132 research outputs found
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
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
Alice: The Rosetta Ultraviolet Imaging Spectrograph
We describe the design, performance and scientific objectives of the
NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet
rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging
spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will
be the first UV spectrograph to study a comet at close range. It is designed to
obtain spatially-resolved spectra of Rosetta mission targets in the 700-2050 A
spectral band with a spectral resolution between 8 A and 12 A for extended
sources that fill its ~0.05 deg x 6.0 deg field-of-view. ALICE employs an
off-axis telescope feeding a 0.15-m normal incidence Rowland circle
spectrograph with a concave holographic reflection grating. The imaging
microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr
and CsI) and employs a 2 D delay-line readout array. The instrument is
controlled by an internal microprocessor. During the prime Rosetta mission,
ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus,
and the nucleus/coma coupling; during cruise to the comet, ALICE will make
observations of the mission's two asteroid flyby targets and of Mars, its
moons, and of Earth's moon. ALICE has already successfully completed the
in-flight commissioning phase and is operating normally in flight. It has been
characterized in flight with stellar flux calibrations, observations of the
Moon during the first Earth fly-by, and observations of comet Linear T7 in 2004
and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing
campaignComment: 11 pages, 7 figure
The Discovery of Argon in Comet C/1995 O1 (Hale-Bopp)
On 30.14 March 1997 we observed the EUV spectrum of the bright comet C/1995
O1 (Hale-Bopp) at the time of its perihelion, using our EUVS sounding rocket
telescope/spectrometer. The spectra reveal the presence H Ly beta, O+, and,
most notably, Argon. Modelling of the retrieved Ar production rates indicates
that comet Hale-Bopp is enriched in Ar relative to cosmogonic expectations.
This in turn indicates that Hale-Bopp's deep interior has never been exposed to
the 35-40 K temperatures necessary to deplete the comet's primordial argon
supply.Comment: 9 pages, 2 figures. ApJ, 545, in press (2000
Chandra's Close Encounter with the Disintegrating Comets 73P/2006 (Schwassmann--Wachmann--3) Fragment B and C/1999 S4 (LINEAR)
On May 23, 2006 we used the ACIS-S instrument on the Chandra X-ray
Observatory (CXO) to study the X-ray emission from the B fragment of comet
73P/2006 (Schwassmann-Wachmann 3) (73P/B). We obtained a total of 20 ks of CXO
observation time of Fragment B, and also investigated contemporaneous ACE and
SOHO solar wind physical data. The CXO data allow us to spatially resolve the
detailed structure of the interaction zone between the solar wind and the
fragment's coma at a resolution of ~ 1,000 km, and to observe the X-ray
emission due to multiple comet--like bodies. We detect a change in the spectral
signature with the ratio of the CV/OVII line increasing with increasing
collisional opacity as predicted by Bodewits \e (2007). The line fluxes arise
from a combination of solar wind speed, the species that populate the wind and
the gas density of the comet. We are able to understand some of the observed
X-ray morphology in terms of non-gravitational forces that act upon an actively
outgassing comet's debris field. We have used the results of the Chandra
observations on the highly fragmented 73P/B debris field to re-analyze and
interpret the mysterious emission seen from comet C/1999 S4 (LINEAR) on August
1st, 2000, after the comet had completely disrupted. We find the physical
situations to be similar in both cases, with extended X-ray emission due to
multiple, small outgassing bodies in the field of view. Nevertheless, the two
comets interacted with completely different solar winds, resulting in
distinctly different spectra.Comment: accepted by ApJ, 44 Pages, including 4 tables and 14 figure
GALEX FUV Observations of Comet C/2004 Q2 (Machholz): The Ionization Lifetime of Carbon
We present a measurement of the lifetime of ground state atomic carbon,
C(^3P), against ionization processes in interplanetary space and compare it to
the lifetime expected from the dominant physical processes likely to occur in
this medium. Our measurement is based on analysis of a far ultraviolet (FUV)
image of comet C/2004 Q2 (Machholz) recorded by the Galaxy Evolution Explorer
(GALEX) on 2005 March 1. The bright CI 1561 A and 1657 A multiplets dominate
the GALEX FUV band. We used the image to create high S/N radial profiles that
extended beyond one million km from the comet nucleus. Our measurements yielded
a total carbon lifetime of 7.1 -- 9.6 x 10^5 s (scaled to 1 AU). Which compares
favorably to calculations assuming solar photoionization, solar wind proton
change exchange and solar wind electron impact ionization are the dominant
processes occurring in this medium and that comet Machholz was embedded in the
slow solar wind. The shape of the CI profiles inside 3x10^5 km suggests that
either the CO lifetime is shorter than previously thought and/or a
shorter-lived carbon-bearing parent molecule, such as CH_4 is providing the
majority of the carbon in this region of the coma of comet Machholz.Comment: 26 pages, 6 figures, accepted for publication in the Astrophysical
Journa
IUE observations of faint comets
Ultraviolet spectra of seven comets taken with the same instrument are presented. Comets P/Encke (1980), P/Tuttle (1980 h), P/Stephan-Oterma (1980 g), and Meier (1980 q) were observed during November-December 1980 with the International Ultraviolet Explorer (IUE) satellite observatory, while comets P/Borrelly (1980 i) and Panther (1980 u) were observed with IUE on 6 March 1981. The spectra of these comets are compared with those of comet Bradfield (1979 X), studied extensively earlier in 1980 with IUE, as well as with each other. In order to simplify the interpretation of the data and to minimize the dependence upon a specific model, the spectra are compared at approximately the same value of heliocentric distance whenever possible. Effects due to heliocentric velocity, geocentric distance, and optical depth are also discussed. All of the cometary spectra are remarkably similar, which suggests that these comets may have a common composition and origin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24271/1/0000537.pd
Simultaneous Swift X-ray and UV views of comet C/2007 N3 (Lulin)
We present an analysis of simultaneous X-Ray and UV observations ofcomet
C/2007 N3 (Lulin) taken on three days between January 2009 and March 2009 using
the Swift observatory. For our X-ray observations, we used basic transforms to
account for the movement of the comet to allow the combination of all available
data to produce an exposure-corrected image. We fit a simple model to the
extracted spectrum and measured an X-ray flux of 4.3+/-1.3 * 10^-13 ergs cm-2
s-1 in the 0.3 to 1.0 keV band. In the UV, we acquired large-aperture
photometry and used a coma model to derive water production rates given
assumptions regarding the distribution of water and its dissociation into OH
molecules about the comet's nucleus.
We compare and discuss the X-ray and UV morphology of the comet. We show that
the peak of the cometary X-ray emission is offset sunward of the UV peak
emission, assumed to be the nucleus, by approximately 35,000 km. The offset
observed, the shape of X-ray emission and the decrease of the X-ray emission
comet-side of the peak, suggested that the comet was indeed collisionally thick
to charge exchange, as expected from our measurements of the comet's water
production rate (6--8 10^28 mol. s-1). The X-ray spectrum is consistent with
solar wind charge exchange emission, and the comet most likely interacted with
a solar wind depleted of very highly ionised oxygen. We show that the measured
X-ray lightcurve can be very well explained by variations in the comet's gas
production rates, the observing geometry and variations in the solar wind flux.Comment: Paper accepted for publication in Astronomy and Astrophysics, 6 March
2012, 12 pages, 8 colour figures, one tabl
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