You-Gang Wang | Searcharxiv

arXiv2017

The local spiral arm in the LAMOST-Gaia common stars?

Using the LAMOST-Gaia common stars, we demonstrate that the in-plane velocity field for the nearby young stars are significantly different from that for the old ones. For the young stars, the probably perturbed velocities similar to the old population are mostly removed from the velocity maps in the $X$--$Y$ plane. The residual velocity field shows that the young stars consistently move along $Y$ with faster $v_ϕ$ at the trailing side of the local arm, while at the leading side, they move slower in azimuth direction. At both sides, the young stars averagely move inward with $v_R$ of $-5\sim-3$ km s$^{-1}$. The divergence of the velocity in $Y$ direction implies that the young stars are associated with a density wave nearby the local arm. We therefore suggest that the young stars may reflect the formation of the local spiral arm by correlating themselves with a density wave. The range of the age for the young stars is around 2 Gyr, which is sensible since the transient spiral arm can sustain that long. We also point out that alternative explanations of the peculiar velocity field for the young population cannot be ruled out only from this observed data.

astro-ph.GA↗

arXiv2015

The stellar kinematics in the solar neighborhood from LAMOST data

We use about 200,000 FGK type main-sequence stars from the LAMOST DR1 data to map the local stellar kinematics. With the velocity de-projection technique, we are able to derive the averaged 3 dimensional velocity and velocity ellipsoids using only the line-of-sight velocity for the stars with various effective temperatures within $100 < |z| < 500$ pc. Using the mean velocities of the cool stars, we derive the solar motion of ($U_{\!\odot}$, $V_{\!\odot}$, $W_{\!\odot}$)=(9.58$\pm2.39$, 10.52$\pm1.96$, 7.01$\pm1.67$)$km\,s^{-1}$ with respect to the local standard of rest. Moreover, we find that the stars with ${T}_{\rm eff}>6000$K show a net asymmetric motion of $\sim3 km\,s^{-1}$ in $\langle W\rangle$ compared to the stars with ${T}_{\rm eff}<6000$K. And their azimuthal velocity increases when $|z|$ increases. This peculiar motion in the warmer stars is likely because they are young and not completely relaxed, although other reasons, such as the resonance induced by the central rotating bar or the spiral structures, and the perturbation of the merging dwarf galaxies, can not be ruled out. The derived velocity dispersions and cross terms for the data are approximately consistent with previous studies. We also find that the vertical gradients of $σ_{U}$ and $σ_V$ are larger than that of $σ_W$ . And the vertical gradient of $σ_U$ shows clear correlation with ${T}_{\rm eff}$, while the other two do not. Finally, our sample shows vertex deviation of about 11$^\circ$, at $300 < |z| < 500$pc, but roughly zero at $100 < |z| < 300$pc.

astro-ph.GA↗