We present colour transformations for the conversion of the Two Micron All Sky Survey (2MASS) photometric system to the Johnson–Cousins UBVRI system and further into the Sloan Digital Sky Survey (SDSS) ugriz system. We have taken SDSS gri magnitudes of stars measured with the 2.5‐m telescope from SDSS Data Release 5 (DR5), and BVRI and JHKs magnitudes from Stetson's catalogue and Cutri et al., respectively. We matched thousands of stars in the three photometric systems by their coordinates and obtained a homogeneous sample of 825 stars by the following constraints, which are not used in previous transformations: (1) the data are dereddened, (2) giants are omitted and (3) the sample stars selected are of the highest quality. We give metallicity, population type and transformations dependent on two colours. The transformations provide absolute magnitude and distance determinations which can be used in space density evaluations at short distances where some or all of the SDSS ugriz magnitudes are saturated. The combination of these densities with those evaluated at larger distances using SDSS ugriz photometry will supply accurate Galactic model parameters, particularly the local space densities for each population.

We investigate radial and vertical metallicity gradients for a sample of red clump stars from the RAdial Velocity Experiment (RAVE) Data Release 3. We select a total of 6781 stars, using a selection of colour, surface gravity and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thin or thick disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We derive almost equal metallicity gradients as a function of the Galactocentric distance for the high‐probability thin‐disc stars and for stars with vertical orbital eccentricities consistent with being dynamically young, ev≤ 0.07, i.e. d[M/H]/dRm=−0.041 ± 0.003 and d[M/H]/dRm=−0.041 ± 0.007 dex kpc−1. Metallicity gradients as a function of the distance from the Galactic plane for the same populations are steeper, i.e. d[M/H]/dzmax=−0.109 ± 0.008 and d[M/H]/dzmax=−0.260 ± 0.031 dex kpc−1, respectively. Rm and zmax are the arithmetic mean of the perigalactic and apogalactic distances, and the maximum distance to the Galactic plane, respectively. Samples including more thick‐disc red clump giant stars show systematically shallower abundance gradients. These findings can be used to distinguish between different formation scenarios of the thick and thin discs.

Using reliable trigonometric measurements, we find that the absolute magnitude of cataclysmic variables depends on the orbital period and de-reddened (J − H) 0 and (H −K s ) 0 colours of 2MASS (Two Micron All Sky Survey) photometric system. The calibration equation covers the ranges 0.03256 and 2.0 < M J < 11.7; It is based on trigonometric parallaxes with relative errors of (σ π /π) ≤ 0.4. By using the period-luminositycolours (PLCs) relation, we estimated the distances of cataclysmic variables with orbital periods and 2MASS observations and compared them with distances found from other methods. We suggest that the PLCs relation can be a useful statistical tool to estimate the distances of cataclysmic variables.

The spatial distribution, galactic model parameters and luminosity function of cataclysmic variables (CVs) in the solar neighbourhood have been determined from a carefully established sample of 459 CVs. The sample contains all of the CVs with distances computed from the Period-Luminosity-Colours (PLCs) relation of CVs which has been recently derived and calibrated with 2MASS photometric data. It has been found that an exponential function fits best to the observational zdistributions of all of the CVs in the sample, non-magnetic CVs and dwarf novae, while the sech 2 function is more appropriate for nova-like stars and polars. The vertical scaleheight of CVs is 158±14 pc for the 2MASS J-band limiting apparent magnitude of 15.8. On the other hand, the vertical scaleheights are 128±20 and 160±5 pc for dwarf novae and nova-like stars, respectively. The local space density of CVs is found to be ∼ 3 × 10 −5 pc −3 which is in agreement with the lower limit of the theoretical predictions. The luminosity function of CVs shows an increasing trend toward higher space densities at low luminosities, implying that the number of short-period systems should be high. The discrepancies between the theoretical and observational population studies of CVs will almost disappear if for the zdependence of the space density the sech 2 density function is used.

Abstract:We 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.