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.