Erratum: ``Observations of Scorpius X-1 with IUE: Ultraviolet Results from a Multiwavelength Campaign'' (ApJ, 376, 278 [1991])

In the published version of our original paper, two sentences were truncated and spliced in the abstract. The abstract (with the missing segment underlined) should read:

``We present ultraviolet results from a multiwavelength campaign on the low-mass X-ray binary Sco X-1. The ultraviolet observations were obtained with the International Ultraviolet Explorer (IUE) and coincided with X-ray observations taken with the Japanese satellite Ginga and other observations from numerous ground-based observatories. Our observations strongly support a direct relationship between the strengths of the UV continuum and line fluxes and the X-ray spectral states. Models predicting UV continuum emission from the X-ray-heated surface of the companion star and from an X-ray-illuminated accretion disk were adjusted for parameters intrinsic to Sco X-1 and fitted to the data. It is found that for Sco X-1, as for Cyg X-2: (1) X-ray heating of the accretion disk is the dominant source of UV emission; (2) the mass accretion rate increases monotonically along the Z-shaped curve in an X-ray color-color diagram; and (3) the disk structure does not change as a function of X-ray spectral state. The accretion disk model gives a best-fit outer disk radius of (6.3+/-0.3)×10¹⁰ cm. Mass accretion rates range from 0.6×10^-8 M_solar yr^-1 in the normal branch (NB) to 1.1×10^-8 M_solar yr^-1 in the flaring branch (FB). The horizontal branch (HB) was not observed simultaneously in the UV and X-rays, but if the weakest state seen from earlier UV observations corresponds to the HB state, the mass accretion rate there is 0.4×10^-8 M_solar yr^-1. UV emission lines from He, C, N, O, and Si are detected; all increase in intensity from the HB to the FB state. A model in which emission lines are due to photoionization of the outer-disk by the X-ray source is developed and gives good agreement with the line fluxes observed in each state. The X-ray:UV:radio flux ratios of Sco X-1 measured at the lower vertex of the Z in the X-ray color-color diagram agree with those previously observed in five other X-ray binaries. We suggest that the flux at this vertex, which several theories identify with an accretion rate at the Eddington limit, may be used as a distance indicator; the distance to Sco X-1 would then be 2.0+/-0.5 kpc.