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]/[H2]~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 15×106 pc cm-6, densities from 0.4 to 5×104 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 0.1-5×106 yr. This evolutionary timescale for W75 N is consistent with that found for early-B stars born in clusters forming more massive stars (M*>25Msolar).
Shepherd D, Kurtz S, Testi L (2004). The Nature of the Massive Young Stars in W75 N. THE ASTROPHYSICAL JOURNAL, 601, 952-961.
The Nature of the Massive Young Stars in W75 N
Testi L
2004
Abstract
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]/[H2]~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 15×106 pc cm-6, densities from 0.4 to 5×104 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 0.1-5×106 yr. This evolutionary timescale for W75 N is consistent with that found for early-B stars born in clusters forming more massive stars (M*>25Msolar).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
