The pointing calibration of the WFCTA tracking system Lingling Ma 18.02.2011 IHEP

Outline Introduction of the WFCTA telescope The method of the pointing direction calibration Night sky background Method ---- the guide of bright stars The results of the calibration Accuracy The pointing error of the tracking system Conclusions

Wild Field Cherenkov Telescope Array. Field of view 256 PMTs (1°×1°) 14°×16° It takes a star 40~50minites to pass through the FOV Step-tracking system How to estimate the pointing accuracy How to estimate the pointing error of the tracking system Trace of crab

Method ----Night sky background The diffuse night sky background The star light A bright star pass through the FOV of a PMT

Method ----The guide of bright stars TD1 catalog Search the trace of the brightest star on the camera by the PMTs with the highest signal Fit the trace to get the pointing direction of telescope Tune the pointing direction by other bright stars Compare the pointing direction with the one given by the tracking system to check the accuracy and the systematics

Results ----accuracy The differences between the positions of the bright stars and the one observed by the telescope in local coordinates are defined as the accuracy of the calibration.

Accuracy Azimuth Elevation The accuracy is better than 0.1°

The pointing error Delta-degree Delta-degree

Conclusions The accuracy of the calibration is better than 0.1° The pointing error of the tracking system Azimuth: 1.5° Elevation: 1.2° More data is expected