"Stellar Prominences" on OB stars to explain wind-line variability

Many O and B stars show unexplained cyclical variability in their winds, i.e. modulation of absorption features on the rotational timescale, but not strictly periodic over longer timescales. For these stars no dipolar magnetic fields have been detected, with upper limits below 300 G. Similar cyclical variability is also found in many optical lines, which are formed at the base of the wind. We propose that these cyclical variations are caused by the presence of multiple, transient, short-lived, corotating magnetic loops, which we call "stellar prominences". We present a simplified model representing these prominences to explain the cyclical optical wind-line variability in the O supergiant lambda Cephei. Other supporting evidence for such prominences comes from the recent discovery of photometric variability in a comparable O star, which was explained by the presence of multiple transient bright spots, presumably of magnetic origin as well.Comment: Contributed paper IAUS 302, Biarritz, August 2013, 4 pages, 3 figure

Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988

Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind

Magnetic fields in O-type stars measured with FORS1 at the VLT

The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of such fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Halpha emission variations, chemical peculiarity, narrow X-ray emission lines and non-thermal radio/X-ray emission. Here we present the results of our studies of magnetic fields in O-type stars, carried out over the last years.Comment: 2 pages, 1 figure, to appear in Proceedings of IAU Symposium 259 "Cosmic Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain, November 3-7, 200

Looking for discrete UV absorption features in the early-type eclipsing binaries μ1 Scorpii and AO Cassiopeiae

A search for discrete absorption components in the ultraviolet spectra of the early-type binaries μ1 Scorpii and AO Cassiopeiae has been undertaken by analyzing material secured with the International Ultraviolet Explorer satellite during an exclusively assigned interval of nearly 50 hr. While the spectra of μ1 Sco definitely do not show the presence of such lines, the spectra of AO Cas do confirm them and permit us to draw some conclusions about where they may be formed.Facultad de Ciencias Astronómicas y Geofísica

Looking for discrete UV absorption features in the early-type eclipsing binaries μ1 Scorpii and AO Cassiopeiae

A search for discrete absorption components in the ultraviolet spectra of the early-type binaries μ1 Scorpii and AO Cassiopeiae has been undertaken by analyzing material secured with the International Ultraviolet Explorer satellite during an exclusively assigned interval of nearly 50 hr. While the spectra of μ1 Sco definitely do not show the presence of such lines, the spectra of AO Cas do confirm them and permit us to draw some conclusions about where they may be formed.Facultad de Ciencias Astronómicas y Geofísica