221 research outputs found
IUE observations of periodic comets Tempel-2, Kopff, and Tempel-1
We summarize the results of observations made between 10 Jun. - 18 Dec. 1988 with the International Ultraviolet Explorer (IUS) of comet P/Tempel-2 during its 1988 appearance. The derived water production rate and relative gas/dust ratio are compared with those of P/Halley, observed with IUE in 1985-86, and other potential Comet Rendezvous/Asteroid Flyby (CRAF) target comets, P/Kopff and P/Tempel-1, both observed with IUE in 1983
Coupled Chemistry-Emission Model for Atomic Oxygen Green and Red-doublet Emissions in Comet C/1996 B2 Hyakutake
The green (5577 \AA) and red-doublet (6300, 6364 \AA) lines are prompt
emissions of metastable oxygen atoms in the S and D states,
respectively, that have been observed in several comets. The value of intensity
ratio of green to red-doublet (G/R ratio) of 0.1 has been used as a benchmark
to identify the parent molecule of oxygen lines as HO. A coupled
chemistry-emission model is developed to study the production and loss
mechanisms of O(S) and O(D) atoms and the generation of red and green
lines in the coma of C/1996 B2 Hyakutake.
The G/R ratio depends not only on photochemistry, but also on the projected
area observed for cometary coma, which is a function of the dimension of the
slit used and geocentric distance of the comet. Calculations show that the
contribution of photodissociation of HO to the green (red) line emission is
30 to 70% (60 to 90%), while CO and CO are the next potential sources
contributing 25 to 50% (5%). The ratio of the photo-production rate of
O(S) to O(D) would be around 0.03 ( 0.01) if HO is the main
source of oxygen lines, whereas it is 0.6 if the parent is CO. Our
calculations suggest that the yield of O(S) production in the
photodissociation of HO cannot be larger than 1%. The model calculated
radial brightness profiles of the red and green lines and G/R ratios are in
good agreement with the observations made on comet Hyakutake in March 1996
Water production models for Comet Bradfield (1979 l)
The IUE observations of Comet Bradfield (1979 l) made 10 January 1980 to 3 March 1980 permit a detailed study of water production for this comet. Brightness measurements are presented for all three water dissociation products, H, O, and OH, and comparisons are made with model predictions. The heliocentric variation of the water production rate was derived
Twentieth century light curves and the nucleus of comet P/Tempel 2
Observations of P/Tempel 2 from 1899 to 1988 corresponding to 13 apparitions are analyzed in order to estimate the perihelion asymmetry of the gas production curve for different periods of its evolution. Using the correlation found by Festou et al. (1990) between the perihelion asymmetries and the delay in perihelion passage due to the action of nongravitational forces, we estimate the mass of the comet to be M approximately equals 1.6 plus or minus 0.5 x 10(exp 14) kg. Assuming a volume of 500 cu km, based on nuclear observations, a density of 0.3 plus or minus 0.1 g/cu cm is obtained
The gas production rate of periodic comet d'Arrest
Comet P/d'Arrest is a potential target for a rendezvous mission to a short period comet. Its light curve is rather peculiar, the comet being active only after perihelion passage. One apparition out of two is easy to observe from the ground. The 1995 apparition of the comet will offer a unique opportunity to characterize the outgassing properties of its nucleus
Heliocentric distance dependencies of the C2 lifetime and C2 parent production rate in comet P/Brorsen-Metcalf (1989o)
Comet P/Brorsen-Metcalf (1989o) has been extensively observed in the visible and in the ultraviolet during its latest apparition of summer 1989. In this paper we report a preliminary determination of the C2 production rates and lifetimes and we compare those rates to the H2O production rates obtained from UV data
The Chemical Composition of an Extrasolar Minor Planet
We report the relative abundances of 17 elements in the atmosphere of the
white dwarf star GD 362, material that, very probably, was contained previously
in a large asteroid or asteroids with composition similar to the Earth/Moon
system. The asteroid may have once been part of a larger parent body not unlike
one of the terrestrial planets of our solar system.Comment: ApJ, in pres
Io: IUE observations of its atmosphere and the plasma torus
Two of the main components of the atmosphere of Io, neutral oxygen and sulfur, were detected with the IUE. Four observations yield brightnesses that are similar, regardless of whether the upstream or the downstream sides of the torus plasma flow around Io is observed. A simple model requires the emissions to be produced by the interaction of O and S columns in the exospheric range with 2 eV electrons. Cooling of the 5 eV torus electrons is required prior to their interaction with the atmosphere of Io. Inconsistencies in the characteristics of the spectra that cannot be accounted for in this model require further analysis with improved atomic data. The Io plasma torus was monitored with the IUE. The long-term stability of the warm torus is established. The observed brightnesses were analyzed using a model of the torus, and variations of less than 30 percent in the composition are observed, the quantitative results being model dependent
Water Production by Comet 103P/Hartley 2 Observed with the SWAN Instrument on the SOHO Spacecraft
Global water production rates were determined from the Lyman-{\alpha}
emission of hydrogen around comet 103P/Hartley 2, observed with the SWAN (Solar
Wind ANisotropies) all-sky camera on the SOHO spacecraft from September 14
through December 12, 2010. This time period included the November 4 flyby by
the EPOXI spacecraft. Water production was 3 times lower than during the 1997
apparition also measured by SWAN. In 2010 it increased by a factor of ~2.5
within one day on September 30 with a similar corresponding drop between
November 24 and 30. The total surface area of sublimating water within {\pm}20
days of perihelion was ~0.5 km^2, about half of the mean cross section of the
nucleus. Outside this period it was ~0.2 km^2. The peak value was 90%, implying
a significant water production by released nucleus icy fragments.Comment: 16 pages, 3 figures, 1 table, accepted for publication in The
Astrophysical Journal Letter
Radial Distribution of Production Rates, Loss Rates and Densities Corresponding to Ion Masses <=40 amu in the Inner Coma of Comet Halley: Composition and Chemistry
In this paper we have studied the chemistry of C, H, N, O, and S compounds
corresponding to ions of masses <=40 amu in the inner coma of the comet
1P/Halley. The production rates, loss rates, and ion mass densities are
calculated using the Analytical Yield Spectrum approach and solving coupled
continuity equation controlled by the steady state photochemical equilibrium
condition. The primary ionization sources in the model are solar EUV photons,
photoelectrons, and auroral electrons of the solar wind origin. The chemical
model couples ion-neutral, electron-neutral, photon-neutral and electron-ion
reactions among ions, neutrals, electrons, and photons through over 600
chemical reactions. Of the 46 ions considered in the model the chemistry of 24
important ions are discussed in this paper. The calculated ion mass densities
are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass
Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km.Comment: pages 42, figures 9 (total 12), tables
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