Calibrated griz Magnitudes of Tycho Stars: All-Sky Photometric Calibration Using Bright Stars

Abstract

Photometric calibration to ∼5% level is frequently needed at arbitrary celestial location. However, existing all-sky astronomical catalogs do not reach this accuracy, and time consuming photometric calibration procedures are required. I fitted the Hipparcos B_T and V_T magnitudes, along with the 2MASS J, H, and K magnitudes of Tycho-2-catalog stars with stellar spectral templates. From the best-fit spectral template derived for each star, I calculated its synthetic SDSS griz magnitudes and constructed an all-sky catalog of griz magnitudes of bright stars (V ≲ 12). Testing this method on SDSS photometric-telescope observations, I find that the photometric accuracy, for a single star, is usually about 0.12, 0.12, 0.10, and 0.08 mag (1 σ), for the g, r, i, and z-bands, respectively. However, by using ∼10 such stars, the typical errors per calibrated field (systematic + statistical) can be reduced to about 0.04, 0.03, 0.02, and 0.02 mag, in the g, r, i, and z-bands, respectively. Therefore, in cases for which several calibration stars can be observed in the field of view of an instrument, accurate photometric calibration is possible.