Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-06-27
Astrophys.J.665:1349-1360,2007
Astronomy and Astrophysics
Astrophysics
Accepted for publication on the Astrophysical Journal
Scientific paper
10.1086/519920
We have investigated the optical thickness of the coronal plasma through the analysis of high-resolution X-ray spectra of a large sample of active stars observed with the High Energy Transmission Grating Spectrometer on Chandra. In particular, we probed for the presence of significant resonant scattering in the strong Lyman series lines arising from hydrogen-like oxygen and neon ions. The active RS CVn-type binaries II Peg and IM Peg and the single M dwarf EV Lac show significant optical depth. For these active coronae, the Lya/Lyb ratios are significantly depleted as compared with theoretical predictions and with the same ratios observed in similar active stars. Interpreting these decrements in terms of resonance scattering of line photons out of the line-of-sight, we are able to derive an estimate for the typical size of coronal structures, and from these we also derive estimates of coronal filling factors. For all three sources we find that the both the photon path length as a fraction of the stellar radius, and the implied surface filling factors are very small and amount to a few percent at most. The measured Lya/Lyb ratios are in good agreement with APED theoretical predictions, thus indicating negligible optical depth, for the other sources in our sample. We discuss the implications for coronal structuring and heating flux requirements. For the stellar sample as a whole, the data suggest increasing quenching of Lya relative to Lyb as function of both L_x/L_bol and the density-sensitive MgXI forbidden to intercombination line ratio, as might generally be expected.
Drake Jeremy J.
Huenemoerder David P.
Peres Giovanni
Testa Paola
No associations
LandOfFree
On X-ray Optical Depth in the Coronae of Active Stars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with On X-ray Optical Depth in the Coronae of Active Stars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and On X-ray Optical Depth in the Coronae of Active Stars will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-256348