Astronomy & Astrophysics

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Issue		A&A Volume 388, Number 3, June IV 2002
Page(s)		899 - 916
Section		Formation, structure and evolution of stars
DOI		10.1051/0004-6361:20020522

A&A 388, 899-916 (2002)
DOI: 10.1051/0004-6361:20020522

Non-radial pulsation, rotation and outburst in the Be star Orionis from the MuSiCoS 1998 campaign

C. Neiner^{1, 2}, A.-M. Hubert¹, M. Floquet¹, S. Jankov^{3, 4}, H. F. Henrichs², B. Foing⁵, J. Oliveira^{5, 6}, S. Orlando^{5, 7}, J. Abbott^{8, 9}, I. K. Baldry¹⁰, T. R. Bedding¹⁰, J. Cami², H. Cao¹¹, C. Catala¹², K. P. Cheng¹³, A. Domiciano de Souza Jr^{14, 3}, E. Janot-Pacheco^{1, 14}, J. X. Hao¹¹, L. Kaper², A. Kaufer¹⁵, N. V. Leister¹⁴, J. E. Neff¹⁶, S. J. O'Toole¹⁰, D. Schäfer¹⁷, S. J. Smartt^{18, 19}, O. Stahl¹⁷, J. Telting^{8, 20}, S. Tubbesing¹⁷ and J. Zorec²¹

¹ GEPI/FRE 2459 du CNRS, Observatoire de Paris-Meudon, France
² Sterrenkundig Instituut Anton Pannekoek, Universiteit van Amsterdam, Netherlands
³ FRESNEL/UMR 6528 du CNRS, Observatoire de la Côte d'Azur (OCA), France
⁴ Astronomical Observatory Beograd, Yugoslavia
⁵ ESA Solar System Division, Space Science Department, ESTEC, The Netherlands
⁶ Department of Physics, Keele University, Staffordshire, UK
⁷ Osservatorio Astronomico di Palermo "G.S. Vaiana", Italy
⁸ Isaac Newton Group (ING), La Palma Island, Spain
⁹ Department of Physics & Astronomy, University College London, UK
¹⁰ School of Physics, University of Sydney 2006, Australia
¹¹ Beijing Astronomical Observatory, China
¹² LESIA, Observatoire de Paris-Meudon, France
¹³ California State University, Fullerton, CA, USA
¹⁴ Instituto Astronomico e Geofisico, Universidade de Sao Paulo, Brazil
¹⁵ European Southern Observatory, Chile
¹⁶ College of Charleston, Charleston, SC, USA
¹⁷ Landessternwarte Heidelberg-Königstuhl, Germany
¹⁸ Institute of Astronomy, University of Cambridge, England
¹⁹ Marshall Space Flight Center, Huntville, AL, USA
²⁰ Nordic Optical Telescope (NOT), La Palma Island, Spain
²¹ Institut d'Astrophysique de Paris (IAP), France

(Received 27 December 2001 / Accepted 29 March 2002)

Abstract
Ori ( HD 37490 , HR 1934 ) is a Be star known to have presented variations. In order to investigate the nature and origin of its short-term and mid-term variability, a study is performed of several spectral lines (H $\alpha$ , H $\delta$ , $\ion{i}$ 4471, 4713, 4921, 5876, 6678, $\ion{C}{ii}$ 4267, 6578, 6583, $\ion{ii}$ 4481, $\ion{iii}$ 4553 and $\ion{ii}$ 6347), based on 249 high signal-to-noise high-resolution spectra taken with 8 telescopes over 22 consecutive nights during the MuSiCoS (Multi SIte COntinuous Spectroscopy) campaign in November-December 1998. The stellar parameters are revisited and the projected rotational velocity ( $v\sin i = 179$ km s ^-1) is redetermined using several methods. With the MuSiCoS 98 dataset, a time series analysis of line-profile variations (LPVs) is performed using the Restricted Local Cleanest (RLC) algorithm and a least squares method. The behaviour of the velocity of the centroid of the lines, the equivalent widths and the apparent vsin i for several lines, as well as Violet and Red components of photospheric lines affected by emission (red $\ion{i}$ lines, $\ion{ii}$ 6347, $\ion{C}{ii}$ 6578, 6583) are analyzed. The non-radial pulsation (NRP) model is examined using phase diagrams and the Fourier-Doppler Imaging (FDI) method. The LPVs are consistent with a NRP mode with l = 2 or 3, |m| = 2 with frequency 1.03 c d ^-1. It is shown that an emission line outburst occurred in the middle of the campaign. Two scenarios are proposed to explain the behaviour of a dense cloud, temporarily orbiting around the star with a frequency 0.46 c d ^-1, in relation to the outburst.

Key words: stars: emission line, Be -- stars: early-type -- stars: individual: Ori -- stars: oscillations -- stars: activity -- line: profiles

Offprint request: C. Neiner, Coralie.Neiner@obspm.fr

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