The Nature of the Massive Young Stars in W 75 N

We have observed the W75 N massive star forming region in SiO(J=2–1 & 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]/[H2] ∼ 5 − 7 × 10−11 which 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 HII regions no collimated, neutral jet was discovered. The ionized gas surrounding the protostars have emission measures ranging from 1 − 15 × 10 pc cm−6, densities from 0.4 − 5 × 10 cm−3, and derived spectral types of the central ionizing stars ranging from B0.5 to B2. Most of the detected sources have spectral indicies which suggest optically thin to moderately optically thick HII 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 years. This evolutionary timescale for W75 N is consistent with that found for early-B stars born in clusters forming more massive stars (M? > 25M ). Subject headings: circumstellar matter – jets and outflows – stars: formation – stars: mass loss – HII regions National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801 Centro de Radioastronomı́a y Astrof́ısica, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, C.P. 58089, Morelia, Mich. Mexico INAF – Osservatorio Astrofisco di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze