Ca II absorption in the circumstellar disk of β Pictoris and 51 Ophiuchi
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Presented here are the results of observations made of the Can Hand K absorption lines in the spectrum of the A5V star β Pictoris, a probable protoplanetary system surrounded by an edge-on circumstellar disc. At times when β Pic was low in the sky, observations were carried out on 51 Ophiuchi, which has been suggested as a possible β Pic like system. Observations were made to further test the Falling Evaporating Bodies (FEB) scenario. Significant activity was again observed, with the bulk of the spectra containing absorptions in a number of different velocity regimes, confirming the clumpy nature of the orbiting gas. The variable absorptions include a very large number of blue-shifted features generally at low relative velocities, appearing to persist for timescales of many days. A large number of long-lived low velocity red-shifted features were also observed, probably largely due to the increased instrumental stability that has been achieved. Many features were observed to last over timescales far longer than the crossing time, in the line of sight, of a single body, lending support to the idea of an infalling stream of comet-like bodies. These long-lived features were generally limited to the low-velocity features (LVFs), although a high-velocity feature at ~200 kms-¹was observed to last over 2 days. Simultaneous observations of the H and K lines have been able to confirm the presence of very high-velocity features (HVFs) lasting only the duration of a single exposure. These are also found to be narrow, shallow features rather than the broader features previously observed and predicted for HVFs. Despite the simultaneity of the H and K line observations, no unequivocal case was observed of the H line being stronger than the K line, as has been suggested when the ionic cloud occults the region of the star rotating away from us. The FEB scenario well explains most of the variable features observed. However the long-lived HVFs seen (as well as some of the LVFs) are not well explained by this scenario. The ability for a feature to last long periods of time requires either a very large number of comets on similar orbits to pass the line of sight continuously for many days or even weeks, otherwise another explanation other than solely the FEB scenario is required to explain the origin of the variations.