Astronomy and Astrophysics, volume 315, 170-178 (1996/11-1)
Simultaneous EUVE & ASCA observations of AB Doradus: temperature structure and abundances of the quiescent corona.
MEWE R., KAASTRA J.S., WHITE S.M. and PALLAVICINI R.
Abstract (from CDS):
We have analyzed EUV and X-ray spectra of the non-flaring state of AB Dor, obtained from simultaneous observations with EUVE and ASCA. The coronal temperature structure and the coronal elemental abundances have been derived by jointly fitting the spectra, including lines and continuum. We have applied a multi-temperature fitting method and we have found that an optically thin plasma model with solar abundances (relative to hydrogen) does not yield a good fit. A 4-T fit allowing the abundances of the more important elements (Fe, S, Si, Mg, Ne, and O) plus four other less important abundances (N, Ar, Ca, and Ni) to vary improves the fit markedly. This results in values of the first 6 abundances relative to solar photospheric values that are significantly (a factor 2-3) below solar except for Ne, which is solar, while most of the remaining four abundances are consistent both with solar and reduced abundances. In the course of the 4-T fitting we have determined a best-fit value for the interstellar hydrogen column density of NH=(2.0±0.5)1018cm–2. We have applied four differential emission measure (DEM) distribution analysis techniques, viz.: (i) regularization method, (ii) polynomial method, (iii) clean algorithm, and (iv) genetic algorithm. The four different methods all yield a qualitatively similar DEM, showing two maxima in the temperature intervals 5-8MK and 20-30MK. Our analysis demonstrates the great value of simultaneous ASCA and EUVE observations in determining the fundamental parameters of stellar coronae.
stars: coronae - pre-main sequence - stars: individual: AB Dor - ultraviolet: stars - X-rays: stars
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