are readily found, although for a few galaxies minor adjustments to the inclination are needed. Reasonable values for the stellar mass-to-light ratios are found, as well as an approximately constant value for the total (gas and stars) mass-to-light ratio. We show that the LSB galaxies investigated here lie on the one, unique Tully-Fisher relation, as predicted by MOND. The scatter on the Tully-Fisher relation can be completely explained by the observed scatter in the total mass-to-light ratio. We address the question of whether MOND can fit any arbitrary rotation curve by constructing a plausible fake model galaxy. While MOND is unable to fit this hypothetical galaxy, a normal dark-halo fit is readily found, showing that dark matter fits are much less selective in producing fits. The good fits to rotation curves of LSB galaxies support MOND, especially because these are galaxies with large mass discrepancies deep in the MOND regime.

GHOSTS IN THE ATTIC: MAPPING THE STELLAR CONTENT OF THE S0 GALAXY NGC 5102

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davidge, T. J.

2010-02-15

The spatial distribution of stars in the nearby S0 galaxy NGC 5102 is investigated using images obtained with WIRCam and MegaCam on the Canada-France-Hawaii Telescope. With the exception of gaps between detector elements, the entire galaxy is surveyed in r' and i', while the J and Ks data extend out to R {sub GC} {approx} 6 kpc, which corresponds to almost 7 disk scale lengths. A modest population of main-sequence stars with M{sub V} < -3.5 and ages {approx}70 Myr are detected throughout the disk, with the majority located in the southern half of the galaxy. The stellar disk inmore » the northern half of the galaxy is warped, following structure that is also seen in H I. Objects with photometric properties that are consistent with those of bright asymptotic giant branch (AGB) stars are seen throughout the disk, and the ratio of C stars to bright M giants is consistent with an overall increase in the star formation rate within the past 1 Gyr. Star-forming activity during the interval 0.1-2 Gyr was more centrally concentrated than during the past {approx}100 Myr. The structure of the disk changes near R {sub GC} {approx} 5 kpc (5.5 disk scale lengths), in the sense that the radial surface density profile defined by red supergiants (RSGs) and bright AGB stars levels off at larger radii. RSGs and bright AGB stars are traced out to a radius of 14 kpc (15.6 scale lengths) along the southern portion of the major axis, while a tentative detection is also made of bright AGB stars at a projected distance of {approx}16 kpc along the southeast minor axis. A large clump of AGB stars that subtends {approx}1 arcmin is identified to the west of the galaxy center. It is argued that this is the remnant of a companion galaxy that triggered past episodes of elevated star-forming activity.« less

The nuclear activity and central structure of the elliptical galaxy NGC 5322

NASA Astrophysics Data System (ADS)

Dullo, Bililign T.; Knapen, Johan H.; Williams, David R. A.; Beswick, Robert J.; Bendo, George; Baldi, Ranieri D.; Argo, Megan; McHardy, Ian M.; Muxlow, Tom; Westcott, J.

2018-04-01

We have analysed a new high-resolution e-MERLIN 1.5 GHz radio continuum map together with HST and SDSS imaging of NGC 5322, an elliptical galaxy hosting radio jets, aiming to understand the galaxy's central structure and its connection to the nuclear activity. We decomposed the composite HST + SDSS surface brightness profile of the galaxy into an inner stellar disc, a spheroid, and an outer stellar halo. Past works showed that this embedded disc counter-rotates rapidly with respect to the spheroid. The HST images reveal an edge-on nuclear dust disc across the centre, aligned along the major-axis of the galaxy and nearly perpendicular to the radio jets. After careful masking of this dust disc, we find a central stellar mass deficit Mdef in the spheroid, scoured by SMBH binaries with final mass MBH such that Mdef/MBH ˜ 1.3-3.4. We propose a three-phase formation scenario for NGC 5322, where a few (2-7) `dry' major mergers involving SMBHs built the spheroid with a depleted core. The cannibalism of a gas-rich satellite subsequently creates the faint counter-rotating disc and funnels gaseous material directly on to the AGN, powering the radio core with a brightness temperature of TB, core ˜ 4.5 × 107 K and the low-power radio jets (Pjets ˜ 7.04 × 1020 W Hz-1), which extend ˜1.6 kpc. The outer halo can later grow via minor mergers and the accretion of tidal debris. The low-luminosity AGN/jet-driven feedback may have quenched the late-time nuclear star formation promptly, which could otherwise have replenished the depleted core.

Serendipitous discovery of a strong-lensed galaxy in integral field spectroscopy from MUSE

NASA Astrophysics Data System (ADS)

Galbany, Lluís; Collett, Thomas E.; Méndez-Abreu, Jairo; Sánchez, Sebastián F.; Anderson, Joseph P.; Kuncarayakti, Hanindyo

2018-06-01

2MASX J04035024-0239275 is a bright red elliptical galaxy at redshift 0.0661 that presents two extended sources at 2″ to the north-east and 1″ to the south-west. The sizes and surface brightnesses of the two blue sources are consistent with a gravitationally-lensed background galaxy. In this paper we present MUSE observations of this galaxy from the All-weather MUse Supernova Integral-field Nearby Galaxies (AMUSING) survey, and report the discovery of a background lensed galaxy at redshift 0.1915, together with other 15 background galaxies at redshifts ranging from 0.09 to 0.9, that are not multiply imaged. We have extracted aperture spectra of the lens and all the sources and fit the stellar continuum with STARLIGHT to estimate their stellar and emission line properties. A trace of past merger and active nucleus activity is found in the lensing galaxy, while the background lensed galaxy is found to be star-forming. Modeling the lensing potential with a singular isothermal ellipsoid, we find an Einstein radius of 1."45±0."04, which corresponds to 1.9 kpc at the redshift of the lens and it is much smaller than its effective radius (reff ˜ 9″"). Comparing the Einstein mass and the STARLIGHT stellar mass within the same aperture yields a dark matter fraction of 18% ± 8 % within the Einstein radius. The advent of large surveys such as the Large Synoptic Survey Telescope (LSST) will discover a number of strong-lensed systems, and here we demonstrate how wide-field integral field spectroscopy offers an excellent approach to study them and to precisely model lensing effects.

The Stellar Populations of Two Ultra-diffuse Galaxies from Optical and Near-infrared Photometry

NASA Astrophysics Data System (ADS)

Pandya, Viraj; Romanowsky, Aaron J.; Laine, Seppo; Brodie, Jean P.; Johnson, Benjamin D.; Glaccum, William; Villaume, Alexa; Cuillandre, Jean-Charles; Gwyn, Stephen; Krick, Jessica; Lasker, Ronald; Martín-Navarro, Ignacio; Martinez-Delgado, David; van Dokkum, Pieter

2018-05-01

We present observational constraints on the stellar populations of two ultra-diffuse galaxies (UDGs) using optical through near-infrared (NIR) spectral energy distribution (SED) fitting. Our analysis is enabled by new Spitzer-IRAC 3.6 and 4.5 μm imaging, archival optical imaging, and the prospector fully Bayesian SED fitting framework. Our sample contains one field UDG (DGSAT I), one Virgo cluster UDG (VCC 1287), and one Virgo cluster dwarf elliptical for comparison (VCC 1122). We find that the optical–NIR colors of the three galaxies are significantly different from each other. We infer that VCC 1287 has an old (≳7.7 Gyr) and surprisingly metal-poor ([Z/Z ⊙] ≲ ‑1.0) stellar population, even after marginalizing over uncertainties on diffuse interstellar dust. In contrast, the field UDG DGSAT I shows evidence of being younger than the Virgo UDG, with an extended star formation history and an age posterior extending down to ∼3 Gyr. The stellar metallicity of DGSAT I is sub-solar but higher than that of the Virgo UDG, with [Z/{Z}ȯ ]=-{0.63}-0.62+0.35; in the case of exactly zero diffuse interstellar dust, DGSAT I may even have solar metallicity. With VCC 1287 and several Coma UDGs, a general picture is emerging where cluster UDGs may be “failed” galaxies, but the field UDG DGSAT I seems more consistent with a stellar feedback-induced expansion scenario. In the future, our approach can be applied to a large and diverse sample of UDGs down to faint surface brightness limits, with the goal of constraining their stellar ages, stellar metallicities, and circumstellar and diffuse interstellar dust content.

Optical/Near-IR spatially resolved study of the H II galaxy Tol 02★

NASA Astrophysics Data System (ADS)

Torres-Campos, A.; Terlevich, E.; Rosa-González, D.; Terlevich, R.; Telles, E.; Díaz, A. I.

2017-11-01

The main goal of this study is to characterize the stellar populations in very low-metallicity galaxies. We have obtained broad U, B, R, I, J, H, K, intermediate Strömgren y and narrow H α and [O III] deep images of the Wolf-Rayet, blue compact dwarf, H II galaxy Tol 02. We have analysed the low surface brightness component, the stellar cluster complexes and the H II regions. The stellar populations in the galaxy have been characterized by comparing the observed broad-band colours with those of single stellar population models. The main results are consistent with Tol 02 being formed by a 1.5 Gyr old disc component at the centre of which a group of eight massive (>104 M⊙) stellar cluster clumps is located. Six of these clumps are 10 Myr old and their near-infrared colours suggest that their light is dominated by Red Supergiant (RSG) stars, the other two are young Wolf-Rayet cluster candidates of ages 3 and 5 Myr, respectively. 12 H II regions in the star-forming region of the galaxy are also identified. These are immersed in a diffuse H α and [O III] emission that spreads towards the north and south covering the old stellar disc. Our spatial-temporal analysis shows that star formation is more likely stochastic and simultaneous within short time-scales. The mismatch between observations and models cannot be attributed alone to a mistreat of the RSG phase and still needs to be further investigated.

Cannibalization and Rebirth in the NGC 5387 System. I. The Stellar Stream and Star-forming Region

NASA Astrophysics Data System (ADS)

Beaton, Rachael L.; Martínez-Delgado, David; Majewski, Steven R.; D'Onghia, Elena; Zibetti, Stefano; Gabany, R. Jay; Johnson, Kelsey E.; Blanton, Michael; Verbiscer, Anne

2014-08-01

We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on, spiral galaxy NGC 5387. An optically blue overdensity coincident with the stream intersection with the NGC 5387 disk was also identified in SDSS and in the Galaxy Evolution Explorer Deep Imaging Survey contributing 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features. The stellar stream is red in color, (B - V) = 0.7, has a stellar mass of 6 × 108 M ⊙, which implies a 1:50 merger ratio, has a circular radius, R circ ~ 11.7 kpc, formed in ~240 Myr, and the progenitor had a total mass of ~4 × 1010 M ⊙. Spectroscopy from LBT+MODS1 was used to determine that the blue overdensity is at the same redshift as NGC 5387, consists of young stellar populations (~10 Myr), is metal-poor (12 + log (O/H) = 8.03), and is forming stars at an enhanced rate (~1-3 M ⊙ yr-1). The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation. Additional exploration of these scenarios is presented in a companion paper. Based on observations with the VATT: the Alice P. Lennon Telescope and the Thomas J. Bannan Astrophysics Facility.

Low Surface Brightness Imaging of the Magellanic System: Imprints of Tidal Interactions between the Clouds in the Stellar Periphery

NASA Astrophysics Data System (ADS)

Besla, Gurtina; Martínez-Delgado, David; van der Marel, Roeland P.; Beletsky, Yuri; Seibert, Mark; Schlafly, Edward F.; Grebel, Eva K.; Neyer, Fabian

2016-07-01

We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts of the stellar disk of the LMC (<10° from the LMC center). These data have higher resolution than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in the northern periphery, with no comparable counterparts in the south. We compare these data to detailed simulations of the LMC disk outskirts, following interactions with its low mass companion, the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field. The simulations are used to assess the origin of the northern structures, including also the low density stellar arc recently identified in the Dark Energy Survey data by Mackey et al. at ˜15°. We conclude that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for 1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are driven by dwarf-dwarf interactions.

IUE investigations of SN 1987A

NASA Technical Reports Server (NTRS)

Kirshner, Robert P.

1989-01-01

IUE observations of the SN 1987A began shortly after the discovery and have been frequent through 1988 and 1989, using the fine error sensor for photometry, low dispersion spectra for the supernova spectrum, and high dispersion observations for the interstellar medium when the supernova was bright and for circumstellar gas surrounding the supernova as the initial event faded. The UV data were very useful in determining which star exploded, assessing the ionizing pulse produced as the shock hit the surface of the star, and in constraining the stellar evolution that preceded the explosion through observations of a circumstellar shell.

The appearance of highly relativistic, spherically symmetric stellar winds

NASA Technical Reports Server (NTRS)

Abramowicz, Marek A.; Novikov, Igor D.; Paczynski, Bohdan

1991-01-01

A nonluminous, steady state, spherically symmetric, relativistic wind, with the opacity dominated by electron scattering appears against a bright background as a dark circle with the radius rd. A luminous wind would appear as a bright spot with a radius rl = rd/2 pi gamma exp 3, where gamma is the Lorentz factor of the wind. The bright wind photosphere is convex for v equal to or less than 2c/3, and appears concave for higher outflow velocities.

A deep narrowband survey for planetary nebulae at the outskirts of M 33

NASA Astrophysics Data System (ADS)

Galera-Rosillo, R.; Corradi, R. L. M.; Mampaso, A.

2018-04-01

Context. Planetary nebulae (PNe) are excellent tracers of stellar populations with low surface brightness, and therefore provide a powerful method to detect and explore the rich system of substructures discovered around the main spiral galaxies of the local group. Aim. We searched the outskirts of the local group spiral galaxy M 33 (the Triangulum) for PNe to gain new insights into the extended stellar substructure on the northern side of the disc and to study the existence of a faint classical halo. Methods: The search is based on wide field imaging covering a 4.5 square degree area out to a maximum projected distance of about 40 kpc from the centre of the galaxy. The PN candidates are detected by the combination of images obtained in narrowband filters selecting the [OIII]λ5007 Å and Hα + [NII] nebular lines and in the continuum g' and r' broadband filters. Results: Inside the bright optical disc of M 33, eight new PN candidates were identified, three of which were spectroscopically confirmed. No PN candidates were found outside the limits of the disc. Fourteen additional sources showing [OIII] excess were also discovered. Conclusions: The absence of bright PN candidates in the area outside the galaxy disc covered by this survey sets an upper limit to the luminosity of the underlying population of 1.6 × 107 L⊙, suggesting the lack of a massive classical halo, which is in agreement with the results obtained using the red giant branch population. Based on observations made with the Isaac Newton Telescope and service observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

The primary role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel; Gaensicke, Boris; Rodriguez-Gil, Pablo; Long, Knox; Marsh, Tom; Steeghs, Danny; Munoz-Darias, Teodoro; Shahbaz, Tariq; Schmidtobreick, Linda; Schreiber, Matthias

2009-02-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) which plays a fundamental role in our understanding of CV structure and evolution. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assesment of their evolutionary state is illusionary. We are monitoring the brightness of a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the binary parameters, white dwarf temperature, and distance to the system for a SW Sex star for the first time. The measured stellar masses and radii will especially be a precious input to the theory of compact binary evolution as a whole.

The local metallicity-surface brightness relationship in galactic disks

NASA Technical Reports Server (NTRS)

Ryder, Stuart D.

1995-01-01

We present the results of a first attempt to employ multiaperture masks to obtain spectrophotometry of H II regions in nearby galaxies. A total of 97 H II regions in six southern spiral galaxies were observed using a combination of multiaperture masks and conventional long-slit spectrophotometry. The oxygen abundances derived from the multiaperture mask observations using the empirical abundance diagnostic R(sub 23) are shown to be consistent with those from long-slit spectra and generally show better reproducibility and object definition. Although the number of objects that can be observed simultaneously with this particular system is still quite limited compared with either imaging spectrophotometry or fiber-fed spectrographs, the spectral resolution offered and high throughput in the blue help make multiaperture spectrophotometry a competitive technique for increasing the sampling of H II regions in both radial distance and luminosity. There is still no clear trend of abundance gradient with either the galaxy's luminosity or its Hubble type, although the extrapolated central abundance does appear to correlate with galaxy luminosity/mass. In order to avoid difficulty in choosing an appropriate normalizing radius, we instead plot the oxygen abundance against the underlying I-band surface brightness at the radial distance of the H II region and confirm the existence of a local metallicity-surface brightness reltaionship within the disks of spiral galaxies. Although the simple closed-boc model of galaxy evolution predicts almost the right form of this relationship, a more realistic multizone model employing expnentially decreasing gas infall provides a more satisfactory fit to the observational data, provided the expected enriched gas return from dying low-mass stars shedding their envelopes at late epochs is properly taken into account. This same model, with a star formation law based upon self-regulating star formation in a three-dimensional disk (Dopita & Ryder 1994), is equally capable of accounting for the observed relationship between recent massive star formation and stellar surface brightness (Ryder & Dopita 1994).

MOST detects corotating bright spots on the mid-O-type giant ξ Persei

NASA Astrophysics Data System (ADS)

Ramiaramanantsoa, Tahina; Moffat, Anthony F. J.; Chené, André-Nicolas; Richardson, Noel D.; Henrichs, Huib F.; Desforges, Sébastien; Antoci, Victoria; Rowe, Jason F.; Matthews, Jaymie M.; Kuschnig, Rainer; Weiss, Werner W.; Sasselov, Dimitar; Rucinski, Slavek M.; Guenther, David B.

2014-06-01

We have used the MOST (Microvariability and Oscillations of STars) microsatellite to obtain four weeks of contiguous high-precision broad-band visual photometry of the O7.5III(n)((f)) star ξ Persei in 2011 November. This star is well known from previous work to show prominent DACs (discrete absorption components) on time-scales of about 2 d from UV spectroscopy and non-radial pulsation with one (l = 3) p-mode oscillation with a period of 3.5 h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails to reveal any periodic light variations above the 0.1 mmag 3σ noise level for periods of a few hours, while several prominent Fourier peaks emerge at the 1 mmag level in the two-day period range. These longer period variations are unlikely due to pulsations, including gravity modes. From our simulations based upon a simple spot model, we deduce that we are seeing the photometric modulation of several corotating bright spots on the stellar surface. In our model, the starting times (random) and lifetimes (up to several rotations) vary from one spot to another yet all spots rotate at the same period of 4.18 d, the best-estimated rotation period of the star. This is the first convincing reported case of corotating bright spots on an O star, with important implications for drivers of the DACs (resulting from corotating interaction regions) with possible bright-spot generation via a breakout at the surface of a global magnetic field generated by a subsurface convection zone.

Extreme emission-line galaxies out to z ~ 1 in zCOSMOS. I. Sample and characterization of global properties

NASA Astrophysics Data System (ADS)

Amorín, R.; Pérez-Montero, E.; Contini, T.; Vílchez, J. M.; Bolzonella, M.; Tasca, L. A. M.; Lamareille, F.; Zamorani, G.; Maier, C.; Carollo, C. M.; Kneib, J.-P.; Le Fèvre, O.; Lilly, S.; Mainieri, V.; Renzini, A.; Scodeggio, M.; Bardelli, S.; Bongiorno, A.; Caputi, K.; Cucciati, O.; de la Torre, S.; de Ravel, L.; Franzetti, P.; Garilli, B.; Iovino, A.; Kampczyk, P.; Knobel, C.; Kovač, K.; Le Borgne, J.-F.; Le Brun, V.; Mignoli, M.; Pellò, R.; Peng, Y.; Presotto, V.; Ricciardelli, E.; Silverman, J. D.; Tanaka, M.; Tresse, L.; Vergani, D.; Zucca, E.

2015-06-01

Context. The study of large and representative samples of low-metallicity star-forming galaxies at different cosmic epochs is of great interest to the detailed understanding of the assembly history and evolution of low-mass galaxies. Aims: We present a thorough characterization of a large sample of 183 extreme emission-line galaxies (EELGs) at redshift 0.11 ≤ z ≤ 0.93 selected from the 20k zCOSMOS bright survey because of their unusually large emission line equivalent widths. Methods: We use multiwavelength COSMOS photometry, HST-ACS I-band imaging, and optical zCOSMOS spectroscopy to derive the main global properties of star-forming EELGs, such as sizes, stellar masses, star formation rates (SFR), and reliable oxygen abundances using both "direct" and "strong-line" methods. Results: The EELGs are extremely compact (r50 ~ 1.3 kpc), low-mass (M∗ ~ 107-1010 M⊙) galaxies forming stars at unusually high specific star formation rates (sSFR ≡ SFR/M⋆ up to 10-7 yr-1) compared to main sequence star-forming galaxies of the same stellar mass and redshift. At rest-frame UV wavelengths, the EELGs are luminous and show high surface brightness and include strong Lyα emitters, as revealed by GALEX spectroscopy. We show that zCOSMOS EELGs are high-ionization, low-metallicity systems, with median 12+log (O/H) = 8.16 ± 0.21 (0.2 Z⊙) including a handful of extremely metal-deficient (<0.1 Z⊙) EELGs. While ~80% of the EELGs show non-axisymmetric morphologies, including clumpy and cometary or tadpole galaxies, we find that ~29% of them show additional low-surface-brightness features, which strongly suggests recent or ongoing interactions. As star-forming dwarfs in the local Universe, EELGs are most often found in relative isolation. While only very few EELGs belong to compact groups, almost one third of them are found in spectroscopically confirmed loose pairs or triplets. Conclusions: The zCOSMOS EELGs are galaxies caught in a transient and probably early period of their evolution, where they are efficiently building up a significant fraction of their present-day stellar mass in an ongoing, galaxy-wide starburst. Therefore, the EELGs constitute an ideal benchmark for comparison studies between low- and high-redshift low-mass star-forming galaxies. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A105

Unidentified point sources in the IRAS minisurvey

NASA Technical Reports Server (NTRS)

Houck, J. R.; Soifer, B. T.; Neugebauer, G.; Beichman, C. A.; Aumann, H. H.; Clegg, P. E.; Gillett, F. C.; Habing, H. J.; Hauser, M. G.; Low, F. J.

1984-01-01

Nine bright, point-like 60 micron sources have been selected from the sample of 8709 sources in the IRAS minisurvey. These sources have no counterparts in a variety of catalogs of nonstellar objects. Four objects have no visible counterparts, while five have faint stellar objects visible in the error ellipse. These sources do not resemble objects previously known to be bright infrared sources.

A New Giant Stellar Structure in the Outer Halo of M31

NASA Astrophysics Data System (ADS)

Zucker, Daniel B.; Kniazev, Alexei Y.; Bell, Eric F.; Martínez-Delgado, David; Grebel, Eva K.; Rix, Hans-Walter; Rockosi, Constance M.; Holtzman, Jon A.; Walterbos, Rene A. M.; Ivezić, Željko; Brinkmann, J.; Brewington, Howard; Harvanek, Michael; Kleinman, S. J.; Krzesinski, Jurek; Lamb, Don Q.; Long, Dan; Newman, Peter R.; Nitta, Atsuko; Snedden, Stephanie A.

2004-09-01

The Sloan Digital Sky Survey has revealed an overdensity of luminous red giant stars ~3° (40 projected kpc) to the northeast of M31, which we have called Andromeda NE. The line-of-sight distance to Andromeda NE is within ~50 kpc of M31; Andromeda NE is not a physically unrelated projection. Andromeda NE has a g-band absolute magnitude of ~-11.6 and a central surface brightness of ~29 mag arcsec-2, making it nearly 2 orders of magnitude more diffuse than any known Local Group dwarf galaxy at that luminosity. Based on its distance and morphology, Andromeda NE is likely undergoing tidal disruption. Andromeda NE's red giant branch color is unlike that of M31's present-day outer disk or the stellar stream reported by Ibata et al., arguing against a direct link between Andromeda NE and these structures. However, Andromeda NE has a red giant branch color similar to that of the G1 clump; it is possible that these structures are both material torn off of M31's disk in the distant past or that these are both part of one ancient stellar stream.

Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades

NASA Astrophysics Data System (ADS)

White, T. R.; Pope, B. J. S.; Antoci, V.; Pápics, P. I.; Aerts, C.; Gies, D. R.; Gordon, K.; Huber, D.; Schaefer, G. H.; Aigrain, S.; Albrecht, S.; Barclay, T.; Barentsen, G.; Beck, P. G.; Bedding, T. R.; Fredslund Andersen, M.; Grundahl, F.; Howell, S. B.; Ireland, M. J.; Murphy, S. J.; Nielsen, M. B.; Silva Aguirre, V.; Tuthill, P. G.

2017-11-01

The most powerful tests of stellar models come from the brightest stars in the sky, for which complementary techniques, such as astrometry, asteroseismology, spectroscopy and interferometry, can be combined. The K2 mission is providing a unique opportunity to obtain high-precision photometric time series for bright stars along the ecliptic. However, bright targets require a large number of pixels to capture the entirety of the stellar flux, and CCD saturation, as well as restrictions on data storage and bandwidth, limit the number and brightness of stars that can be observed. To overcome this, we have developed a new photometric technique, which we call halo photometry, to observe very bright stars using a limited number of pixels. Halo photometry is simple, fast and does not require extensive pixel allocation, and will allow us to use K2 and other photometric missions, such as TESS, to observe very bright stars for asteroseismology and to search for transiting exoplanets. We apply this method to the seven brightest stars in the Pleiades open cluster. Each star exhibits variability; six of the stars show what are most likely slowly pulsating B-star pulsations, with amplitudes ranging from 20 to 2000 ppm. For the star Maia, we demonstrate the utility of combining K2 photometry with spectroscopy and interferometry to show that it is not a `Maia variable', and to establish that its variability is caused by rotational modulation of a large chemical spot on a 10 d time-scale.

Investigating a population of infrared-bright gamma-ray burst host galaxies

NASA Astrophysics Data System (ADS)

Chrimes, Ashley A.; Stanway, Elizabeth R.; Levan, Andrew J.; Davies, Luke J. M.; Angus, Charlotte R.; Greis, Stephanie M. L.

2018-07-01

We identify and explore the properties of an infrared-bright gamma-ray burst (GRB) host population. Candidate hosts are selected by coincidence with sources in WISE, with matching to random coordinates and a false alarm probability analysis showing that the contamination fraction is ˜0.5. This methodology has already identified the host galaxy of GRB 080517. We combine survey photometry from Pan-STARRS, SDSS, APASS, 2MASS, GALEX, and WISE with our own WHT/ACAM and VLT/X-shooter observations to classify the candidates and identify interlopers. Galaxy SED fitting is performed using MAGPHYS, in addition to stellar template fitting, yielding 13 possible IR-bright hosts. A further seven candidates are identified from the previously published work. We report a candidate host for GRB 061002, previously unidentified as such. The remainder of the galaxies have already been noted as potential hosts. Comparing the IR-bright population properties including redshift z, stellar mass M⋆, star formation rate SFR, and V-band attenuation AV to GRB host catalogues in the literature, we find that the infrared-bright population is biased towards low z, high M⋆, and high AV. This naturally arises from their initial selection - local and dusty galaxies are more likely to have the required IR flux to be detected in WISE. We conclude that while IR-bright GRB hosts are not a physically distinct class, they are useful for constraining existing GRB host populations, particularly for long GRBs.

Investigating a population of infrared-bright gamma-ray burst host galaxies

NASA Astrophysics Data System (ADS)

Chrimes, Ashley A.; Stanway, Elizabeth R.; Levan, Andrew J.; Davies, Luke J. M.; Angus, Charlotte R.; Greis, Stephanie M. L.

2018-04-01

We identify and explore the properties of an infrared-bright gamma-ray burst (GRB) host population. Candidate hosts are selected by coincidence with sources in WISE, with matching to random coordinates and a false alarm probability analysis showing that the contamination fraction is ˜ 0.5. This methodology has already identified the host galaxy of GRB 080517. We combine survey photometry from Pan-STARRS, SDSS, APASS, 2MASS, GALEX and WISE with our own WHT/ACAM and VLT/X-shooter observations to classify the candidates and identify interlopers. Galaxy SED fitting is performed using MAGPHYS, in addition to stellar template fitting, yielding 13 possible IR-bright hosts. A further 7 candidates are identified from previously published work. We report a candidate host for GRB 061002, previously unidentified as such. The remainder of the galaxies have already been noted as potential hosts. Comparing the IR-bright population properties including redshift z, stellar mass M⋆, star formation rate SFR and V-band attenuation AV to GRB host catalogues in the literature, we find that the infrared-bright population is biased toward low z, high M⋆ and high AV. This naturally arises from their initial selection - local and dusty galaxies are more likely to have the required IR flux to be detected in WISE. We conclude that while IR-bright GRB hosts are not a physically distinct class, they are useful for constraining existing GRB host populations, particularly for long GRBs.

Eight ultra-faint galaxy candidates discovered in year two of the Dark Energy Survey

DOE PAGES

Drlica-Wagner, A.

2015-11-04

Here, we report the discovery of eight new ultra-faint dwarf galaxy candidates in the second year of optical imaging data from the Dark Energy Survey (DES). Six of these candidates are detected at high confidence, while two lower-confidence candidates are identified in regions of non-uniform survey coverage. The new stellar systems are found by three independent automated search techniques and are identified as overdensities of stars, consistent with the isochrone and luminosity function of an old and metal-poor simple stellar population. The new systems are faint (M V > –4.7more » $$\\mathrm{mag}$$) and span a range of physical sizes (17 $$\\mathrm{pc}$$ < r 1/2 < 181 $$\\mathrm{pc}$$) and heliocentric distances (25 kpc < D ⊙ < 214 kpc). All of the new systems have central surface brightnesses consistent with known ultra-faint dwarf galaxies (μ ≳ 27.5 $$\\mathrm{mag}$$ $$\\mathrm{arcsec}$$ –2). Roughly half of the DES candidates are more distant, less luminous, and/or have lower surface brightnesses than previously known Milky Way satellite galaxies. Most of the candidates are found in the southern part of the DES footprint close to the Magellanic Clouds. We find that the DES data alone exclude (p < 10 –3) a spatially isotropic distribution of Milky Way satellites and that the observed distribution can be well, though not uniquely, described by an association between several of the DES satellites and the Magellanic system. Our model predicts that the full sky may hold ~100 ultra-faint galaxies with physical properties comparable to the DES satellites and that 20%–30% of these would be spatially associated with the Magellanic Clouds.« less

A PAndAS view of M31 dwarf elliptical satellites: NGC 147 and NGC 185

NASA Astrophysics Data System (ADS)

Crnojević, D.; Ferguson, A. M. N.; Irwin, M. J.; McConnachie, A. W.; Bernard, E. J.; Fardal, M. A.; Ibata, R. A.; Lewis, G. F.; Martin, N. F.; Navarro, J. F.; Noël, N. E. D.; Pasetto, S.

2014-12-01

We exploit data from the Pan-Andromeda Archaeological Survey (PAndAS) to study the extended structures of M31's dwarf elliptical companions, NGC 147 and NGC 185. Our wide-field, homogeneous photometry allows us to construct deep colour-magnitude diagrams which reach down to ˜3 mag below the red giant branch (RGB) tip. We trace the stellar components of the galaxies to surface brightness of μg ˜ 32 mag arcsec-2 and show that they have much larger extents (˜5 kpc radii) than previously recognized. While NGC 185 retains a regular shape in its peripheral regions, NGC 147 exhibits pronounced isophotal twisting due to the emergence of symmetric tidal tails. We fit single Sérsic models to composite surface brightness profiles constructed from diffuse light and star counts and find that NGC 147 has an effective radius almost three times that of NGC 185. In both cases, the effective radii that we calculate are larger by a factor of ˜2 compared to most literature values. We also calculate revised total magnitudes of Mg = -15.36 ± 0.04 for NGC 185 and Mg = -16.36 ± 0.04 for NGC 147. Using photometric metallicities computed for RGB stars, we find NGC 185 to exhibit a metallicity gradient of [Fe/H] ˜ -0.15 dex kpc-1 over the radial range 0.125-0.5 deg. On the other hand, NGC 147 exhibits almost no metallicity gradient, ˜-0.02 dex kpc-1 from 0.2 to 0.6 deg. The differences in the structure and stellar populations in the outskirts of these systems suggest that tidal influences have played an important role in governing the evolution of NGC 147.

CHARACTERIZING SPIRAL ARM AND INTERARM STAR FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kreckel, K.; Schinnerer, E.; Meidt, S.

2016-08-20

Interarm star formation contributes significantly to a galaxy’s star formation budget and provides an opportunity to study stellar birthplaces unperturbed by spiral arm dynamics. Using optical integral field spectroscopy of the nearby galaxy NGC 628 with VLT/MUSE, we construct H α maps including detailed corrections for dust extinction and stellar absorption to identify 391 H ii regions at 35 pc resolution over 12 kpc{sup 2}. Using tracers sensitive to the underlying gravitational potential, we associate H ii regions with either arm (271) or interarm (120) environments. Using our full spectral coverage of each region, we find that most physical propertiesmore » (luminosity, size, metallicity, ionization parameter) of H ii regions are independent of environment. We calculate the fraction of H α luminosity due to the background of diffuse ionized gas (DIG) contaminating each H ii region, and find the DIG surface brightness to be higher within H ii regions than in the surroundings, and slightly higher within arm H ii regions. Use of the temperature-sensitive [S ii]/H α line ratio instead of the H α surface brightness to identify the boundaries of H ii regions does not change this result. Using the dust attenuation as a tracer of the gas, we find depletion times consistent with previous work (2 × 10{sup 9} yr) with no differences between the arm and interarm, but this is very sensitive to the DIG correction. Unlike molecular clouds, which can be dynamically affected by the galactic environment, we see fairly consistent properties of H ii regions in both arm and interarm environments. This suggests either a difference in star formation and feedback in arms or a decoupling of dense star-forming clumps from the more extended surrounding molecular gas.« less

Characterizing Spiral Arm and Interarm Star Formation

NASA Astrophysics Data System (ADS)

Kreckel, K.; Blanc, G. A.; Schinnerer, E.; Groves, B.; Adamo, A.; Hughes, A.; Meidt, S.

2016-08-01

Interarm star formation contributes significantly to a galaxy’s star formation budget and provides an opportunity to study stellar birthplaces unperturbed by spiral arm dynamics. Using optical integral field spectroscopy of the nearby galaxy NGC 628 with VLT/MUSE, we construct Hα maps including detailed corrections for dust extinction and stellar absorption to identify 391 H II regions at 35 pc resolution over 12 kpc2. Using tracers sensitive to the underlying gravitational potential, we associate H II regions with either arm (271) or interarm (120) environments. Using our full spectral coverage of each region, we find that most physical properties (luminosity, size, metallicity, ionization parameter) of H II regions are independent of environment. We calculate the fraction of Hα luminosity due to the background of diffuse ionized gas (DIG) contaminating each H II region, and find the DIG surface brightness to be higher within H II regions than in the surroundings, and slightly higher within arm H II regions. Use of the temperature-sensitive [S II]/Hα line ratio instead of the Hα surface brightness to identify the boundaries of H II regions does not change this result. Using the dust attenuation as a tracer of the gas, we find depletion times consistent with previous work (2 × 109 yr) with no differences between the arm and interarm, but this is very sensitive to the DIG correction. Unlike molecular clouds, which can be dynamically affected by the galactic environment, we see fairly consistent properties of H II regions in both arm and interarm environments. This suggests either a difference in star formation and feedback in arms or a decoupling of dense star-forming clumps from the more extended surrounding molecular gas.

STELLAR POPULATIONS AND THE STAR FORMATION HISTORIES OF LSB GALAXIES. V. WFC3 COLOR–MAGNITUDE DIAGRAMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schombert, James; McGaugh, Stacy, E-mail: jschombe@uoregon.edu, E-mail: stacy.mcgaugh@case.edu

2015-09-15

We present WFC3 observations of three low surface brightness (LSB) galaxies from the Schombert et al. LSB catalog that are within 11 Mpc of the Milky Way. Deep imaging at F336W, F555W, and F814W allow the construction of the V − I color–magnitude diagrams (CMD) to M{sub I} = −2. Overall 1869, 465, and 501 stellar sources are identified in the three LSB galaxies F415-3, F608-1, and F750-V1, respectively. The spatial distribution of young blue stars matches the Hα maps from ground-based imaging, indicating that star formation in LSB galaxies follows the same style as in other irregular galaxies. Severalmore » star complexes are identified, matching regions of higher surface brightness as seen from ground-based imaging. The CMD for each LSB galaxy has a similar morphology to Local Volume (LV) dwarf galaxies (i.e., a blue main sequence, blue and red He burning branches, and asymptotic giant branch (AGB) stars). The LSB CMD’s distinguish themselves from nearby dwarf CMD’s by having a higher proportion of blue main sequence stars and fewer AGB stars than expected from their mean metallicities. Current [Fe/H] values below −0.6 are deduced from the position of the red helium-burning branch (rHeB) stars in the V − I diagram. The distribution of stars on the blue helium-burning branch (bHeB) and rHeB from the U − V and V − I CMD indicate a history of constant star formation for the last 100 Myr.« less

Eight ultra-faint galaxy candidates discovered in year two of the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drlica-Wagner, A.

Here, we report the discovery of eight new ultra-faint dwarf galaxy candidates in the second year of optical imaging data from the Dark Energy Survey (DES). Six of these candidates are detected at high confidence, while two lower-confidence candidates are identified in regions of non-uniform survey coverage. The new stellar systems are found by three independent automated search techniques and are identified as overdensities of stars, consistent with the isochrone and luminosity function of an old and metal-poor simple stellar population. The new systems are faint (M V > –4.7more » $$\\mathrm{mag}$$) and span a range of physical sizes (17 $$\\mathrm{pc}$$ < r 1/2 < 181 $$\\mathrm{pc}$$) and heliocentric distances (25 kpc < D ⊙ < 214 kpc). All of the new systems have central surface brightnesses consistent with known ultra-faint dwarf galaxies (μ ≳ 27.5 $$\\mathrm{mag}$$ $$\\mathrm{arcsec}$$ –2). Roughly half of the DES candidates are more distant, less luminous, and/or have lower surface brightnesses than previously known Milky Way satellite galaxies. Most of the candidates are found in the southern part of the DES footprint close to the Magellanic Clouds. We find that the DES data alone exclude (p < 10 –3) a spatially isotropic distribution of Milky Way satellites and that the observed distribution can be well, though not uniquely, described by an association between several of the DES satellites and the Magellanic system. Our model predicts that the full sky may hold ~100 ultra-faint galaxies with physical properties comparable to the DES satellites and that 20%–30% of these would be spatially associated with the Magellanic Clouds.« less

Stellar haloes in massive early-type galaxies

NASA Astrophysics Data System (ADS)

Buitrago, F.

2017-03-01

The Hubble Ultra Deep Field (HUDF) opens up an unique window to witness galaxy assembly at all cosmic distances. Thanks to its extraordinary depth, it is a privileged tool to beat the cosmological dimming, which affects any extragalactic observations and has a very strong dependence with redshift (1 +z)^4. In particular, massive (M_{stellar}>5 × 10^{10} M_⊙) Early Type Galaxies (ETGs) are the most interesting candidates for these studies, as they must grow in an inside-out fashion developing an extended stellar envelope/halo that accounts for their remarkable size evolution (˜5 times larger in the nearby Universe than at z=2-3). To this end we have analysed the 6 most massive ETGs at z <1 in the HUDF12. Because of the careful data reduction and the exhaustive treatment of the Point Spread Function (PSF), we are able to trace the galaxy surface brightness profiles up to the same levels as in the local Universe but this time at = 0.65 (31 mag arcsec^{-2} in all 8 HST bands, ˜ 29 mag arcsec^{-2} restframe or beyond 25 effective radii). This fact enables us to investigate the galactic outskirts or stellar haloes at a previously unexplored era, characterising their light and mass profiles, colors and for the first time the amount of mass in ongoing mergers.

THE SPLASH SURVEY: A SPECTROSCOPIC PORTRAIT OF ANDROMEDA'S GIANT SOUTHERN STREAM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilbert, Karoline M.; Guhathakurta, Puragra; Kollipara, Priya

2009-11-10

The giant southern stream (GSS) is the most prominent tidal debris feature in M31's stellar halo and covers a significant fraction of its southern quadrant. The GSS is a complex structure composed of a relatively metal-rich, high-surface-brightness 'core' and a lower metallicity, lower-surface-brightness 'envelope'. We present spectroscopy of red giant stars in six fields in the vicinity of M31's GSS (including four new fields and improved spectroscopic reductions for two previously published fields) and one field on stream C, an arc-like feature seen in star-count maps on M31's southeast minor axis at R approx 60 kpc. These data are partmore » of our ongoing Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey of M31 using the DEIMOS instrument on the Keck II 10 m telescope. Several GSS-related findings and measurements are presented here. We present the innermost kinematical detection of the GSS core to date (R = 17 kpc). This field also contains the inner continuation of a second kinematically cold component that was originally seen in a GSS core field at R approx 21 kpc. The velocity gradients of the GSS and the second component in the combined data set are parallel over a range of DELTAR = 7 kpc, suggesting that this may represent a bifurcation in the line-of-sight velocities of GSS stars. We present the first kinematical detection of substructure in the GSS envelope (S quadrant, R approx 58 kpc). Using kinematically identified samples, we show that the envelope debris has a approx0.7 dex lower mean photometric metallicity and possibly higher intrinsic velocity dispersion than the GSS core. The GSS is also identified in the field of the M31 dwarf spheroidal satellite And I; the GSS in this field has a metallicity distribution identical to that of the GSS core. We confirm the previous finding of two kinematically cold components in stream C, and measure intrinsic velocity dispersions of approx10 and approx4 km s{sup -1}. This compilation of the kinematical (mean velocity, intrinsic velocity dispersion) and chemical properties of stars in the GSS core and envelope, coupled with published surface-brightness measurements and wide-area star-count maps, will improve constraints on the orbit and internal structure of the dwarf satellite progenitor.« less

Space-based Coronagraphic Imaging Polarimetry of the TW Hydrae Disk: Shedding New Light on Self-shadowing Effects

NASA Astrophysics Data System (ADS)

Poteet, Charles A.; Chen, Christine H.; Hines, Dean C.; Perrin, Marshall D.; Debes, John H.; Pueyo, Laurent; Schneider, Glenn; Mazoyer, Johan; Kolokolova, Ludmilla

2018-06-01

We present Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer coronagraphic imaging polarimetry of the TW Hydrae protoplanetary disk. These observations simultaneously measure the total and polarized intensity, allowing direct measurement of the polarization fraction across the disk. In accord with the self-shadowing hypothesis recently proposed by Debes et al., we find that the total and polarized intensity of the disk exhibits strong azimuthal asymmetries at projected distances consistent with the previously reported bright and dark ring-shaped structures (∼45–99 au). The sinusoidal-like variations possess a maximum brightness at position angles near ∼268°–300° and are up to ∼28% stronger in total intensity. Furthermore, significant radial and azimuthal variations are also detected in the polarization fraction of the disk. In particular, we find that regions of lower polarization fraction are associated with annuli of increased surface brightness, suggesting that the relative proportion of multiple-to-single scattering is greater along the ring and gap structures. Moreover, we find strong (∼20%) azimuthal variation in the polarization fraction along the shadowed region of the disk. Further investigation reveals that the azimuthal variation is not the result of disk flaring effects, but is instead from a decrease in the relative contribution of multiple-to-single scattering within the shadowed region. Employing a two-layer scattering surface, we hypothesize that the diminished contribution in multiple scattering may result from shadowing by an inclined inner disk, which prevents direct stellar light from reaching the optically thick underlying surface component.

FORTY-SEVEN MILKY WAY-SIZED, EXTREMELY DIFFUSE GALAXIES IN THE COMA CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Dokkum, Pieter G.; Merritt, Allison; Geha, Marla

2015-01-10

We report the discovery of 47 low surface brightness objects in deep images of a 3° × 3° field centered on the Coma cluster, obtained with the Dragonfly Telephoto Array. The objects have central surface brightness μ(g, 0) ranging from 24-26 mag arcsec{sup –2} and effective radii r {sub eff} = 3''-10'', as measured from archival Canada-France-Hawaii Telescope images. From their spatial distribution we infer that most or all of the objects are galaxies in the Coma cluster. This relatively large distance is surprising as it implies that the galaxies are very large: with r {sub eff} = 1.5-4.6 kpcmore » their sizes are similar to those of L {sub *} galaxies even though their median stellar mass is only ∼6 × 10{sup 7} M {sub ☉}. The galaxies are relatively red and round, with (g – i) = 0.8 and (b/a) = 0.74. One of the 47 galaxies is fortuitously covered by a deep Hubble Space Telescope Advanced Camera for Surveys (ACS) observation. The ACS imaging shows a large spheroidal object with a central surface brightness μ{sub 475} = 25.8 mag arcsec{sup –2}, a Sérsic index n = 0.6, and an effective radius of 7'', corresponding to 3.4 kpc at the distance of Coma. The galaxy is not resolved into stars, consistent with expectations for a Coma cluster object. We speculate that these ''ultra-diffuse galaxies'' may have lost their gas supply at early times, possibly resulting in very high dark matter fractions.« less

Black hole mass measurement using molecular gas kinematics: what ALMA can do

NASA Astrophysics Data System (ADS)

Yoon, Ilsang

2017-04-01

We study the limits of the spatial and velocity resolution of radio interferometry to infer the mass of supermassive black holes (SMBHs) in galactic centres using the kinematics of circum-nuclear molecular gas, by considering the shapes of the galaxy surface brightness profile, signal-to-noise ratios (S/Ns) of the position-velocity diagram (PVD) and systematic errors due to the spatial and velocity structure of the molecular gas. We argue that for fixed galaxy stellar mass and SMBH mass, the spatial and velocity scales that need to be resolved increase and decrease, respectively, with decreasing Sérsic index of the galaxy surface brightness profile. We validate our arguments using simulated PVDs for varying beam size and velocity channel width. Furthermore, we consider the systematic effects on the inference of the SMBH mass by simulating PVDs including the spatial and velocity structure of the molecular gas, which demonstrates that their impacts are not significant for a PVD with good S/N unless the spatial and velocity scale associated with the systematic effects are comparable to or larger than the angular resolution and velocity channel width of the PVD from pure circular motion. Also, we caution that a bias in a galaxy surface brightness profile owing to the poor resolution of a galaxy photometric image can largely bias the SMBH mass by an order of magnitude. This study shows the promise and the limits of ALMA observations for measuring SMBH mass using molecular gas kinematics and provides a useful technical justification for an ALMA proposal with the science goal of measuring SMBH mass.

The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. II. Sensitivity of the survey and the atlas of synthetic dwarf galaxies

NASA Astrophysics Data System (ADS)

Beccari, G.; Bellazzini, M.; Battaglia, G.; Ibata, R.; Martin, N.; Testa, V.; Cignoni, M.; Correnti, M.

2016-06-01

The searching for StEllar Counterparts of COmpact high velocity clouds (SECCO) survey is devoted to the search for stellar counterparts within ultra compact high velocity clouds that are candidate low-mass, low-luminosity galaxies. We present the results of a set of simulations aimed at the quantitative estimate of the sensitivity of the survey as a function of the total luminosity, size, and distance of the stellar systems we are looking for. For all of our synthetic galaxies we assumed an exponential surface brightness profile and an old and metal-poor population. The synthetic galaxies are simulated both on the images and on the photometric catalogues, taking all the observational effects into account. In the fields where the available observational material is of top quality (≃36% of the SECCO fields), we detect synthetic galaxies as ≥5σ over-densities of resolved stars down to μV,h ≃ 30.0 mag/arcsec2, for D ≤ 1.5 Mpc, and down to μV,h ≃ 29.5 mag/arcsec2, for D ≤ 2.5 Mpc. In the field with the worst observational material of the whole survey, we detect synthetic galaxies with μV,h ≤ 28.8 mag/arcsec2 out to D ≤ 1.0 Mpc, and those with μV,h ≤ 27.5 mag/arcsec2 out to D ≤ 2.5 Mpc. Dwarf galaxies with MV = -10.0, with sizes in the range spanned by known dwarfs, are detected by visual inspection of the images up to D = 5 Mpc independent of the image quality. In the best quality images, dwarfs are partially resolved into stars up to D = 3.0 Mpc and completely unresolved at D = 5 Mpc. As an independent test of the sensitivity of our images to low surface brightness galaxies, we report on the detection of several dwarf spheroidal galaxies probably located in the Virgo cluster with MV ≲ -8.0 and μV,h ≲ 26.8 mag/arcsec2. The nature of the previously discovered SECCO 1 stellar system, also likely located in the Virgo cluster, is rediscussed in comparison with these dwarfs. While specific for the SECCO survey, our study may also provide general guidelines for the detection of faint stellar systems with 8 m class telescopes. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. The LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

The rapid assembly of an elliptical galaxy of 400 billion solar masses at a redshift of 2.3.

PubMed

Fu, Hai; Cooray, Asantha; Feruglio, C; Ivison, R J; Riechers, D A; Gurwell, M; Bussmann, R S; Harris, A I; Altieri, B; Aussel, H; Baker, A J; Bock, J; Boylan-Kolchin, M; Bridge, C; Calanog, J A; Casey, C M; Cava, A; Chapman, S C; Clements, D L; Conley, A; Cox, P; Farrah, D; Frayer, D; Hopwood, R; Jia, J; Magdis, G; Marsden, G; Martínez-Navajas, P; Negrello, M; Neri, R; Oliver, S J; Omont, A; Page, M J; Pérez-Fournon, I; Schulz, B; Scott, D; Smith, A; Vaccari, M; Valtchanov, I; Vieira, J D; Viero, M; Wang, L; Wardlow, J L; Zemcov, M

2013-06-20

Stellar archaeology shows that massive elliptical galaxies formed rapidly about ten billion years ago with star-formation rates of above several hundred solar masses per year. Their progenitors are probably the submillimetre bright galaxies at redshifts z greater than 2. Although the mean molecular gas mass (5 × 10(10) solar masses) of the submillimetre bright galaxies can explain the formation of typical elliptical galaxies, it is inadequate to form elliptical galaxies that already have stellar masses above 2 × 10(11) solar masses at z ≈ 2. Here we report multi-wavelength high-resolution observations of a rare merger of two massive submillimetre bright galaxies at z = 2.3. The system is seen to be forming stars at a rate of 2,000 solar masses per year. The star-formation efficiency is an order of magnitude greater than that of normal galaxies, so the gas reservoir will be exhausted and star formation will be quenched in only around 200 million years. At a projected separation of 19 kiloparsecs, the two massive starbursts are about to merge and form a passive elliptical galaxy with a stellar mass of about 4 × 10(11) solar masses. We conclude that gas-rich major galaxy mergers with intense star formation can form the most massive elliptical galaxies by z ≈ 1.5.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shporer, Avi; Brown, Tim, E-mail: ashporer@lcogt.net; Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106

We present here a small anomalous radial velocity (RV) signal expected to be present in RV curves measured during planetary transits. This signal is induced by the convective blueshift (CB) effect-a net blueshift emanating from the stellar surface, resulting from a larger contribution of rising hot and bright gas relative to the colder and darker sinking gas. Since the CB radial component varies across the stellar surface, the light blocked by the planet during a transit will have a varying RV component, resulting in a small shift of the measured RVs. The CB-induced anomalous RV curve is different than, andmore » independent of, the well-known Rossiter-McLaughlin (RM) effect, where the latter is used for determining the sky-projected angle between the host star rotation axis and the planet's orbital angular momentum axis. The observed RV curve is the sum of the CB and RM signals, and they are both superposed on the orbital Keplerian curve. If not accounted for, the presence of the CB RV signal in the spectroscopic transit RV curve may bias the estimate of the spin-orbit angle. In addition, future very high precision RVs will allow the use of transiting planets to study the CB of their host stars.« less

Mass Profile Decomposition of the Frontier Fields Cluster MACS J0416-2403: Insights on the Dark-matter Inner Profile

NASA Astrophysics Data System (ADS)

Annunziatella, M.; Bonamigo, M.; Grillo, C.; Mercurio, A.; Rosati, P.; Caminha, G.; Biviano, A.; Girardi, M.; Gobat, R.; Lombardi, M.; Munari, E.

2017-12-01

We present a high-resolution dissection of the two-dimensional total mass distribution in the core of the Hubble Frontier Fields galaxy cluster MACS J0416.1‑2403, at z = 0.396. We exploit HST/WFC3 near-IR (F160W) imaging, VLT/Multi Unit Spectroscopic Explorer spectroscopy, and Chandra data to separate the stellar, hot gas, and dark-matter mass components in the inner 300 kpc of the cluster. We combine the recent results of our refined strong lensing analysis, which includes the contribution of the intracluster gas, with the modeling of the surface brightness and stellar mass distributions of 193 cluster members, of which 144 are spectroscopically confirmed. We find that, moving from 10 to 300 kpc from the cluster center, the stellar to total mass fraction decreases from 12% to 1% and the hot gas to total mass fraction increases from 3% to 9%, resulting in a baryon fraction of approximatively 10% at the outermost radius. We measure that the stellar component represents ∼30%, near the cluster center, and 15%, at larger clustercentric distances, of the total mass in the cluster substructures. We subtract the baryonic mass component from the total mass distribution and conclude that within 30 kpc (∼3 times the effective radius of the brightest cluster galaxy) from the cluster center the surface mass density profile of the total mass and global (cluster plus substructures) dark-matter are steeper and that of the diffuse (cluster) dark-matter is shallower than an NFW profile. Our current analysis does not point to a significant offset between the cluster stellar and dark-matter components. This detailed and robust reconstruction of the inner dark-matter distribution in a larger sample of galaxy clusters will set a new benchmark for different structure formation scenarios.

LASR-Guided Variability Subtraction: The Linear Algorithm for Significance Reduction of Stellar Seismic Activity

NASA Astrophysics Data System (ADS)

Horvath, Sarah; Myers, Sam; Ahlers, Johnathon; Barnes, Jason W.

2017-10-01

Stellar seismic activity produces variations in brightness that introduce oscillations into transit light curves, which can create challenges for traditional fitting models. These oscillations disrupt baseline stellar flux values and potentially mask transits. We develop a model that removes these oscillations from transit light curves by minimizing the significance of each oscillation in frequency space. By removing stellar variability, we prepare each light curve for traditional fitting techniques. We apply our model to $\\delta$-Scuti KOI-976 and demonstrate that our variability subtraction routine successfully allows for measuring bulk system characteristics using traditional light curve fitting. These results open a new window for characterizing bulk system parameters of planets orbiting seismically active stars.

The Frequency of Circumnuclear Starbursts in Seyfert Galaxies --- Testing the Starburst-AGN Connection

NASA Astrophysics Data System (ADS)

Schinnerer, E.; Colbert, E.; Armus, L.; Scoville, N. Z.; Heckman, T. M.

We obtained sub-arcsecond medium resolution near-infrared spectra of a sample of nearby bright Seyfert galaxies (8 Seyfert 1s, 11 Seyfert 2s) using the KeckII telescope. The stellar absorption lines present in the spectra were used in conjunction with population synthesis models to determine the age of the circumnuclear stellar population. Initial analysis of a sub-sample of the Seyfert galaxies has provided no evidence for a connection between the age of the circumnuclear stellar population and the Seyfert type. The derived ages for the circumnuclear stellar population are in the range of 10 Myr to < 0.5 Gyr assuming an instantaneous starburst (using the STARBURST99 models).

Tidal features of classical Milky Way satellites in a Λ cold dark matter universe

NASA Astrophysics Data System (ADS)

Wang, M.-Y.; Fattahi, Azadeh; Cooper, Andrew P.; Sawala, Till; Strigari, Louis E.; Frenk, Carlos S.; Navarro, Julio F.; Oman, Kyle; Schaller, Matthieu

2017-07-01

We use the APOSTLE (A Project Of Simulating The Local Environment) cosmological hydrodynamic simulations to examine the effects of tidal stripping on cold dark matter subhaloes that host three of the most luminous Milky Way dwarf satellite galaxies: Fornax, Sculptor and Leo I. We identify simulated satellites that match the observed spatial and kinematic distributions of stars in these galaxies, and track their evolution after infall. We find ˜30 per cent of subhaloes hosting satellites with present-day stellar mass 106-108 M⊙ experience >20 per cent stellar mass-loss after infall. Fornax analogues have earlier infall times compared to Sculptor and Leo I analogues. Star formation in Fornax analogues continues for ˜3-6 Gyr after infall, whereas Sculptor and Leo I analogues stop forming stars <2-3 Gyr after infall. Fornax analogues typically show more significant stellar mass-loss and exhibit stellar tidal tails, whereas Sculptor and Leo I analogues, which are more deeply embedded in their host dark matter haloes at infall, do not show substantial mass-loss due to tides. When additionally comparing the orbital motion of the host subaloes to the measured proper motion of Fornax, we find the matching more difficult; host subhaloes tend to have pericentres smaller than that measured for Fornax itself. From the kinematic and orbital data, we estimate that Fornax has lost 10-20 per cent of its infall stellar mass. Our best estimate for the surface brightness of a stellar tidal stream associated with Fornax is Σ ˜ 32.6 mag arcsec-2, which may be detectable with deep imaging surveys such as DES and LSST.

Improved instrumental magnitude prediction expected from version 2 of the NASA SKY2000 master star catalog

NASA Technical Reports Server (NTRS)

Sande, C. B.; Brasoveanu, D.; Miller, A. C.; Home, A. T.; Tracewell, D. A.; Warren, W. H., Jr.

1998-01-01

The SKY2000 Master Star Catalog (MC), Version 2 and its predecessors have been designed to provide the basic astronomical input data needed for satellite acquisition and attitude determination on NASA spacecraft. Stellar positions and proper motions are the primary MC data required for operations support followed closely by the stellar brightness observed in various standard astronomical passbands. The instrumental red-magnitude prediction subsystem (REDMAG) in the MMSCAT software package computes the expected instrumental color index (CI) [sensor color correction] from an observed astronomical stellar magnitude in the MC and the characteristics of the stellar spectrum, astronomical passband, and sensor sensitivity curve. The computation is more error prone the greater the mismatch of the sensor sensitivity curve characteristics and those of the observed astronomical passbands. This paper presents the preliminary performance analysis of a typical red-sensitive CCDST during acquisition of sensor data from the two Ball CT-601 ST's onboard the Rossi X-Ray Timing Explorer (RXTE). A comparison is made of relative star positions measured in the ST FOV coordinate system with the expected results computed from the recently released Tycho Catalogue. The comparison is repeated for a group of observed stars with nearby, bright neighbors in order to determine the tracker behavior in the presence of an interfering, near neighbor (NN). The results of this analysis will be used to help define a new photoelectric photometric instrumental sensor magnitude system (S) that is based on several thousand bright star magnitudes observed with the PXTE ST's. This new system will be implemented in Version 2 of the SKY2000 MC to provide improved predicted magnitudes in the mission run catalogs.

A family of models for spherical stellar systems

NASA Technical Reports Server (NTRS)

Tremaine, Scott; Richstone, Douglas O.; Byun, Yong-Ik; Dressler, Alan; Faber, S. M.; Grillmair, Carl; Kormendy, John; Lauer, Tod R.

1994-01-01

We describe a one-parameter family of models of stable sperical stellar systems in which the phase-space distribution function depends only on energy. The models have similar density profiles in their outer parts (rho propotional to r(exp -4)) and central power-law density cusps, rho proportional to r(exp 3-eta), 0 less than eta less than or = 3. The family contains the Jaffe (1983) and Hernquist (1990) models as special cases. We evaluate the surface brightness profile, the line-of-sight velocity dispersion profile, and the distribution function, and discuss analogs of King's core-fitting formula for determining mass-to-light ratio. We also generalize the models to a two-parameter family, in which the galaxy contains a central black hole; the second parameter is the mass of the black hole. Our models can be used to estimate the detectability of central black holes and the velocity-dispersion profiles of galaxies that contain central cusps, with or without a central black hole.

Einstein observations of the Hydra A cluster and the efficiency of galaxy formation in groups and clusters

NASA Technical Reports Server (NTRS)

David, L. P.; Arnaud, K. A.; Forman, W.; Jones, C.

1990-01-01

The Einstein imaging proportional counter observations of the poor cluster of galaxies centered on the radio galaxy Hydra A are examined. From the surface brightness profile, it is found that the X-ray-emitting gas in the Hydra A cluster must be condensing out of the intracluster medium at a rate of 600 solar masses/yr. This is one of the largest mass deposition rates observed in a cluster of galaxies. The ratio of gas mass to stellar mass is compared for a variety of systems, showing that this ratio correlates with the gas temperature.

Apollo-16 far-ultraviolet spectra in the Large Magellanic Cloud

NASA Technical Reports Server (NTRS)

Carruthers, G. R.; Page, T.

1977-01-01

Spectra in the wavelength ranges from 900 to 1600 A and 1050 to 1600 A of some OB associations in the Large Magellanic Cloud were obtained from the lunar surface by the Apollo-16 far-ultraviolet camera/spectrograph on April 22, 1972. The observed spectral distributions appear consistent with a stellar model having an effective temperature of 30,000 K, reddened by E(B-V) = 0.3, and characterized by the average far-ultraviolet extinction curve of Bless and Savage (1972). However, the absolute intensity of the far-ultraviolet spectrum of the associations NGC 2050 and 2055 seems somewhat too bright in comparison with ground-based photometry.

Dwarf spheroidal galaxies: Keystones of galaxy evolution

NASA Technical Reports Server (NTRS)

Gallagher, John S., III; Wyse, Rosemary F. G.

1994-01-01

Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

Cheetah: Starspot modeling code

NASA Astrophysics Data System (ADS)

Walkowicz, Lucianne; Thomas, Michael; Finkestein, Adam

2014-12-01

Cheetah models starspots in photometric data (lightcurves) by calculating the modulation of a light curve due to starspots. The main parameters of the program are the linear and quadratic limb darkening coefficients, stellar inclination, spot locations and sizes, and the intensity ratio of the spots to the stellar photosphere. Cheetah uses uniform spot contrast and the minimum number of spots needed to produce a good fit and ignores bright regions for the sake of simplicity.

The Andromeda Optical and Infrared Disk Survey

NASA Astrophysics Data System (ADS)

Sick, Jonathan

The spectral energy distributions of galaxies inform us about a galaxy's stellar populations and interstellar medium, revealing stories of galaxy formation and evolution. How we interpret this light depends in part on our proximity to the galaxy. For nearby galaxies, detailed star formation histories can be extracted from the resolved stellar populations, while more distant galaxies feature the contributions of entire stellar populations within their integrated spectral energy distribution (SED). This thesis aims to resolve whether the techniques used to investigate stellar populations in distant galaxies are consistent with those available for nearby galaxies. As the nearest spiral galaxy, the Andromeda Galaxy (M31) is the ideal testbed for the joint study of resolved stellar populations and panchromatic SEDs. We present the Andromeda Optical and Infrared Disk Survey (ANDROIDS), which adds new near-UV to near-IR (u*g'r'i'JKs) imaging using the MegaCam and WIRCam cameras at the Canada-France-Hawaii telescope to the available M31 panchromatic dataset. To accurately subtract photometric background from our extremely wide-field (14 square degree) mosaics, we present observing and data reduction techniques with sky-target nodding, optimization of image-to-image surface brightness, and a novel hierarchical Bayesian model to trace the background signal while modelling the astrophysical SED. We model the spectral energy distributions of M31 pixels with MAGPHYS (da Cunha et al. 2008) and compare those results to resolved stellar population models of the same pixels from the Panchromatic Hubble Andromeda Treasury (PHAT) survey (Williams et al. 2017). We find substantial (0.3 dex) differences in stellar mass estimates despite a common use of the Chabrier (2003) initial mass function. Stellar mass estimated from the resolved stellar population is larger than any mass estimate from SED models or colour-M/L relations (CMLRs). There is also considerable diversity among CMLR estimators, largely driven by differences in the star formation history prior distribution. We find broad consistency between the star formation history estimated by integrated spectral energy distributions and resolved stars. Generally, spectral energy distribution models yield a stronger inside-out radial metallicity gradient and bias towards younger mean ages than resolved stellar population models.

Automated detectionof very low surface brightness galaxiesin the Virgo cluster

NASA Astrophysics Data System (ADS)

Prole, D. J.; Davies, J. I.; Keenan, O. C.; Davies, L. J. M.

2018-07-01

We report the automatic detection of a new sample of very low surface brightness (LSB) galaxies, likely members of the Virgo cluster. We introduce our new software, DeepScan, that has been designed specifically to detect extended LSB features automatically using the DBSCAN algorithm. We demonstrate the technique by applying it over a 5 deg2 portion of the Next Generation Virgo Survey (NGVS) data to reveal 53 LSB galaxies that are candidate cluster members based on their sizes and colours. 30 of these sources are new detections despite the region being searched specifically for LSB galaxies previously. Our final sample contains galaxies with 26.0 ≤ ⟨μe⟩ ≤ 28.5 and 19 ≤ mg ≤ 21, making them some of the faintest known in Virgo. The majority of them have colours consistent with the red sequence, and have a mean stellar mass of 106.3 ± 0.5 M⊙ assuming cluster membership. After using ProFit to fit Sérsic profiles to our detections, none of the new sources have effective radii larger than 1.5 Kpc and do not meet the criteria for ultra-diffuse galaxy (UDG) classification, so we classify them as ultra-faint dwarfs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oohama, N.; Okamura, S.; Fukugita, M.

A bulge-disk decomposition is made for 737 spiral and lenticular galaxies drawn from a Sloan Digital Sky Survey galaxy sample for which morphological types are estimated. We carry out the bulge-disk decomposition using the growth curve fitting method. It is found that bulge properties, effective radius, effective surface brightness, and also absolute magnitude, change systematically with the morphological sequence; from early to late types, the size becomes somewhat larger, and surface brightness and luminosity fainter. In contrast, disks are nearly universal, their properties remaining similar among disk galaxies irrespective of detailed morphologies from S0 to Sc. While these tendencies weremore » often discussed in previous studies, the present study confirms them based on a large homogeneous magnitude-limited field galaxy sample with morphological types estimated. The systematic change of bulge-to-total luminosity ratio, B/T, along the morphological sequence is therefore not caused by disks but mostly by bulges. It is also shown that elliptical galaxies and bulges of spiral galaxies are unlikely to be in a single sequence. We infer the stellar mass density (in units of the critical mass density) to be OMEGA = 0.0021 for spheroids, i.e., elliptical galaxies plus bulges of spiral galaxies, and OMEGA = 0.00081 for disks.« less

Galaxy Interactions, Tidal Debris, and the Origin of Intracluster Light in the Coma Cluster

NASA Astrophysics Data System (ADS)

Gregg, Michael

1999-07-01

We propose to obtain deep WFPC2 and parallel STIS images of low surface brightness tidal debris that we have recently discovered in the Coma cluster; the material is being stripped from its parent galaxy and added to the general cluster background. These images will enable direct study of the brightest blue and red supergiants, globular clusters, and star forming regions which may be present, or will place strong limits on the numbers of such objects and any recent star formation. We also propose similar observations of the parent spiral, NGC4911, in the core of Coma; it is losing its ISM to the hot cluster gas and as well as the low surface brightness tidal debris. By imaging this galaxy, we will get a high resolution look at the interaction between the galaxy and interstellar medium, as well as any ram-pressure induced star formation. The tidal features in Coma appear to be adding material to the background light and cD galaxy envelopes at a significant rate; determining the nature of the added stellar population and the interactions which produce it are critical to understanding the formation and evolution of cD galaxies and clusters.

Depleted cores, multicomponent fits, and structural parameter relations for luminous early-type galaxies

NASA Astrophysics Data System (ADS)

Dullo, Bililign T.; Graham, Alister W.

2014-11-01

New surface brightness profiles from 26 early-type galaxies with suspected partially depleted cores have been extracted from the full radial extent of Hubble Space Telescope images. We have carefully quantified the radial stellar distributions of the elliptical galaxies using the core-Sérsic model whereas for the lenticular galaxies a core-Sérsic bulge plus an exponential disc model gives the best representation. We additionally caution about the use of excessive multiple Sérsic functions for decomposing galaxies and compare with past fits in the literature. The structural parameters obtained from our fitted models are, in general, in good agreement with our initial study using radially limited (R ≲ 10 arcsec) profiles, and are used here to update several `central' as well as `global' galaxy scaling relations. We find near-linear relations between the break radius Rb and the spheroid luminosity L such that Rb ∝ L1.13±0.13, and with the supermassive black hole mass MBH such that R_b∝ M_BH^{0.83 ± 0.21}. This is internally consistent with the notion that major, dry mergers add the stellar and black hole mass in equal proportion, i.e. MBH ∝ L. In addition, we observe a linear relation R_b∝ R_e^{0.98 ± 0.15} for the core-Sérsic elliptical galaxies - where Re is the galaxies' effective half-light radii - which is collectively consistent with the approximately linear, bright-end of the curved L-Re relation. Finally, we measure accurate stellar mass deficits Mdef that are in general 0.5-4 MBH, and we identify two galaxies (NGC 1399, NGC 5061) that, due to their high Mdef/MBH ratio, may have experienced oscillatory core-passage by a (gravitational radiation)-kicked black hole. The galaxy scaling relations and stellar mass deficits favour core-Sérsic galaxy formation through a few `dry' major merger events involving supermassive black holes such that M_def ∝ M_BH^{3.70 ± 0.76}, for MBH ≳ 2 × 108 M⊙.

Galaxy And Mass Assembly (GAMA): the signatures of galaxy interactions as viewed from small scale galaxy clustering

NASA Astrophysics Data System (ADS)

Gunawardhana, M. L. P.; Norberg, P.; Zehavi, I.; Farrow, D. J.; Loveday, J.; Hopkins, A. M.; Davies, L. J. M.; Wang, L.; Alpaslan, M.; Bland-Hawthorn, J.; Brough, S.; Holwerda, B. W.; Owers, M. S.; Wright, A. H.

2018-06-01

Statistical studies of galaxy-galaxy interactions often utilise net change in physical properties of progenitors as a function of the separation between their nuclei to trace both the strength and the observable timescale of their interaction. In this study, we use two-point auto, cross and mark correlation functions to investigate the extent to which small-scale clustering properties of star forming galaxies can be used to gain physical insight into galaxy-galaxy interactions between galaxies of similar optical brightness and stellar mass. The Hα star formers, drawn from the highly spatially complete Galaxy And Mass Assembly (GAMA) survey, show an increase in clustering on small separations. Moreover, the clustering strength shows a strong dependence on optical brightness and stellar mass, where (1) the clustering amplitude of optically brighter galaxies at a given separation is larger than that of optically fainter systems, (2) the small scale clustering properties (e.g. the strength, the scale at which the signal relative to the fiducial power law plateaus) of star forming galaxies appear to differ as a function of increasing optical brightness of galaxies. According to cross and mark correlation analyses, the former result is largely driven by the increased dust content in optically bright star forming galaxies. The latter could be interpreted as evidence of a correlation between interaction-scale and optical brightness of galaxies, where physical evidence of interactions between optically bright star formers, likely hosted within relatively massive halos, persist over larger separations than those between optically faint star formers.

K2-29 b/WASP-152 b: AN ALIGNED AND INFLATED HOT JUPITER IN A YOUNG VISUAL BINARY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santerne, A.; Barros, S. C. C.; Mena, E. Delgado

In the present paper we report the discovery of a new hot Jupiter, K2-29 b, first detected by the Super-WASP observatory and then by the K2 space mission during its campaign 4. The planet has a period of 3.25 days, a mass of 0.73 ± 0.04 M {sub ♃}, and a radius of 1.19 ± 0.02 R {sub ♃}. The host star is a relatively bright ( V = 12.5) G7 dwarf with a nearby K5V companion. Based on stellar rotation and the abundance of lithium, we find that the system might be as young as ∼450 Myr. The observationmore » of the Rossiter–McLaughlin effect shows that the planet is aligned with respect to the stellar spin. Given the deep transit (20 mmag), the magnitude of the star and the presence of a nearby stellar companion, the planet is a good target for both space- and ground-based transmission spectroscopy, in particular in the near-infrared where both stars are relatively bright.« less

Global Relationships Among the Physical Properties of Stellar Systems.

NASA Astrophysics Data System (ADS)

Burstein, David; Bender, Ralf; Faber, S.; Nolthenius, R.

1997-10-01

The Κ-space three-dimensional parameter system was originally defined to examine the physical properties of dynamically hot elliptical galaxies and bulges (DRGs). The axes of Κ-space are proportional to the logarithm of galaxy mass, mass-to-light ratio, and a third quantity that is mainly surface brightness. In this paper we define self-consistent Κ parameters for disk galaxies, galaxy groups and clusters, and globular clusters and use them to project an integrated view of the major classes of self-gravitating, equilibrium stellar systems in the universe. Each type of stellar system is found to populate its own fundamental plane in Κ-space. At least six different planes are found: (1) the original fundamental plane for DRGs; (2) a nearly-parallel plane slightly offset for Sa-Sc spirals; (3) a plane with different tilt but similar zero point for Scd-Irr galaxies; (4) a plane parallel to the DRG plane but offset by a factor of 10 in mass-to-light ratio for rich galaxy clusters; (5) a plane for galaxy groups that bridges the gap between rich clusters and galaxies; and (6) a plane for Galactic globular clusters. We propose the term "cosmic metaplane" to describe this ensemble of interrelated and interconnected fundamental planes. The projection Κ1-Κ3 (M/L vs M) views all planes essentially edge-on. Planes share the common characteristic that M/L is either constant or increasing with mass. The Κ1-Κ2 projection views all of these planes close to face-on, while Κ2-Κ3 shows variable slopes for different groups owing to the slightly different tilts of the individual planes. The Tully-Fisher relation is the correct compromise projection to view the spiral-irregular planes nearly edge on, analogous to the Dπ-σ relation for DRGs. No stellar system yet violates the rule first found from the study of DRGs, namely, Κ1+Κ2 constant, here chosen to be 8. In physical terms, this says that the maximum global luminosity density of stellar systems varies as M-4/3. Galaxies march away from this "zone of exclusion" (ZOE) in Κ12 as a function of Hubble type: DRGs are closest, with Sm-Irr's being furthest away. The distribution of systems in Κ-space is generally consistent with predictions of galaxy formation via hierarchical clustering and merging. The cosmic metaplane is simply the cosmic virial plane common to all self-gravitating stellar systems, tilted and displaced in mass-to-light ratio for various types of systems due to differences in stellar population and amount of baryonic dissipation. Hierarchical clustering from an n =-1.8 power-law density fluctuation spectrum (plus dissipation) comes close to reproducing the slope of the ZOE, and the progressive displacement of Hubble types from this line is consistent with the formation of early-type galaxies from higher n-σ fluctuations than late Hubble types. The M/L values for galaxy groups containing only a few, mostly spiral galaxies, vary the strongest with M. Moreover, it is these groups that bridge the gap between the two planes defined by the brightest galaxies and the lowest mass rich clusters, giving the cosmic metaplane its striking appearance. Why this is so is but one of four key questions raised by our study. The second question is why the slopes of individual Hubble types in the Κ1-Κ2 lie plane parallel the ZOE. At face value, this appears to suggest less dissipation of massive galaxies within their dark halos compared to lower-mass galaxies of the same Hubble type. The third is why we find isotropic stellar systems only within an effective mass range of 109.5-11.75 Msun. This would seem to imply that dissipation only results in galaxy components flattened by rotation in a limited mass range. The fourth question, perhaps the most basic of all, is how does M/L vary so smoothly with M among all stellar systems so as to give the individual tilts of the various fundamental planes, yet preserve the overall appearance of a metaplane? The answer to this last question must await a more thorough knowledge of how galaxies relate to many parameters, including: their environment, structure, angular momentum acquisition, density, dark matter concentration, the physics of star formation in general, and the formation of the initial mass function in particular. The present investigation is limited by existing data to the B passband and is strongly magnitude-limited, not volume-limited. Rare or hard-to-discover galaxy types, such as R II galaxies, starburst galaxies and low-surface-brightness galaxies, are missing or are under-represented, and use of the B band over-emphasizes stellar population differences. A volume-limited Κ-space survey based on Κ-band photometry and complete to low surface brightness and faint magnitudes is highly desirable but requires data yet to be obtained.

V405 ANDROMEDA REVISITED

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ribeiro, T.; Baptista, R.; Kafka, S.

We present a multi-epoch time-resolved high-resolution optical spectroscopy study of the short-period (P{sub orb} = 11.2 hr) eclipsing M0V+M5V RS CVn binary V405 Andromeda. By means of indirect imaging techniques, namely Doppler imaging, we study the surface activity features of the M0V component of the system. A modified version of a Doppler imaging code, which takes into account the tidal distortion of the surface of the star, is applied to the multi-epoch data set in order to provide indirect images of the stellar surface. The multi-epoch surface brightness distributions show a low intensity 'belt' of spots at latitudes {+-}40{sup 0}more » and a noticeable absence of high latitude features or polar spots on the primary star of V405 Andromeda. They also reveal slow evolution of the spot distribution over {approx}4 yr. An entropy landscape procedure is used in order to find the set of binary parameters that lead to the smoothest surface brightness distributions. As a result, we find M{sub 1} = 0.51 {+-} 0.03 M{sub sun}, M{sub 2} = 0.21 {+-} 0.01 M{sub sun}, R{sub 1} = 0.71 {+-} 0.01 R{sub sun}, and an inclination i = 65{sup 0} {+-} 1{sup 0}. The resulting systemic velocity is distinct for different epochs, raising the possibility of the existence of a third body in the system.« less

The DiskMass Survey. II. Error Budget

NASA Astrophysics Data System (ADS)

Bershady, Matthew A.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.; Martinsson, Thomas

2010-06-01

We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio (Υ_{*}), and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find that a disk inclination range of 25°-35° is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale heights are significant, but can be estimated from radial scale lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction ({F}_bar) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error budget for the key quantities: dynamical disk mass surface density (Σdyn), disk stellar mass-to-light ratio (Υ^disk_{*}), and disk maximality ({F}_{*,max}^disk≡ V^disk_{*,max}/ V_c). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.

A CANDELS-3D-HST synergy: Resolved Star Formation Patterns at 0.7 < z < 1.5

NASA Astrophysics Data System (ADS)

Wuyts, Stijn; Förster Schreiber, Natascha M.; Nelson, Erica J.; van Dokkum, Pieter G.; Brammer, Gabe; Chang, Yu-Yen; Faber, Sandra M.; Ferguson, Henry C.; Franx, Marijn; Fumagalli, Mattia; Genzel, Reinhard; Grogin, Norman A.; Kocevski, Dale D.; Koekemoer, Anton M.; Lundgren, Britt; Lutz, Dieter; McGrath, Elizabeth J.; Momcheva, Ivelina; Rosario, David; Skelton, Rosalind E.; Tacconi, Linda J.; van der Wel, Arjen; Whitaker, Katherine E.

2013-12-01

We analyze the resolved stellar populations of 473 massive star-forming galaxies at 0.7 < z < 1.5, with multi-wavelength broadband imaging from CANDELS and Hα surface brightness profiles at the same kiloparsec resolution from 3D-HST. Together, this unique data set sheds light on how the assembled stellar mass is distributed within galaxies, and where new stars are being formed. We find the Hα morphologies to resemble more closely those observed in the ACS I band than in the WFC3 H band, especially for the larger systems. We next derive a novel prescription for Hα dust corrections, which accounts for extra extinction toward H II regions. The prescription leads to consistent star formation rate (SFR) estimates and reproduces the observed relation between the Hα/UV luminosity ratio and visual extinction, on both a pixel-by-pixel and a galaxy-integrated level. We find the surface density of star formation to correlate with the surface density of assembled stellar mass for spatially resolved regions within galaxies, akin to the so-called "main sequence of star formation" established on a galaxy-integrated level. Deviations from this relation toward lower equivalent widths are found in the inner regions of galaxies. Clumps and spiral features, on the other hand, are associated with enhanced Hα equivalent widths, bluer colors, and higher specific SFRs compared to the underlying disk. Their Hα/UV luminosity ratio is lower than that of the underlying disk, suggesting that the ACS clump selection preferentially picks up those regions of elevated star formation activity that are the least obscured by dust. Our analysis emphasizes that monochromatic studies of galaxy structure can be severely limited by mass-to-light ratio variations due to dust and spatially inhomogeneous star formation histories.

A CANDELS-3d-HST Synergy: Resolved Star Formation Patterns at 0.7 less than z less than 1.5

NASA Technical Reports Server (NTRS)

Wuyts, Stijn; Foerster Schreiber, Natascha M.; Nelson, Erica J.; Van Dokkum, Pieter G.; Brammer, Gabe; Chang, Yu-Yen; Faber, Sandra M.; Ferguson, Henry C.; Franx, Marijn; Fumagalli, Mattia;

K-band observations of boxy bulges - I. Morphology and surface brightness profiles

NASA Astrophysics Data System (ADS)

Bureau, M.; Aronica, G.; Athanassoula, E.; Dettmar, R.-J.; Bosma, A.; Freeman, K. C.

2006-08-01

In this first paper of a series on the structure of boxy and peanut-shaped (B/PS) bulges, Kn-band observations of a sample of 30 edge-on spiral galaxies are described and discussed. Kn-band observations best trace the dominant luminous galactic mass and are minimally affected by dust. Images, unsharp-masked images, as well as major-axis and vertically summed surface brightness profiles are presented and discussed. Galaxies with a B/PS bulge tend to have a more complex morphology than galaxies with other bulge types, more often showing centred or off-centred X structures, secondary maxima along the major-axis and spiral-like structures. While probably not uniquely related to bars, those features are observed in three-dimensional N-body simulations of barred discs and may trace the main bar orbit families. The surface brightness profiles of galaxies with a B/PS bulge are also more complex, typically containing three or more clearly separated regions, including a shallow or flat intermediate region (Freeman Type II profiles). The breaks in the profiles offer evidence for bar-driven transfer of angular momentum and radial redistribution of material. The profiles further suggest a rapid variation of the scaleheight of the disc material, contrary to conventional wisdom but again as expected from the vertical resonances and instabilities present in barred discs. Interestingly, the steep inner region of the surface brightness profiles is often shorter than the isophotally thick part of the galaxies, itself always shorter than the flat intermediate region of the profiles. The steep inner region is also much more prominent along the major-axis than in the vertically summed profiles. Similarly to other recent work but contrary to the standard `bulge + disc' model (where the bulge is both thick and steep), we thus propose that galaxies with a B/PS bulge are composed of a thin concentrated disc (a disc-like bulge) contained within a partially thick bar (the B/PS bulge), itself contained within a thin outer disc. The inner disc likely formed secularly through bar-driven processes and is responsible for the steep inner region of the surface brightness profiles, traditionally associated with a classic bulge, while the bar is responsible for the flat intermediate region of the surface brightness profiles and the thick complex morphological structures observed. Those components are strongly coupled dynamically and are formed mostly of the same (disc) material, shaped by the weak but relentless action of the bar resonances. Any competing formation scenario for galaxies with a B/PS bulge, which represent at least 45 per cent of the local disc galaxy population, must explain equally well and self-consistently the above morphological and photometric properties, the complex gas and stellar kinematics observed, and the correlations between them.

AN ATLAS OF BRIGHT STAR SPECTRA IN THE NEAR-INFRARED FROM CASSINI-VIMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stewart, Paul N.; Tuthill, Peter G.; Nicholson, Philip D.

2015-12-15

We present the Cassini Atlas Of Stellar Spectra (CAOSS), comprised of near-infrared, low-resolution spectra of bright stars recovered from space-based observations by the Cassini spacecraft. The 65 stellar targets in the atlas are predominately M, K, and S giants. However, it also contains spectra of other bright nearby stars including carbon stars and main-sequence stars from A to F. The spectra presented are free of all spectral contamination caused by the Earth's atmosphere, including the detrimental telluric molecular bands which put parts of the near-infrared spectrum out of reach of terrestrial observations. With a single instrument, a spectro-photometric data set is recoveredmore » that spans the near-infrared from 0.8 to 5.1 μm with spectral resolution ranging from R = 53.5 to R = 325. Spectra have been calibrated into absolute flux units after careful characterization of the instrumental spectral efficiency. Spectral energy distributions for most stars match closely with literature values. All final data products have been made available online.« less

Gravitational lensing by a massive black hole at the Galactic center

NASA Technical Reports Server (NTRS)

Wardle, Mark; Yusef-Zadeh, Farhad

1992-01-01

The manifestations of gravitational lensing by a massive black hole at the Galactic center, with particular attention given to lensing of stars in the stellar cluster that lie behind Sgr A*, and of Sgr A east, a nonthermal extended radio source which is known with certainty to lie behind the Galactic center. Lensing of the stellar cluster produces a deficit of stellar images within 10 mas of the center, and a surplus between 30 and 300 mas. The results suggest that the proper motion of the stars will produce brightness variations of stellar images on a time scale of a few years or less. Both images of such a source should be visible, and will rise and fall in luminosity together.

Catching the Next Burst: the periodic young stellar object EC 53 in Serpens Main is sharply brightening at 850 microns and at near-IR H-band and K-band

NASA Astrophysics Data System (ADS)

Johnstone, Doug; Mairs, Steve; Naylor, Tim; Contreras Pena, Carlos; Varricatt, Watson; Hodapp, Klaus; Herczeg, Gregory J.; Lee, Jeong-Eun; Yoo, Hyunju; Bell, Graham S.; Bower, Geoffrey C.; Aikawa, Yuri; Chen, Huei-Ru Vivien; Hatchell, Jennifer; Park, Sunkyung

2018-05-01

As part of our young stellar object (YSO) sub-mm monthly monitoring programme, the JCMT-Transient Survey (Herczeg et al. 2017 ApJ, 849, 43; Johnstone et al. 2018 ApJ, 854, 31), we are using SCUBA2 to monitor the 850 micron peak brightness of the YSO EC 53 (R.A.

Vigorous atmospheric motion in the red supergiant star Antares.

PubMed

Ohnaka, K; Weigelt, G; Hofmann, K-H

2017-08-16

Red supergiant stars represent a late stage of the evolution of stars more massive than about nine solar masses, in which they develop complex, multi-component atmospheres. Bright spots have been detected in the atmosphere of red supergiants using interferometric imaging. Above the photosphere of a red supergiant, the molecular outer atmosphere extends up to about two stellar radii. Furthermore, the hot chromosphere (5,000 to 8,000 kelvin) and cool gas (less than 3,500 kelvin) of a red supergiant coexist at about three stellar radii. The dynamics of such complex atmospheres has been probed by ultraviolet and optical spectroscopy. The most direct approach, however, is to measure the velocity of gas at each position over the image of stars as in observations of the Sun. Here we report the mapping of the velocity field over the surface and atmosphere of the nearby red supergiant Antares. The two-dimensional velocity field map obtained from our near-infrared spectro-interferometric imaging reveals vigorous upwelling and downdrafting motions of several huge gas clumps at velocities ranging from about -20 to +20 kilometres per second in the atmosphere, which extends out to about 1.7 stellar radii. Convection alone cannot explain the observed turbulent motions and atmospheric extension, suggesting that an unidentified process is operating in the extended atmosphere.

Substructures and Tidal Distortions in the Magellanic Stellar Periphery

NASA Astrophysics Data System (ADS)

Mackey, Dougal; Koposov, Sergey; Da Costa, Gary; Belokurov, Vasily; Erkal, Denis; Kuzma, Pete

2018-05-01

We use a new panoramic imaging survey conducted with the Dark Energy Camera to map the stellar fringes of the Large and Small Magellanic Clouds (LMC/SMC) to extremely low surface brightness V ≈ 32 mag arcsec‑2. Our results starkly illustrate the closely interacting nature of the LMC–SMC pair. We show that the outer LMC disk is strongly distorted, exhibiting an irregular shape, evidence for warping, and significant truncation on the side facing the SMC. Large diffuse stellar substructures are present both to the north and south of the LMC, and in the inter-Cloud region. At least one of these features appears as co-spatial with the bridge of RR Lyrae stars that connects the Clouds. The SMC is highly disturbed; we confirm the presence of tidal tails, as well as a large line-of-sight depth on the side closest to the LMC. Young, intermediate-age, and ancient stellar populations in the SMC exhibit strikingly different spatial distributions. In particular, those with ages ∼1.5–4 Gyr exhibit a spheroidal distribution with a centroid offset from that of the oldest stars by several degrees toward the LMC. We speculate that the gravitational influence of the LMC may already have been perturbing the gaseous component of the SMC several Gyr ago. With careful modeling, the variety of substructures and tidal distortions evident in the Magellanic periphery should tightly constrain the interaction history of the Clouds.

A first constraint on the average mass of ultra-diffuse galaxies from weak gravitational lensing

NASA Astrophysics Data System (ADS)

Sifón, Cristóbal; van der Burg, Remco F. J.; Hoekstra, Henk; Muzzin, Adam; Herbonnet, Ricardo

2018-01-01

The recent discovery of thousands of ultra-diffuse galaxies (UDGs) in nearby galaxy clusters has opened a new window into the process of galaxy formation and evolution. Several scenarios have been proposed to explain the formation history of UDGs, and their ability to survive in the harsh cluster environments. A key requirement to distinguish between these scenarios is a measurement of their halo masses which, due to their low surface brightnesses, has proven difficult if one relies on stellar tracers of the potential. We exploit weak gravitational lensing, a technique that does not depend on these baryonic tracers, to measure the average subhalo mass of 784 UDGs selected in 18 clusters at z ≤ 0.09. Our sample of UDGs has a median stellar mass 〈m⋆〉 = 2 × 108 M⊙ and a median effective radius 〈reff〉 = 2.8 kpc. We constrain the average mass of subhaloes within 30 kpc to log mUDG(r < 30 kpc)/M⊙ ≤ 10.99 at 95 per cent credibility, implying an effective virial mass log m200/M⊙ ≤ 11.80, and a lower limit on the stellar mass fraction within 10 kpc of 1.0 per cent. Such mass is consistent with a simple extrapolation of the subhalo-to-stellar mass relation of typical satellite galaxies in massive clusters. However, our analysis is not sensitive to scatter about this mean mass; the possibility remains that extreme UDGs reside in haloes as massive as the Milky Way.

The planetary nebulae population in the nuclear regions of M31: the SAURON view

NASA Astrophysics Data System (ADS)

Pastorello, Nicola; Sarzi, Marc; Cappellari, Michele; Emsellem, Eric; Mamon, Gary A.; Bacon, Roland; Davies, Roger L.; de Zeeuw, P. Tim

2013-04-01

The study of extragalactic planetary nebulae (PNe) in the optical regions of galaxies, where the properties of their stellar population can be best characterized, is a promising ground to better understand the late evolution of stars across different galactic environments. Following a first study of the central regions of M32 that illustrated the power of integral field spectroscopy (IFS) in detecting and measuring the [O III] λ5007 emission of PNe against a strong stellar background, we turn to the very nuclear PN population of M31, within ˜80 pc of its centre. We show that PNe can also be found in the presence of emission from diffuse gas, as commonly observed in early-type galaxies and in the bulge of spirals, and further illustrate the excellent sensitivity of IFS in detecting extragalactic PNe through a comparison with narrow-band images obtained with the Hubble Space Telescope. Contrary to the case of the central regions of M32, the nuclear PNe population of M31 is only marginally consistent with the generally adopted form of the PNe luminosity function (PNLF). In particular, this is due to a lack of PNe with absolute magnitude M5007 brighter than -3, which would only result from a rather unfortunate draw from such a model PNLF. The nuclear stellar population of M31 is quite different from that of the central regions of M32, which is characterized in particular by a larger metallicity and a remarkable ultraviolet (UV) upturn. We suggest that the observed lack of bright PNe in the nuclear regions of M31 is due to a horizontal-branch population that is more tilted towards less massive and hotter He-burning stars, so that its progeny consists mostly of UV-bright stars that fail to climb back up the asymptotic giant branch (AGB) and only a few, if any, bright PNe powered by central post-AGB stars. These results are also consistent with recent reports on a dearth of bright post-AGB stars towards the nucleus of M31, and lend further support to the idea that the metallicity of a stellar population has an impact on the way the horizontal branch is populated and to the loose anticorrelation between the strength of the UV upturn and the specific number of PNe that is observed in early-type galaxies. Finally, our investigation also serves to stress the importance of considering the same spatial scales when comparing the PNe population of galaxies with the properties of their stellar populations.

The Characterization of Galaxy Structure

NASA Astrophysics Data System (ADS)

Zaritsky, Dennis

There is no all-encompassing intuitive physical understanding of galactic structure. We cannot predict the size, surface brightness, or luminosity of an individual galaxy based on the mass of its halo, or other physical characteristics, from simple first principles or even empirical guidelines. We have come to believe that such an understanding is possible because we have identified a simple scaling relation that applies to all gravitationally bound stellar systems,from giant ellipticals to dwarf spheroidals, from spiral galaxies to globular clusters. The simplicity (and low scatter) of this relationship testifies to an underlying order. In this proposal, we outline what we have learned so far about this scaling relationship, what we need to do to refine it so that it has no free parameters and provides the strongest possible test of galaxy formation and evolution models, and several ways in which we will exploit the relationship to explore other issues. Primarily, the proposed work involves a study of the uniform IR surface photometry of several thousand stellar systems using a single data source (the Spitzer S4G survey) to address shortcomings posed by the current heterogeneous sample and combining these data with the GALEX database to study how excursions from this relationship are related to current or on-going star formation. This relationship, like its antecedents the Fundamental Plane or Tully-Fisher relationship, can also be used to estimate distances and stellar mass-to-light ratios. We will describe the key advantages our relationship has relative to the existing work and how we will exploit those using archival NASA data from the Spitzer, GALEX, and WISE missions.

Stellar granulation as the source of high-frequency flicker in Kepler light curves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cranmer, Steven R.; Saar, Steven H.; Bastien, Fabienne A.

2014-02-01

A large fraction of cool, low-mass stars exhibit brightness fluctuations that arise from a combination of convective granulation, acoustic oscillations, magnetic activity, and stellar rotation. Much of the short-timescale variability takes the form of stochastic noise, whose presence may limit the progress of extrasolar planet detection and characterization. In order to lay the groundwork for extracting useful information from these quasi-random signals, we focus on the origin of the granulation-driven component of the variability. We apply existing theoretical scaling relations to predict the star-integrated variability amplitudes for 508 stars with photometric light curves measured by the Kepler mission. We alsomore » derive an empirical correction factor that aims to account for the suppression of convection in F-dwarf stars with magnetic activity and shallow convection zones. So that we can make predictions of specific observational quantities, we performed Monte Carlo simulations of granulation light curves using a Lorentzian power spectrum. These simulations allowed us to reproduce the so-called flicker floor (i.e., a lower bound in the relationship between the full light-curve range and power in short-timescale fluctuations) that was found in the Kepler data. The Monte Carlo model also enabled us to convert the modeled fluctuation variance into a flicker amplitude directly comparable with observations. When the magnetic suppression factor described above is applied, the model reproduces the observed correlation between stellar surface gravity and flicker amplitude. Observationally validated models like these provide new and complementary evidence for a possible impact of magnetic activity on the properties of near-surface convection.« less

The core of the nearby S0 galaxy NGC 7457 imaged with the HST planetary camera

NASA Technical Reports Server (NTRS)

Lauer, Tod R.; Faber, S. M.; Holtzman, Jon A.; Baum, William A.; Currie, Douglas G.; Ewald, S. P.; Groth, Edward J.; Hester, J. Jeff; Kelsall, T.

1991-01-01

A brief analysis is presented of images of the nearby S0 galaxy NGC 7457 obtained with the HST Planetary Camera. While the galaxy remains unresolved with the HST, the images reveal that any core most likely has r(c) less than 0.052 arcsec. The light distribution is consistent with a gamma = -1.0 power law inward to the resolution limit, with a possible stellar nucleus with luminosity of 10 million solar. This result represents the first observation outside the Local Group of a galaxy nucleus at this spatial resolution, and it suggests that such small, high surface brightness cores may be common.

Rosette nebula globules: Seahorse giving birth to a star

NASA Astrophysics Data System (ADS)

Mäkelä, M. M.; Haikala, L. K.; Gahm, G. F.

2017-09-01

Context. The Rosette nebula is an H II region ionized mainly by the stellar cluster NGC 2244. Elephant trunks, globules, and globulettes are seen at the interface where the H II region and the surrounding molecular shell meet. Aims: We have observed a field in the northwestern part of the Rosette nebula where we study the small globules protruding from the shell. Our aim is to measure their properties and study their star-formation history in continuation of our earlier study of the features of the region. Methods: We imaged the region in broadband near-infrared (NIR) JsHKs filters and narrowband H2 1-0 S(1), Pβ, and continuum filters using the SOFI camera at the ESO/NTT. The imaging was used to study the stellar population and surface brightness, create visual extinction maps, and locate star formation. Mid-infrared (MIR) Spitzer IRAC and WISE and optical NOT images were used to further study the star formation and the structure of the globules. The NIR and MIR observations indicate an outflow, which is confirmed with CO observations made with APEX. Results: The globules have mean number densities of 4.6 × 104 cm-3. Pβ is seen in absorption in the cores of the globules where we measure visual extinctions of 11-16 mag. The shell and the globules have bright rims in the observed bands. In the Ks band 20 to 40% of the emission is due to fluorescent emission in the 2.12 μmH2 line similar to the tiny dense globulettes we studied earlier in a nearby region. We identify several stellar NIR excess candidates and four of them are also detected in the Spitzer IRAC 8.0 μm image and studied further. We find an outflow with a cavity wall bright in the 2.124 μmH2 line and at 8.0 μm in one of the globules. The outflow originates from a Class I young stellar object (YSO) embedded deep inside the globule. An Hα image suggests the YSO drives a possible parsec-scale outflow. Despite the morphology of the globule, the outflow does not seem to run inside the dusty fingers extending from the main globule body. Based on observations done at the European Southern Observatory, La Silla, Chile (ESO program 088.C-0630) and with Apex (program O-088.F-9318).Table 1 and APEX CO spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/A82

SMASH: Survey of the MAgellanic Stellar History

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nidever, David L.; Olsen, Knut; Blum, Robert D.

The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg{sup 2} (distributed over ∼2400 square degrees at ∼20% filling factor) to ∼24th mag in ugriz . The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey,more » its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ∼15 mas and the accuracy is ∼2 mas with respect to the Gaia reference frame. The photometric precision is ∼0.5%–0.7% in griz and ∼1% in u with a calibration accuracy of ∼1.3% in all bands. The median 5 σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R  ∼ 18.4 kpc. SMASH DR1 contains measurements of ∼100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.« less

SMASH: Survey of the MAgellanic Stellar History

NASA Astrophysics Data System (ADS)

Nidever, David L.; Olsen, Knut; Walker, Alistair R.; Vivas, A. Katherina; Blum, Robert D.; Kaleida, Catherine; Choi, Yumi; Conn, Blair C.; Gruendl, Robert A.; Bell, Eric F.; Besla, Gurtina; Muñoz, Ricardo R.; Gallart, Carme; Martin, Nicolas F.; Olszewski, Edward W.; Saha, Abhijit; Monachesi, Antonela; Monelli, Matteo; de Boer, Thomas J. L.; Johnson, L. Clifton; Zaritsky, Dennis; Stringfellow, Guy S.; van der Marel, Roeland P.; Cioni, Maria-Rosa L.; Jin, Shoko; Majewski, Steven R.; Martinez-Delgado, David; Monteagudo, Lara; Noël, Noelia E. D.; Bernard, Edouard J.; Kunder, Andrea; Chu, You-Hua; Bell, Cameron P. M.; Santana, Felipe; Frechem, Joshua; Medina, Gustavo E.; Parkash, Vaishali; Serón Navarrete, J. C.; Hayes, Christian

2017-11-01

The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg2 (distributed over ˜2400 square degrees at ˜20% filling factor) to ˜24th mag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ˜15 mas and the accuracy is ˜2 mas with respect to the Gaia reference frame. The photometric precision is ˜0.5%-0.7% in griz and ˜1% in u with a calibration accuracy of ˜1.3% in all bands. The median 5σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R ˜ 18.4 kpc. SMASH DR1 contains measurements of ˜100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.

Deep HST Imaging in 47 Tucanae: A Global Dynamical Model

NASA Astrophysics Data System (ADS)

Heyl, J.; Caiazzo, I.; Richer, H.; Anderson, J.; Kalirai, J.; Parada, J.

2017-12-01

Multi-epoch observations with the Advanced Camera Survey and WFC3 on the Hubble Space Telescope provide a unique and comprehensive probe of stellar dynamics within 47 Tucanae. We confront analytic models of the globular cluster with the observed stellar proper motions that probe along the main sequence from just above 0.8-0.1M ⊙ as well as white dwarfs younger than 1 Gyr. One field lies just beyond the half-light radius where dynamical models (e.g., lowered Maxwellian distributions) make robust predictions for the stellar proper motions. The observed proper motions in this outer field show evidence for anisotropy in the velocity distribution as well as skewness; the latter is evidence of rotation. The measured velocity dispersions and surface brightness distributions agree in detail with a rotating anisotropic model of the stellar distribution function with mild dependence of the proper-motion dispersion on mass. However, the best-fitting models underpredict the rotation and skewness of the stellar velocities. In the second field, centered on the core of the cluster, the mass segregation in proper motion is much stronger. Nevertheless the model developed in the outer field can be extended inward by taking this mass segregation into account in a heuristic fashion. The proper motions of the main-sequence stars yield a mass estimate of the cluster of 1.31+/- 0.02× {10}6{M}⊙ at a distance of 4.7 kpc. By comparing the proper motions of a sample of giant and subgiant stars with the observed radial velocities we estimate the distance to the cluster kinematically to be 4.29 ± 0.47 kpc.

Estimating the HI gas fractions of galaxies in the local Universe

NASA Astrophysics Data System (ADS)

Zhang, Wei; Li, Cheng; Kauffmann, Guinevere; Zou, Hu; Catinella, Barbara; Shen, Shiyin; Guo, Qi; Chang, Ruixiang

2009-08-01

We use a sample of 800 galaxies with HI mass measurements from the HyperLeda catalogue and optical photometry from the fourth data release of the Sloan Digital Sky Survey (SDSS) to calibrate a new photometric estimator of the HI-to-stellar-mass ratio for nearby galaxies. Our estimator, which is motivated by the Kennicutt-Schmidt star formation law, is log10(GHI/S) = -1.73238(g - r) + 0.215182μi - 4.08451, where μi is the i-band surface brightness and g - r is the optical colour estimated from the g- and r-band Petrosian apparent magnitudes. This estimator has a scatter of σ = 0.31 dex in log (GHI/S), compared to σ ~ 0.4 dex for previous estimators that were based on colour alone. We investigate whether the residuals in our estimate of log (GHI/S) depend in a systematic way on a variety of different galaxy properties. We find no effect as a function of stellar mass or 4000 Å break strength, but there is a systematic effect as a function of the concentration index of the light. We then apply our estimator to a sample of 105 emission-line galaxies in the SDSS Data Release 4 (DR4) and derive an estimate of the HI mass function, which is in excellent agreement with recent results from HI blind surveys. Finally, we re-examine the well-known relation between gas-phase metallicity and stellar mass, and ask whether there is a dependence on HI-to-stellar-mass ratio, as predicted by chemical evolution models. We do find that gas-poor galaxies are more metal rich at fixed stellar mass. We compare our results with the semi-analytic models of De Lucia & Blaizot, which include supernova feedback, as well as the cosmological infall of gas.

A common origin for globular clusters and ultra-faint dwarfs in simulations of the first galaxies

DOE PAGES

Ricotti, Massimo; Parry, Owen H.; Gnedin, Nickolay Y.

2016-11-09

In this study, the first in a series on galaxy formation before reionization, we focus on understanding what determines the size and morphology of stellar objects in the first low-mass galaxies, using parsec-scale cosmological simulations performed with an adaptive mesh hydrodynamics code. Although the dense gas in which stars are formed tends to have a disk structure, stars are found in spheroids with little rotation. Halos with masses betweenmore » $${10}^{6}\\,{M}_{\\odot }$$ and $$5\\times {10}^{8}\\,{M}_{\\odot }$$ form stars stochastically, with stellar masses in the range $${10}^{4}\\,{M}_{\\odot }$$ to $$2\\times {10}^{6}\\,{M}_{\\odot }$$. We observe, nearly independent of stellar mass, a large range of half-light radii for the stars, from a few parsecs to a few hundred parsecs and surface brightnesses and mass-to-light ratios ranging from those typical of globular clusters to ultra-faint dwarfs. In our simulations, stars form in dense stellar clusters with high gas-to-star conversion efficiencies and rather uniform metallicities. A fraction of these clusters remain bound after the gas is removed by feedback, but others are destroyed, and their stars, which typically have velocity dispersions of 20–40 km s –1, expand until they become bound by the dark matter halo. We thus speculate that the stars in ultra-faint dwarf galaxies may show kinematic and chemical signatures consistent with their origin in a few distinct stellar clusters. On the other hand, some globular clusters may form at the center of primordial dwarf galaxies and may contain dark matter, perhaps detectable in the outer parts.« less

A common origin for globular clusters and ultra-faint dwarfs in simulations of the first galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ricotti, Massimo; Parry, Owen H.; Gnedin, Nickolay Y.

In this study, the first in a series on galaxy formation before reionization, we focus on understanding what determines the size and morphology of stellar objects in the first low-mass galaxies, using parsec-scale cosmological simulations performed with an adaptive mesh hydrodynamics code. Although the dense gas in which stars are formed tends to have a disk structure, stars are found in spheroids with little rotation. Halos with masses betweenmore » $${10}^{6}\\,{M}_{\\odot }$$ and $$5\\times {10}^{8}\\,{M}_{\\odot }$$ form stars stochastically, with stellar masses in the range $${10}^{4}\\,{M}_{\\odot }$$ to $$2\\times {10}^{6}\\,{M}_{\\odot }$$. We observe, nearly independent of stellar mass, a large range of half-light radii for the stars, from a few parsecs to a few hundred parsecs and surface brightnesses and mass-to-light ratios ranging from those typical of globular clusters to ultra-faint dwarfs. In our simulations, stars form in dense stellar clusters with high gas-to-star conversion efficiencies and rather uniform metallicities. A fraction of these clusters remain bound after the gas is removed by feedback, but others are destroyed, and their stars, which typically have velocity dispersions of 20–40 km s –1, expand until they become bound by the dark matter halo. We thus speculate that the stars in ultra-faint dwarf galaxies may show kinematic and chemical signatures consistent with their origin in a few distinct stellar clusters. On the other hand, some globular clusters may form at the center of primordial dwarf galaxies and may contain dark matter, perhaps detectable in the outer parts.« less

On the AU Microscopii debris disk. Density profiles, grain properties, and dust dynamics

NASA Astrophysics Data System (ADS)

Augereau, J.-C.; Beust, H.

2006-09-01

Context: . AU Mic is a young M-type star surrounded by an edge-on optically thin debris disk that shares many common observational properties with the disk around β Pictoris. In particular, the scattered light surface brightness profile falls off as ˜ r-5 outside 120 AU for β Pictoris and 35 AU for AU Mic. In both cases, the disk color rises as the distance increases beyond these reference radii. Aims: . In this paper, we present the first comprehensive analysis of the AU Mic disk properties since the system was resolved by Kalas et al. (2004, Science, 303, 1990). We explore whether the dynamical model, which successfully reproduces the β Pictoris brightness profile (e.g., Augereau et al. 2001, A&A, 370, 447), could apply to AU Mic. Methods: . We calculate the surface density profile of the AU Mic disk by performing the inversion of the near-IR and visible scattered light brightness profiles measured by Liu (2004, Science, 305, 1442) and Krist et al. (2005, AJ, 129, 1008), respectively. We discuss the grain properties by analysing the blue color of the disk in the visible (Krist et al. 2005) and by fitting the disk spectral energy distribution. Finally, we evaluate the radiation and wind forces on the grains. The impact of the recurrent X-ray and UV-flares on the dust dynamics is also discussed. Results: . We show that irrespective of the mean scattering asymmetry factor of the grains, most of the emission arises from an asymmetric, collisionally-dominated region that peaks close to the surface brightness break around 35 AU. The elementary scatterers at visible wavelengths are found to be sub-micronic, but the inferred size distribution underestimates the number of large grains, resulting in sub-millimeter emissions that are too low compared to the observations. From our inversion procedure, we find that the V- to H-band scattering cross sections ratio increases outside 40 AU, in line with the observed color gradient of the disk. This behavior is expected if the grains have not been produced locally, but placed in orbits of high eccentricity by a size-dependent pressure force, resulting in a paucity of large grains beyond the outer edge of the parent bodies' disk. Because of the low luminosity of AU Mic, radiation pressure is inefficient to diffuse the smallest grains in the outer disk, even when the flares are taken into account. Conversely, we show that a standard, solar-like stellar wind generates a pressure force onto the dust particles that behaves much like a radiation pressure force. With an assumed dot{M} ≃ 3×102 dot{M}⊙, the wind pressure overcomes the radiation pressure, and this effect is enhanced by the stellar flares. This greatly contributes to populating the extended AU Mic debris disk and explains the similarity between the β Pictoris and AU Mic brightness profiles. In both cases, the color gradient beyond 120 AU for β Pictoris and 35 AU for AU Mic, is believed to be a direct consequence of the dust dynamics.

WINGS: WFIRST Infrared Nearby Galaxy Survey

NASA Astrophysics Data System (ADS)

Williams, Benjamin

WFIRST's combination of wide field and high resolution will revolutionize the study of nearby galaxies. We propose to produce and analyze simulated WFIRST data of nearby galaxies and their halos to maximize the scientific yield in the limited observing time available, ensuring the legacy value of WFIRST's eventual archive. We will model both halo structure and resolved stellar populations to optimize WFIRST's constraints on both dark matter and galaxy formation models in the local universe. WFIRST can map galaxy structure down to ~35 mag/square arcsecond using individual stars. The resulting maps of stellar halos and accreting dwarf companions will provide stringent tests of galaxy formation and dark matter models on galactic (and even sub-galactic) scales, which is where the most theoretical tension exists with the Lambda-CDM model. With a careful, coordinated plan, WFIRST can be expected to improve current sample sizes by 2 orders of magnitude, down to surface brightness limits comparable to those currently reached only in the Local Group, and that are >4 magnitudes fainter than achievable from the ground due to limitations in star-galaxy separation. WFIRST's maps of galaxy halos will simultaneously produce photometry for billions of stars in the main bodies of galaxies within 10 Mpc. These data will transform studies of star formation histories that track stellar mass growth as a function of time and position within a galaxy. They also will constrain critical stellar evolution models of the near-infrared bright, rapidly evolving stars that can contribute significantly to the integrated light of galaxies in the near-infrared. Thus, with WFIRST we can derive the detailed evolution of individual galaxies, reconstruct the complete history of star formation in the nearby universe, and put crucial constraints on the theoretical models used to interpret near-infrared extragalactic observations. We propose a three-component work plan that will ensure these gains by testing and optimizing WFIRST observing strategies and providing science guidance to trade studies of observatory requirements such as field of view, pixel scale and filter selection. First, we will perform extensive simulations of galaxies' halo substructures and stellar populations that will be used as input for optimizing observing strategies and sample selection. Second, we will develop a pipeline that optimizes stellar photometry, proper motion, and variability measurements with WFIRST. This software will: maximize data quality & scientific yield; provide essential, independent calibrations to the larger WFIRST efforts; and rapidly provide accurate photometry and astrometry to the community. Third, we will derive quantitative performance metrics to fairly evaluate trade-offs between different survey strategies and WFIRST performance capabilities. The end result of this effort will be: (1) an efficient survey strategy that maximizes the scientific yield of what would otherwise be a chaotic archive of observations from small, un-coordinated programs; (2) a suite of analysis tools and a state-of-the-art pipeline that can be deployed after launch to rapidly deliver stellar photometry to the public; (3) a platform to independently verify the calibration and point spread function modeling that are essential to the primary WFIRST goals, but that are best tested from images of stellar populations. These activities will be carried out by a Science Investigation Team that has decades of experience in using nearby galaxies to inform fundamental topics in astrophysics. This team is composed of researchers who have led the charge in observational and theoretical studies of resolved stellar populations and stellar halos. With our combined background, we are poised to take full advantage of the large field of view and high spatial resolution WFIRST will offer.

High-precision photometry by telescope defocussing - VIII. WASP-22, WASP-41, WASP-42 and WASP-55

NASA Astrophysics Data System (ADS)

Southworth, John; Tregloan-Reed, J.; Andersen, M. I.; Calchi Novati, S.; Ciceri, S.; Colque, J. P.; D'Ago, G.; Dominik, M.; Evans, D. F.; Gu, S.-H.; Herrera-Cordova, A.; Hinse, T. C.; Jørgensen, U. G.; Juncher, D.; Kuffmeier, M.; Mancini, L.; Peixinho, N.; Popovas, A.; Rabus, M.; Skottfelt, J.; Tronsgaard, R.; Unda-Sanzana, E.; Wang, X.-B.; Wertz, O.; Alsubai, K. A.; Andersen, J. M.; Bozza, V.; Bramich, D. M.; Burgdorf, M.; Damerdji, Y.; Diehl, C.; Elyiv, A.; Figuera Jaimes, R.; Haugbølle, T.; Hundertmark, M.; Kains, N.; Kerins, E.; Korhonen, H.; Liebig, C.; Mathiasen, M.; Penny, M. T.; Rahvar, S.; Scarpetta, G.; Schmidt, R. W.; Snodgrass, C.; Starkey, D.; Surdej, J.; Vilela, C.; von Essen, C.; Wang, Y.

2016-04-01

We present 13 high-precision and four additional light curves of four bright southern-hemisphere transiting planetary systems: WASP-22, WASP-41, WASP-42 and WASP-55. In the cases of WASP-42 and WASP-55, these are the first follow-up observations since their discovery papers. We present refined measurements of the physical properties and orbital ephemerides of all four systems. No indications of transit timing variations were seen. All four planets have radii inflated above those expected from theoretical models of gas-giant planets; WASP-55 b is the most discrepant with a mass of 0.63 MJup and a radius of 1.34 RJup. WASP-41 shows brightness anomalies during transit due to the planet occulting spots on the stellar surface. Two anomalies observed 3.1 d apart are very likely due to the same spot. We measure its change in position and determine a rotation period for the host star of 18.6 ± 1.5 d, in good agreement with a published measurement from spot-induced brightness modulation, and a sky-projected orbital obliquity of λ = 6 ± 11°. We conclude with a compilation of obliquity measurements from spot-tracking analyses and a discussion of this technique in the study of the orbital configurations of hot Jupiters.

Determination of Li abundance in Solar type stars of intermediate brightness

NASA Astrophysics Data System (ADS)

Amazo-Gómez, E. M.; Hernandez-Águila, B.; Dagostino, M. C.; Bertone, E.; de la Luz, V.

2014-10-01

The determination of the lithium abundance in stellar atmospheres is of fundamental importance in multiple contexts of contemporary astrophysics. On the one hand, the lithium present in stars with global sub-solar metal abundances provides a strong restriction on the abundance of this element as a result of primordial nucleo-synthesis. On the other hand, Li can be an age indicator for stars with convective envelopes. Additionally, Li abundance appears to be correlated with the presence of sub-stellar companions. We present preliminary results of a project aimed at determining the Li abundance in an extended sample of solar-like stars (spectral type G and luminosity class V) of intermediate brightness. High resolution spectroscopic data (R=65000) were obtained with the CanHiS echelle spectrograph on the 2.11m telescope of the Guillermo Haro Observatory in Cananea, Sonora, Mexico. We report the equivalent widths of a first sub-sample of 33 stars.

Data trove helps pin down the shape of the Milky Way

NASA Astrophysics Data System (ADS)

Clery, Daniel

2018-04-01

On 25 April, hundreds of astronomers around the world got their hands on one of the biggest data dumps in the history of astronomy: the exact positions, motions, brightnesses, and colors of 1.3 billion stars in and around the Milky Way, gathered during the first 2 years of operation by the European Space Agency's €750 million Gaia satellite, launched in 2013. The data—Gaia's second release—will fuel an explosion of studies about the structure of the Milky Way. The trove of stellar positions from Gaia will sharpen our picture of the galaxy's spiral structures, and the data on stellar motions will allow astronomers to wind the clock backward and see how the galaxy evolved over the past 13 billion years. Gaia's color and brightness information, meanwhile, will help astronomers classify stars by composition and pin down where different types are born.

The Ca II V/R ratio and mass loss. [stellar spectral emission lines

NASA Technical Reports Server (NTRS)

Stencel, R. E.

1978-01-01

High-dispersion coude spectrograms of 181 MK standards of types early F through late M, including luminosity classes Ia, Ib, II, and III, are analyzed. It is shown that the brightness ratio of the V and R self-reversed emission peaks (denoted V/R) in the center of the Ca II K line is correlated with spectral type as well as with certain other spectral-type and luminosity-sensitive parameters, including indicators of mass loss and the H-K wing emission lines. The observations indicate that V/R varies smoothly from less than unity in late K and M giants to greater than unity for G giants. This trend appears to be true for bright giants as well but not necessarily for supergiants and seems to hold for the average V/R for a given star, although short-term variations in V/R occur. It is suggested that the V/R values, which can be interpreted in terms of atmospheric motions, may indirectly relate to effects of evolutionary changes in stellar structure and that V/R among late-type stars could be useful as an indicator of both chromospheric activity and the state of stellar evolution.

The DiskMass Survey. VI. Gas and stellar kinematics in spiral galaxies from PPak integral-field spectroscopy

NASA Astrophysics Data System (ADS)

Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Bershady, Matthew A.; Schechtman-Rook, Andrew; Andersen, David R.; Swaters, Rob A.

2013-09-01

We present ionized-gas ([Oiii]λ5007 Å) and stellar kinematics (velocities and velocity dispersions) for 30 nearly face-on spiral galaxies out to as many as three K-band disk scale lengths (hR). These data have been derived from PPak integral-field-unit spectroscopy from 4980-5370 Å observed at a mean resolution of λ/Δλ = 7700 (σinst = 17 km s-1). These data are a fundamental product of our survey and will be used in companion papers to, e.g., derive the detailed (baryonic+dark) mass budget of each galaxy in our sample. Our presentation provides a comprehensive description of the observing strategy and data reduction, including a robust measurement and removal of shift, scale, and rotation effects in the data due to instrumental flexure. Using an in-plane coordinate system determined by fitting circular-speed curves to our velocity fields, we derive azimuthally averaged rotation curves and line-of-sight velocity dispersion (σLOS) and luminosity profiles for both the stars and [Oiii]-emitting gas. Along with a clear presentation of the data, we demonstrate: (1) The [Oiii] and stellar rotation curves exhibit a clear signature of asymmetric drift with a rotation difference that is 11% of the maximum rotation speed of the galaxy disk, comparable to measurements in the solar neighborhood in the Milky Way. (2) The e-folding length of the stellar velocity dispersion (hσ) is 2hR on average, as expected for a disk with a constant scale height and mass-to-light ratio, with a scatter that is notably smaller for massive, high-surface-brightness disks in the most luminous galaxies. (3) At radii larger than 1.5hR, σLOS tends to decline slower than the best-fitting exponential function, which may be due to an increase in the disk mass-to-light ratio, disk flaring, or disk heating by the dark-matter halo. (4) A strong correlation exists between the central vertical stellar velocity dispersion of the disks (σz,0) and their circular rotational speed at 2.2hR (V2.2hROiii), with a zero point indicating that galaxy disks are submaximal. Moreover, weak but consistent correlations exist between σz,0/V2.2hROiii and global galaxy properties such that disks with a fainter central surface brightness in bluer and less luminous galaxies of later morphological types are kinematically colder with respect to their rotational velocities. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Table 2 and Appendices are available in electronic form at http://www.aanda.org

Nebular Line Emission and Stellar Mass of Bright z 8 Galaxies "Super-Eights"

NASA Astrophysics Data System (ADS)

Holwerda, Benne; Bouwens, Rychard; Trenti, Michele; Oesch, Pascal; Labbe, Ivo; Smit, Renske; Roberts-Borsani, Guido; Bernard, Stephanie; Bridge, Joanna

2018-05-01

Searches for the Lyman-alpha emission from the very first galaxies ionizing the Universe have proved to be extremely difficult with limited success beyond z 7 (<3% detections). However, a search of all CANDELS yielded four bright z 8 sources with associated strong Lyman-alpha lines, despite the Universe expected to be 70% neutral at this time. The key to their selection is an extremely red IRAC color ([3.6]-[4.5]> 0.5, Roberts-Borsani+ 2016), indicative of very strong nebular line emission. Do such extreme line emitting galaxies produce most of the photons to reionize the Universe? We propose to expand the sample of bright z 8 galaxies with reliable IRAC colors with seven more Y-band dropouts found with HST and confirmed through HST/Spitzer. The Spitzer observations will test how many of bright z 8 galaxies are IRAC-red and measure both their stellar mass and [OIII]+Hbeta line strength. Together with Keck/VLT spectroscopy, they will address these questions: I) Do all luminous z 8 galaxies show such red IRAC colors ([OIII] emission / hard spectra)? II) Is luminosity or a red IRAC color the dominant predictor for Lyman-alpha emission? III) Or are these sources found along exceptionally transparent sightlines into the early Universe? With 11 bright z 8 sources along different lines-of-sight, all prime targets for JWST, we will aim to determine which of the considered factors (luminosity, color, sight-line) drives the high Lyman-alpha prevalence (100%) and insight into the sources reionizing the Universe.

The Brown Dwarf Kinematics Project (BDKP. III. Parallaxes for 70 Ultracool Dwarfs

DTIC Science & Technology

2012-06-10

highest mass exoplanets (Saumon et al. 1996; Chabrier & Baraffe 1997). In early 2000, the standard stellar spectral classification scheme was extended...Journal, 752:56 (22pp), 2012 June 10 Faherty et al. routine xdimsum was used to perform sky subtractions and mask holes from bright stars.13 3. PARALLAX...epoch. The precise centroids of the stars were measured by binning the stellar profile in the X and Y directions using a box of ∼2′′ around the pixel

The Nonbarred Double-Ringed Galaxy, PGC 1000714

NASA Astrophysics Data System (ADS)

Seigar, Marc; Mutlu Pakdil, Burcin; Mangedarage, Mithila; Treuthardt, Patrick M.

2017-01-01

Hoag-type galaxies are rare peculiar systems which bear strong resemblance to Hoag's Object with an elliptical-like core, a detached outer ring, and no signs of a bar or stellar disk. They represent extreme cases and help us understand the formation of galaxies in general by providing clues on formation mechanisms. The nature of outer rings in Hoag-type galaxies is still debated and may be related either to slow secular evolution, such as dissolution of a barlike structure or to environmental processes, such as galaxy-galaxy interactions or gas infall. Due to a fairly superficial resemblance to Hoag's Object, PGC 1000714 is a good target for detailed study of the peculiar structure of this type. We present the first photometric study of PGC 1000714 that has not yet been described in the literature. Our aim is to evaluate its structure and properties as well as understand the origin of outer rings in such galaxies. Surface photometry of the central body is performed using near-UV, BVRI and JHK images. Based on the photometric data, the nearly round central body follows a de Vaucouleurs profile almost all the way to the center. The detailed photometry reveals a reddish inner ring-shaped structure that shares the same center as the central body. However, no sign of a bar or stellar disk is detected. The outer ring appears as a bump in the surface brightness profile with a peak brightness of 25.8 mag/arcsec^{2} in the B-band and shows no sharp outer boundary. By reconstructing the observed SED for the central body and the rings, we recover the stellar population properties of the galaxy components. Our work suggests different formation histories for the inner and outer rings. We rule out the secular evolution model as being a formation mechanism for the outer ring. The colors of the outer ring are consistent with a feature that may have experienced a burst of star formation due to a possible recent accretion event. In addition, our work supports that the central body may be formed by a relatively dry major merger or in a single, short and highly effective star formation burst, and the inner ring may be formed as a result of intergalactic medium accretion or secular evolution of a possible gaseous disk

Structural properties of faint low surface brightness galaxies

NASA Astrophysics Data System (ADS)

Pahwa, Isha; Saha, Kanak

2018-05-01

We study the structural properties of Low Surface Brightness galaxies (LSB) using a sample of 263 galaxies observed by the Green Bank Telescope (Schneider et al. 1992). We perform 2D decompositions of these galaxies in the SDSS g, r and i bands using the GALFIT software. Our decomposition reveals that about 60% of these galaxies are bulgeless i.e., their light distributions are well modelled by pure exponential disks. The rest of the galaxies were fitted with two components: a Sersic bulge and an exponential disk. Most of these galaxies have bulge-to-total (B/T) ratio less than 0.1. However, of these 104 galaxies, 20% have B/T > 0.1 i.e., hosting significant bulge component and they are more prominent amongst the fainter LSBs. According to g - r colour criteria, most of the LSB galaxies in our sample are blue, with only 7 classified as red LSBs. About 15% of the LSB galaxies (including both blue and red) in our sample host stellar bars. The incidence of bars is more prominent in relatively massive blue LSB galaxies with very high gas fraction. These findings may provide important clues to the formation and evolution of LSB galaxies - in particular on the bar/bulge formation in faint LSB disks.

Relativistic jet activity from the tidal disruption of a star by a massive black hole.

PubMed

Burrows, D N; Kennea, J A; Ghisellini, G; Mangano, V; Zhang, B; Page, K L; Eracleous, M; Romano, P; Sakamoto, T; Falcone, A D; Osborne, J P; Campana, S; Beardmore, A P; Breeveld, A A; Chester, M M; Corbet, R; Covino, S; Cummings, J R; D'Avanzo, P; D'Elia, V; Esposito, P; Evans, P A; Fugazza, D; Gelbord, J M; Hiroi, K; Holland, S T; Huang, K Y; Im, M; Israel, G; Jeon, Y; Jeon, Y-B; Jun, H D; Kawai, N; Kim, J H; Krimm, H A; Marshall, F E; P Mészáros; Negoro, H; Omodei, N; Park, W-K; Perkins, J S; Sugizaki, M; Sung, H-I; Tagliaferri, G; Troja, E; Ueda, Y; Urata, Y; Usui, R; Antonelli, L A; Barthelmy, S D; Cusumano, G; Giommi, P; Melandri, A; Perri, M; Racusin, J L; Sbarufatti, B; Siegel, M H; Gehrels, N

2011-08-24

Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.

Eight new Milky Way companions discovered in first-year Dark Energy Survey data

DOE PAGES

Bechtol, K.

2015-06-30

We report the discovery of eight new Milky Way companions inmore » $$\\sim 1800\\;{\\mathrm{deg}}^{2}$$ of optical imaging data collected during the first year of the Dark Energy Survey (DES). Each system is identified as a statistically significant over-density of individual stars consistent with the expected isochrone and luminosity function of an old and metal-poor stellar population. The objects span a wide range of absolute magnitudes (MV from $-2.2$ to $$-7.4\\;\\mathrm{mag}$$), physical sizes ($$10-170\\;\\mathrm{pc}$$), and heliocentric distances ($$30-330\\;\\mathrm{kpc}$$). Based on the low surface brightnesses, large physical sizes, and/or large Galactocentric distances of these objects, several are likely to be new ultra-faint satellite galaxies of the Milky Way and/or Magellanic Clouds. We introduce a likelihood-based algorithm to search for and characterize stellar over-densities, as well as identify stars with high satellite membership probabilities. As a result, we also present completeness estimates for detecting ultra-faint galaxies of varying luminosities, sizes, and heliocentric distances in the first-year DES data.« less

Rosette globulettes and shells in the infrared

NASA Astrophysics Data System (ADS)

Mäkelä, M. M.; Haikala, L. K.; Gahm, G. F.

2014-07-01

Context. Giant galactic H ii regions surrounding central young clusters show compressed molecular shells, which have broken up into clumps, filaments, and elephant trunks interacting with UV light from central OB stars. Tiny, dense clumps of subsolar mass, called globulettes, form in this environment. Aims: We observe and explore the nature and origin of the infrared emission and extinction in these cool, dusty shell features and globulettes in one H ii region, the Rosette nebula, and search for associated newborn stars. Methods: We imaged the northwestern quadrant of the Rosette nebula in the near-infrared (NIR) through wideband JHKs filters and narrowband H2 1-0 S(1) and Pβ plus continuum filters using the Son of Isaac (SOFI) instrument at the New Technology Telescope (NTT) at European Southern Observatory (ESO). We used the NIR images to study the surface brightness of the globulettes and associated bright rims. We used the NIR JHKs photometry to create a visual extinction map and to search for objects with NIR excess emission. In addition, archival images from Spitzer Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) 24 μm and Herschel Photoconductor Array Camera and Spectrometer (PACS) observations, covering several bands in the mid-infrared and far-infrared, were used to further analyze the stellar population, to examine the structure of the trunks and other shell structures and to study this Rosette nebula photon-dominated region in more detail. Results: The globulettes and elephant trunks have bright rims in the Ks band, which are unresolved in our images, on the sides facing the central cluster. An analysis of 21 globulettes, where surface brightness in the H2 1-0 S(1) line at 2.12 μm is detected, shows that approximately a third of the surface brightness observed in the Ks filter is due to this line: the observed average of the H2/Ks surface brightness is 0.26 ± 0.02 in the globulettes' cores and 0.30 ± 0.01 in the rims. The estimated H2 1-0 S(1) surface brightness of the rims is ˜3-8 × 10-8 Wm-2 sr-1μm-1. The ratio of the surface brightnesses support fluorescence instead of shocks as the H2 excitation mechanism. The globulettes have number densities of n(H2) ˜ 10-4 cm-3 or higher. We estimated masses of individual globulettes and compared them to the results from previous optical and radio molecular line surveys. We confirm that the larger globulettes contain very dense cores, that the density is also high farther out from the core, and that their mass is subsolar. Two NIR protostellar objects were found in an elephant trunk and one was found in the most massive globulette in our study. Based on observations done at the European Southern Observatory, La Silla, Chile (ESO programmes 084.C-0299 and 088.C-0630).Appendix A is only available in electronic form at http://www.aanda.orgTables 5 and 6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A108

Blowin in the Stellar Wind

NASA Image and Video Library

2011-06-13

This image of the Elephant Trunk nebula from NASA Wide-field Survey Explorer shows clouds of dust and gas being pushed and eroded by a massive star. The bright trunk of the nebula near the center is an especially dense cloud.

Hubble Captures View of Mystic Mountain

NASA Image and Video Library

2010-04-22

NASA Hubble Space Telescope captures the chaotic activity atop a three-light-year-tall pillar of gas and dust that is being eaten away by the brilliant light from nearby bright stars in a tempestuous stellar nursery called the Carina Nebula.

Outer-disk reddening and gas-phase metallicities: The CALIFA connection

NASA Astrophysics Data System (ADS)

Marino, R. A.; Gil de Paz, A.; Sánchez, S. F.; Sánchez-Blázquez, P.; Cardiel, N.; Castillo-Morales, A.; Pascual, S.; Vílchez, J.; Kehrig, C.; Mollá, M.; Mendez-Abreu, J.; Catalán-Torrecilla, C.; Florido, E.; Perez, I.; Ruiz-Lara, T.; Ellis, S.; López-Sánchez, A. R.; González Delgado, R. M.; de Lorenzo-Cáceres, A.; García-Benito, R.; Galbany, L.; Zibetti, S.; Cortijo, C.; Kalinova, V.; Mast, D.; Iglesias-Páramo, J.; Papaderos, P.; Walcher, C. J.; Bland-Hawthorn, J.

2016-01-01

We study, for the first time in a statistically significant and well-defined sample, the relation between the outer-disk ionized-gas metallicity gradients and the presence of breaks in the surface brightness profiles of disk galaxies. Sloan Digital Sky Survey (SDSS) g'- and r'-band surface brightness, (g' - r') color, and ionized-gasoxygen abundance profiles for 324 galaxies within the Calar Alto Legacy Integral Field Area (CALIFA) survey are used for this purpose. We perform a detailed light-profile classification, finding that 84% of our disks show down- or up-bending profiles (Type II and Type III, respectively), while the remaining 16% are well fitted by one single exponential (Type I). The analysis of the color gradients at both sides of this break shows a U-shaped profile for most Type II galaxies with an average minimum (g' - r') color of ~0.5 mag and an ionized-gas metallicity flattening associated with it only in the case of low-mass galaxies. Comparatively, more massive systems show a rather uniform negative metallicity gradient. The correlation between metallicity flattening and stellar mass for these systems results in p-values as low as 0.01. Independent of the mechanism having shaped the outer light profiles of these galaxies, stellar migration or a previous episode of star formation in a shrinking star-forming disk, it is clear that the imprint in their ionized-gas metallicity was different for low- and high-mass Type II galaxies. In the case of Type III disks, a positive correlation between the change in color and abundance gradient is found (the null hypothesis is ruled out with a p-value of 0.02), with the outer disks of Type III galaxies with masses ≤1010 M⊙ showing a weak color reddening or even a bluing. This is interpreted as primarily due to a mass downsizing effect on the population of Type III galaxies that recently experienced an enhanced inside-out growth.

The role of stellar radial motions in shaping galaxy surface brightness profiles

NASA Astrophysics Data System (ADS)

Ruiz-Lara, T.; Few, C. G.; Florido, E.; Gibson, B. K.; Pérez, I.; Sánchez-Blázquez, P.

2017-12-01

Aims: The physics driving features such as breaks observed in galaxy surface brightness (SB) profiles remains contentious. Here, we assess the importance of stellar radial motions in shaping their characteristics. Methods: We use the simulated Milky Way-mass cosmological discs from the Ramses Disc Environment Study (RaDES) to characterise the radial redistribution of stars in galaxies displaying type-I (pure exponentials), II (downbending), and III (upbending) SB profiles. We compare radial profiles of the mass fractions and the velocity dispersions of different sub-populations of stars according to their birth and current location. Results: Radial redistribution of stars is important in all galaxies regardless of their light profiles. Type-II breaks seem to be a consequence of the combined effects of outward-moving and accreted stars. The former produce shallower inner profiles (lack of stars in the inner disc) and accumulate material around the break radius and beyond, strengthening the break; the latter can weaken or even convert the break into a pure exponential. Further accretion from satellites can concentrate material in the outermost parts, leading to type-III breaks that can coexist with type-II breaks, but situated further out. Type-III galaxies would be the result of an important radial redistribution of material throughout the entire disc, as well as a concentration of accreted material in the outskirts. In addition, type-III galaxies display the most efficient radial redistribution and the largest number of accreted stars, followed by type-I and II systems, suggesting that type-I galaxies may be an intermediate case between types II and III. In general, the velocity dispersion profiles of all galaxies tend to flatten or even increase around the locations where the breaks are found. The age and metallicity profiles are also affected, exhibiting different inner gradients depending on their SB profile, being steeper in the case of type-II systems (as found observationally). The steep type-II profiles might be inherent to their formation rather than acquired via radial redistribution.

Stellar Vampires Unmasked

NASA Astrophysics Data System (ADS)

2006-10-01

Astronomers have found possible proofs of stellar vampirism in the globular cluster 47 Tucanae. Using ESO's Very Large Telescope, they found that some hot, bright, and apparently young stars in the cluster present less carbon and oxygen than the majority of their sisters. This indicates that these few stars likely formed by taking their material from another star. "This is the first detection of a chemical signature clearly pointing to a specific scenario to form so-called 'Blue straggler stars' in a globular cluster", said Francesco Ferraro, from the Astronomy Department of Bologna University (Italy) and lead-author of the paper presenting the results. Blue stragglers are unexpectedly young-looking stars found in stellar aggregates, such as globular clusters, which are known to be made up of old stars. These enigmatic objects are thought to be created in either direct stellar collisions or through the evolution and coalescence of a binary star system in which one star 'sucks' material off the other, rejuvenating itself. As such, they provide interesting constraints on both binary stellar evolution and star cluster dynamics. To date, the unambiguous signatures of either stellar traffic accidents or stellar vampirism have not been observed, and the formation mechanisms of Blue stragglers are still a mystery. The astronomers used ESO's Very Large Telescope to measure the abundance of chemical elements at the surface of 43 Blue straggler stars in the globular cluster 47 Tucanae [1]. They discovered that six of these Blue straggler stars contain less carbon and oxygen than the majority of these peculiar objects. Such an anomaly indicates that the material at the surface of the blue stragglers comes from the deep interiors of a parent star [2]. Such deep material can reach the surface of the blue straggler only during the mass transfer process occurring between two stars in a binary system. Numerical simulations indeed show that the coalescence of stars should not result in anomalous abundances. ESO PR Photo 37/06 ESO PR Photo 37/06 Abundances in Blue Straggler Stars In the core of a globular cluster, stars are packed extremely close to each other: more than 4000 stars are found in the innermost light-year-sized cube of 47 Tucanae. Thus, stellar collisions are thought to be very frequent and the collision channel for the formation of blue stragglers should be extremely efficient. The chemical signature detected by these observations demonstrates that also the binary mass-transfer scenario is fully active even in a high-density cluster like 47 Tuc. "Our discovery is therefore a fundamental step toward the solution of the long-standing mystery of blue straggler formation in globular clusters," said Ferraro. Measurements of so many faint stars are only possible since the advent of 8-m class telescopes equipped with multiplexing capability spectrographs. In this case, the astronomers used the FLAMES/Giraffe instrument that allows the simultaneous observation of up to 130 targets at a time, making it ideally suited for surveying individual stars in closely populated fields.

Uncovering the Detailed Structure and Dynamics of Andromeda's Complex Stellar Disk

NASA Astrophysics Data System (ADS)

Dorman, Claire; Guhathakurta, Puragra; Seth, Anil; Dalcanton, Julianne; Widrow, Larry; Splash Team, Phat Team

2015-01-01

Lambda cold dark matter (LCDM) cosmology predicts that the disks of Milky Way-mass galaxies should have undergone at least one merger with a large (mass ratio 1:10) satellite in the last several Gyr. However, the stellar disk in the solar neighborhood of the Milky Way is too thin and dynamically cold to have experienced such an impact. The dynamics of the nearby Andromeda galaxy can serve as a second data point, and help us understand whether the Milky Way may simply have had an unusually quiescent merger history, or whether LCDM theory needs to be revisited. Over the last few years, we have carried out a detailed study of the resolved stellar populations in the disk of the Andromeda galaxy using data from two surveys: six-filter Hubble Space Telescope photometry from the recently-completed Panchromatic Hubble Andromeda Treasury (PHAT) survey, and radial velocities derived from Keck/DEIMOS optical spectra obtained as part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) program. These detailed, multidimensional data sets allow us to decouple the structural subcomponents and characterize them individually. We find that an old, dynamically hot (velocity dispersion ~150 km/s) RGB population extends out to 20 kpc (the edge of the visible disk) but has a disk-like surface brightness profile and luminosity function. This population may have originated in the disk but been kicked out subsequently in impacts with satellite galaxies. We also study the kinematics of the disk as a function of the age of stellar tracers, and find a direct correlation between age and velocity dispersion, indicating that Andromeda has undergone a continuous heating or disk settling process throughout its lifetime. Overall, both the velocity dispersion of Andromeda's disk and the slope of the velocity dispersion vs. stellar age curve are several times those of the Milky Way's, suggesting a more active merger history more in line with LCDM cosmological predictions.This research was funded by grants from the NSF and NASA/STScI.

Structure and dynamics of Andromeda's stellar disk

NASA Astrophysics Data System (ADS)

Dorman, Claire Elise

2015-10-01

Lambda cold dark matter (LambdaCDM) cosmology predicts that the disks of Milky Way-mass galaxies should have undergone at least one merger with a large (mass ratio 1:10) satellite in the last several Gyr. However, the stellar disk in the solar neighborhood of the Milky Way is too thin and dynamically cold to have experienced such an impact. The dynamics of the nearby Andromeda galaxy can serve as a second data point, and help us understand whether the Milky Way may simply have had an unusually quiescent merger history, or whether LambdaCDM theory needs to be revisited. Over the last few years, we have carried out a detailed study of the resolved stellar populations in the disk of the Andromeda galaxy using data from two surveys: six-filter Hubble Space Telescope photometry from the recently-completed Panchromatic Hubble Andromeda Treasury (PHAT) survey, and radial velocities derived from Keck/DEIMOS optical spectra obtained as part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar 0Halo (SPLASH) program. These detailed, multidimensional data sets allow us to decouple the structural subcomponents and characterize them individually. We find that an old, dynamically hot (velocity dispersion 150 km/s) RGB population extends out to 20 kpc (the edge of the visible disk) but has a disk-like surface brightness profile and luminosity function. This population may have originated in the disk but been kicked out subsequently in impacts with satellite galaxies. We also study the kinematics of the disk as a function of the age of stellar tracers, and find a direct correlation between age and velocity dispersion, indicating that Andromeda has undergone a continuous heating or disk settling process throughout its lifetime. Overall, both the velocity dispersion of Andromeda's disk and the slope of the velocity dispersion vs. stellar age curve are several times those of the Milky Way's, suggesting a more active merger history more in line with LambdaCDM cosmological predictions.

Optical Multi-Channel Intensity Interferometry - Or: How to Resolve O-Stars in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Trippe, Sascha; Kim, Jae-Young; Lee, Bangwon; Choi, Changsu; Oh, Junghwan; Lee, Taeseok; Yoon, Sung-Chul; Im, Myungshin; Park, Yong-Sun

2014-12-01

Intensity interferometry, based on the Hanbury Brown--Twiss effect, is a simple and inexpensive method for optical interferometry at microarcsecond angular resolutions; its use in astronomy was abandoned in the 1970s because of low sensitivity. Motivated by recent technical developments, we argue that the sensitivity of large modern intensity interferometers can be improved by factors up to approximately 25,000, corresponding to 11 photometric magnitudes, compared to the pioneering Narrabri Stellar Interferometer. This is made possible by (i) using avalanche photodiodes (APD) as light detectors, (ii) distributing the light received from the source over multiple independent spectral channels, and (iii) use of arrays composed of multiple large light collectors. Our approach permits the construction of large (with baselines ranging from few kilometers to intercontinental distances) optical interferometers at the cost of (very) long-baseline radio interferometers. Realistic intensity interferometer designs are able to achieve limiting R-band magnitudes as good as m_R≈14, sufficient for spatially resolved observations of main-sequence O-type stars in the Magellanic Clouds. Multi-channel intensity interferometers can address a wide variety of science cases: (i) linear radii, effective temperatures, and luminosities of stars, via direct measurements of stellar angular sizes; (ii) mass--radius relationships of compact stellar remnants, via direct measurements of the angular sizes of white dwarfs; (iii) stellar rotation, via observations of rotation flattening and surface gravity darkening; (iv) stellar convection and the interaction of stellar photospheres and magnetic fields, via observations of dark and bright starspots; (v) the structure and evolution of multiple stars, via mapping of the companion stars and of accretion flows in interacting binaries; (vi) direct measurements of interstellar distances, derived from angular diameters of stars or via the interferometric Baade--Wesselink method; (vii) the physics of gas accretion onto supermassive black holes, via resolved observations of the central engines of luminous active galactic nuclei; and (viii) calibration of amplitude interferometers by providing a sample of calibrator stars.

Hubble Space Telescope and Spitzer Imaging of Red and Blue Galaxies at z ~ 2.5: A Correlation between Size and Star Formation Activity from Compact Quiescent Galaxies to Extended Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Toft, S.; van Dokkum, P.; Franx, M.; Labbe, I.; Förster Schreiber, N. M.; Wuyts, S.; Webb, T.; Rudnick, G.; Zirm, A.; Kriek, M.; van der Werf, P.; Blakeslee, J. P.; Illingworth, G.; Rix, H.-W.; Papovich, C.; Moorwood, A.

2007-12-01

We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2

Structure of merger remnants. I - Bulgeless progenitors

NASA Technical Reports Server (NTRS)

Hernquist, Lars

1992-01-01

The study examines mergers of identical galaxies consisting of self-gravitating disks and halos in the context of the suggestion that such events may form elliptical galaxies. It is shown that the luminous remnants of such mergers do indeed share many common properties with observed ellipticals. Specifically, the end states of the simulations considered rotate slowly in regions of relatively high surface density, having typical values of less than about 0.2 there. Morphologically, the remnants display a variety of structures, including shells and loops comprising loosely bound material and boxy and disky isophotes. The luminous matter is well-fitted by ellipsoidal generalizations of Hernquists's (1990, 1992) model for elliptical galaxies, implying that the surface brightness profiles are essentially de Vaucouleurs-like over a large radial interval. It is proposed that mergers of pure stellar disks do not represent an attractive mechanism for the production of massive elliptical galaxies.

On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

NASA Astrophysics Data System (ADS)

Windhorst, Rogier A.; Timmes, F. X.; Wyithe, J. Stuart B.; Alpaslan, Mehmet; Andrews, Stephen K.; Coe, Daniel; Diego, Jose M.; Dijkstra, Mark; Driver, Simon P.; Kelly, Patrick L.; Kim, Duho

2018-02-01

We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z ≃ 7–17. Theoretical predictions and recent near-infrared power spectra provide tighter constraints on their sky signal. We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z≳ 7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be μ ≃ {10}4{--}{10}5, with rise times of hours and decline times of ≲ 1 year for cluster transverse velocities of {v}T≲ 1000 km s‑1. Microlensing by intracluster-medium objects can modify transit magnifications but lengthen visibility times. Depending on BH masses, accretion-disk radii, and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require monitoring 3–30 lensing clusters to {AB}≲ 29 mag over a decade.

Discovery of starspots on Vega. First spectroscopic detection of surface structures on a normal A-type star

NASA Astrophysics Data System (ADS)

Böhm, T.; Holschneider, M.; Lignières, F.; Petit, P.; Rainer, M.; Paletou, F.; Wade, G.; Alecian, E.; Carfantan, H.; Blazère, A.; Mirouh, G. M.

2015-05-01

Context. The theoretically studied impact of rapid rotation on stellar evolution needs to be compared with these results of high-resolution spectroscopy-velocimetry observations. Early-type stars present a perfect laboratory for these studies. The prototype A0 star Vega has been extensively monitored in recent years in spectropolarimetry. A weak surface magnetic field was detected, implying that there might be a (still undetected) structured surface. First indications of the presence of small amplitude stellar radial velocity variations have been reported recently, but the confirmation and in-depth study with the highly stabilized spectrograph SOPHIE/OHP was required. Aims: The goal of this article is to present a thorough analysis of the line profile variations and associated estimators in the early-type standard star Vega (A0) in order to reveal potential activity tracers, exoplanet companions, and stellar oscillations. Methods: Vega was monitored in quasi-continuous high-resolution echelle spectroscopy with the highly stabilized velocimeter SOPHIE/OHP. A total of 2588 high signal-to-noise spectra was obtained during 34.7 h on five nights (2 to 6 of August 2012) in high-resolution mode at R = 75 000 and covering the visible domain from 3895-6270 Å. For each reduced spectrum, least square deconvolved equivalent photospheric profiles were calculated with a Teff = 9500 and log g = 4.0 spectral line mask. Several methods were applied to study the dynamic behaviour of the profile variations (evolution of radial velocity, bisectors, vspan, 2D profiles, amongst others). Results: We present the discovery of a spotted stellar surface on an A-type standard star (Vega) with very faint spot amplitudes ΔF/Fc ~ 5 × 10-4. A rotational modulation of spectral lines with a period of rotation P = 0.68 d has clearly been exhibited, unambiguously confirming the results of previous spectropolarimetric studies. Most of these brightness inhomogeneities seem to be located in lower equatorial latitudes. Either a very thin convective layer can be responsible for magnetic field generation at small amplitudes, or a new mechanism has to be invoked to explain the existence of activity tracing starspots. At this stage it is difficult to disentangle a rotational from a stellar pulsational origin for the existing higher frequency periodic variations. Conclusions: This first strong evidence that standard A-type stars can show surface structures opens a new field of research and ask about a potential link with the recently discovered weak magnetic field discoveries in this category of stars. Based on observations obtained with the SOPHIE spectrograph at the 2 m OHP telescope operated by the Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique of France (CNRS).

Dust spectral energy distributions of nearby galaxies: an insight from the Herschel Reference Survey

NASA Astrophysics Data System (ADS)

Ciesla, L.; Boquien, M.; Boselli, A.; Buat, V.; Cortese, L.; Bendo, G. J.; Heinis, S.; Galametz, M.; Eales, S.; Smith, M. W. L.; Baes, M.; Bianchi, S.; De Looze, I.; di Serego Alighieri, S.; Galliano, F.; Hughes, T. M.; Madden, S. C.; Pierini, D.; Rémy-Ruyer, A.; Spinoglio, L.; Vaccari, M.; Viaene, S.; Vlahakis, C.

2014-05-01

Although it accounts only for a small fraction of the baryonic mass, dust has a profound impact on the physical processes at play in galaxies. Thus, to understand the evolution of galaxies, it is essential not only to characterize dust properties per se, but also in relation to global galaxy properties. To do so, we derive the dust properties of galaxies in a volume limited, K-band selected sample, the Herschel Reference Survey (HRS). We gather infrared photometric data from 8 μm to 500 μm from Spitzer, WISE, IRAS, and Herschel for all of the HRS galaxies. Draine & Li (2007, ApJ, 663, 866) models are fit to the data from which the stellar contribution has been carefully removed. We find that our photometric coverage is sufficient to constrain all of the parameters of the Draine & Li models and that a strong constraint on the 20-60 μm range is mandatory to estimate the relative contribution of the photo-dissociation regions to the infrared spectral energy distribution (SED). The SED models tend to systematically underestimate the observed 500 μm flux densities, especially for low-mass systems. We provide the output parameters for all of the galaxies, i.e., the minimum intensity of the interstellar radiation field, the fraction of polycyclic aromatic hydrocarbon (PAH), the relative contribution of PDR and evolved stellar population to the dust heating, the dust mass, and the infrared luminosity. For a subsample of gas-rich galaxies, we analyze the relations between these parameters and the main integrated properties of galaxies, such as stellar mass, star formation rate, infraredluminosity, metallicity, Hα and H-band surface brightness, and the far-ultraviolet attenuation. A good correlation between the fraction of PAH and the metallicity is found, implying a weakening of the PAH emission in galaxies with low metallicities and, thus, low stellar masses. The intensity of the diffuse interstellar radiation field and the H-band and Hα surface brightnesses are correlated, suggesting that the diffuse dust component is heated by both the young stars in star-forming regions and the diffuse evolved population. We use these results to provide a new set of infrared templates calibrated with Herschel observations on nearby galaxies and a mean SED template to provide the z = 0 reference for cosmological studies. For the same purpose, we place our sample on the SFR - M∗ diagram. The templates are compared to the most popular infrared SED libraries, enlightening a large discrepancy between all of them in the 20-100 μm range. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Table 4 and appendices are available in electronic form at http://www.aanda.org

Spatially-Resolved Observations of Giant Stars with SPHERE

NASA Astrophysics Data System (ADS)

Khouri, Theo

2018-04-01

SPHERE on the VLT is an extreme adaptive optics instrument that produces images with unprecedented angular resolution at visible and near-infrared wavelengths. Its primary goal is imaging, low-resolution spectroscopic, and polarimetric characterization of extra-solar planetary systems. Nonetheless, the high spatial resolution and the instrument design optimized for observations in a narrow field of view around bright targets make SPHERE the perfect instrument for obtaining spatially-resolved images of close-by giant, evolved stars. This is particularly true at the shortest wavelengths available with SPHERE, where the angular resolution is best (> 20 mas) and these stars appear larger (< 70 mas). In this talk, I will review how SPHERE has been used to study the surfaces and extended atmospheres of evolved stars and how these observations advance our understanding of the stellar pulsations and convective motions that shape these stars. Moreover, I will present recent results from a monitoring campaign of the star R Doradus using SPHERE with observations taken at twelve epochs over eight months that reveal features on the stellar disc varying on timescales of a few weeks. Finally, I will present quasi-simultaneous observations with SPHERE and ALMA that spatially resolve the stellar discs of two asymptotic giant branch stars, Mira and R Doradus, and discuss what such multi-wavelength observation campaigns can teach us about the processes that shape evolved stars.

Testing Dissipative Magnetosphere Model Light Curves and Spectra with Fermi Pulsars

NASA Technical Reports Server (NTRS)

Brambilla, Gabriele; Kalapotharakos, Constantinos; Harding, Alice K.; Kazanas, Demosthenes

2015-01-01

We explore the emission properties of a dissipative pulsar magnetosphere model introduced by Kalapotharakos et al. comparing its high-energy light curves and spectra, due to curvature radiation, with data collected by the Fermi LAT. The magnetosphere structure is assumed to be near the force-free solution. The accelerating electric field, inside the light cylinder (LC), is assumed to be negligible, while outside the LC it rescales with a finite conductivity (sigma). In our approach we calculate the corresponding high-energy emission by integrating the trajectories of test particles that originate from the stellar surface, taking into account both the accelerating electric field components and the radiation reaction forces. First, we explore the parameter space assuming different value sets for the stellar magnetic field, stellar period, and conductivity. We show that the general properties of the model are in a good agreement with observed emission characteristics of young gamma-ray pulsars, including features of the phase-resolved spectra. Second, we find model parameters that fit each pulsar belonging to a group of eight bright pulsars that have a published phase-resolved spectrum. The sigma values that best describe each of the pulsars in this group show an increase with the spin-down rate (E? ) and a decrease with the pulsar age, expected if pair cascades are providing the magnetospheric conductivity. Finally, we explore the limits of our analysis and suggest future directions for improving such models.

Optical observations of NGC 2915: A nearby blue compact dwarf galaxy

NASA Technical Reports Server (NTRS)

Meurer, G. R.; Mackie, G.; Carignan, C.

1994-01-01

This paper presents B and R band Charge Coupled Device (CCD) images and medium resolution spectroscopy of NGC 2915, a relatively isolated BCD (blue compact dwarf) galaxy at a distance of approximately 5 Mpc. NGC 2915 contains two stellar populations: a high surface brightness blue core population and a red diffuse population. The core population contains all of the H II, and numerous embedded objects. It is the locus of current high mass star formation. The brightest embedded objects are likely to be young ionizing clusters, while many of the fainter objects are likely to be individual supergiant stars with masses up to approximately 25 solar mass, or blends of a few such stars. Curious aligned structures on the SE side of the galaxy are seen and their nature discussed. The spectrum of the core is dominated by bright narrow emission lines like that of a high excitation and low metallicity (less than half solar) H II region. The continuum is flat, with Balmer and Ca II features seen in absorption. The velocity of the Ca II features suggest contamination by galactic interstellar absorption. There is a significant velocity gradient in the spectra, probably indicative of rotation. Outside of its core, NGC 2915 resembles a dE (dwarf elliptical) galaxy, in that it has an exponential surface brightness profile, is red ((B-R)(sub 0) = 1.65), and has a low extrapolated central surface brightness (B(0)(sub c) = 22.44). NGC 2915's properties are compared with other BCDs, concentrating on two morphologically similar BCDs that are near enough to resolve into stars: NGC 1705 and NGC 5253. It is noted that the presence of winds in BCDs invalidates closed box chemical evolution models and the remaining constraints on star formation duration are relatively weak. Some BCDs, including NGC 2915, may be able to maintain their present star formation rate for Gyr time scales. This suggests that the overall evolution of these BCDs may be much slower than the approximately 10 Myr burst time scales commonly quoted. However, shortly after the formation of a massive (10(exp 6) solar mass) cluster a BCD will have all the properties of strong starburst galaxy).

Projected alignment of non-sphericities of stellar, gas, and dark matter distributions in galaxy clusters: analysis of the Horizon-AGN simulation

NASA Astrophysics Data System (ADS)

Okabe, Taizo; Nishimichi, Takahiro; Oguri, Masamune; Peirani, Sébastien; Kitayama, Tetsu; Sasaki, Shin; Suto, Yasushi

2018-04-01

While various observations measured ellipticities of galaxy clusters and alignments between orientations of the brightest cluster galaxies and their host clusters, there are only a handful of numerical simulations that implement realistic baryon physics to allow direct comparisons with those observations. Here we investigate ellipticities of galaxy clusters and alignments between various components of them and the central galaxies in the state-of-the-art cosmological hydrodynamical simulation Horizon-AGN, which contains dark matter, stellar, and gas components in a large simulation box of (100h-1 Mpc)3 with high spatial resolution (˜1 kpc). We estimate ellipticities of total matter, dark matter, stellar, gas surface mass density distributions, X-ray surface brightness, and the Compton y-parameter of the Sunyaev-Zel'dovich effect, as well as alignments between these components and the central galaxies for 120 projected images of galaxy clusters with masses M200 > 5 × 1013M⊙. Our results indicate that the distributions of these components are well aligned with the major-axes of the central galaxies, with the root mean square value of differences of their position angles of ˜20°, which vary little from inner to the outer regions. We also estimate alignments of these various components with total matter distributions, and find tighter alignments than those for central galaxies with the root mean square value of ˜15°. We compare our results with previous observations of ellipticities and position angle alignments and find reasonable agreements. The comprehensive analysis presented in this paper provides useful prior information for analyzing stacked lensing signals as well as designing future observations to study ellipticities and alignments of galaxy clusters.

Projected alignment of non-sphericities of stellar, gas, and dark matter distributions in galaxy clusters: analysis of the Horizon-AGN simulation

NASA Astrophysics Data System (ADS)

Okabe, Taizo; Nishimichi, Takahiro; Oguri, Masamune; Peirani, Sébastien; Kitayama, Tetsu; Sasaki, Shin; Suto, Yasushi

2018-07-01

While various observations measured ellipticities of galaxy clusters and alignments between orientations of the brightest cluster galaxies and their host clusters, there are only a handful of numerical simulations that implement realistic baryon physics to allow direct comparisons with those observations. Here, we investigate ellipticities of galaxy clusters and alignments between various components of them and the central galaxies in the state-of-the-art cosmological hydrodynamical simulation Horizon-AGN, which contains dark matter, stellar, and gas components in a large simulation box of (100h-1 Mpc)3 with high spatial resolution (˜1 kpc). We estimate ellipticities of total matter, dark matter, stellar, gas surface mass density distributions, X-ray surface brightness, and the Compton y-parameter of the Sunyaev-Zel'dovich effect, as well as alignments between these components and the central galaxies for 120 projected images of galaxy clusters with masses M200 > 5 × 1013 M⊙. Our results indicate that the distributions of these components are well aligned with the major axes of the central galaxies, with the root-mean-square value of differences of their position angles of ˜20°, which vary little from inner to the outer regions. We also estimate alignments of these various components with total matter distributions, and find tighter alignments than those for central galaxies with the root-mean-square value of ˜15°. We compare our results with previous observations of ellipticities and position angle alignments and find reasonable agreements. The comprehensive analysis presented in this paper provides useful prior information for analysing stacked lensing signals as well as designing future observations to study ellipticities and alignments of galaxy clusters.

Exoplanet Transits of Stellar Active Regions

NASA Astrophysics Data System (ADS)

Giampapa, Mark S.; Andretta, Vincenzo; Covino, Elvira; Reiners, Ansgar; Esposito, Massimiliano

2018-01-01

We report preliminary results of a program to obtain high spectral- and temporal-resolution observations of the neutral helium triplet line at 1083.0 nm in transiting exoplanet systems. The principal objective of our program is to gain insight on the properties of active regions, analogous to solar plages, on late-type dwarfs by essentially using exoplanet transits as high spatial resolution probes of the stellar surface within the transit chord. The 1083 nm helium line is a particularly appropriate diagnostic of magnetized areas since it is weak in the quiet photosphere of solar-type stars but appears strongly in absorption in active regions. Therefore, during an exoplanet transit over the stellar surface, variations in its absorption equivalent width can arise that are functions of the intrinsic strength of the feature in the active region and the known relative size of the exoplanet. We utilized the Galileo Telescope and the GIANO-B near-IR echelle spectrograph to obtain 1083 nm spectra during transits in bright, well-known systems that include HD 189733, HD 209458, and HD 147506 (HAT-P-2). We also obtained simultaneous auxiliary data on the same telescope with the HARPS-N UV-Visible echelle spectrograph. We will present preliminary results from our analysis of the observed variability of the strength of the He I 1083 nm line during transits.Acknowledgements: Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The NSO is operated by AURA under a cooperative agreement with the NSF.

Tracing the assembly history of NGC 1395 through its Globular Cluster System

NASA Astrophysics Data System (ADS)

Escudero, Carlos G.; Faifer, Favio R.; Smith Castelli, Analía V.; Forte, Juan C.; Sesto, Leandro A.; González, Nélida M.; Scalia, María C.

2018-03-01

We used deep Gemini-South/GMOS g΄r΄i΄z΄ images to study the globular cluster (GC) system of the massive elliptical galaxy NGC 1395, located in the Eridanus supergroup. The photometric analysis of the GC candidates reveals a clear colour bimodality distribution, indicating the presence of `blue' and `red' GC subpopulations. While a negative radial colour gradient is detected in the projected spatial distribution of the red GCs, the blue GCs display a shallow colour gradient. The blue GCs also display a remarkable shallow and extended surface density profile, suggesting a significant accretion of low-mass satellites in the outer halo of the galaxy. In addition, the slope of the projected spatial distribution of the blue GCs in the outer regions of the galaxy, is similar to that of the X-ray halo emission. Integrating up to 165 kpc the profile of the projected spatial distribution of the GCs, we estimated a total GC population and specific frequency of 6000 ± 1100 and SN = 7.4 ± 1.4, respectively. Regarding NGC 1395 itself, the analysis of the deep Gemini/GMOS images shows a low surface brightness umbrella-like structure indicating, at least, one recent merger event. Through relations recently published in the literature, we obtained global parameters, such as Mstellar = 9.32 × 1011 M⊙ and Mh = 6.46 × 1013 M⊙. Using public spectroscopic data, we derive stellar population parameters of the central region of the galaxy by the full spectral fitting technique. We have found that this region seems to be dominated for an old stellar population, in contrast to findings of young stellar populations from the literature.

The Class of Jsolated Stars and Luminous Planetary Nebulae in old stellar populations

NASA Astrophysics Data System (ADS)

Sabach, Efrat; Soker, Noam

2018-06-01

We suggest that stars whose angular momentum (J) does not increase by a companion, star or planet, along their post-main sequence evolution have much lower mass loss rates along their giant branches. Their classification to a separate group can bring insight on their late evolution stages. We here term these Jsolated stars. We argue that the mass loss rate of Jsolated stars is poorly determined because the mass loss rate expressions on the giant branches are empirically based on samples containing stars that experience strong binary interaction, with stellar or sub-stellar companions, e.g., planetary nebula (PN) progenitors. We use our earlier claim for a low mass loss rate of asymptotic giant branch (AGB) stars that are not spun-up by a stellar or substellar companion to show that we can account for the enigmatic finding that the brightest PNe in old stellar populations reach the same luminosity as the brightest PNe in young populations. It is quite likely that the best solution to the existence of bright PNe in old stellar populations is the combination of higher AGB luminosities, as obtained in some new stellar models, and the lower mass loss rates invoked here.

Blue Stragglers in Clusters and Integrated Spectral Properties of Stellar Populations

NASA Astrophysics Data System (ADS)

Xin, Yu; Deng, Licai

Blue straggler stars are the most prominent bright objects in the colour-magnitude diagram of a star cluster that challenges the theory of stellar evolution. Star clusters are the closest counterparts of the theoretical concept of simple stellar populations (SSPs) in the Universe. SSPs are widely used as the basic building blocks to interpret stellar contents in galaxies. The concept of an SSP is a group of coeval stars which follows a given distribution in mass, and has the same chemical property and age. In practice, SSPs are more conveniently made by the latest stellar evolutionary models of single stars. In reality, however, stars can be more complicated than just single either at birth time or during the course of evolution in a typical environment. Observations of star clusters show that there are always exotic objects which do not follow the predictions of standard theory of stellar evolution. Blue straggler stars (BSSs), as discussed intensively in this book both observationally and theoretically, are very important in our context when considering the integrated spectral properties of a cluster, or a simple stellar population. In this chapter, we are going to describe how important the contribution of BSSs is to the total light of a cluster.

Problems and Projects from Astronomy.

ERIC Educational Resources Information Center

Mills, H. R.

1991-01-01

Describes activities to stimulate school astronomy programs. Topics include: counting stars; the Earth's centripetal force; defining astronomical time; three types of sundials; perceptions of star brightness; sunspots and solar radiation; stellar spectroscopy; number-crunching and the molecular structure of the atmosphere; the Earth-Moon common…

Optical long baseline intensity interferometry: prospects for stellar physics

NASA Astrophysics Data System (ADS)

Rivet, Jean-Pierre; Vakili, Farrokh; Lai, Olivier; Vernet, David; Fouché, Mathilde; Guerin, William; Labeyrie, Guillaume; Kaiser, Robin

2018-06-01

More than sixty years after the first intensity correlation experiments by Hanbury Brown and Twiss, there is renewed interest for intensity interferometry techniques for high angular resolution studies of celestial sources. We report on a successful attempt to measure the bunching peak in the intensity correlation function for bright stellar sources with 1 meter telescopes (I2C project). We propose further improvements of our preliminary experiments of spatial interferometry between two 1 m telescopes, and discuss the possibility to export our method to existing large arrays of telescopes.

Ultraviolet photometry from the Orbiting Astronomical Observatory. XXXII - An atlas of ultraviolet stellar spectra

NASA Technical Reports Server (NTRS)

Code, A. D.; Meade, M. R.

1979-01-01

Ultraviolet stellar fluxes are presented in graphs and tables for 164 bright stars in the spectral region from 1200 to 3600 A. The spectra represent a subset of OAO 2 spectrometer data on file at the National Space Science Data Center. The monochromatic flux is given in units of erg per (sq cm-s-A) with a spectral resolution of about 22 A in the region from 3600 to 1850 A and of approximately 12 A in the region from 1850 to 1160 A.

Spectrally resolved interferometric observations of α Cephei and physical modeling of fast rotating stars

NASA Astrophysics Data System (ADS)

Delaa, O.; Zorec, J.; Domiciano de Souza, A.; Mourard, D.; Perraut, K.; Stee, Ph.; Frémat, Y.; Monnier, J.; Kraus, S.; Che, X.; Bério, Ph.; Bonneau, D.; Clausse, J. M.; Challouf, M.; Ligi, R.; Meilland, A.; Nardetto, N.; Spang, A.; McAlister, H.; ten Brummelaar, T.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Goldfinger, P. J.

2013-07-01

Context. When a given observational quantity depends on several stellar physical parameters, it is generally very difficult to obtain observational constraints for each of them individually. Therefore, we studied under which conditions constraints for some individual parameters can be achieved for fast rotators, knowing that their geometry is modified by the rapid rotation which causes a non-uniform surface brightness distribution. Aims: We aim to study the sensitivity of interferometric observables on the position angle of the rotation axis (PA) of a rapidly rotating star, and whether other physical parameters can influence the determination of PA, and also the influence of the surface differential rotation on the determination of the β exponent in the gravity darkening law that enters the interpretation of interferometric observations, using α Cep as a test star. Methods: We used differential phases obtained from observations carried out in the Hα absorption line of α Cep with the VEGA/CHARA interferometer at high spectral resolution, R = 30 000 to study the kinematics in the atmosphere of the star. Results: We studied the influence of the gravity darkening effect (GDE) on the determination of the PA of the rotation axis of α Cep and determined its value, PA = -157-10°+17°. We conclude that the GDE has a weak influence on the dispersed phases. We showed that the surface differential rotation can have a rather strong influence on the determination of the gravity darkening exponent. A new method of determining the inclination angle of the stellar rotational axis is suggested. We conclude that differential phases obtained with spectro-interferometry carried out on the Hα line can in principle lead to an estimate of the stellar inclination angle i. However, to determine both i and the differential rotation parameter α, lines free from the Stark effect and that have collision-dominated source functions are to be preferred.

REFLECTED LIGHT CURVES, SPHERICAL AND BOND ALBEDOS OF JUPITER- AND SATURN-LIKE EXOPLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dyudina, Ulyana; Kopparla, Pushkar; Ingersoll, Andrew P.

Reflected light curves observed for exoplanets indicate that a few of them host bright clouds. We estimate how the light curve and total stellar heating of a planet depends on forward and backward scattering in the clouds based on Pioneer and Cassini spacecraft images of Jupiter and Saturn. We fit analytical functions to the local reflected brightnesses of Jupiter and Saturn depending on the planet’s phase. These observations cover broadbands at 0.59–0.72 and 0.39–0.5 μ m, and narrowbands at 0.938 (atmospheric window), 0.889 (CH4 absorption band), and 0.24–0.28 μ m. We simulate the images of the planets with a ray-tracingmore » model, and disk-integrate them to produce the full-orbit light curves. For Jupiter, we also fit the modeled light curves to the observed full-disk brightness. We derive spherical albedos for Jupiter and Saturn, and for planets with Lambertian and Rayleigh-scattering atmospheres. Jupiter-like atmospheres can produce light curves that are a factor of two fainter at half-phase than the Lambertian planet, given the same geometric albedo at transit. The spherical albedo is typically lower than for a Lambertian planet by up to a factor of ∼1.5. The Lambertian assumption will underestimate the absorption of the stellar light and the equilibrium temperature of the planetary atmosphere. We also compare our light curves with the light curves of solid bodies: the moons Enceladus and Callisto. Their strong backscattering peak within a few degrees of opposition (secondary eclipse) can lead to an even stronger underestimate of the stellar heating.« less

WHEN SHOCK WAVES COLLIDE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartigan, P.; Liao, A. S.; Foster, J.

2016-06-01

Supersonic outflows from objects as varied as stellar jets, massive stars, and novae often exhibit multiple shock waves that overlap one another. When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet. Mach stems are important for interpreting emission-line images of shocked gas because a normal shock produces higher postshock temperatures, and therefore a higher-excitation spectrum than does an oblique shock. In this paper, we summarize the results of a series of numerical simulations and laboratory experiments designed tomore » quantify how Mach stems behave in supersonic plasmas that are the norm in astrophysical flows. The experiments test analytical predictions for critical angles where Mach stems should form, and quantify how Mach stems grow and decay as intersection angles between the incident shock and a surface change. While small Mach stems are destroyed by surface irregularities and subcritical angles, larger ones persist in these situations and can regrow if the intersection angle changes to become more favorable. The experimental and numerical results show that although Mach stems occur only over a limited range of intersection angles and size scales, within these ranges they are relatively robust, and hence are a viable explanation for variable bright knots observed in Hubble Space Telescope images at the intersections of some bow shocks in stellar jets.« less

When shock waves collide

DOE PAGES

Martinez, D.; Hartigan, P.; Frank, A.; ...

2016-06-01

Supersonic outflows from objects as varied as stellar jets, massive stars, and novae often exhibit multiple shock waves that overlap one another. When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet. Mach stems are important for interpreting emission-line images of shocked gas because a normal shock produces higher postshock temperatures, and therefore a higher-excitation spectrum than does an oblique shock. In this paper, we summarize the results of a series of numerical simulations and laboratory experiments designed tomore » quantify how Mach stems behave in supersonic plasmas that are the norm in astrophysical flows. The experiments test analytical predictions for critical angles where Mach stems should form, and quantify how Mach stems grow and decay as intersection angles between the incident shock and a surface change. While small Mach stems are destroyed by surface irregularities and subcritical angles, larger ones persist in these situations and can regrow if the intersection angle changes to become more favorable. Furthermore, the experimental and numerical results show that although Mach stems occur only over a limited range of intersection angles and size scales, within these ranges they are relatively robust, and hence are a viable explanation for variable bright knots observed in Hubble Space Telescope images at the intersections of some bow shocks in stellar jets.« less

Measuring stellar granulation during planet transits

NASA Astrophysics Data System (ADS)

Chiavassa, A.; Caldas, A.; Selsis, F.; Leconte, J.; Von Paris, P.; Bordé, P.; Magic, Z.; Collet, R.; Asplund, M.

2017-01-01

Context. Stellar activity and convection-related surface structures might cause bias in planet detection and characterization that use these transits. Surface convection simulations help to quantify the granulation signal. Aims: We used realistic three-dimensional (3D) radiative hydrodynamical (RHD) simulations from the Stagger grid and synthetic images computed with the radiative transfer code Optim3D to model the transits of three prototype planets: a hot Jupiter, a hot Neptune, and a terrestrial planet. Methods: We computed intensity maps from RHD simulations of the Sun and a K-dwarf star at different wavelength bands from optical to far-infrared that cover the range of several ground- and space-based telescopes which observe exoplanet transits. We modeled the transit using synthetic stellar-disk images obtained with a spherical-tile imaging method and emulated the temporal variation of the granulation intensity generating random images covering a granulation time-series of 13.3 h. We measured the contribution of the stellar granulation on the light curves during the planet transit. Results: We identified two types of granulation noise that act simultaneously during the planet transit: (I) the intrinsic change in the granulation pattern with timescale (e.g., 10 min for solar-type stars assumed in this work) is smaller than the usual planet transit ( hours as in our prototype cases); and (II) the fact that the transiting planet occults isolated regions of the photosphere that differ in local surface brightness as a result of convective-related surface structures. First, we showed that our modeling approach returns granulation timescale fluctuations that are comparable with what has been observed for the Sun. Then, our statistical approach shows that the granulation pattern of solar and K-dwarf-type stars have a non-negligible effect of the light curve depth during the transit, and, consequentially on the determination of the planet transit parameters such as the planet radius (up to 0.90% and 0.47% for terrestrial and gaseous planets, respectively). We also showed that larger (or smaller) orbital inclination angles with respect to values corresponding to transit at the stellar center display a shallower transit depth and longer ingress and egress times, but also granulation fluctuations that are correlated to the center-to-limb variation: they increase (or decrease) the value of the inclination, which amplifies the fluctuations. The granulation noise appears to be correlated among the different wavelength ranges either in the visible or in the infrared regions. Conclusions: The prospects for planet detection and characterization with transiting methods are excellent with access to large amounts of data for stars. The granulation has to be considered as an intrinsic uncertainty (as a result of stellar variability) on the precise measurements of exoplanet transits of planets. The full characterization of the granulation is essential for determining the degree of uncertainty on the planet parameters. In this context, the use of 3D RHD simulations is important to measure the convection-related fluctuations. This can be achieved by performing precise and continuous observations of stellar photometry and radial velocity, as we explained with RHD simulations, before, after, and during the transit periods.

Relativistic jet activity from the tidal disruption of a star by a massive black hole [Discovery of the onset of rapid accretion by a dormant massive black hole

DOE PAGES

Burrows, D. N.; Kennea, J. A.; Ghisellini, G.; ...

2011-08-24

Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased inmore » brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. Furthermore, this event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.« less

Laser-only Adaptive Optics Achieves Significant Image Quality Gains Compared to Seeing-limited Observations over the Entire Sky

NASA Astrophysics Data System (ADS)

Howard, Ward S.; Law, Nicholas M.; Ziegler, Carl A.; Baranec, Christoph; Riddle, Reed

2018-02-01

Adaptive optics laser guide-star systems perform atmospheric correction of stellar wavefronts in two parts: stellar tip-tilt and high-spatial-order laser correction. The requirement of a sufficiently bright guide star in the field-of-view to correct tip-tilt limits sky coverage. In this paper, we show an improvement to effective seeing without the need for nearby bright stars, enabling full sky coverage by performing only laser-assisted wavefront correction. We used Robo-AO, the first robotic AO system, to comprehensively demonstrate this laser-only correction. We analyze observations from four years of efficient robotic operation covering 15000 targets and 42000 observations, each realizing different seeing conditions. Using an autoguider (or a post-processing software equivalent) and the laser to improve effective seeing independent of the brightness of a target, Robo-AO observations show a 39% ± 19% improvement to effective FWHM, without any tip-tilt correction. We also demonstrate that 50% encircled energy performance without tip-tilt correction remains comparable to diffraction-limited, standard Robo-AO performance. Faint-target science programs primarily limited by 50% encircled energy (e.g., those employing integral field spectrographs placed behind the AO system) may see significant benefits to sky coverage from employing laser-only AO.

Unravelling the role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel; Steeghs, Danny; Gaensicke, Boris; Marsh, Tom; Rodriguez-Gil, Pablo; Schmidtobreick, Linda; Long, Knox; Schreiber, Matthias

2007-08-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assesment of their evolutionary state is illusionary. We are monitoring the brightness of a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the mass ratio of the system which, combined with the orbital inclination derived from modelling of either the disc eclipses in the high state or the ellipsoidal modulation in the low state, will eventually provide the first detailed system parameters for any SW Sex star.

Unravelling the role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel

2007-02-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assesment of their evolutionary state is illusionary. We are monitoring the brightness of a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the mass ratio of the system which, combined with the orbital inclination derived from modelling of either the disc eclipses in the high state or the ellipsoidal modulation in the low state, will eventually provide the first detailed system parameters for any SW Sex star.

Digital image profilers for detecting faint sources which have bright companions

NASA Technical Reports Server (NTRS)

Morris, Elena; Flint, Graham; Slavey, Robert

1992-01-01

For this program, an image profiling system was developed which offers the potential for detecting extremely faint optical sources that are located in close proximity to bright companions. The approach employed is novel in three respects. First, it does not require an optical system wherein extraordinary measures must be taken to minimize diffraction and scatter. Second, it does not require detectors possessing either extreme uniformity in sensitivity or extreme temporal stability. Finally, the system can readily be calibrated, or nulled, in space by testing against an unresolved singular stellar source.

DEEP IMAGING OF M51: A NEW VIEW OF THE WHIRLPOOL’S EXTENDED TIDAL DEBRIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watkins, Aaron E.; Mihos, J. Christopher; Harding, Paul

We present deep, wide-field imaging of the M51 system using CWRU’s Burrell Schmidt Telescope at KPNO to study the faint tidal features that constrain its interaction history. Our images trace M51's tidal morphology down to a limiting surface brightness of μ{sub B,lim} ∼ 30 mag arcsec{sup −2} and provide accurate colors (σ{sub B−V}<0.1) down to μ{sub B} ∼ 28. We identify two new tidal streams in the system (the south and northeast plumes) with surface brightnesses of μ{sub B} = 29 and luminosities of ∼10{sup 6}L{sub ⊙,B}. While the northeast plume may be a faint outer extension of the tidalmore » “crown” north of NGC 5195 (M51b), the south plume has no analog in any existing M51 simulation and may represent a distinct tidal stream or disrupted dwarf galaxy. We also trace the extremely diffuse northwest plume out to a total extent of 20′ (43 kpc) from NGC 5194 (M51a) and show it to be physically distinct from the overlapping bright tidal streams from M51b. The northwest plume’s morphology and red color (B−V=0.8) instead argue that it originated from tidal stripping of M51a’s extreme outer disk. Finally, we confirm the strong segregation of gas and stars in the southeast tail and do not detect any diffuse stellar component in the H i portion of the tail. Extant simulations of M51 have difficulty matching both the wealth of tidal structure in the system and the lack of stars in the H i tail, motivating new modeling campaigns to study the dynamical evolution of this classic interacting system.« less

The Next Generation Virgo Cluster Survey (NGVS). XVIII. Measurement and Calibration of Surface Brightness Fluctuation Distances for Bright Galaxies in Virgo (and Beyond)

NASA Astrophysics Data System (ADS)

Cantiello, Michele; Blakeslee, John P.; Ferrarese, Laura; Côté, Patrick; Roediger, Joel C.; Raimondo, Gabriella; Peng, Eric W.; Gwyn, Stephen; Durrell, Patrick R.; Cuillandre, Jean-Charles

2018-04-01

We describe a program to measure surface brightness fluctuation (SBF) distances to galaxies observed in the Next Generation Virgo Cluster Survey (NGVS), a photometric imaging survey covering 104 deg2 of the Virgo cluster in the u*, g, i, and z bandpasses with the Canada–France–Hawaii Telescope. We describe the selection of the sample galaxies, the procedures for measuring the apparent i-band SBF magnitude {\\overline{m}}i, and the calibration of the absolute Mibar as a function of observed stellar population properties. The multiband NGVS data set provides multiple options for calibrating the SBF distances, and we explore various calibrations involving individual color indices as well as combinations of two different colors. Within the color range of the present sample, the two-color calibrations do not significantly improve the scatter with respect to wide-baseline, single-color calibrations involving u*. We adopt the ({u}* -z) calibration as a reference for the present galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack good u* photometry, we use an alternative relation based on a combination of (g-i) and (g-z) colors, with only a slightly larger observed scatter of 0.12 mag. The agreement of our measurements with the best existing distance estimates provides confidence that our measurements are accurate. We present a preliminary catalog of distances for 89 galaxies brighter than B T ≈ 13.0 mag within the survey footprint, including members of the background M and W Clouds at roughly twice the distance of the main body of the Virgo cluster. The extension of the present work to fainter and bluer galaxies is in progress.

The ultraviolet-bright stars of Omega Centauri, M3, and M13

NASA Technical Reports Server (NTRS)

Landsman, Wayne B.; O'Connell, Robert W.; Whitney, Jonathan H.; Bohlin, Ralph C.; Hill, Robert S.; Maran, Stephen P.; Parise, Ronald A.; Roberts, Morton S.; Smith, Andrew A.; Stecher, Theodore P.

1992-01-01

Two new UV-bright stars detected within 2 arcmin of the center of Omega Cen are spectroscopically investigated with the short-wavelength spectrograph of the IUE. The IUE spectra of the UV-bright stars UIT-1 and UIT-2 in the core of Omega Cen superficially resemble those of Population I mid-B stars. The absorption lines of the core UV-bright stars are significantly weaker than in Population I stars, consistent with their membership in the cluster. Synthetic spectra calculated from low-metallicity Kurucz model stellar atmospheres are compared with the spectra. These objects are insufficiently luminous to be classical hydrogen-burning post-AGB stars. They may be evolved hot horizontal branch stars which have been brightened by more than 3 mag since leaving the zero-age horizontal branch. It is inferred from the spectra and luminosity of the core UV-bright stars that similar objects could provide the source of the UV light in elliptical galaxies.

Solar Variability Magnitudes and Timescales

NASA Astrophysics Data System (ADS)

Kopp, Greg

2015-08-01

The Sun’s net radiative output varies on timescales of minutes to many millennia. The former are directly observed as part of the on-going 37-year long total solar irradiance climate data record, while the latter are inferred from solar proxy and stellar evolution models. Since the Sun provides nearly all the energy driving the Earth’s climate system, changes in the sunlight reaching our planet can have - and have had - significant impacts on life and civilizations.Total solar irradiance has been measured from space since 1978 by a series of overlapping instruments. These have shown changes in the spatially- and spectrally-integrated radiant energy at the top of the Earth’s atmosphere from timescales as short as minutes to as long as a solar cycle. The Sun’s ~0.01% variations over a few minutes are caused by the superposition of convection and oscillations, and even occasionally by a large flare. Over days to weeks, changing surface activity affects solar brightness at the ~0.1% level. The 11-year solar cycle has comparable irradiance variations with peaks near solar maxima.Secular variations are harder to discern, being limited by instrument stability and the relatively short duration of the space-borne record. Proxy models of the Sun based on cosmogenic isotope records and inferred from Earth climate signatures indicate solar brightness changes over decades to millennia, although the magnitude of these variations depends on many assumptions. Stellar evolution affects yet longer timescales and is responsible for the greatest solar variabilities.In this talk I will summarize the Sun’s variability magnitudes over different temporal ranges, showing examples relevant for climate studies as well as detections of exo-solar planets transiting Sun-like stars.

SPIDER - I. Sample and galaxy parameters in the grizYJHK wavebands

NASA Astrophysics Data System (ADS)

La Barbera, F.; de Carvalho, R. R.; de La Rosa, I. G.; Lopes, P. A. A.; Kohl-Moreira, J. L.; Capelato, H. V.

2010-11-01

This is the first paper of a series presenting the Spheroids Panchromatic Investigation in Different Environmental Regions (SPIDER). The sample of spheroids consists of 5080 bright (Mr < -20) early-type galaxies (ETGs), in the redshift range of 0.05 to 0.095, with optical (griz) photometry and spectroscopy from the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) and near-infrared (YJHK) photometry from the UKIRT Infrared Deep Sky Survey-Large Area Survey (UKIDSS-LAS) (DR4). We describe how homogeneous photometric parameters (galaxy colours and structural parameters) are derived using grizYJHK wavebands. We find no systematic steepening of the colour-magnitude relation when probing the baseline from g - r to g - K, implying that internal colour gradients drive most of the mass-metallicity relation in ETGs. As far as structural parameters are concerned we find that the mean effective radius of ETGs smoothly decreases, by 30 per cent, from g through K, while no significant dependence on waveband is detected for the axial ratio, Sersic index and a4 parameters. Furthermore, velocity dispersions are remeasured for all the ETGs using STARLIGHT and compared to those obtained by SDSS. The velocity dispersions are rederived using a combination of simple stellar population models as templates, hence accounting for the kinematics of different galaxy stellar components. We compare our (2DPHOT) measurements of total magnitude, effective radius and mean surface brightness with those obtained as part of the SDSS pipeline (PHOTO). Significant differences are found and reported, including comparisons with a third and independent part. A full characterization of the sample completeness in all wavebands is presented, establishing the limits of application of the characteristic parameters presented here for the analysis of the global scaling relations of ETGs.

Comparing pymorph and SDSS photometry - II. The differences are more than semantics and are not dominated by intracluster light

NASA Astrophysics Data System (ADS)

Bernardi, M.; Fischer, J.-L.; Sheth, R. K.; Meert, A.; Huertas-Company, M.; Shankar, F.; Vikram, V.

2017-07-01

The Sloan Digital Sky Survey (SDSS) pipeline photometry underestimates the brightnesses of the most luminous galaxies. This is mainly because (I) the SDSS overestimates the sky background, and (II) single-component or two-component Sérsic-based models better fit the surface brightness profile of galaxies, especially at high luminosities, than the de Vaucouleurs model used by the SDSS pipeline. We use the pymorph photometric reductions to isolate effect (II) and show that it is the same in the full sample as in small group environments, and for satellites in the most massive clusters as well. None of these are expected to be significantly affected by intracluster light (ICL). We only see an additional effect for centrals in the most massive haloes, but we argue that even this is not dominated by ICL. Hence, for the vast majority of galaxies, the differences between pymorph and SDSS pipeline photometry cannot be ascribed to the semantics of whether or not one includes the ICL when describing the stellar mass of massive galaxies. Rather, they likely reflect differences in star formation or assembly histories. Failure to account for the SDSS underestimate has significantly biased most previous estimates of the SDSS luminosity and stellar mass functions, and therefore halo model estimates of the z ˜ 0.1 relation between the mass of a halo and that of the galaxy at its centre. We also show that when one studies correlations, at fixed group mass, with a quantity that was not used to define the groups, then selection effects appear. We show why such effects arise and should not be mistaken for physical effects.

A new approach to detailed structural decomposition from the splash and phat surveys: Kicked-up disk stars in the Andromeda galaxy?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorman, Claire E.; Guhathakurta, Puragra; Widrow, Lawrence M., E-mail: cdorman@ucolick.org, E-mail: raja@ucolick.org, E-mail: widrow@astro.queensu.ca

We characterize the bulge, disk, and halo subcomponents in the Andromeda galaxy (M31) over the radial range 4 kpc < R {sub proj} < 225 kpc. The cospatial nature of these subcomponents renders them difficult to disentangle using surface brightness (SB) information alone, especially interior to ∼20 kpc. Our new decomposition technique combines information from the luminosity function (LF) of over 1.5 million bright (20 < m {sub 814W} < 22) stars from the Panchromatic Hubble Andromeda Treasury survey, radial velocities of over 5000 red giant branch stars in the same magnitude range from the Spectroscopic and Photometric Landscape ofmore » Andromeda's Stellar Halo survey, and integrated I-band SB profiles from various sources. We use an affine-invariant Markov chain Monte Carlo algorithm to fit an appropriate toy model to these three data sets. The bulge, disk, and halo SB profiles are modeled as a Sérsic, exponential, and cored power law, respectively, and the LFs are modeled as broken power laws. We present probability distributions for each of 32 parameters describing the SB profiles and LFs of the three subcomponents. We find that the number of stars with a disk-like LF is 5.2% ± 2.1% larger than the number with disk-like (dynamically cold) kinematics, suggesting that some stars born in the disk have been dynamically heated to the point that they are kinematically indistinguishable from halo members. This is the first kinematical evidence for a 'kicked-up disk' halo population in M31. The fraction of kicked-up disk stars is consistent with that found in simulations. We also find evidence for a radially varying disk LF, consistent with a negative metallicity gradient in the stellar disk.« less

Open-Filter Optical SSA Analysis Considerations

NASA Astrophysics Data System (ADS)

Lambert, J.

2016-09-01

Optical Space Situational Awareness (SSA) sensors used for space object detection and orbit refinement measurements are typically operated in an "open-filter" mode without any spectral filters to maximize sensitivity and signal-to-noise. These same optical brightness measurements are often also employed for size determination (e.g., for orbital debris), object correlation, and object status change. These functions, especially when performed using multiple sensors, are highly dependent on sensor calibration for measurement accuracy. Open-filter SSA sensors are traditionally calibrated against the cataloged visual magnitudes of solar-type stars which have similar spectral distributions as the illuminating source, the Sun. The stellar calibration is performed to a high level of accuracy, a few hundredths of a magnitude, by observing many stars over a range of elevation angles to determine sensor, telescope, and atmospheric effects. However, space objects have individual color properties which alter the reflected solar illumination producing spectral distributions which differ from those of the calibration stars. When the stellar calibrations are applied to the space object measurements, visual magnitude values are obtained which are systematically biased. These magnitudes combined with the unknown Bond albedos of the space objects result in systematically biased size determinations which will differ between sensors. Measurements of satellites of known sizes and surface materials have been analyzed to characterize these effects. The results have combined into standardized Bond albedos to correct the measured magnitudes into object sizes. However, the actual albedo values will vary between objects and represent a mean correction subject to some uncertainty. The objective of this discussion is to characterize the sensor spectral biases that are present in open-filter optical observations and examine the resulting brightness and albedo uncertainties that should accompany object size, correlation, or status change determinations, especially in the SSA analyses of individual space objects using data from multiple sensors.

THE ALBEDOS OF KEPLER'S CLOSE-IN SUPER-EARTHS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demory, Brice-Olivier, E-mail: bod21@cam.ac.uk

Exoplanet research focusing on the characterization of super-Earths is currently limited to the handful of targets orbiting bright stars that are amenable to detailed study. This Letter proposes to look at alternative avenues to probe the surface and atmospheric properties of this category of planets, known to be ubiquitous in our galaxy. I conduct Markov Chain Monte Carlo light-curves analyses for 97 Kepler close-in R{sub P} ≲ 2.0 R {sub ⊕} super-Earth candidates with the aim of detecting their occultations at visible wavelengths. Brightness temperatures and geometric albedos in the Kepler bandpass are constrained for 27 super-Earth candidates. A hierarchicalmore » Bayesian modeling approach is then employed to characterize the population-level reflective properties of these close-in super-Earths. I find median geometric albedos A{sub g} in the Kepler bandpass ranging between 0.16 and 0.30, once decontaminated from thermal emission. These super-Earth geometric albedos are statistically larger than for hot Jupiters, which have medians A{sub g} ranging between 0.06 and 0.11. A subset of objects, including Kepler-10b, exhibit significantly larger albedos (A{sub g} ≳ 0.4). I argue that a better understanding of the incidence of stellar irradation on planetary surface and atmospheric processes is key to explain the diversity in albedos observed for close-in super-Earths.« less

The HD 163296 Circumstellar Disk in Scattered Light: Evidence of Time-Variable Self-Shadowing

NASA Technical Reports Server (NTRS)

Wisniewski, John P.; Clampin, Mark; Grady, Carol A.; Ardila, David R.; Ford, Holland C.; Golimowski, David A.; Illingworth, Garth D.; Krist, John E.

2008-01-01

We present the first multi-color view of the scattered light disk of the Herbig Ae star HD 163296, based on coronagraphic observations from the Hubble Space Telescope Advanced Camera for Surveys (ACS). Radial profile fits of the surface brightness along the disk's semi-major axis indicates that the disk is not continuously flared, and extends to approx.540 AU. The disk's color (V-I)=1.1 at a radial distance of 3.5" is redder than the observed stellar color (V-I)=0.15. This red disk color might be indicative of either an evolution in the grain size distribution (i.e. grain growth) and/or composition, both of which would be consistent with the observed non-flared geometry of the outer disk. We also identify a single ansa morphological structure in our F435W ACS data, which is absent from earlier epoch F606W and F814W ACS data, but corresponds to one of the two ansa observed in archival HST STIS coronagraphic data. Following transformation to similar band-passes, we find that the scattered light disk of HD 163296 is 1 mag arcsec(sup -2) fainter at 3.5" in the STIS data than in the ACS data. Moreover, variations are seen in (i) the visibility of the ansa(e) structures, in (ii) the relative surface brightness of the ansa(e) structures, and in (iii) the (known) intrinsic polarization of the system. These results indicate that the scattered light from the HD 163296 disk is variable. We speculate that the inner disk wall, which Sitko et al. suggests has a variable scale height as diagnosed by near-IR SED variability, induces variable self-shadowing of the outer disk. We further speculate that the observed surface brightness variability of the ansa(e) structures may indicate that the inner disk wall is azimuthally asymmetric. Subject headings: circumstellar matter - stars: individual (HD 163296) - planetary systems: formation - planetary systems: protoplanetary disks

Recombination Line versus Forbidden Line Abundances in Planetary Nebulae

NASA Astrophysics Data System (ADS)

Robertson-Tessi, Mark; Garnett, Donald R.

2005-04-01

Recombination lines (RLs) of C II, N II, and O II in planetary nebulae (PNs) have been found to give abundances that are much larger in some cases than abundances from collisionally excited forbidden lines (CELs). The origins of this abundance discrepancy are highly debated. We present new spectroscopic observations of O II and C II recombination lines for six planetary nebulae. With these data we compare the abundances derived from the optical recombination lines with those determined from collisionally excited lines. Combining our new data with published results on RLs in other PNs, we examine the discrepancy in abundances derived from RLs and CELs. We find that there is a wide range in the measured abundance discrepancy Δ(O+2)=logO+2(RL)-logO+2(CEL), ranging from approximately 0.1 dex (within the 1 σ measurement errors) up to 1.4 dex. This tends to rule out errors in the recombination coefficients as a source of the discrepancy. Most RLs yield similar abundances, with the notable exception of O II multiplet V15, known to arise primarily from dielectronic recombination, which gives abundances averaging 0.6 dex higher than other O II RLs. We compare Δ(O+2) against a variety of physical properties of the PNs to look for clues as to the mechanism responsible for the abundance discrepancy. The strongest correlations are found with the nebula diameter and the Balmer surface brightness; high surface brightness, compact PNs show small values of Δ(O+2), while large low surface brightness PNs show the largest discrepancies. An inverse correlation of Δ(O+2) with nebular density is also seen. A marginal correlation of Δ(O+2) is found with expansion velocity. No correlations are seen with electron temperature, He+2/He+, central star effective temperature and luminosity, stellar mass-loss rate, or nebular morphology. Similar results are found for carbon in comparing C II RL abundances with ultraviolet measurements of C III].

Galaxy And Mass Assembly (GAMA): the galaxy stellar mass function to z = 0.1 from the r-band selected equatorial regions

NASA Astrophysics Data System (ADS)

Wright, A. H.; Robotham, A. S. G.; Driver, S. P.; Alpaslan, M.; Andrews, S. K.; Baldry, I. K.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Colless, M.; da Cunha, E.; Davies, L. J. M.; Graham, Alister W.; Holwerda, B. W.; Hopkins, A. M.; Kafle, P. R.; Kelvin, L. S.; Loveday, J.; Maddox, S. J.; Meyer, M. J.; Moffett, A. J.; Norberg, P.; Phillipps, S.; Rowlands, K.; Taylor, E. N.; Wang, L.; Wilkins, S. M.

2017-09-01

We derive the low-redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial Galaxy And Mass Assembly (GAMA) data set covering 180 deg2. We construct the mass function using a density-corrected maximum volume method, using masses corrected for the impact of optically thick and thin dust. We explore the galactic bivariate brightness plane (M⋆-μ), demonstrating that surface brightness effects do not systematically bias our mass function measurement above 107.5 M⊙. The galaxy distribution in the M-μ plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria. The GSMF is fitted with a double Schechter function, with M^\\star =10^{10.78± 0.01± 0.20} M_{⊙}, φ ^\\star _1=(2.93± 0.40)× 10^{-3} h_{70}^3 Mpc-3, α1 = -0.62 ± 0.03 ± 0.15, φ ^\\star _2=(0.63± 0.10)× 10^{-3} h_{70}^3 Mpc-3 and α2 = -1.50 ± 0.01 ± 0.15. We find the equivalent faint end slope as previously estimated using the GAMA-I sample, although we find a higher value of M^\\star. Using the full GAMA-II sample, we are able to fit the mass function to masses as low as 107.5 M⊙, and assess limits to 106.5 M⊙. Combining GAMA-II with data from G10-COSMOS, we are able to comment qualitatively on the shape of the GSMF down to masses as low as 106 M⊙. Beyond the well-known upturn seen in the GSMF at 109.5, the distribution appears to maintain a single power-law slope from 109 to 106.5. We calculate the stellar mass density parameter given our best-estimate GSMF, finding Ω _\\star = 1.66^{+0.24}_{-0.23}± 0.97 h^{-1}_{70} × 10^{-3}, inclusive of random and systematic uncertainties.

THE SPLASH SURVEY: KINEMATICS OF ANDROMEDA's INNER SPHEROID

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorman, Claire E.; Guhathakurta, Puragra; Fardal, Mark A., E-mail: cdorman@ucolick.org, E-mail: raja@ucolick.org, E-mail: fardal@astro.umass.edu

2012-06-20

The combination of large size, high stellar density, high metallicity, and Sersic surface brightness profile of the spheroidal component of the Andromeda galaxy (M31) within R{sub proj} {approx} 20 kpc suggests that it is unlike any subcomponent of the Milky Way. In this work we capitalize on our proximity to and external view of M31 to probe the kinematical properties of this 'inner spheroid'. We employ a Markov chain Monte Carlo (MCMC) analysis of resolved stellar kinematics from Keck/DEIMOS spectra of 5651 red giant branch stars to disentangle M31's inner spheroid from its stellar disk. We measure the mean velocitymore » and dispersion of the spheroid in each of five spatial bins after accounting for a locally cold stellar disk as well as the Giant Southern Stream and associated tidal debris. For the first time, we detect significant spheroid rotation (v{sub rot} {approx} 50 km s{sup -1}) beyond R{sub proj} {approx} 5 kpc. The velocity dispersion decreases from about 140 km s{sup -1} at R{sub proj} = 7 kpc to 120 km s{sup -1} at R{sub proj} = 14 kpc, consistent to 2{sigma} with existing measurements and models. We calculate the probability that a given star is a member of the spheroid and find that the spheroid has a significant presence throughout the spatial extent of our sample. Lastly, we show that the flattening of the spheroid is due to velocity anisotropy in addition to rotation. Though this suggests that the inner spheroid of M31 more closely resembles an elliptical galaxy than a typical spiral galaxy bulge, it should be cautioned that our measurements are much farther out (2-14r{sub eff}) than for the comparison samples.« less

X-Ray Properties of Low-mass Pre-main Sequence Stars in the Orion Trapezium Cluster

NASA Astrophysics Data System (ADS)

Schulz, Norbert S.; Huenemoerder, David P.; Günther, Moritz; Testa, Paola; Canizares, Claude R.

2015-09-01

The Chandra HETG Orion Legacy Project (HOLP) is the first comprehensive set of observations of a very young massive stellar cluster that provides high-resolution X-ray spectra of very young stars over a wide mass range (0.7-2.3 {M}⊙ ). In this paper, we focus on the six brightest X-ray sources with T Tauri stellar counterparts that are well-characterized at optical and infrared wavelengths. All stars show column densities which are substantially smaller than expected from optical extinction, indicating that the sources are located on the near side of the cluster with respect to the observer as well as that these stars are embedded in more dusty environments. Stellar X-ray luminosities are well above 1031 erg s-1, in some cases exceeding 1032 erg s-1 for a substantial amount of time. The stars during these observations show no flares but are persistently bright. The spectra can be well fit with two temperature plasma components of 10 MK and 40 MK, of which the latter dominates the flux by a ratio 6:1 on average. The total emission measures range between 3-8 × 1054 cm-3 and are comparable to active coronal sources. The fits to the Ne ix He-Like K-shell lines indicate forbidden to inter-combination line ratios consistent with the low-density limit. Observed abundances compare well with active coronal sources underlying the coronal nature of these sources. The surface flux in this sample of 0.6-2.3 {M}⊙ classical T Tauri stars shows that coronal activity increases significantly between ages 0.1 and 10 Myr. The results demonstrate the power of X-ray line diagnostics to study coronal properties of T Tauri stars in young stellar clusters.

VLA and ALMA Imaging of Intense Galaxy-wide Star Formation in z ˜ 2 Galaxies

NASA Astrophysics Data System (ADS)

Rujopakarn, W.; Dunlop, J. S.; Rieke, G. H.; Ivison, R. J.; Cibinel, A.; Nyland, K.; Jagannathan, P.; Silverman, J. D.; Alexander, D. M.; Biggs, A. D.; Bhatnagar, S.; Ballantyne, D. R.; Dickinson, M.; Elbaz, D.; Geach, J. E.; Hayward, C. C.; Kirkpatrick, A.; McLure, R. J.; Michałowski, M. J.; Miller, N. A.; Narayanan, D.; Owen, F. N.; Pannella, M.; Papovich, C.; Pope, A.; Rau, U.; Robertson, B. E.; Scott, D.; Swinbank, A. M.; van der Werf, P.; van Kampen, E.; Weiner, B. J.; Windhorst, R. A.

2016-12-01

We present ≃0.″4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z = 1.3-3.0. These galaxies are selected from sensitive blank-field surveys of the 2‧ × 2‧ Hubble Ultra-Deep Field at λ = 5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z ˜ 2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs), thereby representing a diversity of z ˜ 2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2 ± 1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M ⊙ yr-1 kpc-2, sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3-8 times larger, providing a constraint on the characteristic SFR (˜300 M ⊙ yr-1) above which a significant population of more compact SFGs appears to emerge.

Towards stellar effective temperatures and diameters at 1 per cent accuracy for future surveys

NASA Astrophysics Data System (ADS)

Casagrande, L.; Portinari, L.; Glass, I. S.; Laney, D.; Silva Aguirre, V.; Datson, J.; Andersen, J.; Nordström, B.; Holmberg, J.; Flynn, C.; Asplund, M.

2014-04-01

The apparent size of stars is a crucial benchmark for fundamental stellar properties such as effective temperatures, radii and surface gravities. While interferometric measurements of stellar angular diameters are the most direct method to gauge these, they are still limited to relatively nearby and bright stars, which are saturated in most of the modern photometric surveys. This dichotomy prevents us from safely extending well-calibrated relations to the faint stars targeted in large spectroscopic and photometric surveys. Here, we alleviate this obstacle by presenting South African Astronomical Observatory near-infrared JHK observations of 55 stars: 16 of them have interferometric angular diameters and the rest are in common with the 2 Micron All Sky Survey (2MASS, unsaturated) data set, allowing us to tie the effective temperatures and angular diameters derived via the infrared flux method to the interferometric scale. We extend the test to recent interferometric measurements of unsaturated 2MASS stars, including giants, and the metal-poor benchmark target HD122563. With a critical evaluation of the systematics involved, we conclude that a 1 per cent accuracy in fundamental stellar parameters is usually within reach. Caution, however, must be used when indirectly testing a Teff scale via colour relations as well as when assessing the reliability of interferometric measurements, especially at submilliarcsec level. As a result, rather different effective temperature scales can be compatible with a given subset of interferometric data. We highlight some caveats to be aware of in such a quest and suggest a simple method to check against systematics in fundamental measurements. A new diagnostic combination seismic radii with astrometric distances is also presented.

The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core.

PubMed

Jiménez-Serra, Izaskun; Vasyunin, Anton I; Caselli, Paola; Marcelino, Nuria; Billot, Nicolas; Viti, Serena; Testi, Leonardo; Vastel, Charlotte; Lefloch, Bertrand; Bachiller, Rafael

2016-10-10

The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T<10 K), has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modelling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly-extinguished continuum peak with A V ≥30 mag within the inner 2700 au; and a low-density shell with average A V ~7.5-8 mag located at 4000 au from the core's center and bright in CH 3 OH. Our observations show that CH 3 O, CH 3 OCH 3 and CH 3 CHO are more abundant (by factors ~2-10) toward the low-density shell than toward the continuum peak. Other COMs such as CH 3 OCHO, c-C 3 H 2 O, HCCCHO, CH 2 CHCN and HCCNC show slight enhancements (by factors ≤3) but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modelling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because i) CO starts freezing out onto dust grains driving an active surface chemistry; ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and iii) the density is still moderate to prevent severe depletion of COMs onto grains.

The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core

PubMed Central

Jiménez-Serra, Izaskun; Vasyunin, Anton I.; Caselli, Paola; Marcelino, Nuria; Billot, Nicolas; Viti, Serena; Testi, Leonardo; Vastel, Charlotte; Lefloch, Bertrand; Bachiller, Rafael

2016-01-01

The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T<10 K), has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modelling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly-extinguished continuum peak with AV ≥30 mag within the inner 2700 au; and a low-density shell with average AV ~7.5-8 mag located at 4000 au from the core’s center and bright in CH3OH. Our observations show that CH3O, CH3OCH3 and CH3CHO are more abundant (by factors ~2-10) toward the low-density shell than toward the continuum peak. Other COMs such as CH3OCHO, c-C3H2O, HCCCHO, CH2CHCN and HCCNC show slight enhancements (by factors ≤3) but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modelling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because i) CO starts freezing out onto dust grains driving an active surface chemistry; ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and iii) the density is still moderate to prevent severe depletion of COMs onto grains. PMID:27733899

A Dynamical N-body model for the central region of ω Centauri

NASA Astrophysics Data System (ADS)

Jalali, B.; Baumgardt, H.; Kissler-Patig, M.; Gebhardt, K.; Noyola, E.; Lützgendorf, N.; de Zeeuw, P. T.

2012-02-01

Context. Supermassive black holes (SMBHs) are fundamental keys to understand the formation and evolution of their host galaxies. However, the formation and growth of SMBHs are not yet well understood. One of the proposed formation scenarios is the growth of SMBHs from seed intermediate-mass black holes (IMBHs, 102 to 105 M⊙) formed in star clusters. In this context, and also with respect to the low mass end of the M• - σ relation for galaxies, globular clusters are in a mass range that make them ideal systems to look for IMBHs. Among Galactic star clusters, the massive cluster ω Centauri is a special target due to its central high velocity dispersion and also its multiple stellar populations. Aims: We study the central structure and dynamics of the star cluster ω Centauri to examine whether an IMBH is necessary to explain the observed velocity dispersion and surface brightness profiles. Methods: We perform direct N-body simulations on GPU and GRAPE special purpose computers to follow the dynamical evolution of ω Centauri. The simulations are compared to the most recent data-sets in order to explain the present-day conditions of the cluster and to constrain the initial conditions leading to the observed profiles. Results: We find that starting from isotropic spherical multi-mass King models and within our canonical assumptions, a model with a central IMBH mass of 2% of the cluster stellar mass, i.e. a 5. × 104 M⊙ IMBH, provides a satisfactory fit to both the observed shallow cusp in surface brightness and the continuous rise towards the center of the radial velocity dispersion profile. In our isotropic spherical models, the predicted proper motion dispersion for the best-fit model is the same as the radial velocity dispersion one. Conclusions: We conclude that with the presence of a central IMBH in our models, we reproduce consistently the rise in the radial velocity dispersion. Furthermore, we always end up with a shallow cusp in the projected surface brightness of our model clusters containing an IMBH. In addition, we find that the M/L ratio seems to be constant in the central region, and starts to rise slightly from the core radius outwards for all models independent of the presence of a black hole. Considering our initial parameter space, it is not possible to explain the observations without a central IMBH for ω Centauri. To further strengthen the presence of an IMBH as a unique explanation of the observed light and kinematics more detailed analysis such as investigating the contribution of primordial binaries and different anisotropy profiles should be studied.

REMOVING BIASES IN RESOLVED STELLAR MASS MAPS OF GALAXY DISKS THROUGH SUCCESSIVE BAYESIAN MARGINALIZATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-García, Eric E.; González-Lópezlira, Rosa A.; Bruzual A, Gustavo

2017-01-20

Stellar masses of galaxies are frequently obtained by fitting stellar population synthesis models to galaxy photometry or spectra. The state of the art method resolves spatial structures within a galaxy to assess the total stellar mass content. In comparison to unresolved studies, resolved methods yield, on average, higher fractions of stellar mass for galaxies. In this work we improve the current method in order to mitigate a bias related to the resolved spatial distribution derived for the mass. The bias consists in an apparent filamentary mass distribution and a spatial coincidence between mass structures and dust lanes near spiral arms.more » The improved method is based on iterative Bayesian marginalization, through a new algorithm we have named Bayesian Successive Priors (BSP). We have applied BSP to M51 and to a pilot sample of 90 spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. By quantitatively comparing both methods, we find that the average fraction of stellar mass missed by unresolved studies is only half what previously thought. In contrast with the previous method, the output BSP mass maps bear a better resemblance to near-infrared images.« less

The Dark Matter Halo Profile Of NGC 2976 Via Stellar Kinematics

NASA Astrophysics Data System (ADS)

Adams, Joshua J.; Gebhardt, K.; Hill, G. J.; van den Bosch, R. C. E.; Blanc, G. A.

2011-01-01

The observations of kinematics in low surface brightness (LSB) and dwarf late type galaxies have stubbornly resisted giving clear evidence for the cuspy Navarro-Frenk-White (NFW) dark matter (DM) halo profiles that simulations with ΛCDM inputs predict. Instead, most LSBs and late type dwarfs suggest cored DM halos or the observations are not yet constraining enough to rule out cusps. One viable theory to explain cored DM halos relies on the gravitational perturbation of a growing baryonic disk that is then rapidly removed causing the halo to expand to a cored equilibrium. Weakly self-interacting dark matter has also been invoked to explain cored DM halos. This problem may loom large over small galaxy formation and growth. However, different measurements can be taken to further test the apparent problem. Most previous data have relied on HI or Hα as kinematic tracers. A small number of works have studied the problem with longslit stellar kinematics. Ideally, the advantages of 2D spectroscopic coverage and a collisionless kinematic tracer would be combined. So far, NGC 2976 has made one of the cleanest cases for a cored DM halo via integral field spectroscopy in Hα. We here report on observations of NGC 2976 with the large field-of-view fiber-fed Visible Integral field Replicable Unit Spectrograph Prototype (VIRUS-P) at R=3200 to concurrently measure the gaseous and stellar kinematics and probe the DM halo. We find that the gas and stellar kinematics disagree both in the magnitude of their second velocity moments and their detailed profiles. We unexpectedly find emission features in one of NGC 2976's two large star-forming regions which may be indicative of carbon-rich Wolf-Rayet stars. A putative bar further complicates the use of gaseous tracers. We solve the Jeans equations with stellar kinematics to reevaluate the DM profile in this exemplar galaxy of the core-cusp problem.

The Evolution and Stability of Massive Stars

NASA Astrophysics Data System (ADS)

Shiode, Joshua Hajime

Massive stars are the ultimate source for nearly all the elements necessary for life. The first stars forge these elements from the sparse set of ingredients supplied by the Big Bang, and distribute enriched ashes throughout their galactic homes via their winds and explosive deaths. Subsequent generations follow suit, assembling from the enriched ashes of their predecessors. Over the last several decades, the astrophysics community has developed a sophisticated theoretical picture of the evolution of these stars, but it remains an incomplete accounting of the rich set of observations. Using state of the art models of massive stars, I have investigated the internal processes taking place throughout the life-cycles of stars spanning those from the first generation ("Population III") to the present-day ("Population I"). I will argue that early-generation stars were not highly unstable to perturbations, contrary to a host of past investigations, if a correct accounting is made for the viscous effect of convection. For later generations, those with near solar metallicity, I find that this very same convection may excite gravity-mode oscillations that produce observable brightness variations at the stellar surface when the stars are near the main sequence. If confirmed with modern high-precision monitoring experiments, like Kepler and CoRoT, the properties of observed gravity modes in massive stars could provide a direct probe of the poorly constrained physics of gravity mode excitation by convection. Finally, jumping forward in stellar evolutionary time, I propose and explore an entirely new mechanism to explain the giant eruptions observed and inferred to occur during the final phases of massive stellar evolution. This mechanism taps into the vast nuclear fusion luminosity, and accompanying convective luminosity, in the stellar core to excite waves capable of carrying a super-Eddington luminosity out to the stellar envelope. This energy transfer from the core to the envelope has the potential to unbind a significant amount of mass in close proximity to a star's eventual explosion as a core collapse supernova.

"Almost Darks": HI Mapping and Optical Analysis

NASA Astrophysics Data System (ADS)

Singer, Quinton; Ball, Catie; Cannon, John M.; Leisman, Luke; Haynes, Martha P.; Adams, Elizabeth A.; Bernal Neira, David; Giovanelli, Riccardo; Hallenbeck, Gregory L.; Janesh, William; Janowiecki, Steven; Jozsa, Gyula; Rhode, Katherine L.; Salzer, John Joseph

2017-01-01

We present VLA HI imaging of the "Almost Dark" galaxies AGC 227982, AGC 268363, and AGC 219533. Selected from the ALFALFA survey, "Almost Dark" galaxies have significant HI reservoirs but lack an obvious stellar counterpart in survey-depth ground-based optical imaging. These three HI-rich objects harbor some of the most extreme levels of suppressed star formation amongst the isolated sources in the ALFALFA catalog. Our new multi-configuration, high angular (~20") and spectral (1.7 km/s) resolution HI observations produce spatially resolved column density and velocity distribution moment maps. We compare these images to Sloan Digitized Sky Survey (SDSS) optical images. By localizing the HI gas, we identify previously unknown optical components (offset from the ALFALFA pointing center) for AGC 227982 and AGC 268363, and confirm the association with a very low surface brightness stellar counterpart for AGC 219533. Baryonic masses are derived from VLA flux integral values and ALFALFA distance estimates, giving answers consistent with those derived from ALFALFA fluxes. All three sources appear to have fairly regular HI morphologies and show evidence of ordered rotation.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College.

HI-bearing Ultra Diffuse Galaxies in the ALFALFA Survey

NASA Astrophysics Data System (ADS)

Leisman, Lukas; Janowiecki, Steven; Jones, Michael G.; ALFALFA Almost Darks Team

2018-01-01

The Arecibo Legacy Fast ALFA (Arecibo L-band Feed Array) extragalactic HI survey, with over 30,000 high significance extragalactic sources, is well positioned to locate gas-bearing, low surface brightness sources missed by optical detection algorithms. We investigate the nature of a population of HI-bearing sources in ALFALFA with properties similar to "ultra-diffuse" galaxies (UDGs): galaxies with stellar masses of dwarf galaxies, but radii of L* galaxies. These "HI-bearing ultra-diffuse" sources (HUDS) constitute a small, but pertinent, fraction of the dwarf-mass galaxies in ALFALFA. They are bluer and have more irregular morphologies than the optically-selected UDGs found in clusters, and they appear to be gas-rich for their stellar mass, indicating low star formation efficiency. To illuminate potential explanations for the extreme properties of these sources we explore their environments and estimate their halo properties. We conclude that environmental mechanism are unlikely the cause of HUDS' properties, as they exist in environments equivalent to that of the other ALFALFA sources of similar HI-masses, however, we do find some suggestion that these HUDS may reside in high spin parameter halos, a potential explanation for their "ultra-diffuse" nature.

A PAndAS view of the resolved stellar populations in M31 dwarf elliptical satellites

NASA Astrophysics Data System (ADS)

Crnojević, D.; PAndAS Collaboration

We present the first truly global view of the closest elliptical galaxies, the dwarf elliptical (dE) companions of M31 NGC147 and NGC185. We exploit the deep PAndAS photometric dataset in order to investigate the resolved stellar content and structure of these dEs out to larger distances than ever previously probed. From the analysis of their old red giant branch stars, we derive density maps, full surface brightness profiles and metallicity distribution functions. We find that NGC147 shows pronounced tidal tails likely due to its interaction with M31, while NGC185 retains a regular elliptical shape over its entire extent. The two dEs follow a Sersic profile out to ˜5 kpc, and the effective radii derived in this study are a factor of two larger than previous literature values. While NGC185 shows a significant gradient in metallicity (˜-0.05 dex/kpc), this is almost absent in NGC147. The detailed understanding of nearby dEs is crucial for the studies of more distant objects, and we discuss how internal and environmental processes could have influenced the evolution of NGC147 and NGC185 in light of our results.

HYDRODYNAMICAL INTERACTION OF MILDLY RELATIVISTIC EJECTA WITH AN AMBIENT MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Akihiro; Maeda, Keiichi; Shigeyama, Toshikazu

2017-01-01

The hydrodynamical interaction of spherical ejecta freely expanding at mildly relativistic speeds into an ambient cold medium is studied in semianalytical and numerical ways to investigate how ejecta produced in energetic stellar explosions dissipate their kinetic energy through the interaction with the surrounding medium. We especially focus on the case in which the circumstellar medium (CSM) is well represented by a steady wind at a constant mass-loss rate, having been ejected from the stellar surface prior to the explosion. As a result of the hydrodynamical interaction, the ejecta and CSM are swept by the reverse and forward shocks, leading tomore » the formation of a geometrically thin shell. We present a semianalytical model describing the dynamical evolution of the shell and compare the results with numerical simulations. The shell can give rise to bright emission as it gradually becomes transparent to photons. We develop an emission model for the expected emission from the optically thick shell, in which photons in the shell gradually diffuse out to the interstellar space. Then we investigate the possibility that radiation powered by the hydrodynamical interaction is the origin of an underluminous class of gamma-ray bursts.« less

Radial Color and Mass Profile Trends of Dwarf Irregular Galaxies

NASA Astrophysics Data System (ADS)

Herrmann, Kimberly A.; Hunter, D. A.; THINGS, LITTLE

2014-01-01

Radial stellar surface brightness (SB) profiles of spiral galaxies can be classified into three types: (I) single exponential, (II) truncated: the light falls off with one exponential out to a break radius and then falls off more steeply, and (III) anti-truncated: the light falls off with one exponential out to a break radius and then falls off less steeply. Stellar SB profile breaks are also found in dwarf disk galaxies, but with an additional sub-category of Type II profiles: (FI) flat-inside: the light is roughly constant or increasing and then falls off beyond a break. Additionally, Bakos, Trujillo, & Pohlen (2008) showed that for spirals, each profile type has a characteristic color trend with respect to the break location which can be combined with color mass-to-light ratio relationships to examine radial mass profiles as well. Here we show radial color and mass profile trends for the three main SB types from a large multi-wavelength photometric study of dwarf irregular galaxies (the 141 dwarf parent sample of the LITTLE THINGS galaxies). We explore the similarities and differences between spirals and dwarfs and also between different colors.

Galaxy And Mass Assembly (GAMA): the galaxy stellar mass function at z < 0.06

NASA Astrophysics Data System (ADS)

Baldry, I. K.; Driver, S. P.; Loveday, J.; Taylor, E. N.; Kelvin, L. S.; Liske, J.; Norberg, P.; Robotham, A. S. G.; Brough, S.; Hopkins, A. M.; Bamford, S. P.; Peacock, J. A.; Bland-Hawthorn, J.; Conselice, C. J.; Croom, S. M.; Jones, D. H.; Parkinson, H. R.; Popescu, C. C.; Prescott, M.; Sharp, R. G.; Tuffs, R. J.

2012-03-01

We determine the low-redshift field galaxy stellar mass function (GSMF) using an area of 143 deg2 from the first three years of the Galaxy And Mass Assembly (GAMA) survey. The magnitude limits of this redshift survey are r < 19.4 mag over two-thirds and 19.8 mag over one-third of the area. The GSMF is determined from a sample of 5210 galaxies using a density-corrected maximum volume method. This efficiently overcomes the issue of fluctuations in the number density versus redshift. With H0= 70 km s-1 Mpc-1, the GSMF is well described between 108 and 1011.5 M⊙ using a double Schechter function with ?, ?, α1=-0.35, ? and α2=-1.47. This result is more robust to uncertainties in the flow-model corrected redshifts than from the shallower Sloan Digital Sky Survey main sample (r < 17.8 mag). The upturn in the GSMF is also seen directly in the i-band and K-band galaxy luminosity functions. Accurately measuring the GSMF below 108 M⊙ is possible within the GAMA survey volume but as expected requires deeper imaging data to address the contribution from low surface-brightness galaxies.

Narrow-angle Astrometry with SUSI

NASA Astrophysics Data System (ADS)

Kok, Y.; Ireland, M. J.; Robertson, J. G.; Tuthill, P. G.; Warrington, B. A.; Tango, W. J.

2014-09-01

SUSI (Sydney University Stellar Interferometer) is currently being fitted with a 2nd beam combiner, MUSCA (Micro-arcsecond University of Sydney Companion Astrometry), for the purpose of narrow-angle astrometry. With an aim to achieve ˜10 micro-arcseconds of angular resolution at its best, MUSCA allows SUSI to search for planets around bright binary stars, which are its primary targets. While the first beam combiner, PAVO (Precision Astronomical Visible Observations), is used to track stellar fringes during an observation, MUSCA will be used to measure separations of binary stars. MUSCA is a Michelson interferometer and its setup at SUSI will be described in this poster.

A model for the spectroscopic variations of the peculiar symbiotic star MWC 560

NASA Technical Reports Server (NTRS)

Shore, Steven N.; Aufdenberg, Jason P.; Michalitsianos, A. G.

1994-01-01

In this note, we show that the ultraviolet and optical spectroscopic variability of this unique symbiotic star can be understood in terms of a time variable collimated stellar wind with a rapid acceleration near the source. Using the radial velocities observed during the ultraviolet bright phase, we find that a variation in the mass loss rate of a factor of ten can explain the ultraviolet spectral changes. The acceleration is far faster than normally observed in radiatively driven stellar winds and may be due to mechanical driving of the outflow from the disk.

A catalog of polychromatic bulge-disc decompositions of ˜17.600 galaxies in CANDELS

NASA Astrophysics Data System (ADS)

Dimauro, Paola; Huertas-Company, Marc; Daddi, Emanuele; Pérez-González, Pablo G.; Bernardi, Mariangela; Barro, Guillermo; Buitrago, Fernando; Caro, Fernando; Cattaneo, Andrea; Dominguez-Sánchez, Helena; Faber, Sandra M.; Häußler, Boris; Kocevski, Dale D.; Koekemoer, Anton M.; Koo, David C.; Lee, Christoph T.; Mei, Simona; Margalef-Bentabol, Berta; Primack, Joel; Rodriguez-Puebla, Aldo; Salvato, Mara; Shankar, Francesco; Tuccillo, Diego

2018-05-01

Understanding how bulges grow in galaxies is critical step towards unveiling the link between galaxy morphology and star-formation. To do so, it is necessary to decompose large sample of galaxies at different epochs into their main components (bulges and discs). This is particularly challenging, especially at high redshifts, where galaxies are poorly resolved. This work presents a catalog of bulge-disc decompositions of the surface brightness profiles of ˜17.600 H-band selected galaxies in the CANDELS fields (F160W < 23, 0 < z < 2) in 4 to 7 filters covering a spectral range of 430 - 1600nm. This is the largest available catalog of this kind up to z = 2. By using a novel approach based on deep-learning to select the best model to fit, we manage to control systematics arising from wrong model selection and obtain less contaminated samples than previous works. We show that the derived structural properties are within ˜10 - 20% of random uncertainties. We then fit stellar population models to the decomposed SEDs (Spectral Energy Distribution) of bulges and discs and derive stellar masses (and stellar mass bulge-to-total ratios) as well as rest-frame colors (U,V,J) for bulges and discs separately. All data products are publicly released with this paper and through the web page https://lerma.obspm.fr/huertas/form_CANDELS and will be used for scientific analysis in forthcoming works.

Geometrical evidence for dark matter: X-ray constraints on the mass of the elliptical galaxy NGC 720

NASA Astrophysics Data System (ADS)

Buote, David A.; Canizares, Claude R.

1994-05-01

We describe (1) a new test for dark matter and alternate theories of gravitation based on the relative geometries of the X-ray and optical surface brightness distributions and an assumed form for the potential, of the optical light, (2) a technique to measure the shapes of the total gravitating matter and dark matter of an ellipsoidal system which is insensitive to the precise value of the temperature of the gas and to modest temperature gradients, and (3) a new method to determine the ratio of dark mass to stellar mass that is dependent on the functional forms for the visible star, gas and dark matter distributions, but independent of the distance to the galaxy or the gas temperature. We apply these techniques to X-ray data from the ROSAT Position Sensitive Proportional Counter (PSPC) of the optically flattened elliptical galaxy NGC 720; the optical isophotes have ellipticity epsilon approximately 0.40 extending out to approximately 120 sec. The X-ray isophotes are significantly elongated, epsilon = 0.20-0.30 for semimajor axis a approximately 100 sec. The major axes of the optical and X-ray isophotes are misaligned by approximately 30 deg +/- 15 deg. Spectral analysis of the X-ray data reveals no evidence of temperature gradients or anisotropies and demonstrates that a single-temperature plasma (T approximately 0.6 keV) having subsolar heavy element abundances and a two-temperature model having solar abundances describe the spectrum equally well. Considering only the relative geometries of the X-ray and optical surface brightness distributions and an assumed functional form for the potential of the optical light, we conclude that matter distributed like the optical light cannot produce the observed ellipticities of the X-ray isophotes, independent of the gas pressure, the gas temperature, and the value of the stellar mass; this comparison assumes a state of quasi-hydrostatic equilibrium so that the three-dimensional surfaces of the gas emissivity trace the three-dimensional isopotential surfaces -- we discuss the viability of this assumption for NGC 720. Milgrom's Modification of Newtonian Dynamics (MOND) cannot dispel this manifestation of dark matter. Hence, geometrical considerations require, without mention of pressure or temperature, the presence of an extended, massive dark matter halo in NGC 720. Employing essentially the technique of Buote & Canizares (1992; Buote 1992) we use the shape of the X-ray surface brightness to constrain the shape of the total gravitating matter. The total matter is modeled as either an oblate or prolate spheriod of constant shape and orientation having either a Ferrers (rho approximately r-n) or Hernquist density. Assuming the X-ray gas is in hydrostatic equilibrium, we construct a model X-ray gas distribution for various temperature profiles. We determine the ellipticity of the total gravitating matter to be epsilon approximately 0.50-0.70. Using the single-temperature model we estimate a total mass approximately (0.41-1.4) x 1012 h80 solar mass interior to the ellipsoid of semimajor axis 43.6 h80 kpc. Ferrers densities as steep as r-3 do not fit the data, but the r-2 and Hernquist models yield excellent fits. We estimate the mass distributions of the stars and the gas and fit the dark matter directly. For a given gas equation of state and functional forms for the visible stars, gas, and dark matter, these models yield a distance-independent and temperature-independent measurement of the ratio of dark mass to stellar mass MDM/Mstars. We estimate a minimum MDM/Mstars greater than or equal to 4 which corresponds to a total mass slightly greater than that derived from the single-temperature models for distance D = 20h80 Mpc.

Geometrical evidence for dark matter: X-ray constraints on the mass of the elliptical galaxy NGC 720

NASA Technical Reports Server (NTRS)

Buote, David A.; Canizares, Claude R.

1994-01-01

We describe (1) a new test for dark matter and alternate theories of gravitation based on the relative geometries of the X-ray and optical surface brightness distributions and an assumed form for the potential, of the optical light, (2) a technique to measure the shapes of the total gravitating matter and dark matter of an ellipsoidal system which is insensitive to the precise value of the temperature of the gas and to modest temperature gradients, and (3) a new method to determine the ratio of dark mass to stellar mass that is dependent on the functional forms for the visible star, gas and dark matter distributions, but independent of the distance to the galaxy or the gas temperature. We apply these techniques to X-ray data from the ROSAT Position Sensitive Proportional Counter (PSPC) of the optically flattened elliptical galaxy NGC 720; the optical isophotes have ellipticity epsilon approximately 0.40 extending out to approximately 120 sec. The X-ray isophotes are significantly elongated, epsilon = 0.20-0.30 for semimajor axis a approximately 100 sec. The major axes of the optical and X-ray isophotes are misaligned by approximately 30 deg +/- 15 deg. Spectral analysis of the X-ray data reveals no evidence of temperature gradients or anisotropies and demonstrates that a single-temperature plasma (T approximately 0.6 keV) having subsolar heavy element abundances and a two-temperature model having solar abundances describe the spectrum equally well. Considering only the relative geometries of the X-ray and optical surface brightness distributions and an assumed functional form for the potential of the optical light, we conclude that matter distributed like the optical light cannot produce the observed ellipticities of the X-ray isophotes, independent of the gas pressure, the gas temperature, and the value of the stellar mass; this comparison assumes a state of quasi-hydrostatic equilibrium so that the three-dimensional surfaces of the gas emissivity trace the three-dimensional isopotential surfaces -- we discuss the viability of this assumption for NGC 720. Milgrom's Modification of Newtonian Dynamics (MOND) cannot dispel this manifestation of dark matter. Hence, geometrical considerations require, without mention of pressure or temperature, the presence of an extended, massive dark matter halo in NGC 720. Employing essentially the technique of Buote & Canizares (1992; Buote 1992) we use the shape of the X-ray surface brightness to constrain the shape of the total gravitating matter. The total matter is modeled as either an oblate or prolate spheriod of constant shape and orientation having either a Ferrers (rho approximately r(exp -n)) or Hernquist density. Assuming the X-ray gas is in hydrostatic equilibrium, we construct a model X-ray gas distribution for various temperature profiles. We determine the ellipticity of the total gravitating matter to be epsilon approximately 0.50-0.70. Using the single-temperature model we estimate a total mass approximately (0.41-1.4) x 10(exp 12) h(sub 80) solar mass interior to the ellipsoid of semimajor axis 43.6 h(sub 80) kpc. Ferrers densities as steep as r(exp -3) do not fit the data, but the r(exp -2) and Hernquist models yield excellent fits. We estimate the mass distributions of the stars and the gas and fit the dark matter directly. For a given gas equation of state and functional forms for the visible stars, gas, and dark matter, these models yield a distance-independent and temperature-independent measurement of the ratio of dark mass to stellar mass M(sub DM)/M(sub stars). We estimate a minimum M(sub DM)/M(sub stars) greater than or equal to 4 which corresponds to a total mass slightly greater than that derived from the single-temperature models for distance D = 20h(sub 80) Mpc.

THE EVOLUTION OF EARLY- AND LATE-TYPE GALAXIES IN THE COSMIC EVOLUTION SURVEY UP TO z {approx} 1.2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pannella, Maurilio; Gabasch, Armin; Drory, Niv

2009-08-10

The Cosmic Evolution Survey (COSMOS) allows for the first time a highly significant census of environments and structures up to redshift 1, as well as a full morphological description of the galaxy population. In this paper we present a study aimed to constrain the evolution, in the redshift range 0.2 < z < 1.2, of the mass content of different morphological types and its dependence on the environmental density. We use a deep multicolor catalog, covering an area of {approx}0.7 deg{sup 2} inside the COSMOS field, with accurate photometric redshifts (i {approx}< 26.5 and {delta}z/(z {sub spec} + 1) {approx}more » 0.035). We estimate galaxy stellar masses by fitting the multicolor photometry to a grid of composite stellar population models. We quantitatively describe the galaxy morphology by fitting point-spread function convolved Sersic profiles to the galaxy surface brightness distributions down to F814 = 24 mag for a sample of 41,300 objects. We confirm an evolution of the morphological mix with redshift: the higher the redshift the more disk-dominated galaxies become important. We find that the morphological mix is a function of the local comoving density: the morphology density relation extends up to the highest redshift explored. The stellar mass function of disk-dominated galaxies is consistent with being constant with redshift. Conversely, the stellar mass function of bulge-dominated systems shows a decline in normalization with redshift. Such different behaviors of late-types and early-types stellar mass functions naturally set the redshift evolution of the transition mass. We find a population of relatively massive, early-type galaxies, having high specific star formation rate (SSFR) and blue colors which live preferentially in low-density environments. The bulk of massive (>7 x 10{sup 10} M {sub sun}) early-type galaxies have similar characteristic ages, colors, and SSFRs independently of the environment they belong to, with those hosting the oldest stars in the universe preferentially belonging to the highest density regions. The whole catalog including morphological information and stellar mass estimates analyzed in this work is made publicly available.« less

Interacting Supernovae: Types IIn and Ibn

NASA Astrophysics Data System (ADS)

Smith, Nathan

Supernovae that show evidence of strong shock interaction between their ejecta and pre-existing slower circumstellar material (CSM) constitute an interesting, diverse, and still poorly understood category of explosive transients. The chief reason they are extremely interesting is because they tell us that in a subset of stellar deaths, the progenitor star becomes wildly unstable in the years, decades, or centuries before explosion. This is something that has not been included in standard stellar evolution models but may significantly change the end product and yield of that evolution and complicates our attempts to map SNe to their progenitors. Another reason they are interesting is because CSM interaction is an efficient engine for making bright transients, allowing superluminous transients to arise from normal SN explosion energy, and transients of normal supernova luminosity to arise from sub-energetic explosions or low radioactivity yield. CSM interaction shrouds the fast ejecta in bright shock emission, obscuring our view of the underlying explosion, and the radiation hydrodynamics is challenging to model. The CSM interaction may also be highly nonspherical, perhaps linked to binary interaction in the progenitor system. In some cases, these complications make it difficult to tell the difference between a core-collapse and thermonuclear explosion or to discern between a nonterminal eruption, failed supernova, or weak supernova. Efforts to uncover the physical parameters of individual events and connections to progenitor stars make this a rapidly evolving topic that challenges paradigms of stellar evolution.

Galaxies in x-ray selected clusters and groups in Dark Energy Survey Data I: Stellar mass growth of bright central galaxies since Z similar to 1.2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y.; Miller, C.; McKay, T.

2016-01-10

Using the science verification data of the Dark Energy Survey for a new sample of 106 X-ray selected clusters and groups, we study the stellar mass growth of bright central galaxies (BCGs) since redshift z similar to 1.2. Compared with the expectation in a semi-analytical model applied to the Millennium Simulation, the observed BCGs become under-massive/under-luminous with decreasing redshift. We incorporate the uncertainties associated with cluster mass, redshift, and BCG stellar mass measurements into an analysis of a redshift-dependent BCG-cluster mass relation, m(*) proportional to (M-200/1.5 x 10(14)M(circle dot))(0.24 +/- 0.08)(1+z)(-0.19 +/- 0.34), and compare the observed relation to themore » model prediction. We estimate the average growth rate since z = 1.0 for BCGs hosted by clusters of M-200,M-z = 10(13.8)M(circle dot); at z = 1.0: m(*, BCG) appears to have grown by 0.13 +/- 0.11 dex, in tension at the similar to 2.5 sigma significance level with the 0.40 dex growth rate expected from the semi-analytic model. We show that the build-up of extended intracluster light after z = 1.0 may alleviate this tension in BCG growth rates.« less

Comprehensive stellar population models and the disentanglement of age and metallicity effects

NASA Technical Reports Server (NTRS)

Worthey, Guy

1994-01-01

The construction of detailed models for intermediate and old stellar populations is described. Input parameters include metallicity (-2 less than (Fe/H) less than 0.5), single-burst age (between 1.5 and 17 Gyr), and initial mass function (IMF) exponent. Quantities output include broadband magnitudes, spectral energy distributions, surface brightness fluctuation magnitudes, and a suite of 21 absorption feature indices. The models are checked against a wide variety of available observations. Examinations of model output yield the following conclusions. (1) If the percentage change delta age/delta Z approximately equals 3/2 for two populations, they will appear almost identical in most indices. A few indices break this degeneracy by being either more abundance sensitive (Fe4668, Fe5015, Fe5709, and Fe5782) or more age sensitive (G4300, H beta, and presumably higher order Balmer lines) than usual. (2) Present uncertainties in stellar evolution are of the same magnitude as the effects of IMF and Y in the indices studied. (3) Changes in abundance ratios (like (Mg/Fe)) are predicted to be readily apparent in the spectra of old stellar populations. (4) The I-band flux of a stellar population is predicted to be nearly independent of metallicity and only modestly sensitive to age. The I band is therefore recommended for standard candle work or studies of M/L in galaxies. Other conclusions stem from this work. (1) Intercomparison of models and observations of two TiO indices seem to indicate variation of the (V/Ti) ratio among galaxies, but it is not clear how this observation ties into the standard picture of chemical enrichment. (2) Current estimates of (Fe/H) for the most metal-rich globulars that are based on integrated indices are probably slightly too high. (3) Colors of population models from different authors exhibit a substantial range. At solar metallicity and 13 Gyr, this range corresponds to an age error of roughly +/- 7 Gyr. Model colors from different authors applied in a differential sense have smaller uncertainties. (4) In the present models the dominant error for colors is probably the transformation from stellar atmospheric parameters to stellar colors. (5) Stellar B - V is difficult to model, and current spreads among different authors can reach 0.2 mag. (6) If known defects in the stellar flux library are corrected, the population model colors of this work in passbands redder than U would be accurate to roughly 0.03 mag in an absolute sense. These corrections are not made in the tables of model output.

VizieR Online Data Catalog: Surface photometry of GHASP galaxies (Barbosa+, 2015)

NASA Astrophysics Data System (ADS)

Barbosa, C. E.; Mendes de Oliveira, C.; Amram, P.; Ferrari, F.; Russeil, D.; Epinat, B.; Perret, V.; Adami, C.; Marcelin, M.

2016-04-01

Our data set is constructed using new Rc-band observations taken at the Observatoire de Haute-Provence, supplemented with Sloan Digital Sky Survey archival data, obtained with the purpose of deriving homogeneous photometric profiles and parameters. Our results include Rc-band surface brightness profiles for 170 galaxies and ugriz profiles for 108 of these objects. We catalogue several parameters of general interest for further reference, such as total magnitude, effective radius and isophotal parameters (magnitude, position angle, ellipticity and inclination). We also perform a structural decomposition of the surface brightness profiles using a multi-component method to separate discs from bulges and bars, and to observe the main scaling relations involving luminosities, sizes and maximum velocities. We determine the Rc-band Tully-Fisher relation using maximum velocities derived solely from Hα rotation curves for a sample of 80 galaxies, resulting in a slope of -8.1+/-0.5, zero-point of -3.0+/-1.0 and an estimated intrinsic scatter of 0.28+/-0.07. We note that, unlike the Tully-Fisher relation in the near-infrared derived for the same sample, no change in the slope of the relation is seen at the low-mass end (for galaxies with Vmax<125km/s). We suggest that this different behaviour of the Tully-Fisher relation (with the optical relation being described by a single power law while the near-infrared has two), may be caused by differences in the stellar mass-to-light ratio for galaxies with Vmax<125km/s. (4 data files).

Evolving R Coronae Borealis Stars with MESA

NASA Astrophysics Data System (ADS)

Clayton, Geoffrey C.; Lauer, Amber; Chatzopoulos, Emmanouil; Frank, Juhan

2018-01-01

R Coronae Borealis (RCB) stars form a small class of cool, carbon-rich supergiants that have almost no hydrogen. They undergo extreme, irregular declines in brightness of up to 8 magnitudes due to the formation of thick clouds of carbon dust. Two scenarios have been proposed for the origin of an RCB star: the merger of a CO/He white dwarf (WD) binary and a final helium-shell flash. We are using a combination of 3D hydrodynamics codes and the 1D MESA (Modules for Experiments in Stellar Astrophysics) stellar evolution code including nucleosynthesis to construct post-merger spherical models based on realistic merger progenitor models and on our hydrodynamical simulations, and then following the evolution into the region of the HR diagram where RCB stars are located. We are investigating nucleosynthesis in the dynamically accreting material of CO/He WD mergers which may provide a suitable environment for significant production of 18O and the very low 16O/18O values observed.Our MESA modeling consists of two steps: first mimicking the WD merger event using two different techniques, (a) by choosing a very high mass accretion rate with appropriate abundances and (b) by applying "stellar engineering" to an initial CO WD model to account for the newly merged material by applying an entropy adjusting procedure. Second, we follow the post-merger evolution using a large nuclear reaction network including the effects of convective and rotational instabilities to the mixing of material in order to match the observed RCB abundances. MESA follows the evolution of the merger product as it expands and cools to become an RCB star. We then examine the surface abundances and compare them to the observed RCB abundances. We also investigate how long fusion continues in the He shell near the core and how this processed material is mixed up to the surface of the star. We then model the later evolution of RCB stars to determine their likely lifetimes and endpoints when they have returned to being a WD. Solving the mystery of how the RCB stars evolve will lead to a better understanding of other important types of stellar merger events such as Type Ia SNe.

The stellar population and luminosity function in M31 bulge and Inner Disk Fields

NASA Technical Reports Server (NTRS)

Rich, R. Michael; Mould, J. R.; Graham, James R.

1993-01-01

We report infrared photometry and stellar identifications for stars in five fields in the M31 bulge located from 2 to 11 arcmin from the nucleus. These fields have been chosen such that the bulge/disk star ratio predicted from Kent's (1989) small bulge model varies from 7:1 to 1:5, allowing a study of near pure disk and near pure bulge stellar populations. We reject the hypothesis of Davies et al. (1991) that luminous stars found within 500 pc of the nucleus are due to a contaminating disk population. We find that the bulge contains stars in excess of M(sub bol) = -5 mag and that the bulge luminosity function has a distinct shape different from the disk fields. We find many stars redder than (J-K) = 2 mag, and suggest that these stars may be the counterparts of the IRAS-selected Galactic bulge Miras studied by Whitelock et at. (1991). The number of bright stars (M(sub bol) is less than -5 mag) falls off more rapidly than the r band surface brightness. By building model fields out of a bulge luminosity function and artificial stars, we are able to show that the change in the luminosity function toward the center cannot be explained simply by the mismeasurement of overcrowded star images. However, these tests also raise the possibility that the asymptotic giant branch (AGB) tip may be approximately equal to 1 mag fainter than actually measured in our most crowded field, reaching only M(sub bol) = -5. We compare observed counts of AGB stars with those predicted from theoretical lifetimes using a technique of general interest for this problem, the Fuel Consumption Theorem of Renzini & Buzzoni (1986) Spectral Evolution of Galaxies (Reidel, Dordrecht). Our methodology is generally applicable to the study of other resolved extragalactic stellar populations. The number of observed stars per magnitude up to a luminosity of M(bol) = -5.5 mag is consistent with AGB evolution of the whole population of the innermost bulge field with the standard lifetime on the AGB of 1.3 Myr/mag. We advance the possibility that the bulge of M31 may be younger than the oldest Galactic globular clusters. We note that M33 has recently been found to have an r(exp 1/4)-law spheroid consisting of intermediate-age stars; bulges can form later than the old halo population.

A sudden brightness decrease of the young pre-MS object GM Cep

NASA Astrophysics Data System (ADS)

Munari, U.; Castellani, F.; Giannini, T.; Antoniucci, S.; Lorenzetti, D.

2017-11-01

In the framework of our EXor monitoring programme dubbed EXORCISM (EXOR OptiCal and Infrared Systematic Monitoring - Antoniucci et al. 2013 PPVI, Lorenzetti et al. 2007 ApJ 665, 1182; Lorenzetti et al. 2009 ApJ 693, 1056), we observed a new fading of the optical brightness of the Young Stellar Object (YSO) GM Cep (d=870 pc). This is a well studied variable (Semkov & Peneva 2012 APSS,338,95; Ibryamov et al. 2015 PASA,32,11; Xiao, Kroll, & Henden 2010 AJ, 139, 1527; Sicilia-Aguilar et al. 2008 ApJ,673,382-3) whose light-curve is dominated by recurrent brightness dims, interpreted as non-periodical eclipse events due to orbiting dust structures that move along the line of sight (UXor-type variability - Grinin 1988).

VizieR Online Data Catalog: Calibrator stars catalog for interferometers (Swihart+, 2017)

NASA Astrophysics Data System (ADS)

Swihart, S. J.; Garcia, E. V.; Stassun, K. G.; van Belle, G.; Mutterspaugh, M. W.; Elias, N.

2017-04-01

In order to obtain accurate stellar angular sizes, each star was fit with a model SED using the fitting routine sedFit, written by A. Boden (van Belle & von Braun, 2009, Cat. J/ApJ/694/1085; van Belle et al. 2016, Cat. J/AJ/152/16). We compiled a list of positions, spectral types and visual magnitudes for ~3000 bright (Vmag<6) stars in the northern hemisphere with declinations -15°<δ<82° using the SIMBAD database (Wenger et al., 2000A&AS..143....9W). We chose a brightness limit (Vmag<6) given that most visible light interferometers can obtain scientifically useful data on bright stars. We also removed any stars which appear in the JMMC bad calibrator list. (4 data files).

A distance of 133-137 parsecs to the Pleiades star cluster.

PubMed

Pan, Xiaopei; Shao, M; Kulkarni, S R

2004-01-22

Nearby 'open' clusters of stars (those that are not gravitationally bound) have played a crucial role in the development of stellar astronomy because, as a consequence of the stars having a common age, they provide excellent natural laboratories to test theoretical stellar models. Clusters also play a fundamental part in determining distance scales. The satellite Hipparcos surprisingly found that an extensively studied open cluster--the Pleiades (also known as the Seven Sisters)--had a distance of D = 118 +/- 4 pc (refs 2, 3), about ten per cent smaller than the accepted value. The discrepancy generated a spirited debate because the implication was that either current stellar models were incorrect by a surprising amount or Hipparcos was giving incorrect distances. Here we report the orbital parameters of the bright double star Atlas in the Pleiades, using long-baseline optical/infrared interferometry. From the data we derive a firm lower bound of D > 127 pc, with the most likely range being 133 < D < 137 pc. Our result reaffirms the fidelity of current stellar models.

A Period-Activity Relation for Active RS CVN Stars

NASA Astrophysics Data System (ADS)

Simon, Theodore

Soft X ray observations of RS CVn binaries point to a correlation between L x /Lbol (the X ray to bolometric luminosity ratio that measures the coronal heating rate) and Omega (the stellar angular velocity). This correlation is almost certainly caused by a stellar dynamo, operating in rapidly-rotating late-type stars with deep convection zones. We are proposing to extend the X ray "rotation-activity relation" to the uv transition region and chromospheric emission lines observable with IUE. If the non-radiative heating rates of stellar transition regions and chromospheres are determined largely by magnetic processes associated with a stellar dynamo, then a similar correlation may be found. We have selected a group of recently discovered active long-period systems, which we believe will be very bright at uv wavelengths. One important goal of this program is to determine whether past studies of the "rotation-activity connection" have been compromised by the omission of active long-period RS CVn systems.

Accretion-induced variability links young stellar objects, white dwarfs, and black holes.

PubMed

Scaringi, Simone; Maccarone, Thomas J; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R; Aranzana, Ester; Dhillon, Vikram S; Barros, Susana C C

2015-10-01

The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.

Accretion-induced variability links young stellar objects, white dwarfs, and black holes

PubMed Central

Scaringi, Simone; Maccarone, Thomas J.; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R.; Aranzana, Ester; Dhillon, Vikram S.; Barros, Susana C. C.

2015-01-01

The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies. PMID:26601307

C IV absorption-line variability in X-ray-bright broad absorption-line quasi-stellar objects

NASA Astrophysics Data System (ADS)

Joshi, Ravi; Chand, Hum; Srianand, Raghunathan; Majumdar, Jhilik

2014-07-01

We report the kinematic shift and strength variability of the C IV broad absorption-line (BAL) trough in two high-ionization X-ray-bright quasi-stellar objects (QSOs): SDSS J085551+375752 (at zem ˜ 1.936) and SDSS J091127+055054 (at zem ˜ 2.793). Both these QSOs have shown a combination of profile shifts and the appearance and disappearance of absorption components belonging to a single BAL trough. The observed average kinematic shift of the whole BAL profile resulted in an average deceleration of ˜-0.7 ± 0.1, -2.0 ± 0.1 cm s-2 over rest-frame time-spans of 3.11 and 2.34 yr for SDSS J085551+375752 and SDSS J091127+055054, respectively. To our knowledge, these are the largest kinematic shifts known, exceeding by factors of about 2.8 and 7.8 the highest deceleration reported in the literature; this makes both objects potential candidates to investigate outflows using multiwavelength monitoring of their line and continuum variability. We explore various possible mechanisms to understand the observed profile variations. Outflow models involving many small self-shielded clouds, probably moving in a curved path, provide the simplest explanation for the C IV BAL strength and velocity variations, along with the X-ray-bright nature of these sources.

VizieR Online Data Catalog: GALEX/S4G surface brightness profiles. I. (Bouquin+, 2018)

NASA Astrophysics Data System (ADS)

Bouquin, A. Y. K.; Gil de, Paz A.; Munoz-Mateos, J. C.; Boissier, S.; Sheth, K.; Zaritsky, D.; Peletier, R. F.; Knapen, J. H.; Gallego, J.

2018-03-01

The Spitzer Survey of Stellar Structure in Galaxies (S4

LUMINOUS AND HIGH STELLAR MASS CANDIDATE GALAXIES AT z Almost-Equal-To 8 DISCOVERED IN THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan Haojing; Finkelstein, Steven L.; Huang, Kuang-Han

One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey is to track galaxy evolution back to z Almost-Equal-To 8. Its two-tiered ''wide and deep'' strategy bridges significant gaps in existing near-infrared surveys. Here we report on z Almost-Equal-To 8 galaxy candidates selected as F105W-band dropouts in one of its deep fields, which covers 50.1 arcmin{sup 2} to 4 ks depth in each of three near-infrared bands in the Great Observatories Origins Deep Survey southern field. Two of our candidates have J < 26.2 mag, and are >1 mag brighter than any previously known F105W-dropouts.more » We derive constraints on the bright end of the rest-frame ultraviolet luminosity function of galaxies at z Almost-Equal-To 8, and show that the number density of such very bright objects is higher than expected from the previous Schechter luminosity function estimates at this redshift. Another two candidates are securely detected in Spitzer Infrared Array Camera images, which are the first such individual detections at z Almost-Equal-To 8. Their derived stellar masses are on the order of a few Multiplication-Sign 10{sup 9} M{sub Sun }, from which we obtain the first measurement of the high-mass end of the galaxy stellar mass function at z Almost-Equal-To 8. The high number density of very luminous and very massive galaxies at z Almost-Equal-To 8, if real, could imply a large stellar-to-halo mass ratio and an efficient conversion of baryons to stars at such an early time.« less

Synthesizing Planetary Nebulae for Large Scale Surveys: Predictions for LSST

NASA Astrophysics Data System (ADS)

Vejar, George; Montez, Rodolfo; Morris, Margaret; Stassun, Keivan G.

2017-01-01

The short-lived planetary nebula (PN) phase of stellar evolution is characterized by a hot central star and a bright, ionized, nebula. The PN phase forms after a low- to intermediate-mass star stops burning hydrogen in its core, ascends the asymptotic giant branch, and expels its outer layers of material into space. The exposed hot core produces ionizing UV photons and a fast stellar wind that sweeps up the surrounding material into a dense shell of ionized gas known as the PN. This fleeting stage of stellar evolution provides insight into rare atomic processes and the nucleosynthesis of elements in stars. The inherent brightness of the PNe allow them to be used to obtain distances to nearby stellar systems via the PN luminosity function and as kinematic tracers in other galaxies. However, the prevalence of non-spherical morphologies of PNe challenge the current paradigm of PN formation. The role of binarity in the shaping of the PN has recently gained traction ultimately suggesting single stars might not form PN. Searches for binary central stars have increased the binary fraction but the current PN sample is incomplete. Future wide-field, multi-epoch surveys like the Large Synoptic Survey Telescope (LSST) can impact studies of PNe and improve our understanding of their origin and formation. Using a suite of Cloudy radiative transfer calculations, we study the detectability of PNe in the proposed LSST multiband observations. We compare our synthetic PNe to common sources (stars, galaxies, quasars) and establish discrimination techniques. Finally, we discuss follow-up strategies to verify new LSST-discovered PNe and use limiting distances to estimate the potential sample of PNe enabled by LSST.

SDSS-IV MaNGA: faint quenched galaxies - I. Sample selection and evidence for environmental quenching

NASA Astrophysics Data System (ADS)

Penny, Samantha J.; Masters, Karen L.; Weijmans, Anne-Marie; Westfall, Kyle B.; Bershady, Matthew A.; Bundy, Kevin; Drory, Niv; Falcón-Barroso, Jesús; Law, David; Nichol, Robert C.; Thomas, Daniel; Bizyaev, Dmitry; Brownstein, Joel R.; Freischlad, Gordon; Gaulme, Patrick; Grabowski, Katie; Kinemuchi, Karen; Malanushenko, Elena; Malanushenko, Viktor; Oravetz, Daniel; Roman-Lopes, Alexandre; Pan, Kaike; Simmons, Audrey; Wake, David A.

2016-11-01

Using kinematic maps from the Sloan Digital Sky Survey (SDSS) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we reveal that the majority of low-mass quenched galaxies exhibit coherent rotation in their stellar kinematics. Our sample includes all 39 quenched low-mass galaxies observed in the first year of MaNGA. The galaxies are selected with Mr > -19.1, stellar masses 109 M⊙ < M* < 5 × 109 M⊙, EWHα < 2 Å, and all have red colours (u - r) > 1.9. They lie on the size-magnitude and σ-luminosity relations for previously studied dwarf galaxies. Just six (15 ± 5.7 per cent) are found to have rotation speeds ve, rot < 15 km s-1 at ˜1 Re, and may be dominated by pressure support at all radii. Two galaxies in our sample have kinematically distinct cores in their stellar component, likely the result of accretion. Six contain ionized gas despite not hosting ongoing star formation, and this gas is typically kinematically misaligned from their stellar component. This is the first large-scale Integral Field Unit (IFU) study of low-mass galaxies selected without bias against low-density environments. Nevertheless, we find the majority of these galaxies are within ˜1.5 Mpc of a bright neighbour (MK < -23; or M* > 5 × 1010 M⊙), supporting the hypothesis that galaxy-galaxy or galaxy-group interactions quench star formation in low-mass galaxies. The local bright galaxy density for our sample is ρproj = 8.2 ± 2.0 Mpc-2, compared to ρproj = 2.1 ± 0.4 Mpc-2 for a star-forming comparison sample, confirming that the quenched low-mass galaxies are preferentially found in higher density environments.

Radial Distribution of X-Ray Point Sources Near the Galactic Center

NASA Astrophysics Data System (ADS)

Hong, Jae Sub; van den Berg, Maureen; Grindlay, Jonathan E.; Laycock, Silas

2009-11-01

We present the log N-log S and spatial distributions of X-ray point sources in seven Galactic bulge (GB) fields within 4° from the Galactic center (GC). We compare the properties of 1159 X-ray point sources discovered in our deep (100 ks) Chandra observations of three low extinction Window fields near the GC with the X-ray sources in the other GB fields centered around Sgr B2, Sgr C, the Arches Cluster, and Sgr A* using Chandra archival data. To reduce the systematic errors induced by the uncertain X-ray spectra of the sources coupled with field-and-distance-dependent extinction, we classify the X-ray sources using quantile analysis and estimate their fluxes accordingly. The result indicates that the GB X-ray population is highly concentrated at the center, more heavily than the stellar distribution models. It extends out to more than 1fdg4 from the GC, and the projected density follows an empirical radial relation inversely proportional to the offset from the GC. We also compare the total X-ray and infrared surface brightness using the Chandra and Spitzer observations of the regions. The radial distribution of the total infrared surface brightness from the 3.6 band μm images appears to resemble the radial distribution of the X-ray point sources better than that predicted by the stellar distribution models. Assuming a simple power-law model for the X-ray spectra, the closer to the GC the intrinsically harder the X-ray spectra appear, but adding an iron emission line at 6.7 keV in the model allows the spectra of the GB X-ray sources to be largely consistent across the region. This implies that the majority of these GB X-ray sources can be of the same or similar type. Their X-ray luminosity and spectral properties support the idea that the most likely candidate is magnetic cataclysmic variables (CVs), primarily intermediate polars (IPs). Their observed number density is also consistent with the majority being IPs, provided the relative CV to star density in the GB is not smaller than the value in the local solar neighborhood.

Giant stellar-wind shell associated with the H II region M16

NASA Astrophysics Data System (ADS)

Sofue, Y.; Handa, T.; Fuerst, E.; Reich, W.; Reich, P.

The detection of a giant radio continuum shell associated with the bright H II region M16, one of the most active star-forming sites in the Sagittarius arm, is reported. The shell structure agrees with that predicted by the stellar wind bubble model. The innermost regions of the shell is a cavity dominated by a stellar wind from early-type stars and is bounded by shocked H II gas. The shell is observed as a thermal radio emission loop. The rate of kinetic energy injection from the central O stars is estimated to be 3.3 x 10 to the 36th ergs/s, and the corresponding mass loss rate is 2.6 x 10 to the -6th solar mass/yr, with an age of the shell being about 7 million yr.

The Value of Change: Surprises and Insights in Stellar Evolution

NASA Astrophysics Data System (ADS)

Bildsten, Lars

2018-01-01

Astronomers with large-format cameras regularly scan the sky many times per night to detect what's changing, and telescopes in space such as Kepler and, soon, TESS obtain very accurate brightness measurements of nearly a million stars over time periods of years. These capabilities, in conjunction with theoretical and computational efforts, have yielded surprises and remarkable new insights into the internal properties of stars and how they end their lives. I will show how asteroseismology reveals the properties of the deep interiors of red giants, and highlight how astrophysical transients may be revealing unusual thermonuclear outcomes from exploding white dwarfs and the births of highly magnetic neutron stars. All the while, stellar science has been accelerated by the availability of open source tools, such as Modules for Experiments in Stellar Astrophysics (MESA), and the nearly immediate availability of observational results.

UIT Observations of Early-Type Galaxies and Analysis of the FUSE Spectrum of a Subdwarf B Star

NASA Technical Reports Server (NTRS)

Ohl, Raymond G.; Krebs, Carolyn (Technical Monitor)

2001-01-01

This work covers Ultraviolet Imaging Telescope (UIT) observations of early-type galaxies (155 nm) and Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of a Galactic subdwarf B star (sdB). Early UV space astronomy missions revealed that early-type galaxies harbor a population of stars with effective temperatures greater than that of the main sequence turn-off (about 6,000 K) and UV emission that is very sensitive to characteristics of the stellar population. We present UV (155 nm) surface photometry and UV-B color profiles for 8 E and SO galaxies observed by UIT. Some objects have de Vaucouleurs surface brightness profiles, while others have disk-like profiles, but we find no other evidence for the presence of a disk or young, massive stars. There is a wide range of UV-B color gradients, but there is no correlation with metallicity gradients. SdB stars are the leading candidate UV emitters in old, high metallicity stellar populations (e.g., early-type galaxies). We observed the Galactic sdB star PG0749+658 with FUSE and derived abundances with the aim of constraining models of the heavy element distribution in sdB atmospheres. All of the elements measured are depleted with respect to solar, except for Cr and Mn, which are about solar, and Ni, which is enhanced. This work was supported in part by NASA grants NAG5-700 and NAG5-6403 to the University of Virginia and NAS5-32985 to Johns Hopkins University.

Towards a coherent view of mass loss in Betelgeuse from the photosphere to the interstellar medium

NASA Astrophysics Data System (ADS)

Montarges, Miguel; Kervella, Pierre; Perrin, Guy

2013-06-01

Massive evolved stars contribute to the chemical enrichment of the interstellar medium (ISM), the Galaxy and ultimately the Universe through their mass loss. From the photosphere to the ISM, large convective motions, low surface gravity and high brightness combine to trigger an intense stellar wind. The released material evolves chemically as the distance from the star increases, and eventually forms dust particles. The involved physical and chemical processes are central to apprehend the cosmic impact of massive evolved stars, but they are poorly understood: the surface convection remains essentially uncharacterized, as the composition of the wind, and the role of the magnetic field is unknown. Betelgeuse is the closest red supergiant and therefore it stands out as the best candidate to obtain detailed observations of the close circumstellar environment of a massive evolved star. We are currently running a high angular resolution observations program to obtain a multi-wavelength and multi-epoch characterisation of this star. Using the IOTA interferometer, Haubois et al. reconstructed an image of the photosphere of the star. Within 1 to 100 stellar radii, the VLT and VLTI allowed us to probe the compact molecular envelope of Betelgeuse (the MOLsphere) in the near-infrared, and the extended dusty envelope in the thermal infrared domain. They were recently completed with HST/STIS observations of the chromosphere in the UV, whose location is surprisingly coincident with the MOLsphere. We will present a brief review of our recent results and of our ongoing work on Betelgeuse.

Improving distance estimates to nearby bright stars: Combining astrometric data from Hipparcos, Nano-JASMINE and Gaia

NASA Astrophysics Data System (ADS)

Michalik, Daniel; Lindegren, Lennart; Hobbs, David; Lammers, Uwe; Yamada, Yoshiyuki

2013-02-01

Starting in 2013, Gaia will deliver highly accurate astrometric data, which eventually will supersede most other stellar catalogues in accuracy and completeness. It is, however, limited to observations from magnitude 6 to 20 and will therefore not include the brightest stars. Nano-JASMINE, an ultrasmall Japanese astrometry satellite, will observe these bright stars, but with much lower accuracy. Hence, the Hipparcos catalogue from 1997 will likely remain the main source of accurate distances to bright nearby stars. We are investigating how this might be improved by optimally combining data from all three missions through a joint astrometric solution. This would take advantage of the unique features of each mission: the historic bright-star measurements of Hipparcos, the updated bright-star observations of Nano-JASMINE, and the very accurate reference frame of Gaia. The long temporal baseline between the missions provides additional benefits for the determination of proper motions and binary detection, which indirectly improve the parallax determination further. We present a quantitative analysis of the expected gains based on simulated data for all three missions.

Coronagraphic Imaging with HST and STIS

NASA Technical Reports Server (NTRS)

Grady, C. A.; Proffitt, C.; Malumuth, E.; Woodgate, B. E.; Gull, T. R.; Bowers, C. W.; Heap, S. R.; Kimble, R. A.; Lindler, D.; Plait, P.

2002-01-01

Revealing faint circumstellar nebulosity and faint stellar or substellar companions to bright stars typically requires use of techniques for rejecting the direct, scattered, and diffracted light of the star. One such technique is Lyot coronagraphy. We summarize the performance of the white-light coronagraphic capability of the Space Telescope Imaging spectrograph, on board the Hubble Space Telescope.

Properties of the O-type giants and supergiants in 30 Doradus

NASA Astrophysics Data System (ADS)

Ramírez-Agudelo, O. H.; VFTS Consortium

2017-11-01

We discuss the stellar and wind properties of 72 presumably single O-type giants, bright giants, and supergiants in the 30 Doradus region. This sample constitutes the largest and most homogeneous sample of such stars ever analyzed and offers the opportunity to test models describing their main-sequence evolution.

The VIMOS Ultra-Deep Survey: A major merger origin for the high fraction of galaxies at 2 < z < 6 with two bright clumps

NASA Astrophysics Data System (ADS)

Ribeiro, B.; Le Fèvre, O.; Cassata, P.; Garilli, B.; Lemaux, B. C.; Maccagni, D.; Schaerer, D.; Tasca, L. A. M.; Zamorani, G.; Zucca, E.; Amorín, R.; Bardelli, S.; Hathi, N. P.; Koekemoer, A.; Pforr, J.

2017-11-01

The properties of stellar clumps in star-forming galaxies and their evolution over the redshift range 2 ≲ z ≲ 6 are presented and discussed in the context of the build-up of massive galaxies at early cosmic times. We focused on galaxies with spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS) and stellar masses log 10(M⋆/M⊙) > -0.204 × (z-4.5) + 9.35. We analyzed HST-ACS images to identify clumps within a 20 kpc radius using a method taking into account differential surface brightness dimming and luminosity evolution with redshift. We find that the population of galaxies with more than one clump is dominated by galaxies with two clumps, representing 21-25% of the population, while the fraction of galaxies with three, or four and more, clumps is 8-11% and 7-9%, respectively. The fraction of clumpy galaxies is in the range 35-55% over 2 < z < 6, increasing at higher redshifts, indicating that the fraction of irregular galaxies remains high up to the highest redshifts. The large and bright clumps (M⋆ 109 up to 1010 M⊙) are found to reside predominantly in galaxies with two clumps. Smaller and lower luminosity clumps (M⋆ < 109 M⊙) are found in galaxies with three clumps or more. We interpret these results as evidence for two different modes of clump formation working in parallel. The small low luminosity clumps are likely the result of disk fragmentation, with violent disk instabilities (VDI) forming several long-lived clumps in-situ as suggested from simulations. A fraction of these clumps is also likely coming from minor mergers as confirmed from spectroscopy in several cases. The clumps in the dominating population of galaxies with two clumps are significantly more massive and have properties akin to those in galaxy pairs undergoing massive merging observed at similar redshifts; they appear as more massive than the most massive clumps observed in numerical simulations of disks with VDI. We infer from these properties that the bright and large clumps are most likely the result of major mergers bringing-in ex situ matter onto a galaxy, and we derive a high major merger fraction of 20%. The diversity of clump properties therefore suggests that the assembly of star-forming galaxies at z 2-6 proceeds from several different dissipative processes including an important contribution from major and minor mergers. Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Program 185.A-0791.

Prevalence of Earth-size planets orbiting Sun-like stars.

PubMed

Petigura, Erik A; Howard, Andrew W; Marcy, Geoffrey W

2013-11-26

Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration's Kepler mission. We found 603 planets, including 10 that are Earth size ( ) and receive comparable levels of stellar energy to that of Earth (1 - 2 R[Symbol: see text] ). We account for Kepler's imperfect detectability of such planets by injecting synthetic planet-caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that 11 ± 4% of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to ~200 d. Extrapolating, one finds 5.7(-2.2)(+1.7)% of Sun-like stars harbor an Earth-size planet with orbital periods of 200-400 d.

Prevalence of Earth-size planets orbiting Sun-like stars

PubMed Central

Petigura, Erik A.; Howard, Andrew W.; Marcy, Geoffrey W.

2013-01-01

Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration’s Kepler mission. We found 603 planets, including 10 that are Earth size () and receive comparable levels of stellar energy to that of Earth (). We account for Kepler’s imperfect detectability of such planets by injecting synthetic planet–caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that 11 ± 4% of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to ∼200 d. Extrapolating, one finds % of Sun-like stars harbor an Earth-size planet with orbital periods of 200–400 d. PMID:24191033

The DiskMass Survey. VII. The distribution of luminous and dark matter in spiral galaxies

NASA Astrophysics Data System (ADS)

Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Bershady, Matthew A.; Andersen, David R.; Swaters, Rob A.

2013-09-01

We present dynamically-determined rotation-curve mass decompositions of 30 spiral galaxies, which were carried out to test the maximum-disk hypothesis and to quantify properties of their dark-matter halos. We used measured vertical velocity dispersions of the disk stars to calculate dynamical mass surface densities (Σdyn). By subtracting our observed atomic and inferred molecular gas mass surface densities from Σdyn, we derived the stellar mass surface densities (Σ∗), and thus have absolute measurements of all dominant baryonic components of the galaxies. Using K-band surface brightness profiles (IK), we calculated the K-band mass-to-light ratio of the stellar disks (Υ∗ = Σ∗/IK) and adopted the radial mean (overline{mls}) for each galaxy to extrapolate Σ∗ beyond the outermost kinematic measurement. The derived overline{mls} of individual galaxies are consistent with all galaxies in the sample having equal Υ∗. We find a sample average and scatter of mlab overline{mls}mrab = 0.31 ± 0.07. Rotation curves of the baryonic components were calculated from their deprojected mass surface densities. These were used with circular-speed measurements to derive the structural parameters of the dark-matter halos, modeled as either a pseudo-isothermal sphere (pISO) or a Navarro-Frenk-White (NFW) halo. In addition to our dynamically determined mass decompositions, we also performed alternative rotation-curve decompositions by adopting the traditional maximum-disk hypothesis. However, the galaxies in our sample are submaximal, such that at 2.2 disk scale lengths (hR) the ratios between the baryonic and total rotation curves (Fb2.2hR) are less than 0.75. We find this ratio to be nearly constant between 1-6hR within individual galaxies. We find a sample average and scatter of mlab Fb2.2hRmrab = 0.57 ± 0.07, with trends of larger Fb2.2hR for more luminous and higher-surface-brightness galaxies. To enforce these being maximal, we need to scale Υ∗ by a factor 3.6 on average. In general, the dark-matter rotation curves are marginally better fit by a pISO than by an NFW halo. For the nominal-Υ∗ (submaximal) case, we find that the derived NFW-halo parameters have values consistent with ΛCDM N-body simulations, suggesting that the baryonic matter in our sample of galaxies has only had a minor effect on the dark-matter distribution. In contrast, maximum-Υ∗ decompositions yield halo-concentration parameters that are too low compared to the ΛCDM simulations. Appendix is available in electronic form at http://www.aanda.org

The formation of submillimetre-bright galaxies from gas infall over a billion years.

PubMed

Narayanan, Desika; Turk, Matthew; Feldmann, Robert; Robitaille, Thomas; Hopkins, Philip; Thompson, Robert; Hayward, Christopher; Ball, David; Faucher-Giguère, Claude-André; Kereš, Dušan

2015-09-24

Submillimetre-bright galaxies at high redshift are the most luminous, heavily star-forming galaxies in the Universe and are characterized by prodigious emission in the far-infrared, with a flux of at least five millijanskys at a wavelength of 850 micrometres. They reside in haloes with masses about 10(13) times that of the Sun, have low gas fractions compared to main-sequence disks at a comparable redshift, trace complex environments and are not easily observable at optical wavelengths. Their physical origin remains unclear. Simulations have been able to form galaxies with the requisite luminosities, but have otherwise been unable to simultaneously match the stellar masses, star formation rates, gas fractions and environments. Here we report a cosmological hydrodynamic galaxy formation simulation that is able to form a submillimetre galaxy that simultaneously satisfies the broad range of observed physical constraints. We find that groups of galaxies residing in massive dark matter haloes have increasing rates of star formation that peak at collective rates of about 500-1,000 solar masses per year at redshifts of two to three, by which time the interstellar medium is sufficiently enriched with metals that the region may be observed as a submillimetre-selected system. The intense star formation rates are fuelled in part by the infall of a reservoir gas supply enabled by stellar feedback at earlier times, not through major mergers. With a lifetime of nearly a billion years, our simulations show that the submillimetre-bright phase of high-redshift galaxies is prolonged and associated with significant mass buildup in early-Universe proto-clusters, and that many submillimetre-bright galaxies are composed of numerous unresolved components (for which there is some observational evidence).

Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, X.; Cianciosa, M. R.; Ennis, D. A.

In this research, collimated soft X-ray (SXR) emissivity measurements from multi-channel cameras on the Compact Toroidal Hybrid (CTH) tokamak/torsatron device are incorporated in the 3D equilibrium reconstruction code V3FIT to reconstruct the shape of flux surfaces and infer the current distribution within the plasma. Equilibrium reconstructions of sawtoothing plasmas that use data from both SXR and external magnetic diagnostics show the central safety factor to be near unity under the assumption that SXR iso-emissivity contours lie on magnetic flux surfaces. The reconstruction results are consistent with those using the external magnetic data and a constraint on the location of qmore » = 1 surfaces determined from the sawtooth inversion surface extracted from SXR brightness profiles. The agreement justifies the use of approximating SXR emission as a flux function in CTH, at least within the core of the plasma, subject to the spatial resolution of the SXR diagnostics. Lastly, this improved reconstruction of the central current density indicates that the current profile peakedness decreases with increasing external transform and that the internal inductance is not a relevant measure of how peaked the current profile is in hybrid discharges.« less

Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements

NASA Astrophysics Data System (ADS)

Ma, X.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Herfindal, J. L.; Howell, E. C.; Knowlton, S. F.; Maurer, D. A.; Traverso, P. J.

2018-01-01

Collimated soft X-ray (SXR) emissivity measurements from multi-channel cameras on the Compact Toroidal Hybrid (CTH) tokamak/torsatron device are incorporated in the 3D equilibrium reconstruction code V3FIT to reconstruct the shape of flux surfaces and infer the current distribution within the plasma. Equilibrium reconstructions of sawtoothing plasmas that use data from both SXR and external magnetic diagnostics show the central safety factor to be near unity under the assumption that SXR iso-emissivity contours lie on magnetic flux surfaces. The reconstruction results are consistent with those using the external magnetic data and a constraint on the location of q = 1 surfaces determined from the sawtooth inversion surface extracted from SXR brightness profiles. The agreement justifies the use of approximating SXR emission as a flux function in CTH, at least within the core of the plasma, subject to the spatial resolution of the SXR diagnostics. This improved reconstruction of the central current density indicates that the current profile peakedness decreases with increasing external transform and that the internal inductance is not a relevant measure of how peaked the current profile is in hybrid discharges.

Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements

DOE PAGES

Ma, X.; Cianciosa, M. R.; Ennis, D. A.; ...

2018-01-31

In this research, collimated soft X-ray (SXR) emissivity measurements from multi-channel cameras on the Compact Toroidal Hybrid (CTH) tokamak/torsatron device are incorporated in the 3D equilibrium reconstruction code V3FIT to reconstruct the shape of flux surfaces and infer the current distribution within the plasma. Equilibrium reconstructions of sawtoothing plasmas that use data from both SXR and external magnetic diagnostics show the central safety factor to be near unity under the assumption that SXR iso-emissivity contours lie on magnetic flux surfaces. The reconstruction results are consistent with those using the external magnetic data and a constraint on the location of qmore » = 1 surfaces determined from the sawtooth inversion surface extracted from SXR brightness profiles. The agreement justifies the use of approximating SXR emission as a flux function in CTH, at least within the core of the plasma, subject to the spatial resolution of the SXR diagnostics. Lastly, this improved reconstruction of the central current density indicates that the current profile peakedness decreases with increasing external transform and that the internal inductance is not a relevant measure of how peaked the current profile is in hybrid discharges.« less

Determination of physical parameters of magnetic active regions in stars with different evolutionary stages

NASA Astrophysics Data System (ADS)

Biazzo, K.

2006-11-01

Understanding stellar magnetic activity phenomena is of paramount importance for stellar evolution and for planetary systems formation and their atmosphere and climate. The dynamo process that generates magnetic fields in stars is well understood and there is still no comprehensive model of solar and stellar magnetic activity. Stellar activity is characterized by tracers such as spots, plages, flares and winds. These features are the fingerprints of magnetic field lines and their detailed analysis provides constraints for theoretical models. Our knowledge can only advance if the active stars besides the Sun are included in our study. Therefore, it is essential to accomplish comprehensive studies of active stars with a wide range of stellar parameters and a variety of activity phenomena. In this thesis, I concentrate on emergence of active regions at photospheric and chromospheric levels, namely spots and plages, in stars with different evolutionary stages. Spots are cool areas on the surface of the stars and are supposed to be the result of the blocking effect on convection caused by magnetic flux-tube emersion. Plages are bright areas linked to emersion of magnetic flux tubes from the sub-photospheric convective level. Starspot temperature represents an important parameter for the investigation of stellar magnetic activity, but its precise determination, relying only on light curve inversion techniques, is strongly hampered by the lack of solution uniqueness. Therefore, a method based on line-depth ratios as temperature discriminant has been developed. This technique is capable of resolving temperature differences less than 10 K. Moreover, combining temperature and light curve solutions, I am able to determine in a univocal way starspot temperature and area. Using the net Halpha emission as indicator of plage presence, I have also studied the spot and plage association. As a matter of fact, the residual Halpha profiles, obtained as the difference between the observed spectra and non-active templates, allows to study the chromospheric structures simultaneously to the photospheric ones. In addition, I have also detected the intensity of the HeI-D3 line to analyse the presence of surface features in the high chromosphere. The observations of both standard and target stars have been performed with different instruments. In particular, the spectra have been acquired at Catania Astrophysical Observatory (Italy), Observatoire de Haute-Provence (France) and Nordic Optical Observatory (Canarian Islands). The photometric observations have been obtained at Catania Astrophysical Observatory, Fairnborn Observatory (USA) and Ege University Observatory (Turkey). Finally, starspot and plage physical parameters have been obtained for sixteen stars of different effective temperature and gravity and different evolutionary stages. The main results can be summarized as follows: - starspot temperatures are more similar to solar penumbrae; - dwarf stars tend to have smaller spots compared to giant stars; - stars with higher gravity seem to have cooler (relative to their photosphere) spots compared to stars with lower gravity; - spatial association exists between surface inhomogeneities at different atmospheric levels.

Detecting stellar-wind bubbles through infrared arcs in H II regions

NASA Astrophysics Data System (ADS)

Mackey, Jonathan; Haworth, Thomas J.; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert; Harries, Tim J.

2016-02-01

Mid-infrared arcs of dust emission are often seen near ionizing stars within H II regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional, radiation-hydrodynamics simulations of wind bubbles within H II regions around individual stars to predict the infrared emission properties of the dust within the H II region. We assume that dust and gas are dynamically well-coupled and that dust properties (composition, size distribution) are the same in the H II region as outside it, and that the wind bubble contains no dust. We post-process the simulations to make synthetic intensity maps at infrared wavebands using the torus code. We find that the outer edge of a wind bubble emits brightly at 24 μm through starlight absorbed by dust grains and re-radiated thermally in the infrared. This produces a bright arc of emission for slowly moving stars that have asymmetric wind bubbles, even for cases where there is no bow shock or any corresponding feature in tracers of gas emission. The 24 μm intensity decreases exponentially from the arc with increasing distance from the star because the dust temperature decreases with distance. The size distribution and composition of the dust grains has quantitative but not qualitative effects on our results. Despite the simplifications of our model, we find good qualitative agreement with observations of the H II region RCW 120, and can provide physical explanations for any quantitative differences. Our model produces an infrared arc with the same shape and size as the arc around CD -38°11636 in RCW 120, and with comparable brightness. This suggests that infrared arcs around O stars in H II regions may be revealing the extent of stellar wind bubbles, although we have not excluded other explanations.

Pulsating Stars

NASA Astrophysics Data System (ADS)

Catelan, M.; Smith, H. A.

2015-03-01

This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

Magnetic field strength of a neutron-star-powered ultraluminous X-ray source

NASA Astrophysics Data System (ADS)

Brightman, M.; Harrison, F. A.; Fürst, F.; Middleton, M. J.; Walton, D. J.; Stern, D.; Fabian, A. C.; Heida, M.; Barret, D.; Bachetti, M.

2018-04-01

Ultraluminous X-ray sources (ULXs) are bright X-ray sources in nearby galaxies not associated with the central supermassive black hole. Their luminosities imply they are powered by either an extreme accretion rate onto a compact stellar remnant, or an intermediate mass ( 100-105M⊙) black hole1. Recently detected coherent pulsations coming from three bright ULXs2-5 demonstrate that some of these sources are powered by accretion onto a neutron star, implying accretion rates significantly in excess of the Eddington limit, a high degree of geometric beaming, or both. The physical challenges associated with the high implied accretion rates can be mitigated if the neutron star surface field is very high (1014 G)6, since this suppresses the electron scattering cross-section, reducing the radiation pressure that chokes off accretion for high luminosities. Surface magnetic field strengths can be determined through cyclotron resonance scattering features7,8 produced by the transition of charged particles between quantized Landau levels. Here, we present the detection at a significance of 3.8σ of an absorption line at 4.5 keV in the Chandra spectrum of a ULX in M51. This feature is likely to be a cyclotron resonance scattering feature produced by the strong magnetic field of a neutron star. Assuming scattering off electrons, the magnetic field strength is implied to be 1011 G, while protons would imply a magnetic field of B 1015 G.

The Influence of Atomic Diffusion on Stellar Ages and Chemical Tagging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dotter, Aaron; Conroy, Charlie; Cargile, Phillip

2017-05-10

In the era of large stellar spectroscopic surveys, there is an emphasis on deriving not only stellar abundances but also the ages for millions of stars. In the context of Galactic archeology, stellar ages provide a direct probe of the formation history of the Galaxy. We use the stellar evolution code MESA to compute models with atomic diffusion—with and without radiative acceleration—and extra mixing in the surface layers. The extra mixing consists of both density-dependent turbulent mixing and envelope overshoot mixing. Based on these models we argue that it is important to distinguish between initial, bulk abundances (parameters) and current,more » surface abundances (variables) in the analysis of individual stellar ages. In stars that maintain radiative regions on evolutionary timescales, atomic diffusion modifies the surface abundances. We show that when initial, bulk metallicity is equated with current, surface metallicity in isochrone age analysis, the resulting stellar ages can be systematically overestimated by up to 20%. The change of surface abundances with evolutionary phase also complicates chemical tagging, which is the concept that dispersed star clusters can be identified through unique, high-dimensional chemical signatures. Stars from the same cluster, but in different evolutionary phases, will show different surface abundances. We speculate that calibration of stellar models may allow us to estimate not only stellar ages but also initial abundances for individual stars. In the meantime, analyzing the chemical properties of stars in similar evolutionary phases is essential to minimize the effects of atomic diffusion in the context of chemical tagging.« less

The 6dFGS Fundamental Plane

NASA Astrophysics Data System (ADS)

Springob, Chris M.; Colless, M.; Jones, D. H.; Magoulas, C.; Mould, J. R.; Campbell, L.; Lah, P.; Lucey, J.; Merson, A.; Proctor, R.

2010-01-01

The 6dF Galaxy Survey (6dFGS) is an all southern sky galaxy survey, including 125,000 redshifts and more than 10,000 peculiar velocities, making it the largest peculiar velocity sample to date. In combination with 2MASS surface brightnesses and effective radii, 6dFGS yields the near-infrared Fundamental Plane (FP) for a large and uniform sample. We have fit the FP relation for the galaxies in the peculiar velocity sample using a maximum likelihood method which allows us to precisely account for selection effects and observational errors. We investigate the effects of varying stellar populations and environments on the FP. Finally, we discuss the implications of these results both for our understanding of the origin of the FP for early-type galaxies and bulges and for deriving unbiased distances and peculiar velocities in the local universe.

IC 5181: An S0 Galaxy with Ionized Gas on Polar Orbits

NASA Astrophysics Data System (ADS)

Pizzella, A.; Morelli, L.; Corsini, E. M.; Dalla Bontá, E.; Cesetti, M.

2014-05-01

The nearby S0 galaxy IC 5181 is studied to address the origin of the ionized gas component that orbits the galaxy on polar orbit. We perform detailed photometric and spectroscopic observations measuring the surface brightness distribution of the stars (I band), ionized gas of IC 5181 (Hα narrow band), the ionized-gas and stellar kinematics along both the major and minor axis, and the corresponding line strengths of the Lick indices. We conclude that the galaxy hosts a geometrically and kinematically decoupled component of ionized gas. It is elongated along the galaxy minor axis and in orthogonal rotation with respect to the galaxy disk. The result is suggesting that the gas component is not related to the stars having an external origin. The gas was accreted by IC 5181 on polar orbits from the surrounding environment.

A near-infrared imaging survey of interacting galaxies - The disk-disk merger candidates subset

NASA Technical Reports Server (NTRS)

Stanford, S. A.; Bushouse, H. A.

1991-01-01

Near-infrared imaging obtained for systems believed to be advanced disk-disk mergers are presented and discussed. These systems were chosen from a sample of approximately 170 objects from the Arp Atlas of Peculiar Galaxies which have been imaged in the JHK bands as part of an investigation into the stellar component of interacting galaxies. Of the eight remnants which show optical signs of a disk-disk merger, the near-infrared surface brightness profiles are well-fitted by an r exp 1/4 law over all measured radii in four systems, and out to radii of about 3 kpc in three systems. These K band profiles indicate that most of the remnants in the sample either have finished or are in the process of relaxing into a mass distribution like that of normal elliptical galaxies.

Synchronous x-ray and radio mode switches: a rapid global transformation of the pulsar magnetosphere.

PubMed

Hermsen, W; Hessels, J W T; Kuiper, L; van Leeuwen, J; Mitra, D; de Plaa, J; Rankin, J M; Stappers, B W; Wright, G A E; Basu, R; Alexov, A; Coenen, T; Grießmeier, J-M; Hassall, T E; Karastergiou, A; Keane, E; Kondratiev, V I; Kramer, M; Kuniyoshi, M; Noutsos, A; Serylak, M; Pilia, M; Sobey, C; Weltevrede, P; Zagkouris, K; Asgekar, A; Avruch, I M; Batejat, F; Bell, M E; Bell, M R; Bentum, M J; Bernardi, G; Best, P; Bîrzan, L; Bonafede, A; Breitling, F; Broderick, J; Brüggen, M; Butcher, H R; Ciardi, B; Duscha, S; Eislöffel, J; Falcke, H; Fender, R; Ferrari, C; Frieswijk, W; Garrett, M A; de Gasperin, F; de Geus, E; Gunst, A W; Heald, G; Hoeft, M; Horneffer, A; Iacobelli, M; Kuper, G; Maat, P; Macario, G; Markoff, S; McKean, J P; Mevius, M; Miller-Jones, J C A; Morganti, R; Munk, H; Orrú, E; Paas, H; Pandey-Pommier, M; Pandey, V N; Pizzo, R; Polatidis, A G; Rawlings, S; Reich, W; Röttgering, H; Scaife, A M M; Schoenmakers, A; Shulevski, A; Sluman, J; Steinmetz, M; Tagger, M; Tang, Y; Tasse, C; ter Veen, S; Vermeulen, R; van de Brink, R H; van Weeren, R J; Wijers, R A M J; Wise, M W; Wucknitz, O; Yatawatta, S; Zarka, P

2013-01-25

Pulsars emit from low-frequency radio waves up to high-energy gamma-rays, generated anywhere from the stellar surface out to the edge of the magnetosphere. Detecting correlated mode changes across the electromagnetic spectrum is therefore key to understanding the physical relationship among the emission sites. Through simultaneous observations, we detected synchronous switching in the radio and x-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio-"bright" mode, the x-rays show only an unpulsed, nonthermal component. Conversely, when the pulsar is in a radio-"quiet" mode, the x-ray luminosity more than doubles and a 100% pulsed thermal component is observed along with the nonthermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.

Firework Nova

NASA Image and Video Library

2015-07-02

In Hollywood blockbusters, explosions are often among the stars of the show. In space, explosions of actual stars are a focus for scientists who hope to better understand their births, lives, and deaths and how they interact with their surroundings. Using NASA’s Chandra X-ray Observatory, astronomers have studied one particular explosion that may provide clues to the dynamics of other, much larger stellar eruptions. A team of researchers pointed the telescope at GK Persei, an object that became a sensation in the astronomical world in 1901 when it suddenly appeared as one of the brightest stars in the sky for a few days, before gradually fading away in brightness. Today, astronomers cite GK Persei as an example of a “classical nova,” an outburst produced by a thermonuclear explosion on the surface of a white dwarf star, the dense remnant of a Sun-like star.

Optimized Strategies for Detecting Extrasolar Space Weather

NASA Astrophysics Data System (ADS)

Hallinan, Gregg

2018-06-01

Fully understanding the implications of space weather for the young solar system, as well as the wider population of planet-hosting stars, requires remote sensing of space weather in other stellar systems. Solar coronal mass ejections can be accompanied by bright radio bursts at low frequencies (typically <100 MHz), that are produced as the resulting shockwave propagates through the corona and interplanetary medium.; searches for similar emissions are ongoing from nearby stellar systems. Exoplanets that encounter CMEs can increase in radio luminosity by orders of magnitude at kHz-MHz frequencies. A detection of this radio emission allows the direct measurement of the magnetic field strength of the planet, informing on whether the atmosphere of the planet can survive the intense magnetic activity of its host star. However, both stellar and planetary radio emission are highly variable and optimal strategies for detection of these emissions requires the capability to monitor 1000s of nearby stellar/planetary systems simultaneously. I will discuss optimized strategies for both ground and space-based experiments to take advantage of the highly variable nature of the radio emissions powered by extrasolar space weather to enable detection of stellar CMEs and planetary magnetospheres.

Simulation of the small-scale magnetism in main-sequence stellar atmospheres

NASA Astrophysics Data System (ADS)

Salhab, R. G.; Steiner, O.; Berdyugina, S. V.; Freytag, B.; Rajaguru, S. P.; Steffen, M.

2018-06-01

Context. Observations of the Sun tell us that its granular and subgranular small-scale magnetism has significant consequences for global quantities such as the total solar irradiance or convective blueshift of spectral lines. Aims: In this paper, properties of the small-scale magnetism of four cool stellar atmospheres, including the Sun, are investigated, and in particular its effects on the radiative intensity and flux. Methods: We carried out three-dimensional radiation magnetohydrodynamic simulations with the CO5BOLD code in two different settings: with and without a magnetic field. These are thought to represent states of high and low small-scale magnetic activity of a stellar magnetic cycle. Results: We find that the presence of small-scale magnetism increases the bolometric intensity and flux in all investigated models. The surplus in radiative flux of the magnetic over the magnetic field-free atmosphere increases with increasing effective temperature, Teff, from 0.47% for spectral type K8V to 1.05% for the solar model, but decreases for higher effective temperatures than solar. The degree of evacuation of the magnetic flux concentrations monotonically increases with Teff as does their depression of the visible optical surface, that is the Wilson depression. Nevertheless, the strength of the field concentrations on this surface stays remarkably unchanged at ≈1560 G throughout the considered range of spectral types. With respect to the surrounding gas pressure, the field strength is close to (thermal) equipartition for the Sun and spectral type F5V but is clearly sub-equipartition for K2V and more so for K8V. The magnetic flux concentrations appear most conspicuous for model K2V owing to their high brightness contrast. Conclusions: For mean magnetic flux densities of approximately 50 G, we expect the small-scale magnetism of stars in the spectral range from F5V to K8V to produce a positive contribution to their bolometric luminosity. The modulation seems to be most effective for early G-type stars.

HD 89345: a bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2

NASA Astrophysics Data System (ADS)

Van Eylen, V.; Dai, F.; Mathur, S.; Gandolfi, D.; Albrecht, S.; Fridlund, M.; García, R. A.; Guenther, E.; Hjorth, M.; Justesen, A. B.; Livingston, J.; Lund, M. N.; Pérez Hernández, F.; Prieto-Arranz, J.; Regulo, C.; Bugnet, L.; Everett, M. E.; Hirano, T.; Nespral, D.; Nowak, G.; Palle, E.; Silva Aguirre, V.; Trifonov, T.; Winn, J. N.; Barragán, O.; Beck, P. G.; Chaplin, W. J.; Cochran, W. D.; Csizmadia, S.; Deeg, H.; Endl, M.; Heeren, P.; Grziwa, S.; Hatzes, A. P.; Hidalgo, D.; Korth, J.; Mathis, S.; Montañes Rodriguez, P.; Narita, N.; Patzold, M.; Persson, C. M.; Rodler, F.; Smith, A. M. S.

2018-05-01

We report the discovery and characterization of HD 89345b (K2-234b; EPIC 248777106b), a Saturn-sized planet orbiting a slightly evolved star. HD 89345 is a bright star (V = 9.3 mag) observed by the K2 mission with one-minute time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding the mass and radius to be 1.12^{+0.04}_{-0.01} M_⊙ and 1.657^{+0.020}_{-0.004} R_⊙, respectively. The star appears to have recently left the main sequence, based on the inferred age, 9.4^{+0.4}_{-1.3} Gyr, and the non-detection of mixed modes. The star hosts a "warm Saturn" (P = 11.8 days, Rp = 6.86 ± 0.14 R⊕). Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of 35.7 ± 3.3 M⊕. The data also show that the planet's orbit is eccentric (e ≈ 0.2). An investigation of the rotational splitting of the oscillation frequencies of the star yields no conclusive evidence on the stellar inclination angle. We further obtained Rossiter-McLaughlin observations, which result in a broad posterior of the stellar obliquity. The planet seems to conform to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.

An Unusual Transient in the Extremely Metal-Poor Galaxy SDSS J094332.35+332657.6 (Leoncino Dwarf)

NASA Astrophysics Data System (ADS)

Filho, Mercedes E.; Sánchez Almeida, J.

2018-05-01

We have serendipitously discovered that Leoncino Dwarf, an ultra-faint, low-metallicity record-holder dwarf galaxy, may have hosted a transient source, and possibly exhibited a change in morphology, a shift in the center of brightness, and peak variability of the main (host) source in images taken approximately 40 yr apart; it is highly likely that these phenomena are related. Scenarios involving a Solar System object, a stellar cluster, dust enshrouding, and accretion variability have been considered, and discarded, as the origin of the transient. Although a combination of time-varying strong and weak lensing effects, induced by an intermediate mass black hole (104 - 5 × 105 M⊙) moving within the Milky Way halo (0.1 - 4 kpc), can conceivably explain all of the observed variable galaxy properties, it is statistically highly unlikely according to current theoretical predictions, and, therefore, also discarded. A cataclysmic event such as a supernova/hypernova could have occurred, as long as the event was observed towards the later/late-stage descent of the light curve, but this scenario fails to explain the absence of a post-explosion source and/or host HII region in recent optical images. An episode related to the giant eruption of a luminous blue variable star, a stellar merger or a nova, observed at, or near, peak magnitude may explain the transient source and possibly the change in morphology/center of brightness, but can not justify the main source peak variability, unless stellar variability is evoked.

Galactic Starburst NGC 3603 from X-Rays to Radio

NASA Technical Reports Server (NTRS)

Moffat, A. F. J.; Corcoran, M. F.; Stevens, I. R.; Skalkowski, G.; Marchenko, S. V.; Muecke, A.; Ptak, A.; Koribalski, B. S.; Brenneman, L.; Mushotzky, R.;

Variability Properties of Four Million Sources in the TESS Input Catalog Observed with the Kilodegree Extremely Little Telescope Survey

NASA Astrophysics Data System (ADS)

Oelkers, Ryan J.; Rodriguez, Joseph E.; Stassun, Keivan G.; Pepper, Joshua; Somers, Garrett; Kafka, Stella; Stevens, Daniel J.; Beatty, Thomas G.; Siverd, Robert J.; Lund, Michael B.; Kuhn, Rudolf B.; James, David; Gaudi, B. Scott

2018-01-01

The Kilodegree Extremely Little Telescope (KELT) has been surveying more than 70% of the celestial sphere for nearly a decade. While the primary science goal of the survey is the discovery of transiting, large-radii planets around bright host stars, the survey has collected more than 106 images, with a typical cadence between 10–30 minutes, for more than four million sources with apparent visual magnitudes in the approximate range 7< V< 13. Here, we provide a catalog of 52,741 objects showing significant large-amplitude fluctuations likely caused by stellar variability, as well as 62,229 objects identified with likely stellar rotation periods. The detected variability ranges in rms-amplitude from ∼3 mmag to ∼2.3 mag, and the detected periods range from ∼0.1 to ≳2000 days. We provide variability upper limits for all other ∼4,000,000 sources. These upper limits are principally a function of stellar brightness, but we achieve typical 1σ sensitivity on 30 min timescales down to ∼5 mmag at V∼ 8, and down to ∼43 mmag at V∼ 13. We have matched our catalog to the TESS Input catalog and the AAVSO Variable Star Index to precipitate the follow-up and classification of each source. The catalog is maintained as a living database on the Filtergraph visualization portal at the URL https://filtergraph.com/kelt_vars.

GASS 3505: the prototype of H I-excess, passive galaxies

NASA Astrophysics Data System (ADS)

Geréb, K.; Catinella, B.; Cortese, L.; Bekki, K.; Moran, S. M.; Schiminovich, D.

2016-10-01

We present our multiwavelength analysis of a prototype H I-excess galaxy, GASS 3505, selected based on having a large gas content (M_{H I} = 10^{9.9} M⊙) compared to its little associated star formation activity (˜0.1 M⊙ yr-1) in the GALEX Arecibo SDSS Survey (GASS). Very Large Array observations show that the H I in GASS 3505 is distributed in a regularly rotating, extended (˜50 kpc radius) gas ring. In the SDSS optical image GASS 3505 appears as a bulge-dominated galaxy, however deep optical imaging reveals low surface brightness (≳25 mag arcsec-2) stellar emission around the central bulge. Direct evidence for accretion is detected in form of an extended (˜60 kpc) stellar stream, showing that GASS 3505 has experienced a minor merger in the recent past. We investigate the possibility that the H I ring in GASS 3505 was accreted in such a merger event using N-body and smoothed particle hydrodynamic simulations. The best model that reproduces the general properties (I.e. gas distribution and kinematics, stellar morphology) of the galaxy involves a merger between the central bulge and a gas-rich (M⋆ = 109 M⊙ and M_{H I}/M⋆ = 10) disc galaxy. However, small discrepancies in the observed and modelled properties could suggest that other sources of gas have to be involved in the build-up of the gas reservoir. This work is the first step towards a larger program to investigate the physical mechanisms that drive the large scatter in the gas scaling relations of nearby galaxies.

Particle-physics constraints from the globular cluster M5: neutrino dipole moments

NASA Astrophysics Data System (ADS)

Viaux, N.; Catelan, M.; Stetson, P. B.; Raffelt, G. G.; Redondo, J.; Valcarce, A. A. R.; Weiss, A.

2013-10-01

Stellar evolution is modified if energy is lost in a "dark channel" similar to neutrino emission. Comparing modified stellar evolution sequences with observations provides some of the most restrictive limits on axions and other hypothetical low-mass particles and on non-standard neutrino properties. In particular, a putative neutrino magnetic dipole moment μν enhances the plasmon decay process, postpones helium ignition in low-mass stars, and therefore extends the red giant branch (RGB) in globular clusters (GCs). The brightness of the tip of the RGB (TRGB) remains the most sensitive probe for μν and we revisit this argument from a modern perspective. Based on a large set of archival observations, we provide high-precision photometry for the Galactic GC M5 (NGC 5904) and carefully determine its TRGB position. On the theoretical side, we add the extra plasmon decay rate brought about by μν to the Princeton-Goddard-PUC (PGPUC) stellar evolution code. Different sources of uncertainty are critically examined. The main source of systematic uncertainty is the bolometric correction and the main statistical uncertainty derives from the distance modulus based on main-sequence fitting. (Other measures of distance, e.g., the brightness of RR Lyrae stars, are influenced by the energy loss that we wish to constrain.) The statistical uncertainty of the TRGB position relative to the brightest RGB star is less important because the RGB is well populated. We infer an absolute I-band brightness of MI = -4.17 ± 0.13 mag for the TRGB compared with the theoretical prediction of - 3.99 ± 0.07 mag, in reasonable agreement with each other. A significant brightness increase caused by neutrino dipole moments is constrained such that μν < 2.6 × 10-12 μB (68% CL), where μB ≡ e/2me is the Bohr magneton, and μν < 4.5 × 10-12 μB (95% CL). In these results, statistical and systematic errors have been combined in quadrature. The photometric catalog is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A12

A radio jet from the optical and x-ray bright stellar tidal disruption flare ASASSN-14li.

PubMed

van Velzen, S; Anderson, G E; Stone, N C; Fraser, M; Wevers, T; Metzger, B D; Jonker, P G; van der Horst, A J; Staley, T D; Mendez, A J; Miller-Jones, J C A; Hodgkin, S T; Campbell, H C; Fender, R P

2016-01-01

The tidal disruption of a star by a supermassive black hole leads to a short-lived thermal flare. Despite extensive searches, radio follow-up observations of known thermal stellar tidal disruption flares (TDFs) have not yet produced a conclusive detection. We present a detection of variable radio emission from a thermal TDF, which we interpret as originating from a newly launched jet. The multiwavelength properties of the source present a natural analogy with accretion-state changes of stellar mass black holes, which suggests that all TDFs could be accompanied by a jet. In the rest frame of the TDF, our radio observations are an order of magnitude more sensitive than nearly all previous upper limits, explaining how these jets, if common, could thus far have escaped detection. Copyright © 2016, American Association for the Advancement of Science.

Long-slit optical spectroscopy of powerful far-infrared galaxies - The nature of the nuclear energy source

NASA Technical Reports Server (NTRS)

Armus, Lee; Heckman, Timothy M.; Miley, George K.

1989-01-01

Optical spectroscopic data are presented for a sample of 47 powerful far-IR galaxies chosen for IR spectral shape, and for six other IR-bright galaxies. The stellar absorption lines expected from a population of old stars are generally very weak in the nuclei of the galaxies. Very weak Mg I absorption is found in regions well off the nucleus, implying that the visible spectrum is dominated by young stars and not by an AGN. At least one, and probably five, of the galaxies have detectable WR emission features, providing additional evidence for a young stellar population. About 20 percent of the galaxies have strong Balmer absorption lines, indicating the presence of a substantial intermediate-age stellar population. The equivalent width of the H-alpha emission line can be modeled as arising from a mixture of a large young population and an intermediate-age population of stars.

Optical Region Spectrophotometry: Past and Present

NASA Astrophysics Data System (ADS)

Adelman, Saul J.

In the 1960s and 1970s optical region spectrophotometry achieved the status of a major tool in stellar research. New instrumentation, rotating grating scanners using photomultiplier tubes as detectors, and improved absolute calibrations of Vega made this possible. After this period the use of this technique declined to its near demise at present. The use of Vega as the primary standard has been both a blessing as it is so bright and a curse especially as modeling it correctly requires treating it as a fast rotating star seen nearly pole-on. It may be better to use several stars to define any future absolute calibration. With absolutely calibrated fluxes and Balmer profiles, often Hγ, investigators used the predictions of model atmospheres to find both the effective temperatures and the surface gravities of stars. The fluxes were photometrically calibrated low dispersion spectra with a typical resolution of order 25 Å. A typical data set consisted of 10-15 values covering most of the optical spectral region. At present two instrumental projects ACCESS and the ASTRA Spectrophotometer promise, respectively, a new substantially improved absolute calibration of the optical fluxes of several targets and the availability of a considerable amount of well-calibrated optical flux data for use in studies concerned with stellar properties. They jointly promise to revive optical region spectrophotometric studies.

Tracing the Mass of Early-type Galaxies using Planetary Nebulae

NASA Astrophysics Data System (ADS)

Sluis, A. P. N.; William, T. B.

2002-12-01

We report on observations of two ellipticals (NGC 3379 and NGC 1549) and two S0s (NGC 3384 and NGC 4636) performed with the Rutgers Fabry-Perot (RFP). The observations are part of a larger project to study the distribution of mass in the outer regions of early-type galaxies. Efforts to determine this distribution are generally hampered by the scarcity of useful tracers of the potential at large radii. Ellipticals and S0s have steep surface brightness profiles that make absorption line spectroscopy of the stellar population practically impossible beyond a few kpc from the center. Also, their gas content is low and does not extend far beyond the nucleus. Planetary Nebulae (PNe) offer a way around these problems: as remants of intermediate mass stars we expect them to follow the stellar light distribution and be numerous enough to be an effective tracer. PNe radiate hundreds of solar luminosities in a few emission lines (mostly [OIII] 5007 Å), making it possible to detect them over extragalactic distances and at the same time measure their line of sight velocities using the RFP. We present the photometry and the kinematics of the PN systems as well as some simple dynamical mass models for the four galaxies mentioned above.

The Kepler Mission: A Search for Terrestrial Planets - Development Status

NASA Technical Reports Server (NTRS)

Koch, David; Borucki, W.; Mayer, D.; Caldwell, D.; Jenkens, J.; Dunham, E.; Geary, J.; Bachtell, E.; Deininger, W.; Philbrick, R.

2003-01-01

We have embarked on a mission to detect terrestrial planets. The space mission has been optimized to search for earth-size planets (0.5 to 10 earth masses) in the habitable zone (HZ) of solar-like stars. Given this design, the mission will necessarily be capable of not only detecting Earth analogs, but a wide range of planetary types and characteristics ranging from Mercury-size objects with orbital periods of days to gas-giants in decade long orbits that have undeniable signatures even with only one transit detected. The mission is designed to survey the full range of spectral-type dwarf stars. The approach is to detect the periodic signal of transiting planets. Three or more transits of a star exceeding a combined threshold of eight sigma with a statistically consistent period, brightness change and duration provide a rigorous method of detection. From the relative brightness change the planet size can be calculated. From the period the orbital size can be calculated and its location relative to the HZ determined. Presented here are: the mission goals, the top level system design requirements derived from these goals that drive the flight system design, a number of the trades that have lead to the mission concept, expected photometric performance dependence on stellar brightness and spectral type based on the system 'noise tree' analysis. Updated estimates are presented of the numbers of detectable planets versus size, orbit, stellar spectral type and distances based on a planet frequency hypothesis. The current project schedule and organization are given.

Keck Observations of the UV-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205)

NASA Astrophysics Data System (ADS)

Dixon, William Van Dyke; Chayer, Pierre; Reid, Iain N.

2016-06-01

In color-magnitude diagrams of globular clusters, stars brighter than the horizontal branch and bluer than the red-giant branch are known as UV-bright stars. Most are evolving from the asymptotic giant branch (AGB) to the tip of the white-dwarf cooling curve. To better understand this important phase of stellar evolution, we have analyzed a Keck HIRES echelle spectrum of the UV-bright star Barnard 29 in M13. We begin by fitting the star's H I (Hα, Hβ, and Hγ) and He I lines with a grid of synthetic spectra generated from non-LTE H-He models computed using the TLUSTY code. We find that the shape of the star's Hα profile is not well reproduced with these models. Upgrading from version 200 to version 204M of TLUSTY solves this problem: the Hα profile is now well reproduced. TLUSTY version 204 includes improved calculations for the Stark broadening of hydrogen line profiles. Using these models, we derive stellar parameters of Teff = 21,100 K, log g = 3.05, and log (He/H) = -0.87, values consistent with those of previous authors. The star's Keck spectrum shows photospheric absorption from N II, O II, Mg II, Al III, Si II, Si III, S II, Ar II, and Fe III. The abundances of these species are consistent with published values for the red-giant stars in M13, suggesting that the star's chemistry has changed little since it left the AGB.

Gravity darkening in late-type stars. I. The Coriolis effect

NASA Astrophysics Data System (ADS)

Raynaud, R.; Rieutord, M.; Petitdemange, L.; Gastine, T.; Putigny, B.

2018-02-01

Context. Recent interferometric data have been used to constrain the brightness distribution at the surface of nearby stars, in particular the so-called gravity darkening that makes fast rotating stars brighter at their poles than at their equator. However, good models of gravity darkening are missing for stars that posses a convective envelope. Aim. In order to better understand how rotation affects the heat transfer in stellar convective envelopes, we focus on the heat flux distribution in latitude at the outer surface of numerical models. Methods: We carry out a systematic parameter study of three-dimensional, direct numerical simulations of anelastic convection in rotating spherical shells. As a first step, we neglect the centrifugal acceleration and retain only the Coriolis force. The fluid instability is driven by a fixed entropy drop between the inner and outer boundaries where stress-free boundary conditions are applied for the velocity field. Restricting our investigations to hydrodynamical models with a thermal Prandtl number fixed to unity, we consider both thick and thin (solar-like) shells, and vary the stratification over three orders of magnitude. We measure the heat transfer efficiency in terms of the Nusselt number, defined as the output luminosity normalised by the conductive state luminosity. Results: We report diverse Nusselt number profiles in latitude, ranging from brighter (usually at the onset of convection) to darker equator and uniform profiles. We find that the variations of the surface brightness are mainly controlled by the surface value of the local Rossby number: when the Coriolis force dominates the dynamics, the heat flux is weakened in the equatorial region by the zonal wind and enhanced at the poles by convective motions inside the tangent cylinder. In the presence of a strong background density stratification however, as expected in real stars, the increase of the local Rossby number in the outer layers leads to uniformisation of the surface heat flux distribution.

Stellar granulation as seen in disk-integrated intensity. II. Theoretical scaling relations compared with observations

NASA Astrophysics Data System (ADS)

Samadi, R.; Belkacem, K.; Ludwig, H.-G.; Caffau, E.; Campante, T. L.; Davies, G. R.; Kallinger, T.; Lund, M. N.; Mosser, B.; Baglin, A.; Mathur, S.; Garcia, R. A.

2013-11-01

Context. A large set of stars observed by CoRoT and Kepler shows clear evidence for the presence of a stellar background, which is interpreted to arise from surface convection, i.e., granulation. These observations show that the characteristic time-scale (τeff) and the root-mean-square (rms) brightness fluctuations (σ) associated with the granulation scale as a function of the peak frequency (νmax) of the solar-like oscillations. Aims: We aim at providing a theoretical background to the observed scaling relations based on a model developed in Paper I. Methods: We computed for each 3D model the theoretical power density spectrum (PDS) associated with the granulation as seen in disk-integrated intensity on the basis of the theoretical model published in Paper I. For each PDS we derived the associated characteristic time (τeff) and the rms brightness fluctuations (σ) and compared these theoretical values with the theoretical scaling relations derived from the theoretical model and the measurements made on a large set of Kepler targets. Results: We derive theoretical scaling relations for τeff and σ, which show the same dependence on νmax as the observed scaling relations. In addition, we show that these quantities also scale as a function of the turbulent Mach number (ℳa) estimated at the photosphere. The theoretical scaling relations for τeff and σ match the observations well on a global scale. Quantitatively, the remaining discrepancies with the observations are found to be much smaller than previous theoretical calculations made for red giants. Conclusions: Our modelling provides additional theoretical support for the observed variations of σ and τeff with νmax. It also highlights the important role of ℳa in controlling the properties of the stellar granulation. However, the observations made with Kepler on a wide variety of stars cannot confirm the dependence of our scaling relations on ℳa. Measurements of the granulation background and detections of solar-like oscillations in a statistically sufficient number of cool dwarf stars will be required for confirming the dependence of the theoretical scaling relations with ℳa. Appendices are available in electronic form at http://www.aanda.org

TRACING REJUVENATION EVENTS IN NEARBY S0 GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marino, Antonietta; Bianchi, Luciana; Thilker, David A.

2011-08-01

With the aim of characterizing rejuvenation processes in early-type galaxies, we analyzed five barred S0 galaxies showing a prominent outer ring in ultraviolet (UV) imaging. We analyzed Galaxy Evolution Explorer far-UV (FUV) and near-UV (NUV), and optical data using stellar population models and estimated the age and the stellar mass of the entire galaxies and the UV-bright ring structures. Outer rings consist of young ({approx}<200 Myr old) stellar populations, accounting for up to 70% of the FUV flux but containing only a few percent of the total stellar mass. Integrated photometry of the whole galaxies places four of these objectsmore » on the green valley, indicating a globally evolving nature. We suggest such galaxy evolution is likely driven by bar-induced instabilities, i.e., inner secular evolution, that conveys gas to the nucleus and the outer rings. At the same time, H I observations of NGC 1533 and NGC 2962 suggest external gas re-fueling can play a role in the rejuvenation processes of such galaxies.« less

Source-plane reconstruction of the giant gravitational arc in A2667: A candidate Wolf-Rayet galaxy at z ∼ 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Shuo; Zhu, Zong-Hong; Covone, Giovanni

We present a new analysis of Hubble Space Telescope, Spitzer Space Telescope, and Very Large Telescope imaging and spectroscopic data of a bright lensed galaxy at z = 1.0334 in the lensing cluster A2667. Using this high-resolution imaging, we present an updated lens model that allows us to fully understand the lensing geometry and reconstruct the lensed galaxy in the source plane. This giant arc gives a unique opportunity to view the structure of a high-redshift disk galaxy. We find that the lensed galaxy of A2667 is a typical spiral galaxy with a morphology similar to the structure of itsmore » counterparts at higher redshift, z ∼ 2. The surface brightness of the reconstructed source galaxy in the z {sub 850} band reveals the central surface brightness I(0) = 20.28 ± 0.22 mag arcsec{sup –2} and a characteristic radius r{sub s} = 2.01 ± 0.16 kpc at redshift z ∼ 1. The morphological reconstruction in different bands shows obvious negative radial color gradients for this galaxy. Moreover, the redder central bulge tends to contain a metal-rich stellar population, rather than being heavily reddened by dust due to high and patchy obscuration. We analyze the VIMOS/integral field unit spectroscopic data and find that, in the given wavelength range (∼1800-3200 Å), the combined arc spectrum of the source galaxy is characterized by a strong continuum emission with strong UV absorption lines (Fe II and Mg II) and shows the features of a typical starburst Wolf-Rayet galaxy, NGC 5253. More specifically, we have measured the equivalent widths of Fe II and Mg II lines in the A2667 spectrum, and obtained similar values for the same wavelength interval of the NGC 5253 spectrum. Marginal evidence for [C III] 1909 emission at the edge of the grism range further confirms our expectation.« less

Surface Photometric Properties of HII Galaxies

NASA Astrophysics Data System (ADS)

Vajgel, B.; Telles, E.

2009-05-01

HII galaxies are dwarf galaxies undergoing violent star formation. They were firstly selected by objective-prism spectroscopy and were object of extensive studies to characterize their physical conditions of the interstellar medium. Their SFR together with their low Z raised the question whether some of them can be truly ``young'' galaxies. To infer the SFH, one needs information in a large spectral range. We obtained images in the optical region of the spectrum with the 0.6 m B&C and the 1.6 m telescopes at the Laboratório Nacional de Astrofísica, for a sample of 50 objects in B, V, R and I, which combined with recent evolutionary models, enable us to deduce the stellar population content and its spatial distribution. These seem to be the nearest youngest galaxies that can be studied in detail, and their structural properties offer important indications about the evolutionary relation and the origin of dwarf galaxies in the universe. With this sample we built a morphological catalogue with broad-band photometry, including the structural analysis through the brightness profiles. The initial analysis suggests that the galaxies can be segregated in two broad classes, in agreement with what had already been proposed in the literature; Type I have irregular envelopes with signs of perturbation and turn out to the more luminous sub-sample; while Type II have regular external isophotes and are less luminous. The brightness profiles are well represented by exponential fits, as in irregular and elliptical dwarf galaxies. However, HII galaxies are more compact in comparison with their more diffuse counterparts. We study the behavior of the HII galaxies in the metallicity-luminosity plane. This relation, interpreted as a relation between the mass and the metallicity of dwarf galaxies of low surface brightness (dE and dIrr), has direct implications for their formation and evolution, and over the possible evolutionary links between HII galaxies and other types of dwarf galaxies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan Changshuo; Wang Jianmin, E-mail: wangjm@ihep.ac.c

High spatial resolution observations show that high-redshift galaxies are undergoing intensive evolution of dynamical structure and morphologies displayed by the H{alpha}, H{beta}, [O III], and [N II] images. It has been shown that supernova explosion (SNexp) of young massive stars during the star formation epoch, as kinetic feedback to host galaxies, can efficiently excite the turbulent viscosity. We incorporate the feedback into the dynamical equations through mass dropout and angular momentum transportation driven by the SNexp-excited turbulent viscosity. The empirical Kennicutt-Schmidt law is used for star formation rates (SFRs). We numerically solve the equations and show that there can bemore » intensive evolution of structure of the gaseous disk. Secular evolution of the disk shows interesting characteristics: (1) high viscosity excited by SNexp can efficiently transport the gas from 10 kpc to {approx}1 kpc forming a stellar disk whereas a stellar ring forms for the case with low viscosity; (2) starbursts trigger SMBH activity with a lag of {approx}10{sup 8} yr depending on SFRs, prompting the joint evolution of SMBHs and bulges; and (3) the velocity dispersion is as high as {approx}100 km s{sup -1} in the gaseous disk. These results are likely to vary with the initial mass function (IMF) that the SNexp rates rely on. Given the IMF, we use the GALAXEV code to compute the spectral evolution of stellar populations based on the dynamical structure. In order to compare the present models with the observed dynamical structure and images, we use the incident continuum from the simple stellar synthesis and CLOUDY to calculate emission line ratios of H{alpha}, H{beta}, [O III], and [N II], and H{alpha} brightness of gas photoionized by young massive stars formed on the disks. The models can produce the main features of emission from star-forming galaxies. We apply the present model to two galaxies, BX 389 and BX 482 observed in the SINS high-z sample, which are bulge and disk-dominated, respectively. Two successive rings independently evolving are able to reproduce the main dynamical and emission properties of the two galaxies, such as the Baldwin-Phillips-Terlevich diagram, the relation between line ratios, and H{alpha} brightness. The observed relation between turbulent velocity and the H{alpha} brightness can be explained by the present model. High viscosity excited by SNexp is able to efficiently transport the gas into a bulge to maintain high SFRs or to form a stellar ring close enough to the bulge so that it immigrates into the bulge of its host galaxy. This leads to a fast growing bulge. Implications and future work of the present models have been extensively discussed for galaxy formation in high-z universe.« less

Structure and Feedback in 30 Doradus. I. Observations

NASA Astrophysics Data System (ADS)

Pellegrini, E. W.; Baldwin, J. A.; Ferland, G. J.

2010-11-01

We have completed a new optical imaging and spectrophotometric survey of a 140 × 80 pc2 region of 30 Doradus centered on R136, covering key optical diagnostic emission lines including Hα, Hβ, Hγ, [O III] λλ4363, 4959, 5007, [N II] λλ6548, 6584, [S II] λλ6717, 6731 [S III] λ6312, and in some locations [S III] λ9069. We present maps of fluxes and intensity ratios for these lines, and catalogs of isolated ionizing stars, elephant-trunk pillars, and edge-on ionization fronts. The final science-quality spectroscopic data products are available to the public. Our analysis of the new data finds that, while stellar winds and supernovae undoubtedly produce shocks and are responsible for shaping the nebula, there are no global spectral signatures to indicate that shocks are currently an important source of ionization. We conclude that the considerable region covered by our survey is well described by photoionization from the central cluster where the ionizing continuum is dominated by the most massive O stars. We show that if 30 Dor were viewed at a cosmological distance, its integrated light would be dominated by its extensive regions of lower surface brightness rather than by the bright, eye-catching arcs.

Spatially extended K Iλ7699 emission in the nebula of VY CMa: kinematics and geometry

NASA Astrophysics Data System (ADS)

Smith, Nathan

2004-04-01

Long-slit echelle spectra reveal bright extended emission from the K Iλ7699 resonance line in the reflection nebula surrounding the extreme red supergiant VY Canis Majoris. The central star has long been known for its unusually bright K I emission lines, but this is the first report of intrinsic emission from K I in the nebula. The extended emission is not just a reflected spectrum of the star, but is due to resonant scattering by K atoms in the outer nebula itself, and is therefore a valuable probe of the kinematics and geometry of the circumstellar environment of VY CMa. Dramatic velocity structure is seen in the long-slit spectra, and most lines of sight through the nebula intersect multiple distinct velocity components. A faint `halo' at large distances from the star does appear to show a reflected spectrum, however, and suggests a systemic velocity of +40 km s-1 with respect to the Sun. The most striking feature is blueshifted emission from the filled interior of a large shell seen in images; the kinematic structure is reminiscent of a Hubble flow, and provides strong evidence for asymmetric and episodic mass loss due to localized eruptions on the stellar surface.

HUBBLE WATCHES STAR TEAR APART ITS NEIGHBORHOOD

NASA Technical Reports Server (NTRS)

2002-01-01

NASA's Hubble Space Telescope has snapped a view of a stellar demolition zone in our Milky Way Galaxy: a massive star, nearing the end of its life, tearing apart the shell of surrounding material it blew off 250,000 years ago with its strong stellar wind. The shell of material, dubbed the Crescent Nebula (NGC 6888), surrounds the 'hefty,' aging star WR 136, an extremely rare and short-lived class of super-hot star called a Wolf-Rayet. Hubble's multicolored picture reveals with unprecedented clarity that the shell of matter is a network of filaments and dense knots, all enshrouded in a thin 'skin' of gas [seen in blue]. The whole structure looks like oatmeal trapped inside a balloon. The skin is glowing because it is being blasted by ultraviolet light from WR 136. Hubble's view covers a small region at the northeast tip of the structure, which is roughly three light-years across. A picture taken by a ground-based telescope [lower right] shows almost the entire nebula. The whole structure is about 16 light-years wide and 25 light-years long. The bright dot near the center of NGC 6888 is WR 136. The white outline in the upper left-hand corner represents Hubble's view. Hubble's sharp vision is allowing scientists to probe the intricate details of this complex system, which is crucial to understanding the life cycle of stars and their impact on the evolution of our galaxy. The results of this study appear in the June issue of the Astronomical Journal. WR 136 created this web of luminous material during the late stages of its life. As a bloated, red super-giant, WR 136 gently puffed away some of its bulk, which settled around it. When the star passed from a super-giant to a Wolf-Rayet, it developed a fierce stellar wind - a stream of charged particles released from its surface - and began expelling mass at a furious rate. The star began ejecting material at a speed of 3.8 million mph (6.1 million kilometers per hour), losing matter equal to that of our Sun's every 10,000 years. Then the stellar wind collided with the material around the star and swept it up into a thin shell. That shell broke apart into the network of bright clumps seen in the image. The present-day strong wind of the Wolf-Rayet star has only now caught up with the outer edge of the shell, and is stripping away matter as it flows past [the tongue-shaped material in the upper right of the Hubble image]. The stellar wind continues moving outside the shell, slamming into more material and creating a shock wave. This powerful force produces an extremely hot, glowing skin [seen in blue], which envelops the bright nebula. A shock wave is analogous to the sonic boom produced by a jet plane that exceeds the speed of sound; in a cosmic setting, this boom is seen rather than heard. The outer material is too thin to see in the image until the shock wave hits it. The cosmic collision and subsequent shock wave implies that a large amount of matter resides outside the visible shell. The discovery of this material may explain the discrepancy between the mass of the entire shell (four solar masses) and the amount of matter the star lost when it was a red super-giant (15 solar masses). The nebula's short-term fate is less spectacular. As the stellar wind muscles past the clumps of material, the pressure around them drops. A decrease in pressure means that the clumps expand, leading to a steady decline in brightness and fading perhaps to invisibility. Later, the shell may be compressed and begin glowing again, this time as the powerful blast wave of the Wolf-Rayet star completely destroys itself in a powerful supernova explosion. The nebula resides in the constellation Cygnus, 4,700 light-years from Earth. If the nebula were visible to the naked eye, it would appear in the sky as an ellipse one-quarter the size of the full moon. The observations were taken in June 1995 with the Wide Field and Planetary Camera 2. Scientists selected the colors in this composite image to correspond with the ionization (the process of stripping electrons from atoms) state of the gases, with blue representing the highest and red the lowest observed ionization. Credits: NASA, Brian D. Moore, Jeff Hester, Paul Scowen (Arizona State University), Reginald Dufour (Rice University)

Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres. Comparison with 1D models and HST light curve observations

NASA Astrophysics Data System (ADS)

Hayek, W.; Sing, D.; Pont, F.; Asplund, M.

2012-03-01

We compare limb darkening laws derived from 3D hydrodynamical model atmospheres and 1D hydrostatic MARCS models for the host stars of two well-studied transiting exoplanet systems, the late-type dwarfs HD 209458 and HD 189733. The surface brightness distribution of the stellar disks is calculated for a wide spectral range using 3D LTE spectrum formation and opacity sampling⋆. We test our theoretical predictions using least-squares fits of model light curves to wavelength-integrated primary eclipses that were observed with the Hubble Space Telescope (HST). The limb darkening law derived from the 3D model of HD 209458 in the spectral region between 2900 Å and 5700 Å produces significantly better fits to the HST data, removing systematic residuals that were previously observed for model light curves based on 1D limb darkening predictions. This difference arises mainly from the shallower mean temperature structure of the 3D model, which is a consequence of the explicit simulation of stellar surface granulation where 1D models need to rely on simplified recipes. In the case of HD 189733, the model atmospheres produce practically equivalent limb darkening curves between 2900 Å and 5700 Å, partly due to obstruction by spectral lines, and the data are not sufficient to distinguish between the light curves. We also analyze HST observations between 5350 Å and 10 500 Å for this star; the 3D model leads to a better fit compared to 1D limb darkening predictions. The significant improvement of fit quality for the HD 209458 system demonstrates the higher degree of realism of 3D hydrodynamical models and the importance of surface granulation for the formation of the atmospheric radiation field of late-type stars. This result agrees well with recent investigations of limb darkening in the solar continuum and other observational tests of the 3D models. The case of HD 189733 is no contradiction as the model light curves are less sensitive to the temperature stratification of the stellar atmosphere and the observed data in the 2900-5700 Å region are not sufficient to distinguish more clearly between the 3D and 1D limb darkening predictions. Full theoretical spectra for both stars are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/539/A102, as well as at www.astro.ex.ac.uk/people/sing.

Model-independent Exoplanet Transit Spectroscopy

NASA Astrophysics Data System (ADS)

Aronson, Erik; Piskunov, Nikolai

2018-05-01

We propose a new data analysis method for obtaining transmission spectra of exoplanet atmospheres and brightness variation across the stellar disk from transit observations. The new method is capable of recovering exoplanet atmosphere absorption spectra and stellar specific intensities without relying on theoretical models of stars and planets. We simultaneously fit both stellar specific intensity and planetary radius directly to transit light curves. This allows stellar models to be removed from the data analysis. Furthermore, we use a data quality weighted filtering technique to achieve an optimal trade-off between spectral resolution and reconstruction fidelity homogenizing the signal-to-noise ratio across the wavelength range. Such an approach is more efficient than conventional data binning onto a low-resolution wavelength grid. We demonstrate that our analysis is capable of reproducing results achieved by using an explicit quadratic limb-darkening equation and that the filtering technique helps eliminate spurious spectral features in regions with strong telluric absorption. The method is applied to the VLT FORS2 observations of the exoplanets GJ 1214 b and WASP-49 b, and our results are in agreement with previous studies. Comparisons between obtained stellar specific intensity and numerical models indicates that the method is capable of accurately reconstructing the specific intensity. The proposed method enables more robust characterization of exoplanetary atmospheres by separating derivation of planetary transmission and stellar specific intensity spectra (that is model-independent) from chemical and physical interpretation.

A search for N-type galaxies

NASA Technical Reports Server (NTRS)

Jefferies, J. T.

1971-01-01

A large number of distant clusters of galaxies was examined for the presence of a bright compact galaxy or blue stellar object. Nearly 600 square degrees of sky were searched using glass copies of the National Geographic Society-Palomar Observatory Sky Survey plates, and over 20 fields were selected for observation. The objects were examined for infrared and ultraviolet excesses, using wideband filter photography and spectroscopy. Initial findings include a faint, distant cluster of galaxies near the quasi-stellar radio source 4C 37.43 with a red shift of 0.370. One of these galaxies has an emission line at 6895 A, indicating a possible red shift of 0.377 of the 5007 A line of (0 III).

Comparisons of a standard galaxy model with stellar observations in five fields

NASA Technical Reports Server (NTRS)

Bahcall, J. N.; Soneira, R. M.

1984-01-01

Modern data on the distribution of stellar colors and on the number of stars as a function of apparent magnitude in five directions in the Galaxy are analyzed. It is found that the standard model is consistent with all the available data. Detailed comparisons with the data for five separate fields are presented. The bright end of the spheroid luminosity function and the blue tip of the spheroid horizontal branch are analyzed. The allowed range of the disk scale heights and of fluctuations in the volume density is determined, and a lower limit is set on the disk scale length. Calculations based on the thick disk model of Gilmore and Reid (1983) are presented.

Towards a more realistic population of bright spiral galaxies in cosmological simulations

NASA Astrophysics Data System (ADS)

Aumer, Michael; White, Simon D. M.; Naab, Thorsten; Scannapieco, Cecilia

2013-10-01

We present an update to the multiphase smoothed particle hydrodynamics galaxy formation code by Scannapieco et al. We include a more elaborate treatment of the production of metals, cooling rates based on individual element abundances and a scheme for the turbulent diffusion of metals. Our supernova feedback model now transfers energy to the interstellar medium (ISM) in kinetic and thermal form, and we include a prescription for the effects of radiation pressure from massive young stars on the ISM. We calibrate our new code on the well-studied Aquarius haloes and then use it to simulate a sample of 16 galaxies with halo masses between 1 × 1011 and 3 × 1012 M⊙. In general, the stellar masses of the sample agree well with the stellar mass to halo mass relation inferred from abundance matching techniques for redshifts z = 0-4. There is however a tendency to overproduce stars at z > 4 and to underproduce them at z < 0.5 in the least massive haloes. Overly high star formation rates (SFRs) at z < 1 for the most massive haloes are likely connected to the lack of active galactic nuclei feedback in our model. The simulated sample also shows reasonable agreement with observed SFRs, sizes, gas fractions and gas-phase metallicities at z = 0-3. Remaining discrepancies can be connected to deviations from predictions for star formation histories from abundance matching. At z = 0, the model galaxies show realistic morphologies, stellar surface density profiles, circular velocity curves and stellar metallicities, but overly flat metallicity gradients. 15 out of 16 of our galaxies contain disc components with kinematic disc fraction ranging between 15 and 65 per cent. The disc fraction depends on the time of the last destructive merger or misaligned infall event. Considering the remaining shortcomings of our simulations we conclude that even higher kinematic disc fractions may be possible for Λ cold dark matter haloes with quiet merger histories, such as the Aquarius haloes.

Early-Type Galaxy Star Formation Histories in Different Environments

NASA Astrophysics Data System (ADS)

Fitzpatrick, Patrick; Graves, G.

2014-01-01

We use very high-S/N stacked spectra of ˜29,000 nearby quiescent early-type galaxies (ETGs) from the Sloan Digital Sky Survey (SDSS) to investigate variations in their star formation histories (SFHs) with environment at fixed position along and perpendicular to the Fundamental Plane (FP). We separate galaxies in the three-dimensional FP space defined by galaxy effective radius Re, central stellar velocity dispersion σ, and surface brightness residual from the FP, ΔIe. We use the SDSS group catalogue of Yang et al. to further separate galaxies into three categories by their “identities” within their respective dark matter halos: central “Brightest Group Galaxies” (BGGs); Satellites; and Isolateds (those which are “most massive” in a dark matter halo with no Satellites). Within each category, we construct high-S/N mean stacked spectra to determine mean singleburst ages, [Fe/H], and [Mg/Fe] based on the stellar population synthesis models of R. Schiavon. This allows us to study variations in the stellar population properties (SPPs) with local group environment at fixed structure (i.e., fixed position in FP-space). We find that the SFHs of quiescent ETGs are almost entirely determined by their structural parameters σ and ΔIe. Any variation with local group environment at fixed structure is only slight: Satellites have the oldest stellar populations, 0.02 dex older than BGGs and 0.04 dex older than Isolateds; BGGs have the highest Fe-enrichments, 0.01 dex higher than Isolateds and 0.02 dex higher than Satellites; there are no differences in Mg-enhancement between BGGs, Isolateds, and Satellites. Our observation that, to zeroth-order, the SFHs of quiescent ETGs are fully captured by their structures places important qualitative constraints on the degree to which late-time evolutionary processes (those which occur after a galaxy’s initial formation and main star-forming lifetime) can alter their SFHs/structures.

VLA AND ALMA IMAGING OF INTENSE GALAXY-WIDE STAR FORMATION IN z ∼ 2 GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rujopakarn, W.; Silverman, J. D.; Dunlop, J. S.

2016-12-10

We present ≃0.″4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z  = 1.3–3.0. These galaxies are selected from sensitive blank-field surveys of the 2′ × 2′ Hubble Ultra-Deep Field at λ  = 5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z  ∼ 2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs),more » thereby representing a diversity of z  ∼ 2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2 ± 1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M {sub ⊙} yr{sup −1} kpc{sup −2}, sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3–8 times larger, providing a constraint on the characteristic SFR (∼300 M {sub ⊙} yr{sup −1}) above which a significant population of more compact SFGs appears to emerge.« less

THE SPATIAL DISTRIBUTION OF COMPLEX ORGANIC MOLECULES IN THE L1544 PRE-STELLAR CORE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiménez-Serra, Izaskun; Vasyunin, Anton I.; Caselli, Paola

The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T < 10 K) has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modeling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly extinguished continuum peak with A{sub V}≥ 30 mag within the inner 2700 au; and a low-densitymore » shell with average A{sub V}∼ 7.5–8 mag located at 4000 au from the core’s center and bright in CH{sub 3}OH. Our observations show that CH{sub 3}O, CH{sub 3}OCH{sub 3}, and CH{sub 3}CHO are more abundant (by factors of ∼2–10) toward the low-density shell than toward the continuum peak. Other COMs such as CH{sub 3}OCHO, c-C{sub 3}H{sub 2}O, HCCCHO, CH{sub 2}CHCN, and HCCNC show slight enhancements (by factors ≤3), but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modeling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because (i) CO starts freezing out onto dust grains driving an active surface chemistry; (ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and (iii) the density is still moderate to prevent severe depletion of COMs onto grains.« less

The convective photosphere of the red supergiant CE Tauri. I. VLTI/PIONIER H-band interferometric imaging

NASA Astrophysics Data System (ADS)

Montargès, M.; Norris, R.; Chiavassa, A.; Tessore, B.; Lèbre, A.; Baron, F.

2018-06-01

Context. Red supergiant stars are one of the latest stages in the evolution of massive stars. Their photospheric convection may play an important role in the launching mechanism of their mass loss; however, its characteristics and dynamics are still poorly constrained. Aims: By observing red supergiant stars with near infrared interferometry at different epochs, we expect to reveal the evolution of bright convective features on their stellar surface. Methods: We observed the M2Iab-Ib red supergiant star CE Tau with the VLTI/PIONIER instrument in the H band at two different epochs separated by one month. Results: We derive the angular diameter of the star and basic stellar parameters, and reconstruct two reliable images of its H-band photosphere. The contrast of the convective pattern of the reconstructed images is 5 ± 1% and 6 ± 1% for our two epochs of observation. Conclusions: The stellar photosphere shows few changes between the two epochs. The contrast of the convective pattern is below the average contrast variations obtained on 30 randomly chosen snapshots of the best matching 3D radiative hydrodynamics simulation: 23 ± 1% for the original simulation images and 16 ± 1% for the maps degraded to the reconstruction resolution. We offer two hypotheses to explain this observation. CE Tau may be experiencing a quiet convective activity episode or it could be a consequence of its warmer effective temperature (hence its smaller radius) compared to the simulation. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 298.D-5005(A) and 298.D-5005(B).Reconstructed images as FITS files and basic stellar parameters are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A12Animated gif of the two epochs is available at http://https://www.aanda.org

Insight into the Formation of the Milky Way Through Cold Halo Substructure. I. The ECHOS of Milky Way Formation

NASA Astrophysics Data System (ADS)

Schlaufman, Kevin C.; Rockosi, Constance M.; Allende Prieto, Carlos; Beers, Timothy C.; Bizyaev, Dmitry; Brewington, Howard; Lee, Young Sun; Malanushenko, Viktor; Malanushenko, Elena; Oravetz, Dan; Pan, Kaike; Simmons, Audrey; Snedden, Stephanie; Yanny, Brian

2009-10-01

We identify 10—seven for the first time—elements of cold halo substructure (ECHOS) in the volume within 17.5 kpc of the Sun in the inner halo of the Milky Way. Our result is based on the observed spatial and radial velocity distribution of metal-poor main-sequence turnoff (MPMSTO) stars in 137 Sloan Extension for Galactic Understanding and Exploration lines of sight. We point out that the observed radial velocity distribution is consistent with a smooth stellar component of the Milky Way's inner halo overall, but disagrees significantly at the radial velocities that correspond to our detections. We show that all of our detections are statistically significant and that we expect no false positives. These ECHOS represent the observable stellar debris of ancient merger events in the stellar accretion history of the Milky Way, and we use our detections and completeness estimates to infer a formal upper limit of 0.34+0.02 -0.02 on the fraction of the MPMSTO population in the inner halo that belong to ECHOS. Our detections and completeness calculations also suggest that there is a significant population of low fractional overdensity ECHOS in the inner halo, and we predict that 1/3 of the inner halo (by volume) harbors ECHOS with MPMSTO star number densities n ≈ 15 kpc-3. In addition, we estimate that there are of order 103 ECHOS in the entire inner halo. ECHOS are likely older than known surface brightness substructure, so our detections provide us with a direct measure of the accretion history of the Milky Way in a region and time interval that has yet to be fully explored. In concert with previous studies, our result suggests that the level of merger activity has been roughly constant over the past few Gyr and that there has been no accretion of single stellar systems more massive than a few percent of a Milky Way mass in that interval.

Spectral variability of photospheric radiation due to faculae. I. The Sun and Sun-like stars

NASA Astrophysics Data System (ADS)

Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne C.; Solanki, Sami K.; Krivova, Natalie A.; Yeo, Kok Leng

2017-09-01

Context. Stellar spectral variability on timescales of a day and longer, arising from magnetic surface features such as dark spots and bright faculae, is an important noise source when characterising extra-solar planets. Current 1D models of faculae do not capture the geometric properties and fail to reproduce observed solar facular contrasts. Magnetoconvection simulations provide facular contrasts accounting for geometry. Aims: We calculate facular contrast spectra from magnetoconvection models of the solar photosphere with a view to improve (a) future parameter determinations for planets with early G type host stars and (b) reconstructions of solar spectral variability. Methods: Regions of a solar twin (G2, log g = 4.44) atmosphere with a range of initial average vertical magnetic fields (100 to 500 G) were simulated using a 3D radiation-magnetohydrodynamics code, MURaM, and synthetic intensity spectra were calculated from the ultraviolet (149.5 nm) to the far infrared (160 000 nm) with the ATLAS9 radiative transfer code. Nine viewing angles were investigated to account for facular positions across most of the stellar disc. Results: Contrasts of the radiation from simulation boxes with different levels of magnetic flux relative to an atmosphere with no magnetic field are a complicated function of position, wavelength and magnetic field strength that is not reproduced by 1D facular models. Generally, contrasts increase towards the limb, but at UV wavelengths a saturation and decrease are observed close to the limb. Contrasts also increase strongly from the visible to the UV; there is a rich spectral dependence, with marked peaks in molecular bands and strong spectral lines. At disc centre, a complex relationship with magnetic field was found and areas of strong magnetic field can appear either dark or bright, depending on wavelength. Spectra calculated for a wide variety of magnetic fluxes will also serve to improve total and spectral solar irradiance reconstructions.

Photoionization modeling of the LWS fine-structure lines in IR bright galaxies

NASA Technical Reports Server (NTRS)

Satyapal, S.; Luhman, M. L.; Fischer, J.; Greenhouse, M. A.; Wolfire, M. G.

1997-01-01

The long wavelength spectrometer (LWS) fine structure line spectra from infrared luminous galaxies were modeled using stellar evolutionary synthesis models combined with photoionization and photodissociation region models. The calculations were carried out by using the computational code CLOUDY. Starburst and active galactic nuclei models are presented. The effects of dust in the ionized region are examined.

Resonances in the Photoionization Cross Sections of Atomic Nitrogen Shape the Far-ultraviolet Spectrum of the Bright Star in 47 Tucanae

NASA Astrophysics Data System (ADS)

Dixon, William V.; Chayer, Pierre

2013-08-01

The far-ultraviolet spectrum of the Bright Star (B8 III) in 47 Tuc (NGC 104) shows a remarkable pattern: it is well fit by local thermodynamic equilibrium models at wavelengths longer than Lyβ, but at shorter wavelengths it is fainter than the models by a factor of two. A spectrum of this star obtained with the Far Ultraviolet Spectroscopic Explorer shows broad absorption troughs with sharp edges at 995 and 1010 Å and a deep absorption feature at 1072 Å none of which are predicted by the models. We find that these features are caused by resonances in the photoionization cross sections of the first and second excited states of atomic nitrogen (2s 2 2p 3 2 D 0 and 2 P 0). Using cross sections from the Opacity Project, we can reproduce these features, but only if we use the cross sections at their full resolution, rather than the resonance-averaged cross sections usually employed to model stellar atmospheres. These resonances are strongest in stellar atmospheres with enhanced nitrogen and depleted carbon abundances, a pattern typical of post-asymptotic giant branch stars.

Towards the Detection of Reflected Light from Exo-planets: a Comparison of Two Methods

NASA Astrophysics Data System (ADS)

Rodler, Florian; Kürster, Martin

For exo-planets the huge brightness contrast between the star and the planet constitutes an enormous challenge when attempting to observe some kind of direct signal from the planet. With high resolution spectroscopy in the visual one can exploit the fact that the spectrum reflected from the planet is essentially a copy of the rich stellar absorption line spectrum. This spectrum is shifted in wavelength according to the orbital RV of the planet and strongly scaled down in brightness by a factor of a few times 10-5, and therefore deeply buried in the noise. The S/N of the plantetary signal can be increased by applying one of the following methods. The Least Squares Deconvolution Method (LSDM, eg. Collier Cameron et al. 2002) combines the observed spectral lines into a high S/N mean line profile (star + planet), determined by least-squares deconvolution of the observed spectrum with a template spectrum (from VALD, Kupka et al. 1999). Another approach is the Data Synthesis Method (DSM, eg. Charbonneau et al. 1999), a forward data modelling technique in which the planetary signal is modelled as a scaled-down and RV-shifted version of the stellar spectrum.

Galaxy Selection and the Surface Brightness Distribution

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.; Bothun, Gregory D.; Schombert, James M.

1995-08-01

Optical surveys for galaxies are biased against the inclusion of low surface brightness (LSB) galaxies. Disney [Nature, 263,573(1976)] suggested that the constancy of disk central surface brightness noticed by Freeman [ApJ, 160,811(1970)] was not a physical result, but instead was an artifact of sample selection. Since LSB galaxies do exist, the pertinent and still controversial issue is if these newly discovered galaxies constitute a significant percentage of the general galaxy population. In this paper, we address this issue by determining the space density of galaxies as a function of disk central surface brightness. Using the physically reasonable assumption (which is motivated by the data) that central surface brightness is independent of disk scale length, we arrive at a distribution which is roughly flat (i.e., approximately equal numbers of galaxies at each surface brightness) faintwards of the Freeman (1970) value. Brightwards of this, we find a sharp decline in the distribution which is analogous to the turn down in the luminosity function at L^*^. An intrinsically sharply peaked "Freeman law" distribution can be completely ruled out, and no Gaussian distribution can fit the data. Low surface brightness galaxies (those with central surface brightness fainter than 22 B mag arcsec^-2^) comprise >~ 1/2 the general galaxy population, so a representative sample of galaxies at z = 0 does not really exist at present since past surveys have been insensitive to this component of the general galaxy population.

The inner radio structure of Centaurus A - Clues to the origin of the jet X-ray emission

NASA Technical Reports Server (NTRS)

Burns, J. O.; Feigelson, E. D.; Schreier, E. J.

1983-01-01

VLA observations at 1.4 and 4.9 GHz of the jet and inner lobes of the nearby radio galaxy Centaurus A have been used to construct maps of total intensity and polarization at resolutions of 31 x 10 and 3.6 x 1.1 arcsec. Surface brightness and pressure distributions in the jet, combined with the apparent X-ray emission from the ISM of NGC 5128, indicate that it is thermally confined. A comparison of the radio structure and the optical galaxy shows that the jet in Cen A emerges nearly along the major axis of the elliptical stellar component that is parallel to the angular momentum vector of the dust lane. The outer radio structure bends toward the galaxy minor axis. Evidence is found for a common synchrotron radiation origin of the full spectrum jet emission.

BVR{sub c}I{sub c} observations and analyses on V2421 Cygni, a precontact W UMa binary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samec, R. G.; Shebs, Travis S.; Faulkner, D. R.

2014-01-01

We present the first precision BVRI light curves, synthetic light curve solutions, and a period study for the high amplitude solar type binary, V2421 Cygni. The light curves have the appearance of an Algol (EA) type; however, it is made up of dwarf solar type components in a detached mode with a period of only 0.6331 days with an amplitude of about a full magnitude, i.e., it is a precontact W UMa binary. Flare-like disruptions occur in the light curves following the primary and secondary eclipses possibly due to the line-of-sight track of a gas stream. An associated stream spotmore » and splash spot cause bright equatorial spots on the stellar surface of the primary star. The more massive star is the gainer, making this system a classic, albeit dwarf, Algol.« less

Open Cluster Dynamics via Fundamental Plane

NASA Astrophysics Data System (ADS)

Lin, Chien-Cheng; Pang, Xiao-Ying

2018-04-01

Open clusters (OCs) are important objects for stellar dynamics studies. The short survival timescale of OCs makes them closely related to the formation of Galactic field stars. We motivate to investigate the dynamical evolution of OCs on the aspect of internal effect and the external influence. Firstly, we make use of the known OC catalog to obtain OCs masses, effective radii. Additionally, we estimate OCs kinematics properties by OC members cross-matched with radial velocity and metallicity from SDSSIV/APOGEE2. We then establish the fundamental plane of OCs based on the radial velocity dispersion, the effective radius, and average surface brightness. The deviation of the fundamental plane from the Virial Plane, so called the tilt, and the r.m.s. dispersion of OCs around the average plane are used to indicate the dynamical status of OCs. Parameters of the fitted plane will vary with cluster age and distance.

RVxK2: Simultaneous PRV Program with Kepler/K2 Campaign 16

NASA Astrophysics Data System (ADS)

Xuesong Wang, Sharon; RVxK2 team

2018-01-01

Introducing the RVxK2 program: simultaneous precise radial velocity (PRV) observations with Kepler/K2 Campaign 16, from Dec 7 2017 through Feb 26 2018 (website: rvxk2.com). K2 will provide short cadence photometric data on five carefully selected stars, including the brightest M dwarf in C16 field, a solar analog, and three bright G/K subgiants. K2 will also provide long cadence data on the next three brightest K or M dwarfs in the C16 field. Our campaign includes several precise RV instruments around the globe, including Keck/HIRES, APF, IRTF/iSHELL, SONG, MINERVA, PARAS, representing the first organized, extensive, simultaneous RV campaign with space photometry. Our primary science goal is to characterize and understand stellar jitter and stellar activity. This RV+K2 campaign will provide the community with an unprecedented dataset of RV spectra and precise photometry to study stellar jitter on a broad range of time scales, from minutes to 80 days. We will gather the first ever RV+photometry dataset aiming at characterizing stellar granulation, the most poorly understood term among all astrophysical sources of stellar jitter. This project will also enable the first asteroseismic studies with simultaneous precise RVs and photometry, while searching for planets in the brightest nearby G to M dwarfs in the field.

Infrared Properties of Star Forming Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Vaduvescu, Ovidiu

2005-11-01

Dwarf galaxies are the most common galaxies in the Universe. They are systems believed to consist of matter in a near-primordial state, from which giant galaxies probably form. As such, they are important probes for studying matter in its near-primordial state. In an effort to study the main physical and chemical properties of dwarfs, the present thesis focuses upon the main physical properties of dwarfs. Two classes of star forming dwarf galaxies are considered: dwarf irregulars (dIs), and blue compact dwarfs (BCDs). A third class, dwarf ellipticals (dEs), is studied based on its structural properties and compared with dIs. Possible evolutionary connections are addressed between dIs and BCDs. To measure the luminosity, deep imaging in the near-infrared (NIR) is considered. Compared with the visible, the NIR domain gives a better gauge of the galaxy mass contained in the old stellar populations, minimising the starburst contribution and also the effects of extinction. Two observing samples of star-forming dwarf galaxies are considered. The first includes 34 dIs in the Local Volume closer than 5 Mpc. The second sample includes 16 BCDs in the Virgo Cluster. In six observing runs between 2001 and 2004, we acquired deep NIR images (J and K_s) using the 3.6m Canada-France-Hawaii-Telescope (CFHT) in Hawaii and the 2.1m telescope at the National Astronomical Observatory ''San Pedro Martir'' (OAN-SPM) in Mexico. Deep spectrocopy was acquired in 2003 on the 8.1m Gemini-North telescope in Hawaii. We completed the observed samples with spectroscopic data from the literature, and photometry from the 2MASS survey and GOLDMine database. From a statistical study at CFHT, we derived some strategies necessary to image optimally faint extended sources in the NIR. Due to the airglow variation in the atmosphere and the thermal contribution of the dome, telescope and the instrumentation, repeated observations of the sky must be alternated every 3-4 minutes with the science images, in order to achieve 1% accuracy in surface photometry. We discovered that the NIR surface brightness profiles of dIs can be fitted with a hyperbolic secant (sech) function with only two parameters: the central surface brightness and the scale length. This led to the discovery that BCD profiles could be fitted with a sech component to trace the diffuse component responsible for most of the light, and a Gaussian for the central starburst. For 25 of the 34 observed dIs, we resolved stars as faint as M_K=-7.5 mag out to 5 Mpc. We show that the resolved component comprises more than 50% of the light from star formation bursts within the last 3 Gyr. By separating the resolved sources associated with each galaxy from the unresolved component, we determined for the first time the contribution from the resolved stellar component to the total light in the NIR. In nearly all galaxies, the resolved population up to M_K=-7.5 mag represents less than 5% of the total flux in K_s, with ratios in J 1.5-2 times larger. Compared with the visible, the small contribution of the resolved flux allows us to consider the NIR a better domain to sample the old stellar populations, and thus use it to gauge the stellar mass of star-forming dwarf galaxies. For 29 dIs, colour-magnitude diagrams (CMDs) for the resolved component were derived. Three CMDs include more than 1000 stars in both K_s and J, while another 15 CMDs have more than 100 stars. Most of the CMDs show a main blue finger centered around J-K_s=1 mag. In some cases, a red tail extends from the finger out to J-K_s =+2.5 mag. The colour profiles of the unresolved components show a remarkably constant J-K_s = +0.8 to +1.0 mag, which matches the colour of the main finger in the CMDs. For both dIs and BCDs, we searched for correlations between galaxy size, absolute magnitude, central surface brightness, colours, and the resolved over total ratio (for dIs). Good linear correlations were found between the scale length, and the sech magnitude, and between the isophotal semimajor axis and the sech magnitude. Also, correlations were found between the central surface brightness and the sech magnitude. Overall, galaxies with more luminous old components are larger, redder, and brighter in the centre. Thus, size, colour, and the extent of the central plateau appear to be determined by the mass of the old component. For both dIs and BCDs, the Tully-Fisher relation shows considerable scatter in K_s, especially at low luminosities. The scatter appears to be tied to variations in surface brightness. A new ''fundamental plane'' was discovered for dIs which relates the sech absolute magnitude, the central surface brightness, and the neutral hydrogen line-width. The residuals are low enough (rms 0.4 mag), that it offers considerable potential as a distance indicator for star-forming dwarfs. BCDs appear to lie on the dI fundamental plane, but the scatter is larger, probably due to uncertitudes in their line widths. We used NIR images for 22 dEs in the Virgo cluster taken from the GOLDMine database, and some additional data for 9 other dwarf spheroidals in the Local Group, to examine how closely dEs fit into the dI fundamental plane. Over a 9 mag interval in absolute magnitude, the dEs fall in the plane defined by the dIs. The outstanding overlap suggests a close evolutionary connection between dIs and dEs. Using oxygen abundances of dIs and BCDs from the literature, we studied correlations between metallicity, stellar mass, gas mass, baryonic mass, and gas fractions. Although there is some scatter, metallicity correlates with all four parameters in the sense that more massive systems contain more metals. The oxygen abundance correlates very well with the luminosity in K_s, for both dIs and BCDs. Nevertheless, the two relations appear to be different, with more luminous BCDs being more metal rich than dIs with similar absolute magnitudes. This shift can be biased by not including gas. After the gas mass is considered, BCDs allign with dIs on the same mass-metallicity relation, suggesting similar evolutionary connections. Overall, based on their structural and physical properties, closer links emerge between dIs, BCDs, and dEs. Comparing their structural properties, dIs and BCDs appear to share common origins, with the sech component modeling all the NIR flux for dIs and most of the flux for BCDs. On the fundamental plane, dIs and BCDs also show similar dynamical properties. Thus, BCDs seem to be dIs observed in a bursting phase. Taking into account their gas-to-mass fraction, BCDs cannot be considered closed systems, their shifted position in respect to dIs suggesting flows of gas such as infall of gas clouds. Comparing structural properties, dEs lie in the fundamental plane of dIs, suggesting an intimate link between the two systems, in the sense that dEs could be consider the final outcome of dIs after all gas is removed from the system. Full thesis available online at http://aries.phys.yorku.ca/ ovidiuv/Thesis.pdf (7 MB, 247 pag)

Spectrophotometry of Very Bright Stars in the Southern Sky

NASA Astrophysics Data System (ADS)

Krisciunas, Kevin; Suntzeff, Nicholas B.; Kelarek, Bethany; Bonar, Kyle; Stenzel, Joshua

2017-05-01

We obtained spectra of 20 bright stars in the southern sky, including Sirius, Canopus, Betelgeuse, Rigel, Bellatrix, and Procyon, using the 1.5-m telescope at Cerro Tololo Inter-American Observatory and its grating spectrograph RCSPEC. A 7.5 magnitude neutral density filter was used to keep from saturating the CCD. Our spectra are tied to a Kurucz model of Sirius with T = 9850 K, log g = 4.30, and [Fe/H] = +0.4. Because Sirius is much less problematic than using Vega as a fundamental calibrator, the synthetic photometry of our stars constitutes a Sirius-based system that could be used as a new anchor for stellar and extragalactic photometric measurements.

Observational hints of radial migration in disc galaxies from CALIFA

NASA Astrophysics Data System (ADS)

Ruiz-Lara, T.; Pérez, I.; Florido, E.; Sánchez-Blázquez, P.; Méndez-Abreu, J.; Sánchez-Menguiano, L.; Sánchez, S. F.; Lyubenova, M.; Falcón-Barroso, J.; van de Ven, G.; Marino, R. A.; de Lorenzo-Cáceres, A.; Catalán-Torrecilla, C.; Costantin, L.; Bland-Hawthorn, J.; Galbany, L.; García-Benito, R.; Husemann, B.; Kehrig, C.; Márquez, I.; Mast, D.; Walcher, C. J.; Zibetti, S.; Ziegler, B.; Califa Team

2017-07-01

Context. According to numerical simulations, stars are not always kept at their birth galactocentric distances but they have a tendency to migrate. The importance of this radial migration in shaping galactic light distributions is still unclear. However, if radial migration is indeed important, galaxies with different surface brightness (SB) profiles must display differences in their stellar population properties. Aims: We investigate the role of radial migration in the light distribution and radial stellar content by comparing the inner colour, age, and metallicity gradients for galaxies with different SB profiles. We define these inner parts, avoiding the bulge and bar regions and up to around three disc scale lengths (type I, pure exponential) or the break radius (type II, downbending; type III, upbending). Methods: We analysed 214 spiral galaxies from the CALIFA survey covering different SB profiles. We made use of GASP2D and SDSS data to characterise the light distribution and obtain colour profiles of these spiral galaxies. The stellar age and metallicity profiles were computed using a methodology based on full-spectrum fitting techniques (pPXF, GANDALF, and STECKMAP) to the Integral Field Spectroscopic CALIFA data. Results: The distributions of the colour, stellar age, and stellar metallicity gradients in the inner parts for galaxies displaying different SB profiles are unalike as suggested by Kolmogorov-Smirnov and Anderson-Darling tests. We find a trend in which type II galaxies show the steepest profiles of all, type III show the shallowest, and type I display an intermediate behaviour. Conclusions: These results are consistent with a scenario in which radial migration is more efficient for type III galaxies than for type I systems, where type II galaxies present the lowest radial migration efficiency. In such a scenario, radial migration mixes the stellar content, thereby flattening the radial stellar properties and shaping different SB profiles. However, in light of these results we cannot further quantify the importance of radial migration in shaping spiral galaxies, and other processes, such as recent star formation or satellite accretion, might play a role. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/604/A4

Unbound Young Stellar Systems: Star Formation on the Loose

NASA Astrophysics Data System (ADS)

Gouliermis, Dimitrios A.

2018-07-01

Unbound young stellar systems, the loose ensembles of physically related young bright stars, trace the typical regions of recent star formation in galaxies. Their morphologies vary from small few pc-size associations of newly formed stars to enormous few kpc-size complexes composed of stars few 100 Myr old. These stellar conglomerations are located within the disks and along the spiral arms and rings of star-forming disk galaxies, and they are the active star-forming centers of dwarf and starburst galaxies. Being associated with star-forming regions of various sizes, these stellar structures trace the regions where stars form at various length- and timescales, from compact clusters to whole galactic disks. Stellar associations, the prototypical unbound young systems, and their larger counterparts, stellar aggregates, and stellar complexes, have been the focus of several studies for quite a few decades, with special interest on their demographics, classification, and structural morphology. The compiled surveys of these loose young stellar systems demonstrate that the clear distinction of these systems into well-defined classes is not as straightforward as for stellar clusters, due to their low densities, asymmetric shapes and variety in structural parameters. These surveys also illustrate that unbound stellar structures follow a clear hierarchical pattern in the clustering of their stars across various scales. Stellar associations are characterized by significant sub-structure with bound stellar clusters being their most compact parts, while associations themselves are the brighter denser parts of larger stellar aggregates and stellar complexes, which are members of larger super-structures up to the scale of a whole star-forming galaxy. This structural pattern, which is usually characterized as self-similar or fractal, appears to be identical to that of star-forming giant molecular clouds and interstellar gas, driven mainly by turbulence cascade. In this short review, I make a concise compilation of our understanding of unbound young stellar systems across various environments in the local universe, as it is developed during the last 60 years. I present a factual assessment of the clustering behavior of star formation, as revealed from the assembling pattern of stars across loose stellar structures and its relation to the interstellar medium and the environmental conditions. I also provide a consistent account of the processes that possibly play important role in the formation of unbound stellar systems, compiled from both theoretical and observational investigations on the field.

The Secondary Eclipse and Transit of HD 209458b at 24 micron

NASA Astrophysics Data System (ADS)

Harrington, J.; Luszcz, S.; Deming, D.; Richardson, L. J.; Seager, S.

2005-08-01

We used the Multiband Imaging Photometer on the Spitzer Space Telescope to obtain 24-micron lightcurves for one secondary eclipse and half a transit of extrasolar planet HD 209458b behind/in front of its star. Optimal photometric extraction of the total system brightness gives S/N of ˜100 per 10-sec exposure. We measure the deficit of planetary flux in secondary eclipse at 55 ± 10 μ Jy, or 0.260 ± 0.046% of the stellar flux, giving a brightness temperature of 1130 ± 150 K. The secondary eclipse occurs within 7 min (1σ ) of the mid-time between transits, essentially eliminating the hypothesis that HD 209458b's radius is inflated by tidal dissipation due to an elliptical orbit. Such an orbit would have required a second planet in a resonant orbit. This measurement and a similar, simultaneously-submitted result for TrES-1 by Charbonneau et al. (2005) are the first direct measurements of radiation from confirmed extrasolar planets. We measure a preliminary transit depth of 1.559 ± 0.065% of the stellar flux. The stellar limb-darkening curve is flat to within the errors, as expected for this wavelength. Adopting a stellar radius of 1.18 ± 0.10 R⊙ (Cody and Sasselov 2002) gives a planetary radius of 1.43 ± 0.13 RJ, consistent with that derived from optical measurements. The large error bar prevents us from ruling out a significant wavelength dependence of the eclipsing radius, as might be be expected if a particulate coma were responsible for the inflated optical radius. Spitzer has acquired an additional complete transit; updated results will be presented at the conference. This work was supported by the NASA Origins of Solar Systems program and the Spitzer Space Telescope. LJR is an NRC research associate.

Nebular and Stellar Dust Extinction Across the Disk of Emission-line Galaxies on Kiloparsec Scales

NASA Astrophysics Data System (ADS)

Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam; Nayyeri, Hooshang; Sobral, David; Miller, Sarah

2015-11-01

We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this study.

Patterns of Variation for the Sun and Sun-like Stars

NASA Astrophysics Data System (ADS)

Radick, Richard R.; Lockwood, G. Wesley; Henry, Gregory W.; Hall, Jeffrey C.; Pevtsov, Alexei A.

2018-03-01

We compare patterns of variation for the Sun and 72 Sun-like stars by combining total and spectral solar irradiance measurements between 2003 and 2017 from the SORCE satellite, Strömgren b, y stellar photometry between 1993 and 2017 from Fairborn Observatory, and solar and stellar chromospheric Ca II H+K emission observations between 1992 and 2016 from Lowell Observatory. The new data and their analysis strengthen the relationships found previously between chromospheric and brightness variability on the decadal timescale of the solar activity cycle. Both chromospheric H+K and photometric b, y variability among Sun-like stars are related to average chromospheric activity by power laws on this timescale. Young active stars become fainter as their H+K emission increases, and older, less active, more Sun-age stars tend to show a pattern of direct correlation between photometric and chromospheric emission variations. The directly correlated pattern between total solar irradiance and chromospheric Ca II emission variations shown by the Sun appears to extend also to variations in the Strömgren b, y portion of the solar spectrum. Although the Sun does not differ strongly from its stellar age and spectral class mates in the activity and variability characteristics that we have now studied for over three decades, it may be somewhat unusual in two respects: (1) its comparatively smooth, regular activity cycle, and (2) its rather low photometric brightness variation relative to its chromospheric activity level and variation, perhaps indicating that facular emission and sunspot darkening are especially well-balanced on the Sun.

Revealing stellar brightness profiles by means of microlensing fold caustics

NASA Astrophysics Data System (ADS)

Dominik, M.

2004-09-01

With a handful of measurements of limb-darkening coefficients, galactic microlensing has already proven to be a powerful technique for studying atmospheres of distant stars. Survey campaigns such as OGLE-III are capable of providing ~10 suitable target stars per year that undergo microlensing events involving passages over the caustic created by a binary lens, which last from a few hours to a few days and allow us to resolve the stellar atmosphere by frequent broad-band photometry. For a caustic exit lasting 12 h and a photometric precision of 1.5 per cent, a moderate sampling interval of 30 min (corresponding to ~25-30 data points) is sufficient for providing a reliable measurement of the linear limb-darkening coefficient Γ with an uncertainty of ~8 per cent, which reduces to ~3 per cent for a reduced sampling interval of 6 min for the surroundings of the end of the caustic exit. While some additional points over the remaining parts of the light curve are highly valuable, a denser sampling in these regions provides little improvement. Unless an accuracy of less than 5 per cent is desired, limb-darkening coefficients for several filters can be obtained or observing time can be spent on other targets during the same night. The adoption of an inappropriate stellar brightness profile as well as the effect of acceleration between source and caustic yield distinguishable characteristic systematics in the model residuals. Acceleration effects are unlikely to affect the light curve significantly for most events, although a free acceleration parameter blurs the limb-darkening measurement if the passage duration cannot be accurately determined.

The metallicity of the intracluster medium over cosmic time: further evidence for early enrichment

NASA Astrophysics Data System (ADS)

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn; Simionescu, Aurora; Urban, Ondrej; Werner, Norbert; Zhuravleva, Irina

2017-12-01

We use Chandra X-ray data to measure the metallicity of the intracluster medium (ICM) in 245 massive galaxy clusters selected from X-ray and Sunyaev-Zel'dovich (SZ) effect surveys, spanning redshifts 0 < z < 1.2. Metallicities were measured in three different radial ranges, spanning cluster cores through their outskirts. We explore trends in these measurements as a function of cluster redshift, temperature and surface brightness 'peakiness' (a proxy for gas cooling efficiency in cluster centres). The data at large radii (0.5-1 r500) are consistent with a constant metallicity, while at intermediate radii (0.1-0.5 r500) we see a late-time increase in enrichment, consistent with the expected production and mixing of metals in cluster cores. In cluster centres, there are strong trends of metallicity with temperature and peakiness, reflecting enhanced metal production in the lowest entropy gas. Within the cool-core/sharply peaked cluster population, there is a large intrinsic scatter in central metallicity and no overall evolution, indicating significant astrophysical variations in the efficiency of enrichment. The central metallicity in clusters with flat surface brightness profiles is lower, with a smaller intrinsic scatter, but increases towards lower redshifts. Our results are consistent with other recent measurements of ICM metallicity as a function of redshift. They reinforce the picture implied by observations of uniform metal distributions in the outskirts of nearby clusters, in which most of the enrichment of the ICM takes place before cluster formation, with significant later enrichment taking place only in cluster centres, as the stellar populations of the central galaxies evolve.

The Fundamental Plane of Ultra-Massive Galaxies at z 2

NASA Astrophysics Data System (ADS)

Conselice, Christopher

2016-10-01

The fundamental plane (FP), relating the effective radius, velocity dispersion, and surface brightness is a unique tool for studying the structural, stellar, and dark matter evolution of early-type galaxies, and can reveal how these galaxies have formed and evolved. Thus far, studies have been mostly limited to z<1.3, beyond which the absorption lines used to derive velocity dispersions are redshifted out of the optical. With the advent of sensitive NIR spectrographs on 8m telescopes, it is now possible for the first time to study the FP directly at the epoch (z 2), where lower redshift studies predict it to have formed. Through a large investment of time with the 8m - VLT NIR spectrograph X-SHOOTER, we have derived velocity dispersions for a unique sample of 11 quiescent galaxies at z=2, tripling the number of galaxies with such measurements. We propose to obtain WFC3/IR imaging of these galaxies, which when combined with our ground-based spectroscopy, will allow us to measure accurately the fundamental plane at z 2 for the first time through accurate sizes derived from surface brightness profile fits to the data. This measurement of the FP will further reveal the time-scales and methods of formation for the most massive early type galaxies. The HST observations will also allow us to measure the structures of these galaxies, to search for any extended envelopes or asymmetries, and to examine the properties of their satellite galaxies. Three of our systems also show hints of having close companions through our spectroscopy and WFC3/IR imaging is required to investigate this further.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn

Here, we use Chandra X-ray data to measure the metallicity of the intracluster medium (ICM) in 245 massive galaxy clusters selected from X-ray and Sunyaev–Zel'dovich (SZ) effect surveys, spanning redshifts 0 < z < 1.2. Metallicities were measured in three different radial ranges, spanning cluster cores through their outskirts. We explore trends in these measurements as a function of cluster redshift, temperature and surface brightness ‘peakiness’ (a proxy for gas cooling efficiency in cluster centres). The data at large radii (0.5–1 r500) are consistent with a constant metallicity, while at intermediate radii (0.1–0.5 r500) we see a late-time increase inmore » enrichment, consistent with the expected production and mixing of metals in cluster cores. In cluster centres, there are strong trends of metallicity with temperature and peakiness, reflecting enhanced metal production in the lowest entropy gas. Within the cool-core/sharply peaked cluster population, there is a large intrinsic scatter in central metallicity and no overall evolution, indicating significant astrophysical variations in the efficiency of enrichment. The central metallicity in clusters with flat surface brightness profiles is lower, with a smaller intrinsic scatter, but increases towards lower redshifts. Our results are consistent with other recent measurements of ICM metallicity as a function of redshift. They reinforce the picture implied by observations of uniform metal distributions in the outskirts of nearby clusters, in which most of the enrichment of the ICM takes place before cluster formation, with significant later enrichment taking place only in cluster centres, as the stellar populations of the central galaxies evolve.« less

Absorption line indices in the UV. I. Empirical and theoretical stellar population models

NASA Astrophysics Data System (ADS)

Maraston, C.; Nieves Colmenárez, L.; Bender, R.; Thomas, D.

2009-01-01

Aims: Stellar absorption lines in the optical (e.g. the Lick system) have been extensively studied and constitute an important stellar population diagnostic for galaxies in the local universe and up to moderate redshifts. Proceeding towards higher look-back times, galaxies are younger and the ultraviolet becomes the relevant spectral region where the dominant stellar populations shine. A comprehensive study of ultraviolet absorption lines of stellar population models is however still lacking. With this in mind, we study absorption line indices in the far and mid-ultraviolet in order to determine age and metallicity indicators for UV-bright stellar populations in the local universe as well as at high redshift. Methods: We explore empirical and theoretical spectral libraries and use evolutionary population synthesis to compute synthetic line indices of stellar population models. From the empirical side, we exploit the IUE-low resolution library of stellar spectra and system of absorption lines, from which we derive analytical functions (fitting functions) describing the strength of stellar line indices as a function of gravity, temperature and metallicity. The fitting functions are entered into an evolutionary population synthesis code in order to compute the integrated line indices of stellar populations models. The same line indices are also directly evaluated on theoretical spectral energy distributions of stellar population models based on Kurucz high-resolution synthetic spectra, In order to select indices that can be used as age and/or metallicity indicators for distant galaxies and globular clusters, we compare the models to data of template globular clusters from the Magellanic Clouds with independently known ages and metallicities. Results: We provide synthetic line indices in the wavelength range ~1200 Å to ~3000 Å for stellar populations of various ages and metallicities.This adds several new indices to the already well-studied CIV and SiIV absorptions. Based on the comparison with globular cluster data, we select a set of 11 indices blueward of the 2000 Å rest-frame that allows us to recover well the ages and the metallicities of the clusters. These indices are ideal to study ages and metallicities of young galaxies at high redshift. We also provide the synthetic high-resolution stellar population SEDs.

Big Data in the SHELA Field: Investigating Galaxy Quenching at High Redshifts

NASA Astrophysics Data System (ADS)

Stevans, Matthew L.; Finkelstein, Steven L.; Wold, Isak; Kawinwanichakij, Lalitwadee; Sherman, Sydney; Gebhardt, Karl; Jogee, Shardha; Papovich, Casey J.; Ciardullo, Robin; Gronwall, Caryl; Gawiser, Eric J.; Acquaviva, Viviana; Casey, Caitlin; Florez, Jonathan; HETDEX Team

2017-06-01

We present a measurement of the z ~ 4 Lyman break galaxy (LBG) rest-frame UV luminosity function to investigate the onset of quenching in the early universe. The bright-end of the galaxy luminosity function typically shows an exponential decline far steeper than that of the underlying halo mass function. This is typically attributed to negative feedback from past active galactic nuclei (AGN) activity as well as dust attenuation. Constraining the abundance of bright galaxies at early times (z > 3) can provide a key insight into the mechanisms regulating star formation in galaxies. However, existing studies suffer from low number statistics and/or the inability to robustly remove stellar and AGN contaminants. In this study we take advantage of the unprecedentedly large (24 deg^2) Spitzer/HETDEX Exploratory Large Area (SHELA) field and its deep multi-wavelength photometry, which includes DECam ugriz, NEWFIRM K-band, Spitzer/IRAC, Herschel/SPIRE, and X-ray from XMM-Newton and Chandra. With SHELA’s deep imaging over a large area we are uniquely positioned to study statistically significant samples of massive galaxies at high redshifts (z > 3) when the first massive galaxies began quenching. We select our sample using photometric redshifts from the EAZY software package (Brammer et al. 2008) based on the optical and far-infrared imaging. We directly identify and remove stellar contaminants and AGN with IRAC colors and X-ray detections, respectively. By pinning down the exact shape of the bright-end of the z ~ 4 LBG luminosity function, we provide the deepest probe yet into the baryonic physics dominating star formation and quenching in the early universe.

MAPPING THE CLUMPY STRUCTURES WITHIN SUBMILLIMETER GALAXIES USING LASER-GUIDE STAR ADAPTIVE OPTICS SPECTROSCOPY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menendez-Delmestre, Karin; Goncalves, Thiago S.; Blain, Andrew W.

2013-04-20

We present the first integral-field spectroscopic observations of high-redshift submillimeter-selected galaxies (SMGs) using Laser-Guide Star Adaptive Optics. We target H{alpha} emission of three SMGs at redshifts z {approx} 1.4-2.4 with the OH-Suppressing Infrared Imaging Spectrograph on Keck. The spatially resolved spectroscopy of these galaxies reveals unresolved broad-H{alpha} line regions (FWHM >1000 km s{sup -1}) likely associated with an active galactic nucleus (AGN) and regions of diffuse star formation traced by narrow-line H{alpha} emission (FWHM {approx}< 500 km s{sup -1}) dominated by multiple H{alpha}-bright stellar clumps, each contributing 1%-30% of the total clump-integrated H{alpha} emission. We find that these SMGs hostmore » high star formation rate surface densities, similar to local extreme sources, such as circumnuclear starbursts and luminous infrared galaxies. However, in contrast to these local environments, SMGs appear to be undergoing such intense activity on significantly larger spatial scales as revealed by extended H{alpha} emission over 4-16 kpc. H{alpha} kinematics show no evidence of ordered global motion as would be found in a disk, but rather large velocity offsets ({approx}few Multiplication-Sign 100 km s{sup -1}) between the distinct stellar clumps. Together with the asymmetric distribution of the stellar clumps around the AGN in these objects, it is unlikely that we are unveiling a clumpy disk structure as has been suggested in other high-redshift populations of star-forming galaxies. The SMG clumps in this sample may correspond to remnants of originally independent gas-rich systems that are in the process of merging, hence triggering the ultraluminous SMG phase.« less

The Next Generation Fornax Survey (NGFS). IV. Mass and Age Bimodality of Nuclear Clusters in the Fornax Core Region

NASA Astrophysics Data System (ADS)

Ordenes-Briceño, Yasna; Puzia, Thomas H.; Eigenthaler, Paul; Taylor, Matthew A.; Muñoz, Roberto P.; Zhang, Hongxin; Alamo-Martínez, Karla; Ribbeck, Karen X.; Grebel, Eva K.; Ángel, Simón; Côté, Patrick; Ferrarese, Laura; Hilker, Michael; Lançon, Ariane; Mieske, Steffen; Miller, Bryan W.; Rong, Yu; Sánchez-Janssen, Ruben

2018-06-01

We present the analysis of 61 nucleated dwarf galaxies in the central regions (≲R vir/4) of the Fornax galaxy cluster. The galaxies and their nuclei are studied as part of the Next Generation Fornax Survey using optical imaging obtained with the Dark Energy Camera mounted at Blanco/Cerro Tololo Inter-American Observatory and near-infrared data obtained with VIRCam at VISTA/ESO. We decompose the nucleated dwarfs in nucleus and spheroid, after subtracting the surface brightness profile of the spheroid component and studying the nucleus using point source photometry. In general, nuclei are consistent with colors of confirmed metal-poor globular clusters, but with significantly smaller dispersion than other confirmed compact stellar systems in Fornax. We find a bimodal nucleus mass distribution with peaks located at {log}({{ \\mathcal M }}* /{M}ȯ )≃ 5.4 and ∼6.3. These two nucleus subpopulations have different stellar population properties: the more massive nuclei are older than ∼2 Gyr and have metal-poor stellar populations (Z ≤ 0.02 Z ⊙), while the less massive nuclei are younger than ∼2 Gyr with metallicities in the range 0.02 < Z/Z ⊙ ≤ 1. We find that the nucleus mass ({{ \\mathcal M }}nuc}) versus galaxy mass ({{ \\mathcal M }}gal}) relation becomes shallower for less massive galaxies starting around 108 M ⊙, and the mass ratio {η }n={{ \\mathcal M }}nuc}/{{ \\mathcal M }}gal} shows a clear anticorrelation with {{ \\mathcal M }}gal} for the lowest masses, reaching 10%. We test current theoretical models of nuclear cluster formation and find that they cannot fully reproduce the observed trends. A likely mixture of in situ star formation and star cluster mergers seems to be acting during nucleus growth over cosmic time.

Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies

NASA Technical Reports Server (NTRS)

Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

2012-01-01

We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses <10(sup 7.7) solar mass and Hi line widths <80 kilometers per second. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

Scaling relations and the fundamental line of the local group dwarf galaxies

NASA Astrophysics Data System (ADS)

Woo, Joanna; Courteau, Stéphane; Dekel, Avishai

2008-11-01

We study the scaling relations between global properties of dwarf galaxies in the local group. In addition to quantifying the correlations between pairs of variables, we explore the `shape' of the distribution of galaxies in log parameter space using standardized principal component analysis, the analysis is performed first in the 3D structural parameter space of stellar mass M*, internal velocity V and characteristic radius R* (or surface brightness μ*). It is then extended to a 4D space that includes a stellar population parameter such as metallicity Z or star formation rate . We find that the local group dwarfs basically define a one-parameter `fundamental line' (FL), primarily driven by stellar mass, M*. A more detailed inspection reveals differences between the star formation properties of dwarf irregulars (dI's) and dwarf ellipticals (dE's), beyond the tendency of the latter to be more massive. In particular, the metallicities of dI's are typically lower by a factor of 3 at a given M* and they grow faster with increasing M*, showing a tighter FL in the 4D space for the dE's. The structural scaling relations of dI's resemble those of the more massive spirals, but the dI's have lower star formation rates for a given M* which also grow faster with increasing M*. On the other hand, the FL of the dE's departs from the fundamental plane of bigger ellipticals. While the one-parameter nature of the FL and the associated slopes of the scaling relations are consistent with the general predictions of supernova feedback from Dekel & Woo, the differences between the FL's of the dE's and the dI's remain a challenge and should serve as a guide for the secondary physical processes responsible for these two types.

A Hyper Suprime-Cam View of the Interacting Galaxies of the M81 Group

NASA Astrophysics Data System (ADS)

Okamoto, Sakurako; Arimoto, Nobuo; Ferguson, Annette M. N.; Bernard, Edouard J.; Irwin, Mike J.; Yamada, Yoshihiko; Utsumi, Yousuke

2015-08-01

We present the first results of a wide-field mapping survey of the M81 group conducted with Hyper Suprime-Cam on the Subaru Telescope. Our deep photometry reaches ˜2 mag below the tip of the red giant branch (RGB) and reveals the spatial distribution of both old and young stars over an area of ˜ 100 × 115 kpc at the distance of M81. The young stars (˜30-160 Myr old) closely follow the neutral hydrogen distribution and can be found in a stellar stream between M81 and NGC 3077 and in numerous outlying stellar associations, including the known concentrations of Arp's Loop, Holmberg IX, an arc in the halo of M82, BK3N, and the Garland. Many of these groupings do not have counterparts in the RGB maps, suggesting they may be genuinely young systems. Our survey also reveals for the first time the very extended (≥slant 2× {R}25) halos of RGB stars around M81, M82, and NGC 3077, as well as faint tidal streams that link these systems. The halos of M82 and NGC 3077 exhibit highly disturbed morphologies, presumably a consequence of the recent gravitational encounter and their ongoing disruption. While the halos of M81 and NGC 3077 and the inner halo of M82 have similar {(g-i)}0 colors, the outer halo of M82 is significantly bluer indicating it is more metal poor. Remarkably, our deep panoramic view of the M81 group demonstrates that the complexity long known to be present in HI is equally matched in the low surface brightness stellar component. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

THE MASS PROFILE AND SHAPE OF BARS IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G): SEARCH FOR AN AGE INDICATOR FOR BARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Taehyun; Lee, Myung Gyoon; Sheth, Kartik

2015-01-20

We have measured the radial light profiles and global shapes of bars using two-dimensional 3.6 μm image decompositions for 144 face-on barred galaxies from the Spitzer Survey of Stellar Structure in Galaxies. The bar surface brightness profile is correlated with the stellar mass and bulge-to-total (B/T) ratio of their host galaxies. Bars in massive and bulge-dominated galaxies (B/T > 0.2) show a flat profile, while bars in less massive, disk-dominated galaxies (B/T ∼ 0) show an exponential, disk-like profile with a wider spread in the radial profile than in the bulge-dominated galaxies. The global two-dimensional shapes of bars, however, are rectangular/boxy, independentmore » of the bulge or disk properties. We speculate that because bars are formed out of disks, bars initially have an exponential (disk-like) profile that evolves over time, trapping more disk stars to boxy bar orbits. This leads bars to become stronger and have flatter profiles. The narrow spread of bar radial profiles in more massive disks suggests that these bars formed earlier (z > 1), while the disk-like profiles and a larger spread in the radial profile in less massive systems imply a later and more gradual evolution, consistent with the cosmological evolution of bars inferred from observational studies. Therefore, we expect that the flatness of the bar profile can be used as a dynamical age indicator of the bar to measure the time elapsed since the bar formation. We argue that cosmic gas accretion is required to explain our results on bar profile and the presence of gas within the bar region.« less

The AU Microscopii Debris Disk: Multiwavelength Imaging and Modeling

NASA Astrophysics Data System (ADS)

Fitzgerald, Michael P.; Kalas, Paul G.; Duchêne, Gaspard; Pinte, Christophe; Graham, James R.

2007-11-01

Debris disks around main-sequence stars are produced by the destruction of unseen parent bodies. AU Microscopii (GJ 803) is a compelling object to study in the context of disk evolution across different spectral types, as it is an M dwarf whose nearly edge-on disk may be directly compared to that of its A5 V sibling β Pic. We resolve the disk from 8-60 AU in the near-IR JHK' bands at high resolution with the Keck II Telescope and adaptive optics, and develop a data reduction technique for the removal of the stellar point-spread function. We measure a blue color across the near-IR bands, and confirm the presence of substructure in the inner disk. Some of the structural features exhibit wavelength-dependent positions. Recent measurements of the scattered-light polarization indicate the presence of porous grains. The scattering properties of these porous grains have a strong effect on the inferred structure of the disk relative to the majority of previously modeled grain types. Complementing prior work, we use a Monte Carlo radiative transfer code to compare a relatively simple model of the distribution of porous grains to a broad data set, simultaneously fitting midplane surface brightness profiles and the spectral energy distribution. Our model confirms that the large-scale architecture of the disk is consistent with detailed models of steady state grain dynamics. A belt of parent bodies from 35-40 AU produces dust that is then swept outward by stellar wind and radiation. We infer the presence of very small grains in the region exterior to the belt, down to sizes of ~0.05 μm. These sizes are consistent with stellar mass-loss rates M˙*<<102 M˙solar

Central Stellar Mass Deficits in the Bulges of Local Lenticular Galaxies, and the Connection with Compact z ~ 1.5 Galaxies

NASA Astrophysics Data System (ADS)

Dullo, Bililign T.; Graham, Alister W.

2013-05-01

We have used the full radial extent of images from the Hubble Space Telescope's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to extract surface brightness profiles from a sample of six, local lenticular galaxy candidates. We have modeled these profiles using a core-Sérsic bulge plus an exponential disk model. Our fast rotating lenticular disk galaxies with bulge magnitudes MV <~ -21.30 mag have central stellar deficits, suggesting that these bulges may have formed from "dry" merger events involving supermassive black holes (BHs) while their surrounding disk was subsequently built up, perhaps via cold gas accretion scenarios. The central stellar mass deficits M def are roughly 0.5-2 M BH (BH mass), rather than ~10-20 M BH as claimed from some past studies, which is in accord with core-Sérsic model mass deficit measurements in elliptical galaxies. Furthermore, these bulges have Sérsic indices n ~3, half-light radii Re < 2 kpc and masses >1011 M ⊙, and therefore appear to be descendants of the compact galaxies reported at z ~ 1.5-2. Past studies which have searched for these local counterparts by using single-component galaxy models to provide the z ~ 0 size comparisons have overlooked these dense, compact, and massive bulges in today's early-type disk galaxies. This evolutionary scenario not only accounts for what are today generally old bulges—which must be present in z ~ 1.5 images—residing in what are generally young disks, but it eliminates the uncomfortable suggestion of a factor of three to five growth in size for the compact, z ~ 1.5 galaxies that are known to possess infant disks.

The Resolved Stellar Population in 50 Regions of M83 from HST/WFC3 Early Release Science Observations

NASA Technical Reports Server (NTRS)

Kim, Hwihyun; Whitmore, Bradley C.; Chandar, Rupali; Saha, Abhijit; Kaleida, Catherine C.; Mutchler, Max; Cohen, Seth H.; Calzetti, Daniela; O’Connell, Robert W.; Windhorst, Rogier A.;

Constraining Stellar Coronal Mass Ejections through Multi-wavelength Analysis of the Active M Dwarf EQ Peg

NASA Astrophysics Data System (ADS)

Crosley, M. K.; Osten, R. A.

2018-03-01

Stellar coronal mass ejections remain experimentally unconstrained, unlike their stellar flare counterparts, which are observed ubiquitously across the electromagnetic spectrum. Low-frequency radio bursts in the form of a type II burst offer the best means of identifying and constraining the rate and properties of stellar CMEs. CME properties can be further improved through the use of proposed solar-stellar scaling relations and multi-wavelength observations of CMEs through the use of type II bursts and the associated flares expected to occur alongside them. We report on 20 hr of observation of the nearby, magnetically active, and well-characterized M dwarf star EQ Peg. The observations are simultaneously observed with the Jansky Very Large Array at their P-band (230–470 MHz) and at the Apache Point observatory in the SDSS u‧ filter (λ = 3557 Å). Dynamic spectra of the P-band data, constructed to search for signals in the frequency-time domains, did not reveal evidence of drifting radio bursts that could be ascribed to type II bursts. Given the sensitivity of our observations, we are able to place limits on the brightness temperature and source size of any bursts that may have occurred. Using solar scaling rations on four observed stellar flares, we predict CME parameters. Given the constraints on coronal density and photospheric field strength, our models suggest that the observed flares would have been insufficient to produce detectable type II bursts at our observed frequencies. We consider the implications of these results, and other recent findings, on stellar mass loss.

M Dwarf Mysteries

NASA Astrophysics Data System (ADS)

Henry, Todd J.; Jao, Wei-Chun; Irwin, Jonathan; Dieterich, Sergio; Finch, Charlie T.; Riedel, Adric R.; Subasavage, John P.; Winters, Jennifer; RECONS Team

2017-01-01

During RECONS' 17-year (so far) astrometry/photometry program at the CTIO/SMARTS 0.9m, we have observed thousands of the ubiquitous red dwarfs in the solar neighborhood. During this reconnaissance, a few mysterious characters have emerged ...The Case of the Mercurial Stars: One M dwarf has been fading steadily for more than a decade, at last measure 6% fainter than when it was first observed. Another has grown brighter by 7% over 15 years. Are these brightness changes part of extremely long stellar cycles, or something else entirely?The Case of Identical Stellar Twins that Aren't: Two M dwarfs seem at first to be identical siblings traveling together through the Galaxy. They have virtually identical spectra at optical wavelengths and identical colors throughout the VRIJHK bands. Long-term astrometry indicates that they are, indeed, at the same distance via parallax measurements, and their proper motions match precisely. Yet, one of the twins is FOUR times brighter than the other. Followup work has revealed that the brighter component is a very close spectroscopic double, but no other stars are seen. So, the mystery may be half solved, but why do the close stars remain twice as bright as their widely-separated twin?The Case of the Great Kaboom!: After more than 1000 nights of observing on the reliable 0.9m telescope, with generally routine frames reading out upon the screen, one stellar system comprised of five red dwarfs flared in stunning fashion. Of the two distinct sources, the fainter one (an unresolved double) surpassed the brightness of the brighter one (an unresolved triple), increasing by more than three full magnitudes in the V filter. Which component actually flared? Is this magnificent outburst an unusual event, or in fact typical for this system and other M dwarfs?At the AAS meeting, we hope to probe the cognoscenti who study the Sun's smaller cousins to solve these intriguing M Dwarf Mysteries.This effort has been supported by the NSF through grants AST-0908402, AST-1109445, and AST-1412026, and via observations made possible by the SMARTS Consortium.

Brightness and transparency in the early visual cortex.

PubMed

Salmela, Viljami R; Vanni, Simo

2013-06-24

Several psychophysical studies have shown that transparency can have drastic effects on brightness and lightness. However, the neural processes generating these effects have remained unresolved. Several lines of evidence suggest that the early visual cortex is important for brightness perception. While single cell recordings suggest that surface brightness is represented in the primary visual cortex, the results of functional magnetic resonance imaging (fMRI) studies have been discrepant. In addition, the location of the neural representation of transparency is not yet known. We investigated whether the fMRI responses in areas V1, V2, and V3 correlate with brightness and transparency. To dissociate the blood oxygen level-dependent (BOLD) response to brightness from the response to local border contrast and mean luminance, we used variants of White's brightness illusion, both opaque and transparent, in which luminance increments and decrements cancel each other out. The stimuli consisted of a target surface and a surround. The surround luminance was always sinusoidally modulated at 0.5 Hz to induce brightness modulation to the target. The target luminance was constant or modulated in counterphase to null brightness modulation. The mean signal changes were calculated from the voxels in V1, V2, and V3 corresponding to the retinotopic location of the target surface. The BOLD responses were significantly stronger for modulating brightness than for stimuli with constant brightness. In addition, the responses were stronger for transparent than for opaque stimuli, but there was more individual variation. No interaction between brightness and transparency was found. The results show that the early visual areas V1-V3 are sensitive to surface brightness and transparency and suggest that brightness and transparency are represented separately.

Einstein Observations of X-ray emission from A stars

NASA Astrophysics Data System (ADS)

Golub, L.; Harnden, F. R., Jr.; Maxson, C. W.; Rosner, R.; Vaiana, G. S.; Cash, W., Jr.; Snow, T. P., Jr.

1983-08-01

Results are reported from the combined CfA Stellar Survey of selected bright A stars and an Einstein Guest Observer program for Ap and Am stars. In an initial report of results from the CfA Stellar Surveys by Vaiana et al. (1981) it was noted that the spread in observed X-ray luminosities among the few A stars observed was quite large. The reasons for this large spread was studied by Pallavicini et al. (1981). It was found that the X-ray emission from normal stars is related very strongly to bolometric luminosity for early-type stars and to rotation rate for late-type stars. However, an exception to this rule has been the apparently anomalous behavior of A star X-ray emission, for which the large spread in luminosity showed no apparent correlation with either bolometric luminosity or stellar rotation rate. In the present study, it is shown that the level of emission from normal A stars agrees with the correlation observed for O and B stars.

Resolving the Wind Structure of Eta Carinae

NASA Technical Reports Server (NTRS)

Gull, T.; Hillier, J.; Ishibashi, K.; Davidson, K.

2000-01-01

Space Telescope Imaging Spectrograph (STIS) spectral observations of Eta Carinae have resolved the wind structure of the star(s) from the central point source. These observations were done with a 52 x 0.1" aperture, resolving power of about 5000 and complete spectral coverage from 1640A to 10400A. Various broad stellar Lines are seen to change within the central 0.511 of the nebular region. The Balmer lines, relative to the continuum, drop in strength while some Fe II lines scale with the continuum. Other Fe II lines increase in intensity while still others decrease. The structure to the southeast of the central source shows considerable variation in the stellar line strengths. To the Northwest, the emission is dominated by the very bright nebular knots, Weigelt blobs B and D. Three sets of observations have been done: March 1998, February 1999 and March 2000 to monitor the spectral variations. The stellar, wind and nebular emission changes considerably during this two year period. This work was done under the STIS GTO and HST GO funding.

II Zw 40 - 30 Doradus on Steroids

NASA Astrophysics Data System (ADS)

Leitherer, Claus; Lee, Janice C.; Levesque, Emily M.

2017-11-01

We obtained HST COS G140L spectra of the enigmatic nearby blue compact dwarf galaxy II Zw 40. The galaxy hosts a nuclear super star cluster embedded in a radio-bright nebula, similar to those observed in the related blue compact dwarfs NGC 5253 and Henize 2-10. The ultraviolet spectrum of II Zw 40 is exceptional in terms of the strength of He II 1640, O III] 1666 and C III] 1909. We determined reddening, age, and the cluster mass from the ultraviolet data. The super nebula and the ionizing cluster exceed the ionizing luminosity and stellar mass of the local benchmark 30 Doradus by an order of magnitude. Comparison with stellar evolution models accounting for rotation reveals serious short-comings: these models do not account for the presence of Wolf-Rayet-like stars at young ages observed in II Zw 40. Photoionization modeling is used to probe the origin of the nebular lines and determine gas phase abundances. C/O is solar, in agreement with the result of the stellar-wind modeling.

A Photometric Machine-Learning Method to Infer Stellar Metallicity

NASA Technical Reports Server (NTRS)

Miller, Adam A.

2015-01-01

Following its formation, a star's metal content is one of the few factors that can significantly alter its evolution. Measurements of stellar metallicity ([Fe/H]) typically require a spectrum, but spectroscopic surveys are limited to a few x 10(exp 6) targets; photometric surveys, on the other hand, have detected > 10(exp 9) stars. I present a new machine-learning method to predict [Fe/H] from photometric colors measured by the Sloan Digital Sky Survey (SDSS). The training set consists of approx. 120,000 stars with SDSS photometry and reliable [Fe/H] measurements from the SEGUE Stellar Parameters Pipeline (SSPP). For bright stars (g' < or = 18 mag), with 4500 K < or = Teff < or = 7000 K, corresponding to those with the most reliable SSPP estimates, I find that the model predicts [Fe/H] values with a root-mean-squared-error (RMSE) of approx.0.27 dex. The RMSE from this machine-learning method is similar to the scatter in [Fe/H] measurements from low-resolution spectra..

A Panchromatic View of Star-Forming Regions in the Magellanic Clouds: Characterizing Physical and Evolutionary Parameters of 1,000 Young Stellar Objects

NASA Astrophysics Data System (ADS)

Carlson, Lynn R.

2010-01-01

I discuss newly discovered Young Stellar Objects (YSOs) in several star-forming regions in the Magellanic Clouds. I exploit the synergy between infrared photometry from the Spitzer SAGE (Surveying the Agents of Galaxy Evolution) legacy programs, near-infrared and optical photometry from ground-based surveys, and HST imaging to characterize young stellar populations. This reveals a variety of Main Sequence Stars and Proto-Stars over a wide range of evolutionary stages. Through SED fitting, I characterize the youngest, embedded, infrared-bright YSOs. Complementary color-Magnitude analysis and isochrone fitting of optical data allows a statistical description of more evolved, unembedded stellar and protostellar populations within these same regions. I examine the early evolution of Magellanic star clusters, including propagating and triggered star formation, and take a step toward characterizing evolutionary timescales for YSOs. In this talk, I present an overview of the project and exemplify the analysis by focusing on NGC 602 in the SMC and Henize 206 in the LMC as examples. The SAGE Project is supported by NASA/Spitzer grant 1275598 and NASA NAG5-12595.

Analysis of Mass Profiles and Cooling Flows of Bright, Early-Type Galaxies AO2, AO3 and Surface Brightness Profiles and Energetics of Intracluster Gas in Cool Galaxy Clusters AO3

NASA Technical Reports Server (NTRS)

White, Raymond E., III

1998-01-01

This final report uses ROSAT observations to analyze two different studies. These studies are: Analysis of Mass Profiles and Cooling Flows of Bright, Early-Type Galaxies; and Surface Brightness Profiles and Energetics of Intracluster Gas in Cool Galaxy Clusters.

IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peters, Thomas; Girichidis, Philipp; Gatto, Andrea

2015-11-10

The halo of the Milky Way contains a hot plasma with a surface brightness in soft X-rays of the order 10{sup −12} erg cm{sup −2} s{sup −1} deg{sup −2}. The origin of this gas is unclear, but so far numerical models of galactic star formation have failed to reproduce such a large surface brightness by several orders of magnitude. In this paper, we analyze simulations of the turbulent, magnetized, multi-phase interstellar medium including thermal feedback by supernova explosions as well as cosmic-ray feedback. We include a time-dependent chemical network, self-shielding by gas and dust, and self-gravity. Pure thermal feedback alonemore » is sufficient to produce the observed surface brightness, although it is very sensitive to the supernova rate. Cosmic rays suppress this sensitivity and reduce the surface brightness because they drive cooler outflows. Self-gravity has by far the largest effect because it accumulates the diffuse gas in the disk in dense clumps and filaments, so that supernovae exploding in voids can eject a large amount of hot gas into the halo. This can boost the surface brightness by several orders of magnitude. Although our simulations do not reach a steady state, all simulations produce surface brightness values of the same order of magnitude as the observations, with the exact value depending sensitively on the simulation parameters. We conclude that star formation feedback alone is sufficient to explain the origin of the hot halo gas, but measurements of the surface brightness alone do not provide useful diagnostics for the study of galactic star formation.« less

NGST: Exploring the Fossil Record of Galaxy Formation

NASA Technical Reports Server (NTRS)

Rich, R. Michael

1998-01-01

During this grant period the investigator has accomplished the following: developed and researched the science case for high resolution optical imaging with NGST (Next Generation Space Telescope); presented to the ASWG (Ad-Hoc Science Working Group) on the use of NGST to image and measure the proper motions of white dwarf stars that could account for the MACHO events toward the LMC (Large Magellanic Cloud); wrote proposals for the Design Reference Mission. Three proposals have been written on the following topics: Measuring the faint end of the white dwarf luminosity function to get an independent measure of the age of the oldest stars, measurement of the stellar luminosity function over the full range of age, abundance, and population type, and deep imaging of Local Group halos to measure the relative ages of the oldest stars in the Milky Way and other galaxies; he has introduced simulations of crowded field stellar photometry on a hypothetical population in the M31 halo. Using a physically correct luminosity function and a surface brightness of 24.5 mag/sq. arcsec, NGST imaging in 10 hours easily measures the turnoff and reaches 3 mags down the main sequence in the halo of M31; and has delivered talks at the NGST workshop in Liege, and at the meeting in Paris entitled "Connecting the Distant Universe with the Local Fossil Record".

Characterisation of a candidate dual AGN

NASA Astrophysics Data System (ADS)

Lena, D.; Panizo-Espinar, G.; Jonker, P. G.; Torres, M.; Heida, M.

2018-05-01

We present Chandra and optical observations of a candidate dual AGN discovered serendipitously while searching for recoiling black holes via a cross-correlation between the serendipitous XMM source catalog (2XMMi) and SDSS-DR7 galaxies with a separation no larger than ten times the sum of their Petrosian radii. The system has a stellar mass ratio M1/M2 ≈ 0.7. One of the galaxies (Source 1) shows clear evidence for AGN activity in the form of hard X-ray emission and optical emission-line diagnostics typical of AGN ionisation. The nucleus of the other galaxy (Source 2) has a soft X-ray spectrum, bluer colours, and optical emission line ratios dominated by stellar photoionisation with a "composite" signature, which might indicate the presence of a weak AGN. When plotted on a diagram with X-ray luminosity vs [OIII] luminosity both nuclei fall within the locus defined by local Seyfert galaxies. From the optical spectrum we estimate the electron densities finding n1 < 27 e- cm-3 and n2 ≈ 200 e- cm-3. From a 2D decomposition of the surface brightness distribution we infer that both galaxies host rotationally supported bulges (Sersic index <1). While the active nature of Source 1 can be established with confidence, whether the nucleus of Source 2 is active remains a matter of debate. Evidence that a faint AGN might reside in its nucleus is, however, tantalising.

Extended hard-X-ray emission in the inner few parsecs of the Galaxy.

PubMed

Perez, Kerstin; Hailey, Charles J; Bauer, Franz E; Krivonos, Roman A; Mori, Kaya; Baganoff, Frederick K; Barrière, Nicolas M; Boggs, Steven E; Christensen, Finn E; Craig, William W; Grefenstette, Brian W; Grindlay, Jonathan E; Harrison, Fiona A; Hong, Jaesub; Madsen, Kristin K; Nynka, Melania; Stern, Daniel; Tomsick, John A; Wik, Daniel R; Zhang, Shuo; Zhang, William W; Zoglauer, Andreas

2015-04-30

The Galactic Centre hosts a puzzling stellar population in its inner few parsecs, with a high abundance of surprisingly young, relatively massive stars bound within the deep potential well of the central supermassive black hole, Sagittarius A* (ref. 1). Previous studies suggest that the population of objects emitting soft X-rays (less than 10 kiloelectronvolts) within the surrounding hundreds of parsecs, as well as the population responsible for unresolved X-ray emission extending along the Galactic plane, is dominated by accreting white dwarf systems. Observations of diffuse hard-X-ray (more than 10 kiloelectronvolts) emission in the inner 10 parsecs, however, have been hampered by the limited spatial resolution of previous instruments. Here we report the presence of a distinct hard-X-ray component within the central 4 × 8 parsecs, as revealed by subarcminute-resolution images in the 20-40 kiloelectronvolt range. This emission is more sharply peaked towards the Galactic Centre than is the surface brightness of the soft-X-ray population. This could indicate a significantly more massive population of accreting white dwarfs, large populations of low-mass X-ray binaries or millisecond pulsars, or particle outflows interacting with the surrounding radiation field, dense molecular material or magnetic fields. However, all these interpretations pose significant challenges to our understanding of stellar evolution, binary formation, and cosmic-ray production in the Galactic Centre.

Evidence of differential tidal effects in the old globular cluster population of the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Piatti, A. E.; Mackey, A. D.

2018-04-01

We present for the first time extended stellar density and/or surface brightness radial profiles for almost all the known Large Magellanic Cloud (LMC) old globular clusters (GCs). These were built from DECam images and reach out to ˜ 4 times the GCs' tidal radii. The background subtracted radial profiles reveal that the GCs located closer than ˜ 5 kpc from the LMC centre contain an excess of stars in their outermost regions with respect to the stellar density expected from a King profile. Such a residual amount of stars - not seen in GCs located farther than ˜ 5 kpc from the LMC centre-, as well as the GCs' dimensions, show a clear dependence with the GCs' positions in the galaxy, in the sense that, the farther the GC from the centre of the LMC, the larger both the excess of stars in its outskirts and size. Although the masses of GCs located inside and outside ˜ 5 kpc are commensurate, the outermost regions of GCs located closer than ˜ 5 kpc from the LMC centre appear to have dynamically evolved more quickly. These outcomes can be fully interpreted in the light of the known GC radial velocity disc-like kinematics, from which GCs have been somehow mostly experiencing the influence of the LMC gravitational field at their respective mean distances from the LMC centre.

On the stability of bow shocks generated by red supergiants: the case of IRC -10414

NASA Astrophysics Data System (ADS)

Meyer, D. M.-A.; Gvaramadze, V. V.; Langer, N.; Mackey, J.; Boumis, P.; Mohamed, S.

2014-03-01

In this Letter, we explore the hypothesis that the smooth appearance of bow shocks around some red supergiants (RSGs) might be caused by the ionization of their winds by external sources of radiation. Our numerical simulations of the bow shock generated by IRC -10414 (the first-ever RSG with an optically detected bow shock) show that the ionization of the wind results in its acceleration by a factor of 2, which reduces the difference between the wind and space velocities of the star and makes the contact discontinuity of the bow shock stable for a range of stellar space velocities and mass-loss rates. Our best-fitting model reproduces the overall shape and surface brightness of the observed bow shock and suggests that the space velocity and mass-loss rate of IRC -10414 are ≈50 km s-1 and ≈10-6 M⊙ yr-1, respectively, and that the number density of the local interstellar medium is ≈3 cm-3. It also shows that the bow shock emission comes mainly from the shocked stellar wind. This naturally explains the enhanced nitrogen abundance in the line-emitting material, derived from the spectroscopy of the bow shock. We found that photoionized bow shocks are ≈15-50 times brighter in optical line emission than their neutral counterparts, from which we conclude that the bow shock of IRC -10414 must be photoionized.

Infrared Imaging of Capella with the IOTA Closure Phase Interferometer

NASA Astrophysics Data System (ADS)

Kraus, S.; Schloerb, F. P.; Traub, W. A.; Carleton, N. P.; Lacasse, M.; Pearlman, M.; Monnier, J. D.; Millan-Gabet, R.; Berger, J.-P.; Haguenauer, P.; Perraut, K.; Kern, P.; Malbet, F.; Labeye, P.

2005-07-01

We present infrared aperture synthesis maps produced with the upgraded Infrared Optical Telescope Array interferometer. Michelson interferograms on the close binary system Capella (α Aur) were obtained in the H band between 2002 November 12 and 16 using the IONIC3 beam combiner. With baselines of 15m<=B<=38 m, we were able to determine the relative position of the binary components with milliarcsecond precision and to track their movement along the ~14° arc covered by our observation run. We briefly describe the algorithms used for visibility and closure phase estimation. Three different hybrid mapping and bispectrum fitting techniques were implemented within one software framework and used to reconstruct the source brightness distribution. By dividing our data into subsets, the system could be mapped at three epochs, revealing the motion of the stars. The precise position of the binary components was also determined with model fits, which in addition revealed IAa/IAb=1.49+/-0.10 and apparent stellar uniform-disk diameters of ΘAa=8.9+/-0.6 mas and ΘAb=5.8+/-0.8 mas. To improve the (u,v)-plane coverage, we compensated this orbital motion by applying a rotation-compensating coordinate transformation. The resulting model-independent map with a beam size of 5.4mas×2.6 mas allows the resolution of the stellar surfaces of the Capella giants themselves.

Comparative study of icy patches on comet nuclei

NASA Astrophysics Data System (ADS)

Oklay, Nilda; Pommerol, Antoine; Barucci, Maria Antonietta; Sunshine, Jessica; Sierks, Holger; Pajola, Maurizio

2016-07-01

Cometary missions Deep Impact, EPOXI and Rosetta investigated the nuclei of comets 9P/Tempel 1, 103P/Hartley 2 and 67P/Churyumov-Gerasimenko respectively. Bright patches were observed on the surfaces of each of these three comets [1-5]. Of these, the surface of 67P is mapped at the highest spatial resolution via narrow angle camera (NAC) of the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS, [6]) on board the Rosetta spacecraft. OSIRIS NAC is equipped with twelve filters covering the wavelength range of 250 nm to 1000 nm. Various filters combinations are used during surface mapping. With high spatial resolution data of comet 67P, three types of bright features were detected on the comet surface: Clustered, isolated and bright boulders [2]. In the visible spectral range, clustered bright features on comet 67P display bluer spectral slopes than the average surface [2, 4] while isolated bright features on comet 67P have flat spectra [4]. Icy patches observed on the surface of comets 9P and 103P display bluer spectral slopes than the average surface [1, 5]. Clustered and isolated bright features are blue in the RGB composites generated by using the images taken in NIR, visible and NUV wavelengths [2, 4]. This is valid for the icy patches observed on comets 9P and 103P [1, 5]. Spectroscopic observations of bright patches on comets 9P and 103P confirmed the existence of water [1, 5]. There were more than a hundred of bright features detected on the northern hemisphere of comet 67P [2]. Analysis of those features from both multispectral data and spectroscopic data is an ongoing work. Water ice is detected in eight of the bright features so far [7]. Additionally, spectroscopic observations of two clustered bright features on the surface of comet 67P revealed the existence of water ice [3]. The spectral properties of one of the icy patches were studied by [4] using OSIRIS NAC images and compared with the spectral properties of the active regions observed on comet 67P. Additionally jets rising from the same clustered bright feature were detected visually [4]. We analyzed bright patches on the surface of comets 9P, 103P and 67P using multispectral data obtained by the high-resolution instrument (HRI), medium- resolution instrument (MRI) and OSIRIS NAC using various spectral analysis techniques. Clustered bright features on comet 67P have similar visible spectra to the bright patches on comets 9P and 103P. The comparison of the bright patches includes the published results of the IR spectra. References: [1] Sunshine et al., 2006, Science, 311, 1453 [2] Pommerol et al., 2015, A&A, 583, A25 [3] Filacchione et al., 2016, Nature, 529, 368-372 [4] Oklay et al., 2016, A&A, 586, A80 [5] Sunshine et al. 2012, ACM [6] Keller et al., 2007, Space Sci. Rev., 128, 433 [7] Barucci et al., 2016, COSPAR, B04

Stellar Differential Rotation of F-Stars Using DI and ZDI: The Case of HR1817

NASA Astrophysics Data System (ADS)

Marsden, Stephen

2018-04-01

The measure of surface differential rotation via the motion of spots and/or magnetic features on the stellar surface is a critical part of understanding the stellar dynamo. Here we present several epochs of (Zeeman) Doppler imaging of the young late-F star HR1817 from 2001 until 2011. These results show that HR1817 exhibits a high shear of its surface features, significantly above the solar value. It would appear that F stars, with thin convective zones, have surface differential rotation rates much higher than that of low mass stars.

Imaging Stellar Surfaces with an Agile 12-Telescopes Visible Interferometer for the VLTI

NASA Astrophysics Data System (ADS)

Woillez, Julien

2018-04-01

Imaging stellar surfaces with an optical interferometer requires a large number of telescopes and the extensive use of the bootstrapping technique to reach the high spatial frequencies where the surface details are revealed. An idea would use all 6 dual-star delay lines of VLTI to deploy an agile 12-telescopes single-mode visible interferometer on the Paranal mountain. The concept relies on single-mode fiber technologies that have been demonstrated by the `OHANA and `OHANA IKI projects. We present the expected performance of this concept and explore its potential for the study of stellar surfaces.

The Stellar Imager (SI) Project: Resolving Stellar Surfaces, Interiors, and Magnetic Activity

NASA Technical Reports Server (NTRS)

Carpenter, Kenneth G.; Schrijver, K.; Karovska, M.

2007-01-01

The Stellar Imager (SI) is a UV/Optical. Space-Based Interferometer designed to enable 0.1 milli-arcsec (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. The science of SI focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. Its prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we discuss the science goals, technology needs, and baseline design of the SI mission.

Long-Term Starspot Activity of Some Chromospherically Active Rs CVn and BY Dra Stars

NASA Astrophysics Data System (ADS)

Kozhevnikova, Alla; Ilya, Alekseev

2016-10-01

We present results of our long-term photometric observations of a sample of 15 chromospherically active BY Dra and RS CVn-type stars. Observations were carried out at a 70-cm telescope and multichannel photometer of Kourovka Astronomical Observatory of Ural Federal University and at a 1.25-m telescope of Crimean Astrophysical Observatory from 2003 to 2015 in Johnson B, V, R, I bands. We also use the previously published photometric data for all these stars to find the meaning of historical star's brightness, that we assume as a brightness of unspotted photosphere. Using a renewed zonal spot model for spotted stellar photospheres we determined spot parameters for all observational seasons, as our as published ones, that were spanning almost over 45 years for some stars (e.g. CG Cyg, WY Cnc, EV Lac, V 1396 Cyg). It is shown that the spots were located at low and middle latitudes up to 58 deg., are cooler than the surrounding photosphere by 200 - 2000 K according to the spectral class. The spotted area varied from season to season, comprising 13%-47% of the surface area of the star. Almost half of the stars display drifts of their spots towards the equator and poles during certain time intervals; however, the speeds of the spots' latitude drifts are lower than the analogous speeds for sunspots, by factors of 1.5-4, on average. Activity cycles lasting from 5 to 40 years have been determined or confirmed for majority of the studied stars. As a rule, cycles are expressed in synchronous variations of spot areas, spot latitudes and average photometric star's brightness.

Exploring the extremely low surface brightness sky: distances to 23 newly discovered objects in Dragonfly fields

NASA Astrophysics Data System (ADS)

van Dokkum, Pieter

2016-10-01

We are obtaining deep, wide field images of nearby galaxies with the Dragonfly Telephoto Array. This telescope is optimized for low surface brightness imaging, and we are finding many low surface brightness objects in the Dragonfly fields. In Cycle 22 we obtained ACS imaging for 7 galaxies that we had discovered in a Dragonfly image of the galaxy M101. Unexpectedly, the ACS data show that only 3 of the galaxies are members of the M101 group, and the other 4 are very large Ultra Diffuse Galaxies (UDGs) at much greater distance. Building on our Cycle 22 program, here we request ACS imaging for 23 newly discovered low surface brightness objects in four Dragonfly fields centered on the galaxies NGC 1052, NGC 1084, NGC 3384, and NGC 4258. The immediate goals are to construct the satellite luminosity functions in these four fields and to constrain the number density of UDGs that are not in rich clusters. More generally, this complete sample of extremely low surface brightness objects provides the first systematic insight into galaxies whose brightness peaks at >25 mag/arcsec^2.

On the Red Giant Branch: Ambiguity in the Surface Boundary Condition Leads to ≈100 K Uncertainty in Model Effective Temperatures

NASA Astrophysics Data System (ADS)

Choi, Jieun; Dotter, Aaron; Conroy, Charlie; Ting, Yuan-Sen

2018-06-01

The effective temperature (T eff) distribution of stellar evolution models along the red giant branch (RGB) is sensitive to a number of parameters including the overall metallicity, elemental abundance patterns, the efficiency of convection, and the treatment of the surface boundary condition (BC). Recently there has been interest in using observational estimates of the RGB T eff to place constraints on the mixing length parameter, α MLT, and possible variation with metallicity. Here we use 1D Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution models to explore the sensitivity of the RGB T eff to the treatment of the surface BC. We find that different surface BCs can lead to ±100 K metallicity-dependent offsets on the RGB relative to one another in spite of the fact that all models can reproduce the properties of the Sun. Moreover, for a given atmosphere T–τ relation, we find that the RGB T eff is also sensitive to the optical depth at which the surface BC is applied in the stellar model. Nearly all models adopt the photosphere as the location of the surface BC, but this choice is somewhat arbitrary. We compare our models to stellar parameters derived from the APOGEE-Kepler sample of first ascent red giants and find that systematic uncertainties in the models due to treatment of the surface BC place a limit of ≈100 K below which it is not possible to make firm conclusions regarding the fidelity of the current generation of stellar models.

NEBULAR AND STELLAR DUST EXTINCTION ACROSS THE DISK OF EMISSION-LINE GALAXIES ON KILOPARSEC SCALES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam

We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolutionmore » spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this study.« less

Microlensing Constraints on the Mass of Single Stars from HST Astrometric Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kains, N.; Calamida, A.; Sahu, K. C.

Here, we report on the first results from a large-scale observing campaign aiming to use astrometric microlensing to detect and place limits on the mass of single objects, including stellar remnants. We used the Hubble Space Telescope to monitor stars near the Galactic Center for three years, and we measured the brightness and positions of ~2 million stars at each observing epoch. In addition to this, we monitored the same pointings using the VIMOS imager on the Very Large Telescope. The stars we monitored include several bright microlensing events observed from the ground by the OGLE collaboration. In this paper,more » we present the analysis of our photometric and astrometric measurements for six of these events, and derive mass constraints for the lens in each of them. Although these constraints are limited by the photometric precision of ground-based data, and our ability to determine the lens distance, we were able to constrain the size of the Einstein ring radius thanks to our precise astrometric measurements—the first routine measurements of this type from a large-scale observing program. In conclusion, this demonstrates the power of astrometric microlensing as a tool to constrain the masses of stars, stellar remnants, and, in the future, extrasolar planets, using precise ground- and space-based observations.« less

Microlensing Constraints on the Mass of Single Stars from HST Astrometric Measurements

DOE PAGES

Kains, N.; Calamida, A.; Sahu, K. C.; ...

2017-07-14

Here, we report on the first results from a large-scale observing campaign aiming to use astrometric microlensing to detect and place limits on the mass of single objects, including stellar remnants. We used the Hubble Space Telescope to monitor stars near the Galactic Center for three years, and we measured the brightness and positions of ~2 million stars at each observing epoch. In addition to this, we monitored the same pointings using the VIMOS imager on the Very Large Telescope. The stars we monitored include several bright microlensing events observed from the ground by the OGLE collaboration. In this paper,more » we present the analysis of our photometric and astrometric measurements for six of these events, and derive mass constraints for the lens in each of them. Although these constraints are limited by the photometric precision of ground-based data, and our ability to determine the lens distance, we were able to constrain the size of the Einstein ring radius thanks to our precise astrometric measurements—the first routine measurements of this type from a large-scale observing program. In conclusion, this demonstrates the power of astrometric microlensing as a tool to constrain the masses of stars, stellar remnants, and, in the future, extrasolar planets, using precise ground- and space-based observations.« less

The Orbital and Planetary Phase Variations of Jupiter-sized Planets: Characterizing Present and Future Giants

NASA Astrophysics Data System (ADS)

Mayorga, Laura C.; Jackiewicz, Jason; Rages, Kathy; West, Robert; Knowles, Ben; Lewis, Nikole K.; Marley, Mark S.

2018-01-01

Knowledge of how the brightness and color of a planet varies with viewing angle is essential for the design of future direct imaging missions and deriving constraints on atmospheric properties. However, measuring the phase curves for the solar system gas giants is impossible from the ground. Using data Cassini/ISS obtained during its flyby of Jupiter, I measured Jupiter's phase curve in six bands spanning 400-1000 nm. I found that Jupiter's brightness is less than that of a Lambertian scatterer and that its color varies more with phase angle than predicted by theoretical models. For hot Jupiters, the light from the planet cannot be spatially isolated from that of the star. As a result, determining the planetary phase curve requires removing the phase-dependent contributions from the host star. I consider the effect of varying the stellar model and present a parameterization of the Doppler beaming amplitude that depends upon the planetary mass, orbital period, and the stellar temperature. I consider the detectability of Doppler beaming amplitudes with data from TESS and find that TESS will be less sensitive to this signal than Kepler. This work was supported by the National Science Foundation Graduate Research Fellowship Program and the New Mexico Higher Education Department Graduate Scholarship Program.

On the Nature of Bright Infrared Sources in the Small Magellanic Cloud: Interpreting MSX through the Lens of Spitzer

NASA Astrophysics Data System (ADS)

Kraemer, Kathleen E.; Sloan, G. C.

2015-01-01

We compare infrared observations of the Small Magellanic Cloud (SMC) by the Midcourse Space Experiment (MSX) and the Spitzer Space Telescope to better understand what components of a metal-poor galaxy dominate radiative processes in the infrared. The SMC, at a distance of ~60 kpc and with a metallicity of ~0.1-0.2 solar, can serve as a nearby proxy for metal-poor galaxies at high redshift. The MSX Point Source Catalog contains 243 objects in the SMC that were detected at 8.3 microns, the most sensitive MSX band. Multi-epoch, multi-band mapping with Spitzer, supplemented with observations from the Two-Micron All-Sky Survey (2MASS) and the Wide-field Infrared Survey Explorer (WISE), provides variability information, and, together with spectra from Spitzer for ~15% of the sample, enables us to determine what these luminous sources are. How many remain simple point sources? What fraction break up into multiple stars? Which are star forming regions, with both bright diffuse emission and point sources? How do evolved stars and stellar remnants contribute at these wavelengths? What role do young stellar objects and HII regions play? Answering these questions sets the stage for understanding what we will see with the James Webb Space Telescope (JWST).

Rotation and Mass Loss

NASA Astrophysics Data System (ADS)

Owocki, S.

2008-06-01

Stellar rotation can play an important role in structuring and enhancing the mass loss from massive stars. Initial 1D models focussed on the expected centrifugal enhancement of the line-driven mass flux from the equator of a rotating star, but the review here emphasizes that the loss of centrifugal support away from the stellar surface actually limits the steady mass flux to just the point-star CAK value, with models near critical rotation characterized by a slow, subcritical acceleration. Recent suggestions that such slow outflows might have high enough density to explain disks in Be or B[e] stars are examined in the context of 2D simulations of the ``Wind Compressed Disk'' (WCD) paradigm, together with a review of the tendency for poleward components of the line-driving force to inhibit WCD formation. When one accounts for equatorial gravity darkening, the net tendency is in fact for the relatively bright regions at higher latitude to drive a faster, denser ``bipolar'' outflow. I discuss the potential relevance for the bipolar form of nebulae from LBV stars like η Carinae, but emphasize that, since the large mass loss associated with the eruption of eta Carinae's Homunculus would heavily saturate line-driving, explaining its bipolar form requires development of analogous models for continuum-driven mass loss. I conclude with a discussion of how radiation seems inherently ill-suited to supporting or driving a geometrically thin, but optically thick disk or disk outflow. The disks inferred in Be and B[e] stars may instead be centrifugally ejected, with radiation inducing an ablation flow from the disk surface, and thus perhaps playing a greater role in destroying (rather than creating) an orbiting, circumstellar disk.

Investigating the Magnetospheres of Rapidly Rotating B-type Stars

NASA Astrophysics Data System (ADS)

Fletcher, C. L.; Petit, V.; Nazé, Y.; Wade, G. A.; Townsend, R. H.; Owocki, S. P.; Cohen, D. H.; David-Uraz, A.; Shultz, M.

2017-11-01

Recent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

Surprisingly different star-spot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB

NASA Astrophysics Data System (ADS)

Barnes, J. R.; Jeffers, S. V.; Haswell, C. A.; Jones, H. R. A.; Shulyak, D.; Pavlenko, Ya. V.; Jenkins, J. S.

2017-10-01

We aim to understand how stellar parameters such as mass and rotation impact the distribution of star-spots on the stellar surface. To this purpose, we have used Doppler imaging to reconstruct the surface brightness distributions of three fully convective M dwarfs with similar rotation rates. We secured high cadence spectral time series observations of the 5.5 au separation binary GJ 65, comprising GJ 65A (M5.5V, Prot = 0.24 d) and GJ 65B (M6V, Prot = 0.23 d). We also present new observations of GJ 791.2A (M4.5V, Prot = 0.31 d). Observations of each star were made on two nights with UVES, covering a wavelength range from 0.64 - 1.03μm. The time series spectra reveal multiple line distortions that we interpret as cool star-spots and which are persistent on both nights suggesting stability on the time-scale of 3 d. Spots are recovered with resolutions down to 8.3° at the equator. The global spot distributions for GJ 791.2A are similar to observations made a year earlier. Similar high latitude and circumpolar spot structure is seen on GJ 791.2A and GJ 65A. However, they are surprisingly absent on GJ 65B, which instead reveals more extensive, larger, spots concentrated at intermediate latitudes. All three stars show small amplitude latitude-dependent rotation that is consistent with solid body rotation. We compare our measurements of differential rotation with previous Doppler imaging studies and discuss the results in the wider context of other observational estimates and recent theoretical predictions.

Physical properties of the ionized gas and brightness distribution in NGC4736

NASA Astrophysics Data System (ADS)

Rodrigues, I.; Dottori, H.; Cepa, J.; Vilchez, J.

1998-03-01

In this work we study the galaxy NGC4736, using narrow band interference filters imaging centered at the emission lines {Oii} {3727+3729}, Hβ, {Oiii} {5007}, Hα, {Sii} {6716+6730} and {Siii} {9070} and nearby continua. We have obtained sizes, positions, emission line absolute fluxes, and continua intensities for 90 Hii regions, mainly distributed in a ring-like structure of 3.2kpc in diameter. The Hα luminosities are in the range 37.3 <= log L_Hα <= 39.4 ergs(-1) . The Hii regions size distribution presents a characteristic diameter D_0 = 115pc and verifies the relation log (L_Hα ) ~D(3) . The temperature of the ionizing sources and the metallicity of the Hii regions are respectively in the ranges 3.410(4) <~T_⋆ <~ 4.010(4) K and 8.5 <~12 + log (O/H) <~9.3. The masses of the ionizing clusters are in the range 510(3) <~M_T/M_sun <~210(5) . The continua radial surface brightness distribution is better fitted by the superposition of a de Vaucouleurs', a thin and a thick exponential disk laws. The monochromatic colors show that outside the star forming ring the disk presents a younger stellar population than inside it. Tables 3 and 4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

Linear dark field control: simulation for implementation and testing on the UA wavefront control testbed

NASA Astrophysics Data System (ADS)

Miller, Kelsey; Guyon, Olivier

2016-07-01

This paper presents the early-stage simulation results of linear dark field control (LDFC) as a new approach to maintaining a stable dark hole within a stellar post-coronagraphic PSF. In practice, conventional speckle nulling is used to create a dark hole in the PSF, and LDFC is then employed to maintain the dark field by using information from the bright speckle field. The concept exploits the linear response of the bright speckle intensity to wavefront variations in the pupil, and therefore has many advantages over conventional speckle nulling as a method for stabilizing the dark hole. In theory, LDFC is faster, more sensitive, and more robust than using conventional speckle nulling techniques, like electric field conjugation, to maintain the dark hole. In this paper, LDFC theory, linear bright speckle characterization, and first results in simulation are presented as an initial step toward the deployment of LDFC on the UA Wavefront Control testbed in the coming year.

Wish Upon a Star

NASA Image and Video Library

2015-01-05

What's that bright point of light in the outer A ring? It's a star, bright enough to be visible through the ring! Quick, make a wish! This star -- seen in the lower right quadrant of the image -- was not captured by coincidence, it was part of a stellar occultation. By monitoring the brightness of stars as they pass behind the rings, scientists using this powerful observation technique can inspect detailed structures within the rings and how they vary with location. This view looks toward the sunlit side of the rings from about 44 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 8, 2013. The view was acquired at a distance of approximately 1.1 million miles (1.8 million kilometers) from the rings and at a Sun-Rings-Spacecraft, or phase, angle of 96 degrees. Image scale is 6.8 miles (11 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18297

Long-term Spectroscopic and Photometric Monitoring of Bright Interacting Algol-type Binary Stars

NASA Astrophysics Data System (ADS)

Reed, Phillip A.

2018-01-01

Binary stars have long been used as natural laboratories for studying such fundamental stellar properties as mass. Interacting binaries allow us to examine more complicated aspects such as mass flow between stars, accretion processes, magnetic fields, and stellar mergers. Algol-type interacting binary stars -- consisting of a cool giant or sub-giant donating mass to a much hotter, less evolved, and more massive main-sequence companion -- undergo steady mass transfer and have been used to measure mass transfer rates and to test stellar evolution theories. The method of back-projection Doppler tomography has also been applied to interacting Algols and has produced indirect velocity-space images of the accretion structures (gas streams, accretion disks, etc.) derived from spectroscopic observations of hydrogen and helium emission lines. The accretion structures in several Algol systems have actually been observed to change between disk-like states and stream-like states on timescales as short as several orbital cycles (Richards et al., 2014). Presented here are the first results from a project aimed at studying bright interacting Algol systems with simultaneous mid-resolution (11,000

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Yang; Fang, Min; Yang, Ji

We have carried out {sup 12}CO, {sup 13}CO, and C{sup 18}O observations toward the mixed morphology supernova remnant (SNR) IC 443. The observations cover a 1.°5 × 1.°5 area and allow us to investigate the overall molecular environment of the remnant. Some northern and northeastern partial shell structure of CO gas is around the remnant. One of the partial shells, about 5' extending beyond the northeastern border of the remnant's bright radio shell, seems to just confine the faint radio halo. On the other hand, some faint CO clumps can be discerned along the eastern boundary of the faint remnant'smore » radio halo. Connecting the eastern CO clumps, the northeastern partial shell structures, and the northern CO partial shell, we can see that a half molecular ring structure appears to surround the remnant. The LSR velocity of the half-ring structure is in the range of –5 km s{sup –1} to –2 km s{sup –1}, which is consistent with that of the –4 km s{sup –1} molecular clouds. We suggest that the half-ring structure of the CO emission at V {sub LSR} ∼ –4 km s{sup –1} is associated with the SNR. The structures are possibly swept up by the stellar winds of SNR IC 443's massive progenitor. Based on the Wide-field Infrared Survey Explorer and the Two Micron All Sky Survey near-IR database, 62 young stellar object (YSO) candidates are selected within the radio halo of the remnant. These YSO candidates concentrated along the boundary of the remnant's bright radio shell are likely to be triggered by the stellar winds from the massive progenitor of SNR IC 443.« less

INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cortés, Juan R.; Hardy, Eduardo; Kenney, Jeffrey D. P., E-mail: jcortes@alma.cl, E-mail: ehardy@nrao.cl, E-mail: jeff.kenney@yale.edu

2015-01-01

We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between themore » optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ {sub R}. An evaluation of the galaxies in the λ {sub R} ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects.« less

Ionized Gas Outflows in Infrared-bright Dust-obscured Galaxies Selected with WISE and SDSS

NASA Astrophysics Data System (ADS)

Toba, Yoshiki; Bae, Hyun-Jin; Nagao, Tohru; Woo, Jong-Hak; Wang, Wei-Hao; Wagner, Alexander Y.; Sun, Ai-Lei; Chang, Yu-Yen

2017-12-01

We present the ionized gas properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme optical/IR color, {(i-[22])}{AB}> 7.0, selected with the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). For 36 IR-bright DOGs that show [O III]λ5007 emission in the SDSS spectra, we performed a detailed spectral analysis to investigate their ionized gas properties. In particular, we measured the velocity offset (the velocity with respect to the systemic velocity measured from the stellar absorption lines) and the velocity dispersion of the [O III] line. We found that the derived velocity offset and dispersion of most IR-bright DOGs are larger than those of Seyfert 2 galaxies (Sy2s) at z< 0.3, meaning that the IR-bright DOGs show relatively strong outflows compared to Sy2s. This can be explained by the difference in IR luminosity contributed from active galactic nuclei, {L}{IR} (AGN), because we found that (i) {L}{IR} (AGN) correlates with the velocity offset and dispersion of [O III] and (ii) our IR-bright DOG sample has larger {L}{IR} (AGN) than Sy2s. Nevertheless, the fact that about 75% IR-bright DOGs have a large (>300 km s-1) velocity dispersion, which is a larger fraction compared to other AGN populations, suggests that IR-bright DOGs are good laboratories to investigate AGN feedback. The velocity offset and dispersion of [O III] and [Ne III]λ3869 are larger than those of [O II]λ3727, which indicates that the highly ionized gas tends to show stronger outflows.

The Next Generation Virgo Cluster Survey. IV. NGC 4216: A Bombarded Spiral in the Virgo Cluster

NASA Astrophysics Data System (ADS)

Paudel, Sanjaya; Duc, Pierre-Alain; Côté, Patrick; Cuillandre, Jean-Charles; Ferrarese, Laura; Ferriere, Etienne; Gwyn, Stephen D. J.; Mihos, J. Christopher; Vollmer, Bernd; Balogh, Michael L.; Carlberg, Ray G.; Boissier, Samuel; Boselli, Alessandro; Durrell, Patrick R.; Emsellem, Eric; MacArthur, Lauren A.; Mei, Simona; Michel-Dansac, Leo; van Driel, Wim

2013-04-01

The final stages of mass assembly of present-day massive galaxies are expected to occur through the accretion of multiple satellites. Cosmological simulations thus predict a high frequency of stellar streams resulting from this mass accretion around the massive galaxies in the Local Volume. Such tidal streams are difficult to observe, especially in dense cluster environments, where they are readily destroyed. We present an investigation into the origins of a series of interlaced narrow filamentary stellar structures, loops and plumes in the vicinity of the Virgo Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the Blackbird telescope. Using the deeper, higher-resolution, and precisely calibrated optical CFHT/MegaCam images obtained as part of the Next Generation Virgo Cluster Survey (NGVS), we confirm the previously identified features and identify a few additional structures. The NGVS data allowed us to make a physical study of these low surface brightness features and investigate their origin. The likely progenitors of the structures were identified as either already cataloged Virgo Cluster Catalog dwarfs or newly discovered satellites caught in the act of being destroyed. They have the same g - i color index and likely contain similar stellar populations. The alignment of three dwarfs along an apparently single stream is intriguing, and we cannot totally exclude that these are second-generation dwarf galaxies being born inside the filament from the debris of an original dwarf. The observed complex structures, including in particular a stream apparently emanating from a satellite of a satellite, point to a high rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster where NGC 4216 is located. We discuss the age of the interactions and whether they occurred in a group that is just falling into the cluster and shows signs of the so-called pre-processing before it gets affected by the cluster environment, or in a group which already ventured toward the central regions of Virgo Cluster. In any case, compared to the other spiral galaxies in the Virgo Cluster, but also to those located in lower density environments, NGC 4216 seems to suffer an unusually heavy bombardment. Further studies will be needed to determine whether, given the surface brightness limit of our survey, about 29 mag arcsec-2, the number of observed streams around that galaxy is as predicted by cosmological simulations or conversely, whether the possible lack of similar structures in other galaxies poses a challenge to the merger-based model of galaxy mass assembly. Based on observations obtained with MegaPrime/MegaCam, a joint project of Canada-France-Hawaii Telescope (CFHT) and CEA/DAPNIA, at the CFHT which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Sub-millimetre properties of massive star-forming galaxies at z ~ 2 in SHADES/SXDF

NASA Astrophysics Data System (ADS)

Takagi, T.; Mortier, A. M. J.; Shimasaku, K.; Coppin, K.; Pope, A.; Ivison, R. J.; Hanami, H.; Serjeant, S.; Dunlop, J. S.

2007-05-01

We study the submillimetre (submm) properties of the following NIR-selected massive galaxies at high redshifts: BzK-selected star-forming galaxies (BzKs), distant red galaxies (DRGs) and extremely red objects (EROs). We used the SCUBA HAlf Degree Extragalactic Survey (SHADES), the largest uniform submm survey to date. We detected 6 NIR-selected galaxies in our SCUBA map. Four submm-detected galaxies out of six are found to be detected both at 24 micron and in radio (1.4 GHz), and therefore confirmed as genuine submm-bright galaxies. We identify two submm-bright NIR-selected galaxies are the BzK-DRG-ERO overlapping population. Although this overlapping population is rare, about 12% of this population could be submm galaxies. With a stacking analysis, we detected the 850-micron flux of submm-faint BzKs and EROs in our SCUBA maps. While the contribution from BzKs at z˜2 to submm background is about 10 - 15 % and similar to that from EROs typically at z˜1, BzKs have a higher fraction (˜30%) of flux in resolved sources than EROs do. Therefore, submm flux of BzKs seems to be biased high. From the SED fitting using an evolutionary model of starbursts with radiative transfer, submm-bright NIR-selected galaxies, mostly BzKs, are found to have the stellar mass of >5x1010M[sun] with the bolometric luminosity of >3x1012L[sun]. On the other hand, an average SED of submm-faint BzKs indicates the typical stellar mass of <6x1010M[sun] and therefore less massive.

THE EINSTEIN CROSS: CONSTRAINT ON DARK MATTER FROM STELLAR DYNAMICS AND GRAVITATIONAL LENSING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van de Ven, Glenn; Falcon-Barroso, Jesus; McDermid, Richard M.

2010-08-20

We present two-dimensional line-of-sight stellar kinematics of the lens galaxy in the Einstein Cross, obtained with the GEMINI 8 m telescope, using the GMOS integral-field spectrograph. The stellar kinematics extend to a radius of 4'' (with 0.''2 spaxels), covering about two-thirds of the effective (or half-light) radius R{sub e} {approx_equal} 6'' of this early-type spiral galaxy at redshift z{sub l} {approx_equal} 0.04, of which the bulge is lensing a background quasar at redshift z{sub s} {approx_equal} 1.7. The velocity map shows regular rotation up to {approx}100 km s{sup -1} around the minor axis of the bulge, consistent with axisymmetry. Themore » velocity dispersion map shows a weak gradient increasing toward a central (R < 1'') value of {sigma}{sub 0} = 170 {+-} 9 km s{sup -1}. We deproject the observed surface brightness from Hubble Space Telescope imaging to obtain a realistic luminosity density of the lens galaxy, which in turn is used to build axisymmetric dynamical models that fit the observed kinematic maps. We also construct a gravitational lens model that accurately fits the positions and relative fluxes of the four quasar images. We combine these independent constraints from stellar dynamics and gravitational lensing to study the total mass distribution in the inner parts of the lens galaxy. We find that the resulting luminous and total mass distribution are nearly identical around the Einstein radius R{sub E} = 0.''89, with a slope that is close to isothermal, but which becomes shallower toward the center if indeed mass follows light. The dynamical model fits to the observed kinematic maps result in a total mass-to-light ratio Y{sub dyn} = 3.7 {+-} 0.5 Y{sub sun,I} (in the I band). This is consistent with the Einstein mass M{sub E} = 1.54 x 10{sup 10} M {sub sun} divided by the (projected) luminosity within R{sub E} , which yields a total mass-to-light ratio of Y {sub E} = 3.4 Y{sub sun,I}, with an error of at most a few percent. We estimate from stellar population model fits to colors of the lens galaxy a stellar mass-to-light ratio Y{sub *} from 2.8 to 4.1 Y{sub sun,I}. Although a constant dark matter fraction of 20% is not excluded, dark matter may play no significant role in the bulge of this {approx}L {sub *} early-type spiral galaxy.« less

Analysis of Faint Glints from Stabilized GEO Satellites

NASA Astrophysics Data System (ADS)

Hall, D.; Kervin, P.

2013-09-01

Ground-based telescopes routinely acquire temporal brightness measurements of satellites in geo-stationary and geo-synchronous orbit that provide valuable characterization information. For instance, GEO satellites that are not stabilized tend to rotate, and produce brightnesses that vary in time with frequencies corresponding to rotation rates. Temporal brightness patterns can also be exploited to characterize stabilized GEO satellites. For example, many operational GEO satellites have solar panels that glint when they reflect sunlight towards an observer in a mirror-like fashion. These well-known solar panel glints can be remarkably bright, often exceeding several stellar magnitudes in amplitude. Measured brightnesses and times of these glints can be exploited to estimate the size, segmentation, and alignment of the solar array, valuable information about the satellite's power generation and consumption capabilities. However, satellites can produce other glints in addition to those originating from solar panels. These glints can be much fainter, with amplitudes as small as 0.2 magnitudes. Several observations of GEO satellites show several such glints occurring during the span of a single night. Furthermore, many of these recur from night to night when observed from a single ground-based site, but with subtle, incremental changes in both peak times and brightnesses. These fainter glints must originate from reflective elements mounted on the satellite's main bus, solar panel structure, or other peripheral structures that might be stationary or moving with respect to the main bus. Our analysis indicates that such glints can be exploited for GEO satellite characterization.

Galactic Astronomy in the Ultraviolet

NASA Astrophysics Data System (ADS)

Rastorguev, A. S.; Sachkov, M. E.; Zabolotskikh, M. V.

2017-12-01

We propose a number of prospective observational programs for the ultraviolet space observatory WSO-UV, which seem to be of great importance to modern galactic astronomy. The programs include the search for binary Cepheids; the search and detailed photometric study and the analysis of radial distribution of UV-bright stars in globular clusters ("blue stragglers", blue horizontal-branch stars, RR Lyrae variables, white dwarfs, and stars with UV excesses); the investigation of stellar content and kinematics of young open clusters and associations; the study of spectral energy distribution in hot stars, including calculation of the extinction curves in the UV, optical and NIR; and accurate definition of the relations between the UV-colors and effective temperature. The high angular resolution of the observatory allows accurate astrometric measurements of stellar proper motions and their kinematic analysis.

Low-Resolution Near-infrared Stellar Spectra Observed by the Cosmic Infrared Background Experiment (CIBER)

NASA Astrophysics Data System (ADS)

Kim, Min Gyu; Lee, Hyung Mok; Arai, Toshiaki; Bock, James; Cooray, Asantha; Jeong, Woong-Seob; Kim, Seong Jin; Korngut, Phillip; Lanz, Alicia; Lee, Dae Hee; Lee, Myung Gyoon; Matsumoto, Toshio; Matsuura, Shuji; Nam, Uk Won; Onishi, Yosuke; Shirahata, Mai; Smidt, Joseph; Tsumura, Kohji; Yamamura, Issei; Zemcov, Michael

2017-02-01

We present near-infrared (0.8-1.8 μm) spectra of 105 bright ({m}J < 10) stars observed with the low-resolution spectrometer on the rocket-borne Cosmic Infrared Background Experiment. As our observations are performed above the Earth's atmosphere, our spectra are free from telluric contamination, which makes them a unique resource for near-infrared spectral calibration. Two-Micron All-Sky Survey photometry information is used to identify cross-matched stars after reduction and extraction of the spectra. We identify the spectral types of the observed stars by comparing them with spectral templates from the Infrared Telescope Facility library. All the observed spectra are consistent with late F to M stellar spectral types, and we identify various infrared absorption lines.

An Empirical Decomposition of Near-IR Emission into Galactic and Extragalactic Components

NASA Technical Reports Server (NTRS)

Dwek, Eli; Arendt, Richard G.

2002-01-01

We decompose the COBE/DIRBE observations of the near-IR sky brightness (minus zodiacal light) into Galactic stellar and interstellar medium (ISM) components and an extragalactic background. This empirical procedure allows us to estimate the 4.9 micron cosmic infrared background (CIB) as a function of the CIB intensity at shorter wavelengths. A weak indication of a rising CIB intensity at wavelengths greater than 3.5$ microns hints at interesting astrophysics in the CIB spectrum, or warns that the foreground zodiacal emission may be incompletely subtracted. Subtraction of only the stellar component from the zodiacal-light-subtracted all--sky map reveals the clearest 3.5 micron ISM emission map, which is found to be tightly correlated with the ISM emission at far-IR wavelengths.

A comparison of UV surface brightness and HI surface densities for spiral galaxies

NASA Technical Reports Server (NTRS)

Federman, S. R.; Strom, C.

1990-01-01

Shaya and Federman (1987) suggested that the ambient ultraviolet flux at 1000 A permeating a spiral galaxy controls the neutral hydrogen (HI) surface density in the galaxy. They found that the atomic envelopes surrounding small molecular clouds, because of their great number, provide the major contribution to the HI surface density over the stellar disk. The increase in HI surface density with later Hubble types was ascribed to the stronger UV fields from more high-mass stars in later Hubble types. These hypotheses are based on the observations of nearby diffuse interstellar clouds, which show a sharp atomic-to-molecular transition (Savage et al. 1977), and on the theoretical framework introduced by Federman, Glassgold, and Kwan (1979). Atomic envelopes around interstellar clouds in the solar neighborhood arise when a steady state is reached between photodissociation of H2 and the formation of H2 on grains. The photodissociation process involves photons with wavelengths between 912 A and 1108 A. Shaya and Federman used H-alpha flux as an approximate measure for the far UV flux and made their comparisons based on averages over Hubble type. Here, researchers compare, on an individual basis, UV data obtained with space-borne and balloon-borne instruments for galaxies with measurements of HI surface density (Warmels 1988a, b). The comparisons substantiate the conclusion of Shaya and Federman that the far UV field controls the HI content of spiral galaxies.

The build-up of the cD halo of M 87: evidence for accretion in the last Gyr

NASA Astrophysics Data System (ADS)

Longobardi, A.; Arnaboldi, M.; Gerhard, O.; Mihos, J. C.

2015-07-01

Aims: We present kinematic and photometric evidence for an accretion event in the halo of the cD galaxy M 87 in the last Gyr. Methods: Using velocities for ~300 planetary nebulas (PNs) in the M 87 halo, we identify a chevron-like substructure in the PN phase-space. We implement a probabilistic Gaussian mixture model to identify PNs that belong to the chevron. From analysis of deep V-band images of M 87, we find that the region with the highest density of chevron PNs is a crown-shaped substructure in the light. Results: We assign a total of NPN,sub = 54 to the substructure, which extends over ~50 kpc along the major axis where we also observe radial variations of the ellipticity profile and a colour gradient. The substructure has highest surface brightness in a 20 kpc × 60 kpc region around 70 kpc in radius. In this region, the substructure causes an increase in surface brightness by ≳60%. The accretion event is consistent with a progenitor galaxy with a V-band luminosity of L = 2.8±1.0×109 L⊙ ,V, a colour of (B - V) = 0.76±0.05, and a stellar mass of M = 6.4±2.3×109 M⊙. Conclusions: The accretion of this progenitor galaxy has caused an important modification of the outer halo of M 87 in the last Gyr. This result provides strong evidence that the galaxy's cD halo is growing through the accretion of smaller galaxies as predicted by hierarchical galaxy evolution models. Based on observations made with the VLT at Paranal Observatory under programme 088.B-0288(A) and 093.B-066(A), and with the Subaru Telescope under programme S10A-039.

The metallicity of the intracluster medium over cosmic time: further evidence for early enrichment

DOE PAGES

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn; ...

2017-08-26

Here, we use Chandra X-ray data to measure the metallicity of the intracluster medium (ICM) in 245 massive galaxy clusters selected from X-ray and Sunyaev–Zel'dovich (SZ) effect surveys, spanning redshifts 0 < z < 1.2. Metallicities were measured in three different radial ranges, spanning cluster cores through their outskirts. We explore trends in these measurements as a function of cluster redshift, temperature and surface brightness ‘peakiness’ (a proxy for gas cooling efficiency in cluster centres). The data at large radii (0.5–1 r500) are consistent with a constant metallicity, while at intermediate radii (0.1–0.5 r500) we see a late-time increase inmore » enrichment, consistent with the expected production and mixing of metals in cluster cores. In cluster centres, there are strong trends of metallicity with temperature and peakiness, reflecting enhanced metal production in the lowest entropy gas. Within the cool-core/sharply peaked cluster population, there is a large intrinsic scatter in central metallicity and no overall evolution, indicating significant astrophysical variations in the efficiency of enrichment. The central metallicity in clusters with flat surface brightness profiles is lower, with a smaller intrinsic scatter, but increases towards lower redshifts. Our results are consistent with other recent measurements of ICM metallicity as a function of redshift. They reinforce the picture implied by observations of uniform metal distributions in the outskirts of nearby clusters, in which most of the enrichment of the ICM takes place before cluster formation, with significant later enrichment taking place only in cluster centres, as the stellar populations of the central galaxies evolve.« less

Deep Imaging of the HCG 95 Field. I. Ultra-diffuse Galaxies

NASA Astrophysics Data System (ADS)

Shi, Dong Dong; Zheng, Xian Zhong; Zhao, Hai Bin; Pan, Zhi Zheng; Li, Bin; Zou, Hu; Zhou, Xu; Guo, KeXin; An, Fang Xia; Li, Yu Bin

2017-09-01

We present a detection of 89 candidates of ultra-diffuse galaxies (UDGs) in a 4.9 degree2 field centered on the Hickson Compact Group 95 (HCG 95) using deep g- and r-band images taken with the Chinese Near Object Survey Telescope. This field contains one rich galaxy cluster (Abell 2588 at z = 0.199) and two poor clusters (Pegasus I at z = 0.013 and Pegasus II at z = 0.040). The 89 candidates are likely associated with the two poor clusters, giving about 50-60 true UDGs with a half-light radius {r}{{e}}> 1.5 {kpc} and a central surface brightness μ (g,0)> 24.0 mag arcsec-2. Deep z\\prime -band images are available for 84 of the 89 galaxies from the Dark Energy Camera Legacy Survey (DECaLS), confirming that these galaxies have an extremely low central surface brightness. Moreover, our UDG candidates are spread over a wide range in g - r color, and ˜26% are as blue as normal star-forming galaxies, which is suggestive of young UDGs that are still in formation. Interestingly, we find that one UDG linked with HCG 95 is a gas-rich galaxy with H I mass 1.1× {10}9 M ⊙ detected by the Very Large Array, and has a stellar mass of {M}\\star ˜ 1.8× {10}8 M ⊙. This indicates that UDGs at least partially overlap with the population of nearly dark galaxies found in deep H I surveys. Our results show that the high abundance of blue UDGs in the HCG 95 field is favored by the environment of poor galaxy clusters residing in H I-rich large-scale structures.

A Natal Microcosm

NASA Technical Reports Server (NTRS)

2004-01-01

In the quest to better understand the birth of stars and the formation of new worlds, astronomers have used NASA's Spitzer Space Telescope to examine the massive stars contained in a cloudy region called Sharpless 140. This cloud is a fascinating microcosm of a star-forming region since it exhibits, within a relatively small area, all of the classic manifestations of stellar birth.

Sharpless 140 lies almost 3000 light-years from Earth in the constellation Cepheus. At its heart is a cluster of three deeply embedded young stars, which are each several thousand times brighter than the Sun. Though they are strikingly visible in this image from Spitzer's infrared array camera, they are completely obscured in visible light, buried within the core of the surrounding dust cloud.

The extreme youth of at least one of these stars is indicated by the presence of a stream of gas moving at high velocities. Such outflows are signatures of the processes surrounding a star that is still gobbling up material as part of its formation.

The bright red bowl, or arc, seen in this image traces the outer surface of the dense dust cloud encasing the young stars. This arc is made up primarily of organic compounds called polycyclic aromatic hydrocarbons, which glow on the surface of the cloud. Ultraviolet light from a nearby bright star outside of the image is 'eating away' at these molecules. Eventually, this light will destroy the dust envelope and the masked young stars will emerge.

This false-color image was taken on Oct. 11, 2003 and is composed of photographs obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red).

A Natal Microcosm

NASA Image and Video Library

2004-05-11

In the quest to better understand the birth of stars and the formation of new worlds, astronomers have used NASA's Spitzer Space Telescope to examine the massive stars contained in a cloudy region called Sharpless 140. This cloud is a fascinating microcosm of a star-forming region since it exhibits, within a relatively small area, all of the classic manifestations of stellar birth. Sharpless 140 lies almost 3000 light-years from Earth in the constellation Cepheus. At its heart is a cluster of three deeply embedded young stars, which are each several thousand times brighter than the Sun. Though they are strikingly visible in this image from Spitzer's infrared array camera, they are completely obscured in visible light, buried within the core of the surrounding dust cloud. The extreme youth of at least one of these stars is indicated by the presence of a stream of gas moving at high velocities. Such outflows are signatures of the processes surrounding a star that is still gobbling up material as part of its formation. The bright red bowl, or arc, seen in this image traces the outer surface of the dense dust cloud encasing the young stars. This arc is made up primarily of organic compounds called polycyclic aromatic hydrocarbons, which glow on the surface of the cloud. Ultraviolet light from a nearby bright star outside of the image is "eating away" at these molecules. Eventually, this light will destroy the dust envelope and the masked young stars will emerge. This false-color image was taken on Oct. 11, 2003 and is composed of photographs obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red). http://photojournal.jpl.nasa.gov/catalog/PIA05878