engleski

Investigation of V/R Variations in Be Stars

Despite long lasting observations there is still no unique description or model of the Be phenomenon. One way how to understand the phenomenon is to study systematically the time variations of particular Be stars with a rich enough observational history. For this purpose the bright Be shell stars zeta Tau, V923 Aql and V832 Cyg are chosen. All studied stars were frequently observed at Hvar observatory. Systematic photometric observations from Hvar Observatory and available spectra from Ondrejov and the Dominion Astrophysical Observatory, along with already published data were used to create well-covered observational histories of the studied stars. Additionally V/R variations of the Be star beta Lyr are investigated. Hydrodynamic modeling of the long term cyclic changes of the circumstellar disc of zeta Tau was carried out and reasonable qualitative agreement of model with observations was found. The long term variation of the V/R ratio is interpreted as a prograde moving source of increased emission in the envelope. Phase locked V/R and light variations were found for all stars. Rapid light variations of zeta Tau were found with two close periods and the change between those periods is taking place near the onset of the long term activity phase. Rapid spectral variations of zeta Tau were found with periods of 0\D643 or 1\D334 and 0\D788. Rapid light variations of V923 Aql with the period 0\D845 were found. The double period was suggested for spectroscopic changes. It is demonstrated that at the current stage of development none of the proposed models for V/R variations is sufficient to solely explain the cyclic long term variations of zeta Tau.

binary stars; emission lines; V/R variables; zeta Tau; V923 Aql; V832 Cyg; beta Lyr

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