Haffner 16 Redux: Revisiting a Young Cluster in the Outer Galaxy
  Images and spectra recorded with the Gemini Multi-Object Spectrograph on
Gemini South are used to investigate the stellar content of the open cluster
Haffner 16. The (i', g'-i') color-magnitude diagram (CMD) constructed from
these data samples the cluster main sequence (MS) and 5 magnitudes of the
pre-MS (PMS). The isochrones do not track the PMS on the CMD, in the sense that
the PMS has a shallower slope on the CMD than predicted by the models. Still, a
dip in star counts that is associated with the relaxation of PMS stars onto the
MS is identified near i' = 17. The depth and brightness of this feature - as
well as the morphology of the cluster MS on the CMD - are matched by models
with a slightly sub-solar metallicity that have an age ~ 20 Myr and a distance
modulus of 12.3 +/- 0.2. A light profile of Haffner 16 is constructed in the
WISE W1 filter which suggests that the cluster is surrounded by a diffuse
stellar halo. Spectra are presented of candidate cluster MS and PMS stars
selected according to location on the CMD. The spectra show characteristics
that are suggestive of a sub-solar metallicity. Halpha emission is common among
objects on the PMS locus on the CMD near i' = 18. It is suggested that the
location of the Haffner 16 PMS on the CMD is affected by large-scale cool spot
activity, likely induced by rapid stellar rotation.
