SOHO/SWAN Observations of the Structure and Evolution of the Hydrogen Lyman-α Coma of Comet Hale–Bopp (1995 O1)

Abstract The SWAN all-sky camera on the SOHO spacecraft observed the hydrogen Lyman-alpha coma of Comet Hale–Bopp (1995 O1) from January through May 1997. The observations covered heliocentric distances from 1.75 AU before perihelion to 1.29 AU after, showing the hydrogen coma to vary in brightness, shape, and orientation with the comet's orbital position. The water production rate of the comet was determined from an analysis of these images with a model that accounts for the detailed physics and chemistry. The model incorporates coma dynamics (expansion velocity and kinetic temperatures), which have been shown to be consistent with a variety of other observations. The distribution of brightness in the modeled images reproduces the absolute magnitude and distribution of brightness seen in the observations. We find that the maximum water production rate occurred about 2 weeks after perihelion, and that the magnitude and variation with time are consistent with other published observations which were analyzed in a consistent manner.

[1]  M. Combi,et al.  Monte Carlo particle-trajectory models for neutral cometary gases. II: The spatial morphology of the Lyman-alpha coma , 1988 .

[2]  S. Lederer,et al.  Photometric Behavior of Comet Hale-Bopp (C/1995 O1) Before Perihelion , 1997, Science.

[3]  A. Cochran,et al.  Observational Constraints on the Lifetime of Cometary H2O , 1993 .

[4]  D. K. Prinz,et al.  Validation of the UARS solar ultraviolet irradiances: Comparison with the ATLAS 1 and 2 measurements , 1996 .

[5]  C. Y. Wu,et al.  Velocity distributions of hydrogen atoms and hydroxyl radicals produced through solar photodissociation of water , 1993 .

[6]  P. Feldman,et al.  Water Production Rates in Comet P/Halley from IUE Observations of HI Lyman-β , 1993 .

[7]  M. Combi,et al.  Monte Carlo particle-trajectory models for neutral cometary gases. I. Models and equations. II. The spatial morphology of the Lyman-alpha coma , 1988 .

[8]  M. Combi.  Time-Dependent Gas Kinetics in Tenuous Planetary Atmospheres: The Cometary Coma , 1996 .

[9]  M. Berthé,et al.  First Results from SWAN Lyman α solar wind mapper on SOHO , 1997 .

[10]  P. Feldman,et al.  Post-Perihelion HST Observations of Comet Hale-Bopp , 1999 .

[11]  P. Feldman,et al.  The Activity and Size of the Nucleus of Comet Hale-Bopp (C/1995 O1) , 1997, Science.

[12]  H. Keller,et al.  Multiple Scattering of Hydrogen Lyα Radiation in the Coma of Comet Hyakutake (C/1996 B2) , 2000 .

[13]  K. Powell,et al.  MHD Simulation of Comets: The Plasma Environment of Comet Hale-Bopp , 1997 .

[14]  J. Vial,et al.  Calibrated full disk solar H I Lyman-alpha and Lyman-beta profiles. , 1978 .

[15]  M. Combi.  The outflow speed of the coma of Halley's comet , 1989 .

[16]  Robert L. Millis,et al.  The ensemble properties of comets: Results from narrowband photometry of 85 comets , 1995 .

[17]  M. Berthé,et al.  LYMAN-ALPHA OBSERVATIONS OF COMET HYAKUTAKE WITH SWAN ON SOHO , 1998 .

[18]  J. Bishop.  TRANSPORT OF RESONANT ATOMIC HYDROGEN EMISSIONS IN THE THERMOSPHERE AND GEOCORONA : MODEL DESCRIPTION AND APPLICATIONS , 1999 .

[19]  A. Cochran,et al.  Observation and Analysis of High-Resolution Optical Line Profiles in Comet Hyakutake (C/1996 B2) , 1997 .

[20]  P. Lemaire,et al.  Solar H I Lyman α full disk profile obtained with the SUMER/SOHO spectrometer , 1998 .

[21]  P. Feldman,et al.  Solar Flux Variability and the Lifetimes of Cometary H2O and OH , 1994 .

[22]  J. Bertaux,et al.  LYMAN-ALPHA OBSERVATIONS OF COMET 46 P/WIRTANEN WITH SWAN ON SOHO: H2O PRODUCTION RATE NEAR 1997 PERIHELION , 1999 .

[23]  Robert L. Millis,et al.  Narrowband Photometry of Comet P/Halley: Variation with Heliocentric Distance, Season, and Solar Phase Angle☆ , 1998 .

[24]  T. Rettig,et al.  Ethane Production and Release in Comet C/1995 O1 Hale–Bopp , 2000 .

[25]  R. Lallement,et al.  SWAN: A study of Solar Wind Anisotropies on SOHO with Lyman alpha sky mapping , 1995 .

[26]  A. Stewart,et al.  Pioneer Venus lyman-α observations of comet P/Giacobini-Zinner and the life expectancy of cometary hydrogen , 1986 .

[27]  N. Biver,et al.  Observations of the OH Radical in Comet C/1995 O1 (Hale-Bopp) with the Nançay Radio Telescope , 1997 .

[28]  Dominic J. Benford,et al.  Long-term Evolution of the Outgassing of Comet Hale-Bopp From Radio Observations , 1997 .

[29]  P. Feldman,et al.  IUE observations of H Lyman-α in comet P/Giacobini-Zinner , 1992 .

[30]  K. Powell,et al.  Dust-Gas Interrelations In Comets: Observations And Theory , 1997 .

[31]  A. Stewart,et al.  Analysis of the Pioneer-Venus Lyman-α Image of the Hydrogen Coma of Comet P/Halley , 1991, Science.

[32]  H. Keller,et al.  Predictions of the hydrogen Lyman α coma of Comet Halley , 1985 .

[33]  M. Combi,et al.  Neutral cometary atmospheres. I - An average random walk model for photodissociation in comets , 1980 .