CCD polarimetry as a probe of regions of recent star-formation

Abstract

Chapter 1 of this thesis details the incorporation of a Charged Coupled Device (CCD) detector system with the Durham Imaging Polarimeter. The details include the physical characteristics of the device and the electronics and software associated with the device control and data storage. The introduction of the CCD detector system haa made necessary the inclusion of a super-achromatic half-wave plate in the polarimeter which has an inherent variability in its optic axis. Chapter 2of this work describes fully how suitable corrections for this effect can be made, and derives "first order" results. The CCD performance is examined in comparison with the detector used previously and hence the veracity of the new results is established. Chapter 3 is a relevant summary of the status of the astronomy of the immediate regions of recent star-formation. Chapter 4 describes multicolour polarimetry of NGC2261/R Mon covering the period 1979 to 1986. The data conclusively proves that the polarisation of R Mon must be due to effects close to R Mon (~ 14 astronomical units). This is evident because of the dynamic timescale of the variations of the polarisation of R Mon and the anomalous band of polarisations seen across the head of the nebula. The interpretation presented is an extension of the Elsasser and Staude (1978) method of polarising objects embedded within the confines of a nearly edge-on disk. Detailed polarisations within the main nebula body provide evidence for this extended interpretation and also for an extensive helical magnetic field which may extend into the disk. Also it is seen that R Mon must still be "shrouded" in material preventing light from directly reflecting in the main nebula body. It is not thought that the variations in the region close to R Mon are due to planetary bodies but to accretion from the disk. The results of this re-interpretation of the polarising mechanism are tentatively applied to other similar objects.