explanation blue bibcodes open ADS page with paths to full text
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< T_{eff} < 7300 K, log g >
4 (cgs) and 0.3<(B-V)<SUB>0</SUB><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<{[Fe/H]}<0.5 dex and 2.5< M<SUB>V</SUB><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 M<SUB>V</SUB> > =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<[Fe/H]≤ 0.3 dex and 4<
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< Z≤ 5 kpc, while they are very small positive numbers beyond
Z=5 kpc. All dwarfs with 5< 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< 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>>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<(B-V)<SUB>0</SUB><0.68 mag, -2.0<[Fe/H]<0.4 dex and
3.4< M<SUB>V</SUB><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
(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 < Z <SUB>max</SUB> ⩽ 500 and 500 < 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 < 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 < Z <SUB>max</SUB> ⩽ 500 and 500 <
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> > 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<(B-V)<SUB>0</SUB><1.20 mag, -1.55<[Fe/H]<+0.40 dex and
0.43<M<SUB>V</SUB><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 & 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 & 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.
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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 & 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.
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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.
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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.
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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.
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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.
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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.
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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.
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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 & Saito (1966) and Gulyaev et al.(1994).
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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.