The magnetic field of the pre-main sequence Herbig Ae star HD 190073 ^*

¹ Observatoire de Paris, LESIA, CNRS UMR 8109, 5 place Jules Janssen, 92195 Meudon Principal Cedex, France e-mail: claude.catala@obspm.fr
² Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France
³ Dept. of Physics, Royal Military College of Canada, PO Box 17000, Stn Forces, K7K 4B4, Kingston, Canada
⁴ Dept. of Physics & Astronomy, University of Western Ontario, London, Canada N6A 3K7
⁵ Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, BP 8, 13376 Marseille Cedex 12, France
⁶ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁷ Department of Physics, Engineering Physics, and Astronomy, Queen's University, Kingston, ON K7L 3N6, Canada

Received: 18 August 2006
Accepted: 13 October 2006

Abstract

Context.The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum.

Aims.The particular aim of this paper is to announce the detection of a structured magnetic field in the Herbig Ae star HD 190073, and to discuss various scenarii for the geometry of the star, its environment and its magnetic field.

Methods.We have used the ESPaDOnS spectropolarimeter at CFHT in 2005 and 2006 to obtain high-resolution, high signal-to-noise circular polarization spectra which demonstrate unambiguously the presence of a magnetic field in the photosphere of this star.

Results.Nine circular polarization spectra were obtained, each one showing a clear Zeeman signature. This signature is suggestive of a magnetic field structured on large scales. The signature, which corresponds to a longitudinal magnetic field of  G, does not vary detectably on a one-year timeframe, indicating either an azimuthally symmetric field, a zero inclination angle between the rotation axis and the line of sight, or a very long rotation period. The optical spectrum of HD 190073 exhibits a large number of emission lines. We discuss the formation of these emission lines in the framework of a model involving a turbulent heated region at the base of the stellar wind, possibly powered by magnetic accretion.

Conclusions.This magnetic detection contributes an important new observational discovery which will aid our understanding of stellar magnetism at intermediate masses.