Issue |
A&A
Volume 436, Number 3, June IV 2005
|
|
---|---|---|
Page(s) | 1041 - 1047 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20052834 | |
Published online | 03 June 2005 |
The first observed stellar X-ray flare oscillation: Constraints on the flare loop length and the magnetic field
Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK e-mail: umk@mssl.ucl.ac.uk
Received:
7
February
2005
Accepted:
12
March
2005
We present the first X-ray observation of an oscillation during a stellar
flare. The flare occurred on the active M-type dwarf AT Mic and
was observed with XMM-Newton. The soft X-ray light curve
(0.2–12 keV) is investigated with wavelet analysis. The flare's
extended, flat peak
shows clear evidence for a damped oscillation with a period of around
750 s, an exponential damping time of around 2000 s, and an initial,
relative peak-to-peak amplitude of around 15%.
We suggest that
the oscillation is
a standing magneto-acoustic wave tied to the
flare loop, and find that
the most likely interpretation is a longitudinal, slow-mode
wave, with a resulting loop length of cm. The local
magnetic field strength is found to be 105 ± 50 G. These values are
consistent with (oscillation-independent) flare cooling time models
and pressure balance scaling laws.
Such a flare oscillation provides an excellent opportunity to obtain
coronal properties like the size of a flare loop or the local magnetic
field strength for the otherwise spatially-unresolved star.
Key words: stars: coronae / stars: flare / stars: magnetic fields / stars: oscillations / X-rays: stars / stars: individual: AT Mic
© ESO, 2005
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