Meteoroid stream identification: a new approach -- II. Application to 865 photographic meteor orbits

Abstract

A B S T R A C TThe new criterion D N for meteoroid stream identi®cation, based on variables directly linked to observations, is applied to a set of 865 photographic meteor orbits and the results are compared with those obtained using the well-known and widely used D SH criterion of Southworth & Hawkins, using thresholds for meteor association computed according to Jopek & Froeschle Â. For 15 streams, including the Lyrids, the a Capricornids, the Perseids, the Taurids, the Quadrantids, the Geminids, the Leonids, the Orionids and the southern d Aquarids, the two searches are in very good agreement, with D N often adding a few more members to some streams, at the same level of statistical signi®cance as used for D SH . The Andromedids and the j Leonids, identi®ed as populous streams using D SH , are not recognized using D N ; on the other hand, using D N ®ve additional streams are identi®ed, namely the « Geminids, the Monocerotids, the northern d Aquarids and the rather populous a Virginids and « Piscids. In general, D N gives results essentially equivalent to those obtained with D SH in many circumstances, the most notable exception being for near-ecliptical streams, where the results differ markedly. We show also that the reduced distance function D R can be successfully applied to search for meteor showers resulting from the same meteoroid stream; in our study the Quadrantids and the southern and northern d Aquarid showers have been identi®ed as possibly being originated by a single meteoroid stream.

Meteor stream identification: a new approach - III. The limitations of statistics

“…As in Jopek et al (1999), after having computed all the mutual distances, we processed them with a cluster analysis computer program implementing an algorithm based on the single neighbour linking technique (Lindblad 1971); the values of the meteor association thresholds were estimated with the method described in Jopek & Froeschlé (1997). The only modification with respect to Jopek et al (1999) has been that, instead of determining the thresholds with a single numerical experiment, 10 of these were carried out; this resulted in obtaining the average thresholds and their standard deviations listed in Table 2.…”

“…Valsecchi, Jopek & Froeschlé (1999) introduced a new distance function D N , based on geocentric quantities directly derived from observations. Then, using the single neighbour linking technique (Lindblad 1971) and values for meteor association thresholds obtained according to the prescriptions of Jopek & Froeschlé (1997), Jopek, Valsecchi & Froeschlé (1999) compared the results obtained with D N to those obtained using the classical distance function D SH of Southworth & Hawkins (1963), on a set of 865 precise photographic meteor radiants. The comparison has shown that D N and D SH give similar results on most streams, but give significantly different ones in the case of ecliptical streams.…”

“…A logical step forward from Jopek et al (1999) would be to apply D N to a larger sample of photographic orbits, in order to look for less conspicuous streams.…”

“…We thus decided to do a new search for streams on these two data sets, as well as on the 865 Harvard meteors (HD) published by Whipple (1954), Jacchia & Whipple (1961), Hawkins & Southworth (1958, 1961), already used in Jopek et al (1999).…”

Radar meteoroid orbit stream searches using cluster analysis

“…This time requirement increases steeply as the data set size is increased. Studies such as Jopek, Valsecchi & Froeschle (1999) have no such problems as they are only dealing with a set of ∼10 3 orbits and therefore can perform 10 3 randomized runs or more with no difficulty.…”