  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$\alpha$ 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.

Astrophysics