Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-08-12
Astronomy and Astrophysics
Astrophysics
15 pages (figures imbedded) in A&A format. Accepted by the Astronomy & Astrophysics
Scientific paper
10.1051/0004-6361:20065055
Using the IUE data archive, we have examined the SWP-camera echellograms of 74 B0--B2.5e stars for statistically significant fluctuations in the He II ("Halpha") 1640A line profile. In this sample we found that the HeII line is occasionally variable in 10 stars over short to long timescales. The HeII-variable stars discovered are lambda Eri, omega Ori, mu Cen, 6 Cep, HD 67536, psi-1 Ori, eta Cen, pi Aqr, 2 Vul, and 19 Mon. The most frequent two types of variability are an extended blue wing absorption and a weakening of the line along the profile. Other types of variability are a weak emission in the red wing and occasionally a narrow emission feature. In the overwhelming number of cases, the CIV resonance doublet exhibits a similar response; rarely, it can exhibit a variation in the opposite sense. Similar responses are also often seen in the SiIV doublet, and occasionally even the SiIII 1206A line. We interpret the weakenings of HeII and of high-velocity absorptions of CIV to localized decreases in the photospheric temperature, although this may not be a unique interpretation. We discuss the variable blue wing absorptions and red wing emissions in terms of changes in the velocity law and mass flux carried by the wind. In the latter case, recent experimental models by Venero, Cidale, & Ringuelet require that during such events the wind must be heated to 35kK at some distance from the star.
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