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.

Abstract:We used the data of 701 stars covering the colour index interval 0.32 , B À V # 1.16, with metallicities À1.76 # [Fe/H] # þ0.40 dex. The data were taken from the PASTEL catalogue and estimated metallicity-dependent guillotine factors, which provide a more accurate metallicity calibration. We reduced the metallicities of 11 different authors to the metallicities of Valenti & Fischer (2005), and thus obtained a homogeneous set of data which increased the accuracy of the calibration, i.e. [Fe/H] ¼ À14.316d 0.6 2 À 3.557d 0.6 þ 0.105. Comparison of the metallicity residuals for two sets of data based on the metallicitydependent guillotine factors with the ones obtained via metal-free guillotine factors shows that metallicities estimated by means of the new guillotine factors are more accurate than the other ones. This advantage can be used in the metallicity gradient investigation of the Galactic components, i.e. thin disc, thick disc, and halo.

In this study we present the absolute magnitude calibrations of thin‐disc main‐sequence stars in the optical , and in the near‐infrared . Thin‐disc stars are identified by means of Padova isochrones, and absolute magnitudes for the sample are evaluated via the newly reduced Hipparcos data. The obtained calibrations cover a large range of spectral types: from A0 to M4 in the optical and from A0 to M0 in the near‐infrared. Also, we discuss the effects of binary stars and evolved stars on the absolute magnitude calibrations. The usage of these calibrations can be extended to the estimation of galactic model parameters for the thin disc individually, in order to compare these parameters with the corresponding ones estimated by statistics (which provides galactic model parameters for thin and thick discs and halo simultaneously) to test any degeneracy between them. The calibrations can also be used in other astrophysical researches where distance plays an important role in that study.

We investigate radial metallicity gradients for a sample of dwarf stars from the RAdial Velocity Experiment (RAVE) Data Release 3 (DR3). We select a total of approximately 17 000 F‐type and G‐type dwarfs, using a selection of colour, log g and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thick or thin disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We additionally subsample by colour, to provide samples biased toward young thin‐disc and older thin‐disc stars. We derive a metallicity gradient as a function of Galactocentric radial distance, i.e. d[M/H]/dRm=−0.051 ± 0.005 dex kpc−1, for the youngest sample, F‐type stars with vertical orbital eccentricities ev≤ 0.04. Samples biased toward older thin‐disc stars show systematically shallower abundance gradients.

We analyse a sample of 82 850 stars from the RAdial Velocity Experiment (RAVE) survey, with well‐determined velocities and stellar parameters, to isolate a sample of 18 026 high‐probability thin‐disc dwarfs within 600 pc of the Sun. We derive space motions for these stars, and deduce the solar space velocity with respect to the local standard of rest. The peculiar solar motion we derive is in excellent agreement in radial U⊙ and vertical W⊙ peculiar motions with other recent determinations. Our derived tangential peculiar velocity, V⊙, agrees with very recent determinations, which favour values near 13 km s−1, in disagreement with earlier studies. The derived values are not significantly dependent on the comparison sample chosen, or on the method of analysis. The local Galaxy seems very well dynamically relaxed, in a near symmetric potential.