Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...277..265s&link_type=abstract
Astronomy and Astrophysics, Vol. 277, p. 265 (1993)
Astronomy and Astrophysics
Astrophysics
4
Comets - Orbital Motion - Nongravitational Perturbations - Normal Component Of The Nongravitational Force - P/Clark
Scientific paper
The significance and detectability of a normal component of the nongravitational acceleration that perturbs the motions of periodic comets are examined by comparing the total perturbation effect, calculated from the component's empirical term in the equations of motion integrated over the orbital period, with the cumulative perturbations of the longitude of the ascending node and the orbital inclination brought about by the momentum that is transferred to the nucleus due to water outgassing from discrete active regions. It is shown that the approximation of temporal variations in the recoil acceleration computed using the well-known g(r) law, which is symmetrical with respect to perihelion, implies that the cumulative nongravitational perturbations of the two orbital elements are accounted for in a fashion that is inconsistent with the perturbation theory. The net result is that, in general, the value of the Style II nongravitational parameter that is consistent with the cumulative effect on the inclination, iA3, differs from the parameter's expected value that describes the cumulative effect on the nodal line, ΩA3. The parameter's distributions as functions of the spin vector and the direction of the ejecta's vector (described by the thrust angle) are represented graphically for several heliocentric orbits. Symmetries with respect to particular values of the argument of perihelion, the rotation constants, and the thrust angle that apply in the case of a baseline model (which involves assumptions of a single source and the absence of sublimation lags) are identified. The magnitudes of the parameter A3 derived from orbit- determination runs are found to be generally compatible with the presented interpretation in that they are not excessive, thus supporting the evidence presented in an earlier paper (Sekanina 1993) and based upon information on the transverse and radial components of the recoil force. The values of iA3 and ΩA3 are shown to coincide for certain spin-axis orientations and it is only then that the parameter A3 should reliably be determined from an orbital solution that employs the standard g(r) law. One such scenario appears to be closely approximated by Periodic Comet Clark, for which the data available are shown to provide meaningful constraints on the bulk properties of its nucleus. A potential need for a revision of the non-gravitational terms in the equations of motion is suggested.
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