COmospheres and Beyond.

There is an unexpectedly cool atmospheric layer on top of the Sun's photosphere, likely present in virtually all stars of solar temperature and cooler. The main diagnostic of this mysterious layer is the $\varDelta v$ = 1 (fundamental) rovibrational band system of carbon monoxide in the thermal infrared, near 5 μm. It is thought that strong radiative cooling by the CO bands, themselves, is directly responsible for the depressed thermal structure of the cold layer, thus the moniker "COmosphere." Here, three different views of stellar COmospheres are presented: a survey of the 5 μm CO bands in late-type stars with the PHOENIX cryogenic echelle spectrometer at the Kitt Peak 2.1 m telescope; recent studies of the off-limb CO emissions in the Sun exploiting the McMath-Pierce Fourier transform spectrometer (FTS); and time-resolved integral field spectroscopy of solar surface dynamics using the Imaging Infrared Spectrograph (IRIS) and a new IR adaptive optics system, also on the McMath-Pierce at Kitt Peak. [ABSTRACT FROM AUTHOR]