External perturbations and rate of cometary capture

Abstract

Capture of comets by Sun is attributed to some disturbing force field (Hills 1981; Yabushita 1971, 1972, 1979; Biermann et al. 1983 etc.). In the present exposition an attempt has been made to study the mechanism of the capture process in terms of the perturbation vector-U' imposed on cometary velocity vector-U. For this purpose Hasegawa's (1976) capture hypothesis has been modified. A concise closed form for capture rate has been obtained which gives an insight into the mechanism of this process; consequently a captivity parameter (epsilon) has been defined here which gives a measure for the Sun's total capture efficiency. Under the influence of the external disturbance the magnitude of the Sun's relative velocity vector-V0 is found to be changed to V0 +/- U' for the apex and antepex directions, respectively. Accordingly the total captivity parameter has been split into partial captivity parameters epsilon1 (for apexial direction) and epsilon2 (for antepexial direction) in order to explain the observed anisotropy in capture from the two directions. Further, parameter hyperspace has been scanned for sigma, V0, U', n so that the computed capture rate and anisotropy are in agreement with their observed values. It has been found that the best-fit values sigma = 1.25 km/s, V0 = 1 km/s, U' = 0.2 km/s and n = 1.5 x 10/sup14//cu pc not only conform to physical requirements of the process but are also in agreement with the values obtained by other researchers (Hasegawa 1976; Valtonen & Innanen 1982; Valtonen 1983 etc.).