Optical counterpart of 2A0311–227

Abstract

The X-ray source 2A0311–227 was recently identified independently by Williams¹ and by Griffiths et al.². Williams made a tentative identification from an inspection of low dispersion objective prism Schmidt plates taken at Cerro Tololo Inter-American Observatory for the discovery of active galaxies and quasars. The identifying characteristics were strong emission of H and He II. Griffiths et al. made the identification from an excellent HEAO-1 position followed by spectroscopic observations. The optical position of the object is α = 3 h 12 min 00.0 s, δ = −22° 46′ 48″ (1950). Figure 1 identifies the X-ray source among the neighbouring stars. It has a mag (variable) of about 15. Immediately after the tentative identification by Williams the 1.3-m telescope at McGraw-Hill Observatory on Kitt Peak was scheduled for spectrophotometric observations of the star in question, and we report the results here. A photon-counting spectral scanner was used. The instrument gives a dispersion of 1.15 Å per channel. Exposures of 5 and 10 min were made that covered the spectral region from 4,000 Å to 5,800 Å. A few scans were taken with lower dispersion and broader spectral coverage. The spectrum shows strong emission features, especially H I, He II λ 4686 and the C III–N III blend at λ 4640–4650 (ref. 2).