Peck, LW; (2014) Technical development and scientific preparation for the e-MERLIN Cygnus OB2 radio survey. Doctoral thesis , UCL (University College London).

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Abstract

e-MERLIN is a recent upgrade to the MERLIN radio array. This enhanced facility utilises recent developments in wide bandwidth receivers, a new WIDAR correlator, and a new optical fibre network. This upgrade provides an increase in sensitivity and image fidelity, but also results in a significant increase in data volume. This thesis is motivated by the Cygnus OB2 Radio Survey (COBRaS), an e-MERLIN Legacy project observing the core region of the largest OB association in the northern hemisphere. COBRaS has been awarded ~ 300 hours observing time, resulting in a total Legacy dataset of tens of terabytes. It is not feasible to calibrate this amount of data manually, highlighting the necessity for automated procedures. This thesis primarily contains technical development for e-MERLIN during the commissioning phase and early Legacy observations from COBRaS, which focuses on the creation of automated flagging and calibration pipelines. This includes an automated RFI-mitigation and reduction tool (SERPent), as well as a full calibration pipeline consisting of: phase calibration with fringe fitting, amplitude calibration with the flux calibrator 3C286, bandpass calibration with spectral index and curvature fitting, and automated self-calibration on combined or individual IFs. A program for extracting fluxes for resolved and unresolved sources from radio maps with a detection significance boosting module has also been developed. In addition to the technical work, scientific preparations and initial results for COBRaS are also presented. A catalogue amalgamation routine for the Cyg OB2 association cross correlates previous surveys of Cyg OB2 into one definitive catalogue. Subsequent specific catalogues are compiled from this one catalogue to create an OB star catalogue and candidate catalogue. The predicted mass loss rates and radio fluxes from the winds of O-type stars and early B-type supergiants are determined, and this includes predictions from smooth wind models as well as predictions including the effects of clumping in the winds. The inclusion of an X-ray variability study of the Chandra Cyg OB2 Legacy dataset, provides a multi-wavelength view of the population of Cyg OB2, which complements COBRaS. The first COBRaS 1.6 GHz and 5 GHz radio images of Cyg OB2 are presented with source and flux lists and some initial analysis. The technical developments presented in this thesis are discussed in the context of COBRaS and of future interferometers such as the SKA and its associated pathfinders.

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