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M. Wittkowski (USRA/USNO,MPIfR), NPOI Team
We present direct measurements of the limb-darkened intensity profiles of late-type giants recently obtained with the Navy Prototype Optical Interferometer (NPOI). The use of NPOI's bootstrapping ability and a newly introduced noise bias correction enabled us to measure high-precision squared visibility amplitudes around and beyond the first minimum of the visibility function, in addition to the triple amplitudes and closure phases. We constrain the effective temperatures and surface gravities by directly comparing our interferometric data to a grid of stellar model atmospheres in order to check the consistency of direct observations and theoretical modeling of the limb-darkening effect for stars other than the sun. Obtained effective temperatures and surface gravities are found to be consistent with independent estimates, derived from empirical calibrations or from bolometric fluxes. Furthermore, we determine the angular limb-darkened diameters with a precision as high as 1-2%. These measurements contribute considerably to the small number of direct determinations of this parameter obtained so far.
MW acknowledges support from the Alexander von Humboldt Foundation through a Feodor Lynen Fellowship.
The author(s) of this abstract have provided an email address for comments about the abstract: mw@usno.navy.mil