Resolved spectral variations of the centimetre-wavelength continuum from the ρ Oph W photodissociation region

Centimetre-wavelength radio continuum emission in excess of free–free, synchrotron, and Rayleigh–Jeans dust emission (excess microwave emission, EME), and often called ‘anomalous microwave emission’, is bright in molecular cloud regions exposed to UV radiation, i.e. in photodissociation regions (PDRs). The EME correlates with infrared (IR) dust emission on degree angular scales. Resolved observations of well-studied PDRs are needed to compare the spectral variations of the cm-continuum with tracers of physical conditions and of the dust grain population. The EME is particularly bright in the regions of the ρ Ophiuchi molecular cloud (ρ Oph) that surround the earliest type star in the complex, HD 147889, where the peak signal stems from the filament known as the ρ Oph W PDR. Here, we report on Australia Telescope Compact Array observations of ρ Oph W that resolve the width of the filament. We recover extended emission using a variant of non-parametric image synthesis performed in the sky plane. The multifrequency 17–39 GHz mosaics reveal spectral variations in the centimetre-wavelength continuum. At ∼30 arcsec resolutions, the 17–20 GHz intensities tightly follow the mid-IR, $I_\mathrm{cm} \propto I(8\, \mu$m), despite the breakdown of this correlation on larger scales. However, while the 33–39 GHz filament is parallel to Infrared Array Camera 8 μm, it is offset by 15–20 arcsec towards the UV source. Such morphological differences in frequency reflect spectral variations, which we quantify spectroscopically as a sharp and steepening high-frequency cutoff, interpreted in terms of the spinning dust emission mechanism as a minimum grain size $a_\mathrm{cutoff} \sim 6 \pm 1\,$Å that increases deeper into the PDR

The History of Astrophysics in Antarctica

We examine the historical development of astrophysical science in Antarctica from the early 20th century until today. We find three temporally overlapping eras, each having a rather distinct beginning. These are the astrogeological era of meteorite discovery, the high energy era of particle detectors, and the photon astronomy era of microwave, sub--mm and infrared telescopes, sidelined by a few niche experiments at optical wavelengths. The favourable atmospheric and geophysical conditions are briefly examined, followed by an account of the major experiments and a summary of their results.Comment: 29 pages, 10 figures, 1 table Submitted to PASA in April 200

An ultra-wide bandwidth (704 to 4 032 MHz) receiver for the Parkes radio telescope

We describe an ultra-wide-bandwidth, low-frequency receiver recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band ( ${∼}60$ ), the system temperature is approximately 22 K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver, including its astronomical objectives, as well as the feed, receiver, digitiser, and signal processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified, including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration, and timing stability

Water vapour radiometers for the Australia telescope compact array

In the millimetre wavelength regime of the electromagnetic spectrum used in radio astronomy, poorly mixed pockets of precipitable water vapourcause a change in the refractive index of the atmosphere, thereby inducing an excess path that the signal must travel through. This results in aphase delay for antennae receiving an astronomical signal. In an interferometer such as the Australia Telescope Compact Array (ATCA),variations in phase delay between the antennae thus lead to degradation in the image quality obtainable due to signal decorrelation. This phasefluctuation induced noise increases both with frequency and baseline length. It therefore also puts upper limits on the usable length of baselineswithout experiencing significant decorrelation, thus limiting the spatial resolution of the interferometer.I have developed Water Vapour Radiometers (WVRs) for the ATCA that are capable of determining excess path fluctuations by virtue ofmeasuring small temperature fluctuations in the atmosphere using the 22.2 GHz water vapour line for each of the six antennae. By measuring theline of sight variations of the water vapour, the induced path excess and thus the phase delay can be estimated and corrections can then beapplied during data reduction. This reduces decorrelation of the source signal. I demonstrate how this recovers the telescope's efficiency andimage quality as well as how this improves the telescope's ability to use longer baselines at higher frequencies, thereby resulting in higher spatialresolution.The design process of the WVRs is discussed, including a review of three other WVR systems for comparison with our system design. A detailedsite characterisation is provided with emphasis on millimetre observing conditions and it is determined to what extent WVRs can improve telescopedata. A thorough examination of the frequency space used for the WVRs follows in order to avoid and detect radio frequency interference of bothterrestrial and orbital origin. A detailed description of the WVR hardware design is given and concludes with a detailed account of the atmosphericmodelling and water vapour retrieval mechanisms I have developed. The thesis concludes with a list of future opportunities and developments toimprove the existing WVR system