15 research outputs found
Focus on the future
An assessment is made of what was learned from Halley and recommendations are made for future directions for infrared studies of comets and supporting lab investigations. The following issues are addressed: (1) What steps can be taken to achieve consistent interpretation of Halley infrared data; (2) How successful has the Halley Watch been for infrared studies; (3) What supporting lab research is needed; (4) What are the key infrared observations needed for future comets; and (5) How do current and future NASA programs relate to comet studies
Infrared observations of comets
Selected comets are observed in the near infrared (1 to 2.2 micron) and thermal infrared (3.5 to 20 micron) with the NASA Infrared Telescope Facility (IRTF) and other telescopes as appropriate, in order to characterize the physical properties of the dust grains; their composition, size distribution, emissivity, and albedo. Systematic variations in these properties among comets are looked for, in order to understand the heterogeneity of comet nuclei. Spectrophotometry of the 10 micron silicate emission feature is particularly emphasized. The rate of dust production from the nucleus and its temporal variability are also determined. Knowledge of the dust environment is essential to S/C design and mission planning for NASA's CRAF mission
Infrared Observations of Comets Halley and Wilson and Properties of the Grains
The presented papers and discussions at a workshop held at Cornell Univ. are summarized. The infrared observations of Comet Halley and Comet Wilson are reviewed and they are related to optical properties and composition of cometary grains. Relevant laboratory studies are also discussed. Recommendations are made for future infrared comet observations and supporting laboratory investigations
A Spitzer Study of Comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT)
We present infrared images and spectra of comets 2P/Encke,
67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) as part of a larger
program to observe comets inside of 5 AU from the sun with the Spitzer Space
Telescope. The nucleus of comet 2P/Encke was observed at two vastly different
phase angles (20 degrees and 63 degrees). Model fits to the spectral energy
distributions of the nucleus suggest comet Encke's infrared beaming parameter
derived from the near-Earth asteroid thermal model may have a phase angle
dependence. The observed emission from comet Encke's dust coma is best-modeled
using predominately amorphous carbon grains with a grain size distribution that
peaks near 0.4 microns, and the silicate contribution by mass to the sub-micron
dust coma is constrained to 31%. Comet 67P/Churyumov-Gerasimenko was observed
with distinct coma emission in excess of a model nucleus at a heliocentric
distance of 5.0 AU. The coma detection suggests that sublimation processes are
still active or grains from recent activity remain near the nucleus. Comet
C/2001 HT50 (LINEAR-NEAT) showed evidence for crystalline silicates in the
spectrum obtained at 3.2 AU and we derive a silicate-to-carbon dust ratio of
0.6. The ratio is an order of magnitude lower than that derived for comets
9P/Tempel 1 during the Deep Impact encounter and C/1995 O1 (Hale-Bopp).Comment: Accepted for publication in the Astrophysical Journal 48 pages, 15
figures, 10 table
3 - 14 Micron Spectroscopy of Comets C/2002 O4 (Honig), C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2002 Y1 (Juels-Holvorcem), 69P/Taylor, and the Relationships among Grain Temperature, Silicate Band Strength and Structure among Comet Families
We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002
and February 2003: C/2002 O4 (Honig) on August 1, 2002, C/2002 V1 (NEAT) on
Jan. 9 and 10, 2003, C/2002 X5 (Kudo-Fujikawa) on Jan. 9 and 10, 2003, and
C/2002 Y1 (Juels-Holvorcem) on Feb. 20, 2003. In addition, we include data
obtained much earlier on 69P/Taylor (February 9, 1998) but not previously
published. For Comets Taylor, Honig, NEAT, and Kudo-Fujikawa, the silicate
emission band was detected, being approximately 23%, 12%, 15%, and 10%,
respectively, above the continuum. The data for Comet Juels-Holvorcem were of
insufficient quality to detect the presence of a silicate band of comparable
strength to the other three objects, and we place an upper limit of 24% on this
feature. The silicate features in both NEAT and Kudo-Fujikawa contained
structure indicating the presence of crystalline material. Combining these data
with those of other comets, we confirm the correlation between silicate band
strength and grain temperature of Gehrz & Ney (1992) and Williams et al. (1997)
for dynamically new and long period comets, but the majority of Jupiter family
objects may deviate from this relation. The limited data available on Jupiter
family objects suggest that they may have silicate bands that are slightly
different from the former objects. Finally, when compared to the silicate
emission bands observed in pre-main sequence stars, the dynamically new and
long period comets most closely resemble the more evolved stellar systems,
while the limited data (in quantity and quality) on Jupiter family objects seem
to suggest that these have spectra more like the less-evolved stars.Comment: 45 pages, 12 figure
The NASA Infrared Telescope Facility Comet Halley monitoring program 2: Post-perihelion results
The post perihelion results of a 1 to 20 micrometer infrared monitoring program of Comet Halley are presented. These results complement previous observations of the pre-perihelion passages of Halley. The observations cover the time period of Mar. 1986 to the present time. During the time the comet was observable, two or more observations were obtained per month. The most interesting results were: (1) a detectable change in the J-H and H-K colors of Halley, and (2) a search for a nucleus rotation at J during 20 Feb. to 10 Mar. was unsuccessful. The perihelion J-H and K-K colors were constant at 0.48 + or - 0.01 and 0.17, respectively. A preliminary reduction of the data is given. It is concluded that the colors were at first similar to pre-perihelion and then changed from July onward to be bluer and more similar to the solar colors. This suggests that a change may have occurred in the composition of the dust coma of Halley in July 1986
Cometary Dust in the Debris Disks of HD 31648 and HD 163296: Two ``Baby'' beta Pics
The debris disks surrounding the pre-main sequence stars HD 31648 and HD
163296 were observed spectroscopically between 3 and 14 microns. Both possess a
silicate emission feature at 10 microns which resembles that of the star beta
Pictoris and those observed in solar system comets. The structure of the band
is consistent with a mixture of olivine and pyroxene material, plus an
underlying continuum of unspecified origin. The similarity in both size and
structure of the silicate band suggests that the material in these systems had
a processing history similar to that in our own solar system prior to the time
that the grains were incorporated into comets.Comment: 17 pages, AASTeX, 5 eps figures, accepted for publication in Ap.