Optical and infrared observations of the suspected Be/X-ray transient 4U 0728-25

We present new optical spectra and photometry plus the first infrared photometry of the optical counterpart to the X-ray transient system 4U 0728-25. Our spectral and photometrical analysis lead us to conclude that the primary is an O8-9Ve star with E(B - V) = 0.75 ± 0.02. This revised spectral classification places the star at a distance of 6.1±0.3 kpc. We also present evidence for an unusual faint, blue state that may represent a diskless phase in late 1991.