Triaxial ellipsoid dimensions and rotational pole of 2 Pallas from two stellar occultations

From three stellar occultations we show that it is possible to derive unique triaxial ellipsoid dimensions and a rotational pole for an asteroid. With the two occultations for Pallas, we examine the locus of solutions that fall along a curve in a seven-dimensional parameter space. It appears from this range of solutions that the first occultation (slightly) overestimated the ture size of the outline of the asteroid at that time. Within the errors of this first occultation, however, more plausible solutions are allowed. The best estimate of the lengths of the triaxial ellipsoid axes derived from the two occultations is (in km) (583 ± 18, 527 ± 3, 409 ± 52) and a rotational pole within 10° of RA = 72°, Dec = +3° (or 252°; −3°), corresponding to eliptic coordinates long = 71°, lat = −19°. Combining the occultation model with speckle interferometry results gives a model of (570 ± 22, 525 ± 4, 482 ± 15) km, and for occultation, speckle, and lightcurve methods, a pole at RA = 75°, Dec = +6° (ecliptic coordinates (74°; −17°)), with an error circle of 24° radius. Pallas is more flattened, with a greater b c ratio (and a smaller c) than previously estimated.