共查询到20条相似文献,搜索用时 437 毫秒
1.
Harker David E. Woodward Charles E. McMURTRY Craig W. Goetz J. A. Pipher J. L. Forrest W. J. 《Earth, Moon, and Planets》1997,78(1-3):259-264
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
2.
Hanner M. S. Gehrz R. D. Harker D. E. Hayward T. L. Lynch D. K. Mason C. C. Russell R. W. Williams D. M. Wooden D. H. Woodward C. E. 《Earth, Moon, and Planets》1997,79(1-3):247-264
The dust coma of comet Hale-Bopp was observed in the thermal infrared over a wide range in solar heating (R = 4.9–0.9 AU)
and over the full wavelength range from 3 μm to 160 μm. Unusual early activity produced an extensive coma containing small
warm refractory grains; already at 4.9 AU, the 10 μm silicate emission feature was strong and the color temperature was 30%
above the equilibrium blackbody temperature. Near perihelion the high color temperature, strong silicate feature, and high
albedo indicated a smaller mean grain size than in other comets. The 8–13 μm spectra revealed a silicate emission feature
similar in shape to that seen in P/Halley and several new and long period comets. Detailed spectral structure in the feature
was consistent over time and with different instruments; the main peaks occur at 9.3, 10.0 and 11.2 μm. These peaks can be
identified with olivine and pyroxene minerals, linking the comet dust to the anhydrous chondritic aggregate interplanetary
dust particles. Spectra at 16–40 μm taken with the ISO SWS displayed pronounced emission peaks due to Mg-rich crystalline
olivine, consistent with the 11.2 μm peak.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Wooden Diane H. Harker David E. Woodward Charles E. Koike Chiyoe Butner Harold M 《Earth, Moon, and Planets》1997,78(1-3):285-291
The NASA Ames HIFOGS spectrometer observed comet C/1995 O1 (Hale-Bopp) at epochs including 96 Oct 7–14 UT (2.8 AU), 97 Feb
14–15 UT (1.2 AU), 97 Apr 11 UT (0.93 AU), and 97 Jun 22, 25 UT (1.7 AU). The HIFOGS 7.5–13.5 μm spectrophotometry (R = 360
- 180) of the silicate feature at 2.8 AU is identical in shape to the ISO SWS spectra of comet Hale-Bopp (Crovisier et al.,
1997); the strong 11.2 μm peak in the structured silicate feature is identified as olivine. Upon close passage to the sun,
the HIFOGS spectra at 1.2 AU and 0.93 AU reveals strong peaks at 9.3 μm and 10.0 μm. The post-perihelion 10 μm silicate feature
at 1.7 AU is weaker but has nearly the same shape as the pre-perihelion spectra at 1.2 AU, reverting to its pre-perihelion
shape: there is no change in the dust chemistry by close passage to the sun. The appearance of the strong peaks at 9.3 μm
and 10.0 μm at rh ≲ 1.7 AU is attributed to the rise in the contribution of pryoxenes (clino-pyroxene and orthopyroxene crystals) to the shape
of the feature, and leads to the hypothesis that the pyroxenes are significantly cooler than the olivines. The pyroxenes are
radiating on the Wien side of the blackbody at 2.8 AU and transition to the Rayleigh-Jeans tail of the blackbody upon closer
approach to the Sun. Composite fits to the observed 10 μm silicate features using IDPs and laboratory minerals shows that
a good empirical fit to the spectra is obtained when the pryoxenes are about 150 K cooler than the olivines. The pyroxenes,
because they are cooler and contribute signficantly at perihelion, are more abundant than the olivines. The perihelion temperature
of the pyroxenes implies that the pyroxenes are more Mg-rich than the other minerals including the olivines, amorphous olivines,
and amorphous pyroxenes. The PUMA-1 flyby measurements of comet P/Halley also indicated an overabundance of Mg-rich pryoxenes
compared to olivines. Comet Hale-Bopp's pyroxenes are similar to pyroxere IDPs from the ’Spray‘ class, known for their D-richness
and their unaltered morphologies: Hale-Bopp's Mg-rich pyroxenes may be pristine relic ISM grains.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
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
5.
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
6.
Krzysztof Ziolkowski 《Earth, Moon, and Planets》1995,68(1-3):647-651
A supposition about the common origin of some cometary and asteroidal members of the Taurid complex is analyzed on the basis of their orbital evolution. It is shown that moments, in which the longitudes of perihelion of comet P/Encke, object (2201) Oljato and six other near-Earth asteroids amount to the value of longitude of perihelion of comet 1967 II Rudnicki, are close to the moment of previous perihelion passage of this long-period comet. Although the conjecture about the membership of comet Rudnicki in the Taurid complex is controversial one, nevertheless the presented results seem to be interesting in itself, and yield a contribution in favour of the hypothesis of the breakup of a giant comet some 104 – 105 years ago in the inner Solar System. 相似文献
7.
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
8.
We present a light curve of C/1995 O1 (Hale-Bopp) compiledfrom more than 3000 visual observations of the comet made by members
of the The Astronomer Group world-wide. These observations cover the period from discovery through to the end of 1997. The
light curve shows that the rate of brightening of the comet varied widely at different times, with rapid rates of brightening
at high heliocentric distance pre-perhelion and a comparably rapid post-perihelion fade. There is no evidence that the comet
was suffering a large photometric outburst when first discovered, although a small outburst can be identified at perihelion.
At least five difficult brightening regimes can be identified in the light curve between discovery and perihelion. From 2.5
AU to perihelion the rate of brightening with decreasing heliocentric distance was typical for “fairly” new comets(n ∼ 3.5,
where “n” is the power law exponent of the heliocentric distance), although this was preceded by a period of very slow brightening
with n ∼ 1 from r ∼ 4.0 AU to r ∼ 2.8 AU and followed by an initially more rapid brightening which appears to be related to
the on-set of rapid water sublimation activity. We derive the light curve parameters at different stages of the comet's apparition.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Chandrasekhar T. Ashok N. M. Tej Anandamayee Mondal Soumen Watson P. V. 《Earth, Moon, and Planets》1998,81(2):111-121
During the recent apparition of comet Hale—Bopp (1995 O1) near infrared photometric observations were carried out in the J,
H, K filter bands and also in the 3.0—3.4 μm region at the 1.2 m telescope at Gurushikkar, India. The effective temperature
of the comet was substantially higher than the equilibrium blackbody temperature. A mean superheat value of 1.83 was derived
in the post-perihelion phase which implies that a large fraction of the grain population are made up of small and hot grains
with radii <0.5 μm. High albedo values of ∼0.4 were also derived in the scattering angle range 135° to 160° which could explain
the unusual brightness of comet Hale—Bopp.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
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
11.
Brian M. Cudnik 《Planetary and Space Science》2005,53(6):653-658
Hale-Bopp (C/1995 O1) was the most productive recent comet observed in terms of gas and dust output. Since its discovery in 1995 at a distance of 7.14 AU from the Sun, the comet has been well observed, revealing the dynamics of a rare and large comet. Hale-Bopp showed strong emissions of the principle cometary gases CN, C3, and C2, as well as an abundance of dust. The production rates of these gases were found to be 1.45×1028, 1.71×1028, and , respectively, with dust production, in terms of Afρ, , as measured in the green continuum (5260 Å). The observations for this paper are presented in two groups spanning 10 days each, one group centered near 32 days prior to and the other 21 days after perihelion. The averages of dust and gas production rates show a slightly higher value for each prior to perihelion than after perihelion, consistent with a possible peak in production a few weeks prior to perihelion passage. 相似文献
12.
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
13.
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
14.
Comet 81P/Wild 2 was observed in the thermal infrared over 6 months during its 1997 perihelion passage. The comet was most active in late February, about 3 months preperihelion; dust production declined by a factor of 3 between February and August. For the GIOTTO Halley dust size distribution, maximum dust production rate was ∼2 × 106 g/s. The comet displayed a 10-μm silicate feature about 25% above the continuum, similar to several other Jupiter-family comets, but much lower than that seen in a number of Oort cloud comets.NASA’s STARDUST sample return mission will encounter P/Wild 2 98 days postperihelion in January 2004. Based on our observations at a similar point in the orbit and the Halley size distribution, we predict that the mass fluence on the spacecraft for a 150 km miss distance will be about 8 × 10−6 g/cm2 for particles up to 1 cm in radius. The corresponding areal coverage will be about 10−4. 相似文献
15.
The evolution of the perihelion distance distribution in the Oort cloud was studied over the age of the solar system, under the gravitational perturbations of random passing stars, using a statistical approach. These perturbations are accounted for through an empirical relation relating the change in cometary perihelion distance to the closest-approach comet-star distance; this relation is deduced from a previous study [H. Scholl, A. Cazenave, and A. Brahic, Astron. Astrophys.112, 157–166 (1982)]. Two kinds of initial perihelion distances are considered: (a) perihelion distances <2500 AU, associated with an origin of comets as icy planetesimals in the region of the giant planets, and (b) larger perihelion distances (up to 5 × 104 AU), possibly representative of comet formation as satellite fragments in the accretion disk of the primitive solar nebula. Distant star-comet encounters, as well as rare close encounters, are considered. Several quantities are estimated: (i) number of “new” comets entering into the planetary region, (ii) number of comets escaping the Sun sphere of influence or lost by hyperbolic ejection and (iii) percentage of total comet loss over the age of the solar system. From these quantities, the current and original cloud populations are deduced, as well as the corresponding cloud mass, for the two types of formation scenarios. 相似文献
16.
Woodward Charles E. Gehrz R. D. Mason C. G. Jones T. J. Williams D. M. 《Earth, Moon, and Planets》1998,81(3):217-222
Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed
to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2–18.5 μm infrared (IR) spectrophotometric
and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization
near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron
sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather
than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = Tcolor/TBB ≥ 1.7, the peak of the 10 μm silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity)
of the grains was ≥ 0.4 at a scattering angles, θ ≥ 135°
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Estimating the Size of Hale-Bopp's Nucleus 总被引:1,自引:0,他引:1
A variety of independent methods have been used to estimate the size of the nucleus of comet Hale-Bopp. Several groups have
analyzed optical and infrared images of the comet and claim to detect the signature of the nucleus, despite the presence of
a strong coma. A detection of the nucleus was also claimed during mm- and cm-wave observations of Hale-Bopp shortly before
perihelion. A team of observers detected the occultation of a star by the nucleus of Hale-Bopp in October 1996. The maximum
observed gas production rate of the comet near perihelion can be used to place a lower limit on the size of the nucleus. This
paper critically reviews the many different methods used to constrain the size of Hale-Bopp's nucleus. All of the techniques
are affected by systematic errors that can be difficult to quantify precisely. Nevertheless, the available evidence strongly
suggests that the nucleus of Hale-Bopp has an effective radius of at least 15 km and is probably in the range 20–35 km. Thus,
the prodigious gas and production rates from this comet are naturally explained by its unusually large size.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
The paper presents the results of dynamic simulation for the dust tail formation of comet C/1995 O1 (Hale-Bopp). To simulate
the dust tail, the trajectories of 2 × 106 dust particles were traced. The sizes, ejection moments, outflow directions and velocities of the dust particles were defined
by the Monte Carlo algorithm. The obtained three-dimensional tail was projected on the sky plane to compare it with the observed
images. The brightness distribution in the comet tail was fitted to similar model parameters for three different dates. According
to our model experiments, the observed tails could be formed by particles with sizes from 0.3 to 8.0 μm, ejection velocities
from 0.155 to 0.670 km/s, and power index of the exponential size distribution from −3.6 to −3.7. It is shown that the inclusion
of the particles fragmentation processes leads to a noticeable improvement of the simulation results. 相似文献
19.
SANTOS-SANZ P. SABALISCK N. KIDGER M. R. LICANDRO J. SERRA-RICART M. BELLOT RUBIO L. R. CASAS R. GOMEZ A. SANCHEZ PORTERO J. OSIP D. 《Earth, Moon, and Planets》1997,78(1-3):235-241
We present a comparison between images of comet C/1995 O1 (Hale-Bopp) obtained from 12 March to 9 May 1997, with two telescopes
of the Observatorio del Teide (IAC, Tenerife, Spain) in visible (Johnson-V filter) and three near-infrared narrowband filters
(Brγ (2.166 μm), CO (2.295 μm), and Kcon (2.260 μm)). No significant differences are observed between the images in the three near-infrared bands suggesting that
any CO emission is very weak, or produced by an extended flat source. We do not find evidence for the existence of an additional
infrared component due to emission by warm dust, or to dust grains of diverse composition and/or size. Visible and infrared
images of the same rotational phase look almost identical, supporting the view that the observed jets and shells are mainly
dust structures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
We present results of polarimetric and photometric observations of bright comet C/1995 O1 (Hale-Bopp) obtained at the 0.7
m telescope of Kharkov University Observatory from June 18, 1996 to April 24, 1997. The IHW and HB comet filters were used.
The C2 and C3 production rates for Hale-Bopp are more than one order of magnitude larger and the dust production rates are more than two
orders of magnitude larger than the Halley ones at comparable distances. Hence, Hale-Bopp was one of the most dusty comets.
The average UC-BC and BC-RC colours of the dust were −0.02 and 0.13 mag, respectively. The polarization of comet Hale-Bopp
at small phase angles of 4.8–13.0° was in good agreement with the date for comet P1/Halley at the same phase angles in spite
of the fact that the heliocentric distances of comments differed nearly twice. However, at intermediate phase angles of 34–49°
the polarization of comet Hale-Bopp was significantly larger than the polarization of the other dusty comets. It is the first
case of such a large difference found in the continuum polarization of comets. The wavelength dependence of polarization for
Hale-Bopp was steeper than for other dusty comets. The observed degree of polarization for the anti-sunward side of the coma
was permanently higher than that for the sunward shell side. The polarization phase dependence of Hale-Bopp is discussed and
compared with the polarization curves for other dusty comets. The peculiar polarimetric properties of comet Hale-Bopp are
most likely caused by an over-abundance of small or/and absorbing dust particles in the coma.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献