  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 its optical colours
and the presence of H alpha emission. Our observations indicate that it is an
O9e star. This is the first direct determination of this star's optical
spectral type. The presence of a hotter companion star may in part explain the
large temporal variation observed in this system.
  Extreme variability was observed in 1992 February when 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 the first time that it has been
observed in this system. We use far red spectra of V635 Cas to probe the
circumstellar disk, discussing the various line formation regions. The lines
observed are consistent with a late type Oe star.
  The flux standard Hiltner 102 was also observed. Although it is classified as
a B0 III star, we re-classify it as a O9.7 II star with a slight nitrogen
enhancement.
