Absolute spectrophotometry of Comet Kohoutek 1973f: I. Column densities of cyanogen

Absolute spectrophotometry of the coma of Comet Kohoutek 1973f is discussed for the nights of January 24 and 26, 1974. Specific intensities are measured for spectral features and a continuum band in the wavelength region λλ3460–6062Å. The (0, 0) band of the Δν = 0 sequence of the violet system of the cyanogen molecule is analyzed and column densities of 1.7 × 10¹⁵m^?2 and 3.4 × 10¹⁴m^?2 are found for January 24 and 26, 1974, respectively. The analysis of the bands of C₂ will be reported in a second paper of this series.     

Spectrophotometry of Comet Austin (1982g) during post-perihelion period

Lunar crustal shortening does not seem to be restricted to the lava-filled basins alone; but there are some young scarp-like terra ridges in places around mare areas where they often continue other tectonic structures. This crustal shortening has not reached the same intensity as in the case of the lobate scarp overthrusts on Mercury. Young lunar terra ridges indicate that crustal shortening with an areal extent also took place slightly around mare basins. Thus they link tensional rille tectonics with compressional mare ridge tectonics and indicate that areal heating/bending/extension — cooling/ shortening/compression may describe an important explaining factor in lunar mare- and near-mare tectonics in addition to the volcanic extrusions.     

Spectrophotometry of Comet Bradfield (1980t) during post-perihelion period

Spectrum scans of the head of Comet Bradfield (1980t) covering the wavelength range 365–640 nm were made on two nights when the heliocentric distance of the comet varied from 0.55 to 0.58 AU. The emission features of the CN band at 388 nm and Swan band sequence of C₂ at 474 nm, 516 nm, and 563 nm are identified and absolute fluxes in these bands as well as in the continuum are derived. The continuum energy distribution curves of the comet have been compared with those of the Sun and the star Crv (G5 III). An estimate of the number of C₂ and CN molecules in the head of the comet has been made through the measured intensities of their respective bands lying in this region.     

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 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.     

On the discovery of Comet Kohoutek (1973f)

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

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.     

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.     

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.     

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.     

A search for microwave emission from CH in Comet Kohoutek (1973f)

A search was conducted for the three 9-cm transitions of the ground state Λ-doublet of CH in comet Kohoutek, using the CSIRO 64-m radio telescope and the Onsala Space Observatory's 25.6-m telescope. No lines were detected during the observing periods, and upper limits are given for the corresponding antenna temperatures.     

On the shape and orientation of the tail of Comet Kohoutek (1973f)

Twenty-two photographs of Comet Kohoutek (1973f) have been projected onto the comet's orbital plane under the assumption of a flat tail confined in that plane. The comet has a mixed-type tail; therefore the results concerning Type I and Type II components of the tail are presented separately. The axis of the Type I tail appears to sweep back and forth with respect to the prolonged radius vector in a rather periodical way. Interpretations advanced by some authors for the analogous case of Comet Burnham (1959k) are mentioned briefly. For the Type II tail, a comparison with a theoretical tail model by Sekanina has allowed us to establish when the onset of appreciable dust production occurred. Finally, mention is made of the fact that some peculiarities of the dust tail might be also explained by assuming a three-dimensional model.     

Absolute spectrophotometry of 22 vulpeculae during the eclipse of 1990

The results of broadband photometric observations of 22 Vulpeculae (QS Vulpeculae) between 1984 and 1994 have been considered and unified to produce a composite light curve. The spectral types of the binary components and their contributions to the total luminosity of the binary are estimated using the absolute spectrophotometry of 22 Vulpeculae. The absorption in the visible region is taken to be A(V) = 0 ^m .0.     

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.     

Near-infrared observations of the dust coma of Comet Kohoutek (1973f) with a tilting-filter Fabry-Perot photometer

By means of narrow-band Fabry-Perot filters, which exclude the interference from molecular line fluorescence, the brightness of Comet Kohoutek (1973f) has been measured at 8560 and 8748 Å. Data reduction on the basis of averaged Mie-scattering cross sections indicates that the dust production rate was different before and after perihelion at the same heliocentric distances. This asymmetry suggests that vaporization and dust entrainment were governed by fractionation of a multicomponent mixture of parent molecules in a comparatively porous cometary nucleus.     

Some speculations about the origin of the high speed HCN jets in Comet Kohoutek (1973f)

The origin of the high speed HCN jets observed in Comet Kohoutek (1973f) is considered. It is argued that the occurrence of these jets with Doppler shifts corresponding to velocities of 3–5 km s^–1 with respect to the nucleus cannot be explained in terms of either (a) explosive outbursts of trapped sub-surface volatiles, (b) highly exothermic chemical reactions involving free radicals [or a combination of (a) and (b)] or (c) the outward expansion of the cometary atmosphere with additional heating. Instead, acceleration of the precursor ions of HCN by energetic electrons in the ionospheric current sheets or current arcs is suggested to play an important role. Also, a fraction of the HCN observed by electric discharges, associated with the ionosphere current system through the cometary atmosphere. It is not possible to make a realistic estimate of this fraction at the present time, but that it may be significant cannot be entirely excluded by the existing observations.     

Comet orbits from observations during 1984 and orbital elements for the next perihelion passage

Es wurden korrigierte Bahnen für 21 Kometen, basierend auf in den Minor Planets Circulars publizierten Beobachtungen, berechnet. Die Bahnelemente für die nächsten Periheldurchgänge von kurzperiodischen Kometen sind ebenfalls gegeben.     

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.     

8- to 13-μm spectrophotometry of Comet IRAS-Araki-Alcock

We present spectrophotometry between 8.0 and 13.0 microns at 2% spectral resolution for areas in and near the nuclear condensation of Comet IRAS-Araki-Alcock (1983d) on May 11 and 12, 1983. All the spectra can be fit very well by blackbody curves, and no 10 micron silicate emissions are seen. The temperature structure of the coma suggests the presence of small (radii <5 microns) dust particles within 150 km of the nucleus and larger ones further out. The change in the spatial distribution of the infrared flux between the two nights suggests that an outburst may have occurred sometime on May 11.