Nature of an Ultraviolet Object in Sagittarius

Abstract

WE have obtained a widened spectrogram (April 22, 1968, dispersion 180 Å mm⁻¹) with an image tube spectrograph of the intense ultraviolet object identified with the X-ray source GX3 + 1. In this communication we refer to this object as GX3 + 1. Its magnitude and colours are V=13.4, B−V= +1.0, U−B= −0.9. Very broad emission lines in its spectrum have been reported previously (communications from V. Blanco et al.). Fig. 1 is a linear microphotometer record of the spectrum of GX3 + 1. It shows many very broad emission bands (average width 130 Å at half-intensity); these come from high excitation lines of He II, O III–VI, and C III–IV. Table 1 gives their measured wavelengths, identification, widths and equivalent widths. There is evidence for a mean velocity of about −1,000 km s⁻¹, but this is difficult to estimate because the emission features are so broad and are mostly blends of several lines. There are no broad Balmer lines; the sharp lines of [O III] and H_α come from nebulosity in which the object is embedded, and give some idea of the instrumental profile.