Comet Kohoutek Research Articles

Observations at Nançay of the OH 18-cm lines in comets

Since the apparition of comet Kohoutek 1973 XII, the 18-cm lines of the OH radical have been systematically observed in a number of comets with the Nancay radio telescope. Between 1973 and 1999, 52 comets have been successfully detected. This allowed an evaluation of the cometary water production rates and their evolution with time, as well as a study of several physical processes such as the excitation mechanisms of the OH radio lines, the expansion of cometary atmospheres, their anisotropy in relation to non-gravitational forces, and the Zeeman effect in relation to the cometary magnetic field. Part of these observations and their analysis have already been published. The bulk of the results are now organized in a data base. The present paper is a general presentation of the Nancay cometary data base and a more specific description of the observations of 53 cometary apparitions between 1982 and 1999. Comets observed before 1982 are only partly incorporated in the data base. Observations of comets since 2000 have benefited from a major upgrade of the telescope; they will be presented in forthcoming publications.

Photoelectric photometry of comet Kohoutek (1973 XII = C/1973 E1): the production rates of CN, C 2, and solid refractory particles typical of dynamically new comets

In the past the enterprise to study comet Kohoutek (1973 XII), then called “The Comet of the Century”, was proportionally comparable only with the recent and highly successful one to study comet P/Halley (1986 III). Now over 20 years after this historical endeavour, the original photometric data obtained by Lubos Kohoutek on 14 nights between January 16 and 30, 1974, post-perihelion, when the heliocentric and geocentric distances of the comet were r = 0.66 – 1.00 AU and Δ = 0.81 – 0.96 AU, using the 50 cm (f/15) reflecting telescope of the European Southern Observatory (ESO) in La Silla (Chile) are analysed. Emission fluxes of the bright 388.4 nm CN (0,0) band, the prominent 473.7 nm C 2 (1,0) and 517.2 nm C 2 (0,0) Swan bands, and the 530.0 nm red continuum are studied in the framework of Haser's isotropic radial outflow model. Parent gas production rates of CN, C 2, and the gas-to-dust ( Afϱ parameter) ratio for each observation is determined. An average gas mass loss dM g dt ≈ 1675 kg s −1 is estimated. Using the single particle dust model of Richter and Keller ( Astron. Astrophys. 206, 136–142, 1988) an average total dust production rate dM d dt = 1.6 × 10 4 kg s −1 is calculated, and the average emission lifetimes in the coma for small ( a 1 = 0.6 μm) and large ( a 2 = 600 μm) particles have been estimated in about 2 days (≈ 1.70 × 10 5s) and 2 months (≈ 5.36 × 10 6s), respectively, for a coma of radius R = 2 × 10 5 km.

IUE observations of H Lyman-α in comet P/Giacobini-Zinner

Comet P/Giacobini-Zinner (1985 XIII) was observed during the flyby of the International Cometary Explorer (ICE) satellite and during the 3 preceding months by the International Ultraviolet Explorer (IUE) satellite. Models for the hydrogen abundance and spatial distribution, which were previously used to reproduce the observed spatial distribution of the wide-field Lyman-α comae of Comets Kohoutek and Halley measured by rocket and spacecraft borne instruments, have now been successfully applied to these IUE observations. Vectorial models, which implicitly assume production of cometary OH by dissociation of water molecules, have been routinely used to infer global water production rates from various nucleus-centered IUE observations of comets. However, because of modeling complexities, a large base of Lyman-α observations has not generally been analyzed. One of these modeling complexities is that often the H atom column densities are high enough so that the coma is optically thick to solar Lyman-α radiation which cannot be treated by the standard optically thin models (Haser, vectorial, or Monte Carlo). A spherical radiative transfer model, adapted for application to the H coma, has been used to analyze the IUE observations. This analysis yields water production rates in very good agreement with those calculated from vectorial model analysis of OH observations. The H model makes essentially the same physical assumptions as the vectorial model for OH except for optical density. A further interesting aspect of this dataset is that various offset observations of the Lyman-α brightness were made on August 12, and September 10 and 11, 1985, at sampling distances of 7,500 to 41,000 km. This is much higher spatial resolution that is typically available from the usual rocketborne cameras which have made most of the wide-field measurements of the H distribution in comets. The same H model, in combination with the radiative transfer calculation, also reproduces the observed spatial distribution of H in the inner coma.

Haser model CN, C2 and C3 production rates in some comets

Emission fluxes of CN, C2 and C3 species observed in the coma of some comets are analysed in the framework of Haser model. CN, C2 and C3 production rates are determined using recently derived fluorescence efficiencies and dependence of CN, C2 and C3 production rates on the heliocentric distance is studied. Evidence for a burst type activity around January 15, 1974 in the post-perihelion period of comet Kohoutek (1973f) is observed.

Comets in the space age

view Abstract Citations (24) References (101) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Comets in the space age Whipple, F. L. Abstract The historical development of the study of the nature of comets and their origin is discussed, emphasizing the use of aerospace technology in cometary science. The use of satellites to study the Comet Kohoutek 1973 XII, advances between Kohoutek and P/Halley, and studies of P/Halley during its 1986 return are examined. Consideration is given to data from ground, air, and space sensors, and from the Giotto and Vega spacecraft missions. Also, the physical structure of the nucleus of Comet Halley is described. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167466 Bibcode: 1989ApJ...341....1W Keywords: Comet Nuclei; Cometary Atmospheres; Comets; Giotto Mission; Light Curve; Vega Project; Fractals; Interplanetary Dust; Kohoutek Comet; Magnetohydrodynamics; COMETS; HISTORY; PHYSICAL PROPERTIES; COMET NUCLEI; ORIGIN; FORMATION; DIAGRAMS; KOHOUTEK; HALLEY; ASTRONOMY; LIGHTCURVES; STRUCTURE; COMAE; COMET TAILS; SHAPE; COMPOSITION; DUST; SPACECRAFT OBSERVATIONS; REVIEW; EARTH-BASED OBSERVATIONS; GRAINS; MODELS; HYPOTHESES; COMETESIMALS; COMPARISONS; SATELLITE OBSERVATIONS; Astrophysics; Comets full text sources ADS |

Infrared emission from comets

A brief discussion of the infrared observations from 4 to 20 micrometers of seven comets is presented. The observed infrared emission from comets depends primarily on their heliocentric distance. A model based on grain populations composed of a mixture of silicate and amorphous carbon particles in the mass ratio of about 40 to 1, with a power-law size distribution similar to that inferred for comet Halley, is applied to the observations. The model provides a good match to the observed heliocentric variation of both the 10 micrometers feature and the overall thermal emission from comets West and Halley. Matches to the observations of comet IRAS-Araki-Alcock and the antitail of comet Kohoutek require slightly larger grains. While the model does not match the exact profile and position of the 3.4 micrometers feature discovered in comet Halley, it does produce a qualitative fit to the observed variation of the feature's strength as a function of heliocentric distance. The calculations predict that the continuum under the 3.4 micrometers feature is due primarily to thermal emission from the comet dust when the comet is close to the Sun and to scattered solar radiation at large heliocentric distances, as is observed. A brief discussion of the determination of cometary grain temperatures from the observed infrared emission is presented. It is found that the observed shape of the emission curve from about 4 to 8 micrometers provides the best spectral region for estimating the cometary grain temperature distribution.

Monte Carlo particle-trajectory models for neutral cometary gases. I - Models and equations. II - The spatial morphology of the Lyman-alpha coma

The mathematical derivations of various methods employed in the Monte Carlo particle-trajectory model (MCPTM) are presented, and the application of the MCPTM to the calculation of the photochemical heating of the inner coma through the partial thermalization of cometary hydrogen atoms produced by the photodissociation of water is discussed. This model is then used to explain the observed morphology of the spatially extended Ly-alpha comas of comets. The rocket and Skylab images of the Ly-alpha coma of Comet Kohoutek are examined.

Fluorescence efficiency factors for ionized water vapor

view Abstract Citations (24) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fluorescence Efficiency Factors for Ionized Water Vapor Lutz, Barry L. Abstract Fluorescence efficiency factors and absorption oscillator strengths are presented for the à 2A1-X~ 2B1 transition of H2O+. The abundance of H2O+ in the tail of comet Kohoutek 1973 XII is re-examined and the H2O+/CO+ ratio is found to have been 0.8±0.2. Publication: The Astrophysical Journal Pub Date: April 1987 DOI: 10.1086/184877 Bibcode: 1987ApJ...315L.147L Keywords: Efficiency; Fluorescence; Ionized Gases; Kohoutek Comet; Molecular Ions; Water Vapor; Abundance; Born-Oppenheimer Approximation; Comet Tails; Computational Astrophysics; Ground State; Transition Probabilities; Astrophysics; ABUNDANCES; COMETS; MOLECULAR PROCESSES; TRANSITION PROBABILITIES full text sources ADS |

Absolute spectrophotometry of Comet kohoutek 1973f during post-perihelion passage

Absolute spectrophotometry of the coma of Comet Kohoutek 1973f during post-perihelion period has been presented for seven nights in January 1984. Moderately wide range of heliocentric distance (0.436–0.799 AU) covered during observations allowed us to study the flux variation of emission bands with heliocentric distance. The emission features of CN, CH, C2, C3, and NaI have been identified in this comet. The abundances of CN and C2 have been estimated and the production rates of CN, C2 and C3 have been derived. Production rates of CN and C2 seem to vary as r −0.33 and r −3.50 respectively. The continuum of the comet became more and more redder as the heliocentric distance of the comet increased and phase angle decreased.

Laboratory Infrared Transmission Measurements of Interplanetary Dust and Implications for Remote Observations of Cosmic Particles

AbstractLaboratory infrared absorption spectra of interplanetary dust particles show that most fall into one of three spectral groups (1) designated as “pyroxenes”, “olivines”, and “hydrated silicates”.Comparisons with 10 μm emission data from Comet Kohoutek (2) show that no single spectral type matches the cometary data. However, a reasonable match is obtained by coadding equal amounts of pyroxene and hydrated silicate type spectra.The possibility that the 10 μm feature seen in some comets is due to a combination of these two components can be tested in two ways. First, the pyroxene type spectra show detailed features of variable position and strength within their 10 μm bands. Based on the laboratory data we estimate that comet spectra taken at a resolution of λ/Δλ ~ 200 would be sufficient to find these features, if present. The magnitude of these features is expected to be ≤ 0.1 of the maximum strength of the 10 μm band.Second, the hydrated silicate particles usually have bands at 3.0, 6.2, and 6.9 µm. The first two bands are probably linked to the presence of water while the 6.9 μm band is probably due to carbonates. The 3.0 μm feature is broad and might be hard to separate from thermal background. However, spectra taken at resolutions of λ/Δλ ~ 50 could see the 6.2 and 6.9 μm bands. The strengths of these bands (which are also seen in the spectra of CM meteorites) vary (one particle has a carbonate band that is actually stronger than its corresponding 10 μm silicate band), but are typically ~0.1 the depth of the silicate features. A second, narrow carbonate band at 11.4 μm can also sometimes be seen in particle spectra but its strength is less than that of the 6.9 μm band. This the search for the 6.2 and 6.9 μm bands in astronomical objects, while not requiring high resolutions, would require good S/N.

On the Bimodal Nature of the Particle-Size-Distribution Function of Cometary Dust

AbstractThe bimodal nature of distribution function f(γ) is confirmed by analysing the optical isophotal maps of comets Kohoutek 1973 XII and Bennett 1970 II. Extending the dynamic analysis to the infra-red data of two comets, Kohoutek 1973 XII and IRAS-Araki-Alcock 1983 d, we demonstrate that the secondary component f2(γ), which dominates in the range of large particles, plays a much more important role in emitting the thermal radiation (IR) than in the case of light scattering (optical). The relative weight of two components, measured by their height ratio, g2/g1, should be increased by a factor of about 20, in order to obtain a good fitting to the infra-red data.

Hydrogen production rate from comet Austin 1982g

Meaningful measurements with respect to the cometary Balmer-alpha (H-alpha) emission are difficult and require the use of special equipment. The first ground-based observations of H-alpha emission from a cometary hydrogen corona were conducted on comet Kohoutek 1973 XII with a large-aperture Fabry-Perot spectrometer installed at the McMath solar telescope at Kitt Peak National Observatory. The present investigation is concerned with the second ground-based observations of cometary H-alpha emission carried out during the apparition of comet Austin 1982g. A 150 mm dual-etalon Fabry-Perot spectrometer was employed in the experiment. Use was made of an observatory which is designed for the high spectral resolution study of faint extended sources such as interstellar and geocoronal emission lines. The investigation demonstrates that hydrogen production rates from comets as faint as about 7th magnitude can be routinely measured from the ground at minimal cost.

A search for the 10-micron silicate feature in periodic Comet Grigg-Skjellerup

A 10-micron spectrum of periodic Comet Grigg-Skjellerup was obtained on 22 June 1982 with the UCL array spectrometer at the United Kingdom Infrared Telescope, Mauna Kea. No emission feature is obvious in the spectrum. The observed spectrum can be fit equally well by a model of small hot absorbing grains or by a composite model with less than or equal to 30 percent (3sigma) warm, 'dirty' silicate grains. The latter model is consistent with the silicate abundance in Comet Kohoutek, which did display an emission feature at 10 microns.

Infrared photometry of periodic comets Encke, Chernykh, Kearns-Kwee, Stephan-Oterma, and Tuttle

Nearly simultaneous photometry of the reflected and thermal infrared spectra of periodic comets Encke, Chernykh, Kearns-Kwee, Stephan-Oterma, and Tuttle are presented. The 10-μm, silicate emission feature has been detected for the first time in periodic comets and was observed in three of these objects. The albedo of the dust particles in the comae of these comets is calculted and compared to that of Comet Kohoutek. The peculiar behavior of the dust in Comet Encke is discussed.

Kelvin-Helmholtz instabilities in cometary ion tails

We interpret observations of wave-like phenomena in cometary ion tails in terms of the interaction of the tails with the solar wind through Kelvin-Helmholtz helical instabilities. The calculations are applied to three comets, Comet Kohoutek (1973f), Comet Arend Roland (1957 III) and Comet Morehouse (1908c). Whilst some disagreement is found with earlier work, it is nevertheless shown that, assuming typical parameters, the growth rate of the K-H helical mode should be significant for wavelengths approximately equal to the tail radius.

A search for millimeter-wave emission from HCN and other molecules in Comet Bradfield (1979l)

Millimeter-wave emission from HCN, CS, CH 3OH, and two unidentified lines (previously observed in Comet Kohoutek (1973 XII)) was sought and not detected from Comet Bradfield (1979l) after perihelion passage. Limits on column densities and production rates are derived. In the case of HCN, the production rate is less than that reported for Comet Kohoutek, even after scaling relative to the observed OH emission from each comet.

Plasma dynamics in the tail of Comet Kohoutek 1973 XII

Photographs of Comet Kohoutek 1973 XII from the period 1974, Jan. 19, 0 UT to Jan. 21, 3 UT, collected from many different observatories and assembled in a unified format, are studied. During this time a large-scale tail disturbance was observed which coincides with the passage of a high-speed solar wind stream and an interplanetary sector boundary. Superimposed on a regular outward motion of tail condensations of a speed less than or about 100 km/sec, a kink moves down the tail with almost solar wind velocity. From the shape of the kink the direction of the solar wind adjacent to the tail is deduced. Of particular interest are tail segments where the solar wind flows across the tail. A waviness on the windward side of the tail is explained by differential acceleration, i.e., dense tail clouds are more massive and therefore less accelerated by the solar wind. On the leeward side tail rays point into the down-wind direction. During the large-scale disturbance the overall plasma density seems to be enhanced. While a tail disconnection does not occur in the event studied it is proposed that the tail disconnection observed in other, more dramatic events is caused by the differential acceleration mechanism combined with changes in the ion source. These are possibly due to enhanced charge exchange of cometary neutrals in the compression region in front of the high speed stream. The problem of tail ray formation near tail condensations is discussed but no solution is offered.

Hydrogen production rates from ground-based Fabry-Perot observations of comet Kohoutek

The only ground-based observations of a cometary hydrogen corona that have been obtained up to the present were carried out during the appearance of comet Kohoutek (1973 XII). Hydrogen Balmer alpha (H-alpha) emission from the gas cloud surrounding the comet was detected using a Fabry-Perot spectrometer at Kitt Peak National Observatory. These observations have been reexamined using (1) recently obtained solar full-disk Lyman beta emission line profiles, (2) a new calibration of the absolute sensitivity of the Fabry-Perot spectrometer based on comparison of NGC 7000 with standard stars and the planetary nebula NGC 7662, and (3) corrections for atmospheric extinction instead of the geocoronal H-alpha comparison method used previously to obtain comet H-alpha intensities. The new values for hydrogen production rates are in good agreement with results obtained from Lyman alpha observations of comet Kohoutek.

A model of comet comae. II - Effects of solar photodissociative ionization

Improvements to a computer model of coma photochemistry are described. These include an expansion of the chemical reactions network and new rate constants that have been measured only recently. Photolytic reactions of additional molecules are incorporated, and photolytic branching ratios are treated in far greater detail than previously. A total of 25 photodissociative ionization (PDI) reactions are now considered (as compared to only 3 PDI reactions previously). Solar PDI of the mother molecule CO2 is shown to compete effectively with photoionization of CO in the production of observed CO(+). The CO(+) density peak predicted by the improved model, for CO2 or CO mother molecules, is deep in the inner coma, in better agreement with observation than the old CO2 model. However, neither CO2 nor CO mother molecule calculations reproduce the CO(+)/H2O(+) ratio observed in comet Kohoutek. PDI products of CO2, CO, CH4, and NH3 mother molecules fuel a complex chemistry scheme, producing inner coma abundances of CN, C2, and C3 much greater than previously calculated.

Structures far from the head of comet Kohoutek: II. A discussion of the swan cloud of January 11 and of the general morphology of cometary plasma tails

Photographs taken in New Mexico and in Japan during 1974 January 9–11 show that the “Swan Cloud” observed in comet Kohoutek on January 11 ( C. L. Hyder, J. C. Brandt, and R. G. Roosen, 1974, Icarus 23, 601–610: Paper I) was an advanced stage of a plasma tail disconnection event (DE). The event commenced and evolved with the development of strong tail ray activity, the actual tail disconnection, the merging of the disconnected tail with the new tail to form the Swan, and a new feature not discussed in recent disconnection models—the formation of arcade loops in the space between closing tail rays. An unusual aspect of the event was the deceleration of the rejected tail as it receded from the head. The observed morphological sequence is easily understood in the sector boundary model ( M. B. Niedner, Jr., and J. C. Brandt, 1978, Astrophys. J. 223, 655–670; 1979, Astrophys. J. 234 723–732), in which dayside reconnection of captured interplanetary fields at sector boundary crossings strips away the existing tail, and field capture in the new sector builds a new tail. The associated sector boundary for the event passed Earth of 1974 January 14. The arcade loops are proposed to be reconnected flux tubes between oppositely polarized tail rays in the incipient new tail which followed the disconnection. This interpretation is not only consistent with the magnetic field topology advocated in Alfvén's original model (H. Alfvén, 1957 Tellus 9 92–96), but it may also provide a physical model for some of the features known historically as “condensation,” at least some of which appear to have formed in the same manner.