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Öğe Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya(Oxford University Press, 2023) Kahraman Alicavuş, Filiz; Aliçavuş, Fahri; Pawar, T.; Helminiak, K. G.; Handler, G.; Moharana, A.The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 ± 20 Myr and found that both binary components are situated in the δ Scuti instability strip. The frequency analysis revealed pulsation frequencies between 5.5 and 13.0 d−1 and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.Öğe Mass transfer and tidally tilted pulsation in the Algol-type system TZ Dra(Oxford University Press, 2022) Kahraman Aliçavuş, Filiz; Handler, G.; Aliçavuş, Fahri; De Cat, P.; Bedding, T.; Ekinci, O.Oscillating eclipsing Algols (oEAs) are remarkable systems that allow us to determine accurate fundamental stellar parameters (mass, radius) and probe the stellar interiors through pulsations. TZ Dra is an oEA system containing a δ Scuti component. To examine particular characteristics of such close systems including pulsations and mass transfer, we present a detailed photometric and spectroscopic study of TZ Dra. With the analysis of high-resolution spectra, the orbital parameters were determined by the radial velocity analysis and the atmospheric parameters were derived for the primary component. The binary modelling and the pulsational frequency analysis was carried out using the Transiting Exoplanet Survey Satellite data set. The H α line profiles show the signature of mass transfer from the cool to the hot binary component. The conclusion of mass transfer/mass-loss in the system was supported by the analysis of the orbital period changes. As a result, it was found that there is 3 . 52 × 10 −9 M yr −1 mass-loss from the system most probably through the hotspot and stellar winds. Additionally, most pulsation frequencies originating from the primary component were found to be spaced by harmonics of the orbital frequencies in particular, 12 doublets spaced by 2 f orb were detected from which we infer that this star is a tidally tilted pulsator. A mean p-mode frequency spacing of ≈7.2 d −1 was found as well.Öğe Single-lined eclipsing binaries with ? Scuti components: GQ Dra, RR Lep, and TYC 683-640-1(Oxford University Press, 2024) Kahraman Aliçavuş, Filiz; Aliçavuş, Fahri; Çoban, Çağlar Gani; Handler, G.; De Cat, P.Eclipsing binaries with (a) pulsating component(s) are remarkable objects to investigate the evolution and structure of stellar systems. Detailed studies of such systems are also important to reveal their pulsation properties. The largest sample of pulsating eclipsing binaries is the one containing δ Scuti variables. In this study, we present a comprehensive spectroscopic and photometric study of three such systems, GQ Dra, RR Lep, and TYC 683-640-1. Their orbital parameters were derived from their large-amplitude radial velocity variations. All systems were found to be single-lined eclipsing binaries. We determined the atmospheric parameters of the primary components, which are the more luminous ones. By using the results of the spectroscopic analysis, the binarity of the systems was modelled and the fundamental stellar parameters (mass, radius) of each system were obtained. In addition, the pulsations of the systems were analysed. Both GQ Dra and RR Lep exhibit frequencies that are modulated with the orbital period. Therefore, the pulsating components of these systems are identified as candidate tidally tilted pulsators.Öğe Spectroscopy of hot ? Doradus and A-F hybrid Kepler candidates close to the hot border of the ? Scuti instability strip(Oxford Univ Press, 2020) Alicavus, F. Kahraman; Poretti, E.; Catanzaro, G.; Smalley, B.; Niemczura, E.; Rainer, M.; Handler, G.If gamma Dor-type pulsations are driven by the convective blocking mechanism, a convective envelope at a sufficient depth is essential. There are several hot gamma Dor and hybrid star candidates in which there should not be an adequate convective envelope to excite the gamma Dor-type oscillations. The existence of these hot objects needs an explanation. Therefore, we selected, observed, and studied 24 hot gamma Dor and hybrid candidates to investigate their properties. The atmospheric parameters, chemical abundances, and vsin i values of the candidates were obtained using medium-resolution (R = 46 000) spectra taken with the Fibre-fed Echelle Spectrograph instrument mounted at the Nordic Optical Telescope. We also carried out frequency analyses of the Kepler long- and short-cadence data to determine the exact pulsation contents. We found only five bona fide hot gamma Dor and three bona fide hot hybrid stars in our sample. The other 16 stars were found to be normal gamma Dor, delta Sct, or hybrid variables. No chemical peculiarity was detected in the spectra of the bona fide hot gamma Dor and hybrid stars. We investigated the interplay between rotation and pulsational modes. We also found that the hot gamma Dor stars have higher Gaia luminosities and larger radii compared to main-sequence A-F stars.Öğe The single-sided pulsator CO Camelopardalis(Oxford Univ Press, 2020) Kurtz, D. W.; Handler, G.; Rappaport, S. A.; Saio, H.; Fuller, J.; Jacobs, T.; Schmitt, A.CO Cam (TIC 160268882) is the second 'single-sided pulsator' to be discovered. These are stars where one hemisphere pulsates with a significantly higher amplitude than the other side of the star. CO Cam is a binary star comprised of an Am d Sct primary star with T-eff = 7070 +/- 150 K, and a spectroscopically undetected G main-sequence secondary star. The dominant pulsating side of the primary star is centred on the L1 point. We have modelled the spectral energy distribution combined with radial velocities, and independently the TESS light curve combined with radial velocities. Both of these give excellent agreement and robust system parameters for both stars. The d Sct star is an oblique pulsator with at least four low radial overtone (probably) f modes with the pulsation axis coinciding with the tidal axis of the star, the line of apsides. Preliminary theoretical modelling indicates that the modes must produce much larger flux perturbations near the L1 point, although this is difficult to understand because the pulsating star does not come near to filling its Roche lobe. More detailed models of distorted pulsating stars should be developed. These newly discovered single-sided pulsators offer new opportunities for astrophysical inference from stars that are oblique pulsators in close binary stars.Öğe Tidally trapped pulsations in a close binary star system discovered by TESS(Nature Publishing Group, 2020) Handler, G.; Kurtz, D. W.; Rappaport, S. A.; Saio, H.; Fuller, J.; Jones, D.; Guo, Z.It has long been suspected that tidal forces in close binary stars could modify the orientation of the pulsation axis of the constituent stars. Such stars have been searched for, but until now never detected. Here we report the discovery of tidally trapped pulsations in the ellipsoidal variable HD 74423 in Transiting Exoplanet Survey Satellite (TESS) space photometry data. The system contains a delta Scuti pulsator in a 1.6 d orbit, whose pulsation mode amplitude is strongly modulated at the orbital frequency, which can be explained if the pulsations have a much larger amplitude in one hemisphere of the star. We interpret this as an obliquely pulsating distorted dipole oscillation with a pulsation axis aligned with the tidal axis. This is the first time that oblique pulsation along a tidal axis has been recognized. It is unclear whether the pulsations are trapped in the hemisphere directed towards the companion or in the side facing away from it, but future spectral measurements can provide the solution. In the meantime, the single-sided pulsator HD 74423 stands out as the prototype of a new class of obliquely pulsating stars in which the interactions of stellar pulsations and tidal distortion can be studied. HD 74423 is an unusual binary star system containing two lambda Bootis pulsators. TESS photometry reveals that one of the pair is pulsating along its tidal axis-but only in one hemisphere. Such an odd arrangement provides an interesting laboratory in which to study stellar pulsations and tidal distortion.
