The Study Of Photometric System Of The Nanshan One-meter Wide Telescope At Xinjiang Astronomical Observatory

The flux calibration of the photometry system is an important and basic work.The main factors that affect the flow calibration are the detector response(photometric zero point),color correction items,and airmass.The photometric data is extracted from the image observed by the CCD through the data processing software to obtain the instrumental stellar magnitude of the observed target.The magnitude value reflects the flux counting of the CCD,and makes sense only for the mutual comparison of the flux between the different observed targets in a same image.This flux is called the relative flux.In order to compare and use photometric data more widely,we need to correspond the instrument output value of the target intensity signal to the actual brightness of the target,that is,to convert the instrument stellar magnitude to a standard stellar magnitude system(e.g.Vega magnitude system and AB magnitude system).And then we can obtain the target's actual flux out of atmosphere,which reflects the actual flux value of the celestial body.This procedure is called the absolute flow calibration.Landolt et al.have done a series of work on the UBVRI multi-band standard stars selection and calibration in different sky regions,and have established a Landolt standard star catalog containing the UBVRI photometric system.The photometric calibration relationship of the standard stars and its high accuracy has gained a widespread recognization.In this paper,we mainly derive the flux calibration coefficients through the multicolor photometric observation of the Landolt standard stars,so as to realize the conversion from the instrument magnitude measured by Nanshan one-meter wide-field(NOWT)optical telescope at Xinjiang Astronomical Observatory to the Landolt standard magnitude.This work will promote future development of multicolor photometric research on open clusters,and also provide a calibration method for the ground observation of the space station multi-channel imager(MCI)flux calibration star.The 1m wide-field optical telescope of the Xinjiang Astronomical Observatory's Nanshan Observatory was used to conduct UBVRI multi-band observations on the photometric standard star in the Landolt standard sky area J054610+45 under different airmass.The atmospheric extinction coefficient was obtained according to the Bouguer's law.We used the observation data of the standard field from November 29 th,2017 to January 4th,2019 to obtain photometric zero point as well as color correction items of each band and make a conversion from the NOWT instrument magnitude to the Landolt standard magnitude,which provides a methodological reference to conduct flux calibrations with the telescope for future use.The result shows that the flux calibration correction coefficients of different days will fluctuate to a certain extent.In order to obtain better flow calibration results,it is necessary to observe the standard stars every day to obtain the flux calibration correction coefficients on that day;On the other hand,considering the limitations of practical observation conditions,the atmospheric extinction coefficient could be regarded as constant for a period of time,and the flux calibration using the average atmospheric extinction coefficient over a period of time can still lead to good calibration results.NOWT is in Nanshan,Xinjiang,the northwestern border of China.The climate is dry with little rain.The moderate climate and geographical environment makes this site competent for more than 300 astronomical observation nights every year.Furthermore,there is a lack of optical telescopes near 87.1°E.The installation and operation of NOWT has made up for this vacancy,and is of great significance for time-series photometry.