Narrow band filter photometry of Comet Kohoutek

Narrow band photoelectric measurements of CN(3870), CO⁺(4250), C₂(4700), and C₂(5120) were made on twelve nights in December and January of comet Kohoutek. CN and C₂ appear to be stronger after perihelion, and CO⁺ showed a strong post perihelion increase coincident with the first appearance of a strong gas tail and then decreased to a fairly constant level.     

Infrared observations of Comet Kohoutek (1973f)

Comet Kohoutek has been observed at wavelengths between 1.25 μm and 12.5 μm before and after perihelion passage extending to comet-Sun distance 1 AU. The luminosity and the variation of brightness with comet-Sun distance in the infrared are extraordinarily similar to those of Comet Ikeya-Seki (1965f). Apart from an apparent “silicate” emission feature near 10 μm, the spectrum of the comet between 3.5 μm and 12.5 μm is close to that expected from emission by grey particles. Hotter particles and scattered sunlight produce the bulk of the 1.25- to 3.5 μm emission.     

Infrared photometry and spectrophotometry of Comet Halley

We report on our photometric and spectrophotmetric measurement of Comet Halley in near infrared. The observations confirmed the explosion found in the preceding article and showed the post-explosion behaviour of the comet was different in the visible and the infrared. Water emission lines at 1.4 cm and 1.9 cm were found.     

Infrared photometric and polarimetric observations of Comet Kohoutek 1973f

Comet Kohoutek (1973f) has been observed photometrically and polarimetrically in the near-infrared region. The observed spectra revealed two components, scattered sunlight and thermal emission by dust particles. Color temperatures derived from intensities at 2.2 and 3.5 μm are close to the equilibrium temperature of a gray body with solar heating. Polarizations at 1.0 and 1.65 μm have been found to be ～15 to 20% and perpendicular to the tail direction. Properties of the dust particles in the comet are discussed in relation to these observations.     

Visual observations of Comet Kohoutek from Skylab III

Visual observations of Comet Kohoutek (1973f) by the Skylab III astronauts are presented. They include the sighting of a sunward spike or “anti-tail” on the day after perihelion.     

Solar wind interaction with the tail of Comet Kohoutek

Helical waves of large amplitude observed recently in the tail of Comet Kohoutek are interpreted as stable waves arising due to non-linear evolution of Kelvin-Helmholtz instability. The dispersion equation for waves of a finite amplitude shows that the phase velocity of these waves should approximately coincide with the velocity of the plasma outflow in the tail rather than with the Alfvén velocity. This fact is shown to be in agreement with observations. One may estimate the magnetic field in the Comet Kohoutek tail from both the amplitude of observed helical waves and the pressure balance at the tail boundary. The field turns out to be of the order of the interplanetary magnetic field or less, i.e. ?25 γ near ～0.5 AU.     

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.     

On the discovery of Comet Kohoutek (1973f)

A brief account is given of the circumstances that surrounded the discovery of Comet 1973f.     

Emission band ratios in Comet Kohoutek (1973f)

Preliminary results of a spectrum scanner study of Comet Kohoutek (1973f) are reported. Ratios of band sequence fluxes and their variations with solar distance have been determined for three sequences of C₂, and two sequences of CN from observations obtained on eleven dates. The λ4050 feature of C₃ was visible on two dates, and CH (λ4300) detectable once.     

HCN radio emission from Comet Kohoutek (1973f)

Radio emission spectra of the J = 1?0 ground state transition of H¹²C¹⁴N has been detected in comet Kohoutek (1973f) before and after perihelion passage. The HCN gas production rate is about 10²⁸ molecules sec^?1 at a heliocentric distance of ～0.4 AU. Multiple Doppler shifts in the observed spectrum suggest jets with velocities ranging up to several km sec^?1.     

Tail structure farr from the head of Comet Kohoutek. I

Two tail structures 0.1AU from the head of Comet Kohoutek were photographed during January 1974. One was a wavy structure resembling a helix while the other was an irregular Swan-like cloud. Both features were propagating down the tail at approximately 250km/sec, and the observed speed is probably the phase speed. We discuss the physical origin of these structures and interpret the helix as a kink instability resulting from currents flowing along the tail axis.     

Charge-coupled device photometry of Comet P/Halley

Comet P/Halley has been observed during its approach to perihelion at heliocentric distancesR = 11.0 AU and R = 8.2 AU. No extended coma is seen and limits can be placed on the fraction of the total light contributed by coma. The brightness of the comet varies on a short time scale. The variations may be due to transient activity or to rotation of the irregular nucleus.     

Photoelectric observations of band strengths in Comet Kohoutek (1973f)

Photoelectric observations of the strength of the CN band at 3880 Å and of the C₂ bands at 5165 Å and 5635 Å were obtained on eight nights from January 13, 1974 to February 21, 1974. Observations were limited to the nucleus and inner coma.     

Multiband photometry of Comets Kohoutek,Bennett, Bradfield,and Encke

Observations of Comets Kohoutek (1973f), Bradfield (1974b), and P/Encke have been made at a number of wavelengths between 0.55 and 18 μm. The silicate feature first observed in Comet Bennett (1969i) seems to be a common characteristic of cometary material. The comas of these comets radiate infrared with an effective temperature higher than the black-body temperature at the given distance from the Sun. The albedo of the dust particles is between 0.10 and 0.20. The particles in the coma and tail are small (diameter less than 2 μm), but the particles in the anti-tail of Comet Kohoutek must be larger than about 10 μm diameter. The observations give an absolute upper limit to the diameter of Comet Kohoutek of 30 km. A consistent interpretation would indicate that Comets Kohoutek and Bradfield have nuclear diameters of 5 to 10km, that Bennett was several times larger, and that P/Encke is 10 times smaller. The peculiar behavior of Bradfield showed that the coma of a single comet can abruptly change its dust composition.     

An upper limit on the evolution of carbon monoxide from Comet Kohoutek

An upper limit on the rate evolutio ofComet Kohoutek has been obtained from a search for resonant scatterinf of sunlight near 4.7μm. Thee observations were made approximately two months after perihelion. The rate of evolution of CO at that time appaapparently less than that of CH₃CN observed before perihelion.     

Molecule searches in Comet Kohoutek (1973f) at microwave frequencies

Nine transitions of the possible parent molecules H₂O, NH₃, CH₃OH and N₂O as well as the OH radical were searched for in Comet Kohoutek (1973f) in the frequency range 22.2–25.2 GHz. These molecules were not detected, but the upper limits for the optical depth, mean column density and the production rate are derived for each of the molecules. These results are discussed and compared with the reported detections of HCN and CH₃CN emission and OH absorption.     

Infrared Spectroscopy of Comet Hale-Bopp

High resolution (λ/δλ ∼ 20,000) spectra of comet C/1995 O1 (Hale-Bopp) in the 2–5 μm region were obtained during UT 2–5 March 1997 using CSHELL at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The heliocentric and geocentric distances of the comet were ∼1.1 AU and ∼1.5 AU,respectively. We detected emission lines of the gas-phase molecules H₂O, ₄, C₂H₆, C₂H₂, HCN, and CO and derived absolute production rates and relative abundances for all species. We also used the 2-dimensional nature of the CSHELL data to investigate the spatial distribution of the molecules and find evidence that CO was derived at least partly from an extended source in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.     

JHK photometry of Comet Bowell (1982I)

Comet Bowell (1982I) was observed at JHK (1.25, 1.68, 2.25 μm) with the NASA Infrared Telescope Facility on 10 March 1981, 3–5 June 1981, and 22 February 1982. The inner coma was no brighter near perihelion in February 1982 than it was in 1981. Total are × albedo of the grains within 10⁴ km of the nucleus was ～5 × 10¹²cm².