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LBT Discovery of a Yellow Supergiant Eclipsing Binary in the Dwarf Galaxy Holmberg IX

Published online by Cambridge University Press:  01 December 2007

J. L. Prieto ,
K. Z. Stanek ,
C. S. Kochanek  and
D. R. Weisz
J. L. Prieto
Affiliation:
Department of Astronomy, Ohio State University, Columbus, OH 43210 email: prieto@astronomy.ohio-state.edu, kstanek@astronomy.ohio-state.edu, ckochanek@astronomy.ohio-state.edu
K. Z. Stanek
Affiliation:
Department of Astronomy, Ohio State University, Columbus, OH 43210 email: prieto@astronomy.ohio-state.edu, kstanek@astronomy.ohio-state.edu, ckochanek@astronomy.ohio-state.edu
C. S. Kochanek
Affiliation:
Department of Astronomy, Ohio State University, Columbus, OH 43210 email: prieto@astronomy.ohio-state.edu, kstanek@astronomy.ohio-state.edu, ckochanek@astronomy.ohio-state.edu
D. R. Weisz
Affiliation:
Department of Astronomy, University of Minnesota, Minneapolis, MN 55455 email: dweisz@astro.umn.edu
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Abstract

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In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (MV ≃ −7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 271 days and the light curve is well-fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed of two yellow supergiants (V − I ≃ 1 mag, Teff = 4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however note a second example. The SMC F0 supergiant R47 is a bright (MV ≃ −7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well-fit as a contact binary with a 181 day period. We propose that these massive systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star at the same core evolutionary stage.

Keywords

galaxies: individual (Holmberg IX) – binaries: eclipsing
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S250: Massive Stars as Cosmic Engines , December 2007 , pp. 333 - 338
Copyright
Copyright © International Astronomical Union 2008

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