Serge Pineault

The supernova remnant CTA1 and the surrounding interstellar medium

Dominion Radio Astrophysical Observatory aperture synthesis observations, in the continuum at 1420 MHz and in the 21 cm line of H I, are presented of the supernova remnant (SNR) CTA 1. The angular resolution is 1 arcmin. Full sensitivity to structures of all angular sizes down to this scale has been achieved by combining the aperture synthesis observations with single-antenna data. In the continuum, in addition to the well-known bright arcs giving the SNR the appearance of an incomplete shell structure, diffuse emission can be traced to the north and northeast of the remnant and also in the southwest. Some of these faint features coincide with diffuse [O III] emission. A comparison with the 100 μm coadded IRAS image shows the presence of two cavities of low infrared emissivity adjacent to these regions

VRO 42. 05. 01 - a supernova remnant reenergizing an interstellar cavity

Radio continuum observations are presented of the supernova remnant (SNR) VRO 42.05.01 (G166.0+4.3). An earlier model of this unusual SNR is elaborated. The model depicts the SNR breaking out from a warm medium of intermediate density, in which the supernova occurred, into a hot, tenuous interstellar cavity, presumably formed by one or more previous supernovae or stellar winds. This model is now shown to be quantitatively consistent with hydrodynamical calculations of an SNR breaking out of a cloud. The SNR has renergized a section of the hot cavity of extent about 120 pc. The interface between the warm medium and the hot cavity has been excited into emission around the breakthrough point. It is argued that the linear features, of width 1 pc and length about 80 pc, which are seen crossing the SNR, are regions of this interface where the line of sight is tangential to the surface. 26 references.

Applications of Geometrical Optics to the Kerr Metric. 11. Numerical Results

Numerical integrations are performed to investigate the effects of a strong Kerr gravitational field on optical images. In addition to the well-known intensification due to gravitational focusing, the distortion and orientation of various images, and the rotation of the polarization plane, are obtained in terms of the source position. These effects are analyzed from the point of view of (a) a distant observer looking at a source in a close orbit around a Kerr black hole, and (b) a close observer looking at the distant universe. The rotation of the black hole is found to introduce interesting features which are absent in a spherical field.

Large-Scale Structure and Dynamics of Cassiopeia OB7

A large region (9° × 9°) surrounding the OB association Cassiopeia OB7 has been studied for signs of interaction between the stars and the ambient gas. A large half-shell has been detected in H I around Cas OB7, as well as in the infrared and partially in CO. This half-shell covers a range of 20 km s-1 but could reach 40 km s-1 when extrapolating to the whole shell. The structure is 120 pc across if located at 2 kpc, the distance to Cas OB7. At this distance, we estimate the mass of the shell to be approximately 30,000 M⊙. Interestingly, all Cas OB7 members are located well within the edge of this shell. We believe that there is a strong hint of interaction between the gas and the stars based on morphological evidence. The velocity of both objects (association and shell) and their respective distance are also in agreement. We explain the missing half by an expansion into the interarm region.

VLA and Effelsberg observations of the interstellar medium around the runaway star WR 124

Aims. We present very large array (VLA) and Effelsberg radio continuum and 21 cm H i line observations of the interstellar medium (ISM) surrounding the runaway star WR 124 and the nebula M 1-67. The H I data have been used to investigate the effects that a star with a strong stellar wind and a high peculiar velocity has on the ISM. Methods. The VLA 21 cm H I observations were combined with single-dish Effelsberg observations to produce a series of H I images sensitive to all angular scales from the VLA resolution limit (∼46 �� ) up to the primary field of individual VLA antennae (FWHM = 36 � ). MSX and IRIS images were used to analyze the infrared emission around the star. Because the star is highly supersonic with respect to its local ISM, the observed H I distribution around the star is interpreted in terms of a simple bow shock model. Results. The analysis of the H I data reveals the presence of a cavity centered on the star at an LSR velocity of ∼60 km s −1 , consistent with a distance estimate of 5 kpc for WR 124. A second H I cavity is observed located 10 � to the north of the stellar position, consistent with the direction of motion of WR 124. The VLA continuum image at 8.5 GHz shows a remarkable resemblance to the optical images. All available radio continuum data suggest a purely thermal spectrum for the nebula. The MSX and IRIS infrared data show a changing morphology with wavelength. The dust temperature deduced from the infrared luminosities is in agreement with previous observations of bow shocks.

Ionized gas, molecules and dust in Sh2-132

Fil: Vasquez, Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico La Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

THEORETICAL AND OBSERVATIONAL ASPECTS OF EXPANDING H I SHELLS

We have modeled H I shells expanding into a homogeneous medium in order to explain some of their observational peculiarities. Such peculiarities include difficult-to-observe caps, the presence of stationary rings, expansion velocity determination problems, inaccurate mass measurements, and a systematic discrepancy between H I missing masses and shell masses. Velocity dispersion within the shell, in the form of either thermal or turbulent motions, has been found to be the likely major cause for the absence of observable caps and the presence of stationary rings, hence explaining the apparent lack of ring transition. We discuss different methods generally used to calculate H I shell masses and show that, if one does not take into account the varying shape of the H I background local to the shell, shell masses are likely to be underestimated by a significant factor whose value depends on the relative shell thickness and the ratio of the dispersion to the expansion velocity.

Encounters between degenerate stars and extrasolar comet clouds

Under the assumption that the presence of comet clouds around otherwise normal stars is a common occurrence in the Galaxy, the observational consequences of random penetration encounters between the general Galactic population of degenerate stars and these comet clouds is considered. The only case considered is where the compact stars is a single star. For this scenario, encounters involving neutron stars (NSs) result in impact rates 1000-10,000 times slower than in the model of Tremaine and Zytkow (1986). The rate for white dwarfs (WDs) is larger than the one for NSs by a factor of about 30 times the ratio of the degenerate star number densities. The mean impact rate is significantly increased if the number of comets in a cloud is nearly independent of the mass of the central star. It is concluded that some of the observed gamma-ray bursts may be caused by accretion of comets onto NSs and that this scenario, but with a WD as the accretor, probably contributes to the optical flash background rate. 38 refs.

The Interstellar Environment of the Wolf-Rayet Star WR 143

As part of a systematic study of the environment of Galactic WR stars, a region along the line of sight to Cygnus (l = 77.5°, b = 0°) has been studied. The neutral hydrogen 21 cm line distribution shows the existence of a cavity expanding from the Wolf-Rayet star WR 143. This cavity, created by the stellar wind of the star, has a mean radius of 7 pc (assuming a distance of about 1 kpc), an expansion velocity of more than 8 km s-1, and a missing mass of some 150 M⊙ and seems to be surrounded by an H I shell, likely made up of the gas pushed by the star. Although this hole (also called bubble) is quite conspicuous in H I, there seems to be no trace of it at the other wavelengths studied (radio continuum and infrared). All radio observations were obtained at the Dominion Radio Astrophysical Observatory as part of the Canadian Galactic Plane Survey.

The radio and infrared counterparts of the ring nebula around HD 211564

We report the detection of the radio and infrared (IR) counterparts of the ring nebula around the WN3(h) star HD 211564 (WR 152), located to the south-west of the H II region Sh2 132. Using radio continuum data from the Canadian Galactic Plane Survey, we identified the radio counterparts of the two concentric rings, of about 9 and 16 arcmin in radius, related to the star. After applying a filling factor f = 0.05-0.12, electron densities and ionized masses are in the range 10-16 cm- 3 and 450-700 M ⊙ , respectively. The analysis of the H i gas emission distribution allowed the identification of 5900 M ⊙ of neutral atomic gas with velocities between -52 and -43 km s -1 probably linked to the nebula. The region of the nebula is almost free of molecular gas. Only four small clumps were detected, with a total molecular mass of 790 M ⊙ . About 310 M ⊙ are related to a small IR shell-like source linked to the inner ring, which is also detected in the MSX band A. An IRAS young stellar object candidate is detected in coincidence with the shell-like IR source. We suggest that the optical nebula and its neutral counterparts originated from the stellar winds from the Wolf-Rayet star and its massive progenitor, and are evolving in the envelope of a slowly expanding shell centred at (l, b) = (102°.30, -0°.50) of about 31 pc in radius. The bubbles energy conversion efficiency is in agreement with recent numerical analysis and with observational results.