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1.
A very long series of photographic observations of the comet Hale-Bopp has been made during January–April 1997 at the double
astrograph (400/2000) of the Main Astronomical Observatory (Kyiv, Ukraine). Some of the cometary photos were obtained with
two wide-band filter combinations. One of these combinations isolates C2 emission, another — the nearby dust continuum. The images were digitized by means of AMDPH-XY machine and then calibrated
following the standard procedure. After subtraction of the dust continuum the distribution of surface brightness in the C2 emission coma of comet Hale-Bopp was studied. We found an asymmetric brightness distribution both pre- and post-perihelion.
On 21.77 April 1997 a secondary brightness peak is found at the distance of 1.03 × 105 km from the nucleus. It is possible that this peak is related to the extended source of the C2 molecules.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Lisse C. M. Dennerl K. Englhauser J. Trümper J. Marshall F. E. Petre R. Valinia A. Kellett B. J. Bingham R. 《Earth, Moon, and Planets》1997,77(3):283-291
The discovery of X-ray emission from comets has created a number of questions about the physical mechanism producing the radiation.
There are now a variety of explanations for the emission, from thermal bremsstrahlung of electrons off neutrals or dust, to
charge exchange induced emission from solar wind ions, to scattering of solar X-rays from attogram dust, to reconnection of
solar magnetic field lines. In an effort to understand this new phenomenon, we observed but failed to detect in the X-ray
the very dusty and active comet C/Hale-Bopp 1995 O1 over a two year period, September 1996 to December 1997, using the ROSAT
HRI imaging photometer at 0.1–2.0 keV and the ASCA SIS imaging spectrometer at 0.5–10.0 keV. The results of our Hale-Bopp
non-detections, when combined with spectroscopic imaging 0.08–1.0 keV observations of the comet by EUVE and BeppoSAX, show
that the emission has the same spectral shape and strong variability seen in other comets. Comparison of the ROSAT photometry
of the comet to our ROSAT database of 8 comets strongly suggests that the overall X-ray faintness of the comet was due to
an emission mechanism coupled to gas, and not dust, in the comet’s coma.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
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
4.
Samarasinha Nalin H. Mueller Béatrice E. a. Belton Michael J. S. 《Earth, Moon, and Planets》1997,77(3):189-198
We present constraints on the spin state of comet Hale-Bopp based on coma morphology. Three cases of rotational states are
compatible with near perihelion observations: (1) principal-axis rotation, (2) complex rotational state with a small precessional
angle, or (3) complex rotational state with a large ratio between the component periods. For principal axis rotators, images
from 1996 (pre-perihelion) are consistent with a rotational angular momentum vector, M, directed at ecliptic longitude and
latitude (250°, -5°) while images from late 1997 (post-perihelion) indicate (310°, -40°). This may suggest a change in M.
A complex rotational state with small precessional angle requires only a small or no change in M over the active orbital arc.
In this case, M is directed near ecliptic longitude and latitude (270°, -20°). A rotationally excited nucleus with a large
ratio between component periods requires the nucleus to be nearly spherical. The transformation of dust coma morphology from
near-radial jets to bright arcs and then again to near-radial jets is interpreted as a heliocentric and geocentric distance
dependent evolutionary sequence. The spiral structures seen in CN filters near perihelion (in contrast to sunward side arcs
seen in continuum) can be explained if the precursor of CN molecules (likely sub-micron grains) are emitted from the nucleus
at low levels (≈ 10% of the peak daytime emission) during the nighttime. This may be indicative of a nucleus with a CO-rich
active area(s).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
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
6.
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
7.
Between July 1996 and April 1997, 92 spectra of comet Hale-Bopp were obtained with the 6-meter BTA telescope of the SAO of
the RAS at Mount Pastukhov. The spectra are two-dimensional, which allows one to determine the energy distribution for each
emission along the slit and the energy distribution in wavelength for each individual position in the slit. From the 92 two-dimensional
spectra covering the inner coma, detailed spectral maps of the total near-nuclear region of the comet are available for July
10, 11 and 12, 1996 and April 15, 1997. We propose an hypothesis about an unknown cometary species near λ = 620 nm in the
spectrum obtained July 10, 1996. We also find an effect which may be caused by fluorescence of cometary dust.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
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
9.
Warell Johan LAGERKVIST CLAES-INGVAR Lageros JOHAN S. V. 《Earth, Moon, and Planets》1997,78(1-3):197-203
Dust continuum imaging of comet C/1995 O1 (Hale-Bopp) was carried out with the Swedish Vacuum Solar Telescope (SVST)on La
Palma in April, 1997. Images were reduced according to standard procedure, aligned, averaged, navigated and enhanced with
azimuthal renormalization, rotational derivative, temporal derivative and unsharp masking processing.
The rotational period of the nucleus was determined to 11.5 h and the mean projected dust outflow velocity to 0.41 km s−1. Shell envelopes in the sunward side of the coma were separated by a projected distance of ∼15 000–20 000 km and spiralling
inwards towards smaller radii in the direction of local evening. Small scale inhomogeneities of size 1 000–2 000 km, interpreted
as correlated with variations in dust emission activity, were seen at radii ≤20 000 km. Two overlapping shell systems with
a relative lag angle of ∼55° were evident at the time.
The north pole of the nucleus was directed towards the Earth. The dust emission pattern is very complex and may be due to
several active areas. The shape of the incomplete spiral shell pattern indicates that the angle between the line-of-sight
and the rotational axis of the nucleus was not large.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
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
11.
William Liller 《Planetary and Space Science》1997,45(12):1505-1513
Systematic CCD photometry of Comet 1995 O1 (Hale-Bopp) began in early August 1995 shortly after its discovery (IAU Circular 6187) and continued until mid-November 1996. The light curve derived from a 34″ square centered on the nucleus shows clearly and objectively how the inner regions of the comet brightened during this 15 month period. Possible connections between sudden brightenings and reported outbursts are investigated. During the interval August–December 1995, the magnitude of the comet showed strong evidence of a periodicity of 20±5 days with a full amplitude of approximately 0.20 mag. It is noteworthy that this result spans both the period of 18 days suggested by Sekanina (1995, 1996) and the “superperiod” of 22±2 days reported by Jorda et al. (1997). However, in 1996 neither this periodicity nor any other could be detected with certainty in the photometric data. 相似文献
12.
Images of comet Halley's nucleus taken by the HMC camera during the GIOT-TO encounter in 1986 show that a major part of the total dust production is localized in a few active areas which are the sources of gas-dust jets. The global dust distribution in the inner coma is dominated by two main jets roughly directed to the sun. A combination of a 1D thermal nucleus model with an axisymmetric continuum model of the jet outflow was used to investigate the properties of the inner coma. Detailed investigations show that the characteristics of the observed jets can be reproduced by outgassing from free sublimating active areas of a few km in diameter, a dust to gas ratio of 1–2.5 and a size distribution dominated by the larger grains. It is further shown that most of the observational constraints provided by the HMC data can be met simultaneously by a model of three jets superimposed on a weak background. 相似文献
13.
We describe a 3-dimensional, time-dependent Monte Carlo model developed to analyze the chemical and physical nature of a cometary gas coma. Our model includes the necessary physics and chemistry to recreate the conditions applicable to Comet Hale-Bopp when the comet was near 1 AU from the Sun. Two base models were designed and are described here. The first is an isotropic model that emits particles (parents of the observed gases) from the entire nucleus; the second is a jet model that ejects parent particles solely from discrete active areas on the surface of the comet nucleus, resulting in coma jets. The two models are combined to produce the final model, which is compared with observations. The physical processes incorporated in both base models include: (1) isotropic ejection of daughter molecules (the observed gases) in the parent's frame of reference, (2) solar radiation pressure, (3) solar insolation effects, (4) collisions of daughter products with other molecules in the coma, and (5) acceleration of the gas in the coma. The observed daughter molecules are produced when a parent decays, which is represented by either an exponential decay distribution (photodissociation of the parent gas) or a triangular distribution (production from a grain extended source). Application of this model to the analysis the OH, C2 and CN gas jets observed in the coma of Comet Hale-Bopp is the focus of the accompanying paper [Lederer, S.M., Campins, H., Osip, D.J., 2008. Icarus, in press (this issue)]. 相似文献
14.
Vasundhara R. Chakraborty Pavan Hänel Andreas Heiser Erwin 《Earth, Moon, and Planets》1997,78(1-3):321-328
Persistent jet and shell structures from comet Hale-Bopp showing gradual changes in the shapes and orientations with aspect
angle and solar illumination geometry indicate long lived active sources. A model to simulate the dust features has been applied
to the series of observations from September 1996 to May 1997. Most of the structures can be explained as arising due to ejections
from persistent active regions at comet-o-centric latitudes near +65°, +55°, −5° to −15°, −35° and −65°. The best fitting
pole positions vary between 255° ±10° and 275° ± 10° in right ascension and −45° ± 10° to −75° ± 10° in declination. Lower
limits on the dust and gas production rates at various epochs are presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
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
16.
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
17.
Images of comet Halley's nucleus taken by the HMC camera during the GIOT-TO encounter in 1986 show that a major part of the total dust production is localized in a few active areas which are the sources of gas-dust jets. The global dust distribution in the inner coma is dominated by two main jets roughly directed to the sun. A combination of a 1D thermal nucleus model with an axisymmetric continuum model of the jet outflow was used to investigate the properties of the inner coma. Detailed investigations show that the characteristics of the observed jets can be reproduced by outgassing from free sublimating active areas of a few km in diameter, a dust to gas ratio of 1–2.5 and a size distribution dominated by the larger grains. It is further shown that most of the observational constraints provided by the HMC data can be met simultaneously by a model of three jets superimposed on a weak background. 相似文献
18.
Lederer Susan M. Campins Humberto Osip David J. Schleicher David G. 《Earth, Moon, and Planets》1997,78(1-3):131-136
We report the identification of gas jets in comet Hale-Bopp in OH, NH, CN, C2 and C3. This is the first time OH and NH jets without an obvious optical dust jet counterpart have been identified in narrowband
comet images. We also confirm the existence of CN jets as reported by Larson et al. (1997) and Mueller et al. (1998). Jet
features can be seen in the March and April 1997 datasets, approximately a month before and after perihelion. Our results
contribute to the understanding of both the chemical properties of the comet as well as the physical mechanisms necessary
to produce these features.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
A great deal of attention has been given to the production and spatial distribution of sodium in comets after the discovery
of the sodium tail, by Cremonese et al. (1997a), on Hale-Bopp. The sodium has been observed in several comets in the past,
but the Hale-Bopp represent the first time where it will be deeply analyzed considering the several data and scientists working
on that. The sodium tail stimulated different studies trying to explain the mechanism source and provided the new lifetime
for photoionization of the neutral sodium atom. We took into account other sodium observations performed in this century and
we focalized our attention to comet Hale-Bopp to understand the main sources responsible for the sodium features observed.
We analyzed the sodium tail observations performed by Cremonese et al. (1997b) and Wilson et al. (1998) finding that the Hale-Bopp
had four different tails. The wide field images and the high resolution spectroscopy performed along the sodium tail provided
very important clues to distinguish the two sodium tails observed and their possible sources. Considering most of the data
reported in several papers has been possible to draw a real sketch on what has occurred to the comet during March and April
1997. We are going to demonstrate that the sodium tail observed by Wilson et al. (1998) was not the same reportedby Cremonese
et al. (1997a) and in the images taken by the European Hale-Bopp Team there were two distinct sodium tails. The observations
allowed us to define “narrow sodium tail” the tail reported by Cremonese et al. (1997a), and “diffuse sodium tail” the tail
overimposed to the dust tail. We suggest that the narrow sodium tail was due to a molecular process instead of the diffuse
one due to the release of sodium atoms by the dust particles. Such a conclusion is supported by the spatial distribution of
sodium on the nucleus and in the coma as reported from other authors.
This revised version was published online in July 2006 with corrections to the Cover Date. 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