Estimation of Stellar Instrument Magnitudes Using Synthetic Photometry

Abstract

Stellar instrument magnitudes are of great importance for star trackers. Many methods have been proposed to estimate stellar instrument magnitudes so far, normally making assumption that the dependence among color indices is supposed to be in form of a linear, quadratic or fourth order polynomial fitting function, with one or multiple variables of color indices. Actually, it is not the case especially for stars of all spectral classes over the whole wavelength. Fitting methods cannot be universal, as not all spectral photometry data are available. Moreover, fitting methods may lead to large error with higher order item abandoned. In this paper a novel method of stellar instrument magnitudes computation is proposed by convolving the synthetic photometry spectrum with the optical transmission of star trackers, taking account of the photon-counting nature of modern imaging detectors. This procedure is consistent with the definition of stellar instrument magnitudes, without any assumption. As no high order item is abandoned, the proposed method can achieve much higher accuracy than all existing method. The purpose of this paper is to verify the accuracy of the synthetic photometry method, together with the accuracy of the data source, so as to determine the availability and advantages of the proposed method. Experiments show that the proposed method outperforms the-state-of-art stellar instrument magnitudes computation methods, with an improvement of almost 95.8%, which is meaningful for developing high accuracy navigation catalog especially for star trackers with accuracy less than 1”. As no assumption is needed, the proposed method can be widely used to compute stellar instrument magnitude for stars of various spectral classes.