[ASC-list] WA - Occultation by HYDRA on 27th of June

Emma Donnelly e.donnelly at curtin.edu.au
Mon Jun 6 08:06:53 UTC 2011

Just in case anyone can help ­ please contact Mick directly.
Thank you

------ Forwarded Message
From: Mick Todd <michael.todd at icrar.org>
Date: Mon, 6 Jun 2011 16:00:43 +0800
Subject: Occultation by HYDRA on 27th of June

Dear all
There is predicted to be an occultation of Pluto¹s satellite Hydra of a
bright star (mag ~14) per the attached email below. The current prediction
expects the track to pass right over Exmouth, WA (see the attached pdf of
the path, and the notes in the email below about the error margins).
If anyone knows of available telescopes 10² (25cm) or larger in the vicinity
(meaning within perhaps ~500 km of the path) or of anyone with a portable
setup who may be interested in a field trip to record this event please
contact either myself (michael.todd at icrar.org) or Dr Marc Buie
(buie at boulder.swri.edu). Also, please pass this email along to anyone else
you may think of who might be interested. If they lack a camera there is a
possibility of being able to supply one for this event (see below).
Mick Todd
Curtin University / ICRAR
Perth, Australia
On the 27th of June, (around 14h 20m UTC)  the Pluto system will occult the
bright star 2UCAC 24676603 (14m1). The occultation track will be across the
northern tip of Australia, the northern limit will pass the Philippines.
However, the shadow of Pluto's satellite Hydra is expected to path over
Australia. The orbit of Hydra around Pluto has been updated by Marc Buie,
from the SWRI (Southwest Research Institute, Colorad, USA). The stellar
position will be ubdated to an accuracy of around 10 to 30 milliarcsec, This
gives, together with the current knowledge of the orbit of the Pluto
barycenter, an accuracy of around 500 to 1000km projected on the earth.
However, on the 23rd of June is an occultation of star by Pluto, which will
be measured from Hawaii, which will improve the Pluto position to an
accuracy of about 50 km.
Alltogether, the final improved position of Hydra will have an accuracy of
100 to 200 km, assumed a successful occultation observation on the 23rd of
This will allow an interesting and challenging experiment. because Hydra is
expected to have an diameter of around 100km, there is the possibility, to
set up an "optical fence" with telescopes a few tenth of km apart in the
region, where the shadow of Hydra is expected then.
This would give us the possibility, to determine the shape and position of
Hydra with an unprecedented accuracy. At the moment, the diameter only of
Hydra is just based on assumption about the albedo etc. It looks like, this
will be the last possibility to gain information about Hydra's shape, before
the New Horizons flyby in 2015.
The occultation of Hydra will take place on the 27th of June around 14h 50m
Thed best possible calculated occultation track at present is shown in the
attached graphic (from M. Buie, SWRI). A website from him can be found at
and in a few days a website on the IOTA-ES page can be found (at
An international campaign from observers from the SWRI, the observatory
Paris/Meudon and the IOTA-ES (European Section of the International
Occultation Timing Association) is planned for this reason.
Now my question to you is, can you help to support this campaign either by
observing from your own site, if you are in the region, or with mobile
telescopes, which could be positioned "last minute" in the so determined
occultation zone? Observers from SWRI, Pris/Meudon and IOTa-ES (including
myself) will come to Australia. At the moment, Marc Buie from SWRI will go
to Alice Springs, my own and other places are not determined yet. Any help
would be highly appreciated. In a future publication of the event, all
observers will for sure be coauthors in a possible pepr in a journal.
I will also come to Australia for this event, if we can get enough
telescopes there. We will bring own cameras (including EMCCD cameras from
Paris observatory), or other ones.
We need telescopes in from about 10 inch and larger, where exposure times of
a few tenth of a second will be enough, to record the event.
Its just a standard occultation situation....
DO you know people in your region with 20-30 cm scopes? Regardless, if they
have a camera or not, we may supply one for this event.
By the way, because of the large interest in this observation, you may get
mails from very different persons and/or organizations....
With best regards from Germany
Dr. Wolfgang Beisker
International Occultation Timing Association / European Section Reseach and

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