Study of Stray Light for the Xinglong 1-Meter Optical Telescope

Based on experience and qualitative analyses, some measures are taken to reduce stray light for the Xinglong 1-meter optical telescope. These measures include using baffles painted in black. In this paper, the stray-light propagation in this telescope has been quantitatively analyzed with the code Tracepro, and an improvement design for stray-light supression is proposed and evaluated by calculating its PSNIT (Point Source Normalized Irradiance Transmittance). The calculation results indicate that for the stray-light sources located at off-axis angles beyond 30°, the stray-light PSNIT of the telescope with improved measures should be reduced below 10^-10. Simulations of observations in a night of full moon indicate that for stars of R=15 at 25° away from the moon, the image SNR of the exposures with the telescope in 15~150s can be increased by a factor of about 147%.