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Author name code: bostanci
ADS astronomy entries on 2022-09-14
author:"Bostanci, Z. Funda" 

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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
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 <SUB>
  a </SUB> 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.

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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
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
  (f<SUB>a</SUB> 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 f<SUB>a</SUB> values are clustered
  around 1-3, but can reach up to 11 in a burst where photospheric
  radius expansion is observed. Such f<SUB>a</SUB> 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 f<SUB>a</SUB> 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.

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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
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 (μ<SUB>α</SUB>
  cos δ, μ<SUB>δ</SUB>) = (- 3.02 ± 0.10, - 1.75 ± 0.08) and
  (-3.66 ± 0.07, -2.17 ± 0.06) mas year<SUP>-1</SUP> 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.

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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.
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&lt; T_{eff} &lt; 7300 K, log g &gt;
  4 (cgs) and 0.3&lt;(B-V)<SUB>0</SUB>&lt;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 M<SUB>V</SUB>
  absolute magnitudes. In order to obtain calibrations, (U-B)<SUB>0</SUB>
  and (B-V)<SUB>0</SUB> 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&lt;{[Fe/H]}&lt;0.5 dex and 2.5&lt; M<SUB>V</SUB>&lt;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 &lt; Δ {[Fe/H]}&gt; =0.00± 0.11 dex and &lt;
  Δ M<SUB>V</SUB> &gt; =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.

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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.
2019yCatp017036401C    Altcode:
  Photometric, spectroscopic and astrometric data for 504 F-G type
  main-sequence stars <P />(1 data file).

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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.
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.

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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.
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.

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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.
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 M<SUB>g</SUB> absolute magnitudes for the same stars
  via the re-reduced Hipparcos parallaxes and calibrated the absolute
  magnitude offsets, Δ M<SUB>g</SUB>, 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&lt;[Fe/H]≤ 0.3 dex and 4&lt;
  M<SUB>g</SUB>≤ 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 deg<SUP>2</SUP>. We estimated absolute
  magnitude M<SUB>g</SUB> dependent vertical metallicity gradients as a
  function of vertical distance Z. The gradients are deep in the range
  of 0&lt; Z≤ 5 kpc, while they are very small positive numbers beyond
  Z=5 kpc. All dwarfs with 5&lt; M<SUB>g</SUB>≤ 6 mag are thin-disc
  stars and their distribution shows a mode at (g-r)<SUB>0</SUB>≈
  0.38 mag, while the absolute magnitudes 4&lt; M<SUB>g</SUB> ≤ 5 are
  dominated by thick disc and halo stars, i.e. the apparently bright
  ones (g<SUB>0</SUB>≤ 18 mag) are thick-disc stars with a mode at
  (g-r)<SUB>0</SUB>∼ 0.38 mag, while the halo population is significant
  in the faint stars (g<SUB>0</SUB>&gt;18 mag).

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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.
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. <P />(1
  data file).

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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
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 V<SUB>r</SUB> =
  - 8.3 ± 5.0 km s<SUP>-1</SUP> 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
  μ<SUB>V</SUB> = 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 P<SUB>orb</SUB> = 255 ± 5 Myr.

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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.
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. <P
  />(1 data file).

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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.
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 K<SUB>s</SUB> -band absolute magnitude as -1.54±0.04 mag
  for the sample. The metallicity gradients are calculated with their
  current orbital positions (R <SUB>gc</SUB> and Z) and with their
  orbital properties (R <SUB>m</SUB> and z <SUB>max</SUB>): d[Fe/H]/dR
  <SUB>gc</SUB> = -0.047±0.003 dex kpc<SUP>-1</SUP> for |Z| ≤ 0.5
  kpc and d[Fe/H]/dR <SUB>m</SUB> = -0.025±0.002 dex kpc<SUP>-1</SUP>
  for z <SUB>max</SUB> ≤ 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 <SUB>gc</SUB>
  and R <SUB>m</SUB>. 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 <SUB>m</SUB> = -0.089±0.010,
  -0.073±0.007, -0.053±0.004 and -0.044±0.002 dex kpc<SUP>-1</SUP>
  for e <SUB>p</SUB> ≤ 0.05, e <SUB>p</SUB> ≤ 0.07, e <SUB>p</SUB>
  ≤ 0.10 and e <SUB>p</SUB> ≤ 0.20 sub-samples, respectively, in
  the distance interval z <SUB>max</SUB> ≤ 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.

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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.
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&lt;(B-V)<SUB>0</SUB>&lt;0.68 mag, -2.0&lt;[Fe/H]&lt;0.4 dex and
  3.4&lt; M<SUB>V</SUB>&lt;6.0 mag, respectively. The means and standard
  deviations of the metallicity and absolute magnitude residuals are
  small, i.e. &lt;Δ[Fe/H]_{res}rangle=0 and σ=0.134 dex, and &lt;Δ
  (M<SUB>V</SUB>)_{res}rangle=0 and σ=0.174 mag, respectively, which
  indicate accurate metallicity and photometric parallax estimations.

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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.
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 μ<SUB>V</SUB>=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.

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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.
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. <P
  />(1 data file).

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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.
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 <SUB>max</SUB> ⩽ 825 pc and e <SUB>p</SUB>
  ⩽ 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 &lt; Z <SUB>max</SUB> ⩽ 500 and 500 &lt; Z <SUB>max</SUB> ⩽
  800 pc are d[Fe/H]/dR_m=-0.083± 0.030 and d[Fe/H]/dR_m=-0.048±
  0.037 dex kpc<SUP>-1</SUP>, and d[M/H]/dR_m=-0.063± 0.011 and
  d[M/H]/dR_m=-0.028± 0.057 dex kpc<SUP>-1</SUP>, respectively,
  where R <SUB>m</SUB> is the mean Galactocentric distance. The iron
  and metallicity gradients for less number of stars at further
  vertical distances, 800 &lt; Z <SUB>max</SUB> ⩽ 1500 pc, are
  mostly positive. Compatible iron and metallicity gradients could be
  estimated with guiding radius (R <SUB>g</SUB>) for the same vertical
  distance intervals 0 &lt; Z <SUB>max</SUB> ⩽ 500 and 500 &lt;
  Z <SUB>max</SUB> ⩽ 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<SUP>-1</SUP>; d[M/H]/dR_g=-0.062±
  0.018 and d[M/H]/dR_g=-0.055± 0.045 dex kpc<SUP>-1</SUP>. 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 <SUB>m</SUB> ⩽ 8 kpc,
  nor for the ones at larger distances, R <SUB>m</SUB> &gt; 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<SUP>-1</SUP> and d[Fe/H]/dZ_{max}=-0.119± 0.036 dex
  kpc<SUP>-1</SUP> for the intervals Z <SUB>max</SUB> ⩽ 825 and Z
  <SUB>max</SUB> ⩽ 1500 pc, respectively.

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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.
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.

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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.
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.

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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.
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 <SUB> c </SUB>=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.

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Title: Oscillatory behaviour of chromospheric fine structures in a
    network and a semi-active region
Authors: Bostancı, Zahide Funda; Gültekin, Asuman; Al, Nurol
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.

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Title: A new absolute magnitude calibration for red clump stars
Authors: Bilir, S.; Ak, T.; Ak, S.; Yontan, T.; Bostancı, Z. F.
2013NewA...23...88B    Altcode: 2013arXiv1303.3292B
  We present an M<SUB>V</SUB> 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:
  M<SUB>V</SUB>=0.627(±0.104)(B-V)<SUB>0</SUB>+0.046(±0.043)[Fe/H]+0.262(±0.111).
  The calibration equation is valid in the ranges
  0.42&lt;(B-V)<SUB>0</SUB>&lt;1.20 mag, -1.55&lt;[Fe/H]&lt;+0.40 dex and
  0.43&lt;M<SUB>V</SUB>&lt;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.

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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.
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<SUP>-2</SUP>) ≥ 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 &amp; 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<SUP>-1</SUP>. We estimated the ages using the
  Bayesian procedure of Jørgensen &amp; 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.

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Title: Gamma-ray bursts with extended emission observed with BATSE
Authors: Bostancı, Zahide Funda; Kaneko, Yuki; Göğüş, Ersin
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.
2012grb..confE..25B    Altcode: 2012PoS...152E..25B
  No abstract at ADS

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Title: Cloud modeling of a network region in H\alpha
Authors: Bostanci, Z. F.
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 &amp; 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.
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.
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. <P />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. <P />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. <P />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. <P />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.
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.
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.
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.
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
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 &amp; Saito (1966) and Gulyaev et al.(1994).

---------------------------------------------------------
Title: Physical Parameters of Dark Mottles in Hα
Authors: Bostanci, Z. F.
2005ESASP.596E..53B    Altcode: 2005ccmf.confE..53B
  In April 2002, H<SUB>α</SUB> 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.