OORT CLOUD COMET PERIHELION ASYMMETRIES - GALACTIC TIDE, SHOWER OR OBSERVATIONAL BIAS

We investigate the distribution of Oort cloud comet perihelia. The dat a considered includes comets having orbital elements of the two highes t quality classes with original energies designated as new or young. P erihelion directions are determined in galactic, ecliptic and geocentr ic equatorial coordinates. Asymmetries are detected in the scatter and are studied statistically for evidence of adiabatic galactic tidal dy namics, an impulse-induced shower and observational bias. The only bia s detected is the well-known deficiency of observations with perihelio n distances q > 2.5 AU. There is no significant evidence of a seasonal dependence. Nor is there a substantive hemispherical bias in either e cliptic or equatorial coordinates. There is evidence for a weak stella r shower previously detected by Biermann which accounts for approximat e to 10% of the total observations. Both the q bias and the Biermann s tar track serve to weaken the evidence for a galactic tidal imprint. N evertheless, statistically significant asymmetries in galactic latitud e and longitude of perihelia remain. A latitude asymmetry is produced by a dominant tidal component perpendicular to the galactic disk. The longitude signal implies that approximate to 20% of new comets need an additional dynamical mechanism. Known disk non-uniformities and an hy pothetical bound perturber are discussed as potential explanations. We conclude that the detected dynamical signature of the galactic tide i s real and is not an artifact of observational bias, impulsive showers or poor data.