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Astron. Astrophys. 320, 147-158 (1997)

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ASCA and EUVE observations of II Pegasi: flaring and quiescent coronal emission

R. Mewe 1, J.S. Kaastra 1, G.H.J. van den Oord 2, J. Vink 1 and Y. Tawara 3

1 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Sterrekundig Instituut Utrecht, P.O. Box 80000, 3508 TA Utrecht, The Netherlands
3 Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464, Japan

Received 8 July 1996 / Accepted 17 September 1996


We have analyzed X-ray and EUV spectra of both the quiescent and flaring state of II Peg, obtained from observations with ASCA and EUVE. Coronal temperature structure and abundances have been derived from multi-temperature and differential emission measure (DEM) analyses of the spectra. The abundances are non-solar; in the case of ASCA for most elements (O, Ne, Mg, Si, S, Ar, Ca, Ni) we obtain abundances that are consistent with about 1/2-1/5 of the solar photospheric abundances of Anders and Grevesse (1989), but the Fe abundance is even lower, i.e. 0.1 [FORMULA] solar. The multi-T and DEM fitting analysis shows that the quiescent EUVE and ASCA spectra can be described by two temperature components: 4 and 10 MK (EUVE), 10 and 20 MK (ASCA). The two flares detected by EUVE and ASCA show peak temperatures of 20 and [FORMULA]  35 MK, respectively. The latter flare has a total energy (0.1-10 keV) of 2.7 1034  erg, a peak luminosity of 2.6 1030  erg/s. There is evidence for an increase of a factor [FORMULA]  4 of the iron abundance during the rise phase of the flare. Application of a cooling model yields a loop height of about 8 1010  cm and a plasma density of 8 1010  cm-3.

Key words: stars: coronae – activity – late-type – flare – abundances – II Peg – ultraviolet: stars – X-rays: stars

Send offprint requests to: R. Mewe

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998