A search for millimeter wave spectral lines from comet Sugano-Saigusa-Fujikawa (1983e)

The search for radio spectral lines from Comet Sugano-Saigusa-Fujikawa (1983e) was conducted using the 45-m telescope of Nobeyama Radio Observatory. The frequency ranges of 44.0–46.0 and 47.5–49.5 GHz were surveyed down to $\text{ΔT}{}_{\mathrm{<mtext>A</mtext>}}{}^1\text{(}\text{rms}\text{) = 20–30}\text{mK}$, with a beam size of ～35 arc sec. Upper limits have been established for spectral lines of atomic hydrogen, CS, OCS, SO₂, H₂CO, CH₃OH, HCCCCCN, HCOOCH₃, CH₃OCH₃, and CH₃CH₂CN. The J = 5?4 line from HCCCN in the vibrational ground state possibly has been detected but not confirmed. The suggested total amount of HCCCN in the coma is consistent with the possible picture that HCCCN is the main parent molecule of CN.     

Radioastronomical observations of comets IRAS-Araki-Alcock (1983d) and Sugano-Saigusa-Fujikawa (1983e)

Detections and upper limits to the continuum emission (1 ≤ λ ≤6 cm) and spectral line emission (OH, CO, CS, HCN, HCO⁺, CN, CH₃CN, CH₃C₂H, NH₃, H₂O, HC₃N, CH₃CH₂CN) are reported from radio observations of Comets 1983d and 1983e. Comparison is made with observations of CN at optical wavelengths. These results may be useful in planning future cometary observations.     

Temperature of Comet IRAS-Araki-Alcock (1983d)

Infrared (1.5–20 μm) observations of the nuclear condensation of Comet IRAS-Araki-Alcock (1983d) during the interval 5–8 May 1983 (UT) show that the distribution of 3.5- to 20-μm radiation was blackbody in character with no evidence of 10-μm emission from silicate grains in the coma of the comet. The observed color temperature of the nuclear condensation of the comet was 319 ± 5°K on 7 May and 307 ± 5°K on 8 May. Low-resolution spectrophotometry on 5 May in the 1.5- to 2.6-μm region shows no obvious emission or absorption features, but thermal radiation of approximately the same color temperature as the 3.5- to 20-μm radiation was present along with reflected sunlight. Scans of the nuclear region of the comet indicate that most of the thermal radiation observed at 11.6 and 20.0 μm came from an ≤120-km-diameter, unresolved area centered on the nuclear region. Absolute flux measurements suggest that projected areas (unit emissivity) of 70 and 40 km² were responsible for the thermal radiation from the nuclear condensation on 7 and 8 May, respectively. This large change in total surface area suggests that the amount of dust in the nuclear region of Comet 1983d was highly variable and is consistent with the observation by M.A. Feierberg, F.C. Witteborn, J.R. Johnson, and H. Campins (1984, Icarus, 60, 449–454) of an outburst on 11 May 1983.     

Orbit of comet C/1860 M1 (Great Comet of 1860)

Comet C/1860 M1 (Great Comet of 1860) is one of a large number of comets with parabolic orbits. Given that there are sufficient observations of the comet, 261 in right ascension and 251 in declination, it proves possible to calculate a better orbit. The comet's orbit is hyperbolic, and statistically different from a parabola. The comet, therefore, cannot be considered to be a Near Earth Oject. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new orbit of Comet 1961 V (Wilson-Hubbard)

A definitive orbit of Comet 1961 V (Wilson-Hubbard), based on 84 observations, is given.     

Infrared spectrophotometry of Comet IRAS-Araki-Alcock (1983d): a bare nucleus revealed?

Spectra of the central core and surrounding coma of Comet IRAS-Araki-Alcock (1983d) were obtained at 8–13 μm on 11 May and 2–4 μm on 12 May 1983. Spatially resolved measurements at 10 μm with a 4-arcsec beam showed that the central core was more than 100 times brighter than the inner coma only 8 arcsec away; for radially outflowing dust, the brightness ratio would be a factor of 8. The observations of the central core are consistent with direct detection of a nucleus having a radius of approximately 5 km. The temperature of the sunlit hemisphere was > 300 K. Spectra of the core are featureless, while spectra of the coma suggest weak silicate emission. The spectra show no evidence for icy grains. The dust producton rate on 11.4 May was ～ 10⁵ g/sec, assuming that the gas flux from the dust-producing areas on the nucleus was ～ 10^?5 g/cm²/sec.     

The distribution of dust in the inner coma of comet IRAS-Araki-Alcock (1983d)

High-resolution images of comet IRAS-Araki-Alcock taken on five separate through its closest approach to the Earth are presented. The images were taken in the red and near-infrared, and so consist primarily of continuum scattering from dust grains. The distribution of dust in the inner coma varied widely from day to day, although the dust was emitted primarily in the sunward direction on all days. The main emission exhibited a lag angle consistent with a nuclear rotational vector that was oriented approximately along the line of sight on May 11.3 1983 UT. A curved filament, extending in the sunward direction, was seen in the deepest images obtained on this day as well, and the azimuthal distribution of dust was strongly of dust was strongly peakeed in the sunward direction. The presence of the curved filament is indicative of dust outflow from an active region, on a mantled nucleus. On all days, the brightness falls off slower than the r⁻ expected for uniform outflow, which is interpreted as resulting from fragmentation of the dust grains as they traveled through the coma. The nuclear region appeared stellar on all days. The seeing-limited spatial resolutions was 19 km on May 11.3, but deconvolution of the images with the instrumental profile enables an upper limit of 17 km to be placed on the diameter of the nucleus.     

The time evolution of periodic comet Russel 3, 1983i

The orbit of the newly-discovered comet P/Russel 3 (1983i) is integrated backward and forward to study its evolution within time. Two close approaches with Jupiter in the limited calculation are found: one on December, 1941 and the other on May, 2024. Since its aphelion lies near the Jupiter orbit the orbit of P/Russel 3 appears to be rather unstable.     

Very small dust particles (VSDP's) in comet C/1996 B2 (Hyakutake)

X-ray fluxes observed from comet C/1996 B2 (Hyakutake) are readily explained in terms of scattering by carbonaceous particles with radii of several tens of Angstroms. A few tenths of a megatonne of such particles appear to have been present in the cometary coma on March 26–28 1996.     

A note on the very small grains (VSGs) observed at Halley's comet

The most striking feature in the spatial distribution of the smallest dust grains observed at Halley's comet by the VEGA-1 spacecraft is the sharp glitch at a cometocentric distance of about 180 000 km, which approximately corresponds to the so-called cometopause inside which the contaminated solar wind plasma was rapidly cooled. We propose that this glitch was caused by the electrostatic disruption of larger composite grains which rapidly charged up as they traversed the cometopause. The clear asymmetry in the distribution between the inbound and outbound portion of the spacecraft trajectory is also consistent with the dynamical effects of grain charging although other causes are not excluded.     

Comet Hale-Bopp (1995 O1)

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.     

Spectrophotometry of Comet Bradfield (1987s)

Spectral scans of Comet Bradfield (1987s) at heliocentric distance of 1.539 AU have been observed spectrophotometrically. The column densities and production rates of C₂ and CN have been derived.     

Spectrophotometry of comet Hartley-Good (1985l)

We present spectrophotometric studies of comet Hartley-Good (1985l) in the spectral region 3200–7000 Å. The emission features of molecules CN, CH, C₂, and C₃ are observed. The variation of the emission strength of different species has been studied as a function of heliocentric distance. The abundances (N) and production rates (Q) of the molecules are also estimated.     

Spectrophotometry of comet Levy (1990c)

Two spectrophotometric scans of comet Levy (1990c) have been analysed to estimate Haser model column densities and production rates of CN andC ₂ molecules.     

Photographic observations of Comet Halley (1982i)

Positions of Comet Halley have been measured from the photographic plates taken at Cassegrain focus of the 104-cm telescope of Uttar Pradesh State Observatory.     

Particle sizes in Comet Bennett (1970 II)

The particle size distribution in the coma and tail of Comet Bennett has been determined by several methods, each sensitive to a particular size range. It is confirmed that a minimum value of the particle density (?), size (d), and radiation pressure efficiency (Q_rp) function (?d/Q_rp) exists at about 3–10 sx 10^?5g cm^?2. The existence of such a cutoff is probably due to the decreasing radiation pressure efficiency for particles smaller than the wavelength of the light being scattered. An exact determination of this cutoff may allow identification of the particle type.     

Spectrophotometric observations of Comet Austin (1982g)

Spectrophotometric observations of Comet Austin (1982g) in the bands of CN, C₂, and C₃ are presented, and fit to a Haser model for the cometary brightness distribution. The lifetimes of the parent and daughter molecules, as well as the velocity of the molecules leaving the cometary surface are determined from the model fit. The absolute production rate of molecules is also determined.     

Astrometric positions of Comet Wilson (1986l)

Positions of comet Wilson have been measured from the photographic plates taken at the Cas-segrain focus of the 104-cm reflector of Uttar Pradesh State Observatory, Naini Tal.     

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.     

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.