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  • Articles  (37)
  • Comets  (37)
  • Springer  (37)
  • Oxford University Press
  • 2020-2023
  • 1995-1999  (37)
  • Geosciences  (37)
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  • Articles  (37)
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  • Springer  (37)
  • Oxford University Press
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  • 1
    Electronic Resource
    Electronic Resource
    On the existence of small comets and their interactions with planets (1996)
    Springer
    Earth, moon and planets 72 (1996), S. 243-249 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; small ; search program ; planets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Arguments are presented for a substantial, unexplored population of comets with radii less than 1 km. Known examples confirm this population and extrapolation of any plausible size-distribution function indicates large numbers. However, their accurate numbers, orbital characteristics, and physical properties are unknown. Thus, even though the small comets may be the most frequent cometary bodies impacting the planets, a quantitative evaluation is not currently possible. We advocate an optimized, dedicated search program to characterize this population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00117524
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  • 2
    Electronic Resource
    Electronic Resource
    Comet Hale-Bopp (1995 O1) (1996)
    Springer
    Earth, moon and planets 73 (1996), S. 15-22 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; named objects ; Comet Hale-Bopp (199501) ; photometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00058042
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo Simulations of Oort Cloud Comets: the Influence of Mantle Blow-off on the Inclination Distribution of Jupiter Family (1997)
    Springer
    Earth, moon and planets 77 (1997), S. 239-244 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; Jupiter family ; simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We have developed an efficient Monte Carlo method by which we can evaluate the evolution of comets. There are many poorly known evolutional parameters, and we have investigated the influence of these parameters on the final populations and the inclination distributions of short-period comets. We compare the observed and calculated inclination distributions of different comet populations and obtain a good fit for the inclinations of the Jupiter family comets by assuming a mantle blow-off and a sudden brightening of the comet when its perihelion distance is lowered in a major jump.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006281618542
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  • 4
    Electronic Resource
    Electronic Resource
    What is the Parent of CH in the Coma of Comet C/1995 O1 (Hale-Bopp)? (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 85-91 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; chemistry ; spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The ratio of CH4/CO in comets is an important indicator of the region of their formation. However, it is difficult to measure the quantity of CH+. The Giotto Ion Mass Spectrometer experiment observed a quantity of CH+ which seemed inconsistent with the amount of CH+. Thus, it was proposed that a source of the CH+ was a distributed source in the dust. We tested this hypothesis by observing the CH emission strength in comet Hale-Bopp as a function of dustiness. We see no strong correlation between the dust and the gas. Thus, for Hale-Bopp,dust is unlikely to be a dominant source of CH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006235715217
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  • 5
    Electronic Resource
    Electronic Resource
    Detection Of Soft X-Ray Emission From Comet C/1995 O1 (Hale–Bopp) (1997)
    Springer
    Earth, moon and planets 77 (1997), S. 293-298 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; general-comets ; individual (Hale–Bopp 1995 O1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We report the detection of soft X-rays from comet C/1995 O1 (Hale-Bopp) by the Low Energy Concentrator Spectrometer (LECS) on-board the X-ray satellite, BeppoSAX. The observations took place on 1996 September 10–11 approximately 1 day after a large dust outburst (Schulz et al., 1997–1999). After correcting for the comets motion, a 7σ enhancement was found centered (2.1 ± 1.3) x 105 km from the position of the nucleus, in the general solar direction. The total X-ray luminosity in the 0.1–2.0 keV energy band is 5 x 1016 erg s−1 which is at least a factor of ∼ 3 greater than measured by the Extreme Ultraviolet Explorer (EUVE)4 days later and suggests that the bulk of the emission measured by the LECS is related to the dust outburst. The extracted LECS spectrum is well fit by a thermal bremsstrahlung-like distribution of temperature of 0.29 ± 0.06 keV - consistent with that observed in other comets. We find no evidence for fluorescent carbon or oxygen emission and place 95% confidence limits of 1.0 x 1015 and 7.8 x 1015 erg s−1 to narrow line emission at 0.28 and 0.53 keV, respectively. We calculate that if such lines are present, they constitute at most 18% of the 0.1–2.0 keV continuum luminosity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006253028962
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  • 6
    Electronic Resource
    Electronic Resource
    Collisional Quenching of OH Radio Emission from Comet Hale-Bopp (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 45-51 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; production rates ; OH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Observations of comets in the 18-cm OH transitions offer a means to probe gas production, kinematics, and OH excitation in comets. We present initial results of OH observations of comet Hale-Bopp obtained with the NRAO 43 m antenna located in Greenbank, WV. Maps of the emission provide strong constraints on the amount of quenching of the inversion of the OH ground state Λ-doublet in the coma. Analysis of the total radio OH flux and maps of its radial brightness distribution indicate a quenched region on the order of ∼500,000 km during March and April 1997. This large value is generally consistent with previous observations of radio OH quenching in lower production rate comets when the high production rate of comet Hale-Bopp is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006258908857
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  • 7
    Electronic Resource
    Electronic Resource
    New Molecular Species in Comet C/1995 O1 (Hale-Bopp) Observed with the Caltech Ssubmillimeter Observatory (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 13-20 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; composition ; radio observations ; spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present millimeter-wave observations of HNCO, HC3N, SO, NH2CHO, H13CN, and H3O+ in comet C/1995 O1 (Hale-Bopp)obtained in February–April, 1997 with the Caltech Submillimeter Observatory (CSO). HNCO, first detected at the CSO in comet C/1996B2 (Hyakutake), is securely confirmed in comet Hale-Bopp via observations of three rotational transitions. The derived abundance with respect to H2O is (4-13) × 10-4. HC3N, SO, and NH2CHO are detected for the first time in a comet. The fractional abundance of HC3N based on observations of three rotational lines is (1.9 ± 0.2) × 10-4. Four transitions of SO are detected and the derived fractional abundance, (2-8) ×10-3, is higher than the upper limits derived from UV observations of previous comets. Observations of NH2CHO imply a fractional abundance of (1-8) × 10-4. H3O is detected for the first time from the ground. The H13CN (3-2)transition is also detected and the derived HCN/H13CN abundance ratio is 90 ± 15, consistent with the terrestrial12C/13C ratio. In addition, a number of other molecular species are detected, including HNC, OCS, HCO+, CO+, and CN(the last two are first detections in a comet at radio wavelengths).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006281802554
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  • 8
    Electronic Resource
    Electronic Resource
    The HNC/HCN Ratio in Comets (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 29-35 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; interstellar molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The abundance ratio of the isomers HCN and HNC has been investigated in comet Hale-Bopp (C/1995 O1) through observations of the J = 4−3 rotational transitions of both species for heliocentric distances 0.93 〈 r 〈 3 AU, both pre- and post-perihelion. After correcting for the optical depth of the stronger HCN line, we find that the column density ratio of HNC/HCN in our telescope beam increases significantly as the comet approaches the Sun. We compare this behavior to that predicted from an ion-molecule chemical model and conclude that the HNC is produced insignificant measure by chemical processes in the coma; i.e., for comet Hale-Bopp, HNC is not a parent molecule sublimating from the nucleus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006202823878
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  • 9
    Electronic Resource
    Electronic Resource
    Observations Of Scattered Light From Cometary Dust And Their Interpretation (1997)
    Springer
    Earth, moon and planets 79 (1997), S. 221-245 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; dust ; colour ; polarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This review begins with a discussion of the techniques needed for observations of scattered light from cometary dust. After an introduction into the basic concepts of the scattering process, observations of the phase curves of brightness, colour and polarization are covered. Images of colour and polarization are presented and the observed relation of colour and polarization in jets and shells is discussed. The interpretation of the measurements is based on the power law size distributions of dust grains observed from space. The power index must lie between 2 and 4 to provide the mass budget and visibility of the dust coma in accordance with the basic facts of cometary physics. Application of mechanical (radiation pressure) theory to cometary images allows us to derive related power law distributions for comets not explored by spacecraft. Grain scattering models are presented and compared with observations. A prediction is made of the spatial distribution of Stokes parameters U and V in the presence of aligned particles. Up to now such patterns have not been observed. Future work should include the exploration of comets at small and possibly very small phase angles and a detailed comparison of polarization and colour images of comets with thermal images and with models based on mechanical theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006249703639
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  • 10
    Electronic Resource
    Electronic Resource
    Dust-Gas Interrelations In Comets: Observations And Theory (1997)
    Springer
    Earth, moon and planets 79 (1997), S. 275-306 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; Hale-Bopp ; dynamics ; photochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The development of the expanding atmosphere from the evaporating cometary nucleus has traditionally focused on observing and modeling the separate development of two distinct components, gas and dust,which are coupled dynamically with one another at distances out to a few tens of cometary radii. In the last decade or so, however, direct evidence from observations and suggestions from theory suggest that the dusty-gas coma is a tightly coupled system where material is transferred between the solid and gaseous phase as an important integral part of the basic development of the coma. Comet Hale-Bopp (C/1995 O1) was discovered far from the sun and is the largest and most productive comet, in the sense of release of gas and dust in modern times. This has permitted observations to be made over an unprecedented range of heliocentric distance. This paper presents a review of a range of important issues regarding interrelations between dust and gas in comets, a description of the gas and dust environment for Hale-Bopp, and a summary of the preliminary results from Hale-Bopp which are relevant to these issues. Particular topics include dusty-gas models, dust fading and fragmentation, the role of dust and gas jets, the day/night distribution of gas and dust, and extended sources of gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006257922294
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  • 11
    Electronic Resource
    Electronic Resource
    Dynamical evolution of comets and the problem of cometary fading (1996)
    Springer
    Earth, moon and planets 72 (1996), S. 35-40 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; dynamics ; fading problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Possibilities to explain the observed 1/a-distribution are discussed in the light of improved understanding of the dynamical evolution of long-period comets. It appears that the ‘fading problem’ applies both to single-injection and continuous-injection models. Although uncertainties due to nongravitational effects do not allow detailed results to be drawn from the observed 1/a-distribution at small perihelion distance q, that for q ≳ 1.5 AU shows that a constant fading probability cannot explain all the features of the observed distribution. Assuming that comets can reappear following a period of fading, values for the assumed constant fading and renewal probabilities, and the total cometary flux have been estimated for q 〉 1.5 AU.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00117500
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  • 12
    Electronic Resource
    Electronic Resource
    Light curve behaviour in C/1995 O1 (Hale-Bopp) — II (1996)
    Springer
    Earth, moon and planets 75 (1996), S. 87-94 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; named objects ; C/1995 O1 (Hale-Bopp)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Comet Hale-Bopp is, without doubt, one of the most important objects for cometary science which has ever been observed. The light curve is well-observed from a heliocentric distance 7.2 AU and some information is available at distances as great as 17 AU. This allows the photometric evolution of the comet to be studied as different volatiles dominate the activity. Three different phases of activity are seen as the heliocentric distance reduces during 1996: the initial phase of very fast brightening, characterized by a r −5 law; a “standstill” in the light curve when the brightening law reduced to r −1, which coincides with the initiation of water sublimation at r ~ 4 AU; and a further phase of more rapid brightening with an r −3.5 law, similar to the mean for comets classed as “fairly new”, which initiated at r ~ 4 AU.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00054506
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  • 13
    Electronic Resource
    Electronic Resource
    The Rotational Parameters Of Hale–Bopp (C/1995 O1) From Observations Of The Dust Jets At Pic Du Midi Observatory (1997)
    Springer
    Earth, moon and planets 77 (1997), S. 167-180 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; Hale–Bopp ; period ; rotation ; rotational state ; dust velocity ; dust size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We observed comet Hale-Bopp (C/1995 O1) at Pic du Midi Observatory in 1997 from February 2.24 UT to March 31.89 UT with the 1.05-m telescope equipped with a CCD camera and broad- and narrow-band IHW filters. A total of 30000 images were acquired both during night- and day-time. The images were automatically reduced and all the images obtained within 10 min. were co-added to give a set of ∼1000 images used during the analysis. We can identify two jets on the images. The position angle of the brightest jet from February 2.24 UT to March 5.22 UT is measured using an automatic routine which searches for the averaged position angle of the maximum of brightness at a projected distance of 3200–6100 km from the optocenter. A preliminary model of nucleus rotation is used to fit the data and retrieve the rotational parameters of the nucleus. The best fit is found for a source located at a latitude of 64 ± 3°, a sidereal rotation period of 11.35 ± 0.04 h and a right ascension and declination of the North pole of 275 ± 10° and -57 ± 10°. This preliminary analysis shows no evidence for a precession. Grains with velocities of 450–600 m s−1 and radii 〈;∼ 1 μm dominate the optical scattering cross section in the jets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006234813574
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  • 14
    Electronic Resource
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    X-Ray Emission From Comet Hale–Bopp (1997)
    Springer
    Earth, moon and planets 77 (1997), S. 283-291 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; individual, X-rays ; solar system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006274812124
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  • 15
    Electronic Resource
    Electronic Resource
    Gaseous Jets in Comet Hale-Bopp (1995 O1) (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 131-136 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; Hale-Bopp ; coma morphology ; narrowband imaging ; jets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006280908373
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  • 16
    Electronic Resource
    Electronic Resource
    Evolution of Dust Shells and Jets in the Inner Coma of Comet C/1995 O1 (Hale-Bopp) (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 205-210 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; individual ; C/1995 O1 Hale-Bopp ; dust shells ; spiral jets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Comet Hale-Bopp was observed with the 80 cm reflector + CCD at the Haute-Provence observatory (OHP) and with the 62 cm reflector + CCD at the Saint-Véran observatory (Queyras, France). The morphology of the shells was followed from their first appearence on 1997 Jan. 30, until their disappearance on May 9. These shells spread from the nucleus region with a velocity in agreement with a nuclear rotation period of about 11.33 hours. We report also a short and bright dust ejection on May 8. CN images show a long spiral jet in the tailward side invisible on continuum images. The circumnuclear structures have been followed at Saint-Véran from Apr. 5 to Apr. 11, 1997 with a high spatial resolution (200 km/pixel). We have followed the emergence of a recurrent linear polar jet. Measurements of its expansion show a constant acceleration of material with typical expansion velocity of 1 km/s. The CCD frames show the interconnection between spiral jets and the successive shells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006296932189
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  • 17
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    Spectrocam-10 Thermal Infrared Observations Of The Dust In Comet C/1995 O1 Hale-Bopp (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 265-270 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; infrared ; silicate feature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006217503964
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  • 18
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    Long-term Evolution of the Outgassing of Comet Hale-Bopp From Radio Observations (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 5-11 
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    ISSN: 1573-0794
    Keywords: Comets ; C/1995 O1 (Hale-Bopp) ; radio observations ; molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract C/1995 O1 (Hale-Bopp) has been observed on a regular basis since August 1995 at millimetre and submillimetre wavelengths using IRAM, JCMT, CSO and SEST radio telescopes. The production rates of eight molecular species (CO, HCN, CH3OH, H2CO,H2S, CS, CH3CN,HNC) have been monitored as a function of heliocentric distance(rh from 7 AU pre-perihelion to 4 AU post-perihelion. As comet Hale-Bopp approached and receded from the Sun, these species displayed different behaviours. Far from the Sun, the most volatile species were found in general relatively more abundant in the coma. In comparison to other species, HNC, H2CO and CS showed a much steeper increase of the production rate with decreasing rh. Less than 1.5 AU from the Sun, the relative abundances were fairly stable and approached those found in other comets near 1 AU. The kinetic temperature of the coma, estimated from the relative intensities of the CH3OH and CO lines, increased with decreasing rh, from about10 K at 7 AU to 110 K around perihelion. The expansion velocity of the gaseous species, derived from the line shapes, also increased with a law close torh 3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006229818484
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  • 19
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    Spectroscopy Of Comet Hale-Bopp In The Visible/Near Infrared: Modeling Of Dust Properties (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 305-311 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; C/1995 O1 (Hale-Bopp) ; Solar System
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006234007598
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  • 20
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    Aperture Polarimetry And Photometry Of Comet Hale-Bopp (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 347-352 
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    ISSN: 1573-0794
    Keywords: Comets ; comet Hale-Bopp ; polarization ; dust
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006246310324
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  • 21
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    Infrared Observations Of Dust Emission From Comet Hale-Bopp (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 251-257 
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    ISSN: 1573-0794
    Keywords: Comets ; infrared ; radio ; rotation ; surfaces ; origin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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%.
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    URL: http://dx.doi.org/10.1023/A:1006261303055
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    C/1995 O1 (Hale-Bopp): Gas Production Curves And Their Interpretation (1997)
    Springer
    Earth, moon and planets 79 (1997), S. 55-77 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; cometary activity ; cometary nucleus ; sublimation processes ; numerical modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The discovery of C/1995 O1 (Hale-Bopp) at 7 AU from the Sun provided the first opportunity to follow the activity of a bright comet over a large range of heliocentric distances rh. Production rates of a number of parent molecules and daughter species have been monitored both pre- and postperihelion. CO was found to be the major driver of the activity far from the Sun, surpassed by water within 3 AU whose production rate reached 1031 s−1 at perihelion. Gas production curves obtained for various species show several behaviours with rh. Gas production curves contain important information concerning the physical state of cometary ices, the structure of the nucleus and all the processes taking place inside the nucleus leading to outgassing. They are relevant to the study of several other phenomena such as the sublimation from icy grains, dust mantling or seasonal effects. For some species, such as H2CO or HNC, they permit to constrain their origin in the coma. We discuss models of subsurface gas production in distant comets and predictions of how such a source may vary as the comet moves along its orbit, approaching perihelion and receding again. Features in the observed gas production curves of comet Hale-Bopp are generally interpretable in terms of either subsurface production (typical example: CO at large rh) or free sublimation (typical example: H2O). Possible implications for the vertical stratification of the cometary ices are reviewed, and preference is found for a model with crystallization of amorphous ice close to the nuclear surface.
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    URL: http://dx.doi.org/10.1023/A:1006225030955
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    Summary of Conference (1997)
    Springer
    Earth, moon and planets 79 (1997), S. 309-319 
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    ISSN: 1573-0794
    Keywords: Comets ; comet Hale-Bopp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The recent apparition of comet Hale-Bopp has provided the first opportunity to study a truely “Great Comet” with modern observational equipment, from ground and from space. An enormous amount of data was gathered and is still in the process of being analysed. When compared with elaborate and realistic theoretical considerations, important new insights are now being obtained into the complex physical and chemical processes in the cometary environment. This summary highlights some of the main achievements of this work, as they were presented at the first major international conference on comet Hale-Bopp in February 1998.
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    URL: http://dx.doi.org/10.1023/A:1006214223203
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    The provenance and evolution of comets (1996)
    Springer
    Earth, moon and planets 72 (1996), S. 57-68 
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    ISSN: 1573-0794
    Keywords: Comets ; interstellar dust ; dynamics ; solar neutrino problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The process of comet formation through the hierarchical aggregation of originally submicron-sized interstellar grains to form micron-sized particles and then larger bodies in the protoplanetary disc, culminating in the formation of planetesimals in the disc extending from Jupiter to beyond Neptune, is briefly reviewed. The ‘planetesimal’ theory for the origin of comets implies the existence of distinct cometary reservoirs, with implications for the immediate provenance of observed comets (both long-period and short-period) and their evolution as a result of planetary perturbations and physical decay, for example splitting and sublimation. The principal mode of cometary decay and collisional interaction with the terrestrial planets is through the formation and evolution of streams of cometary debris and hitherto undiscovered ‘families’ of cometary asteroids. Recent dynamical results, in particular the sungrazing and sun-colliding end-state for short-period comet and asteroid orbits, are briefly discussed.
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    URL: http://dx.doi.org/10.1007/BF00117504
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    An analytical model of the Comet's collision with Jupiter (1996)
    Springer
    Earth, moon and planets 73 (1996), S. 23-32 
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    ISSN: 1573-0794
    Keywords: Comets ; Collision ; Jupiter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An important feature observed in the wake of the Jupiter-comet clash was the appearance of the ring structure axisymmetrically positioned around the center of the impact. The persistent expansion of the dark rings and its speed indicated an outward propagating gravity wave (Benka, 1995). We employ an analytical model of constant density, uniform finite depth and inviscid fluid layer to investigate the wave motion produced by the impact of Comet Shoemaker-Levy 9 on the Jovian atmosphere. The relevant thermal effects are neglected and an explosion resulting from the collision is then described by an initial impulsive pressure at the surface of the Jovian atmosphere. Under the assumption that all the kinetic energy of a comet fragment is completely converted into the energy of wave motions in the Jovian atmosphere, an analytical formula describing the relationship between the resulting wave motion in the atmosphere and the parameters of a comet fragment (the radius, density and speed) is derived. Results from the present simple analytical model give a qualitative agreement with observations regarding the distance and speed of the waves.
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    URL: http://dx.doi.org/10.1007/BF00058043
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    Hco+ in the Coma of Comet Hale–Bopp (1997)
    Springer
    Earth, moon and planets 77 (1997), S. 253-258 
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    ISSN: 1573-0794
    Keywords: Comets ; HCO+ ; chemistry ; plasmas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Maps of comet C/1995 O1 (Hale-Bopp) in the millimeter-wave emission of the ion HCO+ revealed a local minimum near the nucleus position, with a maximum about 100,000 km in the antisolar direction. These observed features of the HCO+ emission require a low abundance of HCO+ due to enhanced destruction in the inner coma of the comet, within a region of low electron temperature (Te). To set constraints on the formation of HCO+ in the coma, as well as the location and magnitude of the transition to higher Te, the data are compared with the results of ion-molecule chemistry models.
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    URL: http://dx.doi.org/10.1023/A:1006285703521
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    Observations of the OH Radical in Comet C/1995 O1 (Hale-Bopp) with the Nançay Radio Telescope (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 37-43 
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    ISSN: 1573-0794
    Keywords: Comets ; OH radical ; radio astronomy ; C/1995 O1 (Hale-Bopp)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present OH 18-cm observations of comet Hale-Bopp (C/1995 O1) at the Nançay radio telescope. On nucleus and offset position observations allowed us to obtain both OH production rates and quenching radii. The maximum OH production rate was reached around perihelion, at about1031 s-1.
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    URL: http://dx.doi.org/10.1023/A:1006206924786
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    Sulfur Chemistry at Millimeter Wavelengths in C/Hale-Bopp (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 69-70 
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    ISSN: 1573-0794
    Keywords: Comets ; coma ; radio ; sulfur chemistry ; Hale-Bopp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The recent availability of bright comets has given us an excellent opportunity to study cometary chemistry. Comet Hale-Bopp (1995 O1)gave us the particularly rare opportunity to study a bright and active comet for almost two years. Our program concentrated on millimeter-wave observations of sulfur-bearing molecules in an effort to understand the total sulfur budget of the comet. Using the National Radio Astronomy Observatory 12-m telescope on Kitt Peak we monitored both the long and short-term variations in H2S, CS, and OCS, as well as observing H2CS and SO. This was the first observation of H2CS in any comet (Figure 1). Additionally, we mapped CS with the BIMA interferometer. Variations in the line profiles and changes in line intensity as large as a factor of two were seen in day to day observations of both H2S and CS. An example for H2S is shown in Figure 2. This is the first time we can attempt to study the entire group of sulfur-bearing molecules. Models of the sulfur coma have thus far largely been based on observations of the daughter products CS and atomic sulfur made over the last 18 years using the International Ultraviolet Explorer (IUE) satellite, coupled with radio observations of CS and H2S in several recent comets. Four new sulfur-bearing species have been observed in comets Hale-Bopp and Hyaku take, three of them parent species. The high resolution maps in CS will also allow spatial information to be included in the sulfur model for the first time. C/Hale-Bopp is the first comet in which so many sulfur species have been observed. Analysis of the abundances of these species in comparison to the total atomic sulfur observed should reveal whether or not we can now account for all of the primary sulfur sources in comets. Perhaps the most interesting question that these observations raised was why C/Hale-Bopp appeared to contain so much more SO and SO2 (as observed by others) than any other comet. This spurred the discovery that the UV fluorescence models of these species were incorrect (S. J. Kim, this issue). Analysis of the data and modeling of the sulfur budget are still underway.
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    URL: http://dx.doi.org/10.1023/A:1006275412491
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    Comet Hale-Bopp: Evolution Of Jets And Shells During March 1997 (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 189-195 
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    ISSN: 1573-0794
    Keywords: Comets ; Hale-Bopp ; jets ; shells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Hundreds of high quality CCD images obtained by the GAT group with the 33.5 cm reflector of the Sozzago Astronomical Observatory (SAS) provide a detailed insight into the temporal evolution of comet Hale-Bopp. The images cover the time period from May 1996 until May 1997 and allowed us to analyze various near nucleus phenomena. Among them are jet structures that were visible from August 1996 until May 1997 and shell structures that could be resolved from February 1997 to May 1997. We concentrate on the morphology of these phenomena during March 1997 and investigated them by radial masking techniques that reveal their precise shape and extent. In particular, polar coordinate representations could be used advantageously to derive numerical parameters of these features.
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    URL: http://dx.doi.org/10.1023/A:1006240714442
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    The Visual Light Curve Of C/1995 O1 (Hale-Bopp) From Discovery To Late 1997 (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 169-177 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; named objects ; C/1997 O1 (Hale-Bopp) ; photometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present a light curve of C/1995 O1 (Hale-Bopp) compiledfrom more than 3000 visual observations of the comet made by members of the The Astronomer Group world-wide. These observations cover the period from discovery through to the end of 1997. The light curve shows that the rate of brightening of the comet varied widely at different times, with rapid rates of brightening at high heliocentric distance pre-perhelion and a comparably rapid post-perihelion fade. There is no evidence that the comet was suffering a large photometric outburst when first discovered, although a small outburst can be identified at perihelion. At least five difficult brightening regimes can be identified in the light curve between discovery and perihelion. From 2.5 AU to perihelion the rate of brightening with decreasing heliocentric distance was typical for “fairly” new comets(n ∼ 3.5, where “n” is the power law exponent of the heliocentric distance), although this was preceded by a period of very slow brightening with n ∼ 1 from r ∼ 4.0 AU to r ∼ 2.8 AU and followed by an initially more rapid brightening which appears to be related to the on-set of rapid water sublimation activity. We derive the light curve parameters at different stages of the comet's apparition.
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    URL: http://dx.doi.org/10.1023/A:1006228113533
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    Dust Morphology Of The Inner Coma Of C/1995 O1 (Hale-Bopp) (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 197-203 
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    ISSN: 1573-0794
    Keywords: Comets ; Hale-Bopp ; dust ; coma ; morphology ; rotation ; period
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
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    URL: http://dx.doi.org/10.1023/A:1006292715351
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    High-Dispersion Spectroscopy of the Sodium (NA) Emission within the Inner Coma of C/1995 O1 (Hale-Bopp) (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 93-98 
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    ISSN: 1573-0794
    Keywords: Comets ; sodium ; spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Very-high spectral resolution observations of the neutral Na emission have enabled measurements of the velocity dispersions of the Na atoms within ∼40,000 km of the opto center of Hale-Bopp. Asymmetric Na D line profiles imply both an in situ or core Na source and a secondary Na source at locations within the inner coma. The core velocity distribution had a FWHM of 2 km s-1. The extended source FWHM increased with distance from the nucleus (up to ∼6 km s-1, but appeared smaller in the more dusty regions (∼2.5–3.0 km s-1) of the inner coma. The D2/D1 line strength ratio was consistent with an optically thin inner coma. Within 5,000 km of the opto center the continuum spatial intensity profiles decreased as ∼r-1 while the Na D emission decreased at less than r-1.
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    URL: http://dx.doi.org/10.1023/A:1006239832055
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    UV Photopolarimetric Imaging of C/1995 O1 (Hale-Bopp) with the Wide Field Imaging Survey Polarimeter (WISP) (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 161-167 
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    ISSN: 1573-0794
    Keywords: Comets ; dust ; polarization ; photochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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.
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    URL: http://dx.doi.org/10.1023/A:1006297428846
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    Polarimetry Of Comet Hale-Bopp: Linear And Circular Polarization, Stellar Occultation (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 381-386 
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    ISSN: 1573-0794
    Keywords: Comets ; comet Hale-Bopp ; polarization ; grains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Comet Hale-Bopp was observed with the 2.6-m and 1.25-m telescopes of the Crimean Astrophysical Observatory on March 9 and 11, 1997. We determined the linear and circular polarization in the coma. For the dust coma, the linear polarization varied from 7.8% to 12.4%. The degree of circular polarization was always negative and did not exceed 0.3% with an accuracy of ±0.04% on average. The passage of a bright star through the cometary coma was monitored with polarimetry and photometry. The wavelength dependence and spatial variations of optical thickness of dust are obtained from the stellar occultation.
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    URL: http://dx.doi.org/10.1023/A:1006266914867
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    Cometary Rotation: an Overview (1997)
    Springer
    Earth, moon and planets 79 (1997), S. 35-53 
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    ISSN: 1573-0794
    Keywords: Comets ; nucleus ; rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract I discuss our current understanding of the spin states of cometary nuclei. Cometary spin influences the temporal and spatial patterns of outgassing from the nucleus (through diurnal and seasonal effects) and is in turn influenced by outgassing-driven torques. The current challenge to cometary astronomers is to quantify the interactions between the spin, the outgassing, and the resultant torques on the nucleus, and to understand the role of rotation in determining the basic physical properties of the nucleus.
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    URL: http://dx.doi.org/10.1023/A:1006272914117
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    Dust Activity in Comet Hale-Bopp (1997)
    Springer
    Earth, moon and planets 79 (1997), S. 79-102 
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    ISSN: 1573-0794
    Keywords: Comets ; named objects ; C/1997 O1 (Hale-Bopp) ; dust emission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 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 were observed so frequently between discovery and perihelion + 5 months. Other results from observations carried out during the observing campaign have shown that the dust emission was unusually strong, as witnessed by the considerable jet activity. It is also seen that the dust emission started at an unusually large heliocentric distance and that the dust to gas ratio was particularly large. This final factor is probably one of the key issues in understanding the activity of the comet close to perihelion. Periodicity in the jet activity, which appears to be related to the precession cycle of the comet, is seen clearly in 1995 and, more ambiguously, during 1996. A full understanding of the jet activity in 1995 requires a combination of nucleus topology, the changing solar aspect of the nucleus and precession. However, the stability of the jets seen in 1996 shows that the rotational state must be only minimally excited. A key issue which must be addressed is how typical comet Hale-Bopp's dust and dust activity are in relation to other comets? Whilst the gas activity is found to be absolutely typical (although much greater than for most comets), superheat values suggest that comet Hale-Bopp's dust was highly atypical in some senses, but only when the comet was close to perihelion. These abnormalities should not prevent comet Hale-Bopp from becoming a baseline reference for comparison with other comets.
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    URL: http://dx.doi.org/10.1023/A:1006277015025
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    Comparison of 1998 and 1999 Leonid Light Curve Morphology and Meteoroid Structure (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 351-367 
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    ISSN: 1573-0794
    Keywords: Comets ; dust ; Leonids 1999 ; lightcurves ; meteoroids ; meteors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Photometric low-light level video observations of 1999 Leonid storm meteors have been obtained from two airborne platforms during the Leonid multi-instrument aircraft campaign (Leonid MAC). The 1999 Leonid light curves tend to be skewed towards the end point of the trajectory, while the 1998 Leonid light curves were not. The variation in the light curves from 1998 and 1999 can be explained as an overall reduction in the mass distribution index, α from ∼ 1.95 in 1998 to ∼ 1.75 in 1999. We have interpreted this behaviour as being either indicative of a gradual loss of the "glue" that keeps the grains together, or the fact that the meteoroids sampled in 1998 had a different morphological structure to those sampled in 1999. The early fragmentation of a dustball meteoroid results in a light curve that peaks sooner than that predicted by classical single body ablation theory.
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    URL: http://dx.doi.org/10.1023/A:1017003019448
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