2008/10/23 by Joanne Hughes, George Wallerstein, Anne Bossi
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1088/0004-6256/136/6/2321
20 pages, 7 figures, to appear in the AJ
arxiv created 2008/10/23 · openalex publication_date 2008/11/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
We present Washington CT 1 T 2 photometry of a field central to the Boötes I dwarf spheroidal galaxy, which was discovered as a stellar overdensity in the Sloan Digital Sky Survey (DR5). We show that the Washington filters are much more effective than the Sloan filters in separating the metal-poor turn-off stars in the dwarf galaxy from the foreground stars. We detect 165 objects in the field, and statistically determine that just over 40% of the objects are nonmembers. Our statistical analysis mostly agrees with radial velocity measurements of the brighter stars. We find that there is a distinct main-sequence turn-off and subgiant branch, where there is some evidence of a spread in chemical abundance. Any evidence of an age spread is limited to a few billion years. The brightest seven Boötes I members give a (photometric-color derived) weighted mean iron abundance of [Fe/H] = −2.1 +0.3 −0.5 , and the best-fit isochrone is the 14.1 Gyr, Z = 0.0002 model, with ( m − M ) V = 19.11 and E ( B − V ) = 0.02.