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RR Draconis: An Algol-Type Eclipsing Binary with a Possible Massive Tertiary Companion

Şenavcı H. V., Čeki A., Esmer E. M., Yalçınkaya S., Latković O., Bahar E., Yılmaz M, Bastürk Ö., Özavcı İ., Yörükoğlu O., Selam S. O.

Acta Astronomica

2022

Vol. 72, No. 1

31--53

In this study, we present spectoscopic observations of the eclipsing binary RR Dra carried out with our recently installed T80 telescope in Ankara University Kreiken Observatory and analyze the first radial velocity time series of this system. We simultaneously model TESS light curves along with our radial velocity data to derive absolute parameters of RR Dra system. Additionally, we investigate the period variation of the system using all the available eclipse timings in the literature. In this context, we discuss two possible explanations for the cyclic nature of the eclipse timings: i) light-time effect that corresponds to a high-mass but unseen additional component, ii) magnetic activity of the cooler component. The secular period increase in eclipse timings of RR Dra may be a combination of mass transfer and angular momentum loss, amplified by the presence of circumstellar material.

Analysis of the Most Precise Light Curves of HAT-P-36 Detrended from Spot Signals

Yalçınkaya S., Baştürk Ö., El Helweh F., Esmer E. M., Yörükoğlu O., Yılmaz M., Şenavcı H. V., Kılıçoğlu T., Selam S. O.

Acta Astronomica

2021

Vol. 71, No. 3

223--242

We study the most precise light curves of the planet-host HAT-P-36 that we obtained from the ground primarily with a brand-new 80 cm telescope (T80) very recently installed at Ankara University Kreiken Observatory (AUKR), Turkey and also from the space with Transiting Exoplanet Survey Satellite (TESS). The main objective of the study is to analyze the Transit Timing Variations (TTV) observed in the hot-Jupiter type planet HAT-P-36 b, a strong candidate for orbital decay. Our analysis is based on our own observations as well as those acquired by professional and amateur observers since its discovery. HAT-P-36 displays out-of-transit variability as well as light curve anomalies during the transits of its planet due to stellar spots. We collected and detrended from these anomalies all complete transit light curves we had access to. We modeled transits with EXOFAST and measured the mid-transit times forming a homogeneous data set for a TTV analysis. We found an increase in the orbital period of HAT-P-36 b at a rate of 0.014 s per year from the best fitting quadratic function. This increase is only found in the TTV constructed from the mid-transit times measured from detrended light curves. We refined the values of the system parameters by modeling with EXOFASTv2 the Spectral Energy Distribution of the host star, its archival radial velocity observations from multiple instruments, and the most precise transit light curves from the space and ground covering a wide range of wavelengths. We also analyzed the out-of-transit variability from TESS observations to search for potential rotational modulations through a frequency analysis. We report a statistically significant periodicity in the TESS light curve at 4.22±0.02 d, which might have been caused by instrumental systematics but should be tracked in the future observations of the target.

Orbital Period Analysis of Four Eclipsing Binaries XY Boo, RW Com, MR Del and AK Her

Özavcı İ., Özuyar D., Şenavcı H. V., Yılmaz M, Bahar E., Baştürk Ö., Kılıçoğlu T., Elmaslı A., Çalışkan Ş., İzci D. D., Yörükoğlu O., Selam S. O.

Acta Astronomica

2020

Vol. 70, No. 1

33--52

The orbital period variations of the eclipsing binaries XY Boo, RW Com, MR Del, and AK Her are investigated. This study includes the first orbital period analysis of the detached eclipsing binary MR Del and necessary updates for the remaining stars with addition of new mid-eclipse times calculated from our recent observations carried out at Ankara University Kreiken Observatory. The analysis shows that the period variations may result from mass exchange/loss and a third body for XY Boo, two additional bodies for RW Com, a substellar third component for MR Del, and mass exchange/loss, additional bodies and/or magnetic activity for AK Her. The hypothetical third component of MR Del with an estimated mass of 0.069 M⊙, appears to be very close to the borderline between stars and brown dwarfs.