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The Non-thermal Radio Emitter HD 93250 Resolved by Long Baseline Interferometry

Abstract : 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 timescales of years suggesting either a single star, a binary system seen pole-on view 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) × 10-3 arcsec. At the distance of Carina, this corresponds to a projected physical distance of 3.5 AU. 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 1 to several years despite the lack of measurable radial velocity variations.

Based on observations collected under program IDs 086.D-0586 and 386.D-0198 at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile.

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Submitted on : Tuesday, March 29, 2022 - 12:01:07 PM
Last modification on : Wednesday, March 30, 2022 - 4:12:26 AM

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H. Sana, J. -B. Le Bouquin, M. de Becker, J. -P. Berger, A. de Koter, et al.. The Non-thermal Radio Emitter HD 93250 Resolved by Long Baseline Interferometry. The Astrophysical Journal Letters, 2011, 740, ⟨10.1088/2041-8205/740/2/L43⟩. ⟨insu-03622851⟩

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