The Nature of the Massive Young Stars in W75 N

We have observed the W75 N massive star forming region in SiO ( J = 2-1 and J = 1-0) at 3''-5'' resolution and in 6 cm, 2 cm, and 7 mm continuum emission at 1 4-0 2 resolution. The abundance ratio of [SiO]/[H 2 ] ~ 5-7 × 10 -11 is typical for what is expected in the ambient component of molecular clouds with active star formation. The SiO morphology is diffuse and centered on the positions of the ultracompact H II regions—no collimated, neutral jet was discovered. The ionized gas surrounding the protostars has emission measures ranging from 1 to 15 × 10 6 pc cm -6 , densities from 0.4 to 5 × 10 4 cm -3 , and derived spectral types of the central ionizing stars ranging from B0.5 to B2. Most of the detected sources have spectral indices that suggest optically thin to moderately optically thick H II regions produced by a central ionizing star. The spread in ages between the oldest and youngest early-B protostars in the W75 N cluster is 0.1-5 × 10 6 yr. This evolutionary timescale for W75 N is consistent with that found for early-B stars born in clusters forming more massive stars ( M * > 25 M ☉ ).