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

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 C  and O , which exhibit broad and complex asymmetric profiles with wings extending over more than 1000 km s −1 .T he H Ly α and the C  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 Fe  .U sing an HST/STIS archive spectrum, we checked that the H  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 Fe  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.

[1]  M. Deleuil,et al.  Evidence for wind and accretion in the Herbig Be star HD 100546 from FUSE observations , 2004 .

[2]  S. Lamzin,et al.  Calculation of profiles of the CIV 1550 doublet formed in an accretion shock in a T Tauri star: Axially symmetric radial accretion , 2003 .

[3]  M. Deleuil,et al.  FUSE observations of H2 around the Herbig AeBe stars HD 100546 and HD 163296 , 2003, astro-ph/0306449.

[4]  S. Lamzin.  Calculation of profiles of CIV, NV, OVI, and SiIV resonance lines formed in accretion shocks in T Tauri stars: A plane layer , 2003 .

[5]  Nadine Manset,et al.  ESPaDOnS; an Echelle spectropolarimetric device for the observation of stars , 2003, SPIE Astronomical Telescopes + Instrumentation.

[6]  S. Edwards,et al.  Helium Emission from Classical T Tauri Stars: Dual Origin in Magnetospheric Infall and Hot Wind , 2001 .

[7]  J. Linsky,et al.  Identification of Fe II Emission Lines in FUSE Stellar Spectra , 2001 .

[8]  M. Deleuil,et al.  FUSE and Hubble Space Telescope/STIS Observations of Hot and Cold Gas in the AB Aurigae System , 2001, astro-ph/0103084.

[9]  P. Kalas,et al.  STIS Coronagraphic Imaging of the Herbig Ae Star: HD 163296 , 2000 .

[10]  J. B. Joyce,et al.  On-Orbit Performance of the Far Ultraviolet Spectroscopic Explorer Satellite , 2000, astro-ph/0005531.

[11]  et al,et al.  Overview of the Far Ultraviolet Spectroscopic Explorer Mission , 2000, astro-ph/0005529.

[12]  T. Simon,et al.  Short-term spectroscopic variability in the pre-main sequence Herbig Ae star AB Aurigae during the MUSICOS 96 campaign ? , 1999 .

[13]  M. Hanner,et al.  Cometary Dust in the Debris Disks of HD 31648 and HD 163296: Two “Baby” β Pictoris Stars , 1998, astro-ph/9807229.

[14]  Alfred Vidal-Madjar,et al.  β Pictoris, a young planetary system? A review , 1998 .

[15]  L. Hartmann,et al.  Magnetospheric Accretion Models for the Hydrogen Emission Lines of T Tauri Stars , 1998 .

[16]  V. Mannings,et al.  A High-Resolution Study of Gas and Dust around Young Intermediate-Mass Stars: Evidence for Circumstellar Disks in Herbig Ae Systems , 1997 .

[17]  Andrew Collier Cameron,et al.  Spectropolarimetric observations of active stars , 1997 .

[18]  E. Halbedel.  ROTATIONAL VELOCITY DETERMINATIONS FOR 164 BE AND B STARS , 1996 .

[19]  C. Tout,et al.  X-ray coronae from dynamos in young Ae/Be stars , 1995 .

[20]  C. Català,et al.  Short-term spectral variability in AB Aurigae - Clues for activity in Herbig Ae stars. I - The ultraviolet lines of Mg II and Fe II , 1986 .

[21]  S. Johansson,et al.  Selective excitation of Fe II in the laboratory and late-type stellar atmospheres , 1984 .

[22]  J. Bouvier.  Magnetospheric accretion in T Tauri stars , 2003 .

[23]  C. Jordan,et al.  The outer atmosphere of Tau ‐‐ II. Fluorescent lines , 1999 .

[24]  G. Franco,et al.  Cyclic phenomena in the circumstellar gaseous envelope of the candidate Herbig A0e star HD 163296 , 1998 .