Uncovering fluctuations in atmospheric transmission using the VERITAS pointing monitors

Abstract

Our project encompasses the creation of software that provides nightly estimates of atmospheric transmission and tracks its long-term fluctuations for the VERITAS telescopes. Using archived image files taken from the pointing monitors of the VERITAS telescope, we wrote software that selects stars of appropriate brightness and quantifies their intensity. We then plotted the star intensity as a function of the secant of the telescope angle from the zenith and observed a linear relationship. The ratio of this slope divided by its intercept has a value that is independent of the stars chosen and is proportional to the length of attenuation of light travelling through the atmosphere. By analyzing nightly data for all four telescopes, one can measure the magnitude of the fluctuations in atmospheric transmission using the ratio of the slope over the intercept. This method will allow improvements in the quality of the measurements taken by the VERITAS telescopes, by giving VERITAS control over the effects of the atmosphere on their star intensity data.