Variation in Emission and Absorption Lines and Continuum Flux by Orbital Phase in Vela X - 1

High resolution spectral studies were undertaken at orbital phases (φ) 0, 0.25 and 0.5 on the high-mass X-ray binary (HMXB) Vela X-1 using archival Chandra data. We present (a) the first detailed analysis of the multiple strong narrow emission lines present in φ 0.5 (b) an analysis of the absorption of the continuum in φ 0.5, and (c) the first detection of narrow emission and absorption lines in φ 0.25. Multiple fluorescent and H-and He-like emission lines in the band 1.6 20 Angstrom (Å) in eclipse are partially obscured at φ 0.25 by the X-ray continuum. The φ 0.25 spectrum displays 3 triplets, 2 with a blue-shifted resonance (r) line in absorption and the intercombination (i) and forbidden (f) lines in emission, and shows in absorption other blue-shifted lines seen in emission in eclipse. At φ 0.5 the soft X-ray continuum diminishes revealing an ”eclipse-like” spectrum, however line flux values are around 13-fold those in eclipse. We conclude the doctoral student, Centre for Astronomy, James Cook University