Atmospheric Scintillation in Astronomical Photometry

TL;DR

This paper analyzes atmospheric scintillation noise in ground-based astronomical photometry, showing that traditional estimates underestimate noise levels and providing improved equations and methods for more accurate noise characterization and correction.

Contribution

It introduces new equations for scintillation noise, demonstrates the limitations of previous approximations, and emphasizes the use of real-time turbulence profiles for better noise calibration.

Findings

Median atmospheric turbulence profiles improve scintillation noise estimates.

Scintillation noise is comparable to shot noise for long exposures.

Larger telescopes do not significantly reduce fractional scintillation noise.

Abstract

Scintillation noise due to the Earth's turbulent atmosphere can be a dominant noise source in high-precision astronomical photometry when observing bright targets from the ground. Here we describe the phenomenon of scintillation from its physical origins to its effect on photometry. We show that Young's (1967) scintillation-noise approximation used by many astronomers tends to underestimate the median scintillation noise at several major observatories around the world. We show that using median atmospheric optical turbulence profiles, which are now available for most sites, provides a better estimate of the expected scintillation noise and that real-time turbulence profiles can be used to precisely characterise the scintillation noise component of contemporaneous photometric measurements. This will enable a better understanding and calibration of photometric noise sources and the effectiveness of scintillation correction techniques. We also provide new equations for calculating scintillation noise, including for extremely large telescopes where the scintillation noise will actually be lower than previously thought. These equations highlight the fact that scintillation noise and shot noise have the same dependence on exposure time and so if an observation is scintillation limited, it will be scintillation limited for all exposure times. The ratio of scintillation noise to shot noise is also only weakly dependent on telescope diameter and so a bigger telescope may not yield a reduction in fractional scintillation noise.