Issue |
A&A
Volume 465, Number 2, April II 2007
|
|
---|---|---|
Page(s) | 493 - 499 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20065890 | |
Published online | 22 January 2007 |
Are magnetic hot stars intrinsic X-ray sources?
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: stefan.czesla@hs.uni-hamburg.de
Received:
23
June
2006
Accepted:
12
October
2006
Context. X-ray surveys carried out with the Einstein and ROSAT satellites have resulted in rather unexpected detections of X-ray emission from late B-type and early A-type stars. These stars possess neither winds like early-type stars nor convective envelopes as late-type stars, so that the origin and production mechanism of this X-emission is unclear.
Aims. We investigate whether the presence of large magnetic fields is related to the observed X-ray emission.
Methods.
We carried out Chandra high-angular resolution observations of a sample of late B-type
and A-type stars with measured magnetic fields in the range from kG. Out of
the selected 10 sample stars, 6 objects had been previously detected as X-ray sources, some of them, however, with high positional uncertainty and a low signal-to-noise ratio, while 4 of our sample
stars do have large magnetic fields but no previous detections of X-ray emission.
Results. Our Chandra data confirm all previous ROSAT detections with an extremely high significance, and the limits of the offsets between X-ray and optical positions are greatly improved. In particular, HD 215441, known as Babcock's star with the strongest magnetic field by far (17 kG) of our sample stars, a rather faint and somewhat marginal ROSAT source, can clearly be detected. However, none of the 4 ROSAT non-detections could be detected with the new Chandra observations.
Conclusions. The pure existence of a magnetic field of kiloGauss strength on a late B-type or A-type star is therefore not necessarily a prerequisite for finding X-ray emission among these stars. Understanding the observed X-ray emission from Babcock's star is a challenge for observational and theoretical astrophysics.
Key words: stars: early-type / stars: magnetic fields / stars: activity / X-ray: stars
© ESO, 2007
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