Author name code: bostanci ADS astronomy entries on 2022-09-14 author:"Bostanci, Z. Funda" ------------------------------------------------------------------------ Title: Burst-Disk Interaction in 4U 1636-536 as Observed by NICER Authors: Güver, Tolga; Bostancı, Z. Funda; Boztepe, Tuğba; Göğüş, Ersin; Bult, Peter; Kashyap, Unnati; Chakraborty, Manoneeta; Ballantyne, David R.; Ludlam, R. M.; Malacaria, C.; Jaisawal, Gaurava K.; Strohmayer, Tod E.; Guillot, Sebastien; Ng, Mason Bibcode: 2022ApJ...935..154G Altcode: 2022arXiv220704107G We present the detection of 51 thermonuclear X-ray bursts observed from 4U 1636-536 by the Neutron Star Interior Composition Explorer (NICER) over the course of a 3 yr monitoring campaign. We perform time-resolved spectroscopy for 40 of these bursts and show the existence of a strong soft excess in all the burst spectra. The excess emission can be characterized by the use of a scaling factor (the f a method) to the persistent emission of the source, which is attributed to the increased mass accretion rate onto the neutron star due to Poynting-Robertson drag. The soft excess emission can also be characterized by the use of a model taking into account the reflection of the burst emission off the accretion disk. We also present time-resolved spectral analysis of five X-ray bursts simultaneously observed by NICER and AstroSat, which confirm the main results with even greater precision. Finally, we present evidence for Compton cooling using seven X-ray bursts observed contemporaneously with NuSTAR, by means of a correlated decrease in the hard X-ray lightcurve of 4U 1636-536 as the bursts start. Title: A NICER look at thermonuclear X-ray bursts from Aql X-1 Authors: Güver, Tolga; Boztepe, Tuğba; Ballantyne, D. R.; Bostancı, Z. Funda; Bult, Peter; Jaisawal, Gaurava K.; Göğüş, Ersin; Strohmayer, Tod E.; Altamirano, Diego; Guillot, Sebastien; Chakrabarty, Deepto Bibcode: 2022MNRAS.510.1577G Altcode: 2021MNRAS.tmp.3070G; 2021arXiv211112105G We present spectral and temporal properties of all the thermonuclear X-ray bursts observed from Aql X-1 by the Neutron Star Interior and Composition Explorer (NICER) between 2017 July and 2021 April. This is the first systematic investigation of a large sample of type I X-ray bursts from Aql X-1 with improved sensitivity at low energies. We detect 22 X-ray bursts including two short recurrence burst events in which the separation was only 451 s and 496 s. We perform time resolved spectroscopy of the bursts using the fixed and scaled background (fa method) approaches. We show that the use of a scaling factor to the pre-burst emission is the statistically preferred model in about 68 per cent of all the spectra compared to the fixed background approach. Typically the fa values are clustered around 1-3, but can reach up to 11 in a burst where photospheric radius expansion is observed. Such fa values indicate a very significant increase in the pre-burst emission especially at around the peak flux moments of the bursts. We show that the use of the fa factor alters the best-fitting spectral parameters of the burst emission. Finally, we employed a reflection model instead of scaling the pre-burst emission. We show that reflection models also do fit the spectra and improve the goodness of the fits. In all cases, we see that the disc is highly ionized by the burst emission and the fraction of the reprocessed emission to the incident burst flux is typically clustered around 20 per cent. Title: A study of open clusters Frolov 1 and NGC 7510 using CCD UBV photometry and Gaia DR2 astrometry Authors: Yontan, Talar; Bilir, Selçuk; Ak, Tansel; Akbulut, Burcu; Canbay, Remziye; Banks, Timothy; Paunzen, Ernst; Ak, Serap; Bostancı, Zahide Funda Bibcode: 2021AN....342..538Y Altcode: 2020arXiv201212269Y We present reddening, photometric metallicity, age, and distance estimates for the Frolov 1 and NGC 7510 open clusters based on charge coupled device (CCD) UBV photometric and Gaia data. Photometric observations were collected using the 1 m telescope of the TÜBİTAK National Observatory. Gaia data release 2 (DR2) proper motion data in the direction of two groupings were used to identify cluster membership. We determined mean proper motion values of (μα cos δ, μδ) = (- 3.02 ± 0.10, - 1.75 ± 0.08) and (-3.66 ± 0.07, -2.17 ± 0.06) mas year-1 for Frolov 1 and NGC 7510, respectively. We used two color diagrams to obtain E(B - V) color excesses for Frolov 1 and NGC 7510 of 0.65 ± 0.06 and 1.05 ± 0.05 mag, respectively. We derived the photometric metallicity of Frolov 1 as [Fe/H] = 0.03 ± 0.03 dex and adopted a solar metallicity for NGC 7510. Based on these reddening and metallicities, we determined the distance moduli and ages of the clusters by fitting stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code (PARSEC) isochrones to the cluster color-magnitude diagrams. Isochrone fitting distances for Frolov 1 and NGC 7510 are 2, 864 ± 254 and 2, 818 ± 247 pc, respectively, which correspond to the ages 35 ± 10 Myr and 18 ± 6 Myr. We also calculated mean Gaia distances and compared them with those given in the literature and in this study, concluding that our results are in good agreement with previous work. Finally, we calculated the mass function slopes and found them to be X = -1.21 ± 0.18 for Frolov 1 and X = -1.42 ± 0.27 for NGC 7510. Title: Metallicity and absolute magnitude calibrations for F-G type main-sequence stars in the Gaia era Authors: Çelebi, M.; Bilir, S.; Ak, S.; Ak, T.; Bostancı, Z. F.; Yontan, T. Bibcode: 2019Ap&SS.364..172C Altcode: 2019arXiv191001111C In this study, photometric metallicity and absolute magnitude calibrations were derived using F-G spectral type main-sequence stars in the Solar neighbourhood with precise spectroscopic, photometric and Gaia astrometric data for UBV photometry. The sample consists of 504 main-sequence stars covering the temperature, surface gravity and colour index intervals 5300< T_{eff} < 7300 K, log g > 4 (cgs) and 0.3<(B-V)0<0.8 mag, respectively. Stars with relative trigonometric parallax errors σ _{π }/π ≤ 0.01 were preferred from Gaia DR2 data for the estimation of their MV absolute magnitudes. In order to obtain calibrations, (U-B)0 and (B-V)0 colour indices of stars were preferred and a multi-variable second order equation was used. Calibrations are valid for main-sequence stars in the metallicity and absolute magnitude ranges -2<{[Fe/H]}<0.5 dex and 2.5< MV<6 mag, respectively. The mean value and standard deviation of the differences between original and estimated values for the metal abundance and absolute magnitude are < Δ {[Fe/H]}> =0.00± 0.11 dex and < Δ MV > =0.00± 0.22 mag, respectively. In this work, it has been shown that more precise iron abundance and absolute magnitude values were obtained with the new calibrations, compared to previous calibrations in the literature. Title: VizieR Online Data Catalog: 504 F-G dwarfs photometric metallicities (Celebi+, 2019) Authors: Celebi, M.; Bilir, S.; Ak, S.; Ak, T.; Bostanci, Z. F.; Yontan, T. Bibcode: 2019yCatp017036401C Altcode: Photometric, spectroscopic and astrometric data for 504 F-G type main-sequence stars

(1 data file). Title: CCD UBV photometric and Gaia astrometric study of eight open clusters—ASCC 115, Collinder 421, NGC 6793, NGC 7031, NGC 7039, NGC 7086, Roslund 1 and Stock 21 Authors: Yontan, T.; Bilir, S.; Bostancı, Z. F.; Ak, T.; Ak, S.; Güver, T.; Paunzen, E.; Ürgüp, H.; Çelebi, M.; Akti, B. A.; Gökmen, S. Bibcode: 2019Ap&SS.364..152Y Altcode: 2019arXiv190900345Y In this study, we carried out CCD UBV photometry of eight open clusters, ASCC 115, Collinder 421, NGC 6793, NGC 7031, NGC 7039, NGC 7086, Roslund 1, Stock 21, and determined their reddening, metallicity, distance, age, and mass functions. We used new Gaia Data Release 2 (DR2) astrometric data to separate cluster member stars from the field stars and obtain precise structural and astrophysical parameters. To identify cluster member stars we utilized an unsupervised membership assignment code (UPMASK), which is based on the photometric and astrometric data. The density distributions for the open clusters show good fits with the empirical King model except for Roslund 1 and Stock 21 not having central concentration. The colour excesses and metallicities were derived separately using U-B× B-V two-colour diagrams. Keeping these parameters as constants, we simultaneously calculated distance moduli and ages of the clusters from V× B-V and V × U-B colour-magnitude diagrams using PARSEC theoretical isochrones. Taking into account Gaia DR2 proper motion components and parallaxes of the member stars, we also calculated mean proper motions and distances for the clusters. Distances derived both from isochrone fitting to colour-magnitude diagrams of the clusters and Gaia DR2 trigonometric parallaxes are compatible with each other. Slopes of the mass functions of the eight open clusters are in good agreement with Salpeter (Astrophys. J. 121:161, 1955) value of 1.35. Title: CCD UBV photometric study of five open clusters—Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1 Authors: Bostancı, Z. F.; Yontan, T.; Bilir, S.; Ak, T.; Güver, T.; Ak, S.; Paunzen, E.; Başaran, Ç. S.; Vurgun, E.; Akti, B. A.; Çelebi, M.; Ürgüp, H. Bibcode: 2018Ap&SS.363..143B Altcode: 2018arXiv180600947B In this study, we present CCD UBV photometry of poorly studied open star clusters, Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1, located in the first and second Galactic quadrants. Observations were obtained with T100, the 1-m telescope of the TÜBİTAK National Observatory. Using photometric data, we determined several astrophysical parameters such as reddening, distance, metallicity and ages and from them, initial mass functions, integrated magnitudes and colours. We took into account the proper motions of the observed stars to calculate the membership probabilities. The colour excesses and metallicities were determined independently using two-colour diagrams. After obtaining the colour excesses of the clusters Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1 as 0.19±0.06, 0.15±0.05, 0.32±0.05, 0.12± 0.04, and 0.43±0.06 mag, respectively, the metallicities are found to be 0.00±0.09, 0.02±0.11, 0.03±0.07, 0.01±0.08, and 0.01±0.08 dex, respectively. Furthermore, using these parameters, distance moduli and age of the clusters were also calculated from colour-magnitude diagrams simultaneously using PARSEC theoretical models. The distances to the clusters Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1 are 1050±90, 1610±190, 1210±150, 1060±90, and 1710±250 pc, respectively, while corresponding ages are 400±100, 750±150, 400±100, 600±100, and 175±50 Myr, respectively. Our results are compatible with those found in previous studies. The mass function of each cluster is derived. The slopes of the mass functions of the open clusters range from 1.31 to 1.58, which are in agreement with Salpeter's initial mass function. We also found integrated absolute magnitudes varying from -4.08 to -3.40 for the clusters. Title: Metallicity calibration and photometric parallax estimation: II. SDSS photometry Authors: Tunçel Güçtekin, S.; Bilir, S.; Karaali, S.; Plevne, O.; Ak, S.; Ak, T.; Bostancı, Z. F. Bibcode: 2017Ap&SS.362...17T Altcode: 2016arXiv161108095T We used the updated [Fe/H] abundances of 168 F-G type dwarfs and calibrated them to a third order polynomial in terms of reduced ultraviolet excess, δ_{0.41} defined with ugr data in the SDSS. We estimated the Mg absolute magnitudes for the same stars via the re-reduced Hipparcos parallaxes and calibrated the absolute magnitude offsets, Δ Mg, relative to the intrinsic sequence of Hyades to a third order polynomial in terms of δ_{0.41}. The ranges of the calibrations are -2<[Fe/H]≤ 0.3 dex and 4< Mg≤ 6 mag. The mean of the residuals and the corresponding standard deviation for the metallicity calibration are 0 and 0.137 mag; while, for the absolute magnitude calibration they are 0 and 0.179 mag, respectively. We applied our procedures to 23,414 dwarf stars in the Galactic field with the Galactic coordinates 85° ≤ b≤ 90°, 0° ≤ l≤ 360° and size 78 deg2. We estimated absolute magnitude Mg dependent vertical metallicity gradients as a function of vertical distance Z. The gradients are deep in the range of 0< Z≤ 5 kpc, while they are very small positive numbers beyond Z=5 kpc. All dwarfs with 5< Mg≤ 6 mag are thin-disc stars and their distribution shows a mode at (g-r)0≈ 0.38 mag, while the absolute magnitudes 4< Mg ≤ 5 are dominated by thick disc and halo stars, i.e. the apparently bright ones (g0≤ 18 mag) are thick-disc stars with a mode at (g-r)0∼ 0.38 mag, while the halo population is significant in the faint stars (g0>18 mag). Title: VizieR Online Data Catalog: NGC 225 CCD UBV photometry (Bilir+, 2016) Authors: Bilir, S.; Bostanci, Z. F.; Yontan, T.; Guver, T.; Bakis, V.; Ak, T.; Ak, S.; Paunzen, E.; Eker, Z. Bibcode: 2016yCatp057005801B Altcode: CCD UBVRI images of the open cluster NGC 225 and standard stars selected from Landolt (2009, Cat. J/AJ/137/4186) were acquired on 2012 July 18 using a 1-m Ritchey-Chretien telescope (T100) located at the TUBITAK National Observatory (TUG) in Bakirlitepe, Antalya/Turkey.

(1 data file). Title: CCD UBV photometry and kinematics of the open cluster NGC 225 Authors: Bilir, Selçuk; Bostancı, Z. Funda; Yontan, Talar; Güver, Tolga; Bakış, Volkan; Ak, Tansel; Ak, Serap; Paunzen, Ernst; Eker, Zeki Bibcode: 2016AdSpR..58.1900B Altcode: 2016arXiv160608608B We present the results of CCD UBV photometric and spectroscopic observations of the open cluster NGC 225. In order to determine the structural parameters of NGC 225, we calculated the stellar density profile in the cluster's field. We estimated the probabilities of the stars being physical members of the cluster using the existing astrometric data. The most likely members of the cluster were used in the determination of the astrophysical parameters of the cluster. We calculated the mean radial velocity of the cluster as Vr = - 8.3 ± 5.0 km s-1 from the optical spectra of eight stars in the cluster's field. Using the U - B vs B - V two-colour diagram and UV excesses of the F-G type main-sequence stars, the reddening and metallicity of NGC 225 were inferred as E (B - V) = 0.151 ± 0.047 mag and [Fe /H ] = - 0.11 ± 0.01 dex, respectively. We fitted the colour-magnitude diagrams of NGC 225 with the PARSEC isochrones and derived the distance modulus, distance and age of the cluster as μV = 9.3 ± 0.07 mag, d = 585 ± 20 pc and t = 900 ± 100 Myr, respectively. We also estimated the galactic orbital parameters and space velocity components of the cluster and found that the cluster has a slightly eccentric orbit of e = 0.07 ± 0.01 and an orbital period of Porb = 255 ± 5 Myr. Title: VizieR Online Data Catalog: NGC 6819 CCD UBV photometry (Ak+, 2016) Authors: Ak, T.; Bostanci, Z. F.; Yontan, T.; Bilir, S.; Guver, T.; Ak, S.; Urgup, H.; Paunzen, E. Bibcode: 2016yCatp017036102A Altcode: CCD UBVRI images of the open cluster NGC 6819 and standard stars selected from Landolt (2009, Cat. J/AJ/137/4186) were acquired on 2015 May 18 using a 1-m Ritchey-Chretien telescope (T100) located at the TUBITAK National Observatory (TUG) in Bakirlitepe, Antalya/Turkey.

(1 data file). Title: Local Stellar Kinematics from RAVE data—VII. Metallicity Gradients from Red Clump Stars Authors: Önal Taş, Ö.; Bilir, S.; Seabroke, G. M.; Karaali, S.; Ak, S.; Ak, T.; Bostancı, Z. F. Bibcode: 2016PASA...33...44O Altcode: 2016arXiv160707049O; 2016PASA...33...44T We investigate the Milky Way Galaxy's radial and vertical metallicity gradients using a sample of 47 406 red clump stars from the RAdial Velocity Experiment Data Release 4. Distances are calculated by adopting Ks -band absolute magnitude as -1.54±0.04 mag for the sample. The metallicity gradients are calculated with their current orbital positions (R gc and Z) and with their orbital properties (R m and z max): d[Fe/H]/dR gc = -0.047±0.003 dex kpc-1 for |Z| ≤ 0.5 kpc and d[Fe/H]/dR m = -0.025±0.002 dex kpc-1 for z max ≤ 0.5 kpc. This reaffirms the radial metallicity gradient in the thin disc but highlights that gradients are sensitive to the selection effects caused by the difference between R gc and R m. The radial gradient is flat in the distance interval 0.5-1 kpc from the plane and then becomes positive greater than 1 kpc from the plane. The radial metallicity gradients are also eccentricity dependent. We showed that d[Fe/H]/dR m = -0.089±0.010, -0.073±0.007, -0.053±0.004 and -0.044±0.002 dex kpc-1 for e p ≤ 0.05, e p ≤ 0.07, e p ≤ 0.10 and e p ≤ 0.20 sub-samples, respectively, in the distance interval z max ≤ 0.5 kpc. Similar trend is found for vertical metallicity gradients. Both the radial and vertical metallicity gradients are found to become shallower as the eccentricity of the sample increases. These findings can be used to constrain different formation scenarios of the thick and thin discs. Title: Metallicity calibration and photometric parallax estimation: I. UBV photometry Authors: Tunçel Güçtekin, S.; Bilir, S.; Karaali, S.; Ak, S.; Ak, T.; Bostancı, Z. F. Bibcode: 2016Ap&SS.361..186T Altcode: 2016arXiv160502225T We present metallicity and photometric parallax calibrations for the F and G type dwarfs with photometric, astrometric and spectroscopic data. The sample consists of 168 dwarf stars covering the colour, iron abundance and absolute magnitude intervals 0.30<(B-V)0<0.68 mag, -2.0<[Fe/H]<0.4 dex and 3.4< MV<6.0 mag, respectively. The means and standard deviations of the metallicity and absolute magnitude residuals are small, i.e. <Δ[Fe/H]_{res}rangle=0 and σ=0.134 dex, and <Δ (MV)_{res}rangle=0 and σ=0.174 mag, respectively, which indicate accurate metallicity and photometric parallax estimations. Title: CCD UBV photometry of the open cluster NGC 6819 Authors: Ak, T.; Bostancı, Z. F.; Yontan, T.; Bilir, S.; Güver, T.; Ak, S.; Ürgüp, H.; Paunzen, E. Bibcode: 2016Ap&SS.361..126A Altcode: 2016arXiv160300474A We present the results of CCD UBV observations of the open cluster NGC 6819. We calculated the stellar density profile in the cluster's field to determine the structural parameters of NGC 6819. Using the existing astrometric data, we calculated the probabilities of the stars being physical members of the cluster, and used these objects in the determination of the astrophysical parameters of NGC 6819. We inferred the reddening and metallicity of the cluster as E(B-V)=0.130±0.035 mag and [Fe/H]=+0.051± 0.020 dex, respectively, using the U-B vs B-V two-colour diagram and UV excesses of the F-G type main-sequence stars. We fit the colour-magnitude diagrams of NGC 6819 with the PARSEC isochrones and derived the distance modula, distance and age of the cluster as μV=12.22± 0.10 mag, d=2309±106 pc and t=2.4±0.2 Gyr, respectively. The parameters of the galactic orbit estimated for NGC 6819 indicate that the cluster is orbiting in a slightly eccentric orbit of e=0.06 with a period of P_{orb}= 142 Myr. The slope of the mass function estimated for the cluster is close to the one found for the stars in the solar neighbourhood. Title: VizieR Online Data Catalog: NGC 6866 UBVRI photometry (Bostanci+, 2015) Authors: Bostanci, Z. F.; Ak, T.; Yontan, T.; Bilir, S.; Guver, T.; Ak, S.; Cakirli, O.; Ozdarcan, O.; Paunzen, E.; De Cat, P.; Fu, J. N.; Zhang, Y.; Hou, Y.; Li, G.; Wang, Y.; Zhang, W.; Shi, J.; Wu, Y. Bibcode: 2016yCat..74531095B Altcode: CCD UBVRI images of the open cluster NGC 6866 and standard stars selected from Landolt (2009, Cat. J/AJ/137/4186) were acquired on 2012 July 18 using a 1-m Ritchey-Chretien telescope (T100) located at the TUBITAK National Observatory (TUG) in Bakirlitepe, Antalya/Turkey.

(1 data file). Title: Local Stellar Kinematics from RAVE Data - VI. Metallicity Gradients Based on the F-G Main-Sequence Stars Authors: Plevne, O.; AK, T.; Karaali, S.; Bilir, S.; Ak, S.; Bostanci, Z. F. Bibcode: 2015PASA...32...43P Altcode: 2015arXiv151001749P We estimated iron and metallicity gradients in the radial and vertical directions with the F and G type dwarfs taken from the Radial Velocity Experiment Data Release 4 database. The sample defined by the constraints Z max ⩽ 825 pc and e p ⩽ 0.10 consists of stars with metal abundances and space velocity components agreeable with the thin-disc stars. The radial iron and metallicity gradients estimated for the vertical distance intervals 0 < Z max ⩽ 500 and 500 < Z max ⩽ 800 pc are d[Fe/H]/dR_m=-0.083± 0.030 and d[Fe/H]/dR_m=-0.048± 0.037 dex kpc-1, and d[M/H]/dR_m=-0.063± 0.011 and d[M/H]/dR_m=-0.028± 0.057 dex kpc-1, respectively, where R m is the mean Galactocentric distance. The iron and metallicity gradients for less number of stars at further vertical distances, 800 < Z max ⩽ 1500 pc, are mostly positive. Compatible iron and metallicity gradients could be estimated with guiding radius (R g) for the same vertical distance intervals 0 < Z max ⩽ 500 and 500 < Z max ⩽ 800 pc, i.e. d[Fe/H]/dR_g=-0.083± 0.030 and d[Fe/H]/dR_g=-0.065± 0.039 dex kpc-1; d[M/H]/dR_g=-0.062± 0.018 and d[M/H]/dR_g=-0.055± 0.045 dex kpc-1. F and G type dwarfs on elongated orbits show a complicated radial iron and metallicity gradient distribution in different vertical distance intervals. Significant radial iron and metallicity gradients could be derived neither for the sub-sample stars with R m ⩽ 8 kpc, nor for the ones at larger distances, R m > 8 kpc. The range of the iron and metallicity abundance for the F and G type dwarfs on elongated orbits, [-0.13, -0.01), is similar to the thin-disc stars, while at least half of their space velocity components agree better with those of the thick-disc stars. The vertical iron gradients estimated for the F and G type dwarfs on circular orbits are d[Fe/H]/dZ_{max}=-0.176± 0.039 dex kpc-1 and d[Fe/H]/dZ_{max}=-0.119± 0.036 dex kpc-1 for the intervals Z max ⩽ 825 and Z max ⩽ 1500 pc, respectively. Title: A comprehensive study of the open cluster NGC 6866 Authors: Bostancı, Z. F.; Ak, T.; Yontan, T.; Bilir, S.; Güver, T.; Ak, S.; Çakırlı, Ö.; Özdarcan, O.; Paunzen, E.; De Cat, P.; Fu, J. N.; Zhang, Y.; Hou, Y.; Li, G.; Wang, Y.; Zhang, W.; Shi, J.; Wu, Y. Bibcode: 2015MNRAS.453.1095B Altcode: 2015arXiv150705968B We present CCD UBVRI photometry of the field of the open cluster NGC 6866. Structural parameters of the cluster are determined utilizing the stellar density profile of the stars in the field. We calculate the probabilities of the stars being physical members of the cluster, using their astrometric data, and perform further analyses using only the most probable members. The reddening and metallicity of the cluster were determined by independent methods. The LAMOST spectra and the ultraviolet excess of the F- and G-type main-sequence stars in the cluster indicate that the metallicity of the cluster is about the solar value. We estimated the reddening E(B - V) = 0.074 ± 0.050 mag using the U - B versus B - V two-colour diagram. The distance modula, the distance and the age of NGC 6866 were derived as μ = 10.60 ± 0.10 mag, d = 1189 ± 75 pc and t = 813 ± 50 Myr, respectively, by fitting colour-magnitude diagrams of the cluster with the PARSEC isochrones. The Galactic orbit of NGC 6866 indicates that the cluster is orbiting in a slightly eccentric orbit with e = 0.12. The mass function slope x = 1.35 ± 0.08 was derived by using the most probable members of the cluster. Title: Short gamma-ray bursts with extended emission observed with Swift/BAT and Fermi/GBM Authors: Kaneko, Y.; Bostancı, Z. F.; Göğüş, E.; Lin, L. Bibcode: 2015MNRAS.452..824K Altcode: 2015arXiv150605899K Some short gamma-ray bursts (GRBs) are followed by longer extended emission (EE), lasting anywhere from ∼10 to ∼100 s. These short GRBs with EE can possess observational characteristics of both short and long GRBs (as represented by GRB 060614), and the traditional classification based on the observed duration places some of them in the long GRB class. While GRBs with EE pose a challenge to the compact-binary merger scenario, they may therefore provide an important link between short- and long-duration events. To identify the population of GRBs with EE regardless of their initial classifications, we performed a systematic search of short GRBs with EE using all available data (up to 2013 February) of both Swift/BAT and Fermi/GBM. The search identified 16 BAT and 14 GBM detected GRBs with EE, several of which are common events observed with both detectors. We investigated their spectral and temporal properties for both the spikes and the EE, and examined correlations among these parameters. Here we present the results of the systematic search as well as the properties of the identified events. Finally, their properties are also compared with short GRBs with EE observed with BATSE, identified through our previous search effort. We found several strong correlations among parameters, especially when all of the samples were combined. Based on our results, a possible progenitor scenario of two-component jet is discussed. Title: CCD UBVRI photometry of NGC 6811 Authors: Yontan, T.; Bilir, S.; Bostancı, Z. F.; Ak, T.; Karaali, S.; Güver, T.; Ak, S.; Duran, Ş.; Paunzen, E. Bibcode: 2015Ap&SS.355..267Y Altcode: 2014arXiv1410.3129Y; 2015Ap&SS.tmp....9Y We present the results of CCD UBVRI observations of the open cluster NGC 6811 obtained on 18th July 2012 with the 1 m telescope at the TÜBİTAK National Observatory (TUG). Using these photometric results, we determine the structural and astrophysical parameters of the cluster. The mean photometric uncertainties are better than 0.02 mag in the V magnitude and B- V, V- R, and V- I colour indices to about 0.03 mag for U- B among stars brighter than magnitude V=18. Cluster member stars were separated from the field stars using the Galaxia model of Sharma et al. (2011) together with other techniques. The core radius of the cluster is found to be r c =3.60 arcmin. The astrophysical parameters were determined simultaneously via Bayesian statistics using the colour-magnitude diagrams V versus B- V, V versus V- I, V versus V- R, and V versus R- I of the cluster. The resulting most likely parameters were further confirmed using independent methods, removing any possible degeneracies. The colour excess, distance modulus, metallicity and the age of the cluster are determined simultaneously as E( B- V)=0.05±0.01 mag, μ=10.06±0.08 mag, [ M/ H]=-0.10±0.01 dex and t=1.00±0.05 Gyr, respectively. Distances of five red clump stars which were found to be members of the cluster further confirm our distance estimation. Title: Oscillatory behaviour of chromospheric fine structures in a network and a semi-active region Authors: Bostancı, Zahide Funda; Gültekin, Asuman; Al, Nurol Bibcode: 2014MNRAS.443.1267B Altcode: 2014arXiv1406.4507B In this work, we study the periodicities of oscillations in dark fine structures using observations of a network and a semi-active region close to the solar disc centre. We simultaneously obtained spatially high-resolution time series of white light images and narrow-band images in the Hα line using the 2D Göttingen spectrometer, which were based on two Fabry-Perot interferometers and mounted in the Vacuum Tower Telescope/Observatorio del Teide/Tenerife. During the observations, the Hα line was scanned at 18 wavelength positions with steps of 125 mÅ. We computed series of Doppler and intensity images by subtraction and addition of the Hα ± 0.3 Å and ± 0.7 Å pairs, sampling the upper chromosphere and the upper photosphere, respectively. Then, we obtained power, coherence and phase difference spectra by performing a wavelet analysis to the Doppler fluctuations. Here, we present comparative results of oscillatory properties of dark fine structures seen in a network and a semi-active region. Title: A new absolute magnitude calibration for red clump stars Authors: Bilir, S.; Ak, T.; Ak, S.; Yontan, T.; Bostancı, Z. F. Bibcode: 2013NewA...23...88B Altcode: 2013arXiv1303.3292B We present an MV absolute magnitude calibration including the B-V colour and [Fe/H] metallicity for the red clump stars in the globular and open clusters with a wide range of metallicities: MV=0.627(±0.104)(B-V)0+0.046(±0.043)[Fe/H]+0.262(±0.111). The calibration equation is valid in the ranges 0.42<(B-V)0<1.20 mag, -1.55<[Fe/H]<+0.40 dex and 0.43<MV<1.03 mag. We found that the consistencies in the comparisons of the distances estimated from the calibration equation in this study both with the distances obtained from trigonometric parallaxes and spectrophotometric analysis demonstrate that reliable precise absolute magnitudes for the clump giants can be estimated from the calibration formula. Title: Local Stellar Kinematics from RAVE Data: IV. Solar Neighbourhood Age-Metallicity Relation Authors: Duran, Ş.; Ak, S.; Bilir, S.; Karaali, S.; Ak, T.; Bostanci, Z. F.; Coşkunoǧlu, B. Bibcode: 2013PASA...30...43D Altcode: 2013arXiv1306.5747D We investigated the age-metallicity relation using a sample of 5691 F- and G-type dwarfs from RAdial Velocity Experiment Data Release 3 (RAVE DR3) by applying several constraints. (i) We selected stars with surface gravities log g(cm s-2) ≥ 3.8 and effective temperatures in the 5310 ≤ T_{eff}(K) ≤ 7300 range and obtained a dwarf sample. (ii) We plotted the dwarfs in metallicity sub-samples in the T_{eff}-(J-K_s)_0 plane to compare with the corresponding data of González Hernández & Bonifacio (2009) and identified the ones in agreement. (iii) We fitted the reduced dwarf sample obtained from constraints (i) and (ii) to the Padova isochrones and re-identified those which occupy the plane defined by isochrones with ages t ≤ 13 Gyr. (iv) Finally, we omitted dwarfs with total velocity errors larger than 10.63 km s-1. We estimated the ages using the Bayesian procedure of Jørgensen & Lindegren (2005). The largest age-metallicity slope was found for early F-type dwarfs. We found steeper slopes when we plotted the data as a function of spectral type rather than Galactic population. We noticed a substantial scatter in metallicity distribution at all ages. The metal-rich old dwarfs turned out to be G-type stars which can be interpreted as they migrated from the inner disc or bulge. Title: Gamma-ray bursts with extended emission observed with BATSE Authors: Bostancı, Zahide Funda; Kaneko, Yuki; Göğüş, Ersin Bibcode: 2013MNRAS.428.1623B Altcode: 2013MNRAS.428.1623F; 2012arXiv1210.2399F We present the results of our systematic search for extended emission components following initial short gamma-ray burst (GRB) spikes, using Burst and Transient Source Experiment (BATSE) observations. We performed the extended emission search for both short- and long-duration GRBs to unveil the BATSE population of a new hybrid class of GRBs similar to GRB 060614. For the identified bursts, we investigate temporal and spectral characteristics of their initial spikes as well as their extended emission. Our results reveal that the fraction of GRBs with extended emission is ∼7 per cent of the total number of our BATSE sample. We find that the spectrum of the extended emission is, in general, softer than that of the initial spike, which is in accord with what has been observed in the prototypical bursts, GRB 060614. We also find that the energy fluence of the extended emission varies on a broad range from 0.1 to 40 times of the fluence of the initial spike. We discuss our results in the context of existing physical models, in particular within the two-component jet model. Title: A Study of Gamma-Ray Bursts with extended emission observed with BATSE Authors: Bostanci, Z. F. Bibcode: 2012grb..confE..25B Altcode: 2012PoS...152E..25B No abstract at ADS Title: Cloud modeling of a network region in H\alpha Authors: Bostanci, Z. F. Bibcode: 2011AN....332..815B Altcode: 2011arXiv1108.0675B In this paper, we analyze the physical properties of dark mottles in the chromospheric network using two-dimensional spectroscopic observations in H\alpha obtained with the Göttingen Fabry-Perot Spectrometer in the Vacuum Tower Telescope at the Observatory del Teide, Tenerife. Cloud modeling was applied to measure the mottles' optical thickness, source function, Doppler width, and line-of-sight velocity. Using these measurements, the number density of hydrogen atoms in levels 1 and 2, total particle density, electron density, temperature, gas pressure, and mass density parameters were determined with the method of Tsiropoula & Schmieder (1997). We also analyzed the temporal behaviour of a mottle using cloud parameters. Our result shows that it is dominated by 3 minute signals in source function, and 5 minutes or more in velocity. Title: Cloud modeling of a quiet solar region in Halpha . Authors: Bostanci, Z. F.; Al Erdoğan, N. Bibcode: 2010MmSAI..81..769B Altcode: 2010arXiv1001.3361B We present chromospheric cloud modeling on the basis of Halpha profile-sampling images taken with the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope (DST). We choose the required reference background profile by using theoretical NLTE profile synthesis. The resulting cloud parameters are converted into estimates of physical parameters (temperature and various densities). Their mean values compare well with the VAL-C model. Title: A Study on the Fine Structure of a Quiet Solar Chromospheric Region Near the Disk Center Authors: Bostanci, Z. F. Bibcode: 2009PhDT.........1B Altcode: In this study, the morphological and physical properties of fine structures of a quiet chromospheric region were studied on CCD images and the dynamical characteristics of the investigated region were identified.

The observations were obtained with the Vacuum Tower Telescope in Tenerife, Canary Islands and the Dunn Solar Telescope at the National Solar Observatory, New Mexico, USA. During the observations, time series of high spatial, spectral and temporal resolution images were taken by scanning the Halpha profile at different wavelength steps of narrow bandpasses.

Intensity and Doppler images at the line center and the wing of Halpha were derived by using the standard Doppler-shift and Lambdameter methods. Then these images were used to distinguish variations on the morphology and velocity of fine structures with the height and time.

The cloud model, which has been used extensively in the analysis of Hα contrast profiles was applied to the observations to derive the physical parameters such as the source function, optical depth at the line center, Doppler width and the line of sight velocity of the investigated fine structures. In order to determine physical conditions in these structures, the values of cloud model parameters were used together to derive other parameters such as the number density of hydrogen atoms at levels 1 and 2, total particle density, electron density, temperature, gas pressure, mass density.

Finally, global properties of chromospheric features and time evolution of their physical parameters were discussed in detail and then compared with results obtained by various authors. It is concluded that the dark and the bright mottles observed at the network boundaries on the disk have a similar nature and that they also have similar physical properties with the spicules observed at the limb. Title: Physical Parameters of a Rosette Observed in H-alpha Authors: Al Erdogan, N.; Bostanci, Z. F.; Gultekin, A. Bibcode: 2008ESPM...12.2.29A Altcode: In May 2002, the solar chromosphere was observed in H? with the two-dimensional 'Gottingen' Fabry-Perot spectrometer which is mounted in the German Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife. The data consist of broad-band and narrow-band images which were taken by scanning through this line. For a short period of this time series, we calculated the source function, the line-of-sight velocity, the Doppler width and the optical depth using Becker's cloud model. We also estimated the number densities and the temperature of the structure under investigation. Here, we present several results of this study. Title: Physical Properties of Chromospheric Structures in H-alpha and and CaII 854.2 nm Authors: Bostanci, Z. F.; Rutten, R., R. Jtenbroek, H.; Reardon, K.; Cauzzi, G. Bibcode: 2008ESPM...12.2.45B Altcode: Comprehensive studies of chromospheric structures are the key to understanding their dynamics in different solar regimes and their contribution in heating of the solar atmosphere. High spatial and spectral resolution observations of a quiet chromospheric region were obtained with the Interferometric BIdimensional Spectrometer (IBIS) installed at the Dunn Solar Telescope (DST) of the National Solar Observatory (NSO) on Sacramento Peak, USA. Chromospheric fibrils that were observed simultaneously in the Balmer H? and CaII 854.2 nm line are analysed using the cloud model technique to derive numerical values for the standard cloud model parameters; optical thickness, source function, Dopplerwidth and Dopplershift for the two lines, enabling detailed comparison between these. Title: 2D Observation of a Small Active Region in Hα Authors: Gültekin, A.; Bostanci, Z. F.; Al Erdogan, N. Bibcode: 2007ASPC..368..119G Altcode: A small active region on the solar chromosphere was observed with high spatial and spectral resolution in Hα. The data were obtained with the Göttingen Fabry-Pérot Spectrometer mounted in the Vacuum Tower Telescope at the Observatorio del Teide in May 2002. Intensity and velocity maps for different line widths were derived over the two-dimensional field of view by applying the Lambdameter method. Some physical parameters like the source function, the line-of-sight velocity, the Doppler width, and the optical depth of fibril-like structures were determined using Beckers' cloud model. First results of this study are presented. Title: Temporal Evolution of Mottles in Hα Authors: Bostanci, Z. F.; Erdogan, N. A. Bibcode: 2007ASPC..368..123B Altcode: In April 2002, Hα observations of the solar chromosphere with high spatial and spectral resolution were obtained with the Göttingen Fabry-Pérot Spectrometer mounted in the Vacuum Tower Telescope (VTT) at the Observatorio del Teide. In this work, we analyze a short time sequence of a quiet region with chains of mottles. Some physical parameters of dark mottles are determined by using Beckers' cloud model which takes the source function, the Doppler width, and the velocity to be constant within the cloud along the line of sight. Here, we present the results of our study. Title: Structure and flattening of the solar corona Authors: Özkan, M. T.; Ökten, A.; Oklay, N.; Gültekin, A.; Kara, M.; Bostanci, Z. F.; Bašal, M.; Erdoǧan, N. Al Bibcode: 2007msfa.conf..201O Altcode: In this work, preliminary results of the investigation of the white-light coronal structure and the measurement of flattening parameters are presented. They were obtained using photographic eclipse observations performed during the total solar eclipse of March 29, 2006, in Ilica, Antalya, Turkey. This eclipse practically coincided with the minimum of the 23rd solar cycle. Ludendorff flattening parameters were computed as a function of the distance from the disc centre. The results obtained within the range between 1.1 and 1.83 solar radii seem to be in satisfactory agreement with previous works by Saito (1956), Hata & Saito (1966) and Gulyaev et al.(1994). Title: Physical Parameters of Dark Mottles in Hα Authors: Bostanci, Z. F. Bibcode: 2005ESASP.596E..53B Altcode: 2005ccmf.confE..53B In April 2002, Hα observations of the solar chromosphere with high spatial and high spectral resolution were obtained with the Gottingen Fabry-Perot Spectrometer mounted in Vacuum Tower Telescope at the Observatory del Teide/Tenerife. Intensity and velocity maps for different wavelengths widths were derived over the two-dimensional field of view by applying Lambdameter method. Some physical parameters; like the optical thickness, Doppler width, velocity and source function of dark mottles were determined using Beckers' cloud model (Beckers, 1964). In this work, the obtained results will be discussed.