Photometric Calibration of the Lunar-based Ultraviolet Telescope for Its First Six Months of Operation on the Lunar Surface

We describe the photometric calibration of the Lunar-based Ultraviolet Telescope (LUT), the first robotic astronomical telescope working on the lunar surface, for its first six months of operation on the lunar surface. Two spectral datasets (set A and B) from near-ultraviolet (NUV) to the optical band were constructed with 44 International Ultraviolet Explorer (IUE) standards, because of the LUT's relatively wide wavelength coverage. Set A was obtained by extrapolating the IUE NUV spectra (lambda < 3200 angstrom) to the optical band based upon the theoretical spectra of stellar atmosphere models. Set B was composed of theoretical spectra from 2000 angstrom to 8000 angstrom extracted from the same model grid. In total, seven standards have been observed in 15 observational runs until May 2014. The calibration results show that the photometric performance of LUT is highly stable in its first six months of operation. The magnitude zero points obtained from the two spectral datasets are also consistent with each other, i.e., zp = 17.54 +/- 0.09 mag (set A) and zp = 17.52 +/- 0.07 mag (set B).