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Astron. Astrophys. 320, 273-286 (1997)


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Long-term spectroscopic monitoring of BA-type supergiants

III. Variability of photospheric lines *

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

1 Landessternwarte Heidelberg-Königstuhl, D-69117 Heidelberg, Germany
2 Gothard Astrophysical Observatory, H-9707 Szombathely, Hungary,
3 STScI, Homewood Campus, 3700 San Martin Drive, Baltimore MD 21218, USA
4 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85740 Garching, Germany
5 Universitäts-Sternwarte München, Scheinerstr. 1, D-81679 München, Germany

Received 5 September 1996 / Accepted 26 September 1996

Abstract

We obtained time series of spectra with high [FORMULA] and high resolution in wavelength and time of early-type A and late-type B supergiants (cf. Kaufer et al.  1996a, Paper i, and Kaufer et al.  1996b, Paper ii for the analysis of the variability of the stellar envelopes). In this work we inspect the time variations of the numerous photospheric line profiles in the optical spectrum. We find complex cyclical variations of the radial velocities with a typical velocity dispersion of [FORMULA] [FORMULA]. The corresponding equivalent-width variations are less than 1% of their mean if we assume a common modulation mechanism for both radial velocities and equivalent width. We do not find any depth dependence of the velocity fields in the metallic lines. For [FORMULA] Cyg the Balmer lines show an increase of the radial velocity from H27 to H8 by 3 [FORMULA], which is identified with the onset of the radially accelerating velocity field of the stellar wind. The Clean ed periodograms of the radial-velocity curves show the simultaneous excitation of multiple pulsation modes with periods longer and shorter than the estimated radial fundamental periods of the objects, which might indicate the excitation of non-radial and radial overtones, respectively. The analysis of the line-profile variations (LPV) of the photospheric line spectrum reveals prograde travelling features in the dynamical spectra. The travelling times of these features are in contradiction to the possible rotation periods of these extended, slowly rotating objects. Therefore, we suggest that these features should be identified with non-radial pulsation modes, possibly g-modes, of low order ([FORMULA]).

Key words: stars: early-type, supergiants, emission-line, rotation, pulsation

* Based on observations collected at the European Southern Observatory at La Silla, Chile.

Send offprint requests to:
A. Kaufer e-mail: A.Kaufer@lsw.uni-heidelberg.de

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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