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On the monochromatic brightness variations of comets

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Abstract

A calculation of the non-steady development of a multi-species atmosphere of a comet moving in a near-parabolic heliocentric orbit is presented. The monochromatic brightness variations of the characteristic cometary emission bands due to OH, CN and C2 are then evaluated assuming that the ‘parent molecules’ of these chemically unstable species are respectively H2O, HCN and H2C2 present in a homogeneous H2O clathrate nucleus. For small heliocentric distances where a quasi-steady approximation is valid, the brightness variations follow Levin's (1943) law, provided all the destruction mechanisms of the cometary molecules vary as the inverse square of the heliocentric distance. On the other hand, at large heliocentric distances Levin's law breaks down, essentially due to the large time-scales of residence of the emitting species in the cometary atmosphere. This large residence time at large heliocentric distance also produces an asymmetry between the brightness profiles of the inbound and outbound passages, such that the brightness declines less steeply with distance on the outbound passage than on the inbound. Consequently, the monochromatic brightness of OH at 4 AU outbound is about twice as large as the corresponding value inbound. While some comets show such an effect, others show just the opposite effect. These deviations, which show the limitations of our simple homogeneous model, are discussed qualitatively in terms of the plausible time varying physical structure of the cometary nucleus. The variations of the relative monochromatic brightnesses of the various emissions are also discussed, and the need for extending monochromatic brightness measurements to larger heliocentric distances is stressed.

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References

  1. Code, A. D.: 1970,IAU Trans. 14B, 124.

  2. Delsemme, A. H.: 1971,Science 172, 1126.

  3. Delsemme, A. H.: 1973aAstrophys. Letters 14, 163.

  4. Delsemme, A. H.: 1973b,Space Sci. Rev. 15, 89.

  5. Delsemme, A. H. and Moreau, J. L.: 1973,Astron. Letters 14, 181.

  6. Delsemme, A. H. and Rud, D. A.: 1973,Astron. Astrophys. 28, 1.

  7. Donn, B. and Urey, H. C.: 1956,Astrophys. J. 123, 339.

  8. Feldman, P. D. and Brune, W. H.: 1976,Astrophys. J. (Letters) 209, L45.

  9. Glasstone, S.: 1946,Textbook of Physical Chemistry (2nd ed.), Van Nostrand Co., New York, p. 452.

  10. Ip, W.-H. and Mendis, D. A.: 1976,Icarus 29, 147.

  11. Jacchia, L. G.: 1974,Sky Telesc. 47, 216.

  12. Jackson, W. M.: 1977,J. Photochem. (in press).

  13. Levin, B.: 1943,Astron. Zh. 20, 4.

  14. Mendis, D. A., Holzer, T. E. and Axford, W. I.: 1972,Astrophys. Space Sci. 15, 313.

  15. Mendis, D. A. and Ip, W.-H.: 1974,Nature,249, 536.

  16. Mendis, D. A. and Ip, W.-H.: 1976,Astrophys. Space Sci. 39, 335.

  17. Mendis, D. A. and Ip, W.-H.: 1977,Space Sci. Rev. 20, 145.

  18. Pittich, E. M.: 1972, in G. A. Chebotarev et al. (eds),The Motion Evolution of Orbits and Origin of Comets, Reidel, Dordrecht, p. 283.

  19. Richter, N. B.: 1963,The Nature of Comets, Methuen Press, p. 69.

  20. Vanýsek, V.: 1976, in B. Donnet al. (eds),The Study of Comets, NASA SP-393, p. 1.

  21. Vsekhsvyatsky, S. K.: 1956,Astron. Zh. 33, 516.

  22. Wallis, M. K.: 1972,Science 178, 78.

  23. West, R. C.: 1974,CRC Handbook of Chemistry and Physics, C297 and C-339.

  24. Wurm, K.: 1963, in B. M. Middlehurst and G. P. Kuiper (eds),The Moon Meteorites and Comets, University of chicago Press, p. 573.

  25. Wyckoff, S. and Wehinger, P. A.: 1976,Astrophys. J. 204, 604.

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Mendis, D.A., Brin, G.D. On the monochromatic brightness variations of comets. The Moon and the Planets 18, 77–89 (1978). https://doi.org/10.1007/BF00896699

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Keywords

  • Clathrate
  • Heliocentric Distance
  • Brightness Variation
  • Cometary Nucleus
  • Destruction Mechanism