New insights in the FUV into the activity of the Herbig Ae star HD 163296

¹ Laboratoire d'Astrophysique de Marseille, CNRS - Université de Provence, BP 8, 13376 Marseille Cedex 12, France e-mail: magali.deleuil@oamp.fr
² Observatoire de Paris-Meudon, CNRS, Paris, France
³ Institut d'Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
⁴ Dept. of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Rd., Washington, DC 20015-1305, USA
⁵ Dept. of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, Maryland 21218, USA

Received: 10 June 2004
Accepted: 28 July 2004

Abstract

We present an analysis of the FUSE spectra of HD 163296, a young isolated Herbig Ae star. The spectra in the far UV spectral range are dominated by strong emission lines of and , which exhibit broad and complex asymmetric profiles with wings extending over more than 1000 km s^-1. The Ly α and the emission profiles show evidence for an outflow with a terminal velocity of 270 km s^-1. We also identified several narrower emission lines due to fluorescent decays in . Using an HST/STIS archive spectrum, we checked that the Ly α line, which has a clear type III P Cygni emission profile, is broad enough to provide the photons required to photo-excite the upper levels. As previously explored for the well-known Herbig Ae star AB Aur, most of the spectral features including the fluorescent lines are consistent with the presence of a chromosphere above the photosphere. However, the over-ionized species cannot be produced in this region alone and we discuss two alternative mechanisms to explain such spectral signatures: magnetospheric accretion and a magnetically confined wind. Both interpretations involve a large-scale magnetic field whose detection is now a challenge for the new generation of spectropolarimeters such as ESPaDOnS.