EDP Sciences
Free Access
Volume 403, Number 1, May III 2003
Page(s) 155 - 171
Section Stellar atmospheres
DOI https://doi.org/10.1051/0004-6361:20030257
Published online 29 April 2003

A&A 403, 155-171 (2003)
DOI: 10.1051/0004-6361:20030257

Tomography of a stellar X-ray corona: Coronae Borealis

M. Güdel1, K. Arzner1, M. Audard2 and R. Mewe3

1  Paul Scherrer Institut, Würenlingen & Villigen, CH-5232 Villigen PSI, Switzerland
    e-mail: guedel@astro.phys.ethz.ch; arzner@astro.phys.ethz.ch
2  Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA
    e-mail: audard@astro.columbia.edu
3  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
    e-mail: r.mewe@sron.nl

(Received 9 October 2002 / Accepted 12 February 2003 )

We interpret the X-ray light curve obtained by XMM-Newton during a total X-ray eclipse in the nearby binary star  Coronae Borealis . This system consists of a G5 V main-sequence star orbiting an X-ray dark A0 star. The secondary G star is a young, active solar analog with an age of a few 100 Myr. As the primary A star eclipses active regions on the X-ray bright companion, the light curve drops in consecutive steps to zero; as individual active regions reappear during egress, the flux rises in similar steps. The ingress and egress light curves are combined to reconstruct the 2D distribution of X-ray brightness on and around the G star. Three different methods are applied, and variations due to statistical noise and uncertainties in the binary system parameters are discussed. Although the solutions are non-unique, all reconstructions reveal a similar distribution of X-ray bright regions and large areas with little flux. We present plausible estimates of (lower limits to) the electron densities in the bright regions, obtaining characteristic values between 109- $3\times 10^{10}$ cm -3.

Key words: stars: activity -- stars: coronae -- stars: individual: CrB -- X-rays: stars

Offprint request: M. Güdel, guedel@astro.phys.ethz.ch

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© ESO 2003

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