A chromospheric scenario for the activity of β Pictoris, as revealed by FUSE

¹ Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, BP 8, 13376 Marseille Cedex 12, France
² Université de Provence, Centre de Mathématiques et d'Informatique, 39 rue J. Curie, 13453 Marseille Cedex 13, France e-mail: Magali.Deleuil@astrsp-mrs.fr
³ Laboratory for Astronomy and Solar Physics, Code 681, NASA Goddard Space Flight Center, Greenbelt MD 20771, USA
⁴ Department of Astronomy, University of Maryland, College Park, MD 20742, USA e-mail: lanz@stars.gsfc.nasa.gov
⁵ Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore MD 21218, USA e-mail: akir@pha.jhu.edu
⁶ Institut d'Astrophysique de Paris, CNRS, 98bis Bd Arago, 75014 Paris, France e-mail: lecaveli@iap.fr e-mail: alfred@iap.fr

Corresponding author: J.-C. Bouret, Jean-Claude.Bouret@astrsp-mrs.fr

Received: 5 March 2002
Accepted: 22 April 2002

Abstract

We investigate a chromospheric scenario to explain the characteristics of the far-UV emission lines of β Pictoris, revealed by FUSE spectra of this famous circumstellar disk system. The model assumes a thin region heated up to a few 10⁵ K located close to the stellar photosphere. The resonance lines of at 977 Å and at 1032–1037 Å, seen in emission, are produced in this chromosphere-transition region complex. Using complementary data in the mid and near UV (specifically, a resonance doublet of at 1548–1550 Å and h & k), we show that the whole dataset is remarquably well reproduced by the model. In addition, we investigate the properties of the * multiplet at 1176 Å and conclude that this line likely forms in a weak warm wind, originating from the prominent circumstellar disk of β Pictoris. Finally, radiative losses have been calculated and have provided estimates of the amount of non radiative energy dissipated in the external atmosphere of β Pictoris, which is a measure of the star's activity level. Such behavior for an A5 V star presents a challenge for both evolution and activity models since the former predict that main-sequence A stars should not be active, while the latter are unable to quantitatively account for the characteristics of the chromospheric heating of β Pictoris.