1051 erg less: the Galactic H II region OA 184

Details 1051 erg less: the Galactic H II region OA 184 1051 erg less: the Galactic H II region OA 184

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26a...454..517f&link_type=abstract

Astronomy and Astrophysics, Volume 454, Issue 2, August I 2006, pp.517-526

Astronomy and Astrophysics

Astrophysics

10

Polarization, Ism: Supernova Remnants, H Ii Regions

Scientific paper

Aims.The identification of the object OA 184 as a Galactic Supernova Remnant (SNR) is re-examined, and evidence to the contrary is presented. The aim is to show definitively that OA 184 is actually a Galactic H II region, and to estimate some physical parameters for the nebula (e.g. temperature, density, and magnetic field in the ionized shell). Methods: .To determine the broad spectral properties of OA 184 a multiwavelength approach is used, with historical and new radio data, and existing X-ray and IR data on OA 184 considered. Radio continuum 408 and 1420 MHz Canadian Galactic Plane Survey (CGPS) data, Effelsberg 2695 MHz data, and new Urumqi 5 GHz radio observations in Stokes I, Q, and U are presented. As well, we present CGPS H I line data, and eight radio recombination lines (RRL, H103-110α) observed for this study with the Green Bank Telescope. Results: .An integrated radio spectrum of index α=-0.14 to -0.2 (S(Jy) ∝ να) is determined from four radio frequencies. RRL emission appears at vLSR=-25.8 km s-1 and at the intensity predicted for free-free thermal emission. Q and U maps at λ~6 cm show OA 184 as a depolarizing source, affecting a background filament of polarized non-thermal Galactic emission. An H II shell of thickness less than 0.2° is indicated by this depolarization. CGPS ~1-arcminute resolution H I line maps are presented, and the systemic velocity of the ISM immediately surrounding OA 184 is -26.8 km s-1. The distance of OA 184 is 2.2±0.4 kpc, obtained from a new distance method based on a Galactic H I modelling procedure. A simple model as a shell of ionized hydrogen 4 pc thick is considered, and the RRL observations are used to estimate (under conditions of non-thermodynamic equilibrium) the electron temperature Te=8300 K and density ne=5.3 cm-3. The line of sight magnetic field in the ionized shell is found to be < B∥>≃-2.5~μG (directed away from the Sun). Conclusions: .We conclude that OA 184 is a Galactic H II region energized by the lone O7.5V star BD+41°1144.

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