Optical and Infrared Photometry of the Microquasar GRO J1655−40 in Quiescence

Abstract

We present BVIJK photometry of the black hole candidate GRO J1655-40 in full quiescence. We report a refined orbital period of 2.62191 ± 0.00020 days. The light curves are dominated by ellipsoidal variations from the secondary star. We model the light curves with an upgraded code that includes a more accurate treatment of limb darkening. Previous models containing a large cool disk are ruled out, and, indeed, our data can be fitted with a pure ellipsoidal light curve without any disk contribution. In general agreement with previous results, we derive a confidence region of the correlated quantities inclination and mass ratio, centered on an inclination of 702 ± 19 and mass ratio of 2.6 ± 0.3, resulting in a primary mass M₁ = 6.3 ± 0.5 M_☉ (all 95% confidence). The complex limits and errors on these values and on the possible disk contribution to the light curve are discussed.