Correction to the Photometric Colors of the Gaia Data Release 2 with the Stellar Color Regression Method

Abstract

The second Gaia data release (DR2) delivers accurate and homogeneous photometry data of the whole sky of an exquisite quality, reaching down to the unprecedented millimagnitude (mmag) level for the G, G_RP, and G_BP passbands. However, the presence of magnitude-dependent systematic effects at the 10 mmag level limits its power in scientific exploitation. In this work, using about a half million stars in common with the LAMOST DR5, we apply the spectroscopy-based stellar color regression method to calibrate the Gaia G - G_RP and G_BP - G_RP colors. With an unprecedented precision of about 1 mmag, systematic trends with G magnitude are revealed for both colors in great detail, reflecting changes in instrument configurations. Color-dependent trends are found for the G_BP - G_RP color and for stars brighter than G ∼ 11.5 mag. The maximum correction term of the calibration is about 20 mmag in general and varies by a few mmag/mag. A revised color-color diagram of Gaia DR2 is given, and some applications are briefly discussed.