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Radio emission at centimetre and millimetre wavelengths provides a powerful tool for studying the circumstellar envelopes of evolved stars. These include stars on the asymptotic giant branch (AGB), post-AGB stars and a small number of massive M-type supergiant stars. The AGB stars and M-type supergiants are characterised by extremely high mass-loss rates. The mass loss in such an evolved star is driven by radiation pressure acting on grains which form in the outer stellar atmosphere. The grains are accelerated outwards and transfer momentum to the gas through grain–gas collisions. The outflowing dust and gas thus form an expanding circumstellar envelope through which matter flows from the star to the interstellar medium, at a typical velocity of 15 km s−1. For a recent review of circumstellar mass loss see Chapman, Habing & Killeen (1995).
III Zw 35 is a pair of galaxies characterised by intense OH maser emission, and powerful far-infrared and radio continuum. We have made a detailed study of the galaxy pair based on optical, infrared and radio observations. The brighter northern component is identified as a LINER or Seyfert galaxy and contains an active nuclear region from which radio continuum, OH maser and thermal dust emission are detected. We propose that the northern component has a compact active nucleus deeply embedded in an obscured region of diameter ~ 210 pc within which enhanced star-formation occurs. The lower luminosity, southern component is of low mass and is undergoing starburst activity over an extended region of diameter ~ 5.5 kpc. The origin of the starburst and non-thermal activity appears to be an interaction between the two components.
IAU Commission 40 for Radio Astronomy (hereafter C40) brought together scientists and engineers who carry out observational and theoretical research in radio astronomy and who develop and operate the ground and space-based radio astronomy facilities and instrumentation. As of June 2015, the Commission had approximately 1,100 members from 49 countries, corresponding to nearly 10 per cent of the total IAU membership.
The Parkes 64-m telescope was used to study the OH mainline polarisation properties at 1665 and 1667 MHz for a sample of 36 evolved stars, identified by their far-infrared and OH 1612 MHz maser properties as likely post-AGB stars.
This triennium has seen a phenomenal investment in development of observational radio astronomy facilities in all parts of the globe at a scale that significantly impacts the international community. This includes both major enhancements such as the transition from the VLA to the EVLA in North America, and the development of new facilities such as LOFAR, ALMA, FAST, and Square Kilometre Array precursor telescopes in Australia and South Africa. These developments are driven by advances in radio-frequency, digital and information technologies that tremendously enhance the capabilities in radio astronomy. These new developments foreshadow major scientific advances driven by radio observations in the next triennium. We highlight these facility developments in section 3 of this report. A selection of science highlight from this triennium are summarized in section 2.
We present the morphology and linear polarization of the 22-GHz H2O masers in the high-velocity outflow of two post-AGB sources, d46 (IRAS 15445–5449) and b292 (IRAS 18043–2116). The observations were performed using The Australia Telescope Compact Array. Different levels of saturated maser emission have been detected for both sources. We also present the mid-infrared image of d46 overlaid with the distribution of the maser features that we have observed in the red-shifted lobe of the bipolar structure. The relative position of the observed masers and a previous radio continuum observation suggests that the continnum is produced along the blue-shifted lobe of the jet. It is likely due to synchrontron radiation, implying the presence of a strong magnetic field in the jet. The fractional polarization levels measured for the maser features of d46 indicate that the polarization vectors are tracing the poloidal component of the magnetic field in the emitting region. For the H2O masers of b292 we have measured low levels of fractional linear polarization. The linear polarization in the H2O maser region of this source likely indicates a dominant toroidal or poloidal magnetic field component.
The business meeting of Division X in the IAU 2009GA took place in three sessions during the day of August 6, 2009. The meeting, being well attended, started with the approval for the meeting agenda. Then the triennium reports were made in the first session by the president of Division X, Ren-Dong Nan, and by the chairs of three working groups: “Historic Radio Astronomy WG” by Wayne Orchiston, “Astrophysically Important Lines WG” by Masatoshi Ohishi, and “Global VLBI WG” by Tasso Tzioumis (proxy chair appointed by Steven Tingay). Afterwards, a dozen reports from observatories and worldwide significant projects have been presented in the second session. Business meeting of “Interference Mitigation WG” was located in the third session.
Division X provides a common theme for astronomers using radio techniques to study a vast range of phenomena in the Universe, from exploring the Earth's ionosphere or making radar measurements in the Solar System, via mapping the distribution of gas and molecules in our own Galaxy and in other galaxies, to study the vast explosive processes in radio galaxies and QSOs and the faint afterglow of the Big Bang itself.
We present results of the Australia Telescope Compact Array (ATCA) radio continuum observations of massive stars in the Sco OB1 association. Most stars detected in the program show spectral indices lower than value expected from thermal free-free emission.
The ATCA/VLA Galactic Plane survey detected OH 1612 MHz maser emission from a total of 766 sources. In most cases the detected sources have double-peaked spectral profiles which are characteristic of OH/IR stars. A small number of sources however have irregular spectra and uncertain classifications. We discuss the maser results for two sources with irregular OH spectra, D046 (OH 326.5-0.4) and B292 (OH009.1-0.4). For B292 we detected OH 1720 MHz emission - a transition previously unknown for evolved stars. D046 has exceptionally broad maser profiles and strong non-thermal radio continuum emission. Both are likely to be bipolar post-AGB sources.
Post-AGB sources can be identified from their MSX far-infrared properties. For the ATCA/VLA OH-selected sample, most of the likely post-AGB stars do not have unusual OH 1612 MHz spectra.
We have used the Australia Telescope Compact Array to search for radio continuum emission at λ 3, 6, 13 and 20 cm from a distance-limited sample of 36 southern Wolf-Rayet stars within 3 kpc of the Sun. The observations were taken between 1994 and 1997. Radio continuum emission has been detected from 16 sources at 3 cm. Of these 11 sources were detected at 6 cm, seven sources were detected at 13 cm and 2 sources were detected at 20 cm (Chapman et al. 1999).
We have begun a co-ordinated programme of high angular-resolution radio and infrared measurements to study the physical structure of the circumstellar envelopes surrounding high mass-loss OH-stars. Here we give near-infrared (NIR) angular diameters for 5 stars. For each of these stars the spatial distribution of the OH maser emission at 1612 MHz or 1665 MHz has been previously mapped.
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