OPTICAL SPECTROSCOPY OF V635 CASSIOPEIAE 4U-0115+63/

V635 Cas is the optical counterpart of the X-ray binary system 4U 0115 +63. It was previously tentatively identified as a Be star based on it s optical colours and the presence of H alpha emission. Our observatio ns indicate that it is an O9e star. This is the first direct determina tion of this star's optical spectral type. The presence of a hotter co mpanion star may in part explain the large temporal variation observed in this system. Extreme variability was observed in 1992 February whe n both the H alpha and a series of Paschen lines changed from emission to absorption. This was interpreted as a disk-loss event and it is th e first lime that it has been observed in this system. We use far red spectra of V635 Cas to probe the circumstellar disk, discussing the va rious line formation regions. The lines observed are consistent with a late type Oe star. The flux standard Hiltner 102 was also observed. A lthough it is classified as a B0 III star, we re-classify it as a O9.7 II star with a slight nitrogen enhancement.