Neon and Chemical Fractionation Trends inLate-type Stellar Atmospheres

摘要

A survey of Ne, O and Fe coronal abundances culled from the recent literature for about60 late-type stars confirms that the Ne/O ratio of stellar outer atmospheres is about two times thevalue recently recommended by Asplund et al. The mean Ne/O remains flat from the most activestars down to at least intermediate activity levels (-5 < L_x/L_(bol))< —2), with some evidence fora decline toward the lowest activity levels sampled. The abundances surveyed are all based onemission measure distribution analyses and the mean Ne/O is about 0.1 dex lower than that foundfrom line ratios in the seminal study of mostly active stars by Drake & Testa (2005), but is within thesystematic uncertainties of that study. We also confirm a pattern of strongly decreasing Fe/O withincreasing stellar activity. The observed abundance patterns are reminiscent of the recent finding ofa dependence of the solar Ne/O and Fe/O ratios on active region plasma temperature and indicatea universal fractionation process is at work. The firm saturation in stellar Nei() at higher activitylevels combined with variability in the solar coronal Ne/O leads us to suggest that Ne is generallydepleted in the solar outer atmosphere and photospheric values are reflected in active stellar coronae.The solution to the recent solar model problem would then appear to lie in a combination of theAsplund et al. (2005) O abundance downward revision being too large, and the Ne abundance beingunderestimated for the Sun by about a factor of 2.