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Astron. Astrophys. 334, 188-200 (1998)


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Loop modeling of coronal X-ray spectra

V. One- and two-loop model fitting of G-type star ROSAT/PSPC spectra

R. Ventura 1, A. Maggio 2 and G. Peres 3

1 Osservatorio Astrofisico, Città Universitaria, V. le A. Doria 6, I-95125 Catania, Italy
2 Osservatorio Astronomico, Piazza del Parlamento 1, I-90134 Palermo, Italy
3 Dipartimento di Scienze Fisiche e Astronomiche, sezione di Astronomia, Piazza del Parlamento 1, 90134 Palermo, Italy

Received 11 August 1997 / Accepted 27 January 1998

Abstract

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 [FORMULA] 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 ([FORMULA] K) with pressures ranging from relatively low ([FORMULA] dyn cm-2) to high values ([FORMULA] [FORMULA] dyn cm-2) and hot loops ([FORMULA]) with very high base pressures ([FORMULA] dyn cm-2). We compare the results and the diagnostic power coming from the different approaches and discuss their physical implications.

Key words: stars: coronae – stars: late-type – stars: activity – plasmas – X-rays: stars

Send offprint requests to: rventura@alpha4.ct.astro.it

© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998

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