  Near-IR spectra for a sample of 31 elliptical galaxies in the Coma cluster
are obtained. The galaxies are selected to be ellipticals (no lenticulars),
with a large spatial distribution, covering both the core and outskirt of the
cluster (ie. corresponding to regions with large density contrasts).
Spectroscopic CO (2.3 micron) absorption indices, measuring contribution from
intermediate-age red giant and supergiant stars to the near-IR light of the
ellipticals, are then estimated.
  It is found that the strength of spectroscopic CO features in elliptical
galaxies increases from the core (r < 0.2 deg) to the outskirts (r > 0.2 deg)
of the Coma cluster. Using the Mg2 strengths, it is shown that the observed
effect is not due to metallicity and is mostly caused by the presence of a
younger population (giant and supergiant stars) in ellipticals in outskirts
(low density region) of the cluster.
  Using the spectroscopic CO features, the origin of the scatter on the near-IR
Fundamental Plane of elliptical galaxies is studied. Correcting this relation
for contributions from the red giant and supergiant stars, the rms scatter
reduces from 0.077dex to 0.073dex. Although measurable, the contribution from
these intermediate-age stars to the scatter on the near-IR Fundamental Plane of
ellipticals is only marginal.
  A relation is found between the CO and V-K colours of ellipticals with a
slope 0.036 +/- 0.016. This is studied using stellar synthesis models.
