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1.
Galdemard P. Lagage P. O. Dubreuil D. Jouan R. Masse P. Pantin E. Bockelée-Morvan D. 《Earth, Moon, and Planets》1997,78(1-3):271-277
Comet C/1995 O1 (Hale-Bopp) was observed with camiras, the Saclay mid-infrared camera, mounted on the Nordic Optical Telescope
(Roque de los Muchachos, La Palma), from April 14th to April 25th, 1997. This observing run was part of the European campaign
devoted to Hale-Bopp observations from the Canary Islands (PI R. West). camiras spectro-imaging capabilities, achieved with
a Circular Variable Filter (of spectral resolution R ≈ 50), were used to obtain spectra of the comet in the N atmospheric
window (8–13 μm) over a large field of view (52″ × 78″), at a spatial resolution of ∼1 arcsec. Data were also collected at
shorter wavelengths (in the L and M bands). The silicate dust feature around 10 μm is clearly apparent in the data. The shape
of the feature varies continuously according to the position in the field. A dust model developed at Saclay in the framework
of β-Pictoris dust disk studies was used to interpret the observations. The presence of both olivine and pyroxene with a high
degree of crystallinity is needed to account for the observations. A change in the size distribution of the grains allows
to reproduce the spatial change of the silicate feature according to the position in the field.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
During our monitoring observations of comet Hale-Bopp, we found several sporadic ejections of dust from the nucleus. The most
prominent ejection was observed on May 6–9, 1997, in the post-perihelion phase of the apparition. In this paper, we report
preliminary analysis of this event, in which the total mass of the dust cloud is estimated to be 1.6 × 1011 g.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
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
4.
Hitoshi Hasegawa Takashi Ichikawa Shinsuke Abe Shiomo Hamamura Koji Ohnishi Jun-Ich Watanabe 《Earth, Moon, and Planets》1997,78(1-3):353-358
Near-infrared photometric and polarimetric observations of comet Hale-Bopp (1995 O1) using KONIC (Kiso Observatory Near-Infrared
Camera) are reported. Observations were carried out on March 18 UT and April 26 UT 1997, when the heliocentric distances of
the comet were 0.94 and 1.02 AU, and the phase angles were 48.5 deg and 32.9 deg, respectively. In the J, H, and K′ bands,
we obtained linear polarization of the near-nucleus region of 16.4 ± 1.2, 18.8 ± 1.3, and 15.1 ± 0.9 percent on March 18UT
and 7.1 ± 1.1, 8.9 ± 1.0, and 6.9 ± 0.6 percent on April 26, respectively. These values were higher than those observed for
1P/Halley. The maximum polarization was found at H band on both dates. Polarization maps showed higher polarization regions
toward the anti-solar direction in the J and H bands. No distinct correlation was found between high polarization regions
and bright regions. The projected expansion velocity of the arc structure of the dust jet was 375 ± 35.7 m/s on 17–19 March.
The periodicity was found to be 11.1 ± 2.8 hours.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Polarimetric observations of the light scattered by dust have been carried out at Pic-du-Midi Observatory with the 2 m telescope
in June and September–October 1996, and at Haute-Provence Observatory with the 0.80 m telescope in April 1997. They cover
a total number of 11 nights and a large (6.9°–47.7°) phase angle range. The spatial resolution allows to underline structures
in the coma, as well in the brightness images as in the polarization maps, with a correlation between the regions of bright
structures and the regions of higher polarization. A clear difference appears between the sunward and antisunward side, with
higher polarization on the antisunward side. The phase angle coverage allows us to obtain a polarimetric phase curve for the
whole coma and to compare it with other cometary phase curves. The degree of polarization is higher for Hale-Bopp than for
the comets previously observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
On March 31 and April 1, 1997, simultaneous photometry and polarimetry of comet Hale-Bopp's dust was conducted with the two-channel
focal reducer of the Max-Planck-Institute for Aeronomy attached to the 2 m telescope of Pik Terskol Observatory (Northern
Caucasus). Interference filters at642 nm and 443 nm selected red and blue narrow-band continuum windows. The observations
have been averaged over the one hour of timethe comet could be observed. The polarization maps cover an area of about1 arcmin2 around the nucleus. The values of polarization degree measured close to the nucleus agree very well with observations obtained
with aperture polarimetry. They are lower than in the surrounding coma by about 1%. In our field of view the polarization
increases along the sun-comet line from the solar to the antisolar side by about 3%. The dust shells are visible in the polarization
images. The polarization in the shells is higher by 1 to 2%and this increase is higher in the red than in the blue range.
Therefore the ratio of red to blue polarization (≈ 1.2) increases in the shells by ≈ 0.03. In principle, the polarization
excess in the shells, the ratio of red/blue polarization and the higher integrated polarization as compared to other comets
can be explained by an excess of particles of radius of about 0.1 μm. Such particles, however, are subject to strong radiation
pressure and will be pushed back into the tail before they reach the observed location of the shells. Real Rayleigh particles
cannot explain the observed increase in the ratio of red/blue polarization. One therefore cannot exclude the possibility that
the excess polarization in the shells is caused by fluffy aggregates via effects which are presently not well understood.
The colour map shows features not well related to intensity and polarization, perhaps another dust shell of a different particle
size.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
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
8.
Korsun P. P. Davis S. P. Shavrina A. V. Vasiljeva I. E. Malanushenko V. P. Savanov I. S. 《Earth, Moon, and Planets》1997,78(1-3):119-125
Spectroscopic observations of Comet Hale-Bopp were made at the 2.6 m Shajn Telescope of the Crimean Astrophysical Observatory. Some spectra were obtained with high spectral resolution, FWHM = 0.18–0.4Å, in the coude focus on February 22 and 26, 1997. The observations were made in selected spectral windows (4805–4872 Å,6528–6595 Å, 7186–7253 Å, 8276–8408 Å).The spectrograph slit was centered on the nucleus and had dimensions of 25.2 × 0.6 arcsec2 on the plane of the sky. The continuum spatial profiles were extremely asymmetrical toward the Sun. However, the continuum-subtracted spatial profiles of the molecular emissions were symmetrical relative to the nucleus, except for C2. The shape of the spatial profiles of the C2 emissions is similar to that one of continuum but is more flattened. So, there are evidences that dust can be an additional source of the C2 radicals in the cometary coma. The main aim of our research was identification of the cometary emissions. Using recent laboratory spectroscopic data we identified newlines of C2 associated with the transitions from high rotational levels in the 4805–4872 Å spectral region. We detected cometary Hα emission as well. Emissions of NH2, H2O+,and C2 (Phillips system) were found in the red spectral windows. Some emission features are still unassigned. 相似文献
9.
A Monte Carlo image simulation code for dust features in comets is applied to comet Hale-Bopp in order to model the object's
persistent porcupine-like appearance on high-resolution images taken between May 11 and Nov. 2, 1996. A self-consistent fan
model is proposed, with six isolated sources of dust emission assumed at various locations on the surface of the rotating
nucleus and with the spin axis undergoing a complex motion in an inertial coordinate system. In the framework of this model,
jet pairs represent boundaries of fan-shaped formations described by dust ejected from isolated sources during periods of
time when the Sun is above the local horizon. The spin axis is found to have traveled through a field of 10° by 20° during
the examined period of nearly six months. Still more successful is a fan model with large diurnal dust-emission fluctuations,
which is consistent with an inertially fixed position of the spin axis and requires only three discrete sources. In this scenario,
the dust-emission profile is dominated by several brief flare-ups, or “puffs”, in the production of dust from one of the sources.
The results are insensitive to the spin rate, but the observed dust coma appearance is more typical of a rapidly rotating
comet.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Pittichovâ J. Sekenina Z. Birkle K. Boehnhardt J. Engels D. Keller P. 《Earth, Moon, and Planets》1997,78(1-3):329-338
The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images
of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring
outbursts with a periodicity of 11h21m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one
source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion.
The parent particles were subjected to a radiation pressure acceleration of βp ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized
to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows
even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
Infrared observations of comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp) benefited from the high spectral resolution
and sensitivity of échelle spectrometers now equipping ground-based telescopes and from the availability of the Infrared Space
Observatory (ISO).
From the ground, several hydrocarbons were unambiguously detected for the first time: CH4, C2H2, C2H6. Water was observed through several of its hot vibrational bands, escaping telluric absorption. CO, HCN, NH3 and OCS were also observed, as well as several radicals. This permitted the evaluation of molecular production rates, of
rotational temperature, and — taking advantage of the 1-D imaging of long-slit spectroscopy — of the space distribution of
these species. With ISO, carbon dioxide was directly observed for the second time in a comet (after its detection from the
Vega probes in P/Halley). The spectrum of water was investigated in detail (several bands of vibration and far-infrared rotational
lines), permitting the evaluation of the rotational temperature of water, and of it spin temperature from the ortho-to-para
ratio. Water ice was identified in the grains of Hale-Bopp as far as 7 AU from the ground and possibly at 3 AU with ISO. The
composition of cometary volatiles appears to be strikingly similar to that of interstellar ices.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
Mark R. Kidger 《Earth, Moon, and Planets》1996,73(1):15-22
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
13.
Sekanina and Farrell's model for the striated dust tails of comets describes the formation of striae as a two-step fragmentation
process that is characterized by an ejection time te of parent particles, by their radiation pressure acceleration βp, and by their fragmentation time tf. Of these three, tf is the weakest parameter in that a range oftf offers a set of nearly equivalent solutions. In this context, we comment on Nishioka et al.'s finite-lifetime model, which
is a modification of the fragmentation model. We propose a truncated Gaussian function as a first-approximation distribution
law for particle fragmentation times. We apply this generalized model to a stria in comet Hale-Bopp detected on March 5–15,
1997 and analyzed by Pittichová et al. in a recent paper. We find that in order to fit the stria's estimated width of ∼150
000 km, the fragmentation times cannot be distributed over a period of more than approximately 2 to 3 days.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
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
15.
16.
17.
The polarization distribution of the inner coma of comet Hale-Bopp was measured by CCD imaging around perihelion. The dust
shell positions correlate well with relative maxima of polarization. The images taken in the I-band identify different shell
systems, each showing individual polarization properties. This could be related to differences in the dust properties of the
associated jets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
BRAUNSTEIN M. COMSTOCK R. HOFFMAN P. WOMACK M. DEGLMAN F. PINNICK D. AAKER G. GOLDSCHEN M. JACOBSON A. ZILKA J. FAITH D. MOORE S. RICOTTA J. WEIST A. MODI C. 《Earth, Moon, and Planets》1997,78(1-3):219-227
An optical archive of comet Hale-Bopp was obtained over 28 nights from June 1996 to May 1997 covering a range of heliocentric
distances of r = 4.12 − 0.91. The CCD images were obtained with the 0.8-m University of Washington Manastash Ridge Observatory
and the 0.25-m Pennsylvania State University at Eriemobile observatory. The reduced images clearly document the evolution
of features of the coma, which were dominated by radial jetsfrom r = 4.1 − 2.3 AU, curved fan-shaped jets from r = 1.2 − 1.0
AU, and arcs or shells for 0.9 < r < 1.0 AU. We present the images and derive an average dust expansion velocity of Vdust = 0.67 ± 0.07 km s−1 from measurements of the arc features. The images in thearchive will be made available to other researchers for further study.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Earth, Moon, and Planets - Comet Hale-Bopp has shown an extremely elevated level of dust activity during its apparition. We examine the dust activity of the comet, particularly the dust jets which... 相似文献
20.
LAFFONT CÉLINE ROUSSELOT P. CLAIREMIDI J. MOREELS G. BOICE D. C. 《Earth, Moon, and Planets》1997,78(1-3):211-217
An observation program for measuring the activity of Comet Hale-Bopp was conducted at the Observatoire de Haute Provence from
August 1996 to April 1997. Narrow band images were obtained from the 120 cm telescope. A set of four filters at 513, 516,
527 and 682 nm was used to measure the C2 emission in the (1,1) and (0,0) band and the intensity of the dust-scattered continuum. The luminosity of the central part
of the coma was measured in the continuum and C2 emissions, as a function of heliocentric distance before perihelion. The activity of the comet considerably increased between
October 1996 and February 1997. The images obtained in August, September and October 1996 show the presence of strong jets.
In February, March and April 1997, series of roughly concentric arcs were observed in the sunward hemisphere of the coma.
The arcs were also detected in the spatial distribution of the I(682 nm)/I(527 nm) red color ratio and the I(513 nm)/I(516
nm) C2 emission ratio. Using the I(513 nm)/I(516 nm) ratio as a parameter to measure the degree of excitation of C2 molecules, we can show that the local production of gas, probably resulting from dust fragmentation, should be taken into
account.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献