ABSTRACT
Multiaperture observations of the H2O absorption feature near
2.0 microns
are presented for the nuclei of 37 early-type galaxies, 5 globular clusters,
and for a selection of stars. The H2O absorption is a sensitive
function of effective temperature, and provides a strong constraint on the
contribution of
the very coolest stars to integrated galaxian light. In combination with the
luminosity-sensitive CO absorption, the large H2O absorption
found in galaxies indicates that at two microns a significant
contribution from a stellar giant
component at least as late as M5 in spectral type is present. For our
limited data sample, the amount of H2O absorption shows no
dependence on absolute magnitude for galaxies with
MV 
- 20,
and no dependence on projected aperture size in the range
1.0 
A / D(0)
0.1. The observations are
compared with
recently published synthesis models of Tinsley and Gunn and of O'Connell;
better agreement is found with the latter author's models. It does not
appear that a significant contribution of carbon stars can account for the
discrepancy between the infrared data and the models of Tinsley and Gunn.