A V and I CCD Mosaic Survey of the Ursa Minor Dwarf Spheroidal Galaxy

Details A V and I CCD Mosaic Survey of the Ursa Minor Dwarf Spheroidal Galaxy A V and I CCD Mosaic Survey of the Ursa Minor Dwarf Spheroidal Galaxy

Jun 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aj....115.2359k&link_type=abstract

The Astronomical Journal, Volume 115, Issue 6, pp. 2359-2368.

Astronomy and Astrophysics

Astronomy

45

Galaxies: Dwarf, Galaxies: Individual: Name: Ursa Minor, Galaxies: Stellar Content, Galaxies: Local Group

Scientific paper

We discuss a Johnson-Cousins V- and I-band CCD mosaic survey of the Ursa Minor dwarf spheroidal galaxy (dSph) to V ~ 22. We covered UMi with 27 10.5′ x 10.5′ overlapping CCD frames, each frame consisting of two 300 s exposures in each of V and I. We also observed several regions ~3 deg from UMi to obtain an estimate of contamination by galaxies and Galactic stars. We report the first H-R diagram of an entire dSph. Separation of dwarf stars from foreground stars by color allows a robust estimation of the structural parameters of UMi. We examine earlier evidence of two lumps in the UMi stellar distribution. We detect a statistically significant asymmetry in the stellar distribution of UMi along the major axis. Structure in the stellar distribution of UMi might indicate a tidal origin for UMi's high observed mass-to-light ratio. We demonstrate a technique for obtaining the absolute magnitude of UMi from horizontal-branch star counts compared with M92; this method of luminosity estimation is independent of the distance to UMi. We obtain M_V=-8.87+/-sigmaM_V, where sigmaM_V=0.14 if M92 is a perfect calibrator and sigmaM_V<~0.35 is an upper bound on the error arising from differences in stellar populations. Our value for M_V is consistent with earlier measurements and has a smaller uncertainty.

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