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Astron. Astrophys. 345, 884-904 (1999)

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Short-term spectroscopic variability in the pre-main sequence Herbig Ae star AB Aurigae during the MUSICOS 96 campaign *

C. Catala 1, J.F. Donati 1, T. Böhm 1, J. Landstreet 2, H.F. Henrichs 3, Y. Unruh 4, J. Hao 5, A. Collier Cameron 6, C.M. Johns-Krull 7, L. Kaper 8, T. Simon 9, B.H. Foing 10, H. Cao 5, P. Ehrenfreund 11, A.P. Hatzes 12, L. Huang 5, J.A. deJong 3, E.J. Kennelly 13, E. tenKulve 3, C.L. Mulliss 14, J.E. Neff 15, J.M. Oliveira 10, C. Schrijvers 3, H.C. Stempels 11,10, J.H. Telting 16, N. Walton 16 and D. Yang 5

1 Laboratoire d'Astrophysique de l'OMP, CNRS UMR 5572, Observatoire Midi-Pyrénées, 14, avenue Edouard Belin, F-31400 Toulouse, France
2 Astronomy Department, University of Western Ontario, London, Ontario, Canada
3 Astronomical Institute "Anton Pannekoek", University of Amsterdam, The Netherlands
4 Institute for Astronomy, University of Vienna, Austria
5 Chinese Academy of Sciences, Beijing Astronomical Observatory, P.R. China
6 School of Physics and Astronomy, University of St-Andrews, Scotland
7 JILA, University of Colorado, Boulder, CO, USA
8 European Southern Observatory, Garching bei München, Germany
9 Institute for Astronomy, University of Hawaii, USA
10 Solar System Division, ESA Space Science Department, ESTEC, Noordwijk, The Netherlands
11 Leiden Observatory, The Netherlands
12 Astronomy Department, University of Texas, Austin, TX, USA
13 High Altitude Observatory, Boulder, CO, USA
14 Ritter Astrophysical Research Center, The University of Toledo, OH, USA
15 Department of Astronomy, Penn State University, USA
16 Isaak Newton Group, NFRA/ASTRON, Royal Greenwhich Observatory, La Palma, Spain

Received 17 December 1998 / Accepted 15 February 1999

Abstract

We present results of the spectroscopic monitoring of AB Aur obtained during the MUSICOS 96 campaign. The analysis is mainly focussed on the He I D3 line, on the H[FORMULA] line, and on a set of photospheric lines. The star was monitored irregularly for more than 200 hours.

We confirm the high level of variability of spectral lines in AB Aur. We find that the photospheric lines have a profile differing significantly from a classical rotational profile. The dominant features of this abnormal photospheric profile are a blue component, in absorption, whose velocity is modulated with a 34hr period, and a red component, stable in velocity but of variable intensity, with a possible periodicity near 43 hrs.

The He I D3 line exhibits two well-defined components: a blue component, always in emission with a velocity modulated with a 45hr period, and a red component of variable intensity, alternatively in emission and in absorption, occurring at a fixed velocity, with a variable intensity possibly modulated with a 45 hr period.

The H[FORMULA] line, showing a P Cygni profile, also exhibits pseudo-periodic variations of its blue absorption component, but its variability appears more complicated than that of the other lines studied here.

We suggest that the blue component of the photospheric lines is modulated by the star's rotation, with a period of 34 hrs, due to a highly inhomogeneous photosphere, involving significant radial flows. Our model also involves downflows onto the stellar pole to account for the red components of the photospheric lines and of the He I D3 line.

We propose two different interpretations of the behavior of the blue component of the He I D3 line. In the first one, this component is formed in a wind originating from the star's equatorial regions. In this interpretation, the rotation period of the equatorial regions of the star is 45 hrs, implying a 25% surface differential rotation, with the pole rotating faster than the equator. The second interpretation involves a wind originating from a region of a circumstellar disk, at a distance of 1.6 stellar radii from the star's center, with a rotation period of 45 hrs. We are not able to decide which one of these two interpretations is more likely, on the basis of the data presented here.

Key words: line: profiles – stars: chromospheres – stars: individual: AB Aur – stars: magnetic fields – stars: pre-main sequence

* Based on observations obtained during the MUSICOS 96 MUlti-SIte COntinuous Spectroscopic campaign, collected at the Canada-France Hawaii, the McDonald 2.1m, the La Palma 2.5m Isaak Newton, the Observatoire de Haute-Provence 1.93m, the Xinglong 2.16m, and the Ritter Observatory 1m telescopes

Send offprint requests to: C. Catala (catala@obs-mip.fr)

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999
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