A very large array 3.6 centimeter continuum survey of galactic wolf-rayet stars

Abstract

We report the results of a survey of radio continuum emission of Galactic Wolf-Rayet (WR) stars north of δ = -46°. The observations were obtained at 8.46 GHz (3.6 cm) using the Very Large Array, with an angular resolution of ∼6″ × 9″ and typical rms noise of ∼0.04 mJy beam -1 . Our survey of 34 WR stars resulted in 15 definite, and five probable detections, 13 of these for the first time at radio wavelengths. All detections are unresolved (θ ≲ 5″). Time variations in flux are confirmed in the cases of WR 98a, 104, 105, and 125. WR 79a and WR 89 are also variable in flux, and we suspect they are also nonthermal emitters. Thus, of our sample 20%30% of the detected stars are nonthermal emitters. Average mass-loss rate determinations obtained excluding definite and suspected nonthermal cases give similar values for WN (all subtypes) and WC5-7 stars [M(WN) = (4 ± 3) × 10 -5 M ⊙ yr -1 and M(WC5-7) = (4 ± 2) × 10 -5 M× yr -1 ], while a lower value was obtained for WC8-9 stars [M(WC8-9) = (2 ± 1) × 10 -5 M ⊙ yr -1 ]. Uncertainties in stellar distances largely contribute to the observed scatter in mass-loss rates. Upper limits to the mass-loss rates were obtained in cases of undetected sources and for sources that probably show additional nonthermal emission.