Towards an understanding of the Of?p star HD 191612: optical spectroscopy

Ian D. Howarth, Nolan R. Walborn, Danny J. Lennon, Joachim Puls, Yael Naze, K. Annuk, I. Antokhin, D. Bohlender, H. Bond, J.-F. Donati, L. Georgiev, D. Gies, D. Harmer, A. Herrero, I. Kolka, D. McDavid, T. Morel, I. Negueruela, G. Rauw, P. Reig
Arxiv ID: 0707.0594Last updated: 12/10/2020
We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f?pe-O8fp). The Balmer and HeI lines show strongly variable emission which is highly reproducible on a well-determined 538-d period. Metal lines and HeII absorptions (including many selective emission lines but excluding He II 4686A emission) are essentially constant in line strength, but are variable in velocity, establishing a double-lined binary orbit with P(orb) = 1542d, e=0.45. We conduct a model-atmosphere analysis of the primary, and find that the system is consistent with a O8: giant with a B1: main-sequence secondary. Since the periodic 538-d changes are unrelated to orbital motion, rotational modulation of a magnetically constrained plasma is strongly favoured as the most likely underlying `clock'. An upper limit on the equatorial rotation is consistent with this hypothesis, but is too weak to provide a strong constraint.

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