arXiv subjects

S. Karaali

Publications and source records attributed to S. Karaali.

52 records · Page 3Linked to original sources

arXiv2007

The metallicity distributions in high-latitudes with SDSS

We present metallicities and their variations with different parameters for 36 high-latitude fields covering Galactic longitudes 0<l<360. The metallicities for relatively short vertical distances (z<2.5 kpc) show systematic fluctuations with Galactic longitude, similar to those of the thick-disc scaleheight, which may be interpreted as indicating a common origin, viz., the flare effect of the disc. This suggestion is supported by the metallicity variations which we find as functions of radial distance. The metallicity variation at larger vertical distances (6.5<z<9.5 kpc) is small but monotonic. Three different vertical metallicity gradients could be detected: d[M/H]/dz=-0.22(+/-0.03), d[M/H]/dz=-0.38 (+/-0.06), and d[M/H]/dz=-0.08 (+/-0.07) dex/kpc for the intervals z<3, 3<z<5, and 5<z<10 kpc, respectively. Since our data cover the whole Galactic longitude interval, the resulting metallicity gradients can be interpreted as properties of the larger-scale Galaxy. The first gradient confirms the dissipational formation of the disc at short z-distances. The steeper gradient corresponds to the transition region between different population components of the Galaxy, and finally, the lowest value provides an adequate description of the inner-halo metallicity gradient.

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arXiv2006

Estimation of Galactic model parameters with the SDSS and metallicity distribution in two fields in the anti-centre direction of the Galaxy

We estimated the Galactic model parameters from the SDSS data reduced for two fields in the anti-centre direction of the Galaxy, $l= 180^{o}$, and symmetric relative to the Galactic plane, $b=+45^{o}$ and $b=-45^{o}$. The large size of each field, 60 deg$^{2}$, and the faint limiting apparent magnitude, g=22, give us the chance to determine reliable parameters for three components, thin and thick discs and halo, in the north and south hemispheres of the Galaxy, except the scalelengths for two discs which are adopted from Jurić et al. (2005). Metallicities were evaluated by a recent calibration for SDSS, and absolute magnitudes of stars with $4<M(g)\leq8$ were derived as a function of (g-r) colour and metallicity. Conspicuous differences could not be detected between the corresponding Galactic model parameters for the thin disc of north and south fields, and our results are consistent with the ones in the literature. The same case is valid for the halo, especially the axis ratios for two fields are exactly equal, $κ=0.45$. The metallicity distribution for unevolved G type stars with $5<M(g)\leq6$ shows three substructures relative to the distance from the Galactic plane: for $z^{*}<3$ kpc, the metallicity gradient for two fields is $d[M/H]/dz \sim -0.20(\pm0.02)$ dex kpc$^{-1}$, consistent with the formation scenario of the thin disc. For $5<z^{*}<10$ kpc, $d[M/H]/dz \sim -0.03(\pm0.001)$ dex kpc$^{-1}$ for two fields, confirming that the metallicity gradient for the halo component is close to zero. When we combine these substructures, however, we find a smooth metallicity gradient for two fields, $-0.30(\pm0.04)$ dex kpc$^{-1}$.

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arXiv2006

Galactic longitude dependent Galactic model parameters

We present the Galactic model parameters for thin disc estimated by Sloan Digital Sky Survey (SDSS) data of 14 940 stars with apparent magnitudes $16 =220$ pc ($196\leq H \leq 234$ pc) and $ =1900$ pc ($1561\leq h \leq 2280$ pc) respectively. This result would be useful to explain different numerical values claimed for those parameters obtained by different authors for the fields in different directions of the Galaxy.

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arXiv2005

The investigation of ELAIS field by Vega photometry: Absolute - magnitude dependent on the Galactic model parameters

We estimate the density laws of the Galactic stellar populations as a function of absolute magnitude in a near-polar Galactic field. The density laws are determined by the direct fit to photometric parallaxes from Vega photometry in the ELAIS (l=84.27, b=+44.90; 6.571 deg^2) field both independently for each population and simultaneously for all stellar populations. Stars have been separated into different populations based on their spatial location. The thick disc and halo best fit by an exponential. However, the thin disc best fits by using a sech^2 law for stars at faint absolute magnitudes, (10,11], (11,12] and (12,13], whereas an exponential law for stars at relatively bright absolute magnitudes, (5,6], (6,7], (7,8], (8,9] and (9,10]. The scaleheights for the sech^2 density laws are the equivalent exponential scaleheights. Galactic model parameters are absolute magnitude dependent: The scaleheight for thin disc decreases monotonically from stars at bright absolute magnitudes to stars at faint absolute magnitudes in the range 363-163 pc, except the minimum H=211 pc at (9,10] where sech density law fits better. Its local density is flat at bright absolute magnitudes but it increases at faint absolute magnitudes. For thick disc, the scaleheight is flat within the uncertainties. The local space density of thick disc relative to the local space density for the thin disc is almost flat at absolute magnitude intervals (5,6] and (6,7], 7.59 and 7.41% respectively, whereas it decreases down to 3.31% at absolute magnitude interval (7,8]. The axial ratio for the halo is e=0.60, 0.73 and 0.78 for the absolute magnitude intervals (4,5], (5,6] and (6,7] respectively, and its local space density relative to the local space density for the thin disc is 0.06 and 0.04% for the intervals (5,6], and (6,7] respectively.

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arXiv2005

Parametrization of the Galactic Structure by two exponentials

We parametrized the total structure of the Galaxy in cylindrical coordinates by radial and vertical exponentials up to z=10 kpc, covering thin disc, thick disc, and the inner spheroid. However, we let the scaleheight and scalelength to be a continuous function of distance from the Galactic plane. The standard deviations for the differences between the space densities estimated by means of the newly defined scaleheight and scalelength and the observed space densities for three absolute magnitude intervals, 5<M(g)<=6, 6<M(g)<=7, and 7<M(g)<=8, for the fields SA 114, ELAIS, and #0952+5245 are rather small. The uncertainties for the scaleheight are also small, indicating that this parameter is very sensitive to the distance from the Galactic plane, whereas those for the scalelength are larger.

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arXiv2005

Galactic model parameters for field giants separated from field dwarfs by their 2MASS and V apparent magnitudes

We present a procedure which separates field dwarfs and field giants by their 2MASS and V apparent magnitudes. The procedure is based on the spectroscopically selected standards, hence it is confident. We applied this procedure to stars in two fields, SA 54 and SA 82, and we estimated a full set of Galactic model parameters for giants including their total local space density. Our results are in agreement with the ones appeared recently in the literature.

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arXiv2005

Absolute magnitudes for late-type dwarf stars for Sloan photometry

We present a new formula for absolute magnitude determination for late-type dwarf stars as a function of (g-r) and (r-i) for Sloan photometry. The absolute magnitudes estimated by this approach are brighter than those estimated by colour-magnitude diagrams, and they reduce the luminosity function rather close to the luminosity function of Hipparcos.

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arXiv2004

A different approach for the estimation of Galactic model parameters

We estimated the Galactic model parameters by means of a new approach based on the comparison of the observed space density functions per absolute magnitude interval with a unique density law for each population individually, and via the procedure in situ for the field SA 114 ($l=68^{o}.15$, $b=-48^{o}.38$; 4.239 square-degree; J2000). The separation of stars into different populations has been carried out by their spatial distribution. The new approach reveals that model parameters are absolute magnitude dependent. The scale height for thin disk decreases monotonously from absolutely bright to absolutely faint stars in a range 265-495 pc, but there is a discontunity at the absolute magnitude $M(g^{'})=10$ where the squared secans hiperbolicus density law replaces the exponential one. The range of the scale-height for thick disk, dominant in the absolute magnitude interval $5<M(g^{'})\leq9$, is less: 805-970 pc. The local space density for thick disk relative to thin disk decreases from 9.5% to 5.2% when one goes from the absolutely bright to faint magnitudes. Halo is dominant in three absolute magnitude intervals and the axial ratio for this component is almost the same for these intervals where $c/a \sim 0.7$. The same holds for the local space density relative to the thin disk with range (0.02-0.15)%. The model parameters estimated by comparison of the observed space density functions combined for three populations per absolute magnitude interval with the combined density laws agree with the cited values in the literature. Also each parameter is equal to at least one of the corresponding parameters estimated for different absolute magnitude intervals by the new approach. We argue that the most appropriate Galactic model parameters are those, that are magnitude dependent.

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arXiv2004

New colour-transformations for the Sloan photometry and revised metallicity calibration and equations for photometric parallax estimation

We evaluated new colour-transformations for the Sloan photometry by 224 standards and used them to revise both the equations for photometric parallax estimation and metallicity calibration cited by Karaali et al. (2003). This process improves the metallicity and absolute magnitude estimations by [Fe/H]<=0.3 dex and M^{H}_{g} <= 0.1 mag respectively. There is a high correlation for metallicities and absolute magnitudes derived for two systems, UBV and Sloan, by means of the revised calibrations.

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arXiv2004

Analysis of RGU Photometry in Selected Area 51

A low-latitude anticenter field (l=189, b=+21) is investigated by using the full calibration tools of RGU photometry. The observed RGU data are reduced to the standard system and the separation of dwarfs and evolved stars is carried out by an empirical method. Stars are categorized into three metallicity classes, i.e. -0.25<[M/H]<=+0.50, -1.00<[M/H]<=-0.25, and [M/H]<=-1.00$ dex, and their absolute magnitudes are determined by the corresponding colour-magnitude diagrams. The unusually large scattering in the two-colour diagrams is reduced by excluding 153 extra-galactic objects, identifying them compared with the charts of Basel Astronomical Institute and University of Minnesota, and by the criterion and algorithm of Gaidos et al. (1993). The local logarithmic space density for giants, D(0)=6.75, lies within the local densities of Gliese (1969) and Gliese & Jahreiss (1992). The local luminosity function for the absolute magnitude interval 3<M(G)<=7 agrees with Hipparcos' better than Gliese's, whereas there is a considerable excess for the interval 7 < M(G) <= 8 relative to both luminosity functions. This discrepancy may be due to many reasons, i.e. cumulative catalogue errors, binarity etc.

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arXiv2004

Analysis of UBV Photometry in Selected Area 133

We interpret the de-reddened UBV data for the field SA 133 to deduce the stellar density and metallicity distributions function. The logarithmic local space density for giants, $D^{*}(0)=6.40$, and the agreement of the luminosity function for dwarfs and sub-giants with the one of Hipparcos confirms the empirical method used for their separation. The metallicity distribution for dwarfs gives a narrow peak at [Fe/H]=+0.13 dex, due to apparently bright limiting magnitude, $V_{o}=16.5$, whereas late-type giants extending up to $z \sim4.5$ kpc from the galactic plane have a multimodal distribution. The metallicity distribution for giants gives a steep gradient $d[Fe/H]/dz=-0.75$ dex kpc$^{-1}$ for thin disk and thick disk whereas a smaller value for the halo, i.e. $d[Fe/H]/dz=-0.45$ dex kpc$^{-1}$.

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arXiv2004

Comprehensive analysis of RGU photometry in the direction to M5

The RGU-photographic investigation of an intermediate latitude field in the direction to the Galactic center is presented. 164 extra-galactic objects, identified by comparison of Minnesota and Basel charts, are excluded from the program. Also, a region with size 0.104 square-degrees, contaminated by cluster (M5) stars and affected by background light of the bright star HD 136202 is omitted. Contrary to previous investigations, a reddening of $E(B-V)=0.046$, corresponding to E(G-R)=0.07 mag is adopted. The separation of dwarfs and evolved stars is carried out by an empirical method, already applied in some of our works. A new calibration for the metallicity determination is used for dwarfs, while the absolute magnitude determination for stars of all categories is performed using the procedures given in the literature. There is good agreement between the observed logarithmic space density histograms and the galactic model gradients. Also, the local luminosity function agrees with Gliese's (1969) and Hipparcos' (Jahreiss & Wielen 1997) luminosity functions, for stars with $2<M(G)\leq8$ mag. For giants, we obtained two different local space densities from comparison with two Galactic models, i.e. $D^{*}(0)=6.63$, close to that of Gliese (1969), and $D^{*}(0)=6.79$. A metallicity gradient, $d[Fe/H]/dz= -0.20$ dex/kpc, is detected for dwarfs (only) with absolute magnitudes $4<M(G)\leq6$, corresponding to a spectral type interval F5-K0.

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arXiv2003

A New Procedure for the Photometric Parallax Estimation

We present a new procedure for photometric parallax estimation. The data for 1236 stars provide calibrations between the absolute magnitude offset from the Hyades main-sequence and the UV-excess for different (B-V)o colour-index intervals, i.e.: (0.3 0.4), (0.4 0.5), (0.5 0.6), (0.6 0.7), (0.7 0.8), (0.8 0.9), (0.9 1.0), and (1.0 1.1). The mean difference between the original and estimated absolute magnitudes and the corresponding standard deviation are rather small, +0.0002 and +/-0.0613 mag. The procedure has been adapted to the Sloan photometry by means of colour equations and applied to a set of artificial stars with different metallicity. The comparison of the absolute magnitudes estimated by the new procedure and the canonical one indicates that a single colour-magnitude diagram does not supply reliable absolute magnitudes for stars with large range of metallicity.

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arXiv2003

A CCD Study of High Latitude Galactic Structure: Testing the Model Parameters

We interpret published CCD UBVI data to deduce the stellar density distribution and metallicity distribution function in the region from 2-8 kpc from the Galactic Plane, and compare our results to several star count models. A feature of extant star count models is degeneracy between the adopted scale heights of the thin and thick disks, and their local normalisation. We illustrate the utility of this small data set, and future larger sets (e.g. SDSS), by explicitly considering consistency between the derived density laws, and the implied solar neighbourhood luminosity function. Our data set, from Hall et al.(1996) (l=52, b=-39) contains 566 stars, selected to be consistent with stellar loci in colour-colour diagrams. Our analysis supports the parameterisation of the recent SDSS galaxy model of Chen et al.(2001), except in preferring the stellar halo axis ratio to be 0.84. Photometric metal-abundances have been derived for 329 stars using a new calibration. The vertical distance-dependent metallicity distribution function, if parameterised by a single mean value, can be described by a metallicity gradient -0.2$ dex/kpc for the thin disk and thick disk, and -0.1$ dex/kpc for the inner halo. The data are however better described as the sum of three discrete distribution functions, each of which has a small or zero internal gradient. The changing mix of thin disk, thick disk and halo populations with distance from the plane generates an illusion of a smooth gradient.

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arXiv2003

A New Metallicity Calibration for Dwarfs for the RGU-Photometry

We adopted the procedure of Carney to obtain a metallicity calibration for dwarfs for the RGU-photometry. For this purpose we selected 76 dwarfs of different metallicities from Carney, and Strobel et al., and evaluated their δ(U-G) ultra-violet excess relative to Hyades by transforming their UBV magnitudes to RGU via metallicity dependent equations of Ak-Gungor. The δ_{0.6}/\deltaM normalized factors of Sandage transform δ(U-G) excess at any G-R to δ=δ_{1.08}, i.e.: the ultra-violet excess at G-R=1.08 mag, corresponding to B-V = 0.60 mag in the UBV-system. Finally, the (δ, [Fe/H]) couples were fitted by the equation [Fe/H] = 0.11-2.22d-7.95d^2. This calibration covers the metallicity interval (-2.20, +0.20) dex.

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arXiv2003

New metallicity calibration down to [Fe/H] = -2.75 dex

88 dwarfs, covering the colour index interval 0.37 <(B-V)o <= 1.07 mag, with metallicities -2.70 <= [Fe/H] <= +0.26 dex have been taken from three different sources for new metallicity calibration. The catalogue of Cayrel de Stroble et al. (2001) which includes 65% of the stars in our sample supplies detailed information on abundances for stars with determination based on high resolution spectroscopy. 77 stars which supplies at least one of the following conditions have been used as "corner stones" for constructing the new calibration: (i) the parallax is larger than 10 mas (distance relative to the Sun less than 100 pc) and the galactic latitude is absolutely higher than 30 degrees, (ii) the parallax is rather large, if the galactic latitude is absolutely low and vice versa. Contrary to the previous investigations, a third-degree polynomial fitted for the new calibration: [Fe/H] = 0.10-2.76d-24.04d^2+30.00d^3. The coefficients were evaluated by the least-square method, without regarding the metallicity of Hyades. However, the constant term is in the range of metallicity determined for this cluster i.e.: 0.08 <= [Fe/H] <= 0.11 dex. The mean deviation and the mean error in our work are equal to those of Carney (1979), for [Fe/H] >= -1.75 dex where Carney's calibration is valid.

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