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A progress report is given of investigations related to observations of stellar spectra obtained with the ultraviolet stellar spectrophotometer S59 aboard the ESRO TD-1A satellite. We describe first the processing of the observations: intensity and wavelength calibration, identification of lines, classification of spectra. Thereafter some important groups of lines are dealt with: non-LTE computation of the Mgii lines are presented: apart from the peculiar emission line and shell stars they compare well with the observations; intensity ratios, of Feii and Feiii lines are an important temperature classification criterion. Interstellar UV lines indicate large deficiencies of some metals, as compared to solar values. A new ultraviolet continuous extinction curve is determined. We discuss the strong outstreaming motions observed in α Cygni, and the consequent mass loss of this star (< 3 × 10−10 yr−1and finally we describe the composite spectrum of the (WC8+09I) bnary γ2 Velorum; the ultraviolet continuous spectrum of the WC star is about one magnitude brighter than any theory predicts.

The ultraviolet stellar spectrophotometer S59 of the Utrecht Astronomical Institute uses the stabilization properties of the ESRO TD-1A satellite. This spacecraft scans the sky along eliptic meridians with an orbital precession of one degree per day, thus covering the whole celestial sphere in half a year. This property is combined with a tracking system which points the spectrophotometer during four minutes at stars of sufficient brightness. During this time interval the ultraviolet stellar spectrum is scanned with a resolution of 1.7 Å in three bands of about 100 Å, around 2110, 2545 and 2825 Å. The optical, mechanical and electronic properties of the instrument and its tracking system are described in some detail, as well as the optical and technical performance in laboratory tests and in orbit. Some results obtained during the first half year of operation are briefly described.