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We analyze a 162 ks HETG Chandra observation of the O7.5 III(n)((f)) star xiPer, together with contemporaneous H alpha observations. The X-ray spectrum ofthis 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 periodof 2.086 days, which is thought to be associated with co-rotating interactionregions (CIRs). We examine the Chandra and H alpha data for variability on thistime scale. We find that the X-rays vary by about 15% over the course of theobservations and that this variability is out of phase with variable absorptionon the blue wing of the H alpha profiles (assumed to be a surrogate for the UVabsorption associated with CIRs). While not conclusive, both sets of data areconsistent with models where the CIRs are either a source of X-rays or modulatethem.

CIR Modulation of the X-ray Flux from the O7.5 III(n)((f)) Star xi Persei?