Towards a joint activity profile of the 2007 Aurigids



This plot shows a first reconstruction of the activity profile of the September 1, 2007, Aurigid outburst, based on six independent sources: 5-minute counts by four visual observers in three locations and also from two video cameras in yet another location. The intent is to get a better "feeling" for the overall trend and the reality - or lack - of peaks in addition to the pronounced maximum around 11:15 UTC. Given the shortness of the outburst, the relative spatial proximity of the observers and the brightness distribution skewed heavily towards very bright meteors, no reduction to ZHRs was performed: The counts were taken as they are, only calibrated against each other. (For a more formal analysis of visual counts see the IMO profile, where at the time of this study no profile with sufficient time resolution was present, though.)

The visual observers are Susanne Hüttemeister at Fremont Peak, California, USA, who counted 38 Aurigids between 10:35 and 12:20 UTC, Daniel Fischer at Fremont Peak, California, USA, who counted 21 Aurigids between 11:10 and 12:15 UTC, Wes Stone at Chiloquin, Oregon, USA, who counted 30 Aurigids between 10:40 and 12:00 UTC, and Alan Whitman near Penticton, British Columbia, Canada, who counted 19 Aurigids between 11:20 and 12:10 UTC. (The latter two counts were among the 'best' collected from early MeteorObs postings; several others were rejected because of bad observing conditions or too few meteors seen.) From the 5-minute counts sliding means were calculated (with 1:3:1 weights): The highest numbers of Aurigids seen by the visual observers in a 5-minute intervall were 3.6, 3.8, 4.0 and 4.4, respectively.

The number of meteors seen by the four observers in the interval 11:25 to 11:45 (9, 7, 11 and 7) when all were counting was then used to "reduce" each individual activity profile to an "average" observer (who would have seen 8.5 meteors in that interval), then the mean of the four profiles was calculated. Until 11:10 it's based on only Hüttemeister and Stone (who 'neatly' cancel out fluctuations seen by only one, namely 'peaks' seen by Hüttemeister around 10:50 and Stone at 11:05 UTC), the peak is covered by these two plus Fischer, and after it also Whitman joins in.

The resulting plot is the thick line connecting the filled circles: It shows only one peak, with no other significant maxima; the result is the practically same when working with 10-minute averages (not shown). The full width at half maximum of this main peak is about 30 minutes, very close to the predictions! Other than this peak, only a certain "shoulder" on the descending flank around 11:30 UTC might be real: This, interestingly, would actually correspond to the predicted time of the peak. A major second outburst, perhaps as big as the main peak, at that time - as indicated in some of the (video-based) plots by Chris Peterson - is not seen here, however.

As an independent test, 5-minute counts from the two most successful Armagh video cameras at Lick Observatory - which each got about 20 Aurigids in the interval covered - were added, resulting in the open circles: By coincidence their joint rate turned out to be roughly equal to the rate for one visual observer. The overall trend is pretty close to the visual one, again with a shoulder around 11:30 but little other structure appearing significant. Finally the visual and video plots were added, yielding the dashed upper line connecting the crosses and incorporating now 150 (mostly different) meteors, four times more than any individual groundbased observer could see: the main peak and shoulder shop up, again.

Thusly the author dares to predict that a final analysis of all visual and video data (to accurately combine these into one diagram being an additional challenge) will show a main peak at 11:15 UTC and probably a secondary one at 11:30 UTC - and the hybrid observations from one of the MAC aircraft, i.e. visual counts of intensified video looking look into the atmosphere for enhanced rates, also hint an another increase around 11:32 UTC. It would be worthwhile to look for possible physical and orbital differences (brightnesses = sizes? radiant? chemistry?) of the meteors seen at 11:30 vs. 11:15 UTC - and the modellers should feel invited to postdict both peaks.

Daniel Fischer, 26 September 2007

Note added 15 November 2007: A detailled analysis of visual data from 26 observers who saw 368 Aurigids in total by Rendtel (WGN 35 #5 [October 2007] 108-112) confirms the absence of a significant secondary peak (or any significant substructure at all), with the peak at 11:20±3 UTC and a peak ZHR of 132±26.

Note added 24 October 2007: The data from two other video cameras, both on Fremont Peak, have now been analyzed 'officially' by the IMO video section.

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