Origin of the Universal Correlation between the Flare Temperature and the Emission Measure for Solar and Stellar Flares.

We present a theory to explain the observed universal correlation between flare temperature T and emission measure EM=n2V for solar and stellar flares (including solar microflares observed by Yohkoh as well as protostellar flares observed by ASCA), where n is the electron density and V is the volume. The theory is based on a magnetic reconnection model with heat conduction and chromospheric evaporation, assuming that the gas pressure of a flare loop is comparable to the magnetic pressure. This theory predicts the relation EM~B-5T17/2, which explains well the observed correlation between EM and T in the range of 6x106 K < T<108 K and 1044<EM<1055 cm-3 from solar microflares to protostellar flares, if the magnetic field strength B of a flare loop is nearly constant for solar and stellar flares.