Unbiased analysis shows that IRAS data reliably differentiate between the
early and late stages of stellar evolution because objects at these stages
clearly segregate in infrared color-color diagrams. Structure in these diagrams
is primarily controlled by the density distribution of circumstellar dust. The
density profile around older objects is the steepest, declining as r−2,
while young objects have profiles that vary as r−3/2 and flatter. The
different density profiles reflect the different dynamics that govern the
different environments. Our analysis also shows that high mass star formation
is strongly concentrated within \about 5 kpc around the Galactic center, in
support of other studies.Comment: 11 pages, 3 Postscript figures (included), uses aaspp4.sty. To appear
in Astrophysical Journal Letter