A Cold HII Region in the Molecular Globule G70.7+1.2

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Session 60 -- HII Regions
Display presentation, Thursday, 9:20-4:00, Pauley Room

[60.09] A Cold HII Region in the Molecular Globule G70.7+1.2

J.A. Phillips (Caltech), J.S. Onello (SUNY), S.R. Kulkarni (Caltech)

We have observed an unusual $\lambda$22 cm radio recombination line from the molecular globule G70.7+1.2 using the Arecibo radio telescope and have mapped the radio nebula at 99 GHz with the Owens Valley millimeter interferometer. The H168$\alpha$ spectrum is dominated by a narrow emission line (FWHM 3 km/s) from gas cooler than 185 K, which makes G70.7+1.2 the coolest known HII region. Energy balance arguments suggest that the cold gas was ionized $\lsim 100$ years ago. Recent work shows that a B[e] emission line star is moving through the molecular cloud at supersonic velocity and is preceded by a bow shock typical of compact, cometary HII regions. Aperture synthesis mapping revealed continuum emission from the bow shock and from an HII region of $\sim 0.1$ pc diameter near the emission line star. We speculate that the narrow recombination line could emanate from cold, ionized gas upstream from the bow shock or that the line may originate in a shell of newly ionized gas around a young and growing HII region.

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