scholarly journals Volume-Limited Dependent Galactic Model Parameters

2007 ◽  
Vol 24 (4) ◽  
pp. 208-219 ◽  
Author(s):  
S. Karaali ◽  
S. Bilir ◽  
E. Yaz ◽  
E. Hamzaoğlu ◽  
R. Buser
Keyword(s):  
Axial Ratio ◽  
Absolute Magnitude ◽  
Model Parameters ◽  
Continuous Transition ◽  
Space Density ◽  
Thick Disc ◽  
The Galaxy ◽  
Galactic Model ◽  
Local Space ◽  
Galactic Longitude

AbstractWe estimate 34 sets of Galactic model parameters for three intermediate-latitude fields with Galactic longitudes l = 60°, l = 90°, and l = 180°, 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 < Mg ≤ 5, and 5 < Mg ≤ 6, whereas for the third field (l = 60°) a larger absolute-magnitude interval is adopted, 4 < Mg ≤ 10. The limiting apparent magnitudes of the star samples are g0 = 15 and g0 = 22.5 mag, which provide space densities within distances in the line of sight of ∼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.

scholarly journals Estimation of Galactic Model Parameters in High Latitudes with SDSS

2008 ◽  
Vol 25 (2) ◽  
pp. 69-84 ◽  
Author(s):  
S. Bilir ◽  
A. Cabrera-Lavers ◽  
S. Karaali ◽  
S. Ak ◽  
E. Yaz ◽  
...  
Keyword(s):  
Gravitational Effect ◽  
Mean Value ◽  
Sloan Digital Sky Survey ◽  
Asymmetric Structure ◽  
Model Parameters ◽  
Axis Ratio ◽  
Sky Survey ◽  
The Galaxy ◽  
Galactic Model ◽  
Galactic Longitude

AbstractWe estimated the Galactic model parameters for a set of 36 high-latitude fields included in the currently available Data Release 5 (DR 5) of the Sloan Digital Sky Survey (SDSS), to explore their possible variation with the Galactic longitude. The thick disc scaleheight moves from ∼550 pc at 120 < l < 150° to ∼720 pc at 250 < l < 290°, while the thin disc scaleheight is as large as ∼195 pc in the anticenter direction and ∼15% lower at |l| < 30°. Finally, the axis ratio (c/a) of the halo changes from a mean value of ∼0.55 in the two first quadrants of the Galaxy to ∼0.70 at 190 < l < 300°. For the halo, the reason for the dependence of the model parameters on the Galactic longitude arises from the well known asymmetric structure of this component. However, the variation of the model parameters of the thin and thick discs with Galactic longitude originates from the gravitational effect of the Galactic long bar. Moreover, the excess of stars in quadrant I (quadrant III) over quadrant IV (quadrant II) is in agreement with this scenario.

scholarly journals Estimation of Galactic Model Parameters by Interval Method

1996 ◽  
Vol 169 ◽  
pp. 713-714
Author(s):  
S. A. Kutuzov
Keyword(s):  
Mutual Interaction ◽  
Component Model ◽  
Model Parameters ◽  
Interval Method ◽  
Two Component ◽  
The Galaxy ◽  
Galactic Model

The interval method of estimating model parameters (MPs) for the Galaxy was suggested earlier (Kutuzov 1988). Intervals are proposed to be used both for observational estimates of galactic parameters (GPs) and for the values of MPs. In this work we consider a model as a tool for studying mutual interaction of GPs. Two-component model is considered (Kutuzov, Ossipkov 1989). We have to estimate the array P of eight MPs.

scholarly journals Estimation of Galactic model parameters in high latitudes with the SDSS and SCUSS

2013 ◽  
Vol 9 (S298) ◽  
pp. 404-404
Author(s):  
Cuihua Du ◽  
Yunpeng Jia ◽  
Xiyan Peng
Keyword(s):  
Model Parameters ◽  
High Latitudes ◽  
The South ◽  
Statistical Errors ◽  
Count Method ◽  
Sky Survey ◽  
Star Count ◽  
The Galaxy ◽  
Galactic Model

AbstractBased on the South Galactic Cap U-band Sky Survey (SCUSS) and SDSS observation, we adopted the star-count method to analyze the stellar distribution in different directions of the Galaxy. We find that these model parameters may be variable with observed direction, which cannot simply be attributed to statistical errors.

scholarly journals Estimation of absolute magnitude-dependent Galactic model parameters in intermediate latitude with SDSS and SCUSS

2014 ◽  
Vol 441 (1) ◽  
pp. 503-512 ◽  
Author(s):  
Yunpeng Jia ◽  
Cuihua Du ◽  
Zhenyu Wu ◽  
Xiyan Peng ◽  
Jun Ma ◽  
...  
Keyword(s):  
Absolute Magnitude ◽  
Model Parameters ◽  
Galactic Model

scholarly journals Estimation of Galactic Model Parameters In High Latitude With SDSS and SCUSS

2013 ◽  
Vol 9 (S298) ◽  
pp. 414-414
Author(s):  
Yunpeng Jia ◽  
Cuihua Du
Keyword(s):  
High Latitude ◽  
Absolute Magnitude ◽  
Galactic Structure ◽  
Thin Disk ◽  
Sloan Digital Sky Survey ◽  
Model Parameters ◽  
Structure Parameters ◽  
Sky Survey ◽  
Double Exponential ◽  
Galactic Model

AbstractUsing star counts method, we estimated the Galactic structure parameters in high latitude field (50° ≤ l ≤ 55°, −46° ≤ b ≤ −44°), 10 deg2 field with Sloan Digital Sky Survey (SDSS) and South Galactic Cap of U-band Sky Survey (SCUSS), to explore their possible variations with absolute magnitude. Here we just considered three components: double exponential thin disk and thick disk and a de Vaucouleurs halo. And these parameters were obtained by minimising χ2.

scholarly journals Galactic longitude dependent galactic model parameters

New Astronomy ◽  
2006 ◽  
Vol 12 (3) ◽  
pp. 234-245 ◽  
Author(s):  
S. Bilir ◽  
S. Karaali ◽  
S. Ak ◽  
E. Yaz ◽  
E. Hamzaoğlu
Keyword(s):  
Model Parameters ◽  
Galactic Model ◽  
Galactic Longitude

scholarly journals Comprehensive Analysis of RGU Photometry in the Direction to M5

2004 ◽  
Vol 21 (3) ◽  
pp. 275-283 ◽  
Author(s):  
S. Karaali ◽  
S. Bilir ◽  
R. Buser
Keyword(s):  
Absolute Magnitude ◽  
Empirical Method ◽  
Galactic Centre ◽  
Evolved Stars ◽  
Luminosity Functions ◽  
Galactic Model ◽  
Local Space ◽  
Absolute Magnitudes ◽  
Magnitude Determination ◽  
Good Agreement

AbstractThe RGU-photographic investigation of an intermediate latitude field in the direction to the Galactic centre 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) ≤ 8 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–1, is detected for dwarfs (only) with absolute magnitudes 4 < M(G) ≤ 6, corresponding to a spectral type interval F5–K0.

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