IAU Symposium Abstract S186-010P

The Star Formation History of the Sagittarius Dwarf Spheroidal Galaxy

K.~Mighell1, T.~Armandroff1, A.~Sarajedini1, A.~Layden2, M.~Mateo2, F.~Fusi Pecci3, F.~Ferraro3, R.~Buonanno4
1 Kitt Peak National Observatory, NOAO < mighell@noao.edu, armand@noao.edu, ata@noao.edu >
2 University of Michigan < layden@astro.lsa.umich.edu, mateo@astro.lsa.umich.edu >
3 Universita di Bologna < flavio@astbo3.bo.astro.it, ferraro@astbo3.bo.astro.it >
4 Osservatorio Astronomico di Roma < buonanno@coma.mporzio.astro.it >

The Sagittarius dwarf spheroidal galaxy is the Milky Way's nearest companion, with a galactocentric distance of only 16 kpc. As such, it presents the opportunity to study in detail the interaction between a large galaxy and its nearby satellite. We have obtained deep HST WFPC2 imaging of the Sagittarius dwarf using the F555W and F814W filters. Four fields were observed in Sagittarius, along with two background fields for statistical decontamination of the color-magnitude diagrams. Two of the Sagittarius fields are near the center of the galaxy, and the other two are in the easternmost high-density region. Aperture photometry has been carried out using CCDCAP. The resulting color-magnitude diagrams reveal the turnoff region and approximately 4 magnitudes of the main sequence. The star formation history is determined with the aid of theoretical isochrones. Our complete results on the star formation history of the Sagittarius dwarf will be presented. We will discuss the implications of this star formation history on the Sagittarius dwarf's origin, orbit, and survival.