(meteorobs) Potential gamma-Delphinids return, June 2013

Esko Lyytinen esko.lyytinen at jippii.fi
Sun Apr 28 07:31:13 EDT 2013


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



> Dear meteor observers,
>
> I had one small question about the gamma-Delphinids return predicted on June 11th of this. This prediction is made by Peter Jenniskens and is related in the 2013 Meteor Shower Calendar of the IMO ( http://www.imo.net/files/data/calendar/cal2013.pdf on page 6).
> This prediction is based on observations made on 1930, where an outburst coming from this source was observed by three astronomers. But how was it deduced from these observations that an outburst is possible this year, and not the previous/following years? Was the radiant associated with a know object, allowing such prediction? 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?
>
> Thanks a lot in advance for your answers!
> Clear skies to all!
> Karl
>
>
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