X-ray observations of single-line spectroscopic binaries

Abstract

Observations of three single-line spectroscopic binaries with the Imaging Proportional Counter on the Einstein Observatory are presented. None of the three binaries viz π⁵ Ori, θ² Cru, and 112 Her is detected as an X-ray source, making the presence of a compact secondary in any of these binaries highly unlikely. An extended X-ray source (X-ray size ~3') with an intensity of (2.2±0.25) 10⁻¹² erg cm⁻² s⁻¹ in the 0.3-3.3 KeV energy band has been found at a position 28' away from π⁵ Ori. The X-ray source position is consistent with that of a distant cluster of galaxies, A 520.