The Milky Way Project: Probing Star Formation with First Results on Yellowballs from DR2

TL;DR

This study analyzes yellowballs identified in the Milky Way Project, revealing their role in star formation, especially in intermediate-mass regions, and providing new insights into their properties and evolutionary stages.

Contribution

First detailed characterization of yellowballs from DR2, linking them to star formation stages and expanding the catalog of star-forming regions in the Milky Way.

Findings

20-30% of YBs contain high-mass star formation regions.

Most YBs are intermediate-mass star-forming regions still actively accreting.

Many YBs are new sites of star formation missed by previous surveys.

Abstract

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.