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A. K. Vivas, R. Zinn (Yale University), QUEST Collaboration
The formation and evolution of galaxies is one of the major unsolved problems in astrophysics. Clues to this problem may be found by examining our own galaxy, particularly the ``fossil'' record of the early stages of galactic evolution preserved in the galactic halo stellar populations. If the halo has been built by accretion events, then we do not expect it to have a smooth distribution. The halo may consist of streams of stars that originated in now extinct satellite galaxies. Probably these extinct galaxies contained rich populations of RR Lyrae stars, as do the present satellite galaxies of the Milky Way.
The QUEST RR Lyrae survey is designed to find RR Lyrae stars in the halo of the Milky Way over a range of distances from 4 to 70 Kpc. An important feature of this survey is that it is narrow but long. It has therefore a better chance of crossing one of the debris streams than the customary square survey of equal area. Our observations have partial overlap with the recently discovered clump of stars at Rgal~ 40 Kpc by the Sloan Sky Survey, which may be related to the Sagittarius dwarf spheroidal galaxy. Our survey has detected several more RR Lyrae variables in the clump that were missed by Sloan, and these data strengthen the case that it is a real feature of the halo. We present here a complete description of the RR Lyrae population in the clump. This study demonstrates the potential of our survey for not only finding over-densities in the halo but also for determining important characteristics of their stellar populations.
Research reported herein based on observations at the Observatorio Nacional de Llano del Hato, Venezuela, operated by the Centro de Investigaciones de Astronomia (CIDA) and supported by CONICIT.
The author(s) of this abstract have provided an email address for comments about the abstract: vivas@astro.yale.edu