Comet Kohoutek Research Articles

Microwave continuum radiation from comet Kohoutek 1973f - Emission from the icy-grain halo

view Abstract Citations (20) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Microwave continuum radiation from comet Kohoutek 1973f: emission from the icy-grain halo? Hobbs, R. W. ; Brandt, J. C. ; Maran, S. P. ; Webster, W. J., Jr. ; Swamy, K. S. K. Abstract Cometary emission was measured at 3.71 cm on January 10-11, 1974. A possible detection at 2.8 cm and an upper limit at 11.1 cm are also reported. Interferometer measurements at 3.71 cm show that the angular diameter is less than 1.4 arc sec or less than 850 km at the comet. The corresponding disk brightness temperature is greater than 313 + or - 80 K. The radiation presumably originates in the icy-grain halo postulated by Delsemme. Publication: The Astrophysical Journal Pub Date: November 1975 DOI: 10.1086/153941 Bibcode: 1975ApJ...201..749H Keywords: Comet Nuclei; Continuous Radiation; Kohoutek Comet; Microwave Emission; Brightness Temperature; Granular Materials; Ice; Interferometry; Radio Sources (Astronomy); Astrophysics full text sources ADS |

Molecular production rates in Comet Kohoutek

view Abstract Citations (63) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular production rates in comet Kohoutek. A'Hearn, M. F. ; Cowan, J. J. Abstract Narrow-band photometry was carried out on Comet Kohoutek over a moderately wide range of heliocentric distances (0.66-1.77 AU). Production rates for C2 and CN seem to vary. C3 abundance is comparable to that for CN and C2. The comet was very dusty at large preperihelion distances and, for comparable heliocentric distances, was less dusty after perihelion than before. There was a major outburst of both dust and molecules on 1 and 2 December. The nuclear radius is of order 1 km. Publication: The Astronomical Journal Pub Date: October 1975 DOI: 10.1086/111821 Bibcode: 1975AJ.....80..852A Keywords: Abundance; Astronomical Photometry; Kohoutek Comet; Molecular Interactions; Carbon; Cyanides; Molecular Spectroscopy; Perihelions; Radicals; Rates (Per Time); Spectrophotometry; Astrophysics full text sources ADS |

Occultation of radio source PKS 2025-15 by comet Kohoutek (1973f)

This paper describes the strong fluctuations in the intensity of radio source PKS 2025-15, observed at 327 MHz, during its occultation by comet Kohoutek (1973f) in 1974, January 5. Possible mechanisms which could produce the observed fluctuations are examined. It is difficult to explain the fluctuations in terms of scintillation produced due to the passage of radio waves through the irregular cometary plasma. No detectable radio emission was observed from the comet at 327 MHz.

Spectrophotometry of Comet Kohoutek /1973f = 1973XII/

Spectrum scans have been obtained of Comet Kohoutek with a Fourier spectrometer at heliocentric distances from 0.55 to 1.05 AU. The useful spectral range is roughly 3800-8400 A and the resolution is about 10-15 A at 5000 A. Large variations occurred in the gas-to-dust ratio (pre- versus postperihelion) and in the relative strength of the NH2 bands (with heliocentric distance). There is a smaller change in the ratio of CN to C2 emission. The Swan bands of C2 show the customary anomaly in strengths implying highly non-Boltzmann distributions among vibrational levels. The red and violet CN system fluxes are in slightly better agreement with laboratory data on oscillator strengths than results on previous comets. Other species measured include Na, (O I), CH, and C3.

A Discussion on astronomy in the ultraviolet - Rocket and spacecraft studies of ultraviolet emissions from astrophysical targets

Far-ultraviolet spectral measurements from rockets and spacecraft of a number of astrophysical targets are described. Rocket studies of Arcturus (a Boo) in 1969 provided the first observation of ground state atomic hydrogen and atomic oxygen emissions from the chromosphere of a cool star other than the Sun. More recent rocket measurements show the presence of atomic oxygen (1304 A) emissions and the absence of atomic carbon (1560 and 1657 A). New studies of this star with the Copernicus satellite have provided detailed information about the spectral shape of H Ly a and Mg n 2800 A radiation. Far u.v. spectra of the planets Venus and Jupiter were also obtained during our rocket experiments. Precision photometric measurements of emissions from several bright stars were obtained with the far u.v. spectrometer aboard the Apollo 17 spacecraft. The u.v. background was also observed by the Apollo 17 spectrometer. Apollo 17 u.v. observations showed that solar protons do not produce an atomic hydrogen atmosphere on the Moon. The alternative H 2 formation would not have been detectable. Rocket studies of Comet Kohoutek on 5.1 January 1974 U.T. showed a large atomic hydrogen cloud (Ly a 1216 A), atomic oxygen (1304 A), atomic carbon (1560 and 1657 A) and OH (3090 and 3142 A).

Radio search for HC3N, HCN, OH, and detection of U8.19 in comet Kohoutek /1973f/

Radio search for HC3N, HCN, OH, and detection of U8.19 in comet Kohoutek /1973f/

On the interpretation of the observed cometary scintillations

A previous interpretation of strong fluctuations in the intensity of a radio source observed during its occultation by the plasma tail and head of Comet Kohoutek a few days after the latter's perihelion passage is examined to explain the consequence of this interpretation that plasma irregularities moved toward the cometary nucleus with speeds of between 66 and 94 km/sec. It is shown that this reversed velocity may be associated with a nonlinear wave coupled to the turbulent plasma and propagating toward the nucleus with a typical Alfven speed. The reported abrupt cessation of the radio intensity fluctuations at a distance of 80,000 km from the nucleus is shown to be due to a rather abrupt change in the plasma density.

Upper limit on the radar cross section of the comet Kohoutek

An attempt to observe radar echoes from the comet Kohoutek was made at a radio frequency of 7840 MHz ( λ ∼- 3.8 cm) on 12 January 1974 using the Haystack Observatory radar in Massachusetts. A search for an echo over a range of band-widths covering 2Hz to 66kHz yielded no positive result. The upper limit on the radar cross section is therefore approximately 10 4B 1 2 km 2 , where B is the (unknown) bandwidth of the echo in Hertz. For B ⋍ 100 Hz , it follows that (i) the nucleus, if a perfect spherical reflector, must be less than 250 km in diameter, and (ii) the density of any millimeter-sized particles must be less than 1m −3 for a coma of diameter 10 4km.

Shadow of the head of Comet Kohoutek

An earlier reported shadow of the head of Comet Kohoutek (1973f) was not found in later photographs of the comet. However, linear dark areas were seen and are described as the space between the plasma and the dust tails. The discrepancy in earlier observations is attributed to low resolution in them. Observation of a shadow is also discounted in terms of cometary physics, due to low dust content and the weakness and curvature of the dust tail.

An upper limit for methane production from comet Kohoutek by high resolution tilting-filter photometry at 3.3 μm

We have established an upper limit for the methane production form Comet Kohoutek (1973f) by searching for fluorescence radiation from the P2, P3, and P9 lines at 3.3 μm. The measurements were made on flights aboard the NASA CV990 aircraft using a new and unique high resolution, high throughput tilting-filter photometer. The photometer employed 3 dielectric interference blocking filters on a filter wheel and a 0.2mm thick solid spaced Fabry-Perot etalon with a resolution of 3.7 Å (FWHM), finesse of 43 and 42% peak transmission. The etalon had a tilt range of 6° to give a 50 Å scan. The photometer was mounted on a 12″ Dahl-Kirkham f/30 telescope and the comet was tracked using a gyro-stabilized heliostat mirror. Observations were made on flights on a line from Los Angeles to Vancouver at an altitude of 40 000 ft where the Doppler shifted comet emission lines reached the detector with little or no attenuation by atmospheric methane. The instrument was calibrated in the laboratory and by observing the thermal emission from Venus. On January 8, 1974, at 2 UT, our measurements indicated a production rate upper limit of Q ⩽ 10 29 molecules sec −1 sr −1.

Narrow band filter photometry of Comet Kohoutek

Narrow band photoelectric measurements of CN(3870), CO +(4250), C 2(4700), and C 2(5120) were made on twelve nights in December and January of comet Kohoutek. CN and C 2 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.

The light curve of comet Kohoutek

Visual estimates of total coma brightness define the light curve of Comet Kohoutek between November 24, 1973 and February 6, 1974. These data are well fitted by straight lines on the M-log r diagram. The preperihelion value of n is 2.2, and the post perihelion value is 3.8 up to January 16. A standstill in the decline is suspected between January 16 and 19. If the standstill is ignored the postperihelion data can be fitted less precisely by a single line with n = 3.3. From photoelectric measures on four nights between January 5 and 13 after perihelion, n is found to be 4.1. The average B-V with a 32.4 arc sec diaphragm for those four nights is 0.79 ± 0.04; no clear systematic variation with time is noted.

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.

A search for H 2O and Ch 4 in Comet Kohoutek

A spectroscopic search for H 2O and CH 4 in Comet Kohoutek (1973f) was made using a Pepsios interferometer. No evidence was found for either molecule, allowing us to set an upper limit on their production rates (on about 21 January 1974) of Q(H 2O) < 6.2 × 10 28 sec −1 and Q(CH 4) < 2.0 × 10 30 sec −1. If the cometary surface is water-ice, this production rate leads to a product (1 − A)·( πR 0 2) < 2.2 km 2, where A is the Bond albedo, R 0 is the nuclear radius, and we assume that all the absorbed solar energy is used to evaporate H 2O.

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.

The C-12/C-13 ratio in comet Kohoutek /1973f/

Results are presented for photoelectric scans of the C sub 2 1 to 0 band head at 4737 A at resolutions of 0.14 to 0.50 A in the comet Kohoutek. On the basis of medium-resolution scans and of one high-resolution scan two values are obtained for the C-12/C-13 ratio which are consistent within the experimental errors with the terrestrial values of C-12/C-13 equal to 89. The study also demonstrates the limitations imposed by NH2 blends.

HCN radio emission from Comet Kohoutek (1973f)

Radio emission spectra of the J = 1−0 ground state transition of H 12C 14N has been detected in comet Kohoutek (1973f) before and after perihelion passage. The HCN gas production rate is about 10 28 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.

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

Nine transitions of the possible parent molecules H 2O, NH 3, CH 3OH and N 2O 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 CH 3CN emission and OH absorption.

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.

Microwave search for molecules in Comet Kohoutek

WE report here a molecular radio line search in Comet Kohoutek using the 108–116 GHz spectral line receiver on the NRAO 36-foot telescope during January 14–18, 1974. We discuss some of the reasons for the negative results obtained in our search for transitions of methyl cyanide, cyanogen, cyanoacetylene, propynal and formic acid (all good ‘parent’ molecules for the diatomics and radicals known in the optical spectra of comets).