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Astron. Astrophys. 339, 545-552 (1998)

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[FORMULA] Centauri: coronal temperature structure and abundances from ASCA observations

R. Mewe 1, S.A. Drake 2, J.S. Kaastra 1, C.J. Schrijver 3, J.J. Drake 4, M. Güdel 5, J.H.M.M. Schmitt 6, K.P. Singh 7 and N.E. White 2

1 Space Research Organization Netherlands (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Code 660, Laboratory for High Energy Astrophysics, NASA/GSFC, Greenbelt, MD 20771, USA
3 Stanford-Lockheed Inst. for Space Research, Department H1-12, Bldg. 252, 3251 Hanover St., Palo Alto, CA 94304-1191, USA
4 Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge, MA 02138, USA
5 Paul Scherrer Institut, Würenlingen und Villigen, CH-5232 Villigen PSI, Switzerland
6 Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany
7 Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India

Received 16 July 1997 / Accepted 31 August 1998

Abstract

We have analyzed the X-ray spectrum of the nearby binary [FORMULA] Cen AB (G2V + K1V) that has been obtained from observations with ASCA . The coronal temperature structure and abundances have been derived from multi-temperature fitting and confirmed by a differential emission measure analysis. The corona as seen by ASCA is essentially isothermal with a temperature around 0.3 keV, consistent with the evolutionary picture of coronae of aging solar-type stars. A comparison between the measurements from various instruments indicates a source variability in the coronal flux (which precludes the joint fitting of data from different instruments taken at different epochs) and temperature structure consistent with that discovered in a series of ROSAT observations. The elemental abundances agree with solar photospheric abundances for Ne, Si, and Fe at 1[FORMULA] level, while O appears to be underabundant by a factor of about 3 relative to solar photospheric values, and Mg overabundant by a factor of a few. The abundance ratios with respect to Fe are better determined: [O/Fe] = 0.4[FORMULA]0.14 ([FORMULA] solar, etc.), [Mg/Fe] = 4[FORMULA]1, [Ne/Fe] = 1[FORMULA]0.3, and [Si/Fe] = 6[FORMULA]4.

Key words: stars: coronae – stars: individual: ff Cen – stars: abundances – X-rays: stars

Send offprint requests to: R. Mewe, (R.Mewe@sron.nl)

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© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998
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