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11.
Infrared observations of comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp) benefited from the high spectral resolution
and sensitivity of échelle spectrometers now equipping ground-based telescopes and from the availability of the Infrared Space
Observatory (ISO).
From the ground, several hydrocarbons were unambiguously detected for the first time: CH4, C2H2, C2H6. Water was observed through several of its hot vibrational bands, escaping telluric absorption. CO, HCN, NH3 and OCS were also observed, as well as several radicals. This permitted the evaluation of molecular production rates, of
rotational temperature, and — taking advantage of the 1-D imaging of long-slit spectroscopy — of the space distribution of
these species. With ISO, carbon dioxide was directly observed for the second time in a comet (after its detection from the
Vega probes in P/Halley). The spectrum of water was investigated in detail (several bands of vibration and far-infrared rotational
lines), permitting the evaluation of the rotational temperature of water, and of it spin temperature from the ortho-to-para
ratio. Water ice was identified in the grains of Hale-Bopp as far as 7 AU from the ground and possibly at 3 AU with ISO. The
composition of cometary volatiles appears to be strikingly similar to that of interstellar ices.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
Florence Henry Jacques Crovisier Dominique Bockelée-Morvan Heike Rauer Darek Lis 《Astrophysics and Space Science》2001,277(1-2):303-304
We present radio observations of HCO+, H3O+ and CO+ in Hale-Bopp.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
We report on mid-resolution (R∼2000) spectroscopic observations of Titan, acquired in November 2000 with the Very Large Telescope and covering the range 4.75-5.07 μm. These observations provide a detailed characterization of the CO (1-0) vibrational band, clearly separating for the first time individual CO lines (P10 to P19 lines of 13CO). They indicate that the CO/N2 mixing ratio in Titan’s troposphere is 32±10 ppm. Comparison with photochemical models indicates that CO is not in a steady state in Titan’s atmosphere. The observations confirm that Titan’s 5-μm continuum geometric albedo is ∼0.06, and further indicates a ∼20% albedo decrease over 4.98-5.07 μm. Nonzero flux is detected at the 0.01 geometric albedo level in the saturated core of the 12CO (1-0) band, at 4.75-4.85 μm, providing evidence for backscattering on the stratospheric haze. Finally, emission lines are detected at 4.75-4.835 μm, coinciding in position with lines from the CO(1-0) and/or CO(2-1) bands. Matching them by thermal emission would require Titan’s stratosphere to be much warmer (by ∼ 25 K at 0.1 mbar) than indicated by the methane 7.7-μm emission and the Voyager radio-occultation. We show instead that a nonthermal mechanism, namely solar-excited fluorescence, is a more plausible source for these emissions. Improved observations and laboratory measurements on the vibrational-translational relaxation of CO are needed for further interpretation of these emissions in terms of a CO stratospheric mixing ratio. 相似文献
14.
Bockelée-Morvan Dominique Biver Nicolas Colom Pierre Crovisier Jacques Festou Michel C. Henry Florence Lecacheux Alain Weaver Harold A. 《Earth, Moon, and Planets》2002,90(1-4):459-461
NASA's Deep Space 1 mission flew by Comet 19P/Borrelly on September 22, 2001.We present observations of molecular species obtained with the 30-m telescope of theInstitut de Radioastronomie Millimétrique (IRAM) and the Nançay radio telescopeat and near the time of this flyby. OH, HCN, and CS production rates were measured,while upper limits were deduced for CO, H2CO and H2S. 相似文献
15.
Bockelée-Morvan D. Wink J. Despois D. Colom P. Biver N. Crovisier J. Gautier D. Gérard E. Lellouch E. Moreno R. Paubert G. Rauer H. Davies J. K. Dent W. R. F. 《Earth, Moon, and Planets》1997,78(1-3):67-67
Spectroscopic observations of comet Hale-Boppwere undertaken near perihelion at millimetre wavelengths with the Institut de
Radioastronomie Millimétrique (IRAM) telescopes at Plateau de Bure (France)and Pico Veleta (Spain). They resulted in the first
detections of HCOOH,SO2, NH2CHO and HCOOCH3 in a comet. HDO was detected through its312–221 line at 225.897 GHz,complementing the observation of the 101–000 line at 464.925 GHz at the James Clerk Maxwell Telescope (Meier et al., 1998,Science 279, 842).Several unidentified lines
are present in the spectra. Observations of HC3N, HNCO, OCS, SO, CN, CO+, HCO+, in addition to more ‘classical’species CO, HCN, HNC, CH3CN, CH3OH, H2CO, CS and H2S (Biveret al., this issue) permit us to make out an extensive inventory of the composition of the coma of comet Hale-Bopp
at its perihelion. It presents strong analogies with gas-phase abundances measured in interstellar hot cores and bipolar flows,
which are believed to reflect the composition of interstellar grains.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
J. Boissier D. Bockelée-Morvan N. Biver J. Crovisier R. Moreno E. Lellouch R. Neri 《Earth, Moon, and Planets》2009,105(2-4):89-93
Interferometric observations are essential to probe the molecular emission in the inner cometary atmospheres and study the outgassing from the nucleus. Mapping the continuum emission can provide information about the dust and/or nucleus properties. We present here a summary of the observations of the dust and gas coma of comet 17P/Holmes and nuclear observations of 8P/Tuttle, both carried out with the IRAM interferometer at Plateau de Bure (PdBI) in 2007–2008. The observations of these two comets demonstrate the ability of the PdBI in terms of cometary science. In the near future, several improvements will be made (new receivers at 0.8 mm, a new wide-band correlator) allowing more frequent and more detailed studies of comets. On the long term, NOEMA, an expansion project, may add up to six antennas to the Plateau de Bure Interferometer, and increase the baseline lengths. Such an instrument would offer a complement to ALMA to track comets of the northern hemisphere with about half the sensitivity of ALMA for continuum studies. 相似文献
17.
Davis John K. Geballe Thomas R. Hanner Marthe S. Weaver H. A. Crovisier Jacques Bockelée-Morvan Dominique 《Earth, Moon, and Planets》1997,78(1-3):293-298
We present 10 and 20 μm spectra of comet Hale-Bopp taken at UKIRT on 1996 June 20 and 1996 September 29.The 10 μm spectra
clearly show a strong silicate feature with peaks at 10.0 and 11.2 μm. The 20 μm spectrum on September 29 has strong excess
flux relative to a blackbody and a peak near 19μm, in good agreement with the ISO SWS spectra obtained a week later. However,
the 20 μm spectrum on June 20 has significantly lower flux than would be expected based on a blackbody extrapolation from
the flux at 12.5 μm.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Many new cometary molecules — both parents and daughters — were detected in the exceptionally productive comet C/1995 O1 (Hale-Bopp).The space distribution of several of these species could be investigated from radio interferometry or from long-slit spectroscopy in the infrared. The distinction between parent species — directly sublimated from nucleus ices — and secondary species — resulting from chemical processing in the coma or produced by a secondary source — is not always clear. It is important to assess whether or not observed minor species (HCOOCH3, HCOOH...) could be synthesized by chemical reactions favoured by the high density of the coma of comet Hale-Bopp. Chemical modelling by Rodgers and Charnley suggests that this is notthe case. CO and H2CO are abundant cometary species which partly come from distributed sources. The nature of these sources is still a mystery. A special case, now well documented, is that of HNC, for which the abundance evolution with heliocentric distance could be observed in comet Hale-Bopp and which was observed in several much less productive comets. 相似文献
19.
Leech K. Crovisier J. Bockelée-Morvan D. Brooke T. Y. Hanner M. S. Altieri B. Keller H. U. Lellouch E. Lim T. 《Earth, Moon, and Planets》1997,78(1-3):81-83
Spectra of comet C/1995 O1 (Hale-Bopp) were obtained with the Infrared Space Observatory (ISO) at medium resolution with the
grating spectrometer in the photometer (PHT-S) and/or at high resolution with the short wavelength spectrometer (SWS) and
long wavelength spectrometer (LWS) in April 1996 (Crovisier et al., 1996), September–October 1996 (Crovisier et al., 1997a,
b) and December 1997, at distances from the Sun of 4.6, 2.9 and 3.9 AU, respectively. For the first time, high-resolution
spectra of a comet covering the entire 2.4 to 200 μm spectral range were obtained.
The vibrational bands of H2O, CO2 and CO are detected in emission with PHT-S. Relative production rates of 100:22:70 are derived for H2O:CO2:CO at 3 AU pre-perihelion. H2O is observed at high spectral resolution in the ν3 group of bands around 2.7 μm and the ν2 group around 6 μm with SWS, and in several rotational lines in the 100–180 μm region with LWS. The high signal-to-noise ratio
of the ν3 band observed on September–October 1996 allows accurate determinations of the water rotational temperature (28 K) and of
its ortho-to-para ratio(2.45 ± 0.10, which significantly differs from the high temperature limit and corresponds to a spin
temperature of 25 K).
Longward of 6 μm the spectrum is dominated by dust thermal continuum emission, upon which broad emission features are superimposed.
The wavelengths of the emission peaks correspond to those of Mg-rich crystalline olivine (forsterite). In the September–October
1996 spectra, emission features at 45 and 65 μm and possible absorption at 2.9–3.2 μm suggest that grains of water ice were
present at 3 AU from the Sun.
The observations made post-perihelion in late December 1997 led to the detections of H2O, CO2 and CO at 3.9 AU from the Sun (Figures 1 and 2). The production rates were ≈3.0 × 1028,3.5 × 1028 and ≈1.5 × 1029 s-1, respectively. This corresponds to H2O:CO2:CO = 100:110:500 and confirms that at such distances from the Sun, cometary activity is dominated by sublimation of CO and
CO2 rather than by H2O.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Crovisier Jacques Colom Pierre Gérard Éric Bockelée-Morvan Dominique 《Earth, Moon, and Planets》2002,90(1-4):369-370
The 18 cm lines of OH have been observed in more than 70 comets withthe Nançay radio telescope since 1974. The observations made from1982 to 1999 are now organized in a data base. The Nançay radiotelescope has been recently upgraded, and observations since 2000 aremade with a sensitivity increased by about a factor of two. Twelvecomets were observed from July 2000 to May 2002. 相似文献