The Effect of Rotation on Calibrators for Ground-based Interferometry
NAVAL OBSERVATORY WASHINGTON DC
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We consider the problem introduced by rotation in the use of early-type stars as calibrators for optical interferometry. These objects have high surface brightnesses and hence are relatively bright, even with small angular diameters. However, rotation can introduce changes in the predicted visibilities well in excess of the uncertainties in the various diameter-magnitude-color calibrations. Measurements of the projected rotational velocity constrain these effects, but the constraints are complicated and not easily evaluated when selecting potential calibrators. Furthermore, the magnitude of the variations depends on the details of the interferometer,such as latitude, baseline length, and operating wavelength. Nevertheless, using measured magnitudes, colors parallaxes, and projected rotational velocities, and estimating masses from standard evolutionary grids, we are able to calculate histograms that approximate the probability distribution of the visibilities and allow us to characterize the width of the distribution of squared visibilities and the total range induced by rotation. We have found that proximity to the ZAMS adds a valuable constraint, allowing stars with moderate rotation to be reliable calibrators in a number of cases. Catalogs characterizing the sensitivity of the visibilities of potential calibrators to rotation are presented for a number of standard interferometer configurations.
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