UvA-DARE ( Digital Academic Repository ) X-ray and optical studies of blackhole X-ray transients

t Wee have measure d the brightnes of the optical counterpar t of the black-hol e X-ray binaryy Nova Sco 1994 (GRO J1655-40) during 40 nights between 1995 May 3 andd July 27. From our observations and data from the literature we refine the orbitall period to be 2.62040 0.00098 days. We model the R-band light curve as primarilyy being due to an X-ray heated secondary , using a model that includes a Rochee lobe fillin g secondar y star, the effects of X-ray heating on both the concave accretionn disk and the X-ray illuminated surface of the secondary , shadowing of the secondar yy and disk, and mutual eclipses of the disk and the secondar y star. From thee shape of the light curve we constrai n the inclination of the system to lie in the rangee 65°-76° and constrai n the mass ratio q — MilM2 to lie in the range 3.8-5.5. Thiss implies a mass range for the secondar y star and compact object of 0.95-1. 8 M 00 and 4.9-6.8 M©, respectively. The (V-R) and (R -i) color curves do not show evidencee of significant variability with orbital phase during 1995 June-July, their averagee values being 1.06(3) and 0.86(2) mag, respectively.