Stellar Archaeology in the Galactic halo with the Ultra-Faint Dwarfs: VI. Ursa Major II
M. Dall'Ora (1), K. Kinemuchi (2), V. Ripepi (1), C.T. Rodgers (3), G., Clementini (4), L. Di Fabrizio (5), H.A.Smith (6), M. Marconi (1), I. Musella, (1), C. Greco (7), C.A. Kuehn (6), M. Catelan (8), B.J. Pritzl (9), T.C., Beers (10) ((1) INAF-OACN

TL;DR
This study presents deep photometry and variable star analysis of Ursa Major II, revealing its distance, metallicity spread, and potential multiple stellar populations, enhancing understanding of ultra-faint dwarf galaxy properties.
Contribution
First detailed CMD and variable star analysis of UMa II, providing new insights into its distance, metallicity distribution, and stellar populations.
Findings
Distance to UMa II is approximately 34.7 kpc.
Evidence of metallicity spread indicating multiple stellar populations.
Detection of a bona-fide RR Lyrae star in UMa II.
Abstract
We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf satellite Ursa Major II (UMa II), spanning the magnitude range from V ~ 15 to V ~ 23.5 mag and extending over a 18 {\times} 18 arcmin2 area centered on the galaxy. Our photometry goes down to about 2 magnitudes below the galaxy's main sequence turn-off, that we detected at V ~ 21.5 mag. We have discovered a bona-fide RR Lyrae variable star in UMa II, which we use to estimate a conservative dereddened distance modulus for the galaxy of (m-M)0 = 17.70{\pm}0.04{\pm}0.12 mag, where the first error accounts for the uncertainties of the calibrated photometry, and the second reflects our lack of information on the metallicity of the star. The corresponding distance to UMa II is 34.7 {\pm} 0.6 ({\pm} 2.0) kpc. Our photometry shows evidence of a spread in the galaxy subgiant branch, compatible with a spread in metal abundance…
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