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

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

Corresponding author: C. Neiner, Coralie.Neiner@obspm.fr

Received: 27 December 2001
Accepted: 29 March 2002

Abstract

ω 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 (Hα, Hδ, 4471, 4713, 4921, 5876, 6678, 4267, 6578, 6583, 4481, 4553 and 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 ( 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 vsini for several lines, as well as Violet and Red components of photospheric lines affected by emission (red lines, 6347, 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 or 3, 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.