Hostname: page-component-7c8c6479df-27gpq Total loading time: 0 Render date: 2024-03-28T11:30:36.752Z Has data issue: false hasContentIssue false

Characterization of the Rotation of Cometary Nuclei

Published online by Cambridge University Press:  12 April 2016

Michael J. S. Belton*
Affiliation:
National Optical Astronomy Observatories950 N. Cherry Ave, Tucson, Arizona, 85726

Abstract.

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

I review the primary methods used to determine the spin state of cometary nuclei and the pitfalls and successes experienced in their use. There are in excess of 60 reported determinations of rotational periodicities, but only a few (~4) appear to be reliable, and even these do not necessarily fully describe the true rotational state. An adequate rotational ephemeris is not, at present, available for a single cometary nucleus.

Because recent studies indicate that active cometary nuclei could be in excited spin states, I also review the theory of rigid body rotation from the point of view of remote (astronomical) observers, covering what is known of the effects of nutation on lightcurves, the influence of torques induced by jet activity, and the effects of internal energy and mass dissipation, and nuclear splitting.

The available knowledge on rotation for 8 comets, including P/Halley, is reviewed. Outstanding questions that need early resolution are: (1) Can a consensus be achieved on the rotational state of P/Halley? (2) Is it possible to accurately determine the amplitude of the transverse non-gravitational force associated with rotation? (3) Are the orientations of fan-like comas a valid indicator of the orientation of the spin vector – can definitive observational checks be made in a few cases?

Improved observational and interpretational techniques are needed to advance this field. Improved time-series and zero-date analyses are needed to connect existing and future data sets and to search for multiple periodicities in cometary lightcurves; improved sampling and extension of time-series observations with moderate- and large-aperture telescopes at good sites is needed; near-simultaneous photometric and radiometric observations made when cometary activity is low are particularly significant; well-sampled time-series imaging of near-nuclear phenomena (together with adequate software to analyze them) is essential to diagnose rotational states if nutation is present.

Type
Section IV: The Cometary Nucleus
Copyright
Copyright © Kluwer 1991

References

Abergel, A., Bertaux, J.L., and Dimarellis, E. 1989. Surface features and the rotation state of Halley’s comet nucleus. Annales Geophysicae 7(2), 129140.Google Scholar
A’Hearn, M.F. 1988. Observations of cometary nuclei. Ann. Rev. Earth Planet. Sci. 16, 273293.CrossRefGoogle Scholar
A’Hearn, M.F., Birch, P.V., Feldman, P.D., and Millis, R.L. 1985. Comet Encke: Gas production and lightcurve. Icarus 64, 110.CrossRefGoogle Scholar
A’Hearn, M.F., Hoban, S., Birch, P.V., Bowers, C., Martin, R., and Klinglesmith, D.A. III 1986. Cyanogen jets in comet Halley. Nature 324, 649651.CrossRefGoogle Scholar
A’Hearn, M.F., Campins, H., Schleicher, D.G., and Millis, R.L. 1989. The nucleus of comet P/Tempel 2. Astrophys. J. 347, 11551166.CrossRefGoogle Scholar
Barucci, M.A., Capria, M.T., Harris, A.W., and Fulchignoni, M. 1989. On the shape and albedo variegation of asteroids: Results from Fourier analysis of synthetic and observed asteroid lightcurves. Icarus 78, 311322.CrossRefGoogle Scholar
Belton, M.J.S. 1987. The wobbling nucleus of Halley’s comet. Planetary Report 7(2), 810.Google Scholar
Belton, M.J.S. 1990. Rationalization of Halley’s periods. Icarus, in press.CrossRefGoogle Scholar
Belton, M.J.S., Wallace, L., and Howard, S. 1981. The periods of Neptune: Evidence for atmospheric motions. Icarus 46, 263274.CrossRefGoogle Scholar
Belton, M.J.S., Wehinger, P., Wyckoff, S., and Spinrad, H. 1986. A precise period for P/Halley. In Exploration of Halley’s Comet, ESA SP-250, Vol. 2, 599603.Google Scholar
Belton, M.J.S., and Gandhi, A. 1988. Application of the CLEAN algorithm to cometary lightcurves. Bull. Am. Astron. Soc. 20, 836.Google Scholar
Beisser, K., and Boehnhardt, H., 1987. Dust tail streamers and Halley’s nucleus rotation. In Symposium of the Diversity and Similarity of Comets, ESA SP-278, 665670.Google Scholar
Bertaux, J.L., and Abergel, A. 1986. Some physical characteristics of Halley’s nucleus as inferred from VEGA and Giotto pictures. In Exploration of Halley’s Comet, ESA SP-250, Vol. 2, 341345.Google Scholar
Bobrovnikov, N. T. 1931. Halley’s comet in its apparition of 1909 – 1911. Pub. Lick. Obs. 17, 309482.Google Scholar
Brown, R.H. 1985. Ellipsoidal geometry in asteroid thermal models: The standard radiometric model. Icarus 64, 5363.CrossRefGoogle Scholar
Burns, J.A., and Safronov, V.S. 1973. Asteroid nutation angles. Mon. Not. R. Astr. Soc. 165, 403411.CrossRefGoogle Scholar
Burns, J.A., and Tedesco, E.F. 1979. Asteroid lightcurves: Results for rotations and shapes. In Asteroids. Gehrels, T. (Ed.), Univ. of Arizona Press, Tucson, 495527.Google Scholar
Campbell, D.B., Harmon, J.K, and Shapiro, I.I. 1989. Radar observations of comet Halley. Astrophys. J. 338, 10941105.CrossRefGoogle Scholar
Campins, H., A’Hearn, M.F. and McFadden, L.-A. 1987. The bare nucleus of comet Neujmin 1. Astrophys. J. 316, 847857.CrossRefGoogle Scholar
Celnik, W.E. 1986. The acceleration within the plasma tail, the rotational period of the nucleas, and the aberration of the plasma tail of comet P/Halley. In Exploration of Halley’s Comet, ESA SP-250, Vol. 1, 5358.Google Scholar
Celnik, W.E., and Schmidt-Kaler, Th. 1987. Structure and dynamics of plasma-tail condensations of comet P/Halley 1986 and inferences on the structure and activity of the cometary nucleus. Astron. Astrophys. 187, 233248.Google Scholar
Celnik, W.E., Koczet, P., Schlosser, W., Schulz, R., Svejda, P., and Weissbauer, K. 1988. Structure and dynamics of plasma tail condensations of comet P/Halley 1986. Astron. Astrophys. Suppl. 72, 89127.Google Scholar
Cochran, A.L., and Barker, E.S. 1986. Spectrophotometric observations of comet Halley. In Exploration of Halley’s Comet, ESA SP-250, Vol. 1, 439444.Google Scholar
Colom, P., and Gerard, E. 1988. A search for periodicities in the OH radio emission of comet P/Halley (1986III). Astron. Astrophys. 204, 327336.Google Scholar
Deeming, T.J. 1975a. Fourier analysis with unequally-spaced data. Astrophys. and Space Sci. 36, 137158.CrossRefGoogle Scholar
Deeming, T.J. 1975b. Erratum. Astrophys. and Space Sci. 42, 257.Google Scholar
Dermott, S.F., Harris, A.W., and Murray, C.D. 1984. Asteroid rotation rates. Icarus 57, 1434.CrossRefGoogle Scholar
Dobrovolski, A.R., and Burns, J.A. 1984. Angular momentum drain. A mechanism for despinning asteroids. Icarus 57, 464476.CrossRefGoogle Scholar
Drummond, J.D., Weidenschilling, S.J. Chapman, C.R. and Davies, D.R. 1988. Photometric geodesy of main belt asteroids II. Analysis of lightcurves for poles, periods, and shapes. Icarus 76, 1977.CrossRefGoogle Scholar
Dworetsky, M.M. 1983. A period-finding method for sparse randomly spaced observations or “How long is a piece of string”. Mon. Not. R. Astr. Soc. 203, 917924.CrossRefGoogle Scholar
Farinella, P., Paolicchi, P. and Zappala, V. 1985. On the rotation of cometary nuclei and small asteroids. In Dynamics of comets: Their origin and evolution. Carusi, A. and Valseschi, G.B. (eds.), D. Reidel Publishing Co., Dordrecht, 173178.CrossRefGoogle Scholar
Fay, T.D., and Wisniewski, W.Z. 1978. The lightcurve of the nucleus of comet d’Arrest. Icarus 34, 19.CrossRefGoogle Scholar
Feldman, P.D., A’Hearn, M.F., and Millis, R.L. 1983. Temporal and spatial behavior of the ultra-violet emission of comet IRAS-Araki-Alcock 1983d. Astrophys. J. 282, 799802.CrossRefGoogle Scholar
Ferrin, I. 1988. Has comet Halley retained its primordial angular momentum? Nature 333, 834835.CrossRefGoogle Scholar
Festou, M.C., Lecacheux, J., Kohn, J.L., Encrenaz, T., Baudrand, J., Combes, M., Laques, P., Le Fevre, O., Lemonnier, J.P., LeLievre, G., Mathez, G., Pierre, M., Vidal, J.L., and Wlerick, G. 1986. Photometry and activity of the nucleus of P/Halley at heliocentric distances larger than 6 AU, pre-perihelion. Astron. Astrophys. 169, 336344.Google Scholar
Festou, M.C., Drossart, P., Lecacheux, J., Encrenaz, T., Puel, F., and Kohl-Moreira, J.L. 1987. Periodicities in the lightcurve of P/Halley and the rotation of its nucleus. Astron. Astrophys. 187, 575580.Google Scholar
Goldstein, R.M., Jurgens, R.F., and Sekanina, Z. 1984. A radar study of comet IRAS-Araki-Alcock. Astron. J. 89, 17451754.CrossRefGoogle Scholar
Grun, E., Graser, U., Kohoutek, L., Thiele, T.J., Massonne, L., and Schwehm, G. 1986. Structures in the coma of comet Halley. Nature 321, 144147.CrossRefGoogle Scholar
Hoban, S., Samarasinha, N.H., A’Hearn, M.F., and Klinglesmith, D.A. 1988. An investigation into periodicities in the morphology of CN jets in comet P/Halley. Astron. Astrophys. 195, 331337.Google Scholar
Högbom, J.A. 1974. Aperture synthesis with a non-regular distribution of interferometer baselines. Astron. Astrophys. Suppl. 15, 417426.Google Scholar
Hsieh, K.C., Curtis, C.C., Fan, C.Y., Hunten, D.M., Ip, W.-H., Keppler, E., Richter, A.K., Umlauft, G., Afonin, V.V., Ero, J. Jr., and Somogyi, A.J. 1987. Anisotropy of the neutral gas distribution of comet P/Halley deduced from the NGE/ VEGA 1 measurements. Astron. Astrophys. 187, 375379.Google Scholar
Jewitt, D., and Danielson, G.E. 1984. Charge-coupled device photometry of comet P/Halley. Icarus 60, 435444.CrossRefGoogle Scholar
Jewitt, D., and Meech, K.J. 1985. Rotation of the nucleus of comet P/Arend-Rigaux. Icarus 64, 329335.CrossRefGoogle Scholar
Jewitt, D., and Meech, K. 1987. CCD photometry of comet P/Encke. Astron. J. 93, 15421548.CrossRefGoogle Scholar
Jewitt, D.C., and Meech, K.J. 1988. Optical properties of cometary nuclei and a preliminary comparison with asteroids. Astrophys. J. 328, 974986.CrossRefGoogle Scholar
Jewitt, D., and Luu, J. 1989. A CCD portrait of comet P/Tempel 2. Astron. J. 97, 17661790.CrossRefGoogle Scholar
Joos, G. 1950. Theoretical Physics. Hafner Pub. Co., New York.Google Scholar
Julian, W. II. 1987. Free precession of the comet Halley nucleus. Nature 326, 5758.CrossRefGoogle Scholar
Julian, W.H. 1988a. Precession of triaxial cometary nuclei. Icarus 74, 377382.CrossRefGoogle Scholar
Julian, W.H. 1988b. Forced precession of the comet Halley nucleus. In Proc. of the Lin C.C. Symp., World Scientific Publishing, Singapore, 422427.Google Scholar
Kamel, L., 1988. The rotation, precession and nutation of P/Halley’s nucleus. Astron. Astrophys. 193, L4-L6.Google Scholar
Kamoun, P.D., Campbell, D.B., Ostro, S.J., Pettengill, G.H., and Shapiro, I.I. 1982. Comet Encke: Radar detection of the nucleus. Science 219, 293296.Google Scholar
Kaneda, E., Hirao, K., Takagi, M., Ashihara, O., Itoh, T., and Shimizu, M. 1986a. Strong breathing of the hydrogen coma of comet Halley. Nature 320, 140141.CrossRefGoogle Scholar
Kaneda, E., Ashihara, O., Shimizu, M., Takagi, M., and Hirao, K. 1986b. Observation of comet Halley by the ultraviolet imager of Suisei. Nature 321, 297299.CrossRefGoogle Scholar
Keller, H.U., 1987. The nucleus of comet Halley. In Symposium of the Diversity and Similarity of Comets, ESA SP-278, 447454.Google Scholar
Keller, H.U., and Thomas, N. 1988. On the rotation axis of comet Halley. Nature 333, 146148.CrossRefGoogle Scholar
Kosai, H. 1986. Total visual magnitude and variation of brightness of the comet Halley between 1985 August and 1986 July. In Exploration of Halley’s Comet, ESA SP-250, Vol. 3, 253254.Google Scholar
Kurtz, D.W. 1985. An algorithm for significantly reducing the time necessary to compute a discrete Fourier transform periodogram of unequally spaced data. Mon. Not. R. Astr. Soc. 213, 773776.CrossRefGoogle Scholar
Lafler, T., and Kinman, T.D. 1965. An RR Lyrae star survey with the Lick 20inch astrograph. Astrophys. J. Suppl. 11, 216222.CrossRefGoogle Scholar
Lamy, P.L., and Burns, J.A. 1972. Geometrical approach to torque free motion of a rigid body having internal energy dissipation. Amer. Jrnl. Phys. 40(3), 441445.CrossRefGoogle Scholar
Landau, L.D. and Lifshitz, E.M., 1960. Mechanics. Pergamon Press, Oxford, Chapter VI.Google Scholar
Larson, S.M., and Minton, R.B. 1972. Photographic observations of comet Bennett 1970 II. In Comets: Scientific Data and Missions, Kuiper, G.P. and Roemer, E. (eds.), Univ. of Arizona Press, Tucson, 183208.Google Scholar
Larson, S.M., and Sekanina, Z. 1985. Coma morphology and dust-emission pattern of periodic comet Halley. III. Additional high-resolution images taken in 1910. Astron. J. 90, 823923.CrossRefGoogle Scholar
Larson, S., and Sekanina, Z. 1987a. Dust jet morphology and the lightcurve of Comet Halley. Bull. A.A.S. 19, 866.Google Scholar
Larson, S., Sekanina, Z., Levy, D., Tapia, S., and Senay, M. 1987b. Comet P/Halley near-nucleus phenomena in 1986. Astron. Astrophys. 187, 639644.Google Scholar
Lebofsky, L.A., Sykes, M.V., Tedesco, E.F., Veeder, G.J., Matson, D.L., Brown, R.H., Gradie, J.C., Feierberg, M.A., and Rudy, R.J. 1986. A refined standard thermal model for asteroids based on observations of 1 Ceres and 2 Pallas. Icarus 68, 239251.CrossRefGoogle Scholar
Leibowitz, E.M., and Brosch, N. 1986a. Photoelectric discovery of a 52-hr periodicity in the nuclear activity of P/Halley. Icarus 68, 418429.CrossRefGoogle Scholar
Leibowitz, E.M., and Brosch, N. 1986b. Periodic variations in the near nucleus zone of P/Giacobini-Zinner. Icarus 68, 430441.CrossRefGoogle Scholar
Luu, J., and Jewitt, D. 1990. The nucleus of comet P/Encke. Icarus, in press.CrossRefGoogle Scholar
Manfroid, J., Heck, A., and Mersch, G. 1983. Comparitive study of period determination methods. In Proc. Statistical Methods in Astron. Symp., ESA SP-201, 117121.Google Scholar
Marsden, B.G., Sekanina, Z., and Yeomans, D.K. 1973. Comets and non-gravitational forces. V. Astron. J. 78, 211225.CrossRefGoogle Scholar
McAdoo, D.C., and Burns, J.A. 1974. Approximate axial alignment times for spinning bodies. Icarus 21, 8693.CrossRefGoogle Scholar
McFadden, L.-A., A’Hearn, M.F., Feldman, P.D., Roettger, E.E., Edsall, D.M., and Butterworth, P.S. 1987. Activity of comet P/Halley 23–25 March, 1986: IUE observations. Astron. Astrophys. 187, 333338.Google Scholar
Meech, K.J., Jewitt, D., and Ricker, G.R. 1986. Early photometry of comet Halley: Development of the coma. Icarus 66, 561574.CrossRefGoogle Scholar
Meech, K.J., and Jewitt, D.C. 1987. Observations of comet P/Halley at minimum phase angle. Astron. Astrophys. 187, 585593.Google Scholar
Mendis, D.A., Houpis, H.L.F., and Marconi, M.L. 1985. The physics of comets. Fundamentals of Cosmic Physics 10, 1380.Google Scholar
Millis, R.L., and Schleicher, D.G. 1986. Rotational period of comet Halley. Nature 324, 646649.CrossRefGoogle Scholar
Millis, R.L., A’Hearn, M.F., and Campins, H. 1988. An investigation of the nucleus and coma of P/Arend-Rigaux. Astrophys. J. 324, 11941209.CrossRefGoogle Scholar
Möhlmann, D. 1989. Rotation and free precession of the comet Halley nucleus. Astron. Nachr. 310, 151154.CrossRefGoogle Scholar
Morbey, C.L. 1985. Brightness variations in comet P/Halley determined by the Least Scatter Algorithm. Astron. Express 1, 133136.Google Scholar
Neckel, T., and Munch, G. 1987. Photometry of comet P/Halley at near post-perihelion phases. Astron. Astrophys. 187, 581584.Google Scholar
Ostro, S.J. 1985. Radar observations of asteroids and comets. Pub. Astron. Soc. Pacific 97, 877884.CrossRefGoogle Scholar
Ostro, S.J., and Connelly, R. 1984. Convex profiles from asteroid lightcurves. Icarus 57, 443463.CrossRefGoogle Scholar
Peale, S.J. 1989. On the density of Halley’s comet. Icarus 82, 36349.CrossRefGoogle Scholar
Peale, S.J., and Lissauer, J.J. 1989. Rotation of Halley’s comet. Icarus 79, 396430.CrossRefGoogle Scholar
Percy, J.R. 1977. The application of maximum entropy spectral analysis to the study of short-period variable stars. Mon. Not. R. Astr. Soc. 181, 647656.CrossRefGoogle Scholar
Ponman, T. 1981. The analysis of periodicities in irregularly sampled data. Mon. Not. R. ast. Soc. 196, 583596.CrossRefGoogle Scholar
Pospieszalska-Surdej, A., and Surdej, J. 1985. Determination of the pole orientation of an asteroid. The amplitude-aspect relation revisited. Astron. Astrophys. 149, 186194.Google Scholar
Press, W.H., Flannery, B.P., Teukolsky, S.A., and Vetterling, W.T. 1986. Numerical Recipes. Cambridge University Press, Cambridge.Google Scholar
Reed, L.G., and Welch, G.A. 1988. A search for multiple periods in three Delta Scuti stars. Astron. J. 95, 15101527.CrossRefGoogle Scholar
Rettig, T.W., Kern, J.R., Rucht, R., Baumbaugh, B., Baumbaugh, A.E., Knickerbocker, K.L., and Dawe, J. 1987. Analysis of the coma outburst of comet Halley March 24–25, 1986. In Symposium of the Diversity and Similarity of Comets, ESA SP-278, 265269.Google Scholar
Roberts, D.H., Lehar, J., and Dreher, J.W. 1987. Time-series analysis with CLEAN. Derivation I. of a spectrum. Astron. J. 93, 968989.CrossRefGoogle Scholar
Roemer, E. 1966. The dimensions of cometary nuclei. Mem. Soc. R. Sci. Liege. 15th Series 15, 2328.Google Scholar
Sagdeev, R.Z., Szabo, F., Avanesov, G.A., Cruvellier, P., Szabo, L., Szegö, K., Abergel, A., Balazs, A., Barinov, I.V., Bertaux, J.L., Blamont, J., Detaille, M., Dimarellis, E., Dul’nev, G.N., Endroczy, G., Gardos, M., Kanyo, M., Kostenko, V.I., Krasikov, V.A., Nguyen-Trong, T., Nyitrai, Z., Reny, I., Rusznyak, P., Shamis, V.A., Smith, B., Sukhanov, K.G., Szalai, S., Tarnopolsky, V.I., Toth, I., Tsukanova, G., Valnicek, B.I., Varhalmi, L., Zaiko, Yu.K., Zatsepin, S.I., Ziman, Ya.L., Zsenei, M., and Zhukov, B.S. 1986a. Television observations of comet Halley from VEGA spacecraft. Nature 321, 262266.CrossRefGoogle Scholar
Sagdeev, R.Z., Krasikov, V.A., Szegö, K., Toth, I., Smith, B., Larson, S., Merenyi, E., Shamis, V.A. and Tarnopolsky, V.I. 1986b. Rotation period and spin axis of comet Halley. In Exploration of Halley’s Comet, ESA SP-250, Vol. 2, 335338.Google Scholar
Sagdeev, R.Z., Szegö, K., Smith, B.A., Larson, S., Merenyi, E., Kondor, A., and Toth, I. 1989. The rotation of P/Halley. Astron. J. 97, 546551.CrossRefGoogle Scholar
Samarasinha, N.H., A’Hearn, M.F., Hoban, S., and Klinglesmith, D.A. 1986. CN jets of comet P/Halley – rotational properties. In Exploration of Halley’s Comet, ESA SP-250, Vol. 1, 487492.Google Scholar
Scargle, J.D. 1982. Studies in astronomical time-series analysis. II. Statistical aspects of spectral analysis of unevenly spaced data. Astrophys. J. 263, 835853.CrossRefGoogle Scholar
Schleicher, D.G., Millis, R.L., Tholen, D., Lark, N., Birch, P.V., Martin, R., and A’Hearn, M.F. 1986. The variability of Halley’s comet during the VEGA, Planet-A, and Giotto encounters. In Exploration of Halley’s Comet, ESA SP-250, Vol. 1, 565567.Google Scholar
Schloerb, F.P., Kinzel, W.M., Swade, D.A., and Irvine, W.M. 1987. Observations of HCN in comet P/Halley. Astron. Astrophys. 187, 475480.Google ScholarPubMed
Schlosser, W., Schulz, R., and Koczet, P. 1986. The cyan shells of comet P/Halley. In Exploration of Halley’s Comet, ESA SP-250, Vol. 3, 495498.Google Scholar
Schulz, R. and Schlosser, W. 1989. CN-shell structures and dynamics of the nucleus of comet P/Halley. Astron. Astrophys. 214, 375385.Google Scholar
Sekanina, Z. 1979. Fan-shaped coma, orientation of rotation axis, and surface structure of a cometary nucleus. I. Icarus 37, 420442.CrossRefGoogle Scholar
Sekanina, Z. 1981a. Rotation and precession of cometary nuclei. Ann. Rev. Earth Planet. Sci. 9, 113145.CrossRefGoogle Scholar
Sekanina, Z. 1981b. The distribution of activity of discrete emission areas on the nucleus of periodic comet Swift-Tuttle. Astron. J. 86, 17411773.CrossRefGoogle Scholar
Sekanina, Z. 1982. The problem of split comets in review. In Comets. Wilkening, L.L. (ed.), Univ. of Arizona Press, Tucson, 227250.Google Scholar
Sekanina, Z. 1984. Precession model for the nucleus of periodic comet Kopff. Astron. J. 89, 15731586.CrossRefGoogle Scholar
Sekanina, Z. 1985a. Light variations of periodic comet Halley beyond 7 AU. Astron. Astrophys. 148, 299308.Google Scholar
Sekanina, Z. 1985b. Nucleus studies of comet Halley. Adv. Space Res. 5(12), 307316.CrossRefGoogle Scholar
Sekanina, Z. 1985c. Nucleus precession of periodic comet Sola. Astron. J. 90, 13701381.CrossRefGoogle Scholar
Sekanina, Z., 1985d. Precession model for the nucleus of periodic comet Giacobini-Zinner. Astron. J. 90, 827845.CrossRefGoogle Scholar
Sekanina, Z. 1986. Effects of the law for nongravitational forces on the precession model of comet Encke. Astron. J. 91, 422431.CrossRefGoogle Scholar
Sekanina, Z., 1987a. Anisotropic emission from comets I: Concept and modeling. In Symposium of the Diversity and Similarity of Comets, ESA SP-278, 315322.Google Scholar
Sekanina, Z., 1987b. Anisotropic emission from comets II: Fans versus jets. Periodic Tempel 2. In Symposium of the Diversity and Similarity of Comets, ESA SP-278, 323336.Google Scholar
Sekanina, Z. 1987c. Nucleus of comet Halley as a torque-free rigid rotator. Nature 325, 326328.CrossRefGoogle Scholar
Sekanina, Z., 1988a. Rotation vector of Halley’s comet. In Comet Halley 1986: Worldwide Investigations. Ellis Horwood Lib. of Space, Ser. in Astron.Google Scholar
Sekanina, Z. 1988b. Periodic comet Tempel 2 (1987g). IAU Circ. 4624.Google Scholar
Sekanina, Z. 1988c. Nucleus of comet IRAS-Araki-Alcock (1983 VII). Astron. J. 95, 18761894.CrossRefGoogle Scholar
Sekanina, Z. 1988d. Outgassing asymmetry of periodic comet Encke. I. Apparitions. 1924–1984. Astron. J. 95, 9119240.CrossRefGoogle Scholar
Sekanina, Z. 1988e. Outgassing asymmetry of periodic comet Encke. II. Apparitions 1868–1918 and a study of nucleus evolution. Astron. J. 96, 14551475.CrossRefGoogle Scholar
Sekanina, Z. 1989. Nuclei of two Earth-grazing comets of fan-shaped appearance. Astron. J. 98, 23222345.CrossRefGoogle Scholar
Sekanina, Z., and Larson, S.M. 1984. Coma morphology and dust-emission pattern of periodic comet Halley. II. Nucleus spin vector and modeling of major dust features in 1910. Astron. J. 89, 14081425.CrossRefGoogle Scholar
Sekanina, Z., and Larson, S.M. 1986a. Coma morphology and dust-emission pattern of periodic comet Halley. IV. Spin vector refinement and map of discrete dust sources for 1910. Astron. J. 92, 462482.CrossRefGoogle Scholar
Sekanina, Z., and Larson, S. 1986b. Dust jets in comet Halley observed by Giotto and from the ground. Nature 321, 357361.CrossRefGoogle Scholar
Sekanina, Z., Larson, S.M., Emerson, G., Helin, E.F., and Schmidt, R.E. 1987. The sunward spike of Halley’s comet. Astron. Astrophys. 187, 645649.Google Scholar
Simpson, J.A., Rabinowitz, D., Tuzzolino, A.J., Ksanformality, K.S., and Sagdeev, R.Z. 1987. The dust coma of comet P/Halley: Measurements on the VEGA-1 and VEGA- 2 spacecraft. Astron. Astrophys. 187, 742752.Google Scholar
Smith, B.A., Larson, S.M., Szegö, K., and Sagdeev, R.Z. 1987. Rejection of a proposed 7.4-day rotation period of the comet Halley nucleus. Nature 326, 573574.CrossRefGoogle Scholar
Sommerfeld, A. 1952. Mechanics. Academic Press Inc., New York.Google Scholar
Stellingwerf, R.F. 1978. Period determination using phase-dispersion minimization. Astrophys. J. 224, 953960.CrossRefGoogle Scholar
Sterken, C., Manfroid, J., and Arpigny, C. 1987. Photometry of P/Halley (1982i). Astron. Astrophys. 187, 523525.Google Scholar
Stewart, A.I.F. 1987. Pioneer Venus measurements of H, O, and C production in comet Halley near perihelion. Astron. Astrophys. 187, 369374.Google Scholar
Storrs, A.D., Tokunaga, A.T., Christian, C.A., and Heasley, J.N. 1986. The distribution of dust in the inner coma of comet IRAS-Araki-Alcock. Icarus 66, 143153.CrossRefGoogle Scholar
Trotignon, J.G., Beghin, C., Grard, R., Pedersen, A., Formisiano, V., Mogilevsky, M., and Mikhailov, Y. 1987. Dust observations of comet P/Halley by the plasma-wave analyzer. Astron. Astrophys. 187, 8388.Google Scholar
Vaisberg, O.L., Smirnov, V.N., Gorn, L.S., Iovlev, M.V., Balikchin, M.A., Klimov, S.I., Savin, S.P., Shapiro, V.D., and Shevchenko, V.I. 1986. Dust coma structure of comet Halley from SP-1 detector measurements. Nature 321, 274276.CrossRefGoogle Scholar
Vaisberg, O.L., Smirnov, V., Omelchenko, A., Gorn, L., and Iovlev, M.V. 1987. Spatial and mass distribution of low-mass dust particles (m < 10-10g) in comet P/Halley’s coma. Astron. Astrophys. 187, 753760.Google Scholar
Wallis, M.K. 1984. Rotation of cometary nuclei. Phil. Trans. R. Soc. London. A. 313, 165170.Google Scholar
Watanabe, J. 1987. The rotation of comet 1983 VII IRAS-Araki-Alcock. Pub. Astron. Soc. Japan 39, 485503.Google Scholar
Watanabe, J. 1988. Morphological analysis of near-nucleus images of comet Halley. Ann. Tokyo Astron. Obs. 22, Second Series, No. 1, 130.Google Scholar
Watanabe, J 1989. Rotational motion of the nucleus of comet P/Halley. Pub. Ast. Soc. Japan 41, 897918.Google Scholar
Weidenschilling, S.J. 1981. How fast can an asteroid spin? Icarus 46, 124126.CrossRefGoogle Scholar
West, R.M. 1990. Post-perihelion observations of comet P/Halley. II. r=10.1 AU. Astron. Astrophys. 228, 531538.Google Scholar
West, R.M., and Pedersen, H. 1984. Variability of P/Halley. Astron. Astrophys. 138, L9L10.Google Scholar
West, R.M., and Jorgensen, H.E. 1989. Post perihelion observations of comet P/Halley at r = 8.5 AU. Astron. Astrophys. 218, 307316.Google Scholar
Whipple, F.L. 1950. A comet model. I. The acceleration of comet Encke. Astrophys. J. 111, 375394.CrossRefGoogle Scholar
Whipple, F.L. 1961. Problems of the cometary nucleus. Astron. J. 66, 375380.CrossRefGoogle Scholar
Whipple, F.L. 1978. Rotation period of comet Donati. Nature 273, 134135.CrossRefGoogle Scholar
Whipple, F.L. 1980. Periodic comet Halley. IAU Circ. 3459.Google Scholar
Whipple, F.L. 1981. On observing comets for nuclear rotation. In Modern Observational Techniques for Comets, Brandt, J.C., Donn, B., and Rahe, J. (eds.), JPL Publication 8168.Google Scholar
Whipple, F.L. 1982. The rotation of comet nuclei. In Comets, Wilkening, L.L. (ed.), Univ. of Arizona Press, Tucson, 227250.CrossRefGoogle Scholar
Whipple, F.L. 1983. Cometary nucleus and active regions. In Cometary Exploration, Gombosi, T.I. (ed.). Hungarian Acad. Sci. Budapest, 1, 95110.Google Scholar
Whipple, F.L., and Sekanina, Z. 1979. Comet Encke: Precession of the spin axis, non-gravitational motion, and sublimation. Astron. J. 84, 18941909.CrossRefGoogle Scholar
Whipple, F.L., and Schild, R.E. 1983. Comet IRAS-Araki-Alcock (1983d). An intimate study. Bull. Am. Astron. Soc. 15, 799.Google Scholar
Wilhelm, K. 1987. Rotation and precession of comet Halley. Nature 327, 2730.CrossRefGoogle Scholar
Wilhelm, K., Cosmovici, C.B., Delamere, W.A., Huebner, W.F., Keller, H.U., Reitsema, H., Schmidt, H.U., and Whipple, F.L. 1986. A three-dimensional model of the nucleus of comet Halley. In Exploration of Halley’s Comet, ESA SP-250, Vol. 2, 367369.Google Scholar
Williams, LP., Andrews, P.J., Fitzsimmons, A., and Williams, G.P. 1987. The variation in the brightness of Halley’s comet from ground-based narrow-band photometry. Mon. Not. R. Astr. Soc. 226, 1p4p.CrossRefGoogle Scholar
Wisniewski, W. 1988. Periodic comet Tempel 2 (1987g). IAU Circ. 4603.Google Scholar
Wisniewski, W.Z., Fay, T., and Gehrels, T. 1986. Light variation of comets. In Asteroids, Comets, Meteors II, Lagerkvist, C.I., Lindblad, B.A., Lundstedt, H., and Rickman, H. (eds.), Reprocentralen HSC, Uppsala, 337339.Google Scholar
Yeomans, D.K., and Chodas, P.W. 1989. An asymmetric outgassing model for cometary nongravitational accelerations. Astron. J. 98, 10831093.CrossRefGoogle Scholar