1998/02/07 by S. J. Unger, Unger, S. J., P. Roche +10
Physics and Astronomy · #Astrophysics (astro-ph) #Astrophysics and Star Formation Studies #FOS: Physical sciences #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9802086
6 pages, LaTeX, including 3 tables and 2 PostScript figures, requires l-aa.sty, epsf, and rotate; Astronomy & Astrophysics, accepted
arxiv created 1998/02/07 · openalex publication_date 1998/02/07 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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.