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Multiwavelength monitoring of BD+53 2790, the optical counterpart to 4U~2206+54

P. Blay·I. Negueruela·P. Reig·M. J. Coe·R. H. D. Corbet·J. Fabregat·A. E. Tarasov
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Abstract

We present the results of our long-term monitoring of BD+53 2790, the optical counterpart to the X-ray source 4U~2206+54. Unlike previous studies that classify the source as a Be/X-ray binary, we find that its optical and infrared properties differ from those of typical Be stars: the variability of the V/R ratio is not cyclical; there are variations in the shape and strength of the H$α$ emission line on timescales less than 1 day; and no correlation between the EW and the IR magnitudes or colors is seen. Our observations suggest that BD+53 2790 is very likely a peculiar O9.5V star. In spite of exhaustive searches we cannot find any significant modulation in any emission line parameter or optical/infrared magnitudes. Spectroscopy of the source extending from the optical to the K-band confirms the peculiarity of the spectrum: not only are the He lines stronger than expected for an O9.5V star but also there is no clear pattern of variability. The possibility that BD+53 2790 is an early-type analogue to He-strong stars (like theta^1 Ori C) is discussed.

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P. Blay, I. Negueruela, P. Reig, M. J. Coe, R. H. D. Corbet, J. Fabregat, A. E. Tarasov. 2005-10-13. Multiwavelength monitoring of BD+53 2790, the optical counterpart to 4U~2206+54. https://doi.org/10.1051/0004-6361%3A20053951

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