Mean optical spectrum of M33 X-7

Mean optical spectrum of M33 X-7. The spectrum shown here (connected dots), which was extracted with the SPECRES package in IRAF22, is the sum of the 22 individual spectra that have been velocity-shifted to the rest frame of the secondary star. The solid line is the model spectrum described in the paper. The data were obtained using GMOS on the Gemini North. Twenty-four 40-minute spectra were acquired in service mode between 2006 August 18 and November 16 in good seeing of always < 0.8 arcseconds. In the two-dimensional spectra, the overlap of the profiles of M33 X-7 and the nearby pair of stars was modest.