How achromatic is the stellar scintillation on large telescopes?

Abstract

The atmospheric scintillation of stars is the main reason why the ground-based photometry of astronomical objects has limited accuracy. This becomes particularly noticeable for a variability study with amplitudes of the order of thousandths of stellar magnitude or less. We examine the problem of colour scintillation (i.e. fluctuations of the difference between light intensities measured simultaneously in two different photometric bands). We derive the relations between the colour scintillation power (index) and the atmospheric turbulence, telescope diameter and the characteristics of the photometric channels. Asymptotic dependences for large telescopes (1-10 m) are obtained, which allow us to predict the value of the colour scintillation for a particular telescope and detector. It is shown that the colour scintillation index is ∝ D −3 for measurements with both short (milliseconds) and long (seconds) exposures. We estimate the impact of the atmospheric dispersion, which amplifies colour scintillation away from the zenith. We show that colour scintillation in the long-exposure regime depends strongly on the wind direction in the upper atmosphere.

Angular correlation of the stellar scintillation for large telescopes

“…The author is grateful to his colleagues, who actively participated in obtaining data on optical turbulence at Mt Shatdzhatmaz, and especially to A. Tokovinin and B. Safonov for useful discussions and to M. Sarazin for numerous comments. In a sense, this work is a continuation of the paper Kornilov (2011a), and the author thanks the unknown referee, who stimulated this research by his or her remarks on the previous paper.…”

“…We carry out this integration in polar coordinates, introducing, as dimensionless variables, the frequency q = Df , an aperture shift γ = θ z / D , and wind shear ω = w τ/ D . We rewrite expression (6) in the form of a 2D integral and add the factor sinc 2 (ω q cos ϕ), which describes the averaging by the wind along the x ‐axis (Tokovinin ; Kornilov ): Here, ψ is the position angle of the second object in this coordinate system. Note that the function sinc x = sin x / x is not normalized.…”