With the photometric data from the SDSS survey , the spectroscopic data from the SDSS/SEGUE and the LAMOST surveys , and the astrometric data from the Gaia DR2 , we have identified 67 highly-probable member stars of the GD-1 cold stellar stream spread along almost its entire length ( i.e .
from 126 to 203 degree in Right Ascension ) .
With the accurate spectroscopic ( i.e .
metallicity and line-of-sight velocity ) and astrometric ( i.e .
proper motions ) information , the position-velocity diagrams , i.e . \phi _ { 1 } – \mu _ { \alpha } , \phi _ { 1 } – \mu _ { \delta } and \phi _ { 1 } – { v _ { gsr } } , of the GD-1 stream are well mapped .
The stream has an average metallicity [ Fe/H ] = -1.96 .
The rich information of member stars of the stream now available allow one not only to model its origin , but also to place strong constraints on the mass distribution and the gravitational potential of the Milky Way .