Galactic halo age estimated from LAMOST DR4 and Gaia DR1

The stellar halo is one of the major components in the Milky Way. Research on its age can provide critical constraints on the origin of the stellar halo and further on the formation of our Galaxy. So far, different approaches and samples have been used to estimate the age of the Galactic halo. In our previous paper. we carefully selected 63 field halo turn-off stars within 1 kpc from the literature using a kinematic approach, then estimated the age of the halo. In this following work, we not only update the data from LAMOST DR4 and Gaia DR1, but also try a different method to select a clean halo sample by combining the metallicity and orbital parameters. Then we compare this halo turn-off sample with the GARSTEC model in the B - V vs. metallicity plane. After Monte Carlo simulations are performed, the age is estimated to be 10.5 +/- 1.4Gyr, highly consistent with our previous result and other studies. However. due to the limited common sources between LAMOST DR4 and Gaia DR1, the final sample in this paper is still quite small. The estimated age will be more robust with the much larger Gaia DR2.