A long-term X-ray variability study of the O-type stars σ Orionis and ζ Orionis.
Abstract
X-ray emission in early-type OB stars is thought to be generated by shock-heated gas in the radiatively driven wind of these stars. Calculations of the X-ray production for such a scenario depend on the underlying shock structures, especially the occurrence rate of shocks, cooling length and cooling time which directly influence the source location of the X-rays in the stellar wind. We present a detailed variability analysis of the available ROSAT data for our two program stars σ Ori and ζ Ori. The long-term analysis of both stars covers a time range of 3 years and includes seven pointed PSPC observations, an additional pointed HRI observation for σ Ori and the ROSAT all-sky survey data of both stars. In the case of σ Ori we find no evidence for variability on all analysed time scales. Over a long time range the timing analysis of the X-ray light curve of ζ Ori provides also no evidence for variability. Only during a period of 2 days (September 23-25 1992) did we detect a moderate increase in X-ray count rate by ~ 15%.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 1994
- Bibcode:
- 1994A&A...290..435B
- Keywords:
-
- STARS: {SIGMA} ORI;
- {ZETA} ORI;
- STARS: EARLY-TYPE;
- X-RAYS: STARS