Abstract
Diffraction limited near-infrared H-band
(1.6 μm) NICMOS HST
images are scheduled to be obtained in mid-October
1997 of the young cluster NGC 2070 (age 3.5 Myr)
in the 30 Dor giant HII region in the LMC. The aim
is to search for the low-mass (M < 2
Mʘ) low-luminosity, red
pre-Main Sequence stellar population and to
establish the H-band infrared luminosity function.
With the NICMOS we can now determine whether the
IMF in this prototypical extragalactic starburst
cluster is deficient in subsolar low-mass stars or
not. The best ground-based data can sample only M
> 2 Mʘ. In principle,
NICMOS in the H-band (F160W) is sensitive enough
to reach a magnitude of ~ 23.5 in a relatively
short integration time, which indeed corresponds
to the fantastic possibility to detect young
stellar objects with masses near the hydrogen
burning limit (M=0.1 Mʘ)
according to pre-Main Sequence evolutionary
models. Even if we could reach only H = 22.5 (i.e.
M=0.4 Mʘ), our observations
will still go a long way in directly answering, by
star counts, whether the IMF in starburst galaxies
is low-mass deficient or not, with all the
corresponding far-reaching implications.
The observations would also tell us
whether the 30 Dor cluster can be regarded as a
prototype young globular cluster. This possibility
would be ruled out, if we found NGC 2070 to be
low-mass deficient, because old globular clusters
do have a rich population of low-mass
stars.