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Öğe An astrometric and spectroscopic study of the ? Scuti variable HD 21190 and its wide companion CPD-83A°A 64B(Oxford Univ Press, 2017) Niemczura, E.; Scholz, R. -D.; Hubrig, S.; Jaervinen, S. P.; Schoeller, M.; Ilyin, I.; Alicavus, F. KahramanAlthough pulsations of delta Scuti type are not expected among Ap stars from a theoretical point of view, previous observations of the known delta Scuti star HD 21190 indicated a spectral classification F2 III SrEuSi:, making it the most evolved Ap star known. Our atmospheric chemical analysis based on recent High Accuracy Radial velocity Planet Searcher observations confirms the presence of chemical peculiarities in HD 21190. This star is also the only target known to host a magnetic field along with its delta Scuti pulsation properties. Using an astrometric analysis, we show that HD 21190 forms a physical binary system with the companion CPD -83A degrees A 64B. The presented astrometric and spectroscopic study of the binary components is important to understand the complex interplay between stellar pulsations, magnetic fields and chemical composition.Öğe Analysis of TESS Field Eclipsing Binary Star V948 Her: A Pulsating or Non-pulsating Star?(Natl Astronomical Observatories, Chin Acad Sciences, 2022) Alicavus, F. Kahraman; Ekinci, O.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 located 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 modeling with the literature radial velocity measurements, and the precise fundamental parameters of the system were obtained. The system's age was derived as 1 +/- 0.24 Gyr. The positions of the binary components in the H-R diagram were examined and the primary component was found inside the delta 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 delta Scuti instability strip.Öğe Candidate Eclipsing Binary Systems with a ? Scuti Star in Northern TESS Field(Natl Astronomical Observatories, Chin Acad Sciences, 2022) Alicavus, F. Kahraman; Gumus, D.; Kirmizitas, O.; Ekinci, O.; Cavus, S.; Kaya, Y. T.; Alicavus, F.The 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 eclipse and pulsation variations. The eclipsing binaries are the only way to directly measure the mass and radius of stars with a good accuracy (<= 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 within the northern Transiting Exoplanet Survey Satellite (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 T (eff) values of the targets. As a result of these criteria, we discovered some targets. The orbital variations were first removed from the TESS light curves and frequency analysis was performed on the residuals. The luminosity, and absolute and bolometric magnitudes of the targets were calculated as well. To find how much of these parameters represent the primary (more luminous) binary component, 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 candidate delta Scuti stars and also one Maia variable in eclipsing binary systems.Öğe Detailed spectroscopic and photometric study of three detached eclipsing binaries(Oxford Univ Press, 2019) Alicavus, F. Kahraman; Alicavus, F.Detached eclipsing binaries are remarkable systems to provide accurate fundamental stellar parameters. Fundamental stellar parameters and the metallicity values of stellar systems are needed to deeply understand stellar evolution and formation. In this study, we focus on the detailed spectroscopic and photometric studies of three detached eclipsing binary systems, V372And, V2080Cyg, and CFLyn, to obtain their accurate stellar and atmospheric parameters, and chemical compositions. An analysis of light and radial velocity curves was carried out to derive the orbital and stellar parameters. The disentangled spectra of component stars were obtained for the spectroscopic analysis. Final T-eff, logg, xi, vsiniparameters and the element abundances of component stars were derived by using the spectrum synthesis method. The fundamental stellar parameters were determined with a high certainty for V372And, V2080Cyg (similar to 1-2percent) and with accuracy for CFLyn (similar to 2-6percent). The evolutionary status of the systems was examined and their ages were obtained. It was found that the component stars of V2080Cyg have similar iron abundances, slightly lower than the solar iron abundance. Additionally, we show that the primary component of CFLyn exhibits a non-spherical shape with an 80percent Roche lobe filling factor. It could be estimated that CFLyn will start its first Roche overflow in the next 0.02Gyr.Öğe Determination of Atmospheric Parameters of ? Scuti Stars(Amer Inst Physics, 2017) Alicavus, F. Kahraman; Soydugan, Esin; Kubat, J.; Kotkova, L.Asteroseismology offers an opportunity for examination and detailed understanding of the internal structure of stars by probing their pulsating modes. To obtain reliable results by asteroseismology, accurate atmospheric parameters and metallicities of pulsating stars are required. Hence, in this study we carried out a spectroscopic survey of 8 single delta Scuti stars in detail. The accurate atmospheric parameters (effective temperature, surface gravity), projected rotational velocities and the metallicities of these stars were derived.Öğe Discovery of delta Scuti variables in eclipsing binary systems II. Southern TESS field search(Oxford Univ Press, 2023) Alicavus, F. Kahraman; Coban, C. G.; Celik, E.; Dogan, D. S.; Ekinci, O.; Alicavus, F.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, 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 semidetached EBs considering three steps: the orbital period (P-orb)'s harmonics in the Fourier spectrum, skewness of the light curves, and classification of 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 analysed to see whether the fluxes were 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 analysed. 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 analysed. We also examined our targets to see if any of them showed frequency modulation with the orbital period and discovered one candidate of tidally tilted pulsators.Öğe Discovery of New ? Scuti Stars(Maik Nauka/Interperiodica/Springer, 2022) Kirmizitas, O.; Cavus, S.; Alicavus, F. KahramanPulsating stars are remarkable objects for stellar astrophysics. Their pulsation frequencies allow us to probe the internal structure of stars. One of the most known groups of pulsating stars is delta Scuti variables which could be used to understand the energy transfer mechanism in A-F type stars. Therefore, in the current study, we focused on the discovery of delta Scuti stars. For this investigation, we followed some criteria. First, we inspected TESS database by eye and discovered some single stars that exhibit pulsation-like behaviour. Our second criterion is T-eff and logg range. The delta Scuti stars generally have T-eff and log g value in a range of 6300-8500 K and 3.2-4.3, respectively. Hence, we selected the stars which have TIC T-eff and logg values in these ranges. The other criterion is the pulsating frequency. A frequency analysis was performed for all the candidate stars. In addition, M-V, L and also M-bol parameters of the target stars were determined to calculate the pulsation constants and show their positions in the H-R diagram. The final pulsation type classification was made by considering the frequency ranges and pulsation constants of the stars. As a result of the study, five delta Scuti, one gamma Doradus and four hybrid systems were discovered.Öğe Eclipsing binary stars with a ? Scuti component(Oxford Univ Press, 2017) Alicavus, F. Kahraman; Soydugan, Esin; Smalley, B.; Kubat, J.Eclipsing binaries with a delta Sct component are powerful tools to derive the fundamental parameters and probe the internal structure of stars. In this study, spectral analysis of six primary delta Sct components in eclipsing binaries has been performed. Values of T-eff, v sin i, and metallicity for the stars have been derived from medium-resolution spectroscopy. Additionally, a revised list of delta Sct stars in eclipsing binaries is presented. In this list, we have only given the d Sct stars in eclipsing binaries to show the effects of the secondary components and tidallocking on the pulsations of primary delta Sct components. The stellar pulsation, atmospheric and fundamental parameters (e.g. mass, radius) of 92 d Sct stars in eclipsing binaries have been gathered. Comparison of the properties of single and eclipsing binary member delta Sct stars has been made. We find that single d Sct stars pulsate in longer periods and with higher amplitudes than the primary delta Sct components in eclipsing binaries. The v sin i of delta Sct components is found to be significantly lower than that of single delta Sct stars. Relationships between the pulsation periods, amplitudes and stellar parameters in our list have been examined. Significant correlations between the pulsation periods and the orbital periods, Teff, logg, radius, mass ratio, v sin i and the filling factor have been found.Öğe Spectroscopic survey of ? Doradus stars - I. Comprehensive atmospheric parameters and abundance analysis of ? Doradus stars(Oxford Univ Press, 2016) Alicavus, F. Kahraman; Niemczura, E.; De Cat, P.; Soydugan, Esin; Kolaczkowski, Z.; Ostrowski, J.; Telting, J. H.We present a spectroscopic survey of known and candidate gamma Doradus stars. The high-resolution, high signal-to-noise spectra of 52 objects were collected by five different spectrographs. The spectral classification, atmospheric parameters (T-eff, log g, xi), vsin i and chemical composition of the stars were derived. The stellar spectral and luminosity classes were found between G0-A7 and IV-V, respectively. The initial values for T-eff and log g were determined from the photometric indices and spectral energy distribution. Those parameters were improved by the analysis of hydrogen lines. The final values of T-eff, log g and xi were derived from the iron lines analysis. The T-eff values were found between 6000 K and 7900 K, while log g values range from 3.8 to 4.5 dex. Chemical abundances and vsin i values were derived by the spectrum synthesis method. The vsin i values were found between 5 and 240 km s(-1). The chemical abundance pattern of gamma Doradus stars were compared with the pattern of non-pulsating stars. It turned out that there is no significant difference in abundance patterns between these two groups. Additionally, the relations between the atmospheric parameters and the pulsation quantities were checked. A strong correlation between the vsin i and the pulsation periods of gamma Doradus variables was obtained. The accurate positions of the analysed stars in the Hertzsprung-Russell diagram have been shown. Most of our objects are located inside or close to the blue edge of the theoretical instability strip of gamma Doradus.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.
