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Sample records for main sequence mass

  1. The Star-Forming Main Sequence at Low Galaxy Mass

    NASA Astrophysics Data System (ADS)

    Stierwalt, Sabrina; Johnson, Kelsey E.; Patton, David R.; Besla, Gurtina; Kallivayalil, Nitya; Liss, Sandra; Pearson, Sarah; Privon, George C.; Putman, Mary E.

    2017-01-01

    We present an investigation of the star-forming main sequence at the low mass end. The relation between galaxy stellar mass and star formation rate has been well-studied in the recent literature for a range of redshifts and galaxy type, but almost all of these studies are limited to galaxies with stellar masses above the dwarf galaxy range ( 109 Msun ). Our work, based on the panchromatic TiNy Titans survey of interacting dwarf galaxies, shows that dwarf galaxies extend the well-established main sequence at z=0 down to lower masses. Furthermore, like their more massive counterparts, dwarf mergers appear on an elevated main sequence with higher star formation rates for a given stellar mass. Finally we show that star formation is enhanced to a greater extent in low mass galaxy mergers than for higher mass systems.

  2. Main sequence mass loss and the ages of stars

    NASA Technical Reports Server (NTRS)

    Willson, L. A.

    1989-01-01

    The potentially observable consequences of the pulsation/rotation-induced mass loss from main-sequence A and F stars proposed by Willson et al. (1987) are discussed, reviewing the results of recent investigations. Particular attention is given to (1) evidence for a deficiency in A stars and an excess of F and G stars, as predicted by the theory, (2) cluster HR diagrams and age estimates, and (3) modifications to standard models of solar-system evolution. It is pointed out that the time scales and mass-loss rates required to explain the observed properties of clusters and field stars in this theory are the same as those needed to account for the early development of the solar system.

  3. Dust discs around low-mass main-sequence stars

    NASA Technical Reports Server (NTRS)

    Wolstencroft, R. D.; Walker, Helen J.

    1988-01-01

    The current understanding of the formation of circumstellar disks as a natural accompaniment to the process of low-mass star formation is examined. Models of the thermal emission from the dust disks around the prototype stars Alpha Lyr, Alpha PsA, Beta Pic, and Epsilon Eri are discussed, which indicate that the central regions of three of these disks are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest zone lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud which sweeps up grains crossing its orbit.

  4. Effects of main-sequence mass loss on the turnoff ages of population 1 clusters

    NASA Astrophysics Data System (ADS)

    Guzik, Joyce A.

    Willson, Bowen, and Struck-Marcell have proposed that stars of spectral types A through early-G lose a significant portion of their mass during the early main-sequence phase. The proposed mass loss is driven by pulsation, and facilitated by rapid rotation. One implication of this hypothesis is that the main-sequence turnoff is an invalid indicator of cluster age, as present turnoff stars may have had higher projenitor masses; hence clusters appear older than they actually are. This paper presents examples of cluster HR diagrams synthesized with mass-losing stars of solar metallicity, initial masses 1-2 M, and exponentially-decreasing mass-loss rates with e-folding times 1 to 2 Gyr. The increases in apparent turnoff age of Pop. I clusters, and the potential of the hypothesis to account for blue stragglers as normal stars that have not lost mass (or lost mass more slowly) are discussed.

  5. Mass-loss through the L2 Lagrange point - application to main-sequence EMRI

    NASA Astrophysics Data System (ADS)

    Linial, Itai; Sari, Re'em

    2017-08-01

    We consider stable mass transfer from the secondary to the primary of an extreme mass ratio binary system. We show that when the mass transfer is sufficiently fast, mass leakage occurs through the outer Lagrange point L2, in addition to the usual transfer through L1. We provide an analytical estimate for the mass leakage rate through L2 and find the conditions in which it is comparable to the mass transfer rate through L1. Focusing on a binary system of a main-sequence star and a supermassive black hole, driven by the emission of gravitational radiation, we show that it may sustain stable mass transfer, along with mass-loss through L2. If such a mass transferring system occurs at our Galactic Centre, it produces a gravitational wave signal detectable by future detectors, such as Laser Interferometer Space Antenna (LISA). The signal evolves according to the star's adiabatic index and cooling time. For low-mass stars, the evolution is faster than the Kelvin-Helmholtz cooling rate driving the star out of the main-sequence. In some cases, the frequency and amplitude of the signal may both decrease with time, contrary to the standard chirp of a coalescing binary. Mass-loss through L2, when occurs, decreases the evolution time-scale of the emitted gravitational wave signal by up to a few tens of per cent. We conclude that L2 mass ejection is a crucial factor in analysing gravitational waves signals produced by such systems.

  6. Masses of Pre-Main Sequence Binary Stars-Part 2

    NASA Astrophysics Data System (ADS)

    Simon, Michal

    1991-07-01

    There are still no pre-main sequence stars with reliably known masses. This represents a serious gap in our understanding of low-mass star formation. The goal of this long-term program is to measure the masses of pre-main sequence binaries selected from our survey (ref. 3) of the Taurus star forming region by IR lunar occultation and imaging. We propose to use the Fine Guide Sensors in the Transfer Function Mode to determine the apparent orbits of the binaries. Since the distance to the region is known, the apparent orbits will yield the total masses of the binaries. THIS PROPOSAL CONTAINS ONE FOLLOW-UP VISIT TO HV-TAU-C ONLY. THE REST OF THE EXPOSURES ARE IN 3842.

  7. The faintest stars - The luminosity and mass functions at the bottom of the main sequence

    NASA Technical Reports Server (NTRS)

    Tinney, Christopher G.

    1993-01-01

    We present IR K-band photometry of complete samples of VLM candidates constructed from IIIaF and IVN plates in 10 fields taken as part of the POSSII and UKSRC surveys. Using the I-K colors constructed for these stars we estimate a bolometric luminosity function which extends to M(Bol) = 13.75. We find significant evidence for a luminosity function decreasing toward these luminosities. We also find that our results are consistent with those of studies based on the Nearby Star sample, when those data are presented as a bolometric luminosity function. We convert our observed luminosity function into a mass function, which extends with reasonable statistics to 0.08 solar masses - the H-burning minimum mass. We find significant evidence for features in the mass function at these masses. Specifically, the mass function 'turns over' at 0.25 solar mass, goes through a local minimum at about 0.15 solar mass, and may increase again below 0.1 solar mass - none of these features are predicted by any of the current theories of star formation. Lastly, the mass density we observe just above the H-burning minimum mass makes it difficult to envisage brown dwarfs contributing significant quantities of missing mass without invoking either a mass function in this region significantly steeper than that seen for main-sequence stars, or an extremely low cutoff mass to the mass function.

  8. 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.

  9. Effects of main-sequence mass loss on the turnoff ages of globular clusters

    SciTech Connect

    Guzik, J.A.

    1989-01-01

    Willson, Bowen, and Struck-Marcell have proposed that globular cluster main-sequence turnoff ages can be reconciled with the lower ages of the Galaxy and universe deduced from other methods by incorporating an epoch of early main-sequence mass-loss by stars of spectral types A through early-F. The proposed mass loss is pulsation-driven, and facilitated by rapid rotation. This paper presents stellar evolution calculations of Pop. II (Z = 0.001) mass-losing stars of initial mass 0.8 to 1.6 M/sub /circle dot//, with exponentially-decreasing mass loss rates of e-folding times 0.5 to 2.0 Gyr, evolving to a final mass of 0.7 M/sub /circle dot//. The calculations indicate that a globular cluster with apparent turnoff age 18 Gyr could have an actual age as low as /approximately/12 Gyr. Observational implications that may help to verify the hypothesis, e.g. low C/N abundance ratios among red giants following first dredge-up, blue stragglers, red giant deficiencies, and signatures in cluster mass/luminosity functions, are also discussed.25 refs., 4 figs., 3 tabs.

  10. Uncertainties in the Determination of the Upper Mass Limit for Zero-Age Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Klapp, J.; Langer, N.; Fricke, K. J.

    1987-05-01

    In a recent investigation Klapp et al. 1987 obtained a critical nass of 440 M@ for the overstability of very massive extreme population I stars at the main sequence. In this work we investigate the dependence of Klapp et al. 1987 results upon the program input physics. We find that stars in the 100 - 500 Me range are marginally stable (or unstable) and that this mass range should be considered as a transition region from stability to overstability of very massive stars.

  11. The coronal temperatures of low-mass main-sequence stars

    NASA Astrophysics Data System (ADS)

    Johnstone, C. P.; Güdel, M.

    2015-06-01

    Aims: We study the X-ray emission of low-mass main-sequence stars to derive a reliable general scaling law between coronal temperature and the level of X-ray activity. Methods: We collect ROSAT measurements of hardness ratios and X-ray luminosities for a large sample of stars to derive which stellar X-ray emission parameter is most closely correlated with coronal temperature. We calculate average coronal temperatures for a sample of 24 low-mass main-sequence stars with measured emission measure distributions (EMDs) collected from the literature. These EMDs are based on high-resolution X-ray spectra measured by XMM-Newton and Chandra. Results: We confirm that there is one universal scaling relation between coronal average temperature and surface X-ray flux, FX, that applies to all low-mass main-sequence stars. We find that coronal temperature is related to FX by T̅cor = 0.11 FX0.26, where T̅cor is in MK and FX is in erg s-1 cm-2.

  12. BEYOND THE MAIN SEQUENCE: TESTING THE ACCURACY OF STELLAR MASSES PREDICTED BY THE PARSEC EVOLUTIONARY TRACKS

    SciTech Connect

    Ghezzi, Luan; Johnson, John Asher

    2015-10-20

    Characterizing the physical properties of exoplanets and understanding their formation and orbital evolution requires precise and accurate knowledge of their host stars. Accurately measuring stellar masses is particularly important because they likely influence planet occurrence and the architectures of planetary systems. Single main-sequence stars typically have masses estimated from evolutionary tracks, which generally provide accurate results due to their extensive empirical calibration. However, the validity of this method for subgiants and giants has been called into question by recent studies, with suggestions that the masses of these evolved stars could have been overestimated. We investigate these concerns using a sample of 59 benchmark evolved stars with model-independent masses (from binary systems or asteroseismology) obtained from the literature. We find very good agreement between these benchmark masses and the ones estimated using evolutionary tracks. The average fractional difference in the mass interval ∼0.7–4.5 M{sub ⊙} is consistent with zero (−1.30 ± 2.42%), with no significant trends in the residuals relative to the input parameters. A good agreement between model-dependent and -independent radii (−4.81 ± 1.32%) and surface gravities (0.71 ± 0.51%) is also found. The consistency between independently determined ages for members of binary systems adds further support for the accuracy of the method employed to derive the stellar masses. Taken together, our results indicate that determination of masses of evolved stars using grids of evolutionary tracks is not significantly affected by systematic errors, and is thus valid for estimating the masses of isolated stars beyond the main sequence.

  13. The Solar Neighborhood. XXXVII: The Mass-Luminosity Relation for Main-sequence M Dwarfs

    NASA Astrophysics Data System (ADS)

    Benedict, G. F.; Henry, T. J.; Franz, O. G.; McArthur, B. E.; Wasserman, L. H.; Jao, Wei-Chun; Cargile, P. A.; Dieterich, S. B.; Bradley, A. J.; Nelan, E. P.; Whipple, A. L.

    2016-11-01

    We present a mass-luminosity relation (MLR) for red dwarfs spanning a range of masses from 0.62 {{ M }}⊙ to the end of the stellar main sequence at 0.08 {{ M }}⊙ . The relation is based on 47 stars for which dynamical masses have been determined, primarily using astrometric data from Fine Guidance Sensors (FGS) 3 and 1r, white-light interferometers on the Hubble Space Telescope (HST), and radial velocity data from McDonald Observatory. For our HST/FGS sample of 15 binaries, component mass errors range from 0.4% to 4.0% with a median error of 1.8%. With these and masses from other sources, we construct a V-band MLR for the lower main sequence with 47 stars and a K-band MLR with 45 stars with fit residuals half of those of the V band. We use GJ 831 AB as an example, obtaining an absolute trigonometric parallax, π abs = 125.3 ± 0.3 mas, with orbital elements yielding {{ M }}{{A}}=0.270+/- 0.004 {{ M }}⊙ and {{ M }}{{B}}=0.145+/- 0.002 {{ M }}⊙ . The mass precision rivals that derived for eclipsing binaries. A remaining major task is the interpretation of the intrinsic cosmic scatter in the observed MLR for low-mass stars in terms of physical effects. In the meantime, useful mass values can be estimated from the MLR for the ubiquitous red dwarfs that account for 75% of all stars, with applications ranging from the characterization of exoplanet host stars to the contribution of red dwarfs to the mass of the universe. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  14. X-ray Emission Properties of Intermediate-Mass, Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Povich, Matthew S.; Binder, Breanna; Townsley, Leisa K.; Broos, Patrick S.

    2017-08-01

    Intermediate-mass (2-8 M⊙) main-sequence stars with A to mid-B spectral types occupy an X-ray "desert" of weak intrinsic emission between low- and high-mass stars. Lacking the wind-shock driven emission of massive, O and early B stars or the convectively-driven magnetic reconnection flaring activity of later-type stars, X-ray detections of (non-peculiar) main-sequence AB stars are typically ascribed to the presence of unresolved, lower-mass binary companions. There is mounting evidence, however, that intermediate-mass, pre-main sequence stars (IMPS) with GK spectral types produce intrinsic X-ray emission that rapidly decays with time following the development of a radiative zone as IMPS approach the ZAMS as AB stars. This suggests that X-ray emission from IMPS may be a more luminous analog of the well-studied coronal X-ray emission from lower-mass, T Tauri stars. Statistical studies of young IMPS have been hampered by their scarcety in nearby, unobscured star-forming regions. We present the first results from a spectral-fitting study to measure absorption-corrected X-ray luminosities and plasma temperatures for hundreds of candidate X-ray emitting IMPS found in the MYStIX and MAGiX surveys of massive Galactic star forming regions. Candidate IMPS are placed on the HR diagram via a novel infrared spectral energy distribution modeling technique designed for highly-obscured, young massive star-forming regions. The rapid decay of X-ray emission from these objects has the potential to provide an independent chronometer to constrain star formation rates, and may produce an age-dependent bias in the relationship between the stellar X-ray luminosity function and mass function in distant (>2 kpc) regions observed with relatively shallow X-ray observations.This work is supported by the National Science Foundation under grant CAREER-1454334 and by NASA through Chandra Award 18200040.

  15. The Impact of Starspots on Mass and Age Estimates for Pre-main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Somers, Garrett; Pinsonneault, Marc H.

    2016-01-01

    We investigate the impact of starspots on the evolution of late-type stars during the pre-main sequence (pre-MS). We find that heavy spot coverage increases the radii of stars by 4-10%, consistent with inflation factors in eclipsing binary systems, and suppresses the rate of pre-MS lithium depletion, leading to a dispersion in zero-age MS Li abundance (comparable to observed spreads) if a range of spot properties exist within clusters from 3-10 Myr. This concordance with data implies that spots induce a range of radii at fixed mass during the pre-MS. These spots decrease the luminosity and T eff of stars, leading to a displacement on the HR diagram. This displacement causes isochrone derived masses and ages to be systematically under-estimated, and can lead to the spurious appearance of an age spread in a co-eval population.

  16. Mass functions for globular cluster main sequences based on CCD photometry and stellar models

    NASA Astrophysics Data System (ADS)

    McClure, Robert D.; Vandenberg, Don A.; Smith, Graeme H.; Fahlman, Gregory G.; Richer, Harvey B.; Hesser, James E.; Harris, William E.; Stetson, Peter B.; Bell, R. A.

    1986-08-01

    Main-sequence luminosity functions constructed from CCD observations of globular clusters reveal a strong trend in slope with metal abundance. Theoretical luminosity functions constructed from VandenBerg and Bell's (1985) isochrones have been fitted to the observations and reveal a trend between x, the power-law index of the mass function, and metal abundance. The most metal-poor clusters require an index of about x = 2.5, whereas the most metal-rich clusters exhibit an index of x of roughly -0.5. The luminosity functions for two sparse clusters, E3 and Pal 5, are distinct from those of the more massive clusters, in that they show a turndown which is possibly a result of mass loss or tidal disruption.

  17. Low-Mass Pre-Main-Sequence Stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios A.

    2012-09-01

    The stellar Initial Mass Function (IMF) suggests that stars with sub-solar mass form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming regions. The low-mass stars in such regions are still in their pre-main-sequence (PMS) evolutionary phase, i.e., they have not started their lives on the main-sequence yet. The peculiar nature of these objects and the contamination of their samples by the fore- and background evolved populations of the Galactic disk impose demanding observational techniques, such as X-ray surveying and optical spectroscopy of large samples for the detection of complete numbers of PMS stars in the Milky Way. The Magellanic Clouds, the metal-poor companion galaxies to our own, demonstrate an exceptional star formation activity. The low extinction and stellar field contamination in star-forming regions of these galaxies imply a more efficient detection of low-mass PMS stars than in the Milky Way, but their distance from us make the application of the above techniques unfeasible. Nonetheless, imaging with the Hubble Space Telescope within the last five years yield the discovery of solar and sub-solar PMS stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of such objects are identified as the low-mass stellar content of star-forming regions in these galaxies, changing completely our picture of young stellar systems outside the Milky Way, and extending the extragalactic stellar IMF below the persisting threshold of a few solar masses. This review presents the recent developments in the investigation of the PMS stellar content of the Magellanic Clouds, with special focus on the limitations by single-epoch photometry that can only be circumvented by the detailed study of the observable behavior of these stars in the color-magnitude diagram. The achieved characterization of the low-mass PMS stars in the

  18. Extended main sequence turn-offs in low mass intermediate-age clusters

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Bastian, Nate

    2016-05-01

    We present an imaging analysis of four low mass stellar clusters (≲5000 M⊙) in the outer regions of the LMC in order to shed light on the extended main sequence turn-off (eMSTO) phenomenon observed in high mass clusters. The four clusters have ages between 1-2 Gyr and two of them appear to host eMTSOs. The discovery of eMSTOs in such low mass clusters - more than 5 times less massive than the eMSTO clusters previously studied - suggests that mass is not the controlling factor in whether clusters host eMSTOs. Additionally, the narrow extent of the eMSTO in the two older clusters (~2 Gyr) is in agreement with predictions of the stellar rotation scenario, as lower mass stars are expected to be magnetically braked, meaning that their colour magnitude diagrams should be better reproduced by canonical simple stellar populations. We also performed a structural analysis on all the clusters and found that a large core radius is not a requisite for a cluster to exhibit an eMSTO. Full Table 2, and Tables 3-5 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A50

  19. Luminosity and mass functions of the three main sequences of the globular cluster NGC 2808

    NASA Astrophysics Data System (ADS)

    Milone, A. P.; Piotto, G.; Bedin, L. R.; Cassisi, S.; Anderson, J.; Marino, A. F.; Pietrinferni, A.; Aparicio, A.

    2012-01-01

    High-precision HST photometry has revealed that the globular cluster (GC) NGC 2808 hosts a triple main sequence (MS) corresponding to three stellar populations with different helium abundances. We carried out photometry on ACS/WFC HST images of NGC 2808 with the main purpose of measuring the luminosity function (LF) of stars in the three different MSs, and the binary fraction in the cluster. We used isochrones to transform the observed LFs into mass functions (MFs). We estimate that the fraction of binary systems in NGC 2808 is fbin ≃ 0.05, and find that the three MSs have very similar LFs. The slopes of the corresponding MFs are α = -1.2 ± 0.3 for the red MS, α = -0.9 ± 0.3 for the middle MS, and α = -0.9 ± 0.4 for the blue one, the same, to within the errors. There is marginal evidence of a MF flattening for masses ℳ ≤ 0.6ℳ⊙ for the the reddest (primordial) MS. These results represent the first direct measurement of the present-day MF and LF in distinct stellar populations of a GC, and provide constraints on models of the formation and evolution of multiple generations of stars in these objects. 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, under the programs GO-9899 and GO-10922.Appendices are available in electronic form at http://www.aanda.org

  20. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    SciTech Connect

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F.; SchottelKotte, James; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-06-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M {sub ⊕} and 5 M {sub ⊕}. Assuming H{sub 2}O-(inner HZ) and CO{sub 2}-(outer HZ) dominated atmospheres, and scaling the background N{sub 2} atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H{sub 2}O column depth. For larger planets, the H{sub 2}O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  1. Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass

    NASA Technical Reports Server (NTRS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kotte, James Schottel; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1M and 5M. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (approx.10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing long-wave radiation. Hence the inner edge moves inward (approx.7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  2. Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass

    NASA Technical Reports Server (NTRS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kotte, James Schottel; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1M and 5M. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (approx.10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing long-wave radiation. Hence the inner edge moves inward (approx.7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  3. Standard pre-main sequence models of low-mass stars

    SciTech Connect

    Prada Moroni, P. G.; Degl'Innocenti, S.; Tognelli, E.

    2014-05-09

    The main characteristics of standard pre-main sequence (PMS) models are described. A discussion of the uncer-tainties affecting the current generation of PMS evolutionary tracks and isochrones is also provided. In particular, the impact of the uncertainties in the adopted equation of state, radiative opacity, nuclear cross sections, and initial chemical abundances are analysed.

  4. A theoretical study of acoustic glitches in low-mass main-sequence stars

    SciTech Connect

    Verma, Kuldeep; Antia, H. M.; Basu, Sarbani; Mazumdar, Anwesh E-mail: antia@tifr.res.in E-mail: anwesh@tifr.res.in

    2014-10-20

    There are regions in stars, such as ionization zones and the interface between radiative and convective regions, that cause a localized sharp variation in the sound speed. These are known as 'acoustic glitches'. Acoustic glitches leave their signatures on the oscillation frequencies of stars, and hence these signatures can be used as diagnostics of these regions. In particular, the signatures of these glitches can be used as diagnostics for the position of the second helium ionization zone and that of the base of the envelope convection zone. With the help of stellar models, we study the properties of these acoustic glitches in main-sequence stars. We find that the acoustic glitch due to the helium ionization zone does not correspond to the dip in the adiabatic index Γ{sub 1} caused by the ionization of He II, but to the peak in Γ{sub 1} between the He I and He II ionization zones. We find that it is easiest to study the acoustic glitch that is due to the helium ionization zone in stars with masses in the range 0.9-1.2 M {sub ☉}.

  5. Molecular outflows and mass loss in the pre-main-sequence stars

    NASA Astrophysics Data System (ADS)

    Levreault, Russell M.

    1988-07-01

    Molecular outflows are used here to probe mass loss in premain sequence (PMS) stars. Mass-loss rates are determined for 26 objects ranging in luminosity from four to about 100,000 solar, in mass from 0.5 to 30 solar, and in age from about 10,000 to about a million years. The derived mass-loss rates range from 9 x 10 to the -9th to 9 x 10 to the -4th solar mass/yr, with a typical value of 3 x 10 to the -7th solar mass/yr. PMS objects showing mass loss fall in a clearly demarcated region of the H-R diagram. The mass loss is proportional to bolometric luminosity to the 0.6 power and to stellar mass to the 1.8 power. The implications of these findings for the nature of the PMS mass-loss mechanism, for self-regulated low-mass star formation, and for planetary formation are discussed.

  6. The naked T Tauri stars - The low-mass pre-main sequence unveiled

    NASA Technical Reports Server (NTRS)

    Walter, Frederick M.

    1987-01-01

    The search for low-mass premain-sequence (PMS) stars associated with X-ray sources in regions of star formation is discussed. The survey to date has revealed at least 30 low-mass PMS stars in the Tau-Aur region, and a comparable number in Oph. These stars are the naked T Tau stars, unveiled versions of the well-known classical T Tau stars. The properties of these newly discovered PMS stars and their relation to the classical T Tau stars are discussed, and it is concluded that the naked T Tau stars are the true low-mass PMS stars, and that the observable characteristics defining the classical T Tau stars are due to the interaction of an underlying, fairly normal star with a dominant circumstellar environment. The impact the naked T Tau stars are likely to have on models of the PMS evolution of low-mass stars is considered.

  7. The naked T Tauri stars - The low-mass pre-main sequence unveiled

    NASA Technical Reports Server (NTRS)

    Walter, Frederick M.

    1987-01-01

    The search for low-mass premain-sequence (PMS) stars associated with X-ray sources in regions of star formation is discussed. The survey to date has revealed at least 30 low-mass PMS stars in the Tau-Aur region, and a comparable number in Oph. These stars are the naked T Tau stars, unveiled versions of the well-known classical T Tau stars. The properties of these newly discovered PMS stars and their relation to the classical T Tau stars are discussed, and it is concluded that the naked T Tau stars are the true low-mass PMS stars, and that the observable characteristics defining the classical T Tau stars are due to the interaction of an underlying, fairly normal star with a dominant circumstellar environment. The impact the naked T Tau stars are likely to have on models of the PMS evolution of low-mass stars is considered.

  8. A New Semi-Empirical Technique For Computing Effective Temperatures For Main Sequence Stars From Their Mass And Radii

    NASA Astrophysics Data System (ADS)

    Aslan, Gürkan; Soydugan, Faruk; Eker, Zeki; Bilir, Selçuk; Bakış, Volkan

    2016-07-01

    A semi-empirical technique of improving effective temperature for main sequence stars from their observed mass and radius based on the Stefan-Boltzmann law, was introduced and applied to 450 main-sequence stars with accurate parameters. The method requires a mass-luminosity relation (MLR) and theoretical predictions of radius and effective temperature for stars at zero age main-sequence and at terminal age main-sequence. The MLRs, which act as if a catalyst, are necessary but have no effect on the final result. The present sample of main-sequence stars, which are members of the detached double-lined eclipsing binaries in the solar neighborhood chosen from Eker et al. (2014), have an error histogram for the observed effective temperatures with a peak at 2-3%. Errors of refined effective temperatures by the present method are the propagated errors of the observed masses and radii, that is, the refined temperatures and associated errors are independent of the observational temperatures and their associated errors. The histogram of the refined temperature errors shows a peak at less than 1%. A refined sample of stars (270 out of 450) with masses and radii accurate up to 3% and their refined effective temperatures has been used in this study to improve the classical MLRs. One may prefer, however, to use improved classical MLRs, which allows one to compute effective temperatures as accurate as 3.5%.

  9. Mass loss from pre-main-sequence accretion disks. I - The accelerating wind of FU Orionis

    NASA Technical Reports Server (NTRS)

    Calvet, Nuria; Hartmann, Lee; Kenyon, Scott J.

    1993-01-01

    We present evidence that the wind of the pre-main-sequence object FU Orionis arises from the surface of the luminous accretion disk. A disk wind model calculated assuming radiative equilibrium explains the differential behavior of the observed asymmetric absorption-line profiles. The model predicts that strong lines should be asymmetric and blueshifted, while weak lines should be symmetric and double-peaked due to disk rotation, in agreement with observations. We propose that many blueshifted 'shell' absorption features are not produced in a true shell of material, but rather form in a differentially expanding wind that is rapidly rotating. The inference of rapid rotation supports the proposal that pre-main-sequence disk winds are rotationally driven.

  10. ADIABATIC MASS LOSS IN BINARY STARS. II. FROM ZERO-AGE MAIN SEQUENCE TO THE BASE OF THE GIANT BRANCH

    SciTech Connect

    Ge, Hongwei; Chen, Xuefei; Han, Zhanwen; Webbink, Ronald F. E-mail: rwebbink@illinois.edu

    2015-10-10

    In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z = 0.02) of mass 0.10 M{sub ⊙}–100 M{sub ⊙} from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. For intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio q{sub ad} (throughout this paper, we follow the convention of defining the binary mass ratio as q ≡ M{sub donor}/M{sub accretor}) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, q{sub ad} plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with q{sub ad} declining with decreasing mass, and asymptotically approaching q{sub ad} = 2/3, appropriate to a classical isentropic n = 3/2 polytrope. Our calculated q{sub ad} values agree well with the behavior of time-dependent models by Chen and Han of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems

  11. Looking for very low-mass pre-main sequence objects with SDSS

    SciTech Connect

    Hawley, Suzanne L.,; Covey, K. R.; McGehee, P. M.

    2001-01-01

    Determining the process(es) by which brown dwarfs form is key to understanding their intrinsic nature. If their origins are within circumstellar disks they are akin to giant planets. If, on the other hand, they coalesce from molecular cloud cores, then they share a common lineage with low mass stars. These two mechanisms can be distinguished by investigation of young (< 10 Myr) substellar objects. If brown dwarfs are small failed stars, we expect to find very low mass analogs of the Classical T Tauris, with primordial magnetic fields from the molecular cloud collapse. Accretion onto these objects leads to characteristic magnetic activity signatures such as chromospheric and coronal emission resulting in an ultraviolet excess continuum. The Orion OB1b association (m-M = 7.9, 2 Myr) provides a laboratory for following the strength and occurrence of the accretion process as a function of mass. Studies of the substellar mass function within the sigma Orionis cluster at the southern end of the association indicate that brown dwarfs are common. Based on model isochrones and the SDSS M dwarf sequence we expect the 95% completeness limit of the 'Orion' scans to correspond to 0.1 and 0.03 solar masses for the u and g bands.

  12. The Interior Structure Constants as an Age Diagnostic for Low-mass, Pre-main-sequence Detached Eclipsing Binary Stars

    NASA Astrophysics Data System (ADS)

    Feiden, Gregory A.; Dotter, Aaron

    2013-03-01

    We propose a novel method for determining the ages of low-mass, pre-main-sequence stellar systems using the apsidal motion of low-mass detached eclipsing binaries. The apsidal motion of a binary system with an eccentric orbit provides information regarding the interior structure constants of the individual stars. These constants are related to the normalized stellar interior density distribution and can be extracted from the predictions of stellar evolution models. We demonstrate that low-mass, pre-main-sequence stars undergoing radiative core contraction display rapidly changing interior structure constants (greater than 5% per 10 Myr) that, when combined with observational determinations of the interior structure constants (with 5%-10% precision), allow for a robust age estimate. This age estimate, unlike those based on surface quantities, is largely insensitive to the surface layer where effects of magnetic activity are likely to be most pronounced. On the main sequence, where age sensitivity is minimal, the interior structure constants provide a valuable test of the physics used in stellar structure models of low-mass stars. There are currently no known systems where this technique is applicable. Nevertheless, the emphasis on time domain astronomy with current missions, such as Kepler, and future missions, such as LSST, has the potential to discover systems where the proposed method will be observationally feasible.

  13. The Effects of Post-Main-Sequence Solar Mass Loss on the Stability of Our Planetary System

    NASA Astrophysics Data System (ADS)

    Duncan, Martin J.; Lissauer, Jack J.

    1998-08-01

    We present the results of extensive long-term integrations of systems of planets with orbits initially identical to subsets of the planets within our Solar System, but with the Sun's mass decreased relative to the masses of the planets. For systems based on the giant planets, we find an approximate power-law correlation between the time elapsed until a pair of planetary orbits cross and the solar-to-planetary-mass ratio, provided that this ratio is ≲0.4 times its current value. However, deviations from this relationship at larger ratios suggest that this correlation may not be useful in predicting the lifetime of the current system. Detailed simulations of the evolution of planetary orbits through the solar mass loss phase at the end of the Sun's main-sequence lifetime suggest that the orbits of those terrestrial planets that survive the Sun's red giant phase are likely to remain stable for (possibly much) longer than a billion years and those of the giant planets are likely to remain stable for (possibly much) more than ten billion years. Pluto is likely to escape from its current 2:3 mean-motion resonance with Neptune within a few billion years beyond the Sun's main sequence lifetime if subject only to gravitational forces; its prognosis is likely to be even poorer when nongravitational forces are included. Implications for the effects of stellar mass loss on the stability of other planetary systems are discussed.

  14. Coronal Activity in Low-Mass Pre-Main Sequence Stars: NGC 2264

    NASA Technical Reports Server (NTRS)

    Tebbe, H. J.; Patten, B. M.

    2000-01-01

    We present the preliminary results of an analysis of ROSAT images in the region of the populous young (age approx. 3 Myr) star-forming region NGC 2264. The cluster was imaged with the ROSAT HRI in two sets of pointings -- one set near the central region of the cluster, centered on the star LW Mon, and the other set in the southern part of the cluster, centered near the star V428 Mon, just south of the Cone Nebula. In total 113 unique X-ray sources have been identified in the ROSAT images with signal-to-noise ratios greater than 3. The limiting luminosities (log Lx(ergs/sec)) for 3-sigma detections are estimated to be 30.18, 30.23, and 30.08 for the northern field, southern field, and overlap region between the two fields respectively. Extensive optical photometry, classification spectroscopy, and proper motions, obtained from recent ground-based surveys of this region, were used to identify the most likely optical counterpart to each X-ray source. Although most of our X-ray selected sample appears to be associated with NGC 2264 members, we find that the vast majority of the cluster membership was undetected in the ROSAT HRI survey. The X-ray cumulative luminosity function for solar-mass stars in NGC 2264 shows that most of the low-mass members probably have X-ray luminosities similar to those seen for the X-ray brightest members of older clusters such as IC 2391/IC 2602 (age approx. 50 Myr) and the Pleiades (age approx. 100 Myr). This research was funded in part by the SAO Summer Intern Program and NASA grant NAG5-8120.

  15. Coronal Activity in Low-Mass Pre-Main Sequence Stars: NGC 2264

    NASA Technical Reports Server (NTRS)

    Tebbe, H. J.; Patten, B. M.

    2000-01-01

    We present the preliminary results of an analysis of ROSAT images in the region of the populous young (age approx. 3 Myr) star-forming region NGC 2264. The cluster was imaged with the ROSAT HRI in two sets of pointings -- one set near the central region of the cluster, centered on the star LW Mon, and the other set in the southern part of the cluster, centered near the star V428 Mon, just south of the Cone Nebula. In total 113 unique X-ray sources have been identified in the ROSAT images with signal-to-noise ratios greater than 3. The limiting luminosities (log Lx(ergs/sec)) for 3-sigma detections are estimated to be 30.18, 30.23, and 30.08 for the northern field, southern field, and overlap region between the two fields respectively. Extensive optical photometry, classification spectroscopy, and proper motions, obtained from recent ground-based surveys of this region, were used to identify the most likely optical counterpart to each X-ray source. Although most of our X-ray selected sample appears to be associated with NGC 2264 members, we find that the vast majority of the cluster membership was undetected in the ROSAT HRI survey. The X-ray cumulative luminosity function for solar-mass stars in NGC 2264 shows that most of the low-mass members probably have X-ray luminosities similar to those seen for the X-ray brightest members of older clusters such as IC 2391/IC 2602 (age approx. 50 Myr) and the Pleiades (age approx. 100 Myr). This research was funded in part by the SAO Summer Intern Program and NASA grant NAG5-8120.

  16. HLIMIT 2.0: Towards a Deeper Understanding of the Low Mass End of the Main Sequence

    NASA Astrophysics Data System (ADS)

    Dieterich, Sergio B.; Boss, Alan P.; Weinberger, Alycia J.; Henry, Todd J.; Winters, Jennifer G.; Jao, Wei-Chun; Recons

    2015-01-01

    We describe the observing strategies and scientific goals of a project aimed at providing a deeper understanding of the low mass end of the stellar main sequence. The work outlined here will expand upon the results presented in Dieterich et al. 2014, where radius trends in the local M and L dwarf population were used to gain insight about the stellar/substellar boundary, with evidence for the end of the stellar main sequence at spectral type L2. We now discuss our plans to make the sample volume-complete so that population properties can be studied in a non-biased manner. We also plan to analyze the effects of variations in metallicity using spectroscopy, and link observational properties to known dynamical masses. This work is made possible by the NSF Astronomy and Astrophysics Postdoctoral Fellowship Program through grant AST-1400680. Additional support comes from NSF grants AST-0908402, AST-1109445, AST-1412026, and from the Carnegie Institution for Science. Observations are made possible in part by the SMARTS Consortium.

  17. EVOLUTION OF VERY MASSIVE POPULATION III STARS WITH MASS ACCRETION FROM PRE-MAIN SEQUENCE TO COLLAPSE

    SciTech Connect

    Ohkubo, Takuya; Nomoto, Ken'ichi; Umeda, Hideyuki; Yoshida, Naoki; Tsuruta, Sachiko E-mail: umeda@astron.s.u-tokyo.ac.j E-mail: naoki.yoshida@ipmu.j

    2009-12-01

    We calculate the evolution of zero-metallicity Population III (Pop III) stars whose mass grows from the initial mass of approx1 M{sub sun} by accreting the surrounding gases. Our calculations cover whole evolutionary stages from the pre-main sequence, via various nuclear burning stages, through the final core-collapse or pair-creation instability phases. We adopt two different sets of stellar mass accretion rates as our fiducial models. One is derived from a cosmological simulation of the first generation (PopIII.1) stars, and the other is derived from a simulation of the second generation stars that are affected by radiation from PopIII.1 stars. The latter represents one case of PopIII.2 stars. We also adopt additional models that include radiative feedback effects. We show that the final mass of Pop III.1 stars can be as large as approx1000 M {sub sun}, beyond the mass range (140-300 M{sub sun}) for the pair-instability supernovae. Such massive stars undergo core-collapse to form intermediate-mass black holes, which may be the seeds for merger trees to supermassive black holes. On the other hand, Pop III.2 stars become less massive (approx<40-60 M{sub sun}), being in the mass range of ordinary iron core-collapse stars. Such stars explode and eject heavy elements to contribute to chemical enrichment of the early universe as observed in the abundance patterns of extremely metal-poor stars in the Galactic halo. In view of the large range of possible accretion rates, further studies are important to see if these fiducial models are actually the cases.

  18. Measuring the mass of a pre-main sequence binary star through the orbit of TWA5A

    SciTech Connect

    Konopacky, Q; Ghez, A; Duchene, G; McCabe, C; Macintosh, B

    2007-01-18

    We present the results of a five year monitoring campaign of the close binary TWA 5Aab in the TW Hydrae association, using speckle and adaptive optics on the W.M. Keck 10 m telescopes. These measurements were taken as part of our ongoing monitoring of pre-main sequence (PMS) binaries in an effort to increase the number of dynamically determined PMS masses and thereby calibrate the theoretical PMS evolutionary tracks. Our observations have allowed us to obtain the first determination of this system's astrometric orbit. We find an orbital period of 5.94 {+-} 0.09 years and a semi-major axis of 0.''066 {+-} 0.''005. Combining these results with a kinematic distance, we calculate a total mass of 0.71 {+-} 0.14 M{sub {circle_dot}} (D/44 pc){sup 3}. for this system. This mass measurement, as well as the estimated age of this system, are consistent to within 2{sigma} of all theoretical models considered. In this analysis, we properly account for correlated uncertainties, and show that while these correlations are generally ignored, they increase the formal uncertainties by up to a factor of five and therefore are important to incorporate. With only a few more years of observation, this type of measurement will allow the theoretical models to be distinguished.

  19. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. IV. RECENT STAR FORMATION IN NGC 602

    SciTech Connect

    De Marchi, Guido; Beccari, Giacomo; Panagia, Nino E-mail: gbeccari@eso.org

    2013-09-20

    We have studied the young stellar populations in NGC 602, in the Small Magellanic Cloud, using a novel method that we have developed to combine Hubble Space Telescope photometry in the V, I, and Hα bands. We have identified about 300 pre-main-sequence (PMS) stars, all of which are still undergoing active mass accretion, and have determined their physical parameters (effective temperature, luminosity, age, mass, and mass accretion rate). Our analysis shows that star formation has been present in this field over the last 60 Myr. In addition, we can recognize at least two clear, distinct, and prominent episodes in the recent past: one about 2 Myr ago, but still ongoing in regions of higher nebulosity, and one (or more) older than 30 Myr, encompassing both stars dispersed in the field and two smaller clusters located about 100'' north of the center of NGC 602. The relative locations of younger and older PMS stars do not imply a causal effect or triggering of one generation on the other. The strength of the two episodes appears to be comparable, but the episodes occurring more than 30 Myr ago might have been even stronger than the current one. We have investigated the evolution of the mass accretion rate, M-dot{sub acc}, as a function of the stellar parameters finding that log M-dot{sub acc}≅-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a decreasing function of the metallicity.

  20. Older and colder: The impact of starspots on stellar masses, ages, and lithium during the pre-main sequence

    NASA Astrophysics Data System (ADS)

    Somers, Garrett

    2016-01-01

    Starspots are ubiquitously found on young, active stars on the pre-main sequence (pre-MS), and may cover up to ~50% of their surfaces, but their effects on early stellar evolution have never been fully explored. I study the impact of such extreme spot coverage on pre-MS stellar evolution by modifying an existing stellar evolution code to account for spot effects on both the surface boundary conditions and the transport of energy in the interior. I show that heavy spot coverage systematically increases the radii of young stars, while reducing their luminosity and average surface temperature. Such increased radii may underlie the well-known radius inflation of some young, active stars, while the decreased luminosity and effective temperature displace stars on the HR diagram, leading to systematic under-estimation of stellar masses by up to 2x, and of stellar ages by up to 10x, if spotted stars are interpreted with un-spotted isochrones. The inhomogeneous surfaces of spotted stars also distort the emission spectrum, and can thus explain the anomalous colors of the rapidly rotating K dwarfs of the Pleiades, a young open cluster. I further find that spots reduce the central temperature of stars, leading to a suppression of lithium burning during the pre-MS. As a result, pre-MS stars of equal mass but differing spot properties reach the zero-age main sequence with different surface lithium abundances. I show that this effect can account for the previously unexplained lithium abundance dispersions observed at fixed Teff in the Pleiades, and other young clusters.Synthesizing these results, I argue that the inclusion of spots, a prominent phenomenon on the pre-MS, can explain several outstanding mysteries associated with young stars: inflated radii, age spreads in young clusters, the anomalous colors of rapid rotators, and the lithium abundance dispersions in young star clusters. I discuss implications of under-estimated masses and ages for measuring age spreads in young

  1. New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit

    NASA Astrophysics Data System (ADS)

    Baraffe, Isabelle; Homeier, Derek; Allard, France; Chabrier, Gilles

    2015-05-01

    We present new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and interior structures, thereby superseding the widely used BCAH98 models. The new models include updated molecular linelists and solar abundances, as well as atmospheric convection parameters calibrated on 2D/3D radiative hydrodynamics simulations. Comparison of these models with observations in various colour-magnitude diagrams for various ages shows significant improvement over previous generations of models. The new models can solve flaws that are present in the previous ones, such as the prediction of optical colours that are too blue compared to M dwarf observations. They can also reproduce the four components of the young quadruple system LkCa 3 in a colour-magnitude diagram with one single isochrone, in contrast to any presently existing model. In this paper we also highlight the need for consistency when comparing models and observations, with the necessity of using evolutionary models and colours based on the same atmospheric structures.

  2. Effect of accretion on the pre-main-sequence evolution of low-mass stars and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Elbakyan, Vardan; Hosokawa, Takashi; Sakurai, Yuya; Guedel, Manuel; Yorke, Harold

    2017-09-01

    Aims: The pre-main-sequence evolution of low-mass stars and brown dwarfs is studied numerically starting from the formation of a protostellar or proto-brown dwarf seed and taking into account the mass accretion onto the central object during the initial several Myr of evolution. Methods: The stellar evolution was computed using the STELLAR evolution code with recent modifications. The mass accretion rates were taken from numerical hydrodynamics models by computing the circumstellar disk evolution starting from the gravitational collapse of prestellar cloud cores of various mass and angular momentum. The resulting stellar evolution tracks were compared with the isochrones and isomasses calculated using non-accreting models. Results: We find that mass accretion in the initial several Myr of protostellar evolution can have a strong effect on the subsequent evolution of young stars and brown dwarfs. The disagreement between accreting and non-accreting models in terms of the total stellar luminosity L∗, stellar radius R∗, and effective temperature Teff depends on the thermal efficiency of accretion, that is, on the fraction of accretion energy that is absorbed by the central object. The largest mismatch is found for the cold accretion case, in which essentially all accretion energy is radiated away. The relative deviations in L∗ and R∗ in this case can reach 50% for objects 1.0 Myr old, and they remain notable even for objects 10 Myr old. In the hot and hybrid accretion cases, in which a constant fraction of accretion energy is absorbed, the disagreement between accreting and non-accreting models becomes less pronounced, but still remains notable for objects 1.0 Myr old. These disagreements may lead to an incorrect age estimate for objects of (sub-)solar mass when using the isochrones that are based on non-accreting models, as has also been noted previously. We find that objects with strong luminosity bursts exhibit notable excursions in the L∗-Teff diagram

  3. Precise orbit solution of MML 53, a low-mass, pre-main sequence eclipsing binary in Upper Centaurus Lupus

    NASA Astrophysics Data System (ADS)

    Hebb, L.; Cegla, H. M.; Stassun, K. G.; Stempels, H. C.; Cargile, P. A.; Palladino, L. E.

    2011-07-01

    Aims: We present a double-lined orbit solution for MML 53, the recently discovered low-mass pre-main sequence eclipsing binary. Methods: Using high-resolution spectra from the SMARTS 1.5 m echelle spectrograph, we measure precise radial velocities and derive the orbital parameters of the system. Results: The 2.1 d orbit of the eclipsing pair is circular, and we find the minimum masses of the eclipsing components to be M1sin3i = 0.97 M⊙ and M2sin3i = 0.84 M⊙, with formal uncertainties of 2.0% and an additional systematic uncertainty of ≈2.5% most likely caused by large star spots on the primary star. MML 53 has been previously identified as a member of the Upper Centaurus Lupus (UCL) star forming region (age ~15 Myr). The systemic radial velocity from our orbit solution, vγ = +1.4 ± 0.3 ± 0.8 km s-1 (statistical and systematic), is also consistent with kinematic membership in this association. In addition, we detect a change in vγ between 2006 and 2009 providing further evidence for the presence of a the third body in a wide (several year) orbit.

  4. A Dynamical Mass Measurement for the Pre-Main-Sequence Secondary of the Eclipsing Binary TY CrA

    NASA Astrophysics Data System (ADS)

    Mathieu, R. D.; Casey, B.; Vaz, L. P.; Andersen, J.; Suntzeff, N.; Walter, F.

    1994-05-01

    Using the Danish 50cm telescope at La Silla we have obtained simultaneous uvby light curves of the eclipsing binary TY CrA, located in the Corona Australis star-forming region. We have securely detected the secondary eclipse (2% depth in y). We have also obtained high-resolution (R=15000) echelle spectra in the red. Along with the primary spectrum, absorption lines of the secondary and a previously unknown tertiary component have been found. In particular, both the secondary and tertiary are detected at the Lithium 6708 Angstroms line. Based on temperature insensitive lines the tertiary/secondary luminosity ratio at ~ 6400 Angstroms is ~ 1.5. When combined with our previous single-lined orbital solution for the primary (Casey, B.W., Mathieu, R.D., Suntzeff, N.B., Lee, C.W., and Cardelli, J.A. 1993, Astron. Journal, 105, 2276) the secondary radial-velocity measurements provide a mass ratio of 0.521+/-0.007. Using a modified form of the Wilson-Devinney formalism, our light curve solution gives an inclination angle of 81°, masses and radii of (3.2 M_sun, 1.8 R_sun) and (1.7 M_sun, 2.3 R_sun) for the primary and secondary respectively. Based on both spectral classification and uvby colors we adopt a primary effective temperature of 12,000 +/- 500 K. Using Kurucz atmosphere models for both stars in the WD solution, we derive a temperature of 5,000 K for the secondary, thus fully specifying the system. The primary lies on the ZAMS, while the secondary lies at the base of the Hayashi tracks. The secondary provides the first dynamical mass calibration with which to test theoretical calculations of Hayashi tracks. We will evaluate several modern theoretical pre-main sequence evolutionary models with respect to TY CrA. The vsin i of the secondary spectrum is 40 km/sec, making the secondary rotation synchronous with the orbital motion. Given that the primary is remarkably subsynchronous (Casey et al. 1993 and new spectra), we conclude that the orbit was tidally circularized

  5. Calibrating convective-core overshooting with eclipsing binary systems. The case of low-mass main-sequence stars

    NASA Astrophysics Data System (ADS)

    Valle, G.; Dell'Omodarme, M.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2016-03-01

    Context. Double-lined eclipsing binaries have often been adopted in literature to calibrate the extension of the convective-core overshooting beyond the border defined by the Schwarzschild criterion. Aims: In a robust statistical way, we quantify the magnitude of the uncertainty that affects the calibration of the overshooting efficiency parameter β that is owing to the uncertainty on the observational data. We also quantify the biases on the β determination that is caused by the lack of constraints on the initial helium content and on the efficiencies of the superadiabatic convection and microscopic diffusion. Methods: We adopted a modified grid-based SCEPtER pipeline to recover the β parameter from synthetic stellar data. Our grid spans the mass range [1.1; 1.6] M⊙ and evolutionary stages from the zero-age main sequence (MS) to the central hydrogen depletion. The β estimates were obtained by generalising the maximum likelihood technique described in our previous works. As observational constraint, we adopted the effective temperatures, [Fe/H], masses, and radii of the two stars. Results: By means of Monte Carlo simulations, adopting a reference scenario of mild overshooting β = 0.2 for the synthetic data, and taking typical observational errors into account, we found both large statistical uncertainties and biases on the estimated values of β. For the first 80% of the MS evolution, β is biased by about -0.04, with the 1σ error practically unconstrained in the whole explored range [0.0; 0.4]. In the last 5% of the evolution the bias vanishes and the 1σ error is about 0.05. The 1σ errors are similar when adopting different reference values of β. Interestingly, for synthetic data computed without convective-core overshooting, the estimated β is biased by about 0.12 in the first 80% of the MS evolution, and by 0.05 afterwards. Assuming an uncertainty of ±1 in the helium-to-metal enrichment ratio ΔY/ ΔZ, we found a large systematic uncertainty in the

  6. Strange mode instability driven finite amplitude pulsations and mass-loss in models of massive zero-age main-sequence stars

    NASA Astrophysics Data System (ADS)

    Yadav, Abhay Pratap; Glatzel, Wolfgang

    2017-02-01

    The stability with respect to radial perturbations of massive zero-age main-sequence stars having solar chemical composition and masses between 50 and 150 M⊙ is reinvestigated. As a first step, a linear non-adiabatic stability analysis is performed, confirming the existence of dynamical strange mode instabilities for models with masses above 58 M⊙. For selected models, the evolution of the strange mode instabilities into the non-linear regime is followed by numerical simulation. The final results of strange mode instabilities are thus found to be finite amplitude pulsations with periods between 3 and 24 h. Mean acoustic luminosities capable to drive winds with mass-loss rates of the order of 0.5 × 10-7 M⊙ yr-1, which can at most marginally affect stellar evolution in the vicinity of the zero-age main sequence, are associated with these finite amplitude pulsations.

  7. 2D and 3D Models of Convective Turbulence and Oscillations in Intermediate-Mass Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Guzik, Joyce Ann; Morgan, Taylor H.; Nelson, Nicholas J.; Lovekin, Catherine; Kitiashvili, Irina N.; Mansour, Nagi N.; Kosovichev, Alexander

    2015-08-01

    We present multidimensional modeling of convection and oscillations in main-sequence stars somewhat more massive than the sun, using three separate approaches: 1) Applying the spherical 3D MHD ASH (Anelastic Spherical Harmonics) code to simulate the core convection and radiative zone. Our goal is to determine whether core convection can excite low-frequency gravity modes, and thereby explain the presence of low frequencies for some hybrid gamma Dor/delta Sct variables for which the envelope convection zone is too shallow for the convective blocking mechanism to drive g modes; 2) Using the 3D planar ‘StellarBox’ radiation hydrodynamics code to model the envelope convection zone and part of the radiative zone. Our goals are to examine the interaction of stellar pulsations with turbulent convection in the envelope, excitation of acoustic modes, and the role of convective overshooting; 3) Applying the ROTORC 2D stellar evolution and dynamics code to calculate evolution with a variety of initial rotation rates and extents of core convective overshooting. The nonradial adiabatic pulsation frequencies of these nonspherical models will be calculated using the 2D pulsation code NRO of Clement. We will present new insights into gamma Dor and delta Sct pulsations gained by multidimensional modeling compared to 1D model expectations.

  8. MML 53: a new low-mass, pre-main sequence eclipsing binary in the Upper Centaurus-Lupus region discovered by SuperWASP

    NASA Astrophysics Data System (ADS)

    Hebb, L.; Stempels, H. C.; Aigrain, S.; Collier-Cameron, A.; Hodgkin, S. T.; Irwin, J. M.; Maxted, P. F. L.; Pollacco, D.; Street, R. A.; Wilson, D. M.; Stassun, K. G.

    2010-11-01

    We announce the discovery of a new low-mass, pre-main sequence eclipsing binary, MML 53. Previous observations of MML 53 found it to be a pre-main sequence spectroscopic multiple associated with the 15-22 Myr Upper Centaurus-Lupus cluster. We identify the object as an eclipsing binary for the first time through the analysis of multiple seasons of time series photometry from the SuperWASP transiting planet survey. Re-analysis of a single archive spectrum shows MML 53 to be a spatially unresolved triple system of young stars which all exhibit significant lithium absorption. Two of the components comprise an eclipsing binary with period, P = 2.097891(6) ± 0.000005 and mass ratio, q ~ 0.8. Here, we present the analysis of the discovery data.

  9. A Study of the Wide Main Sequence: The Long-Term Photometric Variability of Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Pewett, Tiffany; Henry, Todd J.; Hosey, Altonio D.; Dieterich, Sergio; Jao, Wei-Chun; Winters, Jennifer G.; Riedel, Adric R.; RECONS Team

    2016-01-01

    The RECONS (REsearch Consortium On Nearby Stars, www.recons.org) team has carried out a long-term photometric variability study using the SMARTS 0.9m telescope at the Cerro Tololo Inter-American Observatory (CTIO). The program has obtained up to 15 years of observations in the V band for hundreds of M dwarf stars. This unique study has provided insight into how the ubiquitous M dwarfs change over decadal timescales, revealing their long-term magnetic cycles and how the presence or lack of such activity may affect their sizes and consequent luminosities, and thus their positions on the H-R Diagram.Using carefully vetted parallaxes and photometric colors, many measured by the RECONS team, we have created a highly accurate H-R Diagram of the nearest (within 25pc) stars using their V-K colors to represent temperatures and absolute V magnitudes as proxies for luminosities. We find that for M dwarfs, the main sequence widens significantly, by up to four magnitudes in MV, corresponding to a factor of almost 40 in optical flux. This spread implies a wide range of stellar radii for M dwarfs of the same temperature. Our study of long-term photometric variability indicates that there is a trend in cyclic activity that is highest for the most luminous red dwarfs and lowest for the rare, cool red subdwarfs. This provides valuable insight into the complex interplay of age, metallicity, and magnetic fields that molds the character of the red dwarfs.This effort has been supported by the NSF through grants AST-0908402, AST-1109445, and AST-1412026, STScI grant HST-GO-13724.001-A, and via observations made possible by the SMARTS Consortium.

  10. Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

    NASA Astrophysics Data System (ADS)

    Stelzer, B.; Huélamo, N.; Micela, G.; Hubrig, S.

    2006-06-01

    Context: .The X-ray emission from B-type main-sequence stars is a longstanding mystery in stellar coronal research. Since there is no theory at hand that explains intrinsic X-ray emission from intermediate-mass main-sequence stars, the observations have often been interpreted in terms of (unknown) late-type magnetically active companion stars. Aims: .Resolving the hypothesized companions requires high spatial resolution observations in the infrared and in X-rays. We use Chandra imaging observations to spatially resolve a sample of main-sequence B-type stars with recently discovered companions at arcsecond separation. Methods: .Our strategy is to search for X-ray emission at the position of both the B-type primary and the faint companion. Results: .We find that all spatially resolved companions are X-ray emitters, but seven out of eleven intermediate-mass stars are also X-ray sources. If this emission is interpreted in terms of additional sub-arcsecond or spectroscopic companions, this implies a high multiplicity of B-type stars. Firm results on B star multiplicity pending, the alternative, that B stars produce intrinsic X-rays, cannot be discarded. An appropriate scenario would be a magnetically confined wind, as suggested for the X-ray emission of the magnetic Ap star IQ Aur. However, the only Ap star in the Chandra sample is not detected in X-rays, and therefore does not support this picture.

  11. Migration and Growth of Protoplanetary Embryos. III. Mass and Metallicity Dependence for FGKM Main-sequence Stars

    NASA Astrophysics Data System (ADS)

    Liu, Beibei; Zhang, Xiaojia; Lin, Douglas N. C.

    2016-06-01

    Radial velocity and transit surveys have found that the fraction of FGKM stars with close-in super-Earth(s) (η ⊕) is around 30%-50%, independent of the stellar mass M * and metallicity Z *. In contrast, the fraction of solar-type stars harboring one or more gas giants (η J) with masses M p > 100 M ⊕ is nearly 10%-15%, and it appears to increase with both M * and Z *. Regardless of the properties of their host stars, the total mass of some multiple super-Earths systems exceeds the core mass of Jupiter and Saturn. We suggest that both super-Earths and supercritical cores of gas giants were assembled from a population of embryos that underwent convergent type I migration from their birthplaces to a transition location between viscously heated and irradiation-heated disk regions. We attribute the cause for the η ⊕-η J dichotomy to conditions required for embryos to merge and to acquire supercritical core mass ({M}{{c}}˜ 10 {M}\\oplus ) for the onset of efficient gaseous envelope accretion. We translate this condition into a critical disk accretion rate, and our analysis and simulation results show that it weakly depends on M * and decreases with metallicity of disk gas Z d. We find that embryos are more likely to merge into supercritical cores around relatively massive and metal-rich stars. This dependence accounts for the observed η J-M *. We also consider the {Z}{{d}}{--}{Z}* dispersed relationship and reproduce the observed η J-Z * correlation.

  12. Disks around Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Trauger, John

    1995-07-01

    About 30 other nearby stars have been shown (Aumann 1985,1988 Sadakane and Nishida 1986) to emit excess infrared flux relative to that expected from their photospheres. It is believed that such emission is the rule rather than the exception and that the limited number is caused by the IRAS detection limits. We propose to observe the prototypical objects Alpha Lyrae. If an optical counterpart to the infrared emission is observed, then the same analysis as that performed on the Beta Pictoris disk will be possible. If not, because of the low scattered light levels in the wings of the HST PSF, stringent limits on the albedo of the disk should be obtained. Only one circumstellar disk has been directly observed around a main sequence star. On the other hand, it is believed that disks are typical byproducts of star formation, and that these disks are the sites where planetary systems are formed. Both of these hypotheses will be tested with the observations proposed here. Firstly, the observations, if they detect the material will constrain its spatial distribution, and test the disk hypothesis. The material surrounding the target stars is presumed but not known to be distributed in a disk. There is not significant extinction towards these targets, but a shell of optically thin material can also fit the existing IRAS observations. The observations also only loosely constrain the radial distribution of the particles. Given a detection, it should be possible to distinguish a disk from

  13. The Ages and Masses of a Million Galactic-disk Main-sequence Turnoff and Subgiant Stars from the LAMOST Galactic Spectroscopic Surveys

    NASA Astrophysics Data System (ADS)

    Xiang, Maosheng; Liu, Xiaowei; Shi, Jianrong; Yuan, Haibo; Huang, Yang; Chen, Bingqiu; Wang, Chun; Tian, Zhijia; Wu, Yaqian; Yang, Yong; Zhang, Huawei; Huo, Zhiying; Ren, Juanjuan

    2017-09-01

    We present estimates of stellar age and mass for 0.93 million Galactic-disk main-sequence turnoff and subgiant stars from the LAMOST Galactic Spectroscopic Surveys. The ages and masses are determined by matching with stellar isochrones using a Bayesian algorithm, utilizing effective temperature {T}{eff}, absolute magnitude {M}V, metallicity [Fe/H], and α-element to iron abundance ratio [α/Fe] deduced from the LAMOST spectra. Extensive examinations suggest the age and mass estimates are robust. Overall, the sample stars have a median error of 34% for the age estimates, and half of the stars older than 2 Gyr have age uncertainties of only 20%-30%. The median error for the mass estimates of the whole sample of stars is ˜8%. The huge data set demonstrates good correlations among stellar age, [Fe/H] ([α/H]), and [α/Fe]. Particularly, double-sequence features are revealed in both the age-[α/Fe] and age-[Fe/H]([α/H]) spaces. In the [Fe/H]-[α/Fe] space, stars of 8-10 Gyr exhibit both the thin and thick disk sequences, while younger (older) stars show only the thin (thick) disk sequence, indicating that the thin disk became prominent 8-10 Gyr ago, while the thick disk formed earlier and was almost quenched 8 Gyr ago. Stellar ages exhibit positive vertical and negative radial gradients across the disk, and the outer disk of R ≳ 9 kpc exhibits a strong flare in stellar age distribution.

  14. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. II. NGC 346 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    De Marchi, Guido; Sirianni, Marco; Panagia, Nino; Sabbi, Elena; Romaniello, Martino; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla E-mail: panagia@stsci.edu

    2011-10-10

    We have studied the properties of the stellar populations in the field of the NGC 346 cluster in the Small Magellanic Cloud, using a novel self-consistent method that allows us to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to identify all stars with excess H{alpha} emission and derive the accretion luminosity L{sub acc} and mass accretion rate M-dot{sub acc} for all of them. The application of this method to existing Hubble Space Telescope (HST)/Advanced Camera for Surveys photometry of the NGC 346 field has allowed us to identify and study 680 bona fide PMS stars with masses from {approx}0.4 M{sub sun} to {approx}4 M{sub sun} and ages in the range from {approx}1 Myr to {approx}30 Myr. Previous investigations of this region, based on the same data, had identified young ({approx}3 Myr old) candidate PMS stars on the basis of their broadband colors. In this study, we show that there are at least two, almost equally numerous, young populations with distinct ages of, respectively, {approx}1 and {approx}20 Myr. We provide accurate physical parameters for all of them. We take advantage of the unprecedented size of our PMS sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters. We find that, regardless of stellar mass, the mass accretion rate decreases with roughly the square root of the age, or about three times slower than predicted by current models of viscous disk evolution, and that more massive stars systematically have a higher mass accretion rate in proportion to their mass. A multivariate linear regression fit reveals that log M-dot{sub acc}{approx_equal}-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a quantity that is higher at lower metallicity. This result is consistent with

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  16. MML 53: A New Low-Mass, Pre-Main Sequence Eclipsing Binary in the Lupus Cloud Discovered By SuperWASP

    NASA Astrophysics Data System (ADS)

    Cegla, Heather; Hebb, L.; Stassun, K. G.; Stempels, H. C.; Cargile, P. A.; Palladino, L. E.; SuperWASP Consortium

    2010-01-01

    We announce the discovery of a new low-mass, pre-main sequence (PMS) eclipsing binary star in the Lupus Cloud, MML 53. This is only the 6th sub-solar mass PMS eclipsing binary known. Previous observations of MML 53 found it to be a spectroscopic multiple associated with the 15-22 Myr Upper Centaurus Lupus (UCL) cluster. Here, we identify the object as an eclipsing binary for the first time through the analysis of photometric time series photometry from the SuperWASP transiting planet survey. We derive an accurate ephemeris for the system and present a double-lined orbit solution based on high resolution spectra. The spectra confirm MML 53 to be a triple system of young stars composed of an eclipsing binary and a stationary third component all of which show strong lithium absorption as expected for low-mass, PMS stars. The 2.1 d orbit of the eclipsing pair is circular, and we find the minimum masses of M1 sin3 i = 0.94 M⊙ and M2 sin3 i = 0.81 M⊙ with formal uncertainties of 2.0 %.We find a systemic radial velocity, vγ = +1.00 ± 0.33 ± 0.81 km s-1, consistent with kinematic membership in the UCL association, and the radii of the component stars are 30 % larger than expected for main sequence stars. Follow-up modeling of high cadence, multi-band light-curve data will provide precise fundamental properties of the components of the system which will ultimately be used to place constraints on theoretical models of PMS stellar evolution. This research is supported by an NSF REU grant to the Vanderbilt Physics & Astronomy Department, and by an NSF PAARE grant to Fisk University.

  17. Large dust particles around main sequence stars

    NASA Astrophysics Data System (ADS)

    Chini, R.; Kruegel, E.; Kreysa, E.

    1990-01-01

    Results are presented on observations of spectra of five nearby main-sequence stars (Vega, Tau-1 Eri, Epsilon Eri, Alpha PsA, and Sirius), carried out from summer 1987 to spring 1989 on the IRAM 30-m telescope on Pico Veleta. It was found that all of these stars, with the possible exception of Sirius, possess an excess at 100 microns, which is interpreted as emission from dust grains, confirming the suggestion of Aumann et al. (1984) that Vega is enshrouded by a shell of large grains. The observations were used to derive precise values for the grain sizes, their temperatures, total mass, and density distribution.

  18. The Gaia-ESO Survey: lithium depletion in the Gamma Velorum cluster and inflated radii in low-mass pre-main-sequence stars

    NASA Astrophysics Data System (ADS)

    Jeffries, R. D.; Jackson, R. J.; Franciosini, E.; Randich, S.; Barrado, D.; Frasca, A.; Klutsch, A.; Lanzafame, A. C.; Prisinzano, L.; Sacco, G. G.; Gilmore, G.; Vallenari, A.; Alfaro, E. J.; Koposov, S. E.; Pancino, E.; Bayo, A.; Casey, A. R.; Costado, M. T.; Damiani, F.; Hourihane, A.; Lewis, J.; Jofre, P.; Magrini, L.; Monaco, L.; Morbidelli, L.; Worley, C. C.; Zaggia, S.; Zwitter, T.

    2017-01-01

    We show that non-magnetic models for the evolution of pre-main-sequence (PMS) stars cannot simultaneously describe the colour-magnitude diagram (CMD) and the pattern of lithium depletion seen in the cluster of young, low-mass stars surrounding γ2 Velorum. The age of 7.5 ± 1 Myr inferred from the CMD is much younger than that implied by the strong Li depletion seen in the cluster M-dwarfs, and the Li depletion occurs at much redder colours than predicted. The epoch at which a star of a given mass depletes its Li and the surface temperature of that star are both dependent on its radius. We demonstrate that if the low-mass stars have radii ˜10 per cent larger at a given mass and age, then both the CMD and the Li-depletion pattern of the Gamma Velorum cluster are explained at a common age of ≃18-21 Myr. This radius inflation could be produced by some combination of magnetic suppression of convection and extensive cool starspots. Models that incorporate radius inflation suggest that PMS stars, similar to those in the Gamma Velorum cluster, in the range 0.2 < M/M⊙ < 0.7, are at least a factor of 2 older and ˜7 per cent cooler than previously thought and that their masses are much larger (by >30 per cent) than inferred from conventional, non-magnetic models in the Hertzsprung-Russell diagram. Systematic changes of this size may be of great importance in understanding the evolution of young stars, disc lifetimes and the formation of planetary systems.

  19. Accretion onto Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Hartmann, Lee; Herczeg, Gregory; Calvet, Nuria

    2016-09-01

    Accretion through circumstellar disks plays an important role in star formation and in establishing the properties of the regions in which planets form and migrate. The mechanisms by which protostellar and protoplanetary disks accrete onto low-mass stars are not clear; angular momentum transport by magnetic fields is thought to be involved, but the low-ionization conditions in major regions of protoplanetary disks lead to a variety of complex nonideal magnetohydrodynamic effects whose implications are not fully understood. Accretion in pre-main-sequence stars of masses ≲1M⊙ (and in at least some 2-3-M⊙ systems) is generally funneled by the stellar magnetic field, which disrupts the disk at scales typically of order a few stellar radii. Matter moving at near free-fall velocities shocks at the stellar surface; the resulting accretion luminosities from the dissipation of kinetic energy indicate that mass addition during the T Tauri phase over the typical disk lifetime ˜3 Myr is modest in terms of stellar evolution, but is comparable to total disk reservoirs as estimated from millimeter-wave dust emission (˜10-2 M⊙). Pre-main-sequence accretion is not steady, encompassing timescales ranging from approximately hours to a century, with longer-timescale variations tending to be the largest. Accretion during the protostellar phase—while the protostellar envelope is still falling onto the disk—is much less well understood, mostly because the properties of the central obscured protostar are difficult to estimate. Kinematic measurements of protostellar masses with new interfometric facilities should improve estimates of accretion rates during the earliest phases of star formation.

  20. Theoretical studies of massive stars. I - Evolution of a 15-solar-mass star from the zero-age main sequence to neon ignition

    NASA Technical Reports Server (NTRS)

    Endal, A. S.

    1975-01-01

    The evolution of a star with mass 15 times that of the sun from the zero-age main sequence to neon ignition has been computed by the Henyey method. The hydrogen-rich envelope and all shell sources were explicitly included in the models. An algorithm has been developed for approximating the results of carbon burning, including the branching ratio for the C-12 + C-12 reaction and taking some secondary reactions into account. Penetration of the convective envelope into the core is found to be unimportant during the stages covered by the models. Energy transfer from the carbon-burning shell to the core by degenerate electron conduction becomes important after the core carbon-burning stage. Neon ignition will occur in a semidegenerate core and will lead to a mild 'flash.' Detailed numerical results are given in an appendix. Continuation of the calculations into later stages and variations with the total mass of the star will be discussed in later papers.

  1. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. I. METHOD AND APPLICATION TO THE SN 1987A FIELD

    SciTech Connect

    De Marchi, Guido; Panagia, Nino; Romaniello, Martino E-mail: panagia@stsci.ed

    2010-05-20

    We have developed and successfully tested a new self-consistent method to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion in a resolved stellar population, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to (1) identify all stars with excess H{alpha} emission, (2) convert the excess H{alpha} magnitude into H{alpha} luminosity L(H{alpha}), (3) estimate the H{alpha} emission equivalent width, (4) derive the accretion luminosity L{sub acc} from L(H{alpha}), and finally (5) obtain the mass accretion rate M-dot{sub acc} from L{sub acc} and the stellar parameters (mass and radius). By selecting stars with an accuracy of 15% or better in the H{alpha} photometry, the statistical uncertainty on the derived M-dot{sub acc} is typically {approx_lt}17% and is dictated by the precision of the H{alpha} photometry. Systematic uncertainties, of up to a factor of 3 on the value of M-dot{sub acc}, are caused by our incomplete understanding of the physics of the accretion process and affect all determinations of the mass accretion rate, including those based on a spectroscopic H{alpha} line analysis. As an application of our method, we study the accretion process in a field of 9.16 arcmin{sup 2} around SN 1987A, using existing Hubble Space Telescope photometry. We identify as bona fide PMS stars a total of 133 objects with a H{alpha} excess above the 4{sigma} level and a median age of 13.5 Myr. Their median mass accretion rate of 2.6 x 10{sup -8} M{sub sun} yr{sup -1} is in excellent agreement with previous determinations based on the U-band excess of the stars in the same field, as well as with the value measured for G-type PMS stars in the Milky Way. The accretion luminosity of these PMS objects shows a strong dependence on their distance from a group of hot massive stars in the field and suggests that the ultraviolet radiation of the latter is rapidly

  2. New low-mass members of the Lupus 3 dark cloud: Further indications of pre-main-sequence evolution strongly affected by accretion

    NASA Astrophysics Data System (ADS)

    Comerón, F.; Fernández, M.; Baraffe, I.; Neuhäuser, R.; Kaas, A. A.

    2003-08-01

    A spectroscopic survey of a small area at the center of the Lupus 3 star-forming core has revealed four new mid-to-late M-type members, including a M7.5 brown dwarf. One of the new members, classified as M5, displays prominent forbidden lines and strong Hα emission (EW(Hα ) = 410 Å), in addition to other permitted lines, and its luminosity is far below that of other members of the region with similar or later spectral types. We estimate a mass accretion rate rate of ~ 1.4 x 10-9 Msun yr-1 for this object, although with uncertainties that do not exclude values as low as 10-10 Msun yr-1. Based on the Hα / [SII] ratio, the detection of HeI, and the CaII infrared triplet, we argue that most of the Hα emission is produced near the surface of the object, probably in accretion columns or at the base of jets, rather than in a low-density extended region. The strong emission-line spectrum superimposed on an unusually faint photospheric continuum thus seems to be a real, intrinsic feature rather than a result of the viewing geometry caused by an edge-on disk blocking the light from the central object. Other Lupus 3 late-type members also display noticeable underluminosity, all of them having EW(Hα ) > 100 Å as a result of the faint underlying continuum. We tentatively interpret these findings as evidence for the pre-main sequence evolution of objects with very low (possibly substellar) initial masses being significantly modified by accretion. Based on observations obtained at the European Southern Observatory using the Very Large Telescope in Cerro Paranal (program 67.C-0549(A)), the ESO New Technology Telescope in La Silla (program 69.B-0126(A)), and the 1.5 Danish telescope, also in La Silla (program 69.C-0423(B)).

  3. A High-resolution Multiband Survey of Westerlund 2 with the Hubble Space Telescope. II. Mass Accretion in the Pre-main-sequence Population

    NASA Astrophysics Data System (ADS)

    Zeidler, Peter; Grebel, Eva K.; Nota, Antonella; Sabbi, Elena; Pasquali, Anna; Tosi, Monica; Bonanos, Alceste Z.; Christian, Carol

    2016-10-01

    We present a detailed analysis of the pre-main-sequence (PMS) population of the young star cluster Westerlund 2 (Wd2), the central ionizing cluster of the H ii region RCW 49, using data from a high-resolution multiband survey with the Hubble Space Telescope. The data were acquired with the Advanced Camera for Surveys in the F555W, F814W, and F658N filters and with the Wide Field Camera 3 in the F125W, F160W, and F128N filters. We find a mean age of the region of 1.04 ± 0.72 Myr. The combination of dereddened F555W and F814W photometry in combination with F658N photometry allows us to study and identify stars with Hα excess emission. With a careful selection of 240 bona-fide PMS Hα excess emitters we were able to determine their Hα luminosity, which has a mean value L({{H}}α )=1.67× {10}-31 {{erg}} {{{s}}}-1. Using the PARSEC 1.2S isochrones to obtain the stellar parameters of the PMS stars, we determined a mean mass accretion rate {\\dot{M}}{{acc}}=4.43× {10}-8 {M}⊙ {{{yr}}}-1 per star. A careful analysis of the spatial dependence of the mass accretion rate suggests that this rate is ˜25% lower in the center of the two density peaks of Wd2 in close proximity to the luminous OB stars, compared to the Wd2 average. This rate is higher with increasing distance from the OB stars, indicating that the PMS accretion disks are being rapidly destroyed by the far-ultraviolet radiation emitted by the OB population.

  4. Photometric Determination of the Mass Accretion Rates of Pre-main-sequence Stars. V. Recent Star Formation in the 30 Dor Nebula

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, Nino; Beccari, Giacomo

    2017-09-01

    We report on the properties of the low-mass stars that recently formed in the central ∼ 2\\buildrel{ \\prime}\\over{.} 7× 2\\buildrel{ \\prime}\\over{.} 7 of 30 Dor, including the R136 cluster. Using the photometric catalog of De Marchi et al., based on observations with the Hubble Space Telescope, and the most recent extinction law for this field, we identify 1035 bona fide pre-main-sequence (PMS) stars showing {{H}}α excess emission at the 4σ level with an {{H}}α equivalent width of 20 Å or more. We find a wide spread in age spanning the range ∼ 0.1{--}50 {Myr}. We also find that the older PMS objects are placed in front of the R136 cluster and are separated from it by a conspicuous amount of absorbing material, indicating that star formation has proceeded from the periphery into the interior of the region. We derive physical parameters for all PMS stars, including masses m, ages t, and mass accretion rates {\\dot{M}}{acc}. To identify reliable correlations between these parameters, which are intertwined, we use a multivariate linear regression fit of the type {log}{\\dot{M}}{acc}=a× {log}t+b× {log}m+c. The values of a and b for 30 Dor are compatible with those found in NGC 346 and NGC 602. We extend the fit to a uniform sample of 1307 PMS stars with 0.5< m/{M}ȯ < 1.5 and t< 16 {Myr} in six star-forming regions in the Large and Small Magellanic Clouds and Milky Way with metallicities in the range of 0.1–1.0 {{Z}}ȯ . We find a=-0.59+/- 0.02 and b=0.78+/- 0.08. The residuals are systematically different between the six regions and reveal a strong correlation with metallicity Z, of the type c=(-3.69+/- 0.02)-(0.30+/- 0.04)× {log}Z/{Z}ȯ . A possible interpretation of this trend is that when the metallicity is higher so is the radiation pressure, and this limits the accretion process, in both its rate and duration. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by

  5. CoRoT 223992193: A new, low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk

    NASA Astrophysics Data System (ADS)

    Gillen, E.; Aigrain, S.; McQuillan, A.; Bouvier, J.; Hodgkin, S.; Alencar, S. H. P.; Terquem, C.; Southworth, J.; Gibson, N. P.; Cody, A.; Lendl, M.; Morales-Calderón, M.; Favata, F.; Stauffer, J.; Micela, G.

    2014-02-01

    We present the discovery of CoRoT 223992193, a double-lined, detached eclipsing binary, comprising two pre-main sequence M dwarfs, discovered by the CoRoT space mission during a 23-day observation of the 3 Myr old NGC 2264 star-forming region. Using multi-epoch optical and near-IR follow-up spectroscopy with FLAMES on the Very Large Telescope and ISIS on the William Herschel Telescope we obtain a full orbital solution and derive the fundamental parameters of both stars by modelling the light curve and radial velocity data. The orbit is circular and has a period of 3.8745745 ± 0.0000014 days. The masses and radii of the two stars are 0.67 ± 0.01 and 0.495 ± 0.007 M⊙ and 1.30 ± 0.04 and 1.11-0.05+0.04 R⊙, respectively. This system is a useful test of evolutionary models of young low-mass stars, as it lies in a region of parameter space where observational constraints are scarce; comparison with these models indicates an apparent age of ~3.5-6 Myr. The systemic velocity is within 1σ of the cluster value which, along with the presence of lithium absorption, strongly indicates cluster membership. The CoRoT light curve also contains large-amplitude, rapidly evolving out-of-eclipse variations, which are difficult to explain using starspots alone. The system's spectral energy distribution reveals a mid-infrared excess, which we model as thermal emission from a small amount of dust located in the inner cavity of a circumbinary disk. In turn, this opens up the possibility that some of the out-of-eclipse variability could be due to occultations of the central stars by material located at the inner edge or in the central cavity of the circumbinary disk. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESAs RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.

  6. Chromospheric variations in main-sequence stars

    NASA Technical Reports Server (NTRS)

    Baliunas, S. L.; Donahue, R. A.; Soon, J. H.; Horne, J. H.; Frazer, J.; Woodard-Eklund, L.; Bradford, M.; Rao, L. M.; Wilson, O. C.; Zhang, Q.

    1995-01-01

    The fluxes in passbands 0.1 nm wide and centered on the Ca II H and K emission cores have been monitored in 111 stars of spectral type F2-M2 on or near the main sequence in a continuation of an observing program started by O. C. Wilson. Most of the measurements began in 1966, with observations scheduled monthly until 1980, when observations were schedueld sevral times per week. The records, with a long-term precision of about 1.5%, display fluctuations that can be idntified with variations on timescales similar to the 11 yr cycle of solar activity as well as axial rotation, and the growth and decay of emitting regions. We present the records of chromospheric emission and general conclusions about variations in surface magnetic activity on timescales greater than 1 yr but less than a few decades. The results for stars of spectral type G0-K5 V indicate a pattern of change in rotation and chromospheric activity on an evolutionary timescale, in which (1) young stars exhibit high average levels of activity, rapid rotation rates, no Maunder minimum phase and rarely display a smooth, cyclic variation; (2) stars of intermediate age (approximately 1-2 Gyr for 1 solar mass) have moderate levels of activity and rotation rates, and occasional smooth cycles; and (3) stars as old as the Sun and older have slower rotation rates, lower activity levels and smooth cycles with occasional Maunder minimum-phases.

  7. CoRoT 223992193: Investigating the variability in a low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk

    NASA Astrophysics Data System (ADS)

    Gillen, E.; Aigrain, S.; Terquem, C.; Bouvier, J.; Alencar, S. H. P.; Gandolfi, D.; Stauffer, J.; Cody, A.; Venuti, L.; Almeida, P. Viana; Micela, G.; Favata, F.; Deeg, H. J.

    2017-02-01

    CoRoT 223992193 is the only known low-mass, pre-main sequence eclipsing binary that shows evidence of a circumbinary disk. The system displays complex photometric and spectroscopic variability over a range of timescales and wavelengths. Using two optical CoRoT runs from 2008 and 2011/2012 (spanning 23 and 39 days), along with infrared Spitzer 3.6 and 4.5 μm observations (spanning 21 and 29 days, and simultaneous with the second CoRoT run), we model the out-of-eclipse light curves, finding that the large scale structure in both CoRoT light curves is consistent with the constructive and destructive interference of starspot signals at two slightly different periods. Using the vsini of both stars, we interpret this as the two stars having slightly different rotation periods: the primary is consistent with synchronisation and the secondary rotates slightly supersynchronously. Comparison of the raw 2011/2012 light curve data to the residuals of our spot model in colour-magnitude space indicates additional contributions consistent with a combination of variable dust emission and obscuration. There appears to be a tentative correlation between this additional variability and the binary orbital phase, with the system displaying increases in its infrared flux around primary and secondary eclipse. We also identify short-duration flux dips preceding secondary eclipse in all three CoRoT and Spitzer bands. We construct a model of the inner regions of the binary and propose that these dips could be caused by partial occultation of the central binary by the accretion stream onto the primary star. Analysis of 15 Hα profiles obtained with the FLAMES instrument on the Very Large Telescope reveal an emission profile associated with each star. The majority of this is consistent with chromospheric emission but additional higher velocity emission is also seen, which could be due to prominences. However, half of the secondary star's emission profiles display full widths at 10% intensity

  8. Habitable zones around main sequence stars.

    PubMed

    Kasting, J F; Whitmire, D P; Reynolds, R T

    1993-01-01

    A one-dimensional climate model is used to estimate the width of the habitable zone (HZ) around our Sun and around other main sequence stars. Our basic premise is that we are dealing with Earth-like planets with CO2/H2O/N2 atmospheres and that habitability requires the presence of liquid water on the planet's surface. The inner edge of the HZ is determined in our model by loss of water via photolysis and hydrogen escape. The outer edge of the HZ is determined by the formation of CO2 clouds, which cool a planet's surface by increasing its albedo and by lowering the convective lapse rate. Conservative estimates for these distances in our own Solar System are 0.95 and 1.37 AU, respectively; the actual width of the present HZ could be much greater. Between these two limits, climate stability is ensured by a feedback mechanism in which atmospheric CO2 concentrations vary inversely with planetary surface temperature. The width of the HZ is slightly greater for planets that are larger than Earth and for planets which have higher N2 partial pressures. The HZ evolves outward in time because the Sun increases in luminosity as it ages. A conservative estimate for the width of the 4.6-Gyr continuously habitable zone (CHZ) is 0.95 to 1.15 AU. Stars later than F0 have main sequence lifetimes exceeding 2 Gyr and, so, are also potential candidates for harboring habitable planets. The HZ around an F star is larger and occurs farther out than for our Sun; the HZ around K and M stars is smaller and occurs farther in. Nevertheless, the widths of all of these HZs are approximately the same if distance is expressed on a logarithmic scale. A log distance scale is probably the appropriate scale for this problem because the planets in our own Solar System are spaced logarithmically and because the distance at which another star would be expected to form planets should be related to the star's mass. The width of the CHZ around other stars depends on the time that a planet is required to

  9. Habitable zones around main sequence stars

    NASA Technical Reports Server (NTRS)

    Kasting, James F.; Whitmire, Daniel P.; Reynolds, Ray T.

    1993-01-01

    A mechanism for stabilizing climate on the earth and other earthlike planets is described, and the physical processes that define the inner and outer boundaries of the habitable zone (HZ) around the sun and main sequence stars are discussed. Physical constraints on the HZ obtained from Venus and Mars are taken into account. A 1D climate model is used to estimate the width of the HZ and the continuously habitable zone around the sun, and the analysis is extended to other main sequence stars. Whether other stars have planets and where such planets might be located with respect to the HZ is addressed. The implications of the findings for NASA's SETI project are considered.

  10. Habitable zones around main sequence stars

    NASA Technical Reports Server (NTRS)

    Kasting, James F.; Whitmire, Daniel P.; Reynolds, Ray T.

    1993-01-01

    A mechanism for stabilizing climate on the earth and other earthlike planets is described, and the physical processes that define the inner and outer boundaries of the habitable zone (HZ) around the sun and main sequence stars are discussed. Physical constraints on the HZ obtained from Venus and Mars are taken into account. A 1D climate model is used to estimate the width of the HZ and the continuously habitable zone around the sun, and the analysis is extended to other main sequence stars. Whether other stars have planets and where such planets might be located with respect to the HZ is addressed. The implications of the findings for NASA's SETI project are considered.

  11. Post-main-sequence planetary system evolution.

    PubMed

    Veras, Dimitri

    2016-02-01

    The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries.

  12. Post-main-sequence planetary system evolution

    PubMed Central

    Veras, Dimitri

    2016-01-01

    The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries. PMID:26998326

  13. Rotational evolution of pre-main sequence stars in Lupus

    NASA Astrophysics Data System (ADS)

    Wichmann, R.; Bouvier, J.; Allain, S.; Krautter, J.

    1998-02-01

    We present results of a study of the rotational periods of Post-TTauri stars (PTTSs) in the Lupus star forming region. These stars have been discovered by spectroscopic follow-up observations of ROSAT x-ray sources. Photometric observations have allowed to determine their luminosity, and by comparison with theoretical evolutionary tracks they were found to be significantly older on average than typical TTauri stars. 46 stars have been monitored photometrically, and for 34 of them photometric variations were found that are consistent with rotational brightness modulations caused by starspots. The large number of data on rotational periods of pre-main-sequence (PMS) / zero-age main-sequence (ZAMS) stars available by now allows us to study the impact of stellar mass on the evolution of angular momentum. For several different mass bins, we compare the available data on rotational periods with theoretical models, and find good agreement between theory and observations for the mass-dependency of the pre-main-sequence evolution of angular momentum. We also study the relation between activity, rotation, mass, and age of low mass stars, and demonstrate that activity is driven by rotation mainly, while it seems to be rather independent of mass and age. Based on observations collected at European Southern Observatory, La Silla, Chile (observing proposals ESO No. 55.E-0575, 57.E-0250).

  14. The Solar system's post-main-sequence escape boundary

    NASA Astrophysics Data System (ADS)

    Veras, Dimitri; Wyatt, Mark C.

    2012-04-01

    The Sun will eventually lose about half of its current mass non-linearly over several phases of post-main-sequence evolution. This mass loss will cause any surviving orbiting body to increase its semimajor axis and perhaps vary its eccentricity. Here, we use a range of solar models spanning plausible evolutionary sequences and assume isotropic mass loss to assess the possibility of escape from the Solar system. We find that the critical semimajor axis in the Solar system within which an orbiting body is guaranteed to remain bound to the dying Sun due to perturbations from stellar mass loss alone is ≈103-104 au. The fate of objects near or beyond this critical semimajor axis, such as the Oort Cloud, outer scattered disc and specific bodies such as Sedna, will significantly depend on their locations along their orbits when the Sun turns off the main sequence. These results are applicable to any exoplanetary system containing a single star with a mass, metallicity and age which are approximately equal to the Sun's, and suggest that few extrasolar Oort Clouds could survive post-main-sequence evolution intact.

  15. THE INFRARED EYE OF THE WIDE-FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE REVEALS MULTIPLE MAIN SEQUENCES OF VERY LOW MASS STARS IN NGC 2808

    SciTech Connect

    Milone, A. P.; Aparicio, A.; Monelli, M. E-mail: aparicio@iac.es; and others

    2012-08-01

    We use images taken with the infrared channel of the Wide Field Camera 3 on the Hubble Space Telescope to study the multiple main sequences (MSs) of NGC 2808. Below the turnoff, the red, the middle, and the blue MS, previously detected from visual-band photometry, are visible over an interval of about 3.5 F160W magnitudes. The three MSs merge together at the level of the MS bend. At fainter magnitudes, the MS again splits into two components containing {approx}65% and {approx}35% of stars, with the most-populated MS being the bluest one. Theoretical isochrones suggest that the latter is connected to the red MS discovered in the optical color-magnitude diagram (CMD) and hence corresponds to the first stellar generation, having primordial helium and enhanced carbon and oxygen abundances. The less-populated MS in the faint part of the near-IR CMD is helium-rich and poor in carbon and oxygen, and it can be associated with the middle and the blue MS of the optical CMD. The finding that the photometric signature of abundance anti-correlation is also present in fully convective MS stars reinforces the inference that they have a primordial origin.

  16. Binary interactions with high accretion rates onto main sequence stars

    NASA Astrophysics Data System (ADS)

    Shiber, Sagiv; Schreier, Ron; Soker, Noam

    2016-07-01

    Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; red novae; red transients). These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to ≈ 10-2 M ⊙ yr-1 for solar type stars, and up to ≈ 1 M ⊙ yr-1 for very massive stars. We speculate that magnetic fields amplified in such extreme conditions might lead to the formation of massive bipolar outflows that can remove most of the disk's energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.

  17. MML 53 - The Brightest Pre-Main-Sequence Eclipsing Binary

    NASA Astrophysics Data System (ADS)

    Stempels, H. C.; Hebb, L.

    2011-12-01

    MML 53 is a newly discovered and bright (V=10.8m) pre-main-sequence eclipsing binary located in the 15-22 Myr old Upper-Centaur-Lupus (UCL) star forming region, with component masses of ˜1.02 M⊙ and ˜0.88 M⊙. This system is the first low-mass pre-main-sequence eclipsing binary discovered outside the ˜10 Myr old Orion star-forming region, and samples a slightly older age. A closer examination of MML 53 reveals that this is a three-component system, where the primary and secondary form a close eclipsing binary. Here we present preliminary results from our recent high-resolution spectroscopic study of this object, including estimates of the individual component masses, radii and temperatures. In addition we find indications that the tertiary in MML 53 interacts gravitationally with the eclipsing components.

  18. Main sequence models for massive zero-metal stars

    NASA Technical Reports Server (NTRS)

    Cary, N.

    1974-01-01

    Zero-age main-sequence models for stars of 20, 10, 5, and 2 solar masses with no heavy elements are constructed for three different possible primordial helium abundances: Y=0.00, Y=0.23, and Y=0.30. The latter two values of Y bracket the range of primordial helium abundances cited by Wagoner. With the exceptions of the two 20 solar mass models that contain helium, these models are found to be self-consistent in the sense that the formation of carbon through the triple-alpha process during premain sequence contraction is not sufficient to bring the CN cycle into competition with the proton-proton chain on the ZAMS. The zero-metal models of the present study have higher surface and central temperatures, higher central densities, smaller radii, and smaller convective cores than do the population I models with the same masses.

  19. Main sequence models for massive zero-metal stars

    NASA Technical Reports Server (NTRS)

    Cary, N.

    1974-01-01

    Zero-age main-sequence models for stars of 20, 10, 5, and 2 solar masses with no heavy elements are constructed for three different possible primordial helium abundances: Y=0.00, Y=0.23, and Y=0.30. The latter two values of Y bracket the range of primordial helium abundances cited by Wagoner. With the exceptions of the two 20 solar mass models that contain helium, these models are found to be self-consistent in the sense that the formation of carbon through the triple-alpha process during premain sequence contraction is not sufficient to bring the CN cycle into competition with the proton-proton chain on the ZAMS. The zero-metal models of the present study have higher surface and central temperatures, higher central densities, smaller radii, and smaller convective cores than do the population I models with the same masses.

  20. Spectroscopic evolution of massive stars on the main sequence

    NASA Astrophysics Data System (ADS)

    Martins, F.; Palacios, A.

    2017-02-01

    Context. The evolution of massive stars depends on several parameters, and the relation between different morphological types is not fully constrained. Aims: We aim to provide an observational view of evolutionary models in the Hertzsprung-Russell diagram, on the main sequence. This view should help compare observations and model predictions. Methods: We first computed evolutionary models with the code STAREVOL for initial masses between 15 and 100 M⊙. We subsequently calculated atmosphere models at specific points along the evolutionary tracks, using the code CMFGEN. Synthetic spectra obtained in this way were classified as if they were observational data: we assigned them a spectral type and a luminosity class. We tested our spectral classification by comparison to observed spectra of various stars with different spectral types. We also compared our results with empirical data of a large number of OB stars. Results: We obtain spectroscopic sequences along evolutionary tracks. In our computations, the earliest O stars (O2-3.5) appear only above 50 M⊙. For later spectral types, a similar mass limit exists, but is lower. A luminosity class V does not correspond to the entire main sequence. This only holds for the 15 M⊙ track. As mass increases, a larger portion of the main sequence is spent in luminosity class III. Above 50 M⊙, supergiants appear before the end of core-hydrogen burning. Dwarf stars (luminosity class V) do not occur on the zero-age main sequence above 80 M⊙. Consequently, the distribution of luminosity class V in the HR diagram is not a diagnostic of the length of the main sequence (above 15 M⊙) and cannot be used to constrain the size of the convective core. The distribution of dwarfs and giants in the HR diagram that results from our calculations agrees well with the location of stars analyzed by means of quantitative spectroscopy. For supergiants, there is a slight discrepancy in the sense that luminosity class I is observed slightly

  1. TIME-SERIES PHOTOMETRY OF STARS IN AND AROUND THE LAGOON NEBULA. I. ROTATION PERIODS OF 290 LOW-MASS PRE-MAIN-SEQUENCE STARS IN NGC 6530

    SciTech Connect

    Henderson, Calen B.; Stassun, Keivan G.

    2012-03-01

    We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of {approx}50,000 stars in the Lagoon Nebula H II region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5 days < P < 10 days; the short-period cutoff corresponds to breakup. We observe no obvious bimodality in the period distribution, but we do find that stars with disk signatures rotate more slowly on average. The stars' X-ray luminosities are roughly flat with rotation period, at the saturation level (log L{sub X} /L{sub bol} Almost-Equal-To -3.3). However, we find a significant positive correlation between L{sub X} /L{sub bol} and corotation radius, suggesting that the observed X-ray luminosities are regulated by centrifugal stripping of the stellar coronae. The period-mass relationship in NGC 6530 is broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the relationship among the slowest rotators differs from that in the ONC and other young clusters. We show that the slope of the period-mass relationship for the slowest rotators can be used as a proxy for the age of a young cluster, and we argue that NGC 6530 may be slightly younger than the ONC, making it a particularly important touchstone for models of angular momentum evolution in young, low-mass stars.

  2. Main Sequence Binary Fraction in Globular Cluster NGC 6397

    NASA Astrophysics Data System (ADS)

    Srinath, Srikar; Cool, A. M.; Anderson, J.

    2011-01-01

    We report preliminary results from a study of main-sequence binaries (MSBs) in the core-collapsed globular cluster NGC 6397 using the Hubble Space Telescope (HST) Advanced Camera for Surveys. We analyze images of the central regions of the cluster extending out to approximately one half-mass radius (rhm = 2.33') taken with the Wide Field Channel in the F435W and F625W filters. After removing non-members using proper motions, we construct a color-magnitude diagram (CMD) containing 15578 cluster stars. Model cluster CMDs indicate that in the range 16 < R < 22, MSBs with mass ratio (q=M2/M1) > 0.6 appear sufficiently far above and redward of the main sequence ridge line to be distinguishable from the single-star sequence. Out of 10835 stars in this magnitude range, we identify an initial set of 137 stars (with primary masses in the range 0.4-0.7 Msun) whose offset from the single-star sequence is statistically significant. A check of quality of fit to the PSF combined with close visual inspection of the images shows that 85 of these stars are well measured and unresolved and are thus good MSB candidates. The resulting upper limit on the fraction of MSBs with q > 0.6 and primaries in the range 0.4-0.7 Msun is 0.8%. We compare our measured fraction and the radial distribution of the MSB candidates to earlier findings based on HST/WFPC2 imaging and explore the significance of the results for the total binary population in NGC 6397. Keywords: binaries: general - globular clusters: individual(NGC 6397) - binary fraction - stars: main sequence binary

  3. Stellar evolution from the zero-age main sequence

    NASA Technical Reports Server (NTRS)

    Mengel, J. G.; Demarque, P.; Sweigart, A. V.; Gross, P. G.

    1979-01-01

    A consistent set of 247 evolutionary sequences extending from the ZAMS to the red-giant branch is presented for Y from 0.10 to 0.40, Z from 0.00001 to 0.10, and masses of 0.55 to 6.90 solar masses. Each sequence is started from a homogeneous ZAMS model, and almost all are evolved to the base of the red-giant branch. It is shown that: (1) the relative position of the main sequence can be determined as a function of composition; (2) theoretical luminosity functions can be derived from the relative evolutionary time scales; (3) a dip in luminosity sometimes occurs at the base of the red-giant branch and is most pronounced at larger Z values; (4) metal-poor stars evolve farther up along the main sequence before turning off toward the red-giant branch; and (5) the onset of helium burning halts the evolution across the Hertzsprung gap for the most massive and most metal-poor models, so that the star remains blue during its phase of core-helium burning.

  4. Are blue supergiants descendants of magnetic main sequence stars?

    NASA Astrophysics Data System (ADS)

    Petermann, Ilka; Langer, Norbert

    2013-06-01

    Red and blue supergiants are, together with luminous blue variables and Wolf-Rayet stars, evolved phases of massive (OB) stars. The position of blue supergiants (BSG) near the main sequence band cannot be reproduced by standard stellar evolution calculations. However, the assumption of a reduced convective core mass during the main sequence (MS) due to strong internal magnetic fields, established in roughly 10% of all stars on the upper MS, can recover this BSG population. For our calculations of the (non-rotating) massive stars at solar metallicity we used the 1D stellar evolution code MESA and compare their evolutionary tracks with positions from stars obtained from the VLT Flames survey of massive stars.

  5. A Coronagraphic Survey for Circumstellar Disks Around Main Sequence and Pre-Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Kalas, Paul George

    1996-12-01

    We search for optical reflection nebulosity around ~100 main sequence and pre-main sequence stars to test the hypothesis that Vega-like stars possess replenished dust disks. A Lyot coronagraph is used to suppress light from the central star and to observe the circumstellar environment closer to planet-forming regions than is possible through direct imaging. A model of scattered light from axisymmetric circumstellar disks is developed to establish the sensitivity limits of our observations. Circumstellar nebulosities are detected around four main sequence stars: β Pic, BD +31o 643, HR 241, and HR 1307. No circumstellar disks are found around ~100 other main sequence stars, including Vega, Fomalhaut, HD 98800, HR 4796, and 51 Oph. Non-detections of disks in the main sequence sample, combined with the sensitivity limits, suggest that the optical scattering cross-section of dust at 102 - 103 AU radii is not strongly correlated to the thermal cross-section at 1-10 AU radii. We show that the prominence of the β Pic disk is primarily a result of its large scattering cross-section, rather than its edge-on inclination or close proximity to the Sun (Kalas & Jewitt 1996). Five types of asymmetry are identified and measured in the disk morphology (Kalas & Jewitt 1995). The observed tilt of the midplane may result from a small inclination (<= 5o) of the disk to our line of sight, combined with a non-isotropic scattering phase function. The remaining four asymmetries indicate a non-axisymmetric distribution of orbiting dust particles between 150 and 800 AU projected radius. The disk may have been gravitationally perturbed in the past 102 to 103 years, though a perturbing agent is not detected. A nebulosity imaged near the B5V double star BD +31o 643 is identified as a circumstellar disk candidate based on its morphological similarity to β Pic and our model disks (Kalas & Jewitt 1997). The disk has a position angle 131o, a projected radius of ~2000 AU, an inclination of i

  6. High-precision Radio and Infrared Astrometry of LSPM J1314+1320AB. II. Testing Pre-main-sequence Models at the Lithium Depletion Boundary with Dynamical Masses

    NASA Astrophysics Data System (ADS)

    Dupuy, Trent J.; Forbrich, Jan; Rizzuto, Aaron; Mann, Andrew W.; Aller, Kimberly; Liu, Michael C.; Kraus, Adam L.; Berger, Edo

    2016-08-01

    We present novel tests of pre-main-sequence models based on individual dynamical masses for the M7 binary LSPM J1314+1320AB. Joint analysis of Keck adaptive optics astrometric monitoring along with Very Long Baseline Array radio data from a companion paper yield component masses of 92.8 ± 0.6 M Jup (0.0885 ± 0.0006 M ⊙) and 91.7 ± 1.0 M Jup (0.0875 ± 0.0010 M ⊙) and a parallactic distance of 17.249 ± 0.013 pc. We find component luminosities consistent with the system being coeval at 80.8 ± 2.5 Myr, according to BHAC15 evolutionary models. The presence of lithium is consistent with model predictions, marking the first test of the theoretical lithium depletion boundary using ultracool dwarfs of known mass. However, we find that the evolutionary model-derived average effective temperature (2950 ± 5 K) is 180 K hotter than that given by a spectral type-{T}{eff} relation based on BT-Settl models (2770 ± 100 K). We suggest that the dominant source of this discrepancy is model radii being too small by ≈13%. In a test mimicking the typical application of models by observers, we derive masses on the H-R diagram using luminosity and BT-Settl temperature. The estimated masses are lower by {46}-19+16 % (2.0σ) than we measure dynamically and would imply that this is a system of ≈50 M Jup brown dwarfs, highlighting the large systematic errors possible in H-R diagram properties. This is the first time masses have been measured for ultracool (≥M6) dwarfs displaying spectral signatures of low gravity. Based on features in the infrared, LSPM J1314+1320AB appears to have higher gravity than typical Pleiades and AB Dor members, opposite the expectation given its younger age. The components of LSPM J1314+1320AB are now the nearest, lowest mass pre-main-sequence stars with direct mass measurements. 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

  7. ON THE DIFFERENTIAL ROTATION OF MASSIVE MAIN-SEQUENCE STARS

    SciTech Connect

    Rogers, T. M.

    2015-12-20

    To date, asteroseismology has provided core-to-surface differential rotation measurements in eight main-sequence stars. These stars, ranging in mass from ∼1.5–9 M{sub ⊙}, show rotation profiles ranging from uniform to counter-rotation. Although they have a variety of masses, these stars all have convective cores and overlying radiative regions, conducive to angular momentum transport by internal gravity waves (IGWs). Using two-dimensional numerical simulations, we show that angular momentum transport by IGWs can explain all of these rotation profiles. We further predict that, should high mass, faster rotating stars be observed, the core-to-envelope differential rotation will be positive, but less than one.

  8. Detecting Mass Loss in Main Belt Asteroids

    NASA Astrophysics Data System (ADS)

    Sandberg, Erik; Rajagopal, Jayadev; Ridgway, Susan E.; Kotulla, Ralf C.; Valdes, Francisco; Allen, Lori

    2016-01-01

    Sandberg, E., Rajagopal, J., Ridgway, S.E, Kotulla, R., Valdes, F., Allen, L.The Dark Energy Camera (DECam) on the 4m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) is being used for a survey of Near Earth Objects (NEOs). Here we attempt to identify mass loss in main belt asteroids (MBAs) from these data. A primary motivation is to understand the role that asteroids may play in supplying dust and gas for debris disks. This work focuses on finding methods to automatically pick out asteroids that have qualities indicating possible mass loss. Two methods were chosen: looking for flux above a certain threshold in the asteroid's radial profile, and comparing its PSF to that of a point source. After sifting through 490 asteroids, several have passed these tests and should be followed up with a more rigorous analysis.Sandberg was supported by the NOAO/KPNO Research Experience for Undergraduates (REU) Program which is funded by the National Science Foundation Research Experiences for Undergraduates Program (AST-1262829)

  9. Evolution of Pre-Main Sequence Stellar Activity

    NASA Astrophysics Data System (ADS)

    Kuin, N. Paul

    The best known low mass pre-main sequence stars, the T Tauri stars. have very active chromospheres and show a variable emission line spectrum. There is a large variety in activity amongst than. Recently another type of pre-main sequence stars was identified which may be post T Tauri stars (PTTS) and were named 'naked T Tauri stars' (NTTS). These PTTS/NTTS are strong X-Ray sources, and do not have a T Tauri type spectrum. The age of these sources is comparable to those of the T Tauri stars, which implies that either the activity evolves much faster in pre-main sequence stars than the timescale in which they move towards the main sequence, or that an external source is responsible for their activity. We propose to obtain low resolution long- and short wavelength RE spectra of two of the PTTS/NTTS and of a T Tauri star of comparable activity. Archival data will be used from three other T Tauri stars having larger activity. The data will enable us to derive models for the chromosphere and transition region. Those will clarify whether there is a gradual change in activity, or a sudden one as way be caused by the closing up of an open magnetic field. Because they cover a large range in chromoshperic activity the models will enable us to improve the alfven wave wind models used for T Tau and RU Lup. In particular the question of the wave dissipation scale length and wave leakage will be considered.

  10. Chromospheric Activity in Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Simon, Theodore

    IUE observations of solar-type stars show a decline of chromospheric and TR emission with age. For main-sequence stars older than 100 million yr, this decay is exponential from a plateau defined by the youngest stars. At an age of ~1 million yr, the pre-main-sequence T Tauri stars have UV emission line fluxes some 2 orders of magnitude above the plateau for mainsequence stars. This suggests that chromospheric activity in the T Tauri stars falls to the levels of the older stars by a separate decay scheme. The decline in pre-mainsequence activity may be caused by the evolutionary shallowing of the convection zone, while on the main-sequence it is due to the star's spindown. This hypothesis needs confirmation, but relatively few T Tauri stars have been observed by IUE. Since the majority of the T Tauri stars thus far observed are probably more massive than the Sun, it may be inappropriate to compare their UV emission with that of the older I Mo dwarf stars. We propose here to observe the ultraviolet chromospheric and TR lines of pre-main-sequence stars we believe to be of ~1 M(sun). We have chosen a sample of low-luminosity M-type T Tauri stars from the T-associations in Lupus; if evolutionary tracks have any validity, a large fraction of those stars should be close to 1 M(sun)in mass. In order to place the stars more accurately on the H-R diagram and to determine their rotation rates (for comparison with the mainsequence stars), we plan concurrent visual spectroscopy and visual-infrared photometry.

  11. Orbital motion in pre-main sequence binaries

    SciTech Connect

    Schaefer, G. H.; Prato, L.; Simon, M.; Patience, J.

    2014-06-01

    We present results from our ongoing program to map the visual orbits of pre-main sequence (PMS) binaries in the Taurus star forming region using adaptive optics imaging at the Keck Observatory. We combine our results with measurements reported in the literature to analyze the orbital motion for each binary. We present preliminary orbits for DF Tau, T Tau S, ZZ Tau, and the Pleiades binary HBC 351. Seven additional binaries show curvature in their relative motion. Currently, we can place lower limits on the orbital periods for these systems; full solutions will be possible with more orbital coverage. Five other binaries show motion that is indistinguishable from linear motion. We suspect that these systems are bound and might show curvature with additional measurements in the future. The observations reported herein lay critical groundwork toward the goal of measuring precise masses for low-mass PMS stars.

  12. Pre-main-sequence disk accretion in Z Canis Majoris

    NASA Technical Reports Server (NTRS)

    Hartmann, L.; Kenyon, S. J.; Hewett, R.; Edwards, S.; Strom, K. M.; Strom, S. E.; Stauffer, J. R.

    1989-01-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.

  13. Pre-main-sequence disk accretion in Z Canis Majoris

    SciTech Connect

    Hartmann, L.; Kenyon, S.J.; Hewett, R.; Edwards, S.; Strom, K.M.; Strom, S.E.; Stauffer, J.R.

    1989-03-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion. 41 references.

  14. Orbital Motion in Pre-main Sequence Binaries

    NASA Astrophysics Data System (ADS)

    Schaefer, G. H.; Prato, L.; Simon, M.; Patience, J.

    2014-06-01

    We present results from our ongoing program to map the visual orbits of pre-main sequence (PMS) binaries in the Taurus star forming region using adaptive optics imaging at the Keck Observatory. We combine our results with measurements reported in the literature to analyze the orbital motion for each binary. We present preliminary orbits for DF Tau, T Tau S, ZZ Tau, and the Pleiades binary HBC 351. Seven additional binaries show curvature in their relative motion. Currently, we can place lower limits on the orbital periods for these systems; full solutions will be possible with more orbital coverage. Five other binaries show motion that is indistinguishable from linear motion. We suspect that these systems are bound and might show curvature with additional measurements in the future. The observations reported herein lay critical groundwork toward the goal of measuring precise masses for low-mass PMS stars.

  15. DISSECTING THE QUASAR MAIN SEQUENCE: INSIGHT FROM HOST GALAXY PROPERTIES

    SciTech Connect

    Sun, Jiayi; Shen, Yue

    2015-05-01

    The diverse properties of broad-line quasars appear to follow a well-defined main sequence along which the optical Fe ii strength increases. It has been suggested that this sequence is mainly driven by the Eddington ratio (L/L{sub Edd}) of the black hole (BH) accretion. Shen and Ho demonstrated with quasar clustering analysis that the average BH mass decreases with increasing Fe ii strength when quasar luminosity is fixed, consistent with this suggestion. Here we perform an independent test by measuring the stellar velocity dispersion σ{sub *} (hence, the BH mass via the M–σ{sub *} relation) from decomposed host spectra in low-redshift Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity, σ{sub *} systematically decreases with increasing Fe ii strength, confirming that the Eddington ratio increases with Fe ii strength. We also found that at fixed luminosity and Fe ii strength, there is little dependence of σ{sub *} on the broad Hβ FWHM. These new results reinforce the framework that the Eddington ratio and orientation govern most of the diversity seen in broad-line quasar properties.

  16. 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.

  17. Spatially Resolved Star Formation Main Sequence of Galaxies

    NASA Astrophysics Data System (ADS)

    Cano-Díaz, M.; Sánchez, S. F.; Zibetti, S.; Ascaribar, Y.; Bland-Hawthorn, J.; Ziegler, B.; González-Delgado, R. M.; Walcher, C. J.; García-Benito, R.; Mast, D.; Mendoza-Pérez, M. A.; Falcón-Barroso, J.; Galbany, L.; Husemann, B.; Kehring, C.; Marino, R. A.; Sánchez-Blázquez, P.; López-Cobá, C.; López-Sánchez, A. R.; Vilchez, J. M.

    2016-06-01

    The relation known as Star Formation Main Sequence (SFMS) of galaxies is defined in terms of stellar mass and star formation rate. This approximately linear relation has been proven to be tight and holds for several star formation indicators at local and at high redshifts. In this talk I will show recent results about our first attempts to study the Spatially Resolved SFMS, using integral field spectroscopic data, coming primarily from the CALIFA survey. I will present as a main result that a local SFMS is found with a slope and zero point of 0.72 +/ 0.04, and -7.95 +/ 0.29 respectively. I will also discuss the influence of characteristics such as environment and morphology in the relation. Finally I will present some extensions of these results for data com in from the MaNGA survey.

  18. Atomic masses from (mainly) experimental data

    SciTech Connect

    Wapstra, A.H.; Audi, G.; Hoekstra, R.

    1988-07-01

    The present list of atomic masses is an update from the 1983 Atomic Mass Table. Two categories of mass values are represented in the tabulation: those derived purely from experimental data, and those calculated with the help of systematic trends also. In order to improve the reliability of the mass values of the latter category, a novel method of extrapolation has been added capitalizing on new formulas for neutron and proton pairing energies. copyright 1988 Academic Press, Inc.

  19. Impact of initial models and variable accretion rates on the pre-main-sequence evolution of massive and intermediate-mass stars and the early evolution of H II regions

    NASA Astrophysics Data System (ADS)

    Haemmerlé, Lionel; Peters, Thomas

    2016-05-01

    Massive star formation requires the accretion of gas at high rate while the star is already bright. Its actual luminosity depends sensitively on the stellar structure. We compute pre-main-sequence tracks for massive and intermediate-mass stars with variable accretion rates and study the evolution of stellar radius, effective temperature and ionizing luminosity, starting at 2 M⊙ with convective or radiative structures. The radiative case shows a much stronger swelling of the protostar for high accretion rates than the convective case. For radiative structures, the star is very sensitive to the accretion rate and reacts quickly to accretion bursts, leading to considerable changes in photospheric properties on time-scales as short as 100-1000 yr. The evolution for convective structures is much less influenced by the instantaneous accretion rate, and produces a monotonically increasing ionizing flux that can be many orders of magnitude smaller than in the radiative case. For massive stars, it results in a delay of the H II region expansion by up to 10 000 yr. In the radiative case, the H II region can potentially be engulfed by the star during the swelling, which never happens in the convective case. We conclude that the early stellar structure has a large impact on the radiative feedback during the pre-main-sequence evolution of massive protostars and introduces an important uncertainty that should be taken into account. Because of their lower effective temperatures, our convective models may hint at a solution to an observed discrepancy between the luminosity distribution functions of massive young stellar objects and compact H II regions.

  20. Massive pre-main-sequence stars in M17

    NASA Astrophysics Data System (ADS)

    Ramírez-Tannus, M. C.; Kaper, L.; de Koter, A.; Tramper, F.; Bik, A.; Ellerbroek, L. E.; Ochsendorf, B. B.; Ramírez-Agudelo, O. H.; Sana, H.

    2017-08-01

    The formation process of massive stars is still poorly understood. Massive young stellar objects (mYSOs) are deeply embedded in their parental clouds; these objects are rare, and thus typically distant, and their reddened spectra usually preclude the determination of their photospheric parameters. M17 is one of the best-studied H ii regions in the sky, is relatively nearby, and hosts a young stellar population. We have obtained optical to near-infrared spectra of previously identified candidate mYSOs and a few OB stars in this region with X-shooter on the ESO Very Large Telescope. The large wavelength coverage enables a detailed spectroscopic analysis of the photospheres and circumstellar disks of these candidate mYSOs. We confirm the pre-main-sequence (PMS) nature of six of the stars and characterise the O stars. The PMS stars have radii that are consistent with being contracting towards the main sequence and are surrounded by a remnant accretion disk. The observed infrared excess and the double-peaked emission lines provide an opportunity to measure structured velocity profiles in the disks. We compare the observed properties of this unique sample of young massive stars with evolutionary tracks of massive protostars and propose that these mYSOs near the western edge of the H ii region are on their way to become main-sequence stars ( 6-20 M⊙) after having undergone high mass accretion rates (Ṁacc 10-4-10-3M⊙yr-1). Their spin distribution upon arrival at the zero age main-sequence is consistent with that observed for young B stars, assuming conservation of angular momentum and homologous contraction. Based on observations collected at the European Southern Observatory at Paranal, Chile (ESO programmes 60.A-9404(A), 085.D-0741, 089.C-0874(A), and 091.C-0934(B)).The full normalised X-shooter spectra are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/604/A78

  1. Infalling Planetesimals in Pre-Main Sequence Stellar Systems

    NASA Technical Reports Server (NTRS)

    Grady, Carol A.; Sitko, Michael L.; Russell, Ray W.; Lynch, David K.; Hanner, Martha S.; Perez, Mario R.; Bjorkman, Karen S.; DeWinter, Dolf

    1999-01-01

    These are exciting times in the study of planetary system formation with a steadily expanding inventory of exo-planet detections, and imaging of dust disks around nearby young and main sequence stars. While these discoveries imply that our Solar System is far from unique, linking the data for the protoplanetary and debris disks to mature planetary systems requires a demonstration that disk evolution proceeds via planetesimal production and growth to the formation of planets. Theoretical studies of planet formation indicate that planetesimals grow, via runaway accretion, to lunar-sized (approx. = 2000 km) embryos in 10(exp 5) years. Recent gas giant planet formation studies have suggested that most of the action in planet formation occurs over 1-16 Myr, with formation of planets similar to Jupiter in t less than 10 Myr, within the time interval that infrared (IR) and optical emission line studies have demonstrated that circumstellar material remains detectable around both solar mass and intermediate mass stars. Direct imaging of exo-planetesimals is not feasible with current and foreseeable technology, since such bodies have substantially less surface area than micron-sized grains distributed in a disk, and thus are inefficient IR emitters. However, such bodies may be indirectly detectable.

  2. Dynamical Mass Constraints on Low-Mass Pre-Main-Sequence Stellar Evolutionary Tracks: An Eclipsing Binary in Orion with a 1.0 M(solar) Primary and a 0.7 M(solar) Secondary

    DTIC Science & Technology

    2004-04-01

    Simon et al. (2000), the distance uncertainty to any particular star in Taurus may be as large as 15%, manifesting itself as a systematic error in...star in Taurus ), which have identical masses and are at identical positions in the H-R diagram. But, disconcertingly, we also find instances of

  3. Scooping helium out in the early B-type main sequence stars

    NASA Astrophysics Data System (ADS)

    Staritsin, E. I.

    The observed process of surface helium enrichment through the main sequence phase of B-stars evolution is analysed on the basis of current hydrodynamical model of matter mixing in rotating star interior. It is shown that shear turbulence and semiconvection are the main processes of partial matter mixing in the interiors of a rotating star with a mass of 8 M⊙. The calculated surface helium enhancement during the second half of main sequence stage of evolution looks like an observable one.

  4. Accretion disc boundary layers around pre-main-sequence stars.

    NASA Astrophysics Data System (ADS)

    Godon, P.

    1996-04-01

    One-dimensional time-dependent calculations of geometrically thin accretion disc boundary layers in pre-main-sequence stars are carried out for mass-accretion rates in the range M˙ = 5×10-7 to 10-4 Msunyr-1, α = 0.005-0.3 and different inner boundary conditions on the temperature. Two kinds of solution are obtained: those with a distinct thermal boundary layer (BL) component and those without a thermal boundary layer. For M˙ up to ≍10-5Msunyr-1, and for a α > αcritic ≍ 0.04, solutions with a thermal BL are obtained. For M˙ ≍ 10-4Msunyr-1 or for α < αcritic solutions without a thermal BL are obtained. The inner boundary condition Fr = σTeff4 leads to hotter solutions and higher threshold values αcritic while the no-flux boundary condition dT/dr=0 leads to cooler solutions. For a very low mass-accretion rate (M˙ ≍ 5×10-7Msunyr-1), the temperature in the disc drops below 104K and the ionization front is adjacent to the outer edge of the hot thermal boundary layer. In the vicinity of the ionization front, the medium becomes slightly optically thin. For a very high mass accretion rate, advection of energy (ζ = Ladv/Lacc ≍ 0.1-0.2) from the boundary layer into the inner boundary becomes important, and the boundary layer luminosity is only a fraction of its expected value.

  5. Habitable Zones of Post-Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2016-05-01

    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 to 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.

  6. The Habitable Zones of Pre-main-sequence Stars

    NASA Astrophysics Data System (ADS)

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2014-12-01

    We calculate the pre-main-sequence habitable zone (HZ) for stars of spectral classes F-M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important for understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet-star separation for cool stars than is the case for the traditional main-sequence (MS) HZ. We use one-dimensional radiative-convective climate and stellar evolutionary models to calculate pre-main-sequence HZ distances for F1-M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 (including the full range of M stars) receive stellar fluxes that exceed the runaway greenhouse threshold, and thus may lose substantial amounts of water initially delivered to them. We predict that M-star planets need to initially accrete more water than Earth did, or, alternatively, have additional water delivered later during the long pre-MS phase to remain habitable. Our findings are also consistent with recent claims that Venus lost its water during accretion.

  7. THE HABITABLE ZONES OF PRE-MAIN-SEQUENCE STARS

    SciTech Connect

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2014-12-20

    We calculate the pre-main-sequence habitable zone (HZ) for stars of spectral classes F-M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important for understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet-star separation for cool stars than is the case for the traditional main-sequence (MS) HZ. We use one-dimensional radiative-convective climate and stellar evolutionary models to calculate pre-main-sequence HZ distances for F1-M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 (including the full range of M stars) receive stellar fluxes that exceed the runaway greenhouse threshold, and thus may lose substantial amounts of water initially delivered to them. We predict that M-star planets need to initially accrete more water than Earth did, or, alternatively, have additional water delivered later during the long pre-MS phase to remain habitable. Our findings are also consistent with recent claims that Venus lost its water during accretion.

  8. Submillimeter Imaging of Dust Around Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Jewitt, David

    1998-01-01

    This grant was to image circumstellar dust disks surrounding main-sequence stars. The delivery of the SCUBA detector we had planned to use for this work was delayed repeatedly, leading us to undertake a majority of the observations with the UKT14 submillimeter detector at the JCMT (James Clerk Maxwell Telescope) and optical imagers and a coronagraph at the University of Hawaii 2.2-m telescope. Major findings under this grant include: (1) We discovered 5 asymmetries in the beta Pictoris regenerated dust disk. The discovery of these asymmetries was a surprise, since smearing due to Keplerian shear should eliminate most such features on timescales of a few thousand years. One exception is the "wing tilt" asymmetry, which we interpret as due to the scattering phase function of dust disk particles. From the wing tilt and a model of the phase function, we find a disk plane inclination to the line of sight of < 5 degrees. Other asymmetries (e.g. the butterfly asymmetry) suggest a disk that has been recently disturbed. We searched for possible nearby perturbers but found no clear candidates. Low mass stars (M dwarfs) and brown dwarfs would have fallen beneath the sensitivity threshhold of our survey, however. (2) We calculated a set of disk models to assess the detectability of dust disks around stars as a function of (a) distance, (b) disk, inclination (c) dust optical depth/mass, and (d) imaging resolution. These models guided our observational strategy on Mauna Kea. (3) We performed a coronagraphic survey of approx. 100 main-sequence stars in search of additional examples of circumstellar disks. The best new candidate disk, around the 5 M(sun) star BD+31deg.643, is distinguished by its large extent (few x 10( exp 3) AU). This disk, if real, cannot be rotationally supported. We suggest that the dust particles are ejected from a smaller, unseen disk (Kuiper Belt?) by strong radiation pressure forces due to the high luminosity central star. (4) SCUBA images of

  9. Submillimeter Imaging of Dust Around Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Jewitt, David

    1998-01-01

    This grant was to image circumstellar dust disks surrounding main-sequence stars. The delivery of the SCUBA detector we had planned to use for this work was delayed repeatedly, leading us to undertake a majority of the observations with the UKT14 submillimeter detector at the JCMT (James Clerk Maxwell Telescope) and optical imagers and a coronagraph at the University of Hawaii 2.2-m telescope. Major findings under this grant include: (1) We discovered 5 asymmetries in the beta Pictoris regenerated dust disk. The discovery of these asymmetries was a surprise, since smearing due to Keplerian shear should eliminate most such features on timescales of a few thousand years. One exception is the "wing tilt" asymmetry, which we interpret as due to the scattering phase function of dust disk particles. From the wing tilt and a model of the phase function, we find a disk plane inclination to the line of sight of < 5 degrees. Other asymmetries (e.g. the butterfly asymmetry) suggest a disk that has been recently disturbed. We searched for possible nearby perturbers but found no clear candidates. Low mass stars (M dwarfs) and brown dwarfs would have fallen beneath the sensitivity threshhold of our survey, however. (2) We calculated a set of disk models to assess the detectability of dust disks around stars as a function of (a) distance, (b) disk, inclination (c) dust optical depth/mass, and (d) imaging resolution. These models guided our observational strategy on Mauna Kea. (3) We performed a coronagraphic survey of approx. 100 main-sequence stars in search of additional examples of circumstellar disks. The best new candidate disk, around the 5 M(sun) star BD+31deg.643, is distinguished by its large extent (few x 10( exp 3) AU). This disk, if real, cannot be rotationally supported. We suggest that the dust particles are ejected from a smaller, unseen disk (Kuiper Belt?) by strong radiation pressure forces due to the high luminosity central star. (4) SCUBA images of

  10. Prof. Hayashi's work on the pre-main sequence evolution and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Nakano, Takenori

    2012-09-01

    Prof. Hayashi's work on the evolution of stars in the pre-main sequence stage is reviewed. The historical background and the process of finding the Hayashi phase are mentioned. The work on the evolution of low-mass stars is also reviewed including the determination of the bottom of the main sequence and evolution of brown dwarfs, and comparison is made with the other works in the same period.

  11. STRUCTURE AND EVOLUTION OF PRE-MAIN-SEQUENCE CIRCUMSTELLAR DISKS

    SciTech Connect

    Isella, Andrea; Carpenter, John M.; Sargent, Anneila I.

    2009-08-10

    We present new subarcsecond ({approx}0.''7) Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of the 1.3 mm continuum emission from circumstellar disks around 11 low- and intermediate-mass pre-main-sequence stars. High-resolution observations for three additional sources were obtained from the literature. In all cases the disk emission is spatially resolved. We adopt a self-consistent accretion disk model based on the similarity solution for the disk surface density and constrain the dust radial density distribution on spatial scales of about 40 AU. Disk surface densities appear to be correlated with the stellar ages where the characteristic disk radius increases from {approx}20 AU to {approx}100 AU over about 5 Myr. This disk expansion is accompanied by a decrease in the mass accretion rate, suggesting that our sample disks form an evolutionary sequence. Interpreting our results in terms of the temporal evolution of a viscous {alpha}-disk, we estimate (1) that at the beginning of the disk evolution about 60% of the circumstellar material was located inside radii of 25-40 AU, (2) that disks formed with masses from 0.05 to 0.4 M {sub sun}, and (3) that the viscous timescale at the disk initial radius is about 0.1-0.3 Myr. Viscous disk models tightly link the surface density {sigma}(R) with the radial profile of the disk viscosity {nu}(R) {proportional_to} R {sup {gamma}}. We find values of {gamma} ranging from -0.8 to 0.8, suggesting that the viscosity dependence on the orbital radius can be very different in the observed disks. Adopting the {alpha} parameterization for the viscosity, we argue that {alpha} must decrease with the orbital radius and that it may vary between 0.5 and 10{sup -4}. From the inferred disk initial radii we derive specific angular momenta, j, for parent cores of (0.8 - 4) x 10{sup -4} km s{sup -1} pc. Comparison with the values of j in dense cores suggests that about 10% of core angular momentum and 30% of the core

  12. Circumstellar Material on and off the Main Sequence

    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 that originates from the small-body population of planetary systems. These bodies tell us something about the chemistry and evolution of protoplanetary disks and the planetary systems they form. What happens to this material as its host star evolves off the main sequence, and how does that inform our understanding of the typical chemistry of rocky bodies in planetary systems? In this talk, I will discuss the composition(s) of circumstellar material on and off the main sequence to begin to answer the question, “Is Earth normal?” In particular, I look at three types of debris disks to understand the typical chemistry of planetary systems—young debris disks, debris disks around giant stars, and dust around white dwarfs. I will review the current understanding on how to infer dust composition for each class of disk, and present new work on constraining dust composition from infrared excesses around main sequence and giant stars. Finally, dusty and polluted white dwarfs hold a unique key to our understanding of the composition of rocky bodies around other stars. In particular, I will discuss WD1145+017, which has a transiting, disintegrating planetesimal. I will review what we know about this system through high speed photometry and spectroscopy and present new work on understanding the complex interplay of physics that creates white dwarf pollution from the disintegration of rocky bodies.

  13. A DOUBLE MAIN SEQUENCE IN THE GLOBULAR CLUSTER NGC 6397

    SciTech Connect

    Milone, A. P.; Aparicio, A.; Marino, A. F.; Piotto, G.; Bedin, L. R.; Anderson, J.; Cassisi, S.; Rich, R. M. E-mail: aparicio@iac.es E-mail: giampaolo.piotto@unipd.it E-mail: bedin@stsci.edu E-mail: rmr@astro.ucla.edu

    2012-01-20

    High-precision multi-band Hubble Space Telescope (HST) photometry reveals that the main sequence of the globular cluster NGC 6397 splits into two components, containing {approx}30% and {approx}70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (1) a primordial population that has a composition similar to field stars, containing {approx}30% of the stars, and (2) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance ({Delta}Y {approx} 0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m{sub F336W}. Theoretical isochrones indicate that this could be due to NH depletion.

  14. The main sequences of NGC 2808: constraints on the early disc accretion scenario

    NASA Astrophysics Data System (ADS)

    Cassisi, Santi; Salaris, Maurizio

    2014-03-01

    A new scenario - early disc accretion - has been proposed very recently to explain the origin of the multiple population phenomenon in Galactic globular clusters. It envisages the possibility that a fraction of low- and very low-mass cluster stars may accrete the ejecta of interacting massive binary (and possibly also fast rotating massive) stars during the fully convective, pre-main sequence stage, to reproduce the CN and ONa anticorrelations observed among stars in individual clusters. This scenario is assumed to be able to explain the presence (and properties) of the multiple populations in the majority of globular clusters in the Milky Way. Here we have considered the well studied cluster NGC 2808, which displays a triple main sequence with well defined and separate He abundances. Knowledge of these abundances allowed us to put strong constraints on the He mass fraction and amount of matter to be accreted by low-mass pre-main sequence stars. We find that the minimum He mass fraction in the accreted gas has to be ~0.44 to produce the observed sequences and that at fixed initial mass of the accreting star, different efficiencies for the accretion are required to produce stars placed onto the multiple main sequences. This may be explained by differences in the orbital properties of the progenitors and/or different spatial distribution of intracluster gas with varying He abundances. Both O-Na and C-N anticorrelations appear naturally along the main sequences, once considering the predicted relationship between He and CNONa abundances in the ejecta of the polluters. As a consequence of the accretion, we predict no discontinuity between the abundance ranges covered by intermediate and blue main sequence stars, but we find a sizeable (several 0.1 dex) discontinuity of the N and Na abundances between objects on the intermediate and red main sequences. There is in principle enough polluting gas with the right He abundances to explain the observed main sequences by early

  15. Solar Luminosity on the Main Sequence, Standard Model and Variations

    NASA Astrophysics Data System (ADS)

    Ayukov, S. V.; Baturin, V. A.; Gorshkov, A. B.; Oreshina, A. V.

    2017-05-01

    Our Sun became Main Sequence star 4.6 Gyr ago according Standard Solar Model. At that time solar luminosity was 30% lower than current value. This conclusion is based on assumption that Sun is fueled by thermonuclear reactions. If Earth's albedo and emissivity in infrared are unchanged during Earth history, 2.3 Gyr ago oceans had to be frozen. This contradicts to geological data: there was liquid water 3.6-3.8 Gyr ago on Earth. This problem is known as Faint Young Sun Paradox. We analyze luminosity change in standard solar evolution theory. Increase of mean molecular weight in the central part of the Sun due to conversion of hydrogen to helium leads to gradual increase of luminosity with time on the Main Sequence. We also consider several exotic models: fully mixed Sun; drastic change of pp reaction rate; Sun consisting of hydrogen and helium only. Solar neutrino observations however exclude most non-standard solar models.

  16. Ultraviolet spectroscopy of pre-main-sequence accretion disks

    NASA Technical Reports Server (NTRS)

    Kenyon, S. J.; Hartmann, L.; Imhoff, C. L.; Cassatella, A.

    1989-01-01

    Low-resolution, ultraviolet spectra of the pre-main-sequence objects Z Canis Majoris, V1057 Cygni, and FU Orionis are presented. Ultraviolet absorption features indicate spectral types of A5 I for FU Ori and F5 I for Z CMa. These results are in reasonable agreement with predictions of simple accretion disk models. The lack of significant veiling of ultraviolet absorption features implies that a hot boundary layer at the inner edge of the disk contributes less than 20 percent of the radiation at 2600-3200 A, which is significantly smaller than expected. It is suggested that accretion has significantly modified the structure of the underlying pre-main-sequence stars in these systems (perhaps by expanding the photosphere or by spinning up a radiative photosphere close to breakup velocity, or both), or that the boundary layer region is much more extended above the disk midplane than standard thin disk theories predict.

  17. Ultraviolet spectroscopy of pre-main-sequence accretion disks

    SciTech Connect

    Kenyon, S.J.; Hartmann, L.; Imhoff, C.L.; Cassatella, A.; Computer Sciences Corp., Greenbelt, MD; International Ultraviolet Explorer Observatory, Madrid )

    1989-09-01

    Low-resolution, ultraviolet spectra of the pre-main-sequence objects Z Canis Majoris, V1057 Cygni, and FU Orionis are presented. Ultraviolet absorption features indicate spectral types of A5 I for FU Ori and F5 I for Z CMa. These results are in reasonable agreement with predictions of simple accretion disk models. The lack of significant veiling of ultraviolet absorption features implies that a hot boundary layer at the inner edge of the disk contributes less than 20 percent of the radiation at 2600-3200 A, which is significantly smaller than expected. It is suggested that accretion has significantly modified the structure of the underlying pre-main-sequence stars in these systems (perhaps by expanding the photosphere or by spinning up a radiative photosphere close to breakup velocity, or both), or that the boundary layer region is much more extended above the disk midplane than standard thin disk theories predict. 26 refs.

  18. Finding the Onset of Convection in Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Simon, Theodore

    2003-01-01

    The primary goal of the work performed under this grant was to locate, if possible, the onset of subphotospheric convection zones in normal main sequence stars by using the presence of emission in high temperature lines in far ultraviolet spectra from the FUSE spacecraft as a proxy for convection. The change in stellar structure represented by this boundary between radiative and convective stars has always been difficult to find by other empirical means. A search was conducted through observations of a sample of A-type stars, which were somewhat hotter and more massive than the Sun, and which were carefully chosen to bridge the theoretically expected radiative/convective boundary line along the main sequence.

  19. 21. General oblique view of main central building mass looking ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    21. General oblique view of main central building mass looking to southeast, showing meeting of north and central building elements. - Fort Ord, Soldiers' Club, California State Highway 1 near Eighth Street, Seaside, Monterey County, CA

  20. A Population Synthesis Study of White Dwarf–Main Sequence Binaries in the Galactic Disk

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    The companion mass ratio distribution (CMRD) of main sequence binaries is a crucial physical quantity for understanding the evolution of stars in binary systems and for constraining models of binary star formation. However, although much work has been done during the last years, the shape of the CMRD remains rather uncertain. We present a population synthesis study of white dwarf-main sequence (WDMS) binaries in the Galactic disk aimed at constraining the properties of the CMRD. To this end, we computed a set of Monte Carlo simulations aimed at reproducing the WDMS binary population observed by the SDSS. We used different prescriptions for the CMRD and we took into account all the known observational biases. We show that our simulations reproduce reasonably well the observed distributions of masses and luminosities of the white dwarf star and of spectral type of the main sequence star. Moreover, our simulations place constraints, albeit weak, on the shape of the CMRD.

  1. Primordial stellar evolution - The pre-main-sequence phase

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.; Palla, F.; Salpeter, E. E.

    1986-01-01

    The quasi-static contraction of primordial stars composed of pure hydrogen and helium gas is studied by following numerically the evolution of a star of five solar masses from the end of protostellar accretion to the onset of hydrogen burning. Although the protostellar core of this mass is radiatively stable and undergoing nonhomologous contraction, its large surface area and luminosity force the star to a partially convective, homologously contracting state within only 100 yr. Deuterium later ignites at an off-center temperature maximum but fails to produce interior convection. The star follows a conventional premain sequence track in the HR diagram, reaching the ZAMS after 1.2 million yr, with a luminosity of 880 solar luminosities and a radius of 1.2 solar radii.

  2. Ultraviolet emission from main-sequence companions of AGB stars

    NASA Astrophysics Data System (ADS)

    Ortiz, Roberto; Guerrero, Martín A.

    2016-09-01

    Although the majority of known binary asymptotic giant branch (AGB) stars are symbiotic systems (i.e. with a white dwarf as a secondary star), main-sequence companions of AGB stars can be more numerous, even though they are more difficult to find because the primary high luminosity hampers the detection of the companion at visual wavelengths. However, in the ultraviolet the flux emitted by a secondary with Teff > 5500 ˜ 6000 K may prevail over that of the primary, and then it can be used to search for candidates to binary AGB stars. In this work, theoretical atmosphere models are used to calculate the UV excess in the GALEX near- and far-UV bands due to a main-sequence companion. After analysing a sample of confirmed binary AGB stars, we propose as a criterium for binarity: (1) the detection of the AGB star in the GALEX far-UV band and/or (2) a GALEX near-UV observed-to-predicted flux ratio >20. These criteria have been applied to a volume-limited sample of AGB stars within 500 pc of the Sun; 34 out of the sample of 58 AGB stars (˜60 per cent) fulfill them, implying to have a main-sequence companion of spectral type earlier than K0. The excess in the GALEX near- and far-UV bands cannot be attributed to a single temperature companion star, thus suggesting that the UV emission of the secondary might be absorbed by the extended atmosphere and circumstellar envelope of the primary or that UV emission is produced in accretion flows.

  3. Environmental impact analysis for the main accidental sequences of ignitor

    SciTech Connect

    Carpignano, A.; Francabandiera, S.; Vella, R.; Zucchetti, M.

    1996-12-31

    A safety analysis study has been applied to the Ignitor machine using Probabilistic Safety Assessment. The main initiating events have been identified, and accident sequences have been studied by means of traditional methods such as Failure Mode and Effect Analysis (FMEA), Fault Trees (FT) and Event Trees (ET). The consequences of the radioactive environmental releases have been assessed in terms of Effective Dose Equivalent (EDEs) to the Most Exposed Individuals (MEI) of the chosen site, by means of a population dose code. Results point out the low enviromental impact of the machine. 13 refs., 1 fig., 3 tabs.

  4. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2003-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  5. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2004-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  6. MAIN-SEQUENCE STAR POPULATIONS IN THE VIRGO OVERDENSITY REGION

    SciTech Connect

    Jerjen, H.; Da Costa, G. S.; Tisserand, P.; Willman, B.; Arimoto, N.; Okamoto, S.; Mateo, M.; Saviane, I.; Walsh, S.; Geha, M.; Jordan, A.; Zoccali, M.; Olszewski, E.; Walker, M.; Kroupa, P.

    2013-05-20

    We present deep color-magnitude diagrams (CMDs) for two Subaru Suprime-Cam fields in the Virgo Stellar Stream (VSS)/Virgo Overdensity (VOD) and compare them to a field centered on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main-sequence stars is detected in all three fields and can be traced as faint as g Almost-Equal-To 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1{sup +1.0}{sub -1.1} Gyr, a median abundance of [Fe/H] = -0.70{sup +0.15}{sub -0.20} dex, and a heliocentric distance of 30.9 {+-} 3.0 kpc for the main sequence of the Sgr Stream Branch A. The dominant main-sequence populations in the two VSS/VOD fields ({Lambda}{sub Sun} Almost-Equal-To 265 Degree-Sign , B{sub Sun} Almost-Equal-To 13 Degree-Sign ) are located at a mean distance of 23.3 {+-} 1.6 kpc and have an age of {approx}8.2 Gyr, and an abundance of [Fe/H] = -0.67{sup +0.16}{sub -0.12} dex, similar to the Sgr Stream stars. These statistically robust parameters, derived from the photometry of 260 main-sequence stars, are also in good agreement with the age of the main population in the Sgr dwarf galaxy (8.0 {+-} 1.5 Gyr). They also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] Almost-Equal-To -0.6 dex, in the Sgr north leading arm. We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law and Majewski based on a triaxial Galactic halo shape that is empirically calibrated with Sloan Digital Sky Survey Sgr A-branch and Two Micron All Sky Survey M-giant stars. We find that the most prominent feature in the CMDs, the main-sequence population at 23 kpc, is not explained by the model. Instead the model predicts in these directions a low-density filamentary structure of Sgr debris stars at {approx}9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42-53 kpc. At best

  7. Main-Sequence Star Populations in the Virgo Overdensity Region

    NASA Astrophysics Data System (ADS)

    Jerjen, H.; Da Costa, G. S.; Willman, B.; Tisserand, P.; Arimoto, N.; Okamoto, S.; Mateo, M.; Saviane, I.; Walsh, S.; Geha, M.; Jordán, A.; Olszewski, E.; Walker, M.; Zoccali, M.; Kroupa, P.

    2013-05-01

    We present deep color-magnitude diagrams (CMDs) for two Subaru Suprime-Cam fields in the Virgo Stellar Stream (VSS)/Virgo Overdensity (VOD) and compare them to a field centered on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main-sequence stars is detected in all three fields and can be traced as faint as g ≈ 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1^{+1.0}_{-1.1} Gyr, a median abundance of [Fe/H] = -0.70^{+0.15}_{-0.20} dex, and a heliocentric distance of 30.9 ± 3.0 kpc for the main sequence of the Sgr Stream Branch A. The dominant main-sequence populations in the two VSS/VOD fields (Λ⊙ ≈ 265°, B ⊙ ≈ 13°) are located at a mean distance of 23.3 ± 1.6 kpc and have an age of ~8.2 Gyr, and an abundance of [Fe/H] = -0.67^{+0.16}_{-0.12} dex, similar to the Sgr Stream stars. These statistically robust parameters, derived from the photometry of 260 main-sequence stars, are also in good agreement with the age of the main population in the Sgr dwarf galaxy (8.0 ± 1.5 Gyr). They also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] ≈-0.6 dex, in the Sgr north leading arm. We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law & Majewski based on a triaxial Galactic halo shape that is empirically calibrated with Sloan Digital Sky Survey Sgr A-branch and Two Micron All Sky Survey M-giant stars. We find that the most prominent feature in the CMDs, the main-sequence population at 23 kpc, is not explained by the model. Instead the model predicts in these directions a low-density filamentary structure of Sgr debris stars at ~9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42-53 kpc. At best there is only marginal evidence for the presence of these populations in our data. Our findings then suggest that while there are

  8. Spatially Resolved Star Formation Main Sequence of Galaxies in the CALIFA Survey

    NASA Astrophysics Data System (ADS)

    Cano-Díaz, M.; Sánchez, S. F.; Zibetti, S.; Ascasibar, Y.; Bland-Hawthorn, J.; Ziegler, B.; González Delgado, R. M.; Walcher, C. J.; García-Benito, R.; Mast, D.; Mendoza-Pérez, M. A.; Falcón-Barroso, J.; Galbany, L.; Husemann, B.; Kehrig, C.; Marino, R. A.; Sánchez-Blázquez, P.; López-Cobá, C.; López-Sánchez, Á. R.; Vilchez, J. M.

    2016-04-01

    The “main sequence of galaxies”—defined in terms of the total star formation rate ψ versus the total stellar mass M *—is a well-studied tight relation that has been observed at several wavelengths and at different redshifts. All earlier studies have derived this relation from integrated properties of galaxies. We recover the same relation from an analysis of spatially resolved properties, with integral field spectroscopic (IFS) observations of 306 galaxies from the CALIFA survey. We consider the SFR surface density in units of log(M ⊙ yr-1 Kpc-2) and the stellar mass surface density in units of log(M ⊙ Kpc-2) in individual spaxels that probe spatial scales of 0.5-1.5 Kpc. This local relation exhibits a high degree of correlation with small scatter (σ = 0.23 dex), irrespective of the dominant ionization source of the host galaxy or its integrated stellar mass. We highlight (i) the integrated star formation main sequence formed by galaxies whose dominant ionization process is related to star formation, for which we find a slope of 0.81 ± 0.02; (ii) for the spatially resolved relation obtained with the spaxel analysis, we find a slope of 0.72 ± 0.04; and (iii) for the integrated main sequence, we also identified a sequence formed by galaxies that are dominated by an old stellar population, which we have called the retired galaxies sequence.

  9. Acoustic Oscillations in Main-Sequence Stars: HD155543

    NASA Astrophysics Data System (ADS)

    Belmonte, J. A.; Pérez Hernández, F.; Roca Cortés, T.

    High-speed photometric techniques have been found useful as a way to study the acoustic mode signature in low main sequence stars. In this work, the discovery of solar-like oscillations associated to the presence of acoustic modes of pulsation in the F2V star HD155543, located outside of the instability strip, is reported. This finding has been obtained through an analysis of a long series of data (184 hours) obtained in 20 nights of observation with two twin three channel photometers attached to two 1.5 m telescopes sited at two observatories, simultaneously: Teide (OT) at Tenerife (Spain) and San Pedro Mártir (SPM) at Baja California Norte (Mexico). The major results yielded have been: the range of frequencies where p-modes signal is present (1 to 3 mHz); an upper limit of 20 µmag for the amplitude of the modes; the mean spacing between modes of equal degree l and consecutive order n, v o = 97.3 ± 0.6 µHz and two possible values of D o, 1.4 or 1.8 µHz. The values of these parameters agree, within the resolution, with those yielded by standard computed models of main sequence stars compatible with the luminosity and effective temperature already known for HD155543. These results open new perspectives for astero-seismology in the near future.

  10. The pre-main sequence spectroscopic binary AK Scorpii revisited

    NASA Astrophysics Data System (ADS)

    Alencar, S. H. P.; Melo, C. H. F.; Dullemond, C. P.; Andersen, J.; Batalha, C.; Vaz, L. P. R.; Mathieu, R. D.

    2003-10-01

    We present an analysis of 32 high-resolution echelle spectra of the pre-main sequence spectroscopic binary AK Sco obtained during 1998 and 2000, as well as a total of 72 photoelectric radial-velocity observations from the period 1986-1994. These data allow considerable improvement of the period and other orbital parameters of AK Sco. Our analysis also includes eight series of photometric observations in the uvby and Geneva seven-color systems from 1987, 1989, 1990, 1992, 1994 and 1997. No eclipses or other periodic variations are seen in the photometry, but the well-determined HIPPARCOS parallax allows us to constrain the orbital inclination of the system to the range 65 degr < i < 70 degr, leading to the following physical parameters for the two near-identical stars: M =1.35 +/- 0.07 \\msun, R =1.59 +/- 0.35 \\rsun, and vsin i =18.5 +/- 1.0 \\kmsn. Disk models have been fit to the spectral energy distribution of AK Sco from 350 nm to 1100 mu m. The above stellar parameters permit a consistent solution with an inner rim temperature of 1250 K, instead of the usual 1500 K corresponding to the dust evaporation temperature. Dynamical effects due to tidal interaction of the binary system are supposed to be responsible for pushing the inner disk radius outwards. Combining simultaneous photometric and spectroscopic data sets allows us to compute the dust obscuration in front of each star at several points over the orbit. The results demonstrate the existence of substructure at scales of just a single stellar diameter, and also that one side of the orbit is more heavily obscured than the other. The spectrum of AK Sco exhibits emission and absorption lines that show substantial variety and variability in shape. The accretion-related lines may show both outflow and infall signatures. The system displays variations at the binary orbital period in both the photospheric and accretion-related line intensities and equivalent widths, although with appreciable scatter. The periodic

  11. Characterization of Detached Main Sequence Binaries Observed by Kepler, SDSS(APOGEE) and Gaia

    NASA Astrophysics Data System (ADS)

    Solis, Christina Oleander; Mason, Paul A.

    2017-01-01

    In addition to finding planets, the Kepler Observatory obtained high precision light curves of eclipsing binaries that have subsequently been observed by SDSS and Gaia. Main sequence eclipsing binaries are important laboratories for stellar astrophysics. The determination of precise temperatures, radii, masses, and orbital parameters constrain evolution theory. We examined 28 main sequence binaries observed using Kepler, SDSS(APOGEE) and Gaia. Combining observed astrometric, photometric, and spectroscopic data places strong constraints on stellar and binary characteristics. We compare derived parameters with model calculations of these binaries and present preliminary results.

  12. Main-sequence turnoff of the Draco dwarf galaxy

    SciTech Connect

    Stetson, P.B.; Mcclure, R.D.; Vandenberg, D.A.

    1985-10-01

    Deep photometry on the B,V system for 182 stars in the dwarf spheroidal galaxy in Draco was obtained with a CCD camera at the Cassegrain focus of the Canada-France-Hawaii 3.6-m telescope. Draco's main-sequence turnoff if found near V(to) = 23.5, which is about 3.4 magnitudes below the galaxy's horizontal branch. This leads to the interpretation that Draco is not measurably younger than the clusters or Ursa Minor: the age of Draco is about 18 Gyr according to current star-revolution chronologies. No blue stragglers are definitely detected in Draco, and it is concluded that any young population in Draco probably represents less than 10 percent of the total. 30 references.

  13. The coronae of main-sequence A stars

    NASA Technical Reports Server (NTRS)

    Simon, Theodore; Drake, Stephen A.

    1993-01-01

    We have undertaken a deep X-ray imaging survey of single, normal, mid-to-late-A- and early-F-type main-sequence stars using the ROSA T PSPC. Eight of the nine such stars in our fields went undetected at very weak emission levels, with upper limits on the normalized X-ray flux in each case of better than log R(x) below -6.3. The only A-F star we detected was 83 Tau, a member of the Hyades that we now belatedly recognize as a possible binary star, whose emission may come from an unidentified companion. Our observations reveal a systematic decline in coronal X-ray brightness with increasing effective temperature, which we attribute to the presence of strong coronal winds. These new results add further weight to earlier suggestions that single A and early-F stars in the field and in nearby older open clusters generally have intrinsically faint coronae.

  14. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2002-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we plan to: (1) Develop much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; (2) Study the dusty emission and accretion rates in these systems, with ages closer to the expected epoch of (giant) planet formation at 3-10 Myr; and (3) Develop detailed model disk structures consistent with observations to infer physical conditions in protoplanetary disks and to constrain possible grain growth as the first stage of planetesimal formation.

  15. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2000-01-01

    The aim of this project was to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we: (1) Developed detailed calculations of disk structure to study physical conditions and investigate the observational effects of grain growth in T Tauri disks; (2) Studied the dusty emission and accretion rates in older disk systems, with ages closer to the expected epoch of (giant) planet formation at 3-10 Myr, and (3) Began a project to develop much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution.

  16. Pre- and main-sequence evolution of solar activity

    NASA Technical Reports Server (NTRS)

    Walter, Frederick M.; Barry, Don C.

    1991-01-01

    The magnetic activity on single solarlike stars declines with stellar age. This has important consequences for the influence of the sun on the early solar system. What is meant by stellar activity, and how it is measured, is reviewed. Stellar activity on the premain-sequence phase of evolution is discussed; the classical T Tauri stars do not exhibit solarlike activity, while the naked T Tauri stars do. The emission surface fluxes of the naked T Tauri stars are similar to those of the youngest main-sequence G stars. The best representation for solarlike stars is a decay proportional to exp(A x t exp 0.5), where A is a function of line excitation temperature. From these decay laws, one can determine the interdependences of the activity, age, and rotation periods. The fluxes of ionizing photons at the earth early in its history are discussed; there was sufficient fluence to account for the observed isotopic ratios of the noble gases.

  17. W134: A new pre-main-sequence double-lined spectroscopic binary

    NASA Technical Reports Server (NTRS)

    Padgett, Deborah L.; Stapelfeldt, Karl R.

    1994-01-01

    We report the discovery that the pre-main-sequence star Walker 134 in the young cluster NGC 2264 is a double-lined spectroscopic binary. Both components are G stars with strong Li I 6708 A absorption lines. Twenty radial velocity measurements have been used to determined the orbital elements of this system. The orbit has a period of 6.3532 +/- 0.0012 days and is circular within the limits of our velocity resolution; e less than 0.01. The total system mass is stellar mass sin(exp 3) i = 3.16 solar mass with a mass ratio of 1.04. Estimates for the orbit inclination angle and stellar radii place the system near the threshold for eclipse observability; howerver, no decrease in brightness was seen during two attempts at photometric monitoring. The circular orbit of W 134 fills an important gap in the period distribution of pre-main-sequence binaries and thereby constrains the effectiveness of tidal orbital circularization during the pre-main sequence.

  18. Possible evidence for metal accretion onto the surfaces of metal-poor main-sequence stars

    SciTech Connect

    Hattori, Kohei; Yoshii, Yuzuru; Beers, Timothy C.; Carollo, Daniela; Lee, Young Sun

    2014-04-01

    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

  19. Multiple main sequence of globular clusters as a result of inhomogeneous big bang nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Moriya, Takashi; Shigeyama, Toshikazu

    2010-02-01

    A new mechanism for enhancing the helium abundance in the blue main sequence stars of ω Centauri and NGC 2808 is investigated. We suggest that helium enhancement was caused by the inhomogeneous big bang nucleosynthesis. Regions with extremely high baryon-to-photon ratios are assumed to be caused by the baryogenesis. Its mass scale is also assumed to be 106M⊙. An example of the mechanisms to realize these two things was already proposed as the Affleck-Dine baryogenesis. As the baryon-to-photon ratio becomes larger, the primordial helium abundance is enhanced. We calculated the big bang nucleosynthesis and found that there exists a parameter region yielding enough helium to account for the split of the main sequence in the aforementioned globular clusters while keeping the abundance of other elements compatible with observations. Our mechanism predicts that heavy elements with the mass number of around 100 is enhanced in the blue main sequence stars. We estimate the time scales of diffusion of the enhanced helium and mass accretion in several stages after the nucleosynthesis to investigate whether these processes diminish the enhancement of helium. We found that the diffusion does not influence the helium content. A cloud with a sufficiently large baryon-to-photon ratio to account for the multiple main sequence collapsed immediately after the recombination. Subsequently, the cloud accreted the ambient matter with the normal helium content. If the star formation occurred both in the collapsed core and the accreted envelope, then the resultant star cluster has a double main sequence.

  20. Multiple main sequence of globular clusters as a result of inhomogeneous big bang nucleosynthesis

    SciTech Connect

    Moriya, Takashi; Shigeyama, Toshikazu

    2010-02-15

    A new mechanism for enhancing the helium abundance in the blue main sequence stars of {omega} Centauri and NGC 2808 is investigated. We suggest that helium enhancement was caused by the inhomogeneous big bang nucleosynthesis. Regions with extremely high baryon-to-photon ratios are assumed to be caused by the baryogenesis. Its mass scale is also assumed to be 10{sup 6}M{sub {center_dot}.} An example of the mechanisms to realize these two things was already proposed as the Affleck-Dine baryogenesis. As the baryon-to-photon ratio becomes larger, the primordial helium abundance is enhanced. We calculated the big bang nucleosynthesis and found that there exists a parameter region yielding enough helium to account for the split of the main sequence in the aforementioned globular clusters while keeping the abundance of other elements compatible with observations. Our mechanism predicts that heavy elements with the mass number of around 100 is enhanced in the blue main sequence stars. We estimate the time scales of diffusion of the enhanced helium and mass accretion in several stages after the nucleosynthesis to investigate whether these processes diminish the enhancement of helium. We found that the diffusion does not influence the helium content. A cloud with a sufficiently large baryon-to-photon ratio to account for the multiple main sequence collapsed immediately after the recombination. Subsequently, the cloud accreted the ambient matter with the normal helium content. If the star formation occurred both in the collapsed core and the accreted envelope, then the resultant star cluster has a double main sequence.

  1. Protein Sequencing with Tandem Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Ziady, Assem G.; Kinter, Michael

    The recent introduction of electrospray ionization techniques that are suitable for peptides and whole proteins has allowed for the design of mass spectrometric protocols that provide accurate sequence information for proteins. The advantages gained by these approaches over traditional Edman Degradation sequencing include faster analysis and femtomole, sometimes attomole, sensitivity. The ability to efficiently identify proteins has allowed investigators to conduct studies on their differential expression or modification in response to various treatments or disease states. In this chapter, we discuss the use of electrospray tandem mass spectrometry, a technique whereby protein-derived peptides are subjected to fragmentation in the gas phase, revealing sequence information for the protein. This powerful technique has been instrumental for the study of proteins and markers associated with various disorders, including heart disease, cancer, and cystic fibrosis. We use the study of protein expression in cystic fibrosis as an example.

  2. The Star Forming Main Sequence and its Scatter as Conequences of the Central Limit Theorem

    NASA Astrophysics Data System (ADS)

    Kelson, Daniel

    2015-01-01

    Star formation rates of disk galaxies strongly correlate with stellar mass, with a small dispersion in specific star formation rate at fixed mass. With such small scattter this main sequence of star formation has been interpreted as deterministic and fundamental. Here it is demonstrated that it is a simple consequence off he central limit theorem. Treating the star formation histories of galaxies as integrable, non-differentiable functions, where stochastic changes in star formation rate in a galaxy's history are not fully independent of each other, we derive the median specific star formation rate for the flat part of the main sequence from 0

  3. Analysis of pre-main-sequence delta-Scuti stars

    NASA Astrophysics Data System (ADS)

    Casey, Michael Patrick

    Information on 72 confirmed or candidate pre-main-sequence delta-Scuti stars is collected and analysed to varying degree of sophistication and completeness. A systematic asteroseismic analysis of around 40 of these stars is performed, putting significant luminosity constraints on many of them simply by comparing the pulsation spectra of the stars to the fundamental and acoustic cut-off frequencies of a dense grid of stellar models. One star in particular, V1366 Ori, appears to be pulsating at or near the acoustic cut-off frequency. Many stars are found to otherwise defy proper asteroseismic analysis, in that matches between observed pulsation spectra and computed values are not able to be found. A simple test reveals that the most likely cause for these problems are the high stellar-rotation rates typically found in this class of star, with v sin i most typically between 60 and 200 km/s. The high rotation rates are found to significantly modify the pulsation spectrum of a star compared to a non-rotating star. These collective results reveal the richness and variety of phenomena within this group of stars, with stars pulsating anywhere from the lowest to the highest possible radial orders, including radial orders just below the acoustic cut-off frequency of some stars. Pulsation in non-radial orders is the normal case, not the exception to the rule, with all stars displaying low-amplitude delta-Scuti variability only.

  4. COMMON WARM DUST TEMPERATURES AROUND MAIN-SEQUENCE STARS

    SciTech Connect

    Morales, Farisa Y.; Werner, M. W.; Bryden, G.; Stapelfeldt, K. R.; Rieke, G. H.; Su, K. Y. L.

    2011-04-01

    We compare the properties of warm dust emission from a sample of main-sequence A-type stars (B8-A7) to those of dust around solar-type stars (F5-K0) with similar Spitzer Space Telescope Infrared Spectrograph/MIPS data and similar ages. Both samples include stars with sources with infrared spectral energy distributions that show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures ({approx}190 K and {approx}60 K for the inner and outer dust components, respectively)-slightly above the ice evaporation temperature for the inner belts. The warm inner dust temperature is readily explained if populations of small grains are being released by sublimation of ice from icy planetesimals. Evaporation of low-eccentricity icy bodies at {approx}150 K can deposit particles into an inner/warm belt, where the small grains are heated to T{sub dust} {approx} 190 K. Alternatively, enhanced collisional processing of an asteroid belt-like system of parent planetesimals just interior to the snow line may account for the observed uniformity in dust temperature. The similarity in temperature of the warmer dust across our B8-K0 stellar sample strongly suggests that dust-producing planetesimals are not found at similar radial locations around all stars, but that dust production is favored at a characteristic temperature horizon.

  5. Planetary Systems Associated with Main-Sequence Stars.

    PubMed

    Brown, H

    1964-09-11

    The luminosity function is used to estimate the number of invisible planet-like objects in the neighborhood of the sun, taking into account the likely chemical composition of planets in relation to the composition of main-sequence stars. There may be about 60 objects more massive than Mars for every visible star. An attempt is made to estimate the distribution of these planet-like cold bodies in relation to stars. It is suggested that stars, together with cold objects, were formed in clusters of bodies of random size distribution. Clusters averaging about 50 bodies each account for the observed distribution of frequencies of double and triple star systems relative to single stars. On this basis, virtually every star should have a planetary system associated with it. As a corollary, systems of cold bodies in which there are no luminous stars should be abundant. The possible distribution of planets around such stars has been studied, making use of the observed orbital characteristics of double star systems. It is concluded that favorable conditions for life processes may be far more abundant than has generally been thought possible.

  6. A TEST OF PRE-MAIN-SEQUENCE LITHIUM DEPLETION MODELS

    SciTech Connect

    Yee, Jennifer C.; Jensen, Eric L. N.

    2010-03-01

    Despite the extensive study of lithium depletion during pre-main-sequence (PMS) contraction, studies of individual stars show discrepancies between ages determined from the Hertzsprung-Russell (H-R) diagram and ages determined from lithium depletion, indicating open questions in the PMS evolutionary models. To further test these models, we present high-resolution spectra for members of the beta Pictoris Moving Group (BPMG), which is young and nearby. We measure equivalent widths of the 6707.8 A Li I line in these stars and use them to determine lithium abundances. We combine the lithium abundance with the predictions of PMS evolutionary models in order to calculate a lithium depletion age for each star. We compare this age to the age predicted by the H-R diagram of the same model. We find that the evolutionary models underpredict the amount of lithium depletion for the BPMG given its nominal H-R diagram age of {approx}12 Myr, particularly for the mid-M stars, which have no observable Li I line. This results in systematically older ages calculated from lithium depletion isochrones than from the H-R diagram. We suggest that this discrepancy may be related to the discrepancy between measured M-dwarf radii and the smaller radii predicted by evolutionary models.

  7. IRAC Observations of Taurus Pre-Main-Sequence Stars

    NASA Technical Reports Server (NTRS)

    Hartmann, L.

    2005-01-01

    We presented infrared photometry obtained with the IRAC camera on the Spitzer Space Telescope of a sample of 82 pre-main-sequence stars and brown dwarfs in the Taurus starforming region. We find a clear separation in some IRAC color-color diagrams between objects with and without disks. A few "transition" objects are noted, which correspond to systems in which the inner disk has been evacuated of small dust. Separating pure disk systems from objects with remnant protostellar envelopes is more difficult at IRAC wavelengths, especially for objects with infall at low rates and large angular momenta. Our results generally confirm the IRAC color classification scheme used in previous papers by Allen et al. and Megeath et al. to distinguish between protostars, T Tauri stars with disks, and young stars without (inner) disks. The observed IRAC colors are in good agreement with recent improved disk models, and in general accord with models for protostellar envelopes derived from analyzing a larger wavelength region. We also comment on a few Taurus objects of special interest. Our results should be useful for interpreting IRAC results in other, less well studied star-forming regions.

  8. IRAC Observations of Taurus Pre-Main-Sequence Stars

    NASA Technical Reports Server (NTRS)

    Hartmann, L.

    2005-01-01

    We presented infrared photometry obtained with the IRAC camera on the Spitzer Space Telescope of a sample of 82 pre-main-sequence stars and brown dwarfs in the Taurus starforming region. We find a clear separation in some IRAC color-color diagrams between objects with and without disks. A few "transition" objects are noted, which correspond to systems in which the inner disk has been evacuated of small dust. Separating pure disk systems from objects with remnant protostellar envelopes is more difficult at IRAC wavelengths, especially for objects with infall at low rates and large angular momenta. Our results generally confirm the IRAC color classification scheme used in previous papers by Allen et al. and Megeath et al. to distinguish between protostars, T Tauri stars with disks, and young stars without (inner) disks. The observed IRAC colors are in good agreement with recent improved disk models, and in general accord with models for protostellar envelopes derived from analyzing a larger wavelength region. We also comment on a few Taurus objects of special interest. Our results should be useful for interpreting IRAC results in other, less well studied star-forming regions.

  9. Common Warm Dust Temperatures Around Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Morales, Farisa; Rieke, George; Werner, Michael; Stapelfeldt, Karl; Bryden, Geoffrey; Su, Kate

    2011-01-01

    We compare the properties of warm dust emission from a sample of main-sequence A-type stars (B8-A7) to those of dust around solar-type stars (F5-KO) with similar Spitzer Space Telescope Infrared Spectrograph/MIPS data and similar ages. Both samples include stars with sources with infrared spectral energy distributions that show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures (∼ 190 K and ∼60 K for the inner and outer dust components, respectively)-slightly above the ice evaporation temperature for the inner belts. The warm inner dust temperature is readily explained if populations of small grains are being released by sublimation of ice from icy planetesimals. Evaporation of low-eccentricity icy bodies at ∼ 150 K can deposit particles into an inner/warm belt, where the small grains are heated to dust Temperatures of -190 K. Alternatively, enhanced collisional processing of an asteroid belt-like system of parent planetesimals just interior to the snow line may account for the observed uniformity in dust temperature. The similarity in temperature of the warmer dust across our B8-KO stellar sample strongly suggests that dust-producing planetesimals are not found at similar radial locations around all stars, but that dust production is favored at a characteristic temperature horizon.

  10. Ordered replication of DNA sequences: synthesis of mouse satellite and adjacent main band sequences.

    PubMed

    Dooley, D C; Ozer, H L

    1979-03-01

    The replication of mouse satellite DNA was delayed when synchronized 3T3 cells were exposed to low concentrations of hydroxyurea during S phase, It appears that the onset of satellite replication is not a time dependent event, but instead requires that a certain amount of main band DNA be synthesized first. Using hydroxyapatite chromatography and S1 nuclease digestion, a procedure was developed to quantitate the synthesis of both satellite and neighboring main band sequences. The replication kinetics of satellite determined by this method agree with previous estimates. Main band sequences adjacent to satellite appear to replicate in concert with satellite DNA. The results are discussed and related to the limitations of the techniques utilized.

  11. The far infra-red SEDs of main sequence and starburst galaxies

    NASA Astrophysics Data System (ADS)

    Cowley, William I.; Béthermin, Matthieu; del P. Lagos, Claudia; Lacey, Cedric G.; Baugh, Carlton M.; Cole, Shaun

    2017-01-01

    We compare observed far infra-red/sub-millimetre (FIR/sub-mm) galaxy spectral energy distributions (SEDs) of massive galaxies (M⋆ ≳ 1010 h-1 M⊙) derived through a stacking analysis with predictions from a new model of galaxy formation. The FIR SEDs of the model galaxies are calculated using a self-consistent model for the absorption and re-emission of radiation by interstellar dust based on radiative transfer calculations and global energy balance arguments. Galaxies are selected based on their position on the specific star formation rate (sSFR) - stellar mass (M⋆) plane. We identify a main sequence of star-forming galaxies in the model, i.e. a well defined relationship between sSFR and M⋆, up to redshift z ˜ 6. The scatter of this relationship evolves such that it is generally larger at higher stellar masses and higher redshifts. There is remarkable agreement between the predicted and observed average SEDs across a broad range of redshifts (0.5 ≲ z ≲ 4) for galaxies on the main sequence. However, the agreement is less good for starburst galaxies at z ≳ 2, selected here to have elevated sSFRs>10 × the main sequence value. We find that the predicted average SEDs are robust to changing the parameters of our dust model within physically plausible values. We also show that the dust temperature evolution of main sequence galaxies in the model is driven by star formation on the main sequence being more burst-dominated at higher redshifts.

  12. The far infra-red SEDs of main sequence and starburst galaxies

    NASA Astrophysics Data System (ADS)

    Cowley, William I.; Béthermin, Matthieu; Lagos, Claudia del P.; Lacey, Cedric G.; Baugh, Carlton M.; Cole, Shaun

    2017-05-01

    We compare observed far infrared/sub-millimetre (FIR/sub-mm) galaxy spectral energy distributions (SEDs) of massive galaxies (M⋆ ≳ 1010 h-1 M⊙) derived through a stacking analysis with predictions from a new model of galaxy formation. The FIR SEDs of the model galaxies are calculated using a self-consistent model for the absorption and re-emission of radiation by interstellar dust based on radiative transfer calculations and global energy balance arguments. Galaxies are selected based on their position on the specific star formation rate (sSFR)-stellar mass (M⋆) plane. We identify a main sequence of star-forming galaxies in the model, i.e. a well-defined relationship between sSFR and M⋆, up to redshift z ˜ 6. The scatter of this relationship evolves such that it is generally larger at higher stellar masses and higher redshifts. There is a remarkable agreement between the predicted and observed average SEDs across a broad range of redshifts (0.5 ≲ z ≲ 4) for galaxies on the main sequence. However, the agreement is less good for starburst galaxies at z ≳ 2, selected here to have elevated sSFRs>10× the main-sequence value. We find that the predicted average SEDs are robust to changing the parameters of our dust model within physically plausible values. We also show that the dust temperature evolution of the main-sequence galaxies in the model is driven by star formation on the main sequence being more burst-dominated at higher redshifts.

  13. Evolution of the Sun and Physical Processes at the Early Stage Before Main Sequence

    NASA Astrophysics Data System (ADS)

    Baturin, V. A.; Oreshina, A. V.; Ayukov, S. V.; Gorshkov, A. B.

    2017-05-01

    We consider basic conceptions about structure and evolution of stars, using our Sun and its possible pre-history in the focus of attention. The Sun is chosen because it is a star with well-studied internal structure, moderate mass, at the middle-age of its life on the Main Sequence (MS). Special attention is given to quasi-stationary evolution before Main Sequence. In comparison with MS, this early pre-Main Sequence (pMS) stage is characterized by faster change of structure parameters and higher luminosity, as well as by dominant role of gravitational sources of energy with respect to nuclear ones. During short time, about 50 Myr, a star undergoes some transformations of its structure: from fully convective to hybrid convective-radiative and finally to radiative-dominated, almost stationary star at the MS. One of the main questions of stellar evolution is if internal structure depends on previous states and if some traces of early evolution exist in later times. One can assume an existence of traces in the surface lithium abundance as well as in some accumulation of heavy elements in the core which occurs during pMS. Previous structure or evolution of a star or its mass change do not leave traces in the internal structure of the present-date Sun.

  14. Mass arsenic poisoning and the public health response in Maine.

    PubMed

    Mills, Dora A; Tomassoni, Anthony J; Tallon, Lindsay A; Kade, Kristy A; Savoia, Elena S

    2013-06-01

    Created in the wake of the September 11, 2001 terrorist attacks, Maine's Office of Public Health Emergency Preparedness within the Maine Center for Disease Control and Prevention undertook a major reorganization of epidemiology and laboratory services and began developing relationships with key partners and stakeholders, and a knowledgeable and skilled public health emergency preparedness workforce. In 2003, these newly implemented initiatives were tested extensively during a mass arsenic poisoning at the Gustav Adolph Lutheran Church in the rural northern community of New Sweden, Maine. This episode serves as a prominent marker of how increased preparedness capabilities, as demonstrated by the rapid identification and administration of antidotes and effective collaborations between key partners, can contribute to the management of broader public health emergencies in rural areas.

  15. Habitable zone lifetimes of exoplanets around main sequence stars.

    PubMed

    Rushby, Andrew J; Claire, Mark W; Osborn, Hugh; Watson, Andrew J

    2013-09-01

    The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star undergoing stellar evolution, possibly including or excluding planets over the course of the star's main sequence lifetime. We describe the time that a planet spends within the HZ as its "habitable zone lifetime." The HZ lifetime of a planet has strong astrobiological implications and is especially important when considering the evolution of complex life, which is likely to require a longer residence time within the HZ. Here, we present results from a simple model built to investigate the evolution of the "classic" HZ over time, while also providing estimates for the evolution of stellar luminosity over time in order to develop a "hybrid" HZ model. These models return estimates for the HZ lifetimes of Earth and 7 confirmed HZ exoplanets and 27 unconfirmed Kepler candidates. The HZ lifetime for Earth ranges between 6.29 and 7.79×10⁹ years (Gyr). The 7 exoplanets fall in a range between ∼1 and 54.72 Gyr, while the 27 Kepler candidate planets' HZ lifetimes range between 0.43 and 18.8 Gyr. Our results show that exoplanet HD 85512b is no longer within the HZ, assuming it has an Earth analog atmosphere. The HZ lifetime should be considered in future models of planetary habitability as setting an upper limit on the lifetime of any potential exoplanetary biosphere, and also for identifying planets of high astrobiological potential for continued observational or modeling campaigns.

  16. Evidence of magnetic field decay in massive main-sequence stars

    NASA Astrophysics Data System (ADS)

    Fossati, L.; Schneider, F. R. N.; Castro, N.; Langer, N.; Simón-Díaz, S.; Müller, A.; de Koter, A.; Morel, T.; Petit, V.; Sana, H.; Wade, G. A.

    2016-08-01

    A significant fraction of massive main-sequence stars show strong, large-scale magnetic fields. The origin of these fields, their lifetimes, and their role in shaping the characteristics and evolution of massive stars are currently not well understood. We compile a catalogue of 389 massive main-sequence stars, 61 of which are magnetic, and derive their fundamental parameters and ages. The two samples contain stars brighter than magnitude 9 in the V-band and range in mass between 5 and 100 M⊙. We find that the fractional main-sequence age distribution of all considered stars follows what is expected for a magnitude limited sample, while that of magnetic stars shows a clear decrease towards the end of the main sequence. This dearth of old magnetic stars is independent of the choice of adopted stellar evolution tracks, and appears to become more prominent when considering only the most massive stars. We show that the decreasing trend in the distribution is significantly stronger than expected from magnetic flux conservation. We also find that binary rejuvenation and magnetic suppression of core convection are unlikely to be responsible for the observed lack of older magnetic massive stars, and conclude that its most probable cause is the decay of the magnetic field, over a time span longer than the stellar lifetime for the lowest considered masses, and shorter for the highest masses. We then investigate the spin-down ages of the slowly rotating magnetic massive stars and find them to exceed the stellar ages by far in many cases. The high fraction of very slowly rotating magnetic stars thus provides an independent argument for a decay of the magnetic fields.

  17. Isolating Added Mass Load Components of CPAS Main Clusters

    NASA Technical Reports Server (NTRS)

    Ray, Eric S.

    2017-01-01

    The current simulation for the Capsule Parachute Assembly System (CPAS) lacks fidelity in representing added mass for the 116 ft Do ringsail Main parachute. The availability of 3-D models of inflating Main canopies allowed for better estimation the enclosed air volume as a function of time. This was combined with trajectory state information to estimate the components making up measured axial loads. A proof-of-concept for an alternate simulation algorithm was developed based on enclosed volume as the primary independent variable rather than drag area growth. Databases of volume growth and parachute drag area vs. volume were developed for several flight tests. Other state information was read directly from test data, rather than numerically propagated. The resulting simulated peak loads were close in timing and magnitude to the measured loads data. However, results are very sensitive to data curve fitting and may not be suitable for Monte Carlo simulations. It was assumed that apparent mass was either negligible or a small fraction of enclosed mass, with little difference in results.

  18. Hepatic capillariasis in Maine presenting as a hepatic mass.

    PubMed

    Klenzak, Jennifer; Mattia, Anthony; Valenti, August; Goldberg, John

    2005-05-01

    We report the first case of hepatic capillariasis in Maine. The patient was a 54-year-old male carpenter who presented with a subacute history of severe abdominal pain, fevers, and weight loss. Initial diagnostic studies suggested a hepatic mass associated with para-aortic lymphadenopathy. The patient underwent open laparotomy for resection of the mass. He was found to have an eosinophilic granuloma in the liver; further evaluation revealed degenerating Capillaria hepatica. The exact route of infection in this case is unknown but is most likely due to accidental ingestion of soil contaminated with mature capillaria eggs. This patient had a low parasite burden and did not exhibit significant peripheral eosinophilia. After treatment with thiabendazole, he recovered uneventfully.

  19. Change in the orbital period of a binary system due to dynamical tides for main-sequence stars

    NASA Astrophysics Data System (ADS)

    Chernov, S. V.

    2017-03-01

    We investigate the change in the orbital period of a binary system due to dynamical tides by taking into account the evolution of a main-sequence star. Three stars with masses of one, one and a half, and two solar masses are considered. A star of one solar mass at lifetimes t = 4.57 × 109 yr closely corresponds to our Sun. We show that a planet of one Jupiter mass revolving around a star of one solar mass will fall onto the star in the main-sequence lifetime of the star due to dynamical tides if the initial orbital period of the planet is less than P orb ≈ 2.8 days. Planets of one Jupiter mass with an orbital period P orb ≈ 2 days or shorter will fall onto a star of one and a half and two solar masses in the mainsequence lifetime of the star.

  20. X-rays across the galaxy population - I. Tracing the main sequence of star formation

    NASA Astrophysics Data System (ADS)

    Aird, J.; Coil, A. L.; Georgakakis, A.

    2017-03-01

    We use deep Chandra imaging to measure the distribution of X-ray luminosities (LX) for samples of star-forming galaxies as a function of stellar mass and redshift, using a Bayesian method to push below the nominal X-ray detection limits. Our luminosity distributions all show narrow peaks at LX ≲ 1042 erg s-1 that we associate with star formation, as opposed to AGN that are traced by a broad tail to higher LX. Tracking the luminosity of these peaks as a function of stellar mass reveals an 'X-ray main sequence' with a constant slope ≈0.63 ± 0.03 over 8.5 ≲ log {M}_{ast }/M_{⊙} ≲ 11.5 and 0.1 ≲ z ≲ 4, with a normalization that increases with redshift as (1 + z)3.79 ± 0.12. We also compare the peak X-ray luminosities with UV-to-IR tracers of star formation rates (SFRs) to calibrate the scaling between LX and SFR. We find that LX ∝ SFR0.83 × (1 + z)1.3, where the redshift evolution and non-linearity likely reflect changes in high-mass X-ray binary populations of star-forming galaxies. Using galaxies with a broader range of SFR, we also constrain a stellar-mass-dependent contribution to LX, likely related to low-mass X-ray binaries. Using this calibration, we convert our X-ray main sequence to SFRs and measure a star-forming main sequence with a constant slope ≈0.76 ± 0.06 and a normalization that evolves with redshift as (1 + z)2.95 ± 0.33. Based on the X-ray emission, there is no evidence for a break in the main sequence at high stellar masses, although we cannot rule out a turnover given the uncertainties in the scaling of LX to SFR.

  1. Lithium abundances among solar-type pre-main-sequence stars

    SciTech Connect

    Strom, K.M.; Wilkin, F.P.; Strom, S.E.; Seaman, R.L. Kitt Peak National Observatory, Tucson, AZ )

    1989-10-01

    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. 26 refs.

  2. The Main-Sequence Luminosity Function of Palomar 5 from THE HUBBLE SPACE TELESCOPE

    NASA Astrophysics Data System (ADS)

    Grillmair, Carl J.; Smith, Graeme H.

    2001-12-01

    A low mass, large core radius, low central concentration, and strong tidal tails suggest that the globular cluster Palomar 5 has lost a large fraction of its initial mass over time. If the dynamical evolution of Pal 5 has been dominated by the effects of mass loss, then theoretical arguments suggest that the luminosity function should be deficient in low-mass stars. Using deep WFPC2 F555W and F814W photometry, we determine the main-sequence luminosity functions both near the cluster center and in a field near the half-light radius. A comparison of these luminosity functions yields no compelling evidence of mass segregation within the cluster, in accord with expectations for low-concentration clusters. On the other hand, a comparison of the global mass function of Pal 5 with that of ω Cen and M55 indicates an increasing deficiency of stars with progressively lower masses. A fit of the observed luminosity function to theoretical models indicates a mass function for Pal 5 of dN/dm~m-0.5, which is notably more deficient in low-mass stars than other globular clusters that have been studied with the Hubble Space Telescope. The flatness of the mass function is consistent with models of the dynamical evolution of globular clusters that have lost ~90% of their original stellar mass. We suggest that, like NGC 6712, Pal 5 has lost a large percentage of its original stellar content as a result of tidal shocking. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.

  3. Theory of winds in late-type evolved and pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Macgregor, K. B.

    1983-01-01

    Recent observational results confirm that many of the physical processes which are known to occur in the Sun also occur among late-type stars in general. One such process is the continuous loss of mass from a star in the form of a wind. There now exists an abundance of either direct or circumstantial evidence which suggests that most (if not all) stars in the cool portion of the HR diagram possess winds. An attempt is made to assess the current state of theoretical understanding of mass loss from two distinctly different classes of late-type stars: the post-main-sequence giant/supergiant stars and the pre-main-sequence T Tauri stars. Toward this end, the observationally inferred properties of the wind associated with each of the two stellar classes under consideration are summarized and compared against the predictions of existing theoretical models. Although considerable progress has been made in attempting to identify the mechanisms responsible for mass loss from cool stars, many fundamental problems remain to be solved.

  4. Orbital Parameters for a Pre-Main Sequence Binary System

    NASA Astrophysics Data System (ADS)

    Karnath, Nicole; Prato, L.; Wasserman, L.

    2011-01-01

    The young system VSB 111 was originally classified as a single-lined spectroscopic binary in the star forming region of NGC 2264. Using the Keck II telescope we measured radial velocities for both the primary and secondary components in the infrared. By combining these data with previous visible light observations of the primary star, we derived the period, eccentricity, and other orbital parameters, as well as the mass ratio of the system. With additional information gained from further observations, for example the inclination derived from the angularly resolved orbit, we will eventually obtain the individual stellar masses, necessary to help to calibrate models of young star evolution. Furthermore, by compiling dozens or even hundreds of mass ratios for young binaries we can use mass ratio distributions to improve our understanding of binary star formation. No infrared excess or any other indication of a circumstellar disk is in evidence for VSB 111, indicating that either the accretion rate has dropped to an undetectable value or that this system has aged enough that its disk has dissipated, if originally present. Given the approximately 900 day period of this system, and its relatively high eccentricity, 0.8, the action of the companion could have been responsible for early dissipation of any disk material.

  5. Infalling Envelopes and Pre-Main Sequence Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    1997-01-01

    The goal of this project is to understand the observed infrared emission of young stellar objects, and explore the implications of this emission for the evolution of dusty envelopes and circumstellar disks. We are using sophisticated radiative transfer methods to compare models with observations, thereby making critical tests of the standard picture of low-mass star formation.

  6. The sub-galactic and nuclear main sequences for local star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Maragkoudakis, A.; Zezas, A.; Ashby, M. L. N.; Willner, S. P.

    2017-04-01

    We describe a sub-galactic main sequence (SGMS) relating star formation rate (SFR) surface density (ΣSFR) and stellar mass density (Σ⋆) for distinct regions within star-forming galaxies, including their nuclei. We use a sample of 246 nearby star-forming galaxies from the 'Star Formation Reference Survey and demonstrate that the SGMS holds down to ∼1 kpc scales with a slope of α = 0.91 and a dispersion of 0.31 dex, similar to the well-known main sequence (MS) measured for globally integrated SFRs and stellar masses. The SGMS slope depends on galaxy morphology, with late-type galaxies (Sc-Irr) having α = 0.97 and early-type spirals (Sa-Sbc) having α = 0.81. The SGMS constructed from subregions of individual galaxies has on average the same characteristics as the composite SGMS from all galaxies. The SGMS for galaxy nuclei shows a dispersion similar to that seen for other subregions. Sampling a limited range of SFR-M⋆ space may produce either sublinearity or superlinearity of the SGMS slope. For nearly all galaxies, both SFR and stellar mass peak in the nucleus, indicating that circumnuclear clusters are among the most actively star-forming regions in the galaxy and the most massive. The nuclear SFR also correlates with total galaxy mass, forming a distinct sequence from the standard MS of star formation. The nuclear MS will be useful for studying bulge growth and for characterizing feedback processes connecting AGN and star formation.

  7. ORBITS, MASSES, AND EVOLUTION OF MAIN BELT TRIPLE (87) SYLVIA

    SciTech Connect

    Fang, Julia; Margot, Jean-Luc; Rojo, Patricio

    2012-08-15

    Sylvia is a triple asteroid system located in the main belt. We report new adaptive optics observations of this system that extend the baseline of existing astrometric observations to a decade. We present the first fully dynamical three-body model for this system by fitting to all available astrometric measurements. This model simultaneously fits for individual masses, orbits, and primary oblateness. We find that Sylvia is composed of a dominant central mass surrounded by two satellites orbiting at 706.5 {+-} 2.5 km and 1357 {+-} 4.0 km, i.e., about 5 and nearly 10 primary radii. We derive individual masses of 1.484{sup +0.016}{sub -0.014} Multiplication-Sign 10{sup 19} kg for the primary (corresponding to a density of 1.29 {+-} 0.39 g cm{sup -3}), 7.33{sup +4.7}{sub -2.3} Multiplication-Sign 10{sup 14} kg for the inner satellite, and 9.32{sup +20.7}{sub -8.3} Multiplication-Sign 10{sup 14} kg for the outer satellite. The oblateness of the primary induces substantial precession and the J{sub 2} value can be constrained to the range of 0.0985-0.1. The orbits of the satellites are relatively circular with eccentricities less than 0.04. The spin axis of the primary body and the orbital poles of both satellites are all aligned within about 2 deg of each other, indicating a nearly coplanar configuration and suggestive of satellite formation in or near the equatorial plane of the primary. We also investigate the past orbital evolution of the system by simulating the effects of a recent passage through 3:1 mean-motion eccentricity-type resonances. In some scenarios this allow us to place constraints on interior structure and past eccentricities.

  8. Water Masses and Nutrient Sources to the Gulf of Maine.

    PubMed

    Townsend, David W; Pettigrew, Neal R; Thomas, Maura A; Neary, Mark G; McGillicuddy, Dennis J; O'Donnell, James

    2015-01-01

    The Gulf of Maine, a semi-enclosed basin on the continental shelf of the northwest Atlantic Ocean, is fed by surface and deep water flows from outside the Gulf: Scotian Shelf Water from the Nova Scotian shelf that enters the Gulf at the surface, and Slope Water that enters at depth and along the bottom through the Northeast Channel. There are two types of Slope Water, Labrador Slope Water (LSW) and Warm Slope Water (WSW); it is these deep water masses that are the major source of dissolved inorganic nutrients to the Gulf. It has been known for some time that the volume inflow of Slope Waters of either type that enters the Gulf of Maine is variable, that it co-varies with the magnitude of inflowing Scotian Shelf Water, and that periods of greater inflows of Scotian Shelf Water have become more frequent in recent years, accompanied by reduced Slope Water inflows. We present here analyses of a ten-year record of data collected by moored sensors in Jordan Basin, in the interior Gulf of Maine, and in the Northeast Channel, along with recent and historical hydrographic and nutrient data, that help reveal the nature of Scotian Shelf Water and Slope Water inflows. Proportional inflows of nutrient-rich Slope Waters and nutrient-poor Scotian Shelf Waters alternate episodically with one another on time scales of months to several years, creating a variable nutrient field upon which the biological productivities of the Gulf of Maine and Georges Bank depend. Unlike decades past, the inflows of Slope Waters of either type do not appear to be correlated with the North Atlantic Oscillation, which had been shown earlier to influence the relative proportions of the two Slope Waters, WSW and LSW, that enter the Gulf. We suggest that of greater importance in recent years are more frequent, episodic influxes of colder, fresher, less dense, and low-nutrient Scotian Shelf Water into the Gulf of Maine, and concomitant reductions in the inflow of deep, nutrient-rich Slope Waters. We also

  9. Confronting uncertainties in stellar physics. II. Exploring differences in main-sequence stellar evolution tracks

    NASA Astrophysics Data System (ADS)

    Stancliffe, R. J.; Fossati, L.; Passy, J.-C.; Schneider, F. R. N.

    2016-02-01

    We assess the systematic uncertainties in stellar evolutionary calculations for low- to intermediate-mass, main-sequence stars. We compare published stellar tracks from several different evolution codes with our own tracks computed using the stellar codes stars and mesa. In particular, we focus on tracks of 1 and 3 M⊙ at solar metallicity. We find that the spread in the available 1 M⊙ tracks (computed before the recent solar composition revision) can be covered by tracks between 0.97-1.01 M⊙ computed with the stars code. We assess some possible causes of the origin of this uncertainty, including how the choice of input physics and the solar constraints used to perform the solar calibration affect the tracks. We find that for a 1 M⊙ track, uncertainties of around 10% in the initial hydrogen abundance and initial metallicity produce around a 2% error in mass. For the 3 M⊙ tracks, there is very little difference between the tracks from the various different stellar codes. The main difference comes in the extent of the main sequence, which we believe results from the different choices of the implementation of convective overshooting in the core. Uncertainties in the initial abundances lead to a 1-2% error in the mass determination. These uncertainties cover only part of the total error budget, which should also include uncertainties in the input physics (e.g., reaction rates, opacities, convective models) and any missing physics (e.g., radiative levitation, rotation, magnetic fields). Uncertainties in stellar surface properties such as luminosity and effective temperature will further reduce the accuracy of any potential mass determinations.

  10. Accreting pre-main-sequence models and abundance anomalies in globular clusters

    NASA Astrophysics Data System (ADS)

    Tognelli, E.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2015-12-01

    We investigated the possibility of producing helium-enhanced stars in globular clusters by accreting polluted matter during the pre-main-sequence phase. We followed the evolution of two different classes of pre-main-sequence accreting models, one which neglects and the other that takes into account the protostellar evolution. We analysed the dependence of the final central helium abundance, of the tracks position in the HR diagram and of the surface lithium abundance evolution on the age at which the accretion of polluted material begins and on the main physical parameters that govern the protostellar evolution. The later is the beginning of the late accretion and the lower are both the central helium and the surface lithium abundances at the end of the accretion phase and in Zero Age Main Sequence (ZAMS). In order to produce a relevant increase of the central helium content the accretion of polluted matter should start at ages lower than 1 Myr. The inclusion of the protostellar evolution has a strong impact on the ZAMS models too. The adoption of a very low seed mass (i.e. 0.001 M⊙) results in models with the lowest central helium and surface lithium abundances. The higher is the accretion rate and the lower is the final helium content in the core and the residual surface lithium. In the worst case - i.e. seed mass 0.001 M⊙ and accretion rate ≥10-5 M⊙ yr-1 - the central helium is not increased at all and the surface lithium is fully depleted in the first few million years.

  11. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2005-01-01

    The aim of this project was to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, premain sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we developed much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measured disk accretion rates in these systems; and constructed detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  12. The evolved slowly pulsating B star 18 Peg. A testbed for upper main sequence stellar evolution

    NASA Astrophysics Data System (ADS)

    Irrgang, Andreas; De Cat, Peter; Tkachenko, Andrew

    2017-09-01

    The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Irrgang et al. ([1]) showed that the B3 III giant 18 Peg is one of the most evolved members of the class of slowly pulsating B (SPB) stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric, more than 6-year orbit. The orbital solution, in combination with the absence of additional signatures of the secondary component in the spectroscopic data and the spectral energy distribution, lead to the conclusion that all the observations of 18 Peg are fully compatible with the assumption that the secondary component is either a main-sequence star with a mass of 1-4 M⊙ or a neutron star.

  13. The Star Formation Main Sequence in the Hubble Space Telescope Frontier Fields

    NASA Astrophysics Data System (ADS)

    Santini, Paola; Fontana, Adriano; Castellano, Marco; Di Criscienzo, Marcella; Merlin, Emiliano; Amorin, Ricardo; Cullen, Fergus; Daddi, Emanuele; Dickinson, Mark; Dunlop, James S.; Grazian, Andrea; Lamastra, Alessandra; McLure, Ross J.; Michałowski, Michał. J.; Pentericci, Laura; Shu, Xinwen

    2017-09-01

    We investigate the relation between star formation rate (SFR) and stellar mass (M), i.e., the main sequence (MS) relation of star-forming galaxies, at 1.3≤slant z< 6 in the first four Hubble Space Telescope (HST) Frontier Fields, on the basis of rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to {log} M/{M}ȯ ∼ 7.5 at z≲ 4 and {log} M/{M}ȯ ∼ 8 at higher redshifts, a factor of ∼10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing mass, suggesting a larger variety of star formation histories in low-mass galaxies. This trend agrees with theoretical predictions and is explained as either a consequence of the smaller number of progenitors of low-mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low-mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.

  14. RADIO AND MID-INFRARED PROPERTIES OF COMPACT STARBURSTS: DISTANCING THEMSELVES FROM THE MAIN SEQUENCE

    SciTech Connect

    Murphy, E. J.; Stierwalt, S.; Armus, L.; Condon, J. J.; Evans, A. S.

    2013-05-01

    We investigate the relationship between 8.44 GHz brightness temperatures and 1.4 to 8.44 GHz radio spectral indices with 6.2 {mu}m polycyclic aromatic hydrocarbon (PAH) emission and 9.7 {mu}m silicate absorption features for a sample of 36 local luminous and ultraluminous infrared galaxies. We find that galaxies having small 6.2 {mu}m PAH equivalent widths (EQWs), which signal the presence of weak PAH emission and/or an excess of very hot dust, also have flat spectral indices. The three active galactic nuclei (AGN) identified through their excessively large 8.44 GHz brightness temperatures are also identified as AGN via their small 6.2 {mu}m PAH EQWs. We also find that the flattening of the radio spectrum increases with increasing silicate optical depth, 8.44 GHz brightness temperature, and decreasing size of the radio source even after removing potential AGN, supporting the idea that compact starbursts show spectral flattening as the result of increased free-free absorption. These correlations additionally suggest that the dust obscuration in these galaxies must largely be coming from the vicinity of the compact starburst itself, and is not distributed throughout the (foreground) disk of the galaxy. Finally, we investigate the location of these infrared-bright systems relative to the main sequence (star formation rate versus stellar mass) of star-forming galaxies in the local universe. We find that the radio spectral indices of galaxies flatten with increasing distance above the main sequence, or in other words, with increasing specific star formation rate. This indicates that galaxies located above the main sequence, having high specific star formation rates, are typically compact starbursts hosting deeply embedded star formation that becomes more optically thick in the radio and infrared with increased distance above the main sequence.

  15. The PISA Pre-Main Sequence accreting models

    NASA Astrophysics Data System (ADS)

    Tognelli, Emanuele; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla

    2013-07-01

    The poster investigates the effect of accretion processes on the evolution of stellar models computed by means of the well tested and updated PROSECCO evolutionary code, under the hypothesis of thin-disk accretion. We analysed the effect on the evolution of the adoption of different parameters as the accretion rate, accretion history, seed mass, and the fraction of the infalling matter energy (alpha_acc) deposed in to the star (accretion energy). We confirm that the most critical parameter is the accretion energy. We show that, depending on alpha_acc the evolution of accreting and non-accreting objects can be completely different, confirming that the adoption of small alpha_acc value (i.e. small accretion energy, cold accretion) produces fainter and more compact models with respect to the ones predicted from non-accreting structures at the same mass and age, models that can not be reconciled with the data available for young objects (i.e. position in the HR diagram, lithium abundances). On the contrary, if a large part of the accretion luminosity is deposed into the star (alpha_acc = 1, hot accretion), at least during the fisrt stages of the accretion phase or during bursts episodes, large radii and luminosities are achievable, with resulting structures much more similar to the non-accreting ones.

  16. The Main Sequence of Explosive Solar Active Regions: Comparison of Emerging and Mature Active Regions

    NASA Technical Reports Server (NTRS)

    Falconer, David; Moore, Ron

    2011-01-01

    For mature active regions, an active region s magnetic flux content determines the maximum free energy the active region can have. Most Large flares and CMEs occur in active regions that are near their free-energy limit. Active-region flare power radiated in the GOES 1-8 band increases steeply as the free-energy limit is approached. We infer that the free-energy limit is set by the rate of release of an active region s free magnetic energy by flares, CMEs and coronal heating balancing the maximum rate the Sun can put free energy into the active region s magnetic field. This balance of maximum power results in explosive active regions residing in a "mainsequence" in active-region (flux content, free energy content) phase space, which sequence is analogous to the main sequence of hydrogen-burning stars in (mass, luminosity) phase space.

  17. Observational Studies of Pre-Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Hutchinson, M. G.

    1988-12-01

    This work investigates selected young stars paying particular attention to their photometric and polarimetric characteristics. The stars observed represent particular sub-classes of the Orion Population of young stars: T Tauri stars of about one solar mass (RY Lup, RU Lup, CoD -33o10685 and AK Sco); Herbig Ae/Be stars of a few solar masses (TY CrA, R CrA, T CrA and V856 Sco); a YY Ori star which is thought to be still accreting matter (S CrA); and an 'isolated' T Tauri star which lies away from a star-forming cloud (V4046 Sgr). Data was acquired at ultraviolet, optical and infrared wavelengths, along with optical polarimetric data. The subsequent analysis of data for the well-studied stars can be summarised as follows: the spectroscopic characteristics of the star are defined; possible mechanisms for the photometric variability are discussed; and given the spectral type of the star, the intrinsic flux distribution is determined and the parameters of the optical and infrared emission are thereby determined. The implications of any photometric variability found are also discussed. A possible model of polarisation is discussed and the wavelength dependence of polarisation in eleven young stars is analysed. It is found that the circumstellar environment plays a role in many of the observed characteristics of the stars studied. Several of the stellar spectra show lines which form in a stellar envelope. Each star is found to be affected by circumstellar extinction and to exhibit infrared emission from circumstellar dust. In most cases the circumstellar dust also gives rise to the optical polarisation. The photometric and/or polarimetric variability exhibited by some of the stars is ascribable to changes in the circumstellar dust shell opacity

  18. NEW X-RAY-SELECTED PRE-MAIN-SEQUENCE MEMBERS OF THE SERPENS MOLECULAR CLOUD

    SciTech Connect

    Oliveira, Isa; Van der Laan, Margriet; Brown, Joanna M.

    2013-11-01

    The study of young stars no longer surrounded by disks can greatly add to our understanding of how protoplanetary disks evolve and planets form. We have used VLT/FLAMES optical spectroscopy to confirm the youth and membership of 19 new young diskless stars in the Serpens Molecular Cloud, identified at X-ray wavelengths. Spectral types, effective temperatures, and stellar luminosities were determined using optical spectra and optical/near-infrared photometry. Stellar masses and ages were derived based on pre-main-sequence evolutionary tracks. The results yield remarkable similarities for age and mass distribution between the diskless and disk-bearing stellar populations in Serpens. We discuss the important implications these similarities may have on the standard picture of disk evolution.

  19. Lithium evolution from Pre-Main Sequence to the Spite plateau: an environmental solution to the cosmological lithium problem

    NASA Astrophysics Data System (ADS)

    Fu, Xiaoting; Bressan, Alessandro; Molaro, Paolo; Marigo, Paola

    2016-08-01

    Lithium abundance derived in metal-poor main sequence stars is about three times lower than the primordial value of the standard Big Bang nucleosynthesis prediction. This disagreement is referred to as the lithium problem. We reconsider the stellar Li evolution from the pre-main sequence to the end of main sequence phase by introducing the effects of overshooting and residual mass accretion. We show that 7Li could be significantly depleted by convective overshooting in the pre-main sequence phase and then partially restored in the stellar atmosphere by residual accretion which follows the Li depletion phase and could be regulated by EUV photo-evaporation. By considering the conventional nuclear burning and diffusion along the main sequence we can reproduce the Spite plateau for stars with initial mass m 0=0.62-0.80 M ⊙, and the Li declining branch for lower mass dwarfs, e.g, m 0=0.57-0.60 M ⊙, for a wide range of metallicities (Z=0.00001 to Z=0.0005), starting from an initial Li abundance A(Li) = 2.72.

  20. Equilibrium model prediction for the scatter in the star-forming main sequence

    NASA Astrophysics Data System (ADS)

    Mitra, Sourav; Davé, Romeel; Simha, Vimal; Finlator, Kristian

    2017-01-01

    The analytic `equilibrium model' for galaxy evolution using a mass balance equation is able to reproduce mean observed galaxy scaling relations between stellar mass, halo mass, star formation rate (SFR), and metallicity across the majority of cosmic time with a small number of parameters related to feedback. Here, we aim to test this data-constrained model to quantify deviations from the mean relation between stellar mass and SFR, i.e. the star-forming galaxy main sequence (MS). We implement fluctuation in halo accretion rates parametrized from merger-based simulations, and quantify the intrinsic scatter introduced into the MS under the assumption that fluctuations in star formation follow baryonic inflow fluctuations. We predict the 1σ MS scatter to be ˜0.2-0.25 dex over the stellar mass range 108-1011 M⊙ and a redshift range 0.5 ≲ z ≲ 3 for SFRs averaged over 100 Myr. The scatter increases modestly at z ≳ 3, as well as by averaging over shorter time-scales. The contribution from merger-induced star formation is generally small, around 5 per cent today and 10-15 per cent during the peak epoch of cosmic star formation. These results are generally consistent with available observations, suggesting that deviations from the MS primarily reflect stochasticity in the inflow rate owing to halo mergers.

  1. ACCRETION RATES ON PRE-MAIN-SEQUENCE STARS IN THE YOUNG OPEN CLUSTER NGC 6530

    SciTech Connect

    Gallardo, Jose; Del Valle, Luciano; Ruiz, Maria Teresa E-mail: ldelvall@das.uchile.cl

    2012-01-15

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first {approx}1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the H{sub {alpha}} emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad H{sub {alpha}} emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR.

  2. Winds in hot main-sequence stars near the static limit

    NASA Technical Reports Server (NTRS)

    Morrison, Nancy D.

    1995-01-01

    This project began with the acquisition of short-wavelength, high-dispersion IUE spectra of selected late O- and early B-type stars that are near the main sequence in open clusters and associations. The profiles of the resonance lines of N(V), Si(IV), and C(IV) were studied, and we found that the C(IV) lines are the most sensitive indicators of mass loss (stellar winds) in stars of this type. The mass loss manifests itself as an extension of the short-wavelength absorption wing of the doublet, while there is no P Cygni-type emission on the long-wavelength side of the line profile. We investigated whether the short-wavelength extension could be caused by blended lines of other ionic species formed in the photosphere. Although blending is present and introduces uncertainty into the estimation of the precise location on the main sequence of the onset of the mass-loss signature, it is a crucial issue only in a few marginal cases. Mass loss certainly overwhelms blending in its influence on the spectrum between spectral types B0 and B1 (effective temperatures in the range 25,000-27,000 K). We defined a parameter called P(sub w), to describe the degree of asymmetry of the C(IV) resonance-line profile, and we studied the dependence of this parameter on the fundamental stellar parameters. For this purpose, we derived new estimates of the stellar T(eff) and log g from a non-LTE, line-blanketed model-atmosphere analysis of these stars (Grigsby, Morrison, and Anderson 1992). In order to estimate the stellar luminosities, we performed an exhaustive search of the literature for the most reliable available estimates of the distances of the clusters and associations to which the program stars belong. The dependence of P(sub w) on stellar temperature and luminosity is also studied.

  3. Masses of asteroids and the total mass of the main asteroid belt

    NASA Astrophysics Data System (ADS)

    Vladimirovna Pitjeva, Elena; Petrovich Pitjev, Nikolay

    2015-08-01

    The renovated database of observations of planets and spacecraft, as well as asteroid data have been used for estimation of masses of asteroids and the total mass of main asteroid belt from their perturbations on motion of solar system bodies. The direct dynamical mass estimations were obtained for about 30 largest asteroids by their gravitation impacts on other bodies. The masses of other large asteroids were estimated by their diameters and evaluated densities. The total contribution of all remaining small asteroids is modeled as a gravitational force from uniform two-dimensional ring with the constant mass distribution in the ecliptic plane. The work was based on the new version of the EPM2014 ephemerides of IAA RAS using more than 800000 positional observations (mostly radar ones) of planets and spacecraft obtained in 1913-2014. For the first time, the two-dimensional asteroid annulus with dimensions corresponding to its observable width has been used instead of one-dimensional ring which applied for modeling perturbation of small asteroids in our previous versions of EPM ephemerides. As a result, the accuracy of the mass of the two-dimensional asteroid annulus has increased by 6 times; orbits of all planets have improved distinctly, in particular, the formal uncertainties of the semi-major axes of the planets decreased by two times. The total mass of the main asteroid belt has been found: Mbelt = (12.25 ± 0.19)×10-10MSun. ≈ 2.5 MCeres.Moreover, the estimation of the total mass of Trans-Neptunian Objects (TNO) including the known masses of 30 largest TNO, Pluto and the evaluated mass of the TNO ring (with a radius of 43 au) was obtained:592×10-10 MSun (or 125 MCeres).

  4. 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.

  5. Critically Rotating Post-Main Sequence Stars Hosting a Viscous Decretion Disk

    NASA Astrophysics Data System (ADS)

    Granada, A.; Sigut, A.; Jones, C.; Georgy, C.; Ekström, S.; Meynet, G.

    2017-02-01

    Stellar evolution calculations of isolated, rotating, intermediate mass stars predict that only a handful of these objects reach the critical limit after the main sequence phase, during the helium burning phase, while describing a blue-loop in the HR diagram. During the red supergiant stage, angular momentum could be dredged-up to the surface so that when the star contracts describing the blue-loop, the surface velocities can reach larger values than those the star had when crossing the Hertzprung-Russell diagram for the first time. Even though these stars might indeed be rare objects, we explore the possibility of such stars undergoing mechanical mass loss and hence forming a viscous decretion disk. By taking into account the angular momentum loss rate from Geneva stellar evolution calculations for a star with 9 solar masses and large rotational rate at the ZAMS (Ω/Ωcrit=0.9), combined with the relations available in the literature we obtain the disk outer radius and disk mass loss rate for such an object. Using BEDISK/BERAY codes, we calculate observables (Hα and other hydrogen lines, forbidden lines, colors) generated in the gaseous component of the resulting star plus disk system and compare them with observations of evolved stars exhibiting the B[e] phenomenon.

  6. Orbital circularization of close binary stars on the pre-main sequence

    NASA Astrophysics Data System (ADS)

    Khaliullin, Kh. F.; Khaliullina, A. I.

    2011-03-01

    The numerical computations of the circularization of close binary systems at the pre-main-sequence (pre-MS) stage of evolution (reported by Zahn and Bouchet in their now well-known paper) are repeated for an extended stellar mass interval of M= 0.1-2.7 M⊙, based on modern evolutionary pre-MS stellar models and on the modified Zahn theory. The new results mostly corroborate those obtained by Zahn and Bouchet in the mass interval M= 0.5-1.25 M⊙ covered by their work. To compare the theoretically expected results with observations, a catalogue is compiled of 70 eclipsing binaries with eccentric orbits and bona fide photometric elements and masses. The pre-MS lifetimes of all these systems are computed as fractions of the circularization time-scale tPMS/tcirc in terms of the Zahn theory and assuming the conservation of angular momentum L. All systems of this catalogue fill almost uniformly the entire domain of the eobs-tPMS/tcirc diagram independently of tPMS/tcirc[i.e. the (tPMS/tcirc)cr= 4 threshold does not separate circular and eccentric systems in this diagram]. This result shows that the computations of the orbital circularization at the pre-MS stage based on the concept of the conservation of L have nothing to do with the actually observed distribution of the eccentricities of close binary systems. The results obtained lead us to the following conclusions. (i) Binaries appear to cross the Hayashi phase in a more detached state than we observe them on the MS, and therefore they are unaffected by tidal circularization at this stage. (ii) Binaries must lose an appreciable fraction of their angular momentum while evolving from the Hayashi phase to the zero-age main sequence. This loss may be a result of the dynamic interaction with the parent disc and other components of the multiple system.

  7. Main-Sequence CMEs as Magnetic Explosions: Compatibility with Observed Kinematics

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Sterling, Alphonse

    2004-01-01

    We examine the kinematics of 26 CMEs of the morphological main sequence of CMEs, those having the classic three-part bubble structure of (1) a bright front eveloping (2) a dark cavity within which rides (3) a bright blob/filamentary feature. Each CME is observed in Yohkoh/SXT images to originate from near the limb (> or equal to 0.7 R(sub Sun) from disk center). The basic data (from the SOHO LASCO CME Catalog) for the kinematics of each CME are the sequence of LASCO images of the CME, the time of each image, the measured radial distance of the front edge of the CME in each image, and the measured angular extent of the CME. About half of our CMEs (12) occur with a flare, and the rest (14) occur without a flare. While the average linear-fit speed of the flare CMEs (1000 km/s) is twice that of the non-flare CMEs (510 km/s), the flare CMEs and the non-flare CMEs are similar in that some have nearly flat velocity-height (radial extent) profiles (little acceleration), some have noticeably falling velocity profiles (noticeable deceleration), and the rest have velocity profiles that rise considerably through the outer corona (blatant acceleration). This suggests that in addition to sharing similar morphology, main-sequence CMEs all have basically the same driving mechanism. The observed radial progression of each of our 26 CMEs is fit by a simple model magnetic plasmoid that is in pressure balance with the radial magnetic field in the outer corona and that propels itself outward by magnetic expansion, doing no net work on its surroundings. On average over the 26 CMEs, this model fits the observations as well as the assumption of constant acceleration. This is compatible with main-sequence CMEs being magnetically driven, basically magnetic explosions, with the velocity profile in the outer corona being largely dictated by the initial Alfien speed in the CME (when the front is at approx. 3 (sub Sun), analogous to the mass of a main-sequence star dictating the luminosity.

  8. Main-Sequence CMEs as Magnetic Explosions: Compatibility with Observed Kinematics

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Sterling, Alphonse

    2004-01-01

    We examine the kinematics of 26 CMEs of the morphological main sequence of CMEs, those having the classic three-part bubble structure of (1) a bright front eveloping (2) a dark cavity within which rides (3) a bright blob/filamentary feature. Each CME is observed in Yohkoh/SXT images to originate from near the limb (> or equal to 0.7 R(sub Sun) from disk center). The basic data (from the SOHO LASCO CME Catalog) for the kinematics of each CME are the sequence of LASCO images of the CME, the time of each image, the measured radial distance of the front edge of the CME in each image, and the measured angular extent of the CME. About half of our CMEs (12) occur with a flare, and the rest (14) occur without a flare. While the average linear-fit speed of the flare CMEs (1000 km/s) is twice that of the non-flare CMEs (510 km/s), the flare CMEs and the non-flare CMEs are similar in that some have nearly flat velocity-height (radial extent) profiles (little acceleration), some have noticeably falling velocity profiles (noticeable deceleration), and the rest have velocity profiles that rise considerably through the outer corona (blatant acceleration). This suggests that in addition to sharing similar morphology, main-sequence CMEs all have basically the same driving mechanism. The observed radial progression of each of our 26 CMEs is fit by a simple model magnetic plasmoid that is in pressure balance with the radial magnetic field in the outer corona and that propels itself outward by magnetic expansion, doing no net work on its surroundings. On average over the 26 CMEs, this model fits the observations as well as the assumption of constant acceleration. This is compatible with main-sequence CMEs being magnetically driven, basically magnetic explosions, with the velocity profile in the outer corona being largely dictated by the initial Alfien speed in the CME (when the front is at approx. 3 (sub Sun), analogous to the mass of a main-sequence star dictating the luminosity.

  9. The N/O Ratio in Early B-Type Main Sequence Stars as an Indicator of Their Evolution

    NASA Astrophysics Data System (ADS)

    Lyubimkov, L. S.

    2016-12-01

    It is shown that, in the case of early B-type main-sequence stars, of the three ratios N/C, C/O, and N/O which are regarded as indicators of stellar evolution, the ratio N/O is more reliable since it seems to be insensitive to overionization of the NII and OII ions. On the other hand, the N/C and C/O ratios, which include carbon, may contain systematic errors for stars with Teff > 18500 K because of neglected overionization of CII ions. The ratio N/O is studied in the atmospheres of 46 early main-sequence B stars. These values of N/O are examined as functions of the effective temperature, age, rotation speed, and mass of the stars. Most early B-stars in the main sequence are found to have [N/O] ≈ 0, which indicates that N/O varies little during the main sequence stage, and this result is independent of the basic parameters listed above. There are two explanations for the large number of stars with [N/O] ≈ 0 : it is predicted theoretically that for an initial rotation velocity V0 < 100 km/s, N/O varies little toward the end of the main sequence stage ([N/O] < 0.2) and observations show that most early main-sequence B-stars do actually have low initial rotation velocities V0. The few early main-sequence B-stars with higher [N/O] = 0.4-0.8 correspond to models with rotation velocities V0 = 200-300 km/s. This conclusion is consistent with earlier data for stars with the same masses in a later stage of evolution: the AFGsupergiant and bright giant stage.

  10. Testing pre-main-sequence models: the power of a Bayesian approach

    NASA Astrophysics Data System (ADS)

    Gennaro, M.; Prada Moroni, P. G.; Tognelli, E.

    2012-02-01

    Pre-main-sequence (PMS) models provide invaluable tools for the study of star-forming regions as they allow us to assign masses and ages to young stars. Thus, it is of primary importance to test the models against observations of PMS stars with dynamically determined masses. We developed a Bayesian method for testing the present generation of PMS models, which allows for a quantitative comparison with observations, largely superseding the widely used isochrones and tracks qualitative superposition. Using the available PMS data, we tested the newest PISA PMS models, establishing good agreement with the observations. The data cover a mass range from ˜0.3 to ˜3.1 M⊙, temperatures from ˜3 × 103 to ˜1.2 × 104 K and luminosities from ˜3 × 10-2 to ˜60 L⊙. Masses are correctly predicted within 20 per cent of the observed values in most of the cases, and for some of them the difference is as small as 5 per cent. Nevertheless, some discrepancies are also observed and critically discussed. By means of simulations, using typical observational errors, we evaluated the spread of log τsim- log τrec, i.e. simulated - recovered age distribution of the single objects. We also found that stars in binary systems simulated as coeval might be recovered as non-coeval, due to observational errors. The actual fraction of fake non-coevality is a complex function of the simulated ages, masses and mass ratios. We demonstrated that it is possible to recover the systems' ages with better precision than for single stars using the composite age-probability distribution, i.e. the product of the components' age distributions. Using this valuable tool, we estimated the ages of the presently observed PMS binary systems.

  11. A Search for Planets and Brown Dwarfs around Post Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Otani, Tomomi; Oswalt, Terry D.

    2016-06-01

    The most promising current theory for the origin of subdwarf B (sdB) stars is that they were formed during binary star evolution. This project was conducted to test this hypothesis by searching for companions around six sdB pulsators using the Observed-minus-Calculated (O-C) method. A star’s position in space will wobble due to the gravitational forces of any companion. If it is emitting a periodic signal, the orbital motion of the star around the system’s center of mass causes periodic changes in the light pulse arrival times. O-C diagrams for six sdB pulsators were constructed from several years’ observations, providing useful limits on suspected companions’ minimum masses and semimajor axes. The results were constrained by “period vs. amplitude” and “mass vs. semimajor axis” models to quantify companion masses and semimajor axes that are consistent with the observational data, if any. Two of our targets, V391 Peg and HS0702+6043, are noted in previous publications to have substellar companions. These were used to validate the method used in this research. The results of this study yielded the same masses and semimajor axes for these two stars as the published values, within the uncertainties. Another of the targets, EC20117-4014, is noted in the literature as a binary system containing an sdB and F5V star, however the orbital period and separation were unknown. The new data obtained in this study contain the signal of a companion candidate with a period of 158.01 days. Several possible mass and semimajor axis combinations for the companion are consistent with the observations. One of the other targets in this study displayed preliminary evidence for a companion that will require further observation. Though still a small sample, these results suggest that planets often survive the post-main-sequence evolution of their parent stars.

  12. Non-linearity and environmental dependence of the star-forming galaxies main sequence

    NASA Astrophysics Data System (ADS)

    Erfanianfar, G.; Popesso, P.; Finoguenov, A.; Wilman, D.; Wuyts, S.; Biviano, A.; Salvato, M.; Mirkazemi, M.; Morselli, L.; Ziparo, F.; Nandra, K.; Lutz, D.; Elbaz, D.; Dickinson, M.; Tanaka, M.; Altieri, M. B.; Aussel, H.; Bauer, F.; Berta, S.; Bielby, R. M.; Brandt, N.; Cappelluti, N.; Cimatti, A.; Cooper, M. C.; Fadda, D.; Ilbert, O.; Le Floch, E.; Magnelli, B.; Mulchaey, J. S.; Nordon, R.; Newman, J. A.; Poglitsch, A.; Pozzi, F.

    2016-01-01

    Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at z < 1.1. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS data sets. We distinguish group environments (Mhalo ˜ 1012.5-14.2 M⊙) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the main sequence (MS) of star-forming galaxies is not a linear relation and there is a flattening towards higher stellar masses (M* > 1010.4-10.6 M⊙), across all environments. At high redshift (0.5 < z < 1.1), the MS varies little with environment. At low redshift (0.15 < z < 0.5), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS towards low SFR is due to an increased fraction of bulge-dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disc-dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold (˜1010.4-1010.6 M⊙) stellar mass, morphology and environment act together in driving the evolution of the star formation activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond z ˜1. The environmental effects appear, instead, at lower redshifts and have a long time-scale.

  13. Mapping the magnetospheric structure at outburst of the pre-main sequence close binary AK Sco

    NASA Astrophysics Data System (ADS)

    Gomez De Castro, Ana

    2013-10-01

    Pre-main sequence {PMS} binaries are surrounded by circumbinary disks from which matter falls onto both components. The material dragged from the circumbinary disk flows onto each star through independent streams channelled by the variable gravitational field. The action of the bar-like potential is most prominent in high eccentricity systems made of two equal mass stars. AK Sco is a unique PMS system composed of two F5 stars that get as close as 11.3 stellar radii at periastron {e=0.47}. AK Sco is an ideal laboratory to study matter infall in binaries and its role in orbit circularization. Our team has reported recently, the discovery of an unexpected 1.3mHz ultra low frequency {ULF} oscillation in the ultraviolet light curve at periastron passage. The oscillation lasted 0.6% of the orbital period. According to our numerical simulations, the cirscumstellar structures get in contact at periastron producing an accretion outburst that triggered of the oscillation. If confirmed, this would unveil a new mechanism for angular momentum loss during pre-main sequence evolution and a new type of interacting binary. The objective of this project is to identify the source of the oscillation and the physical structure of the accretion flow before, during and after the oscillation is triggered. Since the accretion flow radiates in the ultraviolet range, this study requires an ultraviolet {UV} spectroscopic monitoring.

  14. The Main Sequences of Star-forming Galaxies and Active Galactic Nuclei at High Redshift

    NASA Astrophysics Data System (ADS)

    Mancuso, C.; Lapi, A.; Shi, J.; Cai, Z.-Y.; Gonzalez-Nuevo, J.; Béthermin, M.; Danese, L.

    2016-12-01

    We provide a novel, unifying physical interpretation on the origin, average shape, scatter, and cosmic evolution for the main sequences of star-forming galaxies and active galactic nuclei (AGNs) at high redshift z≳ 1. We achieve this goal in a model-independent way by exploiting: (i) the redshift-dependent star formation rate functions based on the latest UV/far-IR data from HST/Herschel, and related statistics of strong gravitationally lensed sources; (ii) deterministic evolutionary tracks for the history of star formation and black hole accretion, gauged on a wealth of multiwavelength observations including the observed Eddington ratio distribution. We further validate these ingredients by showing their consistency with the observed galaxy stellar mass functions and AGN bolometric luminosity functions at different redshifts via the continuity equation approach. Our analysis of the main sequence for high-redshift galaxies and AGNs highlights that the present data are consistently interpreted in terms of an in situ coevolution scenario for star formation and black hole accretion, envisaging these as local, time-coordinated processes.

  15. Estimating the Radius of the Convective Core of Main-sequence Stars from Observed Oscillation Frequencies

    NASA Astrophysics Data System (ADS)

    Yang, Wuming

    2016-10-01

    The determination of the size of the convective core of main-sequence stars is usually dependent on the construction of models of stars. Here we introduce a method to estimate the radius of the convective core of main-sequence stars with masses between about 1.1 and 1.5 M ⊙ from observed frequencies of low-degree p-modes. A formula is proposed to achieve the estimation. The values of the radius of the convective core of four known stars are successfully estimated by the formula. The radius of the convective core of KIC 9812850 estimated by the formula is 0.140 ± 0.028 R ⊙. In order to confirm this prediction, a grid of evolutionary models was computed. The value of the convective-core radius of the best-fit model of KIC 9812850 is 0.149 R ⊙, which is in good agreement with that estimated by the formula from observed frequencies. The formula aids in understanding the interior structure of stars directly from observed frequencies. The understanding is not dependent on the construction of models.

  16. Galaxy Zoo: spiral galaxy morphologies and their relation to the star-forming main sequence

    NASA Astrophysics Data System (ADS)

    Willett, Kyle; Schawinski, Kevin; Masters, Karen; Melvin, Tom; Skibba, Ramin A.; Nichol, Robert; Cheung, Edmond; Lintott, Chris; Simmons, Brooke D.; Kaviraj, Sugata; Keel, William C.; Fortson, Lucy; Galaxy Zoo volunteers

    2015-01-01

    We examine the relationship between stellar mass and star formation rate in disk galaxies at z<0.085, measuring different populations of spirals as classified by their kiloparsec-scale structure. The morphologies of disk galaxies are obtained from the Galaxy Zoo 2 project, which includes the number of spiral arms, the arm pitch angle, and the presence of strong galactic bars. We show that both the slope and dispersion of the star-forming main sequence (SFMS) is constant no matter what the morphology of the spiral disk. We also show that mergers (both major and minor), which represent the strongest conditions for increases in star formation at a constant mass, only boost the SFR above the main relation by 0.3 dex; this is a significant reduction over the increase seen in merging systems at higher redshifts (z > 1). Of the galaxies that do lie significantly above the SFMS in the local Universe, more than 50% are mergers, with a large contribution from the compact green pea galaxies. We interpret our results as evidence that the number and pitch angle of spiral arms, which are imperfect reflections of the galaxy's current gravitational potential, are either fully independent of the various quenching mechanisms for star formation or are completely overwhelmed by the combination of outflows and feedback.

  17. An extensive VLT/X-shooter library of photospheric templates of pre-main sequence stars

    NASA Astrophysics Data System (ADS)

    Manara, C. F.; Frasca, A.; Alcalá, J. M.; Natta, A.; Stelzer, B.; Testi, L.

    2017-09-01

    Context. Studies of the formation and evolution of young stars and their disks rely on knowledge of the stellar parameters of the young stars. The derivation of these parameters is commonly based on comparison with photospheric template spectra. Furthermore, chromospheric emission in young active stars impacts the measurement of mass accretion rates, a key quantity for studying disk evolution. Aims: Here we derive stellar properties of low-mass (M⋆≲ 2 M⊙) pre-main sequence stars without disks, which represent ideal photospheric templates for studies of young stars. We also use these spectra to constrain the impact of chromospheric emission on the measurements of mass accretion rates. The spectra are reduced, flux-calibrated, and corrected for telluric absorption, and are made available to the community. Methods: We derive the spectral type for our targets by analyzing the photospheric molecular features present in their VLT/X-shooter spectra by means of spectral indices and comparison of the relative strength of photospheric absorption features. We also measure effective temperature, gravity, projected rotational velocity, and radial velocity from our spectra by fitting them with synthetic spectra with the ROTFIT tool. The targets have negligible extinction (AV< 0.5 mag) and spectral type from G5 to K6, and from M6.5 to M8. They thus complement the library of photospheric templates presented in our previous publication. We perform synthetic photometry on the spectra to derive the typical colors of young stars in different filters. We measure the luminosity of the emission lines present in the spectra and estimate the noise due to chromospheric emission in the measurements of accretion luminosity in accreting stars. Results: We provide a calibration of the photospheric colors of young pre-main sequence stars as a function of their spectral type in a set of standard broad-band optical and near-infrared filters. The logarithm of the noise on the accretion

  18. Post main sequence evolution of icy minor planets: water retention and white dwarf pollution

    NASA Astrophysics Data System (ADS)

    Malamud, Uri; Perets, Hagai

    2017-06-01

    We investigate the evolution of icy minor planets from the moment of their birth and through the all evolutionary stages of their host stars, including the main sequence, red giant branch and asymptotic giant branch phases. We then asses the degree of water retention in planetary systems around white dwarf, as a function of various parameters. We consider progenitor stars of different masses and metallicities. We also consider minor planets of various sizes, initial orbital distances, compositions and formation times. Our results indicate that water can survive to the white dwarf stage in a variety of circumstances, especially around G, F, A and even some B type stars. We discuss the significance of water retention with respect to white dwarf pollution and also for planet habitability.

  19. A Population Study of Wide-Separation Brown Dwarf Companions to Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Smith, Jeffrey J.

    2005-01-01

    Increased interest in infrared astronomy has opened the frontier to study cooler objects that shed significant light on the formation of planetary systems. Brown dwarf research provides a wealth of information useful for sorting through a myriad of proposed formation theories. Our study combines observational data from 2MASS with rigorous computer simulations to estimate the true population of long-range (greater than 1000 AU) brown dwarf companions in the solar neighborhood (less than 25 pc from Earth). Expanding on Gizis et al. (2001), we have found the margin of error in previous estimates to be significantly underestimated after we included orbit eccentricity, longitude of pericenter, angle of inclination, field star density, and primary and secondary luminosities as parameters influencing the companion systems in observational studies. We apply our simulation results to current L- and T-dwarf catalogs to provide updated estimates on the frequency of wide-separation brown dwarf companions to main sequence stars.

  20. The Discovery of Solar-like Activity Cycles Beyond the End of the Main Sequence?

    NASA Astrophysics Data System (ADS)

    Route, Matthew

    2016-10-01

    The long-term magnetic behavior of objects near the cooler end of the stellar main sequence is poorly understood. Most theoretical work on the generation of magnetism in these ultracool dwarfs (spectral type ≥M7 stars and brown dwarfs) suggests that their magnetic fields should not change in strength and direction. Using polarized radio emission measurements of their magnetic field orientations, I demonstrate that these cool, low-mass, fully convective objects appear to undergo magnetic polarity reversals analogous to those that occur on the Sun. This powerful new technique potentially indicates that the patterns of magnetic activity displayed by the Sun continue to exist, despite the fully convective interiors of these objects, in contravention of several leading theories of the generation of magnetic fields by internal dynamos.

  1. Multiplicity study of young pre-main sequence stars in the Lupus star-forming Region

    NASA Astrophysics Data System (ADS)

    Vogt, Nikolaus; Mugrauer, Markus; Schmidt, Tobias O. B.; Neuhaeuser, Ralph; Ginski, Christian

    2013-07-01

    We have conducted a high contrast imaging search for (sub)stellar companions among 63 young pre-main sequence stars in the Lupus star forming region, using the adaptive optics imager NACO at UT4 of the ESO Paranal observatory. We detected faint co-moving companions around our targets at angular separations between about 0.1 up to several arc seconds (binaries and triple systems). Some of these companions are in the sub stellar mass regime, according to their apparent near infrared photometry at the distance of the Lupus star forming region (about 140pc). We give a progress report to our long-term project, still in execution with the follow-up spectroscopy of detected substellar companion-candidates, and present some first results.

  2. A Population Study of Wide-Separation Brown Dwarf Companions to Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Smith, Jeffrey J.

    2005-01-01

    Increased interest in infrared astronomy has opened the frontier to study cooler objects that shed significant light on the formation of planetary systems. Brown dwarf research provides a wealth of information useful for sorting through a myriad of proposed formation theories. Our study combines observational data from 2MASS with rigorous computer simulations to estimate the true population of long-range (greater than 1000 AU) brown dwarf companions in the solar neighborhood (less than 25 pc from Earth). Expanding on Gizis et al. (2001), we have found the margin of error in previous estimates to be significantly underestimated after we included orbit eccentricity, longitude of pericenter, angle of inclination, field star density, and primary and secondary luminosities as parameters influencing the companion systems in observational studies. We apply our simulation results to current L- and T-dwarf catalogs to provide updated estimates on the frequency of wide-separation brown dwarf companions to main sequence stars.

  3. Domains of pulsational instability of low-frequency modes in rotating upper main sequence stars

    NASA Astrophysics Data System (ADS)

    Szewczuk, Wojciech; Daszyńska-Daszkiewicz, Jadwiga

    2017-07-01

    We determine instability domains on the Hertzsprung-Russell diagram for rotating main sequence stars with masses of 2-20 M⊙. The effects of the Coriolis force are treated wihin the traditional approximation. High-order g modes with harmonic degrees ℓ up to 4 and mixed gravity-Rossby modes with |m| up to 4 are considered. We include the effects of rotation in wider instability strips for a given ℓ compared to the non-rotating case and in an extension of the pulsational instability to hotter and more massive models. We present results for a fixed value of the initial rotation velocity as well as for a fixed ratio of the angular rotation frequency to its critical value. Moreover, we check how the initial hydrogen abundance, metallicity, overshooting from the convective core and opacity affect the pulsational instability domains. The effect of rotation on the period spacing is also discussed.

  4. Fundamental Parameters of Main-Sequence Stars in an Instant with Machine Learning

    NASA Astrophysics Data System (ADS)

    Bellinger, Earl P.; Angelou, George C.; Hekker, Saskia; Basu, Sarbani; Ball, Warrick H.; Guggenberger, Elisabeth

    2016-10-01

    Owing to the remarkable photometric precision of space observatories like Kepler, stellar and planetary systems beyond our own are now being characterized en masse for the first time. These characterizations are pivotal for endeavors such as searching for Earth-like planets and solar twins, understanding the mechanisms that govern stellar evolution, and tracing the dynamics of our Galaxy. The volume of data that is becoming available, however, brings with it the need to process this information accurately and rapidly. While existing methods can constrain fundamental stellar parameters such as ages, masses, and radii from these observations, they require substantial computational effort to do so. We develop a method based on machine learning for rapidly estimating fundamental parameters of main-sequence solar-like stars from classical and asteroseismic observations. We first demonstrate this method on a hare-and-hound exercise and then apply it to the Sun, 16 Cyg A and B, and 34 planet-hosting candidates that have been observed by the Kepler spacecraft. We find that our estimates and their associated uncertainties are comparable to the results of other methods, but with the additional benefit of being able to explore many more stellar parameters while using much less computation time. We furthermore use this method to present evidence for an empirical diffusion-mass relation. Our method is open source and freely available for the community to use.6

  5. A comprehensive set of simulations of high-velocity collisions between main-sequence stars

    NASA Astrophysics Data System (ADS)

    Freitag, Marc; Benz, Willy

    2005-04-01

    We report on a very large set of simulations of collisions between two main-sequence (MS) stars. These computations were carried out with the smoothed particle hydrodynamics method. Realistic stellar structure models for evolved MS stars were used. In order to sample an extended domain of initial parameters space (masses of the stars, relative velocity and impact parameter), more than 14000 simulations were carried out. We considered stellar masses ranging between 0.1 and 75 Msolar and relative velocities up to a few thousand km s-1. To limit the computational burden, a resolution of 1000-32000 particles per star was used. The primary goal of this study was to build a complete data base from which the result of any collision can be interpolated. This allows us to incorporate the effects of stellar collisions with an unprecedented level of realism into dynamical simulations of galactic nuclei and other dense stellar clusters. We make the data describing the initial condition and outcome (mass and energy loss, angle of deflection) of all our simulations available on the Internet. We find that the outcome of collisions depends sensitively on the stellar structure and that, in most cases, using polytropic models is inappropriate. Published fitting formulae for the collision outcomes, established from a limited set of collisions, prove of limited use because they do not allow robust extrapolation to other stellar structures or relative velocities.

  6. The B[e] Phenomenon in Pre-Main-Sequence Herbig Ae/Be Stars

    NASA Astrophysics Data System (ADS)

    Oudmaijer, R. D.

    2017-02-01

    In this review I describe the intermediate mass pre-main-sequence Herbig Ae/Be stars and their role in studies of star formation. They play a particularly important part in understanding the differences between the accretion of matter onto low and high mass stars. Once these differences are understood, further progress can be made in high mass star formation. Given that the B[e] phenomenon is a spectroscopic one, I will present recent developments in the spectroscopic studies of the Herbig Ae/Be stars, and then move to the [e] phenomenon in these object. Based on a large sample, it is found that forbidden lines are present for half of the Herbig Ae/Be stars, implying that the "[e]" phenomenon is widespread in Herbig Ae/Be stars. I will describe how the presence and properties of these lines can be used to our advantage in learning about their circumstellar environments, and their disks in particular. I conclude with a forward look.

  7. STELLAR DIAMETERS AND TEMPERATURES. I. MAIN-SEQUENCE A, F, AND G STARS

    SciTech Connect

    Boyajian, Tabetha S.; McAlister, Harold A.; Gies, Douglas R.; O'Brien, David; Parks, J. Robert; Richardson, Noel D.; Touhami, Yamina; White, Russel; Van Belle, Gerard; Ten Brummelaar, Theo A.; Farrington, Chris; Goldfinger, P. J.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Von Braun, Kaspar; Ridgway, Stephen

    2012-02-10

    We have executed a survey of nearby, main-sequence A-, F-, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars with an average precision of {approx}1.5%. We present new measures of the bolometric flux, which in turn leads to an empirical determination of the effective temperature for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale model isochrones to constrain the masses and ages of the stars. These results are compared to indirect estimates of these quantities obtained by collecting photometry of the stars and applying them to model atmospheres and evolutionary isochrones. We find that for most cases, the models overestimate the effective temperature by {approx}1.5%-4% when compared to our directly measured values. The overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than {approx}1.3 M{sub Sun }. Additionally, we compare our measurements to a large sample of eclipsing binary stars, and excellent agreement is seen within both data sets. Finally, we present temperature relations with respect to (B - V) and (V - K) colors as well as spectral type, showing that calibration of effective temperatures with errors {approx}1% is now possible from interferometric angular diameters of stars.

  8. Molecular and atomic gas along and across the main sequence of star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Saintonge, Amelie; Catinella, Barbara; Cortese, Luca; Genzel, Reinhard; Giovanelli, Riccardo; Haynes, Martha P.; Janowiecki, Steven; Kramer, Carsten; Lutz, Katharina A.; Schiminovich, David; Tacconi, Linda J.; Wuyts, Stijn; Accurso, Gioacchino

    2016-10-01

    We use spectra from the ALFALFA, GASS and COLD GASS surveys to quantify variations in the mean atomic and molecular gas mass fractions throughout the SFR-M* plane and along the main sequence (MS) of star-forming galaxies. Although galaxies well below the MS tend to be undetected in the Arecibo and IRAM observations, reliable mean atomic and molecular gas fractions can be obtained through a spectral stacking technique. We find that the position of galaxies in the SFR-M* plane can be explained mostly by their global cold gas reservoirs as observed in the H I line, with in addition systematic variations in the molecular-to-atomic ratio and star formation efficiency. When looking at galaxies within ±0.4 dex of the MS, we find that as stellar mass increases, both atomic and molecular gas mass fractions decrease, stellar bulges become more prominent, and the mean stellar ages increase. Both star formation efficiency and molecular-to-atomic ratios vary little for massive MS galaxies, indicating that the flattening of the MS is due to the global decrease of the cold gas reservoirs of galaxies rather than to bottlenecks in the process of converting cold atomic gas to stars.

  9. Accretion Rates on Pre-main-sequence Stars in the Young Open Cluster NGC 6530

    NASA Astrophysics Data System (ADS)

    Gallardo, José; del Valle, Luciano; Ruiz, María Teresa

    2012-01-01

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first ~1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the Hα emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad Hα emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciencia e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva

  10. Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123

    NASA Astrophysics Data System (ADS)

    Takada-Hidai, Masahide; Kurtz, Donald W.; Shibahashi, Hiromoto; Murphy, Simon J.; Takata, Masao; Saio, Hideyuki; Sekii, Takashi

    2017-10-01

    A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 - the first main-sequence star with a directly measured core-to-surface rotation profile - based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (Teff = 7600 K, log g = 4.2, ξ = 3.1 km s-1 and [Fe/H] = -0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low [Fe/H] = -0.71 ± 0.11 dex and a high radial velocity of -135.4 ± 0.2 km s-1. These are remarkable among late-A stars. Our best asteroseismic models with this low [Fe/H] have slightly high helium abundance and low masses of 1.4 M⊙. All of these results strongly suggest that KIC 11145123 is a Population II blue straggler; (2) the projected rotation velocity confirms the asteroseismically predicted slow rotation of the star; (3) comparisons of abundance patterns between KIC 11145123 and Am, Ap, and blue stragglers show that KIC 11145123 is neither an Am star nor an Ap star, but has abundances consistent with a blue straggler. We conclude that the remarkably long 100-d rotation period of this star is a consequence of it being a blue straggler, but both pathways for the formation of blue stragglers - merger and mass loss in a binary system - pose difficulties for our understanding of the exceedingly slow rotation. In particular, we show that there is no evidence of any secondary companion star, and we put stringent limits on the possible mass of any such purported companion through the phase modulation technique.

  11. Sensitivity studies for the main r process: nuclear masses

    SciTech Connect

    Aprahamian, A.; Mumpower, M.; Bentley, I.; Surman, R.

    2014-04-15

    The site of the rapid neutron capture process (r process) is one of the open challenges in all of physics today. The r process is thought to be responsible for the creation of more than half of all elements beyond iron. The scientific challenges to understanding the origin of the heavy elements beyond iron lie in both the uncertainties associated with astrophysical conditions that are needed to allow an r process to occur and a vast lack of knowledge about the properties of nuclei far from stability. One way is to disentangle the nuclear and astrophysical components of the question. On the nuclear physics side, there is great global competition to access and measure the most exotic nuclei that existing facilities can reach, while simultaneously building new, more powerful accelerators to make even more exotic nuclei. On the astrophysics side, various astrophysical scenarios for the production of the heaviest elements have been proposed but open questions remain. This paper reports on a sensitivity study of the r process to determine the most crucial nuclear masses to measure using an r-process simulation code, several mass models (FRDM, Duflo-Zuker, and HFB-21), and three potential astrophysical scenarios.

  12. Deep HST Imaging in 47 Tuc and NGC 6397: Main Sequence Turnoff Ages

    NASA Astrophysics Data System (ADS)

    Dotter, Aaron L.; Anderson, J.; Fahlman, G.; Hansen, B.; Hurley, J.; Kalirai, J.; King, I.; Reitzel, D.; Rich, R. M.; Richer, H.; Shara, M.; Stetson, P.; Woodley, K.; Zurek, D.

    2011-01-01

    The ages of Galactic globular clusters provide insight into the formation history of the Milky Way. Utilizing HST photometry of unprecendented depth and wavelength coverage, we determine the main sequence turnoff ages of the nearby globular clusters NGC 6397 and 47 Tuc. The ages are determined by comparing stellar evolution models to the main sequences with a chi-squared minimization technique. Our analysis of 47 Tuc leverages the pronounced 'kink' or 'knee' feature that appears in the lower main sequence in the near-IR. We present our age estimates as probability distributions and construct confidence intervals over input parameters such as metallicity, distance, and reddening.

  13. M4 - A Globular Cluster Hubble Deep Field: The Main Sequence

    NASA Astrophysics Data System (ADS)

    Richer, H. B.; Brewer, J.; Fahlman, G. G.; Gibson, B.; Hansen, B.; Ibata, R.; Limongi, M.; Rich, M. R.; Stetson, P. B.; Shara, M.

    2001-12-01

    A 123 orbit exposure with HST in 2 colors (GO-8679) in a single field of M4 has yielded photometry to V ~ 30, I ~ 28.5. In the proper motion selected cluster color-magnitude diagram constructed from these and earlier epoch data, there is an abrupt termination of the cluster main sequence at about V = 28 (MV = 15.5), fully 2 magnitudes brighter than our limiting magnitude. This is similar to what is seen among field Population II subdwarfs of the same metallicity ([m/H] = -1.3) and suggests that the lowest mass stars capable of burning hydrogen in their cores at this metallicity have been detected. Comparison with the current generation of models suggests that the masses here are near 0.09 Msun. Of particular interest are 6 objects which have proper motions appropriate for cluster membership, are moderately bright, but are undetected in V. The brightest of these will have (V - I) > 4, redder than any known metal poor subdwarf. The nature of these objects is currently unknown but one possibility is that they are recycled brown dwarfs.

  14. Gas Content and Star Formation Efficiency of Massive Main Sequence Galaxies at z~3-4

    NASA Astrophysics Data System (ADS)

    Schinnerer, Eva; Groves, Brent; Karim, Alexander; Sargent, Mark T.; Oesch, Pascal; Le Fevre, Olivier; Tasca, Lidia; Magnelli, Benjamin; Cassata, Paolo; Smolcic, Vernesa

    2016-01-01

    Recent observations have shown that the neutral gas content and star formation efficiency of massive (with log(stellar masses) > 10), normal star forming galaxies, i.e. they reside on the main sequence of star forming galaxies, are steadily decreasing from the peak of star formation activity (at redshifts of z~2) till today. This decrease is coincident with the observed decline in the cosmic star formation rate density over this time range. However, only few observations have probed the evolution of the gas content and star formation efficiency beyond this peak epoch when the cosmic star formation rate density has been increasing, i.e. at redshifts of z~3-4.We will present new ALMA rest-frame 250um continuum detections of 45 massive, normal star forming galaxies in this critical redshift interval selected in the COSMOS deep field. Using the sub-mm continnum as proxy for the cold neutral gas content, we find gas mass fractions and depletions similar to those reported during the peak epoch of star formation. We will discuss our findings in the context of results from lower redshift observations and model expectations.

  15. On The Sfr-M* Main Sequence Archetypal Star-Formation History And Analytical Models

    NASA Astrophysics Data System (ADS)

    Ciesla, Laure; Elbaz, David; Fensch, Jeremy

    2017-06-01

    From the evolution of the main sequence we can build the star formation history (SFH) of MS galaxies, assuming that they follow this relation all their life. We show that this SFH is not only a function of cosmic time but also involve the seed mass of the galaxy. We discuss the implications of this MS SFH on the stellar mass growth, and the entry in the passive region of the UVJ diagram, while the galaxy is still forming stars. We test the ability of different analytical SFH forms found in the literature to probe the SFR of all type of galaxies. Using a sample of GOODS-South galaxies, we show that these SFHs artificially enhance or create a gradient of age, parallel to the MS. A simple model of a MS galaxy, such as those expected from compaction or variation in gas accretion, undergoing some fluctuations provide does not predict such a gradient, that we show is due to SFH assumptions. We propose an improved analytical form, taking into account a flexibility in the recent SFH that we calibrate as a diagnostic to identify rapidly quenched galaxies from large photometric survey.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    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 that 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.

  17. How supercritical are stellar dynamos, or why do old main-sequence dwarfs not obey gyrochronology?

    NASA Astrophysics Data System (ADS)

    Kitchatinov, Leonid; Nepomnyashchikh, Alexander

    2017-09-01

    Asteroseismological determinations of stellar ages have shown that old main-sequence dwarfs do not obey gyrochronology. Their rotation is slow compared to young stars but faster than what gyrochronology predicts. This can be explained by the presence of a maximum rotation period beyond which the large-scale dynamo switches off and stops providing global magnetic fields necessary for stellar spin-down. Assuming this explanation, the excess of stellar dynamo parameters over their marginal values can be estimated for the given spectral type and rotation rate. The estimation gives the dynamo number for the Sun about 10 per cent above its critical value. The corresponding dynamo model provides - though with some further tuning - reasonable results for the Sun. Following the same approach, the differential rotation and marginal dynamo modes are computed for stars between 0.7 and 1.2 solar masses. With an increasing stellar mass, the differential rotation and the ratio of toroidal-to-poloidal field are predicted to increase while the field topology changes from dipolar to mixed quadrupolar-dipolar parity.

  18. Absolute properties of BG Ind - a bright F3 system just leaving the main sequence

    NASA Astrophysics Data System (ADS)

    Rozyczka, M.; Kaluzny, J.; Pych, W.; Konacki, M.; Małek, K.; Mankiewicz, L.; Sokołowski, M.; Żarnecki, A. F.

    2011-07-01

    We present photometric and spectroscopic analysis of the bright detached eclipsing binary BG Ind. The masses of the components are found to be 1.428 ± 0.008 and 1.293 ± 0.008 M⊙ and the radii to be 2.290 ± 0.017 and 1.680 ± 0.038 R⊙ for primary and secondary stars, respectively. Spectra and isochrone fittings coupled with colour indices calibration yield [Fe/H]=-0.2 ± 0.1. At an age of 2.65 ± 0.20 Gyr, BG Ind is well advanced in the main-sequence evolutionary phase - in fact, its primary is at TAMS or just beyond it. Together with three similar systems (BK Peg, BW Aqr and GX Gem), it offers an interesting opportunity to test the theoretical description of overshooting in the critical mass range 1.2-1.5 M⊙. Based in part on data obtained at the South African Astronomical Observatory.

  19. AN OBJECTIVE DEFINITION FOR THE MAIN SEQUENCE OF STAR-FORMING GALAXIES

    SciTech Connect

    Renzini, Alvio; Peng, Ying-jie E-mail: y.peng@mrao.cam.ac.uk

    2015-03-10

    The main sequence (MS) of star-forming (SF) galaxies plays a fundamental role in driving galaxy evolution and our efforts to understand it. However, different studies find significant differences in the normalization, slope, and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate SF galaxies, which may include or exclude galaxies with a specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of SF galaxies. Constructing the 3D SFR–mass–number plot, the MS is then defined as the ridge line of the SF peak, as illustrated with various figures. The advantages of such a definition are manifold. If generally adopted, it will facilitate the inter-comparison of results from different groups using the same SFR and stellar mass diagnostics, or it will highlight the relative systematics of different diagnostics. All of this could help to understand MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies.

  20. THE HIGHLY ECCENTRIC PRE-MAIN-SEQUENCE SPECTROSCOPIC BINARY RX J0529.3+1210

    SciTech Connect

    Mace, G. N.; Prato, L.; Wasserman, L. H.; Franz, O. G.; Schaefer, G. H.; Simon, M.

    2009-03-15

    The young system RX J0529.3+1210 was initially identified as a single-lined spectroscopic binary. Using high-resolution infrared spectra, acquired with NIRSPEC on Keck II, we measured radial velocities for the secondary. The method of using the infrared regime to convert single-lined spectra into double-lined spectra, and derive the mass ratio for the binary system, has been successfully used for a number of young, low-mass binaries. For RX J0529.3+1210, a long-period (462 days) and highly eccentric (0.88) binary system, we determine the mass ratio to be 0.78 {+-} 0.05 using the infrared double-lined velocity data alone, and 0.73 {+-} 0.23 combining visible light and infrared data in a full orbital solution. The large uncertainty in the latter is the result of the sparse sampling in the infrared and the high eccentricity: the stars do not have a large velocity separation during most of their {approx}1.3 yr orbit. A mass ratio close to unity, consistent with the high end of the 1{sigma} uncertainty for this mass ratio value, is inconsistent with the lack of a visible light detection of the secondary component. We outline several scenarios for a color difference in the two stars, such as one heavily spotted component, higher-order multiplicity, or a unique evolutionary stage, favoring detection of only the primary star in visible light, even in a mass ratio {approx}1 system. However, the evidence points to a lower ratio. Although RX J0529.3+1210 exhibits no excess at near-infrared wavelengths, a small 24 {mu}m excess is detected, consistent with circumbinary dust. The properties of this binary and its membership in {lambda} Ori versus a new nearby stellar moving group at {approx}90 pc are discussed. We speculate on the origin of this unusual system and on the impact of such high eccentricity, the largest observed in a pre-main-sequence double-lined system to date, on the potential for planet formation.

  1. PRE-MAIN-SEQUENCE STELLAR POPULATIONS ACROSS SHAPLEY CONSTELLATION III. I. PHOTOMETRIC ANALYSIS AND IDENTIFICATION ,

    SciTech Connect

    Gouliermis, Dimitrios A.; Gennaro, Mario; Henning, Thomas; Da Rio, Nicola; Brandner, Wolfgang; Dolphin, Andrew E.; Robberto, Massimo; Panagia, Nino; Gruendl, Robert A.; Chu, You-Hua; Rosa, Michael; Romaniello, Martino; De Marchi, Guido; Zinnecker, Hans

    2011-09-10

    We present our investigation of pre-main-sequence (PMS) stellar populations in the Large Magellanic Cloud (LMC) from imaging with Hubble Space Telescope Wide-Field Planetary Camera 2. Our targets of interest are four star-forming regions located at the periphery of the super-giant shell LMC 4 (Shapley Constellation III). The PMS stellar content of the regions is revealed through the differential Hess diagrams and the observed color-magnitude diagrams (CMDs). Further statistical analysis of stellar distributions along cross sections of the faint part of the CMDs allowed the quantitative assessment of the PMS stars census, and the isolation of faint PMS stars as the true low-mass stellar members of the regions. These distributions are found to be well represented by a double-Gaussian function, the first component of which represents the main-sequence field stars and the second the native PMS stars of each region. Based on this result, a cluster membership probability was assigned to each PMS star according to its CMD position. The higher extinction in the region LH 88 did not allow the unambiguous identification of its native stellar population. The CMD distributions of the PMS stars with the highest membership probability in the regions LH 60, LH 63, and LH 72 exhibit an extraordinary similarity among the regions, suggesting that these stars share common characteristics, as well as common recent star formation history. Considering that the regions are located at different areas of the edge of LMC 4, this finding suggests that star formation along the super-giant shell may have occurred almost simultaneously.

  2. A candidate infrared companion in the pre-main sequence multiple system V773 Tau

    NASA Astrophysics Data System (ADS)

    Duchene, G.; Ghez, A. M.; McCabe, C.

    2001-12-01

    We present new near-infrared (1.6 and 2.2 micron) adaptive optics images with the 10m-Keck II telescope of the low-mass pre-main sequence multiple system V773 Tau. In addition to the already known unresolved double-lined spectroscopic binary and its 83 milliarcsec companion, our images reveal a fourth star located only 0.21'' (projected distance: 30 AU) away from the brightest component. This object appears to be much redder than the other stars in the system. We also obtained a medium-resolution (R=3500) long-slit spectrum of this object which covers the 2.0-2.4 micron wavelength range. The spectrum of this dim fourth component in the system shows no photospheric feature but has a small Brγ emission line (equivalent width of about 0.5Å). If this object is not an extincted background giant, which the hydrogen emission line seems to exclude, it is very reminiscent of a small class of objects known as "infrared companions" to T Tauri stars. The tight visual binary has been followed over the last years through speckle interferometry technique, and these data indicate a strange behaviour with a large "jump" in position angle. This may reveal some strong photometric variability in the candidate IRC, which would reinforce its status. We also emphasize that such a quadruple system, with four stars located within 30 AU or so, is extremely rare among main sequence solar-type objects while many T Tauri binaries in Taurus turned out to have additionalcompanions when observed with higher resolution and/or sensitivity. This may indicate that this region is all but typical of star formation in the Galaxy.

  3. ROTATION PERIODS OF 34,030 KEPLER MAIN-SEQUENCE STARS: THE FULL AUTOCORRELATION SAMPLE

    SciTech Connect

    McQuillan, A.; Mazeh, T.; Aigrain, S.

    2014-04-01

    We analyzed three years of data from the Kepler space mission to derive rotation periods of main-sequence stars below 6500 K. Our automated autocorrelation-based method detected rotation periods between 0.2 and 70 days for 34,030 (25.6%) of the 133,030 main-sequence Kepler targets (excluding known eclipsing binaries and Kepler Objects of Interest), making this the largest sample of stellar rotation periods to date. In this paper we consider the detailed features of the now well-populated period-temperature distribution and demonstrate that the period bimodality, first seen by McQuillan et al. in the M-dwarf sample, persists to higher masses, becoming less visible above 0.6 M {sub ☉}. We show that these results are globally consistent with the existing ground-based rotation-period data and find that the upper envelope of the period distribution is broadly consistent with a gyrochronological age of 4.5 Gyr, based on the isochrones of Barnes, Mamajek, and Hillenbrand and Meibom et al. We also performed a detailed comparison of our results to those of Reinhold et al. and Nielsen et al., who measured rotation periods of field stars observed by Kepler. We examined the amplitude of periodic variability for the stars with detection rotation periods, and found a typical range between ∼950 ppm (5th percentile) and ∼22,700 ppm (95th percentile), with a median of ∼5600 ppm. We found typically higher amplitudes for shorter periods and lower effective temperatures, with an excess of low-amplitude stars above ∼5400 K.

  4. Dissecting the extended main-sequence turn-off of the young star cluster NGC 1850

    NASA Astrophysics Data System (ADS)

    Correnti, Matteo; Goudfrooij, Paul; Bellini, Andrea; Kalirai, Jason S.; Puzia, Thomas H.

    2017-05-01

    We use the Wide Field Camera 3 onboard the Hubble Space Telescope to obtain deep, high-resolution photometry of the young (˜100 Myr) star cluster NGC 1850 in the Large Magellanic Cloud. We analyse the cluster colour-magnitude diagram (CMD) and find that it hosts an extended main-sequence turn-off (MSTO) and a double main sequence (MS). We demonstrate that these features cannot be due to photometric errors, field star contamination or differential reddening. From a comparison with theoretical models and Monte Carlo simulations, we show that a coeval stellar population featuring a distribution of stellar rotation rates can reproduce the MS split quite well. However, it cannot reproduce the observed MSTO region, which is significantly wider than the simulated ones. Exploiting narrow-band Hα imaging, we find that the MSTO hosts a population of Hα-emitting stars that are interpreted as rapidly rotating Be-type stars. We explore the possibility that the discrepancy between the observed MSTO morphology and that of the simulated simple stellar population (SSP) is caused by the fraction of these objects that are highly reddened, but we rule out this hypothesis. We demonstrate that the global CMD morphology is well reproduced by a combination of SSPs that covers an age range of ˜35 Myr as well as a wide variety of rotation rates. We derive the cluster mass and escape velocity, and use dynamical evolution models to predict their evolution starting at an age of 10 Myr. We discuss these results and their implications in the context of the extended MSTO phenomenon.

  5. Pulsation of Pre-Main Sequence Stars in Young Open Clusters

    NASA Astrophysics Data System (ADS)

    Zwintz, Konstanze; Weiss, Werner W.

    2001-08-01

    The aim of this proposal is to determine observationally the parameter space of the pre-main sequence instability strip. For that purpose we intend to obtain photometric timeseries with high time resolution and low noise level of the stars in young open clusters (IC 4996, NGC 6910 and NGC 6383) and to identify pre-main sequence pulsators. Several cluster members have the spectral types of interest (A-F) and lie between the birthline and the zero-age main sequence. Up to now the number of pre-main sequence pulsators is absolutely inadequate to determine reliably the hot and cool border of the according instability region. Its definition is indispensable for a better understanding of the internal structure and evolution of such stars.

  6. Outbursting Stars, Pre-Main-Sequence Stellar Evolution, Convection, and Lithium Burning

    NASA Astrophysics Data System (ADS)

    Bodenheimer, P.

    2004-12-01

    This historical note summarizes some of the key events related to pre-main-sequence evolution, and in particular the importance of convective energy transport, that led to my Ph. D. dissertation in 1965.

  7. Laser mass spectrometry for DNA sequencing, disease diagnosis, and fingerprinting

    NASA Astrophysics Data System (ADS)

    Chen, C. H. Winston; Taranenko, N. I.; Zhu, Y. F.; Chung, C. N.; Allman, S. L.

    1997-05-01

    Since laser mass spectrometry has the potential for achieving very fast DNA analysis, we recently applied it to DNA sequencing, DNA typing for fingerprinting, and DNA screening for disease diagnosis. Two different approaches for sequencing DNA have been successfully demonstrated. One is to sequence DNA with DNA ladders produced from Sanger's enzymatic method. The other is to do direct sequencing without DNA ladders. The need for quick DNA typing for identification purposes is critical for forensic application. Our preliminary results indicate laser mass spectrometry can possible be used for rapid DNA fingerprinting applications at a much lower cost than gel electrophoresis. Population screening for certain genetic disease can be a very efficient step to reducing medical costs through prevention. Since laser mass spectrometry can provide very fast DNA analysis, we applied laser mass spectrometry to disease diagnosis. Clinical samples with both base deletion and point mutation have been tested with complete success.

  8. Laser mass spectrometry for DNA sequencing, disease diagnosis, and fingerprinting

    SciTech Connect

    Winston Chen, C.H.; Taranenko, N.I.; Zhu, Y.F.; Chung, C.N.; Allman, S.L.

    1997-03-01

    Since laser mass spectrometry has the potential for achieving very fast DNA analysis, the authors recently applied it to DNA sequencing, DNA typing for fingerprinting, and DNA screening for disease diagnosis. Two different approaches for sequencing DNA have been successfully demonstrated. One is to sequence DNA with DNA ladders produced from Snager`s enzymatic method. The other is to do direct sequencing without DNA ladders. The need for quick DNA typing for identification purposes is critical for forensic application. The preliminary results indicate laser mass spectrometry can possibly be used for rapid DNA fingerprinting applications at a much lower cost than gel electrophoresis. Population screening for certain genetic disease can be a very efficient step to reducing medical costs through prevention. Since laser mass spectrometry can provide very fast DNA analysis, the authors applied laser mass spectrometry to disease diagnosis. Clinical samples with both base deletion and point mutation have been tested with complete success.

  9. AN M DWARF COMPANION TO AN F-TYPE STAR IN A YOUNG MAIN-SEQUENCE BINARY

    SciTech Connect

    Eigmüller, Ph.; Csizmadia, Sz.; Erikson, A.; Fridlund, M.; Pasternacki, Th.; Rauer, H.; Eislöffel, J.; Lehmann, H.; Hartmann, M.; Hatzes, A.; Tkachenko, A.; Voss, H.

    2016-03-15

    Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung–Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectroscopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 ± 0.073) M{sub ⊙} and a radius of (1.474 ± 0.040) R{sub ⊙}. The companion is an M dwarf with a mass of (0.188 ± 0.014) M{sub ⊙} and a radius of (0.234 ± 0.009) R{sub ⊙}. The orbital period is (1.35121 ± 0.00001) days. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin–orbit synchronization. This indicates a young main-sequence binary with an age below ∼250 Myr. The mass–radius relation of both components are in agreement with this finding.

  10. Coronagraphic imaging of pre-main-sequence stars: Remnant evvelopes of star formation seen in reflection

    NASA Technical Reports Server (NTRS)

    Nakajima, Tadashi; Golimowski, David A.

    1995-01-01

    We have obtained R- and I-band coronagraphic images of the vicinities of 11 pre-main sequence (PMS) stars to search for faint, small-scale reflection nebulae. The inner radius of the search and the field of view are 1.9 arcsec and 1x1 arcmin, respectively. Reflection nebulae were imaged around RY Tau, T Tau,DG Tau, SU Aur, AB Aur, FU Ori, and Z CMa. No nebulae were detected around HBC 347, GG Tau, V773 Tau, and V830 Tau. Categorically speaking, most of the classical T Tauri program stars and all the FU Orionis-type program stars are associated with the reflection nebulae, while none of the weak-line T Tauri program stars are associated with nebulae. The detected nebulae range in size from 250 to 37 000 AU. From the brightness ratios of the stars and nebulae, we obtain a lower limit to the visual extinction of PMS star light through the nebulae of (A(sub V))(sub neb) = 0.1. The lower limits of masses and volume densities of the nebulae associated with the classical T Tauri stars are 10(exp-6) Solar mass and N(sub H) = 10(exp 5)/cu cm, respectively. Lower limits for the nebulae around FU Orionis stars are 10(exp -5) Solar mass and n(sub H) = 10 (exp 5)/cu cm, respectively. Some reflection nebulae may trace the illuminated surfaces of the optically thick dust nebulae, so these mass estimates are not stringent. All the PMS stars with associated nebulae are strong far-infrared emitters. Both the far-infrared emission and the reflection nebulae appear to originate from the remnant envelopes of star formation. The 100 micrometers emitting regions of SU Aur and FU Ori are likely to be cospatial with the reflection nebulae. A spatial discontinuity between FU Ori and its reflection nebula may explain the dip in the far-infrared spectral energy distribution at 60 micrometers. The warped, disk-like nebulae around T Tau and Z CMa are aligned with and embrace the inner star/circumstellar disk systems. The arc-shaped nebula around DG Tau may be in contact with the coaligned inner

  11. The population of white dwarf-main sequence binaries in the SDSS DR 12

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

    We present a Monte Carlo population synthesis study of white dwarf-main sequence (WD+MS) binaries in the Galactic disc aimed at reproducing the ensemble properties of the entire population observed by the Sloan Digital Sky Survey (SDSS) Data Release 12. Our simulations take into account all known observational biases and use the most up-to-date stellar evolutionary models. This allows us to perform a sound comparison between the simulations and the observational data. We find that the properties of the simulated and observed parameter distributions agree best when assuming low values of the common envelope efficiency (0.2-0.3), a result that is in agreement with previous findings obtained by observational and population synthesis studies of close SDSS WD+MS binaries. We also show that all synthetic populations that result from adopting an initial mass ratio distribution with a positive slope are excluded by observations. Finally, we confirm that the properties of the simulated WD+MS binary populations are nearly independent of the age adopted for the thin disc, on the contribution of WD+MS binaries from the thick disc (0-17 per cent of the total population) and on the assumed fraction of the internal energy that is used to eject the envelope during the common envelope phase (0.1-0.5).

  12. Post-main-sequence debris from rotation-induced YORP break-up of small bodies

    NASA Astrophysics Data System (ADS)

    Veras, Dimitri; Jacobson, Seth A.; Gänsicke, Boris T.

    2014-12-01

    Although discs of dust and gas have been observed orbiting white dwarfs, the origin of this circumstellar matter is uncertain. We hypothesize that the in situ break-up of small bodies such as asteroids spun to fission during the giant branch phases of stellar evolution provides an important contribution to this debris. The YORP (Yarkovsky-O'Keefe-Radviesvki-Paddock) effect, which arises from radiation pressure, accelerates the spin rate of asymmetric asteroids, which can eventually shear themselves apart. This pressure is maintained and enhanced around dying stars because the outward push of an asteroid due to stellar mass loss is insignificant compared to the resulting stellar luminosity increase. Consequently, giant star radiation will destroy nearly all bodies with radii in the range 100 m-10 km that survive their parent star's main-sequence lifetime within a distance of about 7 au; smaller bodies are spun apart to their strongest, competent components. This estimate is conservative and would increase for highly asymmetric shapes or incorporation of the inward drag due to giant star stellar wind. The resulting debris field, which could extend to thousands of au, may be perturbed by remnant planetary systems to reproduce the observed dusty and gaseous discs which accompany polluted white dwarfs.

  13. WHITE-DWARF-MAIN-SEQUENCE BINARIES IDENTIFIED FROM THE LAMOST PILOT SURVEY

    SciTech Connect

    Ren Juanjuan; Luo Ali; Li Yinbi; Wei Peng; Zhao Jingkun; Zhao Yongheng; Song Yihan; Zhao Gang E-mail: lal@nao.cas.cn

    2013-10-01

    We present a set of white-dwarf-main-sequence (WDMS) binaries identified spectroscopically from the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) pilot survey. We develop a color selection criteria based on what is so far the largest and most complete Sloan Digital Sky Survey (SDSS) DR7 WDMS binary catalog and identify 28 WDMS binaries within the LAMOST pilot survey. The primaries in our binary sample are mostly DA white dwarfs except for one DB white dwarf. We derive the stellar atmospheric parameters, masses, and radii for the two components of 10 of our binaries. We also provide cooling ages for the white dwarf primaries as well as the spectral types for the companion stars of these 10 WDMS binaries. These binaries tend to contain hot white dwarfs and early-type companions. Through cross-identification, we note that nine binaries in our sample have been published in the SDSS DR7 WDMS binary catalog. Nineteen spectroscopic WDMS binaries identified by the LAMOST pilot survey are new. Using the 3{sigma} radial velocity variation as a criterion, we find two post-common-envelope binary candidates from our WDMS binary sample.

  14. Absolute Properties of the Upper Main-Sequence Eclipsing Binary Star MU Cassiopeiae

    NASA Astrophysics Data System (ADS)

    Lacy, Claud H. Sandberg; Claret, Antonio; Sabby, Jeffrey A.

    2004-10-01

    We present 6151 differential observations in the V filter measured by a robotic telescope, as well as 29 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, EA-type, 9.65 day period double-lined eclipsing binary star MU Cas. Absolute dimensions of the components are determined with good precision (better than 2% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 4.57+/-0.09 Msolar and 3.67+/-0.04 Rsolar for the hotter, but smaller, less massive and less luminous photometric primary (star A), and 4.66+/-0.10 Msolar and 4.19+/-0.05 Rsolar for the cooler, larger, more massive and more luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 15,100+/-500 K for the primary, 14,750+/-500 K for the secondary-corresponding to spectral types of B5 and B5-and 0.356 mag for Eb-y. The stars are located at a distance of about 1.7 kpc near the plane of the Galactic disk. The orbits of the stars are eccentric, and spectral line widths give observed rotational velocities that are synchronous with the mean orbital motion for both components. The components of MU Cas are upper main-sequence stars with an age of about 65 Myr according to models.

  15. Pulsations and metallicity of the pre-main sequence eclipsing spectroscopic binary RS Cha

    NASA Astrophysics Data System (ADS)

    Alecian, E.; Catala, C.; van't Veer-Menneret, C.; Goupil, M.-J.; Balona, L.

    2005-11-01

    We present new spectroscopic observations of the pre-main sequence eclipsing spectroscopic binary RS Cha. A sample of 174 spectra were obtained with the GIRAFFE spectrograph at the SAAO at 32 000 resolution. The radial velocity curves derived from these spectra were combined with previous observations spanning a period of about 30 years to correct the ephemeris of the system, and the result indicates that the orbital period is not constant. Residuals of the binary radial velocity curve for both components with amplitudes up to a few km s-1 and periods on the order of 1 h are clearly seen in our data, which we interpret as the signatures of delta-Scuti type pulsations. We revisited the masses of both components and determined the surface metallicity Z of both components of the RS Cha system by fitting synthetic spectra to observed spectra in a set of selected spectral regions. The synthetic spectra are calculated with the SYNTH code using stellar atmosphere models computed with the Kurucz ATLAS 9 code, along with a list of lines obtained from the VALD database. A selection of the best spectra and the most relevant spectral regions allowed us to determine Z = 0.028 ± 0.005. We also derived new values of v sin i: 64 ± 6 km s-1 and 70 ± 6 km s-1 for the primary and the secondary star, respectively. Finally, we observationally confirm that the RS Cha system is a synchronized and circularized system.

  16. YSOVAR: SIX PRE-MAIN-SEQUENCE ECLIPSING BINARIES IN THE ORION NEBULA CLUSTER

    SciTech Connect

    Morales-Calderon, M.; Stauffer, J. R.; Rebull, L. M.; Stassun, K. G.; Vrba, F. J.; Prato, L.; Hillenbrand, L. A.; Carpenter, J. M.; Terebey, S.; Angione, J.; Covey, K. R.; Terndrup, D. M.; Gutermuth, R.; Song, I.; Plavchan, P.; Marchis, F.; Garcia, E. V.; Margheim, S.; Luhman, K. L.; Irwin, J. M.

    2012-07-10

    Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for {approx}2400 candidate Orion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass ({theta}{sup 1} Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 M{sub Sun }) and longest-period (ISOY J053505.71-052354.1, P {approx} 20 days) PMS EBs currently known. In two cases ({theta}{sup 1} Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.

  17. High Dispersion Line Profile Studies of TW HYA and Other Pre-Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Linsky, Jeffrey L.

    1984-07-01

    We propose to extend our study of line profiles in T Tauri stars by obtaining a 16 hour SWP-HI spectrum of TW Hya and 6-8 hour LWP-HI spectra of TW Hya, AK Sco, CoD -35 10525 and CoD -33 10685. High dispersion spectra of pre-main sequence (PMS) stars provide unique information on line widths, shifts, and asymmetries, as well as evidence for mass outflow, circumstellar absorption, and diagnostics for the temperature structure of the outer atmosphere layers of these complex yet incredibly important objects. We have previously obtained and studied line profiles in RU Lupi and the prototype star T Tau. RU Lupi has line profiles that are dominated by the wind expansion, for example the MgII and FeII multiplet UV1 profiles are unique in that they have a classical P Cygni shape, whereas T Tau has more symmetric emission profiles indicative of a chromosphere and hotter layers not dominated by expansion. TW Hya is different from these two previously studied stars in that it may be the brightest known example of a post-T Tauri star, and hence less active and older than the other PMS stars. We intend to compare its line profiles with those of RU Lupi and T Tauri in order to understand the differences in the non-thermal mass motions, wind expansion, and thermal structures of these three very different T Tau stars. The requested LWPHI spectra are to obtain MgII and FeII multiplet UV1. profiles of 4 different T Tauri objects so as to infer the expansion and thermal structure in their chromospheric layers.

  18. Lithium abundances for 185 main-sequence stars: Galactic evolution and stellar depletion of lithium

    NASA Astrophysics Data System (ADS)

    Chen, Y. Q.; Nissen, P. E.; Benoni, T.; Zhao, G.

    2001-06-01

    We present a survey of lithium abundances in 185 main-sequence field stars with 5600 <~ Teff <~ 6600 K and -1.4 <~ [Fe/H] <~ +0.2 based on new measurements of the equivalent width of the lambda 6708 Li I line in high-resolution spectra of 130 stars and a reanalysis of data for 55 stars from Lambert et al. (\\cite{Lambert91}). The survey takes advantage of improved photometric and spectroscopic determinations of effective temperature and metallicity as well as mass and age derived from Hipparcos absolute magnitudes, offering an opportunity to investigate the behaviour of Li as a function of these parameters. An interesting result from this study is the presence of a large gap in the log varepsilon (Li) - Teff plane, which distinguishes ``Li-dip'' stars like those first identified in the Hyades cluster by Boesgaard & Tripicco (\\cite{Boesgaard86}) from other stars with a much higher Li abundance. The Li-dip stars concentrate on a certain mass, which decreases with metallicity from about 1.4 Msun at solar metallicity to 1.1 Msun at [Fe/H] =~ -1.0. Excluding the Li-dip stars and a small group of lower mass stars with Teff < 5900 K and log varepsilon (Li) < 1.5, the remaining stars, when divided into four metallicity groups, may show a correlation between Li abundance and stellar mass. The dispersion around the log varepsilon (Li)-mass relation is about 0.2 dex below [Fe/H] =~ -0.4 and 0.3 dex above this metallicity, which cannot be explained by observational errors or differences in metallicity. Furthermore, there is no correlation between the residuals of the log varepsilon (Li)-mass relations and stellar age, which ranges from 1.5 Gyr to about 15 Gyr. This suggests that Li depletion occurs early in stellar life and that parameters other than stellar mass and metallicity affect the degree of depletion, e.g. initial rotation velocity and/or the rate of angular momentum loss. It cannot be excluded, however, that a cosmic scatter of the Li abundance in the Galaxy at a

  19. INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS

    SciTech Connect

    Pecaut, Mark J.; Mamajek, Eric E.

    2013-09-01

    We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVI{sub C} , 2MASS JHK{sub S} and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T {sub eff}) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T {sub eff} and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T {sub eff} scale for pre-MS stars is within ≅100 K of dwarfs at a given spectral type for stars sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

  20. Observational Constraints on the Age-Metallicity Relation from White Dwarf-Main Sequence Binaries

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Anguiano, B.; García-Berro, E.; Freeman, K. C.; Cojocaru, R.; Manser, C. J.; Pala, A. F.; Gänsicke, B. T.; Liu, X.-W.

    2017-03-01

    The age-metallicity relation (AMR) is a fundamental observational property to understand how the Galactic disc formed and evolved chemically in time. However, there is not yet a consensus on the observed properties of the AMR for the solar neighbourhood. This is due primarily to the difficulty of obtaining precise stellar ages for individual field stars. We have started an observational campaign to provide the much needed observational AMR by using white dwarf-main sequence (WDMS) binaries. White dwarfs are natural clocks and can be used to derive accurate ages. Metallicities can be obtained from the main sequence companions. Since white dwarfs and main sequence stars in these binary systems are coeval, these binaries provide an unique opportunity to observationally determine in a robust way the AMR. Here we present the AMR derived from the analysis of a sample of 23 WDMS binaries.

  1. NCBI Mass Sequence Downloader-Large dataset downloading made easy

    NASA Astrophysics Data System (ADS)

    Pina-Martins, F.; Paulo, O. S.

    Sequence databases, such as NCBI, are a very important resource in many areas of science. Downloading small amounts of sequences to local storage can easily be performed using any recent web browser, but downloading tens of thousands of sequences is not as simple. NCBI Mass Sequence Downloader is an open source program aimed at simplifying obtaining large amounts of sequence data from NCBI databases to local storage. It is written in python (can be run under both python 2 and python 3), and uses PyQt5 for the GUI. The program can be run in either graphical or command line mode. Source code is licensed under the GPLv3, and is supported on Linux, Windows and Mac OSX. Available at https://github.com/ElsevierSoftwareX/SOFTX-D-15-00072.git, https://github.com/StuntsPT/NCBI_Mass_Downloader

  2. STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS

    SciTech Connect

    Boyajian, Tabetha S.; McAlister, Harold A.; Jones, Jeremy; White, Russel; Henry, Todd; Gies, Douglas; Jao, Wei-Chun; Parks, J. Robert; Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David; Van Belle, Gerard; Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Muirhead, Philip S.; Lopez-Morales, Mercedes; Ridgway, Stephen; Rojas-Ayala, Barbara; and others

    2012-10-01

    We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for {approx}K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to {approx}2%, {approx}5%, and {approx}4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}5%. These conclusions additionally suggest that

  3. Laser desorption mass spectrometry for DNA analysis and sequencing

    SciTech Connect

    Chen, C.H.; Taranenko, N.I.; Tang, K.; Allman, S.L.

    1995-03-01

    Laser desorption mass spectrometry has been considered as a potential new method for fast DNA sequencing. Our approach is to use matrix-assisted laser desorption to produce parent ions of DNA segments and a time-of-flight mass spectrometer to identify the sizes of DNA segments. Thus, the approach is similar to gel electrophoresis sequencing using Sanger`s enzymatic method. However, gel, radioactive tagging, and dye labeling are not required. In addition, the sequencing process can possibly be finished within a few hundred microseconds instead of hours and days. In order to use mass spectrometry for fast DNA sequencing, the following three criteria need to be satisfied. They are (1) detection of large DNA segments, (2) sensitivity reaching the femtomole region, and (3) mass resolution good enough to separate DNA segments of a single nucleotide difference. It has been very difficult to detect large DNA segments by mass spectrometry before due to the fragile chemical properties of DNA and low detection sensitivity of DNA ions. We discovered several new matrices to increase the production of DNA ions. By innovative design of a mass spectrometer, we can increase the ion energy up to 45 KeV to enhance the detection sensitivity. Recently, we succeeded in detecting a DNA segment with 500 nucleotides. The sensitivity was 100 femtomole. Thus, we have fulfilled two key criteria for using mass spectrometry for fast DNA sequencing. The major effort in the near future is to improve the resolution. Different approaches are being pursued. When high resolution of mass spectrometry can be achieved and automation of sample preparation is developed, the sequencing speed to reach 500 megabases per year can be feasible.

  4. Tandem Mass Spectrum Sequencing: An Alternative to Database Search Engines in Shotgun Proteomics.

    PubMed

    Muth, Thilo; Rapp, Erdmann; Berven, Frode S; Barsnes, Harald; Vaudel, Marc

    2016-01-01

    Protein identification via database searches has become the gold standard in mass spectrometry based shotgun proteomics. However, as the quality of tandem mass spectra improves, direct mass spectrum sequencing gains interest as a database-independent alternative. In this chapter, the general principle of this so-called de novo sequencing is introduced along with pitfalls and challenges of the technique. The main tools available are presented with a focus on user friendly open source software which can be directly applied in everyday proteomic workflows.

  5. Dust around Main-Sequence Stars: Nature or Nurture by the Interstellar Medium?

    NASA Astrophysics Data System (ADS)

    Artymowicz, Pawel; Clampin, Mark

    1997-12-01

    Dust from the interstellar medium (ISM) can collide with and destroy particles in the circumstellar dust disks around main-sequence stars (Vega/β Pic stars). Two current theories tying the occurrence of the Vega/β Pic phenomenon to the erosive influence of the ISM are critically reconsidered here. Using the local standard of rest frame, we find little evidence for a correlated motion (streaming) of prominent disk systems, which one theory suggests would result from a passage about 107 yr ago of these stars, but not the control A-type stars, through the nearby Lupus-Centaurus interstellar cloud complex. Moreover, the prototype system of β Pic could not have retained dust produced in such a passage for much longer than 104 yr. We show theoretically that the ISM sandblasting of disks has minor importance for the structure and evolution of circumstellar disks, except perhaps in their outskirts (usually >400 AU from the stars), where under favorable conditions it may cause asymmetries in observed brightness and color. The ISM neither produces the disks (as in one theory) nor depletes and eliminates them with time (as in another theory), because typical ISM grains are subject to strong radiative repulsion from A- and F-type dwarfs (a few to 100 times stronger than gravity). Atypically large ISM grains are not repelled strongly, but are unimportant on account of their small number density. Dust production and destruction in β Pic-type disks results mainly from their collisional nature enhanced by the radiatively produced eccentricities of particle orbits, rather than from nurture in a hostile ISM. The residence times of the few-micron dust grains predominant in the densest part of the β Pic disk is only 104 yr, or a few dozen orbital periods. Submicronic debris is blown out as β meteoroids, carrying away from this system an equivalent of the solar system's total mass in solids (~120 Earth masses) in only ~65 Myr. This rate of collisional erosion exceeds almost 108

  6. The orbits of subdwarf-B + main-sequence binaries. III. The period-eccentricity distribution

    NASA Astrophysics Data System (ADS)

    Vos, J.; Østensen, R. H.; Vučković, M.; Van Winckel, H.

    2017-09-01

    Context. The predicted orbital-period distribution of the subdwarf-B (sdB) population is bi-modal with peaks at short (<10 days) and long (>500 days) periods. Observationally, many short-period sdB systems are known, but only few wide sdB binaries have been studied in detail. Based on a long-term monitoring programme the wide sdB sample has been increased, discovering an unexpected positive correlation between the eccentricity and orbital period. Aims: In this article we present the orbital solution and spectral analysis of four new systems, BD-7°5977, EC 11031-1348, TYC 2084-448-1 and TYC 3871-835-1, and update the orbital solution of PG 1104+243. Using the whole sample of wide sdB binaries, we aim to find possible correlations between orbital and spectral properties. The ultimate goal is to improve theoretical models of Roche-lobe overflow. Methods: High-resolution spectroscopic time series were obtained to determine the RVs of both the sdB and main sequence (MS) components. Literature photometry was used to construct the spectral-energy distributions, which were fitted with atmosphere models to determine the surface gravities and temperatures of both components in all systems. Spectral parameters of the cool companion were verified using the GSSP code. Furthermore the amount of accreted mass was estimated. Results: Orbital parameters matching the earlier observed period-eccentricity relation were found for three systems, while TYC 2084-448-1 is found to have a lower eccentricity than expected from the period-eccentricity trend indicated by the other systems. Based on new observations, the orbit of PG 1104+243 has a small but significant eccentricity of 0.04 ± 0.02, matching that of the other systems with similar periods. Furthermore, a positive correlation between accreted mass and orbital period was found, as well as a possible relation between the initial mass-ratio and the final period-eccentricity. Conclusions: The wide sdB-binary sample shows interesting

  7. Analysis of flares in the chromosphere and corona of main- and pre-main-sequence M-type stars

    NASA Astrophysics Data System (ADS)

    Crespo-Chacón, I.

    2015-11-01

    This Ph.D. Thesis revolves around flares on main- and pre-main-sequence M-type stars. We use observations in different wavelength ranges with the aim of analysing the effects of flares at different layers of stellar atmospheres. In particular, optical and X-ray observations are used so that we can study how flares affect, respectively, the chromosphere and the corona of stars. In the optical range we carry out a high temporal resolution spectroscopic monitoring of UV Ceti-type stars aimed at detecting non-white-light flares (the most typical kind of solar flares) in stars other than the Sun. With these data we confirm that non-white-light flares are a frequent phenomenon in UV Ceti-type stars, as observed in the Sun. We study and interpret the behaviour of different chromospheric lines during the flares detected on AD Leo. By using a simplified slab model of flares (Jevremović et al. 1998), we are able to determine the physical parameters of the chromospheric flaring plasma (electron density and electron temperature), the temperature of the underlying source, and the surface area covered by the flaring plasma. We also search for possible relationships between the physical parameters of the flaring plasma and other properties such as the flare duration, area, maximum flux and released energy. This work considerably extends the existing sample of stellar flares analysed with good quality spectroscopy in the optical range. In X-rays we take advantage of the great sensitivity, wide energy range, high energy resolution, and continuous time coverage of the EPIC detectors - on-board the XMMNewton satellite - in order to perform time-resolved spectral analysis of coronal flares. In particular, in the UV Ceti-type star CC Eri we study two flares that are weaker than those typically reported in the literature (allowing us to speculate about the role of flares as heating agents of stellar atmospheres); while in the pre-main-sequence M-type star TWA 11B (with no signatures of

  8. MAIN-SEQUENCE STARS MASQUERADING AS YOUNG STELLAR OBJECTS IN THE CENTRAL MOLECULAR ZONE

    SciTech Connect

    Koepferl, Christine M.; Robitaille, Thomas P.; Morales, Esteban F. E.; Johnston, Katharine G.

    2015-01-20

    In contrast to most other galaxies, star formation rates in the Milky Way can be estimated directly from young stellar objects (YSOs). In the central molecular zone the star formation rate calculated from the number of YSOs with 24 μm emission is up to an order of magnitude higher than the value estimated from methods based on diffuse emission (such as free-free emission). Whether this effect is real or whether it indicates problems with either or both star formation rate measures is not currently known. In this paper, we investigate whether estimates based on YSOs could be heavily contaminated by more evolved objects such as main-sequence stars. We present radiative transfer models of YSOs and of main-sequence stars in a constant ambient medium which show that the main-sequence objects can indeed mimic YSOs at 24 μm. However, we show that in some cases the main-sequence models can be marginally resolved at 24 μm, whereas the YSO models are always unresolved. Based on the fraction of resolved MIPS 24 μm sources in the sample of YSOs previously used to compute the star formation rate, we estimate the fraction of misclassified ''YSOs'' to be at least 63%, which suggests that the star formation rate previously determined from YSOs is likely to be at least a factor of three too high.

  9. Head rotation trajectories compared with eye saccades by main sequence relationships.

    PubMed

    Stark, L; Zangemeister, W H; Edwards, J; Grinberg, J; Jones, A; Lehman, S; Lubock, P; Narayan, V; Nystrom, M

    1980-08-01

    A helmet apparatus permitted duration, peak velocity, and peak acceleration measurements as functions of magnitude of horizontal head rotation; these "main sequence" data give evidence for multipulse-step neurological signals appropriate for time optimal control of head rotation similar to those of saccadic eye movements.

  10. Dust Formation around Main Sequence Be Stars with Large Infrared Excess

    NASA Astrophysics Data System (ADS)

    Lee, C.-D.; Liu, S.-Y.; Chen, W.-P.

    2016-11-01

    We present a class of Be stars which have prominent infrared excess emission, yet are not associated with any current or recent star-forming regions. Most of these stars show forbidden lines in the spectra and are among the strongest Balmer emitters. Their infrared excess, extending from near- to mid- or even to far-infrared wavelengths, cannot be explained by free-free emission alone, and must be accounted for by dust thermal emission. A comprehensive “neighborhood census” concludes that these Be stars must have evolved beyond the pre-main sequence stage. The circumstellar dust therefore should be produced in situ by condensation in their expanding envelopes. The freshly made grains could be very small in size, and distributed in a compact disk configuration, in contrast to the case in pre-main sequence Herbig Ae/Be stars that inherit dust grains grown since in parental molecular clouds. This class of main sequence stars hence serves as an additional source of cosmic dust production to the usual post-main sequence stars.

  11. Do C/O > 1 main-sequence stars build carbon planets?

    NASA Astrophysics Data System (ADS)

    Bergfors, Carolina; Farihi, Jay

    2015-12-01

    The existence of rocky yet carbon-dominated planets is predicated on a C-dominated (rather than O-dominated) nebular birthplace. Planet-forming stars with unusually high C/O > 0.8 could provide such a favourable environment. Therefore the highest C/O ratios in potential host stars is of interest, as it has a direct impact on the frequency of C-dominated planetary systems.Interestingly, C/O > 1 main-sequence stars are relatively common, and have distinctive optical spectra dominated by strong molecular carbon features. These dwarf carbon (dC) stars are even more numerous than carbon giants, but their origins may be fundamentally tied to binarity -- where the C/O ratio is increased by C-rich material accreted from an AGB star (now a white dwarf). We are undertaking a survey of dC stars to measure their binary fraction, and to ascertain if any C/O > 1 stars are single and thus favourable to C-rich planet formation.We present first results from our ongoing search for radial velocity companions to dC stars. Multi-epoch observations of 22 systems show clear RV variability for > 70% of targets, suggesting that most, if not all, dC stars are in binary systems. The presence of a formerly more massive companion suggests their C/O > 1 is an enhancement via mass transfer, and not primordial. If correct, C/O > 1 stars may host oxygen-dominated (possibly circumbinary) planets, significantly reducing the Galactic real estate available for carbon planets.

  12. The Rotational Evolution of Solar-like Stars Close to the Zero Age Main Sequence

    NASA Astrophysics Data System (ADS)

    Lanzafame, A. C.; Spada, F.; Lanza, A.; Messina, S.; Collier-Cameron, A.

    We investigate the rotational evolution of solar-like stars approaching and evolving from the zero age main sequence (ZAMS). Most of the observed period distributions in open clusters and young associations available to date are considered. The double zone model, in which the star's radiative core and convective envelope are assumed to rotate as solid bodies, is used to test simple relationships between the core-envelope coupling timescale and rotational properties like the envelope angular velocity or the differential rotation at the core-envelope interface. The trial relationships are tested by fitting the model parameters to available observations via a Monte Carlo Markov Chain method. The synthetic distributions are tested for compatibility with their observational counterparts by means of the Kolmogorov-Smirnov test. A general satisfactory agreement with the observed evolution of rotational periods is found. However, we find it impossible to reconcile the high fraction of fast rotators in Alpha Persei with the rotation period distributions in stellar systems at earlier and later evolutionary stages. Furthermore, the evolution of the rotational period cumulative distribution function of two clusters slightely older than the Pleiades and for which a good number of rotation periods is available, viz. M 50 (130 Myr) and M 35 (150 Myrs), does not follow the evolutionary trend expected from the model. We discuss possible local environmental effects (e.g. early removal of circumstellar discs due to UV radiation and winds from nearby high-mass stars), basic parameters uncertainties (e.g. ages), model oversimplified assumptions, and likely observational biases.

  13. Dissecting the Extended Main Sequence Turn-off of the Young Star Cluster NGC 1850

    NASA Astrophysics Data System (ADS)

    Correnti, Matteo; Goudfrooij, Paul; Bellini, Andrea; Kalirai, Jason S.; Puzia, Thomas H.

    2017-01-01

    We use the Wide Field Camera 3 onboard the Hubble Space Telescope to obtain deep, high-resolution photometry of the young (˜ 100 Myr) star cluster NGC 1850 in the Large Magellanic Cloud. We analyze the cluster colour-magnitude diagram (CMD) and find that it hosts an extended main-sequence turn-off (MSTO) and a double MS. We demonstrate that these features cannot be due to photometric errors, field star contamination, or differential reddening. From a comparison with theoretical models and Monte Carlo simulations, we show that a coeval stellar population featuring a distribution of stellar rotation rates can reproduce the MS split quite well. However, it cannot reproduce the observed MSTO region, which is significantly wider than the simulated ones. Exploiting narrow-band Hα imaging, we find that the MSTO hosts a population of Hα-emitting stars which are interpreted as rapidly rotating Be-type stars. We explore the possibility that the discrepancy between the observed MSTO morphology and that of the simulated simple stellar population (SSP) is caused by the fraction of these objects that are highly reddened, but we rule out this hypothesis. We demonstrate that the global CMD morphology is well-reproduced by a combination of SSPs that cover an age range of ˜ 35 Myr as well as a wide variety of rotation rates. We derive the cluster mass and escape velocity and use dynamical evolution models to predict their evolution starting at an age of 10 Myr. We discuss these results and their implications in the context of the extended MSTO phenomenon.

  14. Absolute Properties of the Main-Sequence Eclipsing Binary Star V885 Cygni

    NASA Astrophysics Data System (ADS)

    Lacy, Claud H. Sandberg; Vaz, Luiz Paulo Ribeiro; Claret, Antonio; Sabby, Jeffrey A.

    2004-09-01

    We present 4179 differential observations in the V filter measured by a robotic telescope, as well as 25 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, EB-type, 1.69 day period double-lined eclipsing binary star V885 Cyg. Absolute dimensions of the components are determined with high precision (better than 1.5% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 2.005+/-0.029 Msolar and 2.345+/-0.012 Rsolar for the hotter, but smaller, less massive and less luminous photometric primary (star A), and 2.234+/-0.026 Msolar and 3.385+/-0.026 Rsolar for the cooler, larger, more massive and more luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 8375+/-150 K for the primary, 8150+/-150 K for the secondary-corresponding to spectral types of A3m and A4m-and 0.058 mag for Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvbyβ photometry. The orbits are circular, and spectral line widths give observed rotational velocities that are synchronous with the orbital motion for both components. The components of V885 Cyg are main-sequence stars with an age of about 500 Myr according to models. Our estimate of the age of this system would seem to favor the hydrodynamic damping formalism of Tassoul & Tassoul in this particular case, since both the components' spins are synchronous and the orbit is circular.

  15. Exploring pre-main-sequence variables of the ONC: the new variables

    NASA Astrophysics Data System (ADS)

    Parihar, Padmakar; Messina, Sergio; Distefano, Elisa; Shantikumar, N. S.; Medhi, Biman J.

    2009-12-01

    Since 2004, we have been engaged in a long-term observing programme to monitor young stellar objects (YSOs) in the Orion Nebula Cluster (ONC). We have collected about 2000 frames in V, R and I broad-band filters on more than 200 nights distributed over five consecutive observing seasons. The high-quality and time-extended photometric data give us an opportunity to address various phenomena associated with young stars. The prime motivations of this project are (i) to explore various manifestations of stellar magnetic activity in very young low-mass stars, (ii) to search for new pre-main-sequence eclipsing binaries and (iii) to look for any EXor and FUor-like transient activities associated with YSOs. Since this is the first paper on this programme, we give a detailed description of the science drivers, the observation and the data reduction strategies as well. In addition to these, we also present a large number of new periodic variables detected from our first 5 yr of time-series photometric data. Our study reveals that about 72 per cent of classical T Tauri stars (CTTS) in our field of view are periodic, whereas only 32 per cent of weak-lined T Tauri stars (WTTS) are periodic. This indicates that inhomogeneity patterns on the surface of CTTS of the ONC stars are much more stable than on WTTS. From our multiyear monitoring campaign, we found that the photometric surveys based on single season are incapable of identifying all periodic variables. And any study on evolution of angular momentum based on single-season surveys must be carried out with caution.

  16. Absolute Properties of the Main-Sequence Eclipsing Binary Star BP Vulpeculae

    NASA Astrophysics Data System (ADS)

    Lacy, Claud H. Sandberg; Torres, Guillermo; Claret, Antonio; Sabby, Jeffrey A.

    2003-10-01

    We present 5236 differential observations in the V filter measured by a robotic telescope, as well as radial velocities from spectroscopic observations, of the detached, eccentric 1.9 day double-lined eclipsing binary star BP Vul. Absolute dimensions of the components are determined with high precision (better than 1% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 1.737+/-0.015 Msolar and 1.852+/-0.014 Rsolar for the primary, and 1.408+/-0.009 Msolar and 1.489+/-0.014 Rsolar for the secondary. The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 7700+/-150 K for the primary, 6800+/-150 K for the secondary-corresponding to spectral types of A7m and F2m-and 0.022 mag for Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvbyβ photometry. Spectral line widths give rotational velocities that are synchronous with the orbital motion for the secondary component, but subsynchronous for the primary component, in a slightly eccentric orbit (e=0.0345). Apsidal motion based on times of minimum light appears to be negative with a period of about 75 years based on recent observations of minima, but this result is not confirmed by the radial velocity measurements, and it is indeterminate when older photographic and visual data are included. The components of BP Vul are main-sequence stars with an age of about 1 Gyr according to models. Some of the observations reported here were obtained with the Multiple Mirror Telescope, a joint facility of the Smithsonian Institution and the University of Arizona.

  17. X-ray Emission from Pre-Main-Sequence Stars - Testing the Solar Analogy

    NASA Technical Reports Server (NTRS)

    Skinner, Stephen L.

    2000-01-01

    This LTSA award funded my research on the origin of stellar X-ray emission and the validity of the solar-stellar analogy. This research broadly addresses the relevance of our current understanding of solar X-ray physics to the interpretation of X-ray emission from stars in general. During the past five years the emphasis has been on space-based X-ray observations of very young stars in star-forming regions (T Tauri stars and protostars), cool solar-like G stars, and evolved high-mass Wolf-Rayet (WR) stars. These observations were carried out primarily with the ASCA and ROSAT space-based observatories (and most recently with Chandra), supplemented by ground-based observations. This research has focused on the identification of physical processes that are responsible for the high levels of X-ray emission seen in pre-main-sequence (PMS) stars, active cool stars, and WR stars. A related issue is how the X-ray emission of such stars changes over time, both on short timescales of days to years and on evolutionary timescales of millions of years. In the case of the Sun it is known that magnetic fields play a key role in the production of X-rays by confining the coronal plasma in loop-like structures where it is heated to temperatures of several million K. The extent to which the magnetically-confined corona interpretation can be applied to other X-ray emitting stars is the key issue that drives the research summarized here.

  18. Laser Desorption Mass Spectrometry for DNA Sequencing and Analysis

    NASA Astrophysics Data System (ADS)

    Chen, C. H. Winston; Taranenko, N. I.; Golovlev, V. V.; Isola, N. R.; Allman, S. L.

    1998-03-01

    Rapid DNA sequencing and/or analysis is critically important for biomedical research. In the past, gel electrophoresis has been the primary tool to achieve DNA analysis and sequencing. However, gel electrophoresis is a time-consuming and labor-extensive process. Recently, we have developed and used laser desorption mass spectrometry (LDMS) to achieve sequencing of ss-DNA longer than 100 nucleotides. With LDMS, we succeeded in sequencing DNA in seconds instead of hours or days required by gel electrophoresis. In addition to sequencing, we also applied LDMS for the detection of DNA probes for hybridization LDMS was also used to detect short tandem repeats for forensic applications. Clinical applications for disease diagnosis such as cystic fibrosis caused by base deletion and point mutation have also been demonstrated. Experimental details will be presented in the meeting. abstract.

  19. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    SciTech Connect

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J.; Basu, S.; Deheuvels, S.; Brandao, I. M.; Cunha, M. S.; Sousa, S. G.; Dogan, G.; Metcalfe, T. S.; Serenelli, A. M.; Garcia, R. A.; Ballot, J.; Weiss, A.; Appourchaux, T.; Casagrande, L.; Cassisi, S.; Creevey, O. L.; Lebreton, Y.; Noels, A.; and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  20. Evolution of the ISM in main-sequence versus starburst galaxies: A motivation for molecular deep fields

    NASA Astrophysics Data System (ADS)

    Aravena, Manuel

    In the last decade, significant progress has been made to understand the evolution with redshift of star formation processes in galaxies. Its is now clear that the majority of galaxies at z<3 form a nearly linear correlation between their stellar mass and star formation rates and appear to create most of their stars in timescales of ~1 Gyr. At the highest luminosities, a significant fraction of galaxies deviate from this main-sequence, showing short duty cycles and thus producing most of their stars in a single burst of star formation within ~100 Myr, being likely driven by major merger activity. Despite the large luminosities of starbursts, main-sequence galaxies appear to dominate the star formation density of the Universe at its peak. While progress has been impressive, a number of questions are still unanswered. In this paper, I briefly review our current observational understanding of this main-sequence vs starburst galaxy paradigm, and address how future observations will help us to have better insights into the fundamental properties of the interstellar medium of these galaxies. Finally, I show recent attempts to conduct molecular deep field observations and the motivation to perform molecular deep field spectroscopy with the Atacama Large Millimeter/submillimeter Array.

  1. The Young Open Clusters King 12, NGC 7788, and NGC 7790: Pre-main-sequence Stars and Extended Stellar Halos

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2012-12-01

    The stellar contents of the open clusters King 12, NGC 7788, and NGC 7790 are investigated using MegaCam images. Comparisons with isochrones yield an age <20 Myr for King 12, 20-40 Myr for NGC 7788, and 60-80 Myr for NGC 7790 based on the properties of stars near the main-sequence turnoff (MSTO) in each cluster. The reddening of NGC 7788 is much larger than previously estimated. The luminosity functions (LFs) of King 12 and NGC 7788 show breaks that are attributed to the onset of pre-main-sequence (PMS) objects, and comparisons with models of PMS evolution yield ages that are consistent with those measured from stars near the MSTO. In contrast, the r' LF of main-sequence stars in NGC 7790 is matched to r' = 20 by a model that is based on the solar neighborhood mass function. The structural properties of all three clusters are investigated by examining the two-point angular correlation function of blue main-sequence stars. King 12 and NGC 7788 are each surrounded by a stellar halo that extends out to a radius of 5 arcmin (~3.4 pc). It is suggested that these halos form in response to large-scale mass ejection early in the evolution of the clusters, as predicted by models. In contrast, blue main-sequence stars in NGC 7790 are traced out to a radius of ~7.5 arcmin (~5.5 pc), with no evidence of a halo. It is suggested that all three clusters may have originated in the same star-forming complex, but not in the same giant molecular cloud. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii.

  2. Sequencing of Oligourea Foldamers by Tandem Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Bathany, Katell; Owens, Neil W.; Guichard, Gilles; Schmitter, Jean-Marie

    2013-03-01

    This study is focused on sequence analysis of peptidomimetic helical oligoureas by means of tandem mass spectrometry, to build a basis for de novo sequencing for future high-throughput combinatorial library screening of oligourea foldamers. After the evaluation of MS/MS spectra obtained for model compounds with either MALDI or ESI sources, we found that the MALDI-TOF-TOF instrument gave more satisfactory results. MS/MS spectra of oligoureas generated by decay of singly charged precursor ions show major ion series corresponding to fragmentation across both CO-NH and N'H-CO urea bonds. Oligourea backbones fragment to produce a pattern of a, x, b, and y type fragment ions. De novo decoding of spectral information is facilitated by the occurrence of low mass reporter ions, representative of constitutive monomers, in an analogous manner to the use of immonium ions for peptide sequencing.

  3. Definition of the Pleiades Main Sequence in the Hertzsprung-Russell Diagram

    NASA Astrophysics Data System (ADS)

    Hansen-Ruiz, C. S.; van Leeuwen, F.

    1997-08-01

    The Pleiades main sequence is intrinsically of very small width. Disturbances to this width come primarily from three sources: local interstellar reddening (related to the reflection nebulae), multiplicity and variations in the distance moduli related to the size of the cluster (~20 pc diameter). Walraven 5-channel photometry can be used to remove most of the reddening related effects. A full literature survey was made concerning multiplicity to provide information needed to correct for multiplicity effects. The locus of the resulting corrected main sequence can be determined using Hipparcos parallaxes (van Leeuwen and Hansen-Ruiz 1997), providing a well defined observational isochrone for the study of stellar evolution and stellar structure. Preliminary results are presented.

  4. On the rate of destruction of lithium in late-type main-sequence stars

    NASA Technical Reports Server (NTRS)

    Christensen-Dalsgaard, J.; Gough, D. O.; Thompson, M. J.

    1992-01-01

    It it shown that the rate of destruction of lithium by nuclear reactions in the outer mixed layers of late-type main-sequence stars depends on both the depth of the region where mixing occurs and the stratification within it. The mixed region includes and probably extends beneath the base of the convection zone. As the star evolves on the main sequence, the properties of the convection zone vary in a simple manner. If the mixed layer behaves similarly, then the mean destruction rate can easily be related to the present local value evaluated at the base of the mixed layer. In the case of the sun, it is found that if mixing is rapid compared with the nuclear destruction rate, then the mean destruction rate is approximately equal to one-half the present local value.

  5. BVI CCD photometry of the broad main-sequence globular cluster NGC 1851

    SciTech Connect

    Alcaino, G.; Liller, W.; Alvarado, F.; Wenderoth, E. )

    1990-03-01

    Three-color CCD C-M diagrams are presented for the globular cluster NGC 1851, showing an extreme breadth of the main-sequence, similar to that of Omega Centauri. It is found that the main-sequence turnoff points are located at V(TO) = 19.44 + or - 0.10, with colors at B-V = 0.54 + or - 0.02, V-I = 0.61 + or - 0.02, and B-I = 1.15 + or - 0.03. The best fit to the VandenBerg and Bell (1985) isochrones is shown to be all C-M diagrams with Y = 0.20, Fe/H abundance ratio = -1.27, and (m-M)v = 15.45. It is concluded that NGC 1851 has a Delta V(TO - HB) = 3.34 + or - 0.10 and an age of 16 + or - 2 Gyr. 29 refs.

  6. Searching for the signatures of terrestrial planets in F-, G-type main-sequence stars

    NASA Astrophysics Data System (ADS)

    González Hernández, J. I.; Delgado-Mena, E.; Sousa, S. G.; Israelian, G.; Santos, N. C.; Adibekyan, V. Zh.; Udry, S.

    2013-04-01

    Context. Detailed chemical abundances of volatile and refractory elements have been discussed in the context of terrestrial-planet formation during in past years. Aims: The HARPS-GTO high-precision planet-search program has provided an extensive database of stellar spectra, which we have inspected in order to select the best-quality spectra available for late type stars. We study the volatile-to-refractory abundance ratios to investigate their possible relation with the low-mass planetary formation. Methods: We present a fully differential chemical abundance analysis using high-quality HARPS and UVES spectra of 61 late F- and early G-type main-sequence stars, where 29 are planet hosts and 32 are stars without detected planets. Results: As for the previous sample of solar analogs, these stars slightly hotter than the Sun also provide very accurate Galactic chemical abundance trends in the metallicity range -0.3 < [Fe/H] < 0.4. Stars with and without planets show similar mean abundance ratios. Moreover, when removing the Galactic chemical evolution effects, these mean abundance ratios, Δ [X/Fe] SUN - STARS, against condensation temperature, tend to exhibit less steep trends with nearly zero or slightly negative slopes. We have also analyzed a subsample of 26 metal-rich stars, 13 with and 13 without known planets, with spectra at S/N ~ 850, on average, in the narrow metallicity range 0.04 < [Fe/H] < 0.19. We find the similar, although not equal, abundance pattern with negative slopes for both samples of stars with and without planets. Using stars at S/N ≥ 550 provides equally steep abundance trends with negative slopes for stars both with and without planets. We revisit the sample of solar analogs to study the abundance patterns of these stars, in particular, 8 stars hosting super-Earth-like planets. Among these stars having very low-mass planets, only four of them reveal clear increasing abundance trends versus condensation temperature. Conclusions: Finally, we

  7. Can the helium-enriched main-sequence donor scenario hide enough hydrogen to explain Type Ia supernovae?

    NASA Astrophysics Data System (ADS)

    Liu, Zheng-Wei; Stancliffe, Richard J.

    2017-09-01

    Hydrodynamical simulations predict that a large amount of hydrogen (≳0.1 M⊙) is removed from a hydrogen-rich companion star by the SN explosion in the single-degenerate scenario of Type Ia supernovae (SNe Ia). However, non-detection of hydrogen-rich material in the late-time spectra of SNe Ia suggests that the hydrogen mass stripped from the progenitor system is ≲0.001-0.058 M⊙. In this Letter, we include thermohaline mixing into self-consistent binary evolution calculations for the helium-enriched main-sequence (HEMS) donor channel of SNe Ia for the first time. We find that the swept-up hydrogen masses expected in this channel are around 0.10-0.17 M⊙, which is higher than the observational limits, although the companion star is strongly helium-enriched when the SN explodes. This presents a serious challenge to the HEMS donor channel.

  8. Evolution and detectability of comet clouds during post-main-sequence stellar evolution

    NASA Technical Reports Server (NTRS)

    Stern, S. Alan; Brandt, John C.; Shull, J. Michael

    1990-01-01

    The destruction of volatile-rich comet disks and Oort-type clouds around luminous post-main-sequence stars is modeled. The models are in agreement with several aspects of existing observations of water and complex molecules in the envelopes of giant and supergiant stars. If confirmed, these results would establish the common existence of Oort-type clouds around other stars and would constitute indirect evidence for sites of past planetary formation.

  9. Evolution and detectability of comet clouds during post-main-sequence stellar evolution

    NASA Technical Reports Server (NTRS)

    Stern, S. Alan; Brandt, John C.; Shull, J. Michael

    1990-01-01

    The destruction of volatile-rich comet disks and Oort-type clouds around luminous post-main-sequence stars is modeled. The models are in agreement with several aspects of existing observations of water and complex molecules in the envelopes of giant and supergiant stars. If confirmed, these results would establish the common existence of Oort-type clouds around other stars and would constitute indirect evidence for sites of past planetary formation.

  10. Post-main-sequence Evolution of Icy Minor Planets. II. Water Retention and White Dwarf Pollution around Massive Progenitor Stars

    NASA Astrophysics Data System (ADS)

    Malamud, Uri; Perets, Hagai B.

    2017-06-01

    Most studies suggest that the pollution of white dwarf (WD) atmospheres arises from the accretion of minor planets, but the exact properties of polluting material, and in particular the evidence for water in some cases, are not yet understood. Here we study the water retention of small icy bodies in exo-solar planetary systems, as their respective host stars evolve through and off the main sequence and eventually become WDs. We explore, for the first time, a wide range of star masses and metallicities. We find that the mass of the WD progenitor star is of crucial importance for the retention of water, while its metallicity is relatively unimportant. We predict that minor planets around lower-mass WD progenitors would generally retain more water and would do so at closer distances from the WD than compared with high-mass progenitors. The dependence of water retention on progenitor mass and other parameters has direct implications for the origin of observed WD pollution, and we discuss how our results and predictions might be tested in the future as more observations of WDs with long cooling ages become available.

  11. Mathematical Assessment of Physical and Chemical Processes from the middle B to the early F Type Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Yuce, Kutluay; Adelman, Saul J.

    2016-07-01

    The middle B to the early F main sequence stars are thought to have some of the most quiet atmospheres. In this part of the HR diagram we find stars with atmospheres in radiative equilibrium. They lack the convective circulations of the middle F and cooler stars and the massive stellar winds of hotter stars. Diffusion theory requires the Chemically Peculiar stars to have relatively quiet atmospheres and if there are no magnetic fields they should lack abundance spots. If we look at stars evolving off the Main Sequence in this part of the HR diagram, we see that the evolutionary paths of stars of different mass do not cross. So if we compare stars with the same effective temperature and surface gravity, we are studying stars of the same luminosity and mass. By comparing their elemental abundances, we might be able to identify physical processes which cause their abundances to be different. In this work we begin with stars whose effective temperatures and surface gravities are similar, and which has been analyzed by us using spectra obtained from the Dominion Astrophysical Observatory.

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

    SciTech Connect

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

    2012-09-10

    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 stars 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.

  13. Testing Scaling Relations for Solar-like Oscillations from the Main Sequence to Red Giants Using Kepler Data

    NASA Astrophysics Data System (ADS)

    Huber, D.; Bedding, T. R.; Stello, D.; Hekker, S.; Mathur, S.; Mosser, B.; Verner, G. A.; Bonanno, A.; Buzasi, D. L.; Campante, T. L.; Elsworth, Y. P.; Hale, S. J.; Kallinger, T.; Silva Aguirre, V.; Chaplin, W. J.; De Ridder, J.; García, R. A.; Appourchaux, T.; Frandsen, S.; Houdek, G.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Broomhall, A. M.; Corsaro, E.; Salabert, D.; Sanderfer, D. T.; Seader, S. E.; Smith, J. C.

    2011-12-01

    We have analyzed solar-like oscillations in ~1700 stars observed by the Kepler Mission, spanning from the main sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power (νmax), the large frequency separation (Δν), and oscillation amplitudes. We show that the difference of the Δν-νmax relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M) s scaling nor the revised scaling relation by Kjeldsen & Bedding is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main sequence to red giants to a precision of ~25%. The residuals show an offset particularly for unevolved stars, suggesting that an additional physical dependency is necessary to fully reproduce the observed amplitudes. We investigate correlations between amplitudes and stellar activity, and find evidence that the effect of amplitude suppression is most pronounced for subgiant stars. Finally, we test the location of the cool edge of the instability strip in the Hertzsprung-Russell diagram using solar-like oscillations and find the detections in the hottest stars compatible with a domain of hybrid stochastically excited and opacity driven pulsation.

  14. Discovery of magnetic A supergiants: the descendants of magnetic main-sequence B stars

    NASA Astrophysics Data System (ADS)

    Neiner, Coralie; Oksala, Mary E.; Georgy, Cyril; Przybilla, Norbert; Mathis, Stéphane; Wade, Gregg; Kondrak, Matthias; Fossati, Luca; Blazère, Aurore; Buysschaert, Bram; Grunhut, Jason

    2017-10-01

    In the context of the high resolution, high signal-to-noise ratio, high sensitivity, spectropolarimetric survey BritePol, which complements observations by the BRITE constellation of nanosatellites for asteroseismology, we are looking for and measuring the magnetic field of all stars brighter than V = 4. In this paper, we present circularly polarized spectra obtained with HarpsPol at ESO in La Silla (Chile) and ESPaDOnS at CFHT (Hawaii) for three hot evolved stars: ι Car, HR 3890 and ε CMa. We detected a magnetic field in all three stars. Each star has been observed several times to confirm the magnetic detections and check for variability. The stellar parameters of the three objects were determined and their evolutionary status was ascertained employing evolution models computed with the Geneva code. ε CMa was already known and is confirmed to be magnetic, but our modelling indicates that it is located near the end of the main sequence, i.e. it is still in a core hydrogen burning phase. ι Car and HR 3890 are the first discoveries of magnetic hot supergiants located well after the end of the main sequence on the Hertzsprung-Russell diagram. These stars are probably the descendants of main-sequence magnetic massive stars. Their current field strength (a few G) is compatible with magnetic flux conservation during stellar evolution. These results provide observational constraints for the development of future evolutionary models of hot stars including a fossil magnetic field.

  15. Exo-Planetary Phoenix: Rebirth of Planetary Systems Beyond the Main Sequence

    NASA Astrophysics Data System (ADS)

    Marengo, M.

    2014-04-01

    Mounting evidence suggests that planetary systems may be a common feature of stars that have evolved beyond the main sequence. Warm debris disks around white dwarfs and "pulsar" planets orbiting a neutron star are a strong indication that planetary systems may, at least in same cases, survive the dramatic phenomena leading to stellar death. A close look at these late evolutionary stages, however, suggests that these systems may be more than mere survivors of doomed pre-existing exo-planetary systems. The circumstellar environment of post-main sequence stars bears surprising similarities to the conditions leading to pre-main sequence planetary formation: a metal-rich environment often characterized by the presence of circumstellar or circumbinary disks. Are these conditions conducive to the birth of a second-generation planetary system, like a phoenix rising from the ashes of ancient worlds? In this talk we will discuss how the physical conditions in the winds of dusty giant stars may be favorable for renewed planetary formation, with particular emphasis on the effects of enhanced metallicity, binarity and the timescales available for the formation of a new generation of planets.

  16. 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.

  17. Rupture complexity of the three main shocks of the 2016 Central Italy seismic sequence

    NASA Astrophysics Data System (ADS)

    Tinti, Elisa; Scognamiglio, Laura; Magnoni, Federica; Casarotti, Emanuele; Michelini, Alberto; Cocco, Massimo

    2017-04-01

    The 2016 Central Italy seismic sequence, started on August 24th, ruptured an almost 60 km long segmented fault system between Amatrice, Norcia and Pieve Torina and is characterized by three main events and more than 45.000 aftershocks. A key feature of the studied sequence is the temporal distribution of the seismic moment release: the largest magnitude event (Mw 6.5, 30th October) occurred two months after the first main shock (Mw 6.0, 24th August) and only four days after the second main event (Mw 5.9, 26th October). All the three main events and most of the aftershocks show NNW-SSE striking focal mechanisms in agreement with the current NE-SW extensional tectonic setting of Central Apennines. To image the rupture history of the three main events of the sequence, we invert the ground velocity time histories obtained from three-component strong motion accelerometers located within 45 km from the faults, filtered between 0.02-0.5 Hz. To improve the fit between data and synthetics we also test complex source geometries and assume rupture segmentation on a number of distinct fault planes. Overall, the retrieved rupture histories display heterogeneous slip distributions with high peak slip values and directivity effects. These features can explain the localized high values of the peak ground motions. Finally, to test the inferred source heterogeneity and directivity, and verify how the topography and geological constraints affect the calculated ground motion, we propagate the retrieved kinematic rupture models within a 3D forward simulation and compare the results to the available observations.

  18. A buried marine depositional sequence (Presumpscot FM. ) N. of the marine limit, Waterboro, Maine

    SciTech Connect

    Morency, R.E. )

    1993-03-01

    Subsurface investigations conducted in Waterboro, ME (York Co.) in connection with studies of two hazardous waste sites and a municipal water supply exploration project, have demonstrated that a laterally extensive sequence of marine deposits underlies surficial sediments mapped as non-esker ice contact glacio-fluvial deposits. The marine deposits consist of a fining-downwards sequence of grey, micaceous sands (fine to medium, grading down to a silty-fine sand), which grade downward into a thick ([plus minus] 30 feet) grey silt/clay unit, which itself shows a fining-downward trend. The stratigraphy is likely correlative to the Presumpscot Formation, as described by Bloom (1963). The bottom of the regressive marine sequence is marked at several locations by a thin layer of sand-sized biotite mica. Lodgement till was encountered only at scattered localities (in boreholes) at each site. The bedrock surface is of considerable relief, with changes of 200--300 feet over short distances detected. The sequence appears to be the record of a rapidly transgressing sea which inundated a valley where outwash had been deposited by meltwater ahead of retreating ice. As the sea retreated, up to 70 feet of sediment was deposited in a continuous, coarsening-upwards sequence. Subsequent to the marine regression, the sediments were reworked in a subaerial (braided stream) environment. The Surficial Geologic Map of Maine shows that the inland limit of late-glacial marine submergence is located approximately 8 miles southwest of Waterboro, in Alfred, Maine. The marine limit in Alfred takes the form of a NNE trending, blunt-ended embayment. The results of this study suggest that the marine embayment once extended northward from Alfred, and is now a buried feature, possibly representing a preglacial valley, which hosted an estuary in late Wisconsonian time.

  19. Applications of mass spectrometry to DNA fingerprinting and DNA sequencing

    SciTech Connect

    Jacobson, K.B.; Buchanan, M.V.; Chen, C.H.; Doktycz, M.J.; McLuckey, S.A.; Arlinghaus, H.F.

    1993-06-01

    DNA fingerprinting and sequencing rely on polyacrylamide gel electrophoresis to determine the sizes of the DNA fragments. Innovative altematives to polyacrylamide gel electrophoresis are under investigation for characterization of such fingerprinting and sequencing. One method uses stable isotopes of tin and other elements to label the DNAwhereas other procedures do not require labels. The detectors in each case are mass spectrometers that detect either the stable isotopes or the DNA fragments themselves. If successful, these methods will speed up the rate of DNA analysis by one or two orders of magnitude.

  20. Applications of mass spectrometry to DNA fingerprinting and DNA sequencing

    SciTech Connect

    Jacobson, K.B.; Buchanan, M.V.; Chen, C.H.; Doktycz, M.J.; McLuckey, S.A. ); Arlinghaus, H.F. )

    1993-01-01

    DNA fingerprinting and sequencing rely on polyacrylamide gel electrophoresis to determine the sizes of the DNA fragments. Innovative altematives to polyacrylamide gel electrophoresis are under investigation for characterization of such fingerprinting and sequencing. One method uses stable isotopes of tin and other elements to label the DNAwhereas other procedures do not require labels. The detectors in each case are mass spectrometers that detect either the stable isotopes or the DNA fragments themselves. If successful, these methods will speed up the rate of DNA analysis by one or two orders of magnitude.

  1. Stellar parameters of main sequence turn-off star candidates observed with LAMOST and Kepler

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Qian; Xiang, Mao-Sheng; Zhang, Xian-Fei; Li, Tan-Da; Bi, Shao-Lan; Liu, Xiao-Wei; Fu, Jian-Ning; Huang, Yang; Tian, Zhi-Jia; Liu, Kang; Ge, Zhi-Shuai; He, Xin; Zhang, Jing-Hua

    2017-01-01

    Main sequence turn-off (MSTO) stars have advantages as indicators of Galactic evolution since their ages can be robustly estimated from atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it is vital to derive accurate stellar parameters. In this work, we select 150 MSTO star candidates from the MSTO star sample of Xiang that have asteroseismic parameters and determine accurate stellar parameters for these stars by combining asteroseismic parameters deduced from Kepler photometry and atmospheric parameters deduced from LAMOST spectra. With this sample, we examine the age determination as well as the contamination rate of the MSTO star sample. A comparison of age between this work and Xiang shows a mean difference of 0.53 Gyr (7%) and a dispersion of 2.71 Gyr (28%). The results show that 79 of the candidates are MSTO stars, while the others are contaminations from either main sequence or sub-giant stars. The contamination rate for the oldest stars is much higher than that for younger stars. The main cause for the high contamination rate is found to be the relatively large systematic bias in the LAMOST surface gravity estimates.

  2. The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

    NASA Astrophysics Data System (ADS)

    Tailo, M.; Di Criscienzo, M.; D'Antona, F.; Caloi, V.; Ventura, P.

    2016-04-01

    We interpret the stellar population of ω Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch (HB) data. The reproduction of the observed colour-magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: (1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed, we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a ˜0.5 Gyr time interval; in particular the most metal-rich population can be coeval (in the above meaning) with the others, if its stars are very helium-rich (Y ˜ 0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = +0.7); (2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub-giant data; (3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal-poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

  3. Carbon Biochemistry and the Ultraviolet Radiation Environments of F, G, and K Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Cockell, Charles S.

    1999-10-01

    The ultraviolet radiation environment of main sequence stars might be a factor in determining the suitability of extrasolar planets for biological evolution and the subsequent radiation of life in exposed habitats. Assuming the validity of the carbon-water chauvinism, the absorbance of DNA in the UV region of the spectrum is used as a theoretical biological dosimeter to elucidate in more detail the photobiological parameter space of anoxic planets orbiting F, G, and K main sequence stars. Planets within the habitable zones of K main sequence stars have particularly favorable UV environments, with biochemically effective irradiances an order of magnitude lower than those believed to have existed on the surface of Archean Earth. Even using the UV shielding and repair habits of present-day terrestrial organisms, the survivability of the photobiological environment of anoxic K star planets can be demonstrated. The biochemically effective irradiances received in the F star radiation environment are more severe, being 6 to 27 times higher than on Archean Earth. Nevertheless, a combination of UV mitigation strategies seen on the present-day Earth suggest that UV radiation is not a constraint on life even in the inner region of the habitable zone. Life in an ocean on an F-star planet could experience a UV radiation regime similar even to that for present-day Earth. These calculations, although limited by our assumptions on the course of biochemical evolution and the UV absorbance of complex extraterrestrial molecules, suggest that life can survive the UV radiation environments of most extrasolar planets.

  4. BVRI main-sequence photometry of the globular cluster M4

    SciTech Connect

    Alcaino, G.; Liller, W.

    1984-09-01

    We present BV and RI photographic photometry of 1421 and 189 stars, respectively, in the intermediate metallicity globular cluster M4 (NGC 6121). This investigation includes the first results of RI main-sequence photometry of a globular cluster. The use of longer wavelengths and longer color baselines provides the potential of improved isochrone fittings and underscores the urgent need for calculations of RI synthetic isochrones to be compared with observations. The Pickering-Racine wedge was used with the ESO 3.6 m telescope, the Las Campanas 2.5 m du Pont telescope, and the CTIO 1 m Yale telescope to extend the photoelectric limit from Vroughly-equal16.1 to Vroughly-equal19.1. We have determined the position of the main-sequence turnoff to lie at V = 16.6 +- 0.2 (m.e.) and B-V = 0.80 +- 0.03 (m.e.). A comparison of our BV observations with the CCD data of Richer and Fahlman shows excellent agreement: the two fifucial main sequences agree at all points to within 0.025 mag and, on average, to 0.013 mag. For the cluster we derive a distance modulus (m-M)/sub V/ = 12.52 +- 0.2 and reddening E(B-V) = 0.44 +- 0.03, results which confirm that at a distance of 2 kpc, M4 is the closest globular clusters to the Sun. Using the isochrones of VandenBerg, we deduce an age 13 +- 2 Gyr. As noted in several other investigations, there is a striking deficiency of stars in certain parts of the color-magnitude diagram; in M4 we find a pronounced gap over approx.0.6 mag at the base of the subgiant branch.

  5. Upper limits on extreme ultraviolet radiation from nearby main sequence and subgiant stars

    NASA Technical Reports Server (NTRS)

    Ayres, T. R.; Linsky, J. L.; Margon, B.; Bowyer, S.

    1978-01-01

    Flux upper limits for 44-800 A radiation were measured in a sample of nearby main sequence stars and one subgiant star with the aid of the Apollo-Soyuz grazing incidence telescope. Comparisons of emission measure upper limits with three different methods for predicting coronal properties cannot yet determine which, if any, are valid. Data for Alpha Centauri A and B are consistent with recent HEAO-1 soft X-ray measurements which suggest that the surface flux of coronal emission from the Alpha Cen system is comparable to that of the 'normal' sun.

  6. Active phenomena in the pre-main sequence Herbig Ae star HD 163296

    NASA Technical Reports Server (NTRS)

    Catala, C.; Praderie, F.; Simon, T.; Talavera, A.; The, P. S.

    1989-01-01

    Observations by IUE of the short-term variability of the Mg II and Ca II resonance lines in the Herbig Ae star HD 163296 are presented. Evidence that these lines show a phenomenon of rotational modulation, similar to the one observed in AB Aur, another Herbig Ae star is found. The variations in the spectrum of HD 163296 are even more conspicuous than in the spectrum of AB Aur. Magnetically structured winds may thus be a widespread phenomenon among the pre-main sequence Herbig Ae/Be stars.

  7. Supersolar metallicity in G0-G3 main-sequence stars with V < 15

    NASA Astrophysics Data System (ADS)

    López-Valdivia, R.; Bertone, E.; Chávez, M.; Tapia-Schiavon, C.; Hernández-Águila, J. B.; Valdés, J. R.; Chavushyan, V.

    2014-11-01

    The basic stellar atmospheric parameters (effective temperature, surface gravity and global metallicity) were determined simultaneously for a sample of 233 stars, limited in magnitude (V < 15), with spectral types between G0 and G3 and luminosity class V (main sequence). The analysis was based on spectroscopic observations collected at the Observatorio Astrofísico Guillermo Haro and using a set of Lick-like indices defined in the spectral range 3800-4800 Å. An extensive set of indices computed in a grid of theoretical spectra was used as a comparison tool in order to determine the photospheric parameters. The method was validated by matching the results from spectra of the asteroids Vesta and Ceres with the Sun parameters. The main results were as follows: (i) the photospheric parameters were determined for the first time for 213 objects in our sample and (ii) a sample of 20 new super-metal-rich star candidates was found.

  8. Main pulmonary artery stenosis caused by fibrocalcified mass in a young infant.

    PubMed Central

    Han, Heon-Seok; Park, Jeong-Hyun; Kim, Deok Soo; Lee, Seog-Jae; Hong, Jang-Soo; Lee, Geon Kook

    2002-01-01

    We present a rare case of main pulmonary artery stenosis secondary to protruding fibrous material in the main pulmonary artery associated with patent ductus arteriosus. A 1-month-old baby boy manifested cardiac murmur. Echocardiogram showed circumferential high echogenic mass inside the main pulmonary artery with pressure gradient of 49 mmHg and patent ductus arteriosus. The mass did not regress during 3 months' follow-up period. Angiographic images showed that the circular filling defect was located at the main pulmonary artery distal to pulmonary valve, and pulmonary valve and both pulmonary arteries were normal. After surgical removal of the circumferential material and ductus ligation, the pressure gradient became negligible. The material was consisted of scarcely cellular fibrous tissue, abundant coagulum of fibrinous material and dense calcification. PMID:12172057

  9. Post-main Sequence Evolution of Icy Minor Planets: Implications for Water Retention and White Dwarf Pollution

    NASA Astrophysics Data System (ADS)

    Malamud, Uri; Perets, Hagai B.

    2016-12-01

    Most observations of polluted white dwarf atmospheres are consistent with accretion of water-depleted planetary material. Among tens of known cases, merely two involve accretion of objects that contain a considerable mass fraction of water. The purpose of this study is to investigate the relative scarcity of these detections. Based on a new and highly detailed model, we evaluate the retention of water inside icy minor planets during the high-luminosity stellar evolution that follows the main sequence. Our model fully considers the thermal, physical, and chemical evolution of icy bodies, following their internal differentiation as well as water depletion, from the moment of their birth and through all stellar evolution phases preceding the formation of the white dwarf. We also account for different initial compositions and formation times. Our results differ from previous studies, which have either underestimated or overestimated water retention. We show that water can survive in a variety of circumstances and in great quantities, and therefore other possibilities are discussed in order to explain the infrequency of water detection. We predict that the sequence of accretion is such that water accretes earlier, and more rapidly, than the rest of the silicate disk, considerably reducing the chance of its detection in H-dominated atmospheres. In He-dominated atmospheres, the scarcity of water detections could be observationally biased. It implies that the accreted material is typically intrinsically dry, which may be the result of the inside-out depopulation sequence of minor planets.

  10. 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.

  11. Alma And Jvla Imaging Of Intense Galaxy-Wide Star Formation In Z 2 Galaxies In The Hudf: Bridging Smgs To The Main Sequence

    NASA Astrophysics Data System (ADS)

    Rujopakarn, Wiphu

    2017-06-01

    We present 0.4'' resolution extinction-independent distributions of star formation and dust in 11 main-sequence star-forming galaxies (SFGs) at z 2. These galaxies are selected from deep ALMA and JVLA surveys of the Hubble Ultra-Deep Field at 1.3 mm and 5 cm. Morphological classification performed on spatially-resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray AGN. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median r_e = 2.4 kpc, thereby providing direct evidence of galaxy-wide star formation in z 2 main-sequence SFGs. In X-ray AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGN, which are found to be cospatial with star formation. The median extinction-independent size of main-sequence SFGs is 2x larger than those of luminous SMGs, providing a constraint on the characteristic SFR of 300 Msun/yr above which a significant population of more compact SFGs appears to emerge, possibly bridging the populations of SMGs to main-sequence SFGs.

  12. X-ray sources in regions of star formation. II - The pre-main-sequence G star HDE 283572

    NASA Technical Reports Server (NTRS)

    Walter, F. M.; Brown, A.; Linsky, J. L.; Rydgren, A. E.; Vrba, F.

    1987-01-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a 'naked' T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars.

  13. Time sequence and time scale of intermediate mass fragment emission

    SciTech Connect

    De Filippo, E.; Pagano, A.; Cardella, G.; Lanzano, G.; Papa, M.; Pirrone, S.; Politi, G.; Wilczynski, J.

    2005-04-01

    Semiperipheral collisions in the {sup 124}Sn+{sup 64}Ni reaction at 35 MeV/nucleon were studied using the forward part of the Charged Heavy Ion Mass and Energy Resolving Array. Nearly completely determined ternary events involving projectilelike fragments (PLF), targetlike fragments (TLF), and intermediate mass fragments (IMF) were selected. A new method of studying the reaction mechanism, focusing on the analysis of the correlations between relative velocities in the IMF+PLF and IMF+TLF subsystems, is proposed. The relative velocity correlations provide information on the time sequence and time scale of the neck fragmentation processes leading to production of IMFs. It is shown that the majority of light IMFs are produced within 40-80 fm/c after the system starts to reseparate. Heavy IMFs are formed at times of about 120 fm/c or later and can be viewed as resulting from two-step (sequential) neck rupture processes.

  14. A surprise at the bottom of the main sequence: Rapid rotation and NO H-alpha emission

    NASA Technical Reports Server (NTRS)

    Basri, Gibor; Marcy, Geoffrey W.

    1995-01-01

    We report Kech Observatory high-resolution echelle spectra from 640-850 nm for eight stars near the faint end of the main sequence. These spectra are the highest resolution spectra of such late-type stars, and clearly resolve the TiO, VO, and atomic lines. The sample includes the field brown-dwarf candidate, BRI 0021-0214 (M9.5+). Very unexpectedly, it shows the most rapid rotation in the entire samples, v sin i approximately 40 km/s, which is 20x faster than typical field nonemission M stars. Equally surprising is that BRI 0021 exhibits no emission or absorptionat H-alpha. We argue that this absence is not simply due to its cool photosphere, but that stellar activity declines in a fundamental way at the end of the main sequence. As it is the first very late M dwarf observed at high spectral resolution, BRI 0021 may be signaling a qualitative change in the angular momentum loss rate among the lowest mass stars. Conventionally, its rapid rotation would have marked BRI 0021 as very young, consistent with the selection effect which arises if the latest-type dwarfs are really brown dwarfs on cooling curves. In any case, it is unprecedented to find no sign of stellar activity in such a rapidly rotating convective star. We also discuss the possible conflict between this observation and the extremely strong H-alpha seen in another very cool star, PC 0025+0447. Extrapolation of M-L relations for BRI 0021 yields M approximately 0.065 solar mass, and the other sample objects have expected masses near the H-burning limit. These include two Pleiades brown-dwarf candidates, four field M6 dwarfs and one late-type T Tauri star. The two Pleiades M6 dwarfs have v sin i of 26 and 37 km/s, H-alpha in emission, and radial velocities consistent with Pleiades M6 dwarfs have v sin i of 26 and 37 km/s, H-alpha in emission, and radial velocities consistent with Pleiades membership. Similarly, the late-type T Tauri star has v sin i approximately 30 km/s and H alpha emission indicate of its

  15. A surprise at the bottom of the main sequence: Rapid rotation and NO H-alpha emission

    NASA Technical Reports Server (NTRS)

    Basri, Gibor; Marcy, Geoffrey W.

    1995-01-01

    We report Kech Observatory high-resolution echelle spectra from 640-850 nm for eight stars near the faint end of the main sequence. These spectra are the highest resolution spectra of such late-type stars, and clearly resolve the TiO, VO, and atomic lines. The sample includes the field brown-dwarf candidate, BRI 0021-0214 (M9.5+). Very unexpectedly, it shows the most rapid rotation in the entire samples, v sin i approximately 40 km/s, which is 20x faster than typical field nonemission M stars. Equally surprising is that BRI 0021 exhibits no emission or absorptionat H-alpha. We argue that this absence is not simply due to its cool photosphere, but that stellar activity declines in a fundamental way at the end of the main sequence. As it is the first very late M dwarf observed at high spectral resolution, BRI 0021 may be signaling a qualitative change in the angular momentum loss rate among the lowest mass stars. Conventionally, its rapid rotation would have marked BRI 0021 as very young, consistent with the selection effect which arises if the latest-type dwarfs are really brown dwarfs on cooling curves. In any case, it is unprecedented to find no sign of stellar activity in such a rapidly rotating convective star. We also discuss the possible conflict between this observation and the extremely strong H-alpha seen in another very cool star, PC 0025+0447. Extrapolation of M-L relations for BRI 0021 yields M approximately 0.065 solar mass, and the other sample objects have expected masses near the H-burning limit. These include two Pleiades brown-dwarf candidates, four field M6 dwarfs and one late-type T Tauri star. The two Pleiades M6 dwarfs have v sin i of 26 and 37 km/s, H-alpha in emission, and radial velocities consistent with Pleiades M6 dwarfs have v sin i of 26 and 37 km/s, H-alpha in emission, and radial velocities consistent with Pleiades membership. Similarly, the late-type T Tauri star has v sin i approximately 30 km/s and H alpha emission indicate of its

  16. New radio detections of early-type pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Skinner, Stephen L.; Brown, Alexander; Linsky, Jeffrey L.

    1990-01-01

    Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out.

  17. Post Main Sequence Orbital Circularization of Binary Stars in the Large and Small Magellanic Clouds.

    SciTech Connect

    Faccioli, L; Alcock, C; Cook, K

    2007-11-20

    We present results from a study of the orbits of eclipsing binary stars (EBs) in the Magellanic Clouds. The samples comprise 4510 EBs found in the Large Magellanic Cloud (LMC) by the MACHO project, 2474 LMC EBs found by the OGLE-II project (of which 1182 are also in the MACHO sample), 1380 in the Small Magellanic Cloud (SMC) found by the MACHO project, and 1317 SMC EBs found by the OGLE-II project (of which 677 are also in the MACHO sample); we also consider the EROS sample of 79 EBs in the bar of the LMC. Statistics of the phase differences between primary and secondary minima allow us to infer the statistics of orbital eccentricities within these samples. We confirm the well-known absence of eccentric orbit in close binary stars. We also find evidence for rapid circularization in longer period systems when one member evolves beyond the main sequence, as also found by previous studies.

  18. Possibility that the far ultraviolet excess in M31 is due to main sequence stars

    NASA Technical Reports Server (NTRS)

    Tinsley, B. M.

    1972-01-01

    The far ultraviolet excess in the central region of M31, observed by OAO-2, could be due to young main sequence stars. More than enough such stars are present in the model for the M31 inner disk population derived by Tinsley and Spinrad (1971) to match line- and color-indices at longer wavelengths. If the far ultraviolet radiation of typical galaxies arises from young stars, the theoretical ultraviolet background is enhanced greatly by evolutionary effects. For evolution at the rate of Tinsley and Spinrad's model for M31, or of Arnett's (1971) linear model for our galaxy, the enhancement is a factor 2.5 to 14, depending on the Hubble constant and the spectrum at wavelengths below 1700 A.

  19. Discovery of ZZ Cetis in detached white dwarf plus main-sequence binaries

    NASA Astrophysics Data System (ADS)

    Pyrzas, S.; Gänsicke, B. T.; Hermes, J. J.; Copperwheat, C. M.; Rebassa-Mansergas, A.; Dhillon, V. S.; Littlefair, S. P.; Marsh, T. R.; Parsons, S. G.; Savoury, C. D. J.; Schreiber, M. R.; Barros, S. C. C.; Bento, J.; Breedt, E.; Kerry, P.

    2015-02-01

    We present the first results of a dedicated search for pulsating white dwarfs (WDs) in detached WD plus main-sequence (MS) binaries. Candidate systems were selected from a catalogue of WD+MS binaries, based on the surface gravities and effective temperatures of the WDs. We observed a total of 26 systems using ULTRACAM mounted on ESO's 3.5 m New Technology Telescope at La Silla. Our photometric observations reveal pulsations in seven WDs of our sample, including the first pulsating WD with an MS companion in a post-common envelope (CE) binary, SDSS J1136+0409. Asteroseismology of these new pulsating systems will provide crucial insight into how binary interactions, particularly the CE phase, affect the internal structure and evolution of WDs. In addition, our observations have revealed the partially eclipsing nature of one of our targets, SDSS J1223-0056.

  20. New radio detections of early-type pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Skinner, Stephen L.; Brown, Alexander; Linsky, Jeffrey L.

    1990-01-01

    Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out.

  1. Theoretical properties of regularities in the oscillation spectra of A-F main-sequence stars

    NASA Astrophysics Data System (ADS)

    Suárez, Juan Carlos; Hernández, Antonio García; Moya, Andrés; Rodrigo, Carlos; Solano, Enrique; Garrido, Rafael; Rodón, José R.

    2014-02-01

    We study the theoretical properties of the regular spacings found in the oscillation spectra of δ Scuti stars. A linear relation between the large separation and the mean density is predicted to be found in the low-frequency domain (i.e. radial orders spanning from 1 to 8, approximately) of the main-sequence δ Scuti stars' oscillation spectrum. This implies an independent direct measure of the average density of δ Scuti stars, analogous to that of the Sun, and places tight constraints on the mode identification and hence on the stellar internal structure and dynamics, and allows a determination the radii of planets orbiting around δ Scuti stars with unprecedented precision. This opens the way for studying the evolution of regular patterns in pulsating stars, and its relation to stellar structure and evolution.

  2. ASCA X-ray observations of pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Skinner, S. L.; Walter, F. M.; Yamauchi, S.

    1996-01-01

    The results of recent Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray observations of two pre-main sequence stars are presented: the weak emission line T Tauri star HD 142361, and the Herbig Ae star HD 104237. The solid state imaging spectrometer spectra for HD 142361 shows a clear emission line from H-like Mg 7, and spectral fits reveal a multiple temperature plasma with a hot component of at least 16 MK. The spectra of HD 104237 show a complex temperature structure with the hottest plasma at temperatures of greater than 30 MK. It is concluded that mechanisms that predict only soft X-ray emission can be dismissed for Herbig Ae stars.

  3. Pre-main-sequence isochrones - III. The Cluster Collaboration isochrone server

    NASA Astrophysics Data System (ADS)

    Bell, Cameron P. M.; Rees, Jon M.; Naylor, Tim; Mayne, N. J.; Jeffries, R. D.; Mamajek, Eric E.; Rowe, John

    2014-12-01

    We present an isochrone server for semi-empirical pre-main-sequence model isochrones in the following systems: Johnson-Cousins, Sloan Digital Sky Survey, Two-Micron All-Sky Survey, Isaac Newton Telescope (INT) Wide-Field Camera and INT Photometric Hα Survey (IPHAS)/UV-Excess Survey (UVEX). The server can be accessed via the Cluster Collaboration webpage http://www.astro.ex.ac.uk/people/timn/isochrones/. To achieve this, we have used the observed colours of member stars in young clusters with well-established age, distance and reddening to create fiducial loci in the colour-magnitude diagram. These empirical sequences have been used to quantify the discrepancy between the models and data arising from uncertainties in both the interior and atmospheric models, resulting in tables of semi-empirical bolometric corrections (BCs) in the various photometric systems. The model isochrones made available through the server are based on existing stellar interior models coupled with our newly derived semi-empirical BCs. As part of this analysis, we also present new cluster parameters for both the Pleiades and Praesepe, yielding ages of 135^{+20}_{-11} and 665^{+14}_{-7} {Myr} as well as distances of 132 ± 2 and 184 ± 2 pc, respectively (statistical uncertainty only).

  4. The evolution of angular momentum among zero-age main-sequence solar-type stars

    NASA Technical Reports Server (NTRS)

    Soderblom, David R.; Stauffer, John R.; Macgregor, Keith B.; Jones, Burton F.

    1993-01-01

    We consider a survey of rotation among F, G, and K dwarfs of the Pleiades in the context of other young clusters (Alpha Persei and the Hyades) and pre-main-sequence (PMS) stars (in Taurus-Auriga and Orion) in order to examine how the angular momentum of a star like the sun evolves during its early life on the main sequence. The rotation of PMS stars can be evolved into distributions like those seen in the young clusters if there is only modest, rotation-independent angular momentum loss prior to the ZAMS. Even then, the ultrafast rotators (UFRs, or ZAMS G and K dwarfs with v sin i equal to or greater than 30 km/s) must owe their extra angular momentum to their conditions of formation and to different angular momentum loss rates above a threshold velocity, for it is unlikely that these stars had angular momentum added as they neared the ZAMS, nor can a spread in ages within a cluster account for the range of rotation seen. Only a fraction of solar-type stars are thus capable of becoming UFRs, and it is not a phase that all stars experience. Simple scaling relations (like the Skumanich relation) applied to the observed surface rotation rates of young solar-type stars cannot reproduce the way in which the Pleiades evolve into the Hyades. We argue that invoking internal differential rotation in these ZAMS stars can explain several aspects of the observations and thus can provide a consistent picture of ZAMS angular momentum evolution.

  5. The evolution of angular momentum among zero-age main-sequence solar-type stars

    NASA Technical Reports Server (NTRS)

    Soderblom, David R.; Stauffer, John R.; Macgregor, Keith B.; Jones, Burton F.

    1993-01-01

    We consider a survey of rotation among F, G, and K dwarfs of the Pleiades in the context of other young clusters (Alpha Persei and the Hyades) and pre-main-sequence (PMS) stars (in Taurus-Auriga and Orion) in order to examine how the angular momentum of a star like the sun evolves during its early life on the main sequence. The rotation of PMS stars can be evolved into distributions like those seen in the young clusters if there is only modest, rotation-independent angular momentum loss prior to the ZAMS. Even then, the ultrafast rotators (UFRs, or ZAMS G and K dwarfs with v sin i equal to or greater than 30 km/s) must owe their extra angular momentum to their conditions of formation and to different angular momentum loss rates above a threshold velocity, for it is unlikely that these stars had angular momentum added as they neared the ZAMS, nor can a spread in ages within a cluster account for the range of rotation seen. Only a fraction of solar-type stars are thus capable of becoming UFRs, and it is not a phase that all stars experience. Simple scaling relations (like the Skumanich relation) applied to the observed surface rotation rates of young solar-type stars cannot reproduce the way in which the Pleiades evolve into the Hyades. We argue that invoking internal differential rotation in these ZAMS stars can explain several aspects of the observations and thus can provide a consistent picture of ZAMS angular momentum evolution.

  6. Exozodiacal Dust Levels for Nearby Main-sequence Stars: A Survey with the Keck Interferometer Nuller

    NASA Astrophysics Data System (ADS)

    Millan-Gabet, R.; Serabyn, E.; Mennesson, B.; Traub, W. A.; Barry, R. K.; Danchi, W. C.; Kuchner, M.; Stark, C. C.; Ragland, S.; Hrynevych, M.; Woillez, J.; Stapelfeldt, K.; Bryden, G.; Colavita, M. M.; Booth, A. J.

    2011-06-01

    The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main-sequence stars in the mid-infrared, in order to assess the prevalence of warm circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN measures circumstellar emission by spatially blocking the star but transmitting the circumstellar flux in a region typically 0.1-4 AU from the star. We find one significant detection (η Crv), two marginal detections (γ Oph and α Aql), and 22 clear non-detections. Using a model of our own solar system's zodiacal cloud, scaled to the luminosity of each target star, we estimate the equivalent number of target zodis needed to match our observations. Our three zodi detections are η Crv (1250 ± 260), γ Oph (200 ± 80), and α Aql (600 ± 200), where the uncertainties are 1σ. The 22 non-detected targets have an ensemble weighted average consistent with zero, with an average individual uncertainty of 160 zodis (1σ). These measurements represent the best limits to date on exozodi levels for a sample of nearby main-sequence stars. A statistical analysis of the population of 23 stars not previously known to contain circumstellar dust (excluding η Crv and γ Oph) suggests that, if the measurement errors are uncorrelated (for which we provide evidence) and if these 23 stars are representative of a single class with respect to the level of exozodi brightness, the mean exozodi level for the class is <150 zodis (3σ upper limit, corresponding to 99% confidence under the additional assumption that the measurement errors are Gaussian). We also demonstrate that this conclusion is largely independent of the shape and mean level of the (unknown) true underlying exozodi distribution.

  7. The slowly pulsating B-star 18 Pegasi: A testbed for upper main sequence stellar evolution

    NASA Astrophysics Data System (ADS)

    Irrgang, A.; Desphande, A.; Moehler, S.; Mugrauer, M.; Janousch, D.

    2016-06-01

    The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Based on a photometric and preliminary asteroseismic analysis, we show that the mid B-type giant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric orbit that is greater than 6 years. Further spectroscopic and photometric monitoring and a sophisticated asteroseismic investigation are required to exploit the full potential of this star as a benchmark object for stellar evolution theory. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 265.C-5038(A), 069.C-0263(A), and 073.D-0024(A). Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), proposals H2005-2.2-016 and H2015-3.5-008. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, proposal W15BN015. Based on observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.

  8. Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases

    NASA Astrophysics Data System (ADS)

    Pizzolato, N.; Maggio, A.; Sciortino, S.

    2000-09-01

    We have investigated the variation of coronal X-ray emission during early post-main-sequence phases for a sample of 120 late-type stars within 100 pc, and with estimated masses in the range 1-3 Msun, based on Hipparcos parallaxes and recent evolutionary models. These stars were observed with the ROSAT/PSPC, and the data processed with the Palermo-CfA pipeline, including detection and evaluation of X-ray fluxes (or upper limits) by means of a wavelet transform algorithm. We have studied the evolutionary history of X-ray luminosity and surface flux for stars in selected mass ranges, including stars with inactive A-type progenitors on the main sequence and lower mass solar-type stars. Our stellar sample suggests a trend of increasing X-ray emission level with age for stars with masses M > 1.5 Msun, and a decline for lower-mass stars. A similar behavior holds for the average coronal temperature, which follows a power-law correlation with the X-ray luminosity, independently of their mass and evolutionary state. We have also studied the relationship between X-ray luminosity and surface rotation rate for stars in the same mass ranges, and how this relationships departs from the Lx ~ vrot2 law followed by main-sequence stars. Our results are interpreted in terms of a magnetic dynamo whose efficiency depends on the stellar evolutionary state through the mass-dependent changes of the stellar internal structure, including the properties of envelope convection and the internal rotation profile.

  9. LESSONS IN DE NOVO PEPTIDE SEQUENCING BY TANDEM MASS SPECTROMETRY

    PubMed Central

    Medzihradszky, Katalin F.; Chalkley, Robert J.

    2015-01-01

    Mass spectrometry has become the method of choice for the qualitative and quantitative characterization of protein mixtures isolated from all kinds of living organisms. The raw data in these studies are MS/MS spectra, usually of peptides produced by proteolytic digestion of a protein. These spectra are “translated” into peptide sequences, normally with the help of various search engines. Data acquisition and interpretation have both been automated, and most researchers look only at the summary of the identifications without ever viewing the underlying raw data used for assignments. Automated analysis of data is essential due to the volume produced. However, being familiar with the finer intricacies of peptide fragmentation processes, and experiencing the difficulties of manual data interpretation allow a researcher to be able to more critically evaluate key results, particularly because there are many known rules of peptide fragmentation that are not incorporated into search engine scoring. Since the most commonly used MS/MS activation method is collision-induced dissociation (CID), in this article we present a brief review of the history of peptide CID analysis. Next, we provide a detailed tutorial on how to determine peptide sequences from CID data. Although the focus of the tutorial is de novo sequencing, the lessons learned and resources supplied are useful for data interpretation in general. PMID:25667941

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

    SciTech Connect

    Goudfrooij, Paul; Kozhurina-Platais, Vera; Kalirai, Jason S.; Correnti, Matteo E-mail: verap@stsci.edu E-mail: correnti@stsci.edu; and others

    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 fraction 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.

  11. Return to [Log-]Normalcy: Rethinking Quenching, The Star Formation Main Sequence, and Perhaps Much More

    NASA Astrophysics Data System (ADS)

    Abramson, Louis E.; Gladders, Michael D.; Dressler, Alan; Oemler, Augustus, Jr.; Poggianti, Bianca; Vulcani, Benedetta

    2016-11-01

    Knowledge of galaxy evolution rests on cross-sectional observations of different objects at different times. Understanding of galaxy evolution rests on longitudinal interpretations of how these data relate to individual objects moving through time. The connection between the two is often assumed to be clear, but we use a simple “physics-free” model to show that it is not and that exploring its nuances can yield new insights. Comprising nothing more than 2094 loosely constrained lognormal star formation histories (SFHs), the model faithfully reproduces the following data it was not designed to match: stellar mass functions at z≤slant 8; the slope of the star formation rate/stellar mass relation (the SFR “Main Sequence”) at z≤slant 6; the mean {sSFR}(\\equiv {SFR}/{M}* ) of low-mass galaxies at z≤slant 7; “fast-” and “slow-track” quenching; downsizing; and a correlation between formation timescale and {sSFR}({M}* ,t) similar to results from simulations that provides a natural connection to bulge growth. We take these findings—which suggest that quenching is the natural downturn of all SFHs affecting galaxies at rates/times correlated with their densities—to mean that: (1) models in which galaxies are diversified on Hubble timescales by something like initial conditions rival the dominant grow-and-quench framework as good descriptions of the data; or (2) absent spatial information, many metrics of galaxy evolution are too undiscriminating—if not inherently misleading—to confirm a unique explanation. We outline future tests of our model but stress that, even if ultimately incorrect, it illustrates how exploring different paradigms can aid learning and, we hope, more detailed modeling efforts.

  12. Molecules and dust in the Large Magellanic Cloud: new colour classifications for post-Main-Sequence stars

    NASA Astrophysics Data System (ADS)

    Markwick-Kemper, Ciska; Leisenring, Jarron; Meixner, Margaret; van Dyk, Schuyler; Szczerba, Ryszard

    In the Large Magellanic Cloud (LMC), as in the Milky Way, dust formation predominantly occurs in the circumstellar environments of evolved stars. The process of dust condensation is not fully understood, and investigating the dust condensation sequence in the low metallicity environment of the LMC (about half of the solar metallicity), may yield additional insights in the dust condensation process. Topics to be studied include the final condensation products, the correlation of the condensation sequence with evolutionary status of the star, degree of crystallinity of the silicates and ratio of carbon-rich dust producing stars. The composition and properties of dust are most easily studied using infrared spectroscopy, and using the high sensitivity of the Infrared Spectrograph (IRS) on board of Spitzer, we were able to observe the thermal emission from circumstellar dust of these stars individually. A sample of 63 post-Main-Sequence stars were selected, using their 2MASS/MSX colours (Egan et al. 2001). We aimed to cover all post-Main-Sequence evolutionary stages, to make an inventory of the dust condensation products, while we placed a certain emphasis on oxygen-rich AGB stars with a intermediate mass-loss rate, to study the existence of a threshold mass-loss rate above which crystalline silicates are observed (Kemper et al. 2001). Here we will present the observed spectra, along with their spectral classification. We find that a large fraction of the stars we observed exhibit spectral features of carbon-rich dust and molecules, such as SiC, C2H2 and MgS. In fact we find that many of these stars are previously classified as oxygen-rich AGB stars, or as OH/IR stars based on their NIR/MIR colours (Egan et al. 2001). These colours are determined for Galactic samples, while in the LMC sample, stars with a carbon-rich chemistry in their outflows occupy a much larger region of the various colour-colour diagrams. In addition, a large fraction of the sample show amorphous

  13. An Analysis of the Population of Extended Main Sequence Turn-off Clusters in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Bastian, Nate

    2016-12-01

    We combine a number of recent studies of the extended main-sequence turn-off (eMSTO) phenomenon in intermediate age stellar (1-2 Gyr) clusters in the Large Magellanic Cloud (LMC) in order to investigate its origin. By employing the largest sample of eMSTO LMC clusters so far used, we show that cluster core radii, masses, and dynamical state are not related to the genesis of eMSTOs. Indeed, clusters in our sample have core radii, masses and age-relaxation time ratios in the range ≈2-6 pc, 3.35-5.50 (log(Mcls/M⊙) and 0.2-8.0, respectively. These results imply that the eMSTO phenomenon is not caused by actual age spreads within the clusters. Furthermore, we confirm from a larger cluster sample recent results including young eMSTO LMC clusters, that the full width at half-maximum at the MSTOs correlates most strongly with cluster age, suggesting that a stellar evolutionary effect is the underlying cause.

  14. Post-main-sequence and POST red giant branch variables with pulsation periods less than one day

    NASA Astrophysics Data System (ADS)

    Eggen, Olin J.

    1994-06-01

    Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5 to 1 solar mass) pulsators are discussed on the basis of four color and H beta light curves published elsewhere. The post-main-sequence variables, called ultrashort period cepheid (USPC) (delta Sct), pulsate in the fundamental and first harmonic modes of radial pulsation and, in many cases, in nonradial modes. The variables for which photometry allows accurate, luminosity estimates and are known to pulsate simultaneously in the fundamental and first harmonic or in the fundamental mode alone, define a PL relation (MV = -2.80 log P - 0.60, fundamental). It is notable that the slope of this relation is in the range of slopes found for classical cepheids. Accurate V photometry is lacking for many of the variables known as 'anomalous cepheids', but the available data divide them into low mass, pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC (delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, for which accurate photometry is available, give remarkably consistent moduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for the clusters, in which they are blue stragglers similar to SX Phe in Kapteyn's star group. The assumption that the four post-giant branch variables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn's star group and RR Lyr in the Groombridge 1830 group, are physical members of these groups and share their V-velocities, leads to a calibration of the photometry for the derivation of reddening, luminosity, and heavy element abundance of 45 field variables. The resulting reddenings are consistent with values obtained by other methods and the metallicities are consistent with the most accurately available spectroscopic determinations of delta S and of Ca II K. The luminosities of the bulk of the variables confirm Sandage's (1993) relation between MV and (Fe/H). Four or five of the field variables are probably binary, including BB Vir

  15. Pulsating stars in NGC 6231. Frequency analysis and photometric mode identification near the main-sequence

    NASA Astrophysics Data System (ADS)

    Meingast, Stefan; Handler, Gerald; Shobbrook, Robert R.

    2013-11-01

    binaries, one new SPB variable, one possible pre-main-sequence pulsator, and another new variable star for which we cannot present a classification. With more than 20 main-sequence pulsators of spectral type B, NGC 6231 becomes the open cluster with the largest population of such pulsating stars known. Appendix A is available in electronic form at http://www.aanda.org

  16. The ALMA Redshift 4 Survey (AR4S). I. The massive end of the z = 4 main sequence of galaxies

    NASA Astrophysics Data System (ADS)

    Schreiber, C.; Pannella, M.; Leiton, R.; Elbaz, D.; Wang, T.; Okumura, K.; Labbé, I.

    2017-03-01

    We introduce the ALMA Redshift 4 Survey (AR4S), a systematic ALMA survey of all the known galaxies with stellar mass (M∗) larger than 5 × 1010M⊙ at 3.5 main sequence of star-forming galaxies was already in place at z = 4, at least among massive galaxies. These new constraints on the properties of the main sequence are in good agreement with the latest predictions from numerical simulations, and suggest that the bulk of star formation in galaxies is driven by the same mechanism from z = 4 to the present day, that is, over at least 90% of the cosmic history. We also discuss the consequences of our results on the population of early quiescent galaxies. This paper is part of a series that will employ these new ALMA observations to explore the star formation and dust properties of the massive end of the z = 4 galaxy population.

  17. CS 22873-139: A very metal-poor main-sequence spectroscopic binary with colors indicative of intermediate age

    NASA Astrophysics Data System (ADS)

    Preston, George W.

    1994-12-01

    CS 22873-139, a metal-deficient ((Fe/H) = -3.1), high-velocity (Vrad = +243 km/s) star with observed UBV colors (B-V = 0.37, U-B = -0.22) that locate it near the main-sequence turnoff of an old metal-poor population (Preston et al. (1991); Beers et al. (1992)), is, in fact, a double-lined spectroscopic binary with a period of 19.16 days, eccentricity e = 0.26, and a mass ratio of approximately 0.88. The observed colors, corrected for reddening, can be matched by those for a family of artificial binaries constructed by use of colors and luminosities taken from isochrones for ages between 3 and 13 Gy, but the strengths of metal lines in the primary and secondary spectra require that the age of the system be less than approximately 8 Gy. The inferred unreddened colors of the primary, (B-V)0,p = 0.30, (U-B)0,p = -0.19, lie blueward of any globular cluster turnoff and near the low-abundance (upper) U-B boundary of BMP stars in the UBV two-color diagram, as discussed by Preston et al. (1994). Were the primary product of binary merger in an initial triple star system, Harrington's (1977) stability criterion requires for the initial close binary a1 less than 5.2 solar radii and P less than 1.5 days. According to Vilhu (1982) such a system will merge in about 109 years, a time much shorter than the main-sequence age deduced for this system, so even if binary merger had taken place the conclusion that CS 22873-139 must be a relatively young metal-poor star is preserved.

  18. First firm spectral classification of an early-B pre-main-sequence star: B275 in M 17

    NASA Astrophysics Data System (ADS)

    Ochsendorf, B. B.; Ellerbroek, L. E.; Chini, R.; Hartoog, O. E.; Hoffmeister, V.; Waters, L. B. F. M.; Kaper, L.

    2011-12-01

    The optical to near-infrared (300 - 2500 nm) spectrum of the candidate massive young stellar object (YSO) B275, embedded in the star-forming region M 17, has been observed with X-shooter on the ESO Very Large Telescope. The spectrum includes both photospheric absorption lines and emission features (H and Ca ii triplet emission lines, 1st and 2nd overtone CO bandhead emission), as well as an infrared excess indicating the presence of a (flaring) circumstellar disk. The strongest emission lines are double-peaked with a peak separation ranging between 70 and 105 km s-1, and they provide information on the physical structure of the disk. The underlying photospheric spectrum is classified as B6-B7, which is significantly cooler than a previous estimate based on modeling of the spectral energy distribution. This discrepancy is solved by allowing for a larger stellar radius (i.e. a bloated star) and thus positioning the star above the main sequence. This constitutes the first firm spectral classification of an early-B pre-main-sequence (PMS) star. We discuss the position of B275 in the Hertzsprung-Russell diagram in terms of PMS evolution. Although the position is consistent with PMS tracks of heavily accreting protostars (Ṁacc ≳ 10-5 M⊙ yr-1), the fact that the photosphere of the object is detectable suggests that the current mass-accretion rate is not very high. Based on observations performed with the ESO Very Large Telescope on Cerro Paranal, Chile, as part of the X-shooter Science Verification program 60.A-9402(A).

  19. 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.

  20. Dynamical Evolution of Short Period Planets in the Multiple Systems during the Host-Stars Contraction to the Main Sequence

    NASA Astrophysics Data System (ADS)

    Nagasawa, M.; Lin, D. N. C.

    2005-05-01

    We study the dynamical evolution of short-period extrasolar planets orbiting young host stars with other eccentric planets. During the fast stages of planet formation, the host-stars are in pre-main sequence stage and are surrounded by protoplanetary disks. As the host-stars evolve onto to the main sequence, the disks are depleted and the stellar radii and the speed of rotation change. All these effects influence the evolution of the orbits of short-period planets. In addition, when the short period planets whose period is less than 6 days have large eccentricities, the tidal dissipation of energy during the circularization would induce interior heating, inflation, Roche lobe overflow, and ultimately mass losses. We study the necessary conditions for the survival of hot Jupiters including the potential of the evolving disk, the potential due to the flattening of the star produced by the increasing stellar rotation, and the post-Newtonian potential of the host star. We find that the short-period planets orbiting around young stellar objects whose spin periods are longer than a few days may be highly vulnerable to the dissipation of the disk and evolution of the stars. Based on these results, we suggest that fast rotators have more short-period planets in multiple systems than slow rotating stars. This work was partly performed while MN held a JSPS Postdoctoral Fellowship for Research Abroad (Heisei 14). This work is supported in part by NASA through grant NAG5-11779 to D. N. C. Lin.

  1. On using occultation and microlensing to find white dwarf and planetary companions of main sequence stars in tranit searches.

    NASA Astrophysics Data System (ADS)

    Agol, E.; Farmer, A.; Mandel, K.

    2002-12-01

    We will prove a gravitational lensing theorem: the magnification of a large source of uniform brightness by a small foreground point-mass lens is M=1+(2RE2-R_L^2)/R_S^2, where RS is the radius of the source and RE and RL are the Einstein radius and size of the lens projected into the source plane; this provides an accurate approximation to the exact magnification for RL,R_E << RS. Remarkably, this result is independent of the shape of the source or position of the lens (except near the edges). We show that this formula can be generalized to include limb-darkening of a circular source by simply inserting the surface-brightness at the position of the foreground object (divided by the average surface-brightness of the star). We use this theorem to compute transit lightcurves in binaries for which the foreground star or planet has a size and Einstein radius much smaller than the background star. White dwarf stars in binaries with semi-major axes of 0.1 AU have a size comparable to their Einstein radii. Thus, white dwarfs orbiting main-sequence stars can show either brightening or eclipse. Since white dwarfs are similar in size to terrestrial planets, we predict how many white dwarf-main sequence binaries might be found in transit searches for terrestrial type planets such as Kepler and Eddington. We estimate that dozens of systems may be found, although the precise number will depend on the properties of low-level variability of the main-sequence stars in these binaries. We also apply these results to planetary transits (RE ~ 0), demonstrating that this simple approximation accurately describes the exact limb-darkened transit lightcurves. Using the HST lightcurve of HD 209458 from Brown et al. (2001), the ratio of the planet radius to stellar radius is measured to be Rp/R_*=0.1207+/- 0.0003 , marginalized over the limb-darkening.

  2. Nearly-uniform internal rotation of solar-like main sequence stars revealed by asteroseismology and spectroscopic measurements

    NASA Astrophysics Data System (ADS)

    Benomar, Othman Michel; Takata, Masao; Shibahashi, Hiromoto; Ceillier, Tugdual; Garcia, Rafael

    2015-08-01

    Stellar pulsations, which can be trapped acoustic waves (p modes), internal gravity waves (g modes) or a mixture of two, have frequencies that depend on the properties of the stellar interior, such as the internal rotation.Helioseismology extensively exploited these pulsations and, by the means of seismic inversion, has revealed a nearly uniform rotation profile, with variations that do not exceed 30% in the radial direction (e.g. Thompson et al. 2003). To conciliate models with observations, an efficient mechanism of transport of angular momentum from the core to the envelope is required.The necessity of an efficient angular momentum transport was also revealed on two main-sequence stars showing p modes and g modes (Kurtz et al. 2014, Saio et al. 2015) and on several evolved stars solar-like showing mixed modes (Deheuvels et al. 2012, 2014).However, the number of stars with a measured internal rotation structure is still limited. For low-mass main-sequence stars showing solar-like oscillations, the measure of the internal rotation profile is limited because only the low degree p modes can be observed by unresolved photometry.Yet, by comparing the average surface rotation with the average of the internal rotation, it is possible to evaluate the degree of differential rotation between deep layers and the surface. The surface rotation can be derived by spectroscopic vsin(i) or by the periodic luminosity variation due to surface spots, while the average internal rotation is determined by asteroseismology, using the so-called rotational splitting.We performed this comparison on 22 solar-like stars of the main sequence. We show that the rotation at the surface and in the interior are generally close to each other. For 10 stars, the difference is clearly too small to be explained by simple evolutionary models that assume local conservation of angular momentum. Furthermore, by adopting a simple two-zone model, we show that 20 out of the 22 stars have a rotation rate in

  3. Post-common envelope binaries from SDSS - VII. A catalogue of white dwarf-main sequence binaries

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Gänsicke, B. T.; Schreiber, M. R.; Koester, D.; Rodríguez-Gil, P.

    2010-02-01

    We present a catalogue of 1602 white-dwarf-main-sequence (WDMS) binaries from the spectroscopic Sloan Digital Sky Survey Data Release 6 (SDSS DR6). Among these, we identify 440 as new WDMS binaries. We select WDMS binary candidates by template fitting all 1.27 million DR6 spectra, using combined constraints in both χ2 and signal-to-noise ratio. In addition, we use Galaxy Evolution Explorer (GALEX) and UKIRT Infrared Sky Survey (UKIDSS) magnitudes to search for objects in which one of the two components dominates the SDSS spectrum. We use a decomposition/fitting technique to measure the effective temperatures, surface gravities, masses and distances to the white dwarfs, as well as the spectral types and distances to the companions in our catalogue. Distributions and density maps obtained from these stellar parameters are then used to study both the general properties and the selection effects of WDMS binaries in the SDSS. A comparison between the distances measured to the white dwarfs and the main-sequence companions shows dsec > dwd for approximately one-fifth of the systems, a tendency already found in our previous work. The hypothesis that magnetic activity raises the temperature of the inter-spot regions in active stars that are heavily covered by cool spots, leading to a bluer optical colour compared to inactive stars, remains the best explanation for this behaviour. We also make use of SDSS-GALEX-UKIDSS magnitudes to investigate the distribution of WDMS binaries, as well as their white-dwarf effective temperatures and companion star spectral types, in ultraviolet to infrared colour space. We show that WDMS binaries can be very efficiently separated from single main-sequence stars and white dwarfs when using a combined ultraviolet, optical and infrared colour selection. Finally, we also provide radial velocities for 1068 systems measured from the NaI λλ8183.27, 8194.81 absorption doublet and/or the Hα emission line. Among the systems with multiple SDSS

  4. A search for pre-main sequence stars in the high-latitude molecular clouds. II - A survey of the Einstein database

    NASA Technical Reports Server (NTRS)

    Caillault, Jean-Pierre; Magnani, Loris

    1990-01-01

    The preliminary results are reported of a survey of every EINSTEIN image which overlaps any high-latitude molecular cloud in a search for X-ray emitting pre-main sequence stars. This survey, together with complementary KPNO and IRAS data, will allow the determination of how prevalent low mass star formation is in these clouds in general and, particularly, in the translucent molecular clouds.

  5. A HIGHLY CONSISTENT FRAMEWORK FOR THE EVOLUTION OF THE STAR-FORMING ''MAIN SEQUENCE'' FROM z ∼ 0-6

    SciTech Connect

    Speagle, J. S.; Steinhardt, C. L.; Silverman, J. D.; Capak, P. L.

    2014-10-01

    Using a compilation of 25 studies from the literature, we investigate the evolution of the star-forming galaxy (SFG) main sequence (MS) in stellar mass and star formation rate (SFR) out to z ∼ 6. After converting all observations to a common set of calibrations, we find a remarkable consensus among MS observations (∼0.1 dex 1σ interpublication scatter). By fitting for time evolution of the MS in bins of constant mass, we deconvolve the observed scatter about the MS within each observed redshift bin. After accounting for observed scatter between different SFR indicators, we find the width of the MS distribution is ∼0.2 dex and remains constant over cosmic time. Our best fits indicate the slope of the MS is likely time-dependent, with our best-fit log SFR(M {sub *}, t) = (0.84 ± 0.02 – 0.026 ± 0.003 × t)log M {sub *} – (6.51 ± 0.24 – 0.11 ± 0.03 × t), where t is the age of the universe in Gyr. We use our fits to create empirical evolutionary tracks in order to constrain MS galaxy star formation histories (SFHs), finding that (1) the most accurate representations of MS SFHs are given by delayed-τ models, (2) the decline in fractional stellar mass growth for a ''typical'' MS galaxy today is approximately linear for most of its lifetime, and (3) scatter about the MS can be generated by galaxies evolving along identical evolutionary tracks assuming an initial 1σ spread in formation times of ∼1.4 Gyr.

  6. Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence.

    PubMed

    Hallinan, G; Littlefair, S P; Cotter, G; Bourke, S; Harding, L K; Pineda, J S; Butler, R P; Golden, A; Basri, G; Doyle, J G; Kao, M M; Berdyugina, S V; Kuznetsov, A; Rupen, M P; Antonova, A

    2015-07-30

    Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons, as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere. Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs.

  7. THE MULTIPLE PRE-MAIN-SEQUENCE SYSTEM HBC 515 IN L1622

    SciTech Connect

    Reipurth, Bo; Aspin, Colin; Herbig, George

    2010-04-15

    The bright pre-main-sequence star HBC 515 (HD 288313) located in the L1622 cometary cloud in Orion has been studied extensively with optical/infrared imaging and ultraviolet/optical/infrared spectroscopy. The spectra indicate that HBC 515 is a weakline T Tauri star (TTS) of spectral type K2V. Adaptive optics imaging in the K band reveals that HBC 515 is a binary with two equally bright components separated by 0.''5. A very faint third component is found 5'' to the northwest. Spitzer IRAC and MIPS observations show that at mid-infrared wavelengths this third source dominates the system, suggesting that it is a protostar still embedded in the nascent cloud of HBC 515. The close association of a weakline TTS with a newborn protostar in a multiple system is noteworthy. Two nearby TTSs are likely associated with the HBC 515 multiple system, and the dynamical evolution of the complex that would lead to such a configuration is considered.

  8. Absolute Ages and Distances of 22 GCs Using Monte Carlo Main-sequence Fitting

    NASA Astrophysics Data System (ADS)

    O'Malley, Erin M.; Gilligan, Christina; Chaboyer, Brian

    2017-04-01

    The recent Gaia Data Release 1 of stellar parallaxes provides ample opportunity to find metal-poor main-sequence stars with precise parallaxes. We select 21 such stars with parallax uncertainties better than σ π /π ≤ 0.10 and accurate abundance determinations suitable for testing metal-poor stellar evolution models and determining the distance to Galactic globular clusters (GCs). A Monte Carlo analysis was used, taking into account uncertainties in the model construction parameters, to generate stellar models and isochrones to fit to the calibration stars. The isochrones that fit the calibration stars best were then used to determine the distances and ages of 22 GCs with metallicities ranging from -2.4 dex to -0.7 dex. We find distances with an average uncertainty of 0.15 mag and absolute ages ranging from 10.8 to 13.6 Gyr with an average uncertainty of 1.6 Gyr. Using literature proper motion data, we calculate orbits for the clusters, finding six that reside within the Galactic disk/bulge, while the rest are considered halo clusters. We find no strong evidence for a relationship between age and Galactocentric distance, but we do find a decreasing age-[Fe/H] relation.

  9. THE EVOLVED MAIN-SEQUENCE CHANNEL: HST AND LBT OBSERVATIONS OF CSS 120422:111127+571239

    SciTech Connect

    Kennedy, M.; Callanan, P.; Garnavich, P.; Littlefield, C.; Szkody, P.; Pogge, R.

    2015-12-20

    The “evolved main-sequence (EMS)” channel is thought to contribute significantly to the population of AM CVn-type systems in the Galaxy, and also to the number of cataclysmic variables (CVs) detected below the period minimum for hydrogen rich systems. CSS 120422:J111127+571239 was discovered by the Catalina Sky Survey in 2012 April. Its period was found to be 56 minutes, well below the minimum, and the optical spectrum is clearly depleted in hydrogen relative to helium, but still has two orders of magnitude more hydrogen than AM CVn stars. Doppler tomography of the Hα line hinted at a spiral structure existing in the disk. Here we present spectroscopy of CSS 120422:J111127+571239 using the Cosmic Origins Spectrograph FUV instrument on the Hubble Space Telescope and using the MODS spectrograph on the Large Binocular Telescope. The UV spectrum shows Si iv, N v, and He ii, but no detectable C iv. The anomalous nitrogen/carbon ratio is seen in a small number of other CVs and confirms a unique binary evolution. We also present and compare the optical spectrum of V418 Ser and advocate that it is also an EMS system.

  10. What Happens to Am Stars After They Leave the Main Sequence?

    NASA Astrophysics Data System (ADS)

    Abt, Helmut A.

    2017-04-01

    The Am, or “Metallic-line,” stars have too strong line strengths of the iron peak elements for their temperatures and too weak He, Ca, etc. Michaud showed that the A4-F2 V stars, which occur in the same area of the main sequence as the Am stars, have radiative zones below their photospheres where diffusion acts to push metals upward into the photospheres by radiation pressure and lets Ca, etc. sink downward, but only if the stars are slow rotators. Slow rotation can be caused by the formation of disks or by tidal interactions in binaries. The Am stars are rich in binaries with P < 100 days; the rapidly rotation A4-F2 V stars have no such binaries. The special peculiarities do not occur in stars above the luminosity class V stars, except among the ρ Puppis stars, so the radiative zones must disappear and the atmospheres become well mixed with the interiors. The suggestion that the ρ Puppis stars are the descendents of the Am stars fails because there are too few ρ Puppis stars by a factor of about 100. Then by searching for binaries among evolved stars I conclude that the Am stars plus A4-F2 V normal stars evolve into A7-F9 IV stars and then into F2-F9 (or later) III stars with normal abundances.

  11. An Ultraviolet Study of Non-periodic Variability in Accreting Pre-Main Sequence Stars: UXors

    NASA Astrophysics Data System (ADS)

    Eaton, N. L.; Herbst, W.

    1994-05-01

    Many earlier type (K0 or hotter) pre-main sequence stars are known to occasionally and irregularly fade by as much as 2-3 magnitudes in V. Such excursions occur on timescales of ten to forty days. They include both G-type T Tauri stars and Herbig Ae/Be stars. We propose UX Ori as a prototype for this class of variable stars and refer to them as UXors. We have used archival IUE spectra and a catalog of UBVRI photometry to study the variations of 5 such objects, namely: RY Lup, RY Tau, CO Ori, BF Ori, and UX Ori. The leading hypothesis for explaining their behavior is variable circumstellar obscuration. Relationships between UV spectral line fluxes and equivalent widths and V magnitude are found and displayed. Some shell features in UX Ori and BF Ori switch from absorption to emission during the minima. The equivalent width of these (emission) features [FeII(1,62,63) and MgII(1)] increases as the star fades. Spectral energy distributions (SEDs) covering the interval of 1200 to 8900 angstroms were constructed for several stars at different V magnitude light levels. A strong depression in the SED around 2200 angstroms, caused by iron lines is quite noticeable in UX Ori and BF Ori when the stars are bright. The source and location of the variable obscuring material is discussed.

  12. An Ultraviolet and Optical Study of Accreting Pre-Main-Sequence Stars: Uxors

    NASA Astrophysics Data System (ADS)

    Eaton, Nancy L.; Herbst, William

    1995-11-01

    UX Ori stars (UXors) are pre-main-sequence stars of both the Herbig Ae/Be and T Tauri type which show aperiodic eclipse-like minima. Their variations have been attributed to occultations by circumstellar material. We use archival IUE spectra and a catalog of UBVRI photometry to study the variations of five such objects, namely, RY Lup, RY Tau, CO Ori, BF Ori, and UX Ori. Relationships between UV spectral line fluxes and equivalent widths and V magnitude are found and displayed. Some shell features in UX Ori and BF Ori switch from absorption to emission during the minima. The equivalent widths of the emission features increase as the star fades. Spectral energy distributions (SEDs) covering the interval of 1200-8900 Å were constructed for several stars at different V magnitude light levels. A strong depression in the SED around 2400 Å, caused primarily by iron absorption lines (the "iron curtain") is quite noticeable in UX Ori and BF Ori when the stars are bright, but is diminished or absent when faint. The data are discussed in the context of the variable circumstellar obscuration hypothesis and provide some additional support for it.

  13. A Radial Velocity Study of Hot Subdwarf B Stars with Cool Main Sequence Companions

    NASA Astrophysics Data System (ADS)

    Barlow, Brad; Wade, R. A.; Liss, S. E.; Stark, M. A.

    2012-01-01

    Many hot subdwarf B (sdB) stars show composite spectra and energy distributions indicative of G- or K-type main sequence companions. Binary population synthesis (BPS) models demonstrate such systems can be formed by Roche lobe overflow but disagree on whether the resulting orbital periods will be long (years) or short (days). Few studies have been carried out to assess the orbital parameters of these composite binaries; what little observations there are suggest the periods are long. To help address this problem, we selected fifteen moderately-bright (V 13) sdB stars with composite spectra for synoptic radial velocity (RV) monitoring. From January 2005 to July 2008, we acquired between 4 and 14 observations of each target using the bench-mounted Medium Resolution Spectrograph on the Hobby-Eberly Telescope. Cross-correlation techniques were used to measure RVs from the cool companion lines with 700 m/s precision. Here we present RV measurements and orbital parameter estimates (when appropriate) for all systems in our sample and discuss the constraints they place on BPS models. Preliminary measurements of PG 1701+359, the most well-studied object in our sample, indicate the orbit has neither a short period nor a high velocity amplitude. This material is based upon work supported by the National Science Foundation under Grant No. AST-0908642.

  14. Near-uniform internal rotation of the main-sequence γ Doradus pulsator KIC 7661054

    NASA Astrophysics Data System (ADS)

    Murphy, Simon J.; Fossati, Luca; Bedding, Timothy R.; Saio, Hideyuki; Kurtz, Donald W.; Grassitelli, Luca; Wang, Edric S.

    2016-06-01

    We used Kepler photometry to determine the internal rotation rate of KIC 7661054, a chemically normal γ Dor star on the main sequence at spectral type F2.5 V. The core rotation period of 27.25 ± 0.06 d is obtained from the rotational splittings of a series of dipole g modes. The surface rotation period is calculated from a spectroscopic projected rotation velocity and a stellar radius computed from models. Literature data, obtained without inclusion of macroturbulence as a line-broadening mechanism, imply that the surface rotates much more quickly than the core, while our detailed analysis suggests that the surface may rotate slightly more quickly than the core and that the rotation profile is uniform within the 1σ uncertainties. We discuss the pitfalls associated with the determination of surface rotation rates of slow rotators from spectroscopy in the absence of asteroseismic constraints. A broad signal is observed at low frequency, which we show cannot be attributed to rotation, contrary to previous suggestions concerning the origin of such signals.

  15. THE ORIGIN OF HVS17, AN UNBOUND MAIN SEQUENCE B STAR AT 50 kpc

    SciTech Connect

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Cohen, Judith G. E-mail: mgeller@cfa.harvard.edu E-mail: jlc@astro.caltech.edu

    2013-09-20

    We analyze Keck Echellette Spectrograph and Imager spectroscopy of HVS17, a B-type star traveling with a Galactic rest frame radial velocity of +445 km s{sup –1} in the outer halo of the Milky Way. HVS17 has the projected rotation of a main sequence B star and is chemically peculiar, with solar iron abundance and sub-solar alpha abundance. Comparing measured T{sub eff} and log g with stellar evolution tracks implies that HVS17 is a 3.91 ± 0.09 M{sub ☉}, 153 ± 9 Myr old star at a Galactocentric distance of r = 48.5 ± 4.6 kpc. The time between its formation and ejection significantly exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk runaway scenario involving massive stars. The observations are consistent, on the other hand, with a hypervelocity star ejection from the Galactic center. We show that Gaia proper motion measurements will easily discriminate between a disk and Galactic center origin, thus allowing us to use HVS17 as a test particle to probe the shape of the Milky Way's dark matter halo.

  16. Magnetic Activity Analysis for a Sample of G-type Main Sequence Kepler Targets

    NASA Astrophysics Data System (ADS)

    Mehrabi, Ahmad; He, Han; Khosroshahi, Habib

    2017-01-01

    The variation of a stellar light curve owing to rotational modulation by magnetic features (starspots and faculae) on the star’s surface can be used to investigate the magnetic properties of the host star. In this paper, we use the periodicity and magnitude of the light-curve variation as two proxies to study the stellar magnetic properties for a large sample of G-type main sequence Kepler targets, for which the rotation periods were recently determined. By analyzing the correlation between the two magnetic proxies, it is found that: (1) the two proxies are positively correlated for most of the stars in our sample, and the percentages of negative, zero, and positive correlations are 4.27%, 6.81%, and 88.91%, respectively; (2) negative correlation stars cannot have a large magnitude of light-curve variation; and (3) with the increase of rotation period, the relative number of positive correlation stars decreases and the negative correlation one increases. These results indicate that stars with shorter rotation period tend to have positive correlation between the two proxies, and a good portion of the positive correlation stars have a larger magnitude of light-curve variation (and hence more intense magnetic activities) than negative correlation stars.

  17. ULTRAVIOLET-SELECTED FIELD AND PRE-MAIN-SEQUENCE STARS TOWARD TAURUS AND UPPER SCORPIUS

    SciTech Connect

    Findeisen, K.; Hillenbrand, L. E-mail: lah@astro.caltech.edu

    2010-04-15

    We have carried out a Galaxy Evolution Explorer (GALEX) Cycle 1 guest investigator program covering 56 deg{sup 2} near the Taurus T association and 12 deg{sup 2} along the northern edge of the Upper Scorpius OB association. We combined photometry in the GALEX far-ultraviolet and near-ultraviolet bands with data from the Two Micron All Sky Survey to identify candidate young ({approx}<100 Myr old) stars as those with an ultraviolet excess relative to older main-sequence stars. Follow-up spectroscopy of a partial sample of these candidates suggests five new members of Taurus, with 8-20 expected from additional observations, and five new members of Upper Scorpius, with three to six expected from additional observations. These candidate new members appear to represent a distributed, non-clustered population in either region, although our sample statistics are as of yet too poor to constrain the nature or extent of this population. Rather, our study demonstrates the ability of GALEX observations to identify young stellar populations distributed over a wide area of the sky. We also highlight the necessity of a better understanding of the Galactic ultraviolet source population to support similar investigations. In particular, we report a large population of stars with an ultraviolet excess but no optical indicators of stellar activity or accretion, and briefly argue against several interpretations of these sources.

  18. Iron-group Abundances in the Metal-poor Main-Sequence Turnoff Star HD~84937

    NASA Astrophysics Data System (ADS)

    Sneden, Christopher; Cowan, John J.; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E.; Den Hartog, Elizabeth A.; Wood, Michael P.

    2016-01-01

    We have derived new, very accurate abundances of the Fe-group elements Sc through Zn (Z = 21-30) in the bright main-sequence turnoff star HD 84937 based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each other. We find no substantial departures from the standard LTE Saha ionization balance in this [Fe/H] = -2.32 star. Noteworthy among the abundances are [Co/Fe] = +0.14 and [Cu/Fe] = -0.83, in agreement with past studies of abundance trends in this and other low-metallicity stars, and < [{{Sc,Ti,V/Fe}}]> = +0.31, which has not been noted previously. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys reveals that they are positively correlated in stars with [Fe/H] < -2 HD 84937 lies at the high end of this correlation. These trends constrain the synthesis mechanisms of Fe-group elements. We also examine the Galactic chemical evolution abundance trends of the Fe-group elements, including a new nucleosynthesis model with jet-like explosion effects.

  19. Phylogenetic reconstruction of Bantu kinship challenges Main Sequence Theory of human social evolution.

    PubMed

    Opie, Christopher; Shultz, Susanne; Atkinson, Quentin D; Currie, Thomas; Mace, Ruth

    2014-12-09

    Kinship provides the fundamental structure of human society: descent determines the inheritance pattern between generations, whereas residence rules govern the location a couple moves to after they marry. In turn, descent and residence patterns determine other key relationships such as alliance, trade, and marriage partners. Hunter-gatherer kinship patterns are viewed as flexible, whereas agricultural societies are thought to have developed much more stable kinship patterns as they expanded during the Holocene. Among the Bantu farmers of sub-Saharan Africa, the ancestral kinship patterns present at the beginning of the expansion are hotly contested, with some arguing for matrilineal and matrilocal patterns, whereas others maintain that any kind of lineality or sex-biased dispersal only emerged much later. Here, we use Bayesian phylogenetic methods to uncover the history of Bantu kinship patterns and trace the interplay between descent and residence systems. The results suggest a number of switches in both descent and residence patterns as Bantu farming spread, but that the first Bantu populations were patrilocal with patrilineal descent. Across the phylogeny, a change in descent triggered a switch away from patrifocal kinship, whereas a change in residence triggered a switch back from matrifocal kinship. These results challenge "Main Sequence Theory," which maintains that changes in residence rules precede change in other social structures. We also indicate the trajectory of kinship change, shedding new light on how this fundamental structure of society developed as farming spread across the globe during the Neolithic.

  20. Carbon, nitrogen, and oxygen abundances in main-sequence stars. II 20 F and G stars

    NASA Astrophysics Data System (ADS)

    Clegg, R. E. S.; Tomkin, J.; Lambert, D. L.

    1981-11-01

    High-resolution Reticon spectra of red and near-infrared C I, N I, and O I lines have been analyzed to determine C, N, and O abundances in a sample of 20 F and G main-sequence stars. Their iron abundances, which have been determined from analysis of additional Reticon spectra of red Fe I lines, cover the Fe/H range from -0.9 to 0.4. Sulfur abundances have also been obtained. It is found that the variations of the carbon and sulfur abundances closely follow those of iron. The oxygen abundance varies much more slowly than iron (O/Fe = 0.48 (+ or - 0.07) Fe/H). This result confirms an earlier conclusion that oxygen is overabundant in more metal-deficient stars. The behavior of the nitrogen abundance appears to be similar to that of iron (N/Fe = 0.0 + or - 0.2). However, the unavailability of nitrogen abundances for the most metal-deficient stars in the sample makes this result less certain than the results for the other elements. These results are discussed in the light of current theories of stellar nucleosynthesis of the elements.

  1. Main sequence of the metal-poor globular cluster M30 (NGC 7099)

    SciTech Connect

    Alcaino, G.; Liller, W.

    1980-10-01

    We present photographic photometry for 673 stars in the metal-poor globular cluster M30 (NGC 7099). The Racine wedge was used with the CTIO 1-m Yale telescope (..delta..m=3/sup m/.60), the CTIO 4-m telescope (..delta..m=6/sup m/.83), and the ESO 3.6-m telescope (..delta..m=4/sup m/.12) to extend the photoelectric limit from Vapprox. =16.3 to Vapprox. =20.4. For the main-sequence turn-off, we have determined its position to lie at V=18.4 +- 0.1 (m.e.) and B-V=0.49 +- 0.03 (m.e.). From these values, we calculate the intrinsic values M/sub v/ =3.87 and (B-V)/sub 0/=0.47. For the cluster as a whole, we derive a distance modulus (m-M)/sub V/=14.53 +- 0.15 and reddening E(B-V)=0.02 +- 0.02. Using the models of Iben and Rood (Astrophys. J. 159, 605 (1970)) and the isochrones of Demarque and McClure ((1977), in Evolution of Galaxies and Stellar Populations, edited by B. Tinsley and R. B. Larson (Yale University Observatory, New Haven), p. 199), we deduce the cluster's age to be 14.5( +- 4.0) x 10/sup 9/ yr. The large uncertainty in this value emphasizes the dire need for more work on cluster evolution.

  2. Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence

    NASA Astrophysics Data System (ADS)

    Hallinan, G.; Littlefair, S. P.; Cotter, G.; Bourke, S.; Harding, L. K.; Pineda, J. S.; Butler, R. P.; Golden, A.; Basri, G.; Doyle, J. G.; Kao, M. M.; Berdyugina, S. V.; Kuznetsov, A.; Rupen, M. P.; Antonova, A.

    2015-07-01

    Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons, as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere. Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs.

  3. The Evolved Main-sequence Channel: HST and LBT Observations of CSS120422:111127+571239

    NASA Astrophysics Data System (ADS)

    Kennedy, M.; Garnavich, P.; Callanan, P.; Szkody, P.; Littlefield, C.; Pogge, R.

    2015-12-01

    The “evolved main-sequence (EMS)” channel is thought to contribute significantly to the population of AM CVn-type systems in the Galaxy, and also to the number of cataclysmic variables (CVs) detected below the period minimum for hydrogen rich systems. CSS 120422:J111127+571239 was discovered by the Catalina Sky Survey in 2012 April. Its period was found to be 56 minutes, well below the minimum, and the optical spectrum is clearly depleted in hydrogen relative to helium, but still has two orders of magnitude more hydrogen than AM CVn stars. Doppler tomography of the Hα line hinted at a spiral structure existing in the disk. Here we present spectroscopy of CSS 120422:J111127+571239 using the Cosmic Origins Spectrograph FUV instrument on the Hubble Space Telescope and using the MODS spectrograph on the Large Binocular Telescope. The UV spectrum shows Si iv, N v, and He ii, but no detectable C iv. The anomalous nitrogen/carbon ratio is seen in a small number of other CVs and confirms a unique binary evolution. We also present and compare the optical spectrum of V418 Ser and advocate that it is also an EMS system.

  4. Detailed Iron-Group Abundances in a Very Metal-Poor Main Sequence Turnoff Star

    NASA Astrophysics Data System (ADS)

    Sneden, Chris; Roederer, Ian U.; Boesgaard, Ann M.; Lawler, James E.; Den Hartog, Elizabeth; Cowan, John J.; Sobeck, Jennifer

    2017-01-01

    We have obtained Keck HIRES and HST STIS high resolution, high signal-to-noise spectra of the very metal-poor ([Fe/H] ~ -2.9) main-sequence turnoff star BD+03 740. A detailed chemical composition analysis based on synthetic spectrum computations has been conducted. Our initial focus has been on the iron-group elements in the Z = 21-28 range. This study takes advantage of recent improvements in neutral and ionzied species transition data for all of these elements except Sc (Z = 21) by the Wisconsin atomic physics group (see a companion presentation on Cr II at this meeting). Several metal-poor abundance surveys have concluded that there are large overabundances of Co and underabundances of Cr with respect to Fe for stars with [Fe/H] < -2.5. Neither of these anomalies is seen in BD+03 740. We discuss the implications of this result for early iron-group synthesis in the Galaxy.This work has been supported by HST STScI Program GO-14232; and NSF grants AST-1211585 and AST-1616040 to CS; AST-1516182 to JEL and EDH; NASA grant NNX16AE96G to JEL

  5. Soft X-ray observations of pre-main sequence stars in the chamaeleon dark cloud

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.; Kriss, Gerard A.

    1987-01-01

    Einstein IPC observations of the nearby Chamaeleon I star forming cloud show 22 well-resolved soft X-ray sources in a 1x2 deg region. Twelve are associated with H-alpha emission line pre-main sequence (PMS) stars, and four with optically selected PMS stars. Several X-ray sources have two or more PMS stars in their error circles. Optical spectra were obtained at CTIO of possible stellar counterparts of the remaining X-ray sources. They reveal 5 probable new cloud members, K7-MO stars with weak or absent emission lines. These naked X-ray selected PMS stars are similar to those found in the Taurus-Auriga cloud. The spatial distributions and H-R diagrams of the X-ray and optically selected PMS stars in the cloud are very similar. Luminosity functions indicate the Chamaeleon stars are on average approximately 5 times more X-ray luminous than Pleiad dwarfs. A significant correlation between L sub x and optical magnitude suggests this trend may continue within the PMS phase of stellar evolution. The relation of increasing X-ray luminosity with decreasing stellar ages is thus extended to stellar ages as young as 1 million years.

  6. 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.

  7. LINEAR RELATION FOR WIND-BLOWN BUBBLE SIZES OF MAIN-SEQUENCE OB STARS IN A MOLECULAR ENVIRONMENT AND IMPLICATION FOR SUPERNOVA PROGENITORS

    SciTech Connect

    Chen Yang; Zhou Ping; Chu Youhua

    2013-05-20

    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{sub b} Almost-Equal-To 1.22 M/M{sub Sun} - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M{sub Sun} 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.

  8. Gaia-ESO Survey: Analysis of pre-main sequence stellar spectra

    NASA Astrophysics Data System (ADS)

    Lanzafame, A. C.; Frasca, A.; Damiani, F.; Franciosini, E.; Cottaar, M.; Sousa, S. G.; Tabernero, H. M.; Klutsch, A.; Spina, L.; Biazzo, K.; Prisinzano, L.; Sacco, G. G.; Randich, S.; Brugaletta, E.; Delgado Mena, E.; Adibekyan, V.; Montes, D.; Bonito, R.; Gameiro, J. F.; Alcalá, J. M.; González Hernández, J. I.; Jeffries, R.; Messina, S.; Meyer, M.; Gilmore, G.; Asplund, M.; Binney, J.; Bonifacio, P.; Drew, J. E.; Feltzing, S.; Ferguson, A. M. N.; Micela, G.; Negueruela, I.; Prusti, T.; Rix, H.-W.; Vallenari, A.; Alfaro, E. J.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme, R.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.; Irwin, M.; Koposov, S. E.; Korn, A. J.; Smiljanic, R.; Van Eck, S.; Walton, N.; Bayo, A.; Bergemann, M.; Carraro, G.; Costado, M. T.; Edvardsson, B.; Heiter, U.; Hill, V.; Hourihane, A.; Jackson, R. J.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Marconi, G.; Martayan, C.; Masseron, T.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Worley, C. C.; Zaggia, S.

    2015-04-01

    Context. The Gaia-ESO Public Spectroscopic Survey is obtaining high-quality spectroscopy of some 100 000 Milky Way stars using the FLAMES spectrograph at the VLT, down to V = 19 mag, systematically covering all the main components of the Milky Way and providing the first homogeneous overview of the distributions of kinematics and chemical element abundances in the Galaxy. Observations of young open clusters, in particular, are giving new insights into their initial structure, kinematics, and their subsequent evolution. Aims: This paper describes the analysis of UVES and GIRAFFE spectra acquired in the fields of young clusters whose population includes pre-main sequence (PMS) stars. The analysis is applied to all stars in such fields, regardless of any prior information on membership, and provides fundamental stellar atmospheric parameters, elemental abundances, and PMS-specific parameters such as veiling, accretion, and chromospheric activity. Methods: When feasible, different methods were used to derive raw parameters (e.g. line equivalent widths) fundamental atmospheric parameters and derived parameters (e.g. abundances). To derive some of these parameters, we used methods that have been extensively used in the past and new ones developed in the context of the Gaia-ESO survey enterprise. The internal precision of these quantities was estimated by inter-comparing the results obtained by these different methods, while the accuracy was estimated by comparison with independent external data, such as effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. A validation procedure based on these comparisons was applied to discard spurious or doubtful results and produce recommended parameters. Specific strategies were implemented to resolve problems of fast rotation, accretion signatures, chromospheric activity, and veiling. Results: The analysis carried out on spectra acquired in young cluster fields during

  9. Mid-IR observations of circumstellar disks. I. Pre-main sequence objects

    NASA Astrophysics Data System (ADS)

    Schütz, O.; Meeus, G.; Sterzik, M. F.

    2005-02-01

    We present new N-band photometry and spectroscopy for a sample of eight pre-main sequence stars including T Tauri, Herbig Ae/Be stars and FU Ori objects using the ESO TIMMI2 camera at the La Silla observatory (Chile). For some objects this is their first N-band spectroscopic observation ever. The FU Ori stars V 346 Nor, V 883 Ori and Z CMa show a broad absorption band which we attribute to silicates, while for BBW 76 we find silicate emission. A comparison with ISO-SWS spectra of V 346 Nor and Z CMa taken in 1996/1997 reveals no differences in spectral shape. All T Tauri and Herbig Ae/Be stars possess N-band emission features. We model the emission spectra with a mixture of silicates consisting of different grain sizes and composition. The Herbig Ae star HD 34282 shows strong features of PAHs but none of silicate, while the emission spectrum of the Herbig Ae star HD 72106 resembles those of solar-system comets and known Herbig sources of evolved dust. We demonstrate that HD 72106 is host to highly processed silicates and find evidence for enstatite, which is not common in young objects. Evolved dust is also seen in the T Tauri stars HD 98800 and MP Mus. We further detected MP Mus at 1200 μm with the bolometer array SIMBA at the SEST in La Silla. The findings of our analysis are given in the context of previous dust studies of young stellar objects. Based on observations collected at the European Southern Observatory, La Silla, Chile (69.C-0073, 70.C-0468, 71.C-0001, 73.C-0372).

  10. Time Variability of the Dust Sublimation Zones in Pre-Main Sequence Disk Systems

    NASA Technical Reports Server (NTRS)

    Sitko, Michael L.; Carpenter, W. J.; Grady, C. A.; Russel, R. W.; Lynch, D. K.; Rudy, R. J.; Mazuk, S. M.; Venturini, C. C.; Kimes, R. L.; Beerman, L. C.; Ablordeppey, K. E.; Puetter, R. C.; Wisnewski, P.; Brafford, S. M.; Polomski, E. R.; Hammel, H. B.; Perry, R. B.; Wilde, J. L.

    2007-01-01

    The dust sublimation zone (DSZ) is the region of pre-main sequence (PMS) disks where dust grains most easily anneal, sublime, and condense out of the gas. Because of this, it is a location where crystalline material may be enhanced and redistributed throughout the rest of the disk. A decade-long program to monitor the thermal emission of the grains located in this region demonstrates that large changes in emitted flux occur in many systems. Changes in the thermal emission between 3 and 13.5 microns were observed in HD 31648 (MWC 480), HD 163296 (MWC 275), and DG Tau. This emission is consistent with it being produced at the DSZ, where the transition from a disk of gas to one of gas+dust occurs. In the case of DG Tau, the outbursts were accompanied by increased emission on the 10 micron silicate band on one occasion, while on another occasion it went into absorption. This requires lofting of the material above the disk into the line of sight. Such changes will affect the determination of the inner disk structure obtained through interferometry measurements, and this has been confirmed in the case of HD 163296. Cyclic variations in the heating of the DSZ will lead to the annealing of large grains, the sublimation of smaller grains, possibly followed by re-condensation as the zone enters a cooling phase. Lofting of dust above the disk plane, and outward acceleration by stellar winds and radiation pressure, can re-distribute the processed material to cooler regions of the disk, where cometesimals form. This processing is consistent with the detection of the preferential concentration of large crystalline grains in the inner few AU of PMS disks using interferometric spectroscopy with the VLTI.

  11. THE QUADRUPLE PRE-MAIN-SEQUENCE SYSTEM LkCa 3: IMPLICATIONS FOR STELLAR EVOLUTION MODELS

    SciTech Connect

    Torres, Guillermo; Latham, David W.; Ruiz-Rodriguez, Dary; Prato, L.; Wasserman, Lawrence H.; Badenas, Mariona; Schaefer, G. H.; Mathieu, Robert D.

    2013-08-10

    We report the discovery that the pre-main-sequence (PMS) object LkCa 3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close ({approx}0.''5) visual pair, with one component being a moderately eccentric 12.94 day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented by new near-infrared (NIR) spectroscopy shows both visual components to be double lined; the second one has a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and NIR flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we also detect the rotational signal of the primary in the 4.06 day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these constraints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting that the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa 3 and the well-known quadruple PMS system GG Tau with the widely used models from the Lyon series for a mixing length parameter of {alpha}{sub ML} = 1.0 strongly favor the Dartmouth models.

  12. The Quadruple Pre-main-sequence System LkCa 3: Implications for Stellar Evolution Models

    NASA Astrophysics Data System (ADS)

    Torres, Guillermo; Ruíz-Rodríguez, Dary; Badenas, Mariona; Prato, L.; Schaefer, G. H.; Wasserman, Lawrence H.; Mathieu, Robert D.; Latham, David W.

    2013-08-01

    We report the discovery that the pre-main-sequence (PMS) object LkCa 3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close (~0.''5) visual pair, with one component being a moderately eccentric 12.94 day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented by new near-infrared (NIR) spectroscopy shows both visual components to be double lined; the second one has a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and NIR flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we also detect the rotational signal of the primary in the 4.06 day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these constraints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting that the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa 3 and the well-known quadruple PMS system GG Tau with the widely used models from the Lyon series for a mixing length parameter of αML = 1.0 strongly favor the Dartmouth models.

  13. VLT/X-shooter spectroscopy of massive pre-main-sequence stars in M17

    NASA Astrophysics Data System (ADS)

    Ramirez-Tannus, Maria Claudia; Kaper, Lex

    2015-08-01

    The formation process of massive stars is still poorly understood. Formation timescales are short, the corresponding accretion rates very high, and the forming stars are hidden from view due to vast amounts of interstellar extinction. On top of that, massive stars are rare, are located at relatively large distances, and play a major role in shaping the interstellar medium due to their strong UV radiation fields and stellar winds. Although massive stars show most spectral features in the UV and optical range, so far only for a handful of massive Young Stellar Objects (mYSOs) optical and near-infrared spectra have been obtained. For some of these their pre-main-sequence (PMS) nature has now been firmly established (e.g. Ochsendorf et al. 2011, Ellerbroek et al. 2013). The objective of our project is to determine the physical properties of mYSOs, to search for signatures remnant of their formation process and to better understand the feedback on their environment.To this aim the optical to near-infrared (300-2500 nm) spectra of six candidate mYSOs (Hanson et al. 1997), deeply embedded in the massive star forming region M17, have been obtained with X-Shooter on the ESO Very Large Telescope. These mYSO candidates have been identified based on their infrared excess and spectral features (double-peaked emission lines, CO band-head emission) indicating the presence of a disk. In most cases, we detect a photospheric spectrum allowing us to measure the physical properties of the mYSO and to confirm its PMS nature. We also uncover many emission features, including forbidden lines, providing information on the (active) formation process of these young (massive) stars.

  14. The Environmental Impacts on the Star Formation Main Sequence: An Hα Study of the Newly Discovered Rich Cluster at z = 1.52

    NASA Astrophysics Data System (ADS)

    Koyama, Yusei; Kodama, Tadayuki; Tadaki, Ken-ichi; Hayashi, Masao; Tanaka, Ichi; Shimakawa, Rhythm

    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 by the passive red massive galaxies residing within rc lsim 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.

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

    SciTech Connect

    Koyama, Yusei; Kodama, Tadayuki; Tadaki, Ken-ichi; Hayashi, Masao; Tanaka, Ichi; Shimakawa, Rhythm

    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 by 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.

  16. EXTENDED MAGNETOSPHERES IN PRE-MAIN-SEQUENCE EVOLUTION: FROM T TAURI STARS TO THE BROWN DWARF LIMIT

    SciTech Connect

    Gomez de Castro, Ana I.; Marcos-Arenal, Pablo

    2012-04-20

    Low-mass pre-main-sequence stars, i.e., T Tauri stars (TTSs), strongly radiate at high energies, from X-rays to the ultraviolet (UV). This excess radiation with respect to main-sequence cool stars (MSCSs) is associated with the accretion process, i.e., it is produced in the extended magnetospheres, in the accretion shocks on the stellar surface, and in the outflows. Although evidence of accretion shocks and outflow contribution to the high-energy excess have been recently addressed, there is not an updated revision of the magnetospheric contribution. This article addresses this issue. The UV observations of the TTSs in the well-known Taurus region have been analyzed together with the XMM-Newton observations compiled in the XEST survey. For the first time the high sensitivity of the Hubble Space Telescope UV instrumentation has allowed measurement of the UV line fluxes of TTSs to M8 type. UV- and X-ray-normalized fluxes have been determined to study the extent and properties of the TTS magnetospheres as a class. They have been compared with the atmospheres of the MSCSs. The main results from this analysis are (1) the normalized fluxes of all the tracers are correlated; this correlation is independent of the broad mass range and the hardness of the X-ray radiation field; (2) the TTS correlations are different than the MSCS correlations; (3) there is a very significant excess emission in O I in the TTSs compared with MSCSs that seems to be caused by recombination radiation from the disk atmosphere after photoionization by extreme UV radiation; the Fe II/Mg II recombination continuum has also been detected in several TTSs and most prominently in AA Tau; and (4) the normalized flux of the UV tracers anticorrelates with the strength of the X-ray flux, i.e., the stronger the X-ray surface flux is, the weaker the observed UV flux. This last behavior is counterintuitive within the framework of stellar dynamo theory and suggests that UV emission can be produced in the

  17. Evidence for a Significant Intermediate-Age Population in the M31 Halo from Main Sequence Photometry

    NASA Technical Reports Server (NTRS)

    Brown, Thomas M.; Ferguson, Henry C.; Smith, Ed; Kimble, Randy A.; Sweigart, Allen V.; Renzini, Alvio; Rich, R. Michael; Vandenberg, Don A.

    2003-01-01

    We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M3l), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at m(sub v) = 30.7 mag. The CMD, constructed from approx. 3 x 10(exp 5) stars, reaches more than 1.5 mag fainter than the old main-sequence turnoff. Our analysis is based on direct comparisons to ACS observations of four globular clusters through the same filters, as well as chi square fitting to a finely-spaced grid of calibrated stellar-population models. We find that the M31 halo contains a major (approx. 30% by mass) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] greater than -0.5) population, as well as a significant globular-cluster age (11-13.5 Gyr) metal-poor population. These findings support the idea that galaxy mergers played an important role in the formation of the M31 halo.

  18. The SDSS spectroscopic catalogue of white dwarf-main-sequence binaries: new identifications from DR 9-12

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Ren, J. J.; Parsons, S. G.; Gänsicke, B. T.; Schreiber, M. R.; García-Berro, E.; Liu, X.-W.; Koester, D.

    2016-06-01

    We present an updated version of the spectroscopic catalogue of white dwarf-main-sequence (WDMS) binaries from the Sloan Digital Sky Survey (SDSS). We identify 938 WDMS binaries within the data releases (DR) 9-12 of SDSS plus 40 objects from DR 1-8 that we missed in our previous works, 646 of which are new. The total number of spectroscopic SDSS WDMS binaries increases to 3294. This is by far the largest and most homogeneous sample of compact binaries currently available. We use a decomposition/fitting routine to derive the stellar parameters of all systems identified here (white dwarf effective temperatures, surface gravities and masses, and secondary star spectral types). The analysis of the corresponding stellar parameter distributions shows that the SDSS WDMS binary population is seriously affected by selection effects. We also measure the Na I λλ 8183.27, 8194.81 absorption doublet and H α emission radial velocities (RV) from all SDSS WDMS binary spectra identified in this work. 98 objects are found to display RV variations, 62 of which are new. The RV data are sufficient enough to estimate the orbital periods of three close binaries.

  19. Evidence for a Significant Intermediate-Age Population in the M31 Halo from Main Sequence Photometry

    NASA Technical Reports Server (NTRS)

    Brown, Thomas M.; Ferguson, Henry C.; Smith, Ed; Kimble, Randy A.; Sweigart, Allen V.; Renzini, Alvio; Rich, R. Michael; Vandenberg, Don A.

    2003-01-01

    We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M3l), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at m(sub v) = 30.7 mag. The CMD, constructed from approx. 3 x 10(exp 5) stars, reaches more than 1.5 mag fainter than the old main-sequence turnoff. Our analysis is based on direct comparisons to ACS observations of four globular clusters through the same filters, as well as chi square fitting to a finely-spaced grid of calibrated stellar-population models. We find that the M31 halo contains a major (approx. 30% by mass) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] greater than -0.5) population, as well as a significant globular-cluster age (11-13.5 Gyr) metal-poor population. These findings support the idea that galaxy mergers played an important role in the formation of the M31 halo.

  20. Kepler-4b: A Hot Neptune-like Planet of a G0 Star Near Main-sequence Turnoff

    NASA Astrophysics Data System (ADS)

    Borucki, William J.; Koch, David G.; Brown, Timothy M.; Basri, Gibor; Batalha, Natalie M.; Caldwell, Douglas A.; Cochran, William D.; Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ronald L.; Howell, Steve B.; Jenkins, Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Monet, David; Rowe, Jason F.; Sasselov, Dimitar

    2010-04-01

    Early time-series photometry from NASA's Kepler spacecraft has revealed a planet transiting the star we term Kepler-4, at R.A. = 19h02m27.s68, δ = +50°08'08farcs7. The planet has an orbital period of 3.213 days and shows transits with a relative depth of 0.87 × 10-3 and a duration of about 3.95 hr. Radial velocity (RV) measurements from the Keck High Resolution Echelle Spectrometer show a reflex Doppler signal of 9.3+1.1 -1.9 m s-1, consistent with a low-eccentricity orbit with the phase expected from the transits. Various tests show no evidence for any companion star near enough to affect the light curve or the RVs for this system. From a transit-based estimate of the host star's mean density, combined with analysis of high-resolution spectra, we infer that the host star is near turnoff from the main sequence, with estimated mass and radius of 1.223+0.053 -0.091 M sun and 1.487+0.071 -0.084 R sun. We estimate the planet mass and radius to be {M P, R P} = {24.5 ± 3.8 M ⊕, 3.99 ± 0.21 R ⊕}. The planet's density is near 1.9 g cm-3 it is thus slightly denser and more massive than Neptune, but about the same size. 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.

  1. KEPLER-4b: A HOT NEPTUNE-LIKE PLANET OF A G0 STAR NEAR MAIN-SEQUENCE TURNOFF

    SciTech Connect

    Borucki, William J.; Koch, David G.; Caldwell, Douglas A.; Jenkins, Jon M.; Lissauer, Jack J.; Rowe, Jason F.; Basri, Gibor; Marcy, Geoffrey W.; Batalha, Natalie M.; Cochran, William D.; Dunham, Edward W.; Gautier, Thomas N.; Gilliland, Ronald L.; Howell, Steve B.; Monet, David

    2010-04-20

    Early time-series photometry from NASA's Kepler spacecraft has revealed a planet transiting the star we term Kepler-4, at R.A. = 19{sup h}02{sup m}27.{sup s}68, {delta} = +50{sup 0}08'08.''7. The planet has an orbital period of 3.213 days and shows transits with a relative depth of 0.87 x 10{sup -3} and a duration of about 3.95 hr. Radial velocity (RV) measurements from the Keck High Resolution Echelle Spectrometer show a reflex Doppler signal of 9.3{sup +1.1} {sub -1.9} m s{sup -1}, consistent with a low-eccentricity orbit with the phase expected from the transits. Various tests show no evidence for any companion star near enough to affect the light curve or the RVs for this system. From a transit-based estimate of the host star's mean density, combined with analysis of high-resolution spectra, we infer that the host star is near turnoff from the main sequence, with estimated mass and radius of 1.223{sup +0.053} {sub -0.091} M {sub sun} and 1.487{sup +0.071} {sub -0.084} R {sub sun}. We estimate the planet mass and radius to be {l_brace}M {sub P}, R {sub P}{r_brace} = {l_brace}24.5 {+-} 3.8 M {sub +}, 3.99 {+-} 0.21 R {sub +}{r_brace}. The planet's density is near 1.9 g cm{sup -3}; it is thus slightly denser and more massive than Neptune, but about the same size.

  2. Long-term evolution of three-planet systems to the post-main sequence and beyond

    NASA Astrophysics Data System (ADS)

    Mustill, Alexander J.; Veras, Dimitri; Villaver, Eva

    2014-01-01

    We study the stability of systems of three giant planets orbiting 3-8 M⊙ stars at orbital distances of >10 au as the host star ages through the main sequence (MS) and well into the white dwarf (WD) stage. Systems are stable on the MS if the planets are separated by more than ˜9 Hill radii. Most systems surviving the MS will remain stable until the WD phase, although planets scattered on to small pericentres in unstable systems can be swallowed by the expanding stellar envelope when the star ascends the giant branches. Mass-loss at the end of the asymptotic giant branch triggers delayed instability in many systems, leading to instabilities typically occurring at WD cooling ages of a few 100 Myr. This instability occurs both in systems that survived the star's previous evolution unscathed, and in systems that previously underwent scattering instabilities. The outcome of such instability around WDs is overwhelmingly the ejection of one of the planets from the system, with several times more ejections occurring during the WD phase than during the MS. Furthermore, few planets are scattered close to the WD, just outside the Roche limit, where they can be tidally circularized. Hence, we predict that planets in WD systems rarely dynamically evolve to become `hot Jupiters'. Nor does it appear that the observed frequency of metal pollution in WD atmospheres can be entirely explained by planetesimals being destabilized following instability in systems of multiple giant planets, although further work incorporating low-mass planets and planetesimals is needed.

  3. A Wide Angle Survey of Young Stellar Associations for Hot Jupiters and Pre-Main Sequence Binaries

    NASA Astrophysics Data System (ADS)

    Oelkers, Ryan J.; Macri, Lucas M.; Marshall, Jennifer L.; Depoy, Darren L.; Garcia Lambas, Diego

    2016-01-01

    The past two decades have seen a significant advancement in the detection, classification and understanding of exoplanets and binary star systems. The vast majority of these systems consist of objects on the main sequence or the giant branch, leading to a dearth of knowledge of properties at early times (<50 Myr). Only a dozen binaries and 1 possible transiting Hot Jupiter are known among pre-main sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well characterized systems is driven by the inherent and aperiodic variability found in pre-main sequence objects which can mask and mimic eclipse signals. Nevertheless a dramatic increase in the total number of systems at early times is required to alleviate the conflict between theory and observation. I have recently completed a photometric survey of 3 nearby (<150 pc) and young (<50 Myr) moving groups with a small aperture telescope. I have discovered over 300 likely pre-main sequence binaries and have ruled out 7 possible transiting Hot Jupiters using techniques developed by reducing crowded, defocused images from an analogous system. I will present the photometric detection and follow-up for these systems, the spectroscopic measurements of pre-main sequence binary candidates and my lower bound on the Hot Jupiter migration timescale.

  4. ALMA observations of α Centauri. First detection of main-sequence stars at 3 mm wavelength

    NASA Astrophysics Data System (ADS)

    Liseau, R.; Vlemmings, W.; Bayo, A.; Bertone, E.; Black, J. H.; del Burgo, C.; Chavez, M.; Danchi, W.; De la Luz, V.; Eiroa, C.; Ertel, S.; Fridlund, M. C. W.; Justtanont, K.; Krivov, A.; Marshall, J. P.; Mora, A.; Montesinos, B.; Nyman, L.-A.; Olofsson, G.; Sanz-Forcada, J.; Thébault, P.; White, G. J.

    2015-01-01

    Context. The precise mechanisms that provide the non-radiative energy for heating the chromosphere and the corona of the Sun and those of other stars constitute an active field of research. By studying stellar chromospheres one aims at identifying the relevant physical processes. Defining the permittable extent of the parameter space can also serve as a template for the Sun-as-a-star. This feedback will probably also help identify stars that potentially host planetary systems that are reminiscent of our own. Aims: Earlier observations with Herschel and APEX have revealed the temperature minimum of α Cen, but these were unable to spatially resolve the binary into individual components. With the data reported in this Letter, we aim at remedying this shortcoming. Furthermore, these earlier data were limited to the wavelength region between 100 and 870 μm. In the present context, we intend to extend the spectral mapping (SED) to longer wavelengths, where the contrast between stellar photospheric and chromospheric emission becomes increasingly evident. Methods: The Atacama Large Millimeter/submillimeter Array (ALMA) is particularly suited to point sources, such as unresolved stars. ALMA provides the means to achieve our objectives with both its high sensitivity of the collecting area for the detection of weak signals and the high spatial resolving power of its adaptable interferometer for imaging close multiple stars. Results: This is the first detection of main-sequence stars at a wavelength of 3 mm. Furthermore, the individual components of the binary α Cen AB are clearly detected and spatially well resolved at all ALMA wavelengths. The high signal-to-noise ratios of these data permit accurate determination of their relative flux ratios, i.e., SyB / SyA> = 0.54 ± 0.04 at 440 μm, = 0.46 ± 0.01 at 870 μm, and = 0.47 ± 0.006 at 3.1 mm, respectively. Conclusions: The previously obtained flux ratio of 0.44±0.18, which was based on measurements in the optical and

  5. Tracing the potential planet-forming regions around seven pre-main-sequence stars

    NASA Astrophysics Data System (ADS)

    Schegerer, A. A.; Wolf, S.; Hummel, C. A.; Quanz, S. P.; Richichi, A.

    2009-07-01

    Aims: We investigate the nature of the innermost regions with radii of several AUs of seven circumstellar disks around pre-main-sequence stars, T Tauri stars in particular. Our object sample contains disks apparently at various stages of their evolution. Both single stars and spatially resolved binaries are considered. In particular, we search for inner disk gaps as proposed for several young stellar objects (YSOs). When analyzing the underlying dust population in the atmosphere of circumstellar disks, the shape of the 10 μm feature should additionally be investigated. Methods: We performed interferometric observations in N band (8-13 μm) with the Mid-Infrared Interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) using baseline lengths of between 54 m and 127 m. The data analysis is based on radiative-transfer simulations using the Monte Carlo code MC3D by modeling simultaneously the spectral energy distribution (SED), N band spectra, and interferometric visibilities. Correlated and uncorrelated N band spectra are compared to investigate the radial distribution of the dust composition of the disk atmosphere. Results: Spatially resolved mid-infrared (MIR) emission was detected in all objects. For four objects (DR Tau, RU Lup, S CrA N, and S CrA S), the observed N band visibilities and corresponding SEDs could be simultaneously simulated using a parameterized active disk-model. For the more evolved objects of our sample, HD 72106 and HBC 639, a purely passive disk-model provides the closest fit. The visibilities inferred for the source RU Lup allow the presence of an inner disk gap. For the YSO GW Ori, one of two visibility measurements could not be simulated by our modeling approach. All uncorrelated spectra reveal the 10 μm silicate emission feature. In contrast to this, some correlated spectra of the observations of the more evolved objects do not show this feature, indicating a lack of small silicates in the inner versus the outer

  6. A Wide Angle Search for Hot Jupiters and Pre-Main Sequence Binaries in Young Stellar Associations

    NASA Astrophysics Data System (ADS)

    Oelkers, Ryan J.; Macri, Lucas M.; Marshall, Jennifer L.; Depoy, Darren L.; Colazo, Carlos; Guzzo, Pablo; Lambas, Diego G.; Quiñones, Ceci; Stringer, Katelyn; Tapia, Luis; Wisdom, Colin

    2016-01-01

    The past two decades have seen a significant advancement in the detection, classification and understanding of exoplanets and binary star systems. The vast majority of these systems consist of stars on the main sequence or on the giant branch, leading to a dearth of knowledge of properties at early times (<50 Myr). Only one transiting planet candidate and a dozen eclipsing binaries are known among pre-main sequence objects, yet these are the systems that can provide the best constraints on stellar and planetary formation models. We have recently completed a photometric survey of 3 young (<50 Myr), nearby (D<150 pc) moving groups with a small-aperture instrument, nicknamed ``AggieCam''. We detected 7 candidate Hot Jupiters and over 200 likely pre-main sequence binaries, which are now being followed up photometrically and spectroscopically.

  7. Theoretical values of convective turnover times and Rossby numbers for solar-like, pre-main sequence stars

    NASA Astrophysics Data System (ADS)

    Landin, N. R.; Mendes, L. T. S.; Vaz, L. P. R.

    2010-02-01

    Context. Magnetic fields are at the heart of the observed stellar activity in late-type stars, and they are presumably generated by a dynamo mechanism at the interface layer (tachocline) between the radiative core and the base of the convective envelope. Aims: Since dynamo models are based on the interaction between differential rotation and convective motions, the introduction of rotation in the ATON 2.3 stellar evolutionary code allows for explorations regarding a physically consistent treatment of magnetic effects in stellar structure and evolution, even though there are formidable mathematical and numerical challenges involved. Methods: As examples of such explorations, we present theoretical estimates for both the local convective turnover time (τ_c), and global convective times (τ_g) for rotating pre-main sequence solar-type stars, based on up-to-date input physics for stellar models. Our theoretical predictions are compared with the previous ones available in the literature. In addition, we investigate the dependence of the convective turnover time on convection regimes, the presence of rotation and atmospheric treatment. Results: Those estimates, as opposed to the use of empirically derived values of τ_c for such matters, can be used to calculate the Rossby number Ro, which is related to the magnetic activity strength in dynamo theories and, at least for main-sequence stars, shows an observational correlation with stellar activity. More important, they can also contribute for testing stellar models against observations. Conclusions: Our theoretical values of τ_c, τ_g and Ro qualitatively agree with those published by Kim & Demarque (1996, ApJ, 457, 340). By increasing the convection efficiency, τ_g decreases for a given mass. FST models show still lower values. The presence of rotation shifts τ_g towards slightly higher values when compared with non-rotating models. The use of non-gray boundary conditions in the models yields values of τ_g smaller

  8. Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars

    NASA Astrophysics Data System (ADS)

    Meunier, N.; Lagrange, A.-M.; Mbemba Kabuiku, L.; Alex, M.; Mignon, L.; Borgniet, S.

    2017-01-01

    Context. In solar-type stars, the attenuation of convective blueshift by stellar magnetic activity dominates the RV (radial velocity) variations over the low amplitude signal induced by low mass planets. Models of stars that differ from the Sun will require a good knowledge of the attenuation of the convective blueshift to estimate its impact on the variations. Aims: It is therefore crucial to precisely determine not only the amplitude of the convective blueshift for different types of stars, but also the dependence of this convective blueshift on magnetic activity, as these are key factors in our model producing the RV. Methods: We studied a sample of main sequence stars with spectral types from G0 to K2 and focused on their temporally averaged properties: the activity level and a criterion allowing to characterise the amplitude of the convective blueshift. This criterion is derived from the dependence of the convective blueshift with the intensity at the bottom of a large set of selected spectral lines. Results: We find the differential velocity shifts of spectral lines due to convection to depend on the spectral type, the wavelength (this dependence is correlated with the Teff and activity level), and on the activity level. This allows us to quantify the dependence of granulation properties on magnetic activity for stars other than the Sun. We are indeed able to derive a significant dependence of the convective blueshift on activity level for all types of stars. The attenuation factor of the convective blueshift appears to be constant over the considered range of spectral types. We derive a convective blueshift which decreases towards lower temperatures, with a trend in close agreement with models for Teff lower than 5800 K, but with a significantly larger global amplitude. Differences also remain to be examined in detail for larger Teff. We finally compare the observed RV variation amplitudes with those that could be derived from our convective blueshift using

  9. A Critical Assessment of Ages Derived Using Pre-Main-Sequence Isochrones in Colour-Magnitude Diagrams

    NASA Astrophysics Data System (ADS)

    Bell, Cameron P. M.

    2012-11-01

    In this thesis a critical assessment of the ages derived using theoretical pre-main-sequence (pre-MS) stellar evolutionary models is presented by comparing the predictions to the low-mass pre-MS population of 14 young star-forming regions (SFRs) in colour-magnitude diagrams (CMDs). Deriving pre-MS ages requires precise distances and estimates of the reddening. Therefore, the main-sequence (MS) members of the SFRs have been used to derive a self-consistent set of statistically robust ages, distances and reddenings with associated uncertainties using a maximum-likelihood fitting statistic and MS evolutionary models. A photometric method for de-reddening individual stars - known as the Q-method - in regions where the extinction is spatially variable has been updated and is presented. The effects of both the model dependency and the SFR composition on these derived parameters are also discussed. The problem of calibrating photometric observations of red pre-MS stars is examined and it is shown that using observations of MS stars to transform the data into a standard photometric system can introduce significant errors in the position of the pre-MS locus in CMD space. Hence, it is crucial that precise photometric studies - especially of pre-MS objects - be carried out in the natural photometric system of the observations. This therefore requires a robust model of the system responses for the instrument used, and thus the calculated responses for the Wide-Field Camera on the Isaac Newton Telescope are presented. These system responses have been tested using standard star observations and have been shown to be a good representation of the photometric system. A benchmark test for the pre-MS evolutionary models is performed by comparing them to a set of well-calibrated CMDs of the Pleiades in the wavelength regime 0.4-2.5 μm. The masses predicted by these models are also tested against dynamical masses using a sample of MS binaries by calculating the system magnitude in a

  10. Monte Carlo Simulations of the Post-Common-Envelope White-Dwarf Main-Sequence Binary Population

    SciTech Connect

    Camacho, Judit; Torres, Santiago; Garcia-Berro, Enrique; Schreiber, Matthias R.

    2010-12-22

    We present a detailed Monte Carlo simulator of the population of binary systems within the solar neighborhood. We have used the most up-to-date stellar evolutionary models, a complete treatment of the Roche lobe overflow episode, as well as a full implementation of the orbital evolution of the binary system. Preliminary results are presented for the population of white-dwarf main-sequence binaries, resulting from a common envelope episode. We also study the role played by the binding energy parameter, {lambda}, and by the common envelope efficiency, {alpha}{sub CE}. Finally, results are compared with the population of identified white-dwarf main-sequence binaries.

  11. Does the upper main sequence extend across the whole H-R diagram. [radiative opacities of stellar evolution models

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    The effect of using Carson's (1976) radiative opacities in evolutionary sequences of stellar models has been studied over the mass range from 7 to 60 solar masses. The opacities are very large in the outer part of the envelope and induce such enormous radii for masses greater than about 30 solar masses for a heavy-element fraction of 0.02 or about 20 solar masses for a heavy-element fraction of 0.04 that the evolutionary tracks during the phase of core hydrogen burning extend across the whole H-R diagram. The choice of the Schwarschild or Ledoux criterion for convection makes very little difference for the behavior of the tracks. Evolution through the effective-temperature range (in logarithms) of 3.6 to 4.0 occurs in all cases on a rapid (secular) time scale. Core helium burning takes place exclusively in the red-supergiant configuration for stellar masses exceeding 8 solar masses (heavy-element fraction of 0.02) or 6 solar masses (heavy-element fraction of 0.04). These stellar models seem to be in significantly better agreement with the observed distribution of bright stars on the H-R diagram than are the older models based on the Cox-Stewart opacities. It can be inferred that a large envelope opacity (e.g., Carson's) exists and that substantial mass loss takes place in very massive late-type supergiants.

  12. Two new SB2 binaries with main sequence B-type pulsators in the Kepler field

    NASA Astrophysics Data System (ADS)

    Pápics, P. I.; Tkachenko, A.; Aerts, C.; Briquet, M.; Marcos-Arenal, P.; Beck, P. G.; Uytterhoeven, K.; Triviño Hage, A.; Southworth, J.; Clubb, K. I.; Bloemen, S.; Degroote, P.; Jackiewicz, J.; McKeever, J.; Van Winckel, H.; Niemczura, E.; Gameiro, J. F.; Debosscher, J.

    2013-05-01

    Context. OB stars are important in the chemistry and evolution of the Universe, but the sample of targets that is well understood from an asteroseismological point of view is still too limited to provide feedback on the current evolutionary models. Aims: We extend this sample with two spectroscopic binary systems. Our goal is to provide orbital solutions, fundamental parameters, and abundances from disentangled high-resolution high signal-to-noise spectra, as well as to analyse and interpret the variations in the Kepler light curve of these carefully selected targets. This way we continue our efforts to map the instability strips of β Cep and slowly pulsating B stars using the combination of high-resolution ground-based spectroscopy and uninterrupted space-based photometry. Methods: We fit Keplerian orbits to radial velocities measured from selected absorption lines of high-resolution spectroscopy using synthetic composite spectra to obtain orbital solutions. We used revised masks to obtain optimal light curves from the original pixel-data from the Kepler satellite, which provided better long-term stability compared to the pipeline-processed light curves. We used various time-series analysis tools to explore and describe the nature of variations present in the light curve. Results: We find two eccentric double-lined spectroscopic binary systems containing a total of three main sequence B-type stars (and one F-type component), of which at least one in each system exhibits light variations. The light curve analysis (combined with spectroscopy) of the system of two B stars points towards the presence of tidally excited g modes in the primary component. We interpret the variations seen in the second system as classical g mode pulsations driven by the κ mechanism in the B type primary, and explain the unexpected power in the p mode region as the result of nonlinear resonant mode excitation. Based on observations made with the Mercator telescope, operated by the

  13. The diagnosis of sarcopenia is mainly driven by muscle mass in hemodialysis patients.

    PubMed

    Bataille, Stanislas; Serveaux, Marianne; Carreno, Elisa; Pedinielli, Nathalie; Darmon, Patrice; Robert, Alain

    2016-10-22

    Sarcopenia is a well-known complication of protein energy wasting in hemodialysis patients. Its diagnosis requires measurements of muscle mass and muscle function. Few studies have reported its prevalence in hemodialysis patients. In this study, we report the prevalence of sarcopenia in this population and evaluate the performance of other parameters for its diagnosis. In this observational cross-sectional study, data from hemodialysis patients from our nephrology department were recorded. Body composition measured by bioimpedancemetry analysis and muscle strength measured by handgrip were recorded. Normal values for sarcopenia were those recommended by the European Working Group on Sarcopenia in Older People (EWGSOP). The median age (interquartile range) of the 111 patients was 77.5 (70.8-84.8) years. A large majority of 88.3% (n = 98) of patients had a low muscle strength; a low muscle mass index was present in 33.3% (n = 37) of the population. Finally, 31.5% (n = 35) of patients had sarcopenia. These latter were older, had longer dialysis vintage, lower BMI, mid-arm circumference and mid-leg circumference, and a lower prealbumin. The best parameter predicting sarcopenia was BMI (ROC curve AUC of 0.79 [0.68-0.91] (p < 0.001) in men and 0.81 [0.68-0.93] (p = 0.003) in women). Mid-arm circumference predicted sarcopenia, but was less accurate than BMI. Mid-leg circumference predicted sarcopenia only in men. Predialysis creatinine or creatinine index could not predict sarcopenia. We report a 31.5% prevalence of sarcopenia in hemodialysis patients. The diagnosis of sarcopenia was mainly driven by muscle mass measurement because muscle strength is low in the large majority of hemodialysis patients. Copyright © 2016 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.

  14. Statistical Study on Main and Residual Accelerations of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Zhang, J.

    2006-05-01

    We present the results of a statistical study on the main and residual accelerations of coronal mass ejections (CMEs). This work is based on a laborious but careful visual search of about 100000 images taken by LASCO (Large Angle Spectrometric Coronagraph) C1 from 1996 Jan. to 1998 Jun. Among a large number of active phenomena seen in the inner corona from 1.1 to 3.0 Rs by C1, we have identified 74 CMEs, which all have counterparts seen by LASCO C2 and C3 from 2 to 30 Rs. Out of these 74 C1 CMEs, 50 CMEs are found to be suitable for a quantitative study on their main acceleration in the inner corona and their residual acceleration in the outer corona. We find that, for the 50 events, the magnitude of the main acceleration ranges from 2.8 m/s2 to 4464.0 m/s2 with a median (average) value of 170.1 (330.9 m/s2 ) and a standard deviation of 644.8 m/s2, whereas the magnitude of the residual acceleration ranges only from -131.0 m/s2 to 52.0 m/s2 with a median (average) value of 3.1 (0.9 m/s2) and a standard deviation of 25.3 m/s2, The distribution of the duration of the main acceleration is from 6 min to 1200 min, with a median (average) value of 54 (180 min) and a standard deviation of 286 min. Apparently, the main acceleration has a wide distribution over almost three orders of magnitude in terms of both magnitude and duration, representing a continuous spectrum of events from extremely gradual ones all the way to extremely impulsive ones. We also find an interesting scaling law between acceleration magnitude (A) and acceleration duration (T) over the entire parameter range, that is A (m/s2) = 10000 T-1 (min); in the logarithmic scale, there is a strong inverse linear correlation between the two parameters, with a correlation coefficient of 0.95.

  15. Deccan Volcanism: a main trigger of environmental changes leading to the KTB mass extinction?

    NASA Astrophysics Data System (ADS)

    Adatte, Thierry; Fantasia, Alicia; Samant, Bandana; Mohabey, Dhananjay; Keller, Gerta; Gertsch, Brian

    2014-05-01

    The nature and causes of mass extinctions in the geological past have remained topics of intense scientific debate for the past three decades. Central to this debate is the question of whether the eruption of large igneous provinces (LIP) was the primary mechanism driving the environmental changes that are commonly regarded as the proximate causes for four of the five major Phanerozoic extinction events. Model results predict that Deccan Traps emplacement was responsible for a strong increase in atmospheric pCO2 accompanied by rapid warming of 4°C that was followed by global cooling. During the warming phase, increased continental weathering of silicates associated with consumption of atmospheric CO2 likely resulted in the drawdown of greenhouse gases that reversed the warming trend leading to global cooling at the end of the Maastrichtian. Massive CO2 input together with massive release of SO2 may thus have triggered the mass extinctions in the marine realm as a result of ocean acidification leading to a carbon crisis and in the terrestrial realms due to acid rains. Global stress conditions related to these climatic changes are well known and documented in planktic foraminifera by a diversity decrease, species dwarfing, dominance of opportunistic species and near disappearance of specialized species. Deccan Traps erupted in three main phases with 6% total Deccan volume in phase-1 (base C30n), 80% in phase-2 (C29r) and 14% in phase-3 (C29n). Recent studies indicate that the bulk (80%) of Deccan trap eruptions (Phase-2) occurred over a relatively short time interval in magnetic polarity C29r, whereas multiproxy studies from central and southeastern India place the Cretaceous-Tertiary (KT) mass extinction near the end of this main phase of Deccan volcanism suggesting a cause-and-effect relationship. In India a strong floral response is observed as a direct response to Deccan volcanic phase-2. In Lameta (infratrappean) sediments preceding the volcanic eruptions

  16. A Wide-field Survey for Transiting Hot Jupiters and Eclipsing Pre-main-sequence Binaries in Young Stellar Associations

    NASA Astrophysics Data System (ADS)

    Oelkers, Ryan J.; Macri, Lucas M.; Marshall, Jennifer L.; DePoy, Darren L.; Lambas, Diego G.; Colazo, Carlos; Stringer, Katelyn

    2016-09-01

    The past two decades have seen a significant advancement in the detection, classification, and understanding of exoplanets and binaries. This is due, in large part, to the increase in use of small-aperture telescopes (<20 cm) to survey large areas of the sky to milli-mag precision with rapid cadence. The vast majority of the planetary and binary systems studied to date consists of main-sequence or evolved objects, leading to a dearth of knowledge of properties at early times (<50 Myr). Only a dozen binaries and one candidate transiting Hot Jupiter are known among pre-main-sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well characterized systems is driven by the inherent and aperiodic variability found in pre-main-sequence objects, which can mask and mimic eclipse signals. Hence, a dramatic increase in the number of young systems with high-quality observations is highly desirable to guide further theoretical developments. We have recently completed a photometric survey of three nearby (<150 pc) and young (<50 Myr) moving groups with a small-aperture telescope. While our survey reached the requisite photometric precision, the temporal coverage was insufficient to detect Hot Jupiters. Nevertheless, we discovered 346 pre-main-sequence binary candidates, including 74 high-priority objects for further study. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.

  17. Persistent Sub-Yearly Chromospheric Variations in Lower Main-Sequence Stars: Tau Booe and alpha Com

    NASA Technical Reports Server (NTRS)

    Maulik, Davesh; Donahue, Robert A.; Baliunas, Sallie L.

    1997-01-01

    The recent discoveries of extrasolar planetary systems around lower main-sequence stars such as tau Booe (HD 120136) has prompted further investigation into their stellar activity. A cursory analysis of tau Booe for cyclic chromospheric activity, based on its 30-yr record of Ca 2 H and K fluxes obtained as part of the HK Project from Mount Wilson Observatory, finds an intermediate, sub-yearly period (approximately 117 d) in chromospheric activity in addition to, and separate from, both its rotation (3.3 d) and long-term variability. As a persistent subyearly period in surface magnetic activity is unprecedented, we investigate this apparent anomaly further by examining chromospheric activity levels of other stars with similar mass, searching for variability in chromospheric activity with periods of less than one year, but longer than measured or predicted rotation. An examination of the time series of 40 mid-to-late F dwarfs yielded one other star for further analysis: alpha Com (HD 114378, P approximately 132 d). The variations for these two stars were checked for persistence and coherence. Based on these determinations, we eliminate the possibilities of rotation, long-term activity cycle, and the evolution of active regions as the cause of this variation in both stars. In particular, for tau Booe we infer that the phenomenon may be chromospheric in origin; however, beyond this, it is difficult to identify anything further regarding the cause of the activity variations, or even whether the observed modulation in the two stars have the same origin.

  18. The confinement of star-forming galaxies into a main sequence through episodes of gas compaction, depletion and replenishment

    NASA Astrophysics Data System (ADS)

    Tacchella, Sandro; Dekel, Avishai; Carollo, C. Marcella; Ceverino, Daniel; DeGraf, Colin; Lapiner, Sharon; Mandelker, Nir; Primack Joel, R.

    2016-04-01

    Using cosmological simulations, we address the properties of high-redshift star-forming galaxies (SFGs) across their main sequence (MS) in the plane of star formation rate (SFR) versus stellar mass. We relate them to the evolution of galaxies through phases of gas compaction, depletion, possible replenishment, and eventual quenching. We find that the high-SFR galaxies in the upper envelope of the MS are compact, with high gas fractions and short depletion times (`blue nuggets'), while the lower SFR galaxies in the lower envelope have lower central gas densities, lower gas fractions, and longer depletion times, consistent with observed gradients across the MS. Stellar-structure gradients are negligible. The SFGs oscillate about the MS ridge on time-scales ˜0.4tHubble (˜1 Gyr at z ˜ 3). The propagation upwards is due to gas compaction, triggered, e.g. by mergers, counter-rotating streams, and/or violent disc instabilities. The downturn at the upper envelope is due to central gas depletion by peak star formation and outflows while inflow from the shrunken gas disc is suppressed. An upturn at the lower envelope can occur once the extended disc has been replenished by fresh gas and a new compaction can be triggered, namely as long as the replenishment time is shorter than the depletion time. The mechanisms of gas compaction, depletion, and replenishment confine the SFGs to the narrow (±0.3 dex) MS. Full quenching occurs in massive haloes (Mvir > 1011.5 M⊙) and/or at low redshifts (z < 3), where the replenishment time is long compared to the depletion time, explaining the observed bending down of the MS at the massive end.

  19. Pulsating low-mass white dwarfs in the frame of new evolutionary sequences. I. Adiabatic properties

    NASA Astrophysics Data System (ADS)

    Córsico, A. H.; Althaus, L. G.

    2014-09-01

    Context. Many low-mass white dwarfs with masses M∗/M⊙ ≲ 0.45, including the so-called extremely low-mass white dwarfs (M∗/M⊙ ≲ 0.20 - 0.25), have recently been discovered in the field of our Galaxy through dedicated photometric surveys. The subsequent discovery of pulsations in some of them has opened the unprecedented opportunity of probing the internal structure of these ancient stars. Aims: We present a detailed adiabatic pulsational study of these stars based on full evolutionary sequences derived from binary star evolution computations. The main aim of this study is to provide a detailed theoretical basis of reference for interpreting present and future observations of variable low-mass white dwarfs. Methods: Our pulsational analysis is based on a new set of He-core white-dwarf models with masses ranging from 0.1554 to 0.4352 M⊙ derived by computing the non-conservative evolution of a binary system consisting of an initially 1 M⊙ ZAMS star and a 1.4 M⊙ neutron star. We computed adiabatic radial (ℓ = 0) and non-radial (ℓ = 1,2) p and g modes to assess the dependence of the pulsational properties of these objects on stellar parameters such as the stellar mass and the effective temperature, as well as the effects of element diffusion. Results: We found that for white dwarf models with masses below ~ 0.18 M⊙, g modes mainly probe the core regions and p modes the envelope, therefore pulsations offer the opportunity of constraining both the core and envelope chemical structure of these stars via asteroseismology. For models with M∗ ≳ 0.18 M⊙, on the other hand, g modes are very sensitive to the He/H compositional gradient and therefore can be used as a diagnostic tool for constraining the H envelope thickness. Because both types of objects have not only very distinct evolutionary histories (according to whether the progenitor stars have experienced CNO-flashes or not), but also have strongly different pulsation properties, we propose to

  20. Full validation of therapeutic antibody sequences by middle-up mass measurements and middle-down protein sequencing.

    PubMed

    Resemann, Anja; Jabs, Wolfgang; Wiechmann, Anja; Wagner, Elsa; Colas, Olivier; Evers, Waltraud; Belau, Eckhard; Vorwerg, Lars; Evans, Catherine; Beck, Alain; Suckau, Detlev

    2016-01-01

    The regulatory bodies request full sequence data assessment both for innovator and biosimilar monoclonal antibodies (mAbs). Full sequence coverage is typically used to verify the integrity of the analytical data obtained following the combination of multiple LC-MS/MS datasets from orthogonal protease digests (so called "bottom-up" approaches). Top-down or middle-down mass spectrometric approaches have the potential to minimize artifacts, reduce overall analysis time and provide orthogonality to this traditional approach. In this work we report a new combined approach involving middle-up LC-QTOF and middle-down LC-MALDI in-source decay (ISD) mass spectrometry. This was applied to cetuximab, panitumumab and natalizumab, selected as representative US Food and Drug Administration- and European Medicines Agency-approved mAbs. The goal was to unambiguously confirm their reference sequences and examine the general applicability of this approach. Furthermore, a new measure for assessing the integrity and validity of results from middle-down approaches is introduced - the "Sequence Validation Percentage." Full sequence data assessment of the 3 antibodies was achieved enabling all 3 sequences to be fully validated by a combination of middle-up molecular weight determination and middle-down protein sequencing. Three errors in the reference amino acid sequence of natalizumab, causing a cumulative mass shift of only -2 Da in the natalizumab Fd domain, were corrected as a result of this work.

  1. Full validation of therapeutic antibody sequences by middle-up mass measurements and middle-down protein sequencing

    PubMed Central

    Resemann, Anja; Jabs, Wolfgang; Wiechmann, Anja; Wagner, Elsa; Colas, Olivier; Evers, Waltraud; Belau, Eckhard; Vorwerg, Lars; Evans, Catherine; Beck, Alain; Suckau, Detlev

    2016-01-01

    ABSTRACT The regulatory bodies request full sequence data assessment both for innovator and biosimilar monoclonal antibodies (mAbs). Full sequence coverage is typically used to verify the integrity of the analytical data obtained following the combination of multiple LC-MS/MS datasets from orthogonal protease digests (so called “bottom-up” approaches). Top-down or middle-down mass spectrometric approaches have the potential to minimize artifacts, reduce overall analysis time and provide orthogonality to this traditional approach. In this work we report a new combined approach involving middle-up LC-QTOF and middle-down LC-MALDI in-source decay (ISD) mass spectrometry. This was applied to cetuximab, panitumumab and natalizumab, selected as representative US Food and Drug Administration- and European Medicines Agency-approved mAbs. The goal was to unambiguously confirm their reference sequences and examine the general applicability of this approach. Furthermore, a new measure for assessing the integrity and validity of results from middle-down approaches is introduced – the “Sequence Validation Percentage.” Full sequence data assessment of the 3 antibodies was achieved enabling all 3 sequences to be fully validated by a combination of middle-up molecular weight determination and middle-down protein sequencing. Three errors in the reference amino acid sequence of natalizumab, causing a cumulative mass shift of only −2 Da in the natalizumab Fd domain, were corrected as a result of this work. PMID:26760197

  2. De Novo Sequencing of Top-Down Tandem Mass Spectra: A Next Step towards Retrieving a Complete Protein Sequence

    PubMed Central

    Vyatkina, Kira

    2017-01-01

    De novo sequencing of tandem (MS/MS) mass spectra represents the only way to determine the sequence of proteins from organisms with unknown genomes, or the ones not directly inscribed in a genome—such as antibodies, or novel splice variants. Top-down mass spectrometry provides new opportunities for analyzing such proteins; however, retrieving a complete protein sequence from top-down MS/MS spectra still remains a distant goal. In this paper, we review the state-of-the-art on this subject, and enhance our previously developed Twister algorithm for de novo sequencing of peptides from top-down MS/MS spectra to derive longer sequence fragments of a target protein. PMID:28248257

  3. The precision analysis of time series photometry and its application to searches for pre-main-sequence objects

    NASA Astrophysics Data System (ADS)

    Oelkers, Ryan James

    The past two decades have seen a significant advancement in the detection, classification and understanding of exoplanets and binary star systems. This is due, in large part, to the increase in use of small aperture telescopes (< 20 cm) to survey large portions of the night sky to milli-mag precision with rapid cadence. The vast majority of the planetary and binary systems studied consist of objects on the main sequence or the giant branch, leading to a dearth of knowledge of properties at early times (<50 Myr). Only a dozen binaries and one possible transiting Hot Jupiter are known among pre-main sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well-characterized systems is driven by the inherent and aperiodic variability found in pre-main-sequence objects which can mask and mimic eclipse signals. Nevertheless, a dramatic increase in the total number of systems at early times is required to alleviate the conflict between theory and observation. We have recently completed a photometric survey of 3 nearby (<150 pc) and young (<50 Myr) moving groups with a small aperture telescope. We discovered over 300 likely pre-main sequence binaries and ruled out 7 possible transiting Hot Jupiters using techniques developed by reducing crowded, defocused images from an analogous system. Using these observations we have determined a lower-limit on the migration timescale for Hot Jupiters to be 11 Myr and have identified numerous high priority pre-main-sequence binary candidates requiring further follow up.

  4. V 3903 Sagittarii: a massive main-sequence (O7V+O9V) detached eclipsing binary

    NASA Astrophysics Data System (ADS)

    Vaz, L. P. R.; Cunha, N. C. S.; Vieira, E. F.; Myrrha, M. L. M.

    1997-11-01

    We present for the first time an analysis based on uvby light curves, Hβ indices and on new spectroscopic data of the massive detached double-lined O-type eclipsing binary V 3903Sgr. The uvby light curves are analysed with the WINK (initial solutions) and the Wilson-Devinney (WD, final solution) programs. Both codes were used in their extended versions, with stellar atmospheres and taking into account the geometric distortions and photometric effects caused by proximity of the components. The spectroscopic CCD observations were analysed with the harmonic ``Wilsing-Russell'' and the ``Lehman-Filhes'' methods. We conclude that V 3903Sgr is one of the rare O-type detached systems where both components are still on the initial phases of the main sequence, with an age of either 1.6x10(6) yrs or 2.5x10(6) yrs (depending on the evolutionary model adopted) at a distance of ~1500pc, the same as for the Lagoon Nebula (Messier8) complex, of which the system is probably a member. We determine the absolute dimensions: M_A=27.27+/-0.55, R_A=8.088+/-% 0.086, M_B=19.01+/-0.44 and R_B=6.125+/-0.060 (solar units). There is no evidence of mass transfer and the system is detached. The orbit is circular, and both components show synchronous rotation, despite their early evolutionary stage. The absolute dimensions determined should be representative for normal single stars. Amongst the massive systems (M>17Msun) with precise absolute dimensions (errors <2%), V 3903Sgr is that with the most massive primary, with the largest mass difference between the components, and it is the youngest one. Based on data collected with the 60$\\,$cm and 1.6$\\,$m telescopes at the Pico dos Dias Observatory, Na\\-tional Laboratory of Astrophysics, LNA-CNPq, Bra\\-só\\-polis, MG, Brazil and with the Danish 50$\\,$cm telescope (SAT) at the European Southern Observatory (ESO), La Silla, Chile

  5. Prospects for detecting decreasing exoplanet frequency with main-sequence age using PLATO

    NASA Astrophysics Data System (ADS)

    Veras, Dimitri; Brown, David J. A.; Mustill, Alexander J.; Pollacco, Don

    2015-10-01

    The space mission PLATO will usher in a new era of exoplanetary science by expanding our current inventory of transiting systems and constraining host star ages, which are currently highly uncertain. This capability might allow PLATO to detect changes in planetary system architecture with time, particularly because planetary scattering due to Lagrange instability may be triggered long after the system was formed. Here, we utilize previously published instability time-scale prescriptions to determine PLATO's capability to detect a trend of decreasing planet frequency with age for systems with equal-mass planets. For two-planet systems, our results demonstrate that PLATO may detect a trend for planet masses which are at least as massive as super-Earths. For systems with three or more planets, we link their initial compactness to potentially detectable frequency trends in order to aid future investigations when these populations will be better characterized.

  6. The CRIRES Search for Planets at the Bottom of the Main Sequence

    NASA Astrophysics Data System (ADS)

    Bean, J.; Seifahrt, A.; Hartman, H.; Nilsson, H.; Wiedemann, G.; Reiners, A.; Dreizler, S.; Henry, T.

    2010-06-01

    We present the first results obtained from our ongoing search for planets around very low-mass stars and brown dwarfs using radial velocities measured with the CRIRES spectrograph on the VLT. High-precision radial velocity measurements for a large sample of these previously neglected stars are enabled by observing at near-infrared wavelengths and using a new type of gas cell that we have developed. Unprecedented long-term near-infrared radial velocity precisions of ~ 5 ms-1 have been demonstrated using CRIRES with the cell. As a first scientific result, data obtained for the very low-mass star VB 10 have been used to refute a claimed planet detection based on astrometry. These results demonstrate the unique sensitivity of our methodology, and confirm its power to detect planets, including potentially habitable ones, around the most numerous stars in the Galaxy.

  7. Stars of type MS with evidence of white dwarf companions. [IUE, Main Sequence (MS)

    NASA Technical Reports Server (NTRS)

    Peery, Benjamin F., Jr.

    1986-01-01

    A search for white dwarf companions of MS-type stars was conducted, using IUE. The overendowments of these stars in typical S-process nuclides suggest that they, like the Ba II stars, may owe their peculiar compositions to earlier mass transfer. Short-wavelength IUE spectra show striking emission line variability in HD35155, HD61913, and 4 Ori; HD35155 and 4 Ori show evidence of white dwarf companions.

  8. A frozen super-Earth orbiting a star at the bottom of the main sequence

    NASA Astrophysics Data System (ADS)

    Kubas, D.; Beaulieu, J. P.; Bennett, D. P.; Cassan, A.; Cole, A.; Lunine, J.; Marquette, J. B.; Dong, S.; Gould, A.; Sumi, T.; Batista, V.; Fouqué, P.; Brillant, S.; Dieters, S.; Coutures, C.; Greenhill, J.; Bond, I.; Nagayama, T.; Udalski, A.; Pompei, E.; Nürnberger, D. E. A.; Le Bouquin, J. B.

    2012-04-01

    Context. Microlensing is a unique method to probe low mass exoplanets beyond the snow line. However, the scientific potential of the new microlensing planet discovery is often unfulfilled due to lack of knowledge of the properties of the lens and source stars. The discovery light curve of the super Earth MOA-2007-BLG-192Lb suffers from significant degeneracies that limit what can be inferred about its physical properties. Aims: High resolution adaptive optics images allow us to solve this problem by resolving the microlensing target from all unrelated background stars, yielding the unique determination of magnified source and lens fluxes. This estimation permits the solution of our microlens model for the mass of the planet and its host and their physical projected separation. Methods: We observed the microlensing event MOA-2007-BLG-192 at high angular resolution in JHKs with the NACO adaptive optics system on the VLT while the object was still amplified by a factor 1.23 and then at baseline 18 months later. We analyzed and calibrated the NACO photometry in the standard 2MASS system in order to accurately constrain the source and the lens star fluxes. Results: We detect light from the host star of MOA-2007-BLG-192Lb, which significantly reduces the uncertainties in its characteristics as compared to earlier analyses. We find that MOA-2007-BLG-192L is most likely a very low mass late type M-dwarf (0.084-0.012+0.015 M⊙) at a distance of 660-70+100 pc orbited by a 3.2-1.8+5.2 M⊕ super-Earth at 0.66-0.22+0.51 AU. We then discuss the properties of this cold planetary system. Based on observations under ESO Prog.IDs: 279.C-5044(A) and 383-C.0495(A).

  9. The Main Sequence of Explosive Solar Active Regions: Discovery and Interpretation

    DTIC Science & Technology

    2009-01-01

    from equilibrium between input of free energy to an explosive active region’s magnetic field in the chromosphere and corona by contortion of the field...coronal mass ejections (CMEs) – Sun: flares 1. INTRODUCTION For an active region’s chromospheric and coronal magnetic field to be able to...reason for this trend is that in the smaller active regions near the front the maximum rate of buildup of free energy in the field in the chromosphere

  10. DeNovoID: a web-based tool for identifying peptides from sequence and mass tags deduced from de novo peptide sequencing by mass spectroscopy.

    PubMed

    Halligan, Brian D; Ruotti, Victor; Twigger, Simon N; Greene, Andrew S

    2005-07-01

    One of the core activities of high-throughput proteomics is the identification of peptides from mass spectra. Some peptides can be identified using spectral matching programs like Sequest or Mascot, but many spectra do not produce high quality database matches. De novo peptide sequencing is an approach to determine partial peptide sequences for some of the unidentified spectra. A drawback of de novo peptide sequencing is that it produces a series of ordered and disordered sequence tags and mass tags rather than a complete, non-degenerate peptide amino acid sequence. This incomplete data is difficult to use in conventional search programs such as BLAST or FASTA. DeNovoID is a program that has been specifically designed to use degenerate amino acid sequence and mass data derived from MS experiments to search a peptide database. Since the algorithm employed depends on the amino acid composition of the peptide and not its sequence, DeNovoID does not have to consider all possible sequences, but rather a smaller number of compositions consistent with a spectrum. DeNovoID also uses a geometric indexing scheme that reduces the number of calculations required to determine the best peptide match in the database. DeNovoID is available at http://proteomics.mcw.edu/denovoid.

  11. THE DUSTIEST POST-MAIN SEQUENCE STARS IN THE MAGELLANIC CLOUDS

    SciTech Connect

    Jones, Olivia C.; Meixner, Margaret; Roman-Duval, Julia; Sargent, Benjamin A.; Boyer, Martha L.; Sewiło, Marta; Hony, Sacha

    2015-10-01

    Using observations from the Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds (MC), we have found 35 evolved stars and stellar end products that are bright in the far-infrared. These 28 (LMC) and 7 (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found 13 low- to intermediate-mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae, and a symbiotic star. We also identify 10 high mass stars, including 4 of the 15 known B[e] stars in the MC, 3 extreme red supergiants that are highly enshrouded by dust, a Luminous Blue Variable, a Wolf–Rayet star, and two supernova remnants. Further, we report the detection of 9 probable evolved objects which were previously undescribed in the literature. These sources are likely to be among the dustiest evolved objects in the MC. The Herschel emission may either be due to dust produced by the evolved star or it may arise from swept-up interstellar medium material.

  12. The Dustiest Post-Main Sequence Stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Jones, Olivia C.; Meixner, Margaret; Sargent, Benjamin A.; Boyer, Martha L.; Sewiło, Marta; Hony, Sacha; Roman-Duval, Julia

    2015-10-01

    Using observations from the Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds (MC), we have found 35 evolved stars and stellar end products that are bright in the far-infrared. These 28 (LMC) and 7 (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found 13 low- to intermediate-mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae, and a symbiotic star. We also identify 10 high mass stars, including 4 of the 15 known B[e] stars in the MC, 3 extreme red supergiants that are highly enshrouded by dust, a Luminous Blue Variable, a Wolf-Rayet star, and two supernova remnants. Further, we report the detection of 9 probable evolved objects which were previously undescribed in the literature. These sources are likely to be among the dustiest evolved objects in the MC. The Herschel emission may either be due to dust produced by the evolved star or it may arise from swept-up interstellar medium material.

  13. Old pre-main-sequence stars. Disc reformation by Bondi-Hoyle accretion

    NASA Astrophysics Data System (ADS)

    Scicluna, P.; Rosotti, G.; Dale, J. E.; Testi, L.

    2014-06-01

    Young stars show evidence of accretion discs which evolve quickly and disperse with an e-folding time of ~3 Myr. This is in striking contrast with recent observations that suggest evidence of numerous >30 Myr old stars with an accretion disc in large star-forming complexes. We consider whether these observations of apparently old accretors could be explained by invoking Bondi-Hoyle accretion to rebuild a new disc around these stars during passage through a clumpy molecular cloud. We combine a simple Monte Carlo model to explore the capture of mass by such systems with a viscous evolution model to infer the levels of accretion that would be observed. We find that a significant fraction of stars may capture enough material via the Bondi-Hoyle mechanism to rebuild a disc of mass ≳1 minimum-mass solar nebula, and ≲10% accrete at observable levels at any given time. A significant fraction of the observed old accretors may be explained with our proposed mechanism. Such accretion may provide a chance for a second epoch of planet formation, and have unpredictable consequences for planetary evolution.

  14. Genome sequence of the necrotrophic fungus Penicillium digitatum, the main postharvest pathogen of citrus

    PubMed Central

    2012-01-01

    Background Penicillium digitatum is a fungal necrotroph causing a common citrus postharvest disease known as green mold. In order to gain insight into the genetic bases of its virulence mechanisms and its high degree of host-specificity, the genomes of two P. digitatum strains that differ in their antifungal resistance traits have been sequenced and compared with those of 28 other Pezizomycotina. Results The two sequenced genomes are highly similar, but important differences between them include the presence of a unique gene cluster in the resistant strain, and mutations previously shown to confer fungicide resistance. The two strains, which were isolated in Spain, and another isolated in China have identical mitochondrial genome sequences suggesting a recent worldwide expansion of the species. Comparison with the closely-related but non-phytopathogenic P. chrysogenum reveals a much smaller gene content in P. digitatum, consistent with a more specialized lifestyle. We show that large regions of the P. chrysogenum genome, including entire supercontigs, are absent from P. digitatum, and that this is the result of large gene family expansions rather than acquisition through horizontal gene transfer. Our analysis of the P. digitatum genome is indicative of heterothallic sexual reproduction and reveals the molecular basis for the inability of this species to assimilate nitrate or produce the metabolites patulin and penicillin. Finally, we identify the predicted secretome, which provides a first approximation to the protein repertoire used during invasive growth. Conclusions The complete genome of P. digitatum, the first of a phytopathogenic Penicillium species, is a valuable tool for understanding the virulence mechanisms and host-specificity of this economically important pest. PMID:23171342

  15. Genome sequence of the necrotrophic fungus Penicillium digitatum, the main postharvest pathogen of citrus.

    PubMed

    Marcet-Houben, Marina; Ballester, Ana-Rosa; de la Fuente, Beatriz; Harries, Eleonora; Marcos, Jose F; González-Candelas, Luis; Gabaldón, Toni

    2012-11-21

    Penicillium digitatum is a fungal necrotroph causing a common citrus postharvest disease known as green mold. In order to gain insight into the genetic bases of its virulence mechanisms and its high degree of host-specificity, the genomes of two P. digitatum strains that differ in their antifungal resistance traits have been sequenced and compared with those of 28 other Pezizomycotina. The two sequenced genomes are highly similar, but important differences between them include the presence of a unique gene cluster in the resistant strain, and mutations previously shown to confer fungicide resistance. The two strains, which were isolated in Spain, and another isolated in China have identical mitochondrial genome sequences suggesting a recent worldwide expansion of the species. Comparison with the closely-related but non-phytopathogenic P. chrysogenum reveals a much smaller gene content in P. digitatum, consistent with a more specialized lifestyle. We show that large regions of the P. chrysogenum genome, including entire supercontigs, are absent from P. digitatum, and that this is the result of large gene family expansions rather than acquisition through horizontal gene transfer. Our analysis of the P. digitatum genome is indicative of heterothallic sexual reproduction and reveals the molecular basis for the inability of this species to assimilate nitrate or produce the metabolites patulin and penicillin. Finally, we identify the predicted secretome, which provides a first approximation to the protein repertoire used during invasive growth. The complete genome of P. digitatum, the first of a phytopathogenic Penicillium species, is a valuable tool for understanding the virulence mechanisms and host-specificity of this economically important pest.

  16. The Radial Distributions of the Two Main-sequence Components in the Young Massive Star Cluster NGC 1856

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    The recent discovery of double main sequences in the young, massive star cluster NGC 1856 has caught significant attention. The observations can be explained by invoking two stellar generations with different ages and metallicities or by a single generation of stars composed of two populations characterized by different rotation rates. We analyzed the number ratios of stars belonging to both main-sequence components in NGC 1856 as a function of radius. We found that their number ratios remain approximately unchanged from the cluster’s central region to its periphery, indicating that both components are homogeneously distributed in space. Through a comparison of the loci of the best-fitting isochrones with the ridge lines of both stellar components, we found that both multiple stellar populations and rapid stellar rotation can potentially explain the observed main-sequence bifurcation in NGC 1856. However, if NGC 1856 were a young representative of the old globular clusters, then the multiple stellar populations model would not be able to explain the observed homogeneity in the spatial distributions of these two components, since all relevant scenarios would predict that the second stellar generation should be formed in a more compact configuration than that of the first stellar generation, while NGC 1856 is too young for both stellar generations to have been fully mixed dynamically. We speculate that the rapid stellar rotation scenario would be the favored explanation of the observed multiple stellar sequences in NGC 1856.

  17. A tale of two anomalies: Depletion, dispersion, and the connection between the stellar lithium spread and inflated radii on the pre-main sequence

    SciTech Connect

    Somers, Garrett; Pinsonneault, Marc H. E-mail: pinsono@astronomy.ohio-state.edu

    2014-07-20

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T{sub eff} is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  18. Detection of methamphetamine and its main metabolite in fingermarks by liquid chromatography-mass spectrometry.

    PubMed

    Zhang, Ting; Chen, Xueguo; Yang, Ruiqin; Xu, Yingjian

    2015-03-01

    A sensitive and efficient method applying liquid chromatography-mass spectrometry for the analysis of methamphetamine and its main metabolite in fingermark deposits was described. Using this method, good linear relationship of methamphetamine was obtained in the range of 0.005μg to 0.5μg per cotton swab, the limit of detection was 1.5ng per cotton swab, the limit of quantitation was 5.0ng per cotton swab and the average values of recovery ratios were above 70.1%. Moreover, the influence factors for the detection of methamphetamine in fingermarks, such as kinds of substrates, development methods and extraction methods, were all discussed in details. The results showed that good recovery ratios could be obtained on painted wood and smooth substrates surfaces. Development methods in commercial powder could not influence the quality of examination of exogenous drug in latent fingermark. Furthermore, the results indicated that the method mentioned here could be applied in the analysis of forensic trace evidences and samples obtained in clinically addicted cases.

  19. Protein sequences from mastodon and Tyrannosaurus rex revealed by mass spectrometry.

    PubMed

    Asara, John M; Schweitzer, Mary H; Freimark, Lisa M; Phillips, Matthew; Cantley, Lewis C

    2007-04-13

    Fossilized bones from extinct taxa harbor the potential for obtaining protein or DNA sequences that could reveal evolutionary links to extant species. We used mass spectrometry to obtain protein sequences from bones of a 160,000- to 600,000-year-old extinct mastodon (Mammut americanum) and a 68-million-year-old dinosaur (Tyrannosaurus rex). The presence of T. rex sequences indicates that their peptide bonds were remarkably stable. Mass spectrometry can thus be used to determine unique sequences from ancient organisms from peptide fragmentation patterns, a valuable tool to study the evolution and adaptation of ancient taxa from which genomic sequences are unlikely to be obtained.

  20. Understanding the scatter in the spatially resolved star formation main sequence of local massive spiral galaxies

    NASA Astrophysics Data System (ADS)

    Abdurro'uf, Akiyama, Masayuki

    2017-08-01

    We investigate the relation between star formation rate (SFR) and stellar mass (M*) at the sub-galactic scale (∼1 kpc) of 93 local (0.01 < z < 0.02) massive (M* > 1010.5 M⊙) spiral galaxies. To derive a spatially resolved SFR and stellar mass, we perform the so-called pixel-to-pixel spectral energy distribution (SED) fitting, which fits an observed spatially resolved multiband SED with a library of model SEDs using Bayesian statistics. We use two bands (far-ultraviolet or FUV and near-ultraviolet or NUV) and five bands (u, g, r, i and z) of imaging data from Galaxy Evolution Explorer (GALEX) and Sloan Digital Sky Survey (SDSS), respectively. We find a tight nearly linear relation between the local surface density of SFR (ΣSFR) and stellar mass (Σ*), which is flattened at high Σ*. The near linear relation between Σ* and ΣSFR suggests a constant specific SFR (sSFR) throughout the galaxies, and the scatter of the relation is directly related to that of the sSFR. Therefore, we analyse the variation of the sSFR in various scales. More massive galaxies on average have lower sSFR throughout them than less massive galaxies. We also find that barred galaxies have a lower sSFR in the core region than non-barred galaxies. However, in the outer region, the sSFRs of barred and non-barred galaxies are similar and lead to a similar total sSFR.

  1. A Monte Carlo sampling method of amino acid sequences adaptable to given main-chain atoms in the proteins.

    PubMed

    Ogata, Koji; Soejima, Kenji; Higo, Junichi

    2006-10-01

    We have developed a computational method of protein design to detect amino acid sequences that are adaptable to given main-chain coordinates of a protein. In this method, the selection of amino acid types employs a Metropolis Monte Carlo method with a scoring function in conjunction with the approximation of free energies computed from 3D structures. To compute the scoring function, a side-chain prediction using another Metropolis Monte Carlo method was performed to select structurally suitable side-chain conformations from a side-chain library. In total, two layers of Monte Carlo procedures were performed, first to select amino acid types (1st layer Monte Carlo) and then to predict side-chain conformations (2nd layers Monte Carlo). We applied this method to sequence design for the entire sequence on the SH3 domain, Protein G, and BPTI. The predicted sequences were similar to those of the wild-type proteins. We compared the results of the predictions with and without the 2nd layer Monte Carlo method. The results revealed that the two-layer Monte Carlo method produced better sequence similarity to the wild-type proteins than the one-layer method. Finally, we applied this method to neuraminidase of influenza virus. The results were consistent with the sequences identified from the isolated viruses.

  2. Soft X-ray observations of pre-main-sequence stars in the Chamaeleon dark cloud

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.; Kriss, Gerard A.

    1989-01-01

    X-ray observations of the Chamaeleon I cloud, a star-forming region, are reported. A total of 22 distinct X-ray sources, most associated with previously identified premain sequence stars, are found. The spatial distributions and HR diagrams of the stars are very similar, suggesting that they are coeval. Luminosity functions suggest that the stars have an average X-ray luminosity (Lx) several times that of the Pleiades dwarfs. The value of Lx is significantly correlated with optical magnitude, though no relation between X-ray emission and any photometric or emission line characteristic is present. It is suggested that a Skumanich-type power-law relation may be present over the entire range of stellar ages between 10 to the 6th and 10 to the 10th yr.

  3. The main challenges that remain in applying high-throughput sequencing to clinical diagnostics.

    PubMed

    Loeffelholz, Michael; Fofanov, Yuriy

    2015-01-01

    Over the last 10 years, the quality, price and availability of high-throughput sequencing instruments have improved to the point that this technology may be close to becoming a routine tool in the diagnostic microbiology laboratory. Two groups of challenges, however, have to be resolved in order to move this powerful research technology into routine use in the clinical microbiology laboratory. The computational/bioinformatics challenges include data storage cost and privacy concerns, requiring analysis to be performed without access to cloud storage or expensive computational infrastructure. The logistical challenges include interpretation of complex results and acceptance and understanding of the advantages and limitations of this technology by the medical community. This article focuses on the approaches to address these challenges, such as file formats, algorithms, data collection, reporting and good laboratory practices.

  4. Soft X-ray observations of pre-main-sequence stars in the Chamaeleon dark cloud

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.; Kriss, Gerard A.

    1989-01-01

    X-ray observations of the Chamaeleon I cloud, a star-forming region, are reported. A total of 22 distinct X-ray sources, most associated with previously identified premain sequence stars, are found. The spatial distributions and HR diagrams of the stars are very similar, suggesting that they are coeval. Luminosity functions suggest that the stars have an average X-ray luminosity (Lx) several times that of the Pleiades dwarfs. The value of Lx is significantly correlated with optical magnitude, though no relation between X-ray emission and any photometric or emission line characteristic is present. It is suggested that a Skumanich-type power-law relation may be present over the entire range of stellar ages between 10 to the 6th and 10 to the 10th yr.

  5. Deep water masses and sediments are main compartments for polychlorinated biphenyls in the Arctic Ocean.

    PubMed

    Sobek, Anna; Gustafsson, Örjan

    2014-06-17

    There is a wealth of studies of polychlorinated biphenyls (PCB) in surface water and biota of the Arctic Ocean. Still, there are no observation-based assessments of PCB distribution and inventories in and between the major Arctic Ocean compartments. Here, the first water column distribution of PCBs in the central Arctic Ocean basins (Nansen, Amundsen, and Makarov) is presented, demonstrating nutrient-like vertical profiles with 5-10 times higher concentrations in the intermediate and deep water masses than in surface waters. The consistent vertical profiles in all three Arctic Ocean basins likely reflect buildup of PCBs transported from the shelf seas and from dissolution and/or mineralization of settling particles. Combined with measurement data on PCBs in other Arctic Ocean compartments collected over the past decade, the total Arctic Ocean inventory of ∑7PCB was estimated to 182 ± 40 t (±1 standard error of the mean), with sediments (144 ± 40 t), intermediate (5 ± 1 t) and deep water masses (30 ± 2 t) storing 98% of the PCBs in the Arctic Ocean. Further, we used hydrographic and carbon cycle parametrizations to assess the main pathways of PCBs into and out of the Arctic Ocean during the 20th century. River discharge appeared to be the major pathway for PCBs into the Arctic Ocean with 115 ± 11 t, followed by ocean currents (52 ± 17 t) and net atmospheric deposition (30 ± 28 t). Ocean currents provided the only important pathway out of the Arctic Ocean, with an estimated cumulative flux of 22 ± 10 t. The observation-based inventory of ∑7PCB of 182 ± 40 t is consistent with the contemporary inventory based on cumulative fluxes for ∑7PCB of 173 ± 36 t. Information on the concentration and distribution of PCBs in the deeper compartments of the Arctic Ocean improves our understanding of the large-scale fate of POPs in the Arctic and may also provide a means to test and improve models used to assess the fate of organic pollutants in the Arctic.

  6. Some aspects of cool main sequence star ages derived from stellar rotation (gyrochronology)

    NASA Astrophysics Data System (ADS)

    Barnes, S. A.; Spada, F.; Weingrill, J.

    2016-09-01

    Rotation periods for cool stars can be measured with good precision by monitoring starspot light modulation. Observations have shown that the rotation periods of dwarf stars of roughly solar metallicity have such systematic dependencies on stellar age and mass that they can be used to derive reliable ages, a procedure called gyrochronology. We review the method and show illustrative cases, including recent ground- and space-based data. The age uncertainties approach 10 % in the best cases, making them a valuable complement to, and constraint on, asteroseismic or other ages. Edited, updated, and refereed version of a presentation at the WE-Heraeus-Seminar in Bad Honnef, Germany: Reconstructing the Milky Way's History: Spectroscopic Surveys, Asteroseismology and Chemodynamical Models

  7. OLD MAIN-SEQUENCE TURNOFF PHOTOMETRY IN THE SMALL MAGELLANIC CLOUD. II. STAR FORMATION HISTORY AND ITS SPATIAL GRADIENTS

    SciTech Connect

    Noel, Noelia E. D.; Gallart, Carme; Hidalgo, Sebastian L.; Aparicio, Antonio; Costa, Edgardo; Mendez, Rene A. E-mail: carme@iac.e E-mail: antapaj@iac.e E-mail: rmendez@das.uchile.c

    2009-11-10

    We present a quantitative analysis of the star formation history (SFH) of 12 fields in the Small Magellanic Cloud (SMC) based on unprecedented deep [(B - R), R] color-magnitude diagrams (CMDs). Our fields reach down to the oldest main-sequence turnoff with a high photometric accuracy, which is vital for obtaining accurate SFHs, particularly at intermediate and old ages. We use the IAC-pop code to obtain the SFH, using synthetic CMDs generated with IAC-star. We obtain the SFH as a function psi(t, z) of age and metallicity. We also consider several auxiliary functions: the initial mass function (IMF), phi(m), and a function accounting for the frequency and relative mass distribution of binary stars, beta(f, q). We find that there are several main periods of enhancement of star formation: a young one peaked at approx0.2-0.5 Gyr old, only present in the eastern and in the central-most fields; two at intermediate ages present in all fields: a conspicuous one peaked at approx4-5 Gyr, and a less significant one peaked at approx1.5-2.5; and an old one, peaked at approx10 Gyr in all fields but the western ones. In the western fields, this old enhancement splits into two, one peaked at approx8 Gyr old and another at approx12 Gyr old. This 'two-enhancement' zone is unaffected by our choice of stellar evolutionary library but more data covering other fields of the SMC are necessary in order to ascertain its significancy. Correlation between star formation rate enhancements and SMC-Milky Way encounters is not clear. Some correlation could exist with encounters taken from the orbit determination of Kallivayalil et al. But our results would also fit in a first pericenter passage scenario like the one claimed by Besla et al. For SMC-Large Magellanic Cloud encounters, we find a correlation only for the most recent encounter approx0.2 Gyr ago. This coincides with the youngest psi(t) enhancement peaked at these ages in our eastern fields. The population younger than 1 Gyr represents

  8. High-resolution Imaging of PHIBSS z ˜ 2 Main-sequence Galaxies in CO J = 1 → 0

    NASA Astrophysics Data System (ADS)

    Bolatto, A. D.; Warren, S. R.; Leroy, A. K.; Tacconi, L. J.; Bouché, N.; Förster Schreiber, N. M.; Genzel, R.; Cooper, M. C.; Fisher, D. B.; Combes, F.; García-Burillo, S.; Burkert, A.; Bournaud, F.; Weiss, A.; Saintonge, A.; Wuyts, S.; Sternberg, A.

    2015-08-01

    We present Karl Jansky Very Large Array observations of the CO J=1-0 transition in a sample of four z˜ 2 main-sequence galaxies. These galaxies are in the blue sequence of star-forming galaxies at their redshift, and are part of the IRAM Plateau de Bure HIgh-z Blue Sequence Survey which imaged them in CO J=3-2. Two galaxies are imaged here at high signal-to-noise, allowing determinations of their disk sizes, line profiles, molecular surface densities, and excitation. Using these and published measurements, we show that the CO and optical disks have similar sizes in main-sequence galaxies, and in the galaxy where we can compare CO J=1-0 and J=3-2 sizes we find these are also very similar. Assuming a Galactic CO-to-H2 conversion, we measure surface densities of {{{Σ }}}{mol}˜ 1200 {M}⊙ pc-2 in projection and estimate {{{Σ }}}{mol}˜ 500-900 {M}⊙ pc-2 deprojected. Finally, our data yields velocity-integrated Rayleigh-Jeans brightness temperature line ratios r31 that are approximately at unity. In addition to the similar disk sizes, the very similar line profiles in J=1-0 and J=3-2 indicate that both transitions sample the same kinematics, implying that their emission is coextensive. We conclude that in these two main-sequence galaxies there is no evidence for significant excitation gradients or a large molecular reservoir that is diffuse or cold and not involved in active star formation. We suggest that r31 in very actively star-forming galaxies is likely an indicator of how well-mixed the star formation activity and the molecular reservoir are.

  9. CCD photometry in the globular cluster NGC 288. I - Blue stragglers and main-sequence binary stars

    NASA Technical Reports Server (NTRS)

    Bolte, Michael

    1992-01-01

    Photometry based on a mosaic of CCD images in B and V is presented for the globular cluster NGC 288. The spatial coverage ranges from the cluster core to about 6 core radii, and stars have been measured over the absolute visual magnitude range -1.2 to 8.4. The cluster is shown to contain a significant number of blue straggler stars in the central regions, and there is an excess of objects brighter and redder than the single-star main-sequence in the color-magnitude plane. These objects are interpreted as a population of main-sequence binary stars. With this interpretation, the explicity measured fraction of binary stars is 10 percent, which sets a lower limit for the total binary population.

  10. On the determination of the He abundance distribution in globular clusters from the width of the main sequence

    NASA Astrophysics Data System (ADS)

    Cassisi, Santi; Salaris, Maurizio; Pietrinferni, Adriano; Hyder, David

    2017-01-01

    One crucial piece of information to study the origin of multiple stellar populations in globular clusters is the range of initial helium abundances ΔY amongst the sub-populations hosted by each cluster. These estimates are commonly obtained by measuring the width in colour of the unevolved main sequence in an optical colour-magnitude diagram (CMD). The measured colour spread is then compared with predictions from theoretical stellar isochrones with varying initial He abundances to determine ΔY. The availability of UV/optical magnitudes, thanks to the Hubble Space Telescope UV Legacy Survey of Galactic GCs project, will allow the homogeneous determination of ΔY for a large Galactic globular cluster sample. From a theoretical point of view, accurate UV CMDs can efficiently disentangle the various sub-populations, and main sequence colour differences in the ACS F606W - (F606W - F814W) diagram allow an estimate of ΔY. We demonstrate that from a theoretical perspective, the (F606W - F814W) colour is an extremely reliable He-abundance indicator. The derivative dY/d(F606W - F814W), computed at a fixed luminosity along the unevolved main sequence, is largely insensitive to the physical assumptions made in stellar model computations, being more sensitive to the choice of the bolometric correction scale, and is only slightly dependent on the adopted set of stellar models. From a theoretical point of view, the (F606W - F814W) colour width of the cluster main sequence is therefore a robust diagnostic of the ΔY range.

  11. The age-metallicity relation in the solar neighbourhood from a pilot sample of white dwarf-main sequence binaries

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Anguiano, B.; García-Berro, E.; Freeman, K. C.; Cojocaru, R.; Manser, C. J.; Pala, A. F.; Gänsicke, B. T.; Liu, X.-W.

    2016-12-01

    The age-metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR for the solar neighbourhood, primarily due to the difficulty in obtaining accurate stellar ages for individual field stars. We have started an observational campaign for providing the much needed observational input by using wide white-dwarf-main-sequence (WDMS) binaries. White dwarfs are `natural' clocks and can be used to derive accurate ages. Metallicities can be obtained from the main-sequence companions. Since the progenitors of white dwarfs and the main-sequence stars were born at the same time, WDMS binaries provide a unique opportunity to observationally constrain in a robust way the properties of the AMR. In this work we present the AMR derived from analysing a pilot sample of 23 WDMS binaries and provide clear observational evidence for the lack of correlation between age and metallicity at young and intermediate ages (0-7 Gyr).

  12. Rotating Stellar Models Can Account for the Extended Main-sequence Turnoffs in Intermediate-age Clusters

    NASA Astrophysics Data System (ADS)

    Brandt, Timothy D.; Huang, Chelsea X.

    2015-07-01

    We show that the extended main-sequence turnoffs seen in intermediate-age Large Magellanic Cloud (LMC) clusters, often attributed to age spreads of several 100 Myr, may be easily accounted for by variable stellar rotation in a coeval population. We compute synthetic photometry for grids of rotating stellar evolution models and interpolate them to produce isochrones at a variety of rotation rates and orientations. An extended main-sequence turnoff naturally appears in color-magnitude diagrams at ages just under 1 Gyr, peaks in extent between ˜1 and 1.5 Gyr, and gradually disappears by around 2 Gyr in age. We then fit our interpolated isochrones by eye to four LMC clusters with very extended main-sequence turnoffs: NGC 1783, 1806, 1846, and 1987. In each case, stellar populations with a single age and metallicity can comfortably account for the observed extent of the turnoff region. The new stellar models predict almost no correlation of turnoff color with rotational v{sin}i. The red part of the turnoff is populated by a combination of slow rotators and edge-on rapid rotators, while the blue part contains rapid rotators at lower inclinations.

  13. Searching for gas giant planets on Solar system scales - a NACO/APP L'-band survey of A- and F-type main-sequence stars

    NASA Astrophysics Data System (ADS)

    Meshkat, T.; Kenworthy, M. A.; Reggiani, M.; Quanz, S. P.; Mamajek, E. E.; Meyer, M. R.

    2015-11-01

    We report the results of a direct imaging survey of A- and F-type main-sequence stars searching for giant planets. A/F stars are often the targets of surveys, as they are thought to have more massive giant planets relative to solar-type stars. However, most imaging is only sensitive to orbital separations >30 au, where it has been demonstrated that giant planets are rare. In this survey, we take advantage of the high-contrast capabilities of the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope. Combined with optimized principal component analysis post-processing, we are sensitive to planetary-mass companions (2-12 MJup) at Solar system scales (≤30 au). We obtained data on 13 stars in the L' band and detected one new companion as part of this survey: an M6.0 ± 0.5 dwarf companion around HD 984. We re-detect low-mass companions around HD 12894 and HD 20385, both reported shortly after the completion of this survey. We use Monte Carlo simulations to determine new constraints on the low-mass (<80 MJup) companion frequency, as a function of mass and separation. Assuming solar-type planet mass and separation distributions, normalized to the planet frequency appropriate for A-stars, and the observed companion mass-ratio distribution for stellar companions extrapolated to planetary masses, we derive a truncation radius for the planetary mass companion surface density of <135 au at 95 per cent confidence.

  14. The space density and kinematics of blue metal-poor main sequence stars near the solar circle

    NASA Astrophysics Data System (ADS)

    Preston, George W.; Beers, Timothy C.; Shectman, Stephen A.

    1994-08-01

    From analysis of a photometrically selected sample of 175 metal-poor field stars with main sequence gravities (hereafter BMPs) and UBV colors blueward of the most metal-poor globular cluster main-sequence turnoffs, 0.15 less than (B-V)0 less than 0.35, and properties of the candidate lists of the HK objective prism survey, we calculate the space density and a suitably defined specific frequency of BMPs within approximately 2 kpc of the Sun. We consider two cases. If we adopt the luminosities and color distribution of globular cluster blue stragglers (hereafter BS) for BMPs the BMP space density is approximately 350 kpc(exp-3), from which we obtain a specific frequency SBMP approximately 8, a value 9 times larger than that of BSs in globular clusters. From this result, we conclude that cluster-type BSs are but a minor component of the field BMPs and that the remainder must be of a different nature. If we adopt luminosities of metal-poor models halfway between the Zero Age Main Sequence and the phase of core hydrogen exhaustion, we obtain a space density of 450 (+300,-150) kpc(exp-3) and a specific frequency SBMP = 10(+5,-3). From a subsample of 107 BMPs with available radial velocities we derive a galactic rotation of 128 km s-1 and an isotropic velocity dispersion of Sigma r phi theta approximately 90 km s-1, values intermediate between those of halo and thick-disk populations. From analysis of a larger sample of stars on 0.15 less than (B-V)0 less than 0.35 binned by a crude line-blanketing parameter, we find that our results are insensitive to adopted BMP selection criteria: none of these subsamples of A- and early F-type stars above the galactic plane possess disk kinematics. The region of the UBV two-color diagram occupied by BMPs could be populated by metal-deficient, main-sequence gravity stars with ages substantially younger than those of the metal-poor halo. Because we cannot imagine how or where the observed local population of BMPs could have been

  15. EPA Awards Funding for Brownfield Cleanup Planning in Lawrence and New Bedford, Mass. and Portland, Maine

    EPA Pesticide Factsheets

    The City of Lawrence, Mass., the City of New Bedford, Mass., and the Greater Portland Council of Governments are among 20 communities in 16 states selected to receive a grant of up to $200,000 from EPA for Brownfields Area-Wide Planning projects...

  16. Determination of the sequences of protein-derived peptides and peptide mixtures by mass spectrometry

    PubMed Central

    Morris, Howard R.; Williams, Dudley H.; Ambler, Richard P.

    1971-01-01

    Micro-quantities of protein-derived peptides have been converted into N-acetylated permethyl derivatives, and their sequences determined by low-resolution mass spectrometry without prior knowledge of their amino acid compositions or lengths. A new strategy is suggested for the mass spectrometric sequencing of oligopeptides or proteins, involving gel filtration of protein hydrolysates and subsequent sequence analysis of peptide mixtures. Finally, results are given that demonstrate for the first time the use of mass spectrometry for the analysis of a protein-derived peptide mixture, again without prior knowledge of the protein or components within the mixture. PMID:5158904

  17. Extreme value statistics for two-dimensional convective penetration in a pre-main sequence star

    NASA Astrophysics Data System (ADS)

    Pratt, J.; Baraffe, I.; Goffrey, T.; Constantino, T.; Viallet, M.; Popov, M. V.; Walder, R.; Folini, D.

    2017-08-01

    Context. In the interior of stars, a convectively unstable zone typically borders a zone that is stable to convection. Convective motions can penetrate the boundary between these zones, creating a layer characterized by intermittent convective mixing, and gradual erosion of the density and temperature stratification. Aims: We examine a penetration layer formed between a central radiative zone and a large convection zone in the deep interior of a young low-mass star. Using the Multidimensional Stellar Implicit Code (MUSIC) to simulate two-dimensional compressible stellar convection in a spherical geometry over long times, we produce statistics that characterize the extent and impact of convective penetration in this layer. Methods: We apply extreme value theory to the maximal extent of convective penetration at any time. We compare statistical results from simulations which treat non-local convection, throughout a large portion of the stellar radius, with simulations designed to treat local convection in a small region surrounding the penetration layer. For each of these situations, we compare simulations of different resolution, which have different velocity magnitudes. We also compare statistical results between simulations that radiate energy at a constant rate to those that allow energy to radiate from the stellar surface according to the local surface temperature. Results: Based on the frequency and depth of penetrating convective structures, we observe two distinct layers that form between the convection zone and the stable radiative zone. We show that the probability density function of the maximal depth of convective penetration at any time corresponds closely in space with the radial position where internal waves are excited. We find that the maximal penetration depth can be modeled by a Weibull distribution with a small shape parameter. Using these results, and building on established scalings for diffusion enhanced by large-scale convective motions, we

  18. RECONCILING THE OBSERVED STAR-FORMING SEQUENCE WITH THE OBSERVED STELLAR MASS FUNCTION

    SciTech Connect

    Leja, Joel; Van Dokkum, Pieter G.; Franx, Marijn; Whitaker, Katherine E.

    2015-01-10

    We examine the connection between the observed star-forming sequence (SFR ∝ M {sup α}) and the observed evolution of the stellar mass function in the range 0.2 < z < 2.5. We find that the star-forming sequence cannot have a slope α ≲ 0.9 at all masses and redshifts because this would result in a much higher number density at 10 < log (M/M {sub ☉}) < 11 by z = 1 than is observed. We show that a transition in the slope of the star-forming sequence, such that α = 1 at log (M/M {sub ☉}) < 10.5 and α = 0.7-0.13z (Whitaker et al.) at log (M/M {sub ☉}) > 10.5, greatly improves agreement with the evolution of the stellar mass function. We then derive a star-forming sequence that reproduces the evolution of the mass function by design. This star-forming sequence is also well described by a broken power law, with a shallow slope at high masses and a steep slope at low masses. At z = 2, it is offset by ∼0.3 dex from the observed star-forming sequence, consistent with the mild disagreement between the cosmic star formation rate (SFR) and recent observations of the growth of the stellar mass density. It is unclear whether this problem stems from errors in stellar mass estimates, errors in SFRs, or other effects. We show that a mass-dependent slope is also seen in other self-consistent models of galaxy evolution, including semianalytical, hydrodynamical, and abundance-matching models. As part of the analysis, we demonstrate that neither mergers nor hidden low-mass quiescent galaxies are likely to reconcile the evolution of the mass function and the star-forming sequence. These results are supported by observations from Whitaker et al.

  19. Duration of inverted metamorphic sequence formation across the Himalayan Main Central Thrust (MCT), Sikkim

    NASA Astrophysics Data System (ADS)

    Cioldi, Stefania; Moulas, Evangelos; Tajcmanová, Lucie; Burg, Jean-Pierre

    2016-04-01

    Collision between the Indian and Eurasian plates since the Eocene (50 Ma) caused the closure of the Neo-Tethys and the underthrusting of India beneath the Tibetan Plateau, generating the 2500 km extended Himalayan belt. The Main Central Thrust (MCT) marks the boundary of the underlying Midland Lower Himalaya metasediments zone (LH) in the south from the overlying high grade metamorphic Higher Himalaya (HH) in the north. Several models considering petrochronology, geothermobarometry and structural geology have been discussed to explain the inverted metamorphic gradient in the LH metasediments without reaching a common agreement. This study investigates the tectonic setting and the timescale of inverted isograds related to crustal-scale thrusting at the MCT in the Sikkim region, northeast India. The aim is to contribute to the understanding of the link between mechanical and thermal evolution of major thrust zones and to clarify the nature and the origin of orogenic heat applying garnet geospeedometry. Garnets provide a sensitive record of metamorphic conditions and are potential chronometer. Their compositional zoning is used as a gauge for rate estimates of element diffusion within the mineral and allows estimating the absolute time of the thermal evolution. Inverse-fitting numerical model considering FRactIonation and Diffusion in GarnEt (FRIDGE) calculates garnet composition profiles by introducing P-T-t paths and bulk-rock composition of a specific sample. P-T conditions were estimated by convectional geothermobarometry supported by phase equilibria modelling and measured garnet chemical compositions. Simulation were compared with measured garnet profiles. Simple step function and FRIDGE preliminary results of Fe-Mg - Ca - Mn garnet fractionation-diffusion modelling indicate very short timescale (between 3 and 6 Ma) for peak metamorphic conditions in the northeast Himalayan collisional system. This duration does not allow thermal re-equilibration. It is an

  20. Novel peptide identification from tandem mass spectra using ESTs and sequence database compression

    PubMed Central

    Edwards, Nathan J

    2007-01-01

    Peptide identification by tandem mass spectrometry is the dominant proteomics workflow for protein characterization in complex samples. Traditional search engines, which match peptide sequences with tandem mass spectra to identify the samples' proteins, use protein sequence databases to suggest peptide candidates for consideration. Although the acquisition of tandem mass spectra is not biased toward well-understood protein isoforms, this computational strategy is failing to identify peptides from alternative splicing and coding SNP protein isoforms despite the acquisition of good-quality tandem mass spectra. We propose, instead, that expressed sequence tags (ESTs) be searched. Ordinarily, such a strategy would be computationally infeasible due to the size of EST sequence databases; however, we show that a sophisticated sequence database compression strategy, applied to human ESTs, reduces the sequence database size approximately 35-fold. Once compressed, our EST sequence database is comparable in size to other commonly used protein sequence databases, making routine EST searching feasible. We demonstrate that our EST sequence database enables the discovery of novel peptides in a variety of public data sets. PMID:17437027

  1. A new method to disentangle the rotational velocities of stars: Application to main-sequence field Stars

    NASA Astrophysics Data System (ADS)

    Curé, M.; Rial, D. F.; Cassetti, J.; Christen, A.

    2014-10-01

    The projected rotational velocity v sin i is a fundamental observable quantity. In order to obtain the rotational velocity distribution of a sample of v sin i, Chandrasekhar & Münch (1950) developed a formalism to obtain this distribution under the assumption that rotational axes are uniformly distributed, but this method is not usually applied due to an intrinsic numerical problem associated to the derivative of an Abel's integral. An alternative iterative method was developed by Lucy (1974) to disentangle the distribution function of this kind of inverse problem, but this method has no convergence criteria. Here we present a new method to disentangle the distribution of rotational velocities, based on Chandrasekhar & Münch (1950) formalism. We obtain the cumulative distribution function (CDF) of the rotational velocities from projected velocities (v sin i) under the standard assumption of uniform distributed rotational axes. Through simulations the method is tested using a) theoretical Maxwellian distribution functions for the rotational velocity distribution and b) with a sample of about 12.500 main-sequence field stars. Our main results are: The method is robust and in just one step gives the cumulative distribution function of rotational velocities. When applied to theoretical distributions it recovers the CDF with very high confidence. When applied to real data, we recover the results from Carvalho et al. (2009) proving that the velocity distribution function of main-sequence field stars is non-Maxwellian and are better described by Tsallis or Kaniadakis distribution functions.

  2. The luminosity function at the end of the main sequence: Results of a deep, large-area, CCD survey for cool dwarfs

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, J. Davy; Mcgraw, John T.; Hess, Thomas R.; Liebert, James; Mccarthy, Donald W., Jr.

    1994-01-01

    late-type M dwarfs are substellar. The luminosity function data together with an empirical derivation of the mass-luminosity relation (from Henry & McCarthy) are used to compute a mass function independent of theory. This mass function increases toward the end of the main sequence, but the observed density of M dwarfs is still insufficient to account for the missing mass. If the increases seen in the luminosity and mass functions are indicative of a large, unseen, substellar population, brown dwarfs may yet add significantly to the mass of the Galaxy.

  3. A long-term UBVRI photometric study of the pre-main sequence star V350 Cep

    NASA Astrophysics Data System (ADS)

    Ibryamov, Sunay; Semkov, Evgeni; Peneva, Stoyanka

    2014-10-01

    Results from UBVRI optical photometric observations of the pre-main sequence star V350 Cep during the period 2004-2014 are presented. The star was discovered in 1977 due to its remarkable increase in brightness by more than 5 mag (R). In previous studies, V350 Cep was considered to be a potential FUor or EXor eruptive variable. Our data suggest that during the period of observations the star maintains its maximum brightness with low amplitude photometric variations. Our conclusion is that V350 Cep was probably an intermediate object between FUors and EXors, similar to V1647 Ori.

  4. Medical Sequencing at the extremes of Human Body Mass

    SciTech Connect

    Ahituv, Nadav; Kavaslar, Nihan; Schackwitz, Wendy; Ustaszewski,Anna; Martin, Joes; Hebert, Sybil; Doelle, Heather; Ersoy, Baran; Kryukov, Gregory; Schmidt, Steffen; Yosef, Nir; Ruppin, Eytan; Sharan,Roded; Vaisse, Christian; Sunyaev, Shamil; Dent, Robert; Cohen, Jonathan; McPherson, Ruth; Pennacchio, Len A.

    2006-09-01

    Body weight is a quantitative trait with significantheritability in humans. To identify potential genetic contributors tothis phenotype, we resequenced the coding exons and splice junctions of58 genes in 379 obese and 378 lean individuals. Our 96Mb survey included21 genes associated with monogenic forms of obesity in humans or mice, aswell as 37 genes that function in body weight-related pathways. We foundthat the monogenic obesity-associated gene group was enriched for rarenonsynonymous variants unique to the obese (n=46) versus lean (n=26)populations. Computational analysis further predicted a significantlygreater fraction of deleterious variants within the obese cohort.Consistent with the complex inheritance of body weight, we did notobserve obvious familial segregation in the majority of the 28 availablekindreds. Taken together, these data suggest that multiple rare alleleswith variable penetrance contribute to obesity in the population andprovide a deep medical sequencing based approach to detectthem.

  5. The Effects of the Overshooting of the Convective Core on Main-sequence Turnoffs of Young- and Intermediate-age Star Clusters

    NASA Astrophysics Data System (ADS)

    Yang, Wuming; Tian, Zhijia

    2017-02-01

    Recent investigations have shown that the extended main-sequence turnoffs (eMSTOs) are a common feature of intermediate-age star clusters in the Magellanic Clouds. The eMSTOs are also found in the color–magnitude diagram of young-age star clusters. The origin of the eMSTOs is still an open question. Moreover, asteroseismology shows that the value of the overshooting parameter {δ }{ov} of the convective core is not fixed for the stars with an approximatelly equal mass. Thus the MSTO of star clusters may be affected by the overshooting of the convective core (OVCC). We calculated the effects of the OVCC with different δ ov on the MSTO of young- and intermediate-age star clusters. If δ ov varies between stars in a cluster, the observed eMSTOs of young- and intermediate-age star clusters can be explained well by the effects. The equivalent age spreads of MSTO caused by the OVCC are related to the age of star clusters and are in good agreement with observed results of many clusters. Moreover, the observed eMSTOs of NGC 1856 are reproduced by the coeval populations with different δ ov. The eMSTOs of star clusters may be relevant to the effects of the OVCC. The effects of the OVCC are similar to that of rotation in some respects. However, the effects cannot result in a significant split of the main sequence of young star clusters at {m}U≲ 21. The presence of a rapid rotation can make the split of the main sequence of young star clusters more significant.

  6. Aspects of oligonucleotide and peptide sequencing with MALDI and electrospray mass spectrometry.

    PubMed

    Owens, D R; Bothner, B; Phung, Q; Harris, K; Siuzdak, G

    1998-09-01

    Biopolymer sequencing with mass spectrometry has become increasingly important and accessible with the development of matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI). Here we examine the use of sequential digestion for the rapid identification of proteolytic fragments, in turn highlighting the general utility of enzymatic MALDI ladder sequencing and ESI tandem mass spectrometry. Analyses were performed on oligonucleotides ranging in size from 2 to 50 residues, on peptides ranging in size from 7 to 44 residues and on viral coat proteins. MALDI ladder sequencing using exonuclease digestion generated a uniform distribution of ions and provided complete sequence information on the oligonucleotides 2-30 nucleic acid residues long. Only partial sequence information was obtained on the longer oligonucleotides. C-terminal peptide ladder sequencing typically provided information from 4 to 7 amino acids into the peptide. Sequential digestion, or endoprotease followed by exoprotease exposure, was also successfully applied to a trypsin digest of viral proteins. Analysis of ladder sequenced peptides by LCMS generated less information than in the MALDI-MS analysis and ESI-MS2 normally provided partial sequence information on both the small oligonucleotides and peptides. In general, MALDI ladder sequencing offered information on a broader mass range of biopolymers than ESI-MS2 and was relatively straightforward to interpret, especially for oligonucleotides.

  7. IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

    NASA Astrophysics Data System (ADS)

    Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

    2017-04-01

    We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

  8. A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

    NASA Astrophysics Data System (ADS)

    Bastian, N.; Niederhofer, F.; Kozhurina-Platais, V.; Salaris, M.; Larsen, S.; Cabrera-Ziri, I.; Cordero, M.; Ekström, S.; Geisler, D.; Georgy, C.; Hilker, M.; Kacharov, N.; Li, C.; Mackey, D.; Mucciarelli, A.; Platais, I.

    2016-07-01

    We present Hubble Space Telescope photometry of NGC 1850, a ˜100 Myr, ˜105 M⊙ cluster in the Large Magellanic Cloud. The colour-magnitude diagram clearly shows the presence of an extended main-sequence turnoff (eMSTO). The use of non-rotating stellar isochrones leads to an age spread of ˜40 Myr. This is in good agreement with the age range expected when the effects of rotation in the main-sequence turnoff (MSTO) stars are wrongly interpreted in terms of age spread. We also do not find evidence for multiple, isolated episodes of star formation bursts within the cluster, in contradiction to scenarios that invoke actual age spreads to explain the eMSTO phenomenon. NGC 1850 therefore continues the trend of eMSTO clusters, where the inferred age spread is proportional to the age of the cluster. While our results confirm a key prediction of the scenario where stellar rotation causes the eMSTO feature, direct measurements of the rotational rate of MSTO stars is required to definitively confirm or refute whether stellar rotation is the origin of the eMSTO phenomenon or if it is due to an as yet undiscovered effect.

  9. Long-term photometric observations of pre-main sequence objects in the field of North America/Pelican Nebula

    NASA Astrophysics Data System (ADS)

    Poljančić, Beljan I.; Jurdana-Šepić, R.; Semkov, E. H.; Ibryamov, S.; Peneva, S. P.; Tsvetkov, M. K.

    2014-08-01

    To broaden the search and study stars in the early evolutionary phase, we investigated a sample of 17 pre-main sequence objects previously detected as either Hα emission-line pre-main sequence stars or T Tauri variables located in the field of the North America/Pelican Nebula complex. Johnson-Cousins B, V, Rc, Ic magnitudes and mean color indices for the program stars are determined from more than 12 400 measurements from archive photographic plates and from CCD data collected at 7 observatories covering the period of almost 60 years from 1954 up to 2013. We complemented previously rare insights on the photometry of the program stars and presented their photometric history, which for almost all program stars is the first long term photometric monitoring on a timescale of 6 decades. Eight program stars are found to be classical T Tauri stars of variability type II, while 6 program stars are weak-line T Tauri stars of variability type I. For the first time, periodicity is found for three stars: V1716 Cyg indicates a 4.15 day period, V2051 Cyg indicates a 384 day period, and V521 Cyg a period of 503 days. Full Tables 4 and 5 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/568/A49

  10. PRE-MAIN-SEQUENCE TURN-ON AS A CHRONOMETER FOR YOUNG CLUSTERS: NGC 346 AS A BENCHMARK

    SciTech Connect

    Cignoni, M.; Tosi, M.; Sabbi, E.; Nota, A.; Degl'Innocenti, S.; Moroni, P. G. Prada; Gallagher, J. S.

    2010-03-20

    We present a novel approach to deriving the age of very young star clusters, by using the Turn-On (TOn). The TOn is the point in the color-magnitude diagram (CMD) where the pre-main sequence (PMS) joins the main sequence (MS). In the MS luminosity function (LF) of the cluster, the TOn is identified as a peak followed by a dip. We propose that by combining the CMD analysis with the monitoring of the spatial distribution of MS stars it is possible to reliably identify the TOn in extragalactic star-forming regions. Compared to alternative methods, this technique is complementary to the turnoff dating and avoids the systematic biases affecting the PMS phase. We describe the method and its uncertainties and apply it to the star-forming region NGC 346, which has been extensively imaged with the Hubble Space Telescope (HST). This study extends the LF approach in crowded extragalactic regions and opens the way for future studies with HST/WFC3, the James Webb Space Telescope and from the ground with adaptive optics.

  11. What is the unusual material orbiting the dustiest main sequence A-type stars HD 131488 and HD 121191?

    NASA Astrophysics Data System (ADS)

    Melis, Carl

    2015-10-01

    Only a small percentage of main sequence stars exhibit excess mid-infrared emission indicative of substantial quantities of warm (T >~ 300 K), inner planetary system material that likely originated in recent transient collisional processes. Detailed study of these events can provide us with insight into how rocky terrestrial-like planets form and evolve through collisional pathways. We have identified two young A-type stars with mid-infrared luminosity brighter than and spectrally distinct from that at any other known main-sequence A-type star. T-ReCS N-band and IRTF SpeX spectroscopy combined with IRAS, Herschel, WISE, and T-ReCS photometric measurements indicate that these stars host two distinct infrared emitting regions, one with characteristic temperatures of >300 K (equivalent to temperatures inside 1 AU in the solar system) and a second of ~100 K (equivalent to the temperature near Saturn). The T-ReCS N-band spectra present an enigma: a putative emission feature with peak wavelength near 6-7 microns is not reproducible with common silicate species. SOFIA-FORCAST narrow-band imaging is the only means available to settling the identity of these strange emission features and hence clarify the nature of the inner planetary system material around these two stars.

  12. Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

    NASA Astrophysics Data System (ADS)

    Messina, S.; Pizzolato, N.; Guinan, E. F.; Rodonò, M.

    2003-11-01

    The maximum amplitude (Amax) of spot-induced brightness variations from long-term V-band photometry and the ratio LX/Lbol between X-ray and bolometric luminosities are suitable indicators of the level of magnetic activity in the photosphere and in the corona of late-type stars, respectively. By using these activity indicators we investigate the dependence of coronal X-ray emission on the level of photospheric starspot activity in a homogeneous sample of low mass main sequence field and cluster stars of different ages (IC 2602, IC 4665, IC 2391, alpha Persei, Pleiades and Hyades). First, the activity-rotation connection at the photospheric level is re-analysed, as well as its dependence on spectral type and age. The upper envelope of Amax increases monotonically with decreasing rotational period (P) and Rossby number (R0) showing a break around 1.1 d that separates two rotation regimes where the starspot activity shows different behaviours. The Amax-P and Amax-R0 relations are fitted with linear, exponential and power laws to look for the function which best represents the trend of the data. The highest values of Amax are found among K-type stars and at the ages of alpha Persei and Pleiades. We also analyse the activity-rotation connection at the coronal level as well as its dependence on spectral type. The level of X-ray emission increases with increasing rotation rate up to a saturation level. The rotational period at which saturation occurs is colour-dependent and increases with advancing spectral type. Also the LX/Lbol-P and LX/Lbol-R0 relations are fitted with linear, exponential and power laws to look for the best fitting function. Among the fastest rotating stars (P<=0.3 d) there is evidence of super-saturation. Also the highest values of LXLbol are found among K-type stars. Finally, the photospheric-coronal activity connection is investigated by using for the first time the largest ever sample of light curve amplitudes as indicators of the magnetic filling

  13. How dusty is α Centauri?. Excess or non-excess over the infrared photospheres of main-sequence stars

    NASA Astrophysics Data System (ADS)

    Wiegert, J.; Liseau, R.; Thébault, P.; Olofsson, G.; Mora, A.; Bryden, G.; Marshall, J. P.; Eiroa, C.; Montesinos, B.; Ardila, D.; Augereau, J. C.; Bayo Aran, A.; Danchi, W. C.; del Burgo, C.; Ertel, S.; Fridlund, M. C. W.; Hajigholi, M.; Krivov, A. V.; Pilbratt, G. L.; Roberge, A.; White, G. J.; Wolf, S.

    2014-03-01

    Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary α Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims: We aim to determine the level of emission from debris around the stars in the α Cen system. This requires knowledge of their photospheres. Having already detected the temperature minimum, Tmin, of α Cen A at far-infrared wavelengths, we here attempt to do the same for the more active companion α Cen B. Using the α Cen stars as templates, we study the possible effects that Tmin may have on the detectability of unresolved dust discs around other stars. Methods: We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in the far infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around α Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunction with radiative transfer calculations, were used to estimate the amount of debris around these stars. Results: For solar-type stars more distant than α Cen, a fractional dust luminosity fd ≡ Ldust/Lstar 2 × 10-7 could account for SEDs that do not exhibit the Tmin effect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared, slight excesses at the 2.5σ level are observed at 24 μm for both α Cen A and B, which, if interpreted as due to zodiacal-type dust emission, would correspond to fd (1-3) × 10-5, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dust grains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the α Cen stars, viz. ≲4 × 10-6 M≤ftmoon of 4 to 1000 μm size

  14. How Dusty Is Alpha Centauri? Excess or Non-excess over the Infrared Photospheres of Main-sequence Stars

    NASA Technical Reports Server (NTRS)

    Wiegert, J.; Liseau, R.; Thebault, P.; Olofsson, G.; Mora, A.; Bryden, G.; Marshall, J. P.; Eiroa, C.; Montesinos, B.; Ardila, D.; Augereau, J. C.; Aran, A. Bayo; Danchi, W. C.; del Burgo, C.; Ertel, S.; Fridlund, M. C. W.; Hajigholi, M.; Krivov, A. V.; Pilbratt, G. L.; Roberge, A.; White, G. J.; Wolf, S.

    2014-01-01

    Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the Cen system. This requires knowledge of their photospheres.Having already detected the temperature minimum, Tmin, of CenA at far-infrared wavelengths, we here attempt to do the same for the moreactive companion Cen B. Using the Cen stars as templates, we study the possible eects that Tmin may have on the detectability of unresolveddust discs around other stars. Methods.We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in thefar infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunctionwith radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than Cen, a fractional dust luminosity fd LdustLstar 2 107 could account for SEDs that do not exhibit the Tmin eect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared,slight excesses at the 2:5 level are observed at 24 m for both CenA and B, which, if interpreted as due to zodiacal-type dust emission, wouldcorrespond to fd (13) 105, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dustgrains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the Cen stars, viz.4106 M$ of 4 to 1000 msize grains, distributed according to n(a) a3:5. Similarly, for filled-in Tmin

  15. GOODS-HERSCHEL: STAR FORMATION, DUST ATTENUATION, AND THE FIR–RADIO CORRELATION ON THE MAIN SEQUENCE OF STAR-FORMING GALAXIES UP TO z ≃ 4

    SciTech Connect

    Pannella, M.; Elbaz, D.; Daddi, E.; Hwang, H. S.; Schreiber, C.; Strazzullo, V.; Aussel, H.; Bethermin, M.; Cibinel, A.; Juneau, S.; Floc’h, E. Le; Leiton, R.; Buat, V.; Charmandaris, V.; Magdis, G.; Ivison, R. J.; Borgne, D. Le; Lin, L.; Morrison, G. E.; and others

    2015-07-10

    We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate–M{sub *} correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR–radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5–4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts.

  16. The Lower Main Sequence of ω Centauri from Deep Hubble Space Telescope NICMOS Near-Infrared Observations

    NASA Astrophysics Data System (ADS)

    Pulone, Luigi; De Marchi, Guido; Paresce, Francesco; Allard, France

    1998-01-01

    A 20" × 20" field located ~7' from the center of the massive galactic globular cluster ω Centauri (NGC 5139) was observed by the NIC2 camera of the Near-Infrared Camera and Multiobject Spectrometer on board the Hubble Space Telescope (HST) through the F110W and F160W broadband filters centered at 1.1 and 1.6 μm for a total of 3000 and 4000 s for the two filters, respectively. Standard photometric analysis of the resulting images yields 340 stars with a signal above a 10 σ threshold in both filters, covering the range of HST m160 magnitudes between 20 and 26, the deepest probe yet of a globular cluster in this wavelength region. These objects form a well-defined sequence in the m160 versus m110-m160 plane that is consistent with the theoretical near-IR color-magnitude diagram expected from recent low-mass stellar model calculations. The resulting stellar luminosity function increases steadily with increasing magnitude up to a peak at m160~=25, where it turns over and drops slowly down to the detection limit set by the incompleteness limit of 60% at m160~=26. With the theoretical mass-luminosity relationship that provides the best fit to the IR color-magnitude diagram, we obtain an excellent fit to the observed luminosity function down to a mass of ~0.2 Msolar with a power-law mass function having a slope of α=-1. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS5-26555.

  17. The VLT-FLAMES Tarantula Survey. XVII. Physical and wind properties of massive stars at the top of the main sequence

    NASA Astrophysics Data System (ADS)

    Bestenlehner, J. M.; Gräfener, G.; Vink, J. S.; Najarro, F.; de Koter, A.; Sana, H.; Evans, C. J.; Crowther, P. A.; Hénault-Brunet, V.; Herrero, A.; Langer, N.; Schneider, F. R. N.; Simón-Díaz, S.; Taylor, W. D.; Walborn, N. R.

    2014-10-01

    The evolution and fate of very massive stars (VMS) is tightly connected to their mass-loss properties. Their initial and final masses differ significantly as a result of mass loss. VMS have strong stellar winds and extremely high ionising fluxes, which are thought to be critical sources of both mechanical and radiative feedback in giant H ii regions. However, how VMS mass-loss properties change during stellar evolution is poorly understood. In the framework of the VLT-Flames Tarantula Survey (VFTS), we explore the mass-loss transition region from optically thin O star winds to denser WNh Wolf-Rayet star winds, thereby testing theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and WNh stars, an unprecedented sample of stars with the highest masses and luminosities known. We perform a spectral analysis of optical VFTS as well as near-infrared VLT/SINFONI data using the non-LTE radiative transfer code CMFGEN to obtain both stellar and wind parameters. For the first time, we observationally resolve the transition between optically thin O star winds and optically thick hydrogen-rich WNh Wolf-Rayet winds. Our results suggest the existence of a "kink" between both mass-loss regimes, in agreement with recent Monte Carlo simulations. For the optically thick regime, we confirm the steep dependence on the classical Eddington factor Γe from previous theoretical and observational studies. The transition occurs on the main sequence near a luminosity of 106.1L⊙, or a mass of 80 ... 90 M⊙. Above this limit, we find that - even when accounting for moderate wind clumping (with fv = 0.1) - wind mass-loss rates are enhanced with respect to standard prescriptions currently adopted in stellar evolution calculations. We also show that this results in substantial helium surface enrichment. Finally, based on our spectroscopic analyses, we are able to provide the most accurate ionising fluxes for VMS known to date, confirming the pivotal role of VMS in ionising and

  18. Sequence determination of protected oligodeoxyribonucleotides containing phosphotriester linkages by californium-252 plasma desorption mass spectrometry.

    PubMed Central

    McNeal, C J; Narang, S A; Macfarlane, R D; Hsiung, H M; Brousseau, R

    1980-01-01

    A mass spectrometric method for determining the sequence and molecular weight of protected oligodeoxyribonucleotides is described. By using the method of 252Cf plasma desorption mass spectrometry [Macfarlane, R. D. & Torgerson, D. F. (1976) Science 191, 920--925], positive-ion mass spectra were obtained for a series of protected oligonucleotides extending to a decanucleotide; the spectra were dominated by the presence of the oligonucleotide molecular ion. The negative-ion mass spectra were characterized by a nested set of fragment ions extending from the 3'- or 5'-terminal nucleotide to the opposite terminal nucleotide, thereby identifying the sequence. The utility of this method has been demonstrated by the sequence determination of protected tetra-, penta-, and hexanucleotides synthesized by the improved phosphotriester method. PMID:6928675

  19. UVI colour gradients of 0.4 < z < 1.4 star-forming main-sequence galaxies in CANDELS: dust extinction and star formation profiles

    NASA Astrophysics Data System (ADS)

    Wang, Weichen; Faber, S. M.; Liu, F. S.; Guo, Yicheng; Pacifici, Camilla; Koo, David C.; Kassin, Susan A.; Mao, Shude; Fang, Jerome J.; Chen, Zhu; Koekemoer, Anton M.; Kocevski, Dale D.; Ashby, M. L. N.

    2017-08-01

    This paper uses radial colour profiles to infer the distributions of dust, gas and star formation in z = 0.4-1.4 star-forming main-sequence galaxies. We start with the standard UVJ-based method to estimate dust extinction and specific star formation rate (sSFR). By replacing J with I band, a new calibration method suitable for use with ACS+WFC3 data is created (i.e. UVI diagram). Using a multi-wavelength multi-aperture photometry catalogue based on CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey), UVI colour profiles of 1328 galaxies are stacked in stellar mass and redshift bins. The resulting colour gradients, covering a radial range of 0.2-2.0 effective radii, increase strongly with galaxy mass and with global AV. Colour gradient directions are nearly parallel to the Calzetti extinction vector, indicating that dust plays a more important role than stellar population variations. With our calibration, the resulting AV profiles fall much more slowly than stellar mass profiles over the measured radial range. sSFR gradients are nearly flat without central quenching signatures, except for M⋆ > 1010.5 M⊙, where central declines of 20-25 per cent are observed. Both sets of profiles agree well with previous radial sSFR and (continuum) AV measurements. They are also consistent with the sSFR profiles and, if assuming a radially constant gas-to-dust ratio, gas profiles in recent hydrodynamic models. We finally discuss the striking findings that SFR scales with stellar mass density in the inner parts of galaxies, and that dust content is high in the outer parts despite low stellar mass surface densities there.

  20. The main properties and peculiarities of the Earth's motion relative to the center of mass

    NASA Astrophysics Data System (ADS)

    Klimov, D. M.; Akulenko, L. D.; Kumakshev, S. A.

    2014-10-01

    The methods of theoretical and celestial mechanics and mathematical statistics have been used to prove that the Earth's motion relative to the center of mass, the polar wobble, in the principal approximation is a combination of two circumferences with a slow trend in the mean position corresponding to the annual and Chandler components. It has been established that the parameters (amplitude and phase shift) of the annual wobble are stable, while those of the Chandler component are less stable and undergo significant variations over the observed time intervals. It has been proven that the behavior of these polar motion parameters is attributable to the gravitational-tidal mechanisms of their excitation.

  1. [Quantification of ventricular mass and function using real-time free-breathing SSFP sequences].

    PubMed

    Bastarrika Alemañ, G; Domínguez Echávarri, P D; Azcárate Agüero, P M; Castaño Rodríguez, S; Fernández Jarne, M E; Gavira Gómez, J J

    2008-01-01

    To compare real-time free-breathing steady-state free precession (SSFP) sequences with conventional breath-hold segmented SSFP sequences on the quantification of ventricular mass and function. Cardiac function and mass were assessed in 15 consecutive patients with cardiopathies who underwent MRI for diverse indications. Sequences were planned in the short axis to include the area from the base to the apex of the ventricle. Two sequences were used: 1) a conventional breath-hold segmented SSFP sequence with 7-mm-thick slices and 3-mm gap between slices and 2) a real-time free-breathing SSFP sequence with 10-mm-thick slices. The systolic and diastolic volumes (VTD, VTS) and ejection fraction (EF) of both ventricles were evaluated and the mass of the left ventricle (LVM) was measured. The correlation between the different sequences was studied for each variable. An excellent correlation was observed between the two sequences on the quantification of cardiac parameters in both ventricles (0.9; p < 0.01). The mean differences for EF, VTD, VTS, and stroke volume (VTD-VTS) were 2.5% (2.1), 5.6 ml (14.2), -0.8 ml (6.4), 6.4 ml (9.4), respectively, for the left ventricle and 1.7% (3.1), 1.8 ml (18.7), -1.9 ml (9.8), 3.7 ml (10.8), respectively, for the right ventricle. The mean difference between the LVM was 4.8 g (6.3). The real-time free-breathing SSFP sequence is useful for the quantification of ventricular mass and function. The correlation with conventional SSFP is excellent. Both sequences allow the cardiac parameters to be precisely quantified and the results are reproducible.

  2. Magnetic Field and Rotation in Lower Main-Sequence Stars: an Empirical Time-dependent Magnetic Bode's Relation?

    NASA Astrophysics Data System (ADS)

    Baliunas, Sallie; Sokoloff, Dmitry; Soon, Willie

    1996-02-01

    We find a significant correlation between the magnetic and rotational moments for a sample of 112 lower main-sequence stars. The rotational moment is calculated from measurements of the rotation period in most of the stars (not from the projected rotational velocity inferred from Doppler broadening). The magnetic moment is computed from a database of homogeneous measurements of the mean level of Ca II H and K emission fluxes sampled for most of the stars over an interval of 25 yr. The slope connecting the logarithm of the magnetic moment and the logarithm of the rotational moment is about +0.5--0.6, with a Pearson correlation coefficient of about +0.9. The scatter of points from the mean relation has a component that is natural and caused by decade-long surface variability.

  3. Spectropolarimetry of the post-main-sequence bipolar nebulae GL 618, M2-56, and M1-92

    NASA Technical Reports Server (NTRS)

    Trammell, Susan R.; Dinerstein, Harriet L.; Goodrich, Robert W.

    1993-01-01

    New high-quality spectropolarimetry of the post-main-sequence bipolar nebulae GL 618, M2-56, and M1-92 is presented which permits accurate separation of the scattered and unscattered components. Shock emission dominates the optical line spectrum of the three nebulae and probably plays a significant role in their dynamical evolution. The central H II region spectrum for GL 6189 is isolated and T(stellar) of 36,000-40,000 and log (N/O) = 0.0 +/- 0.2 are derived. GL 618 and M2-56 have shock velocities of 40-60 km/s; that of M1-92 is 60-100 km/s. Log (N/O) is derived for different regions of the three nebulae. There is an apparent correlation of outflow velocity with chemical abundance.

  4. The Solar Neighborhood. XLI. A Study of the Wide Main Sequence for M Dwarfs—Long-term Photometric Variability

    NASA Astrophysics Data System (ADS)

    Clements, Tiffany D.; Henry, Todd J.; Hosey, Altonio D.; Jao, Wei-Chun; Silverstein, Michele L.; Winters, Jennifer G.; Dieterich, Sergio B.; Riedel, Adric R.

    2017-09-01

    We report findings from a long-term photometric variability study of M dwarfs carried out at the SMARTS 0.9 m telescope at the Cerro Tololo Inter-American Observatory. As part of a multi-faceted effort to investigate the range of luminosities of M dwarfs of a given color on the Hertzsprung–Russell Diagram, 76 M dwarfs have been observed for 3–17 years in the Johnson–Kron–Cousins V band. We find that stars elevated above the center of the main sequence distribution tend to have higher levels of variability, likely caused by magnetic activity, than their fainter counterparts below the center. This study provides insight into how the long-term magnetic activity of these stars may be affecting their sizes, luminosities, and thus positions on the H-R Diagram.

  5. Spectropolarimetry of the post-main-sequence bipolar nebulae GL 618, M2-56, and M1-92

    NASA Technical Reports Server (NTRS)

    Trammell, Susan R.; Dinerstein, Harriet L.; Goodrich, Robert W.

    1993-01-01

    New high-quality spectropolarimetry of the post-main-sequence bipolar nebulae GL 618, M2-56, and M1-92 is presented which permits accurate separation of the scattered and unscattered components. Shock emission dominates the optical line spectrum of the three nebulae and probably plays a significant role in their dynamical evolution. The central H II region spectrum for GL 6189 is isolated and T(stellar) of 36,000-40,000 and log (N/O) = 0.0 +/- 0.2 are derived. GL 618 and M2-56 have shock velocities of 40-60 km/s; that of M1-92 is 60-100 km/s. Log (N/O) is derived for different regions of the three nebulae. There is an apparent correlation of outflow velocity with chemical abundance.

  6. Determining the amount of dust in the habitable zone: a Keck Nuller survey of 26 nearby main sequence stars

    NASA Astrophysics Data System (ADS)

    Mennesson, B.

    2010-10-01

    Because of contrast limitations at high angular resolution, direct observations of debris disks have so far been restricted to the outer (> 10AU) parts of nearby solar systems. The Keck Interferometer Nuller (KIN) was specifically designed to push this limit, and constrain exo-zodiacal emission originating from the "rocky planet forming region", i.e. from ∼0.1 AU to a few AUs. The characterization of exo-zodiacal light at these spatial scales is very revealing as it reflects the host system's specific distribution of planets, dust sources and sinks. Strong exo-zodi emission in the habitable zone is also important to identify, as it can be a hindrance to direct imaging of Earth-like exoplanets. We discuss here the results of a Keck Nuller exo-zodi program targeting 26 nearby main sequence stars, most of which with no previously known infrared excess.

  7. X-ray emission from the pre-main sequence star ZCMa during a FUOri-type outburst

    NASA Astrophysics Data System (ADS)

    Stelzer, Beate

    2007-09-01

    We propose for the first X-ray spectrum of an FUOri object during outburst. The FUOR phenomenon is associated with a sudden increase of the accretion rate in some pre-main sequence (PMS) stars, possibly due to changes in the magnetic field. In the first X-ray survey of FUORs Skinner et al. (2007) have detected two of four targets. None of them was in outburst at the time. The typical two-temperature spectrum of a PMS star requires in the case of FUOri different absorptions for the soft and hard components (Skinner et al. 2006). Our target ZCMa is a young F-type FUOR. In Feb 2008 ZCMa started its so far largest outburst, with a further enhancement ~2 weeks ago. In May 2008 we have detected its magnetic field. Now we aim at an X-ray detection of ZCMa in its `super-outburst'.

  8. Texture analysis of common renal masses in multiple MR sequences for prediction of pathology

    NASA Astrophysics Data System (ADS)

    Hoang, Uyen N.; Malayeri, Ashkan A.; Lay, Nathan S.; Summers, Ronald M.; Yao, Jianhua

    2017-03-01

    This pilot study performs texture analysis on multiple magnetic resonance (MR) images of common renal masses for differentiation of renal cell carcinoma (RCC). Bounding boxes are drawn around each mass on one axial slice in T1 delayed sequence to use for feature extraction and classification. All sequences (T1 delayed, venous, arterial, pre-contrast phases, T2, and T2 fat saturated sequences) are co-registered and texture features are extracted from each sequence simultaneously. Random forest is used to construct models to classify lesions on 96 normal regions, 87 clear cell RCCs, 8 papillary RCCs, and 21 renal oncocytomas; ground truths are verified through pathology reports. The highest performance is seen in random forest model when data from all sequences are used in conjunction, achieving an overall classification accuracy of 83.7%. When using data from one single sequence, the overall accuracies achieved for T1 delayed, venous, arterial, and pre-contrast phase, T2, and T2 fat saturated were 79.1%, 70.5%, 56.2%, 61.0%, 60.0%, and 44.8%, respectively. This demonstrates promising results of utilizing intensity information from multiple MR sequences for accurate classification of renal masses.

  9. Evidence for chemical processing of precometary icy grains in circumstellar environments of pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Tegler, Stephen C.; Weintraub, David A.; Rettig, Terrence W.; Pendleton, Yvonne J.; Whittet, Douglas C. B.; Kulesa, Craig A.

    1995-01-01

    We report the detection of a broad absorption feature near 2166/cm in the spectrum of the Taurus cloud cource Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166/cm absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C triple bonded to N containing compound (called X(C triple bonded to N)) that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components. We find a nonlinear anticorrelation between the abundance of X(C triple bonded to N) and frozen CO components in nonpolar lattices. We find no correlation between the abundance of X(C triple bonded to N) and frozen CO in polar lattices. Because the abundances of frozen CO and H2O are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C triple bonded to N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main-sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.

  10. Evidence for Chemical Processing of Precometary Icy Grains In Circumstellar Environments of Pre-Main-Sequence Stars

    NASA Technical Reports Server (NTRS)

    Teglier, Stephen C.; Weintraub, David A.; Rettig, Terrence W.; Pendleton, Yvonne J.; Whittet, Douglas C.; Kulesa, Craig A.

    1995-01-01

    We report the detection of a broad absorption feature near 2166 cm-1 in the spectrum of the Taurus cloud source Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166 cm-1 absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C=-N containing compound [called X(C=-N)] that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components, We find a nonlinear anticorrelation between the abundance of X(C=-N) and frozen CO in non- polar lattices. We find no correlation between the abundance of X(C=-N) and frozen CO in polar lattices. Because the abundances of frozen CO and H20 are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C=-N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main- sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.

  11. Multiple stellar populations in Magellanic Cloud clusters - V. The split main sequence of the young cluster NGC 1866

    NASA Astrophysics Data System (ADS)

    Milone, A. P.; Marino, A. F.; D'Antona, F.; Bedin, L. R.; Piotto, G.; Jerjen, H.; Anderson, J.; Dotter, A.; Criscienzo, M. Di; Lagioia, E. P.

    2017-03-01

    One of the most unexpected results in the field of stellar populations of the last few years is the discovery that some Magellanic Cloud globular clusters younger than ∼400 Myr exhibit bimodal main sequences (MSs) in their colour-magnitude diagrams (CMDs). Moreover, these young clusters host an extended main-sequence turn-off (eMSTO) in close analogy with what is observed in most ∼1-2 Gyr old clusters of both Magellanic Clouds. We use high-precision Hubble Space Telescope photometry to study the young star cluster NGC 1866 in the Large Magellanic Cloud. We discover an eMSTO and a split MS. The analysis of the CMD reveals that (i) the blue MS is the less populous one, hosting about one-third of the total number of MS stars; (ii) red MS stars are more centrally concentrated than blue MS stars; (iii) the fraction of blue MS stars with respect to the total number of MS stars drops by a factor of ∼2 in the upper MS with mF814W ≲ 19.7. The comparison between the observed CMDs and stellar models reveals that the observations are consistent with ∼200 Myr old highly rotating stars on the red MS, with rotation close to critical value, plus a non-rotating stellar population spanning an age interval between ∼140 and 220 Myr, on the blue MS. Noticeable, neither stellar populations with different ages only, nor coeval stellar models with different rotation rates, properly reproduce the observed split MS and eMSTO. We discuss these results in the context of the eMSTO and multiple MS phenomenon.

  12. Evidence for Chemical Processing of Precometary Icy Grains In Circumstellar Environments of Pre-Main-Sequence Stars

    NASA Technical Reports Server (NTRS)

    Teglier, Stephen C.; Weintraub, David A.; Rettig, Terrence W.; Pendleton, Yvonne J.; Whittet, Douglas C.; Kulesa, Craig A.

    1995-01-01

    We report the detection of a broad absorption feature near 2166 cm-1 in the spectrum of the Taurus cloud source Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166 cm-1 absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C=-N containing compound [called X(C=-N)] that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components, We find a nonlinear anticorrelation between the abundance of X(C=-N) and frozen CO in non- polar lattices. We find no correlation between the abundance of X(C=-N) and frozen CO in polar lattices. Because the abundances of frozen CO and H20 are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C=-N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main- sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.

  13. Evidence for chemical processing of precometary icy grains in circumstellar environments of pre-main-sequence stars

    NASA Astrophysics Data System (ADS)

    Tegler, Stephen C.; Weintraub, David A.; Rettig, Terrence W.; Pendleton, Yvonne J.; Whittet, Douglas C. B.; Kulesa, Craig A.

    1995-01-01

    We report the detection of a broad absorption feature near 2166/cm in the spectrum of the Taurus cloud cource Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166/cm absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C triple bonded to N containing compound (called X(C triple bonded to N)) that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components. We find a nonlinear anticorrelation between the abundance of X(C triple bonded to N) and frozen CO components in nonpolar lattices. We find no correlation between the abundance of X(C triple bonded to N) and frozen CO in polar lattices. Because the abundances of frozen CO and H2O are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C triple bonded to N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main-sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.

  14. THE EFFECTS OF ROTATION ON THE MAIN-SEQUENCE TURNOFF OF INTERMEDIATE-AGE MASSIVE STAR CLUSTERS

    SciTech Connect

    Yang, Wuming; Bi, Shaolan; Liu, Zhie; Meng, Xiangcun E-mail: yangwuming@ynao.ac.cn

    2013-10-20

    The double or extended main-sequence turnoffs (MSTOs) in the color-magnitude diagram (CMD) of intermediate-age massive star clusters in the Large Magellanic Cloud are generally interpreted as age spreads of a few hundred Myr. However, such age spreads do not exist in younger clusters (i.e., 40-300 Myr), which challenges this interpretation. The effects of rotation on the MSTOs of star clusters have been studied in previous works, but the results obtained are conflicting. Compared with previous works, we consider the effects of rotation on the main-sequence lifetime of stars. Our calculations show that rotating models have a fainter and redder MSTO with respect to non-rotating counterparts with ages between about 0.8 and 2.2 Gyr, but have a brighter and bluer MSTO when age is larger than 2.4 Gyr. The spread of the MSTO caused by a typical rotation rate is equivalent to the effect of an age spread of about 200 Myr. Rotation could lead to the double or extended MSTOs in the CMD of the star clusters with ages between about 0.8 and 2.2 Gyr. However, the extension is not significant, and it does not even exist in younger clusters. If the efficiency of the mixing were high enough, the effects of the mixing would counteract the effect of the centrifugal support in the late stage of evolution, and the rotationally induced extension would disappear in the old intermediate-age star clusters, but younger clusters would have an extended MSTO. Moreover, the effects of rotation might aid in understanding the formation of some 'multiple populations' in globular clusters.

  15. Identification of main-sequence stars with mid-infrared excesses: Frequency of beta Pictoris analogs and transition disk systems

    NASA Astrophysics Data System (ADS)

    Uzpen, Brian Robert

    There is solid evidence of life on only one planet in the Universe: Earth. Since current technologies are not capable of directly observing planets, we must rely on secondary indicators, such as circumstellar disks to detect them. Circumstellar disks are commonplace around pre-main-sequence stars; it is believed these disks are a natural byproduct of star formation where planets can form. The general theoretical evolutionary sequence from the optically thick pre-main-sequence stars (T-Tauri and Herbig AeBe) to optically thin "debris disks", is as follows: After particles grow through condensation, they reach a critical value and form planetary cores; these cores accrete the gas around them and form planets. As the available circumstellar material decreases, the inner disk will develop a hole. Circumstellar material dissipates in the outer disk, while particles collide creating a population of grains that re-radiate stellar energy in the far-IR, a characteristic of debris disks. These debris disks represent a final stage of planet formation. Given that most stars originally have circumstellar disks, it is likely that planetary systems are common. Material similar in temperature to Earth emits primarily at ~10 mm (mid-IR wavelengths). By identifying stars with circumstellar material that emits in the mid-IR, it may be possible to locate Earth-like planetary systems; mid-IR excesses may also be an indicator of disks undergoing clearing processes with inner disk holes of a few AU. The purpose of this work is to identify and characterize a large sample of stellar sources with circumstellar disks that re-radiate energy at mid-IR wavelengths and place them in the greater context of disk evolution and planet formation. To achieve this goal, a large number of stellar sources with mid-IR excesses are identified through wide-area Galactic surveys. Far-IR photometry is utilized to confirm the mid-IR excess in a majority of the newly identified sources. Follow-up optical

  16. Proteogenomics: Integrating Next-Generation Sequencing and Mass Spectrometry to Characterize Human Proteomic Variation

    PubMed Central

    Sheynkman, Gloria M.; Shortreed, Michael R.; Cesnik, Anthony J.; Smith, Lloyd M.

    2016-01-01

    Mass spectrometry–based proteomics has emerged as the leading method for detection, quantification, and characterization of proteins. Nearly all proteomic workflows rely on proteomic databases to identify peptides and proteins, but these databases typically contain a generic set of proteins that lack variations unique to a given sample, precluding their detection. Fortunately, proteogenomics enables the detection of such proteomic variations and can be defined, broadly, as the use of nucleotide sequences to generate candidate protein sequences for mass spectrometry database searching. Proteogenomics is experiencing heightened significance due to two developments: (a) advances in DNA sequencing technologies that have made complete sequencing of human genomes and transcriptomes routine, and (b) the unveiling of the tremendous complexity of the human proteome as expressed at the levels of genes, cells, tissues, individuals, and populations. We review here the field of human proteogenomics, with an emphasis on its history, current implementations, the types of proteomic variations it reveals, and several important applications. PMID:27049631

  17. Proteogenomics: Integrating Next-Generation Sequencing and Mass Spectrometry to Characterize Human Proteomic Variation

    NASA Astrophysics Data System (ADS)

    Sheynkman, Gloria M.; Shortreed, Michael R.; Cesnik, Anthony J.; Smith, Lloyd M.

    2016-06-01

    Mass spectrometry-based proteomics has emerged as the leading method for detection, quantification, and characterization of proteins. Nearly all proteomic workflows rely on proteomic databases to identify peptides and proteins, but these databases typically contain a generic set of proteins that lack variations unique to a given sample, precluding their detection. Fortunately, proteogenomics enables the detection of such proteomic variations and can be defined, broadly, as the use of nucleotide sequences to generate candidate protein sequences for mass spectrometry database searching. Proteogenomics is experiencing heightened significance due to two developments: (a) advances in DNA sequencing technologies that have made complete sequencing of human genomes and transcriptomes routine, and (b) the unveiling of the tremendous complexity of the human proteome as expressed at the levels of genes, cells, tissues, individuals, and populations. We review here the field of human proteogenomics, with an emphasis on its history, current implementations, the types of proteomic variations it reveals, and several important applications.

  18. Proteogenomics: Integrating Next-Generation Sequencing and Mass Spectrometry to Characterize Human Proteomic Variation.

    PubMed

    Sheynkman, Gloria M; Shortreed, Michael R; Cesnik, Anthony J; Smith, Lloyd M

    2016-06-12

    Mass spectrometry-based proteomics has emerged as the leading method for detection, quantification, and characterization of proteins. Nearly all proteomic workflows rely on proteomic databases to identify peptides and proteins, but these databases typically contain a generic set of proteins that lack variations unique to a given sample, precluding their detection. Fortunately, proteogenomics enables the detection of such proteomic variations and can be defined, broadly, as the use of nucleotide sequences to generate candidate protein sequences for mass spectrometry database searching. Proteogenomics is experiencing heightened significance due to two developments: (a) advances in DNA sequencing technologies that have made complete sequencing of human genomes and transcriptomes routine, and (b) the unveiling of the tremendous complexity of the human proteome as expressed at the levels of genes, cells, tissues, individuals, and populations. We review here the field of human proteogenomics, with an emphasis on its history, current implementations, the types of proteomic variations it reveals, and several important applications.

  19. The SCUBA-2 Cosmology Legacy Survey: galaxies in the deep 850 μm survey, and the star-forming `main sequence'

    NASA Astrophysics Data System (ADS)

    Koprowski, M. P.; Dunlop, J. S.; Michałowski, M. J.; Roseboom, I.; Geach, J. E.; Cirasuolo, M.; Aretxaga, I.; Bowler, R. A. A.; Banerji, M.; Bourne, N.; Coppin, K. E. K.; Chapman, S.; Hughes, D. H.; Jenness, T.; McLure, R. J.; Symeonidis, M.; Werf, P. van der

    2016-06-01

    We investigate the properties of the galaxies selected from the deepest 850-μm survey undertaken to date with (Submillimetre Common-User Bolometer Array 2) SCUBA-2 on the James Clerk Maxwell Telescope as part of the SCUBA-2 Cosmology Legacy Survey. A total of 106 sources (>5σ) were uncovered at 850 μm from an area of ≃150 arcmin2 in the centre of the COSMOS/UltraVISTA/Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field, imaged to a typical depth of σ850 ≃ 0.25 mJy. We utilize the available multifrequency data to identify galaxy counterparts for 80 of these sources (75 per cent), and to establish the complete redshift distribution for this sample, yielding bar{z} = 2.38± 0.09. We have also been able to determine the stellar masses of the majority of the galaxy identifications, enabling us to explore their location on the star formation rate:stellar mass (SFR:M*) plane. Crucially, our new deep 850-μm-selected sample reaches flux densities equivalent to SFR ≃ 100 M⊙ yr-1, enabling us to confirm that sub-mm galaxies form the high-mass end of the `main sequence' (MS) of star-forming galaxies at z > 1.5 (with a mean specific SFR of sSFR = 2.25 ± 0.19 Gyr-1 at z ≃ 2.5). Our results are consistent with no significant flattening of the MS towards high masses at these redshifts. However, our results add to the growing evidence that average sSFR rises only slowly at high redshift, resulting in log10sSFR being an apparently simple linear function of the age of the Universe.

  20. Mid-IR spectra of pre-main sequence Herbig stars: An explanation for the non-detections of water lines

    NASA Astrophysics Data System (ADS)

    Antonellini, S.; Kamp, I.; Lahuis, F.; Woitke, P.; Thi, W.-F.; Meijerink, R.; Aresu, G.; Spaans, M.; Güdel, M.; Liebhart, A.

    2016-01-01

    Context. The mid-IR detection rate of water lines in disks around Herbig stars disks is about 5%, while it is around 50% for disks around T Tauri stars. The reason for this is still unclear. Aims: In this study, we want to find an explanation for the different detection rates between low mass and high mass pre-main-sequence stars in the mid-IR regime. Methods: We ran disk models with stellar parameters adjusted to spectral types B9 through M2, using the radiation thermo-chemical disk modelling code ProDiMo. We explored also a small parameter space around a standard disk model, considering dust-to-gas mass ratio, disk gas mass, mixing coefficient for dust settling, flaring index, dust maximum size, and size power law distribution index. We produced convolved spectra at the resolution of Spitzer, IRS, JWST MIRI, and VLT VISIR spectrographs. We applied random noise derived from typical Spitzer spectra for a direct comparison with observations. Results: The strength of the mid-IR water lines correlates directly with the luminosity of the central star. The models show that it is possible to suppress the water emission; however, current observations are not sensitive enough to detect mid-IR lines in disks for most of the explored parameters. The presence of noise in the spectra, combined with the high continuum flux (noise level is proportional to the continuum flux), is the most likely explanation for the non-detections towards Herbig stars. Conclusions: Mid-IR spectra with resolution higher than 20 000 are needed to investigate water in protoplanetary disks. Intrinsic differences in disk structure, such as inner gaps, gas-to-dust ratio, dust size and distribution, and inner disk scale height, between Herbig and T Tauri star disks are able to explain a lower water detection rate in disks around Herbig stars.

  1. New clues to the cause of extended main-sequence turnoffs in intermediate-age star clusters in the Magellanic Clouds

    SciTech Connect

    Correnti, Matteo; Goudfrooij, Paul; Kalirai, Jason S.; Girardi, Leo; Puzia, Thomas H.; Kerber, Leandro E-mail: goudfroo@stsci.edu E-mail: leo.girardi@oapd.inaf.it E-mail: lkerber@gmail.com

    2014-10-01

    We use the Wide Field Camera 3 on board the Hubble Space Telescope (HST) to obtain deep, high-resolution images of two intermediate-age star clusters in the Large Magellanic Cloud of relatively low mass (≈10{sup 4} M {sub ☉}) and significantly different core radii, namely NGC 2209 and NGC 2249. For comparison purposes, we also reanalyzed archival HST images of NGC 1795 and IC 2146, two other relatively low-mass star clusters. From the comparison of the observed color-magnitude diagrams with Monte Carlo simulations, we find that the main-sequence turnoff (MSTO) regions in NGC 2209 and NGC 2249 are significantly wider than that derived from simulations of simple stellar populations, while those in NGC 1795 and IC 2146 are not. We determine the evolution of the clusters' masses and escape velocities from an age of 10 Myr to the present age. We find that differences among these clusters can be explained by dynamical evolution arguments if the currently extended clusters (NGC 2209 and IC 2146) experienced stronger levels of initial mass segregation than the currently compact ones (NGC 2249 and NGC 1795). Under this assumption, we find that NGC 2209 and NGC 2249 have estimated escape velocities, V {sub esc} ≳ 15 km s{sup –1} at an age of 10 Myr, large enough to retain material ejected by slow winds of first-generation stars, while the two clusters that do not feature extended MSTOs have V {sub esc} ≲ 12 km s{sup –1} at that age. These results suggest that the extended MSTO phenomenon can be better explained by a range of stellar ages rather than a range of stellar rotation velocities or interacting binaries.

  2. Modeling of Camembert-type cheese mass loss in a ripening chamber: main biological and physical phenomena.

    PubMed

    Hélias, A; Mirade, P-S; Corrieu, G

    2007-11-01

    A model of the mass loss of Camembert-type cheese was established with data obtained from 2 experimental ripening trials carried out in 2 pilot ripening chambers. During these experiments, a cheese was continuously weighed and the relative humidity, temperature, oxygen, and carbon dioxide concentrations in the ripening chamber were recorded online. The aim was to establish a simple but accurate model that would predict cheese mass changes according to available online measurements. The main hypotheses were that 1) the cheese water activity was constant during ripening, 2) the respiratory activity of the microflora played a major role by inducing heat production, combined with important water evaporation, 3) the temperature gradient existing inside the cheese was negligible, and the limiting phenomenon was the convective transfer. The water activity and the specific heat of the cheeses were assessed by offline measurements. The others parameters in the model were obtained from the literature. This dynamic model was built with 2 state variables: the cheese mass and the surface temperature of the cheese. In this way, only the heat transfer coefficient had to be fitted, and it was strongly determined by the airflow characteristics close to the cheeses. Model efficiency was illustrated by comparing the estimated and measured mass and the mass loss rate for the 2 studied runs; the relative errors were less than 1.9 and 3.2% for the mass loss and the mass loss rate, respectively. The dynamic effects of special events, such as room defrosting or changes in chamber relative humidity, were well described by the model, especially in terms of kinetics (mass loss rates).

  3. Synthetic photometry for carbon-rich giants. III. Tracing the sequence of mass-losing galactic C-type Miras

    NASA Astrophysics Data System (ADS)

    Nowotny, W.; Aringer, B.; Höfner, S.; Eriksson, K.

    2013-04-01

    Late-type giant stars in the evolutionary stage of the asymptotic giant branch increasingly lose mass via comparatively slow but dense stellar winds. Not only do these evolved red giants contribute in this way to the enrichment of the surrounding interstellar medium, but the outflows also have a substantial influence on the spectro-photometric appearance of such objects. In the case of carbon-rich atmospheric chemistries, the developing cool circumstellar envelopes contain dust grains mainly composed of amorphous carbon. With increasing mass-loss rates, this leads to more and more pronounced circumstellar reddening. With the help of model calculations we aim at reproducing the observational photometric findings for a large sample of well-characterised galactic C-type Mira variables losing mass at different rates. We used dynamic model atmospheres, describing the outer layers of C-rich Miras, which are severly affected by dynamic effects. Based on the resulting structures and under the assumptions of chemical equilibrium as well as LTE, we computed synthetic spectra and synthetic broad-band photometry (Johnson-Cousins-Glass BVRIJHKL'M). A set of five representative models with different stellar parameters describes a sequence from less to more evolved objects with steadily increasing mass-loss rates. This allowed us to study the significant influence of circumstellar dust on the spectral energy distributions and the (amplitudes of) lightcurves in different filters. We tested the photometric properties (mean NIR magnitudes, colours, and amplitudes) and other characteristics of the models (mass-loss rates, periods, and bolometric corrections) by comparing these with the corresponding observational data adopted from the literature. Using different kinds of diagrams we illustrate where the models are located in a supposed evolutionary sequence defined by observed C-type Mira samples. Based on comparisons of galactic targets with empirical relations derived for C stars

  4. THE MOLECULAR GAS CONTENT OF z = 3 LYMAN BREAK GALAXIES: EVIDENCE OF A NON-EVOLVING GAS FRACTION IN MAIN-SEQUENCE GALAXIES AT z > 2

    SciTech Connect

    Magdis, Georgios E.; Rigopoulou, D.; Daddi, E.; Sargent, M.; Elbaz, D.; Gobat, R.; Tan, Q.; Aussel, H.; Feruglio, C.; Charmandaris, V.; Dickinson, M.; Reddy, N.

    2012-10-10

    We present observations of the CO[J = 3 {yields} 2] emission toward two massive and infrared luminous Lyman break galaxies (LBGs) at z = 3.21 and z = 2.92, using the IRAM Plateau de Bure Interferometer, placing first constraints on the molecular gas masses (M{sub gas}) of non-lensed LBGs. Their overall properties are consistent with those of typical (main-sequence) galaxies at their redshifts, with specific star formation rates {approx}1.6 and {approx}2.2 Gyr{sup -1}, despite their large infrared luminosities (L{sub IR} Almost-Equal-To (2-3) Multiplication-Sign 10{sup 12} L{sub Sun }) derived from Herschel. With one plausible CO detection (spurious detection probability of 10{sup -3}) and one upper limit, we investigate the evolution of the molecular gas-to-stellar mass ratio (M{sub gas}/M{sub *}) with redshift. Our data suggest that the steep evolution of M{sub gas}/M{sub *} of normal galaxies up to z {approx} 2 is followed by a flattening at higher redshifts, providing supporting evidence for the existence of a plateau in the evolution of the specific star formation rate at z > 2.5.

  5. DUSTY OB STARS IN THE SMALL MAGELLANIC CLOUD. I. OPTICAL SPECTROSCOPY REVEALS PREDOMINANTLY MAIN-SEQUENCE OB STARS

    SciTech Connect

    Sheets, Holly A.; Bolatto, Alberto D.; Van Loon, Jacco Th.; Oliveira, Joana M.; Sandstrom, Karin; Simon, Joshua D.; Barba, Rodolfo H.

    2013-07-10

    We present the results of optical spectroscopic follow-up of 125 candidate main sequence OB stars in the Small Magellanic Cloud (SMC) that were originally identified in the S{sup 3}MC infrared imaging survey as showing an excess of emission at 24 {mu}m indicative of warm dust, such as that associated with a transitional or debris disks. We use these long-slit spectra to investigate the origin of the 24 {mu}m emission and the nature of these stars. A possible explanation for the observed 24 {mu}m excess, that these are emission line stars with dusty excretion disks, is disproven for the majority of our sources. We find that 88 of these objects are normal stars without line emission, with spectral types mostly ranging from late-O to early-B; luminosity classes from the literature for a sub-set of our sample indicate that most are main-sequence stars. We further identify 17 emission-line stars, 7 possible emission-line stars, and 5 other objects with forbidden-line emission in our sample. We discover a new O6 Iaf star; it exhibits strong He II 4686 A emission but relatively weak N III 4640 A emission which we attribute to the lower nitrogen abundance in the SMC. Two other objects are identified with planetary nebulae, one with a young stellar object, and two with X-ray binaries. To shed additional light on the nature of the observed 24 {mu}m excess we use optical and infrared photometry to estimate the dust properties of the objects with normal O and B star spectra and compare these properties to those of a sample of hot spots in the Galactic interstellar medium (ISM). We find that the dust properties of the dusty OB star sample resemble the properties of the Galactic sample of hot spots. Some may be runaway systems with bow-shocks resulting from a large velocity difference between star and ISM. We further investigate the nature of these dusty OB stars in a companion paper presenting mid-infrared spectroscopy and additional imaging.

  6. The Space Density and Kinematics of Metal-Poor Blue Main Sequence Stars Near the Solar Circle

    NASA Astrophysics Data System (ADS)

    Preston, G. W.; Beers, T. C.; Shectman, S. A.

    1993-12-01

    We have used UBV photometry to identify 172 blue (0.15 <= (B-V)_o <= 0.35), metal-poor ([Fe/H] <= -1.0) main sequence stars (hereafter BMPs) among candidates from the HK objective-prism/interference-filter survey. The BMP fractions in the principal spectral groups of the survey have been used to estimate the space density of this species within 2 kpc of the sun, nu = 600 kpc(-3) . Accordingly, the specific frequency of the field BMPs, reckoned as the numb