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Title:
A Period and a Prediction for the Of?p Spectrum Alternator HD 191612
Authors:
Walborn, Nolan R.; Howarth, Ian D.; Rauw, Gregor; Lennon, Daniel J.; Bond, Howard E.; Negueruela, Ignacio; Nazé, Yaël; Corcoran, Michael F.; Herrero, Artemio; Pellerin, Anne
Affiliation:
AA(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555 ), AB(Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK; Visiting Observer, Isaac Newton Group, Apartado 321, 38700 Santa Cruz de La Palma, Canary Islands, Spain. ), AC(Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bât B5c, B4000 Liège, Belgium. Also at the Fonds National de Recherche Scientifique, Belgium; Visiting Observer, Observatoire de Haute-Provence, Saint Michel l'Observatoire F-04870, France. The 2004 OHP run was funded by the OPTICON network, supported under the FP6 program of the European Commission. ), AD(Isaac Newton Group, Apartado 321, 38700 Santa Cruz de La Palma, Canary Islands, Spain ), AE(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555 ; Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85726: operated by AURA, Inc., under cooperative agreement with the NS; and Multiple-Mirror Observatory, University of Arizona, Tucson, AZ 85721. ), AF(Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain. Researcher of the Ramón y Cajal program, funded by the Spanish Ministerio de Ciencia y Tecnología (MCyT) and the University of Alicante. This research is partially supported by the Spanish MCyT under grant AYA2002-00814 ; Visiting Observer, Loiano Observatory, Via Orzale 12, 40050 Loiano, Italy. ), AG(Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bât B5c, B4000 Liège, Belgium. Also at the Fonds National de Recherche Scientifique, Belgium ), AH(Universities Space Research Association, 7501 Forbes Boulevard, Suite 206, Seabrook, MD 20706; and Laboratory for High Energy Astrophysics, Goddard Space Flight Center, Greenbelt, MD 20771 ), AI(Instituto de Astrofísica de Canarias, Via Lactea, 38200 La Laguna, Tenerife, Spain ), AJ(Département de physique, de génie physique, et d'optique and Observatoire du mont Mégantic, Université Laval, Québec, QC G1K 7P4, Canada )
Publication:
The Astrophysical Journal, Volume 617, Issue 1, pp. L61-L64. (ApJL Homepage)
Publication Date:
12/2004
Origin:
UCP
Astronomy Keywords:
Stars: Early-Type, Stars: Emission-Line, Be, Stars: Individual: Henry Draper Number: HD 191612, Stars: Mass Loss, Stars: Variables: Other
DOI:
10.1086/427184
Bibliographic Code:
2004ApJ...617L..61W

Abstract

The observational picture of the enigmatic O-type spectrum variable HD 191612 has been sharpened substantially. A symmetrical, low-amplitude light curve with a period near 540 days has recently been reported from Hipparcos photometry. This period satisfies all of the spectroscopy since at least 1982, including extensive new observations during 2003 and 2004, and it has predicted the next transition during 2004 September-October. Measurements of the Hα equivalent width reveal a sharp emission peak in the phase diagram, in contrast to the apparently sinusoidal light curve. The He II absorption-line strength is essentially constant, while He I varies strongly, possibly filled in by emission in the O6 state, thus producing the apparent spectral type variations. The O8 state appears to be the ``normal'' one. Two intermediate O7 observations have been obtained, which fall at the expected phases, but these are the only modern observations of the transitions so far. The period is too long for rotation or pulsation; although there is no direct evidence as yet for a companion, a model in which tidally induced oscillations drive an enhanced wind near periastron of an eccentric orbit appears promising. Further observations during the now predictable transitions may provide a critical test. Ultraviolet and X-ray observations during both states will likely also prove illuminating.
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