Insanoglunun Gunes’ten baska yildizlarin etrafinda da gezegenlerin (otegezegen) var olabilecegi d... more Insanoglunun Gunes’ten baska yildizlarin etrafinda da gezegenlerin (otegezegen) var olabilecegi dusuncesi ile basladigi merak uyandirici arayisi, 1992’de olu bir yildiz kalintisinin cevresinde ilk kez bir gezegenin bulunmasiyla (Wolszczan ve Frail 1992) ilk meyvesini vermis, 1995’te Gunes benzeri bir yildizin etrafinda yorunge hareketi yapan baska bir gezegenin bulunmasi da (Mayor ve Queloz 1995), sadece bilim cevrelerince degil tum dunya kamuoyunca buyuk bir heyecanla karsilanmistir. Bu gelisme, uluslararasi boyutta farkli disiplinlerdeki bilim insanlarini bir araya getirerek, cagimizin en ilgili cekici ve cigir acacak nitelikteki arastirma alanlarindan birinin dogmasina neden olmustur. Bu milat noktasindan gunumuze kadar bu alanda gelistirilen farkli teknikler yardimiyla kesfedilen otegezegen sayisi ise 2000’i asmistir. Onerilen bu proje calismasinin temel amaci dogrultusunda, Ankara Universitesi Kreiken Rasathanesi (AUKR) mevcut teleskoplari ve TUBITAK Ulusal Gozlemevi (TUG) T100 teleskobu yardimiyla otegezegen kesfinde kullanilan Gecis Zamanlari Degisimi (Transit Timing Variations) ve Cift Sistemlerde Donem Degisimi (Timing of the Minima of Low Mass Eclipsing Binaries) yontemleri icin gereken isik egrileri ve minimum zamanlari (tutulma/gecis profilinin merkezine/ortasina karsilik gelen zaman), uluslararasi ortakliklar kapsaminda belirlenen aday yildizlar icin elde edilecek ve yine ayni kapsamda analizleri gerceklestirilecektir. Elde edilecek olan veriler ve analizleri ile literaturde gezegen barindirma olasiligina sahip oldugu one surulen ya da en az bir otegezegen bulundurdugu belirlenmis ancak sisteme bagli baska otegezegenlerin de olabileceginden suphelenilen yildizlara iliskin bulgular degerlendirilip uluslararasi duzeyde literature katki sunulmasi, ulkemiz ve universitemizin, dar anlamda sadece astronominin degil gunumuz biliminin en aktif calisma alanlarindan birinde daha ileri bir duzeye tasinmasi planlanmaktadir.AbstractIntriguing quest of mankind started with the question whether planets exist around other stars gave its first reward when a planet was found in 1992 around a stellar remnant (Wolszczan & Frail 1992) and the discovery of a planet orbiting a Sun-like star in 1995 (Mayor & Queloz 1995) aroused excitement not only in scientific community but also in public all around the world. These discoveries brought scientist from different fields together and led to the birth of a new research area with the potential of opening an era in science. The number of exoplanets discovered with different techniques has exceeded 2000 since then. With this project, it has been aimed to obtain and analyze light curves and eclipse timings (the times corresponding to the eclipse/transit profile minima) of selected exoplanets with 1 meter telescope (T100) in TUBITAK National Observatory (TUG) and the telescopes in Ankara University Kreiken Observatory (AUKR) by making use of “Transit Timing Variations (TTV)” and “Timing of the Minima of Low Mass Eclipsing Binaries” techniques within the framework of international collaborations. It has been planned to evaulate the findings from the data analysis of the potential exoplanet hosting systems, contribute with those findings to the scientific literature, and to improve the know-how in our country and in our university in one of the most active fields of scientific research.
We study the most precise light curves of the planet-host HAT-P-36 that we obtained from the grou... more 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) of 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, based on our own observations as well as that have been acquired by professional and amateur observers since its discovery (Bakos et al. 2012). 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 all the complete transit light curves we had access to from these anomalies, which we modeled with EXOFAST (Eastman et al. 2013) 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 seconds per year from the best fitting quadratic function, which is only found in the TTV constructed by making use of the mid-transit times measured from detrended light curves, against an expectation of an orbital decay based on its parameters. We refined the values of these system parameters by modelling the Spectral Energy Distribution of the host star, its archival radial velocity observations from multiple instruments, and most precise transit light curves from the space and the ground covering a wide range of wavelengths with EXOFASTV2 (Eastman 2017). 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 days, which might have been caused by instrumental systematics but should be tracked in the future observations of the target.
V502 Ophiuchi örten çift yıldız sisteminin 2005 yılında TÜBİTAK Ulusal Gözlemevi'nde, BVR bantlar... more V502 Ophiuchi örten çift yıldız sisteminin 2005 yılında TÜBİTAK Ulusal Gözlemevi'nde, BVR bantlarında elde edilen ışık eğrileri, sistemin fiziksel parametrelerini belirlemek üzere, güncel tayfsal kütle oranı da dikkate alınarak PHOEBE analiz programı ile modellendi. Analiz sonucunda W-türü bir W UMa sistemi olan V502 Oph'nin ışık eğrileri, birinci bileşen üzerinde güneş benzeri soğuk bir lekenin varlığı altında başarılı bir şekilde modellendi ve sisteme ilişkin güncel fiziksel parametreler hesaplandı. Ayrıca, Ankara Üniversitesi Rasathanesi'nde 2009 yılı içinde sistemin ek ışıkölçüm gözlemleri yapılarak yeni minimum zamanları elde edildi. Bu minimum zamanları, literatürden toplanan tüm yayınlanmış minimum zamanları ile birleştirildi ve sistem için güncel bir dönem değişimi analizi gerçekleştirildi. Bu analiz sonucunda ise sistemin yörünge döneminin azalmakta olduğu tespit edildi ve bu azalmaya neden olabilecek mekanizma için bileşenler arası kütle aktarımı önerildi. Anahtar Kelimeler. Örten çift yıldızlar, Yıldızların fotometrik analizi, Yıldızların mutlak boyutları, Yıldızların dönem değişimi analizi.
WASP-43 b is one of the most important candidate for detecting an orbital decay. We investigate p... more WASP-43 b is one of the most important candidate for detecting an orbital decay. We investigate pieces of evidence for this expectation as variations in its transit timings, based on the ground and space observations. The data set include the transit observations at the TÜBİTAK National Observatory of Turkey (TUG) and Transiting Exoplanet Survey Satellite (TESS). We present a global model of the system, based on the most precise photometry from space, ground, and archival radial velocity data. Using the homogenized data set and modeled light curves, we measure the mid-transit times for WASP-43 b. Our analysis agrees with a linear ephemeris which we refine its light elements for future observations of the system. However, there is a negative difference between the transit timings derived from TESS data in two sectors (09 & 35) and a hint of an orbital period decrease in the entire data set. Both findings are statistically insignificant due to the short baseline of observations, which prevents us from drawing firm conclusions about the orbital decay of this ultra-short period planet. However, assuming the effect of this decrease of the period in the planet's orbit, we derive a lower limit for the reduced tidal quality factor as Q ′ * > (4.01 ± 1.15) × 10 5 from the best-fitting quadratic function. Finally, we calculate a probable rotational period for this system as 7.52 days from the out-of-transit flux variation in the TESS light curves due to spot modulation.
NY Virginis is an eclipsing binary system with a subdwarf B primary and an M type dwarf secondary... more NY Virginis is an eclipsing binary system with a subdwarf B primary and an M type dwarf secondary. Recent studies (Qian et al. 2012; Lee et al. 2014) suggested the presence of two circumbinary planets with a few Jovian masses within the system. Lee et al. (2014) examined the orbital stabilities of the suggested planets, using the best-fit parameters derived from their eclipse timing variation analysis. They found that the outer companion should be ejected from the system in about 800 000 years. An observational report from Pulley et al. (2016) pointed out that the recent mideclipse times of the binary deviate significantly from the models suggested by Lee et al. (2014). In fact, variations in the orbital period of the system had already been recognized by many authors, but the parameters of these variations vary significantly as new data accumulate. Here, we analyze the eclipse timing variations of the NY Vir system, using new mid-eclipse times that we have obtained together with earlier published measurements in order to understand the nature of the system and constrain its parameters.
Turkish Journal of Astronomy and Astrophysics, Dec 30, 2022
Geçiş yapan ötegezegenlere ait parametreleri hassas bir şekilde belirleyebilmek için geçiş ışık e... more Geçiş yapan ötegezegenlere ait parametreleri hassas bir şekilde belirleyebilmek için geçiş ışık eğrilerinde görülebilecek zaman değişimlerini tespit etmek oldukça önemlidir. Geçiş ve örtülme ortası zamanları, kenar kararması, yıldız aktivitesi ya da yıldızın basıklığı gibi ışık eğrisi morfolojisini etkileyen nedenlerle ya da sisteme ilave nesneler, yörünge presesyonu, açısal momentum değişimi gibi nedenlerle saniye, dakika veya saat mertebesinde, çoğunlukla çevrimsel şekilde değişebilmektedir. Bu çalışmada manyetik aktivite gösteren barınak yıldızlarda gözlenen yüzey lekelerinin gezegen tarafından örtülmesinin geçiş ortası zamanlarındaki değişime etkileri incelenmektedir.
h i g h l i g h t s Period behavior is examined, sine fit of Qian et al. (2008) is refuted. New R... more h i g h l i g h t s Period behavior is examined, sine fit of Qian et al. (2008) is refuted. New RV results, and new VRI and BVRI light curves are presented. New WD analyses of our data and also the data of Qian et al. (2008). All three models effectively agree within error limits. The spot moves from 2005 to 2013. Follow-up observations are suggested.
We have been carrying out a program for over five years to observe transits of selected exoplanet... more We have been carrying out a program for over five years to observe transits of selected exoplanets with 1 meter Turkish Telescope, T100 (Baştürk et al. 2014, 2015), by making use of the wellestablished defocusing technique (Southworth et al. 2009) to achieve high photometric precision. In this contribution, we review the results of our observing program in timing perspective. The basic idea behind defocusing technique is to have the advantage of posing the detector for longer durations in the observations of bright stars, otherwise observed within very short integration times. Then the effect of the photon noise is diminished, which dominates in the short cadence observations. Longer exposures also help in reducing the noise contribution of the atmospheric scintillation. Noise contributions of the imperfect tracking and flat-fielding are mitigated by integrating over a larger area on the detector as well. Although fewer images can be acquired in a given time, we argue that the timing precision is improved because of better photometric precision. This contribution has been supported by TÜBİTAK-3001 project 116F350.
American Astronomical Society Meeting Abstracts #217, 2011
ABSTRACT The first public data release from the Kepler Space Telescope contained over 156,000 sta... more ABSTRACT The first public data release from the Kepler Space Telescope contained over 156,000 stars which had been monitored continuously for approximately 33 days. With continuous photometric monitoring and unprecedented ultra-high precision, the Kepler dataset is an splendid resource for investigating stellar rotation (and age) via starspots as well as for investigating starspot fractional coverage and distributions, starspot lifetime and differential rotation as a function of spectral type and rotation/age. Here, we narrowed our focus to the 306 planetary candidates, mostly main sequence late F, G and K stars, released during June 2010 (see Boruki et al. 2010). This is an attractive data set for the study of starspots properties since these stars host transiting planets with orbital planes almost exactly aligned with our line-of-sight and will generally have the host stars' rotation axes perpendicular to the planetary orbital plane. Thus, the inclination of the star's rotation axis can be assumed known and should (in most cases) be at right angles to our line-of-sight. Using a Lomb-Scargle Periodogram analysis, we have extracted reliable rotation periods and spot coverages for stars which showed evidence for starspots. From the measured rotation periods, we were able to determine, empirically, the age of the stellar system (using Villanova rotation-age relations) and investigate the potential tidal evolution of the planet-star system. However, we found good evidence that rotation-age relations do not apply to stars that host short-period, Jupiter sized planets. The aforementioned stars show a definite tendency towards star-rotation-planet orbital synchronization. The initial results of this exploratory program will be discussed. This project was initiated at the 2010 Sagan Exoplanet Summer Workshop hosted by NExScI at Caltech. We wish to thank NASA and the organizers of the workshop - in particular Dawn Gelino and Carolyn Brinkworth. EG wishes also to acknowledge support from NSF/RUI Grant AST-10-09903.
In this paper, we present a combined photometric, spectroscopic, and orbital period study of thre... more In this paper, we present a combined photometric, spectroscopic, and orbital period study of three early-type eclipsing binary systems: XZ Aql, UX Her, and AT Peg. As a result, we have derived the absolute parameters of their components and, on that basis, we discuss their evolutionary states. Furthermore, we compare their parameters with those of other binary systems and with theoretical models. An analysis of all available up-to-date times of minima indicated that all three systems studied here show cyclic orbital changes; their origin is discussed in detail. Finally, we performed a frequency analysis for possible pulsational behavior, and as a result we suggest that XZ Aql hosts a δ Scuti component.
The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey... more The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey for transiting planets orbiting bright stars for over ten years. The KELT images have a pixel scale of ∼ 23 pixel −1-very similar to that of NASA's Transiting Exoplanet Survey Satellite (TESS)-as well as a large point spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with higher spatial resolution, cadence, and photometric precision than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1,600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ∼450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1,128 bright stars (6 < V < 13) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observa-KELT-FUN AND KELT FALSE POSITIVES 3 tions. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS.
Insanoglunun Gunes’ten baska yildizlarin etrafinda da gezegenlerin (otegezegen) var olabilecegi d... more Insanoglunun Gunes’ten baska yildizlarin etrafinda da gezegenlerin (otegezegen) var olabilecegi dusuncesi ile basladigi merak uyandirici arayisi, 1992’de olu bir yildiz kalintisinin cevresinde ilk kez bir gezegenin bulunmasiyla (Wolszczan ve Frail 1992) ilk meyvesini vermis, 1995’te Gunes benzeri bir yildizin etrafinda yorunge hareketi yapan baska bir gezegenin bulunmasi da (Mayor ve Queloz 1995), sadece bilim cevrelerince degil tum dunya kamuoyunca buyuk bir heyecanla karsilanmistir. Bu gelisme, uluslararasi boyutta farkli disiplinlerdeki bilim insanlarini bir araya getirerek, cagimizin en ilgili cekici ve cigir acacak nitelikteki arastirma alanlarindan birinin dogmasina neden olmustur. Bu milat noktasindan gunumuze kadar bu alanda gelistirilen farkli teknikler yardimiyla kesfedilen otegezegen sayisi ise 2000’i asmistir. Onerilen bu proje calismasinin temel amaci dogrultusunda, Ankara Universitesi Kreiken Rasathanesi (AUKR) mevcut teleskoplari ve TUBITAK Ulusal Gozlemevi (TUG) T100 teleskobu yardimiyla otegezegen kesfinde kullanilan Gecis Zamanlari Degisimi (Transit Timing Variations) ve Cift Sistemlerde Donem Degisimi (Timing of the Minima of Low Mass Eclipsing Binaries) yontemleri icin gereken isik egrileri ve minimum zamanlari (tutulma/gecis profilinin merkezine/ortasina karsilik gelen zaman), uluslararasi ortakliklar kapsaminda belirlenen aday yildizlar icin elde edilecek ve yine ayni kapsamda analizleri gerceklestirilecektir. Elde edilecek olan veriler ve analizleri ile literaturde gezegen barindirma olasiligina sahip oldugu one surulen ya da en az bir otegezegen bulundurdugu belirlenmis ancak sisteme bagli baska otegezegenlerin de olabileceginden suphelenilen yildizlara iliskin bulgular degerlendirilip uluslararasi duzeyde literature katki sunulmasi, ulkemiz ve universitemizin, dar anlamda sadece astronominin degil gunumuz biliminin en aktif calisma alanlarindan birinde daha ileri bir duzeye tasinmasi planlanmaktadir.AbstractIntriguing quest of mankind started with the question whether planets exist around other stars gave its first reward when a planet was found in 1992 around a stellar remnant (Wolszczan & Frail 1992) and the discovery of a planet orbiting a Sun-like star in 1995 (Mayor & Queloz 1995) aroused excitement not only in scientific community but also in public all around the world. These discoveries brought scientist from different fields together and led to the birth of a new research area with the potential of opening an era in science. The number of exoplanets discovered with different techniques has exceeded 2000 since then. With this project, it has been aimed to obtain and analyze light curves and eclipse timings (the times corresponding to the eclipse/transit profile minima) of selected exoplanets with 1 meter telescope (T100) in TUBITAK National Observatory (TUG) and the telescopes in Ankara University Kreiken Observatory (AUKR) by making use of “Transit Timing Variations (TTV)” and “Timing of the Minima of Low Mass Eclipsing Binaries” techniques within the framework of international collaborations. It has been planned to evaulate the findings from the data analysis of the potential exoplanet hosting systems, contribute with those findings to the scientific literature, and to improve the know-how in our country and in our university in one of the most active fields of scientific research.
We study the most precise light curves of the planet-host HAT-P-36 that we obtained from the grou... more 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) of 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, based on our own observations as well as that have been acquired by professional and amateur observers since its discovery (Bakos et al. 2012). 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 all the complete transit light curves we had access to from these anomalies, which we modeled with EXOFAST (Eastman et al. 2013) 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 seconds per year from the best fitting quadratic function, which is only found in the TTV constructed by making use of the mid-transit times measured from detrended light curves, against an expectation of an orbital decay based on its parameters. We refined the values of these system parameters by modelling the Spectral Energy Distribution of the host star, its archival radial velocity observations from multiple instruments, and most precise transit light curves from the space and the ground covering a wide range of wavelengths with EXOFASTV2 (Eastman 2017). 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 days, which might have been caused by instrumental systematics but should be tracked in the future observations of the target.
V502 Ophiuchi örten çift yıldız sisteminin 2005 yılında TÜBİTAK Ulusal Gözlemevi'nde, BVR bantlar... more V502 Ophiuchi örten çift yıldız sisteminin 2005 yılında TÜBİTAK Ulusal Gözlemevi'nde, BVR bantlarında elde edilen ışık eğrileri, sistemin fiziksel parametrelerini belirlemek üzere, güncel tayfsal kütle oranı da dikkate alınarak PHOEBE analiz programı ile modellendi. Analiz sonucunda W-türü bir W UMa sistemi olan V502 Oph'nin ışık eğrileri, birinci bileşen üzerinde güneş benzeri soğuk bir lekenin varlığı altında başarılı bir şekilde modellendi ve sisteme ilişkin güncel fiziksel parametreler hesaplandı. Ayrıca, Ankara Üniversitesi Rasathanesi'nde 2009 yılı içinde sistemin ek ışıkölçüm gözlemleri yapılarak yeni minimum zamanları elde edildi. Bu minimum zamanları, literatürden toplanan tüm yayınlanmış minimum zamanları ile birleştirildi ve sistem için güncel bir dönem değişimi analizi gerçekleştirildi. Bu analiz sonucunda ise sistemin yörünge döneminin azalmakta olduğu tespit edildi ve bu azalmaya neden olabilecek mekanizma için bileşenler arası kütle aktarımı önerildi. Anahtar Kelimeler. Örten çift yıldızlar, Yıldızların fotometrik analizi, Yıldızların mutlak boyutları, Yıldızların dönem değişimi analizi.
WASP-43 b is one of the most important candidate for detecting an orbital decay. We investigate p... more WASP-43 b is one of the most important candidate for detecting an orbital decay. We investigate pieces of evidence for this expectation as variations in its transit timings, based on the ground and space observations. The data set include the transit observations at the TÜBİTAK National Observatory of Turkey (TUG) and Transiting Exoplanet Survey Satellite (TESS). We present a global model of the system, based on the most precise photometry from space, ground, and archival radial velocity data. Using the homogenized data set and modeled light curves, we measure the mid-transit times for WASP-43 b. Our analysis agrees with a linear ephemeris which we refine its light elements for future observations of the system. However, there is a negative difference between the transit timings derived from TESS data in two sectors (09 & 35) and a hint of an orbital period decrease in the entire data set. Both findings are statistically insignificant due to the short baseline of observations, which prevents us from drawing firm conclusions about the orbital decay of this ultra-short period planet. However, assuming the effect of this decrease of the period in the planet's orbit, we derive a lower limit for the reduced tidal quality factor as Q ′ * > (4.01 ± 1.15) × 10 5 from the best-fitting quadratic function. Finally, we calculate a probable rotational period for this system as 7.52 days from the out-of-transit flux variation in the TESS light curves due to spot modulation.
NY Virginis is an eclipsing binary system with a subdwarf B primary and an M type dwarf secondary... more NY Virginis is an eclipsing binary system with a subdwarf B primary and an M type dwarf secondary. Recent studies (Qian et al. 2012; Lee et al. 2014) suggested the presence of two circumbinary planets with a few Jovian masses within the system. Lee et al. (2014) examined the orbital stabilities of the suggested planets, using the best-fit parameters derived from their eclipse timing variation analysis. They found that the outer companion should be ejected from the system in about 800 000 years. An observational report from Pulley et al. (2016) pointed out that the recent mideclipse times of the binary deviate significantly from the models suggested by Lee et al. (2014). In fact, variations in the orbital period of the system had already been recognized by many authors, but the parameters of these variations vary significantly as new data accumulate. Here, we analyze the eclipse timing variations of the NY Vir system, using new mid-eclipse times that we have obtained together with earlier published measurements in order to understand the nature of the system and constrain its parameters.
Turkish Journal of Astronomy and Astrophysics, Dec 30, 2022
Geçiş yapan ötegezegenlere ait parametreleri hassas bir şekilde belirleyebilmek için geçiş ışık e... more Geçiş yapan ötegezegenlere ait parametreleri hassas bir şekilde belirleyebilmek için geçiş ışık eğrilerinde görülebilecek zaman değişimlerini tespit etmek oldukça önemlidir. Geçiş ve örtülme ortası zamanları, kenar kararması, yıldız aktivitesi ya da yıldızın basıklığı gibi ışık eğrisi morfolojisini etkileyen nedenlerle ya da sisteme ilave nesneler, yörünge presesyonu, açısal momentum değişimi gibi nedenlerle saniye, dakika veya saat mertebesinde, çoğunlukla çevrimsel şekilde değişebilmektedir. Bu çalışmada manyetik aktivite gösteren barınak yıldızlarda gözlenen yüzey lekelerinin gezegen tarafından örtülmesinin geçiş ortası zamanlarındaki değişime etkileri incelenmektedir.
h i g h l i g h t s Period behavior is examined, sine fit of Qian et al. (2008) is refuted. New R... more h i g h l i g h t s Period behavior is examined, sine fit of Qian et al. (2008) is refuted. New RV results, and new VRI and BVRI light curves are presented. New WD analyses of our data and also the data of Qian et al. (2008). All three models effectively agree within error limits. The spot moves from 2005 to 2013. Follow-up observations are suggested.
We have been carrying out a program for over five years to observe transits of selected exoplanet... more We have been carrying out a program for over five years to observe transits of selected exoplanets with 1 meter Turkish Telescope, T100 (Baştürk et al. 2014, 2015), by making use of the wellestablished defocusing technique (Southworth et al. 2009) to achieve high photometric precision. In this contribution, we review the results of our observing program in timing perspective. The basic idea behind defocusing technique is to have the advantage of posing the detector for longer durations in the observations of bright stars, otherwise observed within very short integration times. Then the effect of the photon noise is diminished, which dominates in the short cadence observations. Longer exposures also help in reducing the noise contribution of the atmospheric scintillation. Noise contributions of the imperfect tracking and flat-fielding are mitigated by integrating over a larger area on the detector as well. Although fewer images can be acquired in a given time, we argue that the timing precision is improved because of better photometric precision. This contribution has been supported by TÜBİTAK-3001 project 116F350.
American Astronomical Society Meeting Abstracts #217, 2011
ABSTRACT The first public data release from the Kepler Space Telescope contained over 156,000 sta... more ABSTRACT The first public data release from the Kepler Space Telescope contained over 156,000 stars which had been monitored continuously for approximately 33 days. With continuous photometric monitoring and unprecedented ultra-high precision, the Kepler dataset is an splendid resource for investigating stellar rotation (and age) via starspots as well as for investigating starspot fractional coverage and distributions, starspot lifetime and differential rotation as a function of spectral type and rotation/age. Here, we narrowed our focus to the 306 planetary candidates, mostly main sequence late F, G and K stars, released during June 2010 (see Boruki et al. 2010). This is an attractive data set for the study of starspots properties since these stars host transiting planets with orbital planes almost exactly aligned with our line-of-sight and will generally have the host stars&#39; rotation axes perpendicular to the planetary orbital plane. Thus, the inclination of the star&#39;s rotation axis can be assumed known and should (in most cases) be at right angles to our line-of-sight. Using a Lomb-Scargle Periodogram analysis, we have extracted reliable rotation periods and spot coverages for stars which showed evidence for starspots. From the measured rotation periods, we were able to determine, empirically, the age of the stellar system (using Villanova rotation-age relations) and investigate the potential tidal evolution of the planet-star system. However, we found good evidence that rotation-age relations do not apply to stars that host short-period, Jupiter sized planets. The aforementioned stars show a definite tendency towards star-rotation-planet orbital synchronization. The initial results of this exploratory program will be discussed. This project was initiated at the 2010 Sagan Exoplanet Summer Workshop hosted by NExScI at Caltech. We wish to thank NASA and the organizers of the workshop - in particular Dawn Gelino and Carolyn Brinkworth. EG wishes also to acknowledge support from NSF/RUI Grant AST-10-09903.
In this paper, we present a combined photometric, spectroscopic, and orbital period study of thre... more In this paper, we present a combined photometric, spectroscopic, and orbital period study of three early-type eclipsing binary systems: XZ Aql, UX Her, and AT Peg. As a result, we have derived the absolute parameters of their components and, on that basis, we discuss their evolutionary states. Furthermore, we compare their parameters with those of other binary systems and with theoretical models. An analysis of all available up-to-date times of minima indicated that all three systems studied here show cyclic orbital changes; their origin is discussed in detail. Finally, we performed a frequency analysis for possible pulsational behavior, and as a result we suggest that XZ Aql hosts a δ Scuti component.
The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey... more The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey for transiting planets orbiting bright stars for over ten years. The KELT images have a pixel scale of ∼ 23 pixel −1-very similar to that of NASA's Transiting Exoplanet Survey Satellite (TESS)-as well as a large point spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with higher spatial resolution, cadence, and photometric precision than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1,600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ∼450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1,128 bright stars (6 < V < 13) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observa-KELT-FUN AND KELT FALSE POSITIVES 3 tions. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS.
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Papers by Ozgur Basturk