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Astron. Astrophys. 318, 819-834 (1997)

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Variations of the stellar wind in early-B hypergiants *

Th. Rivinius 1, O. Stahl 1, B. Wolf 1, A. Kaufer 1, Th. Gäng 1, 5, C.A. Gummersbach 1, I. Jankovics 2, J. Kovács 2, H. Mandel 1, J. Peitz 1, Th. Szeifert 1 and H.J.G.L.M. Lamers 3, 4, 5

1 Landessternwarte Königstuhl, D-69117 Heidelberg, Germany
2 Gothard Astrophysical Observatory, H-9707 Szombathely, Hungary
3 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
4 Astronomical Institute, Princetoplein 5, 3584 CC Utrecht, The Netherlands
5 STScI, Homewood Campus, 3700 San Martin Drive, Baltimore MD 21218, USA

Received 12 January 1996 / Accepted 27 April 1996

Abstract

With our fiber-linked echelle spectrograph we monitored three early-B hypergiants with high dispersion and good coverage in time. The program stars [FORMULA]  Sco (HD 152236), HD 169454, and HD 190603 were observed over periods of several months in several seasons. In the years 1990 to 1994, we covered the wavelength range from 4000 Å to 6740 Å and in 1995 from 3450 Å to 8620 Å , respectively. Typically one spectrum of each object was taken every one or two nights.

We found the P Cygni-type profiles of all objects to be variable, both in the emission and in the absorption. Blue-shifted variable absorption features can be seen in many lines. These features are particularly clear in the FeIII [FORMULA] 5127, 5156 lines. They can be traced from photospheric velocities to approximately [FORMULA] [FORMULA]. We find radial-velocity variations of about 20 [FORMULA] in the cores of photospheric lines. These variations have typical time scales of weeks. They show a time delay and a velocity shift between different lines. We interpret this delay as the propagation of disturbances through the innermost layers of the wind. These perturbations originate in the photosphere or the sub-photosphere. The variability of discrete absorption components (DACs) of P Cygni-type profiles can be modeled assuming density perturbations of the order of 10% at the base of the wind. The outward propagation of these perturbations can explain the observed variations. The perturbations move with a velocity law that is slower ([FORMULA]) than that of the ambient wind ([FORMULA]).

The absorption lines show pulsation-like radial-velocity variations with a period of about 12 days. These variations last a few cycles before becoming irregular. Integrating the radial-velocity curve, we derive radius variations of the order of 10% of the stellar radius. These radius variations are correlated with the emission-line variability. The photometric data also indicate possible radial pulsations with this amplitude.

The mass-loss rates of the stars derived from the Balmer-emission components are between 2.7 and [FORMULA] [FORMULA].

Key words: stars: early-type – stars: supergiants – stars: mass loss – stars: individual: i1  Sco – stars: individual: HD 169454 – stars: individual: HD 190603

* Based on observations collected at the European Southern Observatory at La Silla, Chile, on observations at Calar Alto, Spain and on observations with the International Ultraviolet Observer (IUE) at the Villafranca Satellite Tracking Station of the European Space Agency, Madrid, Spain

Send offprint requests to: T.Rivinius@lsw.uni-heidelberg.de

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
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