共查询到20条相似文献,搜索用时 15 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.
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
3.
We present the results of narrowband photoelectric observations of comet Hale-Bopp near perihelion, which were made with the
AZT-14telescope at the station Lisniki of Kyiv University Astronomical Observatory. The standard set of IHW cometary filters
was used. The total number of cometary observations was more than 500 during the interval March 13–April 29, 1997. The comet's
nuclear gas production rates Q of C2 and C3 were calculated using the stellar calibration for these filters. The calculations used the Haser model for a neutral cometary
atmosphere. The value Afρ, which is characteristic of the dust production rate, was determined too. Mean values of the production
rates near perihelion are log Q(C2) = 28.4; log Q(C3) = 27.2; (Afρ)BC = 6.0.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
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
5.
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
6.
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
7.
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
8.
BOEHNHARDT H. BIRKLE K. FIEDLER A. JORDA L. THOMAS N. PESCHKE S. RAUER H. SCHULZ R. SCHWEHM G. TOZZI G. WEST R. 《Earth, Moon, and Planets》1997,78(1-3):179-187
In 1996 comet Hale-Bopp exhibited a porcupine-like coma with straight jets of dust emission from several active regions on
the nucleus. The multi-jet coma geometry developed during the first half of 1996. While the jet orientation remained almost
constant over months, the relative intensity of the jets changed with time. By using the embedded fan model of Sekanina and
Boehnhardt (1997a) the jet pattern of comet Hale-Bopp in 1996 can be interpreted as boundaries of dust emission cones (fans)
from four — possibly five — active regions on the nucleus (for a numerical modelling see part II of the paper by Sekanina
and Boehnhardt, 1997b).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
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
10.
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
11.
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
12.
The comet Hale-Bopp (C/1995 O1) has been observed in the infrared (1–2.5 μm) with the Nordic Optical Telescope (NOT) equipped
with the Arcetri NICMOS3 camera (ARNICA). Two observational campaigns, each one lasting about one week, were made when the
comet heliocentric distance was about 3 AU. The first campaign was at the end of August and the second at the end of September
1996.
During both runs two major outbursts were observed, the more intense of them started the day before the beginning of the second
run. In the images recorded during the first three nights (24.8–26.8 Sept.) of the second run a dust shell expanding in the
northern quadrant with a projected velocity of 0.14–0.28 km/s is clearly evident. The dust production rate increased by at
least a factor ≈3 at the time of the outburst. Also evident on the first night is a change in the IR color that is well correlated
with the dust shell. This is an indication that the material released by the outburst has a different composition and/or size
distribution than that in the “quiescent” dust coma.
In this paper we present preliminary results about the evolution and the photometric characteristics of the dust shell.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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.
Cristiano B. Cosmovici Vojko Bratina Gottfried Schwarz Gianpaolo Tozzi Michael J. Mumma Roberto Stalio 《Astrophysics and Space Science》2006,301(1-4):135-143
We report here on unique post-perihelion (2.3 AU) measurements of Comet Hale-Bopp in the FUV-range (950–1250 Å) by means of the UVSTAR spectrometer from the space shuttle with the main purpose of searching for argon and other FUV emitters. New methods for separating the strong airglow emission at shuttle altitudes are here discussed in detail. Due to our low resolution (15 Å) and S/N ratio the possible rocket-borne detection of argon near perihelion (0.9 AU) could not be confirmed. New species as N2 are suspected but difficult to separate from the strong airglow emission at shuttle altitudes. From the Lyα brightness (1.30± 0.08 kRy) a water production rate Q = 5.9 ± 0.4 × 1029 molecules s?1 could be derived and compared with other post-perihelion observations. 相似文献
15.
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
16.
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
17.
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
18.
An investigation of the activity of Comet C/1995 O1 (Hale-Bopp) with a thermophysical nucleus model that does not rely on the existence of amorphous ice is presented. Our approach incorporates recent observations allowing to constrain important parameters that control cometary activity. The model accounts for heat conduction, heat advection, gas diffusion, sublimation, and condensation in a porous ice-dust matrix with moving boundaries. Erosion due to surface sublimation of water ice leads to a moving boundary. The movement of the boundary is modeled by applying a temperature remapping technique which allows us to account for the loss in the internal energy of the eroded surface material. These kind of problems are commonly referred to as Stefan problems. The model takes into account the diurnal rotation of the nucleus and seasonal effects due to the strong obliquity of Hale-Bopp as reported by Jorda et al. (Jorda, L., Rembor, K., Lecacheux, J., Colom, P., Colas, F., Frappa, E., Lara, L.M. [1997]. Earth Moon Planets 77, 167-180). Only bulk sublimation of water and CO ice are considered without further assumptions such as amorphous ices with certain amount of occluded CO gas. Confined and localized activity patterns are investigated following the reports of Lederer and Campins (Lederer, S.M., Campins, H. [2002]. Earth Moon Planets 90, 381-389) about the chemical heterogeneity of Hale-Bopp and of Bockelée-Morvan et al. (Bockelée-Morvan, D., Henry, F., Biver, N., Boissier, J., Colom, P., Crovisier, J., Despois, D., Moreno, R., Wink, J. [2009]. Astron. Astrophys. 505, 825-843) about a strong CO source at a latitude of 20°. The best fit to the observations of Biver et al. (Biver, N. et al. [2002]. Earth Moon Planets 90, 5-14) is obtained with a low thermal conductivity of 0.01 W m−1 K−1. This is in agreement with recent results of the Deep Impact mission to 9P/Tempel 1 (Groussin, O., A’Hearn, M.F., Li, J.-Y., Thomas, P.C., Sunshine, J.M., Lisse, C.M., Meech, K.J., Farnham, T.L., Feaga, L.M., Delamere, W.A. [2007]. Icarus 187, 16-25) and with previous thermal simulations (Kührt, E. [1999]. Space Sci. Rev. 90, 75-82). The water production curve matches the production rates well from −4 AU pre-perihelion to the outgoing leg while the model does not reproduce so well the water production beyond 4 AU pre-perihelion. The CO production curve is a good fit to the measurements of Biver et al. (2002) over the whole measured heliocentric range from −7 AU pre- to 15 AU post-perihelion. 相似文献
19.
The analysis of the polarized light scattered by cometary dust particles provides information on the physical properties of the solid component of cometary comae for C/1995 O1 Hale-Bopp and 1P/Halley. A model of light scattering by a size distribution of aggregates of up to 256 submicron-sized grains (spherical or spheroidal) mixed with single spheroidal particles has been developed, with its parameters adjusted to fit the phase angle and wavelength dependence of the polarization observations. The particles are built of two materials: a non-absorbing silicates-type material and a more absorbing organic-type material. The model reproduces accurately the inversion angle and the positive branch of the polarization phase curves from the visible to the near-infrared spectral domains. A negative branch of the polarization phase curves appears in our model, although the negative branch is not deep enough to reproduce accurately the observations. Significant differences are shown between the two comets, with dominance of small grains in the coma of Comet C/1995 O1 Hale-Bopp, well fitted by a distribution of the volume-equivalent diameter, a, following a−3.0 with a lower cutoff around 0.20 μm and an upper cutoff of at least 40 μm. For 1P/Halley, the size distribution follows a−2.8 with a lower cutoff around 0.26 μm and an upper cutoff of about 38 μm. The relative amount of organic-type particles is larger for 1P/Halley while the amount of aggregates, significant for both comets, is larger for C/1995 O1 Hale-Bopp. 相似文献
20.
Ziurys LM Savage C Brewster MA Apponi AJ Pesch TC Wyckoff S 《The Astrophysical journal》1999,527(1):L67-L71
Observations of comet Hale-Bopp (C/1995 O1) have been carried out near perihelion (1997 March) at millimeter wavelengths using the NRAO 12 m telescope. The J=1-->0, 2-->1, and 3-->2 lines of HCN at 88, 177, and 265 GHz were measured in the comet as well as the J=3-->2 lines of H13CN, HC15N, and HNC. The N=2-->1 transition of CN near 226 GHz was also detected, and an upper limit was obtained for the J=2-->1 line of HCNH+. From the measurements, column densities and production rates have been estimated. A column density ratio of [HCN]/[HNC] = 7+/-1 was observed near perihelion, while it was found that [HCN]/[HCNH+] greater, similar 1. The production rates at perihelion for HCN and CN were estimated to be Q(HCN) approximately 1x1028 s-1 and Q(CN) approximately 2.6x1027 s-1, respectively, resulting in a ratio of [HCN]/[CN] approximately 3. Consequently, HCN is sufficiently abundant to be the parent molecule of CN in Hale-Bopp, and HCNH+ could be a source of HNC. Finally, carbon and nitrogen isotope ratios of 12C/13C = 109+/-22 and 14N/15N = 330+/-98 were obtained from HCN measurements, in agreement with previous values obtained from J=4-->3 data. Such ratios suggest that comet Hale-Bopp formed coevally with the solar system. 相似文献