NGC 3105: A Young Cluster in the Outer Galaxy
  Images and spectra of the open cluster NGC 3105 have been obtained with GMOS
on Gemini South. The (i', g'-i') color-magnitude diagram (CMD) constructed from
these data extends from the brightest cluster members to g'~23. This is 4 - 5
mag fainter than previous CMDs at visible wavelengths and samples cluster
members with sub-solar masses. Assuming a half-solar metallicity, comparisons
with isochrones yield a distance of 6.6+/-0.3 kpc. An age of at least 32 Myr is
found based on the photometric properties of the brightest stars, coupled with
the apparent absence of pre-main sequence stars in the lower regions of the
CMD. The luminosity function of stars between 50 and 70 arcsec from the cluster
center is consistent with a Chabrier lognormal mass function. However, at radii
smaller than 50 arcsec there is a higher specific frequency of the most massive
main sequence stars than at larger radii. Photometry obtained from archival
SPITZER images reveals that some of the brightest stars near NGC 3105 have
excess infrared emission, presumably from warm dust envelopes. Halpha emission
is detected in a few early-type stars in and around the cluster, building upon
previous spectroscopic observations that found Be stars near NGC 3105. The
equivalent width of the NaD lines in the spectra of early type stars is
consistent with the reddening found from comparisons with isochrones. Stars
with i'~18.5 that fall near the cluster main sequence have a spectral-type A5V,
and a distance modulus that is consistent with that obtained by comparing
isochrones with the CMD is found assuming solar neighborhood intrinsic
brightnesses for these stars.
