Mass and age of red giant branch stars observed with LAMOST and Kepler

NASA Astrophysics Data System (ADS)

Wu, Yaqian; Xiang, Maosheng; Bi, Shaolan; Liu, Xiaowei; Yu, Jie; Hon, Marc; Sharma, Sanjib; Li, Tanda; Huang, Yang; Liu, Kang; Zhang, Xianfei; Li, Yaguang; Ge, Zhishuai; Tian, Zhijia; Zhang, Jinghua; Zhang, Jianwei

2018-04-01

Obtaining accurate and precise masses and ages for large numbers of giant stars is of great importance for unraveling the assemblage history of the Galaxy. In this paper, we estimate masses and ages of 6940 red giant branch (RGB) stars with asteroseismic parameters deduced from Kepler photometry and stellar atmospheric parameters derived from LAMOST spectra. The typical uncertainties of mass is a few per cent, and that of age is ˜20 per cent. The sample stars reveal two separate sequences in the age-[α/Fe] relation - a high-α sequence with stars older than ˜8 Gyr and a low-α sequence composed of stars with ages ranging from younger than 1 Gyr to older than 11 Gyr. We further investigate the feasibility of deducing ages and masses directly from LAMOST spectra with a machine learning method based on kernel based principal component analysis, taking a sub-sample of these RGB stars as a training data set. We demonstrate that ages thus derived achieve an accuracy of ˜24 per cent. We also explored the feasibility of estimating ages and masses based on the spectroscopically measured carbon and nitrogen abundances. The results are quite satisfactory and significantly improved compared to the previous studies.

Surprising Rapid Collapse of Sirius B from Red Giant to White Dwarf Through Mass Transfer to Sirius a

NASA Astrophysics Data System (ADS)

Yousef, Shahinaz; Ali, Ola

2013-03-01

Sirius was observed in antiquity as a red star. In his famous astronomy textbook the Almagest written 140 AD, Ptolemy described the star Sirius as fiery red. He curiously depicted it as one of six red-colored stars. The other five are class M and K stars, such as Arcturus and Betelgeuse. Apparent confirmation in ancient Greek and Roman sources are found and Sirius was also reported red in Europe about 1400 years ago. Sirius must have changed to a white dwarf in the night of Ascension. The star chapter in the Quran started with "by the star as it collapsed (1) your companion have not gone astray nor being misled (2), and in verse 49 which is the rotation period of the companion Sirius B around Sirius A, it is said" He is the Lord of Sirius (49). If Sirius actually was red what could have caused it to change into the brilliant bluish-white star we see today? What the naked eye perceives as a single star is actually a binary star system, consisting of a white main sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. The red color indicates that the star seen then was a red giant. It looks that what they have seen in antiquity was Sirius B which was then a red giant and it collapsed to form a white dwarf. Since there is no evidence of a planetary nebula, then the red Sirius paradox can be solved in terms of stellar evolution with mass transfer. Sirius B was the most massive star which evolved to a red giant and filled the Roche lobe. Mass transfer to Sirius A occurred through the Lagrangian point. Sirius A then became more massive while Sirius B lost mass and shrank. Sirius B then collapsed abruptly into a white dwarf. In the case of Algol, Ptolmy observed it as white star but it was red at the time of El sufi. At present it is white. The rate of mass transfer from Sirius B to Sirius A, and from Algol B to A is estimated from observational data of colour change from red to bullish white to be 0.0021 and 0.0024 M⊙/yr respectively.

Stripped Red Giants - Helium Core White Dwarf Progenitors and their sdB Siblings

NASA Astrophysics Data System (ADS)

Heber, U.

2017-03-01

Some gaps in the mosaic of binary star evolution have recently been filled by the discoveries of helium-core white dwarf progenitors (often called extremely low mass (ELM) white dwarfs) as stripped cores of first-giant branch objects. Two varieties can be distinguished. One class is made up by SB1 binaries, companions being white dwarfs as well. Another class, the so-called EL CVn stars, are composite spectrum binaries, with A-Type companions. Pulsating stars are found among both classes. A riddle is posed by the apparently single objects. There is a one-to-one correspondence of the phenomena found for these new classes of star to those observed for sdB stars. In fact, standard evolutionary scenarios explain the origin of sdB stars as red giants that have been stripped close to the tip of first red giant branch. A subgroup of subluminous B stars can also be identified as stripped helium-cores of red giants. They form an extension of the ELM sequence to higher temperatures. Hence low mass white dwarfs of helium cores and sdB stars in binaries are close relatives in terms of stellar evolution.

Multiple stellar populations in Magellanic Cloud clusters - VI. A survey of multiple sequences and Be stars in young clusters

NASA Astrophysics Data System (ADS)

Milone, A. P.; Marino, A. F.; Di Criscienzo, M.; D'Antona, F.; Bedin, L. R.; Da Costa, G.; Piotto, G.; Tailo, M.; Dotter, A.; Angeloni, R.; Anderson, J.; Jerjen, H.; Li, C.; Dupree, A.; Granata, V.; Lagioia, E. P.; Mackey, A. D.; Nardiello, D.; Vesperini, E.

2018-06-01

The split main sequences (MSs) and extended MS turnoffs (eMSTOs) detected in a few young clusters have demonstrated that these stellar systems host multiple populations differing in a number of properties such as rotation and, possibly, age. We analyse Hubble Space Telescope photometry for 13 clusters with ages between ˜40 and ˜1000 Myr and of different masses. Our goal is to investigate for the first time the occurrence of multiple populations in a large sample of young clusters. We find that all the clusters exhibit the eMSTO phenomenon and that MS stars more massive than ˜1.6 M_{⊙} define a blue and a red MS, with the latter hosting the majority of MS stars. The comparison between the observations and isochrones suggests that the blue MSs are made of slow-rotating stars, while the red MSs host stars with rotational velocities close to the breakup value. About half of the bright MS stars in the youngest clusters are H α emitters. These Be stars populate the red MS and the reddest part of the eMSTO, thus supporting the idea that the red MS is made of fast rotators. We conclude that the split MS and the eMSTO are a common feature of young clusters in both Magellanic Clouds. The phenomena of a split MS and an eMSTO occur for stars that are more massive than a specific threshold, which is independent of the host-cluster mass. As a by-product, we report the serendipitous discovery of a young Small Magellanic Cloud cluster, GALFOR 1.

Understanding the Effects of Space Radiation on Living Organisms and its Implication for Astrobiology

NASA Technical Reports Server (NTRS)

Tarter, Jill C.; Rothschild, Lynn J.

2012-01-01

The planetary environment around a star will be assaulted with various amounts of radiation. including solar and ionizing radiation. The amount and type varies with the type of star, the distance from the star, time of day, and other variables. While some radiation is critical to life on Earth, especially from 400-750 nm (so-called visible and photosynthetically active radiation), the effects of ultraviolet and ionizing radiation can be hazardous and even deadly. This is because life is based on organic carbon, which is susceptible to radiation damage. Radiation regimes in our own solar system address specifically radiation in our solar system with a main sequence star. The possibility remains of planets around red dwarfs. Such stars are much smaller in mass than the Sun (between 0.5 and .08 M(sub Sun), and so their temperature and stellar luminosity are low and peaked in the red. Since red dwarfs comprise about 75% of all stars in the galaxy, the possibility of life on planets around red dwarfs has been examined.

The Mid-infrared View of Red Sequence Galaxies in Abell 2218 with AKARI

NASA Astrophysics Data System (ADS)

Ko, Jongwan; Im, Myungshin; Lee, Hyung Mok; Lee, Myung Gyoon; Hopwood, Ros H.; Serjeant, Stephen; Smail, Ian; Hwang, Ho Seong; Hwang, Narae; Shim, Hyunjin; Kim, Seong Jin; Lee, Jong Chul; Lim, Sungsoon; Seo, Hyunjong; Goto, Tomotsugu; Hanami, Hitoshi; Matsuhara, Hideo; Takagi, Toshinobu; Wada, Takehiko

2009-04-01

We present the AKARI Infrared Camera (IRC) imaging observation of early-type galaxies (ETGs) in A2218 at zsime 0.175. Mid-infrared (MIR) emission from ETGs traces circumstellar dust emission from asymptotic giant branch (AGB) stars or/and residual star formation. Including the unique imaging capability at 11 and 15 μm, our AKARI data provide an effective way to investigate MIR properties of ETGs in the cluster environment. Among our flux-limited sample of 22 red sequence ETGs with precise dynamical and line strength measurements (less than 18 mag at 3 μm), we find that at least 41% have MIR-excess emission. The N3 - S11 versus N3 (3 and 11 μm) color-magnitude relation shows the expected blue sequence, but the MIR-excess galaxies add a red wing to the relation especially at the fainter end. A spectral energy distribution analysis reveals that the dust emission from AGB stars is the most likely cause of the MIR excess, with a low level of star formation being the next possible explanation. The MIR-excess galaxies show a wide spread of N3 - S11 colors, implying a significant spread (2-11 Gyr) in the estimated mean ages of stellar populations. We study the environmental dependence of MIR-excess ETGs over an area out to a half virial radius (~1 Mpc). We find that the MIR-excess ETGs are preferentially located in the outer region. From this evidence, we suggest that the fainter, MIR-excess ETGs have just joined the red sequence, possibly due to the infall and subsequent morphological/spectral transformation induced by the cluster environment.

The dwarf spheroidal galaxy in Draco. I - New BV photometry. II - Galactic foreground reddening

NASA Technical Reports Server (NTRS)

Stetson, P. B.

1979-01-01

BV photoelectric photometry for 39 stars and BV photographic photometry for 514 stars in the field of the Draco dwarf spheroidal galaxy are presented. The color-magnitude diagram for 512 of these field stars is found to display a well-defined red horizontal branch as well as a red giant branch whose observed width is comparable to the accidental photometric error. The results also indicate that a more diffuse sequence of stars lies about 0.1 mag to the blue of the giant branch and that an upper horizontal branch of more massive core helium-burning stars may also be present. The foreground reddening toward Draco is then determined by narrow-band uvby-beta photometry of galactic B-A-F stars.

IMPLICATIONS OF RAPID CORE ROTATION IN RED GIANTS FOR INTERNAL ANGULAR MOMENTUM TRANSPORT IN STARS

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

Tayar, Jamie; Pinsonneault, Marc H., E-mail: tayar.1@osu.edu

2013-09-20

Core rotation rates have been measured for red giant stars using asteroseismology. These data, along with helioseismic measurements and open cluster spin-down studies, provide powerful clues about the nature and timescale for internal angular momentum transport in stars. We focus on two cases: the metal-poor red giant KIC 7341231 ({sup O}tto{sup )} and intermediate-mass core helium burning stars. For both, we examine limiting case studies for angular momentum coupling between cores and envelopes under the assumption of rigid rotation on the main sequence. We discuss the expected pattern of core rotation as a function of mass and radius. In themore » case of Otto, strong post-main-sequence coupling is ruled out and the measured core rotation rate is in the range of 23-33 times the surface value expected from standard spin-down models. The minimum coupling timescale (0.17-0.45 Gyr) is significantly longer than that inferred for young open cluster stars. This implies ineffective internal angular momentum transport in early first ascent giants. By contrast, the core rotation rates of evolved secondary clump stars are found to be consistent with strong coupling given their rapid main-sequence rotation. An extrapolation to the white dwarf regime predicts rotation periods between 330 and 0.0052 days, depending on mass and decoupling time. We identify two key ingredients that explain these features: the presence of a convective core and inefficient angular momentum transport in the presence of larger mean molecular weight gradients. Observational tests that can disentangle these effects are discussed.« less

THE RED SEQUENCE AT BIRTH IN THE GALAXY CLUSTER Cl J1449+0856 AT z = 2

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

Strazzullo, V.; Pannella, M.; Daddi, E.

We use Hubble Space Telescope /WFC3 imaging to study the red population in the IR-selected, X-ray detected, low-mass cluster Cl J1449+0856 at z = 2, one of the few bona fide established clusters discovered at this redshift, and likely a typical progenitor of an average massive cluster today. This study explores the presence and significance of an early red sequence in the core of this structure, investigating the nature of red-sequence galaxies, highlighting environmental effects on cluster galaxy populations at high redshift, and at the same time underlining similarities and differences with other distant dense environments. Our results suggest thatmore » the red population in the core of Cl J1449+0856 is made of a mixture of quiescent and dusty star-forming galaxies, with a seedling of the future red sequence already growing in the very central cluster region, and already characterizing the inner cluster core with respect to lower-density environments. On the other hand, the color–magnitude diagram of this cluster is definitely different from that of lower-redshift z ≲ 1 clusters, as well as of some rare particularly evolved massive clusters at similar redshift, and it is suggestive of a transition phase between active star formation and passive evolution occurring in the protocluster and established lower-redshift cluster regimes.« less

The Nature of Red-Sequence Cluster Spiral Galaxies

NASA Astrophysics Data System (ADS)

Kashur, Lane; Barkhouse, Wayne; Sultanova, Madina; Kalawila Vithanage, Sandanuwa; Archer, Haylee; Foote, Gregory; Mathew, Elijah; Rude, Cody; Lopez-Cruz, Omar

2017-01-01

Preliminary analysis of the red-sequence galaxy population from a sample of 57 low-redshift galaxy clusters observed using the KPNO 0.9m telescope and 74 clusters from the WINGS dataset, indicates that a small fraction of red-sequence galaxies have a morphology consistent with spiral systems. For spiral galaxies to acquire the color of elliptical/S0s at a similar luminosity, they must either have been stripped of their star-forming gas at an earlier epoch, or contain a larger than normal fraction of dust. To test these ideas we have compiled a sample of red-sequence spiral galaxies and examined their infrared properties as measured by 2MASS, WISE, Spitzer, and Herschel. These IR data allows us to estimate the amount of dust in each of our red-sequence spiral galaxies. We compare the estimated dust mass in each of these red-sequence late-type galaxies with spiral galaxies located in the same cluster field but having colors inconsistent with the red-sequence. We thus provide a statistical measure to discriminate between purely passive spiral galaxy evolution and dusty spirals to explain the presence of these late-type systems in cluster red-sequences.

The GALEX/S4G UV-IR Color-Color Diagram: Catching Spiral Galaxies Away from the Blue Sequence

NASA Astrophysics Data System (ADS)

Bouquin, Alexandre Y. K.; Gil de Paz, Armando; Boissier, Samuel; Muñoz-Mateos, Juan-Carlos; Sheth, Kartik; Zaritsky, Dennis; Laine, Jarkko; Gallego, Jesús; Peletier, Reynier F.; Röck, Benjamin R.; Knapen, Johan H.

2015-02-01

We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6 μm photometry for \\gt 2000 galaxies, available for 90% of the S4G sample. We find a very tight GALEX blue sequence (GBS) in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram, which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale (τ) and a degeneracy between τ and dust reddening. The tightness of the GBS provides an unprecedented way of identifying star-forming galaxies and objects that are just evolving to (or from) what we call the GALEX green valley (GGV). At the red end of the GBS, at (NUV-[3.6]) \\gt 5, we find a wider GALEX red sequence (GRS) mostly populated by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the optical red sequence. We find no such dichotomy in terms of stellar mass (measured by {{M}[3.6]}) since both massive ({{M}\\star }\\gt {{10}11}{{M}⊙ }) blue- and red-sequence galaxies are identified. The type that is proportionally more often found in the GGV is the S0-Sa’s, and most of these are located in high-density environments. We discuss evolutionary models of galaxies that show a rapid transition from the blue to the red sequence on a timescale of 108 yr.

Enormous Li Enhancement Preceding Red Giant Phases in Low-mass Stars in the Milky Way Halo

NASA Astrophysics Data System (ADS)

Li, Haining; Aoki, Wako; Matsuno, Tadafumi; Bharat Kumar, Yerra; Shi, Jianrong; Suda, Takuma; Zhao, Gang

2018-01-01

Li abundances in the bulk of low-mass metal-poor stars are well reproduced by stellar evolution models adopting a constant initial abundance. However, a small number of stars have exceptionally high Li abundances, for which no convincing models have been established. We report on the discovery of 12 very metal-poor stars that have large excesses of Li, including an object having more than 100 times higher Li abundance than the values found in usual objects, which is the largest excess in metal-poor stars known to date. The sample is distributed over a wide range of evolutionary stages, including five unevolved stars, showing no clear abundance anomaly in other elements. The results indicate the existence of an efficient process to enrich Li in a small fraction of low-mass stars at the main-sequence or subgiant phase. The wide distribution of Li-rich stars along the red giant branch could be explained by the dilution of surface Li by mixing that occurs when the stars evolve into red giants. Our study narrows down the problem to be solved in order to understand the origins of Li excess found in low-mass stars, suggesting the presence of an unknown process that affects the surface abundances preceding red giant phases. This work is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

AKARI OBSERVATION OF THE NORTH ECLIPTIC POLE (NEP) SUPERCLUSTER AT z = 0.087: MID-INFRARED VIEW OF TRANSITION GALAXIES

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

Ko, Jongwan; Im, Myungshin; Lee, Hyung Mok

2012-02-01

We present the mid-infrared (MIR) properties of galaxies within a supercluster in the north ecliptic pole region at z {approx} 0.087 observed with the AKARI satellite. We use data from the AKARI NEP-Wide (5.4 deg{sup 2}) IR survey and the CLusters of galaxies EVoLution studies (CLEVL) mission program. We show that near-IR (3 {mu}m)-mid-IR (11 {mu}m) color can be used as an indicator of the specific star formation rate and the presence of intermediate-age stellar populations. From the MIR observations, we find that red-sequence galaxies consist not only of passively evolving red early-type galaxies, but also of (1) 'weak-SFGs' (disk-dominatedmore » star-forming galaxies that have star formation rates lower by {approx}4 Multiplication-Sign than blue-cloud galaxies) and (2) 'intermediate-MXGs' (bulge-dominated galaxies showing stronger MIR dust emission than normal red early-type galaxies). These two populations can be a set of transition galaxies from blue, star-forming, late-type galaxies evolving into red, quiescent, early-type ones. We find that the weak-SFGs are predominant at intermediate masses (10{sup 10} M{sub Sun} < M{sub *} < 10{sup 10.5} M{sub Sun }) and are typically found in local densities similar to the outskirts of galaxy clusters. As much as 40% of the supercluster member galaxies in this mass range can be classified as weak-SFGs, but their proportion decreases to <10% at larger masses (M{sub *} > 10{sup 10.5} M{sub Sun }) at any galaxy density. The fraction of the intermediate-MXG among red-sequence galaxies at 10{sup 10} M{sub Sun} < M{sub *} < 10{sup 11} M{sub Sun} also decreases as the density and mass increase. In particular, {approx}42% of the red-sequence galaxies with early-type morphologies are classified as intermediate-MXGs at intermediate densities. These results suggest that the star formation activity is strongly dependent on the stellar mass, but that the morphological transformation is mainly controlled by the environment.« less

A sample of potential disk hosting first ascent red giants

NASA Astrophysics Data System (ADS)

Steele, Amy; Debes, John

2018-01-01

Observations of (sub)giants with planets and disks provide the first set of proof that disks can survive the first stages of post-main-sequence evolution, even though the disks are expected to dissipate by this time. The infrared (IR) excesses present around a number of post-main-sequence (PMS) stars could be due to a traditional debris disk with planets (e.g. kappa CrB), some remnant of enhanced mass loss (e.g. the shell-like structure of R Sculptoris), and/or background contamination. We present a sample of potential disk hosting first ascent red giants. These stars all have infrared excesses at 22 microns, and possibly host circumstellar debris. We summarize the characteristics of the sample to better inform the incidence rates of thermally emitting material around giant stars. A thorough follow-up study of these candidates would serve as the first step in probing the composition of the dust in these systems that have left the main sequence, providing clues to the degree of disk processing that occurs beyond the main-sequence.

Mass loss from red giants - Results from ultraviolet spectroscopy

NASA Technical Reports Server (NTRS)

Linsky, J. L.

1985-01-01

New instrumentation in space, primarily the IUE spacecraft, has enabled the application of ultraviolet spectroscopic techniques to the determination of physical properties and reliable mass loss rates for red giant winds. One important result is the determination of where in the H-R diagram are found stars with hot outer atmospheres and with cool winds. So far it appears that single cool stars, except perhaps the so-called hybrid stars, have either hot outer atmospheres or cool winds but not both. The C II resonance (1335 A) and intersystem (2325 A) multiplets have been used to derive temperatures, densities, and geometrical extents for the chromospheric portions of red giant winds, with the result that the red giants and the earlier giants with hot coronae have qualitatively different chromospheres. Mass loss rates can now be derived accurately from the analysis of asymmetric emission lines, such as the Mg II resonance lines, and from P Cygni profile lines of atoms in the dominant ionization stage when a hot star is available to probe the wind of a red giant. The Zeta Aur systems, consisting of a K-M supergiant and a main sequence B star are important systems for reliable mass loss rates for the red supergiant components are becoming available.

Distance and absolute magnitudes of the brightest stars in the dwarf galaxy Sextans A

NASA Technical Reports Server (NTRS)

Sandage, A.; Carlson, G.

1982-01-01

In an attempt to improve present bright star calibration, data were gathered for the brightest red and blue stars and the Cepheids in the Im V dwarf galaxy, Sextans A. On the basis of a magnitude sequence measured to V and B values of about 22 and 23, respectively, the mean magnitudes of the three brightest blue stars are V=17.98 and B=17.88. The three brightest red supergiants have V=18.09 and B=20.14. The periods and magnitudes measured for five Cepheids yield an apparent blue distance modulus of 25.67 + or - 0.2, via the P-L relation, and the mean absolute magnitudes of V=-7.56 and B=-5.53 for the red supergiants provide additional calibration of the brightest red stars as distance indicators. If Sextans A were placed at the distance of the Virgo cluster, it would appear to have a surface brightness of 23.5 mag/sq arcec. This, together with the large angular diameter, would make such a galaxy easily discoverable in the Virgo cluster by means of ground-based surveys.

Kinematics of Stars from the TGAS (Gaia DR1) Catalogue

NASA Astrophysics Data System (ADS)

Vityazev, V. V.; Popov, A. V.; Tsvetkov, A. S.; Petrov, S. D.; Trofimov, D. A.; Kiyaev, V. I.

2018-04-01

Based on the stellar proper motions of the TGAS (Gaia DR1) catalogue, we have analyzed the velocity field of main-sequence stars and red giants from the TGAS catalogue with heliocentric distances up to 1.5 kpc. We have obtained four variants of kinematic parameters corresponding to different methods of calculating the distances from the parallaxes of stars measured with large relative errors. We have established that within the Ogorodnikov-Milne model changing the variant of distances affects significantly only the solar velocity components relative to the chosen centroid of stars, provided that the solution is obtained in narrow ranges of distances (0.1 kpc). The estimates of all the remaining kinematic parameters change little. This allows the Oort coefficients and related Galactic rotation parameters as well as all the remaining Ogorodnikov-Milne model parameters (except for the solar terms) to be reliably estimated irrespective of the parallax measurement accuracy. The main results obtained from main-sequence stars in the range of distances from 0.1 to 1.5 kpc are: A = 16.29 ± 0.06 km s-1 kpc-1, B = -11.90 ± 0.05 km s-1 kpc-1, C = -2.99 ± 0.06 km s-1 kpc-1, K = -4.04 ± 0.16 km s-1 kpc-1, and the Galactic rotation period P = 217.41 ± 0.60 Myr. The analogous results obtained from red giants in the range from 0.2 to 1.6 kpc are: the Oort constants A = 13.32 ± 0.09 km s-1 kpc-1, B = -12.71 ± 0.06 km s-1 kpc-1, C = -2.04 ± 0.08 km s-1 kpc-1, K = -2.72 ± 0.19 km s-1 kpc-1, and the Galactic rotation period P = 236.03 ± 0.98 Myr. The Galactic rotation velocity gradient along the radius vector (the slope of the Galactic rotation curve) is -4.32 ± 0.08 km s-1 kpc-1 for main-sequence stars and -0.61 ± 0.11 km s-1 kpc-1 for red giants. This suggests that the Galactic rotation velocity determined from main-sequence stars decreases with increasing distance from the Galactic center faster than it does for red giants.

Mass-losing peculiar red giants - The comparison between theory and observations

NASA Technical Reports Server (NTRS)

Jura, M.

1989-01-01

The mass loss from evolved red giants is considered. It seems that red giants on the Asymptotic Giant Branch (AGB) are losing between 0.0003 and 0.0006 solar mass/sq kpc yr in the solar neighborhood. If all the main sequence stars between 1 and 5 solar masses ultimately evolve into white dwarfs with masses of 0.7 solar mass, the predicted mass loss rate in the solar neighborhood from these stars is 0.0008 solar mass/sq kpc yr. Although there are still uncertainties, it appears that there is no strong disagreement between theory and observation.

HABITABLE ZONES OF POST-MAIN SEQUENCE STARS

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

Ramirez, Ramses M.; Kaltenegger, Lisa

Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (∼M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons tomore » super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.« less

Supernova SN 2011fe from an exploding carbon-oxygen white dwarf star.

PubMed

Nugent, Peter E; Sullivan, Mark; Cenko, S Bradley; Thomas, Rollin C; Kasen, Daniel; Howell, D Andrew; Bersier, David; Bloom, Joshua S; Kulkarni, S R; Kandrashoff, Michael T; Filippenko, Alexei V; Silverman, Jeffrey M; Marcy, Geoffrey W; Howard, Andrew W; Isaacson, Howard T; Maguire, Kate; Suzuki, Nao; Tarlton, James E; Pan, Yen-Chen; Bildsten, Lars; Fulton, Benjamin J; Parrent, Jerod T; Sand, David; Podsiadlowski, Philipp; Bianco, Federica B; Dilday, Benjamin; Graham, Melissa L; Lyman, Joe; James, Phil; Kasliwal, Mansi M; Law, Nicholas M; Quimby, Robert M; Hook, Isobel M; Walker, Emma S; Mazzali, Paolo; Pian, Elena; Ofek, Eran O; Gal-Yam, Avishay; Poznanski, Dovi

2011-12-14

Type Ia supernovae have been used empirically as 'standard candles' to demonstrate the acceleration of the expansion of the Universe even though fundamental details, such as the nature of their progenitor systems and how the stars explode, remain a mystery. There is consensus that a white dwarf star explodes after accreting matter in a binary system, but the secondary body could be anything from a main-sequence star to a red giant, or even another white dwarf. This uncertainty stems from the fact that no recent type Ia supernova has been discovered close enough to Earth to detect the stars before explosion. Here we report early observations of supernova SN 2011fe in the galaxy M101 at a distance from Earth of 6.4 megaparsecs. We find that the exploding star was probably a carbon-oxygen white dwarf, and from the lack of an early shock we conclude that the companion was probably a main-sequence star. Early spectroscopy shows high-velocity oxygen that slows rapidly, on a timescale of hours, and extensive mixing of newly synthesized intermediate-mass elements in the outermost layers of the supernova. A companion paper uses pre-explosion images to rule out luminous red giants and most helium stars as companions to the progenitor.

Metallicity Variations in the Type II Globular Cluster NGC 6934

NASA Astrophysics Data System (ADS)

Marino, A. F.; Yong, D.; Milone, A. P.; Piotto, G.; Lundquist, M.; Bedin, L. R.; Chené, A.-N.; Da Costa, G.; Asplund, M.; Jerjen, H.

2018-06-01

The Hubble Space Telescope photometric survey of Galactic globular clusters (GCs) has revealed a peculiar “chromosome map” for NGC 6934. In addition to a typical sequence, similar to that observed in Type I GCs, NGC 6934 displays additional stars on the red side, analogous to the anomalous Type II GCs, as defined in our previous work. We present a chemical abundance analysis of four red giants in this GC. Two stars are located on the chromosome map sequence common to all GCs, and another two lie on the additional sequence. We find (i) star-to-star Fe variations, with the two anomalous stars being enriched by ∼0.2 dex. Because of our small-size sample, this difference is at the ∼2.5σ level. (ii) There is no evidence for variations in the slow neutron-capture abundances over Fe, at odds with what is often observed in anomalous Type II GCs, e.g., M 22 and ω Centauri (iii) no large variations in light elements C, O, and Na, compatible with locations of the targets on the lower part of the chromosome map where such variations are not expected. Since the analyzed stars are homogeneous in light elements, the only way to reproduce the photometric splits on the sub-giant (SGB) and the red giant (RGB) branches is to assume that red RGB/faint SGB stars are enhanced in [Fe/H] by ∼0.2. This fact corroborates the spectroscopic evidence of a metallicity variation in NGC 6934. The observed chemical pattern resembles only partially the other Type II GCs, suggesting that NGC 6934 might belong either to a third class of GCs, or be a link between normal Type I and anomalous Type II GCs. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, and Gemini Telescope at Canada–France–Hawaii Telescope.

Convective-core Overshoot and Suppression of Oscillations: Constraints from Red Giants in NGC 6811

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

Arentoft, T.; Brogaard, K.; Jessen-Hansen, J.

Using data from the NASA spacecraft Kepler , we study solar-like oscillations in red giant stars in the open cluster NGC 6811. We determine oscillation frequencies, frequency separations, period spacings of mixed modes, and mode visibilities for eight cluster giants. The oscillation parameters show that these stars are helium-core-burning red giants. The eight stars form two groups with very different oscillation power spectra; the four stars with the lowest Δ ν values display rich sets of mixed l = 1 modes, while this is not the case for the four stars with higher Δ ν . For the four starsmore » with lowest Δ ν , we determine the asymptotic period spacing of the mixed modes, Δ P , which together with the masses we derive for all eight stars suggest that they belong to the so-called secondary clump. Based on the global oscillation parameters, we present initial theoretical stellar modeling that indicates that we can constrain convective-core overshoot on the main sequence and in the helium-burning phase for these ∼2 M {sub ⊙} stars. Finally, our results indicate less mode suppression than predicted by recent theories for magnetic suppression of certain oscillation modes in red giants.« less

FIRST OBSERVATIONAL SIGNATURE OF ROTATIONAL DECELERATION IN A MASSIVE, INTERMEDIATE-AGE STAR CLUSTER IN THE MAGELLANIC CLOUDS

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

Wu, Xiaohan; Li, Chengyuan; De Grijs, Richard

While the extended main-sequence turnoffs (eMSTOs) found in almost all 1–2 Gyr old star clusters in the Magellanic Clouds are often explained by postulating extended star formation histories (SFHs), the tight subgiant branches (SGBs) seen in some clusters challenge this popular scenario. Puzzlingly, the SGB of the eMSTO cluster NGC 419 is significantly broader at bluer than at redder colors. We carefully assess and confirm the reality of this observational trend. If we would assume that the widths of the features in color–magnitude space were entirely owing to a range in stellar ages, the SFHs of the eMSTO stars andmore » the blue SGB region would be significantly more prolonged than that of the red part of the SGB. This cannot be explained by assuming an internal age spread. We show that rotational deceleration of a population of rapidly rotating stars, a currently hotly debated alternative scenario, naturally explains the observed trend along the SGB. Our analysis shows that a “converging” SGB could be produced if the cluster is mostly composed of rapidly rotating stars that slow down over time owing to the conservation of angular momentum during their evolutionary expansion from main-sequence turnoff stars to red giants.« less

Red giants: then and now

NASA Astrophysics Data System (ADS)

Faulkner, John

Fred Hoyle's work on the structure and evolution of red giants, particularly his pathbreaking contribution with Martin Schwarzschild (Hoyle and Schwarzschild 1955), is both lauded and critically assessed. In his later lectures and work with students in the early 1960s, Hoyle presented more physical ways of understanding some of the approximations used, and results obtained, in that seminal paper. Although later ideas by other investigators will be touched upon, Hoyle's viewpoint - that low-mass red giants are essentially white dwarfs with a serious mass-storage problem - is still extremely fruitful. Over the years, I have further developed his method of attack. Relatively recently, I have been able to deepen and broaden the approach, finally extending the theory to provide a unifying treatment of the structure of low-mass stars from the main sequence though both the red-giant and horizontal-branch phases of evolution. Many aspects of these stars that had remained puzzling, even mysterious, for decades have now fallen into place, and some questions have been answered that were not even posed before. With low-mass red giants as the simplest example, this recent work emphasizes that stars, in general, may have at least two distinct but very important centres: (I) a geometrical centre, and (II) a separate nuclear centre, residing in a shell outside a zero-luminosity dense core for example. This two-centre perspective leads to an explicit, analytical, asymptotic theory of low-mass red-giant structure. It enables one to appreciate that the problem of understanding why such stars become red giants is one of anticipating a remarkable yet natural structural bifurcation that occurs in them. This bifurcation occurs because of a combination of known and understandable facts just summarized namely that, following central hydrogen exhaustion, a thin nuclear-burning shell does develop outside a more-or-less dense core. In the resulting theory, both ρsh/ρolinec and ρsh·ρolinec prove to be important self-consistently derived quantities. I present some striking, explicit, asymptotic analytical theorems and results involving these quantities. Perhaps the most astonishingly unexpected and gratifying single result is this: for the very value Nature gives us for the relevant temperature exponent (η=15; CNO cycle) for nuclear-energy generation, ρsh and ρolinec behave in a well defined, precisely inverse manner for a given value of core-mass, Mc. This emphasizes that the internal behaviour of such stars is definitely anti-homologous rather than homologous: dense cores physically promote diffuse surrounding envelopes. I also extend the ideas yet further in a way which (I) links the structural and evolutionary behaviour of stars from the main sequence through horizontal-branch phases of evolution, and (II) also has implications for post-main-sequence developments in more massive stars. The end results is that the post-main-sequence developments of all stars - low-mass, intermediate-mass, and high-mass - as they expand to become giants, are finally seen to be examples of one underpinning fact: that dense cores with this surrounding shells naturally follow hydrogen exhaustion. While "this has been know all along" from oft-repeated computer calculations, we now know why analytically. That matters to true theorists. What follows is a requested, much expanded version of my Cambridge talk.

Multifrequency observations of symbiotic stars

NASA Technical Reports Server (NTRS)

Kenyon, Scott J.

1988-01-01

The discovery of symbiotic stars is described, and the results of multifrequency observations made during the past two decades are presented. Observational data identify symbiotic stars as long-period binary systems that can be divided into two basic physical classes: detached symbiotics containing a red giant (or a Mira variable), and semidetached symbiotics containing a lobe-filling red giant and a solar-type main sequence star. Three components are typically observed: (1) the cool giant component with an effective temperature of 2500-4000 K, which can be divided by the IR spectral classification into normal M giants (S-types) and heavily reddened Mira variables (D-types); (2) the hot companion displaying a bright blue continuum at UV wavelengths, which is sometimes also an X-ray source; and (3) a gaseous nebula enveloping the binary.

The evolution of rotating stars. III - Predicted surface rotation velocities for stars which conserve total angular momentum

NASA Technical Reports Server (NTRS)

Endal, A. S.; Sofia, S.

1979-01-01

Predicted surface rotation velocities for Population I stars at 10, 7, 5, 3, and 1.5 solar masses are presented. The surface velocities were computed for angular momentum with no radial redistribution, complete redistribution, and partial redistribution as predicted by consideration of circulation currents in rotating stars. Near the main sequence, rotational effects can reduce the moment of inertia of a star, so nonrotating models underestimate the expected velocities for evolving stars. On the red giant branch, angular momentum redistribution reduces the surface velocity by a factor of 2 or more, relative to the velocity expected for no radial redistribution. This removes the discrepancy between predicted and observed rotation rates for the K giants and makes it unlikely that these stars lose significant amounts of angular momentum by stellar winds. Calculations indicate that improved observations of the red giants in the Hyades cluster can be used to determine how angular momentum is redistributed by convection

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets. I. From the PMS to the RGB at solar metallicity

NASA Astrophysics Data System (ADS)

Gallet, F.; Bolmont, E.; Mathis, S.; Charbonnel, C.; Amard, L.

2017-08-01

Context. Star-planet interactions must be taken into account in stellar models to understand the dynamical evolution of close-in planets. The dependence of the tidal interactions on the structural and rotational evolution of the star is of particular importance and should be correctly treated. Aims: We quantify how tidal dissipation in the convective envelope of rotating low-mass stars evolves from the pre-main sequence up to the red-giant branch depending on the initial stellar mass. We investigate the consequences of this evolution on planetary orbital evolution. Methods: We couple the tidal dissipation formalism previously described to the stellar evolution code STAREVOL and apply this coupling to rotating stars with masses between 0.3 and 1.4 M⊙. As a first step, this formalism assumes a simplified bi-layer stellar structure with corresponding averaged densities for the radiative core and the convective envelope. We use a frequency-averaged treatment of the dissipation of tidal inertial waves in the convection zone (but neglect the dissipation of tidal gravity waves in the radiation zone). In addition, we generalize a recent work by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution. Results: On the pre-main sequence the evolution of tidal dissipation is controlled by the evolution of the internal structure of the contracting star. On the main sequence it is strongly driven by the variation of surface rotation that is impacted by magnetized stellar winds braking. The main effect of taking into account the rotational evolution of the stars is to lower the tidal dissipation strength by about four orders of magnitude on the main sequence, compared to a normalized dissipation rate that only takes into account structural changes. Conclusions: The evolution of the dissipation strongly depends on the evolution of the internal structure and rotation of the star. From the pre-main sequence up to the tip of the red-giant branch, it varies by several orders of magnitude, with strong consequences for the orbital evolution of close-in massive planets. These effects are the strongest during the pre-main sequence, implying that the planets are mainly sensitive to the star's early history.

The Optical Gravitational Lensing Experiment: catalogue of stellar proper motions in the OGLE-II Galactic bulge fields

NASA Astrophysics Data System (ADS)

Sumi, T.; Wu, X.; Udalski, A.; Szymański, M.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Woźniak, P.; Żebruń, K.; Szewczyk, O.; Wyrzykowski, Ł.

2004-03-01

We present a proper-motion (μ) catalogue of 5 080 236 stars in 49 Optical Gravitational Lensing Experiment II (OGLE-II) Galactic bulge (GB) fields, covering a range of -11° < l < 11° and -6° < b < 3°, the total area close to 11 deg2. The proper-motion measurements are based on 138-555 I-band images taken during four observing seasons: 1997-2000. The catalogue stars are in the magnitude range 11 < I < 18 mag. In particular, the catalogue includes red clump giants and red giants in the GB, and main-sequence stars in the Galactic disc. The proper motions up to μ= 500 mas yr-1 were measured with a mean accuracy of 0.8-3.5 mas yr-1, depending on the brightness of a star. This catalogue may be useful for studying the kinematics of stars in the GB and the Galactic disc.

On the non-variability of HR 7653 (15 Vul) based on BRITE data

NASA Astrophysics Data System (ADS)

Smalley, B.; Paunzen, E.; Lüftinger, T.; Moffat, A. F. J.; Pigulski, A.; Rucinski, S.; Sikora, J.; Wade, G. A.; Weiss, W.; BEST

2018-02-01

We present space-based BRITE photometric observations of the metallic line (CP1) star HR 7653 (15 Vul). This chemically peculiar star of the upper main sequence was suspected to show variability due to rotation and a magnetic field. Such a variability is quite unusual among the, in general, non-magnetic CP1 stars. We investigated the astrophysical parameters of HR 7653 placing it close to the terminal age main sequence or even in the subgiant phase. The longest BRITE data set has a time base of 18.01 d from which we conclude that there are no coherent long-period variations (>1 d) visible above 2.1 mmag in the red and 6.6 mmag in the blue. Furthermore, we searched for δ Scuti type pulsations. On the basis of a discrete Fourier analysis method, we find no peaks in the Fourier spectra above 0.5 mmag and 8.6 mmag, for the red and blue filters, respectively.

Population gradient in the Sextans dSph: comprehensive mapping of a dwarf galaxy by Suprime-Cam

NASA Astrophysics Data System (ADS)

Okamoto, S.; Arimoto, N.; Tolstoy, E.; Jablonka, P.; Irwin, M. J.; Komiyama, Y.; Yamada, Y.; Onodera, M.

2017-05-01

We present the deep and wide V and Ic photometry of the Sextans dwarf spheroidal galaxy (dSph) taken by the Suprime-Cam imager on the Subaru Telescope, which extends out to the tidal radius. The colour-magnitude diagram (CMD) reaches two magnitudes below the main-sequence (MS) turn-off, showing a steep red giant branch, a blue and a red horizontal branch (BHB and RHB, respectively), a sub-giant branch (SGB), an MS and blue stragglers (BSs). We construct the radial profile of each evolutionary phase and demonstrate that blue HB stars are more spatially extended, while red HB stars are more centrally concentrated than the other components. The colour distribution of SGB stars also varies with the galactocentric distance; the inner SGB stars shift bluer than those in the outskirts. The radial differences in the CMD morphology indicate the existence of the age gradient. The relatively younger stars (˜10 Gyr) are more centrally concentrated than the older ones (˜13 Gyr). The spatial contour maps of stars in different age bins also show that the younger population has a higher concentration and higher ellipticity than the older one. We also detect the centrally concentrated bright BS stars, the number of which is consistent with the idea that a part of these stars belongs to the remnant of a disrupted star cluster discovered in the previous spectroscopic studies.

DUST-CORRECTED COLORS REVEAL BIMODALITY IN THE HOST-GALAXY COLORS OF ACTIVE GALACTIC NUCLEI AT z {approx} 1

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

Cardamone, Carolin N.; Megan Urry, C.; Brammer, Gabriel

2010-09-20

Using new, highly accurate photometric redshifts from the MUSYC medium-band survey in the Extended Chandra Deep Field-South (ECDF-S), we fit synthetic stellar population models to compare active galactic nucleus (AGN) host galaxies to inactive galaxies at 0.8 {<=} z {<=} 1.2. We find that AGN host galaxies are predominantly massive galaxies on the red sequence and in the green valley of the color-mass diagram. Because both passive and dusty galaxies can appear red in optical colors, we use rest-frame near-infrared colors to separate passively evolving stellar populations from galaxies that are reddened by dust. As with the overall galaxy population,more » {approx}25% of the 'red' AGN host galaxies and {approx}75% of the 'green' AGN host galaxies have colors consistent with young stellar populations reddened by dust. The dust-corrected rest-frame optical colors are the blue colors of star-forming galaxies, which imply that these AGN hosts are not passively aging to the red sequence. At z {approx} 1, AGN activity is roughly evenly split between two modes of black hole growth: the first in passively evolving host galaxies, which may be heating up the galaxy's gas and preventing future episodes of star formation, and the second in dust-reddened young galaxies, which may be ionizing the galaxy's interstellar medium and shutting down star formation.« less

Rotational and radial velocities of 1.3-2.2 M {sub ☉} red giants in open clusters

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

Carlberg, Joleen K., E-mail: jcarlberg@dtm.ciw.edu

2014-06-01

This study presents the rotational distribution of red giant (RG) stars in 11 old to intermediate age open clusters. The masses of these stars are all above the Kraft break, so they lose negligible amounts of their birth angular momentum (AM) during the main-sequence (MS) evolution. However, they do span a mass range with quite different AM distributions imparted during formation, with the stars less massive than ∼1.6M {sub ☉} arriving on the MS with lower rotation rates than the more massive stars. The majority of RGs in this study are slow rotators across the entire red giant branch regardlessmore » of mass, supporting the picture that intermediate-mass stars rapidly spin down when they evolve off the MS and develop convection zones capable of driving a magnetic dynamo. Nevertheless, a small fraction of RGs in open clusters show some level of enhanced rotation, and faster rotators are as common in these clusters as in the field RG population. Most of these enhanced rotators appear to be red clump stars, which is also true of the underlying stellar sample, while others are clearly RGs that are above or below the clump. In addition to rotational velocities, the radial velocities (RVs) and membership probabilities of individual stars are also presented. Cluster heliocentric RVs for NGC 6005 and Pismis 18 are reported for the first time.« less

Convective overshooting in the evolution of very massive stars

NASA Technical Reports Server (NTRS)

Stothers, R.; Chin, C.-W.

1981-01-01

Possible convective overshooting in stars of 30-120 solar masses are considered, including a merger between the convective core and the intermediate zone, and penetration by the outer convection zone into the hydrogen-shell region when the star is a supergiant. Convective mixing between the core and inner envelopes is found to lead to a brief renewal of hydrogen burning in the core, and a moderate widening of the main sequence bond in the H-R diagram. Deep penetration by the outer convection zone is found to force the star out of the red supergiant configuration and into a configuration near the main sequence. This would account for the apparent spread of the uppermost part of the main sequence and the concentration of luminous supergiants towards earlier spectral types. In addition, heavy mass loss need not be assumed to achieve the points of agreement, and are tentatively considered unimportant from an evolutionary point of view.

Contribution of Primordial Binary Evolution to the Two Blue-straggler Sequences in Globular Cluster M30

NASA Astrophysics Data System (ADS)

Jiang, Dengkai; Chen, Xuefei; Li, Lifang; Han, Zhanwen

2017-11-01

Two blue-straggler sequences discovered in globular cluster M30 provide a strong constraint on the formation mechanisms of blue stragglers. We study the formation of blue-straggler binaries through binary evolution, and find that binary evolution can contribute to the blue stragglers in both of the sequences. Whether a blue-straggler is located in the blue sequence or red sequence depends on the contribution of the mass donor to the total luminosity of the binary, which is generally observed as a single star in globular clusters. The blue stragglers in the blue sequence have a cool white dwarf companion, while the majority (˜60%) of the objects in the red sequence are binaries that are still experiencing mass transfer. However, there are also some objects for which the donors have just finished the mass transfer (the stripped-core stars, ˜10%) or the blue stragglers (the accretors) have evolved away from the blue sequence (˜30%). Meanwhile, W UMa contact binaries found in both sequences may be explained by various mass ratios, that is, W UMa contact binaries in the red sequence have two components with comparable masses (e.g., mass ratio q ˜ 0.3-1.0), while those in the blue sequence have low mass ratios (e.g., q< 0.3). However, the fraction of the blue sequence in M30 cannot be reproduced by binary population synthesis if we assumed the initial parameters of a binary sample to be the same as those of the field. This possibly indicates that dynamical effects on binary systems are very important in globular clusters.

THE RELATIONSHIP BETWEEN {nu}{sub max} AND AGE t FROM ZAMS TO RGB-TIP FOR LOW-MASS STARS

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

Tang, Y. K.; Gai, N., E-mail: tyk450@163.com, E-mail: ning.gai@hotmail.com

2013-07-10

Stellar age is an important quantity in astrophysics, which is useful for many fields both in the universe and galaxies. It cannot be determined by direct measurements, but can only be estimated or inferred. We attempt to find a useful indicator of stellar age, which is accurate from the zero-age main sequence to the tip of red giant branch for low-mass stars. Using the Yale Rotation and Evolution Code (YREC), a grid of stellar models has been constructed. Meanwhile, the frequency of maximum oscillations' power {nu}{sub max} and the large frequency separation {Delta}{nu} are calculated using the scaling relations. Formore » the stars, the masses of which are from 0.8 M{sub Sun} to 2.8 M{sub Sun }, we can obtain the {nu}{sub max} and stellar age by combing the scaling relations with the four sets of grid models (YREC, Dotter et al., Marigo et al., and YY isochrones). We find that {nu}{sub max} is tightly correlated and decreases monotonically with the age of the star from the main sequence to the red giant evolutionary stages. Moreover, we find that the line shapes of the curves in the Age versus {nu}{sub max} diagram, which is plotted by the four sets of grid models, are consistent for red giants with masses from 1.1 M{sub Sun} to 2.8 M{sub Sun }. For red giants, the differences of correlation coefficients between Age and {nu}{sub max} for different grid models are minor and can be ignored. Interestingly, we find two peaks that correspond to the subgiants and bump of red giants in the Age versus {nu}{sub max} diagram. By general linear least-squares, we make the polynomial fitting and deduce the relationship between log(Age) and log({nu}{sub max}) in red giants' evolutionary state.« less

Stellar Activity at the End of the Main Sequence: GHRS Observations of the M8 Ve Star VB 10

NASA Technical Reports Server (NTRS)

Linsky, Jeffrey L.; Wood, Brian E.; Brown, Alexander; Giampapa, Mark S.; Ambruster, Carol

1995-01-01

We present Goddard High Resolution Spectrograph observations of the M8 Ve star VB 10 (equal to G1 752B), located very near the end of the stellar main sequence, and its dM3.5 binary companion G1 752A. These coeval stars provide a test bed for studying whether the outer atmospheres of stars respond to changes in internal structure as stars become fully convective near mass 0.3 solar mass (about spectral type M5), where the nature of the stellar magnetic dynamo presumably changes, and near the transition from red to brown dwarfs near mass 0.08 solar mass (about spectral type M9), when hydrogen burning ceases at the end of the main sequence. We obtain upper limits for the quiescent emission of VB 10 but observe a transition region spectrum during a large flare, which indicates that some type of magnetic dynamo must be present. Two indirect lines of evidence-scaling from the observed X-ray emission and scaling from a time-resolved flare on AD Leo suggest that the fraction of the stellar bolometric luminosity that heats the transition region of VB 10 outside of obvious flares is comparable to, or larger than, that for G1 752A. This suggests an increase in the magnetic heating rates, as measured by L(sub line)/L(sub bol) ratios, across the radiative/convective core boundary and as stars approach the red/brown dwarf boundary. These results provide new constraints for dynamo models and models of coronal and transition-region heating in late-type stars.

Cannibals in the thick disk: the young α-rich stars as evolved blue stragglers

NASA Astrophysics Data System (ADS)

Jofré, P.; Jorissen, A.; Van Eck, S.; Izzard, R. G.; Masseron, T.; Hawkins, K.; Gilmore, G.; Paladini, C.; Escorza, A.; Blanco-Cuaresma, S.; Manick, R.

2016-10-01

Spectro-seismic measurements of red giants enabled the recent discovery of stars in the thick disk that are more massive than 1.4 M⊙. While it has been claimed that most of these stars are younger than the rest of the typical thick disk stars, we show evidence that they might be products of mass transfer in binary evolution, notably evolved blue stragglers. We took new measurements of the radial velocities in a sample of 26 stars from APOKASC, including 13 "young" stars and 13 "old" stars with similar stellar parameters but with masses below 1.2 M⊙ and found that more of the young starsappear to be in binary systems with respect to the old stars.Furthermore, we show that the young stars do not follow the expected trend of [C/H] ratios versus mass for individual stars. However, with a population synthesis of low-mass stars including binary evolution and mass transfer, we can reproduce the observed [C/N] ratios versus mass. Our study shows how asteroseismology of solar-type red giants provides us with a unique opportunity to study the evolution of field blue stragglers after they have left the main-sequence.

Collaborative observations of HDE 332077

NASA Technical Reports Server (NTRS)

Ake, Thomas B., III

1995-01-01

IUE low dispersion observations were made of the T(sub c)-deficient peculiar red giant (PRG) star, HDE 332077, to test the hypothesis that T(sub c)-poor PRG's are formed as a result of mass transfer from a binary companion rather than from internal thermal pulsing while on the asymptotic red giant branch. Previous ground-based observations of this star indicated that it is a binary, but the secondary star was too massive for an expected white dwarf. A deep, short wavelength prime (SWP) exposure was needed to search for evidence of an A-type main-sequence companion. We obtained a 120 minute LWP exposure (LWP 23479), followed by a collaborative 1230 minute SWP exposure (SWP 45113). These observations were combined with our earlier IUE and optical data on this PRG star to model the spectral energy distribution of the system.

A mysterious dust clump in a disk around an evolved binary star system.

PubMed

Jura, M; Turner, J

1998-09-10

The discovery of planets in orbit around the pulsar PSR1257+12 shows that planets may form around post-main-sequence stars. Other evolved stars, such as HD44179 (an evolved star which is part of the binary system that has expelled the gas and dust that make the Red Rectangle nebula), possess gravitationally bound orbiting dust disks. It is possible that planets might form from gravitational collapse in such disks. Here we report high-angular-resolution observations at millimetre and submillimetre wavelengths of the dusk disk associated with the Red Rectangle. We find a dust clump with an estimated mass near that of Jupiter in the outer region of the disk. The clump is larger than our Solar System, and far beyond where planet formation would normally be expected, so its nature is at present unclear.

High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681

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

O’Malley, Erin M.; Chaboyer, Brian; Knaizev, Alexei

We obtain high-resolution spectra of nine red giant branch stars in NGC 6681 and perform the first detailed abundance analysis of stars in this cluster. We confirm cluster membership for these stars based on consistent radial velocities of 214.5 ± 3.7 km s{sup −1} and find a mean [Fe/H] = −1.63 ± 0.07 dex and [ α /Fe] = 0.42 ± 0.11 dex. Additionally, we confirm the existence of a Na–O anti-correlation in NGC 6681 and identify two populations of stars with unique abundance trends. With the use of HST photometry from Sarajedini et al. and Piotto et al. wemore » are able to identify these two populations as discrete sequences in the cluster CMD. Although we cannot confirm the nature of the polluter stars responsible for the abundance differences in these populations, these results do help put constraints on possible polluter candidates.« less

DISCOVERY OF A RED GIANT WITH SOLAR-LIKE OSCILLATIONS IN AN ECLIPSING BINARY SYSTEM FROM KEPLER SPACE-BASED PHOTOMETRY

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

Hekker, S.; Debosscher, J.; De Ridder, J.

2010-04-20

Oscillating stars in binary systems are among the most interesting stellar laboratories, as these can provide information on the stellar parameters and stellar internal structures. Here we present a red giant with solar-like oscillations in an eclipsing binary observed with the NASA Kepler satellite. We compute stellar parameters of the red giant from spectra and the asteroseismic mass and radius from the oscillations. Although only one eclipse has been observed so far, we can already determine that the secondary is a main-sequence F star in an eccentric orbit with a semi-major axis larger than 0.5 AU and orbital period longermore » than 75 days.« less

Beryllium abundances along the evolutionary sequence of the open cluster IC 4651 - A new test for hydrodynamical stellar models

NASA Astrophysics Data System (ADS)

Smiljanic, R.; Pasquini, L.; Charbonnel, C.; Lagarde, N.

2010-02-01

Context. Previous analyses of lithium abundances in main sequence and red giant stars have revealed the action of mixing mechanisms other than convection in stellar interiors. Beryllium abundances in stars with Li abundance determinations can offer valuable complementary information on the nature of these mechanisms. Aims: Our aim is to derive Be abundances along the whole evolutionary sequence of an open cluster. We focus on the well-studied open cluster IC 4651. These Be abundances are used with previously determined Li abundances, in the same sample stars, to investigate the mixing mechanisms in a range of stellar masses and evolutionary stages. Methods: Atmospheric parameters were adopted from a previous abundance analysis by the same authors. New Be abundances have been determined from high-resolution, high signal-to-noise UVES spectra using spectrum synthesis and model atmospheres. The careful synthetic modeling of the Be lines region is used to calculate reliable abundances in rapidly rotating stars. The observed behavior of Be and Li is compared to theoretical predictions from stellar models including rotation-induced mixing, internal gravity waves, atomic diffusion, and thermohaline mixing. Results: Beryllium is detected in all the main sequence and turn-off sample stars, both slow- and fast-rotating stars, including the Li-dip stars, but is not detected in the red giants. Confirming previous results, we find that the Li dip is also a Be dip, although the depletion of Be is more modest than for Li in the corresponding effective temperature range. For post-main-sequence stars, the Be dilution starts earlier within the Hertzsprung gap than expected from classical predictions, as does the Li dilution. A clear dispersion in the Be abundances is also observed. Theoretical stellar models including the hydrodynamical transport processes mentioned above are able to reproduce all the observed features well. These results show a good theoretical understanding of the Li and Be behavior along the color-magnitude diagram of this intermediate-age cluster for stars more massive than 1.2 M⊙. Based on observations made with the ESO VLT, at Paranal Observatory, under programs 065.L-0427 and 067.D-0126.Current address: European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany.

The Very Slow Wind from the Pulsating Semiregular Red Giant, L2 Puppis

NASA Technical Reports Server (NTRS)

Jura, M.; Chen, C.; Plavchan, P.

2002-01-01

We have obtained 1 1.7 and 17.9 micron images at the Keck I telescope of the circumstellar dust emission from L(sub 2) Pup, which is one of the nearest ( D = 61 pc) mass-losing, pulsating red giants that has a substantial infra-red excess. We propose that the star is losing mass at a rate of approx.3 x 10(exp -7) Solar Mass/yr. Given its relatively low luminosity (approx. 1500 Solar Luminosity), relatively high effective temperature (near 3400 K), relatively short period (approx. 140 days), and inferred gas outflow speed of 3.5 km/s, standard models for dust-driven mass loss do not apply. Instead, the wind may be driven by the stellar pulsations, with radiation pressure on dust being relatively unimportant. as described in some recent calculations. L(sub 2) Pup may serve as the prototype of this phase of stellar evolution, in which a star could lose approx. 15% of its initial main-sequence mass. Subject headings: circumstellar matter - stars: individual (L2 Puppis) - stars: mass loss

ABOUT EXOBIOLOGY: THE CASE FOR DWARF K STARS

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

Cuntz, M.; Guinan, E. F., E-mail: cuntz@uta.edu, E-mail: edward.guinan@villanova.edu

2016-08-10

One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3)more » the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray–UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a “Habitable-Planetary-Real-Estate Parameter” (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be “Goldilocks” stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray–far-UV irradiances for G0 V–M5 V stars over a wide range of ages.« less

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

About Exobiology: The Case for Dwarf K Stars

NASA Astrophysics Data System (ADS)

Cuntz, M.; Guinan, E. F.

2016-08-01

One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3) the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray-UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a “Habitable-Planetary-Real-Estate Parameter” (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be “Goldilocks” stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray-far-UV irradiances for G0 V-M5 V stars over a wide range of ages.

The environmental impacts on the star formation main sequence: An Hα study of the newly discovered rich cluster at z = 1.52

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

Koyama, Yusei; Kodama, Tadayuki; Tadaki, Ken-ichi

2014-07-01

We report the discovery of a strong over-density of galaxies in the field of a radio galaxy at z = 1.52 (4C 65.22) based on our broadband and narrow-band (Hα) photometry with the Subaru Telescope. We find that Hα emitters are located in the outskirts of the density peak (cluster core) dominated by passive red-sequence galaxies. This resembles the situation in lower-redshift clusters, suggesting that the newly discovered structure is a well-evolved rich galaxy cluster at z = 1.5. Our data suggest that the color-density and stellar mass-density relations are already in place at z ∼ 1.5, mostly driven bymore » the passive red massive galaxies residing within r{sub c} ≲ 200 kpc from the cluster core. These environmental trends almost disappear when we consider only star-forming (SF) galaxies. We do not find SFR-density or SSFR-density relations amongst SF galaxies, and the location of the SF main sequence does not significantly change with environment. Nevertheless, we find a tentative hint that star-bursting galaxies (up-scattered objects from the main sequence) are preferentially located in a small group at ∼1 Mpc away from the main body of the cluster. We also argue that the scatter of the SF main sequence could be dependent on the distance to the nearest neighboring galaxy.« less

The Optical Gravitational Lensing Experiment Catalog of stellar proper motions in the OGLE-II Galactic bulge fields

NASA Astrophysics Data System (ADS)

Sumi, T.; Wu, X.; Udalski, A.; Szymański, M.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Woźniak, P.; Zebruń, K.; Szewczyk, O.; Wyrzykowski, L.

2003-12-01

We present proper motion (μ ) catalogue of 5,078,188 stars in 49 Optical Gravitational Lensing Experiment II (OGLE-II) Galactic bulge fields, with the total area close to 11 square degrees. The proper motion measurements are based on 138 - 555 I-band images taken during four observing seasons: 1997-2000. The catalogue stars are in the magnitude range 11 < I < 18 mag. In particular, the catalogue includes Red Clump Giants (RCGs) and Red Giants in the Galactic Bulge, and main sequence stars in the Galactic disc. The proper motions up to μ = 500 mas yr -1 were measured with the mean accuracy of 0.8 ˜ 3.5 mas yr-1, depending on the brightness of a star. This catalogue may be useful for studying the kinematic of stars in the Galactic Bulge and the Galactic disk with Extinction maps in these fields which are construncted by using two-band photometry of RCGs.

Supermassive black holes and central star clusters: Connection with the host galaxy kinematics and color

NASA Astrophysics Data System (ADS)

Zasov, A. V.; Cherepashchuk, A. M.

2013-11-01

The relationship between the masses of the central, supermassive black holes ( M bh) and of the nuclear star clusters ( M nc) of disk galaxies with various parameters galaxies are considered: the rotational velocity at R = 2 kpc V (2), the maximum rotational velocity V max, the indicative dynamical mass M 25, the integrated mass of the stellar population M *, and the integrated color index B-V. The rotational velocities andmasses of the central objects were taken from the literature. Themass M nc correlatesmore closely with the kinematic parameters and the disk mass than M bh, including with the velocity V max, which is closely related to the virial mass of the dark halo. On average, lenticular galaxies are characterized by higher masses M bh compared to other types of galaxies with similar characteristics. The dependence of the blackhole mass on the color index is bimodal: galaxies of the red group (red-sequence) with B-V >0.6-0.7 which are mostly early-type galaxies with weak star formation, differ appreciably from blue galaxies, which have higher values of M nc and M bh. At the dependences we consider between the masses of the central objects and the parameters of the host galaxies (except for the dependence of M bh on the central velocity dispersion), the red-group galaxies have systematically higher M bh values, even when the host-galaxy parameters are similar. In contrast, in the case of nuclear star clusters, the blue and red galaxies form unified sequences. The results agree with scenarios in which most red-group galaxies form as a result of the partial or complete loss of interstellar gas in a stage of high nuclear activity in galaxies whose central black-hole masses exceed 106-107 M ⊙ (depending on the mass of the galaxy itself). The bulk of disk galaxies with M bh > 107 M ⊙ are lenticular galaxies (types S0, E/S0) whose disks are practically devoid of gas.

Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone.

PubMed

Joshi, Manoj M; Haberle, Robert M

2012-01-01

M stars comprise 80% of main sequence stars, so their planetary systems provide the best chance for finding habitable planets, that is, those with surface liquid water. We have modeled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M stars), using spectrally resolved data of Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 μm, combined with M stars emitting a significant fraction of their radiation at these same longer wavelengths, means that the albedos of ice and snow on planets orbiting M stars are much lower than their values on Earth. Our results imply that the ice/snow albedo climate feedback is significantly weaker for planets orbiting M stars than for planets orbiting G-type stars such as the Sun. In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M stars may be 10-30% farther away from the parent star than previously thought.

Lithium-rich very metal-poor stars discovered with LAMOST and Subaru

NASA Astrophysics Data System (ADS)

Aoki, Wako; Li, Haining; Matsuno, Tadafumi; Kumar, Yerra Bharat; Shi, Jianrong; Suda, Takuma; Zhao, Gang

2018-04-01

Lithium is a unique element that is produced in the Big Bang nucleosynthesis but is destroyed by nuclear reactions inside stars. As a result, almost constant lithium abundance is found in unevolved main-sequence metal-poor stars, although the value is systematically lower than that expected from the standard Big Bang nucleosynthesis models, whereas lithium abundances of red giants are more than one order of magnitudes lower than those of unevolved stars. There are, however, a small fraction of metal-poor stars that show extremely high lithium abundances, which is not explained by standard stellar evolution models. We have discovered 12 new very metal-poor stars that have enhancement of lithium by more than 10 times compared with typical metal-poor stars at similar evolutionary stages by the large-scale spectroscopic survey with LAMOST and the follow-up high-resolution spectroscopy with the Subaru Telescope. The sample shows a wide distribution of evolutionary stages from subgiants to red giants with the metallicity of -3.3 <[Fe/H]< -1.6. The chemical abundance ratios of other elements have been obtained by our spectroscopic study, and an estimate of the binary frequency by radial velocity monitoring is ongoing. The observational results provide new constraints on the scenarios to explain lithium-rich metal-poor stars, such as extra mixing during the evolution along the red giant branch, mass-transfer from a companion AGB star, and engulfment of planet-like objects. These explanations are very unlikely for at least some of lithium-rich objects in our sample, suggesting a new mechanism that enhances lithium during the low-mass star evolution.

The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster NGC 6362

NASA Astrophysics Data System (ADS)

Kaluzny, J.; Thompson, I. B.; Rozyczka, M.; Pych, W.; Narloch, W.

2014-12-01

The field of the globular cluster NGC 6362 was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for 69 periodic variable stars including 34 known RR Lyr stars, 10 known objects of other types and 25 newly detected variable stars. Among the latter we identified 18 proper-motion members of the cluster: seven detached eclipsing binaries (DEBs), six SX Phe stars, two W UMa binaries, two spotted red giants, and a very interesting eclipsing binary composed of two red giants - the first example of such a system found in a globular cluster. Five of the DEBs are located at the turnoff region, and the remaining two are redward of the lower main sequence. Eighty-four objects from the central 9×9 arcmin2 of the cluster were found in the region of cluster blue stragglers. Of these 70 are proper motion (PM) members of NGC 6362 (including all SX Phe and two W UMa stars), and five are field stars. The remaining nine objects lacking PM information are located at the very core of the cluster, and as such they are likely genuine blue stragglers.

Linear Relation for Wind-blown Bubble Sizes of Main-sequence OB Stars in a Molecular Environment and Implication for Supernova Progenitors

NASA Astrophysics Data System (ADS)

Chen, Yang; Zhou, Ping; Chu, You-Hua

2013-05-01

We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R b ≈ 1.22 M/M ⊙ - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M ⊙ will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

A TALE OF DWARFS AND GIANTS: USING A z = 1.62 CLUSTER TO UNDERSTAND HOW THE RED SEQUENCE GREW OVER THE LAST 9.5 BILLION YEARS

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

Rudnick, Gregory H.; Tran, Kim-Vy; Papovich, Casey

2012-08-10

We study the red sequence in a cluster of galaxies at z = 1.62 and follow its evolution over the intervening 9.5 Gyr to the present day. Using deep YJK{sub s} imaging with the HAWK-I instrument on the Very Large Telescope, we identify a tight red sequence and construct its rest-frame i-band luminosity function (LF). There is a marked deficit of faint red galaxies in the cluster that causes a turnover in the LF. We compare the red-sequence LF to that for clusters at z < 0.8, correcting the luminosities for passive evolution. The shape of the cluster red-sequence LFmore » does not evolve between z = 1.62 and z = 0.6 but at z < 0.6 the faint population builds up significantly. Meanwhile, between z = 1.62 and 0.6 the inferred total light on the red sequence grows by a factor of {approx}2 and the bright end of the LF becomes more populated. We construct a simple model for red-sequence evolution that grows the red sequence in total luminosity and matches the constant LF shape at z > 0.6. In this model the cluster accretes blue galaxies from the field whose star formation is quenched and who are subsequently allowed to merge. We find that three to four mergers among cluster galaxies during the 4 Gyr between z = 1.62 and z = 0.6 match the observed LF evolution between the two redshifts. The inferred merger rate is consistent with other studies of this cluster. Our result supports the picture that galaxy merging during the major growth phase of massive clusters is an important process in shaping the red-sequence population at all luminosities.« less

Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

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

Zhang, Xianfei; Bi, Shaolan; Hall, Philip D.

It is predicted that orbital decay by gravitational-wave radiation and tidal interaction will cause some close binary stars to merge within a Hubble time. The merger of a helium-core white dwarf with a main-sequence (MS) star can produce a red giant branch star that has a low-mass hydrogen envelope when helium is ignited and thus become a hot subdwarf. Because detailed calculations have not been made, we compute post-merger models with a stellar evolution code. We find the evolutionary paths available to merger remnants and find the pre-merger conditions that lead to the formation of hot subdwarfs. We find thatmore » some such mergers result in the formation of stars with intermediate helium-rich surfaces. These stars later develop helium-poor surfaces owing to diffusion. Combining our results with a model population and comparing to observed stars, we find that some observed intermediate helium-rich hot subdwarfs can be explained as the remnants of the mergers of helium-core white dwarfs with low-mass MS stars.« less

The lowest-metallicity type II supernova from the highest-mass red supergiant progenitor

NASA Astrophysics Data System (ADS)

Anderson, J. P.; Dessart, L.; Gutiérrez, C. P.; Krühler, T.; Galbany, L.; Jerkstrand, A.; Smartt, S. J.; Contreras, C.; Morrell, N.; Phillips, M. M.; Stritzinger, M. D.; Hsiao, E. Y.; González-Gaitán, S.; Agliozzo, C.; Castellón, S.; Chambers, K. C.; Chen, T.-W.; Flewelling, H.; Gonzalez, C.; Hosseinzadeh, G.; Huber, M.; Fraser, M.; Inserra, C.; Kankare, E.; Mattila, S.; Magnier, E.; Maguire, K.; Lowe, T. B.; Sollerman, J.; Sullivan, M.; Young, D. R.; Valenti, S.

2018-05-01

Red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type II supernovae1. However, while such stars are observed with masses >25 M⊙ (ref. 2), detections of >18 M⊙ progenitors remain elusive1. Red supergiants are also expected to form at all metallicities, but discoveries of explosions from low-metallicity progenitors are scarce. Here, we report observations of the type II supernova, SN 2015bs, for which we infer a progenitor metallicity of ≤0.1 Z⊙ from comparison to photospheric-phase spectral models3, and a zero-age main-sequence mass of 17–25 M⊙ through comparison to nebular-phase spectral models4,5. SN 2015bs displays a normal ‘plateau’ light-curve morphology, and typical spectral properties, implying a red supergiant progenitor. This is the first example of such a high-mass progenitor for a ‘normal’ type II supernova, suggesting a link between high-mass red supergiant explosions and low-metallicity progenitors.

Surface effects on the red giant branch

NASA Astrophysics Data System (ADS)

Ball, W. H.; Themeßl, N.; Hekker, S.

2018-05-01

Individual mode frequencies have been detected in thousands of individual solar-like oscillators on the red giant branch (RGB). Fitting stellar models to these mode frequencies, however, is more difficult than in main-sequence stars. This is partly because of the uncertain magnitude of the surface effect: the systematic difference between observed and modelled frequencies caused by poor modelling of the near-surface layers. We aim to study the magnitude of the surface effect in RGB stars. Surface effect corrections used for main-sequence targets are potentially large enough to put the non-radial mixed modes in RGB stars out of order, which is unphysical. Unless this can be circumvented, model-fitting of evolved RGB stars is restricted to the radial modes, which reduces the number of available modes. Here, we present a method to suppress gravity modes (g-modes) in the cores of our stellar models, so that they have only pure pressure modes (p-modes). We show that the method gives unbiased results and apply it to three RGB solar-like oscillators in double-lined eclipsing binaries: KIC 8410637, KIC 9540226 and KIC 5640750. In all three stars, the surface effect decreases the model frequencies consistently by about 0.1-0.3 μHz at the frequency of maximum oscillation power νmax, which agrees with existing predictions from three-dimensional radiation hydrodynamics simulations. Though our method in essence discards information about the stellar cores, it provides a useful step forward in understanding the surface effect in RGB stars.

Surface Compositions of Red Giant Stars in Globular Clusters

NASA Astrophysics Data System (ADS)

Cheng, Eric; Lau, Marie; Smith, Graeme; Chen, Brian

2018-01-01

Globular clusters (GCs) are excellent “laboratories” to study the formation and evolution of our galaxy. In order to understand, more specifically, the chemical compositions and stellar evolution of the stars in GCs, we ask whether or not deep internal mixing occurs in red giants or if in fact the compositions come from the primordial interstellar medium or previous generations of stars. It has been discovered that as a star evolves up the red giant branch, the surface carbon abundance decreases, which is evidence of deep internal mixing. We questioned whether these processes also affect O or Na abundance as a star evolves. We collected measurement data of red giants from GCs out of academic journals and sorted the data into catalogs. Then, we plotted the catalogs into figures, comparing surface O and Na each with stellar luminosity. Statistical tests were ran to quantify the amount of correlation between the variables. Out of 27 GCs, we concluded that eight show a positive correlation between Na and luminosity, and two show a negative correlation between O and luminosity. Properties of GCs were compared to determine if chemical distribution in stars depends on GCs as the self-enrichment scenario suggests. We created histograms of sodium distribution to test for bimodality to examine if there are separate trends in each GC. In six GCs, two different sequences of red giants appear for Na versus luminosity, suggesting evidence that the depth of mixing may differ among each red giant in a GC. This study has provided new evidence that the changing chemical abundances on the surfaces of red giants can be due to stellar evolutionary effects and deep internal mixing, which may not necessarily depend on the GC and may differ in depth among each red giant. Through this study, we learn more about stellar evolution which will eventually help us understand the origins of our universe. Most of this work was carried out by high school students working under the auspices of the Science Internship Program (SIP) at UC Santa Cruz.

The Not So Simple Globular Cluster ω Cen. I. Spatial Distribution of the Multiple Stellar Populations

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

Calamida, A.; Saha, A.; Strampelli, G.

2017-04-01

We present a multi-band photometric catalog of ≈1.7 million cluster members for a field of view of ≈2° × 2° across ω Cen. Photometry is based on images collected with the Dark Energy Camera on the 4 m Blanco telescope and the Advanced Camera for Surveys on the Hubble Space Telescope . The unprecedented photometric accuracy and field coverage allowed us, for the first time, to investigate the spatial distribution of ω Cen multiple populations from the core to the tidal radius, confirming its very complex structure. We found that the frequency of blue main-sequence stars is increasing compared to red main-sequencemore » stars starting from a distance of ≈25′ from the cluster center. Blue main-sequence stars also show a clumpy spatial distribution, with an excess in the northeast quadrant of the cluster pointing toward the direction of the Galactic center. Stars belonging to the reddest and faintest red-giant branch also show a more extended spatial distribution in the outskirts of ω Cen, a region never explored before. Both these stellar sub-populations, according to spectroscopic measurements, are more metal-rich compared to the cluster main stellar population. These findings, once confirmed, make ω Cen the only stellar system currently known where metal-rich stars have a more extended spatial distribution compared to metal-poor stars. Kinematic and chemical abundance measurements are now needed for stars in the external regions of ω Cen to better characterize the properties of these sub-populations.« less

Stellar Multiplicity Meets Stellar Evolution and Metallicity: The APOGEE View

NASA Astrophysics Data System (ADS)

Badenes, Carles; Mazzola, Christine; Thompson, Todd A.; Covey, Kevin; Freeman, Peter E.; Walker, Matthew G.; Moe, Maxwell; Troup, Nicholas; Nidever, David; Allende Prieto, Carlos; Andrews, Brett; Barbá, Rodolfo H.; Beers, Timothy C.; Bovy, Jo; Carlberg, Joleen K.; De Lee, Nathan; Johnson, Jennifer; Lewis, Hannah; Majewski, Steven R.; Pinsonneault, Marc; Sobeck, Jennifer; Stassun, Keivan G.; Stringfellow, Guy S.; Zasowski, Gail

2018-02-01

We use the multi-epoch radial velocities acquired by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to perform a large-scale statistical study of stellar multiplicity for field stars in the Milky Way, spanning the evolutionary phases between the main sequence (MS) and the red clump. We show that the distribution of maximum radial velocity shifts (ΔRVmax) for APOGEE targets is a strong function of log g, with MS stars showing ΔRVmax as high as ∼300 {km} {{{s}}}-1, and steadily dropping down to ∼30 {km} {{{s}}}-1 for log g ∼ 0, as stars climb up the red giant branch (RGB). Red clump stars show a distribution of ΔRVmax values comparable to that of stars at the tip of the RGB, implying they have similar multiplicity characteristics. The observed attrition of high ΔRVmax systems in the RGB is consistent with a lognormal period distribution in the MS and a multiplicity fraction of 0.35, which is truncated at an increasing period as stars become physically larger and undergo mass transfer after Roche Lobe overflow during H-shell burning. The ΔRVmax distributions also show that the multiplicity characteristics of field stars are metallicity-dependent, with metal-poor ([Fe/H] ≲ ‑0.5) stars having a multiplicity fraction a factor of 2–3 higher than metal-rich ([Fe/H] ≳ 0.0) stars. This has profound implications for the formation rates of interacting binaries observed by astronomical transient surveys and gravitational wave detectors, as well as the habitability of circumbinary planets.

The Not So Simple Globular Cluster ω Cen. I. Spatial Distribution of the Multiple Stellar Populations

NASA Astrophysics Data System (ADS)

Calamida, A.; Strampelli, G.; Rest, A.; Bono, G.; Ferraro, I.; Saha, A.; Iannicola, G.; Scolnic, D.; James, D.; Smith, C.; Zenteno, A.

2017-04-01

We present a multi-band photometric catalog of ≈1.7 million cluster members for a field of view of ≈2° × 2° across ω Cen. Photometry is based on images collected with the Dark Energy Camera on the 4 m Blanco telescope and the Advanced Camera for Surveys on the Hubble Space Telescope. The unprecedented photometric accuracy and field coverage allowed us, for the first time, to investigate the spatial distribution of ω Cen multiple populations from the core to the tidal radius, confirming its very complex structure. We found that the frequency of blue main-sequence stars is increasing compared to red main-sequence stars starting from a distance of ≈25‧ from the cluster center. Blue main-sequence stars also show a clumpy spatial distribution, with an excess in the northeast quadrant of the cluster pointing toward the direction of the Galactic center. Stars belonging to the reddest and faintest red-giant branch also show a more extended spatial distribution in the outskirts of ω Cen, a region never explored before. Both these stellar sub-populations, according to spectroscopic measurements, are more metal-rich compared to the cluster main stellar population. These findings, once confirmed, make ω Cen the only stellar system currently known where metal-rich stars have a more extended spatial distribution compared to metal-poor stars. Kinematic and chemical abundance measurements are now needed for stars in the external regions of ω Cen to better characterize the properties of these sub-populations. Based on observations made with the Dark Energy Camera (DECam) on the 4 m Blanco telescope (NOAO) under programs 2014A-0327, 2015A-0151, 2016A-0189, PIs: A. Calamida, A. Rest, and on observations made with the NASA/ESA Hubble Space Telescope, obtained by the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Les galaxies

NASA Astrophysics Data System (ADS)

Combes, Francoise

2016-08-01

Considerable progress has been made on galaxy formation and evolution in recent years, and new issues. The old Hubble classification according to the tuning fork of spirals, lenticulars and ellipticals, is still useful but has given place to the red sequence, the blue cloud and the green valley, showing a real bimodality of types between star forming galaxies (blue) and quenched ones (red). Large surveys have shown that stellar mass and environment density are the two main factors of the evolution from blue to red sequences. Evolution is followed directly with redshift through a look-back time of more than 12 billion years. The most distant galaxy at z=11. has already a stellar mass of a billion suns. In an apparent anti-hierarchical scenario, the most massive galaxies form stars early on, while essentially dwarf galaxies are actively star-formers now. This downsizing feature also applies to the growth of super-massive black holes at the heart of each bulgy galaxy. The feedback from active nuclei is essential to explain the distribution of mass in galaxies, and in particular to explain why the fraction of baryonic matter is so low, lower by more than a factor 5 than the baryonic fraction of the Universe. New instruments just entering in operation, like MUSE and ALMA, provide a new and rich data flow, which is developed in this series of articles.

Cosmic Accretion and Galaxy Co-Evolution: Lessons from the Extended Chandra Deep Field South

NASA Astrophysics Data System (ADS)

Urry, C. Megan

2011-05-01

The Chandra deep fields reveal that most cosmic accretion onto supermassive black holes is obscured by gas and dust. The GOODS and MUSYC multiwavelength data show that many X-ray-detected AGN are faint and red (or even undetectable) in the optical but bright in the infrared, as is characteristic of obscured sources. (N.B. The ECDFS is most sensitive to the AGN that constitute the X-ray background, namely, moderate luminosity AGN, with log Lx=43-44, at moderate redshifts, 0.5

Physical Structure of Four Symbiotic Binaries

NASA Technical Reports Server (NTRS)

Kenyon, Scott J. (Principal Investigator)

1997-01-01

Disk accretion powers many astronomical objects, including pre-main sequence stars, interacting binary systems, and active galactic nuclei. Unfortunately, models developed to explain the behavior of disks and their surroundings - boundary layers, jets, and winds - lack much predictive power, because the physical mechanism driving disk evolution - the viscosity - is not understood. Observations of many types of accreting systems are needed to constrain the basic physics of disks and provide input for improved models. Symbiotic stars are an attractive laboratory for studying physical phenomena associated with disk accretion. These long period binaries (P(sub orb) approx. 2-3 yr) contain an evolved red giant star, a hot companion, and an ionized nebula. The secondary star usually is a white dwarf accreting material from the wind of its red giant companion. A good example of this type of symbiotic is BF Cygni: our analysis shows that disk accretion powers the nuclear burning shell of the hot white dwarf and also manages to eject material perpendicular to the orbital plane (Mikolajewska, Kenyon, and Mikolajewski 1989). The hot components in other symbiotic binaries appear powered by tidal overflow from a very evolved red giant companion. We recently completed a study of CI Cygni and demonstrated that the accreting secondary is a solar-type main sequence star, rather than a white dwarf (Kenyon et aL 1991). This project continued our study of symbiotic binary systems. Our general plan was to combine archival ultraviolet and optical spectrophotometry with high quality optical radial velocity observations to determine the variation of line and continuum sources as functions of orbital phase. We were very successful in generating orbital solutions and phasing UV+optical spectra for five systems: AG Dra, V443 Her, RW Hya, AG Peg, and AX Per. Summaries of our main results for these systems appear below. A second goal of our project was to consider general models for the outbursts of symbiotic stars, with an emphasis on understanding the differences between disk-driven and nuclear-powered eruptions.

The origin and evolution of short-period Miras in the solar neighborhood: Constraints on the life cycle of old stars

NASA Technical Reports Server (NTRS)

Jura, M.

1994-01-01

The spatial distribution of the short-period (P less than 300 days) oxygen-rich Miras in the solar neighborhood can be fitted with an exponential scale height above the Galactic plane of about 600 pc. Using the Gliese catalog of local main-sequence stars, we estimate that the density of suitable G-type progenitor dwarfs within 20 pc of the Sun for these short-period Miras is 6 x 10(exp -4)/cu pc. The portion of the H-R diagram near the main-sequence turnoff of these velocity-selected Gliese stars is intermediate between that of the old open cluster NGC 188 and that of the metal-rich globular cluster, 47 Tuc. We infer that the main-sequence progenitors of the short-period Miras have masses near 1.0 solar mass, and we estimate that these Miras have ages approximately 9 x 10(exp 9). We also identify a few old disk red giants in the neighborhood of the Sun. On the basis of very limited information, we estimate that the total amount of mass lost from these stars during their first ascent up the red giant branch is less than or equal to 0.1 solar mass. We derive a duration of the short-period Mira phase of close to 5 x 10(exp 5) yr. This estimate for the duration of the short period Mira phase is longer than our estimate of 2 x 10(exp 5) yr for the duration of the Mira phase for stars with periods longer than 300 days. From their infrared colors, we estimate a typical mass-loss rate from the short-period Miras of approximately 1 x 10(exp -7) solar mass/yr.

The origin and evolution of short-period Miras in the solar neighborhood: Constraints on the life cycle of old stars

NASA Astrophysics Data System (ADS)

Jura, M.

1994-02-01

The spatial distribution of the short-period (P less than 300 days) oxygen-rich Miras in the solar neighborhood can be fitted with an exponential scale height above the Galactic plane of about 600 pc. Using the Gliese catalog of local main-sequence stars, we estimate that the density of suitable G-type progenitor dwarfs within 20 pc of the Sun for these short-period Miras is 6 x 10-4/cu pc. The portion of the H-R diagram near the main-sequence turnoff of these velocity-selected Gliese stars is intermediate between that of the old open cluster NGC 188 and that of the metal-rich globular cluster, 47 Tuc. We infer that the main-sequence progenitors of the short-period Miras have masses near 1.0 solar mass, and we estimate that these Miras have ages approximately 9 x 109. We also identify a few old disk red giants in the neighborhood of the Sun. On the basis of very limited information, we estimate that the total amount of mass lost from these stars during their first ascent up the red giant branch is less than or equal to 0.1 solar mass. We derive a duration of the short-period Mira phase of close to 5 x 105 yr. This estimate for the duration of the short period Mira phase is longer than our estimate of 2 x 105 yr for the duration of the Mira phase for stars with periods longer than 300 days. From their infrared colors, we estimate a typical mass-loss rate from the short-period Miras of approximately 1 x 10-7 solar mass/yr.

Using the phase shift to asymptotically characterize the dipolar mixed modes in post-main-sequence stars

NASA Astrophysics Data System (ADS)

Jiang, C.; Christensen-Dalsgaard, J.; Cunha, M.

2018-03-01

Mixed modes have been extensively observed in post-main-sequence stars by the Kepler and CoRoT space missions. The mixture of the p and g modes can be measured by the dimensionless coefficient q, the so-called coupling strength factor. In this paper, we discuss the utility of the phase shifts θ from the eigenvalue condition for mixed modes as a tool to characterize dipolar mixed modes from the theoretical as well as the practical point of view. Unlike the coupling strength, whose variation in a given star is very small over the relevant frequency range, the phase shifts vary significantly for different modes. The analysis in terms of θ can also provide a better understanding of the pressure and gravity radial order for a given mixed mode. Observed frequencies of the Kepler red-giant star KIC 3744043 are used to test the method. The results are very promising.

Mass-losing red giants in open clusters

NASA Technical Reports Server (NTRS)

Jura, M.

1987-01-01

Mass-losing stars in open clusters with main-sequence turn-offs at intermediate mass have been searched for by using the IRAS data base. The absence of many strong 60 micron sources in open clusters implies that intermediate-mass stars lose much of their mass during an intense wind phase of rather short duration. For stars of about seven solar masses, this phase, if it exists at all, lasts for not much more than 100,000 yr. For stars of about four solar masses, the intense wind phase appears to last considerably less than 10 million yr; it may well last for less than a million yr.

The empirical Gaia G-band extinction coefficient

NASA Astrophysics Data System (ADS)

Danielski, C.; Babusiaux, C.; Ruiz-Dern, L.; Sartoretti, P.; Arenou, F.

2018-06-01

Context. The first Gaia data release unlocked the access to photometric information for 1.1 billion sources in the G-band. Yet, given the high level of degeneracy between extinction and spectral energy distribution for large passbands such as the Gaia G-band, a correction for the interstellar reddening is needed in order to exploit Gaia data. Aims: The purpose of this manuscript is to provide the empirical estimation of the Gaia G-band extinction coefficient kG for both the red giants and main sequence stars in order to be able to exploit the first data release DR1. Methods: We selected two samples of single stars: one for the red giants and one for the main sequence. Both samples are the result of a cross-match between Gaia DR1 and 2MASS catalogues; they consist of high-quality photometry in the G-, J- and KS-bands. These samples were complemented by temperature and metallicity information retrieved from APOGEE DR13 and LAMOST DR2 surveys, respectively. We implemented a Markov chain Monte Carlo method where we used (G - KS)0 versus Teff and (J - KS)0 versus (G - KS)0, calibration relations to estimate the extinction coefficient kG and we quantify its corresponding confidence interval via bootstrap resampling. We tested our method on samples of red giants and main sequence stars, finding consistent solutions. Results: We present here the determination of the Gaia extinction coefficient through a completely empirical method. Furthermore we provide the scientific community with a formula for measuring the extinction coefficient as a function of stellar effective temperature, the intrinsic colour (G - KS)0, and absorption.

THE AGE SPREAD OF QUIESCENT GALAXIES WITH THE NEWFIRM MEDIUM-BAND SURVEY: IDENTIFICATION OF THE OLDEST GALAXIES OUT TO z {approx} 2

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

Whitaker, Katherine E.; Van Dokkum, Pieter G.; Brammer, Gabriel

2010-08-20

With a complete, mass-selected sample of quiescent galaxies from the NEWFIRM Medium-Band Survey, we study the stellar populations of the oldest and most massive galaxies (>10{sup 11} M{sub sun}) to high redshift. The sample includes 570 quiescent galaxies selected based on their extinction-corrected U - V colors out to z = 2.2, with accurate photometric redshifts, {sigma} {sub z}/(1 + z) {approx} 2%, and rest-frame colors, {sigma}{sub U-V} {approx} 0.06 mag. We measure an increase in the intrinsic scatter of the rest-frame U - V colors of quiescent galaxies with redshift. This scatter in color arises from the spread inmore » ages of the quiescent galaxies, where we see both relatively quiescent red, old galaxies and quiescent blue, younger galaxies toward higher redshift. The trends between color and age are consistent with the observed composite rest-frame spectral energy distributions (SEDs) of these galaxies. The composite SEDs of the reddest and bluest quiescent galaxies are fundamentally different, with remarkably well-defined 4000 A and Balmer breaks, respectively. Some of the quiescent galaxies may be up to four times older than the average age and up to the age of the universe, if the assumption of solar metallicity is correct. By matching the scatter predicted by models that include growth of the red sequence by the transformation of blue galaxies to the observed intrinsic scatter, the data indicate that most early-type galaxies formed their stars at high redshift with a burst of star formation prior to migrating to the red sequence. The observed U - V color evolution with redshift is weaker than passive evolution predicts; possible mechanisms to slow the color evolution include increasing amounts of dust in quiescent galaxies toward higher redshift, red mergers at z {approx}< 1, and a frosting of relatively young stars from star formation at later times.« less

Supernova 1987A - the evolution from blue to red

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

Tuchman, Y.; Wheeler, J.C.

1989-09-01

The evolution of stars with mass comparable to that of the progenitor of SN 1987A from the main sequence to the Hayashi track is critically examined to determine why some models evolve to the red on nuclear time scales, some on thermal time scales, and some not at all. Thermal equilibrium solutions to a parametrized series of structural models with active hydrogen burning shells have two stable solutions with different T(eff) for the same helium core M(He) mass and a minimum M(He) below which no blue thermal equlibrium solution is possible. The dependence of the equilibrium solutions on stellar mass,more » envelope composition, and mass loss are investigated. The solutions quantitatively account for the 'gap' in the HR diagrams of massive stars in the Galaxy and LMC and suggest that the outer envelopes are not substantially enriched in helium during the first passage from the main sequence to the Hayashi track. 23 refs.« less

A Theoretical Probe for Excitation Mechanisms of Sun-like and Mira-like Oscillations of Stars

NASA Astrophysics Data System (ADS)

Xiong, Da-run; Deng, Li-cai

2013-01-01

The linear nonadiabatic oscillations for evolutionary models of 0.6- 3M8 stars are calculated by using a nonlocal and time-dependent convection theory. The results show that in the HR diagram the pulsation-unstable low- temperature stars on the right side of instability strip can be divided into two groups. One group indicates the Sun-like oscillation stars composed of the main- sequence dwarfs, sub-giants and red giants (RGs) of low and intermediate lu- minosities, which are unstable in the intermediate- and high-order (n ≥ 12) p- modes, and stable in the low-order (n ≤ 5) p-modes. Another group indicates the Mira-like stars composed of the bright RGs and asymptotic giant branch (AGB) stars, which are just contrary to Sun-like stars, unstable in low-order (n ≤ 5) p-modes and stable in the intermediate- and high-order (n ≥ 12) p-modes. The oscillations for the red edge of Cepheid (δ Scuti) instability strip, Sun-like and Mira-like stars can be explained uniformly by the coupling between convection and oscillation (CCO). For the low-temperature stars on the right side of in- stability strip, CCO is the dominant excitation and damping mechanism of the oscillations of low- and intermediate-order p-modes, and the turbulent stochas- tic excitation becomes important only for the high-order p-modes of Sun-like oscillations.

Not-so-simple stellar populations in the intermediate-age Large Magellanic Cloud star clusters NGC 1831 and NGC 1868

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

Li, Chengyuan; De Grijs, Richard; Deng, Licai, E-mail: joshuali@pku.edu.cn, E-mail: grijs@pku.edu.cn

2014-04-01

Using a combination of high-resolution Hubble Space Telescope/Wide-Field and Planetary Camera-2 observations, we explore the physical properties of the stellar populations in two intermediate-age star clusters, NGC 1831 and NGC 1868, in the Large Magellanic Cloud based on their color-magnitude diagrams. We show that both clusters exhibit extended main-sequence turn offs. To explain the observations, we consider variations in helium abundance, binarity, age dispersions, and the fast rotation of the clusters' member stars. The observed narrow main sequence excludes significant variations in helium abundance in both clusters. We first establish the clusters' main-sequence binary fractions using the bulk of themore » clusters' main-sequence stellar populations ≳ 1 mag below their turn-offs. The extent of the turn-off regions in color-magnitude space, corrected for the effects of binarity, implies that age spreads of order 300 Myr may be inferred for both clusters if the stellar distributions in color-magnitude space were entirely due to the presence of multiple populations characterized by an age range. Invoking rapid rotation of the population of cluster members characterized by a single age also allows us to match the observed data in detail. However, when taking into account the extent of the red clump in color-magnitude space, we encounter an apparent conflict for NGC 1831 between the age dispersion derived from that based on the extent of the main-sequence turn off and that implied by the compact red clump. We therefore conclude that, for this cluster, variations in stellar rotation rate are preferred over an age dispersion. For NGC 1868, both models perform equally well.« less

BLUE STRAGGLERS IN GLOBULAR CLUSTER 47 TUCANAE

NASA Technical Reports Server (NTRS)

2002-01-01

The core of globular cluster 47 Tucanae is home to many blue stragglers, rejuvenated stars that glow with the blue light of young stars. A ground-based telescope image (on the left) shows the entire crowded core of 47 Tucanae, located 15,000 light-years away in the constellation Tucana. Peering into the heart of the globular cluster's bright core, the Hubble Space Telescope's Wide Field and Planetary Camera 2 separated the dense clump of stars into many individual stars (image on right). Some of these stars shine with the light of old stars; others with the blue light of blue stragglers. The yellow circles in the Hubble telescope image highlight several of the cluster's blue stragglers. Analysis for this observation centered on one massive blue straggler. Astronomers theorize that blue stragglers are formed either by the slow merger of stars in a double-star system or by the collision of two unrelated stars. For the blue straggler in 47 Tucanae, astronomers favor the slow merger scenario. This image is a 3-color composite of archival Hubble Wide Field and Planetary Camera 2 images in the ultraviolet (blue), blue (green), and violet (red) filters. Color tables were assigned and scaled so that the red giant stars appear orange, main-sequence stars are white/green, and blue stragglers are appropriately blue. The ultraviolet images were taken on Oct. 25, 1995, and the blue and violet images were taken on Sept. 1, 1995. Credit: Rex Saffer (Villanova University) and Dave Zurek (STScI), and NASA

Barium Stars: Theoretical Interpretation

NASA Astrophysics Data System (ADS)

Husti, Laura; Gallino, Roberto; Bisterzo, Sara; Straniero, Oscar; Cristallo, Sergio

2009-09-01

Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolution and high S/N. We compare these observations with AGB nucleosynthesis models using different initial masses and a spread of 13C-pocket efficiencies. Once a consistent solution is found for the whole elemental distribution of abundances, a proper dilution factor is applied. This dilution is explained by the fact that the s-rich material transferred from the AGB to the nowadays observed stars is mixed with the envelope of the accretor. We also analyse the mass transfer process, and obtain the wind velocity for giants and subgiants with known orbital period. We find evidence that thermohaline mixing is acting inside main sequence dwarfs and we present a method for estimating its depth.

THE GALEX/S{sup 4}G UV–IR COLOR–COLOR DIAGRAM: CATCHING SPIRAL GALAXIES AWAY FROM THE BLUE SEQUENCE

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

Bouquin, Alexandre Y. K.; Gil de Paz, Armando; Gallego, Jesús

We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6 μm photometry for >2000 galaxies, available for 90% of the S{sup 4}G sample. We find a very tight GALEX blue sequence (GBS) in the (FUV–NUV) versus (NUV–[3.6]) color–color diagram, which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale (τ) and a degeneracy between τ and dust reddening. The tightness of the GBS provides an unprecedented way of identifying star-forming galaxies and objects that are just evolving to (or from) what we call the GALEX green valley (GGV). At the red end of the GBS, atmore » (NUV–[3.6]) > 5, we find a wider GALEX red sequence (GRS) mostly populated by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the optical red sequence. We find no such dichotomy in terms of stellar mass (measured by M{sub [3.6]}) since both massive (M{sub ⋆}>10{sup 11}M{sub ⊙}) blue- and red-sequence galaxies are identified. The type that is proportionally more often found in the GGV is the S0-Sa’s, and most of these are located in high-density environments. We discuss evolutionary models of galaxies that show a rapid transition from the blue to the red sequence on a timescale of 10{sup 8} yr.« less

Metal-poor stars. IV - The evolution of red giants.

NASA Technical Reports Server (NTRS)

Rood, R. T.

1972-01-01

Detailed evolutionary calculations for six Population-II red giants are presented. The first five of these models are followed from the zero age main sequence to the onset of the helium flash. The sixth model allows the effect of direct electron-neutrino interactions to be estimated. The updated input physics and evolutionary code are described briefly. The results of the calculations are presented in a manner pertinent to later stages of evolutions and suitable for comparison with observations.

Stars caught in the braking stage in young Magellanic Cloud clusters

NASA Astrophysics Data System (ADS)

D'Antona, Francesca; Milone, Antonino P.; Tailo, Marco; Ventura, Paolo; Vesperini, Enrico; di Criscienzo, Marcella

2017-08-01

The colour-magnitude diagrams of many Magellanic Cloud clusters (with ages up to 2 billion years) display extended turnoff regions where the stars leave the main sequence, suggesting the presence of multiple stellar populations with ages that may differ even by hundreds of millions of years 1,2,3 . A strongly debated question is whether such an extended turnoff is instead due to populations with different stellar rotations3,4,5,6 . The recent discovery of a 'split' main sequence in some younger clusters (~80-400 Myr) added another piece to this puzzle. The blue side of the main sequence is consistent with slowly rotating stellar models, and the red side consistent with rapidly rotating models7,8,9,10. However, a complete theoretical characterization of the observed colour-magnitude diagram also seemed to require an age spread9. We show here that, in the three clusters so far analysed, if the blue main-sequence stars are interpreted with models in which the stars have always been slowly rotating, they must be ~30% younger than the rest of the cluster. If they are instead interpreted as stars that were initially rapidly rotating but have later slowed down, the age difference disappears, and this 'braking' also helps to explain the apparent age differences of the extended turnoff. The age spreads in Magellanic Cloud clusters are thus a manifestation of rotational stellar evolution. Observational tests are suggested.

Evolution models of helium white dwarf-main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

NASA Astrophysics Data System (ADS)

Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

2018-02-01

It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with a model population, we predict that the mass distribution of single low-mass white dwarfs formed through this channel spans the range 0.37 to 0.5Msolar and peaks between 0.45 and 0.46Msolar. Helium white dwarf--main-sequence star mergers can also lead to the formation of single helium white dwarfs with masses up to 0.51Msolar. In our model the Galactic formation rate of single low-mass white dwarfs through this channel is about 8.7X10^-3yr^-1. Comparing our models with observations, we find that the majority of single low-mass white dwarfs (<0.5Msolar) are formed from helium white dwarf--main-sequence star mergers, at a rate which is about $2$ per cent of the total white dwarf formation rate.

A YOUNG ECLIPSING BINARY AND ITS LUMINOUS NEIGHBORS IN THE EMBEDDED STAR CLUSTER Sh 2-252E

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

Lester, Kathryn V.; Gies, Douglas R.; Guo, Zhao, E-mail: lester@chara.gsu.edu, E-mail: gies@chara.gsu.edu, E-mail: guo@chara.gsu.edu

We present a photometric and light curve analysis of an eccentric eclipsing binary in the K2 Campaign 0 field, which resides in Sh 2-252E, a young star cluster embedded in an H ii region. We describe a spectroscopic investigation of the three brightest stars in the crowded aperture to identify which is the binary system. We find that none of these stars are components of the eclipsing binary system, which must be one of the fainter nearby stars. These bright cluster members all have remarkable spectra: Sh 2-252a (EPIC 202062176) is a B0.5 V star with razor sharp absorption lines, Sh 2-252b is amore » Herbig A0 star with disk-like emission lines, and Sh 2-252c is a pre-main-sequence star with very red color.« less

P-MaNGA: GRADIENTS IN RECENT STAR FORMATION HISTORIES AS DIAGNOSTICS FOR GALAXY GROWTH AND DEATH

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

Li, Cheng; Wang, Enci; Lin, Lin

2015-05-10

We present an analysis of the data produced by the MaNGA prototype run (P-MaNGA), aiming to test how the radial gradients in recent star formation histories, as indicated by the 4000 Å break (D{sub n}(4000)), Hδ absorption (EW(Hδ{sub A})), and Hα emission (EW(Hα)) indices, can be useful for understanding disk growth and star formation cessation in local galaxies. We classify 12 galaxies observed on two P-MaNGA plates as either centrally quiescent (CQ) or centrally star-forming (CSF), according to whether D{sub n}(4000) measured in the central spaxel of each datacube exceeds 1.6. For each spaxel we generate both 2D maps and radialmore » profiles of D{sub n}(4000), EW(Hδ{sub A}), and EW(Hα). We find that CSF galaxies generally show very weak or no radial variation in these diagnostics. In contrast, CQ galaxies present significant radial gradients, in the sense that D{sub n}(4000) decreases, while both EW(Hδ{sub A}) and EW(Hα) increase from the galactic center outward. The outer regions of the galaxies show greater scatter on diagrams relating the three parameters than their central parts. In particular, the clear separation between centrally measured quiescent and star-forming galaxies in these diagnostic planes is largely filled in by the outer parts of galaxies whose global colors place them in the green valley, supporting the idea that the green valley represents a transition between blue-cloud and red-sequence phases, at least in our small sample. These results are consistent with a picture in which the cessation of star formation propagates from the center of a galaxy outward as it moves to the red sequence.« less

The Discovery of an Eccentric Millisecond Pulsar in the Galactic Plane

NASA Astrophysics Data System (ADS)

Champion, David J.; Ransom, Scott M.; Lazarus, Patrick; Camilo, Fernando; Kaspi, Victoria M.; Nice, David J.; Freire, Paulo C. C.; Cordes, James M.; Hessels, Jason W. T.; Bassa, Cees; Lorimer, Duncan R.; Stairs, Ingrid H.; van Leeuwen, Joeri; Arzoumnian, Zaven; Backer, Don C.; Bhat, N. D. Ramesh; Chatterjee, Shami; Crawford, Fronefield; Deneva, Julia S.; Faucher-Giguère, Claude-André; Gaensler, B. M.; Han, Jinlin; Jenet, Fredrick A.; Kasian, Laura; Kondratiev, Vlad I.; Kramer, Michael; Lazio, Joseph; McLaughlin, Maura A.; Stappers, Ben W.; Venkataraman, Arun; Vlemmings, Wouter

2008-02-01

The evolution of binary systems is governed by their orbital properties and the stellar density of the local environment. Studies of neutron stars in binary star systems offer unique insights into both these issues. In an Arecibo survey of the Galactic disk, we have found PSR J1903+0327, a radio emitting neutron star (a ``pulsar'') with a 2.15 ms rotation period, in a 95-day orbit around a massive companion. Observations in the infra-red suggests that the companion may be a main-sequence star. Theories requiring an origin in the Galactic disk cannot account for the extraordinarily high orbital eccentricity observed (0.44) or a main-sequence companion of a pulsar that has spin properties suggesting a prolonged accretion history. The most likely formation mechanism is an exchange interaction in a globular star cluster. This requires that the binary was either ejected from its parent globular cluster as a result of a three-body interaction, or that that cluster was disrupted by repeated passages through the disk of the Milky Way.

The Role of Major Gas-rich Mergers on the Evolution of Galaxies from the Blue Cloud to the Red Sequence

NASA Astrophysics Data System (ADS)

Guo, Rui; Hao, Cai-Na; Xia, X. Y.; Mao, Shude; Shi, Yong

2016-07-01

With the aim of exploring the fast evolutionary path from the blue cloud of star-forming galaxies to the red sequence of quiescent galaxies in the local universe, we select a local advanced merging infrared luminous and ultraluminous galaxy (adv-merger (U)LIRGs) sample and perform careful dust extinction corrections to investigate their positions in the star formation rate-M *, u - r, and NUV - r color-mass diagrams. The sample consists of 89 (U)LIRGs at the late merger stage, obtained from cross-correlating the Infrared Astronomical Satellite Point Source Catalog Redshift Survey and 1 Jy ULIRGs samples with the Sloan Digital Sky Survey DR7 database. Our results show that 74 % +/- 5 % of adv-merger (U)LIRGs are localized above the 1σ line of the local star-forming galaxy main sequence. We also find that all adv-merger (U)LIRGs are more massive than and as blue as the blue cloud galaxies after corrections for Galactic and internal dust extinctions, with 95 % +/- 2 % and 81 % +/- 4 % of them outside the blue cloud on the u - r and NUV - r color-mass diagrams, respectively. These results, combined with the short timescale for exhausting the molecular gas reservoir in adv-merger (U)LIRGs (3× {10}7 to 3× {10}8 years), imply that the adv-merger (U)LIRGs are likely at the starting point of the fast evolutionary track previously proposed by several groups. While the number density of adv-merger (U)LIRGs is only ˜ 0.1 % of the blue cloud star-forming galaxies in the local universe, this evolutionary track may play a more important role at high redshift.

The population of single and binary white dwarfs of the Galactic bulge

NASA Astrophysics Data System (ADS)

Torres, S.; García-Berro, E.; Cojocaru, R.; Calamida, A.

2018-05-01

Recent Hubble Space Telescope observations have unveiled the white dwarf cooling sequence of the Galactic bulge. Although the degenerate sequence can be well fitted employing the most up-to-date theoretical cooling sequences, observations show a systematic excess of red objects that cannot be explained by the theoretical models of single carbon-oxygen white dwarfs of the appropriate masses. Here, we present a population synthesis study of the white dwarf cooling sequence of the Galactic bulge that takes into account the populations of both single white dwarfs and binary systems containing at least one white dwarf. These calculations incorporate state-of-the-art cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres, for both white dwarfs with carbon-oxygen and helium cores, and also take into account detailed prescriptions of the evolutionary history of binary systems. Our Monte Carlo simulator also incorporates all the known observational biases. This allows us to model with a high degree of realism the white dwarf population of the Galactic bulge. We find that the observed excess of red stars can be partially attributed to white dwarf plus main sequence binaries, and to cataclysmic variables or dwarf novae. Our best fit is obtained with a higher binary fraction and an initial mass function slope steeper than standard values, as well as with the inclusion of differential reddening and blending. Our results also show that the possible contribution of double degenerate systems or young and thick-discbulge stars is negligible.

NASA's Swift Mission Observes Mega Flares from a Mini Star

NASA Image and Video Library

2017-12-08

Caption: DG CVn, a binary consisting of two red dwarf stars shown here in an artist's rendering, unleashed a series of powerful flares seen by NASA's Swift. At its peak, the initial flare was brighter in X-rays than the combined light from both stars at all wavelengths under typical conditions. Image Credit: NASA's Goddard Space Flight Center/S. Wiessinger ----- On April 23, NASA's Swift satellite detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf star. The initial blast from this record-setting series of explosions was as much as 10,000 times more powerful than the largest solar flare ever recorded. Read more: 1.usa.gov/1poKiJ5 NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Talks also presented at the Symposium

NASA Astrophysics Data System (ADS)

Eldridge, J. J.; Bray, J. C.; McClelland, L. A. S.; Xiao, L.

2017-11-01

Internal rotation and magnetism are key ingredients that largely affect explosive stellar deaths (Supernovae and Gamma Ray Bursts) and the properties of stellar remnants (White Dwarfs, Neutron Stars and Black Holes). However, the study of these subtle internal stellar properties has been limited to very indirect proxies. In the last couple of years, exciting asteroseismic results have been obtained by the Kepler satellite. Among these results are 1) The direct measure of the degree of radial differential rotation in many evolved low-mass stars and in a few massive stars, and 2) The detection of strong (>105 G) internal magnetic fields in thousands of red giant stars that had convective cores during their main sequence. I will discuss the impact of these important findings for our understanding of massive star evolution.

The γ Dor stars as revealed by Kepler: A key to reveal deep-layer rotation in A and F stars

NASA Astrophysics Data System (ADS)

Salmon, S. J. A. J.; Ouazzani, R.-M.; Antoci, V.; Bedding, T. R.; Murphy, S. J.

2017-09-01

The γ Dor pulsating stars present high-order gravity modes, which make them important targets in the intermediate-and low-mass main-sequence region of the Hertzsprung-Russell diagram. Whilst we have only access to rotation in the envelope of the Sun, the g modes of γ Dor stars can in principle deliver us constraints on the inner layers. With the puzzling discovery of unexpectedly low rotation rates in the core of red giants, the γ Dor stars appear now as unique targets to explore internal angular momentum transport in the progenitors of red giants. Yet, the γ Dor pulsations remain hard to detect from the ground for their periods are close to 1 day. While the CoRoT space mission first revealed intriguing frequency spectra, the almost uninterrupted 4-year photometry from the Kepler mission eventually shed a new light on them. It revealed regularities in the spectra, expected to bear signature of physical processes, including rotation, in the shear layers close to the convective core. We present here the first results of our effort to derive exploitable seismic diagnosis for mid- to fast rotators among γ Dor stars. We confirm their potential to explore the rotation history of this early phase of stellar evolution.

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

Geller, Aaron M.; Leiner, Emily M.; Mathieu, Robert D.

Sub-subgiants are stars that are observed to be redder than normal main-sequence stars and fainter than normal subgiant (and giant) stars in an optical color–magnitude diagram (CMD). The red straggler stars, which lie redward of the red giant branch, may be related and are often grouped together with the sub-subgiants in the literature. These stars defy our standard theory of single-star evolution and are important tests for binary evolution and stellar collision models. In total, we identify 65 sub-subgiants (SSG) and red stragglers (RS) in 16 open and globular star clusters from the literature; 50 of these, including 43 sub-subgiants,more » pass our strict membership selection criteria (though the remaining sources may also be cluster members). In addition to their unique location on the CMD, we find that at least 58% (25/43) of sub-subgiants in this sample are X-ray sources with typical 0.5–2.5 keV luminosities of order 10{sup 30}–10{sup 31} erg s{sup −1}. Their X-ray luminosities and optical–to–X-ray flux ratios are similar to those of RS CVn active binaries. At least 65% (28/43) of the sub-subgiants in our sample are variables, 21 of which are known to be radial-velocity binaries. Typical variability periods are ≲15 days. At least 33% (14/43) of the sub-subgiants are H α emitters. These observational demographics provide strong evidence that binarity is important for sub-subgiant formation. Finally, we find that the number of sub-subgiants per unit mass increases toward lower-mass clusters, such that the open clusters in our sample have the highest specific frequencies of sub-subgiants.« less

Orbital Decay in Binaries with Evolved Stars

NASA Astrophysics Data System (ADS)

Sun, Meng; Arras, Phil; Weinberg, Nevin N.; Troup, Nicholas; Majewski, Steven R.

2018-01-01

Two mechanisms are often invoked to explain tidal friction in binary systems. The ``dynamical tide” is the resonant excitation of internal gravity waves by the tide, and their subsequent damping by nonlinear fluid processes or thermal diffusion. The ``equilibrium tide” refers to non-resonant excitation of fluid motion in the star’s convection zone, with damping by interaction with the turbulent eddies. There have been numerous studies of these processes in main sequence stars, but less so on the subgiant and red giant branches. Motivated by the newly discovered close binary systems in the Apache Point Observatory Galactic Evolution Experiment (APOGEE-1), we have performed calculations of both the dynamical and equilibrium tide processes for stars over a range of mass as the star’s cease core hydrogen burning and evolve to shell burning. Even for stars which had a radiative core on the main sequence, the dynamical tide may have very large amplitude in the newly radiative core in post-main sequence, giving rise to wave breaking. The resulting large dynamical tide dissipation rate is compared to the equilibrium tide, and the range of secondary masses and orbital periods over which rapid orbital decay may occur will be discussed, as well as applications to close APOGEE binaries.

X-ray and Optical Observations of NGC 1788

NASA Astrophysics Data System (ADS)

Alcalá, J. M.; Covino, E.; Wachter, S.; Hoard, D. W.; Sterzik, M. F.; Durisen, R. H.; Freyberg, M.; Cooksey, K.

We report on the results of ROSAT High Resolution Imager (HRI) X-ray observations and optical wide-field spectroscopy and imaging in the star forming region NGC 1788. Several new low mass pre-main sequence (PMS) stars have been found based on intermediate resolution spectroscopy. Many new PMS candidate members of NGC 1788 are selected using the spectroscopically confirmed PMS stars to define the PMS locus in color-magnitude diagrams. Some objects with very red colors detected just above the limiting magnitude of our images, are good candidates for young Brown Dwarfs (BDs). The BD nature of these objects need to be confirmed with subsequent IR observations.

The Optical Gravitational Lensing Experiment. Ellipsoidal Variability of Red Giants in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Soszynski, I.; Udalski, A.; Kubiak, M.; Szymanski, M. K.; Pietrzynski, G.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.; Dziembowski, W. A.

2004-12-01

We used the OGLE-II and OGLE-III photometry of red giants in the Large Magellanic Cloud to select and study objects revealing ellipsoidal variability. We detected 1546 candidates for long period ellipsoidal variables and 121 eclipsing binary systems with clear ellipsoidal modulation. The ellipsoidal red giants follow a period--luminosity (PL) relationship (sequence E), and the scatter of the relation is correlated with the amplitude of variability: the larger the amplitude, the smaller the scatter. We note that some of the ellipsoidal candidates exhibit simultaneously OGLE Small Amplitude Red Giants pulsations. Thus, in some cases the Long Secondary Period (LSP) phenomenon can be explained by the ellipsoidal modulation. We also select about 1600 red giants with distinct LSP, which are not ellipsoidal variables. We discover that besides the sequence D in the PL diagram known before, the LSP giants form additional less numerous sequence for longer periods. We notice that the PL sequence of the ellipsoidal candidates is a direct continuation of the LSP sequence toward fainter stars, what might suggest that the LSP phenomenon is related to binarity but there are strong arguments against such a possibility. About 10% of the presented light curves reveal clear deformation by the eccentricity of the system orbits. The largest estimated eccentricity in our sample is about 0.4. All presented data, including individual BVI observations and finding charts are available from the OGLE Internet archive.

The new galaxy evolution paradigm revealed by the Herschel surveys

NASA Astrophysics Data System (ADS)

Eales, Stephen; Smith, Dan; Bourne, Nathan; Loveday, Jon; Rowlands, Kate; van der Werf, Paul; Driver, Simon; Dunne, Loretta; Dye, Simon; Furlanetto, Cristina; Ivison, R. J.; Maddox, Steve; Robotham, Aaron; Smith, Matthew W. L.; Taylor, Edward N.; Valiante, Elisabetta; Wright, Angus; Cigan, Philip; De Zotti, Gianfranco; Jarvis, Matt J.; Marchetti, Lucia; Michałowski, Michał J.; Phillipps, Steven; Viaene, Sebastien; Vlahakis, Catherine

2018-01-01

The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming 'main sequence' and a separate region of 'passive' or 'red-and-dead' galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically red star-forming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations - they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population.

Digging in the coronal graveyard - A Rosat observation of the red giant Arcturus

NASA Technical Reports Server (NTRS)

Ayres, Thomas R.; Fleming, Thomas A.; Schmitt, Juergen H. M. M.

1991-01-01

A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream.

Tidal Interaction among Red Giants Close Binary Systems in APOGEE Database

NASA Astrophysics Data System (ADS)

Sun, Meng; Arras, Phil; Majewski, Steven R.; Troup, Nicholas William; Weinberg, Nevin N.

2017-01-01

Motivated by the newly discovered close binary systems in the Apache Point Observatory Galactic Evolution Experiment (APOGEE-1), the tidal evolution of binaries containing a red giant branch (RGB) star with a stellar or substellar companion was investigated. The tide raised by the companion in the RGB star leads to exchange of angular momentum between the orbit and the stellar spin, causing the orbit to contract. The tidal dissipation rate is computed using turbulent viscosity acting on the equilibrium tidal flow, where careful attention is paid to the effects of reduced viscosity for close-in companions. Evolutionary models for the RGB stars, from the zero-age main sequence to the present, were acquired from the MESA code. "Standard" turbulent viscosity gives rise to such a large orbital decay that many observed systems have decay times much shorter than the RGB evolution time. Several theories for "reduced" turbulent viscosity are investigated, and reduce the number of systems with uncomfortably short decay times.

The ATLAS3D project - XXVII. Cold gas and the colours and ages of early-type galaxies

NASA Astrophysics Data System (ADS)

Young, Lisa M.; Scott, Nicholas; Serra, Paolo; Alatalo, Katherine; Bayet, Estelle; Blitz, Leo; Bois, Maxime; Bournaud, Frédéric; Bureau, Martin; Crocker, Alison F.; Cappellari, Michele; Davies, Roger L.; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Weijmans, Anne-Marie

2014-11-01

We present a study of the cold gas contents of the ATLAS3D early-type galaxies, in the context of their optical colours, near-ultraviolet colours and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas poor as previously thought, and at least 40 per cent of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation) and removal. Molecular and atomic gas detection rates range from 10 to 34 per cent in red sequence early-type galaxies, depending on how the red sequence is defined, and from 50 to 70 per cent in blue early-type galaxies. Notably, massive red sequence early-type galaxies (stellar masses >5 × 1010 M⊙, derived from dynamical models) are found to have H I masses up to M(H I)/M* ˜ 0.06 and H2 masses up to M(H2)/M* ˜ 0.01. Some 20 per cent of all massive early-type galaxies may have retained atomic and/or molecular gas through their transition to the red sequence. However, kinematic and metallicity signatures of external gas accretion (either from satellite galaxies or the intergalactic medium) are also common, particularly at stellar masses ≤5 × 1010 M⊙, where such signatures are found in ˜50 per cent of H2-rich early-type galaxies. Our data are thus consistent with a scenario in which fast rotator early-type galaxies are quenched former spiral galaxies which have undergone some bulge growth processes, and in addition, some of them also experience cold gas accretion which can initiate a period of modest star formation activity. We discuss implications for the interpretation of colour-magnitude diagrams.

Weighing in on the masses of retired A stars with asteroseismology: K2 observations of the exoplanet-host star HD 212771

NASA Astrophysics Data System (ADS)

Campante, Tiago L.; Veras, Dimitri; North, Thomas S. H.; Miglio, Andrea; Morel, Thierry; Johnson, John A.; Chaplin, William J.; Davies, Guy R.; Huber, Daniel; Kuszlewicz, James S.; Lund, Mikkel N.; Cooke, Benjamin F.; Elsworth, Yvonne P.; Rodrigues, Thaíse S.; Vanderburg, Andrew

2017-08-01

Doppler-based planet surveys point to an increasing occurrence rate of giant planets with stellar mass. Such surveys rely on evolved stars for a sample of intermediate-mass stars (so-called retired A stars), which are more amenable to Doppler observations than their main-sequence progenitors. However, it has been hypothesized that the masses of subgiant and low-luminosity red-giant stars targeted by these surveys - typically derived from a combination of spectroscopy and isochrone fitting - may be systematically overestimated. Here, we test this hypothesis for the particular case of the exoplanet-host star HD 212771 using K2 asteroseismology. The benchmark asteroseismic mass (1.45^{+0.10}_{-0.09} M_{⊙) is significantly higher than the value reported in the discovery paper (1.15 ± 0.08 M⊙), which has been used to inform the stellar mass-planet occurrence relation. This result, therefore, does not lend support to the above hypothesis. Implications for the fates of planetary systems are sensitively dependent on stellar mass. Based on the derived asteroseismic mass, we predict the post-main-sequence evolution of the Jovian planet orbiting HD 212771 under the effects of tidal forces and stellar mass-loss.

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

Smith, Myron A.; Shiao, Bernard; Bianchi, Luciana, E-mail: myronmeister@gmail.com, E-mail: shiao@stsci.edu, E-mail: bianchi@pha.jhu.edu

We report on intriguing photometric properties of Galactic stars observed in the Galaxy Evolution Explorer (GALEX) satellite's far-UV (FUV) and near-UV (NUV) bandpasses, as well as from the ground-based Sloan Digital Sky Survey (SDSS) and the Kepler Input Catalog. The first property is that the (FUV – NUV) color distribution of stars in the Kepler field consists of two well-separated peaks. A second and more perplexing property is that for stars with spectral types G or later the mean (FUV – NUV) color becomes much bluer, contrary to expectation. Investigating this tendency further, we found in two samples of mid-Fmore » through K type stars that 17%-22% of them exhibit FUV excesses relative to their NUV fluxes and spectral types. A correction for FUV incompleteness of the FUV magnitude-limited star sample brings this ratio to 14%-18%. Nearly the same fractions are also discovered among members of the Kepler Eclipsing Binary Catalog and in the published list of Kepler Objects of Interest. These UV-excess ('UVe') colors are confirmed by the negative UV continuum slopes in GALEX spectra of members of the population. The SDSS spectra of some UVe stars exhibit metallic line weakening, especially in the blue. This suggests an enhanced contribution of UV flux relative to photospheric flux of a solar-type single star. We consider the possibility that the UV excesses originate from various types of hot stars, including white dwarf DA and sdB stars, binaries, and strong chromosphere stars that are young or in active binaries. The space density of compact stars is too low to explain the observed frequency of the UVe stars. Our model atmosphere-derived simulations of colors for binaries with main-sequence pairs with a hot secondary demonstrate that the color loci conflict with the observed sequence. As a preferred alternative we are left with the active chromospheres explanation, whether in active close binaries or young single stars, despite the expected paucity of young, chromospherically active stars in the field. We also address a third perplexing color property, namely, the presence of a prominent island of 'UV red' stars surrounded by 'UV blue' stars in the diagnostic (NUV–g), (g – i) color diagram. We find that the subpopulation composing this island is mainly horizontal branch stars. These objects do not exhibit UV excesses and therefore have UV colors typical for their spectral types. This subpopulation appears 'red' in the UV only because the stars' colors are not pulled to the blue by the inclusion of UVe stars.« less

Using He I λ10830 to Diagnose Mass Flows Around Herbig Ae/Be Stars

NASA Astrophysics Data System (ADS)

Cauley, Paul W.; Johns-Krull, Christopher M.

2015-01-01

The pre-main sequence Herbig Ae/Be stars (HAEBES) are the intermediate mass cousins of the low mass T Tauri stars (TTSs). However, it is not clear that the same accretion and mass outflow mechanisms operate identically in both mass regimes. Classical TTSs (CTTSs) accrete material from their disks along stellar magnetic field lines in a scenario called magnetospheric accretion. Magnetospheric accretion requires a strong stellar dipole field in order to truncate the inner gas disk. These fields are either absent or very weak on a large majority of HAEBES, challenging the view that magnetospheric accretion is the dominant accretion mechanism. If magnetospheric accretion does not operate similarly around HAEBES as it does around CTTSs, then strong magnetocentrifugal outflows, which are directly linked to accretion and are ubiquitous around CTTSs, may be driven less efficiently from HAEBE systems. Here we present high resolution spectroscopic observations of the He I λ10830 line in a sample of 48 HAEBES. He I λ10830 is an excellent tracer of both mass infall and outflow which is directly manifested as red and blue-shifted absorption in the profile morphologies. These features, among others, are common in our sample. The occurrence of both red and blue-shifted absorption profiles is less frequent, however, than is found in CTTSs. Statistical contingency tests confirm this difference at a significant level. In addition, we find strong evidence for smaller disk truncation radii in the objects displaying red-shifted absorption profiles. This is expected for HAEBES experiencing magnetospheric accretion based on their large rotation rates and weak magnetic field strengths. Finally, the low incidence of blue-shifted absorption in our sample compared to CTTSs and the complete lack of simultaneous red and blue-shifted absorption features suggests that magnetospheric accretion in HAEBES is less efficient at driving strong outflows. The stellar wind-like outflows that are observed are likely driven, at least in part, by boundary layer accretion. The smaller (or absent) disk truncation radii in HAEBES may have consequences for the frequency of planets in close orbits around main sequence B and A stars.

Constraining the Final Fates of Massive Stars by Oxygen and Iron Enrichment History in the Galaxy

NASA Astrophysics Data System (ADS)

Suzuki, Akihiro; Maeda, Keiichi

2018-01-01

Recent observational studies of core-collapse supernovae suggest that only stars with zero-age main-sequence masses smaller than 16–18 {M}ȯ explode when they are red supergiants, producing Type IIP supernovae. This may imply that more massive stars produce other types of supernovae or they simply collapse to black holes without giving rise to bright supernovae. This failed supernova hypothesis can lead to significantly inefficient oxygen production because oxygen abundantly produced in inner layers of massive stars with zero-age main-sequence masses around 20–30 {M}ȯ might not be ejected into the surrounding interstellar space. We first assume an unspecified population of oxygen injection events related to massive stars and obtain a model-independent constraint on how much oxygen should be released in a single event and how frequently such events should happen. We further carry out one-box galactic chemical enrichment calculations with different mass ranges of massive stars exploding as core-collapse supernovae. Our results suggest that the model assuming that all massive stars with 9–100 {M}ȯ explode as core-collapse supernovae is still most appropriate in explaining the solar abundances of oxygen and iron and their enrichment history in the Galaxy. The oxygen mass in the Galaxy is not explained when assuming that only massive stars with zero-age main-sequence masses in the range of 9–17 {M}ȯ contribute to the galactic oxygen enrichment. This finding implies that a good fraction of stars more massive than 17 {M}ȯ should eject their oxygen layers in either supernova explosions or some other mass-loss processes.

V and K-band Mass-Luminosity Relations for M Dwarf Stars

NASA Astrophysics Data System (ADS)

Benedict, George Frederick; Henry, Todd J.; McArthur, Barbara E.; Franz, Otto; Wasserman, Larry H.; Dieterich, Sergio

2015-08-01

Applying Hubble Space Telescope Fine Guidance Sensor astrometric techniques developed to establish relative orbits for binary stars (Franz et al. 1998, AJ, 116, 1432), determine masses of binary components (Benedict et al. 2001, AJ, 121, 1607), and measure companion masses of exoplanet host stars (McArthur et al. 2010, ApJ, 715, 1203), we derive masses with an average 2% error for 28 components of 14 M dwarf binary star systems. With these and other published masses we update the lower Main Sequence V-band Mass-Luminosity Relation first shown in Henry et al. 1999, ApJ, 512, 864. We demonstrate that a Mass-Luminosity Relation in the K-band has far less scatter. These relations can be used to estimate the masses of the ubiquitous red dwarfs (75% of all stars) to an accuracy of better than 5%.

Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants

NASA Astrophysics Data System (ADS)

Deheuvels, S.; Doğan, G.; Goupil, M. J.; Appourchaux, T.; Benomar, O.; Bruntt, H.; Campante, T. L.; Casagrande, L.; Ceillier, T.; Davies, G. R.; De Cat, P.; Fu, J. N.; García, R. A.; Lobel, A.; Mosser, B.; Reese, D. R.; Regulo, C.; Schou, J.; Stahn, T.; Thygesen, A. O.; Yang, X. H.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Eggenberger, P.; Gizon, L.; Mathis, S.; Molenda-Żakowicz, J.; Pinsonneault, M.

2014-04-01

Context. We still do not understand which physical mechanisms are responsible for the transport of angular momentum inside stars. The recent detection of mixed modes that contain the clear signature of rotation in the spectra of Kepler subgiants and red giants gives us the opportunity to make progress on this question. Aims: Our aim is to probe the radial dependence of the rotation profiles for a sample of Kepler targets. For this purpose, subgiants and early red giants are particularly interesting targets because their rotational splittings are more sensitive to the rotation outside the deeper core than is the case for their more evolved counterparts. Methods: We first extracted the rotational splittings and frequencies of the modes for six young Kepler red giants. We then performed a seismic modeling of these stars using the evolutionary codes Cesam2k and astec. By using the observed splittings and the rotational kernels of the optimal models, we inverted the internal rotation profiles of the six stars. Results: We obtain estimates of the core rotation rates for these stars, and upper limits to the rotation in their convective envelope. We show that the rotation contrast between the core and the envelope increases during the subgiant branch. Our results also suggest that the core of subgiants spins up with time, while their envelope spins down. For two of the stars, we show that a discontinuous rotation profile with a deep discontinuity reproduces the observed splittings significantly better than a smooth rotation profile. Interestingly, the depths that are found to be most probable for the discontinuities roughly coincide with the location of the H-burning shell, which separates the layers that contract from those that expand. Conclusions: We characterized the differential rotation pattern of six young giants with a range of metallicities, and with both radiative and convective cores on the main sequence. This will bring observational constraints to the scenarios of angular momentum transport in stars. Moreover, if the existence of sharp gradients in the rotation profiles of young red giants is confirmed, it is expected to help in distinguishing between the physical processes that could transport angular momentum in the subgiant and red giant branches. Appendices and Tables 3-9 are available in electronic form at http://www.aanda.org

Quenching histories of galaxies and the role of AGN feedback

NASA Astrophysics Data System (ADS)

Smethurst, Rebecca Jane; Lintott, Chris; Simmons, Brooke; Galaxy Zoo Team

2016-01-01

Two open issues in modern astrophysics are: (i) how do galaxies fully quench their star formation and (ii) how is this affected - or not - by AGN feedback? I present the results of a new Bayesian-MCMC analysis of the star formation histories of over 126,000 galaxies across the colour magnitude diagram showing that diverse quenching mechanisms are instrumental in the formation of the present day red sequence. Using classifications from Galaxy Zoo we show that the rate at which quenching can occur is morphologically dependent in each of the blue cloud, green valley and red sequence. We discuss the nature of these possible quenching mechanisms, considering the influence of secular evolution, galaxy interactions and mergers, both with and without black hole activity. We focus particularly on the relationship between these quenched star formation histories and the presence of an AGN by using this new Bayesian method to show a population of type 2 AGN host galaxies have recently (within 2 Gyr) undergone a rapid (τ < 1 Gyr) drop in their star formation rate. With this result we therefore present the first statistically supported observational evidence that AGN feedback is an important mechanism for the cessation of star formation in this population of galaxies. The diversity of this new method also highlights that such rapid quenching histories cannot account fully for all the quenching across the current AGN host population. We demonstrate that slower (τ > 2 Gyr) quenching rates dominate for high stellar mass (log10[M*/M⊙] > 10.75) hosts of AGN with both early- and late-type morphology. We discuss how these results show that both merger-driven and non-merger processes are contributing to the co-evolution of galaxies and supermassive black holes across the entirety of the colour magnitude diagram.

Explosion of a supernova with a red giant companion

NASA Technical Reports Server (NTRS)

Livne, E.; Tuchman, Y.; Wheeler, J. C.

1992-01-01

Two-dimensional numerical simulations of the collision between spherical ejecta from a supernova and a red giant companion are presented. In contrast to previous numerical studies, in which the companion was a main-sequence star or a compact object, the collision consequences are found to have a dramatic impact upon the red giant. In most cases the red giant companion loses most of its envelope in a time scale of 10 exp 7 s with typical velocities about an order of magnitude less than those of the expanding velocity of the supernova shell. We confirm the conclusion of Chugai (1986) that the stripped hydrogen tends to come off as a low-velocity component interior to the supernova ejecta. Possible observational consequences of the results are discussed.

Delayed Gratification Habitable Zones: When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution

NASA Astrophysics Data System (ADS)

Stern, S. Alan

2003-06-01

Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >105 objects >=50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, ~109 Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy.

Delayed gratification habitable zones: when deep outer solar system regions become balmy during post-main sequence stellar evolution.

PubMed

Stern, S Alan

2003-01-01

Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >10(5) objects > or =50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, approximately 10(9) Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy.

Innocent Bystanders: Carbon Stars from the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Green, Paul

2013-03-01

Among stars showing carbon molecular bands (C stars), the main-sequence dwarfs, likely in post-mass transfer binaries, are numerically dominant in the Galaxy. Via spectroscopic selection from the Sloan Digital Sky Survey, we retrieve 1220 high galactic latitude C stars, ~5 times more than previously known, including a wider variety than past techniques such as color or grism selection have netted, and additionally yielding 167 DQ white dwarfs. Of the C stars with proper motion measurements, we identify 69% clearly as dwarfs (dCs), while ~7% are giants. The dCs likely span absolute magnitudes Mi from ~6.5 to 10.5. "G-type" dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C2 bands. We report Balmer emission in 22 dCs, none of which are G-types. We find 8 new DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. Eleven very red C stars with strong red CN bands appear to be "N"-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Leo A. Two such stars within 30' of each other may trace a previously unidentified dwarf galaxy or tidal stream at ~40 kpc. We explore the multiwavelength properties of the sample and report the first X-ray detection of a dC star, which shows strong Balmer emission. Our own spectroscopic survey additionally provides the dC surface density from a complete sample of dwarfs limited by magnitude, color, and proper motion.

The total rate of mass return to the interstellar medium from red giants and planetary nebulae

NASA Technical Reports Server (NTRS)

Knapp, G. R.; Rauch, K. P.; Wilcots, E. M.

1990-01-01

High luminosity post main sequence stars are observed to be losing mass in large amounts into the interstellar medium. The various methods used to estimate individual and total mass loss rates are summarized. Current estimates give MT 0.3 - 0.6 solar mass per year for the whole Galaxy.

Schwarzschild, Martin (1912-97)

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

Astrophysicist, born in Potsdam, Germany, the son of KARL SCHWARZSCHILD, left Germany, became professor at Princeton University. Working with John von Neumann, Schwarzschild used the powers of the newly developed electronic digital computers to work on the theory of stellar structure and evolution. He uncovered phenomena in red giant stars, including how they evolve off the main sequence in the H...

GALAXY EVOLUTION IN THE MID-INFRARED GREEN VALLEY: A CASE OF THE A2199 SUPERCLUSTER

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

Lee, Gwang-Ho; Lee, Myung Gyoon; Sohn, Jubee

2015-02-20

We study the mid-infrared (MIR) properties of the galaxies in the A2199 supercluster at z = 0.03 to understand the star formation activity of galaxy groups and clusters in the supercluster environment. Using the Wide-field Infrared Survey Explorer data, we find no dependence of mass-normalized integrated star formation rates of galaxy groups/clusters on their virial masses. We classify the supercluster galaxies into three classes in the MIR color-luminosity diagram: MIR blue cloud (massive, quiescent, and mostly early-type), MIR star-forming sequence (mostly late-type), and MIR green valley galaxies. These MIR green valley galaxies are distinguishable from the optical green valley galaxiesmore » in the sense that they belong to the optical red sequence. We find that the fraction of each MIR class does not depend on the virial mass of each group/cluster. We compare the cumulative distributions of surface galaxy number density and cluster/group-centric distance for the three MIR classes. MIR green valley galaxies show the distribution between MIR blue cloud and MIR star-forming (SF) sequence galaxies. However, if we fix galaxy morphology, early- and late-type MIR green valley galaxies show different distributions. Our results suggest a possible evolutionary scenario of these galaxies: (1) late-type MIR SF sequence galaxies → (2) late-type MIR green valley galaxies → (3) early-type MIR green valley galaxies → (4) early-type MIR blue cloud galaxies. In this sequence, the star formation of galaxies is quenched before the galaxies enter the MIR green valley, and then morphological transformation occurs in the MIR green valley.« less

Using White Dwarf Companions of Blue Stragglers to Constrain Mass Transfer Physics

NASA Astrophysics Data System (ADS)

Gosnell, Natalie M.; Leiner, Emily; Geller, Aaron M.; Knigge, Christian; Mathieu, Robert D.; Sills, Alison; Leigh, Nathan

2018-06-01

Complete membership studies of old open clusters reveal that 25% of the evolved stars follow pathways in stellar evolution that are impacted by binary evolution. Recent studies show that the majority of blue straggler stars, traditionally defined to be stars brighter and bluer than the corresponding main sequence turnoff, are formed through mass transfer from a giant star onto a main sequence companion, resulting in a white dwarf in a binary system with a blue straggler. We will present constraints on the histories and mass transfer efficiencies for two blue straggler-white dwarf binaries in open cluster NGC 188. The constraints are a result of measuring white dwarf cooling temperatures and surface gravities with HST COS far-ultraviolet spectroscopy. This information sets both the timeline for mass transfer and the stellar masses in the pre-mass transfer binary, allowing us to constrain aspects of the mass transfer physics. One system is formed through Case C mass transfer, leaving a CO-core white dwarf, and provides an interesting test case for mass transfer from an asymptotic giant branch star in an eccentric system. The other system formed through Case B mass transfer, leaving a He-core white dwarf, and challenges our current understanding of the expected regimes for stable mass transfer from red giant branch stars.

Galaxy evolution in groups and clusters: star formation rates, red sequence fractions and the persistent bimodality

NASA Astrophysics Data System (ADS)

Wetzel, Andrew R.; Tinker, Jeremy L.; Conroy, Charlie

2012-07-01

Using galaxy group/cluster catalogues created from the Sloan Digital Sky Survey Data Release 7, we examine in detail the specific star formation rate (SSFR) distribution of satellite galaxies and its dependence on stellar mass, host halo mass and halo-centric radius. All galaxies, regardless of central satellite designation, exhibit a similar bimodal SSFR distribution, with a strong break at SSFR ≈ 10-11 yr-1 and the same high SSFR peak; in no regime is there ever an excess of galaxies in the 'green valley'. Satellite galaxies are simply more likely to lie on the quenched ('red sequence') side of the SSFR distribution. Furthermore, the satellite quenched fraction excess above the field galaxy value is nearly independent of galaxy stellar mass. An enhanced quenched fraction for satellites persists in groups with halo masses down to 3 × 1011 M⊙ and increases strongly with halo mass and towards halo centre. We find no detectable quenching enhancement for galaxies beyond ˜2 Rvir around massive clusters once these galaxies have been decomposed into centrals and satellites. These trends imply that (1) galaxies experience no significant environmental effects until they cross within ˜Rvir of a more massive host halo; (2) after this, star formation in active satellites continues to evolve in the same manner as active central galaxies for several Gyr; and (3) once begun, satellite star formation quenching occurs rapidly. These results place strong constraints on satellite-specific quenching mechanisms, as we will discuss further in companion papers.

Photometry of Southern Hemisphere red dwarf stars

NASA Technical Reports Server (NTRS)

Weistrop, D.

1980-01-01

Results are presented for a photometric investigation of a spectroscopically selected sample of red dwarf stars in the Southern Hemisphere. Absolute magnitudes and distances for the stars are estimated from broadband red colors. Three stars which may be subluminous are identified, as are several stars which may be within 25 pc. The tangential velocity and velocity dispersion of the sample are similar to values found in other studies of nearby late-type stars.

TESTING CONVECTIVE-CORE OVERSHOOTING USING PERIOD SPACINGS OF DIPOLE MODES IN RED GIANTS

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

Montalban, J.; Noels, A.; Dupret, M.-A.

2013-04-01

Uncertainties on central mixing in main-sequence (MS) and core He-burning (He-B) phases affect key predictions of stellar evolution such as late evolutionary phases, chemical enrichment, ages, etc. We propose a test of the extension of extra-mixing in two relevant evolutionary phases based on period spacing ({Delta}P) of solar-like oscillating giants. From stellar models and their corresponding adiabatic frequencies (respectively, computed with ATON and LOSC codes), we provide the first predictions of the observable {Delta}P for stars in the red giant branch and in the red clump (RC). We find (1) a clear correlation between {Delta}P and the mass of themore » helium core (M{sub He}); the latter in intermediate-mass stars depends on the MS overshooting, and hence it can be used to set constraints on extra-mixing during MS when coupled with chemical composition; and (2) a linear dependence of the average value of the asymptotic period spacing (({Delta}P){sub a}) on the size of the convective core during the He-B phase. A first comparison with the inferred asymptotic period spacing for Kepler RC stars also suggests the need for extra-mixing during this phase, as evinced from other observational facts.« less

Magnetic braking of stellar cores in red giants and supergiants

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

Maeder, André; Meynet, Georges, E-mail: andre.maeder@unige, E-mail: georges.meynet@unige.ch

2014-10-01

Magnetic configurations, stable on the long term, appear to exist in various evolutionary phases, from main-sequence stars to white dwarfs and neutron stars. The large-scale ordered nature of these fields, often approximately dipolar, and their scaling according to the flux conservation scenario favor a fossil field model. We make some first estimates of the magnetic coupling between the stellar cores and the outer layers in red giants and supergiants. Analytical expressions of the truncation radius of the field coupling are established for a convective envelope and for a rotating radiative zone with horizontal turbulence. The timescales of the internal exchangesmore » of angular momentum are considered. Numerical estimates are made on the basis of recent model grids. The direct magnetic coupling of the core to the extended convective envelope of red giants and supergiants appears unlikely. However, we find that the intermediate radiative zone is fully coupled to the core during the He-burning and later phases. This coupling is able to produce a strong spin down of the core of red giants and supergiants, also leading to relatively slowly rotating stellar remnants such as white dwarfs and pulsars. Some angular momentum is also transferred to the outer convective envelope of red giants and supergiants during the He-burning phase and later.« less

Physical properties of distant red galaxies in the COSMOS/UltraVISTA field

NASA Astrophysics Data System (ADS)

Ma, Zhongyang; Fang, Guanwen; Kong, Xu; Fan, Lulu

2015-10-01

We present a study on physical properties for a large distant red galaxy (DRG) sample, using the K-selected multi-band photometry catalog of the COSMOS/UltraVISTA field and the CANDELS near-infrared data. Our sample includes 4485 DRGs with (J - K)AB > 1.16 and KAB < 23.4 mag, and 132 DRGs have HST/WFC3 morphological measurements. The results of nonparametric measurements of DRG morphology are consistent with our rest-frame UVJ color classification; quiescent DRGs are generally compact while star-forming DRGs tend to have extended structures. We find the star formation rate (SFR) and the stellar mass of star-forming DRGs present tight "main sequence" relations in all redshift bins. Moreover, the specific SFR (sSFR) of DRGs increases with redshift in all stellar mass bins and DRGs with higher stellar masses generally have lower sSFRs, which indicates that galaxies were much more active on average in the past, and star formation contributes more to the mass growth of low-mass galaxies than to high-mass galaxies. The infrared-derived SFR dominates the total SFR of DRGs which occupy the high-mass range, implying that the J - K color criterion effectively selects massive and dusty galaxies. DRGs with higher M* generally have redder (U - V)rest colors, and the (U - V)rest colors of DRGs become bluer at higher redshifts, suggesting high-mass galaxies have higher internal dust extinctions or older stellar ages and they evolve with time. Finally, we find that DRGs have different overlap among extremely red objects, BzK galaxies, IRAC-selected extremely red objects, and high-z ultraluminous infrared galaxies, indicating that DRGs are not a special population and they can also be selected by other color criteria.

The interstellar redding law in the ultraviolet deduced from filter photometry obtained by the OAO-2 satellite

NASA Technical Reports Server (NTRS)

Laget, M.

1972-01-01

Filter photometry has been obtained of 16 BO stars at ten effective wavelengths in the range 4250-1430 A. The wavelength dependence of the interstellar reddening law, deduced from a least squares fit of the observed values to the reddening line at each band, is found in satisfactory agreement with that derived by Bless and Savage (1972). Toward the shorter wavelengths the increase of the computed probable error of the slope of the mean reddening line suggests that large fluctuations in the law may occur from star to star. Similar computations, separating main-sequence stars and supergiants, indicate that the large fluctuations of the law appear to be well related to the luminosity of the stars; the supergiants show systematically less extinction, this deficiency becoming large toward the far UV. The small number in the sample however, does not allow a general conclusion to be drawn.

Do Close-in Giant Planets Orbiting Evolved Stars Prefer Eccentric Orbits?

NASA Astrophysics Data System (ADS)

Grunblatt, Samuel K.; Huber, Daniel; Gaidos, Eric; Lopez, Eric D.; Barclay, Thomas; Chontos, Ashley; Sinukoff, Evan; Van Eylen, Vincent; Howard, Andrew W.; Isaacson, Howard T.

2018-07-01

The NASA Kepler and K2 Missions have recently revealed a population of transiting giant planets orbiting moderately evolved, low-luminosity red giant branch stars. Here, we present radial velocity (RV) measurements of three of these systems, revealing significantly non-zero orbital eccentricities in each case. Comparing these systems with the known planet population suggests that close-in giant planets around evolved stars tend to have more eccentric orbits than those around main sequence stars. We interpret this as tentative evidence that the orbits of these planets pass through a transient, moderately eccentric phase where they shrink faster than they circularize due to tides raised on evolved host stars. Additional RV measurements of currently known systems, along with new systems discovered by the recently launched NASA Transiting Exoplanet Survey Satellite (TESS) mission, may constrain the timescale and mass dependence of this process.

THE STAR FORMATION HISTORY OF BCGs TO z = 1.8 FROM THE SpARCS/SWIRE SURVEY: EVIDENCE FOR SIGNIFICANT IN SITU STAR FORMATION AT HIGH REDSHIFT

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

Webb, Tracy M. A.; Bonaventura, Nina; Muzzin, Adam

2015-12-01

We present the results of an MIPS-24 μm study of the brightest cluster galaxies (BCGs) of 535 high-redshift galaxy clusters. The clusters are drawn from the Spitzer Adaptation of the Red-Sequence Cluster Survey, which effectively provides a sample selected on total stellar mass, over 0.2 < z < 1.8 within the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey fields. Twenty percent, or 106 clusters, have spectroscopically confirmed redshifts, and the rest have redshifts estimated from the color of their red sequence. A comparison with the public SWIRE images detects 125 individual BCGs at 24 μm ≳ 100 μJy, or 23%. Themore » luminosity-limited detection rate of BCGs in similar richness clusters (N{sub gal} > 12) increases rapidly with redshift. Above z ∼ 1, an average of ∼20% of the sample have 24 μm inferred infrared luminosities of L{sub IR} > 10{sup 12} L{sub ⊙}, while the fraction below z ∼ 1 exhibiting such luminosities is <1%. The Spitzer-IRAC colors indicate the bulk of the 24 μm detected population is predominantly powered by star formation, with only 7/125 galaxies lying within the color region inhabited by active galactic nuclei (AGNs). Simple arguments limit the star formation activity to several hundred million years and this may therefore be indicative of the timescale for AGN feedback to halt the star formation. Below redshift z ∼ 1, there is not enough star formation to significantly contribute to the overall stellar mass of the BCG population, and therefore BCG growth is likely dominated by dry mergers. Above z ∼ 1, however, the inferred star formation would double the stellar mass of the BCGs and is comparable to the mass assembly predicted by simulations through dry mergers. We cannot yet constrain the process driving the star formation for the overall sample, though a single object studied in detail is consistent with a gas-rich merger.« less

Cannonballs Shoot from Star (Artist Concept)

NASA Image and Video Library

2016-10-06

This four-panel graphic illustrates how the binary-star system V Hydrae is launching balls of plasma into space. Panel 1 shows the two stars orbiting each other. One of the stars is nearing the end of its life and has swelled in size, becoming a red giant. In panel 2, the smaller star's orbit carries the star into the red giant's expanded atmosphere. As the star moves through the atmosphere, it gobbles up material from the red giant that settles into a disk around the star. The buildup of material reaches a tipping point and is eventually ejected as blobs of hot plasma along the star's spin axis, as shown in panel 3. This ejection process is repeated every eight years, which is the time it takes for the orbiting star to make another pass through the bloated red giant's envelope, as shown in panel 4. http://photojournal.jpl.nasa.gov/catalog/PIA21071

Adaptive Optics Near-Infrared Imaging of R136 in 30 Doradus: The Stellar Population of a Nearby Starburst

NASA Astrophysics Data System (ADS)

Brandl, B.; Sams, B. J.; Bertoldi, F.; Eckart, A.; Genzel, R.; Drapatz, S.; Hofmann, R.; Loewe, M.; Quirrenbach, A.

1996-07-01

We report 0".15 resolution near-infrared (NIR) imaging of R136, the central region of 30 Doradus in the large Magellanic Cloud. Our 12".8 x 12".8 images were recorded with the MPE camera SHARP II at the 3.6 m ESO telescope, using the adaptive optics system COME ON+. The high spatial resolution and sensitivity (20th magnitude in K) of our observations allow our H- and K-band images to be compared and combined with recent Hubble Space Telescope (HST) WFPC2 data of R136. We fit theoretical models with variable foreground extinction to the observed magnitudes of ˜1000 stars (roughly half of which were detected in HST and NIR bands) and derive the stellar population in this starburst region. We find no red giants or supergiants; however, we detect ˜110 extremely red sources which are probably young, pre-main-sequence low- or intermediate-mass stars. We obtained narrow-band images to identify known and new Wolf-Rayet stars by their He 11(2.189 μm) and Bry (2.166 μm) emission lines. The presence of W-R stars and absence of red supergiants narrow the cluster age to ˜3-5 Myr, while the derived ratio of W-R to 0 stars of 0.05 in the central region favors an age of 3.5 Myr, with a relatively short starburst duration. For the 0 stars, the core radius is found to be 0.1 pc and appears to decrease with increasing stellar mass. The slope of the mass function function is Γ = -1.6 on average, but it steepens with increasing distance from the cluster center from Γ = -1.3 in the inner 0.4 pc to Γ = -2.2 outside 0.8 pc for stars more massive than 12 Msun. The radial variation of the mass function reveals strong mass segregation that is probably due to the cluster's dynamical evolution.

Galaxy Morphology Revealed By SDSS: Blue Elliptical Galaxies

NASA Astrophysics Data System (ADS)

Ann, Hong Bae

The Sloan Digital Sky Survey (SDSS) reveals many new features of galaxy morphologies. Among others, the discovery of blue elliptical galaxies provides some insights into the formation and evolution of galaxies. There seems to be two types of blue elliptical galaxies. One type shows globally blue colors suggesting star formations over the entire galaxy whereas the other type shows blue core that indicates enhanced star formation in the nuclear regions. The former seems to be currently forming galaxies, while the latter is thought to be in transition stage from the blue cloud to the red sequence due to AGN feedback.

The origins of post-starburst galaxies at z < 0.05

NASA Astrophysics Data System (ADS)

Pawlik, M. M.; Taj Aldeen, L.; Wild, V.; Mendez-Abreu, J.; Lahén, N.; Johansson, P. H.; Jimenez, N.; Lucas, W.; Zheng, Y.; Walcher, C. J.; Rowlands, K.

2018-06-01

Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer lines in a volume-limited sample of 189 galaxies with 0.01 < z < 0.05, log ({M}_{\\star }/{M}_{⊙})>9.5 and projected axial ratio b/a > 0.32. We explore their structural properties, environments, emission lines, and star formation histories, and compare them to control samples of star-forming and quiescent galaxies, and simulated galaxy mergers. Excluding contaminants, in which the strong Balmer lines are most likely caused by dust-star geometry, we find evidence for three different pathways through the post-starburst phase, with most events occurring in intermediate-density environments: (1) a significant disruptive event, such as a gas-rich major merger, causing a starburst and growth of a spheroidal component, followed by quenching of the star formation (70 per cent of post-starburst galaxies at 9.5< log ({M}_{\\star}/{M}_{⊙})<10.5 and 60 per cent at log ({M}_{\\star}/{M}_{⊙})>10.5); (2) at 9.5< log ({M}_{\\star}/{M}_{⊙})<10.5, stochastic star formation in blue-sequence galaxies, causing a weak burst and subsequent return to the blue sequence (30 per cent); (3) at log ({M}_{\\star}/{M}_{⊙})>10.5, cyclic evolution of quiescent galaxies which gradually move towards the high-mass end of the red sequence through weak starbursts, possibly as a result of a merger with a smaller gas-rich companion (40 per cent). Our analysis suggests that active galactic nuclei (AGNs) are 'on' for 50 per cent of the duration of the post-starburst phase, meaning that traditional samples of post-starburst galaxies with strict emission-line cuts will be at least 50 per cent incomplete due to the exclusion of narrow-line AGNs.

DISCOVERY OF SUPER-Li-RICH RED GIANTS IN DWARF SPHEROIDAL GALAXIES

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

Kirby, Evan N.; Fu, Xiaoting; Deng, Licai

2012-06-10

Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of kelvin, hot enough for the {sup 7}Li(p, {alpha}){sup 4}He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants-14 of which are new discoveries-among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] {approx}< -0.7) Li-richmore » red giants, and it includes the most-metal-poor Li-enhanced star known ([Fe/H] = -2.82, A(Li){sub NLTE} = 3.15). Because most of the stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. These Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. We consider the possibility that Li enrichment is a universal phase of evolution that affects all stars, and it seems rare only because it is brief.« less

The initial mass function and star formation law in the outer disc of NGC 2915

NASA Astrophysics Data System (ADS)

Bruzzese, S. M.; Meurer, G. R.; Lagos, C. D. P.; Elson, E. C.; Werk, J. K.; Blakeslee, John P.; Ford, H.

2015-02-01

Using Hubble Space Telescope (HST) Advanced Camera for Surveys/Wide Field Camera data we present the photometry and spatial distribution of resolved stellar populations in the outskirts of NGC 2915, a blue compact dwarf with an extended H I disc. These observations reveal an elliptical distribution of red giant branch stars, and a clumpy distribution of main-sequence stars that correlate with the H I gas distribution. We constrain the upper-end initial mass function (IMF) and determine the star formation law (SFL) in this field, using the observed main-sequence stars and an assumed constant star formation rate. Previously published Hα observations of the field, which show one faint H II region, are used to provide further constraints on the IMF. We find that the main-sequence luminosity function analysis alone results in a best-fitting IMF with a power-law slope α = -2.85 and upper-mass limit M_u = 60 M_{⊙}. However, if we assume that all Hα emission is confined to H II regions then the upper-mass limit is restricted to M_u ≲ 20 M_{⊙}. For the luminosity function fit to be correct, we have to discount the Hα observations implying significant diffuse ionized gas or escaping ionizing photons. Combining the HST photometry with H I imaging, we find the SFL has a power-law index N = 1.53 ± 0.21. Applying these results to the entire outer H I disc indicates that it contributes 11-28 per cent of the total recent star formation in NGC 2915, depending on whether the IMF is constant within the disc or varies from the centre to the outer region.

Multiple stellar populations in Magellanic Cloud clusters - III. The first evidence of an extended main sequence turn-off in a young cluster: NGC 1856

NASA Astrophysics Data System (ADS)

Milone, A. P.; Bedin, L. R.; Piotto, G.; Marino, A. F.; Cassisi, S.; Bellini, A.; Jerjen, H.; Pietrinferni, A.; Aparicio, A.; Rich, R. M.

2015-07-01

Recent studies have shown that the extended main-sequence turn-off (eMSTO) is a common feature of intermediate-age star clusters in the Magellanic Clouds (MCs). The most simple explanation is that these stellar systems harbour multiple generations of stars with an age difference of a few hundred million years. However, while an eMSTO has been detected in a large number of clusters with ages between ˜1-2 Gyr, several studies of young clusters in both MCs and in nearby galaxies do not find any evidence for a prolonged star formation history, i. e. for multiple stellar generations. These results have suggested alternative interpretation of the eMSTOs observed in intermediate-age star clusters. The eMSTO could be due to stellar rotation mimicking an age spread or to interacting binaries. In these scenarios, intermediate-age MC clusters would be simple stellar populations, in close analogy with younger clusters. Here, we provide the first evidence for an eMSTO in a young stellar cluster. We exploit multiband Hubble Space Telescope photometry to study the ˜300-Myr old star cluster NGC 1856 in the Large Magellanic Cloud and detected a broadened MSTO that is consistent with a prolonged star formation which had a duration of about 150 Myr. Below the turn-off, the main sequence (MS) of NGC 1856 is split into a red and blue component, hosting 33 ± 5 and 67 ± 5 per cent of the total number of MS stars, respectively. We discuss these findings in the context of multiple-stellar-generation, stellar-rotation, and interacting-binary hypotheses.

Stellar encounters involving neutron stars in globular cluster cores

NASA Technical Reports Server (NTRS)

Davies, M. B.; Benz, W.; Hills, J. G.

1992-01-01

Encounters between a 1.4 solar mass neutron star and a 0.8 solar mass red giant (RG) and between a 1.4 solar mass neutron star (NS) and an 0.8 solar mass main-sequence (MS) star have been successfully simulated. In the case of encounters involving an RG, bound systems are produced when the separation at periastron passage R(MIN) is less than about 2.5 R(RG). At least 70 percent of these bound systems are composed of the RG core and NS forming a binary engulfed in a common envelope of what remains of the former RG envelope. Once the envelope is ejected, a tight white dwarf-NS binary remains. For MS stars, encounters with NSs will produce bound systems when R(MIN) is less than about 3.5 R(MS). Some 50 percent of these systems will be single objects with the NS engulfed in a thick disk of gas almost as massive as the original MS star. The ultimate fate of such systems is unclear.

Red giants and yellow stragglers in the young open cluster NGC 2447

NASA Astrophysics Data System (ADS)

da Silveira, M. D.; Pereira, C. B.; Drake, N. A.

2018-06-01

In this work we analysed, using high-resolution spectroscopy, a sample of 12 single and 4 spectroscopic binary stars of the open cluster NGC 2447. For the single stars, we obtained atmospheric parameters and chemical abundances of Li, C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, Nd, Eu. Rotational velocities were obtained for all the stars. The abundances of the light elements and Eu and the rotational velocities were derived using spectral synthesis technique. We obtained a mean metallicity of [Fe/H] = -0.17 ± 0.05. We found that the abundances of all elements are similar to field giants and/or giants of open clusters, even for the s-process elements, which are enhanced as in other young open clusters. We show that the spectroscopic binaries NGC 2447-26, 38, and 42 are yellow-straggler stars, of which the primary is a giant star and the secondary a main-sequence A-type star.

A case against an X-shaped structure in the Milky Way young bulge

NASA Astrophysics Data System (ADS)

López-Corredoira, Martín

2016-09-01

Context. A number of recent papers have claimed the discovery of an X-shape structure in the bulge of our Galaxy in the population of the red clumps. Aims: We endeavor to analyze the stellar density of bulge stars in the same regions using a different stellar population that is characteristic of the young bulge (≲ 5 Gyr). Particularly, we use F0-F5 main-sequence stars with distances derived through photometric parallax. Methods: We extract these stars from extinction-corrected color-magnitude diagrams in the near-infrared of VISTA-VVV data in some bulge regions and calculate the densities along the line of sight. We take the uncertaintity in the photometric parallax and the contamination of other sources into account, and we see that these errors do not avoid the detection of a possible double peak along some lines of sight as expected for a X-shape bulge if it existed. Results: Only a single peak in the density distribution along the line of sight is observed, so apparently there is no X-shape structure for this population of stars. Nonetheless, the effects of the dispersion of absolute magnitudes in the selected population might be an alternative explanation, although in principle these effects are insufficient to explain this lack of double peak according to our calculations. Conclusions: The results of the present paper do not demonstrate that previous claims of X-shaped bulge using only red clump stars are incorrect, but there are apparently some puzzling questions if we want to maintain the validity of both the red-clump results and the results of this paper.

Red but not dead: unveiling the star-forming far-infrared spectral energy distribution of SpARCS brightest cluster galaxies at 0 < z < 1.8

NASA Astrophysics Data System (ADS)

Bonaventura, N. R.; Webb, T. M. A.; Muzzin, A.; Noble, A.; Lidman, C.; Wilson, G.; Yee, H. K. C.; Geach, J.; Hezaveh, Y.; Shupe, D.; Surace, J.

2017-08-01

We present the results of a Spitzer/Herschel infrared photometric analysis of the largest (716) and the highest-redshift (z = 1.8) sample of brightest cluster galaxies (BCGs), those from the Spitzer Adaptation of the Red-Sequence Cluster Survey Given the tension that exists between model predictions and recent observations of BCGs at z < 2, we aim to uncover the dominant physical mechanism(s) guiding the stellar mass buildup of this special class of galaxies, the most massive in the Universe and uniquely residing at the centres of galaxy clusters. Through a comparison of their stacked, broad-band, infrared spectral energy distributions (SEDs) to a variety of model templates in the literature, we identify the major sources of their infrared energy output, in multiple redshift bins between 0 < z < 1.8. We derive estimates of various BCG physical parameters from the stacked νLν SEDs, from which we infer a star-forming, as opposed to a 'red and dead' population of galaxies, producing tens to hundreds of solar masses per year down to z = 0.5. This discovery challenges the accepted belief that BCGs should only passively evolve through a series of gas-poor, minor mergers since z ˜ 4, but agrees with an improved semi-analytic model of hierarchical structure formation that predicts star-forming BCGs throughout the epoch considered. We attribute the star formation inferred from the stacked infrared SEDs to both major and minor 'wet' (gas-rich) mergers, based on a lack of key signatures (to date) of cooling-flow-induced star formation, as well as a number of observational and simulation-based studies that support this scenario.

The dynamics of post-main sequence planetary systems

NASA Astrophysics Data System (ADS)

Mustill, Alexander James

2017-06-01

The study of planetary systems after their host stars have left the main sequence is of fundamental importance for exoplanet science, as the most direct determination of the compositions of extra-Solar planets, asteroids and comets is in fact made by an analysis of the elemental abundances of the remnants of these bodies accreted into the atmospheres of white dwarfs.To understand how the accreted bodies relate to the source populations in the planetary system, and to model their dynamical delivery to the white dwarf, it is necessary to understand the effects of stellar evolution on bodies' orbits. On the red giant branch (RGB) and asymptotic giant branch (AGB) prior to becoming a white dwarf, stars expand to a large size (>1 au) and are easily deformed by orbiting planets, leading to tidal energy dissipation and orbital decay. They also lose half or more of their mass, causing the expansion of bodies' orbits. This mass loss increases the planet:star mass ratio, so planetary systems orbiting white dwarfs can be much less stable than those orbiting their main-sequence progenitors. Finally, small bodies in the system experience strong non-gravitational forces during the RGB and AGB: aerodynamic drag from the mass shed by the star, and strong radiation forces as the stellar luminosity reaches several thousand Solar luminosities.I will review these effects, focusing on planet--star tidal interactions and planet--asteroid interactions, and I will discuss some of the numerical challenges in modelling systems over their entire lifetimes of multiple Gyr.

GREEN GALAXIES IN THE COSMOS FIELD

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

Pan, Zhizheng; Kong, Xu; Fan, Lulu, E-mail: panzz@mail.ustc.edu.cn, E-mail: xkong@ustc.edu.cn

2013-10-10

We present research on the morphologies, spectra, and environments of ≈2350 'green valley' galaxies at 0.2 < z < 1.0 in the COSMOS field. The bimodality of dust-corrected NUV–r {sup +} color is used to define 'green valley'; it removes dusty star-forming galaxies from galaxies that are truly transitioning between the blue cloud and the red sequence. Morphological parameters of green galaxies are intermediate between those of blue and red galaxy populations, both on the Gini-asymmetry and the Gini-M{sub 20} planes. Approximately 60%-70% of green disk galaxies have intermediate or big bulges, and only 5%-10% are pure disk systems, basedmore » on morphological classification using the Zurich Estimator of Structural Types. The obtained average spectra of green galaxies are intermediate between blue and red ones in terms of [O II], Hα, and Hβ emission lines. Stellar population synthesis on the average spectra shows that green galaxies are on average older than blue galaxies but younger than red galaxies. Green galaxies and blue galaxies have similar projected galaxy density (Σ{sub 10}) distributions at z > 0.7. At z < 0.7, the fractions of M{sub *} < 10{sup 10.0} M{sub ☉} green galaxies located in a dense environment are found to be significantly larger than those of blue galaxies. The morphological and spectral properties of green galaxies are consistent with the transitioning population between the blue cloud and the red sequence. The possible mechanisms for quenching star formation activities in green galaxies are discussed. The importance of active galactic nucleus feedback cannot be well constrained in our study. Finally, our findings suggest that environmental conditions, most likely starvation and harassment, significantly affect the transformation of M{sub *} < 10{sup 10.0} M{sub ☉} blue galaxies into red galaxies, especially at z < 0.5.« less

Dead Star Warps Light of Red Star Artist Animation

NASA Image and Video Library

2013-04-04

This artist concept depicts an ultra-dense dead star, called a white dwarf, passing in front of a small red star. NASA planet-hunting Kepler was able to detect gravitational lensing by measuring a strangely subtle dip in the star brightness.

Significance of Environmental Density in Shocked Poststarburst Galaxy Evolution

NASA Astrophysics Data System (ADS)

Jaliff, Laura

2018-01-01

The Shocked POstarbusrt Galaxy Survey (SPOGS) comprises 1,066 galaxies undergoing the transformation from blue cloud late-type spirals to red sequence non-star-forming early-type ellipticals and lenticulars. They are selected via spectral analysis of ionized gas line ratios, which indicate shocked objects, and Balmer H-δ equivalent width, which select recently formed stars, but not active star formation. E+A galaxies (Zabludoff et al. 1996), like SPOGs, contain young stars but, unlike SPOGs, no emission lines consistent with star formation. They differ in that the quality used to discern SPOGs, their shocks, produces H-α lines that prevent them from being found via the same criteria as E+As. Thus, SPOGs can be found before being entirely stripped of their gas, and, while E+As are largely red and dead, found leaving the green valley, SPOGS are mostly entering it. The environmental density data for SPOGs was retrieved via the NASA Extragalactic Database (NED) radial velocity constrained cone tool, which provides counts and densities within spheres of radii 1, 5, and 10 Mpc from the center of search as well as relative positions and redshifts of objects. The kinematic morphology-density relation (Cappellari et al. 2011) is employed as a point of comparison for how SPOGs’ environmental densities might relate to morphological and spectroscopic factors, including tidal features, asymmetry, and color, in order to fully understand the role of environmental factors in SPOGS object evolution.

2 Micron Spectroscopy within 0&farcs;3 of Sagittarius A*

PubMed

Figer; Becklin; McLean; Gilbert; Graham; Larkin; Levenson; Teplitz; Wilcox; Morris

2000-04-10

We present moderate- (R approximately 2700) and high-resolution (R approximately 22,400) 2.0-2.4 µm spectroscopy of the central 0.1 arcsec2 of the Galaxy obtained with the facility near-infrared spectrometer (NIRSPEC) for the Keck II telescope. The composite spectra do not have any features attributable to the brightest stars in the central cluster; i.e., after background subtraction, W12CO&parl0;2-0&parr0;<2 Å. This stringent limit leads us to conclude that the majority, if not all, of the stars are hotter than typical red giants. Coupled with previously reported photometry, we conclude that the sources are likely OB main-sequence stars. In addition, the continuum slope in the composite spectrum is bluer than that of a red giant and is similar to that of the nearby hot star IRS 16NW. It is unlikely that they are late-type giants stripped of their outer envelopes because such sources would be much fainter than those observed. Given their inferred youth (tauage<20 Myr), we suggest the possibility that the stars have formed within 0.1 pc of the supermassive black hole. We find a newly identified broad-line component (VFWHM approximately 1000 km s-1) toward the 2.2178 µm [Fe iii] line located within a few arcseconds of Sagittarius A*. A similar component is not seen in the Brgamma emission.

Future Interstellar Travel Destinations: Assessing the Suitability of Nearby Red Dwarf Stars as Hosts to Habitable Life-bearing Planets

NASA Astrophysics Data System (ADS)

Guinan, Edward F.; Engle, S. G.

2013-01-01

As part of our NSF/NASA sponsored “Living with a Red Dwarf Star” program, we are carrying out a comprehensive study of red dwarf stars across the electromagnetic spectrum to assess their suitability as hosts for habitable planets. These cool, dim, long-lived, low mass stars comprise >75% of the stars in our Galaxy. Moreover an increasing number of (potentially habitable) large Earth-size planets are being found hosted by red dwarfs. With intrinsically low luminosities (L < 0.02 Lsun), the habitable zones (HZs) of hosted planets are close to their host stars (typically 0.05 AU < HZ <0.4 AU). Our study indicates red dwarf HZ planets without strong (protective) magnetic fields are especially susceptible to atmospheric erosion & loss by the star’s X-UV and wind fluxes. Also, the frequent flaring of young red dwarf stars and tidal-locking of close-in planets could challenge the development of life. But tidal locking of these planets could have some advantages for the developmenet of life. The long lifetimes of the red dwarfs (> 50 BY) could be favorable for the development of complex (possibly even intelligent) life. We discuss our results in the context of nearby red dwarfs as possible destinations for future interstellar missions program. We illustrate this with examples of the red dwarf exoplanet systems: GJ 581 and HD 85512 (both with large HZ Earth-size planets). Also we discuss the nearest star (4.3 LY) - the red dwarf - Proxima Centauri as a potential destination for future interstellar missions such proposed by Icarus Interstellar and the 100-Year Starship and StarVoyager programs. We gratefully acknowledge the support from NSF-Grant AST-10-09903, Chandra Grants GO1-12124X & GO2-13020X and HST Grant GO-10920.

Galaxy and Mass Assembly (GAMA): Morphological transformation of galaxies across the green valley

NASA Astrophysics Data System (ADS)

Bremer, M. N.; Phillipps, S.; Kelvin, L. S.; De Propris, R.; Kennedy, Rebecca; Moffett, Amanda J.; Bamford, S.; Davies, L. J. M.; Driver, S. P.; Häußler, B.; Holwerda, B.; Hopkins, A.; James, P. A.; Liske, J.; Percival, S.; Taylor, E. N.

2018-05-01

We explore constraints on the joint photometric and morphological evolution of typical low redshift galaxies as they move from the blue cloud through the green valley and on to the red sequence. We select Galaxy And Mass Assembly (GAMA) survey galaxies with 10.25 < log(M*/M⊙) < 10.75 and z < 0.2 classified according to their intrinsic u* - r* colour. From single component Sérsic fits, we find that the stellar mass-sensitive K-band profiles of red and green galaxy populations are very similar while g-band profiles indicate more disc-like morphologies for the green galaxies: apparent (optical) morphological differences arise primarily from radial mass-to-light ratio variations. Two-component fits show that most green galaxies have significant bulge and disc components and that the blue to red evolution is driven by colour change in the disc. Together, these strongly suggest that galaxies evolve from blue to red through secular disc fading and that a strong bulge is present prior to any decline in star formation. The relative abundance of the green population implies a typical time-scale for traversing the green valley ˜1-2 Gyr and is independent of environment, unlike that of the red and blue populations. While environment likely plays a rôle in triggering the passage across the green valley, it appears to have little effect on time taken. These results are consistent with a green valley population dominated by (early type) disc galaxies that are insufficiently supplied with gas to maintain previous levels of disc star formation, eventually attaining passive colours. No single event is needed to quench their star formation.

The Contribution of Stellar Winds to Cosmic Ray Production

NASA Astrophysics Data System (ADS)

Seo, Jeongbhin; Kang, Hyesung; Ryu, Dongsu

2018-04-01

Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The wind mechanical energy of a massive star deposited to the interstellar medium can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity by all massive stars in the Galaxy is about Lw ≈ 1.1×1041 ergs, which is about 1/4 of the power of supernova explosions, LSN ≈ 4.8×1041 ergs. If we assume that ˜1-1% of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds are expected to make a significant contribution to GCR production, though lower than that of supernova remnants.

Tests of two convection theories for red giant and red supergiant envelopes

NASA Technical Reports Server (NTRS)

Stothers, Richard B.; Chin, Chao-Wen

1995-01-01

Two theories of stellar envelope convection are considered here in the context of red giants and red supergiants of intermediate to high mass: Boehm-Vitense's standard mixing-length theory (MLT) and Canuto & Mazzitelli's new theory incorporating the full spectrum of turbulence (FST). Both theories assume incompressible convection. Two formulations of the convective mixing length are also evaluated: l proportional to the local pressure scale height (H(sub P)) and l proportional to the distance from the upper boundary of the convection zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red phase of core helium burning. Since the theoretically predicted effective temperatures for cool stars are known to be sensitive to the assigned value of the mixing length, this quantity has been individually calibrated for each evolutionary sequence. The calibration is done in a composite Hertzsprung-Russell diagram for the red giant and red supergiant members of well-observed Galactic open clusters. The MLT model requires the constant of proportionality for the convective mixing length to vary by a small but statistically significant amount with stellar mass, whereas the FST model succeeds in all cases with the mixing lenghth simply set equal to z. The structure of the deep stellar interior, however, remains very nearly unaffected by the choices of convection theory and mixing lenghth. Inside the convective envelope itself, a density inversion always occurs, but is somewhat smaller for the convectively more efficient MLT model. On physical grounds the FST model is preferable, and seems to alleviate the problem of finding the proper mixing length.

Using the XMM-Newton Optical Monitor to Study Cluster Galaxy Evolution

NASA Technical Reports Server (NTRS)

Miller, Neal A.; O'Steen, Richard; Yen, Steffi; Kuntz, K. D.; Hammer, Derek

2012-01-01

We explore the application of XMM Newton Optical Monitor (XMM-OM) ultraviolet (UV) data to study galaxy evolution. Our sample is constructed as the intersection of all Abell clusters with z < 0.05 and having archival XMM-OM data in either the UVM2 or UVW1 filters, plus optical and UV photometry from the Sloan Digital Sky Survey and GALEX, respectively. The 11 resulting clusters include 726 galaxies with measured redshifts, 520 of which have redshifts placing them within their parent Abell clusters. We develop procedures for manipulating the XMM-OM images and measuring galaxy photometry from them, and we confirm our results via comparison with published catalogs. Color-magnitude diagrams (CMDs) constructed using the XMM-OM data along with SDSS optical data show promise for evolutionary studies, with good separation between red and blue sequences and real variation in the width of the red sequence that is likely indicative of differences in star formation history. This is particularly true for UVW1 data, as the relative abundance of data collected using this filter and its depth make it an attractive choice. Available tools that use stellar synthesis libraries to fit the UV and optical photometric data may also be used, thereby better describing star formation history within the past billion years and providing estimates of total stellar mass that include contributions from young stars. Finally, color-color diagrams that include XMM-OM UV data appear useful to the photometric identification of both extragalactic and stellar sources.

THREE DISCRETE GROUPS WITH HOMOGENEOUS CHEMISTRY ALONG THE RED GIANT BRANCH IN THE GLOBULAR CLUSTER NGC 2808

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

Carretta, E., E-mail: eugenio.carretta@oabo.inaf.it

2014-11-10

We present the homogeneous reanalysis of Mg and Al abundances from high resolution UVES/FLAMES spectra for 31 red giants in the globular cluster NGC 2808. We found a well defined Mg-Al anticorrelation reaching a regime of subsolar Mg abundance ratios, with a spread of about 1.4 dex in [Al/Fe]. The main result from the improved statistics of our sample is that the distribution of stars is not continuous along the anticorrelation because they are neatly clustered into three distinct clumps, each with different chemical compositions. One group (P) shows a primordial composition of field stars of similar metallicity, and the other twomore » (I and E) have increasing abundances of Al and decreasing abundances of Mg. The fraction of stars we found in the three components (P: 68%, I: 19%, E: 13%) is in excellent agreement with the ratios computed for the three distinct main sequences in NGC 2808: for the first time there is a clear correspondence between discrete photometric sequences of dwarfs and distinct groups of giants with homogeneous chemistry. The composition of the I group cannot be reproduced by mixing of matter with extreme processing in hot H-burning and gas with pristine, unprocessed composition, as also found in the recent analysis of three discrete groups in NGC 6752. This finding suggests that different classes of polluters were probably at work in NGC 2808 as well.« less

Using the XMM-Newton Optical Monitor to Study Cluster Galaxy Evolution

NASA Astrophysics Data System (ADS)

Miller, Neal A.; O'Steen, Richard; Yen, Steffi; Kuntz, K. D.; Hammer, Derek

2012-02-01

We explore the application of XMM-Newton Optical Monitor (XMM-OM) ultraviolet (UV) data to study galaxy evolution. Our sample is constructed as the intersection of all Abell clusters with z < 0.05 and having archival XMM-OM data in either the UVM2 or UVW1 filters, plus optical and UV photometry from the Sloan Digital Sky Survey and GALEX, respectively. The 11 resulting clusters include 726 galaxies with measured redshifts, 520 of which have redshifts placing them within their parent Abell clusters. We develop procedures for manipulating the XMM-OM images and measuring galaxy photometry from them, and we confirm our results via comparison with published catalogs. Color-magnitude diagrams (CMDs) constructed using the XMM-OM data along with SDSS optical data show promise for evolutionary studies, with good separation between red and blue sequences and real variation in the width of the red sequence that is likely indicative of differences in star formation history. This is particularly true for UVW1 data, as the relative abundance of data collected using this filter and its depth make it an attractive choice. Available tools that use stellar synthesis libraries to fit the UV and optical photometric data may also be used, thereby better describing star formation history within the past billion years and providing estimates of total stellar mass that include contributions from young stars. Finally, color-color diagrams that include XMM-OM UV data appear useful to the photometric identification of both extragalactic and stellar sources.

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets. II. Effect of stellar metallicity

NASA Astrophysics Data System (ADS)

Bolmont, E.; Gallet, F.; Mathis, S.; Charbonnel, C.; Amard, L.; Alibert, Y.

2017-08-01

Observations of hot-Jupiter exoplanets suggest that their orbital period distribution depends on the metallicity of the host stars. We investigate here whether the impact of the stellar metallicity on the evolution of the tidal dissipation inside the convective envelope of rotating stars and its resulting effect on the planetary migration might be a possible explanation for this observed statistical trend. We use a frequency-averaged tidal dissipation formalism coupled to an orbital evolution code and to rotating stellar evolution models in order to estimate the effect of a change of stellar metallicity on the evolution of close-in planets. We consider here two different stellar masses: 0.4 M⊙ and 1.0 M⊙ evolving from the early pre-main sequence phase up to the red-giant branch. We show that the metallicity of a star has a strong effect on the stellar parameters, which in turn strongly influence the tidal dissipation in the convective region. While on the pre-main sequence, the dissipation of a metal-poor Sun-like star is higher than the dissipation of a metal-rich Sun-like star; on the main sequence it is the opposite. However, for the 0.4 M⊙ star, the dependence of the dissipation with metallicity is much less visible. Using an orbital evolution model, we show that changing the metallicity leads to different orbital evolutions (e.g., planets migrate farther out from an initially fast-rotating metal-rich star). Using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more steps are needed to improve our model to try to quantitatively fit our results to the observations. Specifically, we need to improve the treatment of the rotation evolution in the orbital evolution model, and ultimately we need to consistently couple the orbital model to the stellar evolution model.

Very Low Mass Stars with Extremely Low Metallicity in the Milky Way's Halo

NASA Astrophysics Data System (ADS)

Aoki, Wako; Beers, Timothy C.; Takuma, Suda; Honda, Satoshi; Lee, Young Sun

2015-08-01

Large surveys and follow-up spectroscopic studies in the past few decades have been providing chemical abundance data for a growing number of very metal-poor ([Fe/H] <-2) stars. Most of them are red giants or main-sequence turn-off stars having masses near 0.8 solar masses. Lower mass stars with extremely low metallicity ([Fe/H] <-3) have yet to be well explored. Our high-resolution spectroscopic study for very metal-poor stars found with SDSS has identified four cool main-sequence stars with [Fe/H] <-2.5 among 137 objects (Aoki et al. 2013, AJ, 145, 13). The effective temperatures of these stars are 4500--5000 K, corresponding to a mass of around 0.5 solar masses. Our standard analysis of the high-resolution spectra based on 1D-LTE model atmospheres have obtained self-consistent chemical abundances for these objects, assuming small values of micro-turbulent velocities compared with giants and turn-off stars. The low temperature of the atmospheres of these objects enables us to measure their detailed chemical abundances. Interestingly, two of the four stars have extreme chemical abundance patterns: one has the largest excesses of heavy neutron-capture elements associated with the r-process abundance pattern known to date (Aoki et al. 2010, ApJL 723, L201), and the other exhibits low abundances of the alpha-elements and odd-Z elements, suggested to be the signatures of the yields of very massive stars ( >100 solar masses; Aoki et al. 2014, Science 345, 912). Although the sample size is still small, these results indicate the potential of very low-mass stars as probes to study the early stages of the Milky Way's halo formation.

Very Low-Mass Stars with Extremely Low Metallicity in the Milky Way's Halo

NASA Astrophysics Data System (ADS)

Aoki, Wako; Beers, Timothy C.; Suda, Takuma; Honda, Satoshi; Lee, Young Sun

2016-08-01

Large surveys and follow-up spectroscopic studies in the past few decades have been providing chemical abundance data for a growing number of very metal-poor ([Fe/H] <-2) stars. Most of them are red giants or main-sequence turn-off stars having masses near 0.8 solar masses. Lower mass stars with extremely low metallicity ([Fe/H] <-3) are yet to be explored. Our high-resolution spectroscopic study for very metal-poor stars found with SDSS has identified four cool main-sequence stars with [Fe/H] <-2.5 among 137 objects (Aoki et al. 2013). The effective temperatures of these stars are 4500-5000 K, corresponding to a mass of around 0.5 solar masses. Our standard analysis of the high-resolution spectra based on 1D-LTE model atmospheres has obtained self-consistent chemical abundances for these objects, assuming small values of micro-turbulent velocities compared with giants and turn-off stars. The low temperature of the atmospheres of these objects enables us to measure their detailed chemical abundances. Interestingly, two of the four stars have extreme chemical-abundance patterns: one has the largest excesses of heavy neutron-capture elements associated with the r-process abundance pattern known to date (Aoki et al. 2010), and the other exhibits low abundances of the α-elements and odd-Z elements, suggested to be signatures of the yields of very massive stars (> 100 solar masses; Aoki et al. 2014). Although the sample size is still small, these results indicate the potential of very low-mass stars as probes to study the early stages of the Milky Way's halo formation.

The Optical Gravitational Lensing Experiment: Red Clump Stars as a Distance Indicator.

PubMed

Udalski

2000-03-01

We present relation of the mean I-band brightness of red clump stars on metallicity. Red clump stars were proposed to be a very attractive standard candle for distance determination. The calibration is based on 284 nearby red giant stars whose high-quality spectra made it possible to determine accurate individual metal abundances. High-quality parallaxes (sigmapi&solm0;pi<10%) and photometry of these very bright stars come from Hipparcos measurements. Metallicity of the sample covers a large range: -0.6 dex<&sqbl0;Fe&solm0;H&sqbr0;<+0.2 dex. We find a weak dependence of the mean I-band brightness on metallicity ( approximately 0.13 mag dex-1). What is more important, the range of metallicity of the Hipparcos sample partially overlaps with metallicity of field giants in the LMC, thus making it possible to determine the distance to the LMC by almost direct comparison of brightness of the local Hipparcos red clump giants with that of LMC stars. Photometry of field red clump giants in nine low-extinction fields of the LMC halo collected during the OGLE II microlensing survey compared with the Hipparcos red clump stars data yields the distance modulus to the LMC: &parl0;m-M&parr0;LMC=18.24+/-0.08 mag.

Mass-losing M supergiants in the solar neighborhood

NASA Technical Reports Server (NTRS)

Jura, M.; Kleinmann, S. G.

1990-01-01

A list of the 21 mass-losing red supergiants (20 M type, one G type; L greater than 100,000 solar luminosities) within 2.5 kpc of the sun is compiled. These supergiants are highly evolved descendants of main-sequence stars with initial masses larger than 20 solar masses. The surface density is between about 1 and 2/sq kpc. As found previously, these stars are much less concentrated toward the Galactic center than W-R stars, which are also highly evolved massive stars. Although with considerable uncertainty, it is estimated that the mass return by the M supergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpc yr. In the hemisphere facing the Galactic center there is much less mass loss from M supergiants than from W-R stars, but, in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 200,000 and 400,000 yr. During this phase, a star of initially at least 20 solar masses returns perhaps 3-10 solar masses into the interstellar medium.

An outburst powered by the merging of two stars inside the envelope of a giant

NASA Astrophysics Data System (ADS)

Hillel, Shlomi; Schreier, Ron; Soker, Noam

2017-11-01

We conduct 3D hydrodynamical simulations of energy deposition into the envelope of a red giant star as a result of the merger of two close main sequence stars or brown dwarfs, and show that the outcome is a highly non-spherical outflow. Such a violent interaction of a triple stellar system can explain the formation of `messy', I.e. lacking any kind of symmetry, planetary nebulae and similar nebulae around evolved stars. We do not simulate the merging process, but simply assume that after the tight binary system enters the envelope of the giant star the interaction with the envelope causes the two components, stars or brown dwarfs, to merge and liberate gravitational energy. We deposit the energy over a time period of about 9 h, which is about 1 per cent of the the orbital period of the merger product around the centre of the giant star. The ejection of the fast hot gas and its collision with previously ejected mass are very likely to lead to a transient event, I.e. an intermediate luminosity optical transient.

Variable Stars in M13. II.The Red Variables and the Globular Cluster Period-Luminosity Relation

NASA Astrophysics Data System (ADS)

Osborn, W.; Layden, A.; Kopacki, G.; Smith, H.; Anderson, M.; Kelly, A.; McBride, K.; Pritzl, B.

2017-06-01

New CCD observations have been combined with archival data to investigate the nature of the red variables in the globular cluster M13. Mean magnitudes, colors and variation ranges on the UBVIC system have been determined for the 17 cataloged red variables. 15 of the stars are irregular or semi-regular variables that lie at the top of the red giant branch in the color-magnitude diagram. Two stars are not, including one with a well-defined period and a light curve shape indicating it is an ellipsoidal or eclipsing variable. All stars redder than (V-IC)0=1.38 mag vary, with the amplitudes being larger with increased stellar luminosity and with bluer filter passband. Searches of the data for periodicities yielded typical variability cycle times ranging from 30 d up to 92 d for the most luminous star. Several stars have evidence of multiple periods. The stars' period-luminosity diagram compared to those from microlensing survey data shows that most M13 red variables are overtone pulsators. Comparison with the diagrams for other globular clusters shows a correlation between red variable luminosity and cluster metallicity.

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

Schmidt, Edward G., E-mail: eschmidt1@unl.edu

We have obtained VR photometry of 447 Cepheid variable star candidates with declinations north of -14 Degree-Sign 30', most of which were identified using the Northern Sky Variability Survey (NSVS) data archive. Periods and other photometric properties were derived from the combination of our data with the NSVS data. Atmospheric parameters were determined for 81 of these stars from low-resolution spectra. The identification of type II Cepheids based on the data presented in all four papers in this series is discussed. On the basis of spectra, 30 type II Cepheids were identified while 53 variables were identified as cool, mainmore » sequence stars and 283 as red giants following the definitions in Paper III. An additional 30 type II Cepheids were identified on the basis of light curves. The present classifications are compared with those from the Machine-learned All Sky Automated Survey Classification Catalog for 174 stars in common.« less

A Rogues’ Gallery of Andromeda's Dwarf Galaxies. I. A Predominance of Red Horizontal Branches

NASA Astrophysics Data System (ADS)

Martin, Nicolas F.; Weisz, Daniel R.; Albers, Saundra M.; Bernard, Edouard; Collins, Michelle L. M.; Dolphin, Andrew E.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Laevens, Benjamin; Lewis, Geraint F.; Mackey, A. Dougal; McConnachie, Alan; Rich, R. Michael; Skillman, Evan D.

2017-11-01

We present homogeneous, sub-horizontal branch photometry of 20 dwarf spheroidal satellite galaxies of M31 observed with the Hubble Space Telescope. Combining our new data for 16 systems with archival data in the same filters for another four, we show that Andromeda dwarf spheroidal galaxies favor strikingly red horizontal branches or red clumps down to ˜104.2 L ⊙ (M V ˜ -5.8). The age-sensitivity of horizontal branch stars implies that a large fraction of the M31 dwarf galaxies have extended star formation histories (SFHs), and appear inconsistent with early star formation episodes that were rapidly shutdown. Systems fainter than ˜105.5 L ⊙ show the widest range in the ratios and morphologies of red and blue horizontal branches, indicative of both complex SFHs and a diversity in quenching timescales and/or mechanisms, which is qualitatively different from what is currently known for faint Milky Way (MW) satellites of comparable luminosities. Our findings bolster similar conclusions from recent deeper data for a handful of M31 dwarf galaxies. We discuss several sources for diversity of our data such as varying halo masses, patchy reionization, mergers/accretion, and the environmental influence of M31 and the Milky Way on the early evolution of their satellite populations. A detailed comparison between the histories of M31 and MW satellites would shed signifiant insight into the processes that drive the evolution of low-mass galaxies. Such a study will require imaging that reaches the oldest main-sequence turnoffs for a significant number of M31 companions.

CNO isotopes in red giant stars

NASA Technical Reports Server (NTRS)

Wannier, P. G.

1985-01-01

The production and distribution of the CNO nuclides is discussed in light of observed abundance ratios in red giants and in the interstellar medium. Isotope abundances have been measured in the atmospheres and in the recent ejecta of cool giants, including carbon stars, S-type stars and red supergiants as well as in oxygen-rich giants making their first ascent of the giant branch. Several of the observations suggest revision of currently accepted nuclear cross-sections and of the mixing processes operating in giant envelopes. By comparing red giant abundances with high-quality observations of the interstellar medium, conclusions are reached about the contribution of intermediate-mass stars to galactic nuclear evolution. The three oxygen isotopes, O-16, -17 and -18, are particularly valuable for such comparison because they reflect three different stages of stellar nucleosynthesis. One remarkable result comes from observations of O-17/O-18 in several classes of red giant stars. The observed range of values for red giants excludes the entire range of values seen in interstellar molecular clouds. Furthermore, both the observations of stars and interstellar clouds exclude the isotopic ratio found in the solar system.

Seek a Minor Sun: The Distribution of Habitable Planets in the Hertzsprung-Russell-Rosenberg Diagram

NASA Astrophysics Data System (ADS)

Gaidos, Eric

2015-07-01

The Sun-Earth systems has long been used as a template to understand habitable planets around other stars and to develop missions to seek them. However, two decades of exoplanet studies have shown that many, if not most planetary systems around G dwarf stars do not resemble the Solar System. Moreover, an objective census of our Galaxy might ignore solar- type stars and focus on M dwarfs, which constitute some 80% of all stars in the neighborhood. Recent work has shown that M dwarfs have more close-in planets than solar-type stars, and perhaps more planets in the "habitable zone" defined by stellar irradiation. M dwarfs also burn hydrogen over a vastly longer time; slow evolution on the main sequence means a planet can remain habitable for much longer, providing a more permissive environment for the evo- lution of life and intelligence. If M dwarfs are such compelling locales to look for life, why are we ourselves not orbiting a red Sun?

Star formation history: Modeling of visual binaries

NASA Astrophysics Data System (ADS)

Gebrehiwot, Y. M.; Tessema, S. B.; Malkov, O. Yu.; Kovaleva, D. A.; Sytov, A. Yu.; Tutukov, A. V.

2018-05-01

Most stars form in binary or multiple systems. Their evolution is defined by masses of components, orbital separation and eccentricity. In order to understand star formation and evolutionary processes, it is vital to find distributions of physical parameters of binaries. We have carried out Monte Carlo simulations in which we simulate different pairing scenarios: random pairing, primary-constrained pairing, split-core pairing, and total and primary pairing in order to get distributions of binaries over physical parameters at birth. Next, for comparison with observations, we account for stellar evolution and selection effects. Brightness, radius, temperature, and other parameters of components are assigned or calculated according to approximate relations for stars in different evolutionary stages (main-sequence stars, red giants, white dwarfs, relativistic objects). Evolutionary stage is defined as a function of system age and component masses. We compare our results with the observed IMF, binarity rate, and binary mass-ratio distributions for field visual binaries to find initial distributions and pairing scenarios that produce observed distributions.

The black tide model of QSOs

NASA Technical Reports Server (NTRS)

Young, P. J.; Shields, G. A.; Wheeler, J. C.

1977-01-01

The paper develops certain aspects of a model wherein a QSO is a massive black hole located in a dense galactic nucleus, with its growth and luminosity fueled by tidal disruption of passing stars. Cross sections for tidal disruptions are calculated, taking into account the thermal energy of stars, relativistic effects, and partial disruption removing only the outer layers of a star. Accretion rates are computed for a realistic distribution of stellar masses and evolutionary phases, the effect of the black hole on the cluster distribution is examined, and the red-giant disruption rate is evaluated for hole mass of at least 300 million solar masses, the cutoff of disruption of main-sequence stars. The results show that this black-tide model can explain QSO luminosities of at least 1 trillion suns if the black hole remains almost maximally Kerr as it grows above 100 million solar masses and if 'loss-cone' depletion of the number of stars in disruptive orbits is unimportant.

Detection of a Red Supergiant Progenitor Star of a Type II-Plateau Supernova

NASA Astrophysics Data System (ADS)

Smartt, Stephen J.; Maund, Justyn R.; Hendry, Margaret A.; Tout, Christopher A.; Gilmore, Gerard F.; Mattila, Seppo; Benn, Chris R.

2004-01-01

We present the discovery of a red supergiant star that exploded as supernova 2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova explosion, and subsequent HST images confirm the positional coincidence of the supernova with a single resolved star that is a red supergiant of 8+4-2 solar masses. This confirms both stellar evolution models and supernova theories predicting that cool red supergiants are the immediate progenitor stars of type II-plateau supernovae.

CNO isotopes in red giant stars

NASA Technical Reports Server (NTRS)

Wannier, P. G.

1985-01-01

Observational data on CNO abundance ratios in red giants and the interstellar medium (ISM) are analyzed for the implications for the production and distribution of CNO nuclides. The data included isotope abundance measurements for the atmospheres and recent ejecta of cool giants, e.g., carbon stars, S-type stars, red supergiants and oxygen-rich giants beginning an ascent of the giant branch. The contribution of intermediate-mass stars to galactic nuclear evolution is discussed after comparing red giant abundances with ISM abundances, particularly the isotopes O-16, -17 and -18. The O-12/O-18 ratios of red giants are distinctly different from those in interstellar molecular clouds. The CNO values also vary widely from the values found in the solar system.

Extended Star Formation or a Range of Stellar Rotation Velocities? The Nature of Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters

NASA Astrophysics Data System (ADS)

Goudfrooij, Paul

2016-10-01

Recently, deep color-magnitude diagrams (CMDs) from HST data revealed that several massive intermediate-age star clusters in the Magellanic Clouds exhibit extended main-sequence turn-offs (eMSTOs), and in some cases also dual red clumps. This poses serious questions regarding the mechanisms responsible for the formation of massive star clusters and their well-known light-element abundance variations. The nature of eMSTOs is currently a hotly debated topic of study. Several recent studies indicate that the eMSTOs are caused by an age spread of about 100-500 Myr among cluster stars, while other studies indicate that eMSTOs can be caused by a coeval population in which the relevant stars span a range of rotation velocities. Formal evidence to (dis-)prove either scenario still remains at large, mainly because the available stellar tracks that incorporate the effects of rotation are only available for masses > 1.7 Msun whereas the stars in the known eMSTOs of intermediate-age clusters are less massive. To circumvent this issue, we identified a massive star cluster in the Large Magellanic Cloud (LMC) that has the right dynamical properties to host an eMSTO along with an age at which the effects of age spreads to CMD morphology are substantially different from those of spreads of rotation rates: the 600 Myr old cluster NGC 1831. We propose to obtain deep WFC3/UVIS imaging with filters F336W and F814W to analyze the morphologies of the MSTO and upper MS regions of NGC 1831 at high precision and compare with model predictions. This will have a lasting impact on our understanding of the eMSTO phenomenon and of star cluster formation in general.

An Extreme Analogue of ɛ Aurigae: An M-giant Eclipsed Every 69 Years by a Large Opaque Disk Surrounding a Small Hot Source

NASA Astrophysics Data System (ADS)

Rodriguez, Joseph E.; Stassun, Keivan G.; Lund, Michael B.; Siverd, Robert J.; Pepper, Joshua; Tang, Sumin; Kafka, Stella; Gaudi, B. Scott; Conroy, Kyle E.; Beatty, Thomas G.; Stevens, Daniel J.; Shappee, Benjamin J.; Kochanek, Christopher S.

2016-05-01

We present TYC 2505-672-1 as a newly discovered and remarkable eclipsing system comprising an M-type red giant that undergoes a ˜3.45 year long, near-total eclipse (depth of ˜4.5 mag) with a very long period of ˜69.1 years. TYC 2505-672-1 is now the longest-period eclipsing binary system yet discovered, more than twice as long as that of the currently longest-period system, ɛ Aurigae. We show from analysis of the light curve including both our own data and historical data spanning more than 120 years and from modeling of the spectral energy distribution, both before and during eclipse, that the red giant primary is orbited by a moderately hot source (Teff ≈ 8000 K) that is itself surrounded by an extended, opaque circumstellar disk. From the measured ratio of luminosities, the radius of the hot companion must be in the range of 0.1-0.5 R⊙ (depending on the assumed radius of the red giant primary), which is an order of magnitude smaller than that for a main sequence A star and 1-2 orders of magnitude larger than that for a white dwarf. The companion is therefore most likely a “stripped red giant” subdwarf-B type star destined to become a He white dwarf. It is, however, somewhat cooler than most sdB stars, implying a very low mass for this “pre-He-WD” star. The opaque disk surrounding this hot source may be a remnant of the stripping of its former hydrogen envelope. However, it is puzzling how this object became stripped, given that it is at present so distant (orbital semimajor axis of ˜24 au) from the current red giant primary star. Extrapolating from our calculated ephemeris, the next eclipse should begin in early UT 2080 April and end in mid UT 2083 September (eclipse center UT 2081 December 24). In the meantime, radial velocity observations would establish the masses of the components, and high-cadence UV observations could potentially reveal oscillations of the hot companion that would further constrain its evolutionary status. In any case, this system is poised to become an exemplar of a very rare class of systems, even more extreme in several respects than the well studied archetype ɛ Aurigae.

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

Rodriguez, Joseph E.; Stassun, Keivan G.; Lund, Michael B.

We present TYC 2505-672-1 as a newly discovered and remarkable eclipsing system comprising an M-type red giant that undergoes a ∼3.45 year long, near-total eclipse (depth of ∼4.5 mag) with a very long period of ∼69.1 years. TYC 2505-672-1 is now the longest-period eclipsing binary system yet discovered, more than twice as long as that of the currently longest-period system, ϵ Aurigae. We show from analysis of the light curve including both our own data and historical data spanning more than 120 years and from modeling of the spectral energy distribution, both before and during eclipse, that the red giantmore » primary is orbited by a moderately hot source ( T {sub eff} ≈ 8000 K) that is itself surrounded by an extended, opaque circumstellar disk. From the measured ratio of luminosities, the radius of the hot companion must be in the range of 0.1–0.5 R {sub ⊙} (depending on the assumed radius of the red giant primary), which is an order of magnitude smaller than that for a main sequence A star and 1–2 orders of magnitude larger than that for a white dwarf. The companion is therefore most likely a “stripped red giant” subdwarf-B type star destined to become a He white dwarf. It is, however, somewhat cooler than most sdB stars, implying a very low mass for this “pre-He-WD” star. The opaque disk surrounding this hot source may be a remnant of the stripping of its former hydrogen envelope. However, it is puzzling how this object became stripped, given that it is at present so distant (orbital semimajor axis of ∼24 au) from the current red giant primary star. Extrapolating from our calculated ephemeris, the next eclipse should begin in early UT 2080 April and end in mid UT 2083 September (eclipse center UT 2081 December 24). In the meantime, radial velocity observations would establish the masses of the components, and high-cadence UV observations could potentially reveal oscillations of the hot companion that would further constrain its evolutionary status. In any case, this system is poised to become an exemplar of a very rare class of systems, even more extreme in several respects than the well studied archetype ϵ Aurigae.« less

Delayed Gratification Habitable Zones (DG-HZs): When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution

NASA Astrophysics Data System (ADS)

Stern, S. A.

2002-09-01

Late in the Sun's evolution it, like all low and moderate mass stars, it will burn as a red giant, generating 1000s of solar luminosities for a few tens of millions of years. A dozen years ago this stage of stellar evolution was predicted to create observable sublimation signatures in systems where Kuiper Belts (KBs) are extant (Stern et al. 1990, Nature, 345, 305); recently, the SWAS spacecraft detected such systems (Melnick et al. 2001, 412, 160). During the red giant phase, the habitable zone of our solar system will lie in the region where Triton, Pluto-Charon, and KBOs orbit. Compared to the 1 AU habitable zone where Earth resided early in the solar system's history, this "delayed gratification habitable zone (DG-HZ)" will enjoy a far less biologically hazardous environment-- with far lower harmful UV radiation levels from the Sun, and a far quieter collisional environment. Objects like Triton, Pluto-Charon, and KBOs, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Sun's DG-HZ may only be of academic interest owing to its great separation from us in time. However, several 108 approximately solar-type Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our solar system (and as inferred in numerous main sequence stellar disk systems), then DG-HZs form a kind of niche habitable zone that is likely to be numerically common in the galaxy. I will show the calculated temporal evolution of DG-HZs around various stellar types using modern stellar evolution luminosity tracks, and then discuss various aspects of DG-HZs, including the effects of stellar pulsations and mass loss winds. This work was supported by NASA's Origins of Solar Systems Program.

A SIMPLE CONNECTION BETWEEN THE NEAR- AND MID-INFRARED EMISSION OF GALAXIES AND THEIR STAR FORMATION RATES

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

Mentuch, Erin; Abraham, Roberto G.; Zibetti, Stefano

2010-12-20

We have measured the near-infrared colors and the fluxes of individual pixels in 68 galaxies common to the Spitzer Infrared Nearby Galaxies Survey and the Large Galaxy Atlas Survey. Pixels from each galaxy are grouped into regions of increasingly red near-infrared colors. As expected, the majority of pixels are shown to have relatively constant NIR flux ratios (log{sub 10} I{sub 3.6}/I{sub 1.25} = -0.30 {+-} 0.07 and log{sub 10} I{sub 4.5}/I{sub 3.6} = -0.19 {+-} 0.02), representing the blackbody continuum emission of main sequence stars. However, pixels with red NIR colors correspond to pixels with higher H{sub {alpha}} emission andmore » dust extinction. We show that the NIR colors are correlated to both quantities, with the strongest correlation to the intrinsic H{sub {alpha}} emission. In addition, in regions of high star formation, the average intensity of pixels in red-excess regions (at 1.25 {mu}m, 3.6 {mu}m, 4.5 {mu}m, 5.6 {mu}m, 8.0 {mu}m and 24 {mu}m) scales linearly with the intrinsic intensity of H{alpha} emission, and thus with the star formation rate (SFR) within the pixel. This suggests that most NIR-excess regions are not red because their light is being depleted by absorption. Instead, they are red because additional infrared light is being contributed by a process linked to star formation. This is surprising because the shorter wavelength bands in our study (1.25 {mu}m-5.6 {mu}m) do not probe emission from cold (10-20 K) and warm (50-100 K) dust associated with star formation in molecular clouds. However, emission from hot dust (700-1000 K) and/or polycyclic aromatic hydrocarbon (PAH) molecules can explain the additional emission seen at the shorter wavelengths in our study. The contribution from hot dust and/or PAH emission at 2 {mu}m-5 {mu}m and PAH emission at 5.6 {mu}m and 8.0 {mu}m scales linearly with warm dust emission at 24 {mu}m and the intrinsic H{alpha} emission. Since both are tied to the SFR, our analysis shows that the NIR excess continuum emission and PAH emission at {approx}1-8 {mu}m can be added to spectral energy distribution models in a very straightforward way, by simply adding an additional component to the models that scales linearly with SFR.« less

Hot Subluminous Stars

NASA Astrophysics Data System (ADS)

Heber, U.

2016-08-01

Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW Vir systems from eclipse timings. The high incidence of circumbinary substellar objects suggests that most of the planets are formed from the remaining CE material (second generation planets). Several types of pulsating star have been discovered among hot subdwarf stars, the most common are the gravity-mode sdB pulsators (V1093 Her) and their hotter siblings, the p-mode pulsating V361 Hya stars. Another class of multi-periodic pulsating hot subdwarfs has been found in the globular cluster ω Cen that is unmatched by any field star. Asteroseismology has advanced enormously thanks to the high-precision Kepler photometry and allowed stellar rotation rates to be determined, the interior structure of gravity-mode pulsators to be probed and stellar ages to be estimated. Rotation rates turned out to be unexpectedly slow calling for very efficient angular momentum loss on the red giant branch or during the helium core flash. The convective cores were found to be larger than predicted by standard stellar evolution models requiring very efficient angular momentum transport on the red giant branch. The masses of hot subdwarf stars, both single or in binaries, are the key to understand the stars’ evolution. A few pulsating sdB stars in eclipsing binaries have been found that allow both techniques to be applied for mass determination. The results, though few, are in good agreement with predictions from binary population synthesis calculations. New classes of binaries, hosting so-called extremely low mass (ELM) white dwarfs (M < 0.3 M ⊙), have recently been discovered, filling a gap in the mosaic of binary stellar evolution. Like most sdB stars the ELM white dwarfs are the stripped cores of red giants, the known companions are either white dwarfs, neutron stars (pulsars) or F- or A-type main sequence stars (“EL CVn” stars). In the near future, the Gaia mission will provide high-precision astrometry for a large sample of subdwarf stars to disentangle the different stellar populations in the field and to compare the field subdwarf population with the globular clusters’ hot subdwarfs. New fast-moving subdwarfs will allow the mass of the Galactic dark matter halo to be constrained and additional unbound hyper-velocity stars may be discovered. Subdwarf O/B stars and extremely low mass white dwarfs: atmospheric parameters and abundances, formation and evolution, binaries, planetary companions, pulsation, and kinematics.

Hey There Edgar Snow, What Happened to the Red Star over Yan'an?

ERIC Educational Resources Information Center

Boshier, Roger; Huang, Yan

2008-01-01

Edgar Snow scored an extraordinary scoop in 1936 when he persuaded Mao Zedong to tell his story. The resulting book--"Red Star Over China"--was a best-seller in the West and translated editions caused a sensation in China. Adult education was the centrepiece of Communist revolution and featured prominently in Red Star. It is now the…

FOC Imaging of the Dusty Envelopes of Mass-Losing Supergiants

NASA Astrophysics Data System (ADS)

Kastner, Joel

1996-07-01

Stars more massive than 10 M_odot are destined to explode as supernovae {SN}. Pre-SN mass loss can prolong core buildup, and the rate and duration of mass loss therefore largely determines a massive star's post-main sequence evolution and its position in the H-R diagram prior to SN detonation. The envelope ejected by a mass-losing supergiant also plays an important role in the formation and evolution of a SN remnant. We propose to investigate these processes with HST. We will use the FOC to image two massive stars that are in different stages of post-main sequence evolution: VY CMa, the prototype for a class of heavily mass-losing OH/IR supergiants, and HD 179821, a post-red supergiant that is likely in transition to the Wolf-Rayet phase. Both are known to possess compact reflection nebulae, but ground-based techniques are unable to separate the inner nebulosities from the PSF of the central stars. We will use the unparalleled resolution of the FOC to probe the structure of these nebulae at subarcsecond scales. These data will yield the mass loss histories of the central stars and will demonstrate the presence or absence of axisymmetric mass loss and circumstellar disks. In so doing, our HST/FOC program will define the role of mass loss in determining the fates of SN progenitors and SN remnants.

Planets Under a Red Sun Artist Concept

NASA Image and Video Library

2011-04-08

This artist concept illustrates a young, red dwarf star surrounded by three planets. NASA Galaxy Evolution Explorer is helping to identify young, red dwarf stars that are close to us by detecting their ultraviolet light.

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

Clausen, Drew; Wade, Richard A.; Kopparapu, Ravi Kumar

Binaries that contain a hot subdwarf (sdB) star and a main-sequence companion may have interacted in the past. This binary population has historically helped determine our understanding of binary stellar evolution. We have computed a grid of binary population synthesis models using different assumptions about the minimum core mass for helium ignition, the envelope binding energy, the common-envelope ejection efficiency, the amount of mass and angular momentum lost during stable mass transfer, and the criteria for stable mass transfer on the red giant branch and in the Hertzsprung gap. These parameters separately and together can significantly change the entire predictedmore » population of sdBs. Nonetheless, several different parameter sets can reproduce the observed subpopulation of sdB + white dwarf and sdB + M dwarf binaries, which has been used to constrain these parameters in previous studies. The period distribution of sdB + early F dwarf binaries offers a better test of different mass transfer scenarios for stars that fill their Roche lobes on the red giant branch.« less

On the nature of the symbiotic binary AX Persei

NASA Technical Reports Server (NTRS)

Mikolajewska, Joanna; Kenyon, Scott J.

1992-01-01

Photometric and spectroscopic observations of the symbiotic binary AX Persei are presented. This system contains a red giant that fills its tidal lobe and transfers material into an accretion disk surrounding a low-mass main-sequence star. The stellar masses - 1 solar mass for the red giant and about 0.4 solar mass for the companion - suggest AX Per is poised to enter a common envelope phase of evolution. The disk luminosity increases from L(disk) about 100 solar luminosity in quiescence to L(disk) about 5700 solar luminosity in outburst for a distance of d = 2.5 kpc. Except for visual maximum, high ionization permitted emission lines - such as He II - imply an EUV luminosity comparable to the disk luminosity. High-energy photons emitted by a hot boundary layer between the disk and central star ionize a surrounding nebula to produce this permitted line emission. High ionization forbidden lines form in an extended, shock-excited region well out of the binary's orbital plane and may be associated with mass loss from the disk.

The formation and build-up of the red-sequence over the past 9 Gyr in VIPERS

NASA Astrophysics Data System (ADS)

Fritz, Alexander; Abbas, U.; Adami, C.; Arnouts, S.; Bel, J.; Bolzonella, M.; Bottini, D.; Branchini, E.; Burden, A.; Cappi, A.; Coupon, J.; Cucciati, O.; Davidzon, I.; De Lucia, G.; de la Torre, S.; Di Porto, C.; Franzetti, P.; Fumana, M.; Garilli, B.; Granett, B. R.; Guzzo, L.; Ilbert, O.; Iovino, A.; Krywult, J.; Le Brun, V.; Le Fèvre, O.; Maccagni, D.; Małek, K.; Marchetti, A.; Marinoni, C.; Marulli, F.; McCracken, H. J.; Mellier, Y.; Moscardini, L.; Nichol, R. C.; Paioro, L.; Peacock, J. A.; Percival, W. J.; Polletta, M.; Pollo, A.; Scodeggio, M.; Tasca, L. A. M.; Tojeiro, R.; Vergani, D.; Zamorani, G.; Zanichelli, A.; VIPERS Team

2015-02-01

We present the Luminosity Function (LF) and Colour-Magnitude Relation (CMR) using ~45000 galaxies drawn from the VIMOS Public Extragalactic Redshift Survey (VIPERS). Using different selection criteria, we define several samples of early-type galaxies and explore their impact on the evolution of the red-sequence (RS) and the effects of dust. Our results suggest a rapid build-up of the RS within a short time scale. We find a rise in the number density of early-type galaxies and a strong evolution in LF and CMR. Massive galaxies exist already 9 Gyr ago and experience an efficient quenching of their star formation at z = 1, followed by a passive evolution with only limited merging activity. In contrast, low-mass galaxies indicate a different mass assembly history and cause a slow build-up of the CMR over cosmic time.

LIFTING THE DUSTY VEIL WITH NEAR- AND MID-INFRARED PHOTOMETRY. III. TWO-DIMENSIONAL EXTINCTION MAPS OF THE GALACTIC MIDPLANE USING THE RAYLEIGH-JEANS COLOR EXCESS METHOD

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

Nidever, David L.; Zasowski, Gail; Majewski, Steven R., E-mail: dln5q@virginia.edu, E-mail: gz2n@virginia.edu, E-mail: srm4n@virginia.edu

We provide new, high-resolution A(K{sub s} ) extinction maps of the heavily reddened Galactic midplane based on the Rayleigh-Jeans Color Excess ({sup R}JCE{sup )} method. RJCE determines star-by-star reddening based on a combination of near- and mid-infrared photometry. The new RJCE-generated maps have 2' Multiplication-Sign 2' pixels and span some of the most severely extinguished regions of the Galaxy-those covered with Spitzer/IRAC imaging by the GLIMPSE-I, -II, -3D, and Vela-Carina surveys, from 256 Degree-Sign < l < 65 Degree-Sign and, in general, for |b| {<=} 1 Degree-Sign -1.{sup 0}5 (extending up to |b| {<=} 4 Degree-Sign in the bulge). Usingmore » RJCE extinction measurements, we generate dereddened color-magnitude diagrams and, in turn, create maps based on main sequence, red clump, and red giant star tracers, each probing different distances and thereby providing coarse three-dimensional information on the relative placement of dust cloud structures. The maps generated from red giant stars, which reach to {approx}18-20 kpc, probe beyond most of the Milky Way extinction in most directions and provide close to a 'total Galactic extinction' map-at minimum they provide high angular resolution maps of lower limits on A(K{sub s} ). Because these maps are generated directly from measurements of reddening by the very dust being mapped, rather than inferred on the basis of some less direct means, they are likely the most accurate to date for charting in detail the highly patchy differential extinction in the Galactic midplane. We provide downloadable FITS files and an IDL tool for retrieving extinction values for any line of sight within our mapped regions.« less

Star Formation Quenching, How Fast And How Frequently? Inside-Out Or Not?

NASA Astrophysics Data System (ADS)

Lian, Jianhui; Yan, Renbin; Blanton, Michael; Zhang, Kai; Kong, Xu

2017-06-01

Star formation quenching is a critical process that drive galaxies evolving from blue star-forming to red passive stage. This rapid quenching process is necessary in galaxy evolution models to explain the galaxy distribution in NUV-optical colour-colour diagrams1,2 and the buildup of red-sequence from z = 1 to z = 03,4,5. Yet, the mechanism of this quenching process is not fully understood and is of hot debate. Many candidate scenarios, such as strangulation due to shock heating in massive halos, AGN feedback or gas stripping due to environmental effect, have been proposed. To differentiate these scenarios, more constraints on the quenching process and thus the potential physical mechanism are badly needed. The first result we show in this poster is the properties of quenching process we obtained from the galaxy distribution in NUV-optical colour-colour diagrams. Aside from the unclear integrated star formation history (SFH) of galaxies, how the SFH of galaxies varies internally is still poorly understood. One direct probe of the internal variation of SFH is the spatial distribution of colours, i.e. the colour gradient. In the second part of the results of this poster, we explicitly illustrate the definition of 'inside-out growth' and 'inside-out quenching' scenarios and utilize the galaxy distribution in the u-I colour gradients to see which one is more observationally favoured.

On the Origin of Sub-subgiant Stars. II. Binary Mass Transfer, Envelope Stripping, and Magnetic Activity

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

Leiner, Emily; Mathieu, Robert D.; Geller, Aaron M., E-mail: leiner@astro.wisc.edu

Sub-subgiant stars (SSGs) lie to the red of the main sequence and fainter than the red giant branch in cluster color–magnitude diagrams (CMDs), a region not easily populated by standard stellar evolution pathways. While there has been speculation on what mechanisms may create these unusual stars, no well-developed theory exists to explain their origins. Here we discuss three hypotheses of SSG formation: (1) mass transfer in a binary system, (2) stripping of a subgiant’s envelope, perhaps during a dynamical encounter, and (3) reduced luminosity due to magnetic fields that lower convective efficiency and produce large starspots. Using the stellar evolutionmore » code MESA, we develop evolutionary tracks for each of these hypotheses, and compare the expected stellar and orbital properties of these models with six known SSGs in the two open clusters M67 and NGC 6791. All three of these mechanisms can create stars or binary systems in the SSG CMD domain. We also calculate the frequency with which each of these mechanisms may create SSG systems, and find that the magnetic field hypothesis is expected to create SSGs with the highest frequency in open clusters. Mass transfer and envelope stripping have lower expected formation frequencies, but may nevertheless create occasional SSGs in open clusters. They may also be important mechanisms to create SSGs in higher mass globular clusters.« less

Habitability of super-Earth planets around other suns: models including Red Giant Branch evolution.

PubMed

von Bloh, W; Cuntz, M; Schröder, K-P; Bounama, C; Franck, S

2009-01-01

The unexpected diversity of exoplanets includes a growing number of super-Earth planets, i.e., exoplanets with masses of up to several Earth masses and a similar chemical and mineralogical composition as Earth. We present a thermal evolution model for a 10 Earth-mass planet orbiting a star like the Sun. Our model is based on the integrated system approach, which describes the photosynthetic biomass production and takes into account a variety of climatological, biogeochemical, and geodynamical processes. This allows us to identify a so-called photosynthesis-sustaining habitable zone (pHZ), as determined by the limits of biological productivity on the planetary surface. Our model considers solar evolution during the main-sequence stage and along the Red Giant Branch as described by the most recent solar model. We obtain a large set of solutions consistent with the principal possibility of life. The highest likelihood of habitability is found for "water worlds." Only mass-rich water worlds are able to realize pHZ-type habitability beyond the stellar main sequence on the Red Giant Branch.

The redMaPPer Galaxy Cluster Catalog From DES Science Verification Data

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

Rykoff, E. S.

We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied tomore » $$150\\,\\mathrm{deg}^2$$ of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited, and contains 786 clusters with richness $$\\lambda>20$$ (roughly equivalent to $$M_{\\mathrm{500c}}\\gtrsim10^{14}\\,h_{70}^{-1}\\,M_{\\odot}$$) and 0.2 < $z$ <0.9. The DR8 catalog consists of 26311 clusters with 0.08 < $z$ < 0.6, with a sharply increasing richness threshold as a function of redshift for $$z\\gtrsim 0.35$$. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the $$\\sigma_z/(1+z)\\sim 0.01$$ level for $$z\\lesssim0.7$$, rising to $$\\sim0.02$$ at $$z\\sim0.9$$ in DES SV. We make use of $Chandra$ and $XMM$ X-ray and South Pole Telescope Sunyaev-Zeldovich data to show that the centering performance and mass--richness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-$z$ and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.« less

The STREGA survey - II. Globular cluster Palomar 12

NASA Astrophysics Data System (ADS)

Musella, I.; Di Criscienzo, M.; Marconi, M.; Raimondo, G.; Ripepi, V.; Cignoni, M.; Bono, G.; Brocato, E.; Dall'Ora, M.; Ferraro, I.; Grado, A.; Iannicola, G.; Limatola, L.; Molinaro, R.; Moretti, M. I.; Stetson, P. B.; Capaccioli, M.; Cioni, M.-R. L.; Getman, F.; Schipani, P.

2018-01-01

In the framework of the STREGA (STRucture and Evolution of the GAlaxy) survey, two fields around the globular cluster Pal 12 were observed with the aim of detecting the possible presence of streams and/or an extended halo. The adopted stellar tracers are the main sequence, turn-off and red giant branch stars. We discuss the luminosity function and the star counts in the observed region covering about 2 tidal radii, confirming that Pal 12 appears to be embedded in the Sagittarius Stream. Adopting an original approach to separate cluster and field stars, we do not find any evidence of significant extra-tidal Pal 12 stellar populations. The presence of the Sagittarius stream seems to have mimicked a larger tidal radius in previous studies. Indeed, adopting a King model, a redetermination of this value gives rT = 0.22 ± 0.1 deg.

Habitability of planets around red dwarf stars.

PubMed

Heath, M J; Doyle, L R; Joshi, M M; Haberle, R M

1999-08-01

Recent models indicate that relatively moderate climates could exist on Earth-sized planets in synchronous rotation around red dwarf stars. Investigation of the global water cycle, availability of photosynthetically active radiation in red dwarf sunlight, and the biological implications of stellar flares, which can be frequent for red dwarfs, suggests that higher plant habitability of red dwarf planets may be possible.

KPC-SCALE STUDY OF SUBSTRUCTURES INSIDE GALAXIES out to z ~ 1.3

NASA Astrophysics Data System (ADS)

Hemmati, Shoubaneh; Mobasher, B.; Miller, S.; Nayyeri, H.

2014-01-01

Studying the resolved properties of galaxies in kpc scale has the capability to address major questions in galaxy structure formation and stellar properties evolution. We use a unique sample of 129 morphologically inclusive disk-like galaxies in the redshift range 0.2

The Optical Green Valley Versus Mid-infrared Canyon in Compact Groups

NASA Technical Reports Server (NTRS)

Walker, Lisa May; Butterfield, Natalie; Johnson, Kelsey; Zucker, Catherine; Gallagher, Sarah; Konstantopoulos, Iraklis; Zabludoff, Ann; Hornschemeier, Ann E.; Tzanavaris, Panayiotis; Charlton, Jane C.

2013-01-01

Compact groups of galaxies provide conditions similar to those experienced by galaxies in the earlier universe. Recent work on compact groups has led to the discovery of a dearth of mid-infrared transition galaxies (MIRTGs) in Infrared Array Camera (3.6-8.0 micrometers) color space as well as at intermediate specific star formation rates. However, we find that in compact groups these MIRTGs have already transitioned to the optical ([g-r]) red sequence. We investigate the optical color-magnitude diagram (CMD) of 99 compact groups containing 348 galaxies and compare the optical CMD with mid-infrared (mid-IR) color space for compact group galaxies. Utilizing redshifts available from Sloan Digital Sky Survey, we identified new galaxy members for four groups. By combining optical and mid-IR data, we obtain information on both the dust and the stellar populations in compact group galaxies. We also compare with more isolated galaxies and galaxies in the Coma Cluster, which reveals that, similar to clusters, compact groups are dominated by optically red galaxies. While we find that compact group transition galaxies lie on the optical red sequence, LVL (Local Volume Legacy) + (plus) SINGS (Spitzer Infrared Nearby Galaxies Survey) mid-IR (infrared) transition galaxies span the range of optical colors. The dearth of mid-IR transition galaxies in compact groups may be due to a lack of moderately star-forming low mass galaxies; the relative lack of these galaxies could be due to their relatively small gravitational potential wells. This makes them more susceptible to this dynamic environment, thus causing them to more easily lose gas or be accreted by larger members.

Star Shows It Has The Right Stuff

NASA Astrophysics Data System (ADS)

2004-01-01

Astronomers have used an observation by NASA's Chandra X-ray Observatory to make the best case yet that a star can be engulfed by its companion star and survive. This discovery will help astronomers better understand how closely coupled stars, and perhaps even stars and planets, evolve when one of the stars expands enormously in its red giant phase. The binary star system known as V471 Tauri comprises a white dwarf star (the primary) in a close orbit -- one thirtieth of the distance between Mercury and the Sun -- with a normal Sun-like star (the secondary). Chandra's data showed that the hot upper atmosphere of the secondary star has a deficit of carbon atoms relative to nitrogen atoms. "This deficit of carbon atoms is the first clear observational evidence that the normal star was engulfed by its companion in the past," according to Jeremy Drake of the Smithsonian Astrophysical Observatory in Cambridge, MA, who coauthored an article on V471 in The Astrophysical Journal Letters with Marek Sarna of the N. Copernicus Astronomical Center in Poland. The white dwarf star was once a star several times as massive as the Sun. Nuclear fusion reactions in the core of such a star convert carbon into nitrogen over a period of about a billion years. When the fuel in the core of the star is exhausted, the core collapses, triggering more energetic nuclear reactions that cause the star to expand and transform into a red giant before eventually collapsing to become a white dwarf. The carbon-poor material in the core of the red giant is mixed with outer part of the star, so its atmosphere shows a deficit of carbon, as compared with Sun-like stars. The X-ray spectra of a red giant star (top panel) and a Sun-like star (bottom panel) show the large difference in the peaks due to carbon atoms in the two stars. Theoretical calculations indicate that a red giant in a binary system can completely envelop its companion star and dramatically affect its evolution. During this common envelope phase, friction causes the companion star to spiral inward rapidly where it will either be destroyed by the red giant, or it will survive when much of the envelope is spun away. If the companion star manages to survive, it will bear the marks of its ordeal in the form of contamination by carbon-poor material that it accreted while it was inside the red giant envelope. The X-ray spectrum of V471 Tauri in the middle panel shows just this effect - the carbon peak is intermediate between that of a Sun-like star and an isolated red giant star. The data indicate that about 10 percent of the star's mass has been accreted from the red giant. In the future the companion star can return the favor when it expands and dumps material back onto the white dwarf. If enough material is dumped on the white dwarf, it could cause the white dwarf to explode as a supernova. "It's a dog-eat-dog world out there," observed Drake. V471 Tau was observed for approximately one day by Chandra using the Low Energy Transmission Grating and High Resolution Camera on January 24-25, 2002. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

ATLASGAL - towards a complete sample of massive star forming clumps

NASA Astrophysics Data System (ADS)

Urquhart, J. S.; Moore, T. J. T.; Csengeri, T.; Wyrowski, F.; Schuller, F.; Hoare, M. G.; Lumsden, S. L.; Mottram, J. C.; Thompson, M. A.; Menten, K. M.; Walmsley, C. M.; Bronfman, L.; Pfalzner, S.; König, C.; Wienen, M.

2014-09-01

By matching infrared-selected, massive young stellar objects (MYSOs) and compact H II regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ˜1000 embedded young massive stars between 280° < ℓ < 350° and 10° < ℓ < 60° with | b | < 1.5°. Combined with an existing sample of radio-selected methanol masers and compact H II regions, the result is a catalogue of ˜1700 massive stars embedded within ˜1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H II-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H II-region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.

The Unusual S Star Binary HD 191589

NASA Technical Reports Server (NTRS)

Ake, Thomas B.; Johnson, Hollis R.; Wahlgren, Glenn M.; Jorissen, Alain

1996-01-01

Recently, we discovered with International Ultraviolet Explorer (IUE) an F0-F2 IV-V companion to the T(sub c)-deficient S star HD 191589. If the magnitude difference is (delta)V=3.7, as indicated by several arguments, and E(B-V) = 0.0, we obtain a value of M(sub v)= - 1.5 +/- 0.4 for the Peculiar Red Giant (PRG), too faint for it to be a thermally-pulsing asymptotic giant branch star. According to the binary mass-transfer hypothesis for T(sub c)-deficient PRG's, a white dwarf must be the source of the s-process enhancement of the current primary star, but it cannot be seen because of the presence of the secondary. If such is the case, the F-star companion may also have been contaminated by s-process material. High-dispersion IUE observations indicate an enhancement of Zr II in the photosphere of the F-star as well. Thus, HD 191589 is likely a triple system, where what was once the most massive component of the system has polluted both of its companions with s-process material. One of these is the current S star, while the other is the companion still near the main sequence.

The remarkable Red Rectangle: A Stairway to Heaven?

NASA Astrophysics Data System (ADS)

2004-05-01

HD 44179 Nebula hi-res Size hi-res: 865 Kb Credits: NASA/ESA, Hans Van Winckel (Catholic University of Leuven, Belgium) and Martin Cohen (University of California) The HD 44179 nebula, known as the 'Red Rectangle.' This image, taken with the NASA/ESA Hubble Space Telescope, reveals startling new details of one of the most unusual nebulae known in our galaxy. Catalogued as HD 44179, this nebula is more commonly called the 'Red Rectangle' because of its unique shape and colour as seen with ground-based telescopes. Hubble has revealed a wealth of new features in the Red Rectangle that cannot be seen by ground-based telescopes looking through Earth’s turbulent atmosphere. Details of the Hubble study were published in the April 2004 issue of The Astronomical Journal. HD 44179 Nebula hi-res Size hi-res: 1289 Kb Credits: ESA and Vincent Icke (Leiden University, the Netherlands) Simulating the Red Rectangle The NASA/ESA Hubble Space Telescope has revealed a wealth of new features in the Red Rectangle that cannot be seen with ground-based telescopes looking through the Earth’s turbulent atmosphere. Whereas the origins of many of the features in this dying star still remain hidden or even outright mysterious, some are well explained by theorists like the Dutch scientist Vincent Icke from Leiden University in the Netherlands. In 1981 Vincent Icke and collaborators showed that a spherical gas ejection from a dying star hitting a dust torus would give rise to shocks that can produce cone-like outflows similar to the two cones seen in the Hubble image. Meteorologists produce weather forecasts by advanced calculations of temperatures, pressures, velocities and densities for the air masses in our atmosphere and, to some degree, theorists like Icke are doing exactly the same for objects in space. Whether modelling the weather in the Earth’s atmosphere or the processes in distant gaseous nebulae, scientists calculate the motion of the gas by using a complicated set of expressions known as hydrodynamic equations. Most of the matter in the Universe is in the form of gas. The weather on Earth gives rise to spectacular patterns such as thunderclouds and tornadoes in the air masses here. Likewise, the ‘weather’ in gas clouds in space, like the Red Rectangle, can be fascinating. Of the many different parameters in Vincent Icke’s calculations, only the density of the gas and the dust are observed in the Hubble image. The reflection of the gas and dust are shown in this simulated image. The colours show what one would see in scattered light - blue light scatters more than red. The ejected blobs of gas and dust look reddish, the background nebula is whiter. The three images are a time sequence with about 600 years between and show how the Red Rectangle may have been created. HD 44179 Nebula hi-res Size hi-res: 4550 Kb Credits: ESA and Digitized Sky Survey 2 Red Rectangle overview image 1 This is a ground-based view of the sky around the Red Rectangle. The image spans a square of one degree and was constructed from three images from the Digitized Sky Survey 2 taken in blue, infrared and red (shown as blue, green and red respectively). HD 44179 Nebula hi-res Size hi-res: 479 Kb Credits: ESA, ESO and Hans van Winckel (Catholic University of Leuven, Belgium) Red Rectangle overview image 2 This ground-based image was taken with the European Southern Observatory’s New Technology Telescope at La Silla Observatory. The image is constructed from three exposures through a blue filter, hydrogen-alpha filter and a red filter. This image, taken with the NASA/ESA Hubble Space Telescope, reveals startling new details of one of the most unusual nebulae known in our galaxy. Catalogued as HD 44179, this nebula is more commonly called the 'Red Rectangle' because of its unique shape and colour as seen with ground-based telescopes. Hubble has revealed a wealth of new features in the Red Rectangle that cannot be seen by ground-based telescopes looking through the Earth’s turbulent atmosphere. Details of the Hubble study were published in the April 2004 issue of The Astronomical Journal. Hans Van Winckel (Catholic University of Leuven, Belgium), the principal investigator for the Hubble observations, says: “The structure of the Red Rectangle revealed by Hubble is surprisingly complex. The features that impress me most look like the rungs of a ladder, although they are actually projections of gas cones, like a series of nested wine glasses filled to their brim with gas and seen from the side.” Hubble's sharp pictures show that the Red Rectangle is not really rectangular, but has an X-shaped structure, that astronomers interpret as arising from outflows of gas and dust from the star in the centre. The cone-like outflows are ejected from the star in two opposing directions. In addition there are straight linking features that look like the rungs on a ladder, making the Red Rectangle look similar to a spider’s web, a shape unlike that of any other known nebula in the sky. These rungs may have arisen in episodes of mass ejection from the star that occur every few hundred years and could represent a series of ‘smoke rings’, seen almost exactly edge-on from our vantage point. The star at the centre of the Red Rectangle began its life as a star similar to our Sun. It is now nearing the end of its lifetime, and is in the process of ejecting its outer layers to produce the visible nebula. The shedding of the outer layers began about 14 000 years ago, and in a few thousand years, the star will have become smaller and hotter, releasing a flood of ultraviolet light into the surrounding nebula. When this occurs the gas in the nebula will begin to fluoresce, producing a 'planetary nebula'. At the present time, however, the star is still so cool that atoms in the nebula do not glow and the surrounding dust particles are only visible as they reflect light from the central star. Exactly which molecules in the dust cloud are responsible for the striking red colour of the Rectangle is not yet clear, but it is likely that they are some kind of hydrocarbon formed in the cool outflows from the central star. Another remarkable feature of the Red Rectangle, visible only with the superb resolution of the Hubble telescope, is the dark band passing across the central star. This is the shadow of a dense disc of dust that surrounds the star and obscures it from direct view. The light we see streams out along the axis of the disc, and is scattered towards us by dust particles. Astronomers have found that the central star is actually a close pair of stars orbiting each other with a period of about 10.5 months. Interactions between these stars have probably caused the ejection of the thick dust disc that obscures our view of the binary. The disc then funnels subsequent dust and gas outflows out along its axis, forming the bizarre bi-conical structure we see as the rung of the Red Rectangle. The reasons for these fresh periodic ejections of more gas and dust remain unknown. The Red Rectangle was first discovered during a rocket flight in the early 1970s, in which astronomers were searching for strong sources of infrared radiation. This infrared source lies about 2300 light-years from Earth in the direction of the constellation Monoceros. Stars surrounded by clouds of dust are often strong infrared sources because the dust is heated by the starlight and then re-radiates long-wavelength red light. Studies of HD 44179 with ground-based telescopes revealed a rectangular shape in the dust surrounding the star at the centre, leading to the name 'Red Rectangle', coined in 1973 by astronomers Martin Cohen and Mike Merrill. This image was made from observations taken on 17-18 March 1999 with Hubble’s Wide Field Planetary Camera 2.

Double blue straggler sequences in globular clusters: The case of NGC 362

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

Dalessandro, E.; Ferraro, F. R.; Massari, D.

2013-12-01

We used high-quality images acquired with the Wide Field Camera 3 on board the Hubble Space Telescope to probe the blue straggler star (BSS) population of the galactic globular cluster NGC 362. We have found two distinct sequences of BSSs: this is the second case, after M30, where such a feature has been observed. Indeed, the BSS location, their extension in magnitude and color, and their radial distribution within the cluster nicely resemble those observed in M30, thus suggesting that the same interpretative scenario can be applied: the red BSS sub-population is generated by mass-transfer binaries, the blue one bymore » collisions. The discovery of four new W UMa stars, three of which lie along the red BSS sequence, further supports this scenario. We also found that the inner portion of the density profile deviates from a King model and is well reproduced by either a mild power law (α ∼ –0.2) or a double King profile. This feature supports the hypothesis that the cluster is currently undergoing the core-collapse phase. Moreover, the BSS radial distribution shows a central peak and monotonically decreases outward without any evidence of an external rising branch. This evidence is a further indication of the advanced dynamical age of NGC 362; in fact, together with M30, NGC 362 belongs to the family of dynamically old clusters (Family III) in the 'dynamical clock' classification proposed by Ferraro et al. The observational evidence presented here strengthens the possible connection between the existence of a double BSS sequence and a quite advanced dynamical status of the parent cluster.« less

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796. How different are red-giant stars with a mass ratio of 1.015?

NASA Astrophysics Data System (ADS)

Beck, P. G.; Kallinger, T.; Pavlovski, K.; Palacios, A.; Tkachenko, A.; Mathis, S.; García, R. A.; Corsaro, E.; Johnston, C.; Mosser, B.; Ceillier, T.; do Nascimento, J.-D.; Raskin, G.

2018-04-01

Context. Binaries in double-lined spectroscopic systems (SB2) provide a homogeneous set of stars. Differences of parameters, such as age or initial conditions, which otherwise would have strong impact on the stellar evolution, can be neglected. The observed differences are determined by the difference in stellar mass between the two components. The mass ratio can be determined with much higher accuracy than the actual stellar mass. Aim. In this work, we aim to study the eccentric binary system KIC 9163796, whose two components are very close in mass and both are low-luminosity red-giant stars. Methods: We analysed four years of Kepler space photometry and we obtained high-resolution spectroscopy with the Hermes instrument. The orbital elements and the spectra of both components were determined using spectral disentangling methods. The effective temperatures, and metallicities were extracted from disentangled spectra of the two stars. Mass and radius of the primary were determined through asteroseismology. The surface rotation period of the primary is determined from the Kepler light curve. From representative theoretical models of the star, we derived the internal rotational gradient, while for a grid of models, the measured lithium abundance is compared with theoretical predictions. Results: From seismology the primary of KIC 9163796 is a star of 1.39 ± 0.06 M⊙, while the spectroscopic mass ratio between both components can be determined with much higher precision by spectral disentangling to be 1.015 ± 0.005. With such mass and a difference in effective temperature of 600 K from spectroscopy, the secondary and primary are, respectively, in the early and advanced stage of the first dredge-up event on the red-giant branch. The period of the primary's surface rotation resembles the orbital period within ten days. The radial rotational gradient between the surface and core in KIC 9163796 is found to be 6.9-1.0+2.0. This is a low value but not exceptional if compared to the sample of typical single field stars. The seismic average of the envelope's rotation agrees with the surface rotation rate. The lithium'abundance is in agreement with quasi rigidly rotating models. Conclusions: The agreement between the surface rotation with the seismic result indicates that the full convective envelope is rotating quasi-rigidly. The models of the lithium abundance are compatible with a rigid rotation in the radiative zone during the main sequence. Because of the many constraints offered by oscillating stars in binary systems, such objects are important test beds of stellar evolution. Based on observations made with the Kepler space telescope and the Hermes spectrograph mounted on the 1.2 m Mercator Telescope at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

The Mass-loss Return from Evolved Stars to the Large Magellanic Cloud. VI. Luminosities and Mass-loss Rates on Population Scales

NASA Astrophysics Data System (ADS)

Riebel, D.; Srinivasan, S.; Sargent, B.; Meixner, M.

2012-07-01

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ~30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 × 10-5 M ⊙ yr-1, equivalent to a total mass injection rate (including the gas) into the ISM of ~6 × 10-3 M ⊙ yr-1. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K s band as a function of J - K s color, BC_{K_{s}} = -0.40(J-K_{s})^2 + 1.83(J-K_{s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (\\dot{M}_{d}) from C-rich AGB stars, such as log \\dot{M_{d}} = ({-18.90}/({(K_{s}-[8.0])+3.37}))-5.93. We find that a larger fraction of AGB stars exhibiting the "long-secondary period" phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

MINERVA-Red: A Census of Planets Orbiting the Nearest Low-mass Stars to the Sun

NASA Astrophysics Data System (ADS)

Blake, Cullen; Johnson, John; Plavchan, Peter; Sliski, David; Wittenmyer, Robert A.; Eastman, Jason D.; Barnes, Stuart

2015-01-01

Recent results from Kepler and ground-based exoplanet surveys suggest that low-mass stars host numerous small planets. Since low-mass stars are intrinsically faint at optical wavelengths, obtaining the Doppler precision necessary to detect these companions remains a challenge for existing instruments. We describe MINERVA-Red, a project to use a dedicated, robotic, near-infrared optimized 0.7 meter telescope and a specialized Doppler spectrometer to carry out an intensive, multi-year campaign designed to reveal the planetary systems orbiting some of the closest stars to the Sun. The MINERVA-Red cross-dispersed echelle spectrograph is optimized for the 'deep red', between 800 nm and 900 nm, where these stars are relatively bright. The instrument is very compact and designed for the ultimate in Doppler precision by using single-mode fiber input. We describe the spectrometer and the status of the MINERVA-Red project, which is expected to begin routine operations at Whipple Observatory on Mt Hopkins, Arizona, in 2015.

Galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z = 1.58. Red-sequence formation, massive galaxy assembly, and central star formation activity

NASA Astrophysics Data System (ADS)

Fassbender, R.; Nastasi, A.; Santos, J. S.; Lidman, C.; Verdugo, M.; Koyama, Y.; Rosati, P.; Pierini, D.; Padilla, N.; Romeo, A. D.; Menci, N.; Bongiorno, A.; Castellano, M.; Cerulo, P.; Fontana, A.; Galametz, A.; Grazian, A.; Lamastra, A.; Pentericci, L.; Sommariva, V.; Strazzullo, V.; Šuhada, R.; Tozzi, P.

2014-08-01

Context. Recent observational progress has enabled the detection of galaxy clusters and groups out to very high redshifts and for the first time allows detailed studies of galaxy population properties in these densest environments in what was formerly known as the "redshift desert" at z> 1.5. Aims: We aim to investigate various galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z = 1.58, which constitutes the most extreme currently known matter-density peak at this redshift. Methods: We analyzed deep VLT/HAWK-I near-infrared data with an image quality of 0.5'' and limiting Vega magnitudes (50% completeness) of 24.2 in J- and 22.8 in the Ks band, complemented by similarly deep Subaru imaging in i and V, Spitzer observations at 4.5 μm, and new spectroscopic observations with VLT/FORS 2. Results: We detect a cluster-associated excess population of about 90 galaxies, most of them located within the inner 30'' (250 kpc) of the X-ray centroid, which follows a centrally peaked, compact NFW galaxy surface-density profile with a concentration of c200 ≃ 10. Based on the Spitzer 4.5 μm imaging data, we measure a total enclosed stellar mass of M∗500 ≃ (6.3 ± 1.6) × 1012 M⊙ and a resulting stellar mass fraction of f∗,500 = M∗,500/M500 = (3.3 ± 1.4)%, consistent with local values. The total J- and Ks-band galaxy luminosity functions of the core region yield characteristic magnitudes J* and Ks* consistent with expectations from simple zf = 3 burst models. However, a detailed look at the morphologies and color distributions of the spectroscopically confirmed members reveals that the most massive galaxies are undergoing a very active mass-assembly epoch through merging processes. Consequently, the bright end of the cluster red sequence is not in place, while a red-locus population is present at intermediate magnitudes [Ks*, Ks* + 1.6], which is then sharply truncated at magnitudes fainter than Ks* + 1.6. The dominant cluster-core population comprises post-quenched galaxies transitioning toward the red sequence at intermediate magnitudes, while additionally a significant blue-cloud population of faint star-forming galaxies is present even in the densest central regions. Based on a color-color selection performed to separate different cluster galaxy types, we find that the blue star-forming population is concentrated in clumpy structures and dominates in particular at and beyond the R500 radius. On the other hand, the fraction of post-starburst galaxies steadily increases toward the center, while the red-locus population and red-sequence transition galaxies seem to reach their peak fractions already at intermediate cluster-centric radii of about r ~ 200 kpc. Conclusions: Our observations support the scenario in which the dominant effect of the dense z ≃ 1.6 cluster environment is an accelerated mass-assembly timescale (~1 Gyr or shorter) through merging activity that is responsible for driving core galaxies across the mass-quenching threshold of log (M∗/M⊙) ≃ 10.4. Beyond this mass limit, star formation is suppressed on timescales of ~1 Gyr, while the direct environmental quenching process seems to be subdominant and is acting on significantly longer timescales (~2-3 Gyr). Based on observations under programme ID 084.A-0844, 087.A-0351, and 089.A-0419 collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile.J- and Ks-band FITS files are 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/568/A5

High Resolution Spectroscopy of Vega-like Stars: Abundances and Circumstellar Gas

NASA Technical Reports Server (NTRS)

Dunkin, S. K.; Barlow, M. J.; Ryan, Sean G.

1996-01-01

Vega-like stars are main-sequence stars exhibiting excess infrared emission. In an effort to improve the information available on this class of star, 13 stars have been analyzed which have been classed as Vega-like, or have an infra-red excess attributable to dust in their circumstellar environment. In a separate paper stellar properties such as effective temperature and log g have been derived and in this poster we highlight the results of the photospheric abundance analysis also carried out during this work. King recently drew attention to the possible link between Vega-like stars and the photospheric metal-depleted class of A-stars, the Lambda Bootis stars. Since Vega-like stars are thought to have disks of dust, it might be expected that accretion of depleted gas onto the surface of these stars may cause this same phenomenon. In the 6 stars studied for depletions, none showed the extreme underabundance patterns observed in Lambda Bootis stars. However, depletions of silicon and magnesium were found in two of the sample, suggesting that these elements are in silicate dust grains in the circumstellar environment of these stars. Absorption lines attributed to circumstellar gas have been positively identified in three stars in our sample. Individual cases show evidence either of high-velocity outflowing gas, variability in the circumstellar lines observed, or evidence of circumstellar gas in excited lines of Fe II. No previous identification of circumstellar material has been made for two of the stars in question.

Carbon and nitrogen abundances of stellar populations in the globular cluster M 2

NASA Astrophysics Data System (ADS)

Lardo, C.; Pancino, E.; Mucciarelli, A.; Milone, A. P.

2012-12-01

We present CH and CN index analysis and C and N abundance calculations based on the low-resolution blue spectra of red giant branch (RGB) stars in the Galactic globular cluster NGC 7089 (M 2). Our main goal is to investigate the C-N anticorrelation for this intermediate metallicity cluster. The data were collected with DOLORES, the multiobject, low-resolution facility at the Telescopio Nazionale Galileo. We first looked for CH and CN band strength variations and bimodalities in a sample of RGB stars with 17.5 ≤ V ≤ 14.5. Thus we derived C and N abundances under LTE assumption by comparing observed spectra with synthetic models from the spectral features at 4300 Å (G-band) and at ~3883 Å (CN). Spectroscopic data were coupled with UV photometry obtained during the spectroscopic run. We found a considerable star-to-star variation in both A(C) and A(N) at all luminosities for our sample of 35 targets. These abundances appear to be anticorrelated, with a hint of bimodality in the C content for stars with luminosities below the RBG bump (V ~ 15.7), while the range of variations in N abundances is very large and spans almost ~2 dex. We find additional C depletion as the stars evolve off the RGB bump, in fairly good agreement with theoretical predictions for metal-poor stars in the course of normal stellar evolution. We isolated two groups with N-rich and N-poor stars and found that N abundance variations correlate with the (U - V) color in the DOLORES color-magnitude diagram (CMD). The V, (U - V) CMD for this cluster shows an additional RGB sequence, located at the red of the main RGB and amounting to a small fraction of the total giant population. We identified two CH stars detected in previous studies in our U,V images. These stars, which are both cluster members, fall on this redder sequence, suggesting that the anomalous RGB should have a peculiar chemical pattern. Unfortunately, no additional spectra were obtained for stars in this previously unknown RGB branch. 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 (PROGRAM ID: A22TAC_20).Full Table 1 and photometric data are only available 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/548/A107

LIVING WITH A RED DWARF: ROTATION AND X-RAY AND ULTRAVIOLET PROPERTIES OF THE HALO POPULATION KAPTEYN’S STAR

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

Guinan, Edward F.; Engle, Scott G.; Durbin, Allyn, E-mail: scott.engle@villanova.edu

As part of Villanova’s Living with a Red Dwarf program, we have obtained UV, X-ray, and optical data of the Population II red dwarf—Kapteyn’s Star. Kapteyn’s Star is noteworthy for its large proper motions and high radial velocity of ∼+245 km s{sup −1}. As the nearest Pop II red dwarf, it serves as an old age anchor for calibrating activity/irradiance–rotation–age relations, and an important test bed for stellar dynamos and the resulting X-ray–UV emissions of slowly rotating, near-fully convective red dwarf stars. Adding to the notoriety, Kapteyn’s Star has recently been reported to host two super-Earth candidates, one of whichmore » (Kapteyn b) is orbiting within the habitable zone. However, Robertson et al. questioned the planet’s existence since its orbital period may be an artifact of activity, related to the star’s rotation period. Because of its large Doppler-shift, measures of the important, chromospheric H i Lyα 1215.67 Å emission line can be reliably made, because it is mostly displaced from ISM and geo-coronal sources. Lyα emission dominates the FUV region of cool stars. Our measures can help determine the X-ray–UV effects on planets hosted by Kapteyn’s Star, and planets hosted by other old red dwarfs. Stellar X-ray and Lyα emissions have strong influences on the heating and ionization of upper planetary atmospheres and can (with stellar winds and flares) erode or even eliminate planetary atmospheres. Using our program stars, we have reconstructed the past exposures of Kapteyn’s Star's planets to coronal—chromospheric XUV emissions over time.« less

Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67

NASA Astrophysics Data System (ADS)

Souto, Diogo; Cunha, Katia; Smith, Verne V.; Allende Prieto, C.; García-Hernández, D. A.; Pinsonneault, Marc; Holzer, Parker; Frinchaboy, Peter; Holtzman, Jon; Johnson, J. A.; Jönsson, Henrik; Majewski, Steven R.; Shetrone, Matthew; Sobeck, Jennifer; Stringfellow, Guy; Teske, Johanna; Zamora, Olga; Zasowski, Gail; Carrera, Ricardo; Stassun, Keivan; Fernandez-Trincado, J. G.; Villanova, Sandro; Minniti, Dante; Santana, Felipe

2018-04-01

Detailed chemical abundance distributions for 14 elements are derived for eight high-probability stellar members of the solar metallicity old open cluster M67 with an age of ∼4 Gyr. The eight stars consist of four pairs, with each pair occupying a distinct phase of stellar evolution: two G dwarfs, two turnoff stars, two G subgiants, and two red clump (RC) K giants. The abundance analysis uses near-IR high-resolution spectra (λ1.5–1.7 μm) from the Apache Point Observatory Galactic Evolution Experiment survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for 2M08510076+1153115 suggest that this star is a solar twin, exhibiting abundance differences relative to the Sun of ≤0.04 dex for all elements. Chemical homogeneity is found within each class of stars (∼0.02 dex), while significant abundance variations (∼0.05–0.20 dex) are found across the different evolutionary phases; the turnoff stars typically have the lowest abundances, while the RCs tend to have the largest. Non-LTE corrections to the LTE-derived abundances are unlikely to explain the differences. A detailed comparison of the derived Fe, Mg, Si, and Ca abundances with recently published surface abundances from stellar models that include chemical diffusion provides a good match between the observed and predicted abundances as a function of stellar mass. Such agreement would indicate the detection of chemical diffusion processes in the stellar members of M67.

Globular cluster photometry with the Hubble Space Telescope. 3: Blue stragglers and variable stars in the core of M3

NASA Technical Reports Server (NTRS)

Guhathakurta, Puragra; Yanny, Brian; Bahcall, John N.; Schneider, Donald P.

1994-01-01

This paper describes Hubble Space Telescope (HST)/Planetary Camera-I images of the core of the dense globular cluster M3 (NGC 5272). Stellar photometry in the F555W (V) and F785LP (I) bands, with a 1-sigma photometric accuracy of about 0.1 mag, has been used to construct color-magnitude diagrams of about 4700 stars above the main-sequence turnoff within r less than or approximately equal to 1 min of the cluster center. We have also analyzed archival HST F336W (U) images of M3 obtained by the Wide Field/Planetary Camera-I Instrument Definition Team. The UVI data are used to identify 28 blue straggler (BS) stars within the central 0.29 sq. arcmin. The specific frequency of BSs in this region of M3, N(sub BS)/N(sub V less than (V(HB)+2)) = 0.094 +/- 0.019, is about a factor of 2 - 3 higher than that found by Bolte et al. in a recent ground-based study of the same region, but comparable to that seen in the sparse outer parts of the same cluster and in HST observations of the core of the higher density cluster 47 Tuc. The BSs in M3 are slightly more centrally concentrated than red giant branch stars while horizontal branch stars are somewhat less concentrated red giants. The radial distribution of V-selected subgiant and turnoff stars is well fit by a King model with a core radius r(sub core) = 28 arcmin +/- 2 arcmin (90% confidence limits), which corresponds to 1.4 pc. Red giant and horizontal branch stars selected in the ultraviolet data (U less than 18) have a somewhat more compact distribution (r(sub core) = 22.5 arcmin). The HST U data consist of 17 exposures acquired over a span of three days. We have used these data to isolate 40 variable stars for which relative astrometry, brightnesses, colors, and light curves are presented. A Kolmogorov-Smirnov test indicates that, typically, the variability for each star is significant at the 95% level. We identify two variable BS candidates (probably of the SX Phe type), out of a sample of approximately 25 BSs in which variability could have been detected. Most of the variables are RR Lyrae stars on the horizontal branch. All of them have periods P greater than or approximately equal 8 h.

New red giant star in the Kepler open cluster NGC 6819

NASA Astrophysics Data System (ADS)

Komucyeya, E.; Abedigamba, O. P.; Jurua, E.; Anguma, S. K.

2018-05-01

A recent study indicated that 39 red giant stars showing solar-like oscillations were discovered in the field of Kepleropen cluster NGC 6819. The study was based on photometric distance estimates of 27 stars out of the 39. Using photometric method alone may not be adequate to confirm the membership of these stars. The stars were not previously known in literature to belong to the open cluster NGC 6819. In this study, Kepler data was used to study the membership of the 27 stars. A plot of apparent magnitude as a function of the large frequency separation, supplemented with the proper motion and radial velocity values from literature revealed KIC 5112840 to lie on the same plane with the well known members of the cluster. Echelle diagram was constructed, and the median gravity-mode period spacings (ΔP) calculated for KIC 5112840. A value of ΔP = 66.3 s was obtained, thus placing the red giant star KIC 5112840 on the Red Giant Branch stage of evolution. Our evolutionary status result using the approach in this paper is in agreement with what is in the available literature.

The ISOGAL survey

NASA Astrophysics Data System (ADS)

Omont, A.; ISOGAL Collaboration

1999-03-01

ISOGAL is a 7-15 μm ISOCAM survey, with 6'' pixels and sensitivity below 10 mJy, of ~20 deg2, in the galactic plane mostly interior to |l| = 30o. In combination with KJI DENIS data, the ISO images allow detailed studies of cold stellar populations and galactic structures in regions highly obscured throughout the inner Galaxy, with a sensitivity and pixel surface two orders of magnitude better than IRAS. Data reduction is particularly difficult because of the high density of strong sources, of memory effects and of short integration times. However, an improved data reduction is almost complete for all the fields observed, with the use of CIA ISOCAM software and of a special source extraction. The data quality is acceptable, as concerns reliability, completeness and photometric accuracy of the sources, to allow a systematic scientific analysis. A few fields, in the bulge and in the galactic disk, exemplify the results expected from the ~200 fields observed. These results include: A complete census of mass-losing AGB stars in fields of the inner bulge. Even very weak mass-loss are very well characterised, down to the RGB tip. Such stars are by far the most numerous there. They form a very well defined sequence in ISOGAL-DENIS infrared colour-magnitude diagrams. The knowledge of Long Period Variables in two Baade's Window fields confirm that their luminosity is just above the tip of this sequence, and that the spectral type of the stars of the sequence is M6-9III. The same AGB sequence is also quite visible in 7-15 μm colour-magnitude diagrams in the galactic disk, even with a very large extinction. Such AGB stars are thus particularly numerous among the ~105 sources detected by ISOGAL. However, foreground red giants and dusty young stars are also quite numerous. The latter with a few solar masses are detectable through the galactic centre distance. A number of bright young stars are identified on lines of sight close to the Galactic Centre, The combination of ISOGAL and DENIS data allows a detailed estimate of the interstellar extinction for individual stars and lines of sight. Many dark globules and filaments are visible on the 7 and 15 μm images, corresponding to visible extinction larger than ~20-30. The very rich structure of the mid-infrared diffuse emission is often clearly associated with stars.

The Missing Link: Early Methane ("T") Dwarfs in the Sloan Digital Sky Survey.

PubMed

Leggett; Geballe; Fan; Schneider; Gunn; Lupton; Knapp; Strauss; McDaniel; Golimowski; Henry; Peng; Tsvetanov; Uomoto; Zheng; Hill; Ramsey; Anderson; Annis; Bahcall; Brinkmann; Chen; Csabai; Fukugita; Hennessy; Hindsley; Ivezic; Lamb; Munn; Pier; Schlegel; Smith; Stoughton; Thakar; York

2000-06-10

We report the discovery of three cool brown dwarfs that fall in the effective temperature gap between the latest L dwarfs currently known, with no methane absorption bands in the 1-2.5 µm range, and the previously known methane (T) dwarfs, whose spectra are dominated by methane and water. The newly discovered objects were detected as very red objects in the Sloan Digital Sky Survey imaging data and have JHK colors between the red L dwarfs and the blue Gl 229B-like T dwarfs. They show both CO and CH(4) absorption in their near-infrared spectra in addition to H(2)O, with weaker CH(4) absorption features in the H and K bands than those in all other methane dwarfs reported to date. Due to the presence of CH(4) in these bands, we propose that these objects are early T dwarfs. The three form part of the brown dwarf spectral sequence and fill in the large gap in the overall spectral sequence from the hottest main-sequence stars to the coolest methane dwarfs currently known.

Star Masses and Star-Planet Distances for Earth-like Habitability.

PubMed

Waltham, David

2017-01-01

This paper presents statistical estimates for the location and duration of habitable zones (HZs) around stars of different mass. The approach is based upon the assumption that Earth's location, and the Sun's mass, should not be highly atypical of inhabited planets. The results support climate-model-based estimates for the location of the Sun's HZ except models giving a present-day outer-edge beyond 1.64 AU. The statistical approach also demonstrates that there is a habitability issue for stars smaller than 0.65 solar masses since, otherwise, Earth would be an extremely atypical inhabited world. It is difficult to remove this anomaly using the assumption that poor habitability of planets orbiting low-mass stars results from unfavorable radiation regimes either before, or after, their stars enter the main sequence. However, the anomaly is well explained if poor habitability results from tidal locking of planets in the HZs of small stars. The expected host-star mass for planets with intelligent life then has a 95% confidence range of 0.78 M ⊙ < M < 1.04 M ⊙ , and the range for planets with at least simple life is 0.57 M ⊙  < M < 1.64 M ⊙ . Key Words: Habitability-Habitable zone-Anthropic-Red dwarfs-Initial mass function. Astrobiology 17, 61-77.

Star Masses and Star-Planet Distances for Earth-like Habitability

PubMed Central

2017-01-01

Abstract This paper presents statistical estimates for the location and duration of habitable zones (HZs) around stars of different mass. The approach is based upon the assumption that Earth's location, and the Sun's mass, should not be highly atypical of inhabited planets. The results support climate-model-based estimates for the location of the Sun's HZ except models giving a present-day outer-edge beyond 1.64 AU. The statistical approach also demonstrates that there is a habitability issue for stars smaller than 0.65 solar masses since, otherwise, Earth would be an extremely atypical inhabited world. It is difficult to remove this anomaly using the assumption that poor habitability of planets orbiting low-mass stars results from unfavorable radiation regimes either before, or after, their stars enter the main sequence. However, the anomaly is well explained if poor habitability results from tidal locking of planets in the HZs of small stars. The expected host-star mass for planets with intelligent life then has a 95% confidence range of 0.78 M⊙ < M < 1.04 M⊙, and the range for planets with at least simple life is 0.57 M⊙ < M < 1.64 M⊙. Key Words: Habitability—Habitable zone—Anthropic—Red dwarfs—Initial mass function. Astrobiology 17, 61–77. PMID:28103107

Galex and Pan-STARRS1 Discovery of SN IIP 2010aq: The First Few Days After Shock Breakout in a Red Supergiant Star

DTIC Science & Technology

2010-09-01

compare the late- time (φ > 3 d) UV/optical light curve of SN 2010aq with two nearby Type IIP SNe well studied in the UV and optical with the Swift satellite ...following SN shock breakout in a red supergiant star. SN 2010aq was discovered in joint monitoring between the Galaxy Evolution Explorer (GALEX) Time ...simultaneous UV and optical photometry allows us to fit for a progenitor star radius of 700± 200R, the size of a red supergiant star. An excess in UV emission

Star-planet interactions. IV. Possibility of detecting the orbit-shrinking of a planet around a red giant

NASA Astrophysics Data System (ADS)

Meynet, Georges; Eggenberger, Patrick; Privitera, Giovanni; Georgy, Cyril; Ekström, Sylvia; Alibert, Yann; Lovis, Christophe

2017-06-01

The surface rotations of some red giants are so fast that they must have been spun up by tidal interaction with a close companion, either another star, a brown dwarf, or a planet. We focus here on the case of red giants that are spun up by tidal interaction with a planet. When the distance between the planet and the star decreases, the spin period of the star decreases, the orbital period of the planet decreases, and the reflex motion of the star increases. We study the change rate of these three quantities when the circular orbit of a planet of 15 MJ that initially orbits a 2 M⊙ star at 1 au shrinks under the action of tidal forces during the red giant phase. We use stellar evolution models coupled with computations of the orbital evolution of the planet, which allows us to follow the exchanges of angular momentum between the star and the orbit in a consistent way. We obtain that the reflex motion of the red giant star increases by more than 1 m s-1 per year in the last 40 yr before the planet engulfment. During this phase, the reflex motion of the star is between 660 and 710 m s-1. The spin period of the star increases by more than about 10 min per year in the last 3000 yr before engulfment. During this period, the spin period of the star is shorter than 0.7 yr. During this same period, the variation in orbital period, which is shorter than 0.18 yr, is on the same order of magnitude. Changes in reflex-motion and spin velocities are very small and thus most likely out of reach of being observed. The most promising way of detecting this effect is through observations of transiting planets, that is, through changes of the beginning or end of the transit. For the relatively long orbital periods expected around red giants, long observing runs of typically a few years are needed. Interesting star-planet systems that currently are in this stage of orbit-shrinking would be red giants with fast rotation (above typically 4-5 km s-1), a low surface gravity (log g lower than 2), and having a planet at a distance typically smaller than about 0.4-1 au, depending on log g. A space mission like PLATO might be of great interest for detecting planets that are on the verge of being engulfed by red giants. The discovery of a few systems, even only one, would provide very interesting clues about the physics of tidal interaction between a red giant and a planet.

The UK Infrared Telescope M33 monitoring project - IV. Variable red giant stars across the galactic disc

NASA Astrophysics Data System (ADS)

Javadi, Atefeh; Saberi, Maryam; van Loon, Jacco Th.; Khosroshahi, Habib; Golabatooni, Najmeh; Mirtorabi, Mohammad Taghi

2015-03-01

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope, of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. In this fourth paper of the series, we present a search for variable red giant stars in an almost square degree region comprising most of the galaxy's disc, carried out with the WFCAM (Wide Field CAMera) instrument in the K band. These data, taken during the period 2005-2007, were complemented by J- and H-band images. Photometry was obtained for 403 734 stars in this region; of these, 4643 stars were found to be variable, most of which are asymptotic giant branch (AGB) stars. The variable stars are concentrated towards the centre of M33, more so than low-mass, less-evolved red giants. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. Most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey. The photometric catalogue is made publicly available at the Centre de Données astronomiques de Strasbourg.

Serendipitous discovery of a faint dwarf galaxy near a Local Volume dwarf

NASA Astrophysics Data System (ADS)

Makarova, L. N.; Makarov, D. I.; Antipova, A. V.; Karachentsev, I. D.; Tully, R. B.

2018-03-01

A faint dwarf irregular galaxy has been discovered in the HST/ACS field of LV J1157+5638. The galaxy is resolved into individual stars, including the brightest magnitude of the red giant branch. The dwarf is very likely a physical satellite of LV J1157+5638. The distance modulus of LV J1157+5638 using the tip of the red giant branch (TRGB) distance indicator is 29.82 ± 0.09 mag (D = 9.22 ± 0.38 Mpc). The TRGB distance modulus of LV J1157+5638 sat is 29.76 ± 0.11 mag (D = 8.95 ± 0.42 Mpc). The distances to the two galaxies are consistent within the uncertainties. The projected separation between them is only 3.9 kpc. LV J1157+5638 has a total absolute V magnitude of -13.26 ± 0.10 and linear Holmberg diameter of 1.36 kpc, whereas its faint satellite LV J1157+5638 sat has MV = -9.38 ± 0.13 mag and Holmberg diameter of 0.37 kpc. Such a faint dwarf was discovered for the first time beyond the nearest 4 Mpc from us. The presence of main-sequence stars in both galaxies unambiguously indicates the classification of the objects as dwarf irregulars with recent or ongoing star formation events in both galaxies.

Lithium Inventory of 2 Solar Mass Red Clump Stars in Open Clusters: A Test of the Helium Flash Mechanism

NASA Technical Reports Server (NTRS)

Carlberg, Joleen K.; Cunha, Katia; Smith, Verne V.

2016-01-01

The temperature distribution of field Li-rich red giants suggests the presence of a population of Li-rich red clump (RC) stars. One proposed explanation for this population is that all stars with masses near 2 solar mass experience a shortlived phase of Li-richness at the onset of core He-burning. Many of these stars have low C-12/C-13, a signature of deep mixing that is presumably associated with the Li regeneration. To test this purported mechanism of Li enrichment, we measured abundances in 38 RC stars and 6 red giant branch (RGB) stars in four open clusters selected to have RC masses near 2 solar mass. We find six Li-rich stars (A(Li) greater than or equal to 1.50 dex) of which only two may be RC stars. None of the RC stars have Li exceeding the levels observed in the RGB stars, but given the brevity of the suggested Li-rich phase and the modest sample size, it is probable that stars with larger Li-enrichments were missed simply by chance. However, we find very few stars in our sample with low C-12/C-13. Such low C-12/C-13, seen in many field Li-rich stars, should persist even after lithium has returned to normal low levels. Thus, if Li synthesis during the He flash occurs, it is a rare, but potentially long-lived occurrence rather than a short-lived phase for all stars. We estimate a conservative upper limit of the fraction of stars going through a Li-rich phase to be less than 47%, based on stars that have low C-12/C-13 for their observed A(Li).

Evolved stars in the Local Group galaxies - II. AGB, RSG stars and dust production in IC10

NASA Astrophysics Data System (ADS)

Dell'Agli, F.; Di Criscienzo, M.; Ventura, P.; Limongi, M.; García-Hernández, D. A.; Marini, E.; Rossi, C.

2018-06-01

We study the evolved stellar population of the Local Group galaxy IC10, with the aim of characterizing the individual sources observed and to derive global information on the galaxy, primarily the star formation history and the dust production rate. To this aim, we use evolutionary sequences of low- and intermediate-mass (M < 8 M⊙) stars, evolved through the asymptotic giant branch phase, with the inclusion of the description of dust formation. We also use models of higher mass stars. From the analysis of the distribution of stars in the observational planes obtained with IR bands, we find that the reddening and distance of IC10 are E(B - V) = 1.85 mag and d = 0.77 Mpc, respectively. The evolved stellar population is dominated by carbon stars, that account for 40% of the sources brighter than the tip of the red giant branch. Most of these stars descend from ˜1.1 - 1.3 M⊙ progenitors, formed during the major epoch of star formation, which occurred ˜2.5 Gyr ago. The presence of a significant number of bright stars indicates that IC10 has been site of significant star formation in recent epochs and currently hosts a group of massive stars in the core helium-burning phase. Dust production in this galaxy is largely dominated by carbon stars; the overall dust production rate estimated is 7 × 10-6 M⊙/yr.

Tidal Dissipation In Rotating Low Mass Stars: Implications For The Orbital Evolution Of Close In Planets

NASA Astrophysics Data System (ADS)

Gallet, Florian; Bolmont, Emeline; Mathis, Stéphane; Charbonnel, Corinne; Amard, Louis; Alibert, Yann

2017-10-01

Close-in planets represent a large fraction of the population of confirmed exoplanets. To understand the dynamical evolution of these planets, star-planet interactions must be taken into account. In particular, the dependence of the tidal interactions on the structural parameters of the star, its rotation, and its metallicity should be treated in the models. We quantify how the tidal dissipation in the convective envelope of rotating low-mass stars evolves in time. We also investigate the possible consequences of this evolution on planetary orbital evolution. In Gallet et al. (2017) and Bolmont et al. (2017) we generalized the work of Bolmont & Mathis (2016) by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution and non-solar metallicity. We find that during the pre-main sequence the evolution of tidal dissipation is controlled by the evolution of the internal structure of the star through the stellar contraction. On the main-sequence tidal dissipation is strongly driven by the evolution of the surface rotation that is impacted by magnetized stellar winds braking. Finally, during the more evolved phases, the tidal dissipation sharply decreases as radiative core retreats in mass and radius towards the red-giant branch. Using an orbital evolution model, we also show that changing the metallicity leads to diUerent orbital evolutions (e.g., planets migrate farther out from an initially fast rotating metal rich star). By using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more work still remain to be do so as to be able to quantitatively fit our results to the observations.

SDSS-IV MaNGA - the spatially resolved transition from star formation to quiescence

NASA Astrophysics Data System (ADS)

Belfiore, Francesco; Maiolino, Roberto; Maraston, Claudia; Emsellem, Eric; Bershady, Matthew A.; Masters, Karen L.; Bizyaev, Dmitry; Boquien, Médéric; Brownstein, Joel R.; Bundy, Kevin; Diamond-Stanic, Aleksandar M.; Drory, Niv; Heckman, Timothy M.; Law, David R.; Malanushenko, Olena; Oravetz, Audrey; Pan, Kaike; Roman-Lopes, Alexandre; Thomas, Daniel; Weijmans, Anne-Marie; Westfall, Kyle B.; Yan, Renbin

2017-04-01

Using spatially resolved spectroscopy from SDSS-IV MaNGA we have demonstrated that low ionization emission-line regions (LIERs) in local galaxies result from photoionization by hot evolved stars, not active galactic nuclei, hence tracing galactic region hosting old stellar population where, despite the presence of ionized gas, star formation is no longer occurring. LIERs are ubiquitous in both quiescent galaxies and in the central regions of galaxies where star formation takes place at larger radii. We refer to these two classes of galaxies as extended LIER (eLIER) and central LIER (cLIER) galaxies, respectively. cLIERs are late-type galaxies primarily spread across the green valley, in the transition region between the star formation main sequence and quiescent galaxies. These galaxies display regular disc rotation in both stars and gas, although featuring a higher central stellar velocity dispersion than star-forming galaxies of the same mass. cLIERs are consistent with being slowly quenched inside-out; the transformation is associated with massive bulges, pointing towards the importance of bulge growth via secular evolution. eLIERs are morphologically early types and are indistinguishable from passive galaxies devoid of line emission in terms of their stellar populations, morphology and central stellar velocity dispersion. Ionized gas in eLIERs shows both disturbed and disc-like kinematics. When a large-scale flow/rotation is observed in the gas, it is often misaligned relative to the stellar component. These features indicate that eLIERs are passive galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Importantly, quiescent galaxies devoid of line emission reside in denser environments and have significantly higher satellite fraction than eLIERs. Environmental effects thus represent the likely cause for the existence of line-less galaxies on the red sequence.

Abundance patterns of evolved stars with Hipparcos parallaxes and ages based on the APOGEE data base

NASA Astrophysics Data System (ADS)

Jia, Y. P.; Chen, Y. Q.; Zhao, G.; Bari, M. A.; Zhao, J. K.; Tan, K. F.

2018-01-01

We investigate the abundance patterns for four groups of stars at evolutionary phases from sub-giant to red clump (RC) and trace the chemical evolution of the disc by taking 21 individual elemental abundances from APOGEE and ages from evolutionary models with the aid of Hipparcos distances. We find that the abundances of six elements (Si, S, K, Ca, Mn and Ni) are similar from the sub-giant phase to the RC phase. In particular, we find that a group of stars with low [C/N] ratios, mainly from the second sequence of RC stars, show that there is a difference in the transfer efficiency of the C-N-O cycle between the main and the secondary RC sequences. We also compare the abundance patterns of C-N, Mg-Al and Na-O with giant stars in globular clusters from APOGEE and find that field stars follow similar patterns as M107, a metal-rich globular cluster with [M/H] ∼- 1.0, which shows that the self-enrichment mechanism represented by strong C-N, Mg-Al and Na-O anti-correlations may not be important as the metallicity reaches [M/H] > -1.0 dex. Based on the abundances of above-mentioned six elements and [Fe/H], we investigate age versus abundance relations and find some old super-metal-rich stars in our sample. Their properties of old age and being rich in metal are evidence for stellar migration. The age versus metallicity relations in low-[α/M] bins show unexpectedly positive slopes. We propose that the fresh metal-poor gas infalling on to the Galactic disc may be the precursor for this unexpected finding.

Spatially Resolved Spectroscopy of Narrow-line Seyfert 1 Host Galaxies

NASA Astrophysics Data System (ADS)

Scharwächter, J.; Husemann, B.; Busch, G.; Komossa, S.; Dopita, M. A.

2017-10-01

We present optical integral field spectroscopy for five z< 0.062 narrow-line Seyfert 1 (NLS1) galaxies, probing their host galaxies at ≳ 2{--}3 {kpc} scales. Emission lines from the active galactic nucleus (AGN) and the large-scale host galaxy are analyzed separately, based on an AGN-host decomposition technique. The host galaxy gas kinematics indicates large-scale gas rotation in all five sources. At the probed scales of ≳ 2{--}3 {kpc}, the host galaxy gas is found to be predominantly ionized by star formation without any evidence of a strong AGN contribution. None of the five objects shows specific star formation rates (SFRs) exceeding the main sequence of low-redshift star-forming galaxies. The specific SFRs for MCG-05-01-013 and WPVS 007 are roughly consistent with the main sequence, while ESO 399-IG20, MS 22549-3712, and TON S180 show lower specific SFRs, intermediate to the main sequence and the red quiescent galaxies. The host galaxy metallicities, derived for the two sources with sufficient data quality (ESO 399-IG20 and MCG-05-01-013), indicate central oxygen abundances just below the low-redshift mass-metallicity relation. Based on this initial case study, we outline a comparison of AGN and host galaxy parameters as a starting point for future extended NLS1 studies with similar methods.

Observational studies of regions of massive star formation

NASA Astrophysics Data System (ADS)

Cooper, Heather Danielle Blythe

2013-03-01

Massive stars have a profound influence on their surroundings. However, relatively little is known about their formation. The study of massive star formation is hindered by a lack of observational evidence, primarily due to difficulties observing massive stars at early stages in their development. The Red MSX Source survey (RMS survey) is a valuable tool with which to address these issues. Near-infrared H- and K-band spectra were taken for 247 candidate massive young stellar objects (MYSOs), selected from the RMS survey. 195 (∼80%) of the targets are YSOs, of which 131 are massive YSOs (LBOL>5E3L⊙, M>8 M⊙). This is the largest spectroscopic study of massive YSOs to date. This study covers minimally obscured objects right through to very red, dusty sources. Almost all YSOs show some evidence for emission lines, though there is a wide variety of observed properties, with HI, H2 Fe II, and CO among the most commonly observed lines. Evidence for disks and outflows was frequently seen. Comparisons of Brγ and H2 emission with low mass YSOs suggest that the emission mechanism for these lines is the same for low-, intermediate-, and high-mass YSOs, i.e. high-mass YSOs appear to resemble scaled-up versions of low-mass YSOs. It was found that the YSOs form an evolutionary sequence, based on their spectra, consistent with the existing theoretical models. Type I YSOs have strong H2 emission, no ionized lines, and are redder than the other two subtypes. As such, these are considered to be the youngest sources. The Type III sources are bluest, and therefore considered to be the oldest subtype. They have strong H I lines and fluorescent Fe II 1.6878 μm emission. They may also have weak H2 emission. Type III sources may even be beginning to form a mini-H II region. XSHOOTER data from 10 Herbig Be stars were analysed. The evidence suggests that winds and disks are common among Herbig stars, as they are among their main sequence classical Be star counterparts. Line broadening was seen in many of the sources, though it was not possible to identify whether this was due to Stark broadening or electron scattering. The observations and analysis presented in this thesis are an important step forward for the field of massive star formation. They also have the potential to be a starting block for future work.

The Building History of XUV disks of M83& NGC2403 with TRGB Archaeology

NASA Astrophysics Data System (ADS)

Koda, Jin

2015-06-01

We propose deep HSC g & i-band imaging of two extended ultraviolet (XUV) disks of M83 and NGC2403. These galaxies have the prototype XUV disks with the largest size ( 1 deg and 30 arcmin). The Subaru HSC permits unprecedentedly deep imaging over these gigantic XUV disks, including sufficient surrounding areas which are used for sky subtraction and statistical estimation of background contamination. This project probes the building history of the XUV disks using archeological stellar populations, especially the tip of red giant branch (TRGB) stars (age 2-14 Gyr). Their presence and distribution over the XUV disks will reveal any star formation (SF) occurring over the past 2 Gyr, 4-6 Gyr, and beyond - i.e., the epochs preceding the recent (UV-traced) state of SF. Their color depends strongly on metallicity, thus providing an additional measure of star-gas recycling during the evolution of the XUV disks. In addition, we will detect young & massive main sequence stars (<100 Myr) and He-burning stars (100-500 Myr). Comparing various generations of stars, in terms of number densities and spatial distributions, will reveal the much-unexplored SF history in the XUV disks.

WIYN Open Cluster Study. LXXVI. Li Evolution Among Stars of Low/Intermediate Mass: The Metal-deficient Open Cluster NGC 2506

NASA Astrophysics Data System (ADS)

Anthony-Twarog, Barbara J.; Lee-Brown, Donald B.; Deliyannis, Constantine P.; Twarog, Bruce A.

2018-03-01

HYDRA spectra of 287 stars in the field of NGC 2506 from the turnoff through the giant branch are analyzed. With previous data, 22 are identified as probable binaries; 90 more are classified as potential non-members. Spectroscopic analyses of ∼60 red giants and slowly rotating turnoff stars using line equivalent widths and a neural network approach lead to [Fe/H] = ‑0.27 ± 0.07 (s.d.) and [Fe/H] = ‑0.27 ± 0.06 (s.d.), respectively. Li abundances are derived for 145 probable single-star members, 44 being upper limits. Among turnoff stars outside the Li-dip, A(Li) = 3.04 ± 0.16 (s.d.), with no trend with color, luminosity, or rotation speed. Evolving from the turnoff across the subgiant branch, there is a well-delineated decline to A(Li) ∼1.25 at the giant branch base, coupled with the rotational spindown from between ∼20 and 70 km s‑1 to less than 20 km s‑1 for stars entering the subgiant branch and beyond. A(Li) remains effectively constant from the giant branch base to the red giant clump level. A new member above the clump redefines the path of the first-ascent red giant branch; its Li is 0.6 dex below the first-ascent red giants. With one exception, all post-He-flash stars have upper limits to A(Li), at or below the level of the brightest first-ascent red giant. The patterns are in excellent qualitative agreement with the model predictions for low/intermediate-mass stars which undergo rotation-induced mixing at the turnoff and subgiant branch, first dredge-up, and thermohaline mixing beyond the red giant bump.

Massive star formation by accretion. I. Disc accretion

NASA Astrophysics Data System (ADS)

Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.

2016-01-01

Context. Massive stars likely form by accretion and the evolutionary track of an accreting forming star corresponds to what is called the birthline in the Hertzsprung-Russell (HR) diagram. The shape of this birthline is quite sensitive to the evolution of the entropy in the accreting star. Aims: We first study the reasons why some birthlines published in past years present different behaviours for a given accretion rate. We then revisit the question of the accretion rate, which allows us to understand the distribution of the observed pre-main-sequence (pre-MS) stars in the HR diagram. Finally, we identify the conditions needed to obtain a large inflation of the star along its pre-MS evolution that may push the birthline towards the Hayashi line in the upper part of the HR diagram. Methods: We present new pre-MS models including accretion at various rates and for different initial structures of the accreting core. We compare them with previously published equivalent models. From the observed upper envelope of pre-MS stars in the HR diagram, we deduce the accretion law that best matches the accretion history of most of the intermediate-mass stars. Results: In the numerical computation of the time derivative of the entropy, some treatment leads to an artificial loss of entropy and thus reduces the inflation that the accreting star undergoes along the birthline. In the case of cold disc accretion, the existence of a significant swelling during the accretion phase, which leads to radii ≳ 100 R⊙ and brings the star back to the red part of the HR diagram, depends sensitively on the initial conditions. For an accretion rate of 10-3M⊙ yr-1, only models starting from a core with a significant radiative region evolve back to the red part of the HR diagram. We also obtain that, in order to reproduce the observed upper envelope of pre-MS stars in the HR diagram with an accretion law deduced from the observed mass outflows in ultra-compact HII regions, the fraction of the mass that is accreted onto the star should represent a decreasing fraction of the mass outflows when the mass of the accreting object increases. In other words, the accretion efficiency (mass effectively accreted onto the star with respect to the total in falling matter) decreases when the mass of the star increases.

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

Variability of Red Supergiants in M31 from the Palomar Transient Factory

NASA Astrophysics Data System (ADS)

Soraisam, Monika D.; Bildsten, Lars; Drout, Maria R.; Bauer, Evan B.; Gilfanov, Marat; Kupfer, Thomas; Laher, Russ R.; Masci, Frank; Prince, Thomas A.; Kulkarni, Shrinivas R.; Matheson, Thomas; Saha, Abhijit

2018-05-01

Most massive stars end their lives as red supergiants (RSGs), a short-lived evolutionary phase when they are known to pulsate with varying amplitudes. The RSG period–luminosity (PL) relation has been measured in the Milky Way, the Magellanic Clouds and M33 for about 120 stars in total. Using over 1500 epochs of R-band monitoring from the Palomar Transient Factory survey over a five-year period, we study the variability of 255 spectroscopically cataloged RSGs in M31. We find that all RGSs brighter than M K ≈ ‑10 mag (log(L/L ⊙) > 4.8) are variable at Δm R > 0.05 mag. Our period analysis finds 63 with significant pulsation periods. Using the periods found and the known values of M K for these stars, we derive the RSG PL relation in M31 and show that it is consistent with those derived earlier in other galaxies of different metallicities. We also detect, for the first time, a sequence of likely first-overtone pulsations. Comparison to stellar evolution models from MESA confirms the first-overtone hypothesis and indicates that the variable stars in this sample have 12 M ⊙ < M < 24 M ⊙. As these RSGs are the immediate progenitors to Type II-P core-collapse supernovae (SNe), we also explore the implication of their variability in the initial-mass estimates for SN progenitors based on archival images of the progenitors. We find that this effect is small compared to the present measurement errors.

Optical Searches for Baryonic Dark Matter

NASA Astrophysics Data System (ADS)

Graff, David Steven

1997-08-01

Microlensing results suggest that a good fraction of the halo is composed of massive chunks (0.1-1 Msolar) called MACHOs. I examine several optical searches for dim stars to constrain the local density of MACHOs. These searches show that (1) there are few red dwarfs in the galactic halo, and (2) they suggest that there are few brown dwarfs. I also find that (3) there may be sufficiently many white dwarfs in the halo to account for the microlensing results, but only if certain interesting conditions are met. (1) I examine a deep search for halo red dwarfs (Bahcall, Flynn, Gould & Kirhakos 1994). Using new stellar models and parallax observations of low mass, low metallicity stars, I find the halo red dwarf density to be <1% of the halo, while my best estimate of this value is 0.14-0.37%. (2) I derive mass functions (MF) for halo red dwarfs (the faintest hydrogen burning stars) and then extrapolate to place limits on the total mass of halo brown dwarfs (stars not quite massive enough to burn hydrogen). I find that the MF for halo red dwarfs cannot rise more quickly than 1/m2 as one approaches the hydrogen burning limit. Using recent results from star formation theory, I extrapolate the MF into the brown-dwarf regime. Likely extrapolations imply that the total mass of brown dwarfs in the halo is less than ~3% of the local mass density of the halo (~0.3% for the more realistic models I consider). My limits apply to brown dwarfs in the halo that come from the same stellar population as the red dwarfs. (3) A ground based search by Liebert, Dahn & Monet (1988) and a search of the Hubble Deep Field by Flynn, Bahcall & Gould (1996) have found no evidence for a substantial halo population of white dwarfs, implying that the putative halo population is either dim enough or sparse enough to elude detection. I use white dwarf luminosity functions calculated from various main sequence progenitor mass functions to re-examine the implications of these searches in light of recent microlensing results. I show that the minimum age of the white dwarf population depends upon assumptions regarding the initial mass function, atmospheric composition, and their total density. When I compare various theoretical white dwarf luminosity functions in which I vary these three parameters with the non detections of Liebert et al. and Flynn et al., I conclude that if white dwarfs constitute a significant portion of the halo then (I) the Universe must be 11 Gyr old and (II) they must have helium dominated atmospheres. Thus, white dwarfs could be the MACHOs and could make a significant contribution to galactic dark matter.

The Solar Neighborhood. XXV. Discovery of New Proper Motion Stars with 0.40 sec/yr > mu > or = 0.18 sec/yr Between Declinations -47 deg and 00 deg

NASA Technical Reports Server (NTRS)

Boyd, Mark R.; Winters, Jennifer G.; Henry, Todd J.; Jao, Wei-Chun; Finch, Charlie T.; Subasavage, John P.; Hambly, Nigel C.

2011-01-01

We present 2817 new southern proper motion systems with 0.40 sec/yr > mu > or = 0.18 sec/yr and declination between 47 deg and 00 deg. This is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We use the same photometric relations as previous searches to provide distance estimates based on the assumption that the objects are single main-sequence stars. We find 79 new red dwarf systems predicted to be within 25 pc, including a few new components of previously known systems. Two systems--SCR 1731-2452 at 9.5 pc and SCR 1746-3214 at 9.9 pc--are anticipated to be within 10 pc. We also find 23 new white dwarf (WD) candidates with distance estimates of 15-66 pc, as well as 360 new red subdwarf candidates. With this search, we complete the SCR sweep of the southern sky for stars with mu > or = 0.18 sec/yr and R(sub 59F) < or = 16.5, resulting in a total of 5042 objects in 4724 previously unreported proper motion systems. Here we provide selected comprehensive lists from our SCR proper motion search to date, including 152 red dwarf systems estimated to be within 25 pc (9 within 10 pc), 46 WDs (10 within 25 pc), and 598 subdwarf candidates. The results of this search suggest that there are more nearby systems to be found at fainter magnitudes and lower proper motion limits than those probed so far.

Soviet News and Propaganda Highlights from Red Star (The Official Newspaper of the Soviet Defense Establishment) for the Period 1-30 April 1981.

DTIC Science & Technology

1981-04-01

intended to provide daily guidance to the Soviet military political cadre concerning domestic and international issues/events. Men and women in the Soviet... soldier . PART I. SOVIET PERCEPTIONS OF INTERNATIONAL EVENTS. in April 1981, approximately 30 percent of the total space in Red Star re- ported events...of Husak’s speech was reprinted in Red Star. A great number of articles stressed friendship between the Soviet Union and Czechoslovakia. In Bulgaria

Evidence for extended chromospheres surrounding red giant stars

NASA Technical Reports Server (NTRS)

Stencel, R. E.

1982-01-01

Observational evidence and theoretical arguments are summarized which indicate that regions of partially ionized hydrogen extending several stellar radii are an important feature of red giant and supergiant stars. The implications of the existence of extended chromospheres are examined in terms of the nature of the other atmospheres of, and mass loss from cool stars.

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

Tovmassian, G.; González–Buitrago, D.; Zharikov, S.

We studied two objects identified as cataclysmic variables (CVs) with periods exceeding the natural boundary for Roche-lobe-filling zero-age main sequence (ZAMS) secondary stars. We present observational results for V1082 Sgr with a 20.82 hr orbital period, an object that shows a low luminosity state when its flux is totally dominated by a chromospherically active K star with no signs of ongoing accretion. Frequent accretion shutoffs, together with characteristics of emission lines in a high state, indicate that this binary system is probably detached, and the accretion of matter on the magnetic white dwarf takes place through stellar wind from themore » active donor star via coupled magnetic fields. Its observational characteristics are surprisingly similar to V479 And, a 14.5 hr binary system. They both have early K-type stars as donor stars. We argue that, similar to the shorter-period prepolars containing M dwarfs, these are detached binaries with strong magnetic components. Their magnetic fields are coupled, allowing enhanced stellar wind from the K star to be captured and channeled through the bottleneck connecting the two stars onto the white dwarf’s magnetic pole, mimicking a magnetic CV. Hence, they become interactive binaries before they reach contact. This will help to explain an unexpected lack of systems possessing white dwarfs with strong magnetic fields among detached white+red dwarf systems.« less

Studies of Evolved Star Mass Loss: GRAMS Modeling of Red Supergiant and Asymptotic Giant Branch Stars in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, S.; Riebel, D.; Boyer, M.; Meixner, M.

2012-01-01

As proposed in our NASA Astrophysics Data Analysis Program (ADAP) proposal, my colleagues and I are studying mass loss from evolved stars. Such stars lose their own mass in their dying stages, and in their expelled winds they form stardust. To model mass loss from these evolved stars, my colleagues and I have constructed GRAMS: the Grid of Red supergiant and Asymptotic giant branch star ModelS. These GRAMS radiative transfer models are fit to optical through mid-infrared photometry of red supergiant (RSG) stars and asymptotic giant branch (AGB) stars. I will discuss our current studies of mass loss from AGB and RSG stars in the Small Magellanic Cloud (SMC), fitting GRAMS models to the photometry of SMC evolved star candidates identified from the SAGE-SMC (PI: K. Gordon) Spitzer Space Telescope Legacy survey. This work will be briefly compared to similar work we have done for the LMC. I will also discuss Spitzer Infrared Spectrograph (IRS) studies of the dust produced by AGB and RSG stars in the LMC. BAS is grateful for support from the NASA-ADAP grant NNX11AB06G.

Large Magellanic Cloud helium-rich peculiar blue supergiants and SN 1987A

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

Tuchman, Y.; Wheeler, J.C.

1990-11-01

The theoretical distribution of massive stars in the H-R diagram is compared to the revised data of Fitzpatrick and Garmany for the LMC. Preferred models of about 20 M solar masses undergo a thermal contraction at T(eff) about 35,000 K at the end of core hydrogen burning but reestablish thermal equilibrium to the red of the main sequence at T(eff) about 20,000 K after ignition of a hydrogen-burning shell. They then evolve on a nuclear time scale to T(eff) about 6000 K where they lose thermal equilibrium and jump to the Hayashi track. The theoretical and observed distributions agree withmore » two significant exceptions: the blue thermal contraction gap is overpopulated compared to the theory, and there is a ledge crossing the center of the H-R diagram. The hypothesis that some of the observed stars in the blue gap are secondaries that have accreted helium-rich matter from deep within the hydrogen envelope of a red supergiant primary is explored. Some preliminary observational justification is given. 27 refs.« less

Minerva-Red: Small Planets Orbiting Small Stars

NASA Astrophysics Data System (ADS)

Blake, Cullen

2018-06-01

Recent results from Kepler and ground-based exoplanet surveys suggest that low-mass stars are host to numerous small planets. Since low-mass stars are intrinsically faint at optical wavelengths, obtaining the Doppler precision necessary to detect these companions remains a challenge for existing instruments. I will describe MINERVA-Red, a project to use a robotic, near-infrared optimized 0.7-meter telescope and a specialized Doppler spectrometer to carry out an intensive, multi-year campaign designed to reveal the planetary systems orbiting some of the closest stars to the Sun. The MINERVA-Red cross-dispersed echelle spectrograph is optimized for the “deep red”, between 800 nm and 900 nm, where the stars that will be targeted are relatively bright. The instrument is very compact and designed for the ultimate in Doppler precision – it uses a single-mode fiber input. I will describe the spectrometer and the status of the MINERVA-Red project, which is expected to begin routine operations at Whipple Observatory on Mt Hopkins, Arizona, in 2018.

Extended main sequence turnoffs in intermediate-age star clusters: a correlation between turnoff width and early escape velocity

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

Goudfrooij, Paul; Kozhurina-Platais, Vera; Kalirai, Jason S.

2014-12-10

We present a color-magnitude diagram analysis of deep Hubble Space Telescope imaging of a mass-limited sample of 18 intermediate-age (1-2 Gyr old) star clusters in the Magellanic Clouds, including eight clusters for which new data were obtained. We find that all star clusters in our sample feature extended main-sequence turnoff (eMSTO) regions that are wider than can be accounted for by a simple stellar population (including unresolved binary stars). FWHM widths of the MSTOs indicate age spreads of 200-550 Myr. We evaluate the dynamical evolution of clusters with and without initial mass segregation. Our main results are (1) the fractionmore » of red clump (RC) stars in secondary RCs in eMSTO clusters scales with the fraction of MSTO stars having pseudo-ages of ≲1.35 Gyr; (2) the width of the pseudo-age distributions of eMSTO clusters is correlated with their central escape velocity v {sub esc}, both currently and at an age of 10 Myr. We find that these two results are unlikely to be reproduced by the effects of interactive binary stars or a range of stellar rotation velocities. We therefore argue that the eMSTO phenomenon is mainly caused by extended star formation within the clusters; and (3) we find that v {sub esc} ≥ 15 km s{sup –1} out to ages of at least 100 Myr for all clusters featuring eMSTOs, and v {sub esc} ≤ 12 km s{sup –1} at all ages for two lower-mass clusters in the same age range that do not show eMSTOs. We argue that eMSTOs only occur for clusters whose early escape velocities are higher than the wind velocities of stars that provide material from which second-generation stars can form. The threshold of 12-15 km s{sup –1} is consistent with wind velocities of intermediate-mass asymptotic giant branch stars and massive binary stars in the literature.« less

Pulsation Properties of Carbon and Oxygen Red Giants

NASA Astrophysics Data System (ADS)

Percy, J. R.; Huang, D. J.

2015-07-01

We have used up to 12 decades of AAVSO visual observations, and the AAVSO VSTAR software package to determine new and/or improved periods of 5 pulsating biperiodic carbon (C-type) red giants, and 12 pulsating biperiodic oxygen (M-type) red giants. We have also determined improved periods for 43 additional C-type red giants, in part to search for more biperiodic C-type stars, and also for 46 M-type red giants. For a small sample of the biperiodic C-type and M-type stars, we have used wavelet analysis to determine the time scales of the cycles of amplitude increase and decrease. The C-type and M-type stars do not differ significantly in their period ratios (first overtone to fundamental). There is a marginal difference in the lengths of their amplitude cycles. The most important result of this study is that, because of the semiregularity of these stars, and the presence of alias, harmonic, and spurious periods, the periods which we and others derive for these stars—especially the smaller-amplitude ones—must be determined and interpreted with great care and caution. For instance: spurious periods of a year can produce an apparent excess of stars, at that period, in the period distribution.

Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Li, Chengyuan; de Grijs, Richard; Deng, Licai; Milone, Antonino P.

2017-08-01

An increasing number of young massive clusters (YMCs) in the Magellanic Clouds have been found to exhibit bimodal or extended main sequences (MSs) in their color-magnitude diagrams (CMDs). These features are usually interpreted in terms of a coeval stellar population with different stellar rotational rates, where the blue and red MS stars are populated by non- (or slowly) and rapidly rotating stellar populations, respectively. However, some studies have shown that an age spread of several million years is required to reproduce the observed wide turnoff regions in some YMCs. Here we present the ultraviolet-visual CMDs of four Large and Small Magellanic Cloud YMCs, NGC 330, NGC 1805, NGC 1818, and NGC 2164, based on high-precision Hubble Space Telescope photometry. We show that they all exhibit extended main-sequence turnoffs (MSTOs). The importance of age spreads and stellar rotation in reproducing the observations is investigated. The observed extended MSTOs cannot be explained by stellar rotation alone. Adopting an age spread of 35-50 Myr can alleviate this difficulty. We conclude that stars in these clusters are characterized by ranges in both their ages and rotation properties, but the origin of the age spread in these clusters remains unknown.

The CCD photometry of the globular cluster Palomar 1.

NASA Astrophysics Data System (ADS)

Borissova, J.; Spassova, N.

1995-04-01

A CCD photometry of the halo cluster Palomar 1 is presented in the Thuan-Gunn photometric system. The principal sequences of the color-magnitude diagrams are delineated in different spectral bands. The color-magnitude diagrams of the cluster show a well defined red horizontal branch, a subgiant branch and a main-sequence down to about two magnitudes below the main sequence turnoff. The giant branch is absent and the brightest stars are the horizontal branch stars. The age of the cluster determined by comparison with the isochrones of Bell & Vanden Berg (1987) is consistent with an age in the interval 12-14Gyr. A distance modulus of (m-M)_g0_=15.38+/-0.15 magnitude and E(g-r)=0.16 has been derived. An estimate of the cluster structural parameters such as core radius and concentration parameter gives r_c_=1.5pc and c=1.46. A mass estimate of 1.1 10^3^Msun_ and a mass-to-light ratio of 1.79 have been obtained using King's (1966) method. The morphology of color-magnitude diagrams allows Pal 1 to be interpreted as probably a globular cluster rather than an old open one.

THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. VI. LUMINOSITIES AND MASS-LOSS RATES ON POPULATION SCALES

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

Riebel, D.; Meixner, M.; Srinivasan, S.

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to {approx}30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionarymore » parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}, equivalent to a total mass injection rate (including the gas) into the ISM of {approx}6 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K{sub s} band as a function of J - K{sub s} color, BC{sub K{sub s}}= -0.40(J-K{sub s}){sup 2} + 1.83(J-K{sub s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot{sub d}) from C-rich AGB stars, such as log M-dot{sub d} = (-18.90/((K{sub s}-[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.« less

Coolest Orbs on the Block Artist Concept

NASA Image and Video Library

2010-06-24

This artist concept shows hundreds of brown dwarfs deep red, expected to be added to the population of known stars in our solar neighborhood. Our sun and other known stars appear white, yellow or red.

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA. VI. The role of bars in quenching star formation from z = 3 to the present epoch

NASA Astrophysics Data System (ADS)

Gavazzi, G.; Consolandi, G.; Dotti, M.; Fanali, R.; Fossati, M.; Fumagalli, M.; Viscardi, E.; Savorgnan, G.; Boselli, A.; Gutiérrez, L.; Hernández Toledo, H.; Giovanelli, R.; Haynes, M. P.

2015-08-01

A growing body of evidence indicates that the star formation rate per unit stellar mass (sSFR) decreases with increasing mass in normal main-sequence star-forming galaxies. Many processes have been advocated as being responsible for this trend (also known as mass quenching), e.g., feedback from active galactic nuclei (AGNs), and the formation of classical bulges. In order to improve our insight into the mechanisms regulating the star formation in normal star-forming galaxies across cosmic epochs, we determine a refined star formation versus stellar mass relation in the local Universe. To this end we use the Hα narrow-band imaging follow-up survey (Hα3) of field galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Coma and Local superclusters. By complementing this local determination with high-redshift measurements from the literature, we reconstruct the star formation history of main-sequence galaxies as a function of stellar mass from the present epoch up to z = 3. In agreement with previous studies, our analysis shows that quenching mechanisms occur above a threshold stellar mass Mknee that evolves with redshift as ∝ (1 + z)2. Moreover, visual morphological classification of individual objects in our local sample reveals a sharp increase in the fraction of visually classified strong bars with mass, hinting that strong bars may contribute to the observed downturn in the sSFR above Mknee. We test this hypothesis using a simple but physically motivated numerical model for bar formation, finding that strong bars can rapidly quench star formation in the central few kpc of field galaxies. We conclude that strong bars contribute significantly to the red colors observed in the inner parts of massive galaxies, although additional mechanisms are likely required to quench the star formation in the outer regions of massive spiral galaxies. Intriguingly, when we extrapolate our model to higher redshifts, we successfully recover the observed redshift evolution for Mknee. Our study highlights how the formation of strong bars in massive galaxies is an important mechanism in regulating the redshift evolution of the sSFR for field main-sequence galaxies. Based on observations taken at the observatory of San Pedro Martir (Baja California, Mexico), belonging to the Mexican Observatorio Astronómico Nacional.

ACOUSTIC SIGNATURES OF THE HELIUM CORE FLASH

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

Bildsten, Lars; Paxton, Bill; Moore, Kevin

2012-01-15

All evolved stars with masses M {approx}< 2 M{sub Sun} undergo an initiating off-center helium core flash in their M{sub c} Almost-Equal-To 0.48 M{sub Sun} He core as they ascend the red giant branch (RGB). This off-center flash is the first of a few successive helium shell subflashes that remove the core electron degeneracy over 2 Myr, converting the object into a He-burning star. Though characterized by Thomas over 40 years ago, this core flash phase has yet to be observationally probed. Using the Modules for Experiments in Stellar Astrophysics (MESA) code, we show that red giant asteroseismology enabled bymore » space-based photometry (i.e., Kepler and CoRoT) can probe these stars during the flash. The rapid ({approx}< 10{sup 5} yr) contraction of the red giant envelope after the initiating flash dramatically improves the coupling of the p-modes to the core g-modes, making the detection of l = 1 mixed modes possible for these 2 Myr. This duration implies that 1 in 35 stars near the red clump in the H-R diagram will be in their core flash phase. During this time, the star has a g-mode period spacing of {Delta}P{sub g} Almost-Equal-To 70-100 s, lower than the {Delta}P{sub g} Almost-Equal-To 250 s of He-burning stars in the red clump, but higher than the RGB stars at the same luminosity. This places them in an underpopulated part of the large frequency spacing ({Delta}{nu}) versus {Delta}P{sub g} diagram that should ease their identification among the thousands of observed red giants.« less

Progenitors of low-luminosity Type II-Plateau supernovae

NASA Astrophysics Data System (ADS)

Lisakov, Sergey M.; Dessart, Luc; Hillier, D. John; Waldman, Roni; Livne, Eli

2018-01-01

The progenitors of low-luminosity Type II-Plateau supernovae (SNe II-P) are believed to be red supergiant (RSG) stars, but there is much disparity in the literature concerning their mass at core collapse and therefore on the main sequence. Here, we model the SN radiation arising from the low-energy explosion of RSG stars of 12, 25 and 27 M⊙ on the main sequence and formed through single star evolution. Despite the narrow range in ejecta kinetic energy (2.5-4.2 × 1050 erg) in our model set, the SN observables from our three models are significantly distinct, reflecting the differences in progenitor structure (e.g. surface radius, H-rich envelope mass and He-core mass). Our higher mass RSG stars give rise to Type II SNe that tend to have bluer colours at early times, a shorter photospheric phase, and a faster declining V-band light curve (LC) more typical of Type II-linear SNe, in conflict with the LC plateau observed for low-luminosity SNe II. The complete fallback of the CO core in the low-energy explosions of our high-mass RSG stars prevents the ejection of any 56Ni (nor any core O or Si), in contrast to low-luminosity SNe II-P, which eject at least 0.001 M⊙ of 56Ni. In contrast to observations, Type II SN models from higher mass RSGs tend to show an H α absorption that remains broad at late times (due to a larger velocity at the base of the H-rich envelope). In agreement with the analyses of pre-explosion photometry, we conclude that low-luminosity SNe II-P likely arise from low-mass rather than high-mass RSG stars.

Long-orbital-period Prepolars Containing Early K-type Donor Stars. Bottleneck Accretion Mechanism in Action

NASA Astrophysics Data System (ADS)

Tovmassian, G.; González–Buitrago, D.; Zharikov, S.; Reichart, D. E.; Haislip, J. B.; Ivarsen, K. M.; LaCluyze, A. P.; Moore, J. P.; Miroshnichenko, A. S.

2016-03-01

We studied two objects identified as cataclysmic variables (CVs) with periods exceeding the natural boundary for Roche-lobe-filling zero-age main sequence (ZAMS) secondary stars. We present observational results for V1082 Sgr with a 20.82 hr orbital period, an object that shows a low luminosity state when its flux is totally dominated by a chromospherically active K star with no signs of ongoing accretion. Frequent accretion shutoffs, together with characteristics of emission lines in a high state, indicate that this binary system is probably detached, and the accretion of matter on the magnetic white dwarf takes place through stellar wind from the active donor star via coupled magnetic fields. Its observational characteristics are surprisingly similar to V479 And, a 14.5 hr binary system. They both have early K-type stars as donor stars. We argue that, similar to the shorter-period prepolars containing M dwarfs, these are detached binaries with strong magnetic components. Their magnetic fields are coupled, allowing enhanced stellar wind from the K star to be captured and channeled through the bottleneck connecting the two stars onto the white dwarf’s magnetic pole, mimicking a magnetic CV. Hence, they become interactive binaries before they reach contact. This will help to explain an unexpected lack of systems possessing white dwarfs with strong magnetic fields among detached white+red dwarf systems.

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

NASA Astrophysics Data System (ADS)

Nadège, Lagarde

The availability of asteroseismic constraints for a large sample of red-giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. We use a detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al. 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. This study is already published in Lagarde et al. (2015)

High surface magnetic field in red giants as a new signature of planet engulfment?

NASA Astrophysics Data System (ADS)

Privitera, Giovanni; Meynet, Georges; Eggenberger, Patrick; Georgy, Cyril; Ekström, Sylvia; Vidotto, Aline A.; Bianda, Michele; Villaver, Eva; ud-Doula, Asif

2016-09-01

Context. Red giant stars may engulf planets. This may increase the rotation rate of their convective envelope, which could lead to strong dynamo-triggered magnetic fields. Aims: We explore the possibility of generating magnetic fields in red giants that have gone through the process of a planet engulfment. We compare them with similar models that evolve without any planets. We discuss the impact of magnetic braking through stellar wind on the evolution of the surface velocity of the parent star. Methods: By studying rotating stellar models with and without planets and an empirical relation between the Rossby number and the surface magnetic field, we deduced the evolution of the surface magnetic field along the red giant branch. The effects of stellar wind magnetic braking were explored using a relation deduced from magnetohydrodynamics simulations. Results: The stellar evolution model of a red giant with 1.7 M⊙ without planet engulfment and with a time-averaged rotation velocity during the main sequence equal to 100 km s-1 shows a surface magnetic field triggered by convection that is stronger than 10 G only at the base of the red giant branch, that is, for gravities log g> 3. When a planet engulfment occurs, this magnetic field can also appear at much lower gravities, that is, at much higher luminosities along the red giant branch. The engulfment of a 15 MJ planet typically produces a dynamo-triggered magnetic field stronger than 10 G for gravities between 2.5 and 1.9. We show that for reasonable magnetic braking laws for the wind, the high surface velocity reached after a planet engulfment may be maintained sufficiently long to be observable. Conclusions: High surface magnetic fields for red giants in the upper part of the red giant branch are a strong indication of a planet engulfment or of an interaction with a companion. Our theory can be tested by observing fast-rotating red giants such as HD 31994, Tyc 0347-00762-1, Tyc 5904-00513-1, and Tyc 6054-01204-1 and by determining whether they show magnetic fields.

The importance of satellite quenching for the build-up of the red sequence of present-day galaxies

NASA Astrophysics Data System (ADS)

van den Bosch, Frank C.; Aquino, Daniel; Yang, Xiaohu; Mo, H. J.; Pasquali, Anna; McIntosh, Daniel H.; Weinmann, Simone M.; Kang, Xi

2008-06-01

According to the current paradigm, galaxies initially form as disc galaxies at the centres of their own dark matter haloes. During their subsequent evolution, they may undergo a transformation to a red, early-type galaxy, thus giving rise to the build-up of the red sequence. Two important, outstanding questions are (i) which transformation mechanisms are most important and (ii) in what environment do they occur. In this paper, we study the impact of transformation mechanisms that operate only on satellite galaxies, such as strangulation, ram-pressure stripping and galaxy harassment. Using a large galaxy group catalogue constructed from the Sloan Digital Sky Survey, we compare the colours and concentrations of satellites galaxies to those of central galaxies of the same stellar mass, adopting the hypothesis that the latter are the progenitors of the former. On average, satellite galaxies are redder and more concentrated than central galaxies of the same stellar mass, indicating that satellite-specific transformation processes do indeed operate. Central-satellite pairs that are matched in both stellar mass and colour, however, show no average concentration difference, indicating that the transformation mechanisms operating on satellites affect colour more than morphology. We also find that the colour and concentration differences of matched central-satellite pairs are completely independent of the mass of the host halo (not to be confused with the subhalo) of the satellite galaxy, indicating that satellite-specific transformation mechanisms are equally efficient in host haloes of all masses. This strongly rules against mechanisms that are thought to operate only in very massive haloes, such as ram-pressure stripping or harassment. Instead, we argue that strangulation is the main transformation mechanism for satellite galaxies. Finally, we determine the relative importance of satellite quenching for the build-up of the red sequence. We find that roughly 70 per cent of red-sequence satellite galaxies with M* ~ 109h-2Msolar had their star formation quenched as satellites. This drops rapidly with increasing stellar mass, reaching virtually zero at M* ~ 1011h-2Msolar. Therefore, a very significant fraction of red satellite galaxies were already quenched before they became a satellite.

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

Salinas, R.; Pajkos, M. A.; Strader, J.

Intermediate-age star clusters in the Large Magellanic Cloud show extended main sequence turnoffs (MSTOs) that are not consistent with a canonical single stellar population. These broad turnoffs have been interpreted as evidence for extended star formation and/or stellar rotation. Since most of these studies use single frames per filter to do the photometry, the presence of variable stars near the MSTO in these clusters has remained unnoticed and their impact has been totally ignored. We model the influence of Delta Scuti using synthetic CMDs, adding variable stars following different levels of incidence and amplitude distributions. We show that Delta Scutimore » observed at a single phase will produce a broadening of the MSTO without affecting other areas of a CMD such as the upper MS or the red clump; furthermore, the amount of spread introduced correlates with cluster age, as observed. This broadening is constrained to ages ∼1–3 Gyr when the MSTO area crosses the instability strip, which is also consistent with observations. Variable stars cannot explain bifurcarted MSTOs or the extended MSTOs seen in some young clusters, but they can make an important contribution to the extended MSTOs in intermediate-age clusters.« less

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

Casey, Andrew R.; Hawkins, Keith; Koposov, Sergey

The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho- Gaia Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS (≳200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon . For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundancesmore » for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC . We derive and validate effective temperature T {sub eff}, surface gravity log g , and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.« less

V and K-band Mass-Luminosity Relations for M dwarf Stars

NASA Astrophysics Data System (ADS)

Benedict, G. Fritz; Henry, Todd J.; McArthur, Barbara; Franz, Otto G.; Wasserman, Lawrence H.; Dieterich, Sergio

2015-01-01

Applying Hubble Space Telescope Fine Guidance Sensor astrometric techniques developed to establish relative orbits for binary stars (Franz et al. 1998, AJ, 116, 1432), determine masses of binary components (Benedict et al. 2001, AJ, 121, 1607), and measure companion masses of exoplanet host stars (McArthur et al. 2010, ApJ, 715, 1203), we derive masses with an average 2.1% error for 24 components of 12 M dwarf binary star systems. Masses range 0.08 to 0.40 solar masses. With these we update the lower Main Sequence V-band Mass-Luminosity Relation first shown in Henry et al. (1999, ApJ, 512, 864). We demonstrate that a Mass-Luminosity Relation in the K-band has far less scatter than in the V-band. For the eight binary components for which we have component magnitude differences in the K-band the RMS residual drops from 0.5 magnitude in the V-band to 0.05 magnitude in the K-band. These relations can be used to estimate the masses of the ubiquitous red dwarfs that account for 75% of all stars, to an accuracy of 5%, which is much better than ever before.

H I-SELECTED GALAXIES IN THE SLOAN DIGITAL SKY SURVEY. II. THE COLORS OF GAS-RICH GALAXIES

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

West, Andrew A.; Garcia-Appadoo, Diego A.; Dalcanton, Julianne J.

2009-09-15

We utilize color information for an H I-selected sample of 195 galaxies to explore the star formation histories and physical conditions that produce the observed colors. We show that the H I selection creates a significant offset toward bluer colors that can be explained by enhanced recent bursts of star formation. There is also no obvious color bimodality, because the H I selection restricts the sample to bluer, actively star-forming systems, diminishing the importance of the red sequence. Rising star formation rates are still required to explain the colors of galaxies bluer than g - r< 0.3. We also demonstratemore » that the colors of the bluest galaxies in our sample are dominated by emission lines and that stellar population synthesis models alone (without emission lines) are not adequate for reproducing many of the galaxy colors. These emission lines produce large changes in the r - i colors but leave the g - r color largely unchanged. In addition, we find an increase in the dispersion of galaxy colors at low masses that may be the result of a change in the star formation process in low-mass galaxies.« less

Stellar Populations with the LSST

NASA Astrophysics Data System (ADS)

Saha, Abhijit; Olsen, K.; LSST Stellar Populations Collaboration

2006-12-01

The LSST will produce a multi-color map and photometric object catalog of half the sky to g 27.5(5σ). Strategically cadenced time-space sampling of each field spanning ten years will allow variability, proper motion and parallax measurements for objects brighter than g 25. As part of providing an unprecedented map of the Galaxy, the accurate multi-band photometry will permit photometric parallaxes, chemical abundances and a handle on ages via colors at turn-off for main-sequence stars at all distances within the Galaxy, permitting a comprehensive study of star formation histories (SFH) and chemical evolution for field stars. With a geometric parallax accuracy of 1mas, LSST will produce a robust complete sample of the solar neighborhood stars. While delivering parallax accuracy comparable to HIPPARCOS, LSST will extend the catalog to more than a 10 magnitudes fainter limit, and will be complete to MV 15. In the Magellanic Clouds too, the photometry will reach MV +8, allowing the SFH and chemical signatures in the expansive outer extremities to be gleaned from their main sequence stars. This in turn will trace the detailed interaction of the Clouds with the Galaxy halo. The LSST time sampling will identify and characterize variable stars of all types, from time scales of 1hr to several years, a feast for variable star astrophysics. Cepheids and LPVs in all galaxies in the Sculptor, M83 and Cen-A groups are obvious data products: comparative studies will reveal systematic differences with galaxy properties, and help to fine tune the rungs of the distance ladder. Dwarf galaxies within 10Mpc that are too faint to find from surface brightness enhancements will be revealed via over-densities of their red giants: this systematic census will extend the luminosity function of galaxies to the faint limit. Novae discovered by LSST time sampling will trace intergalactic stars out to the Virgo and Fornax clusters.

Galaxy Zoo: Major Galaxy Mergers Are Not a Significant Quenching Pathway

NASA Astrophysics Data System (ADS)

Weigel, Anna K.; Schawinski, Kevin; Caplar, Neven; Carpineti, Alfredo; Hart, Ross E.; Kaviraj, Sugata; Keel, William C.; Kruk, Sandor J.; Lintott, Chris J.; Nichol, Robert C.; Simmons, Brooke D.; Smethurst, Rebecca J.

2017-08-01

We use stellar mass functions to study the properties and the significance of quenching through major galaxy mergers. In addition to SDSS DR7 and Galaxy Zoo 1 data, we use samples of visually selected major galaxy mergers and post-merger galaxies. We determine the stellar mass functions of the stages that we would expect major-merger-quenched galaxies to pass through on their way from the blue cloud to the red sequence: (1) major merger, (2) post-merger, (3) blue early type, (4) green early type, and (5) red early type. Based on their similar mass function shapes, we conclude that major mergers are likely to form an evolutionary sequence from star formation to quiescence via quenching. Relative to all blue galaxies, the major-merger fraction increases as a function of stellar mass. Major-merger quenching is inconsistent with the mass and environment quenching model. At z˜ 0, major-merger-quenched galaxies are unlikely to constitute the majority of galaxies that transition through the green valley. Furthermore, between z˜ 0-0.5, major-merger-quenched galaxies account for 1%-5% of all quenched galaxies at a given stellar mass. Major galaxy mergers are therefore not a significant quenching pathway, neither at z˜ 0 nor within the last 5 Gyr. The majority of red galaxies must have been quenched through an alternative quenching mechanism that causes a slow blue to red evolution. .

A proper motion study of the globular cluster M55

NASA Astrophysics Data System (ADS)

Zloczewski, K.; Kaluzny, J.; Thompson, I. B.

2011-07-01

We have derived the absolute proper motion (PM) of the globular cluster M55 using a large set of CCD images collected with the du Pont telescope between 1997 and 2008. We find (μα cos δ, μδ) = (-3.31 ± 0.10, -9.14 ± 0.15) mas yr-1 relative to background galaxies. Membership status was determined for 16 945 stars with 14 < V < 21 from the central part of the cluster. The PM catalogue includes 52 variables, of which 43 are probable members of M55. This sample not only is dominated by pulsating blue straggler stars, but also includes five eclipsing binaries, three of which are main-sequence objects. The survey also identified several candidate blue, yellow and red straggler stars belonging to the cluster. We detected 15 likely members of the Sgr dSph galaxy located behind M55. The average PM for these stars was measured to be (μα cos δ, μδ) = (-2.23 ± 0.14, -1.83 ± 0.24) mas yr-1.

Carbon stars with oxygen-rich circumstellar material

NASA Technical Reports Server (NTRS)

Jura, Michael; Hawkins, I.

1991-01-01

The IUE satellite was used to search for companions to two carbon-rich stars with oxygen-rich circumstellar envelopes, EU And and V778 Cyg. Depending upon the amount of interstellar extinction and distances (probably between 1 and 2 kpc from the Sun) to these two stars, upper limits were placed between approx. 1.5 and 6 solar mass to the mass of any main sequence companions. For the 'near' distance of 1 kpc, it seems unlikely that there are white dwarf companions because the detection would be expected of ultraviolet emission from accretion of red giant wind material onto the white dwarf. A new model is proposed to explain the oxygen-rich envelopes. If these stars have a high nitrogen abundance, the carbon that is in excess of the oxygen may be carried in the circumstellar envelopes in HCN rather than C2H2 which is a likely key seed molecule for the formation of carbon grains. Consequently, carbon particles may not form; instead, oxygen-rich silicate dust may nucleate from the SiO present in the outflow.

Symbiotic stars

NASA Technical Reports Server (NTRS)

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

Couleurs, etoiles, temperatures.

NASA Astrophysics Data System (ADS)

Spite, F.

The eye is able to distinguish very tiny color differences of contiguous objects (at high light level, cones vision), but it is not a reliable colorimeter. Hot objects (a heated iron rod) emits some red light, a hotter object would provide a yellow-orange light (the filament of a bulb) and a still hotter one a white or even bluish light : this may be at reverse of common life codes, where "red" means hot water and/or danger, and "blue" cool water or cool air. Stars are a good illustration of the link between temperatures and colors. A heated iron rod has a temperature of about 800 K. Let us recall that K is a temperature unit (Kelvin) such that the Kelvin temperature is the Celsius temperature +273).The so called red stars (or cool stars) have temperature around 3000 K, higher than "white-hot iron". The Sun has a still higher temperature (5800 K) and its color is white : the solar light is by definition the "white light", and includes violet, blue, green, yellow, orange and red colors in balanced proportions (the maximum in the yellow-green). It is often said that the Sun is a yellow star. Admittedly, a brief glimpse at the Sun (take care ! never more than a VERY brief glimpse !) provides a perception of yellow light, but such a vision, with the eye overwhelmed by a fierce light, is not able to provide a good evaluation of the solar color : prefer a white sheet of paper illuminated by the Sun at noon and conclude that "the Sun is a white star". It is sometimes asked why red, white and bluish stars are seen in the sky, but no green stars : the solar light has its maximum intensity in the green, but such a dominant green light, equilibrated by some blue and some red light, is what we call "white", so that stars similar to the Sun, with a maximum in the green, are seen as white stars. Faint stars (rods vision of the eye) are also seen as white stars. Spots on the Sun (never look at the Sun ! let us say spots on "projected images of the Sun") appear as black spots : they are in fact bright areas, only slightly less luminous than the undisturbed surface of the Sun, but the eye has a particular of enhancing enormously the contrasts.

Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars

NASA Astrophysics Data System (ADS)

Grunblatt, Samuel K.; Huber, Daniel; Gaidos, Eric; Lopez, Eric D.; Howard, Andrew W.; Isaacson, Howard T.; Sinukoff, Evan; Vanderburg, Andrew; Nofi, Larissa; Yu, Jie; North, Thomas S. H.; Chaplin, William; Foreman-Mackey, Daniel; Petigura, Erik; Ansdell, Megan; Weiss, Lauren; Fulton, Benjamin; Lin, Douglas N. C.

2017-12-01

Despite more than 20 years since the discovery of the first gas giant planet with an anomalously large radius, the mechanism for planet inflation remains unknown. Here, we report the discovery of K2-132b, an inflated gas giant planet found with the NASA K2 Mission, and a revised mass for another inflated planet, K2-97b. These planets orbit on ≈9 day orbits around host stars that recently evolved into red giants. We constrain the irradiation history of these planets using models constrained by asteroseismology and Keck/High Resolution Echelle Spectrometer spectroscopy and radial velocity measurements. We measure planet radii of 1.31 ± 0.11 R J and 1.30 ± 0.07 R J, respectively. These radii are typical for planets receiving the current irradiation, but not the former, zero age main-sequence irradiation of these planets. This suggests that the current sizes of these planets are directly correlated to their current irradiation. Our precise constraints of the masses and radii of the stars and planets in these systems allow us to constrain the planetary heating efficiency of both systems as 0.03{ % }-0.02 % +0.03 % . These results are consistent with a planet re-inflation scenario, but suggest that the efficiency of planet re-inflation may be lower than previously theorized. Finally, we discuss the agreement within 10% of the stellar masses and radii, and the planet masses, radii, and orbital periods of both systems, and speculate that this may be due to selection bias in searching for planets around evolved stars.

THE RED SUPERGIANT CONTENT OF M31

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

Massey, Philip; Evans, Kate Anne, E-mail: kevans@caltech.edu, E-mail: phil.massey@lowell.edu

2016-08-01

We investigate the red supergiant (RSG) population of M31, obtaining the radial velocities of 255 stars. These data substantiate membership of our photometrically selected sample, demonstrating that Galactic foreground stars and extragalactic RSGs can be distinguished on the basis of B V , V R two-color diagrams. In addition, we use these spectra to measure effective temperatures and assign spectral types, deriving physical properties for 192 RSGs. Comparison with the solar metallicity Geneva evolutionary tracks indicates astonishingly good agreement. The most luminous RSGs in M31 are likely evolved from 25–30 M {sub ⊙} stars, while the vast majority evolved frommore » stars with initial masses of 20 M {sub ⊙} or less. There is an interesting bifurcation in the distribution of RSGs with effective temperatures that increases with higher luminosities, with one sequence consisting of early K-type supergiants, and with the other consisting of M-type supergiants that become later (cooler) with increasing luminosities. This separation is only partially reflected in the evolutionary tracks, although that might be due to the mis-match in metallicities between the solar Geneva models and the higher-than-solar metallicity of M31. As the luminosities increase the median spectral type also increases; i.e., the higher mass RSGs spend more time at cooler temperatures than do those of lower luminosities, a result which is new to this study. Finally we discuss what would be needed observationally to successfully build a luminosity function that could be used to constrain the mass-loss rates of RSGs as our Geneva colleagues have suggested.« less

THE SOLAR NEIGHBORHOOD. XXV. DISCOVERY OF NEW PROPER MOTION STARS WITH 0.''40 yr{sup -1} > {mu} {>=} 0.''18 yr{sup -1} BETWEEN DECLINATIONS -47{sup 0} AND 00{sup 0}

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

Boyd, Mark R.; Winters, Jennifer G.; Henry, Todd J.

2011-07-15

We present 2817 new southern proper motion systems with 0.''40 yr{sup -1} > {mu} {>=} 0.''18 yr{sup -1} and declination between -47{sup 0} and 00{sup 0}. This is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We use the same photometric relations as previous searches to provide distance estimates based on the assumption that the objects are single main-sequence stars. We find 79 new red dwarf systems predicted to be within 25 pc, including a few new components of previously known systems. Two systems-SCR 1731-2452 at 9.5 pc and SCR 1746-3214 at 9.9 pc-are anticipatedmore » to be within 10 pc. We also find 23 new white dwarf (WD) candidates with distance estimates of 15-66 pc, as well as 360 new red subdwarf candidates. With this search, we complete the SCR sweep of the southern sky for stars with {mu} {>=} 0.''18 yr{sup -1} and R{sub 59F} {<=} 16.5, resulting in a total of 5042 objects in 4724 previously unreported proper motion systems. Here we provide selected comprehensive lists from our SCR proper motion search to date, including 152 red dwarf systems estimated to be within 25 pc (9 within 10 pc), 46 WDs (10 within 25 pc), and 598 subdwarf candidates. The results of this search suggest that there are more nearby systems to be found at fainter magnitudes and lower proper motion limits than those probed so far.« less

Evolved stars and the origin of abundance trends in planet hosts

NASA Astrophysics Data System (ADS)

Maldonado, J.; Villaver, E.

2016-04-01

Context. Detailed chemical abundance studies have revealed different trends between samples of planet and non-planet hosts. Whether these trends are related to the presence of planets or not is strongly debated. At the same time, tentative evidence that the properties of evolved stars with planets may be different from what we know for main-sequence hosts has recently been reported. Aims: We aim to test whether evolved stars with planets show any chemical peculiarity that could be related to the planet formation process. Methods: In a consistent way, we determine the metallicity and individual abundances of a large sample of evolved (subgiants and red giants) and main-sequence stars that are with and without known planetary companions, and discuss their metallicity distribution and trends. Our methodology is based on the analysis of high-resolution échelle spectra (R ≳ 57 000) from 2-3 m class telescopes. It includes the calculation of the fundamental stellar parameters, as well as individual abundances of C, O , Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn. Results: No differences in the ⟨[X/Fe]⟩ vs. condensation temperature (TC) slopes are found between the samples of planet and non-planet hosts when all elements are considered. However, if the analysis is restricted to only refractory elements, differences in the TC-slopes between stars with and without known planets are found. This result is found to be dependent on the stellar evolutionary stage, as it holds for main-sequence and subgiant stars, while there seems to be no difference between planet and non-planet hosts among the sample of giants. A search for correlations between the TC-slope and the stellar properties reveals significant correlations with the stellar mass and the stellar age. The data also suggest that differences in terms of mass and age between main-sequence planet and non-planet hosts may be present. Conclusions: Our results are well explained by radial mixing in the Galaxy. The sample of giants contains stars that are more massive and younger than their main-sequence counterparts. This leads to a sample of stars that are possibly less contaminated by stars that were not born in the solar neighbourhood, leading to no chemical differences between planet and non-planet hosts. The sample of main-sequence stars may contain more stars from the outer disc (specially the non-planet host sample) which might lead to the differences observed in the chemical trends. Based on observations made with the Mercator Telescope; on observations made with the Nordic Optical Telescope; on observations made with the Italian Telescopio Nazionale Galileo; on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto; and on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 072.C-0488(E), 080.D-0347(A), 081.D-0870(A), 087.C-0831(A), and 183.C-0972(A).Tables B.1-B.3 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/588/A98

The Evolution of Dusty Star formation in Galaxy Clusters to z = 1: Spitzer Infrared Observations of the First Red-Sequence Cluster Survey

NASA Astrophysics Data System (ADS)

Webb, T. M. A.; O'Donnell, D.; Yee, H. K. C.; Gilbank, David; Coppin, Kristen; Ellingson, Erica; Faloon, Ashley; Geach, James E.; Gladders, Mike; Noble, Allison; Muzzin, Adam; Wilson, Gillian; Yan, Renbin

2013-10-01

We present the results of an infrared (IR) study of high-redshift galaxy clusters with the MIPS camera on board the Spitzer Space Telescope. We have assembled a sample of 42 clusters from the Red-Sequence Cluster Survey-1 over the redshift range 0.3 < z < 1.0 and spanning an approximate range in mass of 1014-15 M ⊙. We statistically measure the number of IR-luminous galaxies in clusters above a fixed inferred IR luminosity of 2 × 1011 M ⊙, assuming a star forming galaxy template, per unit cluster mass and find it increases to higher redshift. Fitting a simple power-law we measure evolution of (1 + z)5.1 ± 1.9 over the range 0.3 < z < 1.0. These results are tied to the adoption of a single star forming galaxy template; the presence of active galactic nuclei, and an evolution in their relative contribution to the mid-IR galaxy emission, will alter the overall number counts per cluster and their rate of evolution. Under the star formation assumption we infer the approximate total star formation rate per unit cluster mass (ΣSFR/M cluster). The evolution is similar, with ΣSFR/M cluster ~ (1 + z)5.4 ± 1.9. We show that this can be accounted for by the evolution of the IR-bright field population over the same redshift range; that is, the evolution can be attributed entirely to the change in the in-falling field galaxy population. We show that the ΣSFR/M cluster (binned over all redshift) decreases with increasing cluster mass with a slope (ΣSFR/M_{cluster} \\sim M_{cluster}^{-1.5+/- 0.4}) consistent with the dependence of the stellar-to-total mass per unit cluster mass seen locally. The inferred star formation seen here could produce ~5%-10% of the total stellar mass in massive clusters at z = 0, but we cannot constrain the descendant population, nor how rapidly the star-formation must shut-down once the galaxies have entered the cluster environment. Finally, we show a clear decrease in the number of IR-bright galaxies per unit optical galaxy in the cluster cores, confirming star formation continues to avoid the highest density regions of the universe at z ~ 0.75 (the average redshift of the high-redshift clusters). While several previous studies appear to show enhanced star formation in high-redshift clusters relative to the field we note that these papers have not accounted for the overall increase in galaxy or dark matter density at the location of clusters. Once this is done, clusters at z ~ 0.75 have the same or less star formation per unit mass or galaxy as the field.

Near infra-red astronomy with adaptive optics and laser guide stars at the Keck Observatory

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

Max, C.E.; Gavel, D.T.; Olivier, S.S.

1995-08-03

A laser guide star adaptive optics system is being built for the W. M. Keck Observatory`s 10-meter Keck II telescope. Two new near infra-red instruments will be used with this system: a high-resolution camera (NIRC 2) and an echelle spectrometer (NIRSPEC). The authors describe the expected capabilities of these instruments for high-resolution astronomy, using adaptive optics with either a natural star or a sodium-layer laser guide star as a reference. They compare the expected performance of these planned Keck adaptive optics instruments with that predicted for the NICMOS near infra-red camera, which is scheduled to be installed on the Hubblemore » Space Telescope in 1997.« less

Meridional circulation and CNO anomalies in red giant stars

NASA Technical Reports Server (NTRS)

Sweigart, A. V.; Mengel, J. G.

1979-01-01

The possibility is investigated that meridional circulation driven by internal rotation might lead to the mixing of CNO-processed material from the vicinity of the hydrogen shell into the envelope of a red giant star. This theory of meridional mixing is found to be generally consistent with available data and to be capable of explaining a number of observational results without invoking a radical departure from the standard physics of stellar interiors. It is suggested that meridional circulation must be a normal characteristic of a rotating star and that meridional mixing provides a reasonable framework for understanding many of the CNO anomalies exhibited by weak-G-band and CN-strong stars as well as the low C-12/C-13 ratios measured among field red giants.

The primordial and evolutionary abundance variations in globular-cluster stars: a problem with two unknowns

NASA Astrophysics Data System (ADS)

Denissenkov, P. A.; VandenBerg, D. A.; Hartwick, F. D. A.; Herwig, F.; Weiss, A.; Paxton, B.

2015-04-01

We demonstrate that among the potential sources of the primordial abundance variations of the proton-capture elements in globular-cluster stars proposed so far, such as the hot-bottom burning in massive asymptotic giant branch stars and H burning in the convective cores of supermassive and fast-rotating massive main-sequence (MS) stars, only the supermassive MS stars with M > 104 M⊙ can explain all the observed abundance correlations without any fine-tuning of model parameters. We use our assumed chemical composition for the pristine gas in M13 (NGC 6205) and its mixtures with 50 and 90 per cent of the material partially processed in H burning in the 6 × 104 M⊙ MS model star as the initial compositions for the normal, intermediate, and extreme populations of low-mass stars in this globular cluster, as suggested by its O-Na anticorrelation. We evolve these stars from the zero-age MS to the red giant branch (RGB) tip with the thermohaline and parametric prescriptions for the RGB extra mixing. We find that the 3He-driven thermohaline convection cannot explain the evolutionary decline of [C/Fe] in M13 RGB stars, which, on the other hand, is well reproduced with the universal values for the mixing depth and rate calibrated using the observed decrease of [C/Fe] with MV in the globular cluster NGC5466 that does not have the primordial abundance variations.

Evidence for extended chromospheres surrounding red giant stars

NASA Technical Reports Server (NTRS)

Stencel, R. E.

1981-01-01

There is now an increasing amount of both observational evidence and theoretical arguments that regions of partially ionized hydrogen extending several stellar radii are an important feature of red giant and supergiant stars. This evidence is discussed and the implications of the existence of extended chromospheres in terms of the nature of the outer atmospheres of, and mass loss from, cool stars are examined.

Asteroseismic Diagram for Subgiants and Red Giants

NASA Astrophysics Data System (ADS)

Gai, Ning; Tang, Yanke; Yu, Peng; Dou, Xianghua

2017-02-01

Asteroseismology is a powerful tool for constraining stellar parameters. NASA’s Kepler mission is providing individual eigenfrequencies for a huge number of stars, including thousands of red giants. Besides the frequencies of acoustic modes, an important breakthrough of the Kepler mission is the detection of nonradial gravity-dominated mixed-mode oscillations in red giants. Unlike pure acoustic modes, mixed modes probe deeply into the interior of stars, allowing the stellar core properties and evolution of stars to be derived. In this work, using the gravity-mode period spacing and the large frequency separation, we construct the ΔΠ1-Δν asteroseismic diagram from models of subgiants and red giants with various masses and metallicities. The relationship ΔΠ1-Δν is able to constrain the ages and masses of the subgiants. Meanwhile, for red giants with masses above 1.5 M ⊙, the ΔΠ1-Δν asteroseismic diagram can also work well to constrain the stellar age and mass. Additionally, we calculate the relative “isochrones” τ, which indicate similar evolution states especially for similar mass stars, on the ΔΠ1-Δν diagram.

From starburst to quiescence: testing active galactic nucleus feedback in rapidly quenching post-starburst galaxies

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

Yesuf, Hassen M.; Faber, S. M.; Trump, Jonathan R.

Post-starbursts are galaxies in transition from the blue cloud to the red sequence. Although they are rare today, integrated over time they may be an important pathway to the red sequence. This work uses Sloan Digital Sky Survey, the Galaxy Evolution Explorer, and Wide-field Infrared Survey Explorer observations to identify the evolutionary sequence from starbursts to fully quenched post-starbursts (QPSBs) in the narrow mass range log M(M {sub ☉}) = 10.3-10.7, and identifies 'transiting' post-starbursts (TPSBs) which are intermediate between these two populations. In this mass range, ∼0.3% of galaxies are starbursts, ∼0.1% are QPSBs, and ∼0.5% are the transitingmore » types in between. The TPSBs have stellar properties that are predicted for fast-quenching starbursts and morphological characteristics that are already typical of early-type galaxies. The active galactic nucleus (AGN) fraction, as estimated from optical line ratios, of these post-starbursts is about three times higher (≳ 36% ± 8%) than that of normal star forming galaxies of the same mass, but there is a significant delay between the starburst phase and the peak of nuclear optical AGN activity (median age difference of ≳ 200 ± 100 Myr), in agreement with previous studies. The time delay is inferred by comparing the broadband near-NUV-to-optical photometry with stellar population synthesis models. We also find that starbursts and post-starbursts are significantly more dust obscured than normal star forming galaxies in the same mass range. About 20% of the starbursts and 15% of the TPSBs can be classified as 'dust-obscured galaxies' (DOGs), with a near-UV-to-mid-IR flux ratio of ≳ 900, while only 0.8% of normal galaxies are DOGs. The time delay between the starburst phase and AGN activity suggests that AGNs do not play a primary role in the original quenching of starbursts but may be responsible for quenching later low-level star formation by removing gas and dust during the post-starburst phase.« less

PLANET ENGULFMENT BY {approx}1.5-3 M{sub sun} RED GIANTS

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

Kunitomo, M.; Ikoma, M.; Sato, B.

2011-08-20

Recent radial-velocity surveys for GK clump giants have revealed that planets also exist around {approx}1.5-3 M{sub sun} stars. However, no planets have been found inside 0.6 AU around clump giants, in contrast to solar-type main-sequence stars, many of which harbor short-period planets such as hot Jupiters. In this study, we examine the possibility that planets were engulfed by host stars evolving on the red-giant branch (RGB). We integrate the orbital evolution of planets in the RGB and helium-burning phases of host stars, including the effects of stellar tide and stellar mass loss. Then we derive the critical semimajor axis (ormore » the survival limit) inside which planets are eventually engulfed by their host stars after tidal decay of their orbits. Specifically, we investigate the impact of stellar mass and other stellar parameters on the survival limit in more detail than previous studies. In addition, we make detailed comparisons with measured semimajor axes of planets detected so far, which no previous study has done. We find that the critical semimajor axis is quite sensitive to stellar mass in the range between 1.7 and 2.1 M{sub sun}, which suggests a need for careful comparison between theoretical and observational limits of the existence of planets. Our comparison demonstrates that all planets orbiting GK clump giants that have been detected are beyond the survival limit, which is consistent with the planet-engulfment hypothesis. However, on the high-mass side (>2.1M{sub sun}), the detected planets are orbiting significantly far from the survival limit, which suggests that engulfment by host stars may not be the main reason for the observed lack of short-period giant planets. To confirm our conclusion, the detection of more planets around clump giants, especially with masses {approx}> 2.5M{sub sun}, is required.« less

A New Formation Mechanism for the Hottest Horizontal-Branch Stars

NASA Technical Reports Server (NTRS)

Sweigart, Allen V.; Oegerle, William R. (Technical Monitor)

2002-01-01

Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet color-magnitude diagrams (CMDs) of both omega Cen and NGC 2808. In order to investigate the origin of these subluminous stars, we have constructed a detailed set of evolutionary sequences that follow the evolution of low-mass stars continuously from the zero-age main sequence through the helium-core flash to the HB for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the high temperature gap along the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the main helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the envelope during a late helium-core flash greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous increase in the HB effective temperature. We argue that the hot HB gap observed in NGC 2808 is associated with this theoretically predicted dichotomy in the RB properties. Using new helium- and carbon-rich stellar atmospheres, we show that the changes in the envelope abundances due to flash mixing will suppress the ultraviolet flux in the spectra of hot EHB stars. We suggest that such changes in the emergent spectral energy distribution are primarily responsible for explaining the hot subluminous EHB stars in omega Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations.

Sizing Up Red-Giant Twins

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-02-01

In KIC 9246715, two red-giant stars twins in nearly every way circle each other in a 171-day orbit. This binary pair may be a key to learning about masses and radii of stars with asteroseismology, the study of oscillations in the interiors of stars.Two Ways to MeasureIn order to understand a stars evolution, it is critical that we know its mass and radius. Unfortunately, these quantities are often difficult to pin down!One of the few cases in which we can directly measure stars masses and radii is in eclipsing binaries, wherein two stars eclipse each other as they orbit. If we have a well-sampled light curve for the binary, as well as radial velocities for both stars, then we can determine the stars complete orbital information, including their masses and radii.But there may be another way to obtain stellar mass and radius: asteroseismology. In asteroseismology, oscillations inside stars are used to characterize the stellar interiors. Conveniently, if a star with a convective envelope exhibits solar-like oscillations, these oscillations can be directly compared to those of the Sun. Mass and radius scaling relations which use the Sun as a benchmark and scale based on the stars temperature can then be used to derive the mass and radius of the star.Test Subjects from KeplerSolar-like oscillations from KIC 9246715 are shown in red across different resonant frequencies. The oscillations of a single red-giant star with similar properties are shown upside down in grey for reference. [Rawls et al. 2016]Of course, scaling relations are only useful if we can test them! A team of scientists including Meredith Rawls (New Mexico State University) has identified 18 red-giant eclipsing binaries in the Kepler field of view that also exhibit solar-like oscillations perfect for testing the scaling relations.In a recent study led by Rawls, the team analyzed the first of these binaries, KIC 9246715. Using the Kepler light curves in addition to radial velocity measurements from high-resolution ground-based spectroscopy at the Fred Lawrence Whipple Observatory and Apache Point Observatory, Rawls and collaborators established that the two stars have masses of 2.17 and 2.15 solar masses, and radii of 8.4 and 8.3 solar radii.Not Quite Twins?Intriguingly, when the authors measured the stellar oscillations from the binary, they were only able to pick out one signal. Using the scaling relations, their measurements reveal that the star producing the oscillations has a mass of 2.17 solar masses and radius of 8.3 radii consistent with both red giants in the system, within error bars. This provides excellent confirmation of the scaling relations for obtaining mass and radius, but it also raises a new question: why is only one star of this twin system producing oscillations?Rawls and collaborators have an idea: one star might be more magnetically active than the other, causing the suppression of oscillations in the more active star. The authors observations and detailed modeling support this idea, but similar analyses of the rest of the red-giant eclipsing binaries identified in the Kepler field will help to determine if KIC 9246715 is unusual, or if this behavior is common among such systems.CitationMeredith L. Rawls et al 2016 ApJ 818 108. doi:10.3847/0004-637X/818/2/108

The co-existence of hot and cold gas in debris discs

NASA Astrophysics Data System (ADS)

Rebollido, I.; Eiroa, C.; Montesinos, B.; Maldonado, J.; Villaver, E.; Absil, O.; Bayo, A.; Canovas, H.; Carmona, A.; Chen, Ch.; Ertel, S.; Garufi, A.; Henning, Th.; Iglesias, D. P.; Launhardt, R.; Liseau, R.; Meeus, G.; Moór, A.; Mora, A.; Olofsson, J.; Rauw, G.; Riviere-Marichalar, P.

2018-06-01

Context. Debris discs have often been described as gas-poor discs as the gas-to-dust ratio is expected to be considerably lower than in primordial, protoplanetary discs. However, recent observations have confirmed the presence of a non-negligible amount of cold gas in the circumstellar (CS) debris discs around young main-sequence stars. This cold gas has been suggested to be related to the outgassing of planetesimals and cometary-like objects. Aims: The goal of this paper is to investigate the presence of hot gas in the immediate surroundings of the cold-gas-bearing debris-disc central stars. Methods: High-resolution optical spectra of all currently known cold-gas-bearing debris-disc systems, with the exception of β Pic and Fomalhaut, have been obtained from La Palma (Spain), La Silla (Chile), and La Luz (Mexico) observatories. To verify the presence of hot gas around the sample of stars, we have analysed the Ca II H&K and the Na I D lines searching for non-photospheric absorptions of CS origin, usually attributed to cometary-like activity. Results: Narrow, stable Ca II and/or Na I absorption features have been detected superimposed to the photospheric lines in 10 out of the 15 observed cold-gas-bearing debris-disc stars. Features are found at the radial velocity of the stars, or slightly blue- or red-shifted, and/or at the velocity of the local interstellar medium (ISM). Some stars also present transient variable events or absorptions extended towards red wavelengths (red wings). These are the first detections of such Ca II features in 7 out of the 15 observed stars. Although an ISM origin cannot categorically be excluded, the results suggest that the stable and variable absorptions arise from relatively hot gas located in the CS close-in environment of the stars. This hot gas is detected in at least 80%, of edge-on cold-gas-bearing debris discs, while in only 10% of the discs seen close to face-on. We interpret this result as a geometrical effect, and suggest that the non-detection of hot gas absorptions in some face-on systems is due to the disc inclination and likely not to the absence of the hot-gas component. This gas is likely released in physical processes related in some way to the evaporation of exocomets, evaporation of dust grains, or grain-grain collisions close to the central star. The reduced spectra are only available at the CDS (ascii files) and at the FEROS archive (FITS files) 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/A3

Deep learning classification in asteroseismology

NASA Astrophysics Data System (ADS)

Hon, Marc; Stello, Dennis; Yu, Jie

2017-08-01

In the power spectra of oscillating red giants, there are visually distinct features defining stars ascending the red giant branch from those that have commenced helium core burning. We train a 1D convolutional neural network by supervised learning to automatically learn these visual features from images of folded oscillation spectra. By training and testing on Kepler red giants, we achieve an accuracy of up to 99 per cent in separating helium-burning red giants from those ascending the red giant branch. The convolutional neural network additionally shows capability in accurately predicting the evolutionary states of 5379 previously unclassified Kepler red giants, by which we now have greatly increased the number of classified stars.

Acne at The Bottom Of The Main Sequence

NASA Astrophysics Data System (ADS)

Barnes, John; Haswell, C.; Jenkins, J.; Jeffers, S.; Jones, H. R. A.; Lohr, M.; Pavlenko, Y.

2016-08-01

Starspots are an important manifestation of stellar activity and yet their distribution patterns on the lowest mass stars is not well known. Time series spectra of fully convective M dwarfs taken in the red-optical with UVES reveal numerous line profile distortions which are interpreted as starspots. We derive Doppler images for four M4.5V - M9V stars and find that contrast ratios corresponding to photosphere-spot temperature differences of only 200-300 K are sufficient to model the timeseries spectra. Although more starspot structure is found at high latitudes, spots are reconstructed at a range of phases and latitudes with mean spot filling factors of only a few per cent. The occurrence of low-contrast spots at predominantly high latitudes is in general likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. The recovered starspot patterns are used to assess their effect on precision radial velocity surveys aimed at detecting planets around this population of stars.

Mass Loss during Late Stellar Evolution

NASA Astrophysics Data System (ADS)

Olofsson, Hans

1999-10-01

Extensive post-main sequence mass loss occurs for low- and intermediate-mass (up to ~8MSun) stars on the asymptotic giant branch (AGB), and for the higher-mass stars during their red supergiant evolution. These winds have a profound effect on the evolution of the stars, as well as for the enrichment of the interstellar medium with heavy elements and grain particles. The mass loss on the AGB is the by far most well studied, but a good deal of the basic processes are still not understood or cannot be described in a proper quantitative way, e.g., the mass loss mechanism itself. Furthermore, these objects provide us with fascinating systems, where intricate interplays between various physical and chemical processes take place, and their relative simplicity in terms of geometry, density distribution, and kinematics makes them excellent astrophysical laboratories. In this review we will concentrate on those aspects of AGB mass loss that are particularly well studied using a large millimetre array.

Prospects for Ground-Based Detection and Follow-up of TESS-Discovered Exoplanets

NASA Astrophysics Data System (ADS)

Varakian, Matthew; Deming, Drake

2018-01-01

The Transiting Exoplanet Survey Satellite (TESS) will monitor over 200,000 main sequence dwarf stars for exoplanetary transits, with the goal of discovering small planets orbiting stars that are bright enough for follow-up observations. We here evaluate the prospects for ground-based transit detection and follow-up of the TESS-discovered planets. We focus particularly on the TESS planets that only transit once during each 27.4 day TESS observing window per region, and we calculate to what extent ground-based recovery of additional transits will be possible. Using simulated exoplanet systems from Sullivan et al. and assuming the use of a 60-cm telescope at a high quality observing site, we project the S/N ratios for transits of such planets. We use Phoenix stellar models for stars with surface temperatures from 2500K to 12000K, and we account for limb darkening, red atmospheric noise, and missed transits due to the day-night cycle and poor weather.

New Asteroseismic Scaling Relations Based on the Hayashi Track Relation Applied to Red Giant Branch Stars in NGC 6791 and NGC 6819

NASA Astrophysics Data System (ADS)

Wu, T.; Li, Y.; Hekker, S.

2014-01-01

Stellar mass M, radius R, and gravity g are important basic parameters in stellar physics. Accurate values for these parameters can be obtained from the gravitational interaction between stars in multiple systems or from asteroseismology. Stars in a cluster are thought to be formed coevally from the same interstellar cloud of gas and dust. The cluster members are therefore expected to have some properties in common. These common properties strengthen our ability to constrain stellar models and asteroseismically derived M, R, and g when tested against an ensemble of cluster stars. Here we derive new scaling relations based on a relation for stars on the Hayashi track (\\sqrt{T_eff} \\sim g^pR^q) to determine the masses and metallicities of red giant branch stars in open clusters NGC 6791 and NGC 6819 from the global oscillation parameters Δν (the large frequency separation) and νmax (frequency of maximum oscillation power). The Δν and νmax values are derived from Kepler observations. From the analysis of these new relations we derive: (1) direct observational evidence that the masses of red giant branch stars in a cluster are the same within their uncertainties, (2) new methods to derive M and z of the cluster in a self-consistent way from Δν and νmax, with lower intrinsic uncertainties, and (3) the mass dependence in the Δν - νmax relation for red giant branch stars.

THE REDMAPPER GALAXY CLUSTER CATALOG FROM DES SCIENCE VERIFICATION DATA

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

Rykoff, E. S.; Rozo, E.; Hollowood, D.

We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to 150 deg(2) of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited and contains 786 clusters with richness lambda > 20 (roughly equivalent to M500c greater than or similar to 10(14) h(70)(-1)M(circle dot)) and 0.2 < z < 0.9. The DR8 catalog consists of 26,311 clusters with 0.08 < z < 0.6, with a sharplymore » increasing richness threshold as a function of redshift for z greater than or similar to 0.35. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the sigma(z)/(1+ z) similar to 0.01 level for z greater than or similar to 0.7, rising to similar to 0.02 at z similar to 0.9 in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev-Zeldovich data to show that the centering performance and mass-richness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.« less

MASS OUTFLOW AND CHROMOSPHERIC ACTIVITY OF RED GIANT STARS IN GLOBULAR CLUSTERS. II. M13 AND M92

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

Meszaros, Sz.; Dupree, A. K.; Szalai, T.

High-resolution spectra of 123 red giant stars in the globular cluster M13 and 64 red giant stars in M92 were obtained with Hectochelle at the MMT telescope. Emission and line asymmetries in H{alpha} and Ca II K are identified, characterizing motions in the extended atmospheres and seeking differences attributable to metallicity in these clusters and M15. On the red giant branch, emission in H{alpha} generally appears in stars with T {sub eff} {approx}< 4500 K and log L/L {sub sun}{approx}> 2.75. Fainter stars showing emission are asymptotic giant branch (AGB) stars or perhaps binary stars. The line-bisector for H{alpha} revealsmore » the onset of chromospheric expansion in stars more luminous than log (L/L {sub sun}) {approx} 2.5 in all clusters, and this outflow velocity increases with stellar luminosity. However, the coolest giants in the metal-rich M13 show greatly reduced outflow in H{alpha} most probably due to decreased T {sub eff} and changing atmospheric structure. The Ca II K{sub 3} outflow velocities are larger than shown by H{alpha} at the same luminosity and signal accelerating outflows in the chromospheres. Stars clearly on the AGB show faster chromospheric outflows in H{alpha} than RGB objects. While the H{alpha} velocities on the RGB are similar for all metallicities, the AGB stars in the metal-poor M15 and M92 have higher outflow velocities than in the metal-rich M13. Comparison of these chromospheric line profiles in the paired metal-poor clusters, M15 and M92, shows remarkable similarities in the presence of emission and dynamical signatures, and does not reveal a source of the 'second-parameter' effect.« less

On the Detection and Characterization of Polluted White Dwarfs

NASA Astrophysics Data System (ADS)

Steele, Amy; Debes, John H.; Deming, Drake

2017-06-01

There is evidence of circumstellar material around main sequence, giant, and white dwarf stars. What happens to this material after the main sequence? With this work, we focus on the characterization of the material around WD 1145+017. The goals are to monitor the white dwarf—which has a transiting, disintegrating planetesimal and determine the composition of the evaporated material for that same white dwarf by looking at high-resolution spectra. We also present preliminary results of follow-up photometric observations of known polluted WDs. If rocky bodies survive red giant branch evolution, then the material raining down on a WD atmosphere is a direct probe of main sequence cosmochemistry. If rocky bodies do not survive the evolution, then this informs the degree of post-main-sequence processing. These case studies will provide the community with further insight about debris disk modeling, the degree of post-main-sequence processing of circumstellar material, and the composition of a disintegrating planetesimal.

Asteroseismology can reveal strong internal magnetic fields in red giant stars.

PubMed

Fuller, Jim; Cantiello, Matteo; Stello, Dennis; Garcia, Rafael A; Bildsten, Lars

2015-10-23

Internal stellar magnetic fields are inaccessible to direct observations, and little is known about their amplitude, geometry, and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can be identified with asteroseismology. The fields can manifest themselves via depressed dipole stellar oscillation modes, arising from a magnetic greenhouse effect that scatters and traps oscillation-mode energy within the core of the star. The Kepler satellite has observed a few dozen red giants with depressed dipole modes, which we interpret as stars with strongly magnetized cores. We find that field strengths larger than ~10(5) gauss may produce the observed depression, and in one case we infer a minimum core field strength of ≈10(7) gauss. Copyright © 2015, American Association for the Advancement of Science.

Panel 1: A pulsating red giant star and a compact, hot white dwarf star orbit each other.

NASA Technical Reports Server (NTRS)

2002-01-01

Panel 1: A pulsating red giant star and a compact, hot white dwarf star orbit each other. Panel 2: The red giant sheds much of its outer layers in a stellar wind. The white dwarf helps concentrate the wind along a thin equatorial plane. The white dwarf accretes some of this escaping gas forming a disk around the itself. Panel 3: When enough gas accumulates on the white dwarf's surface it explodes as a nova outburst. Most of the hot gas forms a pair of expanding bubbles above and below the equatorial disk. Panel 4: A few thousand years after the bubbles expand into space, the white dwarf goes through another nova outburst and makes another pair of bubbles, which form a distinctive hourglass shape.

Color-magnitude relations in nearby galaxy clusters

NASA Astrophysics Data System (ADS)

Rasheed, Mariwan A.; Mohammad, Khalid K.

2018-06-01

The rest-frame (g-r) /Mr color-magnitude relations of 12 Abell-type clusters are analyzed in the redshift range (0.02≲ z ≲ 0.10) and within a projected radius of 0.75 Mpc using photometric data from SDSS-DR9. We show that the color-magnitude relation parameters (slope, zero-point, and scatter) do not exhibit significant evolution within this low-redshift range. Thus, we can say that during the look-back time of z ˜ 0.1 all red sequence galaxies evolve passively, without any star formation activity.

Clear Evidence for the Presence of Second-generation Asymptotic Giant Branch Stars in Metal-poor Galactic Globular Clusters

NASA Astrophysics Data System (ADS)

García-Hernández, D. A.; Mészáros, Sz.; Monelli, M.; Cassisi, S.; Stetson, P. B.; Zamora, O.; Shetrone, M.; Lucatello, S.

2015-12-01

Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation (FG) with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch (RGB)). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M13, M5, M3, and M2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the Apache Point Observatory Galactic Evolution Experiment survey with ground-based optical photometry, we identify SG Al-rich AGB stars in these four GCs and show that Al-rich RGB/AGB GC stars should be Na-rich. Our observations provide strong support for present, standard stellar models, i.e., without including a strong mass-loss efficiency, for low-mass HB stars. In fact, current empirical evidence is in agreement with the predicted distribution of FG and SG stars during the He-burning stages based on these standard stellar models.

Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

NASA Astrophysics Data System (ADS)

Meyer, D. M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V. V.; Mignone, A.; Izzard, R. G.; Kaper, L.

2014-11-01

At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional axisymmetric hydrodynamical simulations following the evolution of the circumstellar medium of these stars in the Galactic plane from the main sequence to the red supergiant phase. We find that thermal conduction is an important process governing the shape, size and structure of the bow shocks around hot stars, and that they have an optical luminosity mainly produced by forbidden lines, e.g. [O III]. The Hα emission of the bow shocks around hot stars originates from near their contact discontinuity. The Hα emission of bow shocks around cool stars originates from their forward shock, and is too faint to be observed for the bow shocks that we simulate. The emission of optically thin radiation mainly comes from the shocked ISM material. All bow shock models are brighter in the infrared, i.e. the infrared is the most appropriate waveband to search for bow shocks. Our study suggests that the infrared emission comes from near the contact discontinuity for bow shocks of hot stars and from the inner region of shocked wind for bow shocks around cool stars. We predict that, in the Galactic plane, the brightest, i.e. the most easily detectable bow shocks are produced by high-mass stars moving with small space velocities.

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.

Empirically Calibrated Asteroseismic Masses and Radii for Red Giants in the Kepler Fields

NASA Astrophysics Data System (ADS)

Pinsonneault, Marc; Elsworth, Yvonne; Silva Aguirre, Victor; Chaplin, William J.; Garcia, Rafael A.; Hekker, Saskia; Holtzman, Jon; Huber, Daniel; Johnson, Jennifer; Kallinger, Thomas; Mosser, Benoit; Mathur, Savita; Serenelli, Aldo; Shetrone, Matthew; Stello, Dennis; Tayar, Jamie; Zinn, Joel; APOGEE Team, KASC Team, APOKASC Team

2018-01-01

We report on the joint asteroseismic and spectroscopic properties of a sample of 6048 evolved stars in the fields originally observed by the Kepler satellite. We use APOGEE spectroscopic data taken from Data Release 13 of the Sloan Digital Sky Survey, combined with asteroseismic data analyzed by members of the Kepler Asteroseismic Science Consortium. With high statistical significance, the different pipelines do not have relative zero points that are the same as the solar values, and red clump stars do not have the same empirical relative zero points as red giants. We employ theoretically motivated corrections to the scaling relation for the large frequency spacing, and adjust the zero point of the frequency of maximum power scaling relation to be consistent with masses and radii for members of star clusters. The scatter in calibrator masses is consistent with our error estimation. Systematic and random mass errors are explicitly separated and identified. The measurement scatter, and random uncertainties, are three times larger for red giants where one or more technique failed to return a value than for targets where all five methods could do so, and this is a substantial fraction of the sample (20% of red giants and 25% of red clump stars). Overall trends and future prospects are discussed.

RED GIANTS IN ECLIPSING BINARY AND MULTIPLE-STAR SYSTEMS: MODELING AND ASTEROSEISMIC ANALYSIS OF 70 CANDIDATES FROM KEPLER DATA

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

Gaulme, P.; McKeever, J.; Rawls, M. L.

2013-04-10

Red giant stars are proving to be an incredible source of information for testing models of stellar evolution, as asteroseismology has opened up a window into their interiors. Such insights are a direct result of the unprecedented data from space missions CoRoT and Kepler as well as recent theoretical advances. Eclipsing binaries are also fundamental astrophysical objects, and when coupled with asteroseismology, binaries provide two independent methods to obtain masses and radii and exciting opportunities to develop highly constrained stellar models. The possibility of discovering pulsating red giants in eclipsing binary systems is therefore an important goal that could potentiallymore » offer very robust characterization of these systems. Until recently, only one case has been discovered with Kepler. We cross-correlate the detected red giant and eclipsing-binary catalogs from Kepler data to find possible candidate systems. Light-curve modeling and mean properties measured from asteroseismology are combined to yield specific measurements of periods, masses, radii, temperatures, eclipse timing variations, core rotation rates, and red giant evolutionary state. After using three different techniques to eliminate false positives, out of the 70 systems common to the red giant and eclipsing-binary catalogs we find 13 strong candidates (12 previously unknown) to be eclipsing binaries, one to be a non-eclipsing binary with tidally induced oscillations, and 10 more to be hierarchical triple systems, all of which include a pulsating red giant. The systems span a range of orbital eccentricities, periods, and spectral types F, G, K, and M for the companion of the red giant. One case even suggests an eclipsing binary composed of two red giant stars and another of a red giant with a {delta}-Scuti star. The discovery of multiple pulsating red giants in eclipsing binaries provides an exciting test bed for precise astrophysical modeling, and follow-up spectroscopic observations of many of the candidate systems are encouraged. The resulting highly constrained stellar parameters will allow, for example, the exploration of how binary tidal interactions affect pulsations when compared to the single-star case.« less

Star Formation, Quenching And Chemical Enrichment In Local Galaxies From Integral Field Spectroscopy

NASA Astrophysics Data System (ADS)

Belfiore, Francesco

2017-08-01

Within the currently well-established ΛCDM cosmological framework we still lack a satisfactory understanding of the processes that trigger, regulate and eventually quench star formation on galactic scales. Gas flows (including inflows from the cosmic web and supernovae-driven outflows) are considered to act as self-regulatory mechanisms, generating the scaling relations between stellar mass, star formation rate and metallicity observed in the local Universe by large spectroscopic surveys. These surveys, however, have so far been limited by the availability of only one spectrum per galaxy. The aim of this dissertation is to expand the study of star formation and chemical abundances to resolved scales within galaxies by using integral field spectroscopy (IFS) data, mostly from the ongoing SDSS-IV MaNGA survey. In the first part of this thesis I demonstrate the ubiquitous presence of extended low ionisation emission-line regions (LIERs) in both late- and early-type galaxies. By studying the Hα equivalent width and diagnostic line ratios radial profiles, together with tracers of the underlying stellar population, I show that LIERs are not due to a central point source but to hot evolved (post-asymptotic giant branch) stars. In light of this, I suggest a new classification scheme for galaxies based on their line emission. By analysing the colours, star formation rates, morphologies, gas and stellar kinematics and environmental properties of galaxies with substantial LIER emission, I identify two distinct populations. Galaxies where the central regions are LIER-like, but show star formation at larger radii are late types in which star formation is slowly quenched inside-out. This transformation is associated with massive bulges. Galaxies dominated by LIER emission at all radii, on the other hand, are red-sequence galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Quiescent galaxies devoid of line emission reside in denser environments, which suggests environmental effects as a likely cause for the existence of line-less galaxies on the red sequence. In the second part of this dissertation I focus on the study of resolved chemical abundances by characterising the gas phase oxygen and nitrogen abundance gradients in a large sample of star forming galaxies. I analyse the deviations from an exponential profile at small and large radii and the dependence of the gradients on stellar mass. These findings are interpreted in the context of the inside-out paradigm of disc growth. I then demonstrate the necessity of gas flows, which are responsible for the observed flattening of the metallicity and N/O ratio gradients at large radii. Finally, I present a case study based on one nearby galaxy (NGC 628), in which I combine IFS and cold gas data to derive a spatially resolved metal bud- get and estimate the mass of metals lost by the galaxy throughout its lifetime. By using simple physically-motivated models of chemical evolution I infer the average outflow loading factor to be of order unity.

VLT/PIONIER Imaging of Red Supergiant Stars

NASA Astrophysics Data System (ADS)

Montargès, Miguel

2018-04-01

PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) was the first 4-telescope instrument installed at the Very Large Telescope Interferometer (VLTI) in 2010. Benefiting from the multiple interferometric configurations available at the Cerro Paranal observatory, it can efficiently image stellar surfaces. With their large linear sizes, nearby red supergiant stars are among the most interesting targets for such instrument. Near infrared interferometry allows to study their surface in order to get a better understanding of their mass loss, mostly by constraining the characteristics of their photospheric features. I will review recent results obtain with VLTI/PIONIER on red supergiant stars, and emphasize the different techniques used to analyze these observations.

Omega Centauri Looks Radiant in Infrared

NASA Technical Reports Server (NTRS)

2008-01-01

[figure removed for brevity, see original site] Poster Version

A cluster brimming with millions of stars glistens like an iridescent opal in this image from NASA's Spitzer Space Telescope. Called Omega Centauri, the sparkling orb of stars is like a miniature galaxy. It is the biggest and brightest of the 150 or so similar objects, called globular clusters, that orbit around the outside of our Milky Way galaxy. Stargazers at southern latitudes can spot the stellar gem with the naked eye in the constellation Centaurus.

Globular clusters are some of the oldest objects in our universe. Their stars are over 12 billion years old, and, in most cases, formed all at once when the universe was just a toddler. Omega Centauri is unusual in that its stars are of different ages and possess varying levels of metals, or elements heavier than boron. Astronomers say this points to a different origin for Omega Centauri than other globular clusters: they think it might be the core of a dwarf galaxy that was ripped apart and absorbed by our Milky Way long ago.

In this new view of Omega Centauri, Spitzer's infrared observations have been combined with visible-light data from the National Science Foundation's Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile. Visible-light data with a wavelength of .55 microns is colored blue, 3.6-micron infrared light captured by Spitzer's infrared array camera is colored green and 24-micron infrared light taken by Spitzer's multiband imaging photometer is colored red.

Where green and red overlap, the color yellow appears. Thus, the yellow and red dots are stars revealed by Spitzer. These stars, called red giants, are more evolved, larger and dustier. The stars that appear blue were spotted in both visible and 3.6-micron-, or near-, infrared light. They are less evolved, like our own sun. Some of the red spots in the picture are distant galaxies beyond our own.

Spitzer found very little dust around any but the most luminous, coolest red giants, implying that the dimmer red giants do not form significant amounts of dust. The space between the stars in Omega Centauri was also found to lack dust, which means the dust is rapidly destroyed or leaves the cluster.

GROUND-BASED Paα NARROW-BAND IMAGING OF LOCAL LUMINOUS INFRARED GALAXIES. I. STAR FORMATION RATES AND SURFACE DENSITIES

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

Tateuchi, Ken; Konishi, Masahiro; Motohara, Kentaro

2015-03-15

Luminous infrared galaxies (LIRGs) are enshrouded by a large amount of dust produced by their active star formation, and it is difficult to measure their activity in optical wavelengths. We have carried out Paα narrow-band imaging observations of 38 nearby star forming galaxies including 33 LIRGs listed in the IRAS Revised Bright Galaxy Sample catalog with the Atacama Near InfraRed camera on the University of Tokyo Atacama Observatory (TAO) 1.0 m telescope (miniTAO). Star formation rates (SFRs) estimated from the Paα fluxes, corrected for dust extinction using the Balmer decrement method (typically A{sub V} ∼ 4.3 mag), show a good correlation with thosemore » from the bolometric infrared luminosity of the IRAS data within a scatter of 0.27 dex. This suggests that the correction of dust extinction for the Paα flux is sufficient in our sample. We measure the physical sizes and surface densities of infrared luminosities (Σ{sub L(IR)}) and the SFR (Σ{sub SFR}) of star forming regions for individual galaxies, and we find that most of the galaxies follow a sequence of local ultra-luminous or luminous infrared galaxies (U/LIRGs) on the L(IR)-Σ{sub L(IR)} and SFR-Σ{sub SFR} plane. We confirm that a transition of the sequence from normal galaxies to U/LIRGs is seen at L(IR) = 8 × 10{sup 10} L {sub ☉}. Also, we find that there is a large scatter in physical size, different from normal galaxies or ULIRGs. Considering the fact that most U/LIRGs are merging or interacting galaxies, this scatter may be caused by strong external factors or differences in their merging stages.« less

THE K2 M67 STUDY: AN EVOLVED BLUE STRAGGLER IN M67 FROM K2 MISSION ASTEROSEISMOLOGY

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

Leiner, Emily; Mathieu, Robert D.; Stello, Dennis

Yellow straggler stars (YSSs) fall above the subgiant branch in optical color–magnitude diagrams (CMDs), between the blue stragglers and the red giants. YSSs may represent a population of evolved blue stragglers, but none have the direct and precise mass and radius measurements needed to determine their evolutionary states and formation histories. Here we report the first asteroseismic mass and radius measurements of such a star, the yellow straggler S1237 in the open cluster M67. We apply asteroseismic scaling relations to a frequency analysis of the Kepler K2 light curve and find a mass of 2.9 ± 0.2 M {sub ⊙}more » and a radius of 9.2 ± 0.2 R{sub ⊙}. This is more than twice the mass of the main-sequence turnoff in M67, suggesting that S1237 is indeed an evolved blue straggler. S1237 is the primary in a spectroscopic binary. We update the binary orbital solution and use spectral energy distribution fitting to constrain the CMD location of the secondary star. We find that the secondary is likely an upper main-sequence star near the turnoff, but a slightly hotter blue straggler companion is also possible. We then compare the asteroseismic mass of the primary to its mass from CMD fitting, finding that the photometry implies a mass and radius more than 2 σ below the asteroseismic measurement. Finally, we consider formation mechanisms for this star and suggest that S1237 may have formed from dynamical encounters resulting in stellar collisions or a binary merger.« less

Gravity mode offset and properties of the evanescent zone in red-giant stars

NASA Astrophysics Data System (ADS)

Hekker, S.; Elsworth, Y.; Angelou, G. C.

2018-03-01

Context. The wealth of asteroseismic data for red-giant stars and the precision with which these data have been observed over the last decade calls for investigations to further understand the internal structures of these stars. Aim. The aim of this work is to validate a method to measure the underlying period spacing, coupling term, and mode offset of pure gravity modes that are present in the deep interiors of red-giant stars. We subsequently investigate the physical conditions of the evanescent zone between the gravity mode cavity and the pressure mode cavity. Methods: We implement an alternative mathematical description compared to what is used in the literature to analyse observational data and to extract the underlying physical parameters that determine the frequencies of mixed modes. This description takes the radial order of the modes explicitly into account, which reduces its sensitivity to aliases. Additionally, and for the first time, this method allows us to constrain the gravity mode offset ɛg for red-giant stars. Results: We find that this alternative mathematical description allows us to determine the period spacing ΔΠ and the coupling term q for the dipole modes within a few percent of values found in the literature. Additionally, we find that ɛg varies on a star-by-star basis and should not be kept fixed in the analysis. Furthermore, we find that the coupling factor is logarithmically related to the physical width of the evanescent region normalised by the radius at which the evanescent zone is located. Finally, the local density contrast at the edge of the core of red-giant branch models shows a tentative correlation with the offset ɛg. Conclusions: We are continuing to exploit the full potential of the mixed modes to investigate the internal structures of red-giant stars; in this case we focus on the evanescent zone. It remains, however, important to perform comparisons between observations and models with great care as the methods employed are sensitive to the range of input frequencies.

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints - The open cluster NGC 6633 and field stars-

NASA Astrophysics Data System (ADS)

Lagarde, Nadège; Miglio, Andrea; Eggenberger, Patrick; Morel, Thierry; Montalbàn, Josefina; Mosser, Benoit

2015-08-01

The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations.We use the first detailed spectroscopic study of CoRoT red-giant stars (Morel et al 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars.In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red-giant branch.We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red-giants targets. Tighter constraints on the physics of the models would be possible if there were detailed knowledge of the core rotation rate and the asymptotic period spacing.

Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds

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

Li, Chengyuan; De Grijs, Richard; Deng, Licai

An increasing number of young massive clusters (YMCs) in the Magellanic Clouds have been found to exhibit bimodal or extended main sequences (MSs) in their color–magnitude diagrams (CMDs). These features are usually interpreted in terms of a coeval stellar population with different stellar rotational rates, where the blue and red MS stars are populated by non- (or slowly) and rapidly rotating stellar populations, respectively. However, some studies have shown that an age spread of several million years is required to reproduce the observed wide turnoff regions in some YMCs. Here we present the ultraviolet–visual CMDs of four Large and Smallmore » Magellanic Cloud YMCs, NGC 330, NGC 1805, NGC 1818, and NGC 2164, based on high-precision Hubble Space Telescope photometry. We show that they all exhibit extended main-sequence turnoffs (MSTOs). The importance of age spreads and stellar rotation in reproducing the observations is investigated. The observed extended MSTOs cannot be explained by stellar rotation alone. Adopting an age spread of 35–50 Myr can alleviate this difficulty. We conclude that stars in these clusters are characterized by ranges in both their ages and rotation properties, but the origin of the age spread in these clusters remains unknown.« less

Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low-Mass White Dwarfs

NASA Astrophysics Data System (ADS)

Kalirai, Jasonjot S.; Bergeron, P.; Hansen, Brad M. S.; Kelson, Daniel D.; Reitzel, David B.; Rich, R. Michael; Richer, Harvey B.

2007-12-01

We present the first detailed study of the properties (temperatures, gravities, and masses) of the NGC 6791 white dwarf population. This unique stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H]~+0.4) open clusters in our Galaxy and has a color-magnitude diagram (CMD) that exhibits both a red giant clump and a much hotter extreme horizontal branch. Fitting the Balmer lines of the white dwarfs in the cluster using Keck/LRIS spectra suggests that most of these stars are undermassive, =0.43+/-0.06 Msolar, and therefore could not have formed from canonical stellar evolution involving the helium flash at the tip of the red giant branch. We show that at least 40% of NGC 6791's evolved stars must have lost enough mass on the red giant branch to avoid the flash and therefore did not convert helium into carbon-oxygen in their core. Such increased mass loss in the evolution of the progenitors of these stars is consistent with the presence of the extreme horizontal branch in the CMD. This unique stellar evolutionary channel also naturally explains the recent finding of a very young age (2.4 Gyr) for NGC 6791 from white dwarf cooling theory; helium-core white dwarfs in this cluster will cool ~3 times slower than carbon-oxygen-core stars, and therefore the corrected white dwarf cooling age is in fact >~7 Gyr, consistent with the well-measured main-sequence turnoff age. These results provide direct empirical evidence that mass loss is much more efficient in high-metallicity environments and therefore may be critical in interpreting the ultraviolet upturn in elliptical galaxies. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council 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.

New asteroseismic scaling relations based on the Hayashi track relation applied to red giant branch stars in NGC 6791 and NGC 6819

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

Wu, T.; Li, Y.; Hekker, S., E-mail: wutao@ynao.ac.cn, E-mail: ly@ynao.ac.cn, E-mail: hekker@mps.mpg.de

2014-01-20

Stellar mass M, radius R, and gravity g are important basic parameters in stellar physics. Accurate values for these parameters can be obtained from the gravitational interaction between stars in multiple systems or from asteroseismology. Stars in a cluster are thought to be formed coevally from the same interstellar cloud of gas and dust. The cluster members are therefore expected to have some properties in common. These common properties strengthen our ability to constrain stellar models and asteroseismically derived M, R, and g when tested against an ensemble of cluster stars. Here we derive new scaling relations based on amore » relation for stars on the Hayashi track (√(T{sub eff})∼g{sup p}R{sup q}) to determine the masses and metallicities of red giant branch stars in open clusters NGC 6791 and NGC 6819 from the global oscillation parameters Δν (the large frequency separation) and ν{sub max} (frequency of maximum oscillation power). The Δν and ν{sub max} values are derived from Kepler observations. From the analysis of these new relations we derive: (1) direct observational evidence that the masses of red giant branch stars in a cluster are the same within their uncertainties, (2) new methods to derive M and z of the cluster in a self-consistent way from Δν and ν{sub max}, with lower intrinsic uncertainties, and (3) the mass dependence in the Δν - ν{sub max} relation for red giant branch stars.« less

Growing up in a megalopolis: environmental effects on galaxy evolution in a supercluster at z ˜ 0.65 in UKIDSS UDS

NASA Astrophysics Data System (ADS)

Galametz, Audrey; Pentericci, Laura; Castellano, Marco; Mendel, Trevor; Hartley, Will G.; Fossati, Matteo; Finoguenov, Alexis; Almaini, Omar; Beifiori, Alessandra; Fontana, Adriano; Grazian, Andrea; Scodeggio, Marco; Kocevski, Dale D.

2018-04-01

We present a large-scale galaxy structure Cl J021734-0513 at z ˜ 0.65 discovered in the UKIDSS UDS field, made of ˜20 galaxy groups and clusters, spreading over 10 Mpc. We report on a VLT/VIMOS spectroscopic follow-up program that, combined with past spectroscopy, allowed us to confirm four galaxy clusters (M200 ˜ 1014 M⊙) and a dozen associated groups and star-forming galaxy overdensities. Two additional filamentary structures at z ˜ 0.62 and 0.69 and foreground and background clusters at 0.6 < z < 0.7 were also confirmed along the line of sight. The structure subcomponents are at different formation stages. The clusters have a core dominated by passive galaxies and an established red sequence. The remaining structures are a mix of star-forming galaxy overdensities and forming groups. The presence of quiescent galaxies in the core of the latter shows that `pre-processing' has already happened before the groups fall into their more massive neighbours. Our spectroscopy allows us to derive spectral index measurements e.g. emission/absorption line equivalent widths, strength of the 4000 Å break, valuable to investigate the star formation history of structure members. Based on these line measurements, we select a population of `post-starburst' galaxies. These galaxies are preferentially found within the virial radius of clusters, supporting a scenario in which their recent quenching could be prompted by gas stripping by the dense intracluster medium. We derive stellar age estimates using Markov Chain Monte Carlo-based spectral fitting for quiescent galaxies and find a correlation between ages and colours/stellar masses which favours a top-down formation scenario of the red sequence. A catalogue of ˜650 redshifts in UDS is released alongside the paper (via MNRAS online data).

Asteroseismic Diagram for Subgiants and Red Giants

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

Gai, Ning; Tang, Yanke; Yu, Peng

Asteroseismology is a powerful tool for constraining stellar parameters. NASA’s Kepler mission is providing individual eigenfrequencies for a huge number of stars, including thousands of red giants. Besides the frequencies of acoustic modes, an important breakthrough of the Kepler mission is the detection of nonradial gravity-dominated mixed-mode oscillations in red giants. Unlike pure acoustic modes, mixed modes probe deeply into the interior of stars, allowing the stellar core properties and evolution of stars to be derived. In this work, using the gravity-mode period spacing and the large frequency separation, we construct the ΔΠ{sub 1}–Δ ν asteroseismic diagram from models ofmore » subgiants and red giants with various masses and metallicities. The relationship ΔΠ{sub 1}–Δ ν is able to constrain the ages and masses of the subgiants. Meanwhile, for red giants with masses above 1.5 M {sub ⊙}, the ΔΠ{sub 1}–Δ ν asteroseismic diagram can also work well to constrain the stellar age and mass. Additionally, we calculate the relative “isochrones” τ , which indicate similar evolution states especially for similar mass stars, on the ΔΠ{sub 1}–Δ ν diagram.« less

The dimensionality of stellar chemical space using spectra from the Apache Point Observatory Galactic Evolution Experiment

NASA Astrophysics Data System (ADS)

Price-Jones, Natalie; Bovy, Jo

2018-03-01

Chemical tagging of stars based on their similar compositions can offer new insights about the star formation and dynamical history of the Milky Way. We investigate the feasibility of identifying groups of stars in chemical space by forgoing the use of model derived abundances in favour of direct analysis of spectra. This facilitates the propagation of measurement uncertainties and does not pre-suppose knowledge of which elements are important for distinguishing stars in chemical space. We use ˜16 000 red giant and red clump H-band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and perform polynomial fits to remove trends not due to abundance-ratio variations. Using expectation maximized principal component analysis, we find principal components with high signal in the wavelength regions most important for distinguishing between stars. Different subsamples of red giant and red clump stars are all consistent with needing about 10 principal components to accurately model the spectra above the level of the measurement uncertainties. The dimensionality of stellar chemical space that can be investigated in the H band is therefore ≲10. For APOGEE observations with typical signal-to-noise ratios of 100, the number of chemical space cells within which stars cannot be distinguished is approximately 1010±2 × (5 ± 2)n - 10 with n the number of principal components. This high dimensionality and the fine-grained sampling of chemical space are a promising first step towards chemical tagging based on spectra alone.

Multi-periodic pulsations of a stripped red-giant star in an eclipsing binary system.

PubMed

Maxted, Pierre F L; Serenelli, Aldo M; Miglio, Andrea; Marsh, Thomas R; Heber, Ulrich; Dhillon, Vikram S; Littlefair, Stuart; Copperwheat, Chris; Smalley, Barry; Breedt, Elmé; Schaffenroth, Veronika

2013-06-27

Low-mass white-dwarf stars are the remnants of disrupted red-giant stars in binary millisecond pulsars and other exotic binary star systems. Some low-mass white dwarfs cool rapidly, whereas others stay bright for millions of years because of stable fusion in thick surface hydrogen layers. This dichotomy is not well understood, so the potential use of low-mass white dwarfs as independent clocks with which to test the spin-down ages of pulsars or as probes of the extreme environments in which low-mass white dwarfs form cannot fully be exploited. Here we report precise mass and radius measurements for the precursor to a low-mass white dwarf. We find that only models in which this disrupted red-giant star has a thick hydrogen envelope can match the strong constraints provided by our data. Very cool low-mass white dwarfs must therefore have lost their thick hydrogen envelopes by irradiation from pulsar companions or by episodes of unstable hydrogen fusion (shell flashes). We also find that this low-mass white-dwarf precursor is a type of pulsating star not hitherto seen. The observed pulsation frequencies are sensitive to internal processes that determine whether this star will undergo shell flashes.

The RAVE-on Catalog of Stellar Atmospheric Parameters and Chemical Abundances for Chemo-dynamic Studies in the Gaia Era

NASA Astrophysics Data System (ADS)

Casey, Andrew R.; Hawkins, Keith; Hogg, David W.; Ness, Melissa; Rix, Hans-Walter; Kordopatis, Georges; Kunder, Andrea; Steinmetz, Matthias; Koposov, Sergey; Enke, Harry; Sanders, Jason; Gilmore, Gerry; Zwitter, Tomaž; Freeman, Kenneth C.; Casagrande, Luca; Matijevič, Gal; Seabroke, George; Bienaymé, Olivier; Bland-Hawthorn, Joss; Gibson, Brad K.; Grebel, Eva K.; Helmi, Amina; Munari, Ulisse; Navarro, Julio F.; Reid, Warren; Siebert, Arnaud; Wyse, Rosemary

2017-05-01

The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho-Gaia Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS (≳200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon. For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundances for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We derive and validate effective temperature T eff, surface gravity log g, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.

The Origin of the Ultraluminous X-Ray Sources

NASA Astrophysics Data System (ADS)

Wiktorowicz, Grzegorz; Sobolewska, Małgorzata; Lasota, Jean-Pierre; Belczynski, Krzysztof

2017-09-01

Recently, several ultraluminous X-ray (ULX) sources were shown to host a neutron star (NS) accretor. We perform a suite of evolutionary calculations, which show that, in fact, NSs are the dominant type of ULX accretor. Although black holes (BH) dominate early epochs after the star-formation burst, NSs outweigh them after a few 100 Myr and may appear as late as a few gigayears after the end of the star-formation episode. If star formation is a prolonged and continuous event (I.e., not a relatively short burst), NS accretors dominate the ULX population at any time in the solar metallicity environment, whereas BH accretors dominate when the metallicity is sub-solar. Our results show a very clear (and testable) relation between the companion/donor evolutionary stage and the age of the system. A typical NSULX consists of a ˜ 1.3 {M}⊙ NS and ˜ 1.0 {M}⊙ Red Giant. A typical BH ULX consists of a ˜ 8 {M}⊙ BH and ˜ 6 {M}⊙ main-sequence star. Additionally, we find that the very luminous ULXs ({L}X≳ {10}41 erg s-1) are predominantly BH systems (˜ 9 {M}⊙ ) with Hertzsprung-gap donors (˜ 2 {M}⊙ ). Nevertheless, some NSULX systems may also reach extremely high X-ray luminosities (≳1041 erg s-1).

The nature of the ultraluminous X-ray sources

NASA Astrophysics Data System (ADS)

Wiktorowicz, G.; Sobolewska, M.; Lasota, J.; Belczynski, K.

2017-10-01

Recently, several ultraluminous X-ray (ULX) sources were shown to host a neutron star (NS) accretor. We perform a suite of evolutionary calculations which show that, in fact, NSs are the dominant type of ULX accretor. Although black holes (BH) dominate early epochs after the star-formation burst, NSs outweigh them after a few 100 Myr and may appear as late as a few Gyr after the end of the star formation episode. If star formation is a prolonged and continuous event (i.e., not a relatively short burst), NS accretors dominate ULX population at any time in solar metallicity environment, whereas BH accretors dominate when the metallicity is sub-solar. Our results show a very clear (and testable) relation between the companion/donor evolutionary stage and the age of the system. A typical NS ULX consists of a ˜1.3 M_⊙ NS and ˜1.0 M_⊙ Red Giant. A typical BH ULX consist of a ˜8 M_⊙ BH and ˜6 M_⊙ main-sequence star. Additionally, we find that the very luminous ULXs (L_X>˜10^{41} erg/s) are predominantly BH systems (˜9 M_⊙) with Hertzsprung gap donors (˜2 M_⊙). Nevertheless, some NS ULX systems may also reach extremely high X-ray luminosities (>˜10^{41} erg/s)

Giant star seismology

NASA Astrophysics Data System (ADS)

Hekker, S.; Christensen-Dalsgaard, J.

2017-06-01

The internal properties of stars in the red-giant phase undergo significant changes on relatively short timescales. Long near-uninterrupted high-precision photometric timeseries observations from dedicated space missions such as CoRoT and Kepler have provided seismic inferences of the global and internal properties of a large number of evolved stars, including red giants. These inferences are confronted with predictions from theoretical models to improve our understanding of stellar structure and evolution. Our knowledge and understanding of red giants have indeed increased tremendously using these seismic inferences, and we anticipate that more information is still hidden in the data. Unraveling this will further improve our understanding of stellar evolution. This will also have significant impact on our knowledge of the Milky Way Galaxy as well as on exo-planet host stars. The latter is important for our understanding of the formation and structure of planetary systems.

Classification of O Stars in the Yellow-Green: The Exciting Star VES 735

NASA Astrophysics Data System (ADS)

Kerton, C. R.; Ballantyne, D. R.; Martin, P. G.

1999-05-01

Acquiring data for spectral classification of heavily reddened stars using traditional criteria in the blue-violet region of the spectrum can be prohibitively time consuming using small to medium sized telescopes. One such star is the Vatican Observatory emission-line star VES 735, which we have found excites the H II region KR 140. In order to classify VES 735, we have constructed an atlas of stellar spectra of O stars in the yellow-green (4800-5420 Å). We calibrate spectral type versus the line ratio He I lambda4922:He II lambda5411, showing that this ratio should be useful for the classification of heavily reddened O stars associated with H II regions. Application to VES 735 shows that the spectral type is O8.5. The absolute magnitude suggests luminosity class V. Comparison of the rate of emission of ionizing photons and the bolometric luminosity of VES 735, inferred from radio and infrared measurements of the KR 140 region, to recent stellar models gives consistent evidence for a main-sequence star of mass 25 M_solar and age less than a few million years with a covering factor 0.4-0.5 by the nebular material. Spectra taken in the red (6500-6700 Å) show that the stellar Hα emission is double-peaked about the systemic velocity and slightly variable. Hβ is in absorption, so that the emission-line classification is ``(e)''. However, unlike the case of the more well-known O(e) star zeta Oph, the emission from VES 735 appears to be long-lived rather than episodic.

Kepler-432 b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star

NASA Astrophysics Data System (ADS)

Ortiz, Mauricio; Gandolfi, Davide; Reffert, Sabine; Quirrenbach, Andreas; Deeg, Hans J.; Karjalainen, Raine; Montañés-Rodríguez, Pilar; Nespral, David; Nowak, Grzegorz; Osorio, Yeisson; Palle, Enric

2015-01-01

We study the Kepler object Kepler-432, an evolved star ascending the red giant branch. By deriving precise radial velocities from multi-epoch high-resolution spectra of Kepler-432 taken with the CAFE spectrograph at the 2.2 m telescope of Calar Alto Observatory and the FIES spectrograph at the Nordic Optical Telescope of Roque de Los Muchachos Observatory, we confirm the planetary nature of the object Kepler-432 b, which has a transit period of 52 days. We find a planetary mass of Mp = 5.84 ± 0.05MJup and a high eccentricity of e = 0.478 ± 0.004. With a semi-major axis of a = 0.303 ± 0.007 AU, Kepler-432 b is the first bona fide warm Jupiter detected to transit a giant star. We also find a radial velocity linear trend of γ˙ = 0.44 ± 0.04 m s-1 d-1, which suggests the presence of a third object in the system. Current models of planetary evolution in the post-main-sequence phase predict that Kepler-432 b will be most likely engulfed by its host star before the latter reaches the tip of the red giant branch. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie (Heidelberg) and the Instituto de Astrofísica de Andalucía (IAA-CSIC, Granada).Based on observations obtained with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Table 3 is available in electronic form at http://www.aanda.org

THE QUENCHING TIMESCALE AND QUENCHING RATE OF GALAXIES

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

Lian, Jianhui; Kong, Xu; Yan, Renbin

2016-11-20

The average star formation rate (SFR) in galaxies has been declining since the redshift of 2. A fraction of galaxies quench and become quiescent. We constrain two key properties of the quenching process: the quenching timescale and the quenching rate among galaxies. We achieve this by analyzing the galaxy number density profile in NUV- u color space and the distribution in NUV- u versus u - i color–color diagram with a simple toy-model framework. We focus on galaxies in three mass bins between 10{sup 10} and 10{sup 10.6} M {sub ⊙}. In the NUV- u versus u - i color–colormore » diagram, the red u - i galaxies exhibit a different slope from the slope traced by the star-forming galaxies. This angled distribution and the number density profile of galaxies in NUV- u space strongly suggest that the decline of the SFR in galaxies has to accelerate before they turn quiescent. We model this color–color distribution with a two-phase exponential decline star formation history. The models with an e-folding time in the second phase (the quenching phase) of 0.5 Gyr best fit the data. We further use the NUV- u number density profile to constrain the quenching rate among star-forming galaxies as a function of mass. Adopting an e-folding time of 0.5 Gyr in the second phase (or the quenching phase), we found the quenching rate to be 19%/Gyr, 25%/Gyr and 33%/Gyr for the three mass bins. These are upper limits of the quenching rate as the transition zone could also be populated by rejuvenated red-sequence galaxies.« less

The masses of retired A stars with asteroseismology: Kepler and K2 observations of exoplanet hosts

NASA Astrophysics Data System (ADS)

North, Thomas S. H.; Campante, Tiago L.; Miglio, Andxsrea; Davies, Guy R.; Grunblatt, Samuel K.; Huber, Daniel; Kuszlewicz, James S.; Lund, Mikkel N.; Cooke, Benjamin F.; Chaplin, William J.

2017-12-01

We investigate the masses of 'retired A stars' using asteroseismic detections on seven low-luminosity red-giant and sub-giant stars observed by the NASA Kepler and K2 missions. Our aim is to explore whether masses derived from spectroscopy and isochrone fitting may have been systematically overestimated. Our targets have all previously been subject to long-term radial velocity observations to detect orbiting bodies, and satisfy the criteria used by Johnson et al. to select survey stars which may have had A-type (or early F-type) main-sequence progenitors. The sample actually spans a somewhat wider range in mass, from ≈ 1 M⊙ up to ≈ 1.7 M⊙. Whilst for five of the seven stars the reported discovery mass from spectroscopy exceeds the mass estimated using asteroseismology, there is no strong evidence for a significant, systematic bias across the sample. Moreover, comparisons with other masses from the literature show that the absolute scale of any differences is highly sensitive to the chosen reference literature mass, with the scatter between different literature masses significantly larger than reported error bars. We find that any mass difference can be explained through use of different constraints during the recovery process. We also conclude that underestimated uncertainties on the input parameters can significantly bias the recovered stellar masses, which may have contributed to the controversy on the mass scale for retired A stars.

The Search for Hot Jupiters using Red Buttes Observatory

NASA Astrophysics Data System (ADS)

Sorber, Rebecca L.; Kar, Aman; Hancock, Daniel A.; Leuquire, Jacob D.; Suhaimi, Afiq; Kasper, David; Jang-Condell, Hannah

2018-01-01

The goal of this research is to use the University of Wyoming’s Red Buttes Observatory (RBO) to perform manual, remote, or automated observations of transiting exoplanet candidates. The data contributes to discovery of star systems that include never before identified exoplanets. RBO houses a 0.6-meter telescope and is located approximately 10 miles south of the University of Wyoming’s campus. Our targets are catalogued by the KELT (Kilodegree Extremely Little Telescope) Survey, a photometric search for transiting exoplanets around bright main sequence stars. The KELT Follow-up Network (KELT-FUN), a collaboration of small-aperture telescope users located all over the world, confirms new exoplanet candidates. As part of KELT-FUN, students use the RBO to monitor candidates identified by the KELT team. RBO typically detects transits around stars that are 8-12 in V magnitude, with transit durations of ~1-4 hours and full depth relative changes in brightness above 2 mmags. Using AstroImageJ, we process the data and we look for any indication of a transit occurrence in the processed lightcurve which might confirm the presence of the potential exoplanet. Our team has contributed over 50 light curves to KELT-FUN to date. We are able to compare our data with simultaneous observations by other members of KELT-FUN to maximize the utility of our observations. This project gives undergraduates an authentic scientific research experience, learning how to operate an observatory, process data, and participate in a scientific collaboration.

Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes.

PubMed

Beck, Paul G; Montalban, Josefina; Kallinger, Thomas; De Ridder, Joris; Aerts, Conny; García, Rafael A; Hekker, Saskia; Dupret, Marc-Antoine; Mosser, Benoit; Eggenberger, Patrick; Stello, Dennis; Elsworth, Yvonne; Frandsen, Søren; Carrier, Fabien; Hillen, Michel; Gruberbauer, Michael; Christensen-Dalsgaard, Jørgen; Miglio, Andrea; Valentini, Marica; Bedding, Timothy R; Kjeldsen, Hans; Girouard, Forrest R; Hall, Jennifer R; Ibrahim, Khadeejah A

2011-12-07

When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes; indirect evidence supports this. Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected 'mixed modes'. By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior.

Sublimating comets as the source of nucleation seeds for grain condensation in the gas outflow from AGB stars

NASA Technical Reports Server (NTRS)

Whitmire, D. P.; Matese, John J.; Reynolds, R. T.

1989-01-01

A growing amount of observational and theoretical evidence suggests that most main sequence stars are surrounded by disks of cometary material. The dust production by comets in such disks is investigated when the central stars evolve up the red giant and asymptotic giant branch (AGB). Once released, the dust is ablated and accelerated by the gas outflow and the fragments become the seeds necessary for condensation of the gas. The origin of the requisite seeds has presented a well known problem for classical nucleation theory. This model is consistent with the dust production observed in M giants and supergiants (which have increasing luminosities) and the fact that earlier supergiants and most WR stars (whose luminosities are unchanging) do not have significant dust clouds even though they have significant stellar winds. Another consequence of the model is that the spatial distribution of the dust does not, in general, coincide with that of the gas outflow, in contrast to the conventional condensation model. A further prediction is that the condensation radius is greater that that predicted by conventional theory which is in agreement with IR interferometry measurements of alpha-Ori.

Why stars become red giants

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

Applegate, J.H.

1988-06-01

It is shown that a radiative envelope in which the Kramers opacity law holds cannot transport a luminosity larger than a critical value, and it is argued that the transition to red giant structure is triggered by the star's luminosity exceeding the critical value. If the Kramers law is used for all temperatures and densities, the radius of the star diverges as the critical luminosity is approached. In real stars the radiative envelope expands as the luminosity increases until the star intersects the Hayashi track. Once on the Hayashi track, luminosities in excess of the critical luminosity can be accommodatedmore » by forcing most of the mass of the envelope into the convection zone. 17 references.« less

High-resolution spectra of stars in globular clusters. VI - Oxygen-deficient red giant stars in M13

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

Brown, J.A.; Wallerstein, G.; Oke, J.B.

From high-resolution, high signal-to-noise spectra, abundances of carbon, nitrogen, and oxygen and the C-12/C-13 ratio for five red giants in M13, including star II-67, which has previously been reported to be deficient in oxygen have been determined. Three of the five stars exhibit substantial oxygen deficiencies; O/Fe values range from +0.5 to less than about 0.3. The sum of the CNO nuclides is the same for all stars, which is interpreted as evidence that mixing of CNO-cycled material into the envelope is the cause of the variations in oxygen abundance. 41 refs.

Red and nebulous objects in dark clouds - A survey

NASA Technical Reports Server (NTRS)

Cohen, M.

1980-01-01

A search on the NGS-PO Sky Survey photographs has revealed 150 interesting nebulous and/or red objects, mostly lying in dark clouds and not previously catalogued. Spectral classifications are presented for 55 objects. These indicate a small number of new members of the class of Herbig-Haro objects, a significant number of new T Tauri stars, and a few emission-line hot stars. It is argued that hot, high-mass stars form preferentially in the dense cores of dark clouds. The possible symbiosis of high and low mass stars is considered. A new morphology class is defined for cometary nebulae, in which a star lies on the periphery of a nebulous ring.

Galaxy Zoo: evidence for diverse star formation histories through the green valley

NASA Astrophysics Data System (ADS)

Smethurst, R. J.; Lintott, C. J.; Simmons, B. D.; Schawinski, K.; Marshall, P. J.; Bamford, S.; Fortson, L.; Kaviraj, S.; Masters, K. L.; Melvin, T.; Nichol, R. C.; Skibba, R. A.; Willett, K. W.

2015-06-01

Does galaxy evolution proceed through the green valley via multiple pathways or as a single population? Motivated by recent results highlighting radically different evolutionary pathways between early- and late-type galaxies, we present results from a simple Bayesian approach to this problem wherein we model the star formation history (SFH) of a galaxy with two parameters, [t, τ] and compare the predicted and observed optical and near-ultraviolet colours. We use a novel method to investigate the morphological differences between the most probable SFHs for both disc-like and smooth-like populations of galaxies, by using a sample of 126 316 galaxies (0.01 < z < 0.25) with probabilistic estimates of morphology from Galaxy Zoo. We find a clear difference between the quenching time-scales preferred by smooth- and disc-like galaxies, with three possible routes through the green valley dominated by smooth- (rapid time-scales, attributed to major mergers), intermediate- (intermediate time-scales, attributed to minor mergers and galaxy interactions) and disc-like (slow time-scales, attributed to secular evolution) galaxies. We hypothesize that morphological changes occur in systems which have undergone quenching with an exponential time-scale τ < 1.5 Gyr, in order for the evolution of galaxies in the green valley to match the ratio of smooth to disc galaxies observed in the red sequence. These rapid time-scales are instrumental in the formation of the red sequence at earlier times; however, we find that galaxies currently passing through the green valley typically do so at intermediate time-scales.†

JUPITER WILL BECOME A HOT JUPITER: CONSEQUENCES OF POST-MAIN-SEQUENCE STELLAR EVOLUTION ON GAS GIANT PLANETS

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

Spiegel, David S.; Madhusudhan, Nikku, E-mail: dave@ias.edu, E-mail: Nikku.Madhusudhan@yale.edu

When the Sun ascends the red giant branch (RGB), its luminosity will increase and all the planets will receive much greater irradiation than they do now. Jupiter, in particular, might end up more highly irradiated than the hot Neptune GJ 436b and, hence, could appropriately be termed a 'hot Jupiter'. When their stars go through the RGB or asymptotic giant branch stages, many of the currently known Jupiter-mass planets in several-AU orbits will receive levels of irradiation comparable to the hot Jupiters, which will transiently increase their atmospheric temperatures to {approx}1000 K or more. Furthermore, massive planets around post-main-sequence starsmore » could accrete a non-negligible amount of material from the enhanced stellar winds, thereby significantly altering their atmospheric chemistry as well as causing a significant accretion luminosity during the epochs of most intense stellar mass loss. Future generations of infrared observatories might be able to probe the thermal and chemical structure of such hot Jupiters' atmospheres. Finally, we argue that, unlike their main-sequence analogs (whose zonal winds are thought to be organized in only a few broad, planetary-scale jets), red-giant hot Jupiters should have multiple, narrow jets of zonal winds and efficient day-night redistribution.« less

A Real Shooting Star

NASA Technical Reports Server (NTRS)

2007-01-01

[figure removed for brevity, see original site] Click on the image for movie of A Real Shooting Star

This artist's animation illustrates a star flying through our galaxy at supersonic speeds, leaving a 13-light-year-long trail of glowing material in its wake. The star, named Mira (pronounced my-rah) after the latin word for 'wonderful,' sheds material that will be recycled into new stars, planets and possibly even life. NASA's Galaxy Evolution Explorer discovered the long trail of material behind Mira during its survey of the entire sky in ultraviolet light.

The animation begins by showing a close-up of Mira -- a red-giant star near the end of its life. Red giants are red in color and extremely bloated; for example, if a red giant were to replace our sun, it would engulf everything out to the orbit of Mars. They constantly blow off gas and dust in the form of stellar winds, supplying the galaxy with molecules, such as oxygen and carbon, that will make their way into new solar systems. Our sun will mature into a red giant in about 5 billion years.

As the animation pulls out, we can see the enormous trail of material deposited behind Mira as it hurls along between the stars. Like a boat traveling through water, a bow shock, or build up of gas, forms ahead of the star in the direction of its motion. Gas in the bow shock is heated and then mixes with the cool hydrogen gas in the wind that is blowing off Mira. This heated hydrogen gas then flows around behind the star, forming a turbulent wake.

Why does the trailing hydrogen gas glow in ultraviolet light? When it is heated, it transitions into a higher-energy state, which then loses energy by emitting ultraviolet light - a process known as fluorescence.

Finally, the artist's rendering gives way to the actual ultraviolet image taken by the Galaxy Evolution Explorer

Mira is located 350 light-years from Earth in the constellation Cetus, otherwise known as the whale. Coincidentally, Mira and its 'whale of a tail' can be found in the tail of the whale constellation.

High star formation activity in the central region of a distant cluster at z = 1.46

NASA Astrophysics Data System (ADS)

Hayashi, Masao; Kodama, Tadayuki; Koyama, Yusei; Tanaka, Ichi; Shimasaku, Kazuhiro; Okamura, Sadanori

2010-03-01

We present an unbiased deep [OII] emission survey of a cluster XMMXCS J2215.9-1738 at z = 1.46, the most distant cluster to date with a detection of extended X-ray emission. With wide-field optical and near-infrared cameras (Suprime-Cam and MOIRCS, respectively) on Subaru telescope, we performed deep imaging with a narrow-band filter NB912 (λc = 9139 Å, Δλ = 134 Å) as well as broad-band filters (B,z',J and Ks). From the photometric catalogues, we have identified 44 [OII] emitters in the cluster central region of 6 × 6 arcmin2 down to a dust-free star formation rate (SFR) of 2.6Msolaryr-1 (3σ). Interestingly, it is found that there are many [OII] emitters even in the central high-density region. In fact, the fraction of [OII] emitters to the cluster members as well as their SFRs and equivalent widths stay almost constant with decreasing cluster-centric distance up to the cluster core. Unlike clusters at lower redshifts (z <~ 1) where star formation activity is mostly quenched in their central regions, this higher redshift XMMXCS J2215.9-1738 cluster shows its high star formation activity even at its centre, suggesting that we are beginning to enter the formation epoch of some galaxies in the cluster core eventually. Moreover, we find a deficit of galaxies on the red sequence at magnitudes fainter than ~M* + 0.5 on the colour-magnitude diagram. This break magnitude is brighter than that of lower redshift clusters, and it is likely that we are seeing the formation phase of more massive red galaxies in the cluster core at z ~ 1. These results may indicate inside-out and down-sizing propagation of star formation activity in the course of cluster evolution.

A Brief Glossary of Commonly Used Astronomical Terms.

ERIC Educational Resources Information Center

Harrington, Sherwood

A glossary of 50 astronimical terms is presented. Among terms included are: Asteroid; Big Bang; Binary Star; Black Hole; Comet; Constellation; Eclipse; Equinox; Galaxy; Globular Cluster; Local Group; Magellanic Clouds; Nebula; Neutron Star; Nova; Parsec; Quasar; Radio Astronomy; Red Giant; Red Shift; S.E.T.I.; Solstice; Supernova; and White Dwarf.…

Which of Kepler's Stars Flare?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-12-01

The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a function of Rossby number, which traces stellar rotation. Higher rotation rates correspond to lower Rossby numbers, so these data indicate that more rapidly rotating stars are more likely to exhibit flares. [Van Doorsselaere et al. 2017]Roughly 3.5% of Kepler stars in this sample are flaring stars.24 new A stars are found to show flaring activity. This is interesting because A stars arent thought to have an outer convective zone, which should prevent a magnetic dynamo from operating. Yet these flaring-star detections add to the body of evidence that at least some A stars do show magnetic activity.Most flaring stars in the sample are main-sequence stars, but 653 giants were found to have flaring activity. As with A stars, its unexpected that giant stars would have strong magnetic fields their increase in size and gradual spin-down over time should result in weakening of the surface fields. Nevertheless, it seems that the flare incidence of giant stars is similar to that of F or G main-sequence stars.All stellar types appear to have a small fraction of flare stars stars with an especially high rate of flare occurrence.Rapidly rotating stars are more likely to flare, tend to flare more often, and tend to have stronger flares than slowly rotating stars.As a next step, the authors plan to apply their flare detection algorithm to the larger sample of all Kepler data. In the meantime, this study has both deepened a few mysteries and moved us a step closer in our understanding of which stars flare and why.CitationTom Van Doorsselaere et al 2017 ApJS 232 26. doi:10.3847/1538-4365/aa8f9a

The Multiple Stellar Populations in the Ancient LMC Globular Clusters Hodge 11 and NGC 2210

NASA Astrophysics Data System (ADS)

Chaboyer, Brian; Gilligan, Christina; Wagner-Kaiser, Rachel; Mackey, Dougal; Sarajedini, Ata; Cummings, Jeffrey; Grocholski, Aaron; Geisler, Doug; Cohen, Roger; Villanova, Sandro; Yang, Soung-Chul; Parisi, Celeste

2018-01-01

Hubble Space telescope images of the ancient LMC globular clusters Hodge 11 and NGC 2210 in the F336W, F606W and F814W filters were obtained between June 2016 and April 2017. These deep images has been analyzed with the Dolphot software package. High quality photometry has been obtained from three magnitudes brighter than the horizontal branch, to about four magnitudes fainter than the main sequence turn-off. Both clusters show an excess of red main sequence stars in the F336W filter, indicating that multiple stellar populations exist in both clusters. Hodge 11 shows irregularities in its horizontal branch morphology, which is indicative of the presence of an approximately 0.1 dex internal helium abundance spread.

Wolf-Rayet stars as starting points or as endpoints of the evolution of massive stars?

NASA Technical Reports Server (NTRS)

Lamers, H. J. G. L. M.; Maeder, A.; Schmutz, W.; Cassinelli, J. P.

1991-01-01

The paper investigates the evidence for the two interpretations of Wolf-Rayet stars suggested in the literature: (1) massive premain-sequence stars with disks and (2) massive stars which have lost most of their H-rich layers in a stellar wind is investigated. The abundance determinations which are done in two different ways and which lead to different conclusions are discussed. The composition is solar, which would suggest interpretation (1), or the CNO abundances are strongly anomalous, which would suggest interpretation (2). Results from evolutionary calculations, stellar statistics, the existence of Ofpe/WN9 transition stars and W-R stars with evolved companions show overwhelming evidence that W-R stars are not premain-sequence stars but that they are in a late stage of evolution. Moreover, the fact that W-R stars are usually in clear regions of space, whereas massive premain-sequence stars are embedded in ultracompact H II regions also shows that W-R stars are not young premain-sequence stars.

HADES RV Programme with HARPS-N at TNG . III. Flux-flux and activity-rotation relationships of early-M dwarfs

NASA Astrophysics Data System (ADS)

Maldonado, J.; Scandariato, G.; Stelzer, B.; Biazzo, K.; Lanza, A. F.; Maggio, A.; Micela, G.; González-Álvarez, E.; Affer, L.; Claudi, R. U.; Cosentino, R.; Damasso, M.; Desidera, S.; González Hernández, J. I.; Gratton, R.; Leto, G.; Messina, S.; Molinari, E.; Pagano, I.; Perger, M.; Piotto, G.; Rebolo, R.; Ribas, I.; Sozzetti, A.; Suárez Mascareño, A.; Zanmar Sanchez, R.

2017-02-01

Context. Understanding stellar activity in M dwarfs is crucial for the physics of stellar atmospheres and for ongoing radial velocity exoplanet programmes. Despite the increasing interest in M dwarfs, our knowledge of the chromospheres of these stars is far from being complete. Aims: We test whether the relations between activity, rotation, and stellar parameters and flux-flux relationships previously investigated for main-sequence FGK stars and for pre-main-sequence M stars also hold for early-M dwarfs on the main-sequence. Although several attempts have been made so far, here we analyse a large sample of stars undergoing relatively low activity. Methods: We analyse in a homogeneous and coherent way a well-defined sample of 71 late-K/early-M dwarfs that are currently being observed in the framework of the HArps-N red Dwarf Exoplanet Survey (HADES). Rotational velocities are derived using the cross-correlation technique, while emission flux excesses in the Ca II H & K and Balmer lines from Hα up to Hɛ are obtained by using the spectral subtraction technique. The relationships between the emission excesses and the stellar parameters (projected rotational velocity, effective temperature, kinematics, and age) are studied. Relations between pairs of fluxes of different chromospheric lines (flux-flux relationships) are also studied and compared with the literature results for other samples of stars. Results: We find that the strength of the chromospheric emission in the Ca II H & K and Balmer lines is roughly constant for stars in the M0-M3 spectral range. Although our sample is likely to be biased towards inactive stars, our data suggest that a moderate but significant correlation between activity and rotation might be present, as well as a hint of kinematically selected young stars showing higher levels of emission in the calcium line and in most of the Balmer lines. We find our sample of M dwarfs to be complementary in terms of chromospheric and X-ray fluxes with those of the literature, extending the analysis of the flux-flux relationships to the very low flux domain. Conclusions: Our results agree with previous works suggesting that the activity-rotation-age relationship known to hold for solar-type stars also applies to early-M dwarfs. We also confirm previous findings that the field stars which deviate from the bulk of the empirical flux-flux relationships show evidence of youth. 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 Astrofísica de Canarias.

VizieR Online Data Catalog: U,V photometry in M2 (NGC 7089) (Lardo+, 2012)

NASA Astrophysics Data System (ADS)

Lardo, C.; Pancino, E.; Mucciarelli, A.; Milone, A. P.

2012-10-01

We present U, V photometry of the globular cluster M2. Stars within 1' and outside of 4' from the cluster center are excluded from the CMD to reduce blending effects and the field star contamination, respectively. We imposed on all stars the selection limits of CHI<2.0 and -1

HUBBLE HERITAGE PROJECT'S FIRST ANNIVERSARY(NGC 2261)

NASA Technical Reports Server (NTRS)

2002-01-01

NGC 2346, in contrast to the first two young objects, is a so-called 'planetary nebula,' which is ejected from Sun-like stars which are near the ends of their lives. NGC 2346 is remarkable because its central star is known to be actually a very close pair of stars, orbiting each other every 16 days. It is believed that the binary star was originally more widely separated. However, when one component of the binary evolved, expanded in size, and became a red-giant star, it literally swallowed its companion star. The companion star then spiralled downwards inside the red giant, and in the process spewed out gas into a ring around the binary system. Later on, when the hot core of the red giant was exposed, it developed a faster stellar wind, which emerged perpendicularly to the ring and inflated two huge 'bubbles.' This two-stage process is believed to have resulted in the butterfly-like shape of the nebula. NGC 2346 lies about 2,000 light-years away from us, and is about one-third of a light-year in size. The Hubble Heritage team made this image from observations of NGC 2346 acquired by Massimo Stiavelli (STScI), Inge Heyer (STScI), and collaborators. Image Credit: NASA/The Hubble Heritage Team (AURA/STScI).

A Star on the Run

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-10-01

Usually stars that are born together tend to move together but sometimes stars can go rogue and run away from their original birthplace. A pair of astronomers have now discovered the first runaway red supergiant (RSG) ever identified in another galaxy. With a radial velocity discrepancy of 300 km/s, its also the fastest runaway massive star known. Discrepant Speeds: When massive stars form in giant molecular clouds, they create what are known as OB associations: groups of hot, massive, short-lived stars that have similar velocities because theyre moving through space together. But sometimes stars that appear to be part of an OB association dont have the same velocity as the rest of the group. These stars are called runaways.What causes an OB star to run away is still debated, but we know that a fairly significant fraction of OB stars are runaways. In spite of this, surprisingly few runaways have been found that are evolved massive stars i.e., the post-main-sequence state of OB stars. This is presumably because these evolved stars have had more time to move away from their birthplace, and its more difficult to identify a runaway without the context of its original group. An Evolved Runaway: Difference between observed velocity and expected velocity, plotted as a function of expected velocity. The black points are foreground stars. The red points are expected RSGs, clustered around a velocity difference of zero. The green pentagon is the runaway RSG J004330.06+405258.4. [Evans Massey 2015]Despite this challenge, a recent survey of RSGs in the galaxy M31 has led to the detection of a massive star on the run! Kate Evans (Lowell Observatory and California Institute of Technology) and Philip Massey (Lowell Observatory and Northern Arizona University) discovered that RSG J004330.06+405258.4 is moving through the Andromeda Galaxy with a radial velocity thats off by about 300 km/s from the radial velocity expected for its location.Evans and Massey discovered this rogue star via a photometric survey of RSGs in M31, followed up by spectroscopy with the Multiple Mirror Telescope. They determined that the star is also separated from other massive stars in the disk of the galaxy by about 4.6 kpc which is roughly the distance it would be expected to travel, given its discrepant motion, in an assumed age of about 10 Myr.The authors suggest that this star may be a high-mass analog of hypervelocity stars stars within the Milky Way that are moving fast enough to escape the galaxy. The authors demonstrate that the total discrepant speed of RSG J004330.06+405258.4 is probably comparable to the escape velocity of M31s disk.But whether or not this star is moving fast enough to escape turns out to be moot: it will only live another million years, which means it wont have enough time to leave the galaxy before ending its life in a spectacular supernova. Citation: Kate Anne Evans and Philip Massey 2015 AJ 150 149. doi:10.1088/0004-6256/150/5/149

Infra-Red Characteristics of Faint Galactic Carbon Stars from the First Byurakan Spectral Sky Survey

NASA Astrophysics Data System (ADS)

Kostandyan, G. R.; Gigoyan, K. S.

2017-07-01

Infra-Red (IR) astronomical databases, namely, IRAS, 2MASS, WISE, and Spitzer, are used to analyze photometric data of 126 carbon (C) stars whose spectra are visible in the First Byurakan Survey (FBS) (Markarian et al. 1989) low-resolution (lr) spectral plates. In this work several IR color-color diagrams are studied. Early and late-type C stars are separated in the JHK Near-Infra-Red (NIR) color-color plots, as well as in the WISE W3-W4 versus W1-W2 diagram. Late N-type Asymptotic Giant Branch (AGB) stars are redder in W1-W2, while early-types (CH and R giants) are redder in W3-W4 as expected. Objects with W2-W3 > 1.0m show double-peaked spectral energy distribution (SED), indicating the existence of the circumstellar envelopes around them. 26 N-type stars have IRAS Point Source Catalog (PSC) associations. The reddest object among the targets is N-type C star FBS 2213+421, which belong to the group of the cold post-AGB R Coronae Borealis (R CrB) variables (Rossi et al. 2016).

Photometry, Astrometry, and Discoveries of Ultracool Dwarfs in the Pan-STARRS 3π Survey

NASA Astrophysics Data System (ADS)

Best, William M. J.; Magnier, Eugene A.; Liu, Michael C.; Deacon, Niall; Aller, Kimberly; Zhang, Zhoujian; Pan-STARRS1 Builders

2018-01-01

The Pan-STARRS1 3π Survey (PS1)'s far-red optical sensitivity makes it an exceptional new resource for discovering and characterizing ultracool dwarfs. We present a PS1-based catalog of photometry and proper motions of nearly 10,000 M, L, and T dwarfs, along with our analysis of the kinematics of nearby M6-T9 dwarfs, building a comprehensive picture of the local ultracool population. We highlight some especially interesting ultracool discoveries made with PS1, including brown dwarfs with spectral types in the enigmatic L/T transition, wide companions to main sequence stars that serve as age and metallicity bechmarks for substellar models, and free-floating members of the nearby young moving groups and star-forming regions with masses down to ≈5 MJup. With its public release, PS1 will continue to be a vital tool for studying the ultracool population.

Spectroscopy of hot subdwarf binaries

NASA Astrophysics Data System (ADS)

Kreuzer, Simon; Irrgang, Andreas; Heber, Ulrich

2018-06-01

We present a status report of our spectroscopic analysis of subdwarf binaries consisting of a subdwarf and a F/G/K-type main-sequence companion. These systems selected from SDSS photometry show significant excess in the (infra-)red which can not be explained by interstellar reddening. Inspection of SDSS spectra revealed that most of them are composite spectrum sdB binaries. Once their spectra are disentangled, a detailed spectral analysis can be carried out. It reveals Teff, log g and the metal abundance of each individual star. The cool companion is of particular interest, because its spectrum reveals the original chemical composition of the binary.

Near-infrared spectroscopy of candidate red supergiant stars in clusters

NASA Astrophysics Data System (ADS)

Messineo, Maria; Zhu, Qingfeng; Ivanov, Valentin D.; Figer, Donald F.; Davies, Ben; Menten, Karl M.; Kudritzki, Rolf P.; Chen, C.-H. Rosie

2014-11-01

Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims: We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods: We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks< 7 mag) in GLIMPSE and 2MASS images. Results: A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M⊙ to 15 M⊙. Two red supergiants are located at Galactic coordinates (l,b) = (16.°7, -0.°63) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b) = (49.°3, + 0.°72) and at a distance of ~7.0 kpc. Conclusions: Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps. Based on observations collected at the European Southern Observatory (ESO Programme 60.A-9700(E), and 089.D-0876), and on observations collected at the UKIRT telescope (programme ID H243NS).MM is currently employed by the MPIfR. Part of this work was performed at RIT (2009), at ESA (2010), and at the MPIfR.Tables 3, 4, and 6 are available in electronic form at http://www.aanda.org

An Introduction to the Sun and Stars

NASA Astrophysics Data System (ADS)

Green, Simon F.; Jones, Mark H.

2015-02-01

Introduction; 1. Seeing the Sun; 2. The working Sun; 3. Measuring stars; 4. Comparing stars; 5. The formation of stars; 6. The main sequence life of stars; 7. The life of stars beyond the main sequence; 8. The death of stars; 9. The remnants of stars; Conclusion; Answers and comments; Appendices; Glossary; Further reading; Acknowledgements; Figure references; Index.

Observations of red-giant variable stars by Aboriginal Australians

NASA Astrophysics Data System (ADS)

Hamacher, Duane W.

2018-04-01

Aboriginal Australians carefully observe the properties and positions of stars, including both overt and subtle changes in their brightness, for subsistence and social application. These observations are encoded in oral tradition. I examine two Aboriginal oral traditions from South Australia that describe the periodic changing brightness in three pulsating, red-giant variable stars: Betelgeuse (Alpha Orionis), Aldebaran (Alpha Tauri), and Antares (Alpha Scorpii). The Australian Aboriginal accounts stand as the only known descriptions of pulsating variable stars in any Indigenous oral tradition in the world. Researchers examining these oral traditions over the last century, including anthropologists and astronomers, missed the description of these stars as being variable in nature as the ethnographic record contained several misidentifications of stars and celestial objects. Arguably, ethnographers working on Indigenous Knowledge Systems should have academic training in both the natural and social sciences.

Ring of Stellar Death

NASA Technical Reports Server (NTRS)

2004-01-01

This false-color image from NASA's Spitzer Space Telescope shows a dying star (center) surrounded by a cloud of glowing gas and dust. Thanks to Spitzer's dust-piercing infrared eyes, the new image also highlights a never-before-seen feature -- a giant ring of material (red) slightly offset from the cloud's core. This clumpy ring consists of material that was expelled from the aging star.

The star and its cloud halo constitute a 'planetary nebula' called NGC 246. When a star like our own Sun begins to run out of fuel, its core shrinks and heats up, boiling off the star's outer layers. Leftover material shoots outward, expanding in shells around the star. This ejected material is then bombarded with ultraviolet light from the central star's fiery surface, producing huge, glowing clouds -- planetary nebulas -- that look like giant jellyfish in space.

In this image, the expelled gases appear green, and the ring of expelled material appears red. Astronomers believe the ring is likely made of hydrogen molecules that were ejected from the star in the form of atoms, then cooled to make hydrogen pairs. The new data will help explain how planetary nebulas take shape, and how they nourish future generations of stars.

This image composite was taken on Dec. 6, 2003, by Spitzer's infrared array camera, and is composed of images obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red).

Stellar Snowflake Cluster

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Figure 1 Stellar Snowflake Cluster Combined Image [figure removed for brevity, see original site] Figure 2 Infrared Array CameraFigure 3 Multiband Imaging Photometer

Newborn stars, hidden behind thick dust, are revealed in this image of a section of the Christmas Tree cluster from NASA's Spitzer Space Telescope, created in joint effort between Spitzer's infrared array camera and multiband imaging photometer instruments.

The newly revealed infant stars appear as pink and red specks toward the center of the combined image (fig. 1). The stars appear to have formed in regularly spaced intervals along linear structures in a configuration that resembles the spokes of a wheel or the pattern of a snowflake. Hence, astronomers have nicknamed this the 'Snowflake' cluster.

Star-forming clouds like this one are dynamic and evolving structures. Since the stars trace the straight line pattern of spokes of a wheel, scientists believe that these are newborn stars, or 'protostars.' At a mere 100,000 years old, these infant structures have yet to 'crawl' away from their location of birth. Over time, the natural drifting motions of each star will break this order, and the snowflake design will be no more.

While most of the visible-light stars that give the Christmas Tree cluster its name and triangular shape do not shine brightly in Spitzer's infrared eyes, all of the stars forming from this dusty cloud are considered part of the cluster.

Like a dusty cosmic finger pointing up to the newborn clusters, Spitzer also illuminates the optically dark and dense Cone nebula, the tip of which can be seen towards the bottom left corner of each image.

This combined image shows the presence of organic molecules mixed with dust as wisps of green, which have been illuminated by nearby star formation. The larger yellowish dots neighboring the baby red stars in the Snowflake Cluster are massive stellar infants forming from the same cloud. The blue dots sprinkled across the image represent older Milky Way stars at various distances along this line of sight. This image is a five-channel, false-color composite, showing emission from wavelengths of 3.6 and 4.5 microns (blue), 5.8 microns (cyan), 8 microns (green), and 24 microns (red).

The top right (fig. 2) image from the infrared array camera show that the nebula is still actively forming stars. The wisps of red (represented as green in the combined image) are organic molecules mixed with dust, which has been illuminated by nearby star formation. The infrared array camera picture is a four-channel, false-color composite, showing emission from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red).

The bottom right image (fig. 3) from the multiband imaging photometer shows the colder dust of the nebula and unwraps the youngest stellar babies from their dusty covering. This is a false-color image showing emission at 24 microns (red).

Cool Companions of White Dwarfs from 2MASS

NASA Astrophysics Data System (ADS)

Hoard, D. W.; Wachter, S.; Sturch, L. K.; Widhalm, A. M.; Weiler, K. P.; Wellhouse, J. W.; Gibiansky, M.

2006-12-01

Detecting low mass stellar companions to white dwarfs (WDs) offers many advantages compared to main sequence primaries. In the latter case, faint low mass companions are often hidden in the glare of the more luminous main sequence primary, and radial velocity variations are small and, therefore, difficult to detect. Since WDs are less luminous than main sequence stars, the brightness contrast compared to a potential faint companion is significantly reduced. Most importantly, the markedly different spectral energy distributions of the WDs and their low mass companions makes the detection and separation of the two components relatively straightforward even with simple broad-band multi-color photometry. We have shown in Wachter et al. (2003) that the 2MASS near-IR color-color diagram can easily and efficiently identify candidates for unresolved WD + red dwarf binaries. Our follow-up observations (e.g., Farihi et al. 2006) have shown that a large fraction of these candidates are confirmed as previously unknown binary stars. Here, we present results from our full survey of the 2235 WDs from the McCook & Sion (1999) Catalog using the 2MASS All-Sky Data Release. We have identified an additional large sample of candidate WD + red dwarf binaries, as well as a number of systems that may contain extremely low mass stellar or substellar companions. Support for this work was provided by the National Aeronautics and Space Administration (NASA) under an Astrophysics Data Program grant issued through the Office of Space Science. This research made use of the NASA/Infrared Processing and Analysis Center (IPAC) Infrared Science Archive, which is operated by the Jet Propulsion Laboratory/California Institute of Technology (CIT), under contract with NASA, and data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and IPAC/CIT, funded by NASA and the National Science Foundation.

ALMA observations of the nearby AGB star L2 Puppis. I. Mass of the central star and detection of a candidate planet

NASA Astrophysics Data System (ADS)

Kervella, P.; Homan, W.; Richards, A. M. S.; Decin, L.; McDonald, I.; Montargès, M.; Ohnaka, K.

2016-12-01

Six billion years from now, while evolving on the asymptotic giant branch (AGB), the Sun will metamorphose from a red giant into a beautiful planetary nebula. This spectacular evolution will impact the solar system planets, but observational confirmations of the predictions of evolution models are still elusive as no planet orbiting an AGB star has yet been discovered. The nearby AGB red giant L2 Puppis (d = 64 pc) is surrounded by an almost edge-on circumstellar dust disk. We report new observations with ALMA at very high angular resolution (18 × 15 mas) in band 7 (ν ≈ 350 GHz) that allow us to resolve the velocity profile of the molecular disk. We establish that the gas velocity profile is Keplerian within the central cavity of the dust disk, allowing us to derive the mass of the central star L2 Pup A, mA = 0.659 ± 0.011 ± 0.041 M⊙ (± 6.6%). From evolutionary models, we determine that L2 Pup A had a near-solar main-sequence mass, and is therefore a close analog of the future Sun in 5 to 6 Gyr. The continuum map reveals a secondary source (B) at a radius of 2 AU contributing fB/fA = 1.3 ± 0.1% of the flux of the AGB star. L2 Pup B is also detected in CO emission lines at a radial velocity of vB = 12.2 ± 1.0 km s-1. The close coincidence of the center of rotation of the gaseous disk with the position of the continuum emission from the AGB star allows us to constrain the mass of the companion to mB = 12 ± 16 MJup. L2 Pup B is most likely a planet or low-mass brown dwarf with an orbital period of about five years. Its continuum brightness and molecular emission suggest that it may be surrounded by an extended molecular atmosphere or an accretion disk. L2 Pup therefore emerges as a promising vantage point on the distant future of our solar system.

Carbon and nitrogen abundances in red giant stars in the globular cluster 47 Tucanae

NASA Technical Reports Server (NTRS)

Dickens, R. J.; Bell, R. A.; Gustafsson, B.

1979-01-01

The effects of changes in temperature, gravity, overall metal abundance, and carbon and nitrogen abundances have been investigated for model stellar spectra and colors representing globular-cluster giants of moderate metal deficiency. The results are presented in the form of spectral atlases and theoretical color-color diagrams. Using these results, approximate abundances of carbon and nitrogen have been derived for some red giant stars in 47 Tuc, from intermediate- and low-dispersion spectra and from intermediate- and narrow-band photometry. In all the normal giants studied, nitrogen is overabundant by up to about a factor of 5 (the precise value depends on the adopted carbon abundance), with different enhancements for different giants. The observational material is not sufficient to distinguish between a normal carbon abundance and a slight carbon depletion for the giant-branch stars, but carbon appears to be somewhat depleted in stars on the asymptotic giant branch. A most probable value of M/H = -0.8 for the overall cluster metal abundance is suggested from analysis of Stromgren photometry of red horizontal-branch stars.

MINERVA-Red: A telescope dedicated to the discovery of planets orbiting the nearest low-mass stars

NASA Astrophysics Data System (ADS)

Sliski, David; Blake, Cullen; Johnson, John A.; Plavchan, Peter; Wittenmyer, Robert A.; Eastman, Jason D.; Barnes, Stuart; Baker, Ashley

2017-01-01

Results from Kepler and ground-based exoplanet surveys suggest that M-dwarfs host numerous small sized planets. Additionally, the discovery of the Earth-sized exoplanets orbiting Proxima Centauri and Trappist 1 demonstrate that these stars can host terrestrial planets in their habitable zones. Since low-mass stars are intrinsically faint at optical wavelengths, obtaining 1 m/s Doppler resolution to detect their planetary companions remains a challenge for instruments designed for sun-like stars. We describe a novel, high-cadence approach aimed at detecting and characterizing planets orbiting the closest low-mass stars to the Sun. MINERVA-Red is an echelle spectrograph optimized for the 'deep red', between 800 nm and 900 nm, where M-dwarfs are brightest. The spectrograph will be temperature controlled at 20C +/- 10mk and in a vacuum chamber which maintains a pressure below 0.01 mbar while using a Fabry-Perot etalon and U/Ne lamp for wavelength calibration. The spectrometer will operate with a robotic, 0.7-meter telescope at Mt. Hopkins, Arizona. We expect first light in 2017.

Rapidly rotating neutron stars in general relativity: Realistic equations of state

NASA Technical Reports Server (NTRS)

Cook, Gregory B.; Shapiro, Stuart L.; Teukolsky, Saul A.

1994-01-01

We construct equilibrium sequences of rotating neutron stars in general relativity. We compare results for 14 nuclear matter equations of state. We determine a number of important physical parameters for such stars, including the maximum mass and maximum spin rate. The stability of the configurations to quasi-radial perturbations is assessed. We employ a numerical scheme particularly well suited to handle rapid rotation and large departures from spherical symmetry. We provide an extensive tabulation of models for future reference. Two classes of evolutionary sequences of fixed baryon rest mass and entropy are explored: normal sequences, which behave very much like Newtonian sequences, and supramassive sequences, which exist for neutron stars solely because of general relativistic effects. Adiabatic dissipation of energy and angular momentum causes a star to evolve in quasi-stationary fashion along an evolutionary sequence. Supramassive sequences have masses exceeding the maximum mass of a nonrotating neutron star. A supramassive star evolves toward eventual catastrophic collapse to a black hole. Prior to collapse, the star actually spins up as it loses angular momentum, an effect that may provide an observable precursor to gravitational collapse to a black hole.

Astrophysics of Red Supergiants

NASA Astrophysics Data System (ADS)

Levesque, Emily M.

2017-12-01

'Astrophysics of Red Supergiants' is the first book of its kind devoted to our current knowledge of red supergiant stars, a key evolutionary phase that is critical to our larger understanding of massive stars. It provides a comprehensive overview of the fundamental physical properties of red supergiants, their evolution, and their extragalactic and cosmological applications. It serves as a reference for researchers from a broad range of fields (including stellar astrophysics, supernovae, and high-redshift galaxies) who are interested in red supergiants as extreme stages of stellar evolution, dust producers, supernova progenitors, extragalactic metallicity indicators, members of massive binaries and mergers, or simply as compelling objects in their own right. The book is accessible to a range of experience levels, from graduate students up to senior researchers.

Dust clouds around red giant stars - Evidence of sublimating comet disks?

NASA Technical Reports Server (NTRS)

Matese, John J.; Whitmire, Daniel P.; Reynolds, Ray T.

1989-01-01

The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

Additional red and reddened stars in Cyg OB2 association

NASA Technical Reports Server (NTRS)

Parthasarathy, M.; Jain, S. K.

1989-01-01

Several new red and reddened stars are detected in the most heavily reddened associations Cyg OB2. About 47 IRAS sources are detected in Cyg OB2. Their flux distributions, and colors, suggest that they are young stellar objects embedded in dust envelopes or disks (some of them may be proto stars) and are most likely members of the Cyg OB2 association. The large values of the flux ratio L sub IR/L sub VIS suggests that the central objects are obscured because of very large extinction.

PROBING THE DEEP END OF THE MILKY WAY WITH KEPLER : ASTEROSEISMIC ANALYSIS OF 854 FAINT RED GIANTS MISCLASSIFIED AS COOL DWARFS

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

Mathur, S.; García, R. A.; Beck, P. G.

Asteroseismology has proven to be an excellent tool to determine not only global stellar properties with good precision, but also to infer the stellar structure, dynamics, and evolution for a large sample of Kepler stars. Prior to the launch of the mission, the properties of Kepler targets were inferred from broadband photometry, leading to the Kepler Input Catalog (KIC). The KIC was later revised in the Kepler Star Properties Catalog, based on literature values and an asteroseismic analysis of stars that were unclassified in the KIC. Here, we present an asteroseismic analysis of 45,400 stars that were classified as dwarfsmore » in the Kepler Star Properties Catalog. We found that around 2% of the sample shows acoustic modes in the typical frequency range that put them in the red-giant category rather than the cool dwarf category. We analyze the asteroseismic properties of these stars, derive their surface gravities, masses, and radii, and present updated effective temperatures and distances. We show that the sample is significantly fainter than the previously known oscillating giants in the Kepler field, with the faintest stars reaching down to a Kepler magnitude of Kp ∼ 16. We demonstrate that 404 stars are at distances beyond 5 kpc and that the stars are significantly less massive than for the original Kepler red-giant sample, consistent with a population of distant halo giants. A comparison with a galactic population model shows that up to 40 stars might be genuine halo giants, which would increase the number of known asteroseismic halo stars by a factor of 4. The detections presented here will provide a valuable sample for galactic archeology studies.« less

The Mass-loss Return from Evolved Stars to the Large Magellanic Cloud. IV. Construction and Validation of a Grid of Models for Oxygen-rich AGB Stars, Red Supergiants, and Extreme AGB Stars

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, S.; Meixner, M.

2011-02-01

To measure the mass loss from dusty oxygen-rich (O-rich) evolved stars in the Large Magellanic Cloud (LMC), we have constructed a grid of models of spherically symmetric dust shells around stars with constant mass-loss rates using 2Dust. These models will constitute the O-rich model part of the "Grid of Red supergiant and Asymptotic giant branch star ModelS" (GRAMS). This model grid explores four parameters—stellar effective temperature from 2100 K to 4700 K luminosity from 103 to 106 L sun; dust shell inner radii of 3, 7, 11, and 15 R star; and 10.0 μm optical depth from 10-4 to 26. From an initial grid of ~1200 2Dust models, we create a larger grid of ~69,000 models by scaling to cover the luminosity range required by the data. These models are available online to the public. The matching in color-magnitude diagrams and color-color diagrams to observed O-rich asymptotic giant branch (AGB) and red supergiant (RSG) candidate stars from the SAGE and SAGE-Spec LMC samples and a small sample of OH/IR stars is generally very good. The extreme AGB star candidates from SAGE are more consistent with carbon-rich (C-rich) than O-rich dust composition. Our model grid suggests lower limits to the mid-infrared colors of the dustiest AGB stars for which the chemistry could be O-rich. Finally, the fitting of GRAMS models to spectral energy distributions of sources fit by other studies provides additional verification of our grid and anticipates future, more expansive efforts.

A Large and Pristine Sample of Standard Candles across the Milky Way: ∼100,000 Red Clump Stars with 3% Contamination

NASA Astrophysics Data System (ADS)

Ting, Yuan-Sen; Hawkins, Keith; Rix, Hans-Walter

2018-05-01

Core helium-burning red clump (RC) stars are excellent standard candles in the Milky Way. These stars may have more precise distance estimates from spectrophotometry than from Gaia parallaxes beyond 3 kpc. However, RC stars have values of T eff and {log}g that are very similar to some red giant branch (RGB) stars. Especially for low-resolution spectroscopic studies where T eff, {log}g, and [Fe/H] can only be estimated with limited precision, separating RC stars from RGB through established methods can incur ∼20% contamination. Recently, Hawkins et al. demonstrated that the additional information in single-epoch spectra, such as the C/N ratio, can be exploited to cleanly differentiate RC and RGB stars. In this second paper of the series, we establish a data-driven mapping from spectral flux space to independently determined asteroseismic parameters, the frequency and the period spacing. From this, we identify 210,371 RC stars from the publicly available LAMOST DR3 and APOGEE DR14 data, with ∼9% of contamination. We provide an RC sample of 92249 stars with a contamination of only ∼3%, by restricting the combined analysis to LAMOST stars with S/Npix ≥ 75. This demonstrates that high-signal-to-noise ratio (S/N), low-resolution spectra covering a broad wavelength range can identify RC samples at least as pristine as their high-resolution counterparts. As coming and ongoing surveys such as TESS, DESI, and LAMOST will continue to improve the overlapping training spectroscopic-asteroseismic sample, the method presented in this study provides an efficient and straightforward way to derive a vast yet pristine sample of RC stars to reveal the three-dimensional (3D) structure of the Milky Way.

VizieR Online Data Catalog: CCD photometry of Pal 1 (Borissova+ 1995)

NASA Astrophysics Data System (ADS)

Borissova, J.; Spassova, N.

1997-06-01

A CCD photometry of the halo cluster Palomar 1 is presented in the Thuan-Gunn photometric system. The principal sequences of the color-magnitude diagrams are delineated in different spectral bands. The color- magnitude diagrams of the cluster show a well defined red horizontal branch, a subgiant branch and a main-sequence down to about two magnitudes below the main sequence turnoff. The giant branch is absent and the brightest stars are the horizontal branch stars. The age of the cluster determined by comparison with the isochrones of Bell & VandenBerg (1987ApJS...63..335B) is consistent with an age in the interval 12-14Gyr. A distance modulus of (m-M)g0=15.38+/-0.15 magnitude and E(g-r)=0.16 has been derived. An estimate of the cluster structural parameters such as core radius and concentration parameter gives rc=1.5pc and c=1.46. A mass estimate of 1.1x103M⊙ and a mass-to-light ratio of 1.79 have been obtained using King's (1966AJ.....71...64K) method. The morphology of color-magnitude diagrams allows Pal 1 to be interpreted as probably a globular cluster rather than an old open one. For a description of the uvgr photometric system, see e.g. (1 data file).

VizieR Online Data Catalog: CONCH-SHELL catalog of nearby M dwarfs (Gaidos+, 2014)

NASA Astrophysics Data System (ADS)

Gaidos, E.; Mann, A. W.; Lepine, S.; Buccino, A.; James, D.; Ansdell, M.; Petrucci, R.; Mauas, P.; Hilton, E. J.

2015-04-01

Lepinet et al. 2011 (J/AJ/142/138) selected candidate M dwarfs as stars that were (i) bright (J<10), (ii) red (V-J>2.7), (iii) had absolute magnitudes or reduced proper motions, proxies for absolute magnitudes, consistent with the main sequence and (iv) infrared Two Micron All-Sky Survey (2MASS; Skrutskie et al. 2006, Cat. II/246) JHKS colours that are consistent with M dwarfs. In this work, we constructed a revised catalogue of J<9 M dwarfs using modified criteria and new photometry from APASS. Spectroscopic observations with a resolution if ~1000 were achieved at the SuperNova Integral Field Spectrograph (SNIFS) on the University of Hawaii 2.2m telescope on Maunakea, Hawaii, the Mark III spectrograph and Boller & Chivens CCDS spectrograph (CCDS) on the 1.3m McGraw-Hill telescope at the MDM Observatory on Kitt Peak, Arizona, the REOSC spectrograph on the 2.15m Jorge Sahade telescope at the Complejo Astronomico El Leoncito Observatory (CASLEO), Argentina, and the RC spectrograph on the 1.9m Radcliffe telescope at the South African Astronomical Observatory. We obtained a total of 3071 spectra of 2583 stars or 86% of the catalog over the span 2002-2014 of more than 11 years. 425 stars were observed twice, 14 stars were observed thrice, and 6 stars had more than four observations. (2 data files).

UVIT observations of the star-forming ring in NGC 7252: Evidence of possible AGN feedback suppressing central star formation

NASA Astrophysics Data System (ADS)

George, K.; Joseph, P.; Mondal, C.; Devaraj, A.; Subramaniam, A.; Stalin, C. S.; Côté, P.; Ghosh, S. K.; Hutchings, J. B.; Mohan, R.; Postma, J.; Sankarasubramanian, K.; Sreekumar, P.; Tandon, S. N.

2018-05-01

Context. Some post-merger galaxies are known to undergo a starburst phase that quickly depletes the gas reservoir and turns it into a red-sequence galaxy, though the details are still unclear. Aims: Here we explore the pattern of recent star formation in the central region of the post-merger galaxy NGC 7252 using high-resolution ultraviolet (UV) images from the UVIT on ASTROSAT. Methods: The UVIT images with 1.2 and 1.4 arcsec resolution in the FUV and NUV are used to construct a FUV-NUV colour map of the central region. Results: The FUV-NUV pixel colour map for this canonical post-merger galaxy reveals a blue circumnuclear ring of diameter 10'' (3.2 kpc) with bluer patches located over the ring. Based on a comparison to single stellar population models, we show that the ring is comprised of stellar populations with ages ≲300 Myr, with embedded star-forming clumps of younger age (≲150Myr). Conclusions: The suppressed star formation in the central region, along with the recent finding of a large amount of ionised gas, leads us to speculate that this ring may be connected to past feedback from a central super-massive black hole that has ionised the hydrogen gas in the central 4'' 1.3 kpc.

Multiplicity of the Galactic Senior Citizens: A High-resolution Search for Cool Subdwarf Companions

NASA Astrophysics Data System (ADS)

Ziegler, Carl; Law, Nicholas M.; Baranec, Christoph; Riddle, Reed L.; Fuchs, Joshua T.

2015-05-01

Cool subdwarfs are the oldest members of the low-mass stellar population. Mostly present in the galactic halo, subdwarfs are characterized by their low-metallicity. Measuring their binary fraction and comparing it to solar-metallicity stars could give key insights into the star formation process early in the Milky Way’s history. However, because of their low luminosity and relative rarity in the solar neighborhood, binarity surveys of cool subdwarfs have suffered from small sample sizes and incompleteness. Previous surveys have suggested that the binary fraction of red subdwarfs is much lower than for their main-sequence cousins. Using the highly efficient Robo-AO system, we present the largest high-resolution survey of subdwarfs, sensitive to angular separations (ρ ≥slant 0.″ 15) and contrast ratios ({Δ }{{m}i} ≤slant 6) invisible in past surveys. Of 344 target cool subdwarfs, 43 are in multiple systems, 19 of which are newly discovered, for a binary fraction of 12.5 ± 1.9%. We also discovered seven triple star systems for a triplet fraction of 2.0 ± 0.8%. Comparisons to similar surveys of solar-metallicity dwarf stars gives a ∼3σ disparity in luminosity between companion stars, with subdwarfs displaying a shortage of low-contrast companions. We also observe a lack of close subdwarf companions in comparison to similar-mass dwarf multiple systems.

LONG-TERM LIGHT CURVE OF HIGHLY VARIABLE PROTOSTELLAR STAR GM CEP

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

Xiao Limin; Kroll, Peter; Henden, Arne A.

2010-04-15

We present data from the archival plates at Harvard College Observatory and Sonneberg Observatory showing the field of the solar-type pre-main-sequence star GM Cep. A total of 186 magnitudes of GM Cep have been measured on these archival plates, with 176 in blue sensitivity, six in visible, and four in red. We combine our data with data from the literature and from the American Association of Variable Star Observers to depict the long-term light curves of GM Cep in both B and V wavelengths. The light curves span from 1895 until now, with two densely sampled regions (1935-1945 in themore » B band, and 2006 until now in the V band). The long-term light curves do not show any fast rise behavior as predicted by an accretion mechanism. Both the light curves and the magnitude histograms confirm the conclusion that the light curves are dominated by dips (possibly from extinction) superposed on some quiescence state, instead of outbursts caused by accretion flares. Our result excludes the possibility of GM Cep being a FUor, EXor, or McNeil's Nebula-type star. Several special cases of T Tauri stars were checked, but none of these light curves were compatible with that of GM Cep. The lack of periodicity in the light curve excludes the possibility of GM Cep being a KH 15D system.« less

Monash Chemical Yields Project (Monχey) Element production in low- and intermediate-mass stars

NASA Astrophysics Data System (ADS)

Doherty, Carolyn; Lattanzio, John; Angelou, George; Campbell, Simon W.; Church, Ross; Constantino, Thomas; Cristallo, Sergio; Gil-Pons, Pilar; Karakas, Amanda; Lugaro, Maria; Stancliffe, Richard

The Monχey project will provide a large and homogeneous set of stellar yields for the low- and intermediate- mass stars and has applications particularly to galactic chemical evolution modelling. We describe our detailed grid of stellar evolutionary models and corresponding nucleosynthetic yields for stars of initial mass 0.8 M⊙ up to the limit for core collapse supernova (CC-SN) ~ 10 M⊙. Our study covers a broad range of metallicities, ranging from the first, primordial stars (Z = 0) to those of super-solar metallicity (Z = 0.04). The models are evolved from the zero-age main-sequence until the end of the asymptotic giant branch (AGB) and the nucleosynthesis calculations include all elements from H to Bi. A major innovation of our work is the first complete grid of heavy element nucleosynthetic predictions for primordial AGB stars as well as the inclusion of extra-mixing processes (in this case thermohaline) during the red giant branch. We provide a broad overview of our results with implications for galactic chemical evolution as well as highlight interesting results such as heavy element production in dredge-out events of super-AGB stars. We briefly introduce our forthcoming web-based database which provides the evolutionary tracks, structural properties, internal/surface nucleosynthetic compositions and stellar yields. Our web interface includes user- driven plotting capabilities with output available in a range of formats. Our nucleosynthetic results will be available for further use in post processing calculations for dust production yields.

Supernova shock breakout from a red supergiant.

PubMed

Schawinski, Kevin; Justham, Stephen; Wolf, Christian; Podsiadlowski, Philipp; Sullivan, Mark; Steenbrugge, Katrien C; Bell, Tony; Röser, Hermann-Josef; Walker, Emma S; Astier, Pierre; Balam, Dave; Balland, Christophe; Carlberg, Ray; Conley, Alex; Fouchez, Dominique; Guy, Julien; Hardin, Delphine; Hook, Isobel; Howell, D Andrew; Pain, Reynald; Perrett, Kathy; Pritchet, Chris; Regnault, Nicolas; Yi, Sukyoung K

2008-07-11

Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic "core-collapse" supernova. Such events are usually only detected at least a few days after the star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy Evolution Explorer space telescope reveal a radiative precursor from the supernova shock before the shock reached the surface of the star and show the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve confirm that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a way to probe the physics of core-collapse supernovae and the internal structures of their progenitor stars.

ASTEROSEISMIC CLASSIFICATION OF STELLAR POPULATIONS AMONG 13,000 RED GIANTS OBSERVED BY KEPLER

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

Stello, Dennis; Bedding, Timothy R.; Benomar, Othman

2013-03-10

Of the more than 150,000 targets followed by the Kepler Mission, about 10% were selected as red giants. Due to their high scientific value, in particular for Galaxy population studies and stellar structure and evolution, their Kepler light curves were made public in late 2011. More than 13,000 (over 85%) of these stars show intrinsic flux variability caused by solar-like oscillations making them ideal for large-scale asteroseismic investigations. We automatically extracted individual frequencies and measured the period spacings of the dipole modes in nearly every red giant. These measurements naturally classify the stars into various populations, such as the redmore » giant branch, the low-mass (M/M{sub Sun} {approx}< 1.8) helium-core-burning red clump, and the higher-mass (M/M{sub Sun} {approx}> 1.8) secondary clump. The period spacings also reveal that a large fraction of the stars show rotationally induced frequency splittings. This sample of stars will undoubtedly provide an extremely valuable source for studying the stellar population in the direction of the Kepler field, in particular when combined with complementary spectroscopic surveys.« less

Interacting supernovae from photoionization-confined shells around red supergiant stars

NASA Astrophysics Data System (ADS)

Mackey, Jonathan; Mohamed, Shazrene; Gvaramadze, Vasilii V.; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M.-A.; Moriya, Takashi J.; Neilson, Hilding R.

2014-08-01

Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction.

Interacting supernovae from photoionization-confined shells around red supergiant stars.

PubMed

Mackey, Jonathan; Mohamed, Shazrene; Gvaramadze, Vasilii V; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M-A; Moriya, Takashi J; Neilson, Hilding R

2014-08-21

Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction.

Lithium abundances among solar-type pre-main-sequence stars

NASA Technical Reports Server (NTRS)

Strom, Karen M.; Wilkin, Francis P.; Strom, Stephen E.; Seaman, Robert L.

1989-01-01

Measurements of Li I 6707 A line strengths were carried out for two samples of pre-main-sequence (PMS) stars (L 1641 and Taurus-Auriga), and the Li abundances estimated for PMS stars are compared with those deduced from observations of Li line strengths for main-sequence stars in the Alpha Persei cluster. It was found that the maximum Li abundances among the PMS stars with solar mass values greater than 1.0 exceed the maximum abundances for Alpha Per stars by at least 0.3 dex. Some PMS stars, including few apparently young stars, showed large (greater than 1.0 dex) Li depletion, and some apparently old PMS stars showed little or no depletion.

Eagle Nebula Flaunts its Infrared Feathers

NASA Technical Reports Server (NTRS)

2007-01-01

[figure removed for brevity, see original site] Figure 1 [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 2 Figure 3

This set of images from NASA's Spitzer Space Telescope shows the Eagle nebula in different hues of infrared light. Each view tells a different tale. The left picture shows lots of stars and dusty structures with clarity. Dusty molecules found on Earth called polycyclic aromatic hydrocarbons produce most of the red; gas is green and stars are blue.

The middle view is packed with drama, because it tells astronomers that a star in this region violently erupted, or went supernova, heating surrounding dust (orange). This view also reveals that the hot dust is shell shaped, another indication that a star exploded.

The final picture highlights the contrast between the hot, supernova-heated dust (green) and the cooler dust making up the region's dusty star-forming clouds and towers (red, blue and purple).

The left image is a composite of infrared light with the following wavelengths: 3.6 microns (blue); 4.5 microns (green); 5.8 microns (orange); and 8 microns (red). The right image includes longer infrared wavelengths, and is a composite of light of 4.5 to 8.0 microns (blue); 24 microns (green); and 70 microns (red). The middle image is made up solely of 24-micron light.

RE-INFLATED WARM JUPITERS AROUND RED GIANTS

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

Lopez, Eric D.; Fortney, Jonathan J.

2016-02-10

Since the discovery of the first transiting hot Jupiters, models have sought to explain the anomalously large radii of highly irradiated gas giants. We now know that the size of hot Jupiter radius anomalies scales strongly with a planet's level of irradiation and numerous models like tidal heating, ohmic dissipation, and thermal tides have since been developed to help explain these inflated radii. In general, however, these models can be grouped into two broad categories: models that directly inflate planetary radii by depositing a fraction of the incident irradiation into the interior and models that simply slow a planet's radiativemore » cooling, allowing it to retain more heat from formation and thereby delay contraction. Here we present a new test to distinguish between these two classes of models. Gas giants orbiting at moderate orbital periods around post-main-sequence stars will experience enormous increases to their irradiation as their host stars move up the sub-giant and red-giant branches. If hot Jupiter inflation works by depositing irradiation into the planet's deep interiors then planetary radii should increase in response to the increased irradiation. This means that otherwise non-inflated gas giants at moderate orbital periods of >10 days can re-inflate as their host stars evolve. Here we explore the circumstances that can lead to the creation of these “re-inflated” gas giants and examine how the existence or absence of such planets can be used to place unique constraints on the physics of the hot Jupiter inflation mechanism. Finally, we explore the prospects for detecting this potentially important undiscovered population of planets.« less

Star System Bonanza Illustration

NASA Image and Video Library

2014-02-27

This illustration shows the unusual orbit of planet Kepler-413b around a close pair of orange and red dwarf stars. The planet 66-day orbit is tilted 2.5 degrees with respect to the plane of the binary stars orbit.

A survey for red varibles INT he LMC - II

NASA Astrophysics Data System (ADS)

Reid, Neill; Glass, I. S.; Catchpole, R. M.

1988-05-01

Infrared photometry of a sample of 126 variables drawn from a 16 sq deg area of the northern LMC is presented. Most of these stars were previously unknown and the majority prove the be long period red-giant variables. Most of the latter stars fall within two groups in the /K(0), log(P)/ diagram, the lower luminosity ones being Miras which obey a definite period-luminosity relation. Using the latter stars as distance estimators is discussed. The /M(bol), P/ diagram is compared with the theoretical tracks calculated by Wood, Bessell & Fox (1983), and it is found that the distribution of stars is probably consistent with a lull in star formation in the LMC from about 10 to the 9th - 2 x 10 to the 8th yr ago, although this conclusion depends strongly on the luminosity at which stars of different initial mass enter the thermally pulsing AGB.

Lighting up a Dead Star's Layers

NASA Technical Reports Server (NTRS)

2006-01-01

This image from NASA's Spitzer Space Telescope shows the scattered remains of an exploded star named Cassiopeia A. Spitzer's infrared detectors 'picked' through these remains and found that much of the star's original layering had been preserved.

In this false-color image, the faint, blue glow surrounding the dead star is material that was energized by a shock wave, called the forward shock, which was created when the star blew up. The forward shock is now located at the outer edge of the blue glow. Stars are also seen in blue. Green, yellow and red primarily represent material that was ejected in the explosion and heated by a slower shock wave, called the reverse shock wave.

The picture was taken by Spitzer's infrared array camera and is a composite of 3.6-micron light (blue); 4.5-micron light (green); and 8.0-micron light (red).

SDSS-IV MaNGA: Spatially Resolved Star Formation Main Sequence and LI(N)ER Sequence

NASA Astrophysics Data System (ADS)

Hsieh, B. C.; Lin, Lihwai; Lin, J. H.; Pan, H. A.; Hsu, C. H.; Sánchez, S. F.; Cano-Díaz, M.; Zhang, K.; Yan, R.; Barrera-Ballesteros, J. K.; Boquien, M.; Riffel, R.; Brownstein, J.; Cruz-González, I.; Hagen, A.; Ibarra, H.; Pan, K.; Bizyaev, D.; Oravetz, D.; Simmons, A.

2017-12-01

We present our study on the spatially resolved Hα and M * relation for 536 star-forming and 424 quiescent galaxies taken from the MaNGA survey. We show that the star formation rate surface density ({{{Σ }}}{SFR}), derived based on the Hα emissions, is strongly correlated with the M * surface density ({{{Σ }}}* ) on kiloparsec scales for star-forming galaxies and can be directly connected to the global star-forming sequence. This suggests that the global main sequence may be a consequence of a more fundamental relation on small scales. On the other hand, our result suggests that ∼20% of quiescent galaxies in our sample still have star formation activities in the outer region with lower specific star formation rate (SSFR) than typical star-forming galaxies. Meanwhile, we also find a tight correlation between {{{Σ }}}{{H}α } and {{{Σ }}}* for LI(N)ER regions, named the resolved “LI(N)ER” sequence, in quiescent galaxies, which is consistent with the scenario that LI(N)ER emissions are primarily powered by the hot, evolved stars as suggested in the literature.

What's Old is New in the Large Magellanic Cloud

NASA Technical Reports Server (NTRS)

2006-01-01

[figure removed for brevity, see original site] Poster Version Large Magellanic Cloud

This vibrant image from NASA's Spitzer Space Telescope shows the Large Magellanic Cloud, a satellite galaxy to our own Milky Way galaxy.

The infrared image, a mosaic of 300,000 individual tiles, offers astronomers a unique chance to study the lifecycle of stars and dust in a single galaxy. Nearly one million objects are revealed for the first time in this Spitzer view, which represents about a 1,000-fold improvement in sensitivity over previous space-based missions. Most of the new objects are dusty stars of various ages populating the Large Magellanic Cloud; the rest are thought to be background galaxies.

The blue color in the picture, seen most prominently in the central bar, represents starlight from older stars. The chaotic, bright regions outside this bar are filled with hot, massive stars buried in thick blankets of dust. The red color around these bright regions is from dust heated by stars, while the red dots scattered throughout the picture are either dusty, old stars or more distant galaxies. The greenish clouds contain cooler interstellar gas and molecular-sized dust grains illuminated by ambient starlight.

Astronomers say this image allows them to quantify the process by which space dust -- the same stuff that makes up planets and even people -- is recycled in a galaxy. The picture shows dust at its three main cosmic hangouts: around the young stars, where it is being consumed (red-tinted, bright clouds); scattered about in the space between stars (greenish clouds); and in expelled shells of material from old stars (randomly-spaced red dots).

The Large Magellanic Cloud, located 160,000 light-years from Earth, is one of a handful of dwarf galaxies that orbit our own Milky Way. It is approximately one-third as wide as the Milky Way, and, if it could be seen in its entirety, would cover the same amount of sky as a grid of about 480 full moons. About one-third of the entire galaxy can be seen in the Spitzer image.

This picture is a composite of infrared light captured by Spitzer. Light with wavelengths of 3.6 (blue) and 8 (green) microns was captured by the telescope's infrared array camera; 24-micron light (red) was detected by the multiband imaging photometer.

What Old is New in the Large Magellanic Cloud

NASA Image and Video Library

2006-09-01

This vibrant image from NASA's Spitzer Space Telescope shows the Large Magellanic Cloud, a satellite galaxy to our own Milky Way galaxy. The infrared image, a mosaic of 300,000 individual tiles, offers astronomers a unique chance to study the lifecycle of stars and dust in a single galaxy. Nearly one million objects are revealed for the first time in this Spitzer view, which represents about a 1,000-fold improvement in sensitivity over previous space-based missions. Most of the new objects are dusty stars of various ages populating the Large Magellanic Cloud; the rest are thought to be background galaxies. The blue color in the picture, seen most prominently in the central bar, represents starlight from older stars. The chaotic, bright regions outside this bar are filled with hot, massive stars buried in thick blankets of dust. The red color around these bright regions is from dust heated by stars, while the red dots scattered throughout the picture are either dusty, old stars or more distant galaxies. The greenish clouds contain cooler interstellar gas and molecular-sized dust grains illuminated by ambient starlight. Astronomers say this image allows them to quantify the process by which space dust -- the same stuff that makes up planets and even people -- is recycled in a galaxy. The picture shows dust at its three main cosmic hangouts: around the young stars, where it is being consumed (red-tinted, bright clouds); scattered about in the space between stars (greenish clouds); and in expelled shells of material from old stars (randomly-spaced red dots). The Large Magellanic Cloud, located 160,000 light-years from Earth, is one of a handful of dwarf galaxies that orbit our own Milky Way. It is approximately one-third as wide as the Milky Way, and, if it could be seen in its entirety, would cover the same amount of sky as a grid of about 480 full moons. About one-third of the entire galaxy can be seen in the Spitzer image. This picture is a composite of infrared light captured by Spitzer. Light with wavelengths of 3.6 (blue) and 8 (green) microns was captured by the telescope's infrared array camera; 24-micron light (red) was detected by the multiband imaging photometer. http://photojournal.jpl.nasa.gov/catalog/PIA07137

Stellar Work of Art

NASA Technical Reports Server (NTRS)

2008-01-01

[figure removed for brevity, see original site] Poster Version

This painterly portrait of a star-forming cloud, called NGC 346, is a combination of multiwavelength light from NASA's Spitzer Space Telescope (infrared), the European Southern Observatory's New Technology Telescope (visible), and the European Space Agency's XMM-Newton space telescope (X-ray).

The infrared observations highlight cold dust in red, visible data show glowing gas in green, and X-rays show very warm gas in blue. Ordinary stars appear as blue spots with white centers, while young stars enshrouded in dust appear as red spots with white centers.

The colorful picture demonstrates that stars in this region are being created by two different types of triggered star formation one involving wind, and the other, radiation. Triggered star formation occurs when massive stars spur new, smaller stars into existence. The first radiation-based mechanism is demonstrated near the center of the cloud. There, radiation from the massive stars is eating away at the surrounding dust cloud, creating shock waves that compress gas and dust into new stars. This compressed material appears as an arc-shaped orange-red filament, while the new stars within this filament are still blanketed with dust and cannot be seen.

The second wind-based mechanism is at play higher up in the cloud. The isolated, pinkish blob of stars at the upper left was triggered by winds from a massive star located to the left of it. This massive star blew up in a supernova explosion 50,000 years ago, but before it died, its winds pushed gas and dust together into new stars. While this massive star cannot be seen in the image, a bubble created when it exploded can be seen near the large, white spot with a blue halo at the upper left (this white spot is actually a collection of three stars).

NGC 346 is the brightest star-forming region in the Small Magellanic Cloud, an irregular dwarf galaxy that orbits our Milky Way galaxy, 210,000 light-years away.

ENHANCED WARM H{sub 2} EMISSION IN THE COMPACT GROUP MID-INFRARED ''GREEN VALLEY''

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

Cluver, M. E.; Ogle, P.; Guillard, P.

2013-03-10

We present results from a Spitzer mid-infrared spectroscopy study of a sample of 74 galaxies located in 23 Hickson Compact Groups (HCGs), chosen to be at a dynamically active stage of H I depletion. We find evidence for enhanced warm H{sub 2} emission (i.e., above that associated with UV excitation in star-forming regions) in 14 galaxies ({approx}20%), with 8 galaxies having extreme values of L(H{sub 2} S(0)-S(3))/L(7.7 {mu}m polycyclic aromatic hydrocarbon), in excess of 0.07. Such emission has been seen previously in the compact group HCG 92 (Stephan's Quintet), and was shown to be associated with the dissipation of mechanicalmore » energy associated with a large-scale shock caused when one group member collided, at high velocity, with tidal debris in the intragroup medium. Similarly, shock excitation or turbulent heating is likely responsible for the enhanced H{sub 2} emission in the compact group galaxies, since other sources of heating (UV or X-ray excitation from star formation or active galactic nuclei) are insufficient to account for the observed emission. The group galaxies fall predominantly in a region of mid-infrared color-color space identified by previous studies as being connected to rapid transformations in HCG galaxy evolution. Furthermore, the majority of H{sub 2}-enhanced galaxies lie in the optical ''green valley'' between the blue cloud and red sequence, and are primarily early-type disk systems. We suggest that H{sub 2}-enhanced systems may represent a specific phase in the evolution of galaxies in dense environments and provide new insight into mechanisms which transform galaxies onto the optical red sequence.« less

A CN Band Survey of Red Giants in the Globular Cluster M53

NASA Astrophysics Data System (ADS)

Martell, S. L.; Smith, G. H.

2004-12-01

We investigate the star-to-star variations in λ 3883 CN bandstrength among red giant stars in the low-metallicity globular cluster M53 ([Fe/H] = --2.0). Our data were taken with the Kast spectrograph on the 3-meter Shane telescope at Lick Observatory in April 2001. Star-to-star variations in CN bandstrength are common in intermediate- and high-metallicity globular clusters ([Fe/H] ≥ --1.6). Our data were obtained to test whether that variation will also be present in a low-metallicity globular cluster, or whether it will be suppressed by the overall lack of metals in the stars. Our preliminary result is that the λ 3883 CN band is weak in our program stars, which span the brightest magnitude of the red giant branch. On visual inspection, the M53 giants appear to be similar in their CN bandstrength to the four CN-weak giants in NGC 6752 whose average spectrum is plotted in Fig. 4 of Norris et al. (1981, ApJ, 244, 205). This work is planned to form part of a larger study of the metallicity dependence of CN bandstrength and carbon abundance behavior on the upper giant branch of globular clusters. This work is supported by NSF grant AST 00-98453 and by an award from the ARCS foundation, Northern California Chapter.

Primordial black holes in globular clusters

NASA Technical Reports Server (NTRS)

Sigurdsson, Steinn; Hernquist, Lars

1993-01-01

It has recently been recognized that significant numbers of medium-mass back holes (of order 10 solar masses) should form in globular clusters during the early stages of their evolution. Here we explore the dynamical and observational consequences of the presence of such a primordial black-hole population in a globular cluster. The holes initially segregate to the cluster cores, where they form binary and multiple black-hole systems. The subsequent dynamical evolution of the black-hole population ejects most of the holes on a relatively short timescale: a typical cluster will retain between zero and four black holes in its core, and possibly a few black holes in its halo. The presence of binary, triple, and quadruple black-hole systems in cluster cores will disrupt main-sequence and giant stellar binaries; this may account for the observed anomalies in the distribution of binaries in globular clusters. Furthermore, tidal interactions between a multiple black-hole system and a red giant star can remove much of the red giant's stellar envelope, which may explain the puzzling absence of larger red giants in the cores of some very dense clusters.

Differential rotation in main-sequence solar-like stars: Qualitative inference from asteroseismic data

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

Lund, Mikkel N.; Christensen-Dalsgaard, Jørgen; Miesch, Mark S., E-mail: mikkelnl@phys.au.dk

2014-08-01

Understanding differential rotation of Sun-like stars is of great importance for insight into the angular momentum transport in these stars. One means of gaining such information is that of asteroseismology. By a forward modeling approach we analyze in a qualitative manner the impact of different differential rotation profiles on the splittings of p-mode oscillation frequencies. The optimum modes for inference on differential rotation are identified along with the best value of the stellar inclination angle. We find that in general it is not likely that asteroseismology can be used to make an unambiguous distinction between a rotation profile such asmore » a conical Sun-like profile and a cylindrical profile. In addition, it seems unlikely that asteroseismology of Sun-like stars will result in inferences on the radial profile of the differential rotation, such as can be done for red giants. At best, one could possibly obtain the sign of the radial differential rotation gradient. Measurements of the extent of the latitudinal differential from frequency splitting are, however, more promising. One very interesting aspect that could likely be tested from frequency splittings is whether the differential rotation is solar-like or anti-solar-like in nature, in the sense that a solar-like profile has an equator rotating faster than the poles.« less

The effects of diffusion in hot subdwarf progenitors from the common envelope channel

NASA Astrophysics Data System (ADS)

Byrne, Conor M.; Jeffery, C. Simon; Tout, Christopher A.; Hu, Haili

2018-04-01

Diffusion of elements in the atmosphere and envelope of a star can drastically alter its surface composition, leading to extreme chemical peculiarities. We consider the case of hot subdwarfs, where surface helium abundances range from practically zero to almost 100 percent. Since hot subdwarfs can form via a number of different evolution channels, a key question concerns how the formation mechanism is connected to the present surface chemistry. A sequence of extreme horizontal branch star models was generated by producing post-common envelope stars from red giants. Evolution was computed with MESA from envelope ejection up to core-helium ignition. Surface abundances were calculated at the zero-age horizontal branch for models with and without diffusion. A number of simulations also included radiative levitation. The goal was to study surface chemistry during evolution from cool giant to hot subdwarf and determine when the characteristic subdwarf surface is established. Only stars leaving the giant branch close to core-helium ignition become hydrogen-rich subdwarfs at the zero-age horizontal branch. Diffusion, including radiative levitation, depletes the initial surface helium in all cases. All subdwarf models rapidly become more depleted than observations allow. Surface abundances of other elements follow observed trends in general, but not in detail. Additional physics is required.

The circumstellar dust envelopes of red giant stars. I - M giant stars with the 10-micron silicate emission band

NASA Technical Reports Server (NTRS)

Hashimoto, O.; Nakada, Y.; Onaka, T.; Kamijo, F.; Tanabe, T.

1990-01-01

Spherical dust envelope models of red giant stars are constructed by solving the radiative transfer equations of the generalized two-stream Eddington approximation. The IRAS observations of M giant stars which show the 10-micron silicate emission band in IRAS LRS spectra are explained by the models with the dirty silicate grains with K proportional to lambda exp -1.5 for lambda greather than 28 microns. Under the assumption of steady mass flow in the envelope, this model analysis gives the following conclusions: (1) the strength of the silicate emission peak at 10 microns is a good indicator of the mass loss rate of the star, (2) no stars with the 10-microns silicate emission feature are observed in the range of mass loss rate smaller than 7 x 10 to the -8th solar mass/yr, and (3) the characteristic time of the mass loss process of M stars does not exceed a few 10,000 years.

Survival of a brown dwarf after engulfment by a red giant star.

PubMed

Maxted, P F L; Napiwotzki, R; Dobbie, P D; Burleigh, M R

2006-08-03

Many sub-stellar companions (usually planets but also some brown dwarfs) orbit solar-type stars. These stars can engulf their sub-stellar companions when they become red giants. This interaction may explain several outstanding problems in astrophysics but it is unclear under what conditions a low mass companion will evaporate, survive the interaction unchanged or gain mass. Observational tests of models for this interaction have been hampered by a lack of positively identified remnants-that is, white dwarf stars with close, sub-stellar companions. The companion to the pre-white dwarf AA Doradus may be a brown dwarf, but the uncertain history of this star and the extreme luminosity difference between the components make it difficult to interpret the observations or to put strong constraints on the models. The magnetic white dwarf SDSS J121209.31 + 013627.7 may have a close brown dwarf companion but little is known about this binary at present. Here we report the discovery of a brown dwarf in a short period orbit around a white dwarf. The properties of both stars in this binary can be directly observed and show that the brown dwarf was engulfed by a red giant but that this had little effect on it.

Witnessing the Birth of the Red Sequence: ALMA High-resolution Imaging of [C II] and Dust in Two Interacting Ultra-red Starbursts at z = 4.425

NASA Astrophysics Data System (ADS)

Oteo, I.; Ivison, R. J.; Dunne, L.; Smail, I.; Swinbank, A. M.; Zhang, Z.-Y.; Lewis, A.; Maddox, S.; Riechers, D.; Serjeant, S.; Van der Werf, P.; Biggs, A. D.; Bremer, M.; Cigan, P.; Clements, D. L.; Cooray, A.; Dannerbauer, H.; Eales, S.; Ibar, E.; Messias, H.; Michałowski, M. J.; Pérez-Fournon, I.; van Kampen, E.

2016-08-01

Exploiting the sensitivity and spatial resolution of the Atacama Large Millimeter/submillimeter Array, we have studied the morphology and the physical scale of the interstellar medium—both gas and dust—in SGP 38326, an unlensed pair of interacting starbursts at z = 4.425. SGP 38326 is the most luminous star bursting system known at z > 4, with a total IR luminosity of L IR ˜ 2.5 × 1013 L ⊙ and a star formation rate of ˜ 4500 M ⊙ yr-1. SGP 38326 also contains a molecular gas reservoir among the most massive yet found in the early universe, and it is the likely progenitor of a massive, red-and-dead elliptical galaxy at z ˜ 3. Probing scales of ˜0.″1 or ˜800 pc we find that the smooth distribution of the continuum emission from cool dust grains contrasts with the more irregular morphology of the gas, as traced by the [C II] fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved [C II] emission reveals that the dynamics of the two interacting components of SGP 38326 are each compatible with disk-like, ordered rotation, but also reveals an ISM which is turbulent and unstable. Our observations support a scenario where at least a subset of the most distant extreme starbursts are highly dissipative mergers of gas-rich galaxies.

WITNESSING THE BIRTH OF THE RED SEQUENCE: ALMA HIGH-RESOLUTION IMAGING OF [C II] AND DUST IN TWO INTERACTING ULTRA-RED STARBURSTS AT z = 4.425

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

Oteo, I.; Ivison, R. J.; Dunne, L.

Exploiting the sensitivity and spatial resolution of the Atacama Large Millimeter/submillimeter Array, we have studied the morphology and the physical scale of the interstellar medium—both gas and dust—in SGP 38326, an unlensed pair of interacting starbursts at z = 4.425. SGP 38326 is the most luminous star bursting system known at z > 4, with a total IR luminosity of L {sub IR} ∼ 2.5 × 10{sup 13} L {sub ⊙} and a star formation rate of ∼ 4500 M {sub ⊙} yr{sup −1}. SGP 38326 also contains a molecular gas reservoir among the most massive yet found in themore » early universe, and it is the likely progenitor of a massive, red-and-dead elliptical galaxy at z ∼ 3. Probing scales of ∼0.″1 or ∼800 pc we find that the smooth distribution of the continuum emission from cool dust grains contrasts with the more irregular morphology of the gas, as traced by the [C ii] fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved [C ii] emission reveals that the dynamics of the two interacting components of SGP 38326 are each compatible with disk-like, ordered rotation, but also reveals an ISM which is turbulent and unstable. Our observations support a scenario where at least a subset of the most distant extreme starbursts are highly dissipative mergers of gas-rich galaxies.« less

SU-F-I-24: Feasibility of Magnetic Susceptibility to Relative Electron Density Conversion Method for Radiation Therapy

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

Ito, K; Kadoya, N; Chiba, M

2016-06-15

Purpose: The aim of this study is to develop radiation treatment planning using magnetic susceptibility obtained from quantitative susceptibility mapping (QSM) via MR imaging. This study demonstrates the feasibility of a method for generating a substitute for a CT image from an MRI. Methods: The head of a healthy volunteer was scanned using a CT scanner and a 3.0 T MRI scanner. The CT imaging was performed with a slice thickness of 2.5 mm at 80 and 120 kV (dual-energy scan). These CT images were converted to relative electron density (rED) using the CT-rED conversion table generated by a previousmore » dual-energy CT scan. The CT-rED conversion table was generated using the conversion of the energy-subtracted CT number to rED via a single linear relationship. One T2 star-weighted 3D gradient echo-based sequence with four different echo times images was acquired using the MRI scanner. These T2 star-weighted images were used to estimate the phase data. To estimate the local field map, a Laplacian unwrapping of the phase and background field removal algorithm were implemented to process phase data. To generate a magnetic susceptibility map from the local field map, we used morphology enabled dipole inversion method. The rED map was resampled to the same resolution as magnetic susceptibility, and the magnetic susceptibility-rED conversion table was obtained via voxel-by-voxel mapping between the magnetic susceptibility and rED maps. Results: A correlation between magnetic susceptibility and rED is not observed through our method. Conclusion: Our results show that the correlation between magnetic susceptibility and rED is not observed. As the next step, we assume that the voxel of the magnetic susceptibility map comprises two materials, such as water (0 ppm) and bone (-2.2 ppm) or water and marrow (0.81ppm). The elements of each voxel were estimated from the ratio of the two materials.« less

First results from the IllustrisTNG simulations: the galaxy colour bimodality

NASA Astrophysics Data System (ADS)

Nelson, Dylan; Pillepich, Annalisa; Springel, Volker; Weinberger, Rainer; Hernquist, Lars; Pakmor, Rüdiger; Genel, Shy; Torrey, Paul; Vogelsberger, Mark; Kauffmann, Guinevere; Marinacci, Federico; Naiman, Jill

2018-03-01

We introduce the first two simulations of the IllustrisTNG project, a next generation of cosmological magnetohydrodynamical simulations, focusing on the optical colours of galaxies. We explore TNG100, a rerun of the original Illustris box, and TNG300, which includes 2 × 25003 resolution elements in a volume 20 times larger. Here, we present first results on the galaxy colour bimodality at low redshift. Accounting for the attenuation of stellar light by dust, we compare the simulated (g - r) colours of 109 < M⋆/M⊙ < 1012.5 galaxies to the observed distribution from the Sloan Digital Sky Survey. We find a striking improvement with respect to the original Illustris simulation, as well as excellent quantitative agreement with the observations, with a sharp transition in median colour from blue to red at a characteristic M⋆ ˜ 1010.5 M⊙. Investigating the build-up of the colour-mass plane and the formation of the red sequence, we demonstrate that the primary driver of galaxy colour transition is supermassive black hole feedback in its low accretion state. Across the entire population the median colour transition time-scale Δtgreen is ˜1.6 Gyr, a value which drops for increasingly massive galaxies. We find signatures of the physical process of quenching: at fixed stellar mass, redder galaxies have lower star formation rates, gas fractions, and gas metallicities; their stellar populations are also older and their large-scale interstellar magnetic fields weaker than in bluer galaxies. Finally, we measure the amount of stellar mass growth on the red sequence. Galaxies with M⋆ > 1011 M⊙ which redden at z < 1 accumulate on average ˜25 per cent of their final z = 0 mass post-reddening; at the same time, ˜18 per cent of such massive galaxies acquire half or more of their final stellar mass while on the red sequence.

History and destiny of an emerging early-type galaxy. New IFU insights on the major-merger remnant NGC 7252

NASA Astrophysics Data System (ADS)

Weaver, J.; Husemann, B.; Kuntschner, H.; Martín-Navarro, I.; Bournaud, F.; Duc, P.-A.; Emsellem, E.; Krajnović, D.; Lyubenova, M.; McDermid, R. M.

2018-06-01

Context. The merging of galaxies is one key aspect in our favourite hierarchical ΛCDM Universe and is an important channel leading to massive quiescent elliptical galaxies. Understanding this complex transformational process is ongoing. Aims: We aim to study NGC 7252, which is one of the nearest major-merger galaxy remnants, observed 1 Gyr after the collision of presumably two gas-rich disc galaxies. It is therefore an ideal laboratory to study the processes inherent to the transformation of disc galaxies to ellipticals. Methods: We obtained wide-field IFU spectroscopy with the VLT-VIMOS integral-field spectrograph covering the central 50'' × 50'' of NGC 7252 to map the stellar and ionised gas kinematics, and the distribution and conditions of the ionised gas, revealing the extent of ongoing star formation and recent star formation history. Results: Contrary to previous studies, we find the inner gas disc not to be counter-rotating with respect to the stars. In addition, the stellar kinematics appear complex with a clear indication of a prolate-like rotation component which suggests a polar merger configuration. The ongoing star formation rate is 2.2 ± 0.6 M⊙ yr-1 and implies a typical depletion time of 2 Gyr given the molecular gas content. Furthermore, the spatially resolved star formation history suggests a slight radial dependence, moving outwards at later times. We confirm a large AGN-ionised gas cloud previously discovered 5 kpc south of the nucleus, and find a higher ionisation state of the ionised gas at the galaxy centre relative to the surrounding gas disc. Although the higher ionisation towards the centre is potentially degenerate within the central star forming ring, it may be associated with a low-luminosity AGN. Conclusions: Although NGC 7252 has been classified as post-starburst galaxy at the centre, the elliptical-like major-merger remnant still appears very active. A central kpc-scale gas disc has presumably re-formed quickly within the last 100 Myr after final coalescence. The disc features ongoing star formation, implying Gyr long timescale to reach the red sequence through gas consumption alone. While NGC 7252 is useful to probe the transformation from discs to ellipticals, it is not well-suited to study the transformation from blue to red at this point.

Analyzing the Effects of Stellar Evolution on White Dwarf Ages

NASA Astrophysics Data System (ADS)

Moss, Adam; Von Hippel, Ted, Dr.

2018-01-01

White dwarfs are among the oldest objects in our Galaxy, thus if we can determine their ages, we can derive the star formation history of our Galaxy. As part of a larger project that will use Gaia parallaxes to derive the ages of tens of thousands of white dwarfs, we explore the impact on the total white dwarf age of various modern models of main sequence and red giant branch stellar evolution, as well as uncertainties in progenitor metallicity. In addition, we study the effect on white dwarf ages caused by uncertainties in the Initial Final Mass Relation, which is the mapping between zero age main sequence and white dwarf masses. We find that for old and high mass white dwarfs, uncertainties in these factors have little effect on the total white dwarf age.

NGC 6819: testing the asteroseismic mass scale, mass loss and evidence for products of non-standard evolution

NASA Astrophysics Data System (ADS)

Handberg, R.; Brogaard, K.; Miglio, A.; Bossini, D.; Elsworth, Y.; Slumstrup, D.; Davies, G. R.; Chaplin, W. J.

2017-11-01

We present an extensive peakbagging effort on Kepler data of ∼50 red giant stars in the open star cluster NGC 6819. By employing sophisticated pre-processing of the time series and Markov chain Monte Carlo techniques we extracted individual frequencies, heights and line widths for hundreds of oscillation modes. We show that the 'average' asteroseismic parameter δν02, derived from these, can be used to distinguish the stellar evolutionary state between the red giant branch (RGB) stars and red clump (RC) stars. Masses and radii are estimated using asteroseismic scaling relations, both empirically corrected to obtain self-consistency and agreement with independent measures of distance, and using updated theoretical corrections. Remarkable agreement is found, allowing the evolutionary state of the giants to be determined exclusively from the empirical correction to the scaling relations. We find a mean mass of the RGB stars and RC stars in NGC 6819 to be 1.61 ± 0.02 and 1.64 ± 0.02 M⊙, respectively. The difference ΔM = -0.03 ± 0.01 M⊙ is almost insensitive to systematics, suggesting very little RGB mass loss, if any. Stars that are outliers relative to the ensemble reveal overmassive members that likely evolved via mass transfer in a blue straggler phase. We suggest that KIC 4937011, a low-mass Li-rich giant, is a cluster member in the RC phase that experienced very high mass loss during its evolution. Such over- and undermassive stars need to be considered when studying field giants, since the true age of such stars cannot be known and there is currently no way to distinguish them from normal stars.

Collisions of Terrestrial Worlds: The Occurrence of Extreme Mid-infrared Excesses around Low-mass Field Stars

NASA Astrophysics Data System (ADS)

Theissen, Christopher A.; West, Andrew A.

2017-04-01

We present the results of an investigation into the occurrence and properties (stellar age and mass trends) of low-mass field stars exhibiting extreme mid-infrared (MIR) excesses ({L}{IR}/{L}* ≳ 0.01). Stars for the analysis were initially selected from the Motion Verified Red Stars (MoVeRS) catalog of photometric stars with Sloan Digital Sky Survey, 2MASS, and WISE photometry and significant proper motions. We identify 584 stars exhibiting extreme MIR excesses, selected based on an empirical relationship for main-sequence W1-W3 colors. For a small subset of the sample, we show, using spectroscopic tracers of stellar age (Hα and Li I) and luminosity class, that the parent sample is most likely comprised of field dwarfs (≳ 1 Gyr). We also develop the Low-mass Kinematics (LoKi) galactic model to estimate the completeness of the extreme MIR excess sample. Using Galactic height as a proxy for stellar age, the completeness-corrected analysis indicates a distinct age dependence for field stars exhibiting extreme MIR excesses. We also find a trend with stellar mass (using r - z color as a proxy). Our findings are consistent with the detected extreme MIR excesses originating from dust created in a short-lived collisional cascade (≲100,000 years) during a giant impact between two large planetismals or terrestrial planets. These stars with extreme MIR excesses also provide support for planetary collisions being the dominant mechanism in creating the observed Kepler dichotomy (the need for more than a single mode, typically two, to explain the variety of planetary system architectures Kepler has observed), rather than different formation mechanisms.

Magnetic fields in single late-type giants in the Solar vicinity: How common is magnetic activity on the giant branches?

NASA Astrophysics Data System (ADS)

Konstantinova-Antova, Renada; Aurière, Michel; Charbonnel, Corinne; Drake, Natalia; Wade, Gregg; Tsvetkova, Svetla; Petit, Pascal; Schröder, Klaus-Peter; Lèbre, Agnes

2014-08-01

We present our first results on a new sample containing all single G, K and M giants down to V = 4 mag in the Solar vicinity, suitable for spectropolarimetric (Stokes V) observations with Narval at TBL, France. For detection and measurement of the magnetic field (MF), the Least Squares Deconvolution (LSD) method was applied (Donati et al. 1997) that in the present case enables detection of large-scale MFs even weaker than the solar one (the typical precision of our longitudinal MF measurements is 0.1-0.2 G). The evolutionary status of the stars is determined on the basis of the evolutionary models with rotation (Lagarde et al. 2012; Charbonnel et al., in prep.) and fundamental parameters given by Massarotti et al. (1998). The stars appear to be in the mass range 1-4 M ⊙, situated at different evolutionary stages after the Main Sequence (MS), up to the Asymptotic Giant Branch (AGB). The sample contains 45 stars. Up to now, 29 stars are observed (that is about 64% of the sample), each observed at least twice. For 2 stars in the Hertzsprung gap, one is definitely Zeeman detected. Only 5 G and K giants, situated mainly at the base of the Red Giant Branch (RGB) and in the He-burning phase are detected. Surprisingly, a lot of stars ascending towards the RGB tip and in early AGB phase are detected (8 of 13 observed stars). For all Zeeman detected stars v sin i is redetermined and appears in the interval 2-3 km/s, but few giants with MF possess larger v sin i.

Detection of the Tip of Red Giant Branc in NGC 5128

NASA Technical Reports Server (NTRS)

Soria, Roberto; Mould, Jeremy R.; Watson, Alan M.; Gallagher, John S., III; Ballester, Gilda E.; Burrows, Christopher J.; Casertano, Stefano; Clarke, John T.; Crisp, David; Griffiths, Richard E.;

Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. VI. First chromosphere model of a late-type giant

NASA Astrophysics Data System (ADS)

Wedemeyer, Sven; Kučinskas, Arūnas; Klevas, Jonas; Ludwig, Hans-Günter

2017-10-01

Aims: Although observational data unequivocally point to the presence of chromospheres in red giant stars, no attempts have been made so far to model them using 3D hydrodynamical model atmospheres. We therefore compute an exploratory 3D hydrodynamical model atmosphere for a cool red giant in order to study the dynamical and thermodynamic properties of its chromosphere, as well as the influence of the chromosphere on its observable properties. Methods: Three-dimensional radiation hydrodynamics simulations are carried out with the CO5BOLD model atmosphere code for a star with the atmospheric parameters (Teff ≈ 4010 K, log g = 1.5, [ M / H ] = 0.0), which are similar to those of the K-type giant star Aldebaran (α Tau). The computational domain extends from the upper convection zone into the chromosphere (7.4 ≥ log τRoss ≥ - 12.8) and covers several granules in each horizontal direction. Using this model atmosphere, we compute the emergent continuum intensity maps at different wavelengths, spectral line profiles of Ca II K, the Ca II infrared triplet line at 854.2 nm, and Hα, as well as the spectral energy distribution (SED) of the emergent radiative flux. Results: The initial model quickly develops a dynamical chromosphere that is characterised by propagating and interacting shock waves. The peak temperatures in the chromospheric shock fronts reach values of up to 5000 K, although the shock fronts remain quite narrow. Similar to the Sun, the gas temperature distribution in the upper layers of red giant stars is composed of a cool component due to adiabatic cooling in the expanding post-shock regions and a hot component due to shock waves. For this red giant model, the hot component is a rather flat high-temperature tail, which nevertheless affects the resulting average temperatures significantly. Conclusions: The simulations show that the atmospheres of red giant stars are dynamic and intermittent. Consequently, many observable properties cannot be reproduced with static 1D models, but require advanced 3D hydrodynamical modelling. Furthermore, including a chromosphere in the models might produce significant contributions to the emergent UV flux.

The AMBRE project: The thick thin disk and thin thick disk of the Milky Way

NASA Astrophysics Data System (ADS)

Hayden, M. R.; Recio-Blanco, A.; de Laverny, P.; Mikolaitis, S.; Worley, C. C.

2017-11-01

We analyze 494 main sequence turnoff and subgiant stars from the AMBRE:HARPS survey. These stars have accurate astrometric information from Gaia DR1, providing reliable age estimates with relative uncertainties of ±1 or 2 Gyr and allowing precise orbital determinations. The sample is split based on chemistry into a low-[Mg/Fe] sequence, which are often identified as thin disk stellar populations, and high-[Mg/Fe] sequence, which are often associated with thick disk stellar populations. We find that the high-[Mg/Fe] chemical sequence has extended star formation for several Gyr and is coeval with the oldest stars of the low-[Mg/Fe] chemical sequence: both the low- and high-[Mg/Fe] sequences were forming stars at the same time. We find that the high-[Mg/Fe] stellar populations are only vertically extended for the oldest, most-metal poor and highest [Mg/Fe] stars. When comparing vertical velocity dispersion for the low- and high-[Mg/Fe] sequences, the high-[Mg/Fe] sequence has lower vertical velocity dispersion than the low-[Mg/Fe] sequence for stars of similar age. This means that identifying either group as thin or thick disk based on chemistry is misleading. The stars belonging to the high-[Mg/Fe] sequence have perigalacticons that originate in the inner disk, while the perigalacticons of stars on the low-[Mg/Fe] sequence are generally around the solar neighborhood. From the orbital properties of the stars, the high-[Mg/Fe] and low-[Mg/Fe] sequences are most likely a reflection of the chemical enrichment history of the inner and outer disk populations, respectively; radial mixing causes both populations to be observed in situ at the solar position. Based on these results, we emphasize that it is important to be clear in defining what populations are being referenced when using the terms thin and thick disk, and that ideally the term thick disk should be reserved for purely geometric definitions to avoid confusion and be consistent with definitions in external galaxies.

Seeing Red in NGC 1978, NGC 55, and NGC 3109

NASA Astrophysics Data System (ADS)

Davidge, T. J.

2018-04-01

Spectra of the intermediate-age star cluster NGC 1978 and the dwarf irregular galaxies NGC 55 and NGC 3109 are discussed. The spectra were recorded with the Gemini Multi-object Spectrograph on Gemini South and span the 0.7–1.1 μm wavelength interval. Five slit pointings were observed in NGC 1978, and these are used to examine stochastic effects on the integrated red light from an intermediate-age cluster. The removal of either the brightest M giant or the brightest C star from the co-added spectrum has minor effects on the equivalent withs of the Ca triplet. The most robust signature of C stars in the integrated cluster spectrum at these wavelengths is the CN band head near 7900 Å. The equivalent widths of Ca triplet lines in the NGC 1978 spectrum and in the spectra of individual cluster stars are larger than expected for a scaled-solar abundance system. It is suggested that these stars have a lower than expected surface gravity, which might occur if the stars in NGC 1978 have been subject to extra mixing processes, as suggested by Lederer et al. The near-infrared color profile of NGC 1978 is shown to contain a prominent red cusp in the central 10 arcsec, and the suppression of light from this cusp does not affect the depth of the Ca lines in the integrated spectrum. The NGC 55 spectra run parallel to the major axis, and a gradient is found in the strength of the Ca lines, in the sense that the Ca lines weaken with increasing distance from the disk plane. Comparisons with models suggest that the disk light is dominated by stars with ages 1–2 Gyr, in agreement with star-forming histories (SFHs) obtained from the analysis of color–magnitude diagrams (CMDs). The NGC 55 spectra also sample a large star-forming complex. The age of this complex inferred from comparisons with models is broadly consistent with that estimated from a near-infrared CMD of the same region. The CN band head at 7900 Å in this part of NGC 55 is detected, but this is likely a signature of red supergiants (RSGs) rather than C stars. The NGC 3109 observations sample three different parts of that galaxy but have a low signal-to-noise ratio. Comparisons with models suggest that the light from the NGC 3109 disk at red wavelengths is dominated by RSGs with ages of at most a few tens of Myr, in qualitative agreement with SFHs that are based on photometric measurements.

H-ATLAS/GAMA: the nature and characteristics of optically red galaxies detected at submillimetre wavelengths

NASA Astrophysics Data System (ADS)

Dariush, A.; Dib, S.; Hony, S.; Smith, D. J. B.; Zhukovska, S.; Dunne, L.; Eales, S.; Andrae, E.; Baes, M.; Baldry, I.; Bauer, A.; Bland-Hawthorn, J.; Brough, S.; Bourne, N.; Cava, A.; Clements, D.; Cluver, M.; Cooray, A.; De Zotti, G.; Driver, S.; Grootes, M. W.; Hopkins, A. M.; Hopwood, R.; Kaviraj, S.; Kelvin, L.; Lara-Lopez, M. A.; Liske, J.; Loveday, J.; Maddox, S.; Madore, B.; Michałowski, M. J.; Pearson, C.; Popescu, C.; Robotham, A.; Rowlands, K.; Seibert, M.; Shabani, F.; Smith, M. W. L.; Taylor, E. N.; Tuffs, R.; Valiante, E.; Virdee, J. S.

2016-02-01

We combine Herschel/SPIRE submillimetre (submm) observations with existing multiwavelength data to investigate the characteristics of low-redshift, optically red galaxies detected in submm bands. We select a sample of galaxies in the redshift range 0.01 ≤ z ≤ 0.2, having >5σ detections in the SPIRE 250 μm submm waveband. Sources are then divided into two sub-samples of red and blue galaxies, based on their UV-optical colours. Galaxies in the red sample account for ≈4.2 per cent of the total number of sources with stellar masses M* ≳ 1010 M⊙. Following visual classification of the red galaxies, we find that ≳30 per cent of them are early-type galaxies and ≳40 per cent are spirals. The colour of the red-spiral galaxies could be the result of their highly inclined orientation and/or a strong contribution of the old stellar population. It is found that irrespective of their morphological types, red and blue sources occupy environments with more or less similar densities (I.e. the Σ5 parameter). From the analysis of the spectral energy distributions of galaxies in our samples based on MAGPHYS, we find that galaxies in the red sample (of any morphological type) have dust masses similar to those in the blue sample (I.e. normal spiral/star-forming systems). However, in comparison to the red-spirals and in particular blue systems, red-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies in the red-elliptical sample have much lower mean star formation/specific star formation rates in contrast to their counterparts in the blue sample. Our results support a scenario where dust in early-type systems is likely to be of an external origin.

Gravity, Rotation, Ages, and Magnetism of Solar-like Stars and Red Giants observed by Kepler and K2

NASA Astrophysics Data System (ADS)

Mathur, Savita

Scientific Objectives: Asteroseismology has proved to be a very powerful tool thanks to the high-precision data obtained by the space missions such as Kepler and CoRoT. Solar-like oscillations have been detected and reported for around 15,600 red giants and 540 main-sequence stars observed by the nominal Kepler mission. Hence, these stars have their surface gravities, masses, and radii obtained with seismology. However, according to the latest Kepler star properties catalog (Mathur et al., in prep.) more than 24,000 red giants, 127,000 FGK dwarfs, and 10,000 subgiants were targeted. K2 has been observing 90,000 red giants and dwarfs. Moreover, the continuous photometric data of 4 yrs (resp. 3 mo) collected by Kepler (resp. K2) contain the signature of other phenomena such as convection, rotation, and magnetism, which are very important to understand stellar evolution and can also be used to obtain precise fundamental stellar parameters even when pulsations are not detected. We propose to perform the largest homogeneous analysis to date of seismic oscillations, convection, and rotation/magnetic activity across the full range of stellar spectral types and evolutionary states present in the K2 and Kepler missions. We will use the longest publicly available time series to derive the most accurate surface gravities, rotation periods, evolutionary states, and magnetic activity levels to characterize rotation-age-magnetic activity relationships and oscillations-magnetism interaction. Relevance: The determination of the gravity, mass, radius, and age of planet host stars allow us to better characterize the planetary systems. By studying the stellar surface rotation periods, we can better understand the angular momentum transport involved during the stellar evolution and have more accurate rotation-age relationships. Finally, the study of the magnetic activity of a large number of stars will allow us to put the Sun in a broader context. This work will also have an impact on galactic evolution study. Methodology: We will analyse the data with the new version of the A2Z pipeline (Mathur et al. 2010) on the stars where no acoustic modes have been detected or completely characterized so far. In the case that still no modes are observed, we will study the convective background as it has been shown that the granulation timescale is proportional to the surface gravity of the star (Mathur et al. 2011). We will develop and automate the recent method developed by Kallinger et al. (2016) that proved it is possible to measure logg very precisely with the auto-correlation function for stars where the modes are slightly above the Nyquist frequency, i.e. subgiants for the long cadence data. We will analyze dwarfs and subgiants observed by Kepler and K2 to look for their rotation periods following Garcia et al. (2014). This method was shown to have the best combination of completeness and reliability according to hare and hounds benchmarks (Aigrain et al., 2015). We will calibrate gyrochronology relation with the best-characterized dwarfs as done by van Saders et al. (2016) and apply it to dwarfs when applicable to estimate their ages. For the stars where a reliable rotation period is determined we will compute a photometric magnetic proxy as defined in Mathur et al. (2014). In many cases we will have complementary spectroscopic observations (e.g. Gaia). Data: We will analyse the Kepler Q0-Q17 data calibrated with the KADACS software (Garcia et al. 2011; Mathur et al. in prep.) and the K2 C1 to C7 data processed by Vanderburg & Johnson (2014).

Magnitude Bias of Microlensed Sources toward the Large Magellanic Cloud.

PubMed

Zhao; Graff; Guhathakurta

2000-03-20

There are lines of evidence suggesting that some of the observed microlensing events in the direction of the Large Magellanic Cloud (LMC) are caused by ordinary star lenses as opposed to dark MACHOs in the Galactic halo. Efficient lensing by ordinary stars generally requires the presence of one or more additional concentrations of stars along the line of sight to the LMC disk. If such a population behind the LMC disk exists, then the source stars (for lensing by LMC disk objects) will be drawn preferentially from the background population and will show systematic differences from LMC field stars. One such difference is that the (lensed) source stars will be farther away than the average LMC field stars, and this should be reflected in their apparent baseline magnitudes. We focus on red clump stars; these should appear in the color-magnitude diagram at a few tenths of a magnitude fainter than the field red clump. Suggestively, one of the two near-clump confirmed events, MACHO-LMC-1, is a few tenths of magnitude fainter than the clump.

Evolutionary paths among different red galaxy types at 0.3 < z < 1.5 and the build-up of massive E-S0's

NASA Astrophysics Data System (ADS)

Gallego, Jesús; Prieto, Mercedes; Eliche-Moral, M. Carmen; Balcells, Marc; Cristóbal-Hornillos, David; Erwin, Peter; Abreu, David; Domínguez-Palmero, Lilian; Hempel, Angela; López-Sanjuan, Carlos; Guzmán, Rafael; Pérez-González, Pablo G.; Barro, Guillermo; Zamorano, Jaime

2013-07-01

Some recent observations seem to disagree with hierarchical theories of galaxy formation on the role of major mergers in a late build-up of massive early-type galaxies. We re-address this question by analysing the morphology, structural distortion level, and star formation enhancement of a sample of massive galaxies (M* > 5 × 1010M⊙) lying on the Red Sequence and its surroundings at 0.3 < z < 1.5. We have used an initial sample of ~1800 sources with Ks < 20.5 mag over an area ~155 arcmin2 on the Groth Strip, combining data from the Rainbow Extragalactic Database and the GOYA Survey. Red galaxy classes that can be directly associated to intermediate stages of major mergers and to their final products have been defined. For the first time we report observationally the existence of a dominant evolutionary path among massive red galaxies at 0.6 < z < 1.5, consisting in the conversion of irregular disks into irregular spheroids, and of these ones into regular spheroids. This result points to: 1) the massive red regular galaxies at low redshifts derive from the irregular ones populating the Red Sequence and its neighbourhood at earlier epochs up to z ~ 1.5; 2) the progenitors of the bulk of present-day massive red regular galaxies have been blue disks that have migrated to the Red Sequence majoritarily through major mergers at 0.6 < z < 1.2 (these mergers thus starting at z ~ 1.5); 3) the formation of E-S0's that end up with M* > 1011M⊙ at z = 0 through gas-rich major mergers has frozen since z ~ 0.6. Our results support that major mergers have played the dominant role in the definitive build-up of present-day E-S0's with M* > 1011M⊙ at 0.6 < z < 1.2, in good agreement with the hierarchical scenario proposed in the Eliche-Moral et al. (2010a) model (see also Eliche-Moral et al. 2010b). This study is published in Prieto et al. (2012). Supported by the Spanish Ministry of Science and Innovation (MICINN) under projects AYA2009-10368, AYA2006-12955, AYA2010-21887-C04-04, and AYA2009-11137, by the Madrid Regional Government through the AstroMadrid Project (CAM S2009/ESP-1496), and by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006-00070: ``First Science with the GTC'' (http://www.iac.es/consolider-ingenio-gtc/). S. D. H. & G.

CHARACTERIZING THE POPULATION OF BRIGHT INFRARED SOURCES IN THE SMALL MAGELLANIC CLOUD

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

Kraemer, K. E.; Sloan, G. C.; Wood, P. R.

We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to observe stars in the Small Magellanic Cloud (SMC) selected from the Point Source Catalog of the Midcourse Space Experiment (MSX). We concentrate on the dust properties of the oxygen-rich evolved stars. The dust composition has smaller contributions from alumina compared to the Galaxy. This difference may arise from the lower metallicity in the SMC, but it could be a selection effect, as the SMC sample includes more stars that are brighter and thus more massive. The distribution of the SMC stars along the silicate sequence looks moremore » like the Galactic sample of red supergiants than asymptotic giant branch stars (AGBs). While many of the SMC stars are definitively on the AGB, several also show evidence of hot bottom burning. Three of the supergiants show PAH emission at 11.3 μ m. Two other sources show mixed chemistry, with both carbon-rich and oxygen-rich spectral features. One, MSX SMC 134, may be the first confirmed silicate/carbon star in the SMC. The other, MSX SMC 049, is a candidate post-AGB star. MSX SMC 145, previously considered a candidate OH/IR star, is actually an AGB star with a background galaxy at z  = 0.16 along the same line of sight. We consider the overall characteristics of all the MSX sources, the most infrared-bright objects in the SMC, in light of the higher sensitivity and resolution of Spitzer , and compare them with the object types expected from the original selection criteria. This population represents what will be seen in more distant galaxies by the upcoming James Webb Space Telescope ( JWST ). Color–color diagrams generated from the IRS spectra and the mid-infrared filters on JWST show how one can separate evolved stars from young stellar objects (YSOs) and distinguish among different classes of YSOs.« less

Characterizing the Population of Bright Infrared Sources in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Kraemer, K. E.; Sloan, G. C.; Wood, P. R.; Jones, O. C.; Egan, M. P.

2017-01-01

We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to observe stars in the Small Magellanic Cloud (SMC) selected from the Point Source Catalog of the Midcourse Space Experiment (MSX). We concentrate on the dust properties of the oxygen-rich evolved stars. The dust composition has smaller contributions from alumina compared to the Galaxy. This difference may arise from the lower metallicity in the SMC, but it could be a selection effect, as the SMC sample includes more stars that are brighter and thus more massive. The distribution of the SMC stars along the silicate sequence looks more like the Galactic sample of red supergiants than asymptotic giant branch stars (AGBs). While many of the SMC stars are definitively on the AGB, several also show evidence of hot bottom burning. Three of the supergiants show PAH emission at 11.3 μm. Two other sources show mixed chemistry, with both carbon-rich and oxygen-rich spectral features. One, MSX SMC 134, may be the first confirmed silicate/carbon star in the SMC. The other, MSX SMC 049, is a candidate post-AGB star. MSX SMC 145, previously considered a candidate OH/IR star, is actually an AGB star with a background galaxy at z = 0.16 along the same line of sight. We consider the overall characteristics of all the MSX sources, the most infrared-bright objects in the SMC, in light of the higher sensitivity and resolution of Spitzer, and compare them with the object types expected from the original selection criteria. This population represents what will be seen in more distant galaxies by the upcoming James Webb Space Telescope (JWST). Color-color diagrams generated from the IRS spectra and the mid-infrared filters on JWST show how one can separate evolved stars from young stellar objects (YSOs) and distinguish among different classes of YSOs.

Dwarf Star Erupts in Giant Flare

NASA Technical Reports Server (NTRS)

2005-01-01

This movie taken by NASA'S Galaxy Evolution Explorer shows one of the largest flares, or star eruptions, ever recorded at ultraviolet wavelengths. The star, called GJ 3685A, just happened to be in the Galaxy Evolution Explorer's field of view while the telescope was busy observing galaxies. As the movie demonstrates, the seemingly serene star suddenly exploded once, then even more intensely a second time, pouring out in total about one million times more energy than a typical flare from our Sun. The second blast of light constituted an increase in brightness by a factor of at least 10,000.

Flares are huge explosions of energy stemming from a single location on a star's surface. They are caused by the brief destruction of a star's magnetic fields. Many types of stars experience them, though old, small, rapidly rotating 'red dwarfs' like GJ 3685A tend to flare more frequently and dramatically. These stars, called flare stars, can experience powerful eruptions as often as every few hours. Younger stars, in general, also erupt more often. One of the reasons astronomers study flare stars is to gain a better picture and history of flare events taking place on the Sun.

A preliminary analysis of the GJ 3685A flare shows that the mechanisms underlying stellar eruptions may be more complex than previously believed. Evidence for the two most popular flare theories was found.

Though this movie has been sped up (the actual flare lasted about 20 minutes), time-resolved data exist for each one-hundredth of a second. These observations were taken at 2 p.m. Pacific time, April 24, 2004. In the still image, the time sequence starts in the upper left panel, continues in the upper right, then moves to the lower left and ends in the lower right.

The circular and linear features that appear below and to the right of GJ 3685A during the flare event are detector artifacts caused by the extreme brightness of the flare.

The Morphological Evolution, AGN Fractions, Dust Content, Environments, and Downsizing of Massive Green Valley Galaxies at 0.5 < z < 2.5 in 3D-HST/CANDELS

NASA Astrophysics Data System (ADS)

Gu, Yizhou; Fang, Guanwen; Yuan, Qirong; Cai, Zhenyi; Wang, Tao

2018-03-01

To explore the evolutionary connection among red, green, and blue galaxy populations, based on a sample of massive ({M}* > {10}10 {M}ȯ ) galaxies at 0.5 < z < 2.5 in five 3D-HST/CANDELS fields, we investigate the dust content, morphologies, structures, active galactic nucleus (AGN) fractions, and environments of these three populations. Green valley galaxies are found to have intermediate dust attenuation and reside in the middle of the regions occupied by quiescent and star-forming galaxies in the UVJ diagram. Compared with blue and red galaxy populations at z < 2, green galaxies have intermediate compactness and morphological parameters. The above findings seem to favor the scenario that green galaxies are at a transitional phase when star-forming galaxies are being quenched into quiescent status. The green galaxies at z < 2 show the highest AGN fraction, suggesting that AGN feedback may have played an important role in star formation quenching. For the massive galaxies at 2 < z < 2.5, both red and green galaxies are found to have a similarly higher AGN fraction than the blue ones, which implies that AGN feedback may help to keep quiescence of red galaxies at z > 2. A significant environmental difference is found between green and red galaxies at z < 1.5. Green and blue galaxies at z > 0.5 seem to have similar local density distributions, suggesting that environment quenching is not the major mechanism to cease star formation at z > 0.5. The fractions of three populations as functions of mass support a “downsizing” quenching picture that the bulk of star formation in more massive galaxies is completed earlier than that of lower-mass galaxies.

CHEMICAL ABUNDANCES IN A SAMPLE OF RED GIANTS IN THE OPEN CLUSTER NGC 2420 FROM APOGEE

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

Souto, Diogo; Cunha, K.; Smith, V.

NGC 2420 is a ∼2 Gyr old well-populated open cluster that lies about 2 kpc beyond the solar circle, in the general direction of the Galactic anti-center. Most previous abundance studies have found this cluster to be mildly metal-poor, but with a large scatter in the obtained metallicities. Detailed chemical abundance distributions are derived for 12 red-giant members of NGC 2420 via a manual abundance analysis of high-resolution ( R = 22,500) near-infrared ( λ 1.5–1.7 μ m) spectra obtained from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The sample analyzed contains six stars that are identified asmore » members of the first-ascent red giant branch (RGB), as well as six members of the red clump (RC). We find small scatter in the star-to-star abundances in NGC 2420, with a mean cluster abundance of [Fe/H] = −0.16 ± 0.04 for the 12 red giants. The internal abundance dispersion for all elements (C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Co and Ni) is also very small (∼0.03–0.06 dex), indicating a uniform cluster abundance distribution within the uncertainties. NGC 2420 is one of the clusters used to calibrate the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). The results from this manual analysis compare well with ASPCAP abundances for most of the elements studied, although for Na, Al, and V there are more significant offsets. No evidence of extra-mixing at the RGB luminosity bump is found in the {sup 12}C and {sup 14}N abundances from the pre-luminosity-bump RGB stars in comparison to the post-He core-flash RC stars.« less

Chromospheres and mass loss in metal-deficient giant stars

NASA Technical Reports Server (NTRS)

Dupree, A. K.; Hartmann, L.; Avrett, E. H.

1984-01-01

Semiempirical atmospheric models indicate that the characteristic emission in the wings of the H-alpha line observed in Population II giant stars can arise naturally within static chromospheres. Radial expansion gives an asymmetric, blueshifted H-alpha core accompanied by greater emission in the red line wing than in the blue wing. Wind models with extended atmospheres suggest mass loss rates much smaller than 2 x 10 to the -9th solar mass per yr. Thus H-alpha provides no evidence that steady mass loss can significantly affect the evolution of stars on the red giant branch of globular clusters.

Resolved photometry of extragalactic young massive star clusters

NASA Astrophysics Data System (ADS)

Larsen, S. S.; de Mink, S. E.; Eldridge, J. J.; Langer, N.; Bastian, N.; Seth, A.; Smith, L. J.; Brodie, J.; Efremov, Yu. N.

2011-08-01

Aims: We present colour-magnitude diagrams (CMDs) of young massive star clusters in several galaxies located well beyond the Local Group. The richness of these clusters allows us to obtain large samples of post-main sequence stars and test how well the observed CMDs are reproduced by canonical stellar isochrones. Methods: We use imaging of seven clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793 obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope and carry out PSF-fitting photometry of individual stars in the clusters. The clusters have ages in the range ~(5-50) × 106 years and masses of ~105 M⊙-106 M⊙. Although crowding prevents us from obtaining photometry in the inner regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. Results: In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2 mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. We find that this spread can be reproduced by including an age spread of ~(10-30) × 106 years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role. Conclusions: Colour-magnitude diagrams can be successfully obtained for massive star clusters out to distances of at least 4-5 Mpc. Comparing such CMDs with models based on canonical isochrones we find several areas of disagreement. One interesting possibility is that an age spread of up to ~30 Myr may be present in some clusters. The data presented here may provide useful constraints on models for single and/or binary stellar evolution. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555Tables 4-10 are only 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/532/A147

The Cosmic Skidmark: witnessing galaxy transformation at z = 0.19

NASA Astrophysics Data System (ADS)

Murphy, David N. A.

2015-02-01

We present an early-look analysis of the ``Cosmic Skidmark''. Discovered following visual inspection of the Geach, Murphy & Bower (2011) SDSS Stripe 82 cluster catalogue generated by ORCA (an automated cluster algorithm searching for red-sequences; Murphy, Geach & Bower 2012), this z = 0.19 1.4L* galaxy appears to have been caught in the rare act of transformation while accreting onto an estimated 1013-1014 h -1 M⊙-mass galaxy group. SDSS spectroscopy reveals clear signatures of star formation whilst deep optical imaging reveals a pronounced 50 kpc cometary tail. Pending completion of our ALMA Cycle 2 and IFU observations, we show here preliminary analysis of this target.

On the red giant titanium oxide bands

NASA Astrophysics Data System (ADS)

Hanni, L.; Sitska, J.

1985-12-01

The dependence of TiO absorption in cool oxygen-sequence giant stars on the Teff and log g of their atmospheres is investigated theoretically on the basis of spectra simulated using the computer program described by Hanni (1983) and the giant model atmospheres of Johnson et al. (1980). The temperature dependence of the intensity jumps at the head of the alpha(1.0) band is determined from simulated spectra, and the jumps are related to spectral types using the calibration of Ridgway et al. (1980). The results are presented in tables and graphs and shown to be in good agreement with the empirical Teff/intensity-jump correlation of Boyarchuk (1969).

Lithium in lower-main-sequence stars of the Alpha Persei cluster

NASA Technical Reports Server (NTRS)

Balachandran, Suchitra; Lambert, David L.; Stauffer, John R.

1988-01-01

Lithium abundances are presented for main-sequence stars of spectral types F, G, and K in the young open cluster Alpha Per. For 46 cluster members, a correlation between Li abundance and projected rotational velocity v sin i is found: all of the Li-poor stars are slow rotators. Two explanations are proposed to account for the correlation: (1) that the Li depletion is introduced following a rapid spin-down phase experienced by young low-mass stars, and that this episode of Li depletion may be the dominant one determining the spread of Li abundances among young low-mass main-sequence stars, and (2) that star formation has occurred over a finite period such that the older stars have undergone a spin-down and depletion of Li by a means that may or may not depend on rotation. The Li abundance in the warm and rapidly rotating stars appears to be undepleted, as is predicted by recent models of pre-main-sequence stars. The depletion observed in the cool stars exceeds the level predicted by these models.

Variation in the genomic locations and sequence conservation of STAR elements among staphylococcal species provides insight into DNA repeat evolution

PubMed Central

2012-01-01

Background Staphylococcus aureus Repeat (STAR) elements are a type of interspersed intergenic direct repeat. In this study the conservation and variation in these elements was explored by bioinformatic analyses of published staphylococcal genome sequences and through sequencing of specific STAR element loci from a large set of S. aureus isolates. Results Using bioinformatic analyses, we found that the STAR elements were located in different genomic loci within each staphylococcal species. There was no correlation between the number of STAR elements in each genome and the evolutionary relatedness of staphylococcal species, however higher levels of repeats were observed in both S. aureus and S. lugdunensis compared to other staphylococcal species. Unexpectedly, sequencing of the internal spacer sequences of individual repeat elements from multiple isolates showed conservation at the sequence level within deep evolutionary lineages of S. aureus. Whilst individual STAR element loci were demonstrated to expand and contract, the sequences associated with each locus were stable and distinct from one another. Conclusions The high degree of lineage and locus-specific conservation of these intergenic repeat regions suggests that STAR elements are maintained due to selective or molecular forces with some of these elements having an important role in cell physiology. The high prevalence in two of the more virulent staphylococcal species is indicative of a potential role for STAR elements in pathogenesis. PMID:23020678

Calibration and characterisation of the Gaia Red Clump

NASA Astrophysics Data System (ADS)

Ruiz-Dern, L.; Babusiaux, C.; Arenou, F.; Danielski, C.; Turon, C.; Sartoretti, P.

2018-04-01

We present new empirical Colour-Colour and Effective Temperature-Colour Gaia Red Clump calibrations. The selected sample takes into account high photometric quality, good spectrometric metallicity, homogeneous effective temperatures and low interstellar extinctions. From those calibrations we developed a method to derive the absolute magnitude, temperature and extinction of the Gaia RC. We tested our colour and extinction estimates on stars with measured spectroscopic effective temperatures and Diffuse Interstellar Band (DIB) constraints. Within the Gaia Validation team these calibrations are also being used, together with asteroseismic constraints, to check the parallax zero-point with Red Clump stars.

Galaxy Packs Big Star-Making Punch

NASA Image and Video Library

2013-04-23

The tiny red spot in this image is one of the most efficient star-making galaxies ever observed, converting gas into stars at the maximum possible rate. The galaxy is shown here is from NASA WISE, which first spotted the rare galaxy in infrared light.

SEARCH FOR RED DWARF STARS IN GLOBULAR CLUSTER NGC 6397

NASA Technical Reports Server (NTRS)

2002-01-01

Left A NASA Hubble Space Telescope image of a small region (1.4 light-years across) in the globular star cluster NGC 6397. Simulated stars (diamonds) have been added to this view of the same region of the cluster to illustrate what astronomers would have expected to see if faint red dwarf stars were abundant in the Milky Way Galaxy. The field would then contain 500 stars, according to theoretical calculations. Right The unmodified HST image shows far fewer stars than would be expected, according to popular theories of star formation. HST resolves about 200 stars. The stellar density is so low that HST can literally see right through the cluster and resolve far more distant background galaxies. From this observation, scientists have identified the surprising cutoff point below which nature apparently doesn't make many stars smaller that 1/5 the mass of our Sun. These HST findings provide new insights into star formation in our Galaxy. Technical detail:The globular cluster NGC 6397, one of the nearest and densest agglomerations of stars, is located 7,200 light-years away in the southern constellation Ara. This visible-light picture was taken on March 3, 1994 with the Wide Field Planetary Camera 2, as part the HST parallel observing program. Credit: F. Paresce, ST ScI and ESA and NASA

Red giants seismology

NASA Astrophysics Data System (ADS)

Mosser, B.; Samadi, R.; Belkacem, K.

2013-11-01

The space-borne missions CoRoT and Kepler are indiscreet. With their asteroseismic programs, they tell us what is hidden deep inside the stars. Waves excited just below the stellar surface travel throughout the stellar interior and unveil many secrets: how old is the star, how big, how massive, how fast (or slow) its core is dancing. This paper intends to paparazze the red giants according to the seismic pictures we have from their interiors.

Determining Mass-Loss Rates of Evolved Stars in the Galactic Bulge from Infrared Surveys

NASA Astrophysics Data System (ADS)

Riley, Allyssa; Sargent, Benjamin A.; Srinivasan, Sundar; Meixner, Margaret; Kastner, Joel H.

2018-06-01

To investigate the relationship between mass loss from evolved stars and host galaxy metallicity, we are computing the dust mass loss budget due to red supergiant (RSG) and asymptotic giant branch (AGB) stars in the Galactic Bulge and comparing this result to that previously obtained for the Magellanic Clouds. We construct spectral energy distributions (SEDs) for our candidate RSG and AGB stars using observations from various infrared surveys, including the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Because Robitaille et al (2008, AJ, 136, 2413) have already identified Intrinsically Red Objects from the GLIMPSE I and II surveys, we use their method as a starting point and expand the study by using the GLIMPSE 3D survey. Because AGB stars can be variable, we also match the GLIMPSE I, II, and 3D sources to other surveys, such as DEEP GLIMPSE, WISE, VVV, and DENIS, in order to characterize the variability across the spectral energy distribution (SED) of each source. This allows us to determine the source’s average SED over multiple epochs. We use extinction curves derived from Spitzer studies of extinction in the Galaxy to determine the extinction corrections for our sample. To establish mass-loss rates of evolved stars in the Bulge, we use the Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS) of dust-enshrouded evolved stars (2011, A&A, 532, A54; 2011, ApJ, 728, 93). This allows us to determine the total mass return to the Bulge from these stars. This work has been supported by NASA ADAP grant 80NSSC17K0057.

MOTION VERIFIED RED STARS (MoVeRS): A CATALOG OF PROPER MOTION SELECTED LOW-MASS STARS FROM WISE, SDSS, AND 2MASS

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

Theissen, Christopher A.; West, Andrew A.; Dhital, Saurav, E-mail: ctheisse@bu.edu

2016-02-15

We present a photometric catalog of 8,735,004 proper motion selected low-mass stars (KML-spectral types) within the Sloan Digital Sky Survey (SDSS) footprint, from the combined SDSS Data Release 10 (DR10), Two Micron All-Sky Survey (2MASS) point-source catalog (PSC), and Wide-field Infrared Survey Explorer (WISE) AllWISE catalog. Stars were selected using r − i, i − z, r − z, z − J, and z − W1 colors, and SDSS, WISE, and 2MASS astrometry was combined to compute proper motions. The resulting 3,518,150 stars were augmented with proper motions for 5,216,854 earlier type stars from the combined SDSS and United States Naval Observatory B1.0 catalog (USNO-B). We used SDSS+USNO-B proper motionsmore » to determine the best criteria for selecting a clean sample of stars. Only stars whose proper motions were greater than their 2σ uncertainty were included. Our Motion Verified Red Stars catalog is available through SDSS CasJobs and VizieR.« less

Magnesium Isotope Ratios in ω Centauri Red Giants

NASA Astrophysics Data System (ADS)

Da Costa, G. S.; Norris, John E.; Yong, David

2013-05-01

We have used the high-resolution observations obtained at the Anglo-Australian Telescope with Ultra-High Resolution Facility (R ~ 100,000) and at Gemini-S with b-HROS (R ~ 150,000) to determine magnesium isotope ratios for seven ω Cen red giants that cover a range in iron abundance from [Fe/H] = -1.78 to -0.78 dex, and for two red giants in M4 (NGC 6121). The ω Cen stars sample both the "primordial" (i.e., O-rich, Na- and Al-poor) and the "extreme" (O-depleted, Na- and Al-rich) populations in the cluster. The primordial population stars in both ω Cen and M4 show (25Mg, 26Mg)/24Mg isotopic ratios that are consistent with those found for the primordial population in other globular clusters with similar [Fe/H] values. The isotopic ratios for the ω Cen extreme stars are also consistent with those for extreme population stars in other clusters. The results for the extreme population stars studied indicate that the 26Mg/24Mg ratio is highest at intermediate metallicities ([Fe/H] < -1.4 dex), and for the highest [Al/Fe] values. Further, the relative abundance of 26Mg in the extreme population stars is notably higher than that of 25Mg, in contrast to model predictions. The 25Mg/24Mg isotopic ratio in fact does not show any obvious dependence on either [Fe/H] or [Al/Fe] nor, intriguingly, any obvious difference between the primordial and extreme population stars.

Flaring Red Dwarf Star (Illustration)

NASA Image and Video Library

2017-06-06

This illustration shows a red dwarf star orbited by a hypothetical exoplanet. Red dwarfs tend to be magnetically active, displaying gigantic arcing prominences and a wealth of dark sunspots. Red dwarfs also erupt with intense flares that could strip a nearby planet's atmosphere over time, or make the surface inhospitable to life as we know it. By mining data from the Galaxy Evolution Explorer (GALEX) spacecraft, a team of astronomers identified dozens of flares at a range of durations and strengths. The team measured events with less total energy than many previously detected flares from red dwarfs. This is important because, although individually less energetic and therefore less hostile to life, smaller flares might be much more frequent and add up over time to produce a cumulative effect on an orbiting planet. https://photojournal.jpl.nasa.gov/catalog/PIA21473

SEISMIC DIAGNOSTICS OF RED GIANTS: FIRST COMPARISON WITH STELLAR MODELS

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

Montalban, J.; Miglio, A.; Noels, A.

2010-10-01

The clear detection with CoRoT and KEPLER of radial and non-radial solar-like oscillations in many red giants paves the way for seismic inferences on the structure of such stars. We present an overview of the properties of the adiabatic frequencies and frequency separations of radial and non-radial oscillation modes for an extended grid of models. We highlight how their detection allows a deeper insight into the internal structure and evolutionary state of red giants. In particular, we find that the properties of dipole modes constitute a promising seismic diagnostic tool of the evolutionary state of red giant stars. We comparemore » our theoretical predictions with the first 34 days of KEPLER data and predict the frequency diagram expected for red giants in the CoRoT exofield in the galactic center direction.« less

Star Surface Polluted by Planetary Debris

NASA Astrophysics Data System (ADS)

2007-07-01

Looking at the chemical composition of stars that host planets, astronomers have found that while dwarf stars often show iron enrichment on their surface, giant stars do not. The astronomers think that the planetary debris falling onto the outer layer of the star produces a detectable effect in a dwarf star, but this pollution is diluted by the giant star and mixed into its interior. "It is a little bit like a Tiramisu or a Capuccino," says Luca Pasquini from ESO, lead-author of the paper reporting the results. "There is cocoa powder only on the top!' ESO PR Photo 29/07 ESO PR Photo 29/07 The Structure of Stars Just a few years after the discovery of the first exoplanet it became evident that planets are preferentially found around stars that are enriched in iron. Planet-hosting stars are on average almost twice as rich in metals than their counterparts with no planetary system. The immediate question is whether this richness in metals enhances planet formation, or whether it is caused by the presence of planets. The classic chicken and egg problem. In the first case, the stars would be metal-rich down to their centre. In the second case, debris from the planetary system would have polluted the star and only the external layers would be affected by this pollution. When observing stars and taking spectra, astronomers indeed only see the outer layers and can't make sure the whole star has the same composition. When planetary debris fall onto a star, the material will stay in the outer parts, polluting it and leaving traces in the spectra taken. A team of astronomers has decided to tackle this question by looking at a different kind of stars: red giants. These are stars that, as will the Sun in several billion years, have exhausted the hydrogen in their core. As a result, they have puffed up, becoming much larger and cooler. Looking at the distribution of metals in fourteen planet-hosting giants, the astronomers found that their distribution was rather different from normal planet-hosting stars. "We find that evolved stars are not enriched in metals, even when hosting planets," says Pasquini. "Thus, the anomalies found in planet-hosting stars seem to disappear when they get older and puff up!" Looking at the various options, the astronomers conclude that the most likely explanation lies in the difference in the structure between red giants and solar-like stars: the size of the convective zone, the region where all the gas is completely mixed. In the Sun, this convective zone comprises only 2% of the star's mass. But in red giants, the convective zone is huge, encompassing 35 times more mass. The polluting material would thus be 35 times more diluted in a red giant than in a solar-like star. "Although the interpretation of the data is not straightforward, the simplest explanation is that solar-like stars appear metal-rich because of the pollution of their atmospheres," says co-author Artie Hatzes, Director of the Thüringer Landessternwarte Tautenburg (Germany) where some of the data were obtained. When the star was still surrounded by a proto-planetary disc, material enriched in more heavy elements would fall onto the star, thereby polluting its surface. The metal excess produced by this pollution, while visible in the thin atmospheres of solar-like stars, is completely diluted in the extended, massive atmospheres of the giants.

Sparsely-Observed Pulsating Red Giants in the AAVSO Observing Program

NASA Astrophysics Data System (ADS)

Percy, J. R.

2018-06-01

This paper reports on time-series analysis of 156 pulsating red giants (21 SRa, 52 SRb, 33 SR, 50 Lb) in the AAVSO observing program for which there are no more than 150-250 observations in total. Some results were obtained for 68 of these stars: 17 SRa, 14 SRb, 20 SR, and 17 Lb. These results generally include only an average period and amplitude. Many, if not most of the stars are undoubtedly more complex; pulsating red giants are known to have wandering periods, variable amplitudes, and often multiple periods including "long secondary periods" of unknown origin. These results (or lack thereof) raise the question of how the AAVSO should best manage the observation of these and other sparsely-observed pulsating red giants.

EVOLUTION OF THE MASS-METALLICITY RELATIONS IN PASSIVE AND STAR-FORMING GALAXIES FROM SPH-COSMOLOGICAL SIMULATIONS

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

Romeo Velona, A. D.; Gavignaud, I.; Meza, A.

2013-06-20

We present results from SPH-cosmological simulations, including self-consistent modeling of supernova feedback and chemical evolution, of galaxies belonging to two clusters and 12 groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming (SF) activity, as parameterized by their specific star formation rate (sSFR), across a redshift range up to z = 2. The overall ZM relation for the composite population evolves according to a redshift-dependent quadratic functional form that is consistent with other empirical estimates, provided that the highest mass bin of the brightest central galaxies is excluded. Its slope shows irrelevantmore » evolution in the passive sample, being steeper in groups than in clusters. However, the subsample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. The scatter of the passive sample is dominated by low-mass galaxies at all redshifts and keeps constant over cosmic times. The mean metallicity is highest in cluster cores and lowest in normal groups, following the same environmental sequence as that previously found in the red sequence building. The ZM relation for the SF sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The SF galaxies make up a tight sequence in the SFR-M{sub *} plane at high redshift, whose scatter increases with time alongside the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the SF galaxies, while on the contrary more active galaxies in terms of simple SFR are also metal-richer. Finally, the [O/Fe] abundance ratio is presented too: we report a strong increasing evolution with redshift at given mass, especially at z {approx}> 1. The expected increasing trend with mass is recovered when only considering the more massive galaxies. We discuss these results in terms of the mechanisms driving the evolution within the high- and low-mass regimes at different epochs: mergers, feedback-driven outflows, and the intrinsic variation of the star formation efficiency.« less

Star formation is boosted (and quenched) from the inside-out: radial star formation profiles from MaNGA

NASA Astrophysics Data System (ADS)

Ellison, Sara L.; Sánchez, Sebastian F.; Ibarra-Medel, Hector; Antonio, Braulio; Mendel, J. Trevor; Barrera-Ballesteros, Jorge

2018-02-01

The tight correlation between total galaxy stellar mass and star formation rate (SFR) has become known as the star-forming main sequence. Using ˜487 000 spaxels from galaxies observed as part of the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we confirm previous results that a correlation also exists between the surface densities of star formation (ΣSFR) and stellar mass (Σ⋆) on kpc scales, representing a `resolved' main sequence. Using a new metric (ΔΣSFR), which measures the relative enhancement or deficit of star formation on a spaxel-by-spaxel basis relative to the resolved main sequence, we investigate the SFR profiles of 864 galaxies as a function of their position relative to the global star-forming main sequence (ΔSFR). For galaxies above the global main sequence (positive ΔSFR) ΔΣSFR is elevated throughout the galaxy, but the greatest enhancement in star formation occurs at small radii (<3 kpc, or 0.5Re). Moreover, galaxies that are at least a factor of 3 above the main sequence show diluted gas phase metallicities out to 2Re, indicative of metal-poor gas inflows accompanying the starbursts. For quiescent/passive galaxies that lie at least a factor of 10 below the star-forming main sequence, there is an analogous deficit of star formation throughout the galaxy with the lowest values of ΔΣSFR in the central 3 kpc. Our results are in qualitative agreement with the `compaction' scenario in which a central starburst leads to mass growth in the bulge and may ultimately precede galactic quenching from the inside-out.

The photosphere of red supergiant stars as seen by optical interferometry

NASA Astrophysics Data System (ADS)

Montargès, M.; Kervella, P.; Perrin, G.; Chiavassa, A.; Norris, R.; Ridgway, S. T.; Decin, L.

2017-12-01

During the end of their lives, massive stars become red supergiant (RSG) stars. At this stage, they are forging heavy elements in their cores that are transported up to the photosphere thanks to convection and expelled to the interstellar medium through the star's mass loss. Cooling in the outer atmosphere causes these elements to become molecules and dust that are the building blocks of future planetary systems and eventually life. One of the scenarios to explain the launch of material from the photosphere involves convection that leads to an increased scale height and facilitates mass ejection. We present here observations of several bright features on the surface of nearby RSG stars using near infrared (NIR) interferometry. They are interpreted as being the top of convective cells. We compare them with 3D convective simulation predictions. These inhomogeneities are bright and large enough to cause a photocenter displacement that might bias parallax measurements.

Evidence for a warm wind from the red star in symbiotic binaries

NASA Technical Reports Server (NTRS)

Friedjung, M.; Stencel, R. E.; Viotti, R.

1983-01-01

A systematic redshift of the high ionization resonance emission lines with respect to the intercombination lines is found from an examination of the ultraviolet spectra of symbiotic stars obtained with IUE. After consideration of other possibilities, this is most probably explained by photon scattering in an expanding envelope optically thick to the resonance lines. Line formation in a wind, or at the base of a wind is therefore suggested. Reasons are also given indicating line formation of the most ionized species in a region with an electron temperature of the order of 100,000 K, probably around the cool star. The behavior of the emission line width with ionization energy seems to support this model. The cool components of symbiotic stars appear to differ from normal red giants, which do not have winds of this temperature. An explanation in terms of a higher rotation velocity due to the binary nature of these stars is suggested.

Amplitude Variations in Pulsating Red Giants. II. Some Systematics

NASA Astrophysics Data System (ADS)

Percy, J. R.; Laing, J.

2017-12-01

In order to extend our previous studies of the unexplained phenomenon of cyclic amplitude variations in pulsating red giants, we have used the AAVSO time-series analysis package vstar to analyze long-term AAVSO visual observations of 50 such stars, mostly Mira stars. The relative amount of the variation, typically a factor of 1.5, and the time scale of the variation, typically 20-35 pulsation periods, are not significantly different in longer-period, shorter-period, and carbon stars in our sample, and they also occur in stars whose period is changing secularly, perhaps due to a thermal pulse. The time scale of the variations is similar to that in smaller-amplitude SR variables, but the relative amount of the variation appears to be larger in smaller-amplitude stars, and is therefore more conspicuous. The cause of the amplitude variations remains unclear, though they may be due to rotational modulation of a star whose pulsating surface is dominated by the effects of large convective cells.

Stellar structure model in hydrostatic equilibrium in the context of f({\\mathscr{R}})-gravity

NASA Astrophysics Data System (ADS)

André, Raíla; Kremer, Gilberto M.

2017-12-01

In this work we present a stellar structure model from the f({\\mathscr{R}})-gravity point of view capable of describing some classes of stars (white dwarfs, brown dwarfs, neutron stars, red giants and the Sun). This model is based on f({\\mathscr{R}})-gravity field equations for f({\\mathscr{R}})={\\mathscr{R}}+{f}2{{\\mathscr{R}}}2, hydrostatic equilibrium equation and a polytropic equation of state. We compare the results obtained with those found by Newtonian theory. It has been observed that in these systems, where high curvature regimes emerge, stellar structure equations undergo modifications. Despite the simplicity of this model, the results are satisfactory. The estimated values of pressure, density and temperature of the stars are within those determined by observations. This f({\\mathscr{R}})-gravity model has proved to be necessary to describe stars with strong fields such as white dwarfs, neutron stars and brown dwarfs, while stars with weaker fields, such as red giants and the Sun, are best described by Newtonian theory.

Finding η Car Analogs in Nearby Galaxies Using Spitzer. II. Identification of An Emerging Class of Extragalactic Self-Obscured Stars

NASA Astrophysics Data System (ADS)

Khan, Rubab; Kochanek, C. S.; Stanek, K. Z.; Gerke, Jill

2015-02-01

Understanding the late-stage evolution of the most massive stars such as η Carinae is challenging because no true analogs of η Car have been clearly identified in the Milky Way or other galaxies. In Khan et al., we utilized Spitzer IRAC images of 7 nearby (lsim 4 Mpc) galaxies to search for such analogs, and found 34 candidates with flat or red mid-IR spectral energy distributions. Here, in Paper II, we present our characterization of these candidates using multi-wavelength data from the optical through the far-IR. Our search detected no true analogs of η Car, which implies an eruption rate that is a fraction 0.01 <~ F <~ 0.19 of the core-collapse supernova (ccSN) rate. This is roughly consistent with each M ZAMS >~ 70 M ⊙ star undergoing one or two outbursts in its lifetime. However, we do identify a significant population of 18 lower luminosity (log (L/L ⊙) ~= 5.5-6.0) dusty stars. Stars enter this phase at a rate that is a fraction 0.09 <~ F <~ 0.55 of the ccSN rate, and this is consistent with all 25 < M ZAMS < 60 M ⊙ stars undergoing an obscured phase at most lasting a few thousand years once or twice. These phases constitute a negligible fraction of post-main-sequence lifetimes of massive stars, which implies that these events are likely to be associated with special periods in the evolution of the stars. The mass of the obscuring material is of order ~M ⊙, and we simply do not find enough heavily obscured stars for theses phases to represent more than a modest fraction (~10% not ~50%) of the total mass lost by these stars. In the long term, the sources that we identified will be prime candidates for detailed physical analysis with the James Webb Space Telescope.

Signatures of progenitors of Type Ia supernovae

NASA Astrophysics Data System (ADS)

Hoeflich, P.; Chakraborty, S.; Comaskey, W.; Fisher, A.; Hristov, B.; Collins, D.; Diamond, T. R.; Dragulin, P.; Hsiao, E. Y.; Sadler, B.

Thermonuclear Supernovae (SNe Ia) are one of the building blocks of modern cosmology and laboratories for the explosion physics of White Dwarf star/s (WD) in close binary systems. The second star may be a WD (double degenerate systems, DD), or a non-degenerated star (SD) with a main sequence star, red giant or a helium star as companion \\citep{branch95,nomoto03,wang2012}. Light curves and spectra of the explosion look similar because a 'stellar amnesia' \\citep{h06}. Basic nuclear physics determines the progenitor structure and the explosion physics, breaking the link between progenitor evolution, and the explosion, resulting in three main classes of explosion scenarios: a) dynamical merging of two WD and a heating on time scales of seconds \\citep{webbink84,isern11}, b) surface helium detonations on top of a WD which ignite the central C/O by a detonation wave traveling inwards \\citep{n82,hk96,Kromer2010}; c) compressional heating in an accreting WD approaching the Chandrasekar mass on time of up to 108 years which may originated from SD and DD systems \\citep{WI73,Piersanti2004}. Simulations of the explosions depend on the inital conditions at the onset of the explosions, namely the mass and angular momentum of the WD(s). For all scenarios, diversity in SNe Ia must be expected because the WD originates from a range of Main Sequence masses (MMS < 8 M_⊙) and metallicities Z. Moreover, there is growing evidence that magnetic fields B may have to be added to the 'mix'. Only with recent advances in observations ranging from X-ray to radio, high precision spectroscopy, polarimetry and photometry and in the time-domain astronomy we obtain constraints for progenitor, on the explosion scenarios and links emerge between the progenitors and their environment with LCs and spectral signatures needed for high precision cosmology. It is too early to give final answers but we present our personal view. We will give some examples from the theory point of view and discuss future prospects with upcoming ground based, ELT, GMT and space based such as JWST, Euclide and WFIRST instruments.

A Census of Broad-line Active Galactic Nuclei in Nearby Galaxies: Coeval Star Formation and Rapid Black Hole Growth

NASA Astrophysics Data System (ADS)

Trump, Jonathan R.; Hsu, Alexander D.; Fang, Jerome J.; Faber, S. M.; Koo, David C.; Kocevski, Dale D.

2013-02-01

We present the first quantified, statistical map of broad-line active galactic nucleus (AGN) frequency with host galaxy color and stellar mass in nearby (0.01 < z < 0.11) galaxies. Aperture photometry and z-band concentration measurements from the Sloan Digital Sky Survey are used to disentangle AGN and galaxy emission, resulting in estimates of uncontaminated galaxy rest-frame color, luminosity, and stellar mass. Broad-line AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rarer in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that broad-line AGNs occur during a different phase in galaxy evolution. More luminous broad-line AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars. The data favor processes that simultaneously fuel both star formation activity and rapid supermassive black hole accretion. If AGNs cause feedback on their host galaxies in the nearby universe, the evidence of galaxy-wide quenching must be delayed until after the broad-line AGN phase.

Hubble Space Telescope Imaging of the Mass-losing Supergiant VY Canis Majoris

NASA Astrophysics Data System (ADS)

Kastner, Joel H.; Weintraub, David A.

1998-04-01

The highly luminous M supergiant VY CMa is a massive star that appears to be in its final death throes, losing mass at high rate en route to exploding as a supernova. Subarcsecond-resolution optical images of VY CMa, obtained with the Faint Object Camera (FOC) aboard the Hubble Space Telescope, vividly demonstrate that mass loss from VY CMa is highly anisotropic. In the FOC images, the optical ``star'' VY CMa constitutes the bright, well-resolved core of an elongated reflection nebula. The imaged nebula is ~3" (~4500 AU) in extent and is clumpy and highly asymmetric. The images indicate that the bright core, which lies near one edge of the nebula, is pure scattered starlight. We conclude that at optical wavelengths VY CMa is obscured from view along our line of sight by its own dusty envelope. The presence of the extended reflection nebula then suggests that this envelope is highly flattened and/or that the star is surrounded by a massive circumstellar disk. Such axisymmetric circumstellar density structure should have profound effects on post-red supergiant mass loss from VY CMa and, ultimately, on the shaping of the remnant of the supernova that will terminate its post-main-sequence evolution.

A new reduction of the blanco cosmology survey: An optically selected galaxy cluster catalog and a

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

Bleem, L. E.; Stalder, B.; Brodwin, M.

2015-01-01

The Blanco Cosmology Survey is a four-band (griz) optical-imaging survey of ≈80 deg2 of the southern sky. The survey consists of two fields centered approximately at (R.A., decl.) = (23h, -55°) and (5h30m, -53°) with imaging sufficient for the detection of Lmore » $$\\star$$ galaxies at redshift z ≤ 1. In this paper, we present our reduction of the survey data and describe a new technique for the separation of stars and galaxies. We search the calibrated source catalogs for galaxy clusters at z ≤ 0.75 by identifying spatial over-densities of red-sequence galaxies and report the coordinates, redshifts, and optical richnesses, λ, for 764 galaxy clusters at z ≤ 0.75. This sample, >85% of which are new discoveries, has a median redshift of z = 0.52 and median richness λ(0.4L$$\\star$$) = 16.4. Accompanying this paper we also release full survey data products including reduced images and calibrated source catalogs. These products are available at http://data.rcc.uchicago.edu/dataset/blanco-cosmology-survey.« less

Different Characteristics of the Bright Branches of the Globular Clusters M15 and M92

NASA Astrophysics Data System (ADS)

Cho, Dong-Hwan; Lee, Sang-Gak

2007-05-01

We carried out relatively wide-field BVI CCD photometric observations of the globular clusters M15 (NGC 7078) and M92 (NGC 6341) using the 1.8 m telescope of the Bohyun Optical Astronomy Observatory. We present color-magnitude diagrams (V vs. B-V, V vs. V-I, and V vs. B-I) of M15 and M92. We found asymptotic giant branch (AGB) bumps at VbumpAGB=15.20+/-0.05 mag and VbumpAGB=14.50+/-0.05 mag for M15 and M92, respectively. We identified the red giant branch (RGB) bumps of the two clusters. We have estimated the population ratios R and R2 for M15 and M92 in two cases: when only normal horizontal-branch (HB) stars are used and when all the HB stars are used. We have compared the observed RGB luminosity functions of M15 and M92 with the theoretical RGB luminosity functions of Bergbusch & VandenBerg and found no significant ``extra stars'' in the comparisons. This implies that the HB morphology difference between M15 and M92 is not certain due to the results of deep mixing in the RGB sequence.

Identifying Multiple Populations in M71 using CN

NASA Astrophysics Data System (ADS)

Gerber, Jeffrey M.; Friel, Eileen D.; Vesperini, Enrico

2018-01-01

It is now well established that globular clusters (GCs) host multiple stellar populations characterized by differences in several light elements. While these populations have been found in nearly all GCs, we still lack an entirely successful model to explain their formation. A key constraint to these models is the detailed pattern of light element abundances seen among the populations; different techniques for identifying these populations probe different elements and do not always yield the same results. We study a large sample of stars in the GC M71 for light elements C and N, using the CN and CH band strength to identify multiple populations. Our measurements come from low-resolution spectroscopy obtained with the WIYN-3.5m telescope for ~150 stars from the tip of the red-giant branch down to the main-sequence turn-off. The large number of stars and broad spatial coverage of our sample (out to ~3.5 half-light radii) allows us to carry out a comprehensive characterization of the multiple populations in M71. We use a combination of the various spectroscopic and photometric indicators to draw a more complete picture of the properties of the populations and to investigate the consistency of classifications using different techniques.

Star formation in the cluster merger DLSCL J0916.2+2953

DOE PAGES

Mansheim, A. S.; Lemaux, B. C.; Dawson, W. A.; ...

2017-01-13

We investigate star formation in DLSCL J0916.2+2953, a dissociative merger of two clusters at z=0.53 that has progressed 1:1 +1.3 -0.4 Gyr since rst pass-through. We attempt to reveal the effects a collision may have had on the evolution of the cluster galaxies by tracing their star formation history. We probe current and recent activity to identify a possible star formation event at the time of the merger using EW(Hδ), EW([OII]), and Dn(4000) measured from the composite spectra of 64 cluster and 153 coeval eld galaxies. We supplement Keck DEIMOS spectra with DLS and HST imaging to determine the color,more » stellar mass, and morphology of each galaxy and conduct a comprehensive study of the populations in this complex structure. Spectral results indicate the average cluster and cluster red sequence galaxies experienced no enhanced star formation relative to the surrounding eld during the merger, ruling out a predominantly merger-quenched population. We nd that the average blue galaxy in the North cluster is currently active and in the South cluster is currently post-starburst having undergone a recent star formation event. While the North activity could be latent or long- term merger effects, a young blue stellar population and irregular geometry suggest the cluster was still forming prior the collision. While the South activity coincides with the time of the merger, the blue early-type population could be a result of secular cluster processes. The evidence suggests that the dearth or surfeit of activity is indiscernible from normal cluster galaxy evolution.« less

Monash Chemical Yields Project (Monχey) - Element production in low- and intermediate-mass stars of metallicities Z = 0 to 0.04

NASA Astrophysics Data System (ADS)

Doherty, Carolyn Louise; Lattanzio, John; Angelou, George; Wattana Campbell, Simon; Church, Ross; Constantino, Thomas; Cristallo, Sergio; Gil-Pons, Pilar; Karakas, Amanda; Lugaro, Maria; Stancliffe, Richard James

2015-08-01

The Monχey project provides a large and homogeneous set of stellar yields for the low- and intermediate- mass stars and has applications particularly to galactic chemical evolution modelling.We present a detailed grid of stellar evolutionary models and corresponding nucleosynthetic yields for stars of initial mass 0.8 M⊙ up to the limit for core collapse supernova ≈ 10 M⊙. Our study covers a broad range of metallicities, ranging from the first, primordial stars (Z=0) to those of super-solar metallicity (Z=0.04). The models are evolved from the zero-age main-sequence until the end of the asymptotic giant branch (AGB) and the nucleosynthesis calculations include all elements from H to Bi.A major innovation of our work is the first complete grid of heavy element nucleosynthetic predictions for primordial AGB stars as well as the inclusion of extra-mixing processes (in this case thermohaline) during the red giant branch. We provide a broad overview of our results with implications for galactic chemical evolution as well as highlight interesting results such as heavy element production in dredge-out events of super-AGB stars.We briefly introduce our easy to use web-based database which provides the evolutionary tracks, structural properties, internal/surface nucleosynthetic compositions and stellar yields. Our web interface includes user- driven plotting capabilities with output available in a range of formats. Our nucleosynthetic results are available for further use in post processing calculations for dust production yields.

Debris Disks Among the Shell Stars: Insights from Spitzer

NASA Technical Reports Server (NTRS)

Roberge, Aki; Weinberger, Alycia; Teske, Johanna

2008-01-01

Shell stars are a class of early-type stars that show narrow absorption lines in their spectra that appear to arise from circumstellar class. This observationally defined class contains a variety of objects, including evolved stars and classical Be stars. However, some of the main sequence shell stars harbor debris disks and younger protoplanetary disks, though this aspect of the class has been largely overlooked. We surveyed a set of main sequence stars for cool dust using Spitzer MIPS and found four additional systems with IR excesses at both 24 and 70 microns. This indicates that the stars have both circumstellar gas and dust, and are likely to be edge-on debris disks. Our estimate of the disk fraction among nearby main sequence shell stars is 48% +/- 14%. We discuss here the nature of the shell stars and present preliminary results from ground-based optical spectra of the survey target stars. We will also outline our planned studies aimed at further characterization of the shell star class.

On Helium-Dominated Stellar Evolution: The Mysterious Role of the O(He)-Type Stars

NASA Technical Reports Server (NTRS)

Reindl, N.; Rauch, T.; Werner, K.; Kruk, J. W.; Todt, H.

2014-01-01

Context. About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are not yet understood. Aims. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. A precise analysis of their photospheric abundances will establish constraints to their evolution. Methods. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques. Results. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf (WD) merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star. Conclusions. A helium-dominated stellar evolutionary sequence exists that may be fed by different types of mergers or CE scenarios. It appears likely that all these pass through the O(He) phase just before they become WDs.

ALE OF TWO CLUSTERS YIELDS SECRETS OF STAR BIRTH IN THE EARLY UNIVERSE

NASA Technical Reports Server (NTRS)

2002-01-01

This NASA Hubble Space Telescope (HST) image shows rich detail, previously only seen in neighboring star birth regions, in a pair of star clusters 166,000 light-years away in the Large Magellanic Cloud (LMC), in the southern constellation Doradus. The field of view is 130 light-years across and was taken with the Wide Field Planetary Camera 2. HST's unique capabilities -- ultraviolet sensitivity, ability to see faint stars, and high resolution -- have been utilized fully to identify three separate populations in this concentration of nearly 10,000 stars down to the 25th magnitude (more that twice as many as can be seen over the entire sky with the naked eye on a clear night on Earth). The field of view is only 130 light-years across. Previous observations with ground-based telescopes resolve less than 1,000 stars in the same region. About 60 percent of the stars belong to the dominant yellow cluster called NGC 1850, which is estimated to be 50 million years old. A scattering of white stars in the image are massive stars that are only about 4 million years old and represent about 20 percent of the stars in the image. (The remainder are field stars in the LMC.) Besides being much younger, the white stars are much more loosely distributed than the yellow cluster. The significant difference between the two cluster ages suggests these are two separate star groups that lie along the same line of sight. The younger, more open cluster probably lies 200 light-years beyond the older cluster. If it were in the foreground, then dust contained in the white cluster would obscure stars in the older yellow cluster. To observe two well-defined star populations separated by such a small gap of space is unusual. This juxtaposition suggests that supernova explosions in the older cluster might have triggered the birth of the younger cluster. This color composite image is assembled from exposures taken in ultraviolet, visible, and near-infrared light. Yellow stars correspond to Main Sequence stars (like our Sun) with average surface temperatures of 6000 Kelvin; red stars are cool giants and supergiants (3500 K); white stars are hot young stars (25,000 K or more) that are bright in ultraviolet. Credit: R. Gilmozzi, Space Telescope Science Institute/European Space Agency; Shawn Ewald, JPL; and NASA

A Study Of The Kinematics Of Stellar Sub-populations In M31's Disk And Spheroid Using PHAT And SPLASH Data

NASA Astrophysics Data System (ADS)

Guhathakurta, Puragra; Dorman, C.; Seth, A.; Dalcanton, J.; Gilbert, K.; Howley, K.; Johnson, L. C.; Kalirai, J.; Krause, T.; Lang, D.; Williams, B.; PHAT Team; SPLASH Collaboration

2012-01-01

We present a comparative study of the kinematics of different types of stars in the Andromeda galaxy (M31). Our fields of study span a range of projected radii from 2 to 15 kpc in the NE and SE quadrants of M31's disk and spheroid. The kinematical part of this study is based on radial velocity measurements of a few thousand stars obtained using the Keck II telescope and DEIMOS spectrograph as part of the SPLASH survey. The DEIMOS spectra have a spectral resolution of about 1.5 Angstrom (FWHM) and cover the wavelength range 6500-9000 Angstrom. The stellar populations part of this study - specifically, the division of stars into sub-populations - is based on high spatial resolution Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) and Wide-Field Camera 3 (WFC3) images and photometry in six filters: two ultraviolet bands (F275W and F336W), two optical bands (F475W and F814W), and two near-infrared bands (F110W and F160W). The stellar sub-populations we study include metal-rich, metal-intermediate, and metal-poor red giants, asymptotic giant branch stars, He-burning blue loop stars, massive main sequence stars, planetary nebulae, and X-ray binaries. Kinematical information allows us to measure the fraction of each sub-population that is associated with M31's disk versus its spheroid. The excellent synergy between HST and Keck provides insight into the relationship between the dynamical, star formation, and chemical enrichment histories of the structural sub-components of M31 and, by association, other large spiral galaxies. This research was supported by the National Science Foundation, NASA, and the Science Internship Program (SIP) at UCSC.

The search for multiple populations in Magellanic Cloud Clusters IV: Coeval multiple stellar populations in the young star cluster NGC 1978

NASA Astrophysics Data System (ADS)

Martocchia, S.; Niederhofer, F.; Dalessandro, E.; Bastian, N.; Kacharov, N.; Usher, C.; Cabrera-Ziri, I.; Lardo, C.; Cassisi, S.; Geisler, D.; Hilker, M.; Hollyhead, K.; Kozhurina-Platais, V.; Larsen, S.; Mackey, D.; Mucciarelli, A.; Platais, I.; Salaris, M.

2018-04-01

We have recently shown that the ˜2 Gyr old Large Magellanic Cloud star cluster NGC 1978 hosts multiple populations in terms of star-to-star abundance variations in [N/Fe]. These can be seen as a splitting or spread in the sub-giant and red giant branches (SGB and RGB) when certain photometric filter combinations are used. Due to its relative youth, NGC 1978 can be used to place stringent limits on whether multiple bursts of star-formation have taken place within the cluster, as predicted by some models for the origin of multiple populations. We carry out two distinct analyses to test whether multiple star-formation epochs have occurred within NGC 1978. First, we use UV CMDs to select stars from the first and second population along the SGB, and then compare their positions in optical CMDs, where the morphology is dominantly controlled by age as opposed to multiple population effects. We find that the two populations are indistinguishable, with age differences of 1 ± 20 Myr between them. This is in tension with predictions from the AGB scenario for the origin of multiple populations. Second, we estimate the broadness of the main sequence turnoff (MSTO) of NGC 1978 and we report that it is consistent with the observational errors. We find an upper limit of ˜65 Myr on the age spread in the MSTO of NGC 1978. This finding is in conflict with the age spread scenario as origin of the extendend MSTO in intermediate age clusters, while it fully supports predictions from the stellar rotation model.

The search for multiple populations in Magellanic Cloud clusters - IV. Coeval multiple stellar populations in the young star cluster NGC 1978

NASA Astrophysics Data System (ADS)

Martocchia, S.; Niederhofer, F.; Dalessandro, E.; Bastian, N.; Kacharov, N.; Usher, C.; Cabrera-Ziri, I.; Lardo, C.; Cassisi, S.; Geisler, D.; Hilker, M.; Hollyhead, K.; Kozhurina-Platais, V.; Larsen, S.; Mackey, D.; Mucciarelli, A.; Platais, I.; Salaris, M.

2018-07-01

We have recently shown that the ˜2 Gyr old Large Magellanic Cloud star cluster NGC 1978 hosts multiple populations in terms of star-to-star abundance variations in [N/Fe]. These can be seen as a splitting or spread in the subgiant and red giant branches (SGB and RGB) when certain photometric filter combinations are used. Because of its relative youth, NGC 1978 can be used to place stringent limits on whether multiple bursts of star formation have taken place within the cluster, as predicted by some models for the origin of multiple populations. We carry out two distinct analyses to test whether multiple star formation epochs have occurred within NGC 1978. First, we use ultraviolet colour-magnitude diagrams (CMDs) to select stars from the first and second population along the SGB, and then compare their positions in optical CMDs, where the morphology is dominantly controlled by age as opposed to multiple population effects. We find that the two populations are indistinguishable, with age differences of 1 ± 20 Myr between them. This is in tension with predictions from the asymptotic giant branch scenario for the origin of multiple populations. Second, we estimate the broadness of the main-sequence turn-off (MSTO) of NGC 1978 and we report that it is consistent with the observational errors. We find an upper limit of ˜65 Myr on the age spread in the MSTO of NGC 1978. This finding is in conflict with the age spread scenario as origin of the extended MSTO in intermediate-age clusters, while it fully supports predictions from the stellar rotation model.

On The Origin Of Two-Shell Supernova Remnants

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

2006-08-01

It is known that proper motion of massive stars causes them to explode far from the geometric centers of their wind-driven bubbles and thereby affects the symmetry of the resulting diffuse supernova remnants (SNRs). We use this fact to explain the origin of SNRs consisting of two partially overlapping shells (e.g. 3C 400.2, Cygnus Loop, Kes32, etc.), whose unusual morphology is usually treated in terms of the collision (or superposition) of two separate SNRs or breakout phenomena in a region with a density discontinuity. We propose that a SNR of this type is a natural consequence of an off-centered cavity supernova (SN) explosion of a moving massive star, which ended its evolution near the edge of the main-sequence (MS) wind-driven bubble. Our proposal implies that one of the shells is the former MS bubble reenergized by the SN blast wave. The second shell, however, could originate in two somewhat different ways, depending on the initial mass of the SN progenitor star. It could be a shell swept-up by the SN blast wave expanding through the unperturbed ambient interstellar medium if the massive star ends its evolution as a red supergiant (RSG). Or it could be the remainder of a pre-existing shell (adjacent to the MS bubble) swept-up by the fast progenitor's wind during the late evolutionary phases if after the RSG phase the star evolves through the Wolf-Rayet phase. In both cases the resulting (two-shell) SNR should be associated only with one (young) neutron star (thus one can somewhat improve the statistics of neutron star/SNR associations since the two-shell SNRs are quite numerous). We discuss several criteria to discern the SNRs formed by SN explosion after the RSG or WR phase.

Constraints on core collapse from the black hole mass function

NASA Astrophysics Data System (ADS)

Kochanek, C. S.

2015-01-01

We model the observed black hole mass function under the assumption that black hole formation is controlled by the compactness of the stellar core at the time of collapse. Low-compactness stars are more likely to explode as supernovae and produce neutron stars, while high-compactness stars are more likely to be failed supernovae that produce black holes with the mass of the helium core of the star. Using three sequences of stellar models and marginalizing over a model for the completeness of the black hole mass function, we find that the compactness ξ2.5 above which 50% of core collapses produce black holes is ξ _{2.5}^{50%}=0.24 (0.15 < ξ _{2.5}^{50%} < 0.37 at 90% confidence). The models also predict that f = 0.18 (0.09 < f < 0.39) of core collapses fail. We tested four other criteria for black hole formation based on ξ2.0 and ξ3.0, the compactnesses at enclosed masses of 2.0 or 3.0 rather than 2.5 M⊙, the mass of the iron core MFe, and the mass inside the oxygen burning shell MO. We found that ξ2.0 works as well as ξ2.5, while ξ3.0, MFe and MO are significantly worse. As expected from the high compactness of 20-25 M⊙ stars, black hole formation in this mass range provides a natural explanation of the red supergiant problem.

Innocent Bystanders and Smoking Guns: Dwarf Carbon Stars

NASA Astrophysics Data System (ADS)

Green, Paul J.

2014-01-01

As far as we know, most carbon throughout the Universe is created and dispersed by AGB stars. So it was at first surprising to find that the carbon stars most prevalent in the Galaxy are in fact dwarfs. We suspect that dC stars are most likely innocent bystanders in post-mass transfer binaries, and may be predominantly metal-poor. Among 1200 C stars found in the SDSS (Green 2013), we confirm 724 dCs, of which a dozen are DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. The dCs likely span absolute magnitudes M_i from about 6.5 to 10.5. G-type dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C_2 bands. Eleven very red C stars with strong red CN bands appear to be N-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Le A. Two such stars within 30arcmin of each other may trace a previously unidentified dwarf galaxy or tidal stream at ~40 kpc. We describe follow-up projects to study the spatial, kinematic, and binary properties of these C-enriched dwarfs.

Galaxy And Mass Assembly (GAMA): bivariate functions of Hα star-forming galaxies

NASA Astrophysics Data System (ADS)

Gunawardhana, M. L. P.; Hopkins, A. M.; Taylor, E. N.; Bland-Hawthorn, J.; Norberg, P.; Baldry, I. K.; Loveday, J.; Owers, M. S.; Wilkins, S. M.; Colless, M.; Brown, M. J. I.; Driver, S. P.; Alpaslan, M.; Brough, S.; Cluver, M.; Croom, S.; Kelvin, L.; Lara-López, M. A.; Liske, J.; López-Sánchez, A. R.; Robotham, A. S. G.

2015-02-01

We present bivariate luminosity and stellar mass functions of Hα star-forming galaxies drawn from the Galaxy And Mass Assembly (GAMA) survey. While optically deep spectroscopic observations of GAMA over a wide sky area enable the detection of a large number of 0.001 < SFRHα (M⊙ yr-1) < 100 galaxies, the requirement for an Hα detection in targets selected from an r-band magnitude-limited survey leads to an incompleteness due to missing optically faint star-forming galaxies. Using z < 0.1 bivariate distributions as a reference we model the higher-z distributions, thereby approximating a correction for the missing optically faint star-forming galaxies to the local star formation rate (SFR) and M densities. Furthermore, we obtain the r-band luminosity functions (LFs) and stellar mass functions of Hα star-forming galaxies from the bivariate LFs. As our sample is selected on the basis of detected Hα emission, a direct tracer of ongoing star formation, this sample represents a true star-forming galaxy sample, and is drawn from both photometrically classified blue and red subpopulations, though mostly from the blue population. On average 20-30 per cent of red galaxies at all stellar masses are star forming, implying that these galaxies may be dusty star-forming systems.

Ionized and Molecular Gas in IC 860: Evidence for an Outflow

NASA Astrophysics Data System (ADS)

Adams, Carson; Alatalo, Katherine; Medling, Anne M.

2018-01-01

Galaxies at present-day fall predominantly in two distinct populations, as either blue, star-forming spirals or red, quiescent early-type galaxies. Blue galaxies appear to evolve onto the red sequence as star formation is quenched. The absence of a significant population falling in the intermediate ‘green valley’ implies that these transitions must occur rapidly. Identifying the initial properties of and pathways taken by these ‘dying galaxies’ is essential to building a complete understanding of galactic evolution. In this work, we investigate these phenomena in action within IC860 — a nearby, early-type spiral in the initial stages of undergoing a rapid transition in the presence of a powerful AGN-driven molecular outflow. As a shocked, post-starburst galaxy with an intermediate-age stellar population which lies on the blue end of the green valley, IC860 provides a window into the early stages of galaxy transition and AGN feedback. We present Hubble Space Telescope imaging of IC860 showing a violent, dusty outflow originating from a compact core. We find that the mean velocity map of the CO(1-0) from CARMA suggests a dynamically excited bar funneling molecular gas into the galactic center. Finally, we present kinematic maps of ionized gas emission lines as well as sodium D absorption tracing neutral winds obtained by the Wide-Field Spectrograph.

Planets around Low-mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425*

NASA Astrophysics Data System (ADS)

Bowler, Brendan P.; Liu, Michael C.; Mawet, Dimitri; Ngo, Henry; Malo, Lison; Mace, Gregory N.; McLane, Jacob N.; Lu, Jessica R.; Tristan, Isaiah I.; Hinkley, Sasha; Hillenbrand, Lynne A.; Shkolnik, Evgenya L.; Benneke, Björn; Best, William M. J.

2017-01-01

We report the discovery of an extremely red planetary-mass companion to 2MASS J22362452+4751425, a ≈0.6 M⊙ late-K dwarf likely belonging to the ˜120 Myr AB Doradus moving group. 2M2236+4751 b was identified in multi-epoch NIRC2 adaptive optics imaging at Keck Observatory at a separation of 3\\buildrel{\\prime\\prime}\\over{.} 7, or 230 ± 20 AU in projection at the kinematic distance of 63 ± 5 pc to its host star. Assuming membership in the AB Dor group, as suggested from its kinematics, the inferred mass of 2M2236+4751 b is 11-14 MJup. Follow-up Keck/OSIRIS K-band spectroscopy of the companion reveals strong CO absorption similar to other faint red L dwarfs and lacks signs of methane absorption, despite having an effective temperature of ≈900-1200 K. With a (J-K)MKO color of 2.69 ± 0.12 mag, the near-infrared slope of 2M2236+4751 b is redder than all of the HR 8799 planets and instead resembles the ≈23 Myr isolated planetary-mass object PSO J318.5-22, implying that similarly thick photospheric clouds can persist in the atmospheres of giant planets at ages beyond 100 Myr. In near-infrared color-magnitude diagrams, 2M2236+4751 b is located at the tip of the red L dwarf sequence and appears to define the “elbow” of the AB Dor substellar isochrone separating low-gravity L dwarfs from the cooler young T dwarf track. 2M2236+4751 b is the reddest substellar companion to a star and will be a valuable benchmark to study the shared atmospheric properties of young low-mass brown dwarfs and extrasolar giant planets. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Laboratory submillimeter transition frequencies of Li-7H and Li-6H. [used for abundance investigations in red giant stars

NASA Technical Reports Server (NTRS)

Plummer, G. M.; Herbst, E.; De Lucia, F. C.

1984-01-01

The fundamental (J = 1 - 0) rotational transition frequencies of Li-7H and Li-6H in their ground (v = 0) vibrational states and of Li-7H in its first excited (v = 1) vibrational state have been measured in the laboratory. Use of these transition frequencies should permit astronomical investigations of LiH abundances in red giant stars of high lithium abundance.

THE YOUNG OPEN CLUSTER BERKELEY 55

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

Negueruela, Ignacio; Marco, Amparo, E-mail: ignacio.negueruela@ua.es, E-mail: amparo.marco@ua.es

We present UBV photometry of the highly reddened and poorly studied open cluster Berkeley 55, revealing an important population of B-type stars and several evolved stars of high luminosity. Intermediate-resolution far-red spectra of several candidate members confirm the presence of one F-type supergiant and six late supergiants or bright giants. The brightest blue stars are mid-B giants. Spectroscopic and photometric analyses indicate an age 50 {+-} 10 Myr. The cluster is located at a distance d Almost-Equal-To 4 kpc, consistent with other tracers of the Perseus Arm in this direction. Berkeley 55 is thus a moderately young open cluster withmore » a sizable population of candidate red (super)giant members, which can provide valuable information about the evolution of intermediate-mass stars.« less

Metallicity of Young and Old Stars in Irregular Galaxies

NASA Astrophysics Data System (ADS)

Tikhonov, N. A.

2018-01-01

Based on archived images obtained with the Hubble Space Telescope, stellar photometry for 105 irregular galaxies has been conducted. We have shown the red supergiant and giant branches in the obtained Hertzsprung-Russel diagrams. Using the TRGB method, distances to galaxies and metallicity of red giants have been determined. The color index ( V - I) of the supergiant branch at the luminosity level M I = -7 was chosen as the metallicity index of red supergiants. For the galaxies under study, the diagrams have been built, in which the correlation can be seen between the luminosity of galaxies ( M B ) and metallicity of red giants and supergiants. The main source of variance of the results in the obtained diagrams is, in our opinion, uncertainty inmeasurements of galaxy luminosities and star-forming outburst. The relation between metallicity of young and old stars shows that main enrichment of galaxies with metals has taken place in the remote past. Deviations of some galaxies in the obtained relation can possibly be explained with the fall of the intergalactic gas on them, although, this inconsiderably affects metallicities of the stellar content.

Deep mixing of 3He: reconciling Big Bang and stellar nucleosynthesis.

PubMed

Eggleton, Peter P; Dearborn, David S P; Lattanzio, John C

2006-12-08

Low-mass stars, approximately 1 to 2 solar masses, near the Main Sequence are efficient at producing the helium isotope 3He, which they mix into the convective envelope on the giant branch and should distribute into the Galaxy by way of envelope loss. This process is so efficient that it is difficult to reconcile the low observed cosmic abundance of 3He with the predictions of both stellar and Big Bang nucleosynthesis. Here we find, by modeling a red giant with a fully three-dimensional hydrodynamic code and a full nucleosynthetic network, that mixing arises in the supposedly stable and radiative zone between the hydrogen-burning shell and the base of the convective envelope. This mixing is due to Rayleigh-Taylor instability within a zone just above the hydrogen-burning shell, where a nuclear reaction lowers the mean molecular weight slightly. Thus, we are able to remove the threat that 3He production in low-mass stars poses to the Big Bang nucleosynthesis of 3He.

CANDELS+3D-HST: Compact SFGs at z ∼ 2-3, the progenitors of the first quiescent galaxies

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

Barro, G.; Faber, S. M.; Koo, D. C.

We analyze the star-forming and structural properties of 45 massive (log(M/M{sub ☉}) >10) compact star-forming galaxies (SFGs) at 2 < z < 3 to explore whether they are progenitors of compact quiescent galaxies at z ∼ 2. The optical/NIR and far-IR Spitzer/Herschel colors indicate that most compact SFGs are heavily obscured. Nearly half (47%) host an X-ray-bright active galactic nucleus (AGN). In contrast, only about 10% of other massive galaxies at that time host AGNs. Compact SFGs have centrally concentrated light profiles and spheroidal morphologies similar to quiescent galaxies and are thus strikingly different from other SFGs, which typically aremore » disk-like and sometimes clumpy or irregular. Most compact SFGs lie either within the star formation rate (SFR)-mass main sequence (65%) or below it (30%), on the expected evolutionary path toward quiescent galaxies. These results show conclusively that galaxies become more compact before they lose their gas and dust, quenching star formation. Using extensive HST photometry from CANDELS and grism spectroscopy from the 3D-HST survey, we model their stellar populations with either exponentially declining (τ) star formation histories (SFHs) or physically motivated SFHs drawn from semianalytic models (SAMs). SAMs predict longer formation timescales and older ages ∼2 Gyr, which are nearly twice as old as the estimates of the τ models. Both models yield good spectral energy distribution fits, indicating that the systematic uncertainty in the age due to degeneracies in the SFH is of that order of magnitude. However, SAM SFHs better match the observed slope and zero point of the SFR-mass main sequence. Contrary to expectations, some low-mass compact SFGs (log(M/M{sub ☉}) =10-10.6) have younger ages but lower specific SFRs than that of more massive galaxies, suggesting that the low-mass galaxies reach the red sequence faster. If the progenitors of compact SFGs are extended SFGs, state-of-the-art SAMs show that mergers and disk instabilities (DIs) are both able to shrink galaxies, but DIs are more frequent (60% versus 40%) and form more concentrated galaxies. We confirm this result via high-resolution hydrodynamic simulations.« less

Mass Loss from Dusty AGB and Red Supergiant Stars in the Magellanic Clouds and in the Galaxy

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, Sundar; Meixner, Margaret; Kastner, Joel

2016-01-01

Asymptotic giant branch (AGB) and red supergiant (RSG) stars are evolved stars that eject large parts of their mass in outflows of dust and gas. As part of an ongoing effort to measure mass loss from evolved stars in our Galaxy and in the Magellanic Clouds, we are modeling mass loss from AGB and RSG stars in these galaxies. Our approach is twofold. We pursue radiative transfer modeling of the spectral energy distributions (SEDs) of AGB and RSG stars in the Large Magellanic Cloud (LMC), in the Small Magellanic Cloud (SMC), and in the Galactic bulge and in globular clusters of the Milky Way. We are also constructing detailed dust opacity models of AGB and RSG stars in these galaxies for which we have infrared spectra; e.g., from the Spitzer Space Telescope Infrared Spectrograph (IRS). Our sample of infrared spectra largely comes from Spitzer-IRS observations. The detailed dust modeling of spectra informs our choice of dust properties to use in radiative transfer modeling of SEDs. We seek to determine how mass loss from these evolved stars depends upon the metallicity of their host environments. BAS acknowledges funding from NASA ADAP grant NNX15AF15G.

A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars.

PubMed

Stello, Dennis; Cantiello, Matteo; Fuller, Jim; Huber, Daniel; García, Rafael A; Bedding, Timothy R; Bildsten, Lars; Aguirre, Victor Silva

2016-01-21

Magnetic fields play a part in almost all stages of stellar evolution. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes. Intermediate-mass stars do not have deep convective envelopes, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process. These stars do have convective cores that might produce internal magnetic fields, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface. Here we report the strength of dipolar oscillation modes for a sample of 3,600 red giant stars. About 20 per cent of our sample show mode suppression, by strong magnetic fields in the cores, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6-2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.

Flickering Aldebaran #3

NASA Image and Video Library

2006-10-13

As Cassini watches the rings pass in front of bright red giant star Aldebaran, the star light fluctuates, providing information about the concentrations of ring particles within the various radial features in the rings

Flickering Aldebaran #2

NASA Image and Video Library

2006-10-11

As Cassini watches the rings pass in front of bright red giant star Aldebaran, the star light fluctuates, providing information about the concentrations of ring particles within the various radial features in the rings

Infrared Detection of Very Low Mass Stars.

NASA Astrophysics Data System (ADS)

Probst, Ronald George

We present in this thesis a review of very-low -mass ((TURN)0.1 M(,0)) star research, and results of two observational programs directed at the photometric detection of low mass binary companions in the infrared. Present theoretical desiderata are model atmospheres for very cool dwarf stars and determination of the minimum protostellar mass with all relevant physics included. Luminosities for these stars are well determined, but the effective temperature scale is uncertain and abundance analyses are lacking. Masses are known for very few, and with large relative errors. The luminosity function for M(,v) > 13 is very uncertain. Astrometric methods provide at present the only means of detecting very low mass objects in significant numbers. Completion of the near-star parallax catalogue and measurement of additional low-mass binaries are important observational programs. The potential of photometric selection of red dwarf binaries is explored in Chapter II. Separation of binaries from single stars by color anomalies alone is found impractical. Detection by overluminosity in the HR diagram is hampered by the intrinsic spread of the field star population. However, we find that application of both kinematic and photometric criteria allows binaries to be detected with only moderate contamination by single stars; we discuss several binary suspects selected in this way. Our approach uses an infrared bandpass to provide temperature resolution in the color baseline, and we present JHK photometry for 60 stars, including recent parallax stars with M(,v)>14. We examine the status of the least luminous stars; there is no conclusive evidence that they are not hydrogen-burning objects. Chapter III presents a survey of (TURN)100 white dwarfs at 2 (mu) for infrared excess indicative of low -luminosity cool companions. White dwarf-red dwarf composites are detectable by infared color anomalies down to M(,v)(TURN)21 for the red dwarf component, and our survey is complete to absolute magnitudes on this level. Candidates for astrometric mass determination are suggested. Several stars are found to be composites containing an accretion disk or a hot subdwarf + dK secondary. We find very few new low-luminosity companions to normal white dwarfs. This does not appear to be a selection effect, nor is there reason to believe that all parent systems have been altered or destroyed in the mass loss phase. Our strongly negative result constrains the luminosity function for red dwarf companions to decline steeply past M(,v) (DBLTURN) 13. This may reflect a general decline in the initial mass function for star formation, or a failure of systems with large mass ratios to form or remain bound in the parent star-forming regions.

Imaging and spectroscopic observations of a strange elliptical bubble in the northern arm of the spiral galaxy NGC 6946

NASA Astrophysics Data System (ADS)

Efremov, Yuri N.; Moiseev, Alexei V.

2016-09-01

NGC 6946, known as the Fireworks galaxy because of its high supernova rate and high star formation, is embedded in a very extended H I halo. Its northern spiral arm is well detached from the galactic main body. We found that this arm contains a large (˜300 pc in size) Red Ellipse, named according to a strong contamination of the Hα emission line on its optical images. The ellipse is accompanied by a short parallel arc and a few others still smaller and less regular; a bright star cluster is seen inside these features. The complicated combination of arcs seems to be unique; it is only a bit similar to some SNRs. However, the long-slit spectral data obtained with the Russian 6-m telescope did not confirm the origin of the nebula as a result of a single SN outburst. The emission-line spectrum corresponds to the photoionization by young hot stars with a small contribution of shock ionization. The most likely explanation of the Red Ellipse is a superbubble created by a collective feedback of massive stars in the star cluster located in the NE side of the Red Ellipse. However, the very regular elliptical shape of the nebulae seems strange.

A Study of the Multiple Populations in M10

NASA Astrophysics Data System (ADS)

Gerber, Jeffrey M.; Friel, Eileen D.; Vesperini, Enrico

2017-06-01

We present an analysis of CN and CH band strengths which allow the identification of multiple populations in red giant stars in the globular cluster M10. Our measurements come from low-resolution spectroscopy obtained for ~140 red and asymptotic giant branch stars over two observation runs using Hydra on the WIYN 3.5m telescope. We sort the stars into nitrogen normal and enhanced populations based on the distribution of CN band strength as a function of magnitude. Once the stars are sorted into first and second generation (CN normal and enhanced, respectively), we compare this analysis to other ways of determining multiple stellar populations such as with the light elements Na and O and photometric indicators, particularly the UV photometry from the Hubble Space Telescope. C and N abundances are determined by matching observed CN and CH band measurements with those produced by synthetic spectra created with the Synthetic Spectrum Generator (SSG). The large sample size also allows us to study characteristics like radial distribution, and evolutionary effects such as the depletion of carbon (and subsequent nitrogen enrichment) as a star climbs the red giant branch. We find a rate of carbon depletion as a function of time for both populations in M10 and compare our result to M13, a cluster similar in metallicity.

A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host.

PubMed

Gaudi, B Scott; Stassun, Keivan G; Collins, Karen A; Beatty, Thomas G; Zhou, George; Latham, David W; Bieryla, Allyson; Eastman, Jason D; Siverd, Robert J; Crepp, Justin R; Gonzales, Erica J; Stevens, Daniel J; Buchhave, Lars A; Pepper, Joshua; Johnson, Marshall C; Colon, Knicole D; Jensen, Eric L N; Rodriguez, Joseph E; Bozza, Valerio; Novati, Sebastiano Calchi; D'Ago, Giuseppe; Dumont, Mary T; Ellis, Tyler; Gaillard, Clement; Jang-Condell, Hannah; Kasper, David H; Fukui, Akihiko; Gregorio, Joao; Ito, Ayaka; Kielkopf, John F; Manner, Mark; Matt, Kyle; Narita, Norio; Oberst, Thomas E; Reed, Phillip A; Scarpetta, Gaetano; Stephens, Denice C; Yeigh, Rex R; Zambelli, Roberto; Fulton, B J; Howard, Andrew W; James, David J; Penny, Matthew; Bayliss, Daniel; Curtis, Ivan A; DePoy, D L; Esquerdo, Gilbert A; Gould, Andrew; Joner, Michael D; Kuhn, Rudolf B; Labadie-Bartz, Jonathan; Lund, Michael B; Marshall, Jennifer L; McLeod, Kim K; Pogge, Richard W; Relles, Howard; Stockdale, Christopher; Tan, T G; Trueblood, Mark; Trueblood, Patricia

2017-06-22

The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extrasolar planets now known, only six have been found that transit hot, A-type stars (with temperatures of 7,300-10,000 kelvin), and no planets are known to transit the even hotter B-type stars. For example, WASP-33 is an A-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, WASP-33b (ref. 1); the planet is itself as hot as a red dwarf star of type M (ref. 2). WASP-33b displays a large heat differential between its dayside and nightside, and is highly inflated-traits that have been linked to high insolation. However, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. Here we report observations of the bright star HD 195689 (also known as KELT-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b. At approximately 10,170 kelvin, the host star is at the dividing line between stars of type A and B, and we measure the dayside temperature of KELT-9b to be about 4,600 kelvin. This is as hot as stars of stellar type K4 (ref. 5). The molecules in K stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. Furthermore, KELT-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.

What Makes Red Giants Tick? Linking Tidal Forces, Activity, and Solar-Like Oscillations via Eclipsing Binaries

NASA Astrophysics Data System (ADS)

Rawls, Meredith L.; Gaulme, Patrick; McKeever, Jean; Jackiewicz, Jason

2016-01-01

Thanks to advances in asteroseismology, red giants have become astrophysical laboratories for studying stellar evolution and probing the Milky Way. However, not all red giants show solar-like oscillations. It has been proposed that stronger tidal interactions from short-period binaries and increased magnetic activity on spotty giants are linked to absent or damped solar-like oscillations, yet each star tells a nuanced story. In this work, we characterize a subset of red giants in eclipsing binaries observed by Kepler. The binaries exhibit a range of orbital periods, solar-like oscillation behavior, and stellar activity. We use orbital solutions together with a suite of modeling tools to combine photometry and spectroscopy in a detailed analysis of tidal synchronization timescales, star spot activity, and stellar evolution histories. These red giants offer an unprecedented opportunity to test stellar physics and are important benchmarks for ensemble asteroseismology.

Accurate radio and optical positions for the radio star HD 36705 (AB Doradus)

NASA Technical Reports Server (NTRS)

White, Graeme L.; Jauncey, David L.; Batty, Michael J.; Peters, W. L.; Gulkis, S.

1988-01-01

Arc-second position measurements of the active star HD 36705 (AB Dor) and of the variable radio source found nearby are presented. These measurements show that the radio source is clearly identified with HD 36705 and not with the nearby red-dwarf star Rst 137B.

THE SUPER LITHIUM-RICH RED GIANT RAPID ROTATOR G0928+73.2600: A CASE FOR PLANET ACCRETION?

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

Carlberg, Joleen K.; Majewski, Steven R.; Rood, Robert T.

2010-11-01

We present the discovery of a super lithium-rich K giant star, G0928+73.2600. This red giant (T {sub eff} = 4885 K and log g = 2.65) is a fast rotator with a projected rotational velocity of 8.4 km s{sup -1} and an unusually high lithium abundance of A(Li) = 3.30 dex. Although the lack of a measured parallax precludes knowing the exact evolutionary phase, an isochrone-derived estimate of its luminosity places the star on the Hertzsprung-Russell diagram in a location that is not consistent with either the red bump on the first ascent of the red giant branch or withmore » the second ascent on the asymptotic giant branch, the two evolutionary stages where lithium-rich giant stars tend to cluster. Thus, even among the already unusual group of lithium-rich giant stars, G0928+73.2600 is peculiar. Using {sup 12}C/{sup 13}C as a tracer for mixing-more mixing leads to lower {sup 12}C/{sup 13}C-we find {sup 12}C/{sup 13}C = 28, which is near the expected value for standard first dredge-up mixing. We can therefore conclude that 'extra' deep mixing has not occurred. Regardless of the ambiguity of the evolutionary stage, the extremely large lithium abundance and the rotational velocity of this star are unusual, and we speculate that G0928+73.2600 has been enriched in both lithium and angular momentum from a sub-stellar companion.« less

Mapping Milky Way Halo Structure with Blue Horizontal Branch Stars

NASA Astrophysics Data System (ADS)

Martin, Charles; Newberg, Heidi Jo; Carlin, Jeffrey L.

2017-01-01

The use of blue horizontal brach (BHB) and red giant branch stars as tracers of stellar debris streams is a common practice and has been useful in the confirmation of kinematic properties of previously identified streams. This work explores less common ways of untangling the velocity signatures of streams traveling radially to our line of sight, and to peer toward the higher density region of the Galactic Center using data from the Sloan Digital Sky Survey (SDSS). Using spectra of BHB stars, we are able to kinematically distinguish moving groups in the Milky Way halo. The results of this thesis advance our knowledge of the following stellar halo substructures: the Pisces Stellar Stream, the Hercules-Aquila Cloud, the Hercules Halo Stream, and the Hermus Stream. A study of red giant stars led to the kinematic discovery of the Pisces Stellar Stream. Red giant stars were also examined to determine that the previously identified velocity signature that was suggested for the Hercules-Aquila Cloud was due to disk star contamination and errors in preliminary SDSS velocities. The Hercules Halo Stream is a previously unidentified structure that could be related to the Hercules-Aquila Cloud, and was discovered as a velocity excess of SDSS BHB stars. We identify a group of 10 stars with similar velocities that are spatially coincident with the Hermus Stream. An orbit is fit to the Hermus Stream that rules out a connection with the Phoenix Stream.This work was supported by NSF grants AST 09-37523, 14-09421, 16-15688, the NASA/NY Space Grant fellowship, and contributions made by The Marvin Clan, Babette Josephs, Manit Limlamai, and the 2015 Crowd Funding Campaign to Support Milky Way Research.

Flickering Aldebaran #1

NASA Image and Video Library

2006-10-09

As Cassini watches the rings pass in front of the bright red giant star Aldebaran, the star light fluctuates, providing information about the concentrations of ring particles within the various radial features in the rings

Neisseria gonorrhoeae Sequence Typing for Antimicrobial Resistance, a Novel Antimicrobial Resistance Multilocus Typing Scheme for Tracking Global Dissemination of N. gonorrhoeae Strains.

PubMed

Demczuk, W; Sidhu, S; Unemo, M; Whiley, D M; Allen, V G; Dillon, J R; Cole, M; Seah, C; Trembizki, E; Trees, D L; Kersh, E N; Abrams, A J; de Vries, H J C; van Dam, A P; Medina, I; Bharat, A; Mulvey, M R; Van Domselaar, G; Martin, I

2017-05-01

A curated Web-based user-friendly sequence typing tool based on antimicrobial resistance determinants in Neisseria gonorrhoeae was developed and is publicly accessible (https://ngstar.canada.ca). The N. gonorrhoeae Sequence Typing for Antimicrobial Resistance (NG-STAR) molecular typing scheme uses the DNA sequences of 7 genes ( penA , mtrR , porB , ponA , gyrA , parC , and 23S rRNA) associated with resistance to β-lactam antimicrobials, macrolides, or fluoroquinolones. NG-STAR uses the entire penA sequence, combining the historical nomenclature for penA types I to XXXVIII with novel nucleotide sequence designations; the full mtrR sequence and a portion of its promoter region; portions of ponA , porB , gyrA , and parC ; and 23S rRNA sequences. NG-STAR grouped 768 isolates into 139 sequence types (STs) ( n = 660) consisting of 29 clonal complexes (CCs) having a maximum of a single-locus variation, and 76 NG-STAR STs ( n = 109) were identified as unrelated singletons. NG-STAR had a high Simpson's diversity index value of 96.5% (95% confidence interval [CI] = 0.959 to 0.969). The most common STs were NG-STAR ST-90 ( n = 100; 13.0%), ST-42 and ST-91 ( n = 45; 5.9%), ST-64 ( n = 44; 5.72%), and ST-139 ( n = 42; 5.5%). Decreased susceptibility to azithromycin was associated with NG-STAR ST-58, ST-61, ST-64, ST-79, ST-91, and ST-139 ( n = 156; 92.3%); decreased susceptibility to cephalosporins was associated with NG-STAR ST-90, ST-91, and ST-97 ( n = 162; 94.2%); and ciprofloxacin resistance was associated with NG-STAR ST-26, ST-90, ST-91, ST-97, ST-150, and ST-158 ( n = 196; 98.0%). All isolates of NG-STAR ST-42, ST-43, ST-63, ST-81, and ST-160 ( n = 106) were susceptible to all four antimicrobials. The standardization of nomenclature associated with antimicrobial resistance determinants through an internationally available database will facilitate the monitoring of the global dissemination of antimicrobial-resistant N. gonorrhoeae strains. © Crown copyright 2017.

MAGNESIUM ISOTOPE RATIOS IN {omega} CENTAURI RED GIANTS

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

Da Costa, G. S.; Norris, John E.; Yong, David

2013-05-20

We have used the high-resolution observations obtained at the Anglo-Australian Telescope with Ultra-High Resolution Facility (R {approx} 100,000) and at Gemini-S with b-HROS (R {approx} 150,000) to determine magnesium isotope ratios for seven {omega} Cen red giants that cover a range in iron abundance from [Fe/H] = -1.78 to -0.78 dex, and for two red giants in M4 (NGC 6121). The {omega} Cen stars sample both the ''primordial'' (i.e., O-rich, Na- and Al-poor) and the ''extreme'' (O-depleted, Na- and Al-rich) populations in the cluster. The primordial population stars in both {omega} Cen and M4 show ({sup 25}Mg, {sup 26}Mg)/{sup 24}Mgmore » isotopic ratios that are consistent with those found for the primordial population in other globular clusters with similar [Fe/H] values. The isotopic ratios for the {omega} Cen extreme stars are also consistent with those for extreme population stars in other clusters. The results for the extreme population stars studied indicate that the {sup 26}Mg/{sup 24}Mg ratio is highest at intermediate metallicities ([Fe/H] < -1.4 dex), and for the highest [Al/Fe] values. Further, the relative abundance of {sup 26}Mg in the extreme population stars is notably higher than that of {sup 25}Mg, in contrast to model predictions. The {sup 25}Mg/{sup 24}Mg isotopic ratio in fact does not show any obvious dependence on either [Fe/H] or [Al/Fe] nor, intriguingly, any obvious difference between the primordial and extreme population stars.« less

Mass-loss From Evolved Stellar Populations In The Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Riebel, David

2012-01-01

I have conducted a study of a sample of 30,000 evolved stars in the Large Magellanic Cloud (LMC) and 6,000 in the Small Magellanic Cloud (SMC), covering their variability, mass-loss properties, and chemistry. The initial stages of of my thesis work focused on the infrared variability of Asymptotic Giant Branch (AGB) stars in the LMC. I determined the period-luminosity (P-L) relations for 6 separate sequences of 30,000 evolved star candidates at 8 wavelengths, as a function of photometrically assigned chemistry, and showed that the P-L relations are different for different chemical populations (O-rich or C-rich). I also present results from the Grid of Red supergiant and Asymptotic giant branch star ModelS (GRAMS) radiative transfer (RT) model grid applied to the evolved stellar population of the LMC. GRAMS is a pre-computed grid of RT models of RSG and AGB stars and surrounding circumstellar dust. Best-fit models are determined based on 12 bands of photometry from the optical to the mid-infrared. Using a pre-computed grid, I can present the first reasonably detailed radiative transfer modeling for tens of thousands of stars, allowing me to make statistically accurate estimations of the carbon-star luminosity function and the global dust mass return to the interstellar medium from AGB stars, both key parameters for stellar population synthesis models to reproduce. In the SAGE-Var program, I used the warm Spitzer mission to take 4 additional epochs of observations of 7500 AGB stars in the LMC and SMC. These epochs, combined with existing data, enable me to derive mean fluxes at 3.6 and 4.5 microns, that will be used for tighter constraints for GRAMS, which is currently limited by the variability induced error on the photometry. This work is support by NASA NAG5-12595 and Spitzer contract 1415784.

Dwarf Galaxies Swimming in Tidal Tails

NASA Technical Reports Server (NTRS)

2005-01-01

This false-color infrared image from NASA's Spitzer Space Telescope shows little 'dwarf galaxies' forming in the 'tails' of two larger galaxies that are colliding together. The big galaxies are at the center of the picture, while the dwarfs can be seen as red dots in the red streamers, or tidal tails. The two blue dots above the big galaxies are stars in the foreground.

Galaxy mergers are common occurrences in the universe; for example, our own Milky Way galaxy will eventually smash into the nearby Andromeda galaxy. When two galaxies meet, they tend to rip each other apart, leaving a trail, called a tidal tail, of gas and dust in their wake. It is out of this galactic debris that new dwarf galaxies are born.

The new Spitzer picture demonstrates that these particular dwarfs are actively forming stars. The red color indicates the presence of dust produced in star-forming regions, including organic molecules called polycyclic aromatic hydrocarbons. These carbon-containing molecules are also found on Earth, in car exhaust and on burnt toast, among other places. Here, the molecules are being heated up by the young stars, and, as a result, shine in infrared light.

This image was taken by the infrared array camera on Spitzer. It is a 4-color composite of infrared light, showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange), and 8.0 microns (red). Starlight has been subtracted from the orange and red channels in order to enhance the dust features.

The Formation and Evolution of the Large Magellanic Cloud from Selected Clusters and Star Fields

NASA Astrophysics Data System (ADS)

Olsen, Knut Anders Grova

We have obtained deep Hubble Space Telescope color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, WGC 1898, NGC 1916, NGC 2005, and NGC 2019. The data have been carefully calibrated and the effects of crowding on the photometric accuracy have been thoroughly investigated. The observations have been used to produce V-I,V color-magnitude diagrams of the clusters and of the background field stars, which we have separated from each other through a statistical cleaning technique. The cluster color-magnitude diagrams show that the clusters are old, with main sequence turnoffs at V~ 22.5 and well-developed horizontal branches. We used the slopes of the red giant branches to measure the abundances, which we find to be 0.3 dex higher, on average, than previously measured spectroscopic abundances. In two cases there is significant variable reddening across at least part of the image, but only for NGC 1916 does differential reddening preclude accurate measurements of the CMD characteristics. The mean reddenings of the clusters, measured both from the color of the red giant branch and through comparison with Milky Way clusters, are <=0.10 magnitudes in E(B-V) in all cases. By matching tbe color-magnitude diagrams of the clusters to fiducial sequences of the Milky Way globular clusters M3, M5, and M55, we find that the mean difference of the LMC and Milky Way cluster ages is 1.0 ± 1.2 Gyr, calculated such that a positive difference indicates that the LMC clusters are older. Through Monte Carlo simulations, errors in the individual measurements of the ages relative to Milky Way clusters are found to be ~<1.0 Gyr. We find a similar chronology by comparing the horizontal branch morphologies and abundances with HB evolutionary tracks, assuming that age is the 'second parameter'. These results imply that the LMC formed at the same time as the Milky Way Galaxy. The evolution of the LMC following its formation has been studied through an analysis of the field star CMDs. We used an automated technique to disentangle the evolutionary tracks of varying age and composition that are represented in the CMDs. We computed star formation rates as a function of age for a number of models having different initial mass function slopes, distances, and uniform reddenings, assuming that the chemical evolution follows that implied by LMC clusters. Our results show that the LMC has been actively forming stars over the last 4 Gyr, with evidence for a decline in the last 0.5-1 Gyr. While the NGC 1754 field, which lies in the disk, has had only a low level of star formation after the globular cluster formation epoch until 4 Gyr ago, we find that the bar has been actively forming stars for the past 6-8 Gyr. We find that these qualitative results are robust against errors in the model parameters. (Abstract shortened by UMI.)* ftn*Originally published in DAI Vol. 59, No. 6. Reprinted here with corrected author name.

Low coverage sequencing of three echinoderm genomes: the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis.

PubMed

Long, Kyle A; Nossa, Carlos W; Sewell, Mary A; Putnam, Nicholas H; Ryan, Joseph F

2016-01-01

There are five major extant groups of Echinodermata: Crinoidea (feather stars and sea lillies), Ophiuroidea (brittle stars and basket stars), Asteroidea (sea stars), Echinoidea (sea urchins, sea biscuits, and sand dollars), and Holothuroidea (sea cucumbers). These animals are known for their pentaradial symmetry as adults, unique water vascular system, mutable collagenous tissues, and endoskeletons of high magnesium calcite. To our knowledge, the only echinoderm species with a genome sequence available to date is Strongylocentrotus pupuratus (Echinoidea). The availability of additional echinoderm genome sequences is crucial for understanding the biology of these animals. Here we present assembled draft genomes of the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis from Illumina sequence data with coverages of 12.5x, 22.5x, and 21.4x, respectively. These data provide a resource for mining gene superfamilies, identifying non-coding RNAs, confirming gene losses, and designing experimental constructs. They will be important comparative resources for future genomic studies in echinoderms.

DISCOVERY OF RELATIVELY HYDROGEN-POOR GIANTS IN THE GALACTIC GLOBULAR CLUSTER ω CENTAURI

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

Hema, B. P.; Pandey, Gajendra, E-mail: hema@iiap.res.in, E-mail: pandey@iiap.res.in

2014-09-10

In this Letter, the results of our low-resolution spectroscopic survey for identifying hydrogen-deficient stars in the red giant sample of the globular cluster ω Cen are reported. Spectral analyses were carried out on the basis of the strengths of the (0, 0) MgH band and the Mg b triplet. In our sample, four giants were identified with weak/absent MgH bands in their observed spectra, which was unexpected for their well determined stellar parameters. The Mg abundances for the program stars were determined from the subordinate lines of the MgH band to the blue of the Mg b triplet, using the spectral synthesis technique. Themore » derived Mg abundances for the program stars were as expected for the red giants of ω Cen, except for the four identified candidates. The determined Mg abundances of these four candidates are much lower than that expected for the red giants of ω Cen, and are unacceptable based on the strengths of the Mg b triplet in their observed spectra. Hence, a plausible explanation for the weak/absent MgH bands in the observed spectra of these stars is a relatively lower abundance of hydrogen in their atmospheres. These giants may belong to the group of helium-enriched red giants of ω Cen.« less

Mapping RNA-seq Reads with STAR

PubMed Central

Dobin, Alexander; Gingeras, Thomas R.

2015-01-01

Mapping of large sets of high-throughput sequencing reads to a reference genome is one of the foundational steps in RNA-seq data analysis. The STAR software package performs this task with high levels of accuracy and speed. In addition to detecting annotated and novel splice junctions, STAR is capable of discovering more complex RNA sequence arrangements, such as chimeric and circular RNA. STAR can align spliced sequences of any length with moderate error rates providing scalability for emerging sequencing technologies. STAR generates output files that can be used for many downstream analyses such as transcript/gene expression quantification, differential gene expression, novel isoform reconstruction, signal visualization, and so forth. In this unit we describe computational protocols that produce various output files, use different RNA-seq datatypes, and utilize different mapping strategies. STAR is Open Source software that can be run on Unix, Linux or Mac OS X systems. PMID:26334920

Mapping RNA-seq Reads with STAR.

PubMed

Dobin, Alexander; Gingeras, Thomas R

2015-09-03

Mapping of large sets of high-throughput sequencing reads to a reference genome is one of the foundational steps in RNA-seq data analysis. The STAR software package performs this task with high levels of accuracy and speed. In addition to detecting annotated and novel splice junctions, STAR is capable of discovering more complex RNA sequence arrangements, such as chimeric and circular RNA. STAR can align spliced sequences of any length with moderate error rates, providing scalability for emerging sequencing technologies. STAR generates output files that can be used for many downstream analyses such as transcript/gene expression quantification, differential gene expression, novel isoform reconstruction, and signal visualization. In this unit, we describe computational protocols that produce various output files, use different RNA-seq datatypes, and utilize different mapping strategies. STAR is open source software that can be run on Unix, Linux, or Mac OS X systems. Copyright © 2015 John Wiley & Sons, Inc.

The evolutionary sequence of post-starburst galaxies

NASA Astrophysics Data System (ADS)

Wilkinson, C. L.; Pimbblet, K. A.; Stott, J. P.

2017-12-01

There are multiple ways in which to select post-starburst galaxies in the literature. In this work, we present a study into how two well-used selection techniques have consequences on observable post-starburst galaxy parameters, such as colour, morphology and environment, and how this affects interpretations of their role in the galaxy duty cycle. We identify a master sample of H δ strong (EWH δ > 3Å) post-starburst galaxies from the value-added catalogue in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7) over a redshift range 0.01 < z < 0.1. From this sample we select two E+A subsets, both having a very little [O II] emission (EW_[O II] > -2.5 Å) but one having an additional cut on EWHα (>-3 Å). We examine the differences in observables and AGN fractions to see what effect the H α cut has on the properties of post-starburst galaxies and what these differing samples can tell us about the duty cycle of post-starburst galaxies. We find that H δ strong galaxies peak in the 'blue cloud', E+As in the 'green valley' and pure E+As in the 'red sequence'. We also find that pure E+As have a more early-type morphology and a higher fraction in denser environments compared with the H δ strong and E+A galaxies. These results suggest that there is an evolutionary sequence in the post-starburst phase from blue discy galaxies with residual star formation to passive red early-types.

The SAMI Galaxy Survey: spatially resolving the main sequence of star formation

NASA Astrophysics Data System (ADS)

Medling, Anne M.; Cortese, Luca; Croom, Scott M.; Green, Andrew W.; Groves, Brent; Hampton, Elise; Ho, I.-Ting; Davies, Luke J. M.; Kewley, Lisa J.; Moffett, Amanda J.; Schaefer, Adam L.; Taylor, Edward; Zafar, Tayyaba; Bekki, Kenji; Bland-Hawthorn, Joss; Bloom, Jessica V.; Brough, Sarah; Bryant, Julia J.; Catinella, Barbara; Cecil, Gerald; Colless, Matthew; Couch, Warrick J.; Drinkwater, Michael J.; Driver, Simon P.; Federrath, Christoph; Foster, Caroline; Goldstein, Gregory; Goodwin, Michael; Hopkins, Andrew; Lawrence, J. S.; Leslie, Sarah K.; Lewis, Geraint F.; Lorente, Nuria P. F.; Owers, Matt S.; McDermid, Richard; Richards, Samuel N.; Sharp, Robert; Scott, Nicholas; Sweet, Sarah M.; Taranu, Dan S.; Tescari, Edoardo; Tonini, Chiara; van de Sande, Jesse; Walcher, C. Jakob; Wright, Angus

2018-04-01

We present the ˜800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on H α emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/H β, [N II]/H α, [S II]/H α, and [O I]/H α line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main-sequence population has centrally concentrated star formation similar to late-type galaxies, while galaxies >3σ below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.

Are sdAs helium core stars?

NASA Astrophysics Data System (ADS)

Pelisoli, Ingrid; Kepler, S. O.; Koester, Detlev

2017-12-01

Evolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

Atomic diffusion and mixing in old stars. V. A deeper look into the globular cluster NGC 6752

NASA Astrophysics Data System (ADS)

Gruyters, Pieter; Nordlander, Thomas; Korn, Andreas J.

2014-07-01

Context. Abundance trends in heavier elements with evolutionary phase have been shown to exist in the globular cluster NGC 6752 ([Fe / H] = -1.6). These trends are a result of atomic diffusion and additional (non-convective) mixing. Studying such trends can provide us with important constraints on the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. Aims: Taking advantage of a larger data sample, we investigate the reality and the size of these abundance trends and address questions and potential biases associated with the various stellar populations that make up NGC 6752. Methods: We perform an abundance analysis by combining photometric and spectroscopic data of 194 stars located between the turnoff point and the base of the red giant branch. Stellar parameters are derived from uvby Strömgren photometry. Using the quantitative-spectroscopy package SME, stellar surface abundances for light elements such as Li, Na, Mg, Al, and Si as well as heavier elements such as Ca, Ti, and Fe are derived in an automated way by fitting synthetic spectra to individual lines in the stellar spectra, obtained with the VLT/FLAMES-GIRAFFE spectrograph. Results: Based on uvby Strömgren photometry, we are able to separate three stellar populations in NGC 6752 along the evolutionary sequence from the base of the red giant branch down to the turnoff point. We find weak systematic abundance trends with evolutionary phase for Ca, Ti, and Fe which are best explained by stellar-structure models including atomic diffusion with efficient additional mixing. We derive a new value for the initial lithium abundance of NGC 6752 after correcting for the effect of atomic diffusion and additional mixing which falls slightly below the predicted standard BBN value. Conclusions: We find three stellar populations by combining photometric and spectroscopic data of 194 stars in the globular cluster NGC 6752. Abundance trends for groups of elements, differently affected by atomic diffusion and additional mixing, are identified. Although the statistical significance of the individual trends is weak, they all support the notion that atomic diffusion is operational along the evolutionary sequence of NGC 6752. Based on data collected at the ESO telescopes under programs 079.D-0645(A) and 081.D-0253(A).Full Tables 2 and 8 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/A72

Examining the infrared variable star population discovered in the Small Magellanic Cloud using the SAGE-SMC survey

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

Polsdofer, Elizabeth; Marengo, M.; Seale, J.

2015-02-01

We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program “Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud” (SAGE-SMC) and the “Spitzer Survey of the Small Magellanic Cloud” (S{sup 3}MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer’s InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0 μm bands, and the Multiband Imaging Photometer for Spitzer 24 μm band. Anmore » error-weighted flux difference between each pair of three epochs (“variability index”) is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ∼2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.« less

Dark Star-Making Factory

NASA Image and Video Library

2009-10-02

In this infrared view from the Herschel Observatory, a European Space Agency mission, blue shows the warmest dust, and red, the coolest. The choppy clouds of gas and dust are just starting to condense into new stars.

Condensation onto grains in the outflows from mass-losing red giants

NASA Technical Reports Server (NTRS)

Jura, M.; Morris, M.

1985-01-01

In the outflows from red giants, grains are formed which are driven by radiation pressure. For the development of a model of the outflows, a detailed understanding of the interaction between the gas and dust is critical. The present investigation is concerned with condensation processes which occur after the grains nucleate near the stars. A physical process considered results from the cooling of the grains as they flow away from the star. Molecules which initially do not condense onto the grains can do so far from the star. It is shown that for some species this effect can be quite important in determining their gas-phase abundances in the outer circumstellar envelope. One of the major motivations of this investigation was provided by the desire to understand the physical conditions and molecular abundances in the outflows from the considered stars.

Infrared Studies of the Variability and Mass Loss of Dusty Asymptotic Giant Branch Stars in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Sargent, Benjamin; Groenewegen, M. A. T.

2018-01-01

The asymptotic giant branch (AGB) phase is one of the last phases of a star's life. AGB stars lose mass in an outflow in which dust condenses and is pushed away from the star. Extreme AGB stars are so named because their very red colors suggest very large amounts of dust, which in turn suggests extremely high mass loss rates. AGB stars also vary in brightness, and studies show that extreme AGB stars tend to have longer periods than other AGB stars and are more likely to be fundamental mode pulsators than other AGB stars. Extreme AGB stars are difficult to study, as their colors are so red due to their copious amounts of circumstellar dust that they are often not detected at optical wavelengths. Therefore, they must be observed at infrared wavelengths to explore their variability. Using the Spitzer Space Telescope, my team and I have observed a sample of extreme AGB stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) over Cycles 9 through 12 during the Warm Spitzer mission. For each cycle, we typically observed a set of extreme AGB stars at both 3.6 and 4.5 microns wavelength approximately monthly for most of a year. These observations reveal a wide range of variability properties. I present results from our analysis of the data obtained from these Spitzer variability programs, including light curve analyses and comparison to period-luminosity diagrams. Funding is acknowledged from JPL RSA # 1561703.

An empirical mass-loss law for Population II giants from the Spitzer-IRAC survey of Galactic globular clusters

NASA Astrophysics Data System (ADS)

Origlia, L.; Ferraro, F. R.; Fabbri, S.; Fusi Pecci, F.; Dalessandro, E.; Rich, R. M.; Valenti, E.

2014-04-01

Aims: The main aim of the present work is to derive an empirical mass-loss (ML) law for Population II stars in first and second ascent red giant branches. Methods: We used the Spitzer InfraRed Array Camera (IRAC) photometry obtained in the 3.6-8 μm range of a carefully chosen sample of 15 Galactic globular clusters spanning the entire metallicity range and sampling the vast zoology of horizontal branch (HB) morphologies. We complemented the IRAC photometry with near-infrared data to build suitable color-magnitude and color-color diagrams and identify mass-losing giant stars. Results: We find that while the majority of stars show colors typical of cool giants, some stars show an excess of mid-infrared light that is larger than expected from their photospheric emission and that is plausibly due to dust formation in mass flowing from them. For these stars, we estimate dust and total (gas + dust) ML rates and timescales. We finally calibrate an empirical ML law for Population II red and asymptotic giant branch stars with varying metallicity. We find that at a given red giant branch luminosity only a fraction of the stars are losing mass. From this, we conclude that ML is episodic and is active only a fraction of the time, which we define as the duty cycle. The fraction of mass-losing stars increases by increasing the stellar luminosity and metallicity. The ML rate, as estimated from reasonable assumptions for the gas-to-dust ratio and expansion velocity, depends on metallicity and slowly increases with decreasing metallicity. In contrast, the duty cycle increases with increasing metallicity, with the net result that total ML increases moderately with increasing metallicity, about 0.1 M⊙ every dex in [Fe/H]. For Population II asymptotic giant branch stars, we estimate a total ML of ≤0.1 M⊙, nearly constant with varying metallicity. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.Appendix A is available in electronic form at http://www.aanda.org

A Glimpse of the Milky Way

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Figure 1

In visible light, the bulk of our Milky Way galaxy's stars are eclipsed behind thick clouds of galactic dust and gas. But to the infrared eyes of NASA's Spitzer Space Telescope, distant stars and dust clouds shine with unparalleled clarity and color.

In this panoramic image (center row, fig. 1) from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire project, a plethora of stellar activity in the Milky Way's galactic plane, reaching to the far side of our galaxy, is exposed. This image spans 9 degrees of sky (approximately the width of a fist held out at arm's length).

The red clouds indicate the presence of large organic molecules (mixed with the dust), which have been illuminated by nearby star formation. The patches of black are dense obscuring dust clouds impenetrable by even Spitzer's super-sensitive infrared eyes. Bright arcs of white throughout the image are massive stellar incubators.

With over 160 megapixels, the full detail in this panorama cannot be appreciated without zooming in to various areas of interest (top and bottom rows, fig. 1). Bubbles, or holes, in the red clouds are formed by the powerful outflows from massive groups of forming stars. Wisps of green indicate the presence of hot hydrogen gas. Star clusters can also be seen as the groupings of blue, yellow, and green specks inside some of the red nebulae, or star-forming clouds.

In contrast to the plentiful examples of stellar youth in this montage, Spitzer also sees an object called a planetary nebula (top row, middle, fig. 1). Such nebulae are the final gasp of dying stars like our sun, whose outer layers are blown into space, leaving a burnt out core of a star, called a white dwarf, behind.

Although this panoramic image captures a large range of the galaxy, it represents only 7.5 percent of the primary Glimpse survey, which will image most of the star formation regions in our galaxy.

The infrared images were captured with the Spitzer's infrared array camera. The pictures are 4-channel false-color composites, showing emission from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange), and 8.0 microns (red).

Caution: Images are best resolution available and are very large.

Abundances of the light elements from UV (HST) and red (ESO) spectra in the very old star HD 84937

NASA Astrophysics Data System (ADS)

Spite, M.; Peterson, R. C.; Gallagher, A. J.; Barbuy, B.; Spite, F.

2017-04-01

Aims: In order to provide a better basis for the study of mechanisms of nucleosynthesis of the light elements beyond hydrogen and helium in the oldest stars, the abundances of C, O, Mg, Si, P, S, K, and Ca have been derived from UV-HST and visible-ESO high resolution spectra in the old, very metal-poor star HD 84937, at a metallicity that is 1/200 that of the Sun's. For this halo main-sequence turnoff star, the abundance determination of P and S are the first published determinations. Methods: The LTE profiles of the lines were computed and fitted to the observed spectra. Wherever possible, we compared the abundances derived from the UV spectrum to abundances derived from the visible or near-infrared spectra, and also corrected the derived abundances for non-LTE effects. Three-dimensional (3D) CO5BOLD model atmospheres have been used to determine the abundances of C and O from molecular CH and OH bands. Results: The abundances of these light elements relative to iron in HD 84937 are found to agree well with the abundances of these elements in classical metal-poor stars. Our HD 84937 carbon abundance determination points toward a solar (or mildly enhanced above solar) value of [C/Fe]. The modest overabundance of the α elements of even atomic number Z, typical of halo turnoff stars, is confirmed in this example. The odd-Z element P is found to be somewhat deficient in HD 84937, at [P/Fe] = -0.32, which is again consistent with the handful of existing determinations for turnoff stars of such low metallicity. We show that the abundance of oxygen, deduced from the OH band from 3D computations, is not compatible with the abundance deduced from the red oxygen triplet. This incompatibility is explained by the existence of a chromosphere heating the shallow layers of the atmosphere where the OH band, in 3D computations, is mainly formed. Conclusions: The abundance ratios are compared to the predictions of models of galactic nucleosynthesis and evolution. Based on observations made with the NASA/ESA Hubble Space Telescope obtained under program GO-14161 at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA) and on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere (Archives of programmes 080.D-0347(A), 082.B-0610(A), 266.D-5655(A), and 073.D-0024(A) ).

VizieR Online Data Catalog: Vatican Emission-line stars (Coyne+ 1974-1983)

NASA Astrophysics Data System (ADS)

Coyne, G. V.; Lee, T. A.; de Graeve, E.; Wisniewski, W.; Corbally, C.; Otten, L. B.; MacConnell, D. J.

2009-10-01

The survey represents a search for Hα emission-line stars, and was conducted with a 12{deg} objective prism on the Vatican Schmidt telescope. The Vatican Emission Stars (VES) survey covers the galactic plane (|b|<=5{deg}) between galactic longitudes 58 and 174{deg}. The catalog was re-examined by B. Skiff (Lowell Observatory), and tne VES stars were cross-identified with modern surveys: GSC (Cat. I/255), Tycho-2 (I/256), 2MASS (II/246), IRAS point source catalog (II/125), MSX6C (V/114), CMC14 (I/304), GSC-2.3 (I/305), UCAC2 (I/289). Cross-identifications are also supplied with HD/BD/GCVS names, and with Dearborn catalog of red stars (II/68). Many of the stars in the first four papers are not early-type emission-line stars, but instead M giants, where the sharp TiO bandhead at 6544{AA} was mistaken for H-{alpha} emission on the objective-prism plates. Based on the revision of paper V and a later list prepared by Jack MacConnell, a column identifies the "non H-alpha" stars explicitly. The links with the Dearborn, IRAS, and MSX catalogues help identify the red stars. These and other identifications and comments are given in the remarks at the end of each line, or in longer notes in a separate file, indicated by an asterisk (*) next to the star number. (3 data files).

VizieR Online Data Catalog: Vatican Emission-line stars (Coyne+ 1974-1983)

NASA Astrophysics Data System (ADS)

Coyne, G. V.; Lee, T. A.; de Graeve, E.; Wisniewski, W.; Corbally, C.; Otten, L. B.; MacConnell, D. J.

2008-03-01

The survey represents a search for Hα emission-line stars, and was conducted with a 12{deg} objective prism on the Vatican Schmidt telescope. The Vatican Emission Stars (VES) survey covers the galactic plane (|b|<=5{deg}) between galactic longitudes 58 and 174{deg}. The catalog was re-examined by B. Skiff (Lowell Observatory), and tne VES stars were cross-identified with modern surveys: GSC (Cat. I/255), Tycho-2 (I/256), 2MASS (II/246), IRAS point source catalog (II/125), MSX6C (V/114), CMC14 (I/304), GSC-2.3 (I/305), UCAC2 (I/289). Cross-identifications are also supplied with HD/BD/GCVS names, and with Dearborn catalog of red stars (II/68). Many of the stars in the first four papers are not early-type emission-line stars, but instead M giants, where the sharp TiO bandhead at 6544{AA} was mistaken for H-{alpha} emission on the objective-prism plates. Based on the revision of paper V and a later list prepared by Jack MacConnell, a column identifies the "non H-alpha" stars explicitly. The links with the Dearborn, IRAS, and MSX catalogues help identify the red stars. These and other identifications and comments are given in the remarks at the end of each line, or in longer notes in a separate file, indicated by an asterisk (*) next to the star number. (2 data files).

The Chemical Composition Contrast between M3 and M13 Revisited: New Abundances for 28 Giant Stars in M3

NASA Astrophysics Data System (ADS)

Sneden, Christopher; Kraft, Robert P.; Guhathakurta, Puragra; Peterson, Ruth C.; Fulbright, Jon P.

2004-04-01

We report new chemical abundances of 23 bright red giant members of the globular cluster M3, based on high-resolution (R~45,000) spectra obtained with the Keck I telescope. The observations, which involve the use of multislits in the HIRES Keck I spectrograph, are described in detail. Combining these data with a previously reported small sample of M3 giants obtained with the Lick 3 m telescope, we compare metallicities and [X/Fe] ratios for 28 M3 giants with a 35-star sample in the similar-metallicity cluster M13, and with Galactic halo field stars having [Fe/H]<-1. For elements having atomic number A>=A(Si), we derive little difference in [X/Fe] ratios in the M3, M13, or halo field samples. All three groups exhibit C depletion with advancing evolutionary state beginning at the level of the red giant branch ``bump,'' but the overall depletion of about 0.7-0.9 dex seen in the clusters is larger than that associated with the field stars. The behaviors of O, Na, Mg, and Al are distinctively different among the three stellar samples. Field halo giants and subdwarfs have a positive correlation of Na with Mg, as predicted from explosive or hydrostatic carbon burning in Type II supernova sites. Both M3 and M13 show evidence of high-temperature proton-capture synthesis from the ON, NeNa, and MgAl cycles, while there is no evidence for such synthesis among halo field stars. But the degree of such extreme proton-capture synthesis in M3 is smaller than it is in M13: the M3 giants exhibit only modest deficiencies of O and corresponding enhancements of Na, less extreme overabundances of Al, fewer stars with low Mg and correspondingly high Na, and no indication that O depletions are a function of advancing evolutionary state, as has been claimed for M13. We have also considered NGC 6752, for which Mg isotopic abundances have been reported by Yong et al. Giants in NGC 6752 and M13 satisfy the same anticorrelation of O abundances with the ratio (25Mg+26Mg)/24Mg, which measures the relative contribution of rare to abundant isotopes of Mg. This points to a scenario in which these abundance ratios arose in the ejected material of 3-6 Msolar cluster stars, material that was then used to form the atmospheres of the presently evolving low-mass cluster stars. It also suggests that the low oxygen abundance seen among the most evolved M13 giants arose in hot bottom O-to-N processing in these same intermediate-mass cluster stars. Thus, mixing is required by the dependence of some abundance ratios on luminosity, but an earlier nucleosynthesis process in a hotter environment than giants or main-sequence stars is required by the variations previously seen in stars near the main sequence. The nature and the site of the earlier process is constrained but not pinpointed by the observed Mg isotopic ratio. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Reconciling mass functions with the star-forming main sequence via mergers

NASA Astrophysics Data System (ADS)

Steinhardt, Charles L.; Yurk, Dominic; Capak, Peter

2017-06-01

We combine star formation along the 'main sequence', quiescence and clustering and merging to produce an empirical model for the evolution of individual galaxies. Main-sequence star formation alone would significantly steepen the stellar mass function towards low redshift, in sharp conflict with observation. However, a combination of star formation and merging produces a consistent result for correct choice of the merger rate function. As a result, we are motivated to propose a model in which hierarchical merging is disconnected from environmentally independent star formation. This model can be tested via correlation functions and would produce new constraints on clustering and merging.

Two New Super Li-rich Core He-burning Giants: A New Twist to the Long Tale of Li Enhancement in K Giants

NASA Astrophysics Data System (ADS)

Bharat Kumar, Yerra; Singh, Raghubar; Eswar Reddy, B.; Zhao, Gang

2018-05-01

In this Letter we report two new super Li-rich K giants, KIC2305930 and KIC12645107, with Li abundances exceeding that of the interstellar medium (ISM; A(Li) ≥ 3.2 dex). Importantly, both of the giants have been classified as core He-burning red clump (RC) stars based on asteroseismic data from Kepler mission. Also, both of the stars are found to be low mass (M ≈ 1.0 M ⊙), which, together with an evidence of their evolutionary status of being RC stars, implies that the stars have gone through both the luminosity bump and He-flash during their red giant branch (RGB) evolution. The stars’ large Li abundance and evolutionary phase suggest that Li enrichment occurred very recently, probably at the tip of the RGB either during He-flash, an immediate preceding event on the RGB, or by some kind of external event such as merger of an RGB star with white dwarf. The findings will provide critical constraints to theoretical models for understanding of Li enhancement origin in RGB stars.

Far-infrared data for symbiotic stars. II - The IRAS survey observations

NASA Technical Reports Server (NTRS)

Kenyon, S. J.; Fernandez-Castro, T.; Stencel, R. E.

1988-01-01

IRAS survey data for all known symbiotic binaries are reported. S type systems have 25 micron excesses much larger than those of single red giant stars, suggesting that these objects lose mass more rapidly than do normal giants. D type objects have far-IR colors similar to those of Mira variables, implying mass-loss rate of about 10 to the -6th solar masses/yr. The near-IR extinctions of the D types indicate that their Mira components are enshrouded in optically thick dust shells, while their hot companions lie outside the shells. If this interpretation of the data is correct, then the very red near-IR colors of D type symbiotic stars are caused by extreme amounts of dust absorption rather than dust emission. The small group of D prime objects possesses far-IR colors resembling those of compact planetary nebulae or extreme OH/IR stars. It is speculated that these binaries are not symbiotic stars at all, but contain a hot compact star and an exasymptotic branch giant which is in the process of ejecting a planetary nebula shell.

Red Star Ruby (Sunrise) and blond qualities of Jaffa grapefruits and their influence on plasma lipid levels and plasma antioxidant activity in rats fed with cholesterol-containing and cholesterol-free diets.

PubMed

Gorinstein, Shela; Leontowicz, Hanna; Leontowicz, Maria; Drzewiecki, Jerzy; Jastrzebski, Zenon; Tapia, María S; Katrich, Elena; Trakhtenberg, Simon

2005-09-23

Bioactive compounds of peels and peeled red Star Ruby (Sunrise) and blond qualities of Jaffa grapefruits were analyzed and their antioxidant potential was assessed. The dietary fibers were determined according to Prosky et al., the total polyphenol content by Folin-Ciocalteu method and measured at 765 nm, minerals and trace elements by atomic absorption spectrometer, phenolic and ascorbic acids by HPLC and the antioxidant potential by two different antioxidant assays (DPPH and beta-carotene linoleate model system). It was found that the contents of most studied bioactive compounds in both qualities are comparable. Only the contents of total polyphenols and flavonoids were higher in red grapefruits, but not significant. The antioxidant potentials of red peeled grapefruits and their peels were significantly higher than of blond peeled grapefruits and their peels (P<0.05 in both cases). Diets supplemented with peeled red and blond qualities of Jaffa grapefruits and their peels have increased the plasma antioxidant capacity and improved plasma lipid levels, especially in rats fed with cholesterol added diet. In conclusion, both qualities of Jaffa grapefruits contain high quantities of bioactive compounds, but the antioxidant potential of red grapefruits is significantly higher. Diets supplemented with both qualities of Jaffa grapefruits improve the plasma lipid levels and increase the plasma antioxidant activity, especially in rats fed with cholesterol added diets. Jaffa grapefruits, especially their red Star Ruby quality, could be a valuable supplementation for diseases-preventing diets.

Big Black Holes Mean Bad News for Stars (diagram)

NASA Technical Reports Server (NTRS)

2006-01-01

[figure removed for brevity, see original site] Poster Version Suppression of Star Formation from Supermassive Black Holes

This diagram illustrates research from NASA's Galaxy Evolution Explorer showing that black holes -- once they reach a critical size -- can put the brakes on new star formation in elliptical galaxies.

In this graph, galaxies and their supermassive black holes are indicated by the drawings (the black circle at the center of each galaxy represents the black hole). The relative masses of the galaxies and their black holes are reflected in the sizes of the drawings. Blue indicates that the galaxy has new stars, while red means the galaxy does not have any detectable new stars.

The Galaxy Evolution Explorer observed the following trend: the biggest galaxies and black holes (shown in upper right corner) are more likely to have no observable star formation (red) than the smaller galaxies with smaller black holes. This is evidence that black holes can create environments unsuitable for stellar birth.

The white line in the diagram illustrates that, for any galaxy no matter what the mass, its black hole must reach a critical size before it can shut down star formation.

The red/infrared evolution in galaxies - Effect of the stars on the asymptotic giant branch

NASA Technical Reports Server (NTRS)

Chokshi, Arati; Wright, Edward L.

1987-01-01

The effect of including the asymptotic giant branch (AGB) population in a spectral synthesis model of galaxy evolution is examined. Stars on the AGB are luminous enough and also evolve rapidly enough to affect the evolution of red and infrared colors in galaxies. The validity of using infrared colors as distance indicators to galaxies is then investigated in detail. It is found that for z of 1 or less infrared colors of model galaxies behave linearly with redshift.

Soviet News and Propaganda Analysis Based on RED STAR (The Official Newspaper of the Soviet Defense Establishment) for the Period 1-30 November 1982. Volume 2, Number 11, 1982.

DTIC Science & Technology

1982-01-01

massive propaganda war, based on lies. Patriotic Lebanese attack Israeli forces. • Israelis increase repression and terror against Lebanese. - For...e Israelis increase repression and terror against Lebanese. An analysis of the amount of space by topicp devoted to articles about Israel and Lebanon...Israeli repressions/ terror .............. 21% (4) United States aid/interactions .......... 4% 100% *Represents percent of space in Red Star for Israel

A Spectroscopic Survey of Field Red Horizontal-branch Stars

NASA Astrophysics Data System (ADS)

Afşar, Melike; Bozkurt, Zeynep; Böcek Topcu, Gamze; Casetti-Dinescu, Dana I.; Sneden, Christopher; Şehitog̅lu, Gizem

2018-06-01

A metallicity, chemical composition, and kinematic survey has been conducted for a sample of 340 candidate field red horizontal-branch (RHB) stars. Spectra with high resolution and high signal-to-noise ratio were gathered with the McDonald Observatory 2.7 m Tull and the Hobby–Eberly Telescope echelle spectrographs, and were used to determine effective temperatures, surface gravities, microturbulent velocities, [Fe/H] metallicities, and abundance ratios [X/Fe] for seven α and Fe-group species. The derived temperatures and gravities confirm that at least half of the candidates are true RHB stars, with (average) parameters T eff ∼ 5000 K and log g ∼ 2.5. From the α abundances alone, the thin and thick Galactic populations are apparent in our sample. Space motions for 90% of the program stars were computed from Hipparcos and Gaia parallaxes and proper motions. Correlations between chemical compositions and Galactic kinematics clearly indicate the existence of both thin-disk and thick-disk RHB stars.

Induced nucleation of carbon dust in red giant stars

NASA Technical Reports Server (NTRS)

Cadwell, Brian J.; Wang, Hai; Feigelson, Eric D.; Frenklach, Michael

1994-01-01

This study quantitatively tests the proposed model of induced nucleation of carbonaceous grains in carbon-rich red giant stars. Induced nucleation is the process of grain growth initiated by the presence of reactive surfaces provided by seed particles. The numerical study was performed using a deailed chemical kinetic model of carbon deposition, grain coagulation, and homogeneous nucleation of polycyclic aromatic hydrocarbons (PAHs). The model uses a method of moments to keep track of developing grain population in the forming dust shell. We test the efficiency of grain formation for large ranges of dust shell parameters typical for carbon stars. Our model is capable of producing a range of optically thick and thin dust shells in carbon stars. Results are in accord with (IRAS) spectral classes of carbon stars. The resulting composite grains produced are consistent with those recently found in ancient meteorites. This model also provides a realistic explanation for high abundances of (PAHs) in the interstellar medium and some planetary nebulae.

Spitzer-IRS Spectroscopic Studies of Oxygen-Rich Asymptotic Giant Branch Star and Red Supergiant Star Dust Properties

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, Sundar; Speck, Angela; Volk, Kevin; Kemper, Ciska; Reach, William T.; Lagadec, Eric; Bernard, Jean-Philippe; McDonald, Iain; Meixner, Margaret

2015-01-01

We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of Oxygen-rich (O-rich) asymptotic giant branch (AGB) and red supergiant (RSG) stars. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper) and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We present an update of our investigation of differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

Unexplained Cases of Allergic Reactions Linked to Red Meat

MedlinePlus

... that starts after being bitten by a lone star tick may cause unexplained cases of recurrent anaphylaxis. ... after eating meat. Previous studies have linked lone star tick bites to this unusual food allergy. The ...

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Star formation history of passive red galaxies

NASA Astrophysics Data System (ADS)

Siudek, M.; Małek, K.; Scodeggio, M.; Garilli, B.; Pollo, A.; Haines, C. P.; Fritz, A.; Bolzonella, M.; de la Torre, S.; Granett, B. R.; Guzzo, L.; Abbas, U.; Adami, C.; Bottini, D.; Cappi, A.; Cucciati, O.; De Lucia, G.; Davidzon, I.; Franzetti, P.; Iovino, A.; Krywult, J.; Le Brun, V.; Le Fèvre, O.; Maccagni, D.; Marchetti, A.; Marulli, F.; Polletta, M.; Tasca, L. A. M.; Tojeiro, R.; Vergani, D.; Zanichelli, A.; Arnouts, S.; Bel, J.; Branchini, E.; Ilbert, O.; Gargiulo, A.; Moscardini, L.; Takeuchi, T. T.; Zamorani, G.

2017-01-01

Aims: We trace the evolution and the star formation history of passive red galaxies, using a subset of the VIMOS Public Extragalactic Redshift Survey (VIPERS). The detailed spectral analysis of stellar populations of intermediate-redshift passive red galaxies allows the build up of their stellar content to be followed over the last 8 billion years. Methods: We extracted a sample of passive red galaxies in the redshift range 0.4

The accelerated build-up of the red sequence in high-redshift galaxy clusters

NASA Astrophysics Data System (ADS)

Cerulo, P.; Couch, W. J.; Lidman, C.; Demarco, R.; Huertas-Company, M.; Mei, S.; Sánchez-Janssen, R.; Barrientos, L. F.; Muñoz, R. P.

2016-04-01

We analyse the evolution of the red sequence in a sample of galaxy clusters at redshifts 0.8 < z < 1.5 taken from the HAWK-I Cluster Survey (HCS). The comparison with the low-redshift (0.04 < z < 0.08) sample of the WIde-field Nearby Galaxy-cluster Survey (WINGS) and other literature results shows that the slope and intrinsic scatter of the cluster red sequence have undergone little evolution since z = 1.5. We find that the luminous-to-faint ratio and the slope of the faint end of the luminosity distribution of the HCS red sequence are consistent with those measured in WINGS, implying that there is no deficit of red galaxies at magnitudes fainter than M_V^{ast } at high redshifts. We find that the most massive HCS clusters host a population of bright red sequence galaxies at MV < -22.0 mag, which are not observed in low-mass clusters. Interestingly, we also note the presence of a population of very bright (MV < -23.0 mag) and massive (log (M*/M⊙) > 11.5) red sequence galaxies in the WINGS clusters, which do not include only the brightest cluster galaxies and which are not present in the HCS clusters, suggesting that they formed at epochs later than z = 0.8. The comparison with the luminosity distribution of a sample of passive red sequence galaxies drawn from the COSMOS/UltraVISTA field in the photometric redshift range 0.8 < zphot < 1.5 shows that the red sequence in clusters is more developed at the faint end, suggesting that halo mass plays an important role in setting the time-scales for the build-up of the red sequence.