Further X-ray detections of Herbig stars

Abstract

The interpretation of X-ray detections from Herbig Ae/Be stars is disputed as it is not clear if 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. 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 to test the T Tauri hypothesis by spatially resolving known visual companions from the primaries. Here we report on six as yet unpublished Chandra exposures from our X-ray survey of Herbig stars.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 further A/B-type stars that are serendipitously in the Chandra field-of-view. In this sample we record a detection rate of 100%, i.e. all A/B-type stars display X-ray emission at levels of log(L_x/L_bol) ~ -5...-7. The analysis of hardness ratios confirms that HAeBe's have hotter and/or more absorbed X-ray emitting plasma than more evolved B-type stars. Radiative winds are ruled out as exclusive emission mechanism on 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 open if 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.

11 pages; accepted for publication in Astronomy & Astrophysics Main Journal

References in corpus (12)

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Cited by in corpus (18)

• X-Ray Spectroscopy of Stars
• Diagnosing Mass Flows Around Herbig Ae/Be Stars Using the He I 10830 Line
• The Gould Belt Very Large Array Survey IV: The Taurus-Auriga complex
• Photoevaporative Dispersal of Protoplanetary Disks around Evolving Intermediate-mass Stars
• Herbig Stars: A Quarter Century of Progress
• A gas density drop in the inner 6 AU of the transition disk around the Herbig Ae star HD 139614: Further evidence for a giant planet inside the disk?
• Evolution of X-ray Activity in <25 Myr Old Pre-Main Sequence Stars
• X-ray emission processes in stars
• Chandra and Spitzer Imaging of the Infrared Cluster in NGC 2071
• Burn Out or Fade Away? On the X-ray and Magnetic Death of Intermediate Mass Stars
• X-ray and optical spectroscopy of the massive young open cluster IC1805
• Herbig AeBe stars: Multiplicity and consequences
• K-band GRAVITY/VLTI interferometry of "extreme" Herbig Be stars. The size-luminosity relation revisited
• Accretion, jets and winds: High-energy emission from young stellar objects
• Multiwavelength Observations of the RV Tauri Variable System U Monocerotis: Long-Term Variability Phenomena That Can Be Explained by Binary Interactions with a Circumbinary Disk
• The near-infrared companion to HD94660 (=KQ Vel)
• X-ray Super-Flares From Pre-Main Sequence Stars: Flare Modeling
• Star Forming Regions