HIGH SPECTRAL RESOLUTION OBSERVATIONS AND KINEMATIC MODELING OF THE 1667 MHZ HYPERFINE TRANSITION OF OH IN COMETS HALLEY (1982I), GIACOBINI-ZINNER (1984E), HARTLEY-GOOD (1985L), THIELE (1985M), AND WILSON (1986L)

被引:22
作者
TACCONIGARMAN, LE
SCHLOERB, FP
CLAUSSEN, MJ
机构
[1] UNIV MASSACHUSETTS,COLL RADIO ASTRON OBSERV 5,AMHERST,MA 01003
[2] UNIV MASSACHUSETTS,DEPT PHYS & ASTRON,AMHERST,MA 01003
[3] USN,RES LAB,CTR ADV SPACE SENSING,WASHINGTON,DC 20375
关键词
Comets; Radio sources: lines;
D O I
10.1086/169450
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
As a first step toward understanding the kinematics of cometary comae we have undertaken an analysis of the 18 cm OH lines in comets. This work builds on past OH excitation and kinematic studies to meld them into a complete and self-consistent model for a cometary coma. We model the kinematics via the vectorial formalism and employ the powerful Monte Carlo technique in an effort to reproduce the high-sensitivity, high spectral resolution 18 cm OH line profiles of comets Halley, Giacobini-Zinner, Hartley-Good, Thiele, and Wilson which were obtained at the 43 m telescope of the National Radio Astronomy Observatory at Green Bank, West Virginia. We have made estimates of the gas production rates using a "simple" A-doublet quenching correction to the 18 cm data and find that the long standing UV/radio gas production rate disparity can be diminished. We have derived gas expansion velocities and coma anisotropies from observations covering a wide range of heliocentric distances and gas production rates. The inferred ratio of dayside gas emission to nightside gas emission for all comets in this study, except P/Giacobini-Zinner, is 1.39(+0.13-0.12). This value is consistent with that derived from in situ observations of the neutral gas in the coma of comet Halley and is independent of both gas productivity and heliocentric distance. For P/Giacobini-Zinner we infer anomalously high gas outflow anisotropies for which there is no clear explanation. The derived outflow velocities are consistent with those derived from a variety of other indicators of the coma expansion velocity and suggest that the gas production of a comet plays a critical role in determining the coma kinematics for active comets near the Sun. We find, however, that the outflow velocities at large heliocentric distances are consistently lower than the predictions of one-dimensional coma dynamical models.
引用
收藏
页码:672 / 686
页数:15
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