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1.
2.
The correlation between specific meteorites and asteroids is a long-standing problem. The best-known correlation seems to
be the HED–Vesta, although several problems still remain to be solved. We report the spectral reflectance analysis (0.4–2.5 μm)
of a set of HED meteorites, taken from the RELAB database and three V-type asteroids, taken from MIT-UH-IRTF Joint Campaign
for NEO Reconnaissance. We used the Modified Gaussian Model to fit the spectra to a series of overlapping, modified Gaussian
absorptions. The fitted individual bands are validated against established laboratory calibrations. With spectral resolution
extending to the near-infrared, we are able to resolve the presence of both high-calcium pyroxene (HCP) and low-calcium pyroxene
(LCP) and, thus, use the HCP/(HCP + LCP) ratios to remotely trace igneous processing on the parent asteroids. A search of
this mineral provides a useful probe of differentiation. The high HCP/(HCP + LCP) ratios found require extensive differentiation
of these asteroids and/or their primordial parent body. The degree of melting obtained for the eucrites, using the former
ratio, is comparable with that obtained for all V-type asteroids here analyzed, suggesting a comparable geologic history. 相似文献
3.
Ľubor Kresák 《Earth, Moon, and Planets》1980,22(1):83-98
The dynamics of larger interplanetary bodies is reviewed, with emphasis on evolutionary problems, interrelations, and open questions. Observational biases distinguishing the sample of known objects from the whole population are briefly discussed. A schematic division of the solar system into zones with different regimes of motion, and a rough taxonomy of orbit types are attempted. The role of individual major planets in controlling the dynamical evolution of interplanetary objects, in particular by stabilizing resonances and destabilizing close encounters, is compared. There are significant evolution asymmetries due to boundary conditions and preferential evolutionary paths; individual major displacements in the phase space of orbital elements conserve the Tisserand invariant with respect to the planet responsible, thus favouring certain evolutionary sequences against others. Very limited lifetimes of some orbit types imply a long-term balance between source and sink, and require a continuous supply of objects from other types of orbits. In this respect, the ultimate fate of extinct comets is of particular interest. Under very specific conditions, nongravitational effects of mass loss can result in stabilization of a formerly unstable orbit. Since the dividing line between the two basic interplanetary populations distinguished by origin and composition — the asteroids and the comets — is essentially that between stable and unstable motion, orbital data can be used to specify which of the known asteroid-like objects may be devolatilized cometary nuclei.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy. 相似文献
4.
As the rate of replenishment of short-lived Apollo-Amor asteroids from the main belt seems to be insufficient to compensate for their losses, the idea was put forward that most of them are inactive cometary nuclei. However, the observational and theoretical evidence is inconclusive about whether it is possible to transform cometary nuclei into asteroid-like objects. There is good evidence that Apollo-Amor asteroids represent the last parent bodies of most, or even all, classes of meteorites. But meteorites cannot be formed within cometary nuclei having a constitution like Whipple's classical model, and alternative models seem to be unsatisfactory. Therefore, it is concluded that the cometary origin of most Apollo-Amor asteroids is implausible and they are genuine asteroids coming from the main belt. The process of their losses and replenishment must be studied further. 相似文献
5.
We present near-infrared spectra of 23 B-type asteroids obtained with the NICS camera-spectrograph at the 3.56 m Telescopio Nazionale Galileo. We also compile additional visible and near-infrared spectra of another 22 B-type asteroids from the literature. A total of 45 B-types are analyzed. No significant trends in orbital properties of our sample were detected when compared with all known B-types and all known asteroids. The reflectance spectra of the asteroids in the 0.8–2.5 μm range show a continuous shape variation, from a monotonic negative (blue) slope to a positive (red) slope. This continuous spectral trend is filling the gap between the two main groups of B-types published by Clark et al. ([2010]. J. Geophys. Res., 115, 6005–6027). We found no clear correlations between the spectral slope and the asteroids’ sizes or heliocentric distances. We apply a clustering technique to reduce the volume of data to six optimized “average spectra” or “centroids”, representative of the whole sample. These centroids are then compared against meteorite spectra from the RELAB database. We found carbonaceous chondrites as the best meteorite analogs for the six centroids. There is a progressive change in analogs that correlates with the spectral slope: from CM2 chondrites (water-rich, aqueously altered) for the reddest centroid, to CK4 chondrites (dry, heated/thermally altered) for the bluest one. 相似文献
6.
V. V. Busarev 《Solar System Research》2011,45(1):43-52
The reflectance spectra of asteroids 10 Hygiea (C-type), 135 Hertha (M-type), and 196 Philomela (S-type) are obtained in a
range of 0.40–0.91 μm with different time intervals. In this paper, the technique of the spectral measurements of asteroids
is analyzed and the reflectance spectra of Hygiea, Hertha, and Philomela are interpreted. The main physical and chemical factors
and processes influencing the spectral characteristics of asteroids are considered. It is determined that the spectra of Hertha
and Hygiea contain variations exceeding the measurement errors several times at different relative rotation phases, whereas
spectral variations of Philomela caused by its rotation hardly exceed the error limits. Most probably, these variations are
caused by local manifestations of the impact metamorphism of the material of asteroids in serious impact events. Results show
that, to determine the prevailing spectral type and the corresponding mineralogy of each asteroid, one should estimate and
take into account the changes in its spectral characteristics for a time interval comparable to the rotation period. 相似文献
7.
Two asteroids 2001 QQ199 and 2004 AE9 and two comets P/LINEAR-Catalina and P/LINEAR are found to be quasi-satellites of Jupiter
at present time. The Tisserand parameters of these four bodies lie between 2.3 and 2.5, which means two asteroids might be
Jupiter family comets and will show a cometary’s activity in the near future. 相似文献
8.
V-type asteroids in the inner Main Belt (a < 2.5 AU) and the HED meteorites are thought to be genetically related to one another as collisional fragments from the surface of the large basaltic Asteroid 4 Vesta. We investigate this relationship by comparing the near-infrared (0.7-2.5 μm) spectra of 39 V-type asteroids to laboratory spectra of HED meteorites. The central wavelengths and areas spanned by the 1 and 2 μm pyroxene-olivine absorption bands that are characteristic of planetary basalts are measured for both the asteroidal and meteoritic data. The band centers are shown to be well correlated, however the ratio of areas spanned by the 1 and 2 μm absorption bands are much larger for the asteroids than for the meteorites. We argue that this offset in band area ratio is consistent with our currently limited understanding of the effects of space weathering, however we cannot rule out the possibility that this offset is due to compositional differences. Several other possible causes of this offset are discussed.Amongst these inner Main Belt asteroids we do not find evidence for non-Vestoid mineralogies. Instead, these asteroids seem to represent a continuum of compositions, consistent with an origin from a single differentiated parent body. In addition, our analysis shows that V-type asteroids with low inclinations (i < 6°) tend to have band centers slightly shifted towards long wavelengths. This may imply that more than one collision on Vesta’s surface was responsible for producing the observed population of inner belt V-type asteroids. Finally, we offer several predictions that can be tested when the Dawn spacecraft enters into orbit around Vesta in the summer of 2011. 相似文献
9.
E. N. Slyuta 《Solar System Research》2009,43(5):443-452
Physical-mechanical properties of cometary nuclei matter are described in detail. As compared to other Solar System bodies,
cometary nuclei are characterized by low strength properties. The ultimate tensile strength of cometary matter and cometary
nuclei on the whole is about 2 kPa. An analysis performed based on a rheological model of a self-gravitating triaxial solid
body showed that cometary nuclei less than 50–60 km (this actually being all known comets) are characterized by a constant
ultimate tensile strength which is determined only by the matter composition and structure. The effective ultimate tensile
strength for bodies larger than 50–60 km is determined by the body mass and figure parameters and increases according to the
quadratic law depending on the body dimensions and mass. Such an increase of the effective strength can explain the absence
or deficit of cometary nuclei more than 60 km in size, since it can significantly affect the parameters of the parent body
destruction and the formation of a secondary population. The dependence of the mechanism and character of destruction on the
parameters of the figure for Kuiper objects more than 50–60 km is size can yield a deficit of the population of the bodies
whose figure parameters are a/c > 1.75 with respect to the bodies with a/c < 1.75 figure parameters. 相似文献
10.
Near-infrared (J, H and K bands) spectra of nine dark asteroids (chosen among a sample of supposed primitive objects between C and D classes) have been obtained at the Mauna Kea Observatory (Hawaii) with the 2.2-m telescope using KSPEC as spectrograph. The aim of this work was to search for evidence of the presence of organic materials in these objects as found in other planetary bodies as 5145 Pholus, and in some cometary nuclei. A careful analysis of the data has revealed flat or slightly redder spectra than the solar one for all observed asteroids. No evidence of distinct absorption features was found. 相似文献
11.
Comets in the near-Earth object population 总被引：1，自引：0，他引：1
Francesca DeMeo 《Icarus》2008,194(2):436-449
Because the lifespan of near-Earth objects (NEOs) is shorter than the age of the Solar System, these objects originate elsewhere. Their most likely sources are the main asteroid belt and comets. Through physical observations we seek to identify potential dormant or extinct comets among “asteroids” catalogued as NEOs and thereby determine the fraction of “comet candidates” within the total NEO population. Both discovery statistics and dynamical models indicate that candidate cometary objects in near-Earth space are predominantly found among those having a jovian Tisserand parameter Tj<3. Therefore, we seek to identify comet candidates among asteroid-like NEOs using three criteria: Tj<3, spectral parameters (C, D, T, or P taxonomic types), and/or low (<0.075) albedos. We present new observations for 20 NEOs having Tj<3, consisting of visible spectra, near-infrared spectra, and/or albedo measurements obtained using the NASA Infrared Telescope Facility, the Kitt Peak National Observatory 4 m, and the Magellan Observatory 6.5-m. Four of our “asteroid” targets have been subsequently confirmed as low activity comets. Thus our sample includes spectra of the nuclei of Comets 2002 EX12 = 169P (NEAT), 2001 WF2 = 182P (LONEOS), 2003 WY25 = D/1891 W1 (Blanplain), and Halley Family Comet 2006 HR30 = P/2006 HR30 (Siding Spring). From the available literature, we tabulate physical properties for 55 NEOs having Tj<3, and after accounting for possible bias effects, we estimate that 54±10% of NEOs in Tj<3 orbits have “comet-like” spectra or albedos. Bias corrected discovery statistics [Stuart, J.S., Binzel, R.P., 2004. Icarus 170, 295-311] estimate 30±5% of the entire NEO population resides in orbits having Tj<3. Combining these two factors suggests that 16±5% of the total discovered “asteroid-like” NEO population has “comet-like” dynamical and physical properties. Outer main-belt asteroids typically have similar taxonomic and albedo properties as our “comet candidates.” Using the model of Bottke et al. [Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.M., Levison, H., Michel, P., Metcalfe, T.S., 2002. Icarus 156, 399-433] to evaluate source region probabilities, we conclude that 8±5% of the total asteroid-like NEO population have the requisite orbital properties, physical properties, and dynamical likelihood to have originated as comets from the outer Solar System. 相似文献
12.
M.E. Ockert-Bell B.E. Clark M.K. Shepard R.A. Isaacs E.A. Cloutis S. Fornasier S.J. Bus 《Icarus》2010,210(2):674-692
We have conducted a radar-driven observational campaign of 22 main-belt asteroids (MBAs) focused on Bus–DeMeo Xc- and Xk-type objects (Tholen X and M class asteroids) using the Arecibo radar and NASA Infrared Telescope Facilities (IRTF). Sixteen of our targets were near-simultaneously observed with radar and those observations are described in a companion paper (Shepard, M.K., and 19 colleagues [2010]. Icarus, in press). We find that most of the highest metal-content asteroids, as suggested by radar, tend to exhibit silicate absorption features at both 0.9 and 1.9 μm, and the lowest metal-content asteroids tend to exhibit either no bands or only the 0.9 μm band. Eleven of the asteroids were observed at several rotational longitudes in the near-infrared and significant variations in continuum slope were found for nine in the spectral regions 1.1–1.45 μm and 1.6–2.3 μm. We utilized visible wavelength data (Bus, S.J., Binzel, R.P. [2002b]. Icarus 158, 146–177; Fornasier, S., Clark, B.E., Dotto, E., Migliorini, A., Ockert-Bell, M., Barucci, M.A. [2010]. Icarus 210, 655–673.) for a more complete compositional analysis of our targets. Compositional evidence is derived from our target asteroid spectra using two different methods: (1) a χ2 search for spectral matches in the RELAB database, and (2) parametric comparisons with meteorites. This paper synthesizes the results of the RELAB search and the parametric comparisons with compositional suggestions based on radar observations. We find that for six of the seven asteroids with the highest iron abundances, our spectral results are consistent with the radar evidence (16 Psyche, 216 Kleopatra, 347 Pariana, 758 Mancunia, 779 Nina, and 785 Zwetana). Three of the seven asteroids with the lowest metal abundances, our spectral results are consistent with the radar evidence (21 Lutetia, 135 Hertha, 497 Iva). The remaining seven asteroids (22 Kalliope, 97 Klotho, 110 Lydia, 129 Antigone, 224 Oceana, 678 Fredegundis, and 771 Libera) have ambiguous compositional interpretations when comparing the spectral analogs to the radar analogs. The number of objects with ambiguous results from this multi-wavelength survey using visible, near-infrared, and radar wavelengths indicates that perhaps a third diagnostic wavelength region (such as the mid-infrared around 2–4 μm, the mid-infrared around 10–15 μm, and/or the ultraviolet around 0.2–0.4 μm) should be explored to resolve the discrepancies. 相似文献
13.
We present new near-infrared spectra of 20 Trojan asteroids. The spectra were recorded at the NASA Infrared Telescope Facility (IRTF) using the recently commissioned medium-resolution spectrograph SpeX and at the Multiple Mirror Telescope (MMT) using the instrument FSPEC. Spectra of all of these objects were measured in K-band (1.95-2.5 μm), 8 of these in L-band (2.8-4.0 μm), and 14 in the range 0.8-2.5 μm. These observations nearly double the number of published 0.8-2.5 μm spectra of Trojan asteroids and provide the first systematic study of the L-band region for these distant asteroids. The data show that the red spectral slope measured in the near-IR extends through the L-band, though it is not as steep here as at shorter wavelengths. A significant diversity is apparent in the near-IR spectral slopes of this sampling of objects. Most of the spectra do not contain any definitive absorption features characteristic of surface composition (e.g., H2O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. A few objects may display spectral activity, and the reliability of these possible features is discussed. While these spectra are generally compatible with silicate surfaces to explain the spectral slope mixed with some fraction of low albedo material, there is no absolute indication of silicates. The spectral slope could also be explained by the presence of hydrocarbons, but the lack of absorption features, especially in L-band where very strong fundamental absorptions from these molecules appear, constrains the character and abundance of these materials at the surface. 相似文献
14.
Near-infrared spectra (∼0.90 to ∼1.65 μm) are presented for 181 main-belt asteroids, more than half having diameters less than 20 km. These spectra were measured using a specialized grism at the NASA Infrared Telescope Facility, where the near-infrared wavelength coverage is designed to complement visible wavelength CCD measurements for enhanced mineralogic interpretation. We have focused our analysis on asteroids that appear to have surfaces dominated by olivine or pyroxene since these objects can be best characterized with spectral coverage only out to 1.65 μm. Olivine-dominated A-type asteroids have distinctly redder slopes than olivine found in meteorites, possibly due to surface alteration effects such as micro-meteoroid bombardment simulated by laser irradiation laboratory experiments. K-type asteroids observed within the Eos family tend to be well matched by laboratory spectra of CO3 chondrites, while those independent of the Eos family have a variety of spectral properties. The revealed structure of the 1-μm band for 3628 Bo?němcová appears to refute its previously proposed match to ordinary chondrite meteorites. Bo?němcová displays a 1-μm band that is unlike that for any currently measured meteorite; however, spectra out to 2.5 μm are needed to conclusively argue that Bo?němcová has a surface mineralogy different from that of ordinary chondrites. Extending the spectral coverage of Vestoids out to ∼1.65 μm continues to be consistent with the “genetic” relationship of almost all observed Vestoids with Vesta and the howardites, eucrites, and diogenites. Eucrites/howardites provide the best spectral matches to the observed Vestoids. 相似文献
15.
THOMAS H. BURBINE 《Meteoritics & planetary science》1998,33(2):253-258
Abstract— I review the dynamical and compositional evidence for possibly linking CM chondrites and asteroids having G-class taxonomic designations. Three G asteroids have been identified through previous theoretical studies as being likely meteorite source bodies due to their locations near resonances. Two of these objects, 19 Fortuna and 13 Egeria, have spectral properties that are consistent with such a linkage with CM chondrites. Fortuna has a similar strength 0.7 μm absorption feature and near-infrared spectral slope to CM chondrites but a weaker ultraviolet feature. Egeria also has the characteristic 0.7 μm feature of CM chondrite spectra but does not match as well in the near-infrared. However, since the 0.7 μm feature is apparent in the spectra of approximately one-half of measured C-type asteroids, no definitive statement about any linkages can be made. Ceres is spectrally different from known meteorites in the 3 μm wavelength region and cannot be convincingly linked with any meteorite group. 相似文献
16.
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
17.
Absorption bands near 0.43 and 0.60–0.80 m, with a relative intensity of approximately 5–10%, were discovered in the reflectance spectra of five M asteroids (21, 75, 161, 201, and 497) and two S asteroids (11 and 198). It is highly probable that these absorption bands are related to oxidized and/or hydrated silicates that incorporate OH structural groups. Absorbed water in the surface material of about 24% of the known M asteroids and three E asteroids has been identified by a group of astronomers at the University of Arizona (Rivkin et al., 1995; Rivkin, 1997; Rivkin et al., 2000) on the basis of the characteristic 3-m absorption band. In addition to this, four of the six E-type asteroids observed spectrally in the visible region quite recently were found to have an absorption band at 0.5 m (Burbine et al., 1998; Fornasier and Lazzarin, 2001), which could likewise be associated with the presence of hydrated silicates in their material. The above data contradict the generally accepted viewpoint on the nature of M, S, and E asteroids, which is based on their common observed characteristics as bodies that arose at high temperatures (in the 1000–2000°C range). This contradiction, however, can be eliminated if use is made of the cosmogonic model developed by V.S. Safronov and co- workers. According to this model, the initial evolution of the main-belt asteroids was directly influenced by the process of the growth of Jupiter and was later controlled by its gravitational field. 相似文献
18.
We present reflected light spectral observations from 0.4 to 2.5 μm of 24 asteroids chosen from the population of asteroids initially classified as Tholen X-type objects (Tholen, 1984). The X complex in the Tholen taxonomy comprises the E, M and P classes which have very different inferred mineralogies but which are spectrally similar to each other, with featureless spectra in visible wavelengths.The data were obtained during several observing runs in the 2004-2007 years at the NTT, TNG and IRTF telescopes. Sixteen asteroids were observed in the visible and near-infrared wavelength range, seven objects in the visible wavelength range only, and one object in the near-infrared wavelength range only. We find a large variety of near-infrared spectral behaviors within the X class, and we identify weak absorption bands in spectra of 11 asteroids. Our spectra, together with albedos published by Tedesco et al. (2002), can be used to suggest new Tholen classifications for these objects. We describe 1 A-type (1122), 1 D-type (1328), 1 E-type (possibly, 3447 Burckhalter), 10 M-types (77, 92, 184, 337, 417, 741, 758, 1124, 1146 and 1355), 5 P-types (275, 463, 522, 909, 1902), and 6 C-types (50, 220, 223, 283, 517, and 536). In order to constrain the possible composition of these asteroids, we perform a least-squares search through the RELAB spectral database. Many of the best fits are consistent with meteorite analogue materials suggested in the published literature. In fact, we find that seven of the new M-types can be fit with metallic iron (or pallasite) materials, and that the low albedo C/P-type asteroids are best fitted with CM meteorites, some of which have been subjected to heating episodes or laser irradiation. Our method of searching for meteorite analogues emphasizes the spectral characteristics of brightness and shape, and de-emphasizes minor absorption bands. Indeed, faint absorption features like the 0.9 μm band seen on four newly classified M-type asteroids are not reproduced by the iron meteorites. In these cases, we have searched for geographical mixture models that can fit the asteroid spectrum, minor bands, and albedo. We find that a few percent (less than 3%) of orthopyroxene added to iron or pallasite meteorite, results in good spectral matches, reproducing the weak spectral feature around 0.9 μm seen on 92 Undina, 417 Suevia, and 1124 Stroobantia. For 337 Devosa, a mixture model that better reproduces its spectral behavior and the 0.9 μm feature is made with Esquel pallasite enriched with goethite (2%).Finally, we consider the sample of the X-type asteroids we have when we combine the present observations with previously published observations for a total of 72 bodies. This sample includes M and E-type asteroid data presented in
[Fornasier et al., 2008] and [Fornasier et al., 2010]. We find that the mean visible spectral slopes for the different E, M and P Tholen classes are very similar, as expected. An analysis of the X-type asteroid distribution in the main belt is also reported, following both the Tholen and the Bus-DeMeo taxonomies (DeMeo et al., 2009). 相似文献
19.
T. H. Jarrett C. A. Beichman D. Van Buren N. Gautier C. Jorquera C. Bruce 《Experimental Astronomy》1994,3(1-4):133-134
In a joint effort between engineers and scientists at the Jet Propulsion Laboratory and the California Institute of Technology, a near-infrared (0.8–2.6 m) direct imaging system has been developed and integrated into the Caltech Palomar Observatory detector series. The camera system has been tested and operated in a science mode at the prime-focus (f/3.3) of the Hale 5-m Telescope. This paper outlines the system components and performance, including discussion of the detector linearity. 相似文献
20.
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