Searching for Infall: Aperture Synthesis HCO +(1--0) and SiO(2--1) Observations of the G45.47+0.05 Region

Details Searching for Infall: Aperture Synthesis HCO +(1--0) and SiO(2--1) Observations of the G45.47+0.05 Region Searching for Infall: Aperture Synthesis HCO +(1--0) and SiO(2--1) Observations of the G45.47+0.05 Region

May 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...462..339w&link_type=abstract

Astrophysical Journal v.462, p.339

Astronomy and Astrophysics

Astronomy

13

Ism: H Ii Regions, Ism: Individual Alphanumeric: G45.47+0.05, Ism: Kinematics And Dynamics, Ism: Molecules, Radio Lines: Ism

Scientific paper

We report 5" resolution observations of the HCO+(1-0) and SiO(2-1) lines toward the G45.47+0.05 ultracompact H II region obtained with the OVRO millimeter array. We find no evidence for the spherical infall suggested by inverse P Cygni profiles observed in high-excitation NH3 lines at 40" resolution. Instead, we find multiple velocity components in HCO+ and SiO emission that suggest the presence of a protocluster of OB stars. We speculate that emission and absorption from separate sites of activity in the region conspire to mimic the inverse P Cygni infall signature. However, the observations do not entirely rule out a collapse localized to the ultracompact H II region, since absorption in the HCO+(1-0) line from low-excitation foreground gas may mask emission at velocities associated with infalling material. A new VLA 8.4 GHz D-array observation shows that the nearby "cometary" ultracompact H II region G45.45 +0.06 lies within the northwest wall of an ionized shell with ˜30" diameter. Unfortunately, this bright source within the VLA field of view precluded a search for faint centimeter continuum sources associated with the molecular line peaks.

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