A new UBV and proper motion survey in the anticentre direction at intermediate latitude: kinematics of the galaxy's stellar populations

Abstract

We present the results from a new complete absolute proper motion survey in the direction of intermediate galactic latitude (L = 167.5 °, b = 47.4 °) with respect to background galaxies and quasars, using a set of Tautenburg and OCA (Observatoire de la Cote d'Azur) Schmidt plates, obtained at different epochs separated by approximately 25 years. Photometric U, B and V survey has been done for 4167 objects covering 18.8 square degree field and proper motions have been calculated for 1888 objects for a 8.6 deg² area. The resulting catalogs are complete down to V = 17, B = 19 and U = 16.5. An average proper motion accuracy of 0."25 per century was achieved for stars brighter than V = 16, with the uncertainties increasing to ∼ 0."4 per century at V > 16. The photometric accuracy ranges between 0.07 to 0.10 in the three bands. We utilize our photometric and absolute proper motions data to investigate the structure and kinematics of the Galaxy. We have determined ultraviolet excesses and distances for a sub-sample of 2685 stars in the color range 0.3 ≤ (B-V) ≤ 0.9 and with V ≤ 17. Thus we have been able to probe the kinematical distribution of F and G-type stars to distances up to 3.5 kpc from the plane. We obtain a value -0.21 ± 0.1 kpc^-1 for the galactic radial gradient of velocity dispersion(∂lnσ²_U+W/∂r. By comparing the ratio of stars in this direction to the number of stars towards galactic center at intermediate latitude (l =3 °, b = 47 °), give a strong evidence that the scale length of old disk is rather short (2-2.5 kpc). Because of the kinematical biases inherent in our data sample, we can not present definite kinematical parameters for the intermediate population, but reasonable estimates would be an asymmetric drift of 57 ±4 km/s and velocity dispersion σ_V of 60 ± 3 km/s at a mean distance (above the plane) of z = 2 kpc.