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Re: (meteorobs) June Bootids of 1921 and 1927
Jure wrote about June Bootids (JBO):
>But then, in 1927 in Russia (!!) folx saw an outburst of
>500 meteors per hour on June 27.
You are right. Please see our description of this event
in the article in MNRAS 308, 887. It would be tedious to
rewrite the story here.
Best wishes, Rainer
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\subsection{The 1927 June Bo\"otids}
The next enhanced June Bo\"otid activity after the 1916 event
occurred in 1927 for which we find two main records: an observers
group in Tashkent (summary in Sytinsky 1928; details are given
in Sytinskaja 1928) and an observation by Dole in the USA
(reported by King 1928). Although very large meteor numbers
were reported, both reports do not necessarily indicate a June
Bo\"otid outburst similar to the 1916 event occurred.
Dole gave two active radiants, the Coronids at $\alpha=235^\circ$,
$\delta=+30^\circ$ with which he associated 130~meteors, and the
Ursa Majorids at $\alpha=215^\circ$, $\delta=+57^\circ$, with
which he associated 145~meteors. The maximum was found on
June 29 and June 30 with 35 Coronids, 65 Ursa Majorids
and 48 Coronids, 37 Ursa Majorids respectively. The same note
by King gives Dole's Orionid rates: 499~Orionids in total,
at maximum 97 Orionids were seen on October~23. On the one hand,
the Orionids usually furnish a maximum ZHR
of about 25 implying that the possible June Bo\"otid rates
were as high as that at best. On the other hand, we should bear
in mind that northern June nights are shorter than October nights,
i.e. the meteors were probably seen in a shorter period of time.
We can, nevertheless, conclude that the 1927 activity was not as
high as in 1916 and did not exceed a value of about 30.
The second report (Sytinskaja 1928) gives enormous meteor
numbers for the end of June. The nights of early June and
early July with mainly sporadic activity free of major
showers indicate that the observations were carried out
under extremely good sky conditions, stellar limiting
magnitudes are assumed to be between $+7.0$~mag and $+7.5$~mag.
Fig.~\ref{figtashkent} shows the uncorrected hourly rates
(including sporadics)
for the most active observers of the Tashkent group, and
it becomes obvious that the actual activity did not exceed
sporadic activity by more than a factor of two.
A limiting magnitude of $+7.5$~mag results in reasonable
sporadic rates before and after the event. With this assumption
we can calculate the hourly rate, corrected for the limiting
magnitude and radiant elevation, from the meteors actually
associated with the June Bo\"otids.
It turns out that the ZHR did not exceed 10 indicating that
the observers applied a very stringent shower association.
Taking the total-rate graph and the ZHR as well as the results
from Dole's observations into account, we can conclude that
{\it the ZHR did not exceed a value of about 30 in 1927.}
...taken from
Arlt, Rendtel, Brown, Velkov, Hocking, Jones (1999)
Monthly Not. Roy. Astr. Soc. 308, 887.
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--
Rainer Arlt -- Astrophysikalisches Institut Potsdam -- www.aip.de
Visual Commission - International Meteor Organization -- www.imo.net
rarlt@aip.de -- phone: +49-331-7499-533 -- fax: +49-331-7499-526
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