- ID:
- ivo://CDS.VizieR/J/ApJ/891/85
- Title:
- Manganese abundances in GC & dSph galaxies
- Short Name:
- J/ApJ/891/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Manganese abundances are sensitive probes of the progenitors of TypeIa supernovae (SNe Ia). In this work, we present a catalog of manganese abundances in dwarf spheroidal satellites of the Milky Way, measured using medium-resolution spectroscopy. Using a simple chemical evolution model, we infer the manganese yield of SNe Ia in the Sculptor dwarf spheroidal galaxy (dSph) and compare to theoretical yields. The sub-solar yield from SNIa ([Mn/Fe]_Ia_=-0.30_-0.03_^+0.03^ at [Fe/H]=-1.5dex, with negligible dependence on metallicity) implies that sub-Chandrasekhar-mass (sub-MCh) white dwarf progenitors are the dominant channel of SNe Ia at early times in this galaxy, although some fraction (>~20%) of M_Ch_ Type Ia or Type Iax SNe are still needed to produce the observed yield. First-order corrections for deviations from local thermodynamic equilibrium increase the inferred [Mn/Fe]_Ia_ by as much as ~0.3dex. However, our results also suggest that the nucleosynthetic source of SNe Ia may depend on environment. In particular, we find that dSphs with extended star formation histories (Leo I, Fornax dSphs) appear to have higher [Mn/Fe] at a given metallicity than galaxies with early bursts of star formation (Sculptor dSph), suggesting that M_Ch_ progenitors may become the dominant channel of SNe Ia at later times in a galaxy's chemical evolution.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/557/A19
- Title:
- Mass and age of extreme low-mass white dwarfs
- Short Name:
- J/A+A/557/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The number of detected extremely low mass (ELM) white dwarf stars has increased drastically in recent year thanks to the results of many surveys. In addition, some of these stars have been found to exhibit pulsations, making them potential targets for asteroseismology. We provide a fine and homogeneous grid of evolutionary sequences for helium (He) core white dwarfs for the whole range of their expected masses (0.15<~M_*_/M_{sun}_<~0.45), including the mass range for ELM white dwarfs (M_*_/M_{sun}_<~0.20). The grid is appropriate for mass and age determination of these stars, as well as to study their adiatabic pulsational properties. White dwarf sequences have been computed by performing full evolutionary calculations that consider the main energy sources and processes of chemical abundance changes during white dwarf evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/419/L5
- Title:
- Masses and radii of DA white dwarfs in SDSS DR1
- Short Name:
- J/A+A/419/L5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the sample of 1175 new nonmagnetic DA white dwarfs with the effective temperatures T_eff_>=12000K, which were extracted from the Data Release 1 of the Sloan Digital Sky Survey. We determined masses, radii, and bolometric luminosities of stars in the sample. The above parameters were derived from the effective temperatures T_eff_ and surface gravities logg published in the DR1, and the new theoretical M-R relations for carbon-core and oxygen-core white dwarfs. Mass distribution of white dwarfs in this sample exhibits the peak at M=0.562M_{sun}_ (carbon-core stars), and the tail towards higher masses. Both the shape of the mass distribution function and the empirical mass-radius relation are practically identical for white dwarfs with either pure carbon or pure oxygen cores.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A157
- Title:
- Massive O-type stars near ZAMS elusive detection
- Short Name:
- J/A+A/638/A157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The apparent lack of massive O-type stars near the Zero Age Main Sequence, or ZAMS, (at ages <2Myr) has been a topic widely discussed in the last 40 years. Different explanations for the elusive detection of these young massive stars have been proposed from both the observational and theoretical side, but no firm conclusions have been reached yet. The aim of this work is to perform a reassessment of this empirical result benefiting from the high quality spectroscopic observations of (more than 400) Galactic O-type stars gathered by the IACOB and OWN surveys. We use effective temperatures and surface gravities resulting from a homogeneous, semi-automatized, IACOB-GBAT/FASTWIND spectroscopic analysis to locate our sample of stars in the Kiel and spectroscopic Hertzsprung-Russell (HR) diagrams. We evaluate the completeness of our magnitude limited sample of stars - as well as the existence of potential observational biases affecting the compiled sample - using information from the Galactic O star catalog (GOSC). We discuss limitations and possible systematics of our analysis methodology, and compare our results with other recent studies using smaller samples of Galactic O-type stars. We mainly base our discussion on the distribution of stars in the spectroscopic HR diagram in order to avoid the use of still uncertain distances to most of the stars in our sample. However, we also perform a more detailed study of the young cluster Trumpler-14 as an illustrative example of how Gaia cluster distances can help to construct the associated classical HR diagram. We find that the apparent lack of massive O-type stars near the zero-age main sequence with initial evolutionary masses in the range between ~30 and 70M_{sun}_ still persist despite using spectroscopic results from a large, non-biased sample of stars. We do not find any correlations between the dearth of stars close to the ZAMS and obvious observational biases, limitations of our analysis methodology, and/or the use of one example spectroscopic HR diagram instead of the classical one. Finally, by investigating the impact of the efficiency of mass accretion during the formation process of massive stars, we conclude that an adjustment of the mass accretion rate towards lower values than canonically assumed could reconcile the hotter boundary of the empirical distribution of optically detected O-type stars in the spectroscopic HR diagram and the theoretical birthline for stars with masses above 30M_{sun}_. Last, we also discuss how the presence of a small sample of O2-O3.5 stars found much closer to the ZAMS than the main distribution of Galactic O-type star could be explained in the context of this scenario taking also into account the effect of non-standard star evolution (e.g. binary interaction, mergers, and/or homogeneous evolution).
- ID:
- ivo://CDS.VizieR/J/other/Sci/359.69
- Title:
- Massive stars in 30 Dor
- Short Name:
- J/other/Sci/359.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses (M_{sun}_). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1My. The IMF is densely sampled up to 200 Embedded Image and contains 32+/-12% more stars above 30M_{sun}_ than predicted by a standard Salpeter IMF. In the mass range of 15 to 200M_{sun}_, the IMF power-law exponent is 190^+0.37^_-0.26_, shallower than the Salpeter value of 2.35.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/3765
- Title:
- Mass-loss rates in LMC and SMC O stars
- Short Name:
- J/MNRAS/470/3765
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a combination of BVJHK and Spitzer [3.6], [5.8] and [8.0] photometry to determine infrared (IR) excesses for a sample of 58 Large Magellanic Cloud and 46 Small Magellanic Cloud O stars. This sample is ideal for determining IR excesses because the very small line-of-sight reddening minimizes uncertainties due to extinction corrections. We use the core-halo model developed by Lamers & Waters to translate the excesses into mass-loss rates and demonstrate that the results of this simple model agree with the more sophisticated CMFGEN models to within a factor of 2. Taken at face value, the derived mass-loss rates are larger than those predicted by Vink et al. (2001A&A...369..574V), and the magnitude of the disagreement increases with decreasing luminosity. However, the IR excesses need not imply large mass-loss rates. Instead, we argue that they probably indicate that the outer atmospheres of O stars contain complex structures and that their winds are launched with much smaller velocity gradients than normally assumed. If this is the case, it could affect the theoretical and observational interpretations of the 'weak wind' problem, where classical mass-loss indicators suggest that the mass-loss rates of lower luminosity O stars are far less than expected.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/71
- Title:
- Mass-loss return from LMC evolved stars. VI.
- Short Name:
- J/ApJ/753/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ~30000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry.
- ID:
- ivo://CDS.VizieR/VI/156
- Title:
- M-dwarf Lum-Temp-Radius relationships
- Short Name:
- VI/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is growing evidence that M-dwarf stars suffer radius inflation when compared to theoretical models, suggesting that models are missing some key physics required to completely describe stars at effective temperatures (TSED) less than about 4000K. The advent of Gaia DR2 distances finally makes available large datasets to determine the nature and extent of this effect.We employ an all-sky sample, comprising of >15000 stars, to determine empirical relation-ships between luminosity, temperature and radius.This is accomplished using only geometric distances and multiwave-band photometry, by utilising a modified spectral energy distribution fitting method. The radii we measure show an inflation of 3-7% compared to models, but nomore than a 1-2% intrinsic spread in the inflated sequence. We show that we are currently able to determine M-dwarf radii to an accuracy of 2.4% using our method. However, we determine that this is limited by the precision of metallicity measurements, which contribute 1.7% to the measured radius scatter. We also present evidence that stellar magnetism is currently unable to explain radius inflation in M-dwarfs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/1844
- Title:
- M dwarfs rotation-activity relation
- Short Name:
- J/MNRAS/463/1844
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the relation between stellar rotation and magnetic activity for a sample of 134 bright, nearby M dwarfs observed in the Kepler Two-Wheel (K2) mission during campaigns C0 to C4. The K2 lightcurves yield photometrically derived rotation periods for 97 stars (79 of which without previous period measurement), as well as various measures for activity related to cool spots and flares. We find a clear difference between fast and slow rotators with a dividing line at a period of ~10d at which the activity level changes abruptly. All photometric diagnostics of activity (spot cycle amplitude, flare peak amplitude and residual variability after subtraction of spot and flare variations) display the same dichotomy, pointing to a quick transition between a high-activity mode for fast rotators and a low-activity mode for slow rotators. This unexplained behavior is reminiscent of a dynamo mode-change seen in numerical simulations that separates a dipolar from a multipolar regime. A substantial number of the fast rotators are visual binaries. A tentative explanation is accelerated disk evolution in binaries leading to higher initial rotation rates on the main-sequence and associated longer spin-down and activity lifetimes. We combine the K2 rotation periods with archival X-ray and UV data. X-ray, FUV and NUV detections are found for 26, 41, and 11 stars from our sample, respectively. Separating the fast from the slow rotators, we determine for the first time the X-ray saturation level separately for early- and for mid-M stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/146
- Title:
- M dwarfs with IR excess
- Short Name:
- J/ApJ/794/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) spectroscopic catalog, we searched the WISE AllWISE catalog to investigate the occurrence of warm dust, as inferred from IR excesses, around field M dwarfs (dMs). We developed SDSS/WISE color selection criteria to identify 175 dMs (from 70841) that show IR flux greater than the typical dM photosphere levels at 12 and/or 22{mu}m, including seven new stars within the Orion OB1 footprint. We characterize the dust populations inferred from each IR excess and investigate the possibility that these excesses could arise from ultracool binary companions by modeling combined spectral energy distributions. Our observed IR fluxes are greater than levels expected from ultracool companions (>3{sigma}). We also estimate that the probability the observed IR excesses are due to chance alignments with extragalactic sources is <0.1%. Using SDSS spectra we measure surface gravity-dependent features (K, Na, and CaH 3) and find <15% of our sample indicates low surface gravities. Examining tracers of youth (H{alpha}, UV fluxes, and Li absorption), we find <3% of our sample appear young, indicating we are observing a population of field stars >~1Gyr, likely harboring circumstellar material. We investigate age-dependent properties probed by this sample, studying the disk fraction as a function of Galactic height. The fraction remains small and constant to |Z|~700pc and then drops, indicating little to no trend with age. Possible explanations for disks around field dMs include (1) collisions of planetary bodies, (2) tidal disruption of planetary bodies, or (3) failed planet formation.