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Session 14 - Various Stellar Surveys.
Display session, Wednesday, January 07
Exhibit Hall,

[14.05] Limb-Darkening Observations with the Navy Prototype Optical Interferometer

T. A. Pauls, D. Mozurkewich, J. T. Armstrong (NRL), A. R. Hajian, C. A. Hummel (USNO)

We report stellar limb-darkening observations using three elements of the Navy Prototype Optical Interferometer. Observing with 20 spectral channels covering the wavelength range 520 - 850 nm, we have implemented a phase bootstrapping technique in which short baselines with high visibilities are used to keep the longer baselines with low visibilities in phase. This technique enables us to extend the spatial frequency coverage beyond the first zero of the stellar visibility function for a number of K giant stars that range in size from 5 to 7 milli-arcseconds. The data are inconsistent with a uniform brightness stellar disk, but are well fit by adopting a limb-darkening law based on model stellar atmosphere calculations. These three-element observations also allow determination of the closure phase, which shows a jump of 180 degrees at the position of the first zero in the visibility amplitude, as expected. This represents the first non-zero closure phase measured with separate apertures on a single star at optical wavelengths.

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