Very metal-poor stars in the solar vicinity: age determination

Abstract

The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the Universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and super-impose isochrones from different sources in the stars color-magnitude diagram built up with different photometric systems. We highlight subtle metallicity effects when using the Johnson photometry for low metallicity stars and finally adopt Gaia photometry. An automatic fitting method is devised to assign ages to each individual star taking into account the uncertainties in the input parameters. The mean age of the sample turns out to be $13.9\pm 0.5$ Gyr using Padova isochrones, and $13.7\pm 0.4$ Gyr using BASTI isochrones. We found also a group of very metal-poor stars ($\left[\frac{Fe}{H}\right]$: -2.7 -2.0 dex) with relatively young ages, in the range 8 --10 Gyr.

23 pages, 16 eps figures, accepted for publication in the Astrophysical Journal

References in corpus (12)

• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties
• HD 140283: A Star in the Solar Neighborhood that Formed Shortly After the Big Bang
• Revising the ages of planet-hosting stars
• Four-hundred Very Metal-Poor Stars Studied with LAMOST and Subaru. II. Elemental abundances
• Timing the Early Assembly of the Milky Way with the H3 Survey
• The Best and Brightest Metal-Poor Stars
• Three Ancient Halo Subgiants: Precise Parallaxes, Compositions, Ages, and Implications for Globular Clusters
• The all-sky PLATO input catalogue
• Constraints on the Distance Moduli, Helium and Metal Abundances, and Ages of Globular Clusters from their RR Lyrae and Non-Variable Horizontal-Branch Stars. I. M3, M15, and M92
• Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
• Ancient Very Metal-Poor Stars Associated With the Galactic Disk in the H3 Survey

Cited by in corpus (3)

• Some Old Globular Clusters (and Stars) Inferring That the Universe Is Older Than Commonly Accepted
• Very metal-poor stars in the solar vicinity: kinematics and abundance analysis
• Evolution of Size, Mass, and Density of Galaxies Since Cosmic Dawn