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Paper: Spectrum Disentangling of AK Her and VW Cep
Volume: 435, Binaries – Key to Comprehension of the Universe
Page: 251
Authors: Lee, C.-U.; Kim, C.-H.; Kim, H.-I.; Kim, S.-L.; Lee, J. W.
Abstract: We introduce a spectrum disentangling experiment to find third- or forth- components in close binaries. The aim of this experiment is to detect the extra components' spectral lines after subtracting the combined synthetic spectra from observed spectra. The experiment has been applied to two close binaries, AK Her and VW Cep. Their orbital periods show sinusoidal changes in their O–C diagrams, which can be explained by two effects; the light-time effects (LITE) which indicates the possibility of multiple systems, and the intrinsic orbital period variations probably caused by spot cycles due to magnetic activities on the late type close binaries. To disentangle each component's spectral line from observed spectra, high resolution spectra with high signal to noise ratio (SNR) are essential. High spectral resolution (R=30K) and high SNR (>100) spectra near Hα of AK Her and VW Cep have been obtained using Bohyunsan Optical Echelle Spectrograph (BOES) which is attached to an 1.8m telescope at Bohyunsan Optical Astronomy Observatory in Korea. Exposure time of each observation does not exceed 2% of orbital period, and the observations show good phase coverage. From the experiment we found that there was no obvious spectrum lines from the residuals in case of AK Her, but relatively sharp Hα absorption lines were detected after subtracting combined synthetic spectra in VW Cep. The averaged sharp Hα absorption line of subtracted spectra has an equivalent width of about 0.175 at 6562.16 Å.
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