The enigmatic X-rays from the Herbig star HD 163296: Jet, accretion, or corona?^*

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: moritz.guenther@hs.uni-hamburg.de

Received: 22 September 2008
Accepted: 26 November 2008

Abstract

Context. Herbig Ae/Be stars (HAeBe) are pre-main sequence objects in the mass range 2  <  < 8 . Their X-ray properties are uncertain and, as yet, unexplained.

Aims. We want to elucidate the X-ray generating mechanism in HAeBes.

Methods. We present an XMM-Newton observation of the HAeBe HD 163296. We analyse the light curve, the broad band and the grating spectra, fit emission measures and abundances and apply models for accretion and wind shocks.

Results. We find three temperature components ranging from 0.2 keV to 2.7 keV. The He-like triplet indicates an X-ray formation region in a low density environment with a weak UV photon field, i.e. above the stellar surface. This makes an origin in an accretion shock unlikely; instead we suggest a shock at the base of the jet for the soft component and a coronal origin for the hot component. A mass outflow of  yr^-1 is sufficient to power the soft X-rays.

Conclusions. HD 163296 is thought to be single, so this data represent genuine HAeBe X-ray emission. HD 163296 might be prototypical for its class.