Using Gaia DR2 to solve differential color refraction and charge transfer efficiency issues

TL;DR

This paper presents a Gaia DR2-based method to calibrate differential color refraction and correct charge transfer efficiency issues, significantly improving ground-based astrometric accuracy.

Contribution

The authors develop a simple Gaia DR2-based calibration method for DCR and CTE-related errors applicable to ground-based telescopic observations.

Findings

DCR correction reduces residuals from 19 mas to 3 mas for G-mag 15 stars.

CTE correction eliminates systematic errors up to 30 mas.

Method improves positional accuracy in ground-based astrometry.

Abstract

The Gaia DR2 catalog released in 2018 gives information about more than one billion stars, including their extremely precise positions that are not affected by the atmosphere, as well as the magnitudes in the G, RP, and BP passbands. This information provides great potential for the improvement of the ground-based astrometry. Based on Gaia DR2, we present a convenient method to calibrate the differential color refraction (DCR). This method only requires observations with dozens of stars taken through a selected filter. Applying this method to the reduction of observations captured through different filters by the 1-m and 2.4-m telescopes at Yunnan Observatory, the results show that the mean of the residuals between observed and computed positions (O-C) after DCR correction is significantly reduced. For our observations taken through an N (null) filter, the median of the mean (O-C) for well-exposed stars (about 15 G-mag) decreases from 19 mas to 3 mas, thus achieving better accuracy, i.e. mean (O-C). Another issue correlated is a systematic error caused by the poor charge transfer efficiency (CTE) when a CCD frame is read out. This systematic error is significant for some of the observations captured by the 1-m telescope at Yunnan Observatory. Using a sigmoidal function to fit and correct the mean (O-C), a systematic error up to 30 mas can be eliminated.