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ABSTRACT: As one of the prime targets of interstellar chemistry study, Orion BN/KL
clearly shows different molecular distributions between large nitrogen- (e.g.,
C2H5CN) and oxygen-bearing (e.g., HCOOCH3) molecules. However, acetone
(CH3)2CO, a special complex O-bearing molecule, has been shown to have a very
different distribution from other typical O-bearing molecules in the BN/KL
region. We searched for acetone within our IRAM Plateau de Bure Interferometer
3 mm and 1.3 mm data sets. Twenty-two acetone lines were searched within these
data sets. The angular resolution ranged from 1.8 X 0.8 to 6.0 X 2.3 arcsec^2,
and the spectral resolution ranged from 0.4 to 1.9 km s-1. Nine of the acetone
lines appear free of contamination. Three main acetone peaks (Ace-1, 2, and 3)
are identified in Orion BN/KL. The new acetone source Ace-3 and the extended
emission in the north of the hot core region have been found for the first
time. An excitation temperature of about 150 K is determined toward Ace-1 and
Ace-2, and the acetone column density is estimated to be 2-4 X 10^16 cm-2 with
a relative abundance of 1-6 X 10^-8 toward these two peaks. Acetone is a few
times less abundant toward the hot core and Ace-3 compared with Ace-1 and
Ace-2.
We find that the overall distribution of acetone in BN/KL is similar to that
of N-bearing molecules, e.g., NH3 and C2H5CN, and very different from those of
large O-bearing molecules, e.g., HCOOCH3 and (CH3)2O. Our findings show the
acetone distribution is more extended than in previous studies and does not
originate only in those areas where both N-bearing and O-bearing species are
present. Moreover, because the N-bearing molecules may be associated with
shocked gas in Orion BN/KL, this suggests that the formation and/or destruction
of acetone may involve ammonia or large N-bearing molecules in a shocked-gas
environment.
04/2013;
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ABSTRACT: We used several data sets from the Plateau de Bure Interferometer to map the
dimethyl ether emission in Orion-KL with different arcsec spatial resolutions
and different energy levels to compare with our previous methyl formate maps.
Our data show remarkable similarity between the dimethyl ether (CH3OCH3) and
the methyl formate (HCOOCH3) distributions even on a small scale (1.8"x0.8" or
about 500 AU). This long suspected similarity, seen from both observational and
theoretical arguments, is demonstrated with unprecedented confidence, with a
correlation coefficient of maps of 0.8.
A common precursor is the simplest explanation of our correlation.
Comparisons with previous laboratory work and chemical models suggest the major
role of grain surface chemistry and a recent release, probably with little
processing, of mantle molecules by shocks. In this case the CH3O radical
produced from methanol ice would be the common precursor (whereas ethanol,
C2H5OH, is produced from the radical CH2OH). The alternative gas phase scheme,
where protonated methanol CH3OH2+ is the common precursor to produce methyl
formate and dimethyl ether through reactions with HCOOH and CH3OH, is also
compatible with our data. Our observations cannot yet definitely allow a choice
between the different chemical processes, but the tight correlation between the
distributions of HCOOCH3 and CH3OCH3 strongly contrasts with the different
behavior we observe for the distributions of ethanol and formic acid. This
provides a very significant constraint on models.
12/2012;
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ABSTRACT: Deuterated molecules have been detected and studied toward Orion BN/KL in the
past decades, mostly with single-dish telescopes. However, high angular
resolution data are critical not only for interpreting the spatial distribution
of the deuteration ratio but also for understanding this complex region in
terms of cloud evolution involving star-forming activities and stellar
feedbacks. We present here the first high angular resolution (1.8 arcsec \times
0.8 arcsec) images of deuterated methanol CH2DOH in Orion BN/KL observed with
the IRAM Plateau de Bure Interferometer from 1999 to 2007 in the 1 to 3 mm
range. Six CH2DOH lines were detected around 105.8, 223.5, and 225.9 GHz. In
addition, three E-type methanol lines around 101-102 GHz were detected and were
used to derive the corresponding CH3OH rotational temperatures and column
densities toward different regions across Orion BN/KL. The strongest CH2DOH and
CH3OH emissions come from the Hot Core southwest region with an LSR velocity of
about 8 km/s. We derive [CH2DOH]/[CH3OH] abundance ratios of 0.8-1.3\times10^-3
toward three CH2DOH emission peaks. A new transition of CH3OD was detected at
226.2 GHz for the first time in the interstellar medium. Its distribution is
similar to that of CH2DOH. Besides, we find that the [CH2DOH]/[CH3OD] abundance
ratios are lower than unity in the central part of BN/KL. Furthermore, the HDO
3(1,2)-2(2,1) line at 225.9 GHz was detected and its emission distribution
shows a shift of a few arcseconds with respect to the deuterated methanol
emission that likely results from different excitation effects. The deuteration
ratios derived along Orion BN/KL are not markedly different from one clump to
another. However, various processes such as slow heating due to ongoing star
formation, heating by luminous infrared sources, or heating by shocks could be
competing to explain some local differences observed for these ratios.
06/2012;
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ABSTRACT: We report the first subarcsecond (065 × 051) image of the dimethyl ether molecule, (CH3)2O, toward the Orion Kleinmann-Low nebula. The observations were carried at 43.4 GHz with the Expanded Very Large Array (EVLA). The distribution of the lower energy transition 61, 5-60, 6, EE (E u = 21 K) mapped in this study is in excellent agreement with the published dimethyl ether emission maps imaged with a lower resolution. The main emission peaks are observed toward the Compact Ridge and Hot Core southwest components, at the northern parts of the Compact Ridge and in an intermediate position between the Compact Ridge and the Hot Core. A notable result is that the distribution of dimethyl ether is very similar to that of another important larger O-bearing species, the methyl formate (HCOOCH3), imaged at a lower resolution. Our study shows that higher spectral resolution (WIDAR correlator) and increased spectral coverage provided by the EVLA offer new possibilities for imaging complex molecular species. The sensitivity improvement and the other EVLA improvements make this instrument well suited for high sensitivity, high angular resolution, and molecular line imaging.
The Astrophysical Journal Letters 08/2011; 739(1):L12. · 5.53 Impact Factor
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ABSTRACT: Observations of the CO J(1-0) 115 GHz and J(2-1) 230 GHz lines in comet C/1995 O1 (Hale-Bopp) were performed with the IRAM Plateau de Bure interferometer on 11 March, 1997. The observations were conducted in both single-dish (ON-OFF) and interferometric modes with 0.13 km s-1 spectral resolution. Images of CO emission with 1.7 to 3" angular resolution were obtained. The ON-OFF and interferometric spectra show a velocity shift with sinusoidal time variations related to the Hale-Bopp nucleus rotation of 11.35 h. The peak position of the CO images moves perpendicularly to the spin axis direction in the plane of the sky. This suggests the presence of a CO jet, which is active night and day at about the same extent, and is spiralling with nucleus rotation. The high quality of the data allows us to constrain the characteristics of this CO jet. We have developed a 3-D model to interpret the temporal evolution of CO spectra and maps. The CO coma is represented as the combination of an isotropic distribution and a spiralling gas jet, both of nucleus origin. Spectra and visibilities (the direct output of interferometric data) analysis shows that the CO jet comprises ~40% the total CO production and is located at a latitude ~20 degrees North on the nucleus surface. Our inability to reproduce all observational characteristics shows that the real structure of the CO coma is more complex than assumed, especially in the first thousand kilometres from the nucleus. The presence of another moving CO structure, faint but compact and possibly created by an outburst, is identified. Comment: 20 pages, 26 figures. Accepted for publication in Astronomy & Astrophysics
06/2009;
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N. Biver,
D. Bockelée-Morvan,
J. Crovisier,
J. K. Davies,
H. E. Matthews,
J. E. Wink,
H. Rauer,
P. Colom,
W. R. F. Dent, D. Despois,
R. Moreno,
G. Paubert,
D. Jewitt,
and M. Senay
[show abstract]
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ABSTRACT: Molecular radio lines were monitored in comet C/1996 B2 (Hyakutake) from 1996 February 10 to June 23, using the James Clerk Maxwell Telescope and the 30 m telescope and the Plateau de Bure interferometer of the Institut de Radioastronomie Millimétrique. We report on observations of HCN, CH3OH, CO, H2CO, CS, and H2S and on the evolution of their production rates with heliocentric distance (rh), from 1.86 down to 0.24 AU at perihelion. Most production rates increased roughly as r down to 0.6 AU preperihelion. Closer to the Sun, they stalled before decreasing beyond 0.6 AU postperihelion, when observations resumed. The CS/HCN ratio varied as r from 1.2 to 0.24 AU. A rapid increase of the mean gas temperature in the coma is measured, and the gas expansion velocity increased from 0.55 to 1.6 km s-1, as the comet approached the Sun from 1.6 to 0.3 AU. Molecular abundances of the minor species around 1 AU are similar to those observed in other comets, while the CO abundance relative to water is high (≈22%). Coarse mapping was used to check the comet's position and to investigate the density distribution of the molecules within the coma. It provides constraints on the size of the extended source of formaldehyde, found to be between 1.2 and 2 times the scale length of H2CO itself. The density distribution of CS is compatible with its production from the photodissociation of a short-lived molecule such as CS2. The density distribution observed for CO can be mostly explained by a nuclear source.
The Astronomical Journal 12/2007; 118(4):1850. · 4.03 Impact Factor
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ABSTRACT: We present observations of rotational lines of H2S, SO and CS performed in comet C/1995 O1 (Hale-Bopp) in March 1997 with the Plateau de Bure interferometer (IRAM). The observations provide informations on the spatial and velocity distributions of these molecules. They can be used to constrain their photodissociation rate and their origin. We use a radiative transfer code which allows us to compute synthetic line profiles and interferometric maps, to be compared to the observations. Both single-dish spectra and interferometric spectral maps show a day/night asymmetry in the outgassing. From the analysis of the spectral maps, including the astrometry, we show that SO and CS present in addition a jet-like structure that may be the gaseous counterpart of the dust high-latitude jet observed in optical images. A CS rotating jet is also observed. Using the astrometry provided by continuum radio maps obtained in parallel, we conclude that there is no need to invoke of nongravitational forces acting on this comet, and provide an updated orbit. The radial extension of H2S is found to be consistent with direct release from the nucleus. SO displays an extended radial distribution. Assuming that SO2 is the parent of SO, the photodissociation rate of SO is measured to be 1.5 E-4 s-1 at 1 AU from the Sun. This is lower than most laboratory-based estimates and may suggest that SO is not solely produced by SO2 photolysis. From the observations of J(2-1) and J(5-4) CS lines, we deduce a CS photodissociation rate of 1 to 5 E-5 s-1. The photodissociation rate of CS2, the likely parent of CS, cannot be constrained due to insufficient resolution, but our data are consistent with published values. These observations illustrate the cometary science that will be performed with the future ALMA interferometer. Comment: Accepted for publication in Astronomy & Astrophysics
09/2007;
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S. Gulkis,
M. Frerking,
J. Crovisier,
G. Beaudin,
P. Hartogh,
P. Encrenaz,
T. Koch,
C. Kahn,
Y. Salinas,
R. Nowicki, [......],
N. Biver,
T. Encrenaz, D. Despois,
W. Ip,
E. Lellouch,
I. Mann,
D. Muhlemann,
H. Rauer,
P. Schloerb,
T. Spilker
[show abstract]
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ABSTRACT: The European Space Agency Rosetta Spacecraft, launched on March 2, 2004 toward Comet 67P/Churyumov-Gerasimenko, carries a relatively small and lightweight millimeter-submillimeter spectrometer instrument, the first of its kind launched into deep space. The instrument will be used to study the evolution of outgassing water and other molecules from the target comet as a function of heliocentric distance. During flybys of the asteroids (2867) Steins and (21) Lutetia in 2008 and 2010 respectively, the instrument will measure thermal emission and search for water vapor in the vicinity of these asteroids.
The instrument, named MIRO (Microwave Instrument for the Rosetta Orbiter), consists of a 30-cm diameter, offset parabolic reflector telescope followed by two heterodyne receivers. Center-band operating frequencies of the receivers are near 190 GHz (1.6 mm) and 562 GHz (0.5 mm). Broadband continuum channels are implemented in both frequency bands for the measurement of near surface temperatures and temperature gradients in Comet 67P/Churyumov-Gerasimenko and the asteroids (2867) Steins and (21) Lutetia. A 4096 channel CTS (Chirp Transform Spectrometer) spectrometer having 180 MHz total bandwidth and 44 kHz resolution is, in addition to the continuum channel, connected to the submillimeter receiver. The submillimeter radiometer/spectrometer is fixed tuned to measure four volatile species – CO, CH<sub>3</sub>OH, NH<sub>3</sub> and three, oxygen-related isotopologues of water, H<sub>2</sub> <sup>16</sup>O, H<sub>2</sub> <sup>17</sup>O and H<sub>2</sub> <sup>18</sup>O. The basic quantities measured with the MIRO instrument are surface temperature, gas production rates and relative abundances, and velocity and excitation temperature of each species, along with their spatial and temporal variability. This paper provides a short discussion of the scientific objectives of the investigation, and a detailed discussion of the MIRO instrument system.
Space Science Reviews 01/2007; 128(1-4):561-597. · 3.61 Impact Factor
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J. Crovisier,
N. Biver,
D. Bockelée-Morvan,
J. Boissier,
P. Colom,
R. Moreno,
D. C. Lis,
G. Paubert, D. Despois,
M. Gunnarsson,
H. A. Weaver
[show abstract]
[hide abstract]
ABSTRACT: In 2003-2005 seven comets were investigated at millimeter to
submillimeter wavelengths using CSO and IRAM-30m facilities: C/2002 V1
(NEAT), C/2002 X5 (Kudo-Fujikawa), 2P/Encke, C/2002 T7 (LINEAR), C/2001
Q4 (NEAT), C/2004 Q2 (Machholz) and 9P/Tempel 1. With these
observations, we can further extend our comparative study of the
molecular composition of comets (Biver et al. 2002, EMP 90, 323) and
improve our understanding on the evolution of molecular abundances with
heliocentric distance (rh) (between rh = 0.1 and
2.8 AU from the Sun). The sample is also very diverse, with comets of
the shortest (3.3 years) and long orbital period: 9000 to 30 million
years. A total of 12 molecules: HCN, CH3OH, CS, CO,
H2CO, H2S, HNC, CH3CN, SO, HNCO,
HC3N and HCOOH were observed and detected in at least one
comet, in some cases for the second time since their identification in
comet Hale-Bopp in 1997. We present our main results, including the
following findings: (1) The HNC/HCN production rate ratio appears to
plateau at a maximum value around 0.2 for rh < 0.5 AU,
after initially increasing with decreasing heliocentric distance; (2)
The CH3OH/HCN ratio, on the other hand, seems to decrease
towards the Sun, as observed in C/2002 X5 and C/2002 T7; (3) HDO was
searched for in C/2004 Q2 (Machholz) and the upper limit obtained for
the D/H ratio in water (< 0.00023; 3-σ ) is lower, though only
marginally, than the value of 0.0003 measured in other long period
comets; (4) Both comets 2P and C/2002 T7, the comets having the shortest
and longest orbital periods among the sample, have a high methanol
abundance (about 4% relative to water). The abundances of all molecules
detected and searched for are presented and a comparison between comets,
including comet Hale-Bopp, is shown.
07/2005; 37:646.
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ABSTRACT: Comets are among the most primitive bodies of the Solar System, and their chemical composition is rich in information on the protosolar nebula and its possible connection with interstellar cloud chemistry. Comets are also a source of light atoms and probably of prebiotic organic molecules for the early Earth. We know better and better cometary volatiles through spectroscopy, mainly at infrared and radio wavelengths. Another crucial component of cometary matter — organic refractories — is however still poorly characterized. We summarize here the ∼ 30 abundances and ∼ 20 upper limits obtained on cometary volatiles and highlight a few species and problems: ethylene glycol, NS, HNC/HCN, 14 N/ 15 N, CN origin, CS2, PAHs, and H2O measurements. Comet-to-comet variations and comet internal heliocentric variations can now be studied, and cometary comas are mapped with a variety of techniques. We list temperature indicators: they can help understand the relation between IS and cometary matters, which present both a global similarity, and marked differences, like the high ethylene glycol content of comets. We conclude by picking up a few key problems to be addressed by future ground-based and space instruments or by cometary sample analysis. For many species, however, laboratory data are missing on spectroscopy, photodissociation and collisions with H2O.
01/2005; 231.
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ABSTRACT: From radio spectroscopic observations of comets, more than 22 molecules,
radicals and ions, plus several isotopologues, were detected, the
majority of them being recently revealed in comets C/1996 B2 (Hyakutake)
and C/1995 O1 (Hale-Bopp). Among them were acetic acid, formic acid,
methyl formate... detected in radio spectra obtained at the IRAM 30-m
telescope and Plateau de Bure interferometer and at the Caltech
Sumillimeter Observatory in spring 1997 (Bockelée-Morvan et
al., 2000, Astron. Astrophys., 353, 1101). In addition, upper limits
were obtained for several species, including complex organic molecules
such as ethanol, acetic acid, glycolaldehyde, glycine... (Crovisier et
al., 2004, Astron. Astrophys., 418, 1141). Ethylene glycol (HOCH2CH2OH)
was recently identified from about ten rotational lines in the archival
spectra of comet C/1995 O1 (Hale-Bopp) (Crovisier et al., 2004, Astron.
Astrophys., 418, L35). The identification was made just after the
rotational lines of this molecule were included in the Cologne Database
for Molecular Spectroscopy. The production rate of ethylene glycol is
~0.25% that of water, making it one of the most abundant organic
molecules in cometary ices. This detection strengthens the similarity
between interstellar and cometary material. It outlines the possible
role of cometary impacts in the origin of life by seeding the early
Earth with prebiotic molecules.
11/2004; -1:71.
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M Gunnarsson,
D Bockelée-Morvan,
A Winnberg,
H Rickman,
J Crovisier,
N Biver,
P Colom,
J ~K Davies, D Despois,
F Henry,
L ~E ~B Johansson,
R Moreno,
G Paubert,
F ~T Rantakyrö
åp. 04/2003; 402:383-393.
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[show abstract]
[hide abstract]
ABSTRACT: Comets may deliver simple (HCN, H2CO...) or more complex
(amino acids, nuclear bases...) molecules important for prebiotic
chemistry on the early Earth. We present a (provisional) reference list
of 27 cometary volatile abundances (plus 8 upper limits), and discuss
its validity limits. Recent results are detailed. Glycine upper limit is
not stringent (<0.5% H2O) and says nothing on its possible
presence in organic refractories. Comet contribution to Earth oceans
appears low (<10%). Future work needed to improve our appreciation of
the importance of comets for prebiotic chemistry is outlined.
10/2002; 518:123-127.
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J. Crovisier,
N. Biver,
R. Moreno,
D. C. Lis,
D. Bockelée-Morvan,
M. Womack,
P. Colom,
F. Henry,
A. Lecacheux,
G. Paubert, D. Despois,
H. A. Weaver
[show abstract]
[hide abstract]
ABSTRACT: Comet C/1999 T1 (McNaught-Hartley) was observed at radio wavelengths
using the Swedish-ESO Submillimetre Telescope (SEST), Caltech
Submillimeter Observatory (CSO), Institut de RadioAstronomie
Millimétrique (IRAM) 30-m, and Nançay telescopes between
September 2000 and February 2001. Comet C/2001 A2 (LINEAR) was also
observed with the CSO, IRAM and Nançay telescopes, as well as
with the Kitt Peak 12-m Radio Telescope, between April and July 2001.
The lines of OH, HCN, CH3OH, H2CO, H2S,
CS, were detected in both comets. In addition, CO was detected in C/1999
T1, and HNC and CH3CN were detected in C/2001 A2. These two
Oort cloud comets presented similar intrinsic activity levels, with a
water outgassing rate peaking at around 1029 molecules
s-1 near perihelion. However, C/2001 A2 showed a much steeper
heliocentric evolution of its activity, and a dramatic outburst of ≈
4 magnitudes at 1.3 AU inbound. The gaseous composition of these comets
also presents some significant differences: CO is much more abundant
(with respect to HCN and CH3OH) in C/1999 T1, while another
very volatile molecule, H2S, is more abundant in C/2001 A2.
In C/2001 A2, the HNC, CS and H2CO abundances (relative to
HCN or H2S and CH3OH) show variations with
heliocentric distance and/or cometary activity. Similar behaviors were
seen in comet C/1995 O1 (Hale-Bopp). Sensitive searches of
HC3N and OCS in C/2001 A2 suggest that these species are
depleted with respect to HCN, CH3CN or H2S, in
comparison with what was measured in comet Hale-Bopp.
10/2001; 33:1121.
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08/1999; 31:1123.
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[show abstract]
[hide abstract]
ABSTRACT: We present millimetre and submillimetre observations of comet C/1995 (Hale-Bopp) undertaken near perihelion with the Caltech Submillimeter Observatory and the 30m telescope and Plateau-de-Bure interferometer of the Institut de Radioastronomie Millimetrique. From a spectral molecular survey, six new cometary molecular species have been identified for the first time in a comet: SO, SO2, HC3N, NH2CHO, HCOOH, and HCOOCH3. Relative abundances with respect to water are 0.3% (SO), 0.2% (SO2),0.02% (HC3N), 0.01-0.02% (NH2CHO), 0.09% (HCOOH), and 0.08% (HCOOCH3). Several rotational transitions of OCS and HNCO, whose first identifications were made previously in comet C/1996 B2 (Hyakutake), have also been detected, confirming that these molecular species are ubiquitous compounds of cometary atmospheres. Inferred abundances of OCS and HNCO relative to water in comet Hale-Bopp are 0.4% and 0.1%, respectively. During this observational campaign, we also observed rotational lines of HCN, HNC, CH3CN, CO, CH3OH, H2CO, H2S, and CS. In combination with results of other observations, a comprehensive view of the volatile composition of the coma of comet Hale-Bopp is obtained. A quantitative comparison shows that chemical abundances in comet Hale-Bopp parallel those inferred in interstellar ices, hot molecular cores and bipolar flows around protostars. This suggests that the processes at work in the interstellar medium, in particular grain surface chemistry, played a major role in the formation of cometary ices. It supports models in which cometary volatiles formed in the interstellar medium and suffered little processing in the Solar Nebula.
Astronomy and Astrophysics 02/1999; · 4.59 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Comet Hale-Bopp has been observed in October and March 1997 at the IRAM
Plateau de Bure Interferometer. Millimetre lines of 8 molecules (HCN,
HNC, CO, H_2CO, H_2S, SO, CS and CH_3OH) have been mapped with spatial
resolutions of 1 to 3 arcsec. Both spectra and maps present temporal
modulations linked to the nucleus rotation period of 11.3 hours, showing
the presence of rotating molecular structures in the coma. The rotating
CO jet remains equally active during both day and night, indicating CO
production from below the surface. The analysis of the radial
distribution of the molecules shows that some species are not directly
released from the nucleus. Best evidences are for H_2CO et SO. The
comparaison between HCN and HNC maps shows that these two species have
similar photodissociation lifetimes. Evidences that HNC is produced in
the coma are seen, supporting its formation in the coma by chemical
reactions, as proposed for explaining the heliocentric variation of its
abundance. Simultaneous maps of several lines of CH_3OH at 241 GHz allow
us to study the evolution of the rotation temperature with distance to
nucleus. The coldest temperatures found in the outer coma agree with
excitation model.
08/1998; 30:1071.
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D. C. Lis,
D. M. Mehringer,
D. Benford,
M. Gardner,
T. G. Phillips,
D. Bockelee-Morvan,
N. Biver,
P. Colom,
J. Crovisier, D. Despois,
H. Rauer
[show abstract]
[hide abstract]
ABSTRACT: We present millimeter-wave observations of HNCO, HC3N, SO, NH2CHO, H(13)CN, and H3O(+) in comet C/1995 O1 (Hale-Bopp) obtained in February-April, 1997 with the Caltech Submillimeter Observatory (CSO). HNCO, first detected at the CSO in comet C/1996 B2 (Hyakutake), is securely confirmed in comet Hale-Bopp via observations of three rotational transitions. The derived abundance with respect to H2O is (4-13) x 10(exp -4). HC3N, SO, and NH2CHO are detected for the first time in a comet. The fractional abundance of HC3N based on observations of three rotational lines is (1.9 +/- 0.2) x 10(exp -4). Four transitions of SO are detected and the derived fractional abundance, (2-8) x 10(exp -3), is higher than the upper limits derived from UV observations of previous comets. Observations of NH2CHO imply a fractional abundance of (1-8) x 10(exp -4). H3O(+) is detected for the first time from the ground. The H(13)CN (3-2) transition is also detected and the derived HCN/H(13)CN abundance ratio is 90 +/- 15, consistent with the terrestrial C-13/C-12 ratio. in addition, a number of other molecular species are detected, including HNC, OCS, HCO(+), CO(+), and CN (the last two are first detections in a comet at radio wavelengths).
05/1998;
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D. Bockelee-Morvan,
D. Gautier,
D. C. Lis,
K. Young,
J. Keene,
T. G. Phillips,
T. Owen,
J. Crovisier,
P. F. Goldsmith,
E. A. Bergin, D. Despois,
A. Wootten
[show abstract]
[hide abstract]
ABSTRACT: The close approach to the Earth of comet C/1996 B2 (Hyakutake) in March 1996 allowed searches for minor volatile species outgassing from the nucleus. We report the detection of deuterated water (HDO) through its 1(sub 01)-0(sub 00) rotational transition at 464.925 GHz using the Caltech Submillimeter Observatory. We also present negative results of a sensitive research for the J(5-4) line of deuterated hydrogen cyanide (DCN) at 362.046 GHz. Simultaneous observations of two rotational lines of methanol together with HDO in the same spectrum allow us to determine the average gas temperature within the telescope beam to be 69 +/- 10 K. We are thus able to constrain the excitation conditions in the inner coma and determine reliably the HDO production rate as (1.20 +/- 0.28) x 10(exp 26)/s on March 23-24, 1996. Available IR, UV and radio measurements lead to a water production rate of (2.1 +/- 0.5) x 10(exp 29)/s at the time of our HDO observations. The resulting D/H ratio in cometary water is thus (29 +/- 10) x 10(exp -5) in good agreement with the values of (30.8(sub - 5.3, sup +3.8) (Balsiger et al. 1995) and (31.6 +/- 3.4) x 10(exp -5) (Eberhardt et al. 1995) determined in comet P/Halley from in situ ion mass spectra. The inferred 3 a upper limit for the D/H ratio in HCN is 1%. Deuterium abundance is a key parameter for studying the origin and the early evolution of the Solar System and of its individual bodies. Our HDO measurement confirms that, in cometary water, deuterium is enriched by a factor of at least 10 relative to the protosolar ratio, namely the D/H ratio in H2 in the primitive Solar Nebula which formed from the collapse of the protosolar cloud. This indicates that cometary water has preserved a major part of the high D/H ratio acquired in this protosolar cloud through ion-molecule isotopic exchanges or grain-surface reactions and was not re-equilibrated with H2 in the Solar Nebula. Scenarios of formation of comets consistent with these results are discussed.
02/1998;
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J. Wink,
D. Bockelée-Morvan, D. Despois,
P. Colom,
N. Biver,
J. Crovisier,
E. Gérard,
E. Lellouch,
J. K. Davies,
W. R. F. Dent,
L. Jorda
[show abstract]
[hide abstract]
ABSTRACT: Comet C/1995 O1 (Hale-Bopp) has been observed on October 5 and 25, 1996 and from March 6 to March 22, 1997 with the Institut
de Radioastronomie Millimétrique (IRAM) interferometer at Plateau de Bure (France). Millimetre lines of HCN,HNC, CO, H2CO, CH3OH, H2S, CS and SO were mapped with spatial resolutions of 1.5–3.5 arc sec. These observations allow us to investigate whether these
species are released by the nucleus or produced in the coma by extended sources or photo-processes. The brightness distribution
of the HCN J (1-0) line is consistent with release from the nucleus. The HNC J (1-0) distribution deviates from that of HCN
in the innermost coma, and indicates production of HNC in the coma. This is in agreement with the heliocentric variation of
the HNC/HCN ratio (Biver et al., 1997, Science 275, 1915; Irvine et al., 1998, this issue) and formation by chemical reactions
(Rodgers and Charnley, 1998, Ap. J. 501, L227; Irvine et al., 1998, Nature 393, 547). There is clear evidence that SO is a
photo dissociation product. The observations also confirm that H2CO is mainly produced by an extended source, as first evidenced in comet P/Halley. The contribution of the nucleus to the
total H2CO production rate does not exceed 6%. The molecular lines have also been monitored hourly with the five antennas of the interferometer
in single-dish mode. The line velocity shifts show aperiodic modulation linked to the nucleus rotation. The amplitude of the
modulation differs from one species to another. The periodic modulation seen for the CO J (2-1) line on March 11 suggests
that a significant fraction of CO is released continuously night and day by an active source situated at equatorial latitudes
on the nucleus surface.
Earth Moon and Planets 06/1997; 78(1):63-63. · 0.67 Impact Factor
