arXiv subjects

F. Kahraman Alicavus

Publications and source records attributed to F. Kahraman Alicavus.

10 recordsLinked to original sources

arXiv2025

Photometric investigation of WY Leo: An Eclipsing binary system with Delta Scuti component

Eclipsing binary stars with Delta Scuti components are exceptional systems for gaining a deeper understanding of stellar systems. WY Leo is one such system, exhibiting Delta Scuti-type oscillations. However, it has not been extensively studied in the literature. WY Leo was observed by Transiting Exoplanet Survey Satellite (TESS), providing two sectors of high-quality photometric data. This study focuses on the photometric analysis of WY Leo. Binary modeling was performed, and the system's fundamental stellar parameters, such as mass and radius, were determined. The pulsational properties of WY Leo were also investigated, revealing that the more luminous star exhibits Delta Scuti type oscillations with a period of 0.052 days. The position of the primary component was examined on the HR diagram, and it was found to lie within the Delta Scuti instability strip.

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arXiv2025

Eclipsing binary systems with $β$ Cephei components. V1216 Sco

We present a detailed analysis of the high-mass binary system V1216 Sco, an eclipsing Algol-type binary hosting a $β$ Cephei pulsator, with an orbital period of 3.92 days. This system was analyzed using TESS photometry and high-resolution spectroscopy from SALT HRS to investigate its orbital parameters, stellar properties, and evolutionary history. The TESS light curve, comprising over 12000 data points, revealed five independent pulsation frequencies within the beta Cephei range of 5 to 7 d$^{-1}$. Spectroscopic analysis provided radial velocities and disentangled atmospheric parameters, enabling precise orbital and evolutionary modeling. The system features a primary star of 11.72 M$_{\odot}$ and a secondary of 4.34 M$_{\odot}$. The secondary star has a radius near its Roche lobe, indicating recent or ongoing mass transfer. Evolutionary modeling with MESA-binary suggests that V1216 Sco underwent a case A mass transfer scenario, where mass transfer began while the donor was still on the main sequence. The system's evolutionary models indicate an age of 15 to 30 million years, highlighting the significant impact of binary interactions on stellar evolution. This study underscores the value of combining observational and theoretical approaches to understanding complex systems like V1216 Sco, emphasizing the role of mass transfer in shaping binary star evolution.

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arXiv2023

Discovery of Delta Scuti variables in eclipsing binary systems II.Southern TESS field search

The presence of pulsating stars in eclipsing binary systems (EBs) makes these objects significant since they allow us to investigate the stellar interior structure and evolution. Different types of pulsating stars could be found in EBs such as Delta Scuti variables. Delta Scuti stars in EBs have been known for decades and the increasing number of such systems is important for understanding pulsational structure. Hence, in this study, a research was carried out on the southern TESS field to discover new Delta Scuti stars in EBs. We produced an algorithm to search for detached and semi-detached EBs considering three steps; the orbital period (P$_{orb}$)'s harmonics in the Fourier spectrum, skewness of the light curves, and classification of \textsc{UPSILON} program. If two of these steps classify a system as an EB, the algorithm also identifies it as an EB. The TESS pixel files of targets were also analyzed to see whether the fluxes are contaminated by other systems. No contamination was found. We researched the existence of pulsation through EBs with a visual inspection. To confirm Delta Scuti-type oscillations, the binary variation was removed from the light curve, and residuals were analyzed. Consequently, we identified 42 Delta Scuti candidates in EBs. The P$_{orb}$, $L$, and M$_{V}$ of systems were calculated. Their positions on the H-R diagram and the known orbital-pulsation period relationship were analyzed. We also examined our targets to find if any of them show frequency modulation with the orbital period and discovered one candidate of tidally tilted pulsators.

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arXiv2023

Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya

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 $\pm$ 20 Myr and found that both binary components are situated in the Delta Scuti instability strip. The frequency analysis revealed pulsation frequencies between the 5.5 - 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.

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arXiv2022

Candidate eclipsing binary systems with a Delta Scuti star in Northern TESS field

Existence of pulsating stars in eclipsing binaries has been known for decades. These types of objects are extremely valuable systems for astronomical studies as they exhibit both eclipsing and pulsation variations. The eclipsing binaries are the only way to directly measure the mass and radius of stars with a good accuracy ($\leq$1\%), while the pulsations are a unique way to probe the stellar interior via oscillation frequencies. There are different types of pulsating stars existing in eclipsing binaries. One of them is the Delta Scuti variables. Currently, the known number of Delta Scuti stars in eclipsing binaries is around 90 according to the latest catalog of these variables. An increasing number of these kinds of variables is important to understand the stellar structure, evolution and the effect of binarity on the pulsations. Therefore, in this study, we focus on discovering new eclipsing binaries with Delta Scuti component(s). We searched for the northern TESS field with a visual inspection by following some criteria such as light curve shape, the existence of pulsation like variations in the out-of-eclipse light curve and the Teff values of the targets. As a result of these criteria, we determined some targets. The TESS light curves of the selected targets first were removed from the binarity and frequency analysis was performed on the residuals. The luminosity, absolute and bolometric magnitudes of the targets were calculated as well. To find how much of these parameters represent the primary binary component (more luminous) we also computed the flux density ratio of the systems by utilizing the area of the eclipses. In addition, the positions of the systems in the H-R diagram were examined considering the flux density ratios. As a consequence of the investigation, we defined 38 candidates Delta Scuti and also one Maia variable in eclipsing binary systems.

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arXiv2021

Analysis of TESS field eclipsing binary star V948 Her: a pulsating or non-pulsating star?

Pulsating stars occupy a significant place in the H-R diagram and it was thought that all stars inside the classical instability strip should pulsate. However, recent studies showed that there are many non-pulsating stars placed inside the classical instability strip. The existence of these non-pulsating stars is still a mystery. To deeply understand the properties of these non-pulsating and pulsating stars, one needs precise fundamental stellar parameters (e.g mass). For this purpose, the eclipsing binaries are unique systems. Hence, in this study, we present the TESS data analysis of one candidate pulsating eclipsing binary system V948\,Her. TESS data were used for the binary modelling with the literature radial velocity measurements and the precise fundamental parameters of the system were obtained. The system's age was derived as 1$\pm$0.24 Gyr. The positions of the binary components in the H-R diagram were examined and the primary component was found inside the $δ$\,Scuti instability strip. However, in the frequency analysis of TESS data, we found no significant pulsation frequencies. Only the harmonics of the orbital periods were obtained in the analysis. Therefore, the system was classified as a non-pulsator. V948\,Her is an important object to understand the nature of non-pulsating stars inside the $δ$\,Scuti instability strip.

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arXiv2021

Mass transfer and tidally tilted pulsation in the Algol-type system TZ Dra

Oscillating eclipsing Algols (oEAs) are remarkable systems which 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 TESS 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 $3.52 \times 10^{-9}$ $M_\odot$/year 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, twelve doublets spaced by $2f_{\rm orb}$ were detected from which we infer that this star a tidally tilted pulsator. A mean p-mode frequency spacing of $\approx 7.2 $d$^{-1}$ was found as well.

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arXiv2020

Tidally Trapped Pulsations in a close binary star system discovered by TESS

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 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.

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arXiv2020

Spectroscopy of hot Gamma Doradus and A-F hybrid Kepler candidates close to the hot border of the Delta Scuti instability strip

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 theγDor-type oscillations. The existence of these hot objects needs an explanation. Therefore, we selected, observed and studied 24 hotγDor and hybrid candidates to investigate their properties. The atmospheric parameters, chemical abundances and vsini values of the candidates were obtained using medium-resolution (R= 46 000)spectra taken with the FIES instrument mounted at the NordicOptical Telescope. We also carried out frequency analyses of theKeplerlong- and short-cadence data to determine the exact pulsation contents. We found only five bona-fide hotγDor and three bona-fide hot hybrid stars in our sample. The other 16 stars were found to benormalγDor,δSct, or hybrid variables. No chemical peculiarity was detected in the spectra of the bona-fide hotγDor and hybrid stars. We investigated the interplay between rotation and pulsational modes. We also found that the hotγDor stars havehigherGaialuminosities and larger radii compared to main-sequence A-F stars.

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arXiv2019

The first view of $δ$ Scuti and $γ$ Doradus stars with the TESS mission

We present the first asteroseismic results for $δ$ Scuti and $γ$ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilise the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung-Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, $γ$ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74% for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young $δ$ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.

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