Table 3

Table 3

Statistics of the parameters of four meteor showers found in the amor data. Mean (x), standard deviation (c), standard error in the mean (a/y/N) and representative (median) uncertainty (Unc.) are shown for each shower of size N. Parameters experiencing daily motion are corrected to central solar longitudes.

graphic and radar; Lindblad [7] photographic, TV and combined photographic/TV; and Taylor [13] mean orbits respectively. The best agreement is with Taylor's mean and this is fortuitous as his mean orbit derives from meteors detected on the original configuration of the amor system (circa 1990). The level of agreement indicates continuity and consistency in the measurement of this shower at amor's 26.2 MHz transmission frequency thus inspiring confidence in the quality of the long-term amor calibration regime. Lindblad [7] notes that Cook [3] derived his value from a single photographic meteor—it is ignored here. Lindblad's [6] photographic mean shows a particularly high level of dissimilarity: it differs from the amor mean orbit determination in the method of detection and also in the number of meteors forming the mean (Lindblad uses 11 orbits while ~ 103 amor orbits are used currently). It is quite possible that the different meteoroid size ranges probed yield different orbital means or that the small sample of Lindblad may have led to an inaccurate mean. In support of the latter, the amor shower is found to be much more similar to the radar mean of Lindblad [6] and to the (closer to radar size range) TV mean of Lindblad [7].

In the case of the cap two photographic means listed by Kronk [5] and the radar mean of Weiss [14] agree best with the amor mean orbit at dissimilarities of 0.06, 0.06 and 0.05 respectively. These are followed by Kronk's other mean orbit at Dsh = 0.24, an unacceptably high value for stream association of near-ecliptic stream comparisons. Finally the radar orbits of Sekanina are even more dissimilar with Dsh = 0.3 for Sekanina

[10] and an extreme Dsh = 1-18 for Sekanina [11]. These very large dissimilarities are not unexpected given the very low inclination angle (0.9°) in Sekanina [10] and the very hyperbolic eccentricity (1.92) in Sekanina [11]; such parameter values are both outside the range expected for this shower. Kronk's [5] third orbit which also disagrees badly, having a dissimilarity of 0.24, likewise has a very low inclination of 1.1°.

The dsx has not been detected in many major orbit reducing studies—the daytime nature of this shower renders it only visible by radar methods. Nilsson [8] and Sekanina

[11] present mean orbits obtained, in both cases from nine orbits, at the Adelaide and Harvard Radio Project radars respectively. Nine meteors is a rather meager sample of these relatively high uncertainty orbits on which to base a mean; Nilsson, however, agrees well with the current result at DSH — 0.03 while Sekanina's mean is very dissimilar with Dsh = 0.21 which is expected given the ~ 10° difference between his inclination angle and that provided by both amor and Nilsson. The inclination angle in the latter studies is closer to that generally accepted.

On further examination of the shower candidates (Peaks 1 and 2 of Section 2) no match for Peak 1 is found while Peak 2 on close analysis is found to be similar to the omicron Cetids tabulated by Sekanina [11]. A dissimilarity of Dsh = 0.09 between the mean orbits of the latter and the former indicates excellent agreement.

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