The investigation of fip effect for selected post-AGB stars

In the frame work thesis, element abundance analysis for nine post-AGB stars (AR Sgr, CE Vir, DF Cyg, DY Aql, HP Lyr, SS Gem, SZ Mon, TT Oph, and UZ Oph) was performed via high resolution échelle spectra obtained with 2.1 m Otto Struve telescope and Sandiford Échelle spectrometer at the McDonald Observatory and the presence of first ionization potential effect (i.e. FIP) was investigated by evaluation of these abundances. For some of the program stars, low resolution échelle spectra from TFOSC spectrometer and RTT-150 telescope of the TÜBİTAK National Observatory were also present. The FIP that is scrutinized with an alternative method also known as gas-dust winnowing effect and shed light onto physical nature of the object of interest is a powerful method that is used to explain abundance anomalies exhibited in the spectra of RV Tauri type variable stars. The FIP is an up-to-date theory known for its effects in Sun and solar like stars also to be tested as an chromospheric activity indicator and characterized with lower Solar photospheric abundances computed for elements (Mg, Si, Ca, Fe,...) with ionization potential energies less than 8 eV compared to those detected in the Solar Corona. The method, in its application stage, enforces the sources to be exposed to an accurate element abundance analysis. In the context of the thesis, the FIP effect was examined in the frame work of abundances computed for C, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and s- and/or r-process contributed elements (e.g. Y and Nd). The model stellar atmospheres in local thermodynamic equilibrium (LTE) was taken into consideration for their chemical abundance analyses. In order to be used in abundance analysis, at the stage of compilation of the up-to-date atomic data, the atomic data library and sources by Akdeniz University Space Sciences and Technologies Department High Resolution Stellar Spectroscopy Group (HRSS) was exploited. At the stage of converting line intensities measured in stellar spectra to abundance values, the equivalent width method and spectrum synthesis technique was used. The atomic data used in abundance analysis was tested by using solar spectrum and in a way to reproduce solar photospheric abundance. For the majority of sources, the lists for atomic transitions that are used in abundance analysis were provided for the first time. When the results of abundances analysis was assessed, the FIP was seen to dominate in all sources except Ar Sgr. For AR Sgr, neither the presence of gas-dust seperation nor FIP was detected. The distribution of abundances in FIP vs. [X/H] diagrams due to an additional source is probable and the source should be spectroscopically followed. The FIP effect for DY Aql was investigated for the first time in the scope of this thesis and it was found to present the FIP effect. DF Cyg that is found to show FIP effect in this thesis was classified as a binary system in the literature on the basis of its photometric analysis. Active chromospheric structure that is belong to source is thought to cause a similar effect too. In the near future, the study is planned to be extended by identification of atomic transitions that can be used for detection of chromospheric activity. In the additional infrared spectra to be obtained, the element abundances acquired in the optical region is planned to be confirmed with the measurements in the infrared region in the sources presenting FIP behaviour. In the view of the fact that these sources are pulsating variables, the determination of pulsation-sensitive transitions have importance. For this reason, the nature of pulsation-sensitive atomic transitions is planned to be understood via periodic follow up of the radial velocity measurements of the thesis stars and via evaluation of these data with the photometric data to be provided from the literature.