(meteorobs) Potential gamma-Delphinids return, June 2013

[Roberto Gorelli]

On Sun, 28 Apr 2013 11:31:13 +0000
  Esko Lyytinen <esko.lyytinen at jippii.fi> wrote:
> 
> Dear Karl and others,
> 
> The possibility of an outburst from this was originally predicted in 
> this paper:
> http://adsabs.harvard.edu/abs/2003Icar..162..443L
> http://www.sciencedirect.com/science/article/pii/S0019103502000714
> This could earlier be freely downloaded, but maybe not any more. A 
> earlier (working) link that I tested now, did not work.
> 
> The theory behind this is discussed in this paper and there are also 
> given some quite certain predictions and some quite uncertain.
> 
> The main assumptions in this (case and similar to the others) are 
>that 
> the outburst in 1930 was real and secondly that it was from a 
> 1-revolution dust trail of a long period comet ( which practically 
>do 
> not make definite outbursts other than from 1-rev. trail). And 
>thirdly 
> this is based on the derived radiant ( in case of not known parent 
>comet 
> as in this case).
> In this we consider a long period comet to be one with the orbital 
> period from a few hundreds years (like the Lyrids) to a few 
>thousands 
> years something like with the Aurigids. (Longer than a few thousand 
> years will probably have the dust tails too much stretched adn 
> consequently have a  too small density of meteoroids, (unless of 
> especially big comet)).
> 
> In principle this (the theory) is about similar to the 2007 
>predicted ( 
> and observed) Aurigids outburts and some observed and post predicted 
> Lyrids ourbursts. The parent comet of these are however known. The 
>alpha 
> Monocerotids parent comet is not known, but all the observed 
>outbursts 
> can be post-predicted or linked mutually. Actually the latest of 
>these 
> in 1995 was predicted beforehand (by Jenniskens) by means of a more 
> 
> approximate treatment by means of the Solar system barycentre (see 
>also 
> below near the end).
> With actual computer calculations also the timings can be linked to 
>each 
> other with an accuracy of about 15 minutes ( I recall). This AMO 
>post 
> prediction however has the radiant very accurately known from the 
>1995 
> video observations.
> In practically any (without known parent orbit) case (if we do not 
>have 
> enough of diverse observations from several outbursts) one can not 
>tell 
> if the encouter was very central or not and these calculations have 
>been 
> made by assuming that they were central.
> 
> As to the gamma-Delphinids, I read in that paper:
> "The remaining six showers, the a-Lyncids (aLy), the
> a-Pyxisids (aPx), the o-Orionids (oOr), the e-Eridanids (eEr), the 
> g-Delphinids (gDe), and the a-Circinids (aCi) are less well 
>documented 
> (Jenniskens 1995, Jenniskens et al. 1997). Future returns need to 
> establish that these are indeed long-period comet dust trail 
>encounters."
> 
> Then further:
> "The first complication is that possible errors in the reported 
>radiant 
> position can introduce large variations in the calculated trail 
> positions because of relatively close encounters with one of the big 
> planets."
> 
> This latest is a general remark, not specially for the gamma 
>Delphinds. 
> A sensitiviy test was amde for each of these by shifting the radiant 
> about 5 degrees in declination and also (in another calculation) in 
>the 
> RA direction.
> And this case fortunately seems to be relatively non-sensitve for 
>errors 
> in the radiant.
> An error of about 10 degrees (to any direction) in the radiant, does 
>not 
> seem to nullify the prediction.
> Now the nominal rD-rE distance is +0.00021 au, quite good.
> 
> As a conclusion. IF the 1930 outburts was real and IF the case is of 
> long period, then probably some level outburst is expected to 
>happen. 
> Then the timing also should be quite good, to about (almost) the 
> accuracy of the observations of this in 1930, (well) better than an 
>hour 
> is expected now.
> 
> If it is not of a long period, then probabaly nothing is observed, 
>at 
> least based on this predition. There is of course the possibility of 
> some other type shower and some meteors of this might bee seen. Then 
> also not much of the timing of these can be said from this, except 
> probably around the same solar longitude.
> 
> As it appears from this, also negative observations are valuable. 
>And if 
> an outburst is observed, then hopefully a more reliable radiant can 
>be 
> derived from video and/or photographs of these.
> 
> Table 3. in the Jenniskens book  “Meteor Showers & Their Parent 
>Comets” 
> (Cambridge University Press, 200
> 6), "
> has the table data of that paper.
> And I see that the "2013 Meteor Shower Calendar of the IMO" 
>mentioned 
> (with link) by Karl, seems to contain the description of the 1930 
> observations.
> 
> Karl also asked:
> 
> "Or is it just that we will be, in 2013, in a planetary 
>configuration exactly similar to this of 1930? In that case, which 
>planetary influences seems to be of importance?
> "
> With an about similar planetary configuration to some previous, the 
>trail passes (near the node in question) at about the same distance 
>from the Sun. So, for example the mentioned prediaction of 1995 AMO's 
>was 60 years from the observed 1935 outburst, and in 60 years Jupiter 
>makes about 5 revolutions and Saturn about 2, resulting an about 
>similar configuration. But the trail encounters can also happen in 
>quite different planetary situations. The distance of the trail from 
>the Sun (near the node in question) varies typically by a few 
>hundredths of au. And if the encounter is not near one extreme of 
>these variation (as it is with the Lyrids, might say unfortunately 
>because some of the "waves" are too small to reach enough), then an 
>encouner can happen at two different "phases" of these variations 
>caused primarily by Jupiter and secondly Saturn etc.
> If I recall this correctly, the 2007 Aurigids outburst could not be 
>actually predicted by means of similar planetary configuration, 
>although Jupiter was not so far from the 1994 situation.
> 
> 
> Esko

I agree with Esko, one or two years ago I wrote in this list for a 
possible out-burst of Gamma Delphinids utilizing the work of 
Jenniskens
by means of a more approximate treatment by means of the Solar system 
barycentre (http://adsabs.harvard.edu/abs/2003Icar..162..443L)
but as I remember nobody saw this meteors. The best it's observe too 
this year, in negative case we can only waste time but if we not 
observe and the shower occur .....
Best greetings.
Roberto Gorelli