The Photometric System of Tsinghua-NAOC 80-cm Telescope at NAOC Xinglong Observatory

TL;DR

This paper systematically evaluates the photometric performance of the Tsinghua-NAOC 80-cm Telescope at Xinglong Observatory, providing calibration, limiting magnitudes, and analysis of sky background changes over eight years.

Contribution

It offers a comprehensive calibration and performance analysis of the TNT telescope, including transformation relationships and long-term sky background assessment.

Findings

Accurate transformation between instrumental and standard magnitudes established.

Limiting magnitudes and photometric precision quantified.

Sky background at Xinglong Observatory has gradually worsened over years.

Abstract

Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at Xinglong bservatory of NAOC, with main scientific goals of monitoring various transients in the universe such as supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. We present in this paper a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations on twelve photometric nights, spanning the period from year 2004 to year 2012, we derived an accurate transformation relationship between the instrumental $ubvri$ magnitudes and standard Johnson $UBV$ and Cousins $RI$ magnitudes. In particular, the color terms and the extinction coefficients of different passbands are well determined. With these data, we also obtained the limiting magnitudes and the photometric precision of TNT. It is worthwhile to point out that the sky background at Xinglong Observatory may become gradually worse over the period from year 2005 to year 2012 (e.g., $\sim$21.4 mag vs. $\sim$20.1 mag in the V band).