Abstract:
We present observations of the active M-dwarf binary AT Mic (dM4.5e+dM4.5e) obtained with the orbital
observatory AstroSat. During 20 ks of observations, in the far-ultraviolet (130–180 nm) and soft X-ray (0.3–7 keV)
spectral ranges, we detected both quiescent emission and at least five flares on different components of the binary.
The X-ray flares were typically longer than and delayed (by 5–6 minutes) with respect to their ultraviolet
counterparts, in agreement with the Neupert effect. Using X-ray spectral fits, we estimated the parameters of the
emitting plasma. The results indicate the presence of a hot multi-thermal corona with average temperatures in the
range of ∼7–15 MK and emission measure of ∼(2.9–4.5) × 1052 cm−3
; both the temperature and the emission
measure increased during the flares. The estimated abundance of heavy elements in the corona of AT Mic is
considerably lower than at the Sun (∼0.18–0.34 of the solar photospheric value); the coronal abundance increased
during the flares due to chromospheric evaporation. The detected flares had the energies of ∼1031–1032 erg; the
energy-duration relations indicate the presence of magnetic fields stronger than in typical solar flares.
