A spectroscopic study of the rapidly oscillating peculiar A star HD 134214

Abstract

Photometric studies were made of 10 peculiar-A-type (Ap) stars looking for long period oscillations typical of rapidly-oscillating Ap stars (roAp stars) using the 0.75-rn telescope at the South African Astronomical Observatory. Although a
promising candidate pulsator was found in HD 156869, no such oscillations were seen in these stars. Further spectroscopic observations did discover a 21 mm pulsation in HD 116114 and as a result further investigations were confined to spectroscopy.
In addition a theoretical model of the atmosphere of an roAp star was developed involving a standing wave with a running wave component. This model appears to be more consistent with previous results from roAp stars and also with the results presented in this thesis, in terms of pulsation phase and amplitude behaviour.
Using high resolution VLT/UVES spectroscopic data, an abundance analysis has been performed for the rapidly oscillating Ap star HD 134214, the shortest period roAp star known. An atmosphere with Te ff = 7800K and logg = 4.2 and calculated with the package ATLA99 was found to fit the data best, with a microturbulence of 0.5kmr'. It was possible to identify 139 good quality Fei lines and 38 Fell lines of similar quality, so that the above atmospheric parameters could be calculated with a good level of confidence. The problems in determining these parameters are discussed in detail, along with the limitations of previous work.
The abundance analysis was performed using the programs WIIDTH9 to calculate abundances from measured equivalent widths and SYNTH in order to fit calculated profiles, There were 610 lines identified which had abundances calculated,
covering 46 different ion species. The abundance pattern found is similar to that seen in other Ap stars, with the Fe peak elements being in general either of solar abundance or slightly overabundant. The rare earth elements are very overabundant compared with the solar values and an abundance anomaly of 1.2 and 1.4dex is seen between the first and second ions of Pr and Nd. This is similar to that seen in other Ap stars and is suggestive that these elements may be stratified in the atmosphere of HD 134214 and other Ap stars.
The lines used in the abundance analysis were then investigated for evidence of pulsations. As is typical for the Ap stars, the rare earth elements showed the strongest pulsations. Most of the lines show phases that are concentrated within
the range —0.5 to 0.5, but Priii, Tbiii and Thin show significant deviations from this value. The lines of La ii and Nd iii show evidence of a running wave in the atmosphere and it is postulated that these lines are probing regions close to nodes of the pulsation, where the amplitude becomes low and the running component of the wave begins to dominate, causing the phase to run away. It is tentatively suggested that Nd ii may be situated at an antinode, with Lali and Nd iii probing the nodes on either side.
Despite the analyses that have been performed it is not clear what marks HD 134214 as different from other roAp stars and causes it to show such a small pulsation period. Both the abundance patterns and pulsational behaviour of the star in every other way seem to be typical of many other roAp stars.