Extreme Ultraviolet Explorer Observations of λ Andromedae

Abstract

Extreme-ultraviolet spectra (70-740 Å) and light curves (75-175 Å) of the spectroscopic binary system λ Andromedae (HD 222107) were obtained with the Extreme Ultraviolet Explorer (EUVE) satellite in 1997 July and August. Two flares were detected during the observations that spanned 15 days, or almost 3/4 of the orbital period of 20.5 days, with a total exposure time of 283 ks. The emission measure distribution (EMD) of λ And derived from a line-based analysis shows an increasing slope with temperatures over the range logT_e (K)=6.5-7.3 as well as a remarkable narrow enhancement or ``bump'' around logT_e (K)=6.9. Both flaring and quiescent EUVE spectra were obtained. During the flares, small changes were detected in both the general slope of the EMD and the height of the bump, but the bump remained very stable in its temperature. Electron densities of logN_e (cm^-3)~12.3 are indicated at temperatures of logT_e (K)=7 using Fe XXI and Fe XXII emission features, and those densities increase to logN_e (cm^-3)~12.9 during flaring episodes.