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1.
Comet Hale-Bopp is, without doubt, one of the most important objects for cometary science which has ever been observed. The light curve is well-observed from a heliocentric distance 7.2 AU and some information is available at distances as great as 17 AU. This allows the photometric evolution of the comet to be studied as different volatiles dominate the activity. Three different phases of activity are seen as the heliocentric distance reduces during 1996: the initial phase of very fast brightening, characterized by a r –5 law; a standstill in the light curve when the brightening law reduced to r –1, which coincides with the initiation of water sublimation at r ~ 4 AU; and a further phase of more rapid brightening with an r –3.5 law, similar to the mean for comets classed as fairly new, which initiated at r ~ 4 AU.  相似文献   

2.
Comet outburst activity and the structure of solar wind streams were compared on the basis of Pioneer 10, 11, Vela 3 and IMP 7, 8 measurements at the heliocentric distance r ≈ 1–6 AU. It is shown that the solar wind velocity waves which are evolving into corotating shock waves beyond the Earth orbit may be responsible for comet outburst activity. The correlation between variations of comet outburst activity with heliocentric distance and the behavior of the solar wind velocity waves is established. The closeness of the characteristic times for the velocity waves and comet outburst activity (7–8 days at r = 1 AU) as well as the simultaneous growth of both the characteristic times with r are noted. The observed distribution of the comet outburst activity parameters during the 11-year cycle is also in good agreement with the phase distributions during the 11-year cycle of variations of the coronal hole areas and the rate of change of the sunspot area δS p.  相似文献   

3.
Considerable interest has been raised by the discovery of Comet Hale-Bopp (1995 O1) and the possibility that it might become a very bright object in Spring 1997. The evidence to support either of the conflicting hypothesis (an intrinsically bright comet or a faint comet in a very large outburst) is too limited to reach solid conclusions and may remain so for some months yet. The pre-discovery observations encountered to date provide some limits to photometric models and suggest that the comet may be intrinsically bright, but do not yet permit a firm discrimination, even between extreme scenarios, due to the enormous extrapolation that must be made from the heliocentric distance at discovery, to that of perihelion.  相似文献   

4.
Lisse  C. M.  Fernández  Y. R.  A'hearn  M. F.  Kostiuk  T.  Livengood  T. A.  Käufl  H. U.  Hoffmann  W. F.  Dayal  A.  Ressler  M. E.  Hanner  M. S.  Fazio  G. G.  Hora  J. L.  Peschke  S. B.  Grün  E.  Deutsch  L. K. 《Earth, Moon, and Planets》1997,78(1-3):251-257
We present infrared imaging and photometry of the bright, giant comet C/1995 O1 (Hale-Bopp). The comet was observed in an extended infrared and optical observing campaign in 1996–1997. The infrared morphology of the comet was observed to change from the 6 to 8 jet “porcupine” structure in 1996 to the “pinwheel” structure seen in 1997; this has implications for the position of the rotational angular momentum vector. Long term light curves taken at 11.3 μm indicate a dust production rate that varies with heliocentric distance as ∶ r−1.4. Short term light curves taken at perihelion indicate a rotational periodicity of 11.3 hours and a projected dust outflow speed of ∶ 0.4 km s−1. The spectral energy distribution of the dust on October 31, 1996 is well modeled by a mixture of 70% silicaceous and 30% carbonaceous non-porous grains, with a small particle dominated size distribution like that seen for comet P/Halley (McDonnell et al., 1991), an overall dust production rate of 2 × 105 kg s−1, a dust-to-gas ratio of ∶5, and an albedo of 39%. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
We describe 5 to 18 μm broadband images and R ∼ 100 spectra of comet Hale-Bopp taken with SpectroCam-10 on the 5 m Hale telescope during six runs between 1996 June and 1997 April. Our data show the gradual warming of dust grains as the comet approached perihelion. In June, the 10 μm silicate emission feature was already stronger than observed in any other comet, and it increased to about 3 times the continuum level near perihelion. Spectral structure attributed to a crystalline olivine grain component remained relatively constant, but other features associated with pyroxenes appeared to vary with heliocentric distance. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

6.
We present observational data for two long-period and three dynamically new comets observed at heliocentric distances between 5.8 to 14.0 AU. All of the comets exhibited activity beyond the distance at which water ice sublimation can be significant. We have conducted experiments on gas-laden amorphous ice samples and show that considerable gas emission occurs when the ice is heated below the temperature of the amorphous-crystalline ice phase transition (T∼137 K). We propose that annealing of amorphous water ice is the driver of activity in comets as they first enter the inner Solar System. Experimental data show that large grains can be ejected at low velocity during annealing and that the rate of brightening of the comet should decrease as the heliocentric distance decreases. These results are consistent with both historical observations of distant comet activity and with the data presented here. If observations of the onset of activity in a dynamically new comet are ever made, the distance at which this occurs would be a sensitive indicator of the temperature at which the comet had formed or represents the maximum temperature that it has experienced. New surveys such as Pan STARRS, may be able to detect these comets while they are still inactive.  相似文献   

7.
The comet Hale-Bopp (C/1995 O1) has been observed in the infrared (1–2.5 μm) with the Nordic Optical Telescope (NOT) equipped with the Arcetri NICMOS3 camera (ARNICA). Two observational campaigns, each one lasting about one week, were made when the comet heliocentric distance was about 3 AU. The first campaign was at the end of August and the second at the end of September 1996. During both runs two major outbursts were observed, the more intense of them started the day before the beginning of the second run. In the images recorded during the first three nights (24.8–26.8 Sept.) of the second run a dust shell expanding in the northern quadrant with a projected velocity of 0.14–0.28 km/s is clearly evident. The dust production rate increased by at least a factor ≈3 at the time of the outburst. Also evident on the first night is a change in the IR color that is well correlated with the dust shell. This is an indication that the material released by the outburst has a different composition and/or size distribution than that in the “quiescent” dust coma. In this paper we present preliminary results about the evolution and the photometric characteristics of the dust shell. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
The object P/2010 TO20 LINEAR-Grauer, discovered at a heliocentric distance of over 5 AU, and at first classified as a Trojan, is now believed to be a comet. This paper reports special observations of the object that have allowed a significant refinement of its orbit and investigation of its dynamic evolution. It is shown that P/2010 TO20 LINEAR-Grauer is not a Trojan yet demonstrates unusual dynamic features. In particular, the object moves in a temporary satellite orbit relative to Jupiter over the observation interval. The comet has been in the Hill sphere for about two years and has made one revolution around the planet. The jovicentric distance function has two minima, and the smallest distance is 0.075 AU. Our estimates show that, with a probability of 0.76, the comet is likely to move in a Jupiter family orbit with a perihelion distance of less than 2.5 AU. The average time for such a transition is around forty thousand years.  相似文献   

9.
Presented here are results from photometric analysis on broadband images taken of comet 21P/Giacobini‐Zinner from May 24, 2011 to October 24, 2011. As the parent body of the Draconids, a meteor shower known for outbursting, 21P was studied for its dust production activity, Afρ, focusing on how it changes with heliocentric distance. An expected increase in dust production with a decrease in heliocentric distance was observed. The comet went from heliocentric distance of 3.05 –1.77 AU during the observed time that corresponded to an apparent magnitude of 19.61 to 15.72 and Afρ of 16.48 cm to 284.17 cm. These values can be extrapolated to estimate a peak Afρ value at perihelion of 3824 cm. The images were obtained using a 0.5‐meter f/8.1 Ritchey‐Chrétien telescope located in Mayhill, New Mexico.  相似文献   

10.
Despois  D. 《Earth, Moon, and Planets》1997,79(1-3):103-124
We present here a review of the radio observations of the remarkable comet Hale-Bopp C/1995 O1 in which most major radio astronomical facilities have been involved. These observations started in August 1995, soon after the discovery of the comet (it was then at ∼7 AU from the sun), and well before its perihelion on April 1st, 1997; they are still going on, hopefully up to end of 1998. Extended cartographies have been obtained using multibeam receivers and on-the-fly techniques. High spatial resolution (a few ″) has been achieved with interferometers. Submillimetric observations are playing an increasing role, and high resolution (R ∼ 106−107) spectroscopy of cometary lines is now performed from decimetric to submillimetric wavelengths. The number of species observed at radio wavelengths now reaches ∼28,when it was ∼14 for comet C/1996 B2 Hyakutake. Most of these species are parent molecules. However, ions have been observed for the first time at radio wavelengths, and their velocities measured. Several isotopic species (involving D,13C,34S,15N) have been sought, allowing isotopic enrichment determinations. The abundances of cometary molecules present many similarities and some differences with the abundances of interstellar molecules in regions where grain mantles are believed to be evaporated to the gas phase (hot cores, bipolar flows). They will be discussed for their implications on the origin of cometary ices and of comets themselves. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
Comet P/Halley has been observed during its approach to perihelion at heliocentric distancesR = 11.0 AU and R = 8.2 AU. No extended coma is seen and limits can be placed on the fraction of the total light contributed by coma. The brightness of the comet varies on a short time scale. The variations may be due to transient activity or to rotation of the irregular nucleus.  相似文献   

12.
Peschke  S. B.  Grün  E.  Böhnhardt  H.  Campins  H.  Osip  D. J.  Hanner  M. S.  Heinrichsen  I.  Knacke  R. F.  Leinert  Ch.  Lemke  D.  Stickel  M.  Lisse  C. M.  Sykes  M.  Zarnecki  J. 《Earth, Moon, and Planets》1997,78(1-3):299-304
Comet Hale-Bopp has been observed five times with ISOPHOT, the photometer on board the Infrared Space Observatory (ISO), four times before its perihelion passage at heliocentric distances of 4.92, 4.58, 2.93 and 2.81 AU, and at 3.91 AU postperihelion. Each time, multi-filter photometry covering the range between 3.6–175 μm with eight to ten filters was performed to sample the spectral energy distribution of the comet. These measurements were used to determine dust temperatures for the cometary coma. The evolution of the strength of the silicate feature can be followed in the data as well as the flux deficit at longer wavelengths. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

13.
We present 1- to 5-μm broadband and CVF images of comet Hale-Bopp taken 1997 February 10.5 UT, 50 days before perihelion. All the images exhibit a nonspherical coma with a bright “ridge” in the direction of the dust tail approximately 10″ from the coma. Synthetic aperture spectrophotometry implies that the optically important grains are of a radius ≤0.4 μm; smallest radius for any comet seen to date. The variation of the integrated surface brightness with radial distance from the coma (ρ) in all the images closely follows the “steady state” ρ−1 model for comet dust ablation (Gehrz and Ney, 1992). The near-infrared colors taken along the dust tail are not constant implying the dust grain properties vary with coma distance. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

14.
Weaver  H. A.  Brooke  T. Y.  Chin  G.  Kim  S. J.  Bockelée-Morvan  D.  Davies  J. K. 《Earth, Moon, and Planets》1997,78(1-3):71-80
High resolution (λ/δλ ∼ 20,000) spectra of comet C/1995 O1 (Hale-Bopp) in the 2–5 μm region were obtained during UT 2–5 March 1997 using CSHELL at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The heliocentric and geocentric distances of the comet were ∼1.1 AU and ∼1.5 AU,respectively. We detected emission lines of the gas-phase molecules H2O, 4, C2H6, C2H2, HCN, and CO and derived absolute production rates and relative abundances for all species. We also used the 2-dimensional nature of the CSHELL data to investigate the spatial distribution of the molecules and find evidence that CO was derived at least partly from an extended source in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
A class of comets, of which Comet Kohoutek (1973f) is typical, show total as well as monochromatic brightness asymmetries about perihelion. They are fainter after perihelion than before at the same heliocentric distance. A model of the cometary nucleus consisting of a growing non-volatile dust mantle surrounding a volatile icy core is used to discuss this phenomenon.Numerical results are obtained for Comet Kohoutek (1973f). It is found that dust mantles of thickness in the range of 10–75 cm can be grown by perihelion passage for various values of the thermal conductivity of the dust if there is no substantial dust blow-off by the sublimating volatiles.The thermal conductivity of the dust mantle is quite small and is dominated by radiative conductivity for heliocentric distances 2 AU. Since the radiative conductivity is larger for larger grain size, the thickest mantle corresponds to coarsest matrix.The strong insulation provided by the growing dust layer progressively suppresses the surface temperature of the volatile core below its quasi-equilibrium value had there been no mantle. As a consequence the production rate of the parent-molecules as well as the monochromatic brightness of their daughter products increases less steeply than in the mantleless case, as the comet approaches perihelion. Furthermore, there are significant monochromatic brightness asymmetries about perihelion, which are enhanced if there is a greater dust blow-off before perihelion than after, as is believed to be the case with Comet Kohoutek (1973f). Estimates of this asymmetry of 1 × 2 magnitudes for the OH brightness at a heliocentric distance × 1 AU are consistent with the rather limited observations.  相似文献   

16.
We systematically surveyed the orbits of short-period (SP) comets that show a large change of perihelion distance (q) between 1–2 AU (visible comets) and 4–5 AU (invisible comets) during 4400 years. The data are taken from Cosmo-DICE (Nakamura and Yoshikawa 1991a), which is a long-term orbital evolution project for SP comets. Recognizing that q is the most critical element for observability of comets, an invisibility factor (f), defined as the ratio of unobservable time span to observable span during 4400 years, is calculated for each of the large-q-change comets. A detection limit for each comet is obtained from the heliocentric distance at discovery and/or the absolute magnitude at recent apparitions. A mean f value for 35 SP comets with 2.9 J (J is the Tisserand's invariant) is found to be 19.8. This implies that for each visible SP comet of this J-range, at every epoch of time, there exist about 20 invisible comets near the capture orbits by Jupiter, under the assumptions of steady-state flux and ergodicity for the SP-comet population.  相似文献   

17.
This paper reports on the detection of a satellite around the principal nucleus of comet Hale-Bopp. As shown elsewhere, a successful morphological model for the comet's dust coma necessitates the postulation of overlapping jet activity from a comet pair. The satellite has been detected digitally on images taken with the Hubble Space Telescope's Wide Field Planetary Camera 2 in the planetary mode on five days in May–October 1996. An average satellite-to-primary signal ratio is 0.21 ± 0.03, which implies that the satellite is ∼30 km in diameter, assuming the main nucleus is ∼70 km across. To avoid collision, the separation distance must exceed 50–60 km at all times. The satellite's projected distances on the images vary from 160 to 210 km, or 0.06 to 0.10 arcsec. The satellite was not detected in October 1995, presumably because of its subpixel separation from the primary. The radius of the gravitational sphere of action of the principal nucleus 70 km in diameter is 370–540 km at perihelion, increasing linearly with the Sun's distance: the satellite appears to be in a fairly stable orbit. Its orbital period at ∼180 km is expected to be ∼2–3 days, much shorter than the intervals between the HST observations. If the main nucleus should be no more than 42 km across, Weaver et al.'s upper limit, the satellite's orbit could become unstable, with the object drifting away from the main nucleus after perihelion. Potentially relevant ground-based detections of close companions are reported. Efforts to determine the satellite's orbit and the total mass of the system will get under way in the near future. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

18.
McCARTHY  D.  STOLOVY  S.  KERN  S.  SCHNEIDER  G.  FERRO  A.  SPINRAD  H.  BLACK  J.  SMITH  B. 《Earth, Moon, and Planets》1997,78(1-3):243-249
Near-infrared images of comet Hale-Bopp (C/1995 O1) were obtained from NICMOS/HST on UT August 27–28, 1997, when the comet emerged from the 50 degree solar elongation limit at 2.99 AU from Earth. Diffraction-limited images were obtained with camera 2 filters centered at 1.87, 1.90, 2.04 and 2.22 μm with ∼0.2″ resolution (0.076″/pixel; 165 km/pixel). Over the 1.7-hour baseline of observation, a recent (<7 hours) outburst is seen in the form of an expanding spiral arm with a projected expansion velocity of ∼80 m/s. Other asymmetric features include a jet emanating from the nucleus and several static linear features. Comparisons of the flux distribution in the 2.04 and 2.22 μm filters indicate that the region near the nucleus exhibits a slight, ∼3%, water ice absorption. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
One of the goals of comet research is the determination of the chemical composition of the nucleus because it provides us with the clues about the composition of the nebula in which comet nuclei formed. It is well accepted that photo-chemical reactions must be considered to establish the abundances of mother molecules in the coma as they are released from the comet nucleus or from distributed dust sources in the coma. However, the mixing ratios of mother molecules in the coma changes with heliocentric distance. To obtain the abundances in the nucleus relative to those in the coma, we must turn our attention to the release rates of mother molecules from the nucleus as a function of heliocentric distance. For this purpose, we assume three sources for the coma gas: the surface of the nucleus (releasing mostly water vapor), the dust in the coma (the distributed source of several species released from dust particles), and the interior of the porous nucleus (the source of many species more volatile than water). The species diffusing from the interior of the nucleus are released by heat transported into the interior. Thus, the ratio of volatiles relative to water in the coma is a function of the heliocentric distance and provides important information about the chemical composition and structure of the nucleus. Our goal is to determine the abundance ratios of various mother molecules relative to water from many remote-sensing observations of the coma as a function of heliocentric distance. Comet Hale-Bopp is ideal for this purpose since it has been observed using instruments in many different wavelength regions over large ranges of heliocentric distances. The ratios of release rates of species into the coma are than modeled assuming various chemical compositions of the spinning nucleus as it moves from large heliocentric distance through perihelion. Since the heat flow into the nucleus will be different after perihelion from that before perihelion, we can also expect different gas release rates after perihelion compared to those observed before perihelion. Since not all the data are available yet, we report on progress of these calculations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

20.
Ignacio Ferrín 《Icarus》2005,178(2):493-516
We present the secular light curves of eight comets listed in the title. Two plots per comet are needed to study these objects: a reduced magnitude (to Δ=1 AU = geocentric distance) vs time, and a reduced magnitude vs LogR (R=heliocentric distance). A total of over 16 new parameters, are measured from both plots, and give an unprecedented amount of information to characterize these objects: the onset of sublimation (RON), the offset of sublimation (ROFF), the time lag at perihelion (LAG), the absolute magnitude (m(1,1)), the maximum magnitude at perihelion (mMAX(1,LAG)), the nuclear magnitudes (VN), the amplitude of the secular light curve (ASEC), plus several others, and the photometric functions needed to describe the envelope. The most significant findings of this investigation are: (a) The envelope of the observations is the best representation of the secular light curve. (b) The H10 photometric system is unable to explain the curves and a new set of photometric rules and functions is used. (c) Only four comets exhibit power laws in their secular light curves, and only partially: 1P, 19P, 21P, and 81P. All others have to be described by more complex functions. Of the four, three exhibit a break of the power law, requiring two laws pre-perihelion and one post-perihelion. The reason for this behavior is not understood. (d) We predict the existence of a photometric anomaly in the secular light curve of 67P/Churyumov-Gerasimenko, evidenced by a region of diminished activity from −119 to −6 days before perihelion, that might be interpreted as a topographic effect or the turn off of an active region. (e) We define a photometric parameter (P-AGE) that attempts to measure the relative age of a comet through the activity exhibited in the secular light curve. 81P/Wild 2 (a comet that has recently entered the inner Solar System) is confirmed as a young object, while 28P/Neujmin 1 is confirmed as a very old comet. (f) Arranging the comets by P-AGE also classifies them by shape. A preliminary classification is achieved. (g) The old controversy of what is a nuclear magnitude is clearly resolved.  相似文献   

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