The age-velocity dispersion relation of the Galactic discs from the LAMOST-GAIA data

主讲人 (Speaker): 俞锦程

主讲人单位 (Speaker's Institute): 中国国家天文台

邀请人 (Invited by): 汤柏添

时间 (Time): 星期一, 2018/07/30 - 15:00 to 16:00

地点 (Location): 珠海校区海滨红楼17栋206

摘要 (Abstract):

We present the age-velocity dispersion relation (AVR) in three dimensions in the solar neighbourhood using 3,564 commonly observed sub-giant/red-giant branch stars selected from LAMOST, which gives the age and radial velocity, and Gaia, which measures the distance and proper motion. The stars are separated into metal-poor ([Fe/H]<-0.2 dex and metal-rich ([Fe/H]>-0.2 dex) groups, so that the metal-rich stars are mostly alpha-poor, while the metal-poor group are mostly contributed by alpha-enhanced stars. Thus, the old and metal-poor stars likely belong to the chemically defined thick disc population, while the metal-rich sample is dominated by the thin disc. The AVR for the metal-poor sample shows an abrupt increase at >7 Gyr, which is contributed by the thick disc component. On the other hand, most of the thin disc stars with [Fe/H]>-0.2 dex display a power-law like AVR with indices of about 0.3--0.4 and 0.5 for the in-plane and vertical dispersions, respectively. This is consistent with the scenario that the disc is gradually heated by the spiral arms and/or the giant molecular clouds. Moreover, the older thin disc stars (>7 Gyr) have a rounder velocity ellipsoid, i.e.~sigma_phi / sigma_z is close to 1.0, probably due to the more efficient heating in vertical direction. Particularly for the old metal-poor sample located with |z|>270 pc, the vertical dispersion is even larger than its azimuthal counterpart. Finally, the vertex deviations and the tilt angles are plausibly around zero with large uncertainties.

主讲人简介 (Speaker's CV):

俞锦程于2012年获得中国科学院上海天文台博士学位，2012至2016年期间在智利天主教大学从事博士后工作，2016年至2017年为国家天文台博士后。他的主要研究方向为星团的动力学演化以及银河系结构与演化。