Simulation of optical interstellar scintillation

TL;DR

This paper presents a comprehensive simulation of optical interstellar scintillation, modeling how light from distant stars fluctuates as it passes through turbulent molecular clouds, and discusses the potential for current telescopes to detect this phenomenon.

Contribution

It introduces a detailed simulation framework for interstellar scintillation, linking cloud structure to observable stellar light fluctuations, and evaluates detection capabilities with existing telescopes.

Findings

Simulated light curves show modulation index varies with turbulence strength and source size.

Current 4m telescopes can potentially detect interstellar scintillation effects.

Distinct desynchronized signals can confirm interstellar origin of scintillation.

Abstract

Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected on a longer time scale when the light of remote stars crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths. The aim of the study described in this paper is to fully simulate the scintillation process, starting from the molecular cloud description as a fractal object, ending with the simulations of fluctuating stellar light curves. Fast Fourier transforms are first used to simulate fractal clouds. Then, the illumination pattern resulting from the crossing of background star light through these refractive clouds is calculated from a Fresnel integral that also uses fast Fourier transform techniques. Regularisation procedure and computing limitations are discussed, along with the effect of spatial and temporal coherency (source size and wavelength passband). We quantify the expected modulation index of stellar light curves as a function of the turbulence strength --characterised by the diffraction radius $R_{diff}$-- and the projected source size, introduce the timing aspects, and establish connections between the light curve observables and the refractive cloud. We extend our discussion to clouds with different structure functions from Kolmogorov-type turbulence. Our study confirms that current telescopes of ~4m with fast-readout, wide-field detectors have the capability of discovering the first interstellar optical scintillation effects. We also show that this effect should be unambiguously distinguished from any other type of variability through the observation of desynchronised light curves, simultaneously measured by two distant telescopes.