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Paper: A Period for the Of?p Spectrum Alternator HD 191612
Volume: 367, Massive Stars in Interactive Binaries
Page: 401
Authors: Walborn, N.R.; Howarth, I.D.
Abstract: The Of?p star HD 191612 was found in 2001 to display two peculiar, recurrent spectral states at optical wavelengths. In one, the spectral type is near O6 and there are strong wind diagnostics, including a P Cygni profile at Hα; while in the other it is O8 with Hα predominantly in absorption. Other peculiar spectral features alternate correlatively. In 2004, with the aid of Hipparcos photometry, the spectral variations have been found to be periodic and predictable. Hence, we are planning or proposing optical, UV, and X-ray observations at critical extreme and transition phases, to enable progress toward a physical interpretation. The predicted Fall 2004 transition, from the O8 to the O6 state, is already being observed optically. Although by no means proven, the most promising current model for this bizarre behavior is tidally induced nonradial pulsations driving enhanced mass loss near periastron in an eccentric binary. Hence, this object may provide new information about massive-binary evolution.
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