Browsing by Author "Derman, Ethem"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Light-curve and period changes of AB Andromedae(1994) Derman, Ethem; Akalın, A; Selam, Salim O; Müyesseroğlu, Zekeriya; Demirçan, Osman; Fen FakültesiNew photoelectric observations of AB And obtained between 1989 and 1992 have been used, together with all available light curves from the literature, to study the light-curve variation of the system and its probable connection with the orbital period variation. A long-term brightness variation in the light levels is detected. The maximum brightness occurred in 1970 (±3 yr). A period study based on all available times of minimum light (of which 22 are newly determined) reveals that the photometric period of the system oscillates around a mean value (P0≈0.331890d) with an oscillation period of ≈88.0\textpm0.2 yr and a half-amplitude of 0.000 003 76 d. Such a variation can be caused by either (i) a period modulation due to the magnetic activity cycle of the active primary component, or (ii) a light-traveltime effect due to a third body in the system. It is shown that the third body, if it exists, can only be a white dwarf; this can be checked by ultraviolet spectroscopy. The rms light variation of the system predicted by Applegate's theory of the magnetic activity modulation of the orbital period is found to be comparable with the observed amplitude of long-term brightness variations of the system. However, the brightness variation is found to be 90° out of phase with the O–C curve. Such a phase shift can be explained in terms of the damping effect of the convective zone. The theory predicts a subsurface magnetic field of 7.4 kG for the primary component of AB And.Item Light-curve and period changes of AB-Andromedae(1994) Selam, Selim; Derman, Ethem; Müyesseroğlu, Zekeriya; Akalın, Aynur; Demircan, Osman; Fen FakültesiNew photoelectric observations of AB And obtained between 1989 and 1992 have been used, together with all available light curves from the literature, to study the light-curve variation of the system and its probable connection with the orbital period variation. A long-term brightness variation in the light levels is detected. The maximum brightness occurred in 1970 (+/- 3 yr). A period study based on all available times of minimum light (of which 22 are newly determined) reveals that the photometric period of the system oscillates around a mean value (P0 almost-equal-to 0.331 890 d) with an oscillation period of almost-equal-to 88.0 +/- 0.2 yr and a half-amplitude of 0.000 003 76 d. Such a variation can be caused by either (i) a period modulation due to the magnetic activity cycle of the active primary component, or (ii) a light-traveltime effect due to a third body in the system. It is shown that the third body, if it exists, can only be a white dwarf; this can be checked by ultraviolet spectroscopy. The rms light variation of the system predicted by Applegate's theory of the magnetic activity modulation of the orbital period is found to be comparable with the observed amplitude of long-term brightness variations of the system. However, the brightness variation is found to be 90-degrees out of phase with the O - C curve. Such a phase shift can be explained in terms of the damping effect of the convective zone. The theory predicts a subsurface magnetic field of 7.4 kG for the primary component of AB And.Item Minimum zamanın saptanmasında dalga boyunun etkisinin incelenmesi(Fen Bilimleri Enstitüsü, 1995) Kitaplı, Nurtekin; Derman, Ethem; Astronomi ve Uzay BilimleriIn the present thesis, the wavelength dependence of the observed times of minima of eclipsing binaries were analysed. Many times of minima of different type eclipsing binaries in different wavelength extracted from the literature and some times of minima calculated using the orginal observation with the Kwee Van Woerden method and minima times database constructed. As man? published times of minima are generali? the average of different colors in papers. It had been necesserfly recalculate many of me minima times. A statistical work was done using rrrinima times in hard and the different behaivours of the eclipsing binaries in different colors were investigated. As a result, of this investigation, it was seen that the RS CVn systems and O-B and G spectral type systems are in a different nature in contrast to other eclipsing binary systems. It was arived that the differences between the minima times in different colors are great in these systems. KEY WORDS: Minima times. Changing Minima times according to colours, Light curve.Item Robotik teleskop arşivlerinden farklı gök cisimlerinin saptanması(Fen Bilimleri Enstitüsü, 2010) Güçsav, Burak Bülent; Derman, Ethem; Astronomi ve Uzay BilimleriRobotic telescopes are indispensable for digital sky surveys. The fully or semiautomatic pipelines designed for the purpose of the survey can yield quick pre-analysisof bulk amount of data. ROTSE-III telescope network which consists of 4 telescopesgeographically distributed around the world, has been formed for the ground basedoptical follow-up observations of Gamma Ray Bursts. The idle time of the telescopesare in use of independent research facilities. The ROTSE-IIId telescope located at TUG,Bakırlıtepe is part of the ROTSE-III network. In this thesis, by the use of data obtainedfrom the %30 Turkish time identification of pre known or possible new exploration ofvariable stars has been studied. The ROTSE-IIId telescope pipeline, automaticly makesthe astrometrical and photometrical transformations, obtains the morphology of theobjects identified in the CCD frame and files all the information gathered in catalogfiles.Besides the ROTSE-III pipeline, a fresh-design one which can process raw CCDdata is demonstrated and the results obtained are compared with the current. As the firstresults, 152 short and long period variable stars have been identified, which at least 20of them are non-existant in the GCVS catalog. Considering the relatively huge amountof data, it was decided to use a paralel computer clusterItem Transit timing analysis in the HAT-P-32 system(2014) Derman, Ethem; Fen FakültesiWe present the results of 45 transit observations obtained for the transiting exoplanet HATP-32b. The transits have been observed using several telescopes mainly throughout the YETI (Young Exoplanet Transit Initiative) network. In 25 cases, complete transit light curves with a timing precision better than 1.4min have been obtained. These light curves have been used to refine the system properties, namely inclination i, planet-to-star radius ratio Rp/Rs, and the ratio between the semimajor axis and the stellar radius a/Rs. First analyses by Hartman et al. suggests the existence of a second planet in the system, thus we tried to find an additional body using the transit timing variation (TTV) technique. Taking also the literature data points into account, we can explain all mid-transit times by refining the linear ephemeris by 21ms. Thus, we can exclude TTV amplitudes of more than∼1.5minItem Transit timing analysis in the HAT-P-32 system(2014) Derman, Ethem; Fen FakültesiWe present the results of 45 transit observations obtained for the transiting exoplanet HATP-32b. The transits have been observed using several telescopes mainly throughout the YETI (Young Exoplanet Transit Initiative) network. In 25 cases, complete transit light curves with a timing precision better than 1.4 min have been obtained. These light curves have been used to refine the system properties, namely inclination i, planet-to-star radius ratio R-p/R-s, and the ratio between the semimajor axis and the stellar radius a/R-s. First analyses by Hartman et al. suggests the existence of a second planet in the system, thus we tried to find an additional body using the transit timing variation (TTV) technique. Taking also the literature data points into account, we can explain all mid-transit times by refining the linear ephemeris by 21 ms. Thus, we can exclude TTV amplitudes of more than similar to 1.5min.