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

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 χ2 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 (Tmax ' 1.5− 5 × 106 K) with pressures ranging from relatively low (p0 ' 2− 10 dyn cm−2) to high values (p0 ' 100 dyn cm−2) and hot loops (Tmax ' 1 − 3 × 107) with very high base pressures (p0 ' 102 − 2.4 × 104 dyn cm−2). We compare the results and the diagnostic power coming from the different approaches and discuss their physical implications.