(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



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