Description of source "g21A" from Chambers et al. (2011)

Single SED fits were performed for most green sources (Y-Z09), but g21 was best fit by two sources, designated g21A (11.8 ± 2.5 M_0) and g21B (23.8 ± 6.6 M_0). These sources are seen as distinct lobes of 4.5 µm emission in Figure 21, and appear to be in the same star-forming region, which is foreground to the Galactic center and in the vicinity of RCW 137. Like many of the other green sources, g21A and g21B are associated with an IRDC and are coincident with 24 µm emission. There is one 6.7 GHz maser that is located <10 arcsec from g21A and g21B (7 arcsec and 1 arcsec, respectively). Because it is closer to g21B, we associate the maser with that source. This maser consists of a single, bright emission feature at 23 km s−1 in the C10 data. No 44 GHz masers are detected toward either of the g21 sources.