An international team led by Dr. Tian Haijun of China Three Gorges University (CTGU) and Liu Chao of National Astronomical Observatories of China (NAOC) combined Gaia DR1, PS1, SDSS and 2MASS astrometry to construct a catalog of proper motions (dubbed GPS1) consisting of ~350 million sources across three-fourths of the sky down to a magnitude of mr<20. GPS1 has a characteristic systematic error of less than 0.3 mas/yr, and a typical precision of 1.5-2.0mas/yr. The proper motions have been validated using galaxies, open clusters, distant giant stars and QSOs. In comparison with other published faint proper motion catalogs, GPS1's systematic error (<0.3 mas/yr) should be nearly an order of magnitude better than that of PPMXL and UCAC4 (>2.0 mas/yr). Similarly, its precision (~1.5mas/yr) is a four-fold improvement relative to PPMXL and UCAC4 (~6.0mas/yr). This work has been published online in the Astrophysical Journal Supplement Series (ApJS, 232, 4T, 2017).

In recent decades, several high-precision and large photometric surveys have been completed or are being carried out in the world. The time baseline is from 2000 to 2015. They provide an unprecedented opportunity to build the best current proper motion catalog across much of the sky. After the first 14 months of observation, the ESA Gaia mission published its first data release (Gaia DR1) on September 14, 2016. It consists of around 1.14 billion astrometrical sources with high accurate position coordinates in J2015.0. The average positional uncertainty of the sources with G<20 mag is better than 16.6 mas. After a survey of more than 5 years, the Pan-STARRS (PS1) has collected multi-detection positions for billions of stars across three-fourths of the sky, with average positional uncertainty of~15 mas. The SDSS and 2MASS released the photometric data 10~20 years ago, with positional accuracies of 25 mas and 100 mas, respectively. Dr. Tian Haijun obtained permission to use these data during his MPIA visit in 2016, and rapidly completed the construction of GPS1.

The proper motion catalog GPS1, particularly when combined with LAMOST, provides vital information for understanding the stellar kinematics and dynamic mechanisms, and reveals the origin and evolutionary history of the Milky Way. Reviewers have commented that GPS1 has the potential to be a valuable asset to the community until (and perhaps beyond) the Gaia DR2 release.

Dr. Branimir Sesar and Prof. Hans-Walter Rix at MPIA have contributed to this work as key co-authors. The work was supported by the National Natural Science Foundation of China (NSFC) and fellowships from the China Scholarship Council (CSC) and Max Planck Institute for Astronomy (MPIA).

The distribution of GPS1 proper motion uncertainties for stars with 14<mr<18 in the equatorial Mollweide projection maps (top) and the variation of the proper motion precisions with the magnitude (bottom) (Image from NAOC)

For more information, please contact:

Dr. Tian Haijun

China Three Gorges University

hjtian@lamost.org

Source: NAOC