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

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DOI: 10.1111/j.1365-2966.2006.09891.x
arXiv ID: astro-ph/0511643
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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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