Publications of the MPIfR
Optical & Infrared
Interferometry Group
Skinner, Stephen L.; Güdel, Manuel;
Audard, Marc; Smith, Kester
New Perspectives on the X-Ray Emission of HD
104237 and Other Nearby Herbig Ae/Be Stars from XMM-Newton and Chandra
The Astrophysical Journal, Volume 614, Issue 1, pp.
221-234 (2004)
Abstract
The origin of the X-ray emission from Herbig Ae/Be stars is not yet
known. These intermediate-mass pre-main-sequence stars lie on radiative
tracks and are not expected to emit X-rays via solar-like magnetic
processes, nor are their winds powerful enough to produce X-rays by
radiative wind shocks as in more massive O-type stars. The emission
could originate in unseen low-mass companions, or it may be intrinsic
to
the Herbig stars themselves if they still have primordial magnetic
fields or can sustain magnetic activity via a nonsolar dynamo. We
present new X-ray observations of the nearby Herbig Ae star HD 104237
(=DX Cha) with XMM-Newton, whose objective is to clarify the origin of
the emission. Several X-ray emission lines are clearly visible in the
CCD spectra, including the high-temperature Fe Kα complex. The
emission can be accurately modeled as a multitemperature thermal plasma
with cool (kT<1 keV) and hot (kT>~3 keV) components. The presence
of a hot component is compelling evidence that the X-rays originate in
magnetically confined plasma, either in the Herbig star itself or in
the
corona of an as yet unseen late-type companion. The X-ray temperatures
and luminosity (logLX=30.5 ergs s-1) are within
the range expected for a T Tauri companion, but high-resolution Chandra
and Hubble Space Telescope images constrain the separation of a
putative
companion to less than 1". We place these new results into broader
context by comparing the X-ray and bolometric luminosities of a sample
of nearby Herbig stars with those of T Tauri stars and classical
main-sequence Be stars. We also test the predictions of a model that
attributes the X-ray emission of Herbig stars to magnetic activity that
is sustained by a shear-powered dynamo.
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