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Title:
Investigating the spectroscopic, magnetic and circumstellar variability of the O9 subgiant star HD 57682
Authors:
Grunhut, J. H.; Wade, G. A.; Sundqvist, J. O.; ud-Doula, A.; Neiner, C.; Ignace, R.; Marcolino, W. L. F.; Rivinius, Th.; Fullerton, A.; Kaper, L.; Mauclaire, B.; Buil, C.; Garrel, T.; Ribeiro, J.; Ubaud, S.
Affiliation:
AA(Department of Physics, Engineering Physics and Astronomy, Queens University, Kingston, Ontario K7L 3N6 Canada; Department of Physics, Royal Military College of Canada, PO Box 17000 Station Forces Kingston, Ontario K7K 7B4 Canada), AB(Department of Physics, Royal Military College of Canada, PO Box 17000 Station Forces Kingston, Ontario K7K 7B4 Canada), AC(University of Delaware, Bartol Research Institute, Newark, DE 19716 USA), AD(Penn State Worthington Scranton, 120 Ridge View Drive Dunmore, PA 18512 USA), AE(LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen 92190 Meudon, France), AF(Department of Physics and Astronomy, East Tennessee State University, Johnson City, TN 37614 USA), AG(Universidade Federal do Rio de Janeiro, Observatório do Valongo Ladeira Pedro Antônio 43 CEP 20080-090 Rio de Janeiro, Brazil), AH(ESO - European Organisation for Astronomical Research in the Southern Hemisphere, Casilla, 19001 Santiago 19 Chile), AI(Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218 USA), AJ(Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904 1098 XH Amsterdam, the Netherlands), AK(Observatoire du Val de l'Arc, route de Peynier 13530 Trets, France), AL(Castanet Tolosan Observatory, 6 place Clémence Isaure 31320 Castanet Tolosan, France), AM(Observatoire de Juvignac, 19 avenue du Hameau du Golf 34990 Juvignac, France), AN(Obervatorio do Instituto Geografico do Exercito, R. Venezuela 29, 3 Esq. 1500-618 Lisboa, Portugal), AO(Observatoire des Quatres chemins, Calade, 06410 Biot France)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 426, Issue 3, pp. 2208-2227. (MNRAS Homepage)
Publication Date:
11/2012
Origin:
WILEY
Astronomy Keywords:
techniques: polarimetric, circumstellar matter, stars: individual: HD 57682, stars: magnetic field, stars: rotation, stars: winds, outflows
DOI:
10.1111/j.1365-2966.2012.21799.x
Bibliographic Code:
2012MNRAS.426.2208G

Abstract

The O9IV star HD 57682, discovered to be magnetic within the context of the Magnetism in Massive Stars (MiMeS) survey in 2009, is one of only eight convincingly detected magnetic O-type stars. Among this select group, it stands out due to its sharp-lined photospheric spectrum. Since its discovery, the MiMeS Collaboration has continued to obtain spectroscopic and magnetic observations in order to refine our knowledge of its magnetic field strength and geometry, rotational period and spectral properties and variability. In this paper we report new Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) spectropolarimetric observations of HD 57682, which are combined with previously published ESPaDOnS data and archival Halpha spectroscopy. This data set is used to determine the rotational period (63.5708 ± 0.0057 d), refine the longitudinal magnetic field variation and magnetic geometry (dipole surface field strength of 880 ± 50 G and magnetic obliquity of 79° ± 4° as measured from the magnetic longitudinal field variations, assuming an inclination of 60°) and examine the phase variation of various lines. In particular, we demonstrate that the Halpha equivalent width undergoes a double-wave variation during a single rotation of the star, consistent with the derived magnetic geometry. We group the variable lines into two classes: those that, like Halpha, exhibit non-sinusoidal variability, often with multiple maxima during the rotation cycle, and those that vary essentially sinusoidally. Based on our modelling of the Halpha emission, we show that the variability is consistent with emission being generated from an optically thick, flattened distribution of magnetically confined plasma that is roughly distributed about the magnetic equator. Finally, we discuss our findings in the magnetospheric framework proposed in our earlier study. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii.

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