Journal Article

Low-velocity streams in the solar neighbourhood caused by the Galactic bar

I. Minchev, C. Boily, A. Siebert and O. Bienayme

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 4, pages 2122-2130
Published in print October 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17060.x
Low-velocity streams in the solar neighbourhood caused by the Galactic bar

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We find that a steady-state bar induces transient features at low velocities in the solar neighbourhood velocity distribution due to the initial response of the disc, following the formation of the bar. We associate these velocity streams with two quasi-periodic orbital families, librating around the stable x1(1) and x1(2) orbits near the bar's outer Lindblad resonance. In a reference frame moving with the bar, these otherwise stationary orbits precess on a time-scale dependent on the strength of the bar, consistent with predictions from a simple Hamiltonian model for the resonance. This behaviour allows the two orbital families to reach the solar neighbourhood and manifest themselves as clumps in the uv plane moving away from (x1(2)), and towards (x1(1)) the Galactic centre. Depending on the bar parameters and time since its formation, this model is consistent with the Pleiades and Coma Berenices, or Pleiades and Sirius moving groups seen in the Hipparcos stellar velocity distribution, if the Milky Way bar angle is 30°≲ϕ0≲ 45° and its pattern speed is Ωb0= 1.82 ± 0.07, where Ω0 is the angular velocity of the local standard of rest. Since the process is recurrent, we can achieve a good match about every six local standard of rest rotations. However, to be consistent with the fraction of stars in the Pleiades, we estimate that the Milky Way bar formed ∼2 Gyr ago. This model argues against a common dynamical origin for the Hyades and Pleiades moving groups.

Keywords: Galaxy: bulge; Galaxy: disc; Galaxy: evolution; Galaxy: kinematics and dynamics; solar neighbourhood; Galaxy: structure

Journal Article.  6734 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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