Loop modeling of coronal X-ray spectra. V. One- and two-loop model fitting of G-type star ROSAT/PSPC spectra

Astronomy and Astrophysics – Astrophysics

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Stars: Coronae, Stars: Late-Type, Stars: Activity, Plasmas, X-Rays: Stars

Scientific paper

As part of a systematic study devoted to the diagnostic of solar-like coronal structures in late-type stars, we have analyzed ROSAT/PSPC X-ray spectra of eight main sequence G-type stars in the solar neighborhood. We have fitted the X-ray spectra adopting two different classes of models: the usual two-component isothermal models and the more physically meaningful hydrostatic loop models. The two-component isothermal models yield fairly acceptable chi (2) values, however they allow limited physical insight on the stellar coronal structures; on the other hand, the one-loop model fitting provides unreliable long loops, namely orders of magnitude larger than the stellar radius, in the majority of the cases studied. A more realistic physical description of the observed coronae comes from the two-loop modeling approach: two distinct classes of loops with different characteristics seem to dominate the X-ray emission of our sample of G-type stars: relatively cool loops (T_max =~ 1.5 - 5 x 10(6) K) with pressures ranging from relatively low (p_0 =~ 2 - 10 dyn cm(-2) ) to high values (p_0 =~ 100 dyn cm(-2) ) and hot loops (T_max =~ 1 - 3 x 10(7) ) with very high base pressures (p_0 =~ 10(2) - 2.4 x 10(4) dyn cm(-2) ). We compare the results and the diagnostic power coming from the different approaches and discuss their physical implications.

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