Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...310..577w&link_type=abstract
Astronomy and Astrophysics, v.310, p.577-591
Astronomy and Astrophysics
Astrophysics
19
Stars: Wolf-Rayet, Stars: Hd 50896, X-Rays: Stars
Scientific paper
We present an analysis of 8 X-ray observations of HD 50896 obtained in our Guest Observer programmes with the XRT+PSPC on the ROSAT satellite, covering the energy range [0.1-2.5keV]. Our first observation, obtained in AO2, covered an integration time of 7ksec on 29 March 1992. This was followed by a further 7 PSPC observations, during AO3, at roughly daily intervals during 20-26 September 1992. The total PSPC count rates show evidence for variability at the <=30% level on timescales of <=1day, together with larger (x1.7) epoch-changes. We find no evidence for significant variations on very short timescales (<=1hour) previously reported from Einstein X-ray data. No `phase-dependent' modulation is apparent in the PSPC total count rates, or spectral fits, within the 3.766d optical period of the source. Single component spectral fitting (blackbody emission + photoelectric absorption) to the derived mean PSPC spectrum yields kT=0.28keV, and logN(H)=20.6. The latter is very close to the line-of-sight interstellar hydrogen column to HD 50896 of logN(H)_ism_=20.7, implying that the observed X-ray emission from the source has undergone negligible absorption in the WN 5 wind. With an adopted distance of 1.8kpc, the mean X-ray luminosity in the PSPC energy range is 3.1x10^32^erg/s, whilst the overall observed variations span the range [2.2-3.8]x10^32^erg/s. Adopting a mass loss rate of 5x10^-5^Msun_/yr, and a wind terminal velocity of vinfinity_=2000km/s, we estimate the 0.28keV X-ray emergent emission has a characteristic radius of >=1000Rsun_. A re-analysis of archival Einstein IPC X-ray [0.2-4kev] observations of HD 50896 at three different epochs confirms substantial variability (L_x_~[3-9]x10^32^erg/s), but shows no significant changes in spectral shape, for which kT~0.4keV is derived - compatible with that deduced from our ROSAT data. We conclude that the observed PSPC and previous IPC X-ray emission from HD 50896 originates via mechanisms intrinsic to the WR wind, probably in shocked gas produced by radiatively-induced instabilities of the kind being predicted theoretically by Owocki and co-workers.
Stevens Ian R.
Willis Alan J.
No associations
LandOfFree
ROSAT X-ray observations of the Wolf-Rayet star HD 50896 (WN 5). does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with ROSAT X-ray observations of the Wolf-Rayet star HD 50896 (WN 5)., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and ROSAT X-ray observations of the Wolf-Rayet star HD 50896 (WN 5). will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1303662