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.     

Spectrophotometric study of periodic Comet Halley (1982i)

Spectral scans of the head of periodic Comet Halley (1982i) have been presented and analysed in detail in the optical region (3200–7000 Å); for ten nights during pre-perihelion period. Emission features due to NH, CN, CH, C₃, and C₂ molecules have been identified. The behaviour of the variation of different emission lines strength as a function of heliocentric distance has been investigated. It is found that the comet exhibits night-to-night variation of brightness. The abundances and production rates of CN and C₂ species have also been derived.     

An analysis of spectrophotometric observations of comets Austin (1982g) and Bradfield (1980t)

Post-perihelion observed emission fluxes at 388 nm (CN) and 516 nm (C₂) of the coma of comets Austin (1982g) and Bradfield (1980t) are analysed in the framework of the Haser model. Ratios of Haser model CN and C₂ parent production rates with expansion velocity show that each comet behaves normally. For comet Austin (1982g), the Q _CN/v and Q _c2/v values decrease with increase of heliocentric distance of comet. For an assumed %; activity of the total spherical surface area of the nucleus, the water vaporization theory coupled with derived water production rates from the International Ultraviolet Explorer H and OH flux data yields a nuclear diameter of about 6 km for comet Austin (1982g). For comet Bradfield (1980t), the derived nuclear diameter is expected to be of about 1 km. In each comet, the dust mass production rates as well as ratio of dust-to-gas mass production rates decrease with increase of heliocentric distance of comet.     

Narrowband photometry of comet Okazaki-Levy-Rudenko 1989r

The results of the photoelectric photometry with the narrowband CN, C₃, C₂ and Blue Continuum (BC) IHW interference filters are presented. Observations were carried out with a set of diaphragms of different effective radii. On the base of the Haser model the production rates of the radicals have been obtained. The CN and C₂ molecules scale lengths (3.4 × 10⁵ km and 8.5 × 10⁴ km respectively for 1.0 AU heliocentric distance) have been also derived. The dust continuum spectrum is negligibly low in comparison with the molecular one, which stay in agreement with the results of other observations of comet Okazaki-Levy-Rudenko.     

Spectrophotometry of P/Halley (1982i)

Spectral scans of the head of periodic Comet Halley (1982i) have been presented in the optical region (3200–7000 Å) for six nights. Emission features due to NH, CN, CH, C₃, C₂ and NH₂ molecules have been identified. It is found that the comet exhibits night-to-night variation of emission bands. The abundances and production rates of CN and C₂ species have been derived.     

The effect of using different scale lengths on the production rates of Comet 46P/Wirtanen

The variations in production rates for Comet 46P/Wirtanen for the species H₂O and the parents of C₂ and CN are examined from the point of view of a variety of commonly used scale lengths. The calculations are carried out as a function of heliocentric distance. It is shown that, by using a common set of scale lengths, the results of various investigators can be brought into acceptable accord. The resulting production rates of H₂O and the parents of C₂ and CN versus heliocentric distance are recalculated and plotted versus the heliocentric distance r_H. The curves show reasonable agreement with a slope of ∼r_H⁻⁴. The water production rate near perihelion of 46P/Wirtanen is close to .     

Spectrophotometry of comet West (1975n) after the perihelion passage

In the wavelength range 350 to 650 nm, the flux distribution of comet West (1975n) is presented for various dates following perihelion passage. The variations with heliocentric distance, in the flux of the emission features of the CN band at 388 nm, the C₂ bands at 474 nm, 516 nm and 563 nm and Na at 589 nm, have been discussed. It is concluded that the comet was dust rich.     

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.     

Gas and dust release from comet West (1976VI) nuclear fragments

Emission fluxes of CN, G₂ and C₃ carbon-bearing molecular species observed in the spectra of the nuclear fragment A and D of comet West (1976VI) are analysed in the framework of Haser's two-component model with radial outflow symmetry. Gas production rates have been derived and their ratios obtained. We find these vary as Q r ⁿ (where 1.0r2.6 is the heliocentric distance in AU) with photometric parametern = -4.11 (CN), -2.68 (C₂), -1.89 (C₃) andQ _x /Q _y r ⁿ withn = 2.22 (C₃/CN), 1.42 (C₂/CN), -0.79 (C₂/C₃). The gas-to-dust ratio, dust production rates in arbitrary units, total number of dust particles in the field of view and an effective radius R_eff 2.0 km for the principal nuclear fragmentA is also estimated.     

Light curve behaviour in C/1995 O1 (Hale-Bopp) — II

Comet Hale-Bopp is, without doubt, one of the most important objects for cometary science which has ever been observed. The light curve is well-observed from a heliocentric distance 7.2 AU and some information is available at distances as great as 17 AU. This allows the photometric evolution of the comet to be studied as different volatiles dominate the activity. Three different phases of activity are seen as the heliocentric distance reduces during 1996: the initial phase of very fast brightening, characterized by a r ^–5 law; a standstill in the light curve when the brightening law reduced to r ^–1, which coincides with the initiation of water sublimation at r ~ 4 AU; and a further phase of more rapid brightening with an r ^–3.5 law, similar to the mean for comets classed as fairly new, which initiated at r ~ 4 AU.     

Spectral studies of comet C/2001 Q4 (NEAT)

The paper presents the results of the spectral observations of comet C/2001 Q4 (NEAT) acquired with the Zeiss-600 telescope of the Andrushevka astronomical observatory in May 2004. The spectrum of the comet was obtained in the range of 3600–8200 Å. We identified a number of emission features in the spectrum of comet C/2001 Q4 (NEAT). The emission bands of C₂, C₃, CN, CH, NH₂, H₂O⁺ were detected in the spectrum of the comet, and their intensities were determined. The ratios of gas-production rates Q(C₂)/Q(CN) = 0.23, Q(C₃)/Q(CN) = ?0.79, and Q(NH₂)/Q(CN) = ?0.029 were determined with the Haser model.     

Photometric studies of comet C/2009 P1 (Garradd) before the perihelion

The results of the photometric observations of comet C/2009 P1 (Garradd) performed at the 60-cm Zeiss-600 telescope of the Terskol observatory have been analyzed. During the observations, the comet was at the heliocentric and geocentric distances of 1.7 and 2.0 AU, respectively. The CCD images of the comet were obtained in the standard narrowband interference filters suggested by the International research program for comet Hale-Bopp and correspondingly designated the “Hale-Bopp (HB) set.” These filters were designed to isolate the BC (λ4450/67 Å), GC (λ5260/56 Å) and RC (λ7128/58 Å) continua and the emission bands of C₂ (λ5141/118 Å), CN (λ3870/62 Å), and C₃ (λ4062/62 Å). From the photometric data, the dust production rate of the comet and its color index and color excess were determined. The concentration of C₂, CN, and C₃ molecules and their production rates along the line of sight were estimated. The obtained results show that the physical parameters of the comet are close to the mean characteristics typical of the dynamically new comets.     

Models of the cometary coma in which abundances are calculated for various heliocentric distances

One-dimensional radial models of the chemistry in cometary comae have been constructed for heliocentric distances ranging from 2 to 0.125 AU. The coma's opacity to solar radiation is included and photolytic reaction rates are calculated. A parent volatile mixture similar to that found in interstellar molecular clouds is assumed. Profiles through the coma of number density and column density are presented for H₂O, OH, O, CN, C₂, C₃, CH, and NH₂. Whole-coma abundances are presented for NH₂, CH, C₂, C₃, CN, OH, CO⁺, H₂O⁺, CH⁺, N₂⁺, and CO₂⁺.     

Spectrophotometric scan of comet 1973 XII Kohoutek

Photoelectric spectrophotometric scans of Comet 1973 XII Kohoutek were made on November 25.85 and 28.85 UT, 1973. The vibrational temperature of C₂, the total numbers of CN and of C₂, and the production rates for CN and C₂ are derived from the observed fluxes. The temperature of C₂ was 4900 K on 25.85 November and 4300 K on 28.85 November. Mean abundance ratio of C₂ to CN was about 2.7. From the variation of production rates with heliocentric distance, it is shown that there was an outburst on 25.85 November in both CN and C₂ productions. For C₂, the production rates are derived by using two coma models, i.e. the Haser's parent-daughter model and the model relevant to a proposition of Yamamoto (1981b) that C₂ is formed via two-step photodissociation of its parent molecules. By comparing the production rate derived from the two models, it can be supported that C₂ is formed via two-step photodissociation rather than one-step photodissociation. In consequence, it is shown that the variation of the production rate with heliocentric distance is largely modified compared with that derived from the Haser's model.     

Rapid changes of brightness in P/Halley

Scanner observations of the coma of periodic comet Encke (P/Encke) are presented for four nights in March 1984 during its post-perihelion period. The strong emission features of CN and C₂ molecules have been identified and the abundances of CN and C₂ are estimated. The production rates of these molecules have also been derived from their band luminosities. No trace of sodium emission has been found in this comet.     

Some requirements of a colliding comet source of gamma ray bursts

Colliding comets in the Solar System may be an important source of gamma ray bursts. The spherical gamma ray comet cloud required by the results of the Venera Satellites (Mazets and Golenetskii, 1987) and the BATSE detector on the Compton Satellite (Meeganet al., 1992a, b) is neither the Oort Cloud nor the Kuiper Belt. To satisfy observations ofN(>P _max) vsP _max for the maximum gamma ray fluxes,P _max > 10^–5 erg cm^–2 s^–1 (about 30 bursts yr^–1), the comet density,n, should increase asn a ¹ from about 40 to 100 AU wherea is the comet heliocentric distance. The turnover above 100 AU requiresn a ^–1/2 to 200 AU to fit the Venera results andn a ^1/4 to 400 AU to fit the BATSE data. Then the masses of comets in the 3 regions are from: 40–100 AU, about 9 earth masses,m _E; 100–200 AU about 25m _E; and 100–400 AU, about 900m _E. The flux of 10^–5 erg cm^–2 s^–1 corresponds to a luminosity at 100 AU of 3 × 10²⁶ erg s^–1. Two colliding spherical comets at a distance of 100 AU, each with nucleus of radiusR of 5 km, density of 0.5 g cm^–3 and Keplerian velocity 3 km s^–1 have a combined kinetic energy of 3 × 10²⁸ erg, a factor of about 100 greater than required by the burst maximum fluxes that last for one second. Betatron acceleration in the compressed magnetic fields between the colliding comets could accelerate electrons to energies sufficient to produce the observed high energy gamma rays. Many of the additional observed features of gamma ray bursts can be explained by the solar comet collision source.     

Photopolarimetric studies of comet Austin

Photopolarimetric observations of comet Austin with the IAU/IHW filter system were obtained on the 2.34 m Vainu Bappu Telescope (VBT) of the Indian Institute of Astrophysics, at Kavalur, India, during pre-perihelion phase on February 20,1990 and on the 1.2 m telescope of the Physical Research Laboratory at Gurusikhar, Mount Abu during postperihelion phase on May 2 and 4, 1990. The comet appeared bluer than a solar analog during post-perihelion phase on May 2 and 4. The percent polarization shows a sharp increase towards the red on May 2 and 4. The dominant sizes of the dust particles appear to lie in a narrow range of 0.1 to 0.5 Μm. Regarding the molecular band emission, CN and C₂ bands are quite strong; C₃ emission was also found to be strong though the observations on May 2 and 4 show significant variation as compared to C₂ emission. Molecular band polarization for CN, C₃, C₂ and H₂ O+ have been calculated. It has been found that emission polarization in CN, C₂ and C₃ is between 1–7% (phase angle between 107.4–109 degrees). For CN and C₂ the polarization values are close to the theoretically predicted values, but for C₃ the polarization value falls much below the theoretically predicted value. A similar result was found for comet Halley.     

Postperihelion interference filter photometry of the “annual” comet P/Encke

Interference filter photometry was taken of Comet Encke on June 14, 1974 (1.07 AU heliocentric distance, postperihelion) at the CTIO (Cerro Tololo Interamerican Observatory) 150-cm reflector. Production rates were calculated of 4.1 × 10²³ mol sec^?1 of CN, 5.3 × 10²³ mol sec^?1 of C₃, and 4.3 × 10²⁴ mol sec^?1 of C₂. These are about three times smaller than at comparable heliocentric distance preperihelion, assuming a value of 100 for the ratio H₂O/ (C₂ + C₃ + CN). An upper limit was placed on the production of nonvolatiles at about one-third that of volatiles in mass by assuming a bulk density of 1 g cm^?3, a particle geometric albedo of 0.1, and a phase function of 0.2.     

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.     

The spectrum of comet C/2009 R1 (McNaught) in 4140–5240 Å wavelength region

The spectroscopic observations of comet C/2009 R1 (McNaught) were carried out with the 2 m Zeiss-RCC Telescope of Pik Terskol Observatory operated by the International Center for Astronomical and Medico-Ecological Research (Ukraine, Russia). The Multi Mode Cassegrain spectrometer was used to obtain spectra of moderate spectral resolving power with a wavelength coverage from 4140 to 5240 Å. The spectrum is characterized by the extremely low continuum level and strong molecular features. 192 emission lines of C₂, CN, CH, NH₂, CO⁺, and CH⁺ have been identified by the comparison of the observed and theoretical spectra of the molecules. The ratios of the gas production rates of Q(C₂)/Q(CN)=1.32, Q(CH)/Q(CN)=0.49, and Q(NH₂)/Q(CN)=0.81 were derived using a Haser model.