Volume 563, March 2014
|Number of page(s)||17|
|Section||Galactic structure, stellar clusters and populations|
|Published online||07 March 2014|
Constraints on the Galactic bar from the Hercules stream as traced with RAVE across the Galaxy⋆
1 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
2 University of Leicester, University Road, Leicester LE1 7RH, UK
3 Université de Strasbourg, CNRS, Observatoire, 11 rue de l’Université, 67000 Strasbourg, France
4 Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 Sydney, Australia
5 RSAA Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611 Canberra, Australia
6 Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE, UK
7 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
8 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12–14, 69120 Heidelberg, Germany
9 Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
10 INAF Osservatorio Astronomico di Padova, 36012 Asiago (VI), Italy
11 Senior CIfAR Fellow. University of Victoria, Victoria BC Canada V8P 5C2, Canada
12 Department of Physics and Astronomy, Macquarie University, NSW 2109 Sydney, Australia
13 Research Centre for Astronomy, Astrophysics and Astrophotonics, Macquarie University, NSW 2109 Sydney, Australia
14 Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
15 Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK
16 Johns Hopkins University, Homewood Campus, 3400 N Charles Street, Baltimore MD 21218, USA
17 University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, 1000 Ljubljana, Slovenia
18 Center of excellence Space-SI, Askerceva 19, 1000 Ljubljana, Slovenia
Received: 6 September 2013
Accepted: 16 January 2014
Non-axisymmetries in the Galactic potential (spiral arms and bar) induce kinematic groups such as the Hercules stream. Assuming that Hercules is caused by the effects of the outer Lindblad resonance of the Galactic bar, we model analytically its properties as a function of position in the Galaxy and its dependence on the bar’s pattern speed and orientation. Using data from the RAVE survey we find that the azimuthal velocity of the Hercules structure decreases as a function of Galactocentric radius, in a manner consistent with our analytical model. This allows us to obtain new estimates of the parameters of the Milky Way’s bar. The combined likelihood function of the bar’s pattern speed and angle has its maximum for a pattern speed of Ωb = (1.89 ± 0.08) × Ω0, where Ω0 is the local circular frequency. Assuming a solar radius of 8.05 kpc and a local circular velocity of 238 km s-1, this corresponds to Ωb = 56 ± 2 km s-1 kpc-1. On the other hand, the bar’s orientation φb cannot be constrained with the available data. In fact, the likelihood function shows that a tight correlation exists between the pattern speed and the orientation, implying that a better description of our best fit results is given by the linear relation Ωb/Ω0 = 1.91 + 0.0044(φb(deg) − 48), with standard deviation of 0.02. For example, for an angle of φb = 30 deg the pattern speed is 54.0 ± 0.5 km s-1 kpc-1. These results are not very sensitive to the other Galactic parameters such as the circular velocity curve or the peculiar motion of the Sun, and are robust to biases in distance.
Key words: Galaxy: kinematics and dynamics / Galaxy: structure / Galaxy: disk / Galaxy: evolution
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2014
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.