A different approach for the estimation of Galactic model parameters

Abstract

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.Comment: 14 pages, including 16 figures and 16 tables, accepted for publication in MNRA

Luminosity–colour relations for red clump stars

“…There is a good agreement between the Galactic model parameters estimated in this study and the ones appeared in the literature (cf. Karaali et al 2004;Cabrera-Lavers et al 2005;Bilir et al 2006b,c).…”

Parametrization of the Galactic structure by two exponentials

“…114 and ELAIS are almost symmetric relative to the galactic plane, and the galactic coordinates of the centre of ELAIS and #0952+5245 almost coincide with one another, however their sizes are quite different. For the field SA 114, we transfered the mean z * distances from the galactic plane and the corresponding logarithmic space densities D * for the absolute magnitude intervals 5 < M (g ′ ) ≤ 6, 6 < M (g ′ ) ≤ 7, and 7 < M (g ′ ) ≤ 8 from the work of Karaali et al (2004), whereas the z * and D * data for the same absolute magnitude intervals, for the fields ELAIS and #0952+5245 were recently evaluated by Bilir, Karaali & Gilmore (2005) and Karaali et al (2005), respectively. The space densities for these intervals extend up to ∼10 kpc from the galactic plane and cover thin and thick discs, and spheroid.…”

“…For example, Chen et al (2001) and Siegel et al (2002) give 6.5-13 and 6-10 per cent, respectively, for the relative local density for the thick disc. In the paper of Karaali, Bilir & Hamzaoglu (2004), we discussed the large range of these parameters and claimed that Galactic model parameters are absolute magnitude dependent. We showed that the range of the model parameters estimated for a unique absolute magnitude interval is considerably smaller.…”

The Galactic kinematics of cataclysmic variables

“…Although the thick disc component of the Galaxy was discovered more than 30 years ago (Gilmore & Reid 1983), there is still not a consensus for the numerical values of the parameters of this component. Especially, there is a degeneracy between the space density in the Solar Neighbourhood and the scale height of the thick disc component (Siegel et al 2002;Karaali et al 2004;Bilir et al 2006Bilir et al , 2008. Thus, we have decided to find a value for Z (distance from the Galactic plane), for which the space densities of thin and thick discs are almost equal, by performing Monte Carlo simulations with a wide range of parameters.…”