arXiv subjects

S. Bilir

Publications and source records attributed to S. Bilir.

At least 73 records · Page 4Linked to original sources

arXiv2014

Effective Temperatures of Selected Main-sequence Stars with Most Accurate Parameters

In this study, the distributions of the double-lined detached binaries (DBs) on the planes of mass-luminosity, mass radius and mass-effective temperature have been studied. We improved the classical mass-luminosity relation based on the database of DBs by Eker et al. (2004a). With accurate observational data available to us, a method for improving effective temperatures for eclipsing binaries with accurate masses and radii were suggested.

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arXiv2014

CCD UBVRI photometry of NGC 6811

We present the results of CCD UBVRI observations of the open cluster NGC 6811 obtained on 18th July 2012 with the 1m 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$\pm$0.01 mag, $μ=10.06\pm0.08$ mag, [M/H]=-0.10$\pm$0.01 dex and t=1.00$\pm$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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arXiv2014

Galactic model parameters of cataclysmic variables: Results from a new absolute magnitude calibration with 2MASS and WISE

In order to determine the spatial distribution, Galactic model parameters and luminosity function of cataclysmic variables (CVs), a $J$-band magnitude limited sample of 263 CVs has been established using a newly constructed period-luminosity-colours (PLCs) relation which includes $J$, $K_{s}$ and $W1$-band magnitudes in 2MASS and WISE photometries, and the orbital periods of the systems. This CV sample is assumed to be homogeneous regarding to distances as the new PLCs relation is calibrated with new or re-measured trigonometric parallaxes. Our analysis shows that the scaleheight of CVs is increasing towards shorter periods, although selection effects for the periods shorter than 2.25 h dramatically decrease the scaleheight: the scaleheight of the systems increases from 192 pc to 326 pc as the orbital period decreases from 12 to 2.25h. The $z$-distribution of all CVs in the sample is well fitted by an exponential function with a scaleheight of 213$^{+11}_{-10}$ pc. However, we suggest that the scaleheight of CVs in the Solar vicinity should be $\sim$300 pc and that the scaleheights derived using the sech$^2$ function should be also considered in the population synthesis models. The space density of CVs in the Solar vicinity is found 5.58(1.35)$\times 10^{-6}$ pc$^{-3}$ which is in the range of previously derived space densities and not in agreement with the predictions of the population models. The analysis based on the comparisons of the luminosity function of white dwarfs with the luminosity function of CVs in this study show that the best fits are obtained by dividing the luminosity functions of white dwarfs by a factor of 350-450.

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arXiv2014

Absolute Magnitude Calibration for Dwarfs Based on the Colour-Magnitude Diagrams of Galactic Clusters

We present two absolute magnitude calibrations for dwarfs based on colour-magnitude diagrams of Galactic clusters. The combination of the $M_g$ absolute magnitudes of the dwarf fiducial sequences of the clusters M92, M13, M5, NGC 2420, M67 and NGC 6791 with the corresponding metallicities provides absolute magnitude calibration for a given $(g-r)_0$ colour. The calibration is defined in the colour interval $0.25\leq (g-r)_0 \leq 1.25$ mag and it covers the metallicity interval $-2.15\leq \lbrack Fe/H\rbrack \leq +0.37$ dex. The absolute magnitude residuals obtained by the application of the procedure to another set of Galactic clusters lie in the interval $-0.15 \leq ΔM_g \leq +0.12$ mag. The mean and standard deviation of the residuals are $<ΔM_g>=-0.002$ and $σ=0.065$ mag, respectively. The calibration of the $M_J$ absolute magnitude in terms of metallicity is carried out by using the fiducial sequences of the clusters M92, M13, 47 Tuc, NGC 2158 and NGC 6791. It is defined in the colour interval $0.90 \leq (V-J)_0 \leq 1.75$ mag and it covers the same metallicity interval of the $M_g$ calibration. The absolute magnitude residuals obtained by the application of the procedure to the cluster M5 ($\lbrack Fe/H\rbrack=-1.40$ dex) and 46 solar metallicity, $-0.45 \leq \lbrack Fe/H\rbrack \leq +0.35$ dex, field stars lie in the interval -0.29 and +0.35 mag. However, the range of 87 per cent of them is rather shorter, $-0.2 \leq ΔM_J \leq +0.2$ mag. The mean and standard deviation of all residuals are $<ΔM_J>=0.05$ and $σ$=0.13 mag, respectively. The derived relations are applicable to stars older than 4 Gyr for the $M_g$ calibration, and older than 2 Gyr for the $M_J$ calibration. The cited limits are the ages of the youngest calibration clusters in the two systems.

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arXiv2014

Transit Timing Analysis in the HAT-P-32 system

We present the results of 45 transit observations obtained for the transiting exoplanet HAT-P-32b. The transits have been observed using several telescopes mainly throughout the YETI network. In 25 cases, complete transit light curves with a timing precision better than $1.4\:$min have been obtained. These light curves have been used to refine the system properties, namely inclination $i$, planet-to-star radius ratio $R_\textrm{p}/R_\textrm{s}$, and the ratio between the semimajor axis and the stellar radius $a/R_\textrm{s}$. First analyses by Hartman et al. (2011) suggest the existence of a second planet in the system, thus we tried to find an additional body using the transit timing variation (TTV) technique. Taking also literature data points into account, we can explain all mid-transit times by refining the linear ephemeris by 21ms. Thus we can exclude TTV amplitudes of more than $\sim1.5$min.

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arXiv2014

Study of Eclipsing Binary and Multiple Systems in OB Associations II. The Cygnus OB Region: V443 Cyg, V456 Cyg and V2107 Cyg

Three presumably young eclipsing binary systems in the direction of the Cygnus OB1, OB3 and OB9 associations are studied. Component spectra are reconstructed and their orbits are determined using light curves and spectra disentangling techniques. V443 Cyg and V456 Cyg have circular orbits, while the light curve of V2107\,Cyg imposes a slightly eccentric orbit ($e=0.045\pm0.03)$. V443 Cyg harbours F-type stars, and not young early-A stars as previously suggested in the literature based on photometry solely. It appears to be situated in the foreground (distance $0.6\pm0.2$ kpc) of the young stellar populations in Cygnus. V456 Cyg, at a distance of $0.50\pm0.03$ kpc consists of a slightly metal-weak A--type and an early--F star. The age of both systems, on or very near to the main sequence, remains uncertain by an order of magnitude. V2107 Cyg is a more massive system ($8.9\pm2$ and $4.5\pm1.2 M_\odot$) at $1.5\pm0.5$ kpc and, also kinematically, a strong candidate-member of Cyg OB1. The more massive component is slightly evolved and appears to undergo non-radial $βCep$-type pulsations. The Doppler signal of the secondary is barely detectable. A more extensive study is important to fix masses more precisely, and an asteroseismological study would then become appropriate. Nevertheless, the position of the primary in the HR-diagram confines the age already reasonably well to $20\pm5$ Myr, indicating for Cyg OB1 a similar extent of star formation history as established for Cyg OB2.

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arXiv2014

The Catalogue of Stellar Parameters from the Detached Double-Lined Eclipsing Binaries in the Milky Way

The most accurate stellar astrophysical parameters were collected from the solutions of the light and the radial velocity curves of 257 detached double-lined eclipsing binaries in the Milky Way. The catalogue contains masses, radii, surface gravities, effective temperatures, luminosities, projected rotational velocities of the component stars and the orbital parameters. The number of stars with accurate parameters increased 67 per cent in comparison to the most recent similar collection by Torres et al. (2010). Distributions of some basic parameters were investigated. The ranges of effective temperatures, masses and radii are $2750<T_{eff}$(K)$<43000$, $0.18<M/M_{\odot}<33$ and $0.2<R/R_{\odot}<21.2$, respectively. Being mostly located in one kpc in the Solar neighborhood, the present sample covers distances up to 4.6 kpc within the two local Galactic arms Carina-Sagittarius and Orion Spur. The number of stars with both mass and radius measurements better than 1 per cent uncertainty is 93, better than 3 per cent uncertainty is 311, and better than 5 per cent uncertainty is 388. It is estimated from the Roche lobe filling factors that 455 stars (88.5 per cent of the sample) are spherical within 1 per cent of uncertainty.

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arXiv2014

Colour Transformations between BVRc and g'r'i' Photometric Systems for Giant Stars

The transformation equations from $BVR_c$ to $g'r'i'$ magnitudes and vice versa for the giants were established from a sample of 80 stars collected from Soubiran et al. (2010) with confirmed surface gravity ($2\leq \log g$ (cms$^{-2}$)$ \leq3$) at effective temperatures $4000<T_{eff} (K)<16000$. The photometric observations, all sample stars at $g'r'i'$ and 65 of them at $BVR_c$, were obtained at TÜBİTAK National Observatory (TUG) 1m (T100) telescope, on the Taurus Mountains in Turkey. The $M_V$ absolute magnitudes of the giant stars were estimated from the absolute magnitude-temperature data for the giant stars by Sung et al. (2013) using the $T_{eff}$ from the intrinsic colours considered in this study. The transformation equations could be considered to be valid through the ranges of the following magnitudes and colours involved: $7.10<V_0<14.50$, $7.30<g'_0<14.85$, $-0.20<(B-V)_0<1.41$, $-0.11<(V-R_c)_0<0.73$, $-0.42<(g'-r')_0<1.15$, and $-0.37<(r'-i')_0<0.47$ mag. The transformations were successfully applied to the synthetic $BVR_c$ data of 427 field giants in order to obtain the $g'r'i'$ magnitudes and colours. Comparisons of these data with the $g'r'i'$ observations of giants in this study show that the mean residuals and standard deviations lie within [-0.010, 0.042] and [0.028, 0.068] mag, respectively.

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arXiv2014

Local stellar kinematics from RAVE data- V. Kinematic investigation of the Galaxy with red clump stars

We investigated the space velocity components of 6610 red clump (RC) stars in terms of vertical distance, Galactocentric radial distance and Galactic longitude. Stellar velocity vectors are corrected for differential rotation of the Galaxy which is taken into account using photometric distances of RC stars. The space velocity components estimated for the sample stars above and below the Galactic plane are compatible only for the space velocity component in the direction to the Galactic rotation of the thin disc stars. The space velocity component in the direction to the Galactic rotation (V) shows a smooth variation relative to the mean Galactocentric radial distance (Rm), while it attains its maximum at the Galactic plane. The space velocity components in the Galactic centre (U) and in the vertical direction (W) show almost flat distributions relative to Rm with small changes in their trends at Rm=7.5 kpc. U values estimated for the RC stars in quadrant 180<l<=270 are larger than the ones in quadrants 0<l<=90 and 270<l<=360. The smooth distribution of the space velocity dispersions reveals that the thin and thick discs are kinematically continuous components of the Galaxy. Based on the W space velocity components estimated in the quadrants 0<l<=90 and 270<l<=360, in the inward direction relative to the Sun, we showed that RC stars above the Galactic plane move towards the North Galactic Pole, whereas those below the Galactic plane move in the opposite direction. In the case of quadrant 180<l<=270, their behaviour is different, i.e. the RC stars above and below the Galactic plane move towards the Galactic plane. We stated that the Galactic long bar is the probable origin of many, but not all, of the detected features.

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arXiv2013

The early-type near-contact binary system V337 Aql revisited

The close binary V337 Aql consists of two early B-type components with an orbital period of 2.7339 d. New multi-band photometric observations of the system together with published radial velocities enabled us to derive the absolute parameters of the components. The simultaneous light and radial velocity curves solution yields masses and radii of \emph{M$_{1}$}=17.44$\pm$0.31 \emph{M$_\odot$} and \emph{R$_{1}$}=9.86$\pm$0.06 \emph{R$_\odot$} for the primary and \emph{M$_{2}$}=7.83$\pm$0.18 \emph{M$_\odot$} and \emph{R$_{2}$}=7.48$\pm$0.04 \emph{R$_\odot$} for the secondary component. Derived fundamental parameters allow us to calculate the photometric distance as 1355$\pm$160 pc. The present analysis indicates that the system is a near-contact semi-detached binary, in which a primary star is inside its Roche lobe with a filling ratio of 92 percent and the secondary star fills its Roche lobe. From \emph{O-C} data analysis, an orbital period decrease was determined with a rate of -7.6 $\times$ 10$^{-8}$ yr$^{-1}$. Kinematic analysis reveals that V337 Aql has a circular orbit in the Galaxy and belongs to a young thin-disc population.

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arXiv2013

Local stellar kinematics from RAVE data: IV. Solar neighbourhood age-metallicity relation

We investigated the age-metallicity relation using a sample of 5691 F and G type dwarfs from RAVE DR3 by applying several constraints: i) We selected stars with surface gravities log g < 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 Gonzalez Hernandez & 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. We estimated the ages using the Bayesian procedure of Jorgensen & 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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arXiv2013

Absolute Magnitude Calibration for Red Clump Stars

We combined the ($K_s$, $J-K_s$) data in Laney et al. (2012) with the $V$ apparent magnitudes and trigonometric parallaxes taken from the Hipparcos catalogue and used them to fit the $M_{K_s}$ absolute magnitude to a linear polynomial in terms of $V-K_s$ colour. The mean and standard deviation of the absolute magnitude residuals, -0.001 and 0.195 mag, respectively, estimated for 224 red clump stars in Laney et al. 2012 are (absolutely) smaller than the corresponding ones estimated by the procedure which adopts a mean $M_{K_s}=-1.613$ mag absolute magnitude for all red clump stars, -0.053 and 0.218 mag, respectively. The statistics estimated by applying the linear equation to the data of 282 red clump stars in Alves (2000) are larger, $ΔM_{K_s}=0.209$ and $σ=0.524$ mag, which can be explained by a different absolute magnitude trend, i.e. condensation along a horizontal distribution.

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arXiv2013

First identification and absolute magnitudes of the red clump stars in the Solar neighbourhood for WISE

We present the first determination of absolute magnitudes for the red clump (RC) stars with the Wide-field Infrared Survey Explorer (WISE). We used recently reduced parallaxes taken from the Hipparcos catalogue and identified 3889 RC stars with the WISE photometry in the Solar neighbourhood. Mode values estimated from the distributions of absolute magnitudes and a colour of the RC stars in WISE photometry are M_{W1}=-1.635(0.026), M_{W3}=-1.606(0.024) and (W1-W3)_0=-0.028(0.001) mag. These values are consistent with those obtained from the transformation formulae using 2MASS data. Distances of the RC stars estimated by using their M_{W1} and M_{W3} absolute magnitudes are in agreement with the ones calculated by the spectrophotometric method, as well. These WISE absolute magnitudes can be used in astrophysical researches where distance plays an important role.

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arXiv2013

A New Absolute Magnitude Calibration for Red Clump Stars

We present an M_V 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_V = 0.627(0.104)(B-V)o+0.046(0.043)[Fe/H]+0.262(0.111). The calibration equation is valid in the ranges 0.42<(B-V)o<1.20 mag, -1.55<[Fe/H]<+0.40 dex and 0.43<M_V<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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arXiv2012

Research Performance of Turkish Astronomers in the Period of 1980-2010

We investigated the development of astronomy and astrophysics research productivity in Turkey in terms of publication output and their impacts as reflected in the Science Citation Index (SCI) for the period 1980-2010. It includes 838 refereed publications, including 801 articles, 16 letters, 15 reviews, and six research notes. The number of papers were prominently increased after 2000 and the average number of papers per researcher is calculated as 0.89. Total number of received citations for 838 papers is 6938, while number of citations per papers is approximately 8.3 in 30 years. Publication performance of Turkish astronomers and astrophysicists was compared with those of seven countries that have similar gross domestic expenditures on research and development, and members of Organization for Economic Co-operation and Development (OECD). Our study reveals that the output of astronomy and astrophysics research in Turkey has gradually increased over the years.

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arXiv2012

Population types of cataclysmic variables in the solar neighbourhood

The Galactic orbital parameters of 159 cataclysmic variables in the Solar neighbourhood are calculated, for the first time, to determine their population types using published kinematical parameters. Population analysis shows that about 6 per cent of cataclysmic variables in the sample are members of the thick disc component of the Galaxy. This value is consistent with the fraction obtained from star count analysis. The rest of the systems in the sample are found to be in the thin disc component of the Galaxy. Our analysis revealed no halo CVs in the Solar vicinity. About 60 per cent of the thick disc CVs have orbital periods below the orbital period gap. This result is roughly consistent with the predictions of population synthesis models developed for cataclysmic variables. A kinematical age of 13 Gyr is obtained using total space velocity dispersion of the most probable thick disc CVs which is consistent with the age of thick disc component of the Galaxy.

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arXiv2012

Luminosity-Colour Relations for Red Clump Stars

We calibrated the $M_V$, $M_J$, $M_{K_s}$ and $M_g$ absolute magnitudes of red clump stars in terms of colours. $M_V$ and $M_g$ are strongly dependent on colour, while the dependence of $M_J$ and $M_{K_s}$ on colour is rather weak. The calibration of $M_V$ and $M_{K_s}$ absolute magnitudes is tested on 101 RC stars in the field SA 141. The Galactic model parameters estimated with this sample are in good agreement with earlier studies.

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arXiv2012

Absolute Magnitude Calibration for Red Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. III-Calibration with 2MASS

We present two absolute magnitude calibrations, $M_{J}$ and $M_{K_s}$, for red giants with the colour magnitude diagrams of five Galactic clusters with different metallicities i.e. M92, M13, M71, M67, and NGC 6791. The combination of the absolute magnitudes of the red giant sequences with the corresponding metallicities provides calibration for absolute magnitude estimation for red giants for a given colour. The calibrations for $M_{J}$ and $M_{K_s}$ are defined in the colour intervals $1.3\leq(V-J)_{0}\leq2.8$ and $1.75 \leq (V-K_{s})_{0}\leq 3.80$ mag, respectively, and they cover the metallicity interval $-2.15 \leq \lbrack Fe/H \rbrack \leq +0.37$ dex. The absolute magnitude residuals obtained by the application of the procedure to another set of Galactic clusters lie in the intervals $-0.08<ΔM_{J}\leq +0.34$ and $-0.10< ΔM_{K_s}\leq +0.27$ mag for $M_{J}$ and $M_{K_s}$, respectively. The means and standard deviations of the residuals are $<ΔM_{J}>= 0.137$ and $σ_{M_J}=0.080$, and $<ΔM_{K_s}>=0.109$ and $σ_{M_{K_{s}}}=0.123$ mag. The derived relations are applicable to stars older than 4 Gyr, the age of the youngest calibrating cluster.

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