2010AJ....140..595W -
Astron. J., 140, 595-601 (2010/August-0)
XMM-Newton observations of the enigmatic long period eclipsing binary epsilon Aurigae: constraining the physical models.
WOLK S.J., PILLITTERI I., GUINAN E. and STENCEL R.
Abstract (from CDS):
We report on an XMM-Newton observation of the unusual, long period (F0 supergiant + cool disk companion) eclipsing binary star ε Aurigae observed in X-rays prior to the onset of the 2009-2011 eclipse phase. While it appears certain that a disk-like body is obscuring the star, it remains unclear what kind of object is at the center of the disk. The XMM-Newton observation had a duration of ∼25 ks. The X-ray image does not show a source at the optical position of the star. We have determined a limiting X-ray flux of about 2.5x10–15 erg/cm2/s. This flux is equivalent to a luminosity of about log LX∼ 29.3-29.7 erg/s for an unabsorbed source at the assumed distance, estimated to be between 650 and 1300 pc. The direct emission from an otherwise unobscured primary is excluded at a level above LX∼ 4x1029 erg/s. We explore the physical constraints that these limits put on the primary and several proposed models for the system secondary. For a black hole, we find that the direct absorption required by the disk is approximately NH≥ 1025/cm2. While not unreasonable for a protoplanetary disk, the lack of secondary X-rays makes this model unlikely. For high-mass models, in which the disk harbors pre-main-sequence stars, we find a minimum disk absorption of NH≥ 1023/cm2. Since this is not unlikely for a protoplanetary disk, this is not a significant constraint. For low-mass models, in which the disk harbors older stars, the known line-of-sight absorption is nearly enough to account for the non-detection. The data do not discriminate between these models.
Abstract Copyright:
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Journal keyword(s):
binaries: eclipsing - stars: chemically peculiar - stars: individual: Epsilon Aurigae
Simbad objects:
7
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