Yazar "Hamzaoglu, E." seçeneğine göre listele
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Öğe Galactic longitude dependent galactic model parameters(Elsevier Science Bv, 2006) Bilir, S.; Karaali, S.; Ak, S.; Yaz, E.; Hamzaoglu, E.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 < g(o) <= 21 in six intermediate latitude fields in the first Galactic quadrant. Star/galaxy separation was performed by using the SDSS photometric pipeline and the isodensity contours in the (g - r)(o) - (r - i)(o) two colour diagram. The separation of thin disc stars is carried out by the bimodal distribution of stars in the (g - r)o histogram, and the absolute magnitudes were evaluated by a procedure presented in the literature (Bilir, S., Karaali, S., Tuncel, S. 2005. AN 326, 321). Exponential density law fits better to the derived density functions for the absolute magnitude intervals 8 < M(g) <= 9 and 11 < M(g) <= 12, whereas sech/sech(2) laws are more appropriate for absolute magnitude intervals 9 < M(g) <= 10 and 10 < M(g) <= 11. We showed that the scaleheight and scatelength are Galactic longitude dependent. The average values and ranges of the scaleheight and the scalelength are < H > = 220 pc (196 <= H <= 234 pc) and < H > = 1900 pc (1561 <= h <= 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. (c) 2006 Elsevier B.V. All rights reserved.Öğe A universal vertical stellar density distribution law for the Galaxy(Springer, 2009) Karaali, S.; Hamzaoglu, E.; Bilir, S.We reduced the observational logarithmic space densities in the vertical direction up to 8 kpc from the galactic plane, for stars with absolute magnitudes (5,6], (6,7] and [5,10] in the fields #0952+5245 and SA114, to a single exponential density law. One of three parameters in the quadratic expression of the density law corresponds to the local space density for stars with absolute magnitudes in question. There is no need of any definition for scaleheights or population types. We confirm with the arguments of non-discrete thin and thick discs for our Galaxy and propose a single structure up to several kiloparsecs from the galactic plane. The logarithmic space densities evaluated by this law for the ELAIS field fit to the observational ones. Whereas, there are considerable offsets for the logarithmic space densities produced by two sets of classical galactic model parameters from the observational ones, for the same field.Öğe Volume-limited dependent Galactic model parameters(Csiro Publishing, 2007) Karaali, S.; Bilir, S.; Yaz, E.; Hamzaoglu, E.; Buser, R.We estimate 34 sets of Galactic model parameters for three intermediate-latitude fields with Galactic longitudes l = 60 degrees, l = 90 degrees, and l= 180 degrees, and we discussed their dependence on the volume. Also, we confirm the variation of these parameters with absolute magnitude and Galactic longitude. The star samples in two fields are restricted with bright and unit absolute-magnitude intervals, 4 < M-g <= 5, and 5 < M-g <= 6, whereas for the third field (l= 60 degrees) a larger absolute-magnitude interval is adopted, 4 < M-g <= 10. The limiting apparent magnitudes of the star samples are g(0) = 15 and g(0) = 22.5 mag, which provide space densities within distances in the line of sight of similar to 0.9 and 25 kpc. The Galactic model parameters for the thin disc are not volume dependent. However, the ones for the thick disc and halo do show spectacular trends in their variation with volume, except for the scalelength of the thick disc. The local space density of the thick disc increases, whereas the scaleheight of the same Galactic component decreases monotonically. However, both model parameters approach asymptotic values at large distances. The relative local space density of the halo estimated by fitting the density laws to the space densities evaluated for all volumes is constant, except for the small ones. However it is absolute-magnitude and Galactic-longitude dependent. The axial ratio of the halo increases abruptly for the volumes where a thick disc is dominant, whereas it approaches an asymptotic value gradually for larger volumes, indicating a continuous transition from a disc-like structure to a spherical one at the outermost region of the Galaxy. The variation of the Galactic model parameters with absolute magnitude can be explained by their dependence on the stellar luminosity, whereas the variation with volume and Galactic longitude at short distances is a bias in analysis.
