Stars are generally characterized by a decrease in their temperature from the interior (where the temperature is typically millions of degrees Kelvin) to the surface (where the temperature is thousands or tens of thousands of degrees Kelvin). In the sun and other stars with surface (i.e., photospheric) temperatures of roughly 6000 K and less the temperature rises sharply in the transparent, outermost layers due to energy deposited from magnetic surface activities. In the sun, the region in which the temperature starts rising has traditionally been known as the chromosphere. More recently, the processes giving rise to this temperature inversion have been called the "molecular cooling catastrophes" because radiative cooling by CO and other molecules appears to be responsible for it. The Principal Investigator (PI) proposes to study the regions of temperature inversion in the atmospheres of late-type stars and compare them to those of the sun. The observational input data will be spatially-unresolved spectra of these stars, which the PI and his collaborators have accumulated over the past three years. This data will be processed by computer codes capable of solving the molecular non-local thermodynamic equilibrium (NLTE) problem.
