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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 Hα 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 +53º2790 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 θ^1 Ori C) is discussed.Blay Serrano, Pedro Jose, Pere.Blay@uv.es ; Reig Torres, Pablo, Pablo.Reig@uv.es ; Fabregat Llueca, Juan, Juan.Fabregat@uv.e

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