Angular Diameter of the Asteroids Vesta and Pallas Determined from Speckle Observations

The technique of speckle interferometric measurement of asteroids is applied to Vesta and Pallas, yielding diameters of 550 or - 23 and 673 or - 55 km, respectively. The improved Vesta speckle diameter is in excellent agreement with other measurements for Vesta. However, the derived Pallas diameter is slightly larger than other measurements. This is perhaps attributable to systematic errors arising as an objects angular diameter nears the seeing disk size. It is alo pointed out that it is necessary to carefully normalize and center speckle frames before applying the autocorrelation, cross-correlation subtraction method developed by Worden et al.