Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21714705h&link_type=abstract
American Astronomical Society, AAS Meeting #217, #147.05; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Using the SPIcam imager at the Apache Point 3.5-m telescope, we have observed the ultra-faint dSph, UMa II (d 30 kpc), and the WLM dIrr galaxy (d 930 kpc) in Washington and Strömgren filters. UMa II is a nearby metal-poor system ([Fe/H] -2.5), within the dark matter halo of the Milky Way, with few red giant branch stars above the horizontal branch. Previous spectroscopic studies have confirmed that UMa II is old ( 12 Gyr), contains some stars more metal-poor than [Fe/H]=-3.0, and has a 1.0 dex metallicity spread. The WLM Galaxy is more metal rich (mean [Fe/H] -1.3) than UMa II, with the bright RGB population being dominated by young and relatively more metal-rich stars. There is a metallicity gradient within the WLM dIrr, with the inner-galaxy population being at least 0.3 dex more metal rich ([Fe/H] -1.1) than the outer halo ([Fe/H] -1.4). We present our new imaging data and compare the stellar population color-magnitude diagrams with theoretical models to determine the best photometric methods of quantifying metallicity spreads in these diverse populations. We show that photometric metallicities can be determined to 0.2 dex for bright RGB stars and to 0.15 dex for well-defined giant branches.
We acknowledge support from NSERC Discovery Grants and the M.J. Murdock Charitable Trust.
Hankins A.
Hughes Joanne D.
Leaman Ryan
McCormick Katherine
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