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 superimpose isochrones from different sources on 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 ± 0.5 Gyr using Padova isochrones, and 13.7 ± 0.4 Gyr using BASTI isochrones. We found also a group of very metal-poor stars ([Fe/H] = −2.7 to −2.0 dex) with relatively young ages, in the range 8–10 Gyr.

Very metal-poor stars in the solar vicinity: kinematics and abundance analysis

“…Distance is one of the most important parameters in dynamics studies. In Plotnikova et al (2022) we compared the best distances, estimated out of four different techniques: Gaia DR3 parallaxes (Gaia Collaboration et al (2022)), Gaia EDR3 (Gaia Collaboration (2021)) corrected by Lindegren et al (2021), the distances derived by Bailer-Jones et al (2021), andQueiroz et al (2019) (StarHorse). Our choice was made based on the best fit of the data with the isochrones in the color-magnitude diagram.…”

“…CONCLUSIONS Three main parameters that can be used to obtain the origin of the star are: kinematics, chemistry and age. In this study, we explored all three of them for a sample of 28 very metal-poor stars for whom we had previously derived ages ( (Plotnikova et al 2022)). Kinematics and chemistry are routinely used to assign stars to different components of the Milky Way galaxy, or to the various accreted systems that have been identified over the years in the Galactic halo.…”

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Very metal-poor stars contain crucial information on the Milky Way's infancy. In our previous study (Plotnikova et al 2022) we derived a mean age of ∼ 13.7 Gyr for a sample of these stars in the Sun's vicinity. In this work, we investigate the chemical and kinematics properties of these stars with the goal of obtaining some insights on their origin and their parent population.

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Very Metal-poor Stars in the Solar Vicinity: Kinematics and Abundance Analysis

“…As the main target for this investigation, we chose the data set of 28 very metal-poor stars for which we derived precise ages (Plotnikova et al 2022). These stars are of particular interest because they are very metal-poor and their average age is 13.7 ± 0.4 Gyr.…”

“…In this work, we build on Plotnikova et al (2022) and study the kinematics and abundances of a sample of very metal-poor stars in the solar vicinity. Therefore, the layout of this study is as follows.…”