Globular clusters with Gaia

Abstract

The treatment of crowded fields in Gaia data will only be a reality in a few years from now. In particular, for globular clusters, only the end-of-mission data (public in 2022-2023) will have the necessary full crowding treatment and will reach sufficient quality for the faintest stars. As a consequence, the work on the deblending and decontamination pipelines is still ongoing. We describe the present status of the pipelines for different Gaia instruments, and we model the end-of-mission crowding errors on the basis of available information. We then apply the nominal post-launch Gaia performances, appropriately worsened by the estimated crowding errors, to a set of 18 simulated globular clusters with different concentration, distance, and field contamination. We conclude that there will be 10 3 -10 4 stars with astrometric performances virtually untouched by crowding (contaminated by <1 mmag) in the majoritiy of clusters. The most limiting factor will be field crowding, not cluster crowding: the most contaminated clusters will only contain 10-100 clean stars. We also conclude that: (i) the systemic proper motions and parallaxes will be determined to 1% or better up to 15 kpc, and the nearby clusters will have radial velocities to a few km s −1 ; (ii) internal kinematics will be of unprecendented quality, cluster masses will be determined to 10% up to 15 kpc and beyond, and it will be possible to identify differences of a few km s −1 or less in the kinematics (if any) of cluster sub-populations up to 10 kpc and beyond; (iii) the brightest stars (V 17 mag) will have space-quality, wide-field photometry (mmag errors), and all Gaia photometry will have 1-3% errors on the absolute photometric calibration.

New Constraints on the Nuclear Equation of State from the Thermal Emission of Neutron Stars in Quiescent Low-mass X-Ray Binaries

“…Within the framework of Gaia's Data Release 2 (DR2; Gaia Collaboration et al 2018a), trigonometric parallaxes have already become available for large numbers of stars belonging to dozens of GCs. Still, as discussed in detail by Pancino et al (2017) and more recently also emphasized by Gaia Collaboration et al (2018c), systematic uncertainties still preclude the determination of reliable distances based on the available Gaia data for such crowded fields as Galactic GCs -even though, by the end of the mission, GC distances that are accurate to within the 1% level can be expected (Pancino et al 2017). Confronting the Gaia-DR2 data with distances from the literature, as independently compiled in the Harris (1996Harris ( , 2010 catalog, a relatively small systematic offset, at the level of 0.029 mas, was found (Gaia Collaboration et al 2018b), in the sense that parallaxes derived by Gaia are smaller than those implied by the distances given in Harris (2010).…”

A family of lowered isothermal models

“…Radial velocity measurements of stars in the outer parts of GCs are expensive because of the contamination of non-member stars (Da Costa 2012). The upcoming data of the ESA-Gaia mission will improve this situation: the availability of all-sky proper motions and photometry measurements will facilitate membership selection, and for several nearby GC the proper motions will be of sufficient quality that they can be used for dynamical modelling and to unveil the properties of the hidden lowenergy stars Pancino et al 2013;Sollima et al 2015). The models presented in this paper allow for higher level of inference of physical properties of GCs from these upcoming data.…”

Evolutionary history of four binary blue stragglers from the globular clustersωCen, M 55, 47 Tuc, and NGC 6752

“…However, uncertainties of stellar evolution models still remain the primary factor impeding the accurate determination of the absolute ages of globular clusters. Observational uncertainties will dramatically decrease when Gaia parallaxes become available (distances to many GCs will be known with an accuracy better than one per cent; Pancino et al 2013). If the theory is to catch up with observations, much more effort in exposing and diagnosing its problems is needed.…”