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A 30-day contiguous photometric run with the MOST satellite on the WN5-6bstar WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 +/- 0.55days along with a number of harmonics at periods P/n, with n ~ 2,3,4,5 and 6,and a few other possible stray periodicities and/or stochastic variability ontimescales longer than about a day. Spectroscopic RV studies fail to reveal anyplausible companion with a period in this range. Therefore, we conjecture thatthe observed light-curve cusps of amplitude ~ 0.01 mag that recur at a 4.08 daytimescale may arise in the inner parts, or at the base of, a corotatinginteraction region (CIR) seen in emission as it rotates around with the star atconstant angular velocity. The hard X-ray component seen in WR 110 could thenbe a result of a high velocity component of the CIR shock interacting with theambient wind at several stellar radii. Given that most hot, luminous starsshowing CIRs have two CIR arms, it is possible that either the fundamentalperiod is 8.2 days or, more likely in the case of WR 110, there is indeed asecond weaker CIR arm for P = 4.08 days, that occurs ~ two thirds of a rotationperiod after the main CIR. If this interpretation is correct, WR 110 thereforejoins the ranks with three other single WR stars, all WN, with confirmed CIRrotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far thelowest amplitude photometric modulation. This illustrates the power of beingable to secure intense, continuous high-precision photometry from space-basedplatforms such as MOST. It also opens the door to revealing low-amplitudephotometric variations in other WN stars, where previous attempts have failed.If all WN stars have CIRs at some level, this could be important for revealingsources of magnetism or pulsation in addition to rotation periods.

WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?