Citation:
Dupree A K, Gursky H, Black J H, Davis R J, Hartmann L, Matilsky T, Raymond J C, Hammerschlag-Hensberge G, van den Heuvel E P J, Burger M, et al. Simultaneous ultraviolet, optical and X-ray observations of the X-raysource Vel X-1 (HD 77581). \apj. 1980;238 :969-981.