CaII absorption in the circumstellar disk of Beta Pictoris and other A-type stars
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Presented here are the results of observations made at the Mount John Observatory (MJUO) during the spectroscopic campaigns to observe beta Pictoris in 1992, 1993, 1994 and observations conducted in 1995 to characterise the behaviour of the Ca II H and K lines and to test the Falling Evaporating Bodies scenario. Using the method of division by a reference spectrum both narrow and broad variable absorption features in both the redshifted and blue shifted sides of the Ca II H and K lines are clearly detected. The large data set obtained allows the determination of the evolution in terms of velocity, equivalent width, FWHM and timescales of variability of the variable absorption features. These are then compared with the results on Lagrange-Henri et al. (1996) in their paper on the 1992 observing campaign.
Lagrange-Henri et al. find that there are 2 velocity regimes and this is confirmed in the MJUO data. The higher the redshift, the smaller the variability timescales and the smaller the absorbing cloud. In contrast the low velocity features tend to be longer lived and to have the deeper absorptions. The correlation between the FWHM and velocity of the features found by Lagrange-Henri et al. is confirmed, but with the larger set of data the correlation is found to be somewhat weaker. Significant activity was seen in each set of observations with long lived absorption features at low velocity almost always being present and it has been found that ¼ of all features observed are most likely due to more than one FEB.
The effect of stellar rotation is suggested in the data of some of the strong and more variable absorption features. However conclusive evidence of the changes in equivalent width are not forthcoming. Large numbers of high velocity features are also observed and are seen to vary in timescales no longer than the crossing time for an orbiting body to pass across the stellar disk. This lends further support to the FEB scenario as an explanation for the variable absorption features. The measurement of the filling factors of the clouds of ions indicate that these clouds do in indeed cover large fractions of the stellar disk and some of the lines even exhibit pK/pH less than 1, as predicted.
The FEB scenario appears to explain many of the characteristics of the variable absorption features very well, simulations can reproduce many of the absorptions however there are some cases where the FEB scenario fails to adequately explain the observations. The ability for some of the long-lived features to last as long as they are observed would require either large numbers of bodies on similar orbits crossing the line of sight for many weeks, or that there is some other explanation for the origin of the absorptions.