  The recent discovery of a ~9.5-d period in the X-ray lightcurve of the
massive X-ray binary 4U2206+54 has opened the possibility that it is a Be/X-ray
binary with an unusually close orbit, which, together with its low intrinsic
luminosity, suggests that the system is actually a Be + WD binary, in which a
white dwarf accretes material from the dense circumstellar disc surrounding a
classical Be star. In this paper we present new X-ray observations and for the
first time high-resolution optical spectroscopy of the source. We show that
both the X-ray behaviour and the characteristics of the optical counterpart, BD
+53 2790, are more consistent with a neutron star accreting from the wind of an
early-type star. The X-ray lightcurve shows irregular flaring and no
indications of pulsations, while the very high hydrogen column density supports
accretion from a dense wind. BD +53 2790 is shown not to be a classical Be
star, as believed until now, but rather a very peculiar late O-type active
star, exhibiting emission components in the HeII lines, complex spectral
variability and strong wind resonance lines in the ultraviolet. Though many of
the characteristics of the spectrum resemble those of the He-rich stars, the
absence of HeI variability makes a connection unlikely. The spectrum is
compatible with a composite of two stars of similar spectral type, though
circumstantial evidence points to a single very peculiar active early-type
star. This adds weight to the growing evidence that the traditional
subdivisions of supergiant and Be/X-ray binaries fail to cover the whole
phenomenology of massive X-ray binaries.
