SIMBAD references

The Chandra High Energy Transmission Grating Spectrometer (HETG) spectra of the coronally active binary stars σ Gem and HR 1099 are among the highest fluence observations for such systems taken at high spectral resolution in X-rays with this instrument. This allows us to compare their properties in detail to solar flare spectra obtained with the Russian CORONAS-F spacecraft's RESIK instrument at similar resolution in an overlapping bandpass. Here we emphasize the detailed comparisons of the 3.3-6.1Å region (including emission from highly ionized S, Si, Ar, and K) from solar flare spectra to the corresponding σ Gem and HR 1099 spectra. We also model the larger wavelength range of the HETG, from 1.7 to 25Å–having emission lines from Fe, Ca, Ar, Si, Al, Mg, Ne, O, and N–to determine coronal temperatures and abundances. σ Gem is a single-lined coronally active long-period binary which has a very hot corona. HR 1099 is a similar, but shorter period, double-lined system. With very deep HETG exposures we can even study emission from some of the weaker species, such as K, Na, and Al, which are important since they have the lowest first ionization potentials, a parameter well known to be correlated with elemental fractionation in the solar corona. The solar flare temperatures reach ~20 MK, comparable to the σ Gem and HR 1099 coronae. During the Chandra exposures, σ Gem was slowly decaying from a flare and its spectrum is well characterized by a collisional ionization equilibrium plasma with a broad temperature distribution ranging from 2 to 60 MK, peaking near 25 MK, but with substantial emission from 50 MK plasma. We have detected K XVIII and Na XI emission which allow us to set limits on their abundances. HR 1099 was also quite variable in X-rays, also in a flare state, but had no detectable K XVIII. These measurements provide new comparisons of solar and stellar coronal abundances, especially at the lowest first ionization potential (FIP) values. The low FIP elements do not show enhancement in the stellar coronae as they do in the Sun, except perhaps for K in σ Gem. While σ Gem and HR 1099 differ in their emission measure distributions, they have very similar elemental abundances.