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G. Brammer (CTIO / Williams College), S. Wachter, D. W. Hoard (CTIO), A. P. Smale (GSFC)
We present photometry results of the search for the orbital period of the low mass X-ray binary (LMXB) system X1556-60. The optical counterpart of X1556-60 was identified by Charles et al. in 1979, but subsequent studies failed to detect significant periodicity in optical variations. Smale (1991) reported a possible period of 9.1 hr (0.3807 day) but added that a further independent study would be needed for confirmation. We present the period analysis of two observation runs taken at the Cerro Tololo Inter-American Observatory in 1997 and 2000 with the 1.5 m and 0.9 m telescope respectively. Our data indicate possible periods of 0.46229 day and 0.43993 day for the data from 1997 and 2000 respectively, and neither data set provided any evidence for the 0.3807 day candidate period of Smale (1991). We will also present RXTE data taken contemporaneously with the 1997 data set. This research was part of the 2001 CTIO REU program, funded by the NSF.