The Milky Way Project: Probing Star Formation with First Results on
  Yellowballs from DR2
  Yellowballs (YBs) were first discovered during the Milky Way Project
citizen-science initiative (MWP; Simpson et al. 2012). MWP users noticed
compact, yellow regions in Spitzer Space Telescope mid-infrared (MIR) images of
the Milky Way plane and asked professional astronomers to explain these "yellow
balls." Follow-up work by Kerton et al. (2015) determined that YBs likely trace
compact photo-dissociation regions associated with massive and
intermediate-mass star formation. YBs were included as target objects in a
version of the Milky Way Project launched in 2016 (Jayasinghe et al. 2016),
which produced a listing of over 6000 YB locations. We have measured distances,
cross-match associations, physical properties, and MIR colors of ~500 YBs
within a pilot region covering the l= 30 - 40 degrees, b= +/- 1 degree region
of the Galactic plane. We find 20-30% of YBs in our pilot region contain
high-mass star formation capable of becoming expanding H II regions that
produce MIR bubbles. A majority of YBs represent intermediate-mass star-forming
regions whose placement in evolutionary diagrams suggest they are still
actively accreting, and may be precursors to optically-revealed Herbig Ae/Be
nebulae. Many of these intermediate-mass YBs were missed by surveys of massive
star-formation tracers and thus this catalog provides information for many new
sites of star formation. Future work will expand this pilot region analysis to
the entire YB catalog.
