Model-Independent Diagnostics of Highly Reddened Milky Way Star
  Clusters: Age Calibration
  The next generation near- and mid-infrared Galactic surveys will yield a
large number of new highly obscured star clusters. Detailed characterization of
these new objects with spectroscopy is time-consuming. Diagnostic tools that
will be able to characterize clusters based only on the available photometry
will be needed to study large samples of the newly found objects. The
brightness difference between the red clump and the main-sequence turn-off
point have been used as a model-independent age calibrator for clusters with
ages from a few 10$^8$ to 10$^{10}$ yr in the optical. Here we apply for the
first time the method in the near-infrared. We calibrated this difference in
$K$-band, which is likely to be available for obscured clusters, and we apply
it to a number of test clusters with photometry comparable to the one that will
be yielded by the current or near-future surveys. The new calibration yields
reliable ages over the range of ages for which the red clump is present in
clusters. The slope of the relation is smoother than that of the corresponding
$V$-band relation, reducing the uncertainty in the age determinations with
respect to the optical ones.
