共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
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
3.
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
4.
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
5.
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
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.
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.
Vanscheidt R. Bleul H. Manthey E. Jütte M. Pohlen M. Schmidtobreick L. Altmann M. Dieball A. Geffert M. Sanner J. Notni P. Schmoll J. 《Earth, Moon, and Planets》1998,81(3):223-231
Extensive widefield CCD direct imaging of C/1995 O1 (Hale-Bopp) at UBVRI was carried out at Hoher List Observatory with the
1.06 m telescope (field of view 20′ × 20′) and at Potsdam Observatory with the 0.70 m telescope (field of view 8′ × 8′). The
corresponding spatial resolution is 850–1000 km pix-1and 525–590 km pix-1, respectively. The data covers 25 nights from February 20 to April 21, 1997.
In order to quantify the various features in the apparent inner coma we introduce a new tomographic method that minimizes
the morphological bias caused by image processing. The tomographic analysis leads to quantitative maps refering to the position
and intensity of the dust ejections for each image frame. Variability and periodicity within the inner coma can be thoroughly
deduced due to various sets of consecutive nights in the observation period mentioned above. The results are compared with
applications of adaptive Laplace filtering.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
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
10.
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
11.
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
12.
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
13.
S. Young † C. Packham R. E. Mason J. T. Radomski C. M. Telesco 《Monthly notices of the Royal Astronomical Society》2007,378(3):888-892
We present spatially resolved 10-μm spectra of the nucleus of IC 5063 that are near-diffraction-limited. The observations were obtained with T-ReCS, the mid-infrared (mid-IR) imager and spectrometer on the 8.1-m Gemini South telescope, with the slit aligned at a position angle on the sky along the direction of the cone of narrow-line emission. The spectra cover the nucleus and the inner reaches of the ionization cones at a spatial resolution of approximately 0.4 arcsec (90 pc). Individual spectra, extracted in steps in the spatial direction along the slit, reveal variations in continuum slope and silicate feature profile and depth on subarcsecond scales, illustrating in unprecedented detail the complexity of the circumnuclear regions of this galaxy at mid-IR wavelengths. The dust population in the vicinity of the narrow-line region, north-west of the nuclear position, is significantly warmer than that to the south-east of the nucleus. This is consistent with an observation of the cooler dust associated with the outer reaches of the postulated torus that obscures the type 1 nucleus in this object. 相似文献
14.
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
15.
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
16.
A. Chalabaev E. Le Coarer P. Rabou Y. Magnard P. Petmezakis D. Le Mignant 《Experimental Astronomy》2002,14(3):147-181
The GraF instrument using a Fabry-Perot interferometer cross-dispersed with a grating was one of the first integral-field
and long-slit spectrographs built for and used with an adaptive optics system. We describe its concept, design, optimal observational
procedures and the measured performances. The instrument was used in 1997–2001 at the ESO3.6 m telescope equipped with ADONIS
adaptive optics and SHARPII+camera. The operating spectral range was 1.2–2.5 μm. We used the spectral resolution from 500
to 10 000 combined with the angular resolution of 0.1″–0.2″. The quality of GraF data is illustrated by the integral field
spectroscopy of the complex0.9″ × 0.9″ central region of η Car in the1.7 μm spectral range at the limit of spectral and angular
resolutions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
We review the composition of Jupiter-family comet (JFC) dust as inferred from infrared spectroscopy. We find that JFCs have silicate emission features with fluxes roughly 20-25% over the dust continuum (emission strength 1.20-1.25), similar to the weakest silicate features in Oort Cloud (OC) comets. We discuss the grain properties that alter the silicate emission feature (composition, size, and structure/shape), and emphasize that thermal emission from the comet nucleus can have significant influence on the derived silicate emission strength. Recent evidence suggests that grain porosity is the is different between JFCs and OC comets, but more observations and models of silicates in JFCs are needed to determine if a consistent set of grain parameters can explain their weak silicate emission features. Models of 8 m telescope and Spitzer Space Telescope observations have shown that JFCs have crystalline silicates with abundances similar to or less than those found in OC comets, although the crystalline silicate mineralogy of comets 9P/Tempel and C/1995 O1 (Hale-Bopp) differ from each other in Mg and Fe content. The heterogeneity of comet nuclei can also be assessed with mid-infrared spectroscopy, and we review the evidence for heterogeneous dust properties in the nucleus of comet 9P/Tempel. Models of dust formation, mixing in the solar nebula, and comet formation must be able to explain the observed range of Mg and Fe content and the heterogeneity of comet 9P/Tempel, although more work is needed in order to understand to what extent do comets 9P/Tempel and Hale-Bopp represent comets as a whole. 相似文献
18.
Previous analysis of imaging spectroscopy data in the 0.4–1 μm spectral range of comet Hale-Bopp, have shown the presence
of two regions on the sunward and antisunward sides of the nucleus exhibiting different continuum emission (Bellucci, 1998,
hereafter paper I). In this work we present the modeling of the continuum emission in terms of size distribution and composition
of the dust grains. The spectra are fitted by micron sized olvine grains. A mechanism to explain the spatial gradient is also
proposed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Harris W. M. Nordsieck K. H. Scherb F. Mierkiewicz E. J. 《Earth, Moon, and Planets》1997,78(1-3):161-167
We report on the reduction and analysis of UVpolarimetric images of CI (λ1657 Å) and dust continuum (2696 Å emissions from C/1995 O1 (Hale-Bopp) taken using the Wide Field Imaging Survey Polarimeter (WISP) sounding rocket on 8 April, 1997. These observations represent the first imaging polarimetry of comets in the UV, and were performed in consort with ground based measurements of gas and dust polarization and distribution. The continuum results show 9% polarization across the image field with a polarization phase angle close to the 129° prediction. Comparison with ground based data implies minimal color dependence for Hale-Bopp in either the degree of polarization and in the position angle. The carbon polarimetry implies that most production occurs in the dense inner coma, and that it leaves that area in thermodynamic equilibrium. Its radial profile further constrains the carbon outflow speed to be sufficient to travel ≥5 × 106 km without photoionization. 相似文献
20.
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