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ABSTRACT We analyse the kinematics of disc stars observed by the RAdial Velocity Experiment (RAVE) survey in and beyond the solar neighbourhood. We detect significant overdensities in the velocity distributions using a technique based on the wavelet transform. We find that the main local kinematic groups are large-scale features, surviving at least up to ∼1 kpc from the Sun in the direction of antirotation, and also at below the Galactic plane. We also find that for regions located at different radii than the Sun, the known groups appear shifted in the v R- vφ velocity plane. For example, the Hercules group has a larger azimuthal velocity for regions inside the solar circle and a lower value outside. We have also discovered a new group at in the solar neighbourhood and confirmed the significance of other previously found groups. Some of these trends detected for the first time are consistent with dynamical models of the effects of the bar and the spiral arms. More modelling is required to definitively characterize the non-axisymmetric components of our Galaxy using these groups. [ABSTRACT FROM AUTHOR]

Diffuse interstellar bands (DIBs) are usually observed in spectra of hot stars, where interstellar lines are rarely blended with stellar ones. The need for hot stars is a strong limitation in the number of sightlines we can observe and their distribution in the Galaxy, as hot stars are rare and concentrated in the Galactic plane. We are introducing a new method, where interstellar lines can be observed in spectra of cool stars in large spectroscopic surveys. The method is completely automated and does not require prior knowledge of the stellar parameters. The main step is a construction of the stellar spectrum, which is done by finding other observed spectra that lack interstellar features and are otherwise very similar to the spectrum in question. Such spectra are then combined into a single stellar spectrum template, matching the stellar component of the observed spectrum. We demonstrate the performance of this new method on a sample of 482,430 Radial Velocity Experiment survey spectra. However, many spectra have to be combined (48 on average) in order to achieve a signal-to-noise ratio high enough to measure the profile of the DIB at 8620 Å, hence limiting the spatial information about the interstellar medium. We compare its equivalent width with extinction maps and with Bayesian reddening, calculated for individual stars, and provide a linear relation between the equivalent width and reddening. Separately from the introduced method, we calculate equivalent widths of the DIB in spectra of hot stars with known extinction and compare all three linear relations. [ABSTRACT FROM AUTHOR]

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 and 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 u– v plane moving away from , and towards 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 and its pattern speed is , where 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. [ABSTRACT FROM AUTHOR]