Erratum: Probing the Galaxys bars via the Hercules stream

The paper ‘Probing the Galaxy’s bars via the Hercules stream’ was published in Mon. Not. R. Astron. Soc. 405, 545–552 (2010). An error in the correction for the solar motion has been found in our analysis of the effects of a Galactic bar (or bars) on the velocity space of stars near the Sun. Correcting this error, the conclusions of our analysis change slightly. The measured pattern speed for both bars changes from 1.93± 0.03 to 1.87± 0.02 times the local circular frequency. This is in good agreement with previous measurements for the Galactic bar. This correction does not change our conclusion that both the Galactic bar and the new ‘long bar’ can generate a feature like the Hercules stream in the solar neighbourhood, and further that the Arcturus stream could be associated with the ‘long bar’. Fig. 1 shows the distribution of stars in local velocity space (U, V). After properly making the correction for the solar motion [i.e. (U , V ) = (11.1, 12.2) km s−1, Schonrich, Binney & Dehnen (2010)], the positions of the Pleiades, Sirius and Hyades streams are around (0, −10), (20, 20), and (−25, −5) km s−1, respectively. The position of the Hercules stream is (−25,−30) km s−1. The other corrected figures are shown in Figs 2–9. We derive a revised best fitting OLR (Outer Lindblad Resonance) of 1.87 ± 0.02, assuming that the position of the secondary feature is at V =−30 ± 5 km s−1. This is in good agreement with Minchev, Nordhaus & Quillen (2007), who use a completely different method to measure this quantity. Assuming the slower solar velocity correction from Dehnen & Binney (1998) shifts the Hercules feature to V = −35 km s−1, the value for the OLR must be higher, the initial estimate of 1.90 ± 0.03 stands. The position of the ‘tertiary feature’, which we associate with the Arcturus stream in the dual bar models, is now at V ∼ −80. The estimated value for the dual bar model’s OLR is reduced to 1.90 ± 0.03, slightly higher than estimates for a singular bar. The values for the pattern speed for the Galactic bar and the long bar are 55.9 and 54.9 km s−1 kpc−1, respectively. Corotation for the long bar thus takes place at the tip of the bar at a Galactocentric radius of 3.9 kpc. The Galactic bar does not have a corotation radius, as before.