2002A&A...382..921B -
Astronomy and Astrophysics, volume 382, 921-934 (2002/2-2)
Radio and submillimetre observations of {epsilon Ori}.
BLOMME R., PRINJA R.K., RUNACRES M.C. and COLLEY S.
Abstract (from CDS):
In common with other early-type stars, ε Ori (B0 Ia) shows evidence for structure in its stellar wind. Variations in optical and ultraviolet line profiles reveal the presence of large-scale structure in the inner wind. The detection of X-rays and the existence of black troughs in saturated ultraviolet lines are indicative of small-scale structure. The geometric extent of both types of structure is poorly known. In principle, large-scale structure can be detected directly from very high spatial resolution observations that resolve the stellar wind. A simpler technique is to look for the presence of additional flux compared to that expected from a smooth wind. The run of this excess flux as a function of wavelength indicates how fast structure decays in the wind. If there is variability in the excess flux, it shows us that the structure must be large-scale. Such variability is suggested by two previous 6 cm radio observations of ε Ori: Abbott et al. (
1980ApJ...238..196A) found 1.6±0.5mJy, while Scuderi et al. (
1998A&A...332..251S) measured only 0.60±0.06mJy. This could indicate that the large-scale structure persists beyond ∼50R
*. To further investigate this variability, we used the Very Large Array (VLA) to monitor ε Ori over a 5-day period in February 1999. We supplemented our data with observations from the VLA archive. In an attempt to resolve the stellar wind, we also obtained a series of high spatial resolution observations with the Multi-Element Radio Linked Interferometer Network (MERLIN) during January-March 1999. From this combined material we find no evidence for variability and we conclude that the Abbott et al. (
1980ApJ...238..196A) flux determination is in error. The data do show substantial excess flux at millimetre wavelengths, compared to a smooth wind. This excess is confirmed by a submillimetre observation which we obtained with the James Clerk Maxwell Telescope (JCMT). The behaviour of ε Ori is therefore similar to what had been found previously for
α Cam,
δ Ori A,
κ Ori and
ζ Pup. While the present data do not allow very strong constraints, they show that considerable structure must persist up to at least ∼10R
* in the wind of ε Ori. The combined radio fluxes are used to derive a mass-loss rate of log{dot}(M)(M
☉/yr)=-5.73±0.04. This value is in good agreement with the Hα mass-loss rate. The good agreement between Hα and radio mass-loss rates for hot stars in general remains puzzling, as it implies that the same amount of structure is present in very different formation regions.
Abstract Copyright:
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Journal keyword(s):
stars: early-type - stars: individual: ε Ori - stars: mass-loss - stars: winds, outflows - continuum: stars radio
Simbad objects:
21
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