Hydrodynamic Modeling of a Flare Loop Connecting the Accretion Disk and Central Core of Young Stellar Objects

Abstract

Many young stellar objects, such as protostars and T-Tauri stars, show strong flare activity. In this paper we present a hydrodynamic simulation of a flare loop that connects the central star and the accretion disk, and discuss the evaporation of the chromosphere of the central star and the disk. We assumed a long ( >10R☉) loop length, and that the flare energy is deposited near the half-way point between the disk and the stellar surface. We found that in some cases all of the plasma in the accretion disk is heated to the flare temperature and spreads over the flare loop. The condition for this ``disk disappearance'' was examined. The X-ray spectrum expected when we observe the simulation result was synthesized by taking into account the instrumental response of ASCA/GIS. However, we could not find any clear observational signature of the existence of the disk, because the bulk properties of a flare loop are determined by the flare heating flux and loop length, and not by the involvement of the disk. We found that the synthesized spectrum is reasonably fitted with a two-temperature model, and that the temperature of the hotter component is several factors lower than the maximum temperature of the simulation result.