HSTbanner

AR 16625 (Archival Research)

Sun Jul 14 02:17:47 GMT 2024

Principal Investigator: Kevin McKinnon
PI Institution: Canadian Institute for Theoretical Astrophysics
Investigators (xml)

Title: Combining HST and Gaia to Measure Proper Motions of Distant Halo Stars: Resolving Kinematic Inhomogeneity in the Milky Way
Cycle: 29

Abstract
The Milky Way's stellar halo contains information about the Galaxy's accretion history, its growth through time, and its dynamical interactions with satellites. From our location in the Galaxy, we can use measurements of individual stars to trace the history of our Galaxy's satellite accretion, measuring inhomogeneity and substructure in the kinematics and abundances in the halo caused by these interactions. To measure these properties, full positional, kinematic, and chemical abundance data is needed for halo stars along many lines of sight. Spectra can constrain distance and measure line of sight velocity and chemistry, but the tangential velocities require measuring proper motions (PMs). Precise astrometry with HST has been used to determine PMs for stars in the Milky Way halo from deep, multi-epoch data, but this is only available for a few fields. Gaia's third data release (EDR3) offers unprecedented spatial coverage by providing PMs across the whole sky, but the relatively short time baseline limits its accuracy for faint stars. Here, we propose to develop tools that will combine single-epoch HST archival images with Gaia measurements to measure more accurate PMs for many more stars at G>18 mag on many more fields in the halo. This will enhance the scientific impact of both observatories beyond their individual capabilities. Archival HST images will be matched with Gaia to increase the PM precision for faint halo stars in Gaia's catalog (18