Radio astronomy techniques : the use of radio instruments from single dish radio telescopes to radio interferometers

摘要

New radio telescopes under development, will significantly enhance the capabilitiesof radio astronomy in the Southern Hemisphere. South Africa, inparticular, is actively involved in the development of a new array (MeerKAT)as well as in the expansion of existing very long baseline interferometer arraysin the south. Participation in these new developments demands a thoroughunderstanding of radio astronomy techniques, and data analysis, and thisthesis focusses on two projects with the aim of gaining such experience.The Southern Hemisphere very long baselines array is not well servedwith calibrator sources and there are significant gaps in the present calibratordistribution on the sky. An adequately dense, well distributed, set of strong,compact calibrator or reference sources is needed. With this in mind, observationsusing the Southern Hemisphere long baseline array were conducted toinvestigate a sample of candidate calibrator sources. The compactness of thesources was investigated and new potential calibrators have been identified.Single antenna radio spectroscopy of OH masers has identified sourcesof 1720 MHz emission associated with supernova remnants at the shock interfacebetween the expanding supernova remnant and a molecular cloud.Models indicate that these masers are shock excited and can only be producedunder tight physical constraints. Outows from newly-formed starscreate nebulous regions known as Herbig-Haro objects when they interactwith the surrounding medium, and these regions are potentially similar tothose seen in supernova remnants. If conditions behind the shock fronts ofHerbig-Haro objects are able to support 1720-MHz OH masers they couldbe a useful diagnostic tool for star formation. A survey toward Herbig-Haroobjects using a single-dish radio telescope did detect 1720-MHz OH lines inemission, but neither their spectral signature nor follow-up observations withthe Very Large Array showed evidence of maser emission.