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D.J. Sand (Caltech), A.M. Ghez (UCLA)
Over the past six years, Ghez et al. (1998, 2000) have conducted a proper motion study of the galactic center using the Keck telescope in the K bandpass in order to ascertain the existence, position and mass of the central supermassive black hole. Using this data set, a systematic search for both short and long term variables within about 4 arcseconds of the galactic center was undertaken. Sample sources had to appear in all twenty observed epochs and in over fifty percent of the contributing shift-and-add frames. Employing a reduced chi-squared test for variability, twelve of the fifty sources were found to be variable. Of these, IRS 16SW (P= 9.72 days) and S2-7 (P=33.63 days) exhibited periodicity. Several possible explanations for the source of this periodicity are explored. Some variability in general is expected due to the possible location of many of the sources on the asymptotic giant branch along with several others that may be luminous blue variables. In comparison with previous variability studies that have searched to 13 K mag, we were able to study sources down to a K magnitude of 15 and so have been able to check for variability in several of the high-velocity sources within 1 arcsecond of the galactic center. As the proper motion survey continues and more epochs are obtained, the sample size should increase and the variability detection statistics improve. A census and characterization of the variable sources at the galactic center will contribute to a better understanding of the stellar population and evolution of the region.