The EUVE point of view of AD Leo

Abstract

All the Extreme Ultraviolet Explorer (EUVE) observations of AD Leo, totalling, 1.1 Ms of exposure time, have been employed to analyze the corona of this single M dwarf. The light curves show a well defined quiescent stage, and a distribution of amplitude of variability following a power law with a ∼-2.4 index. The flaring behavior exhibits much similarity with other M active stars like FK Aqr or YY Gem, and flares behave differently from late type active giants and subgiants. The Emission Measure Distribution (EMD) of the summed spectrum, as well as that of quiescent and flaring stages, were obtained using a line-based method. The average EMD is dominated by material at log T(K) ∼ 6.9, with a second peak around log T(K) ∼ 6.3, and a large increase in the amount of material with log T(K) ≳ 7.1 during flares, material almost absent during quiescence. The results are interpreted as the combination of three families of loops with maximum temperatures at log T(K) ∼ 6.3, ∼6.9 and somewhere beyond log T(K) ≳ 7.1. A value of the abundance of [Ne/Fe] = 1.05 ± 0.08 was measured at log T(K) ∼ 5.9. No significative increment of neon abundance was detected between quiescence and flaring states.