ASCA and EUVE Observations of II Pegasi: Flaring and Quiescent Coronal Emission

R. Mewe, J.S. Kaastra, G.H.J. van Den, J. Vink, Y. Tawara

Astronomy and Astrophysics, v. 320, p. 147-158


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, Geochim. Cosmochim. Acta 53, 197), but the Fe abundance is even lower, i.e. 0.1xSolar. The multi-T and DEM fitting analysis shows that the quiescent EUVE and ASCA spectra can be described by two temperature components: 4 and 10MK (EUVE), 10 and 20MK (ASCA). The two flares detected by EUVE and ASCA show peak temperatures of 20 and >35MK, respectively. The latter flare has a total energy (0.1-10keV) of 2.7x10^34^erg, a peak luminosity of 2.6x10^30^erg/s. There is evidence for an increase of a factor ~4 of the iron abundance during the rise phase of the flare. Application of a cooling model yields a loop height of about 8x10^10^cm and a plasma density of 8x10^10^cm^-3^.

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