XMM-NEWTON OBSERVATIONS OF THE ENIGMATIC LONG PERIOD ECLIPSING BINARY EPSILON AURIGAE: CONSTRAINING THE PHYSICAL MODELS
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Astronomy, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States)
- Department of Physics and Astronomy, University of Denver, Denver, CO 80208 (United States)
We report on an XMM-Newton observation of the unusual, long period (F0 supergiant + cool disk companion) eclipsing binary star {epsilon} 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 {approx}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 2.5 x 10{sup -15} erg cm{sup -2} s{sup -1}. This flux is equivalent to a luminosity of about log L{sub X} {approx} 29.3-29.7 erg s{sup -1} 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 L{sub X} {approx} 4 x 10{sup 29} erg s{sup -1}. 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 N{sub H} {>=} 10{sup 25} cm{sup -2}. 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 N{sub H} {>=} 10{sup 23} cm{sup -2}. 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.
- OSTI ID:
- 21443259
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 140, Issue 2; Other Information: DOI: 10.1088/0004-6256/140/2/595; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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