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Start Over Subject stellar ages Validation Level 2
1. Absolute polarimetry observations of 33 pulsars
ID:
ivo://CDS.VizieR/J/MNRAS/453/4485
Title:
Absolute polarimetry observations of 33 pulsars
Short Name:
J/MNRAS/453/4485
Date:
21 Oct 2021
Publisher:
CDS
Description:
Absolute polarimetry observations of 33 pulsars were carried out with the Green Bank Telescope in the 1100-1900 MHz band using the Green Bank Ultimate Pulsar Processing Instrument. This group was selected to help complete a larger sample for which accurate proper-motion measurements were available. A combination of profile analysis using the core/double cone model and polarization-angle fitting methods were applied to estimate the "fiducial" longitude of the magnetic axis for each star and refer the linear polarization angle at that point to infinite frequency. As had been found previously, a number of the pulsars are found to have fiducial polarization directions that fall either along or at right angles to their proper-motion directions, whereas upwards of a third of the stars studied show alignments that are neither parallel nor orthogonal.
2. Abundances and ages of stars in the Milky Way bulge
ID:
ivo://CDS.VizieR/J/ApJ/900/4
Title:
Abundances and ages of stars in the Milky Way bulge
Short Name:
J/ApJ/900/4
Date:
14 Mar 2022 07:37:10
Publisher:
CDS
Description:
The age and chemical characteristics of the Galactic bulge link to the formation and evolutionary history of the Galaxy. Data-driven methods and large surveys enable stellar ages and precision chemical abundances to be determined for vast regions of the Milky Way, including the bulge. Here, we use the data-driven approach of The Cannon, to infer the ages and abundances for 125367 stars in the Milky Way, using spectra from Apache Point Observatory Galaxy Evolution Experiment (apogee) DR14. We examine the ages and metallicities of 1654 bulge stars within R_GAL_<3.5kpc. We focus on fields with b<12{deg}, and out to longitudes of l<15{deg}. We see that stars in the bulge are about twice as old ({tau}=8Gyr), on average, compared to those in the solar neighborhood ({tau}=4Gyr), with a larger dispersion in [Fe/H] (~0.38 compared to 0.23dex). This age gradient comes primarily from the low-{alpha} stars. Looking along the Galactic plane, the very central field in the bulge shows by far the largest dispersion in [Fe/H] ({sigma}[Fe/H]~0.4dex) and line-of- sight velocity ({sigma}vr~90km/s), and simultaneously the smallest dispersion in age. Moving out in longitude, the stars become kinematically colder and less dispersed in [Fe/H], but show a much broader range of ages. We see a signature of the X-shape within the bulge at a latitude of b=8{deg}, but not at b=12{deg}. Future apogee and other survey data, with larger sampling, affords the opportunity to extend our approach and study in more detail, to place stronger constraints on models of the Milky Way.
3. Abundances in the local region. I. G and K giants
ID:
ivo://CDS.VizieR/J/AJ/150/88
Title:
Abundances in the local region. I. G and K giants
Short Name:
J/AJ/150/88
Date:
21 Oct 2021
Publisher:
CDS
Description:
Parameters and abundances for 1133 stars of spectral types F, G, and K of luminosity class III have been derived. In terms of stellar parameters, the primary point of interest is the disagreement between gravities derived with masses determined from isochrones, and gravities determined from an ionization balance. This is not a new result per se, but the size of this sample emphasizes the severity of the problem. A variety of arguments led to the selection of the ionization-balance gravity as the working value. The derived abundances indicate that the giants in the solar region have Sun-like total abundances and abundance ratios. Stellar evolution indicators have also been investigated with the Li abundances and the [C/Fe] and C/O ratios, indicating that standard processing has been operating in these stars. The more salient result for stellar evolution is that the [C/Fe] data across the red-giant clump indicates the presence of mass-dependent mixing in accord with standard stellar evolution predictions.
4. Abundances in the local region. II. F, G, and K dwarfs
ID:
ivo://CDS.VizieR/J/AJ/153/21
Title:
Abundances in the local region. II. F, G, and K dwarfs
Short Name:
J/AJ/153/21
Date:
21 Oct 2021
Publisher:
CDS
Description:
Parameters and abundances have been derived for 1002 stars of spectral types F, G, and K, and luminosity classes IV and V. After culling the sample for rotational velocity and effective temperature, 867 stars remain for discussion. Twenty-eight elements are considered in the analysis. The {alpha}, iron-peak, and Period 5 transition metal abundances for these stars show a modest enhancement over solar averaging about 0.05dex. The lanthanides are more abundant, averaging about +0.2dex over solar. The question is: Are these stars enhanced, or is the Sun somewhat metal-poor relative to these stars? The consistency of the abundances derived here supports an argument for the latter view. Lithium, carbon, and oxygen abundances have been derived. The stars show the usual lithium astration as a function of mass/temperature. There are more than 100 planet-hosts in the sample, and there is no discernible difference in their lithium content, relative to the remaining stars. The carbon and oxygen abundances show the well-known trend of decreasing [x/Fe] ratio with increasing [Fe/H].
5. Abundances in the local region. III. Southern dwarfs
ID:
ivo://CDS.VizieR/J/AJ/155/111
Title:
Abundances in the local region. III. Southern dwarfs
Short Name:
J/AJ/155/111
Date:
21 Oct 2021
Publisher:
CDS
Description:
Stellar parameters and abundances have been derived from a sample of 907 F, G, and K dwarfs. The high-resolution, high signal-to-noise spectra utilized were acquired with the HARPS spectrograph of the European Southern Observatory. The stars in the sample with -0.2<[Fe/H]<+0.2 have abundances that strongly resemble that of the Sun, except for the lithium content and the lanthanides. Near the solar temperature, stars show two orders of magnitude range in lithium content. The average content of stars in the local region appears to be enhanced at about the +0.1 level relative to the Sun for the lanthanides. There are over 100 planet hosts in this sample, and there is no discernible difference between them and the non-hosts regarding their lithium content.
6. Abundances of neutron-capture elements
ID:
ivo://CDS.VizieR/J/A+A/649/A126
Title:
Abundances of neutron-capture elements
Short Name:
J/A+A/649/A126
Date:
22 Feb 2022
Publisher:
CDS
Description:
The aim of this work is to determine abundances of neutron-capture elements for thin- and thick-disc F, G, and K stars in several selected sky fields near the North Ecliptic Pole and to compare the results with the Galactic chemical evolution models, to explore elemental gradients according to stellar ages, mean galactocentric distances, and maximum heights above the Galactic plane. The observational data were obtained with the 1.65 meter telescope at the Moletai Astronomical Observatory and a fibre-fed high-resolution spectrograph covering a full visible wavelength range (4000-8500{AA}). Elemental abundances were determined using a differential line-by-line spectrum synthesis using the TURBOSPECTRUM code with the MARCS stellar model atmospheres and accounting for the hyperfine-structure effects. Results. We determined abundances of Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu for 424 thin- and 82 thick-disc stars. The sample of thick-disc stars shows a clearly visible decrease of [Eu/Mg] with increasing metallicity compared to the thin-disc stars, bringing more evidences of different chemical evolution in these two Galactic components. Abundance correlation with age slopes for the investigated thin-disc stars are slightly negative for the majority of s-process dominated elements, while r-process dominated elements have positive correlations. Our sample of thin-disc stars with ages spanning from 0.1 to 9Gyrs gives the [Y/Mg]=0.022(+/-0.015)-0.027(+/-0.003)/age[Gyr] relation. However, for the thick-disc stars, when taking into account also data from other studies, we found that [Y/Mg] cannot serve as an age indicator. The radial abundance-to-iron gradients in the thin disc are negligible for the s-process dominated elements and become positive for the r-process dominated elements, the vertical gradients are negative for the light s-process dominated elements and become positive for the r-process dominated elements. In the thick disc, the radial abundance-to-iron slopes are negligible and the vertical ones are predominantly negative.
7. Abundances of stars hosting planets
ID:
ivo://CDS.VizieR/J/ApJ/720/1290
Title:
Abundances of stars hosting planets
Short Name:
J/ApJ/720/1290
Date:
21 Oct 2021
Publisher:
CDS
Description:
The metal content of planet-hosting stars is an important ingredient that may affect the formation and evolution of planetary systems. Accurate stellar abundances require the determinations of reliable physical parameters, namely, the effective temperature, surface gravity, microturbulent velocity, and metallicity. This work presents the homogeneous derivation of such parameters for a large sample of stars hosting planets (N=117), as well as a control sample of disk stars not known to harbor giant, closely orbiting planets (N=145). Stellar parameters and iron abundances are derived from an automated analysis technique developed for this work. As previously found in the literature, the results in this study indicate that the metallicity distribution of planet-hosting stars is more metal rich by ~0.15 dex when compared to the control sample stars. A segregation of the sample according to planet mass indicates that the metallicity distribution of stars hosting only Neptunian-mass planets (with no Jovian-mass planets) tends to be more metal poor in comparison with that obtained for stars hosting a closely orbiting Jovian planet. The significance of this difference in metallicity arises from a homogeneous analysis of samples of FGK dwarfs which do not include the cooler and more problematic M dwarfs.
8. A combined Chandra & LAMOST study of stellar activity
ID:
ivo://CDS.VizieR/J/ApJ/871/193
Title:
A combined Chandra & LAMOST study of stellar activity
Short Name:
J/ApJ/871/193
Date:
21 Oct 2021
Publisher:
CDS
Description:
We probed stellar X-ray activity over a wide range of stellar parameters, using Chandra and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) data. We measured the X-ray-to-bolometric luminosity ratio (R_X_=L_X_/L_bol_) for 484 main-sequence stars and found a bimodal distribution for G and K types. We interpret this bimodality as evidence of two subpopulations with different coronal temperatures, which are caused by different coronal heating rates. Using the metallicity and velocity information, we find that both of the subpopulations are mostly located in the thin disk. We find no trend of R_X_ with stellar age for stars older than ~4Gyr; there is a trough in the R_X_ versus age distribution, with the lowest range of R_X_ appearing at ages around 2Gyr. We then examined the correlation between R_X_ and R_H{alpha}_ (proxy of chromospheric activity): we find that the two quantities are well correlated, as found in many earlier studies. Finally, we selected a sample of 12 stars with X-ray flares and studied the light-curve morphology of the flares. The variety of flare profiles and timescales observed in our sample suggests the contribution of different processes of energy release.
9. Active Kepler stars differential rotation
ID:
ivo://CDS.VizieR/J/A+A/583/A65
Title:
Active Kepler stars differential rotation
Short Name:
J/A+A/583/A65
Date:
21 Oct 2021
Publisher:
CDS
Description:
In addition to the discovery of hundreds of exoplanets, the high-precision photometry from the CoRoT and Kepler satellites has led to measurements of surface rotation periods for tens of thousands of stars, which can potentially be used to infer stellar ages via gyrochronology. Our main goal is to derive ages of thousands of field stars using consistent rotation period measurements derived by different methods. Multiple rotation periods are interpreted as surface differential rotation (DR). We study the dependence of DR with rotation period and effective temperature. We reanalyze a previously studied sample of 24,124 Kepler stars using different approaches based on the Lomb- Scargle periodogram. Each quarter (Q1-Q14) is treated individually using a prewhitening approach. Additionally, the full time series and their different segments are analyzed.
10. Age and colors of massive white dwarf stars
ID:
ivo://CDS.VizieR/J/A+A/465/249
Title:
Age and colors of massive white dwarf stars
Short Name:
J/A+A/465/249
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present evolutionary calculations and colors for massive white dwarfs with oxygen-neon cores for masses between 1.06 and 1.28M_{sun}_. The evolutionary stages computed cover the luminosity range from log(L/L_{sun}_)~0.5 down to -5.2. Our cooling sequences are based on evolutionary calculations that take into account the chemical composition expected from massive white dwarf progenitors that burned carbon in partially degenerate conditions. The use of detailed non-gray model atmospheres provides us with accurate outer boundary conditions for our evolving models at low effective temperatures.

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