共查询到20条相似文献，搜索用时 31 毫秒
1.
On 4 July 2005 at 5:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the 110-101 ortho-water ground-state rotational transition in Comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS and we derive an upper limit of 1.8×107 kg on the water ice evaporated by the impact. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before and after the impact. Episodes of increased activity with alternated with periods with low outgassing (). We estimate that 9P/Tempel 1 vaporized a total of N∼4.5×1034 water molecules (∼1.3×109 kg) during June-September 2005. Our observations indicate that only a small fraction of the nucleus of Tempel 1 appears to be covered with active areas. Water vapor is expected to emanate predominantly from topographic features periodically facing the Sun as the comet rotates. We calculate that appreciable asymmetries of these features could lead to a spin-down or spin-up of the nucleus at observable rates. 相似文献
2.
We report the detection of the nucleus of Comet 22P/Kopff with the Planetary Camera of the Hubble Space Telescope (HST) and with the Infrared Camera of the Infrared Space Observatory (ISOCAM). The HST observations were performed on 18 July 1996, 16 days after its perihelion passage of 2 July 1996, when it was at Rh=1.59 AU from the Sun and Δ=0.57 AU from the Earth. A sequence of images taken with four broad-band filters was repeated eight times over a 12-h time interval. The ISOCAM observations were performed on 15 October 1996, 106 days after the perihelion passage, when the comet was at Rh=1.89 AU from the Sun and Δ=1.32 AU from the Earth. Seven images were obtained with a broad-band filter centered at 11.5 μm. In both instances, the spatial resolution was appropriate to separate the signal of the nucleus from that of the coma. We determine the Johnson-Kron-Cousins BVRI magnitudes of the nucleus. The visible lightcurves constrain neither the rotation period nor the ratio of semiaxes. We favor the solution of a rather spherical nucleus, although the situation of a pole-on view of an irregular body cannot be excluded. The systematic decreasing trend of the lightcurves could suggest a period of several days. Combining the visible and infrared observations, we find that an ice-dust mixed model is ruled out, while the standard thermal model leads to a nuclear radius of Rn=1.67±0.18 km of albedo pv=0.042±0.006. The red color of the nucleus is characterized by a nearly constant gradient of S′=14±5% per kÅ from 400 to 800 nm. We estimate a fractional active area of 0.35 which places 22P/Kopff in the class of highly active short-period comets. At Rh=1.59 AU, the dust coma is characterized by a red color with a reflectivity gradient S′=17±3% per kÅ, compatible with that of the nucleus, and Afρ=545 cm, yielding a dust production rate of Qd=130 kg sec−1. 相似文献
3.
Prior to the impact event, Deep Impact monitored the ambient inner coma of Comet 9P/Tempel 1 at high spatial resolution in July 2005. Gaseous H2O and CO2 are unambiguously detected in the infrared spectra collected with the HRI-IR spectrometer aboard Deep Impact. Detailed distribution maps of these volatiles in the inner coma, within 60 km from the nucleus, are produced from the integrated emission bands of H2O (2.66 μm) and CO2 (4.26 μm). Uncorrelated asymmetries are determined in the spatial distribution of both species indicating chemical heterogeneities within the nucleus. Although present at some abundance surrounding the entire nucleus, H2O has a pronounced enhancement in abundance in the sunward direction rotational phases, evidence that the dominant process of subliming water ice from the nucleus is solar heating. In contrast, CO2 is enhanced in the regions near the negative rotational pole of the nucleus, suggesting localized outgassing there. Both species show an increase in radiance above the limb of the nucleus toward Ecliptic North. The distribution maps also suggest that the process of dust removal from the nucleus is strongly connected to the outgassing of volatiles. Detailed study of these coma asymmetries gives insight to the relative abundances of the dominant molecular components of the inner coma, source regions of the native volatiles, anisotropic outgassing of the nucleus, and the formation and evolution of the nucleus. A quiescent water production rate for Tempel 1 on July 4, 2005, is estimated to be . 相似文献
4.
The investigation of fragmented comets provides information on the physical properties and internal structure of cometary nuclei, as well as insights into the mechanisms responsible for cometary breakups. The Jupiter-family Comet 73P/Schwassmann-Wachmann 3 (73P/SW3) fragmented non-tidally into at least four components, and probably more, in the autumn of 1995. Fragment C was detected with the Wide Field Planetary Camera 2 (WFPC2) of the Hubble Space Telescope (HST) on 26 November 2001 when it was 3.26 AU from the Sun and 2.34 AU from the Earth. The high spatial resolution of the HST allowed us to separate the signal of the fragment from that of its coma, and to determine its R magnitude in the Johnson-Kron-Cousins photometric system from four images taken with the F675W filter. Assuming a spherical body with a geometric albedo of 0.04 and a linear phase coefficient of 0.04 mag deg−1 for the R band, we derived an effective radius of . The pre-breakup radius of the original nucleus was estimated to be 1.1 km, which implies that the volume of fragment C is ∼25% of the total volume of the pre-breakup nucleus. The limited temporal coverage of our observations preclude deriving an accurate shape or rotational period; our measurements are consistent with a rather spherical body but an elongated shape cannot be excluded. Fragment C was very active despite its rather large heliocentric distance, with an estimated dust production rate of (∼130 metric tons day−1). A very large fraction of the surface area of fragment C must have been sublimating to sustain such a high level of activity. Fragment C may be recovered at its next return in 2006, if it does not experience further fragmentation. 相似文献
5.
Near-simultaneous R- and J-band photometric measurements of the short-period Comets 2P/Encke and the Deep Impact mission target 9P/Tempel 1 were obtained. The resulting R-J colors are +0.82±0.08 mag and +1.46±0.13 mag for Encke and Tempel 1, respectively. Tempel 1's color is redder than the solar R-J color index of +0.76. The Tempel 1 observations directly detected the nucleus while the Encke observations likely suffered from coma contamination. 相似文献
6.
On UT 2000 August 21 we obtained simultaneous visible and mid-infrared observations of Comet 9P/Tempel 1, the target of the upcoming NASA Discovery Program mission Deep Impact. The comet was still quite active while 2.55 AU from the Sun (post-perihelion). Two independent analyses of our data, one parameterizing the coma morphology and the other modeling infrared spectrophotometry, show that the nucleus's cross section at the time the data were taken corresponds to an effective radius of 3.0±0.2 km. Based on visible-wavelength photometry of the comet taken during this observing run and others in the summer of 2000, all of which show the rotational modulation of the nucleus's brightness, we find that the infrared data were obtained near the maximum of the light curve. If we assume that the nucleus's light curve had a peak-to-valley range of 0.6±0.2 mag, then the mean effective radius is 2.6±0.2 km. Visible-wavelength photometry of the nucleus, including data published by other groups, lets us constrain the nucleus's R-band geometric albedo: 0.072±0.016. The nucleus's flux contributed about 85% of the light in the mid-infrared images. 相似文献
7.
Paul D. Feldman Stephan R. McCandliss Harold A. Weaver Michael J.S. Belton 《Icarus》2007,187(1):113-122
We report on the Hubble Space Telescope program to observe periodic Comet 9P/Tempel 1 in conjunction with NASA's Deep Impact Mission. Our objectives were to study the generation and evolution of the coma resulting from the impact and to obtain wide-band images of the visual outburst generated by the impact. Two observing campaigns utilizing a total of 17 HST orbits were carried out: the first occurred on 2005 June 13-14 and fortuitously recorded the appearance of a new, short-lived fan in the sunward direction on June 14. The principal campaign began two days before impact and was followed by contiguous orbits through impact plus several hours and then snapshots one, seven, and twelve days later. All of the observations were made using the Advanced Camera for Surveys (ACS). For imaging, the ACS High Resolution Channel (HRC) provides a spatial resolution of 36 km (16 km pixel−1) at the comet at the time of impact. Baseline images of the comet, made prior to impact, photometrically resolved the comet's nucleus. The derived diameter, 6.1 km, is in excellent agreement with the 6.0±0.2 km diameter derived from the spacecraft imagers. Following the impact, the HRC images illustrate the temporal and spatial evolution of the ejecta cloud and allow for a determination of its expansion velocity distribution. One day after impact the ejecta cloud had passed out of the field-of-view of the HRC. 相似文献
8.
The article presents results of CCD photometry in R-band of a dynamically new Comet C/2001 K5 (LINEAR), obtained at a heliocentric distance of about 5.6 AU, after the perihelion passage. Being so distant from the Sun, this comet was extremely active (Afρ close to 2000 cm), exhibiting quite well developed dust coma and tail. During the observations, general photometric behavior of the comet with heliocentric distance r was well described by the 2.5nlog(r) function with coefficient n=5. The radial profiles of the coma were found to be undulated, with mean slope of the dependence between cometary magnitude and 2.5log of aperture radius (at comet distance) equal to . The light curve of Comet LINEAR exhibited short-term variability which we attributed to cyclic changes of dust emission, induced by nucleus rotation. Model computations by some authors have revealed that active comets can change their spin status quite substantially even during a single orbital revolution. Thus, attempting to search for a rotation frequency, we have modified the classical PDM approach by including the spin acceleration term. Such DynamicalPDM (DPDM) method revealed the most reliable solution for the frequency f0=0.019048±0.000013 h−1 and its first time-derivative (index “zero” denotes reference to the mid time of the whole observing run), indicating a rapid spin-down of the nucleus. These parameters are equivalent to the rotation period of 52.499±0.036 h and its relative increment of 0.02729±0.00013. We present the most probable evolution of the rotation frequency of Comet LINEAR, based on the results of periodicity analysis and a simple, almost parameter independent, dynamical model of nucleus rotation. It is also shown that the DPDM may be an effective tool for determination of a nucleus radius, which provided us with the value of 1.53±0.25 km for Comet LINEAR. 相似文献
9.
The Wide Field Camera (WFC) on the Hubble Space Telescope and the Low Resolution Imaging Spectrograph (LRIS) on the Keck II telescope have been used to image 21 distant dynamically new, long-period (LP) and short-period (SP) Jupiter-family (JF) comet nuclei (near aphelion), as part of a long-term program to search for physical differences between short-period comets and Oort cloud comets. WFC data were obtained on Comets C/1987 H1 (Shoemaker) and C/1984 K1 (Shoemaker) during Cycle 5 (1995 December) and on C/1988 B1 (Shoemaker), C/1987 F1 (Torres), and C/1983 O1 (?ernis) during Cycle 6 (1997 April, May, and June). The HST comets were at heliocentric distances 20.4 < r[AU] < 29.5. Each comet observation was allocated 7 orbits, for ≈3.6 hrs of integration. The most difficult part of the image reduction was the removal of cosmic rays. We present our scheme for cosmic ray removal. None of the HST comet nuclei was detected to the 3-σ level at mR∼27. The inferred upper limits to the nucleus radii are . The SP comets range in radius between , with a median value of RN∼1.61 km. The LP comets ranged in size between <4.0-56 km. Over a range of radii between 1-10 km, the nuclei can be fit with a cumulative distribution N(>RN)∝RN−α with α=1.45±0.05, and for nuclei in the range 2-5 km, α=1.91±0.06. Statistical analysis and modeling shows that the slopes of the observed TNO and JF comet distributions are not compatible, suggesting that the intrinsic distribution of JF comet nuclei is a differential a−3.5 power law truncated at small nucleus radii between 0.3 and 2.0 km. 相似文献
10.
We present results from CCD observations of Comet 2P/Encke acquired at Steward Observatory's 2.3 m Bok Telescope on Kitt Peak. The observations were carried out in October 2002 when the comet was near aphelion. Rotational lightcurves in B-, V-, and R-filters were acquired over two nights of observations, and analysed to study the physical and color properties of the nucleus. The average apparent R-filter magnitude across both nights corresponds to a mean effective radius of 3.95±0.06 km, and this value is similar to that found for the V- and B-filters. Taking the observed brightness range, we obtain a/b?1.44±0.06 for the semi-axial ratio of Encke's nucleus. Applying the axial ratio to the R-filter photometry gives nucleus semi-axes of [3.60±0.09]×[5.20±0.13] km, using the empirically-derived albedo and phase coefficient. No coma or tail was seen despite deep imaging of the comet, and flux limits from potential unresolved coma do not exceed a few percent of the total measured flux, for standard coma models. This is consistent with many other published data sets taken when the comet was near aphelion. Our data includes the first detailed time series multi-color measurements of a cometary nucleus, and significant color variations were seen on October 3, though not repeated on October 4. The average color indices across both nights are: (V−R)=0.39±0.06 and (B−V)=0.73±0.06 (). We analysed the R-filter time-series photometry using the method of Harris et al. [Harris, A.W., Young, J.W., Bowell, E., Martin, L.J., Millis, R.L., Poutanen, M., Scaltriti, F., Zappala, V., Schober, H.J., Debehogne, H., Zeigler, K.W., 1989. Icarus 77, 171-186] to constrain the rotation period of the comet's nucleus, and find that a period of ∼11.45 h will satisfy the data, however the errors bars are large. We have successfully linked our data with the September 2002 data from Fernández et al. [Fernández, Y.R., Lowry, S.C., Weissman, P.R., Mueller, B.E.A., Samarasinha, N.H., Belton, M.J.S., Meech, K.J., 2005. Icarus 175, 194-214]—taken just 2-3 weeks before the current data set—and we show that a rotation period of just over 11 h works extremely well for the combined data set. The resulting best-fit period is 11.083±0.003 h, consistent with the Fernández et al. value. 相似文献
11.
Direct sublimation of a comet nucleus surface is usually considered to be the main source of gas in the coma of a comet. However, evidence from a number of comets including the recent spectacular images of Comet 103P/Hartley 2 by the EPOXI mission indicates that the nucleus alone may not be responsible for all, or possibly at times even most, of the total amount of gas seen in the coma. Indeed, the sublimation of icy grains, which have been injected into the coma, appears to constitute an important source. We use the fully-kinetic Direct Simulation Monte Carlo model of Tenishev et al. (Tenishev, V.M., Combi, M.R., Davidsson, B. [2008]. Astrophys. J., 685, 659?677; Tenishev, V.M., Combi, M.R., Rubin, M. [2011]. Astrophys. J., 732) to reproduce the measurements of column density and rotational temperature of water in Comet 73P-B/Schwassmann–Wachmann 3 obtained with a very high spatial resolution of ～30 km using IRCS/Subaru in May 2006 (Bonev, B.P., Mumma, M.J., Kawakita, H., Kobayashi, H., Villanueva, G.L. [2008]. Icarus, 196, 241?248). For gas released solely from the cometary nucleus at a heliocentric distance of 1 AU, modeled rotational temperatures start at 110 K close to the surface and decrease to only several tens of degrees by 10–20 nucleus radii. However, the measured decay of both rotational temperature and column density with distance from the nucleus is much slower than predicted by this simple model. The addition of a substantial (distributed) source of gas from icy grains in the model slows the decay in rotational temperature and provides a more gradual drop in column density profiles. Together with a contribution of rotational heating of water molecules by electrons, the combined effects allow a much better match to the IRCS/Subaru observations. From the spatial distributions of water abundance and temperature measured in 73P/SW3-B, we have identified and quantified multiple mechanisms of release. The application of this tool to other comets may permit such studies over a range of heliocentric and geocentric distances. 相似文献
12.
The results of the multiaperture photometry of Comet Shoemaker-Levy 1991 T2 in the pre-perihelion and P/deVico in the post-perihelion period with the narrowband CN, C2 and Blue Continuum (BC) IHW filters are presented. A Haser model of the molecular coma was used for the determination of the parent and daughter scale-lengths and production rates of the radicals. The comets showed some substantial differences between their parent scale-lengths. The CN parent scale-length (at 1.0 AU) was 16×103 km for Comet Shoemaker-Levy and 39×103 for P/deVico, the C2 parent scale-lengths were respectively 29×103 and 54×103 km. Such divergences could be interpreted in the frame of different scenarios of emission of cometary parents, either from a nucleus or from a volume source. The daughter scale-lengths for these comets were quite similar, namely: 306×103 and 318×103 km for CN and 69×103 and 66×103 km for C2. We determined the Afρ parameter for apertures of different radii. A Monte Carlo model of the dust coma was used to obtain the dust ejection velocity. It was of the order of 0.1 km s−1 for both comets. The power index of the distribution of the β-parameter of dust particles (ratio of light pressure to the solar gravitation) was of the order of 3 for C/Shoemaker-Levy and close to 2 for P/deVico. The dependence on heliocentric distance (rh) of the radical and dust production rates for P/deVico in the range of 0.7-1.0 AU was described by the power law function with a power index equal to: 5.55±0.14 for CN, 5.70±0.24 for C2 and 5.22±0.19 for dust. Relative abundances of the dynamically new Comet Shoemaker-Levy and short-period P/deVico were quite similar with an enhancement of C2 comparing with standard values taken from A'Hearn et al. (1995). 相似文献
13.
Comet Hale-Bopp was imaged at wavelengths from 1.87 to 2.22 μm by HST/NICMOS in post-perihelion observations starting on UT 1997 August 27.95. Diffraction-limited (∼02) images were obtained at high signal-to-noise (∼1500) to probe the composition and dynamics of the inner coma and also the size and activity of the nucleus. The velocities of several unusual morphological features over a 1.7 h period, indicate that a significant outburst occurred 7.4 h prior to these images while the comet was at a heliocentric distance of 2.49 AU. Similar features are also apparent after re-analysis of pre-perihelion ground-based images. The inner coma (radius ?2500 km) is dominated by an “arc” feature, which expanded and became more diffuse with time. This feature can be modeled as the bright central portion of a “jet of outburst” from a near-equatorial region of the nucleus. Less prominent, time-variable linear and circular morphologies are also apparent. The expansion rates of both the arc feature and the circular morphologies imply a common origin and also suggest a grain size distribution with two broad maxima. In addition, several static linear features extend to the edge of the field of view (21,100 km). Radial brightness profiles are highly asymmetric and only approach a ρ−1 decline at distances ?15,000 km. Images in a narrow-band filter at 2.04 μm exhibit a ∼4% absorption feature relative to nearly simultaneous images at wavelengths of 2.22, 1.90, and 1.87 μm. This absorption is attributed to H2O ice in the coma grains. The spatial distribution and expansion velocity of the absorption at 2.04 μm indicate that these grains are associated with the outburst. The constancy of the absorption feature indicates no appreciable sublimation over 1.7 h. The unresolved nucleus has a flux density consistent with a 40±10 km diameter assuming a 4% geometric albedo. 相似文献
14.
The target of the Deep Impact space mission (NASA), Comet 9P/Tempel 1, was observed from two nights before impact to eight nights after impact using the FORS spectrographs at the ESO VLT UT1 and UT2 telescopes. Low resolution optical long-slit spectra were obtained to study the evolution of the gas coma around the Deep Impact event. Following first results of this observing campaign on the CN and dust activity [Rauer, H., Weiler, M., Sterken, C., Jehin, E., Knollenberg, J., Hainaut, O., 2006. Astron. Astrophys. 459, 257-263], this work presents a study of the complete dataset on CN, C2, C3, and NH2 activity of Comet 9P/Tempel 1. An extended impact gas cloud was observed moving radially outwards. No compositional differences between this impact cloud and the undisturbed coma were found as far as the observed radicals are concerned. The gas production rates before and well after impact indicate no change in the cometary activity on an intermediate time scale. Over the observing period, the activity of Comet 9P/Tempel 1 was found to be related to the rotation of the cometary nucleus. The rotational lightcurve for different gaseous species provides indications for compositional differences among different parts of the nucleus surface. 相似文献
15.
O. Groussin P. Lamy M. Kelley M. A'Hearn J. Licandro S. Lowry C. Snodgrass 《Icarus》2009,199(2):568-1670
We detected the nucleus of Comet 22P/Kopff at 4.87 AU from the Sun with the two IRS peak-up cameras of the Spitzer Space Telescope on April 19, 2007. Using the thermal model of [Groussin, O., and 15 colleagues, 2007. Icarus 187, 16-25], we derive a nucleus size of 1.89±0.16 km, in agreement with [Lamy, P., Toth, I., Jorda, L., Groussin, O., A'Hearn, M.F., Weaver, H.A., 2002. Icarus 156, 442-455], and a thermal inertia . 相似文献
16.
CCD images of comet P/Grigg-Skjellerup, obtained for astrometric purposes with the 3.5 m telescope at the Calar Alto Observatory/Spain, were used for an analysis of the activity status of the nucleus and for a search of faint coma structures. The nucleus was found essentially inactive beyond 2.7 AU solar distance both inbound and outbound (observations on 12–13 August, 1986, 21–23 October, 1986, 22 August, 1988, 18 October, 1988, 9 and 12 September, 1991 and 3 December, 1991). The coma of the comet was well developed in May and July 1987 with a diameter of at least 190 000 km on 24 May, 1987 and of at least 80 000 km on 24 July 1987. The coma showed a cone of diffuse brightness enhancement in the sunward hemisphere. The orientation of the cone axis changed from the Sun direction in May 1987 towards about North in July 1987, i.e., it was almost perpendicular to the projected Sun-nucleus line on the sky. The cone opening angle became smaller from about 100 in May to about 50 in July 1987. A weak and narrow plasma tail was found in the images of May 1987. 相似文献
17.
Multiple non-resonance fluorescence lines of water (H2O) were detected in Comet 153/P Ikeya-Zhang (2002 C1) between UT 2002 March 21.9 (Rh=0.51 AU) and April 13.9 (Rh=0.78 AU), using the Cryogenic Echelle Spectrometer (CSHELL) at the NASA Infrared Telescope Facility. Analysis of 2.9-μm water lines enabled accurate determination of rotational temperatures on three dates. The derived H2O rotational temperatures were 138+6−5, 141+10−9, and 94±3 K on UT 2002 March 22.0, March 23.0, and April 13.8, respectively. Water production rates were retrieved from spectral lines measured in nineteen separate grating settings over seven observing periods. The derived heliocentric dependence of the water production rate was Q=(9.2±1.1)×1028[Rh(−3.21±0.26)] molecules s−1. The spatial distribution of H2O in the coma was consistent with its release directly from the nucleus (as a native source) on all dates. 相似文献
18.
Jian-Yang Li Michael F. A'Hearn Christopher J. Crockett Carey M. Lisse Lucy A. McFadden Jessica M. Sunshine Joe Veverka 《Icarus》2007,187(1):41-55
The photometric properties of the nucleus of Comet 9P/Tempel 1 are studied from the disk-resolved color images obtained by Deep Impact (DI). Comet Tempel 1 has typical photometric properties for comets and dark asteroids. The disk-integrated spectrum of the nucleus of Tempel 1 between 309 and 950 nm is linear without any features at the spectral resolution of the filtered images. At V-band, the red slope of the nucleus is 12.5±1% per 100 nm at 63° phase angle, translating to B-V=0.84±0.01, V-R=0.50±0.01, and R-I=0.49±0.02. No phase reddening is confirmed. The phase function of the nucleus of Tempel 1 is constructed from DI images and earlier ground-based observations found from the literature. The phase coefficient is determined to be β=0.046±0.007 mag/deg between 4° and 117° phase angle. Hapke's theoretical scattering model was used to model the photometric properties of this comet. Assuming a single Henyey-Greenstein function for the single-particle phase function, the asymmetry factor of Tempel 1 was fitted to be g=−0.49±0.02, and the corresponding single-scattering albedo (SSA) was modeled to be 0.039±0.005 at 550 nm wavelength. The SSA spectrum shows a similar linear slope to that of the disk-integrated spectrum. The roughness parameter is found to be 16°±8°, and independent of wavelength. The Minnaert k parameter is modeled to be 0.680±0.014. The photometric variations on Tempel 1 are relatively small compared to other comets and asteroids, with a ∼20% full width at half maximum of albedo variation histogram, and ∼3% for color. Roughness variations are evident in one small area, with a roughness parameter about twice the average and appearing to correlate with the complex morphological texture seen in high-resolution images. 相似文献
19.
Ignacio Ferrín 《Icarus》2007,187(1):326-331
In support of the Deep Impact Mission, we have updated the secular light curve of 9P/Tempel 1 presented in Paper I [Ferrín, I., 2005. Icarus 178, 493-516], with new data sets. The secular light curves (SLC) of the comet are presented in the log and time plots (Figs. 1 and 2) and provide a clear profile of the overall shape of the envelope. We arrive at the following conclusions: (1) Improved values of 18 photometric parameters are derived including the turn on and turn off points, RON=−3.47±0.05 AU, ROFF=+4.20±0.05 AU, and TON=−410±25 d, TOFF=+555±25 d. (2) The improved SLC shows a most interesting and peculiar shape, with a linear power law of slope n=7.7±0.1 from RON=−3.47 AU to RBP=−2.08±0.05 AU, and then converts to a law with curvature. The break point of the power law at RBP=−2.08 AU, mV(1,R)=14.0±0.1 mag, is interpreted as a change in sublimating something more volatile than water ice (most probably CO2), to water ice sublimation. In other words, the comet's sublimation is controlled by two different substances. (3) The photometric-age (defined in Paper I) and the time-age of the comet [Ferrín, I., 2006. Icarus. In press] are recomputed, and results in a value P-AGE=21±2 and T-AGE=11±2 comet years. Thus 9P is a young comet. (4) The comet is active almost up to aphelion since the turn off point has been determined at ROFF=+4.20±0.05 AU while aphelion takes place at Q=+4.74 AU. (5) The comet exhibits activity post-aphelion which is not understood. Two hypothesis are advanced to explain this behavior. 相似文献
20.
Broadband imaging of Comet 67P/Churyumov–Gerasimenko has provided more data on the characterisation of the target of the ESA
Rosetta Mission. The comet monitoring between r
h=2.37 and r
h=2.78 AU postperihelion shows a prominent dust coma which extends up to ≈ 25,000 km from the nucleus, and a long dust structure
in approximately anti-tail direction, reaching at least 230,000 km, identified as a neck-line structure. The non-isotropic
dust emission is detected from the structures in the inner coma, and it is reflected on the slope of linear fits of surface
brightness profiles vs. cometocentric projected distance in log–log representation as m ≈ 0.83−0.941. Besides the long dust spike at position angle of 295°, the morphological study of the dust coma confirms the
presence of two structures at position angles of
95 and
195° where the overabundance of dust can be as high as 50% at ρ ≤ 30,000 km. The A
f ρ parameter derived from our R broadband data is 26.0 and 29.8 cm at r
h=2.37 and 2.48 AU postperihelion. The dust reflectivity S′(λ), a measurement of the dust colour, is 0.061±0.019, a rather neutral colour. 相似文献