New X-ray detections of Herbig stars

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Autor/in:
Erscheinungsjahr:
2009
Medientyp:
Text
Schlagworte:
  • Disks
  • Protoplanetary disks
  • Outer disk
  • Galaxies
  • Stars
  • Planets
  • Stars: coronae
  • Stars: pre-main sequence
  • Stars: Early-type
  • X-rays: Stars
  • Stars: activity
  • Stars: binaries: general
  • Disks
  • Protoplanetary disks
  • Outer disk
  • Galaxies
  • Stars
  • Planets
Beschreibung:
  • Context. The interpretation of X-ray detections from Herbig Ae/Be stars is disputed as it is not clear whether these intermediate-mass pre-main sequence stars are able to drive a dynamo and ensuing phenomena of magnetic activity. Alternative X-ray production mechanisms, related to stellar winds, star-disk magnetospheres, or unresolved late-type T Tauri star companions have been proposed. Aims. The companion hypothesis can be tested by resolving Herbig stars in X-rays from their known visual secondaries. Furthermore, their global X-ray properties (such as detection rate, luminosity, temperature, variability) may give clues to the emission mechanism by comparison to other types of stars, e.g. similar-age but lower-mass T Tauri stars, similar-mass but more evolved main-sequence A-and B-type stars, and with respect to model predictions. Methods. In a series of papers we have been investigating high-resolution X-ray Chandra images of Herbig Ae/Be and main-sequence B-type stars where known close visual companions are spatially separated from the primaries. Results. Here we report on six as yet unpublished Chandra exposures from our X-ray survey of Herbig stars. The target list comprises six Herbig stars with known cool companions, and three other A/B-type stars that are serendipitously in the Chandra field-of-view. In this sample we record a detection rate of 1.00%; i.e. all A/B-type stars display X-ray emission at levels of log(Lx/L bol) ∼ -5... - 7. The analysis of hardness ratios confirms that HAeBes have hotter and/or more absorbed X-ray emitting plasma than more evolved B-type stars. Conclusions. Radiative winds are ruled out as an exclusive emission mechanism on the basis of the high X-ray temperatures. Confirming earlier results, the X-ray properties of Herbig Ae/Be stars are not vastly different from those of their late-type companion stars (if such are known). The diagnostics provided by the presently available data leave it open whether the hard X-ray emission of Herbig stars is due to young age or indicative of further coronally active low-mass companion stars. In the latter case, our detection statistics imply a high fraction of higher order multiple systems among Herbig stars. © ESO 2009.
Lizenz:
  • info:eu-repo/semantics/openAccess
Quellsystem:
Forschungsinformationssystem der UHH
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oai:www.edit.fis.uni-hamburg.de:publications/511980b4-e2f0-40b0-997a-000ba6ca28f1