Determination of the local standard of rest using the LSS-GAC DR1

Abstract

We re-estimate the peculiar velocity of the Sun with respect to the local standard of rest (LSR) using a sample of local stars within 600 pc of the Sun, selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST; also named the Guoshoujing Telescope) Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC). The sample consists of 94,332 FGK main-sequence stars with well-determined radial velocities and atmospheric parameters. To derive the LSR, two independent analyses are applied to the data. Firstly, we determine the solar motion by comparing the observed velocity distribution to that generated with the analytic formulism of Schönrich & Binney that has been demonstrated to show excellent agreement with rigorous torus-based dynamics modelling by Binney & McMillan. Secondly, we propose that cold populations of thin disc stars, selected by applying an orbital eccentricity cut, can be directly used to determine the LSR without the need of asymmetric drift corrections. Both approaches yield consistent results of solar motion in the direction of Galactic rotation, V ⊙ , that are much higher than the standard value adopted hitherto, derived from Strömgren's equation. The newly deduced values of V ⊙ are 1-2 km s −1 smaller than the more recent estimates derived from the Geneva-Copenhagen Survey (GCS) sample of stars in the solar neighbourhood (within 100 pc). We attribute the small difference to the presence of several well-known moving groups in the GCS sample that, fortunately, hardly affect the LSS-GAC sample. The newly derived radial (U ⊙ ) and vertical (W ⊙ ) components of the solar motion agree well with the previous studies. In addition, for all components of the solar motion, the values yielded by stars of different spectral types in the LSS-GAC sample are consistent with each other, suggesting that the local disk is well relaxed and that the LSR reported in the current work is robust. Our final recommended LSR is, (U ⊙ , V ⊙ , W ⊙ ) = (7.01 ± 0.20, 10.13 ± 0.12, 4.95 ± 0.09) km s −1 .

The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution

“…Both estimates are more than 10 km s −1 higher than the values estimated from stars in the solar neighborhood (e.g. Schönrich, Binney & Dehnen 2010;Huang et al 2015b) as well as the value deduced in the current study. We note however, the analyses of both and Bovy et al (2015) assume a certain shape of the RC -a flat RC in fact.…”

“…To do so, we first convert the observed V helio los to the Galactic standard of rest (GSR) frame by, VGSR = V helio los +U⊙ cos b cos l+V φ,⊙ cos b sin l+W⊙ sin b, (8) where U⊙ and W⊙ are taken from Huang et al (2015b), and V φ,⊙ is again set to the value as adopted in Section 3.1. Next, we calculate the GSR line-of-sight velocity dispersion, σGSR, by dividing HKGs into different radial bins.…”

“…The value of Ω⊙ is well constrained by the proper motions of Sgr A * measured by Reid & Brunthaler (2004). For VR,⊙, we take the value of −7.01 km s −1 determined by Huang et al (2015b). Table 1 summaries all the fixed parameters employed in our kinematical model.…”

“…To compare those earlier results with ours, we have used the data (i.e. distances, radial velocities and errors) of H II regions published by Fich et al (1989) and those of carbon stars of 60 l 150 • published by Demers & Battinelli (2007), and recalculate the circular velocities, adopting the same value of R0 assumed in the current study, the value of Vc(R0) deduced from the current study, as well as the solar peculiar velocities in the radial and vertical directions (U⊙, W⊙) from Huang et al (2015b) for consistency reason. The results are presented in Fig.…”

Discovery of Two New Hypervelocity Stars from the LAMOST Spectroscopic Surveys

“…V c (R 0 ) + V ⊙ , is set to the value yielded by the proper motion of Sgr A * (Reid & Brunthaler 2004) and R 0 = 8.34 kpc (Reid et al 2014). The values of the solar motion in the radial and vertical directions are adopted from Huang et al (2015), i.e. (U ⊙ , W ⊙ ) = (7.01, 4.95) km s −1 .…”