Investigating the low-frequency stability of BiSON's resonant scattering spectrometers

Davies, Guy (2011). Investigating the low-frequency stability of BiSON's resonant scattering spectrometers. University of Birmingham. Ph.D.

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Abstract

The main focus of the thesis is the study of low-degree low-frequency solar p modes from the analysis of high-resolution power spectra generated from 20 years of high-quality data collected by the Birmingham Solar Oscillations Network (BiSON) Resonant Scattering Spectrometers (RSS). To that end we present a novel model of the RSS and its observations that allows for the determination of a significant improvement in calibration for ground-based Sun-as-a-star Doppler velocity observations. We show that the previously neglected multiple scattering in the RSS vapour cell is significant and demonstrate its impact on the spatial weighting to the solar disk, combining the new instrumental weighting with a detailed treatment of terrestrial atmospheric effects and a model of the solar surface velocity field. The resulting simulation allows for the development of a new and successful correction for differential atmospheric extinction generating up to a 25% increase in the signal-to-noise ratio at low frequencies (0.8 to 1.3 mHz). The improvement in signal to noise allows for the detection of low-frequency p modes with small associated errors in frequency and together with the fitting of mode structure, produces estimates of mode linewidth and power. Over the frequency range 972 to 1850 microHz we find the exponent of the frequency-linewidth dependence to be 7.5(0.4).

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):