TheGaia-ESO Survey: open clusters inGaia-DR1

Abstract

Context. Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. Aims. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. Methods. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. Results. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. Conclusions. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets.

Differential abundances of open clusters and their tidal tails: Chemical tagging and chemical homogeneity

“…Open Clusters (OCs) of different ages and chemical compositions are ideal to test on star formation and evolution theories and have long been used to better understand the history of the Galactic disc. Several spectroscopic surveys dedicate a significant observing time to OCs such as Gaia-ESO survey (Gilmore et al 2012;Randich et al 2013), APOGEE (Majewski et al 2017), OCCASO (Casamiquela et al 2019), among others. In these surveys, OCs provide fundamental material for calibrating the stellar parameters, in particular, the dependencies of abundances as a function of stellar parameters (Jofré et al 2019).…”

The Gaia-ESO Survey: a new approach to chemically characterising young open clusters

“…However, while the number of studies on intermediate-age and old OCs (τ 600 Myr) is conspicuous, less attention has been payed to the chemical composition of young OCs (YOCs, ages younger than ∼ 150 Myr) and starforming regions (SFRs). The Gaia-ESO public spectroscopic Survey (Gilmore et al 2012;Randich et al 2013) places special emphasis on observations of OCs covering the age range from a few million to several billion years, analysed in a homogeneous way. It therefore offers the opportunity of deriving the metallicity and abundances of a significant number of young objects (Spina et al 2014a,b).…”

On the Chemical and Kinematic Consistency between N-rich Metal-poor Field Stars and Enriched Populations in Globular Clusters

“…With the release of Gaia DR2 (Gaia Collaboration et al 2018;Katz et al 2018), proper motions of billions of stars are now available to the astronomical community. Combining with radial velocities from large spectroscopic surveys, like Sloan Digital Sky Survey (SDSS, Eisenstein et al 2011;Blanton et al 2017), Gaia-ESO survey (Gilmore et al 2012;Randich et al 2013), and LAM-OST Galactic spectroscopic survey Zhao et al 2012), the wealthy 6D information of billions of stars have challenged and even overthrown many aspects of our understanding of the Milky Way (MW). The discovery of snail shells in the phase space distribution of MW disk stars (Antoja et al 2018) has inspired the debates about their origin: whether they are generated by the passage of a dwarf galaxy (probably Sagittarius dwarf galaxy) through the MW disk (Binney & Schönrich 2018), or they are the echo of the MW bar buckling (Khoperskov et al 2019).…”