Most of our knowledge of the chromosphere of the sun is based on spectral features which originate in hot plasmas. However, the chromosphere is very inhomogeneous and also contains relatively cool regions. The infrared bands from CO will be observed to study this cooler gas in the sun and other stars. Numerical simulations will be constructed to understand these observations in conjunction with observations of the hot plasma. This work will shed light on the elusive question of the source of heating of the solar chromosphere.
