Year: 2026
Type: article
Abstract: We present proper motion (PM) measurements for Draco II, an ultrafaint dwarf satellite of the Milky Way. These PMs are measured using two epochs of Hubble Space Telescope (HST)/Advanced Camera for Surveys imaging separated by a 7 yr temporal baseline. Measuring the PMs of low-luminosity systems is difficult due to the low number of member stars, requiring a precise inertial reference frame. We construct reference frames using three different sets of external sources: (1) stars with Gaia Data Release 3 data, (2) stationary background galaxies, and (3) a combination of the two. We show that all three reference frames give consistent PM results. We find that for this sparse, low-luminosity regime including background galaxies into the reference frame improves our measurement by up to ∼2× versus using only Gaia astrometric data. Using 301 background galaxies as a reference frame, we find that Draco II’s systemic PM is ( μ α * , μ δ ) = ( 1.043 ± 0.029 , 0.879 ± 0.028 ) mas yr −1 , which is the most precise measurement of the three we present in this paper.
Source: The Astrophysical Journal
Authors: Jack T. Warfield, Kevin A. McKinnon, Sangmo Tony Sohn, Nitya Kallivayalil, Alessandro Savino, Roeland P. van der Marel, Andrew B. Pace, Christopher T. Garling, Niusha Ahvazi, Paul Bennet, Roger E. Cohen, Matteo Correnti, Mark A. Fardal, Kristen. B. W. McQuinn, Max J. B. Newman, Eduardo Vitral
Institutions: University of Virginia, University of Toronto, Space Telescope Science Institute, University of California, Berkeley, Johns Hopkins University, Rutgers, The State University of New Jersey, Astronomical Observatory of Rome, Agenzia Spaziale Italiana, National Institute for Astrophysics, Eureka Scientific, Royal Observatory, University of Edinburgh
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W7127055417