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Massive X-ray binaries are usually classified depending on the properties ofthe donor star in classical, supergiant and Be X-ray binaries. The massiveX-ray binary 4U 2206+54 does not fit in any of these groups, and deserves adetailed study to understand how the transfer of matter and the accretion on tothe compact object take place. To this end we study an IUE spectrum of thedonor and obtain a wind terminal velocity (v_inf) of ~350 km/s, which isabnormally slow for its spectral type. We also analyse here more than 9 yearsof available RXTE/ASM data. We study the long-term X-ray variability of thesource and find it to be similar to that observed in the wind-fed supergiantsystem Vela X-1, reinforcing the idea that 4U 2206+54 is also a wind-fedsystem. We find a quasi-period decreasing from ~270 to ~130 d, noticed inprevious works but never studied in detail. We discuss possible scenarios andconclude that long-term quasi-periodic variations in the mass-loss rate of theprimary are probably driving such variability in the measured X-ray flux. Weobtain an improved orbital period of 9.5591 d with maximum X-ray flux at MJD51856.6. Our study of the orbital X-ray variability in the context of windaccretion suggests a moderate eccentricity around 0.15. Moreover, the low valueof v_inf solves the long-standing problem of the relatively high X-rayluminosity for the unevolved nature of the donor, BD +53 2790, which isprobably an O9.5 V star. We note that changes in v_inf and/or the mass-lossrate of the primary alone cannot explain the diferent patterns displayed by theorbital X-ray variability. We finally emphasize that 4U 2206+54, together withLS 5039, could be part of a new population of wind-fed HMXBs with main sequencedonors, the natural progenitors of supergiant X-ray binaries. (Abridged)Comment: 12 pages, 9 figures; to appear in A&A; corrected typos, updated  references; matches published versio

Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow wind and a moderately eccentric orbit