Stellar scintillation on large and extremely large telescopes

Abstract

The accuracy of ground-based astronomical photometry is limited by two factors: photon statistics and stellar scintillation arising when starlight passes through the Earth's atmosphere. This paper examines the theoretical role of the outer scale L O of the optical turbulence (OT), which suppresses the low-frequency component of the scintillation. It is shown that for typical values of L O ∼ 25-50 m, this effect becomes noticeable for telescopes of diameter about 4 m. On extremely large, 30-40 m, telescopes with exposures longer than a few seconds, the inclusion of the outer scale in the calculation reduces the scintillation power by more than a factor of 10 relative to conventional estimates. The details of this phenomenon are discussed for various models of non-Kolmogorov turbulence. In addition, a quantitative description of the influence of the telescope central obscuration on the measured scintillation noise is introduced and combined with the effect of the outer scale. Evaluation of the scintillation noise on future TMT and E-ELT telescopes predicts an amplitude of approximately 10 μmag for a 60-s exposure.

Atmospheric scintillation in astronomical photometry

“…In the case of a large telescope, this increase in the scintillation noise due to the central obscuration needs to be compared to the expected reduction in scintillation noise due to outer scale effects (as discussed in Section 5) (Kornilov 2012b). …”

Scintillation correction for astronomical photometry on large and extremely large telescopes with tomographic atmospheric reconstruction

“…It is this function that gives the intensity fluctuations an intrinsic spatial scale of r F = √ λz. A(f) is the aperture filter function and is defined by (2J 1 (πDf)/(πDf)) 2 for a circular aperture (Kornilov 2012). z is the propagation distance to the turbulent layer and the altitude of the layer is then h = zcos (γ ), with γ being the zenith angle of the observation.…”