- ID:
- ivo://CDS.VizieR/J/A+A/575/A18
- Title:
- Revising the ages of planet-hosting stars
- Short Name:
- J/A+A/575/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This article aims to measure the age of stars with planets (SWP) through stellar tracks and isochrones computed with the Padova & Trieste Stellar Evolutionary Code (PARSEC). We developed algorithms based on two different techniques for determining the ages of field stars: isochrone placement and Bayesian estimation. Their application to a synthetic sample of coeval stars shows the intrinsic limits of each method. For instance, the Bayesian computation of the modal age tends to select the extreme age values in the isochrones grid. Therefore, we used the isochrone placement technique to measure the ages of 317 SWP. We found that ~6% of SWP have ages lower than 0.5Gyr. The age distribution peaks in the interval [1.5, 2]Gyr, then it decreases. However, ~7% of the stars are older than 11Gyr. The Sun turns out to be a common star that hosts planets, when considering its evolutionary stage. Our SWP age distribution is less peaked and slightly shifted towards lower ages if compared with ages in the literature and based on the isochrone fit. In particular, there are no ages below 0.5Gyr in the literature.
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- ID:
- ivo://CDS.VizieR/J/A+A/530/A115
- Title:
- Rotating massive MS stars evolutionary models
- Short Name:
- J/A+A/530/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a dense grid of evolutionary tracks and isochrones of rotating massive main-sequence stars. We provide three grids with different initial compositions tailored to compare with early OB stars in the Small and Large Magellanic Clouds and in the Galaxy. Each grid covers masses ranging from 5 to 60M_{sun}_ and initial rotation rates between 0 and about 600km/s. To calibrate our models we used the results of the VLT-FLAMES Survey of Massive Stars. We determine the amount of convective overshooting by using the observed drop in rotation rates for stars with surface gravities logg<3.2 to determine the width of the main sequence. We calibrate the efficiency of rotationally induced mixing using the nitrogen abundance determinations for B stars in the Large Magellanic cloud. We describe and provide evolutionary tracks and the evolution of the central and surface abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/291/155
- Title:
- Rotating neutron stars models. I.
- Short Name:
- J/A+A/291/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+AS/108/455
- Title:
- Rotating neutron stars models. II.
- Short Name:
- J/A+AS/108/455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/606/A55
- Title:
- Rotational mixing in CEMP-s stars
- Short Name:
- J/A+A/606/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars with s-process enrichment (CEMP-s) are believed to be the products of mass transfer from an asymptotic giant branch (AGB) companion, which has long since become a white dwarf. The surface abundances of CEMP-s stars are thus commonly assumed to reflect the nucleosynthesis output of the first AGB stars. We have previously shown that, for this to be the case, some physical mechanism must counter atomic diffusion (gravitational settling and radiative levitation) in these nearly fully radiative stars, which otherwise leads to surface abundance anomalies clearly inconsistent with observations. Here we take into account angular momentum accretion by these stars. We compute in detail the evolution of typical CEMP-s stars from the zero-age main sequence, through the mass accretion, and up the red giant branch for a wide range of specific angular momentum ja of the accreted material, corresponding to surface rotation velocities, v_rot_, between about 0.3 and 300km/s. We find that only for j_a_>~10^17^cm^2^/s (v_rot_>20km/s, depending on mass accreted) angular momentum accretion directly causes chemical dilution of the accreted material. This could nevertheless be relevant to CEMP-s stars, which are observed to rotate more slowly, if they undergo continuous angular momentum loss akin to solar-like stars. In models with rotation velocities characteristic of CEMP-s stars, rotational mixing primarily serves to inhibit atomic diffusion, such that the maximal surface abundance variations (with respect to the composition of the accreted material) prior to first dredge-up remain within about 0.4dex without thermohaline mixing or about 0.5-1.5dex with thermohaline mixing. Even in models with the lowest rotation velocities (v_rot_<~1km/s), rotational mixing is able to severely inhibit atomic diffusion, compared to non-rotating models. We thus conclude that it offers a natural solution to the problem posed by atomic diffusion and cannot be neglected in models of CEMP-s stars.
- ID:
- ivo://CDS.VizieR/J/AJ/156/89
- Title:
- RVs & predicted transit-times for the K2-24 system
- Short Name:
- J/AJ/156/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While planets between the size of Uranus and Saturn are absent within the solar system, the star K2-24 hosts two such planets, K2-24b and c, with radii equal to 5.4 R_{Earth}_ and 7.5 R_{Earth}_, respectively. The two planets have orbital periods of 20.9 days and 42.4 days, residing only 1% outside the nominal 2:1 mean-motion resonance. In this work, we present results from a coordinated observing campaign to measure planet masses and eccentricities that combines radial velocity measurements from Keck/HIRES and transit-timing measurements from K2 and Spitzer. K2-24b and c have low, but nonzero, eccentricities of e_1_~e_2_~0.08. The low observed eccentricities provide clues to the formation and dynamical evolution of K2-24b and K2-24c, suggesting that they could be the result of stochastic gravitational interactions with a turbulent protoplanetary disk, among other mechanisms. K2-24b and c are 19.0_-2.1_^+2.2^ M_{Earth}_ and 15.4_-1.8_^+1.9^ M_{Earth}_, respectively; K2-24c is 20% less massive than K2-24b, despite being 40% larger. Their large sizes and low masses imply large envelope fractions, which we estimate at 26_-3_^+3^ % and 52_-3_^+5^ %. In particular, K2-24c's large envelope presents an intriguing challenge to the standard model of core-nucleated accretion that predicts the onset of runaway accretion when f_env_~50%.
- ID:
- ivo://CDS.VizieR/J/A+A/484/815
- Title:
- Scaled solar tracks and isochrones
- Short Name:
- J/A+A/484/815
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In many astrophysical contexts, the helium content of stars may differ significantly from those usually assumed in evolutionary calculations. In order to improve upon this situation, we have computed tracks and isochrones in the range of initial masses 0.15-20M_{sun}_ for a grid of 39 chemical compositions with the metal content Z between 0.0001 and 0.070 and helium content Y between 0.23 and 0.46. ************************************************************************** * * * Sorry, but the author(s) never supplied the tabular material * * announced in the paper * * * **************************************************************************
- ID:
- ivo://CDS.VizieR/J/A+A/508/355
- Title:
- Scaled solar tracks and isochrones
- Short Name:
- J/A+A/508/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extend our theoretical computations for low-mass stars to intermediate-mass and massive stars, for which few databases exist in the literature. Evolutionary tracks and isochrones are computed for initial masses 2.50-20M_{sun}_ for a grid of 37 chemical compositions with metal content Z between 0.0001 and 0.070 and helium content Y between 0.23 and 0.40 to enable users to obtain isochrones for ages as young as about 10^7^ years and to simulate stellar populations with different helium-to-metal enrichment laws. The Padova stellar evolution code is identical to that used in the first paper of this series. Synthetic TP-AGB models allow stellar tracks and isochrones to be extended until the end of the thermal pulses along the AGB. We provide software tools for the bidimensional interpolation (in Y and Z) of the isochrones from very old ages down to about 10^7^ years. This lower limit depends on chemical composition. The extension of the blue loops and the instability strip of Cepheid stars are compared and the Cepheid mass-discrepancy is discussed. The location of red supergiants in the H-R diagram is in good agreement with the evolutionary tracks for masses from 10 to 20M_{sun}_. Tracks and isochrones are available in tabular form for the adopted grid of chemical compositions in the extended plane Z-Y in three photometric systems. An interactive web interface allows users to obtain isochrones of any chemical composition inside the provided Z-Y range and also to simulate stellar populations with different Y(Z) helium-to-metal enrichment laws.
- ID:
- ivo://CDS.VizieR/J/ApJS/210/3
- Title:
- SDSS bulge, disk and total stellar mass estimates
- Short Name:
- J/ApJS/210/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of bulge, disk, and total stellar mass estimates for ~660000 galaxies in the Legacy area of the Sloan Digital Sky Survey Data (SDSS) Release 7. These masses are based on a homogeneous catalog of g- and r-band photometry described by Simard et al. (2011, Cat. J/ApJS/196/11), which we extend here with bulge+disk and Sersic profile photometric decompositions in the SDSS u, i, and z bands. We discuss the methodology used to derive stellar masses from these data via fitting to broadband spectral energy distributions (SEDs), and show that the typical statistical uncertainty on total, bulge, and disk stellar mass is ~0.15 dex. Despite relatively small formal uncertainties, we argue that SED modeling assumptions, including the choice of synthesis model, extinction law, initial mass function, and details of stellar evolution likely contribute an additional 60% systematic uncertainty in any mass estimate based on broadband SED fitting. We discuss several approaches for identifying genuine bulge+disk systems based on both their statistical likelihood and an analysis of their one-dimensional surface-brightness profiles, and include these metrics in the catalogs. Estimates of the total, bulge and disk stellar masses for both normal and dust-free models and their uncertainties are made publicly available here.
- ID:
- ivo://CDS.VizieR/J/AJ/132/271
- Title:
- SFR of M31 from resolved stars in near-IR
- Short Name:
- J/AJ/132/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss H and K observations of three fields in the bulge and disk of M31 obtained with the ALTAIR adaptive optics system and NIRI instrument on Gemini North. These are the highest resolution and deepest near-infrared observations obtained to date of the inner regions of M31 and demonstrate the promise of ground-based adaptive optics for studying the crowded regions of nearby galaxies. We have combined our observations with previously published Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer observations of nine M31 fields and have derived the coarse star formation histories of M31's bulge and inner disk. From fits to the MK luminosity functions, we find the stellar population mix to be dominated by old, nearly solar-metallicity stars. The old populations, which we define as having age >=6Gyr, indeed dominate the star formation histories at all radii independent of the relative contributions of bulge and disk stars. Although all of our fields contain some bulge contribution, our results suggest that there is no age difference between the bulge and disk to the limit of our precision.
