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    LIGHT AND FREQUENCY ANALYSIS OF DETACHED ECCENTRIC BINARY SYSTEM DT CAM WITH PRE-MAIN SEQUENCE COMPONENT
    (Univ Nacional Autonoma Mexico, Inst De Astronomia, 2024) Ozdemir, Tuncay; Gurol, Birol
    In this study we analyzed TESS data of detached eccentric binary system DT Cam and we obtained the first physical parameters of the components. We found that the out-of-eclipse variation of the system shows a small amplitude periodic feature. Most of the frequencies obtained are related with the orbital variation except one, for which the period was determined as <^>x0.605 days. The masses and radii of the primary and secondary components were calculated as M1 = 1.793M0, M2 = 1.414M0, R1 = 1.355R0, and R2 = 1.522R0, respectively. Considering the physical properties of the primary component we concluded that it is a rotational variable. We found that the massive component is smaller than the low-mass component. It seems that the secondary component is a pre-main sequence star, which is important for the understanding of stellar structure and evolution.
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    On oxygen-rich SR variables in the solar neighborhood
    (Tubitak Scientific & Technological Research Council Turkey, 2018) Ozdemir, Tuncay
    Brightness distribution of variable stars was investigated based on good Hipparcos parallaxes of semiregular variables (SRVs) in the solar neighborhood, and it is shown that the order of the variability types Lb, SR, SRb, SRa, and Mira is, statistically, an order of increasing brightness along the red giant branch and asymptotic giant branch. In addition, it is also shown that the majority of Miras are above and majority of SRVs are below the tip of the red giant branch. The periods of SRVs that fall in Wood's sequence C (fundamental mode) of large Magellanic clouds were identified. Statistically, the order of SR, SRb, and Mira variables with increasing period and increasing absolute magnitude is the same in six infrared (IR) band wavelengths. The slope of the P-L relation for SR + SRb variables in sequence C increases systematically with wavelength in the near IR. This indicates that circumstellar IR emission increases with increasing period from the shorter period SRVs to Miras, which is consistent with the high mass loss rate found in long period Miras. (J-K)-M-K diagram suggests that the sequence Lb, SR, SRb, SRab (emission), and Mira may be an evolutionary sequence.