CIR modulation of the X-ray flux from the O7.5 III(n)((f)) star Persei?

Abstract

We analyse a 162 ks high energy transmission grating Chandra observation of the O7.5 III(n)((f)) star ξ Per, together with contemporaneous Hα observations. The X-ray spectrum of this star is similar to other single O stars, and not pathological in any way. Its UV wind lines are known to display cyclical time variability, with a period of 2.086 d, which is thought to be associated with corotating interaction regions (CIRs). We examine the Chandra and Hα data for variability on this time-scale. We find that the X-rays vary by ∼15 per cent over the course of the observations and that this variability is out of phase with variable absorption on the blue wing of the Hα profiles (assumed to be a surrogate for the UV absorption associated with CIRs). While not conclusive, both sets of data are consistent with models where the CIRs are either a source of X-rays or modulate them.