The galactic plane region near - I. HII region NRAO 655

Free access article

Issue		A&A Volume 367, Number 2, February IV 2001


Page(s)		635 - 651
Section		Diffuse matter in space
DOI		http://dx.doi.org/10.1051/0004-6361:20000432

A&A 367, 635-651 (2001)
DOI: 10.1051/0004-6361:20000432

The galactic plane region near $\mathsf{\ell=93^\circ}$

I. HII region NRAO 655

T. Foster¹ and D. Routledge²

¹ Dept. of Physics, University of Alberta, Edmonton, Canada
² Dept. of Electrical and Computer Engineering, University of Alberta, Edmonton, Canada

(Received 29 August 2000 / Accepted 24 November 2000)

Abstract
We present new Canadian Galactic Plane Survey radio continuum and $\lambda$ 21 cm H I line observations of NRAO 655 (G93.4+1.8), plus radio recombination line observations, and optical H $\alpha$ -line observations. The radio spectrum of NRAO 655 confirms its emission as thermal. From the $\lambda$ 21 cm H I data we find an atomic hydrogen cavity associated with this object at $v \simeq -71.5$ km s^-1. The cavity corresponds in position and size to the brightest radio continuum emission from NRAO 655. The corresponding kinematic distance is 8.8 kpc, placing NRAO 655 in the Perseus Arm. NRAO 655's linear size is therefore 70 pc $\times$ 130 pc. To confirm the $\lambda$ 21 cm H I velocity we present the first recombination line detection of NRAO 655 (H158 $\alpha$ line, $v \simeq -71$ km s^-1), and the first observations of a molecular cloud coinciding with NRAO 655 (at $v \simeq -72$ km s^-1). The first optical detection of $\lambda$ 656 nm H $\alpha$ emission line features in NRAO 655 is also presented, and the H $\alpha$ emission line brightness is determined. We suggest that the eastward extension of this strongly asymmetric object originates in a champagne outflow, and we estimate its age. We show that a single early-type star cannot be responsible for the outflow, whereas a group of later-type stars would suffice. A partial H I shell is seen adjacent to the brightest part of NRAO 655; we suggest that it has been formed by dissociation of H₂ in the molecular cloud.

Key words: HII regions -- radio continuum: ISM -- radio lines: ISM -- ISM: jets and outflows -- ISM: individual objects: NRAO 655

Offprint request: D. Routledge, routle@ee.ualberta.ca

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