(meteorobs) re Early PERs from around the lamba AND
wisetdf at Safe-mail.net
wisetdf at Safe-mail.net
Sun Jul 10 08:16:40 EDT 2011
Hi Each
Not directly related, but possibly of passing interest for the upcoming week(s), I've been playing with the SonotaCo database recently to see if there's anything of interest in the objects tagged as sporadics in their orbits' database, playing with good ol' D criterion matches against comet orbits and against themselves, dusting off bits of software kit I haven't played with in over a decade since looking at the DMS video orbits database. Some intriguing bits and pieces hidden away in there there are.
One thing that cropped up and was confusing me in a big way was a "shower" centred upon the 15th July, and annoyingly only for 2009 despite the database carrying data for 2007 and 2008 also. Until I more thoroughly checked the IMO shower calendars and noticed that this "Cassiopeia" shower ideally matched the 15th July track position for the Perseids in the 2010 calendar.
The radiants marked here to the lower right http://oi51.tinypic.com/2rrotom.jpg can be compared to that year's IMO shower calendar plot.
Trouble is I'm not much of an orbital dynamicist, if at all, and the orbits although self consistent and with some similarities with 109P/Swift-Tuttle are also distinctly different, a plot of the orbits here :-
http://oi54.tinypic.com/zmo5ye.jpg and a comparison with 109P/Swift-Tuttle (those on the left two orbits of 109P, those on the right a representative 15th July meteor orbit) here http://oi56.tinypic.com/b3px94.jpg
I did find a paper on nodal regression published soon after the recovery of 109P back in the early nineties, and it did seem to fit in with this sort of thing, but that'd mean a bunched up lump of meteors had been staying on this old orbit thousands if not tens of thousands of years. And really bunched too, given this particular "outburst" was in 2009 only out of the 2007 to 2009 dataset. Not sure how the radiant tracks of meteor showers are derived, but obviously people have been seeing things from the July 15th ish radiant region for some time now for it to be part of the radiant drift data used in IMO Calendar 2010.
I tried a population index of 2.5 'standard' plugging to the ZHR calculation for the object but the resulting ZHR was ridiculously high, nearly 200. Some of this might be due to the SonotaCo magnitude distribution going down to only magnitude 2, so the data are biased towards the bright end, but it also does contain some remarkably bright meteors for some known and suspected very weak showers at times, or so it seems to me personally, so I'm not sure how well the data are calibrated in terms of magnitude, and/or whether video magnitudes have a different nature to the classical visual ones in this case. I don't remember such problems when I used to look at the DMS and MSSWG video meteor databases about a decade ago.
Anyway, a plot of number of objects as y axis against 0.1 degree bins of Solar Longitude as x axis lives here http://oi56.tinypic.com/wa1wtz.jpg , showing there was something of a tight peak of about a dozen objects in a relatively short period of time, suggesting that it might not just be a case of being an intermittent "subshower", but also a case of actually managing to be lucky enough to catch the thing in action!
Those are the same objects as per the orbit and radiant plots (some of the radiant points are superposed) and I suppose some are distant enough from the central time to be coincident, but the orbit plots look tight.
I'll cut and paste the data below (credit for data goes to the SonotaCo meteor orbits' catalogue) anyway, so folk can make their own mind up.
And finally, the small handful of radiants also plotted to the left of the main bunch (nearer theta Cas) are centred around the 24th/25th July, cover more than one year (2008 was a leap year remember), and the representative orbit for those is the middle one in the plot at http://oi56.tinypic.com/b3px94.jpg .
I also forgot to note that I used a somewhat stricter than usual threshold of 0.06 for the Southworth and Hawkins d criterion, usually a value of around 0.1 is used, but I'm trying to get results that're as certain as possible out of the orbit database. Also I'm using a variant of it due to Jopek where certain biases relating to the perihelia of the orbits are supposed to be allowed for, as I'd pretty good success in the past. One of the main problems with S&H and especially with Drummond's d' variant are that they tend to find too many co-orbitals, both within data and when data are crossmatched in parent body searches, ones that give ill fitting matches on orbit plots. That doesn't mean these objects are false alarms, orbits can evolve, but although that's fair enough for well known and well established orbits, it's not all that helpful when suspect and working showers are what you're trying to tie down, and/or when you're seeing if any novel stuff is hidden away in the data.
Anyway, do people have much experience of early pre-outbursts from Perseids? Or aware of much literature of pre-historical nodal regression type papers for this stream?
Cheers
John
John Greaves
The following was cut and paste as per tab delimiting, the email will no doubt word wrap it, the last line per entry is the mag, first line ending in -0.40 last line in 0.15, and all data are taken directly from the SontocaCo freely available dataset, and interesting and at times marvellous resource as far as I can tell, so far.
LOCALTIME SOL RA_O DC_O VG Q E PERI NODE INCL STREAM MAG
_20080712_015439 109.629684 2.325366 47.551559 58.403439 1.005475 0.990062 167.961426 109.629662 109.635796 _spo -0.40
_20090713_031635 110.391182 4.551586 48.957436 56.217018 0.996620 0.846449 163.191193 110.391228 107.319664 _spo -0.20
_20090713_224839 111.167297 1.781986 49.840515 57.274673 1.005186 0.974008 167.805466 111.167351 106.809860 _spo 0.55
_20090714_000949 111.221062 3.468987 52.375057 56.134445 0.993621 0.979456 162.651962 111.221100 103.576767 _spo 0.30
_20090714_010715 111.259094 3.457310 50.684189 57.144806 0.999957 0.994184 165.320175 111.259140 105.959045 _spo 0.20
_20090715_010406 112.210197 4.637526 50.581871 57.388336 0.999381 0.989148 165.062561 112.210258 106.770470 _spo 2.00
_20090715_020458 112.251015 5.850009 50.235859 57.210270 0.997158 0.951007 163.954575 112.251076 107.295746 _spo -1.20
_20090715_034642 112.318390 7.869231 50.364601 58.180618 0.991146 1.015674 161.912277 112.318451 108.403282 _spo 0.50
_20090715_040440 112.330299 6.681388 48.809349 58.204128 1.000297 0.963381 165.375290 112.330368 109.813560 _spo -0.20
_20090715_214034 113.029724 4.420552 51.461441 56.119022 0.998875 0.896912 164.467972 113.029778 105.608650 _spo 1.65
_20090715_225751 113.080925 7.591912 49.999508 56.951805 0.990358 0.879655 160.944656 113.080994 108.572159 _spo 0.80
_20090715_230320 113.084557 5.624743 49.233330 58.320419 1.002340 0.978847 166.406799 113.084625 109.696625 _spo 0.68
_20090715_234706 113.113548 6.353703 50.281727 58.238655 0.997894 1.013937 164.534897 113.113617 108.546921 _spo -0.45
_20090716_010630 113.166145 6.123416 49.622238 56.489708 1.000115 0.855540 164.842163 113.166214 107.779099 _spo 1.05
_20090716_011810 113.173866 7.888161 48.944996 56.881100 0.994552 0.840095 162.340927 113.173943 109.437157 _spo 0.95
_20090716_014148 113.189529 6.703249 50.673702 56.547447 0.996010 0.899624 163.256119 113.189583 106.781151 _spo 0.08
_20090716_015559 113.198921 6.267118 50.471809 56.904343 0.998984 0.925460 164.647049 113.198982 107.074951 _spo 0.57
_20090716_024833 113.233757 7.287750 48.578125 58.364773 1.001713 0.953257 166.015091 113.233826 110.542381 _spo 0.90
_20090716_025054 113.235306 5.598749 52.216824 56.220871 0.997903 0.953812 164.299484 113.235352 104.411926 _spo 0.50
_20090716_030402 113.244003 6.057698 49.214104 58.037449 1.004584 0.968908 167.512863 113.244072 109.116089 _spo 0.90
_20090716_031934 113.254303 6.160591 51.083866 56.304256 0.999058 0.905912 164.594910 113.254356 105.888054 _spo 0.20
_20090716_032449 113.257774 5.842781 50.934311 57.408806 1.001655 0.992931 166.132568 113.257828 106.695869 _spo -1.00
_20090716_033930 113.267509 10.491576 49.602917 58.451515 0.985788 0.973784 159.871643 113.267578 110.396957 _spo 0.45
_20090717_011547 114.126328 8.707150 50.276642 58.229649 0.994593 0.989569 163.120483 114.126396 109.196396 _spo 0.60
_20080718_012720 115.332756 6.642590 51.481300 57.014786 1.004302 0.958457 167.394318 115.332764 106.472542 _spo 0.15
More information about the meteorobs
mailing list