modeling of coronal X - ray spectraV . One - and two - loop model tting of G - type star ROSAT / PSPC

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 tted the X-ray spectra adopting two diierent 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 2 values, however they allow limited physical insight on the stellar coronal structures; on the other hand, the one-loop model tting 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 coro-nae comes from the two-loop modeling approach: two distinct classes of loops with diierent characteristics seem to dominate the X-ray emission of our sample of G-type stars: relatively cool loops (T max ' 1:5 ? 5 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 10 7) with very high base pressures (p 0 ' 10 2 ? 2:4 10 4 dyn cm ?2). We compare the results and the diagnostic power coming from the diierent approaches and discuss their physical implications.