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Issue A&A
Volume 411, Number 3, December I 2003
Page(s) 509 - 515
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20031389



A&A 411, 509-515 (2003)
DOI: 10.1051/0004-6361:20031389

The X-ray spectra of the flaring and quiescent states of AT Microscopii observed by XMM-Newton

A. J. J. Raassen1, 2, R. Mewe1, M. Audard3 and M. Güdel4

1  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2  Astronomical Institute "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3  Columbia Astrophysics Laboratory, Mail code 5247, 550 West 120th Street, New York, NY 10027, USA
4  Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland

(Received 3 February 2003 / Accepted 29 August 2003 )

Abstract
The X-ray spectrum of the late-type M-dwarf binary AT Mic (dM4.5e+dM4.5e) is observed in the wavelength range 1-40 Å by means of RGS and EPIC-MOS on board XMM-Newton. During the exposure a flare occured. We have performed a 3-temperature fit and a DEM-modeling to the flaring and quiescent part of the spectrum. We report the coronal temperature distribution, emission measures, and abundances of the flaring and quiescent state of this bright X-ray source. The temperature range stretches from about 1 to 60 MK. The total volume emission measure in this temperature interval is ${\sim} 12.2 \times 10^{51}$ cm -3 for the quiescent state and ${\sim} 19.5 \times 10^{51}$ cm -3 for the flare state. This difference is due to the contribution of the hot temperature component. The high-resolution spectrum of AT Mic, obtained by RGS, is dominated by the H- and He-like transitions of C, N, O, and Ne and by Fe XVII lines, produced by the plasma with temperatures from 1 to 10 MK. The EPIC-MOS spectrum below 10 Å shows H- and He-like Ne, Si and the iron K-shell transitions. They are produced by the hot component (30 MK). The iron K-shell is more prominent in the flare state. The abundance pattern in the quiescent state of AT Mic shows the depletion of low-FIP elements relative to high-FIP elements, indicating the presence of an I(nverse)FIP effect in this active star. In the flare state, however, some flattening of this IFIP effect is present.


Key words: stars: individual: AT Mic -- stars: coronae -- stars: late-type -- missions: -- XMM-Newton

Offprint request: A. J. J. Raassen, a.j.j.raassen@sron.nl

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