Spectral and time analysis of the coronal X-ray emission from Capella observed with Chandra/LETG
Abstract
We present a detailed analysis of two X-ray spectra of Capella, taken eleven months apart, obtained with the LETGS of the handra Observatory. We have identified the strongest emission lines, including several Fe lines with ionization level from FeXVI to FeXXIII. We have determined the electron density Ne and the relevant temperature T using the line ratios of the OVII, NeIX, MgXI and SiXIII He-like triplets, finding Ne values in the range 10^10-10^12 cm-3; from the Ne and T values we have derived volumes and pressures of the emitting plasma vs temperatures. Emission measure distribution em(T), with element abundances, has been reconstructed for each observation with the Markov-Chain Monte Carlo method proposed by Kashyap &Drake (1998). The em(T) distribution obtained has a sharp peak around log T=6.8-6.9 and no significant amount of plasma has been found for log T>7.2. From the em(T) shape we have derived information about the population of loops at different temperatures. We have compared the results obtained from each observation finding that during the first one the whole coronal emission was 3% stronger; there also appears to be a tendency, albeit a marginal one, for hotter lines to show the largest changes between the two observations. We have also performed a detailed search for short-term variability with the Collura et al. (1987) method testing photon arrival times of individual lines (the investigated time scale range is 10^2-10^4 s), thus testing the variability of coronal plasma in a narrow temperature range. In all the cases analysed we have found that emission was compatible with a constant source, therefore we can only pose upper limits of 5%-10% to the source variability, suggesting that the intense X- ray emission is due to stable structures like loops and not to flare activity.
- Publication:
-
34th COSPAR Scientific Assembly
- Pub Date:
- 2002
- Bibcode:
- 2002cosp...34E3034A