Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 412, Issue 3, Pages 2026-2032Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2010.18037.x
Keywords
stars: kinematics and dynamics; Galaxy: fundamental parameters; Galaxy: kinematics and dynamics
Categories
Funding
- Anglo-Australian Observatory
- Astrophysical Institute Potsdam
- Australian Research Council
- German Research foundation
- National Institute for Astrophysics at Padova
- Johns Hopkins University
- Netherlands Research School for Astronomy
- Natural Sciences and Engineering Research Council of Canada
- Slovenian Research Agency
- Swiss National Science Foundation
- National Science Foundation of the USA [AST-0908326]
- Netherlands Organisation for Scientific Research
- Particle Physics and Astronomy Research Council of the UK
- Opticon
- Strasbourg Observatory
- University of Basel
- University of Cambridge
- University of Groningen
- Science and Technology Facilities Council [ST/G002479/1, PP/D001242/1, ST/H00243X/1, ST/G002509/1, PP/D001528/1] Funding Source: researchfish
- UK Space Agency [PP/D006570/1] Funding Source: researchfish
- STFC [ST/G002509/1, PP/D001242/1, ST/G002479/1, PP/D001528/1] Funding Source: UKRI
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Using a sample of 213 713 stars from the Radial Velocity Experiment (RAVE) survey, limited to a distance of 2 kpc from the Sun and to |z| < 1 kpc, we report the detection of a velocity gradient of disc stars in the fourth quadrant, directed radially from the Galactic Centre. In the direction of the Galactic Centre, we apply a simple method independent of stellar proper motions and of Galactic parameters to assess the existence of this gradient in the RAVE data. This velocity gradient corresponds to vertical bar K + C vertical bar > rsim 3 km s-1 kpc-1, where K and C are the Oort constants measuring the local divergence and radial shear of the velocity field, respectively. In order to illustrate the effect, assuming a zero radial velocity of the local standard of rest we then reconstruct the two-dimensional Galactocentric velocity maps using two different sets of proper motions and photometric distances based either on isochrone fitting or on K-band magnitudes, and considering two sets of values for the Galactocentric radius of the Sun and local circular speed. Further observational confirmation of our finding with line-of-sight velocities of stars at low latitudes, together with further modelling, should help constrain the non-axisymmetric components of the Galactic potential, including the bar, the spiral arms and possibly the ellipticity of the dark halo.
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