Free Access
Astron. Astrophys. Suppl. Ser.
Volume 120, Number 3, December_II 1996
Page(s) 431 - 450
Azimuthal structures in the wind and chromosphere of the Herbig Ae star AB Aurigae. Results from the MUSICOS 1992 campaign DOI: 10.1051/aas:1996295

Astronomy and Astrophysics Supplement Series, Vol. 120, December II 1996, 431-450

Azimuthal structures in the wind and chromosphere of the Herbig Ae star AB Aurigae. gif Results from the MUSICOS 1992 campaign

T. Böhm , C. Catala , J.-F. Donati , A. Welty, J. Baudrand , C.J. Butler , B. Carter , A. Collier-Cameron , J. Czarny , B. Foing , K. Ghosh , J. Hao , E. Houdebine , L. Huang , S. Jiang , J.E. Neff , D. Rees , M. Semel , T. Simon , A. Talavera , D. Zhai and F. Zhao
Send offprint requests to: T. Böhm (German address)

European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching, Germany
Département d'Astrophysique Extragalactique et de Cosmologie et Unité de Recherche associée au CNRS 173 et à l'Université Paris 7, Observatoire de Paris, Section de Meudon, 92195 Meudon Principal Cedex, France
Laboratoire d'Astrophysique et Unité de Recherche associée au CNRS 285, Observatoire Midi-Pyrénées, France
Pennsylvania State University, Department of Astronomy and Astrophysics, 525 Davey Laboratory, University Park, PA 16802, U.S.A.
Armagh Observatory, Armagh BT61 9DG, N. Ireland, UK
University of New South Wales, Australia
School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, Scotland KY16 9SS
Solar System Division, ESA Space Science Department, ESTEC (SO), postbus 299, NL-2200 AG, Noordwijk, The Netherlands
Indian Institute of Astrophysics, Vainu Bappu Observatory, Kavalur, Alangayam 635701, Tamilnadu, India
Beijing Astronomical Observatory, China
CSIRO Division of Radiophysics, Epping, NSW 2121, Australia
Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822, U.S.A.
LAEFF/INTA, P.O. Box 50727, 28080 Madrid, Spain

Received February 22; accepted May 2, 1996


The observations of the MUSICOS 1992 campaign concerned three scientific programs, among which was the study of azimuthal structures in the wind and chromosphere of the pre-main sequence Herbig Ae star AB Aur. The He I 5876 Å line of AB Aur, which is formed in the expanding chromosphere of this star, most probably in the innermost parts of its wind, was continuously monitored at a spectral resolution of 30000 for about 4 days. The line was discovered to be variable in a spectacular way, the profile changing from pure emission to a composite profile including a deep absorption component in the course of a few hours. In this paper we present strong clues that suggest a rotational modulation of the line, with a period corresponding to the stars rotation period of 32 hrs. We confirmed the covariation of several non-photospheric spectral lines, formed at very different radial distances of the star, which strengthens the idea that the variability is the signature of azimuthal structures in the wind of AB Aur, most probably due to magnetically confined streams or loops emanating from the stellar surface. We present the data collected during the MUSICOS 1992 campaign, but also a data set of the He I D3 line obtained with FOE at KPNO during the years 1991--1994 and a series of IUE spectra containing the Mg II h & k UV lines obtained one month prior to the campaign. A thorough discussion of the possible interpretations of the spectacular variations of the He I 5876 Å\ line is presented.

Key words: line: formation --- line: profiles --- stars: magnetic fields --- stars: pre-main sequence --- stars: AB Aur --- stars: emission line, Be

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