Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-10-04
ApJ, 740, L43 (2011)
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
9 pages, 4 figures, published in ApJL
Scientific paper
10.1088/2041-8205/740/2/L43
As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4 III(fc)) is X-ray overluminous for its spectral type and has an unusually hard X-ray spectrum. Two different scenarios have been invoked to explain its X-ray properties: wind-wind interaction and magnetic wind confinement. Yet, HD 93250 shows absolutely constant radial velocities over time scales of years suggesting either a single star, a binary system seen pole-one or a very long period and/or highly eccentric system. Using the ESO Very Large Telescope Interferometer, we resolved HD 93250 as a close pair with similar components. We measured a near-infrared flux ratio of 0.8+/-0.1 and a separation of 1.5+/-0.2 x 10E-03 arcsec. At the distance of Carina, this corresponds to a projected physical distance of 3.5 A.U. While a quantitative investigation would require a full characterization of the orbit, the binary nature of HD 93250 allows us to qualitatively explain both its X-ray flux and hardness and its non-thermal radio emission in the framework of a colliding wind scenario. We also discuss various observational biases. We show that, due to line-blending of two similar spectral components, HD 93250 could have a period as short as one to several years despite the lack of measurable radial velocity variations.
Berger Jean Philippe
de Becker Michael
de Koter Alex
Le Bouquin Jean-Baptiste
Mérand Antoine
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