Farhang Habibi, Marc Moniez, Reza Ansari, Sohrab Rahvar
Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected at longer time scale when the light of remote stars crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelength. 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 to the simulated realisations of fluctuating stellar light curves. Fast Fourier Transforms are first used to simulate realisations of fractal clouds. Then, the illumination pattern resulting from the crossing of background star light through these refractive clouds is calculated from a Fresnel integral also using Fast Fourier Transform techniques. Regularisation procedure and computing limitations are discussed, as well as 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 to discover 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.
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http://arxiv.org/abs/1301.0514
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