The intrinsically bright Wolf-Rayet stars of type WN 7. III. The probable single Sco OB 1 star HD 151932 with variable He I envelope.
Abstract
Summary. HD 151932 is a WN 7 star without Of-type central absorption lines. It is located near the young open cluster NGC 6231 in the core of the association Sco OB 1. Photographic coude' spectroscopy, scanner spectrophotometry and photoelectric narrow-band photometry are used to analyse the nature of the star. Radial velocities of emission lines and He ii, N m-v violet shifted absorption lines from 32 coude' plates taken between 1970 and 1977 along with the photoelectric observations in 1975 indicate from their constancy that HD 151932 is probably another single Wolf-Rayet star of type WN 7. Photoelectric scanner observations of the spectral region 6450-8500 A show that the apparent near-infrared excess of HD 151932 with respect to other WN 7 stars can be accounted for simply by normal Interstellar reddening rather than having to evoke an unseen red companion, as suggested elsewhere in the literature. Whereas the He ii and N iii-v absorption edges have constant velocity indicating a stable inner part of the expanding WR envelope, the He I absorptions show different degrees of variability: rapid variations in 1971, stability (at least for Hei 5876) in 1975 and slow velocity changes in 1977. The variations can be explained by assuming small relative changes of the particle density in the envelope, causing virtually only its outer layers to vary through zones of different expansion velocity. According to the interstellar line velocities and diffuse interstellar band equivalent widths, HD 151932 is a member bf the association Sco OB 1 from which an absolute magnitude My = - 6' 5 is deduced. Photographic continuum measurements between 3550 and 5950 A in comparison to 0 8 f-type supergiants allow only the determination of lower limits of the effective temperature Teff =33,000 K and the bolometric magnitude Mbol = - 9rn.6 using 0-type star model atmospheres. Key words: Wolf-Rayet stars - coude' spectroscopy - scanner spectrophotometry - narrow-b and photoelectric photometry - individual star: HD 151932
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 1979
- Bibcode:
- 1979A&A....72..332S
- Keywords:
-
- Hot Stars;
- O Stars;
- Stellar Envelopes;
- Stellar Models;
- Stellar Spectrophotometry;
- Supergiant Stars;
- Wolf-Rayet Stars;
- Atmospheric Models;
- Line Spectra;
- Radial Velocity;
- Spectral Line Width;
- Stellar Atmospheres;
- Astrophysics;
- Absorption Lines:Wolf-Rayet Stars;
- Photometry:Wolf-Rayet Stars;
- Radial Velocities:Wolf-Rayet Stars;
- Spectra:Wolf-Rayet Stars;
- Wolf-Rayet Stars:Envelopes