  In our previous paper, we have presented a theory to explain the observed
universal correlation between the emission measure ($EM=n^2 V$) and temperature
(T) for solar/stellar flares on the basis of the magnetic reconnection model
with heat conduction and chromospheric evaporation. Here n is the electron
density and V is the volume. By extending our theory to general situations, we
examined the EM-T diagram in detail, and found the following properties: 1) The
universal correlation sequence (``main sequence flares'') with $EM \propto
T^{17/2}$ corresponds to the case of constant heating flux or equivalently the
case of constant magnetic field strength in the reconnection model. 2) The EM-T
diagram has a forbidden region, where gas pressure of flares exceeds magnetic
pressure. 3) There is a coronal branch with $EM \propto T^{15/2}$ for $T< 10^7$
K, and $EM \propto T^{13/2}$ for $T> 10^7$ K. This branch is situated left side
of the main sequence flares in the EM-T diagram. 4) There is another forbidden
region determined by the length of flare loop; a lower limit of flare loop is
$10^7$ cm. Small flares near this limit correspond to nanoflares observed by
SOHO/EIT. 5) We can plot flare evolution track on the EM-T diagram. A flare
evolves from the coronal branch to main sequence flares, then returns to the
coronal branch eventually. These properties of the EM-T diagram are similar to
those of the HR diagram for stars, and thus we propose that the EM-T diagram is
quite useful to estimate the physical quantities (loop length, heating flux,
magnetic field strength, total energy and so on) of flares and corona when
there is no spatially resolved imaging observations.
