Comets

Festou, M. C.; Rickman, H.; West, R. M.

doi:10.1007/bf00872923

Cited by 61 publications

(16 citation statements)

References 371 publications

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“…Everhart (1967b), taking more careful account of selection effects, found ∼60 yr −1 with q ≤ 4 AU, of which roughly 35 yr −1 would pass within 3 AU. Assuming one in three of these is dynamically new (Festou et al 1993b), we find new 12 yr −1 . The number of V 1 comets produced in our simulation (see below) is 1368; hence our simulation corresponds to a time interval …”

Section: Resultsmentioning

confidence: 77%

The Evolution of Long-Period Comets

Wiegert

Tremaine

1999

Icarus

174

210

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We study the evolution of long-period comets by numerical integration of their orbits, a more realistic dynamical approach than the Monte Carlo and analytic methods previously used to study this problem. We follow the comets from their origin in the Oort cloud until their final escape or destruction, in a model solar system consisting of the Sun, the four giant planets and the Galactic tide. We also examine the effects of nongravitational forces as well as the gravitational forces from a hypothetical solar companion or circumsolar disk. We confirm the conclusion of Oort and other investigators that the observed distribution of long-period comet orbits does not match the expected steady-state distribution unless there is fading or some similar physical process that depletes the population of older comets. We investigate several simple fading laws. We can match the observed orbit distribution if the fraction of comets remaining observable after m apparitions is ∝m −0.6±0.1 (close to the fading law originally proposed by Whipple 1962); or if approximately 95% of comets live for only a few (∼6) returns and the remainder last indefinitely. Our results also yield statistics such as the expected perihelion distribution, distribution of aphelion directions, frequency of encounters with the giant planets and the rate of production of Halley-type comets.

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Section: Resultsmentioning

confidence: 77%

The Evolution of Long-Period Comets

Wiegert

Tremaine

1999

Icarus

174

210

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“…According to them, about 35 of 60 LP comets would pass their perihelion per year within 3 AU. To obtain the flux of new comets, in the second step, the authors utilized the conclusion by Festou et al (1993) that one in three LP comets is dynamically new. It is clear that it is derived from the rates of new and old comets in the catalogue, without taking the fading effect into account and, consequently, the different discovery efficiency.…”

Section: Oort-cloud-population Estimatesmentioning

confidence: 99%

The fading problem and the population of the Oort cloud

Neslušan

2006

A&A

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Context. The discovery efficiency of the dynamically new comets has been assumed to be approximately the same as that of all long-period (LP) comets when estimating the population of the Oort cloud. On the other hand, studies of the so-called fading problem have implied a strong difference in the discovery efficiencies of both new and old comets. Some authors have attempted to explain this discrepancy by suggesting that old comets disappeared due to the extinction or disintegration of their nuclei. Aims. We attempt to answer the question of whether the absolute brightness of old comets steeply decreases in time or whether their nuclei become extinct, dormant, or disintegrated. Moreover, we analyse the impact of the highly different discovery efficiencies on an estimate of the Oort-cloud population. Methods. The dominance of the fading over the extinction, dormant-phase, or disintegration is demonstrated with the help of the distributions of the reciprocal semi-major axes of the original orbits of the LP comets and a more moderate decrease in discoveries of new comets with increasing perihelion distance. The comet discoveries within the LINEAR sky survey are also used to support our conclusion.Results. The demonstrated dominance of the fading implies the relatively higher discovery efficiency of new comets. Its ignorance causes an overestimation of the actual intrinsic flux of new comets through the zone of visibility compared to the corresponding intrinsic flux of all LP comets. This overestimate is also documented by a significantly smaller amount of new comets with perihelia q < ≈ 3 AU discovered within the LINEAR. Conclusions. The actual intrinsic flux of new comets must be about one order of magnitude lower than has been derived before. Its reduction implies a one-order-of-magnitude less numerous population for the Oort cloud. Moreover, such the reduction also solves (or, at least, weakens) the problem of too high a mass of the comet cloud, as well as the problem of too numerous a population of predicted Halley-type objects or too high a space density of interstellar comets.

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“…Detections of this species have been proposed but are viewed as questionable by Festou et al (1993). Korsun and Lipatov (1993) listed some tentative optical line identifications.…”

Section: Hcomentioning

confidence: 99%

“…Because the spectra of comets are diverse (Festou et al 1993), future efforts at fine identification will be aided by information on the strengths of the fines in different comets. Therefore, in this paper, we present a fist of unidentified features remaining after a line-identification study of two échelle spectra of Comet C/1996 B2.…”

Section: Introductionmentioning

confidence: 99%

High-Resolution Optical Spectra of the Head of the Comet C/1996 B2 (Hyakutake)

Morrison

Knauth

Mulliss

et al. 1997

PASP

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ABSTRACT. On 1996 March 23 and 27, we obtained high-resolution (R -26,000) échelle spectra by manually guiding on the head of Comet C/1996 B2 (Hyakutake). The two spectra cover different but slightly overlapping sets of nine disjoint 70 À regions of the green, yellow, and red. The continuum signal-to-noise ratio is in the range 40-100 per spectral resolution element. We used line lists from the standard astronomical literature to identify lines of [O i], Nal, C 2 , NH 2 , CN, and H 2 0 + , we unsuccessfully sought evidence for CO + , and we obtained upper limits on HCO line strengths. In addition, we used laboratory data to make new identifications, by wavelength coincidence only, of lines of NH 2 . For the lines that remain unidentified, we have listed measured wavelengths and relative fluxes, in order to aid future efforts at identification. Our spectra include the green and one of the red lines of [O i], and the indicated photon flux ratio of X5577 / (X6300 + X6364) is in the range 0.12-0.16, consistent with formation of the excited O atoms from photodissociation of H 2 0.

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Comets

Cited by 61 publications

References 371 publications

The Evolution of Long-Period Comets

The Evolution of Long-Period Comets

The fading problem and the population of the Oort cloud

High-Resolution Optical Spectra of the Head of the Comet C/1996 B2 (Hyakutake)

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