Silvina Cichowolski

The Interstellar Medium around Galactic WN Stars: WR 2, WR 128, and WR 151

The neutral hydrogen distribution has been studied in the direction of three Galactic Wolf-Rayet (W-R) stars, using the 100 m Effelsberg radio telescope. Neutral hydrogen voids, regions of low H I emissivity, are observed over a 10–16 km s-1 velocity range for the stars WR 2 (=HD 6327), WR 128 (=HD 187282), and WR 151 (=CX Cep). These minima are interpreted as the observable 21 cm counterpart of the interstellar bubble created by the powerful winds of W-R stars and their progenitors. The H I cavities are elongated structures having an axial ratio ranging from 1.3 (WR 151) to 2.0 (WR 128). As pointed out in previous studies, the W-R stars are always off-center with respect to either the geometric center of the H I void or the absolute minimum inside the cavity. This offset ranges from 40% to 70% of the H I holes minor axis. The major axes of these cavities are ~30 pc for both WR 2 and WR 128, and ~50 pc for WR 151. The missing H I mass amounts to 96 M⊙ (WR 128), 200 M⊙ (WR 2), and 480 M⊙ (WR 151). Some of the physical parameters of the ring nebula associated with WR 128, such as its expansion velocity, 80 ± 22 km s-1, radius, 6.3 ± 0.2 pc, and characteristic age, (7.4 ± 2.4) × 104 yr, are derived from a simple geometric model that accounts for the discrepancy between the radial velocity of the H I hole and the ring nebula related to WR 128.

GSH 91.5+2-114: A large H i shell in the outer part of the Galaxy

GSH 91.5 + 2 - 114 is a large HI shell located in the outer Galaxy at a kinematic distance of about 15 kpc. It was first identified in the Canadian Galactic Plane Survey (CGPS) by Pineault et al. (2002, ASP Conf. Ser., 276, 332) as being possibly associated with objects possessing infrared colors, which indicates strong stellar winds. The H I shell has no obvious continuum counterpart in the CGPS radio images at 408 and 1420 MHz or in the IRAS images. We found no evidence for early-type massive stars, most likely as a result of the large extinction that is expected for this large distance. An analysis of the energetics and of the main physical parameters of the H I shell shows that this shell is likely the result of the combined action of the stellar winds and supernova explosions of many stars. We investigate whether a number of slightly extended regions characterized by a thermal radio continuum and located near the periphery of the HI shell could be the result of star formation triggered by the expanding shell.

Radio observations of interstellar bubbles surrounding massive stars

We show radio continuum observations of the WR ring nebulae around WR 101 and WR 113 obtained using the VLA and HI 21em line data of the interstellar bubble around the 0 type stars BD +24 3866 and BD+25° 3952 obtained with the DRAO Synthesis Telescope. We review previous .radio continuum and H I line results toward WR and O-type stars.