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(meteorobs) IRAS-Araki-Alcockid meteors (eta Lyrids)

At 11:38 07-05-2000 +0200, Jurre A. wrote:

>where is the Eta Lyrid radiant located and what is the
>speed of the meteors. I'd like to check my plots for any
>shower members. .

(Message from Marco Langbroek, via Casper ter Kuile):

Hi Jurre,

The theoretical radiant position of Iras-Araki-Alcock meteors (eta Lyrids) 
is at RA 19h 15m, dec. +44, on the Lyra/Cygnus border, and indeed this is 
where Koen and I see our eta Lyrid meteors coming from for several years 
now. The maximum theoretically should be on May 8/9. Koen and I have 
observed activity  from the radiant for a week or so around this date the 
past decade. It are mediumfast to fast meteors, theoretically they should 
have a speed of 44 km/s (comparable to Quadrantids, slightly slower than 
April Lyrids). Don't expect high numbers: we usually see say 1-2 
streammembers per hour around the maximum at best. But last two nights and 
certainly last night Koen and I found them quite active, although that 
partly is due to the fact that this was the first time we observed them 
from our dark observing site Biddinghuizen instead of from our home locations.

Especially later during the night, the radiant is well located for 
observations (approaching zenith!). Observations this year are still 
possible for a few days untill the moon starts to interfere.

Very little actually is known about the stream. If I remember correctly, I 
believe the Japanese have been the first to observe them in the middle 
eighties.

You also wrote:
" And another thing. What is the orbital
period of IRAS-Araki-Alcock, it appears that the meteoroid
cloud (I presume there is no continuous stream as it is
a long period comet) is quite 'long' as the comet passed
perihelion in 1983"

I do not exactly remember the correct periodicity (anyone else knows?) of 
IRAS-Araki-Alcock, but if I remember correctly it was something like 44 000 
years?
Most likely the stream IS 'continuous'  however! While this might seem 
counterintuitive to see meteors from long period comets like this, there 
are a number of other examples. The September Aurigids from comet 1911 
Kiess, and the November alpha Monocerotids for example, are due to (very) 
long period comets as well (note: the alpha Monocerotids are sometimes 
still given a 10 year periodicity; however, our 1995 photographic and video 
orbits have shown that the stream has a period of tens of thousands of 
years [1]).

These streams are very interresting from another point too, and that is one 
of the reasons why Koen and I are targetting the eta Lyrid stream for 
several years now: like the alpha Monocerotids and Aurigids which are 
indeed known to do so, the eta Lyrids from Iras-Araki-Alcock are a possible 
candidate to produce the freak erratic "Far comet type" outbursts, such as 
the already mentioned other  two streams do (the 1995 alpha Monocerotid 
example is well known, and in 1994 Bob Lunsford and George Zay for example 
catched an Aurigid outburst [2]). There is no way of predicting when the 
stream might produce such an event however as long as there are no previous 
chance records. They might happen as little as once-twice per 60 years.... 
The orbital geometry of the parent comet however is very favourable in 
principle, the orbit appraches that of earth up to about 0.003 AU! Reason 
to keep a watchfull eye on the stream around maximum each year...

- Marco Langbroek
    Dutch Meteor Society

[1]   P.Jenniskens, H. Betlem, M. de Lignie and M. Langbroek: Astrophysical 
Journal 479 (1997), 441-447.

[2]   P. Jenniskens: Astronomy & Astrophysics 317 (1997), 953-961.

Casper ter Kuile, Dutch Meteor Society (DMS)
Akker 145, NL-3732 XD, De Bilt, The Netherlands
Tel. +(31)-30-2203170, Fax. +(31)-30-2202695
GSM-BEN: +(31)-6-24242445, GSM-KPN: +(31)-6-53270844
E-mail_1: casper.ter.kuile@planetdot nl
E-mail_2: casper.ter.kuile@dmsweb.org
E-mail_3: webmaster@dmsweb.org
DMS website: http://www.dmsweb.org
Mirrorsite: http://home.wanadoodot nl/dms

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