PI: Andrew A. Cole, University of Massachusetts, email@example.com
Address: LGRT-B, Room 619E, 710 North Pleasant Street, Amherst, MA 01003-9305, USA
CoI: Tammy Smecker-Hane, University of California, Irvine
CoI: Ata Sarajedini, University of Florida
Title: Chemical Evolution of the Outer Disk and Halo of M33: Subtracting the Milky Way Foreground
Abstract: We propose to image fields in the outer disk and stellar halo of M33 using the KPNO 4-meter telescope, Mosaic camera and V, I and DDO51 filters. Our goal is to identify a sample of red gaint stars for subsequent spectroscopy so that we can accurately define the metallicity distribution function (MDF) as a function of radius. Contamination by Galactic foreground dwarfs will be sizeable because of the surface density of M33 stars is low. In addition, the velocity separation between M33 and Galactic stars is not large enough to reliably discriminate them \it post facto. The DDO51 filter measures the absorption strength of a Mg \small I triplet and MgH bandhead, which are highly sensitive to surface gravity for late-type stars. Giants and dwarfs are thus separated by ~0.2 mag in the (V-I, 51-V) plane, allowing us to target M33 giants for spectroscopy with high reliability. This strategy will roughly double the efficiency of our spectroscopy campaign. We will obtain spectra of ~ 500 M33 red giants with the Keck II 10-meter telescope, and derive chemical abundances with random errors of ~ 0.15 dex per star. Defining the MDF will be key to accurately inferring its M33's star-formation history, which will in turn provide strong contraints on theories of galaxy formation. Our program adds value to the M33 photometry obtained by Massey et al. in an NOAO Survey program by extending it to larger radii and providing dwarf/giant discrimination. In addition, our data will define photometric zeropoints for scheduled ACS/HST imaging of M33 halo fields.
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360