Spectroscopic modeling of oscillating Algol-type stars

Tkachenko, Andrii GND

The aim of this thesis is to provide a computer program that is able to analyze time series of high-resolution spectra of double-lined spectroscopic eclipsing binaries to derive the stellar and system parameters of their components and to apply the program to spectra of oEA stars. We analyzed time-series of high-resolution spectra of the two brightest oEA stars (i.e., Algol-type eclipsing binaries with oscillating primary components) RZCas and TWDra using the KOREL program (orbital solutions + decomposed spectra of the binary components), the SynthV program (spectral analysis of the decomposed spectra), and the newly developed Shellspec07_inverse program (optimized stellar parameters from composite line profiles at all orbital phases). The results show that it is possible to derive the stellar and system parameters of the two target stars spectroscopically with an accuracy that is comparable to that obtained from the light curve analysis. We assume that the secondary of RZCas shows a large dark spot on its surface pointing toward the primary, presumably originating from a cooling mechanism by the enthalpy transport via the inner Lagrangian point. Both stars have been observed during two different epochs. In 2007 and 2008, the TWDra system can be well modeled without including any Algol-typical effects like a gas stream or an accretion annulus into the calculations. We conclude that it was in a quiet state during both years. The same result was obtained for RZCas when observed in 2006. The O-C residuals of our solution based on the spectra from 2001 show a complex distribution of circumbinary matter, however, pointing to the occurrence of an episode of rapid mass transfer. This assumption is supported by the deduced change of the orbital period of RZCas of 2 seconds between the two epochs of observations that can be explained in terms of angular momentum transfer between the accelerated rotation of the outer layers of the primary and the orbit. A first attempt to include the calculation of line profile variations due to non-radial pulsations into Shellspec07_inverse gave encouraging results. We could derive some common relationships between system parameters and the pulsation characteristics of the primary and show that the Shellspec07_inverse program can be used for a future mode identification based on radial velocity measurements.

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Tkachenko, Andrii: Spectroscopic modeling of oscillating Algol-type stars. 2011.

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