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Observations of A0535+26 (HDE 245770) by the ANS in September 1975 and March 1976 when it was at the X-ray low state are discussed. Also observed were 58 early-type stars lying within 10 deg of HDE 245770; these stars are used to derive a localized extinction curve. On the basis of the depth of the 2200 A interstellar absorption feature observed in the ANS flux distribution of HDE 245770 and the shape of the localized extinction curve, an E(B-V) = 0.72 is derived for HDE 245770. Observations were made of this system during its X-ray flare-up (October 1980) and quiescent (November 1981) states by the IUE. It is noted that the fine error sensor on board the IUE detected an increase in the optical brightness of HDE 245770 during the X-ray outburst. This greatly corroborates the identification of HDE 245770 as the optical counterpart of A0535+26. No significant change in the absorption-line profiles during the X-ray high and low periods is found, indicating that there was no significant increase in the stellar wind density when the X-ray flare-up occurred. The UV continuum level increased by less than 6 percent when it was near peak X-ray luminosity. The UV spectrum of HDE 245770 suggests that it is a B0 V or a B0 III star with its dereddened continuum slope slightly in favor of being a giant.

The early-type eclipsing binary Delta Pictoris has been studied with 260 observations in each of five UV bands. These are the most accurate observations to date, and no strong evidence for light-curve complications produced by circumstellar material has been found. Combined light curves from four epochs separated by intervals of six months do not show any strong dips or shoulders as seen in earlier investigations. The strength of th C IV wavelength 1550 line is independent of phase to better than 0.01 m. The root-mean-square scatterer shown by the light curves ranges from 0.006 m to 0.014 and may be evidence that either or both of the components are intrinsically variable. The integrated colors of the system are consistent with a B1 V spectral type and very little interstellar extinction. A detached solution of the light curves for a Roche model well with the spectroscopic mass ratio, but a semidetached solution cannot be ruled out.

Ultraviolet observations of three dwarf Cepheids (VZ Cnc, SX Phe, and AI Vel) are presented. The UV light curves are consistent with those in the visual region. When compared to standard stars, all three dwarf Cepheids exhibit flux deficiencies at the shortest observed wavelengths. The most extreme deficiencies appear for SX Phe; these may be related to the other properties previously noted for this star, including low metallicity, high space motion, and low luminosity.

In 1979-80, ultraviolet spectrophotometry of RY Sgr was obtained by the International Ultraviolet Explorer (IUE) during the star's recovery from its 1977-78 minimum. The wavelength dependence of the extinction of this R Coronae Borealis-type variable was determined by comparison of spectra obtained at different times but with nearly the same pulsational phase. The measured wavelength dependence is compatible with theoretical predictions of extinction by spherical graphite particles having a radius of 0.043 micron and with the extinction observed for amorphorus carbon smoke.

Complete ultraviolet light curves for HZ Her immediately after a well-defined X-ray turn-on in 1975 are obtained. The features of the curve are found to correspond well with features seen in the optical. The absolute level of emission at maximum light at 1550 A is in good agreement with the calculations of the X-ray reflection effect of Milgrom and Salpeter (1975). It is found that at 1550 A approximately 20% of the light at maximum comes from the accretion disk. Similar observations of Cyg X-1 make it possible to determine the degree of reddening, equivalent to E(B-V) = 0.95 + or - 0.07, from the strength of the 2200 A interstellar absorption feature. The distance inferred from this amount of reddening requires that the optical star be luminous and, therefore, massive. Observations obtained during the May 1975 X-ray transition show ultraviolet excess when compared with the data obtained six months later.

Four low-resolution UV spectra of v1 Sgr (cK2) were obtained with the IUE satellite to investigate the nature of the hot component in this object, which was detected in the Astronomical Netherlands Satellite UV photometric data. The IUE results show that the spectral energy distribution of v1 Sgr in the FUV is comparable to that of a B9 star. FUV flux level, when compared with that of the mid-ultraviolet flux level, indicates that the luminosity of the hot component is roughly equivalent to that of a main-sequence star, assuming that the mid-ultraviolet flux is dominated almost entirely by a K2 I object. No discernible spectral features are present in the FUV, contrary to what may be expected in a star of B9 spectral type. Two possible interpretations are suggested: the hot component is a rapidly rotating star, or an accretion disk surrounding a central object which could be a collapsed star is being observed.