Yellowballs (YBs) were first discovered during the Milky Way Project (MWP) citizen science initiative. The 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+ (2015, J/ApJ/799/153) determined that YBs likely trace compact photodissociation regions associated with massive and intermediate-mass star formation. The YBs were included as target objects in a version of the MWP launched in 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{deg}-40{deg}, b={+/-}1{deg} region of the Galactic plane. We find that ~20-30% of YBs in our pilot region contain high-mass star formation capable of becoming expanding HII 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; thus, this catalog provides information for many new sites of star formation.

Cone search capability for table J/ApJ/911/28/table1 (DR2 yellowballs (YBs))

Cone search capability for table J/ApJ/911/28/ybpilot (Yellowballs DR2 pilot region cross-matches (Table 2) and MIR photometry (Table 6))

Cone search capability for table J/ApJ/911/28/table3 (YB position, velocity, and Bayesian distance)

Cone search capability for table J/ApJ/911/28/table4 (Physical properties of YB-Hi-GAL matched sources)