At least 16 fragments were detected in images of comet C/1999 S4 (LINEAR) taken on 5 August 2000 with the Hubble Space Telescope (HST) and on 6 August with the Very Large Telescope (VLT). Photometric ...analysis of the fragments indicates that the largest ones have effective spherical diameters of about 100 meters, which implies that the total mass in the observed fragments was about 2 × 109kilograms. The comet's dust tail, which was the most prominent optical feature in August, was produced during a major fragmentation event, whose activity peaked on UT 22.8 ± 0.2 July 2000. The mass of small particles (diameters less than about 230 micrometers) in the tail was about 4 × 108kilograms, which is comparable to the mass contained in a large fragment and to the total mass lost from water sublimation after 21 July 2000 (about 3 × 108kilograms). HST spectroscopic observations during 5 and 6 July 2000 demonstrate that the nucleus contained little carbon monoxide ice (ratio of carbon monoxide to water is less than or equal to 0.4%), which suggests that this volatile species did not play a role in the fragmentation of C/1999 S4 (LINEAR).
We report on simultaneous optical and infrared observations of the Halley Family comet 8P/Tuttle performed with the ESO Very Large Telescope. Such multi-wavelength and coordinated observations are a ...good example of what can be done to support space missions. From high resolution optical spectroscopy of the CN (0,0) 388 nm and NH
2
(0,9,0) 610 nm bands using UVES at UT2 we determined
12
C/
13
C = 90 ± 10 and
14
N/
15
N = 150 ± 20 in CN and we derived a nuclear spin temperature of NH
3
of 29 ± 1 K. These values are similar to those found in Oort-Cloud and Jupiter Family comets. From low resolution long slit spectroscopy with FORS1 at UT2 we determined the CN, C
3
and C
2
production rates and the parent and daughter scale lengths up to 5.2 10
5
km tailward. From high resolution IR spectroscopy with CRIRES at UT1 we measured simultaneously the production rates and mixing ratios of H
2
O, HCN, C
2
H
2
, CH
4
, C
2
H
6
, and CH
3
OH.
The 12C14N/12C15N and 12C14N/13C14N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C/1999 S4 ...(LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant within the uncertainties. The mean values are 12C/13C $\simeq$ 90 and 14N/15N $\simeq145$ for the eight comets. These results strengthen the view that CN radicals originate from refractory organics formed in the protosolar molecular cloud and subsequently incorporated in comets.
Analysis of Hubble Space Telescope (HST) images of comet Hale-Bopp (C/1995 O1) suggests that the effective diameter of the nucleus is between 27 to 42 kilometers, which is at least three times larger ...than that of comet P/Halley. The International Ultraviolet Explorer and HST spectra showed emissions from OH (a tracer of H$_2$O) and CS (a tracer of CS$_2$) starting in April 1996, and from the CO Cameron system (which primarily traces CO$_2$) starting in June 1996. The variation of the H$_2$O production rate with heliocentric distance was consistent with sublimation of an icy body near its subsolar point. The heliocentric variation in the production rates of CS$_2$ and dust was different from that of H$_2$O, which implies that H$_2$O sublimation did not control the CS$_2$ or dust production during these observations.
The Hubble Space Telescope made systematic observations of the split comet P/Shoemaker-Levy 9 (SL9) (P designates a periodic comet) starting in July 1993 and continuing through mid-July 1994 when the ...fragments plunged into Jupiter's atmosphere. Deconvolutions of Wide Field Planetary Camera images indicate that the diameters of some fragments may have been as large as ∼2 to 4 kilometers, assuming a geometric albedo of 4 percent, but significantly smaller values (that is, <1 kilometer) cannot be ruled out. Most of the fragments (or nuclei) were embedded in circularly symmetric inner comae from July 1993 until late June 1994, implying that there was continuous, but weak, cometary activity. At least a few nuclei fragmented into separate, condensed objects well after the breakup of the SL9 parent body, which argues against the hypothesis that the SL9 fragments were swarms of debris with no dominant, central bodies. Spectroscopic observations taken on 14 July 1994 showed an outburst in magnesium ion emission that was followed closely by a threefold increase in continuum emission, which may have been caused by the electrostatic charging and subsequent explosion of dust as the comet passed from interplanetary space into the jovian magnetosphere. No OH emission was detected, but the derived upper limit on the H$_2$O production rate of ∼10$^{27}$ molecules per second does not necessarily imply that the object was water-poor.
Post-perihelion observations of Comet Hale–Bopp (C/1995 O1) were made with the Hubble Space Telescope (HST) on 27 August 1997 (r=2.48 AU; Δ=2.99 AU), 11 November 1997 (r=3.38 AU; Δ=3.31 AU), and 19 ...February 1998 (r=4.44 AU; Δ=4.40 AU) using the newly installed Space Telescope Imaging Spectrograph (STIS). The STIS CCD was used to image the comet, and useful spectroscopy was obtained between 2000 and 3190 Å using the G230LB, G230MB, and G230L gratings. The morphology of the images closely resembled that obtained at similar heliocentric distances preperihelion, but the dust production rates may have been slightly lower post-perihelion. We find no evidence for any companions to the nucleus in the STIS images, but fairly bright objects (up to ∼20% of the brightness of the main nucleus) could be easily “hidden” within the strong coma jets. Emissions from OH and CS were observed in the spectra and were used to derive production rates for H2O and CS2. As with the dust, the gas production rates appear to be somewhat smaller post-perihelion than preperihelion. The two-dimensional STIS data allowed us to map the spatial distribution of the OH emission with a spatial resolution of ∼0.″1, and the ∼6-Å spectral resolution of the G230MB grating permitted a detailed examination of the OH excitation. The relative intensities of the rotational lines in the OH(0,0) band are fairly well matched by a standard fluorescence excitation model. The OH spatial brightness profile was slightly asymmetric (∼20% brightness differences when comparing two different directions), and the intensity peak was offset by ∼3200 km from the continuum peak for both the August and November 1997 observations. Perhaps this offset may be explained by asymmetric ejection of H2O molecules from the nucleus, but we have not attempted to model this effect. Except for this offset, conventional models for the spatial distribution of OH provide a good match to the data from November 1997. The observed spatial profile for the August 1997 observation is well matched by our model at large cometocentric distances but is considerably flatter near the nucleus (within ∼2″ of the continuum peak) than predicted. The available evidence strongly suggests that an optical depth effect, rather than the production of OH from a population of icy grains in the coma, is responsible for the observed flattening of the OH spatial brightness profile.
Ultraviolet (UV) spectra of comet P/Hartley 2 (1991 XV) taken with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) in 1991 September reveal several bands of the Cameron system ...of CO (a 3 Pi-X 1 Sigma). These band are most likely due to 'prompt' emission from CO2 and, thus, provide a direct tracer of the CO2 abundance in the nucleus. Photodissociative excitation of CO2 is probably the largest contributor to the Cameron band emission, but significant contributions from electron impact excitation of CO, electron impact dissociation of CO2, and dissociative recombination of CO2(+), are also possible. Using our estimate that photodissociative excitation is responsible for approximately 60% of the total excitation of the Cameron system, we derive Q(sub CO2) approximately 2.6 x 10(exp 27) molecules/s, which implies CO2/H20 approximately 4%. If all of the Cameron band emission is due to photodissociative excitation, then CO2/H2O = 7 +/- 2%. For the largest possible contributions from the other excitation mechanisms considered, the CO2 abundance could be as a small as aproximately 2-3%. We did not detect CO Fourth Positive Group emission in our data and derive an upper limit of CO/H2O less than or equal to 1% (3 sigma) for CO coming directly from the nucleus. Comparison of the relative CO2 and CO abundances in P/Hartley 2 to those in P/Halley (CO2/H2O approximately 3%-4%, CO/H20 approximately 4% for the nucleus source) indicates that selective devolatilization of the nucleus may have occurred for P/Hartley 2. A relatively large CO2/CO ratio (i.e., approximately greater than 1) seems to be a common property of cometary nuclei. Since gas phase chemistry, in either the solar nebula or the interstellar medium (ISM), appears incapable of producing large relative CO2 abundances, the CO2 in cometary nuclei is probably produced either by UV and/or cosmic ray irradiation of ISM grains prior to the formation of the Solar System, or by condensation fractionation in the solar nebula.
On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational ...campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.
Anomalous Nitrogen Isotope Ratio in Comets Arpigny, Claude; Jehin, Emmanuël; Manfroid, Jean ...
Science (American Association for the Advancement of Science),
09/2003, Letnik:
301, Številka:
5639
Journal Article, Web Resource
Recenzirano
High-resolution spectra of the$CN B^2 \Sigma^+-X^2 \Sigma^+$(0,0) band at 390 nanometers yield isotopic ratios for comets C/1995 O1 (Hale-Bopp) and C/2000 WM1 (LINEAR) as follows:$165 \pm 40$and$115 ...\pm 20$for12C/13C,$140 \pm 35$and$140 \pm 30$for14N/15N. Our N isotopic measurements are lower than the terrestrial$^{14}N/^{15}N = 272$and the ratio for Hale-Bopp from measurements of HCN, the presumed parent species of CN. This isotopic anomaly suggests the existence of other parent(s) of CN, with an even lower N isotopic ratio. Organic compounds like those found in interplanetary dust particles are good candidates.
Theoretical resonance fluorescence calculations are presented of the triatomic CSUB3/SUB radical and are compared with observations of the CSUB3/SUB emission in comets Hale-Bopp and de Vico. A ...theoretical model of the CSUB3/SUB vibration-rotational structure in the ASUP1/SUPPiSUBu/SUB - XSUP1/SUPSigmaSUBg/SUB SUP+/SUP electronic system is introduced. The model takes into account the detailed structure of the bending mode nuSUB2/SUB which is responsible for the emission of the 4050 à group. A total of 1959 levels are considered, with 515 levels in the ground state. The main effort is to model high-resolution spectra of the 4050 à emission in comets C/1995 O1 Hale-Bopp and 122P/1995 S1 de Vico. The agreement between observed and theoretical spectra is good for a value of the dipole moment derivative of dmu/dr ~ 2.5 Debye à SUP-1/SUP. The modeled CSUB3/SUB emission exhibits a pronounced Swings effect. Based on observations made with William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, and on observations made at the McDonald Observatory, which is operated by the University of Texas at Austin, USA.
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