12 September 2012 Precise stellar diameters from coherently averaged visibilities
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Abstract
Optical interferometry is the only means of directly measuring the sizes of stars. The most precise angular diameter measurements, however, depend on measuring complex fringe visibilities V at spatial frequencies where Re(V ) crosses zero. We can then use the spatial frequency B⊥/λ0 of the zero crossing as a measure of the stellar diameter via θUD,0 ≈ 1.22λ0/B⊥, where λ0 and is the wavelength at which Re(V ) = 0 when observed with a baseline length B⊥ projected toward the star, and θUD,0 is the equivalent uniform disk diameter. The variation in limb darkening with wavelength leads to a corresponding variation in θUD,0 with λ, even at fixed B, which allows us to measure the limb darkening in detail and probe the structure of the atmosphere. However, in order to take meaningful data at those spatial frequencies, we need some form of bootstrapping, in wavelength, baseline length, or both. Reduction of these bootstrapped data benefits greatly from the increase in SNR offered by coherent averaging. We demonstrate the effect of limb darkening on θUD,0(λ) with simulated observations based on model atmospheres, and compare them to coherently averaged NOI data.
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J. T. Armstrong, A. M. Jorgensen, H. R. Neilson, D. Mozurkewich, E. K. Baines, and H. R. Schmitt "Precise stellar diameters from coherently averaged visibilities", Proc. SPIE 8445, Optical and Infrared Interferometry III, 84453K (12 September 2012); doi: 10.1117/12.926508; https://doi.org/10.1117/12.926508
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