AAS 205th Meeting, 9-13 January 2005
Session 141 Our Friendly Neighbors: M31 and M33
Poster, Thursday, January 13, 2005, 9:20am-4:00pm, Exhibit Hall

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[141.03] Separating M33 Red Giant Stars From Foreground Milky Way Dwarfs

M. Teig, T. Smecker-Hane, M. Hood (UCI)

Our goal is to quantify the kinematics and chemical abundances of the stellar populations (thin disk and thick disk and/or halo) of the nearby spiral galaxy M33 in order to test sophisticated models of galaxy formation. We are using the DEIMOS spectrograph at the Keck II 10-meter telescope to obtain spectra surrounding the Ca II near-infrared triplet lines for approximately 1000 red giant stars throughout M33's disk and halo. From the spectra we will measure the radial velocities and chemical abundances of the stars and distinguish the separate stellar populations. One critical step in our project is our use of V, I, and DDO51-band imaging to separate M33 red giants from foreground Milky Way dwarf stars, because the radial velocities of these stars overlap significantly. Our imaging has been done using the Kitt Peak National Observatory 4-meter telescope and MOSAIC camera. A star's flux in the DDO51 filter (centered at 5100 Å; width of 150 Å) is a measure of the strength of the Mg I lines that are highly dependent on the star's surface gravity. Thus when plotted in a (V-I) vs. (DDO51-V) diagram, most M33 red giants are easily discriminated from foreground Galactic dwarfs. We will present photometric results from a field located SE of M33's core along the minor axis, the first of four fields that we have observed. We also will show fiducials from globular and open star clusters that illustrate this technique's lack of metallicity dependence, and thus its power.

We gratefully acknowledge financial support from grants NSF AST-0307863 and STScI/NASA GO-9837 to Tammy Smecker-Hane.

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