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Astron. Astrophys. 329, 769-775 (1998)

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1. Introduction

The fragmentation of meteoroids during their flight in the atmosphere has been observed many times both visually and photographically. The amount of data evidencing fragmentation led Levin (1963) to the conclusion that, if fragmentation were not taken into consideration in processing the observations, erroneous results would result. According to Levin (1961), the following basic forms of fragmentation were recognized (see also Lebedinets 1980, Bronshten 1983):

  • 1) disintegration of meteoroid into several pieces;
  • 2) simultaneous detachment of much small debris from the parent meteor body (PMB), being classified as a flare;
  • 3) progressive fragmentation during which also daughter particles fragment, and so on;
  • 4) quasi-continuous fragmentation (QCF) during which a large number of small further nonfragmenting particles detaches from PMB.

Observations show that the QCF should be of greatest interest. First, this kind of fragmentation is most probable and frequently observed in practice. Second, there exist many facts (e. g. McCrosky 1958, Babadzhanov & Kramer 1968, Hawkes & Jones 1975, Lebedinets 1980, Bronshten 1983, Millman 1983) pointing out the QCF as the mechanism of disintegration of PMB. Third, the kinds of ablation of PMB such as pure evaporation or flare can be considered a special case of QCF. Fourth, QCF can explain the observed shapes of the radar-underdense Fresnel diffraction characteristics (e. g. Novikov & Pecina 1990). The basic physical mechanisms causing QCF are well known and were listed by Lebedinets (1980, 1987). The first numerical values of fragmentation energies were published by Lebedinets (1980) and Novikov et al. (1984 b). Their more precise values corresponding to various kinds of meteor matter were published by Lebedinets (1986), and by Babadzhanov (1993) - see his Table 2.

The basic theory of light curves of meteoroids ablating via QCF has been put forward by Simonenko (1973). Further development has been carried out by Lebedinets (1980), Kalenichenko (1980) and Novikov et al. (1984a). Novikov & Konovalova (1995) utilized the theory of QCF in processing light curves without going into details of the derivation of basic formulae, and without treating the ionization.

Novikov et al. (1996a, 1996b) have used the theory of QCF of PMB to infer the bulk densities of meteoroids and to describe quantitatively the evolution and the structure of meteor coma observed photographically by the method of instantaneous exposure. However, the theory of QCF was not described by the authors. Here we derive the formulae describing both the light and ionization curves of meteors ablating by QCF of PMB; we also rectify some mistakes present in the old version of the theory of Novikov et al. (1984a), and in Novikov & Konovalova (1996), and present the above formulae in compact form being more convenient for meteor physicists. To demonstrate the capability of the new approach, we solve the model tasks concerning determination of some parameters of PMB.

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997