  Molecular absorption lines of OH (99 lines) and CH (105 lines) are measured
for the carbon-enhanced metal-poor star BD+44 493 with [Fe/H]=-3.8. The
abundances of oxygen and carbon determined from individual lines based on an
1D-LTE analysis exhibit significant dependence on excitation potentials of the
lines; d log e/d chi ~ -0.15 - -0.2 dex/eV, where e and chi are elemental
abundances from individual spectral lines and their excitation potentials,
respectively. The dependence is not explained by the uncertainties of stellar
parameters, but suggests that the atmosphere of this object possesses a cool
layer that is not reproduced by the 1D model atmosphere. This result agrees
with the predictions by 3D model calculations. Although absorption lines of
neutral iron exhibit similar trend, it is much weaker than found in molecular
lines and that predicted by 3D LTE models.
