Journal Article

Probing the Galaxy's bars via the Hercules stream

Esko Gardner and Chris Flynn

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 405, issue 1, pages 545-552
Published in print June 2010 | ISSN: 0035-8711
Published online June 2010 | e-ISSN: 1365-2966 | DOI:
Probing the Galaxy's bars via the Hercules stream

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It has been suggested that a resonance between a rotating bar and stars in the solar neighbourhood can produce the so called ‘Hercules stream’. Recently, a second bar may have been identified in the Galactic centre, the so called ‘long bar’, which is longer and much flatter than the traditional Galactic bar and has a similar mass. We looked at the dynamical effects of both bars, separately and together, on orbits of stars integrated backwards from local position and velocities and a model of the Galactic potential which includes the bars directly. Both bars can produce Hercules like features and allow us to measure the rotation rate of the bar(s). We measure a pattern speed, for both bars, of 1.93 ± 0.03 times the local circular frequency. This is slightly higher than previous measurements for the Galactic bar, but is mainly because we adopt a slightly different solar motion. Finally, we identify a new kinematic feature in local velocity space, caused by the long bar, which is tempting to identify with the high-velocity ‘Arcturus’ stream.

Keywords: Galaxy: centre; Galaxy: kinematics and dynamics; solar neighbourhood; Galaxy: structure

Journal Article.  5915 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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