IUE Investigations at the Core of M 79

Extract

As a result of their investigation of 27 galactic globular clusters with the ANS satellite van Albada, de Boer and Dickens (1981) classified M 79 (NGC 1904) as an “extremely blue” cluster. It was also found to be a low luminosity x-ray source based on data acquired with the Einstein X-ray Observatory (Grindlay 1981). In this brief paper we discuss the stellar spectra extracted from two short wavelength (SWP) IUE images acquired at the “center of light” of M 79. Discrete peaks in the “spatially resolved”, cross-dispersion profile suggested the presence of at least three hot stars in the large aperture in both images (Fig. 1). The images in question are SWP 25303 and SWP 28936 for which it is important to note here that 1) the orientation of the large aperture on the plane of the sky differs for the two images by nearly 180° and 2) the target coordinates, determined from offset maneuvers with respect to a nearby SAO star, are nearly coincident. The cross-dispersion profile observed in the first spectrum is thus repeated in the second case, but is “flipped” left for right. Features immediately apparent in both images include a broad, asymmetric peak, almost certainly the blend of two or more components, and a second peak well separated from this blend and most likely a single star. In Fig. 2 we show the cross-dispersion profile of SWP 28936 and the best fit to that profile, assuming three components. From fits such as this and similar ones in other wavelength bins, we ultimately obtain from each image the entire SWP spectrum of each individual component.