Presented in this thesis is an analysis of absorption features identified in Ca II H & K absorption profiles obtained via observations taken of β Pic at the University of Canterbury Mount John Observatory (UC MJO) using the 1.0m McLellan telescope equipped with the HERCULES spectrograph and the Fairchild 486 back-illuminated CCD in 2017.

This study mainly focused on analysing the absorptions identified across 2017 by analysing the median spectrum for a night. However, for the specific night of the 3rd of December 2017, the sequence of spectra obtained on the night were fitted individually to gain an insight into the variability of the different features throughout the course of the night.

Significant activity was observed, with the bulk of the spectra containing absorptions in a number of different velocity regimes, confirming the clumpy nature of the orbiting gas. A large number of blue-shifted features with a range of velocities were observed, while some features with high blue-shift velocities (< −40 km s₋¹) were also observed which could last over several successive days. Low velocity features (LVFs; v < 40 km s₋¹), which were responsible for an asymmetric broadening of the stable, deep circumstellar feature, were observed on successive nights. This supported the predictions of the “Falling Evaporating Bodies” (FEB) scenario by Beust et al.(1990) [1] regarding the long possible lifetime of the LVFs (on the order of days). While several high velocity features (HVFs; v > 40 km s₋¹) were identified, only one HVF was identified on two consecutive nights (on the 5th December to 6th December 2017) with sufficiently close radial velocities and widths (measured by the Full Width at Half Maximum (FWHM)). This feature is not well-explained by the FEB scenario. The HVFs identified on the night of 3rd of December 2017 were present throughout the course of the night which supported the FEB model’s prediction that HVFs have a lifetime on the order of hours.

The predictions of the FEB scenario were also supported in regards to the ex- pected increase in the FWHM of the features with an increase in radial velocity and also the expected decrease in the depths of the features with an increase in radial velocity. These results agreed well with similar studies carried out by previous authors such as Lagrange-Henri et al. (1996) [2], Petterson et al. (1999) [3] and Persson et al. (1998) [4] as was discussed by these authors. It was found that the LVFs (v < 40 km s₋¹) had the highest depths of the absorption features and also could have very

high coverage of the stellar disk, as shown by the high filling factors (approaching unity). Some features in the velocity regime (40−60 km s−1) were also found to have high depths and filling factors. HVFs with velocities beyond 60 km s−1 were found to be restricted mainly to low depths. This agreed with the findings of Petterson et al. (1996) [5] and Persson et al. (1998) [4], but as some HVFs lying in the velocity range of 40 − 60 km s−1 were found to have high depths in this study, this did not agree with the published studies of Lagrange-Henri et al. (1996) [2] and Petterson et al. (1999) [3] who found all HVFs (v > 40 km s₋¹) restricted to low depths. With the exception of the HVF which lasted on consecutive nights, the FEB scenario well explains most of the variable features observed.

A plot of the absorption depth against the surface ratio,α, produced by Kiefer et al. (2014) [6] claimed that there were two families of exocomets around β Pic. However, perhaps due to insufficient quality data, no major clustering of points was observed in our data based on the two depth regimes (pK < 0.4 and pK > 0.4) and we could not verify this aspect of the analysis by Kiefer et al. (2014).

Due to a predicted β Pic b Hill sphere transit event in 2017, predicted from April 2017 to January 2018 (Wang et al. 2016), Ca II H & K absorption profiles collected within this time period were analysed to look for any effects of this transit. It was hypothesised that the Hill sphere transit could have an impact on the depth of the circumstellar feature due to density variations of circumstellar material, or the frequency of exocometary transits due to perturbations induced by the gravitational field of the planet or the planet’s possible satellites. However, no discernible effect was seen on the depth of the circumstellar feature when compared to the study conducted by Barnes et al. (2000) [7], or on the rate of exocometary transits when compared to the studies by Lagrange-Henri et al.(1996) [2],Barnes et al. (2000) [7] and Kiefer et al. (2014) [6] who conducted their studies when a β Pic b Hill sphere transit was not predicted.