SIMBAD references

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 HII region, and to estimate some physical parameters for the nebula (e.g. temperature, density, and magnetic field in the ionized shell). 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 1420MHz Canadian Galactic Plane Survey (CGPS) data, Effelsberg 2695MHz data, and new Urumqi 5 GHz radio observations in Stokes I, Q, and U are presented. As well, we present CGPS HI line data, and eight radio recombination lines (RRL, H103-110α) observed for this study with the Green Bank Telescope. An integrated radio spectrum of index α=-0.14 to -0.2 (S(Jy)∝ν^α) is determined from four radio frequencies. RRL emission appears at v_LSR=-25.8km/s and at the intensity predicted for free-free thermal emission. Q and U maps at λ 6cm show OA 184 as a depolarizing source, affecting a background filament of polarized non-thermal Galactic emission. An HII shell of thickness less than 0.2° is indicated by this depolarization. CGPS ∼1-arcminute resolution HI line maps are presented, and the systemic velocity of the ISM immediately surrounding OA 184 is -26.8km/s. The distance of OA 184 is 2.2±0.4kpc, obtained from a new distance method based on a Galactic HI modelling procedure. A simple model as a shell of ionized hydrogen 4pc thick is considered, and the RRL observations are used to estimate (under conditions of non-thermodynamic equilibrium) the electron temperature T_e=8300K and density n_e=5.3cm^–3. The line of sight magnetic field in the ionized shell is found to be <B_||≥~-2.5µG (directed away from the Sun). We conclude that OA 184 is a Galactic HII region energized by the lone O7.5V star BD+41°1144.