Trans-Neptunian Objects including Pluto, Charon, Hydra and Nix
For the year 2012...
High precision predictions
The observation of
occultation of stars by Trans-Neptunion Objects (TNO) is one of
the most challenging astronomical projects in these times.
Occultation Astronomy is the only precise method, to determine the
diameter and shape of these far away objects as well as to detect
possible gas envelopes of these objects such as Pluto's
The precision of
pre-event astrometry has been increased in the past few years so
far, that successful observations can be carried out right now.
Pluto's orbit has been pinpointed with an accuracy much better
than its radius, so that planning of expeditions can be done far
ahead of the event.
However, last minute
astrometry is still needed urgently, such as it is for standard
asteroids occultation work. The required precision however, has to
be much better, around 10 milliarcsec.
We have to be very
thankful to the group around Marcelo Assafin in Brazil (the RIO
Team), who does astrometry with large instruments from Pico dos
Diaz observatory in Brazil as well as from ESO sites in Chile. He
is analyzing these high precision images with his software package
PRAIA. Bruno Sicardy in Paris/Meudon Observatory calculates the
predictions for the objects. IOTA-ES can have access to these
predictions as soon as they are provided.
Because of the growing
number of occultations predicted, IOTA-ES presents on its site
only an excerpt of all predictions, for stars brighter then 17m5
and only for those events, where a reasonable area of visibility
on earth exists or with a special point of interest.
in mind, that recently a small telescope of only 38cm diameter was
able to record a star of 17m in 1 second exposure time with a
camera as simple as the QHY6. And for many objects, even
occultation observations with a time resolution of 2 seconds are
very valuable research data. The diameter of the TNOs can be
pinpointed with a precision of around 5% in many cases!!
With best regards from
are the predictions done?
A good description of
the process of predictions as has been done for Pluto and its
satellites can be found in A&A 515, A32 (2010), "Precise
predictions of stellar occultations by Pluto, Charon, Nix, and
Hydra for 2008–2015" by M. Assafin et al. .
summarize, an astrometric star catalog of the path of the Pluto
system has been generated in 2007 with the ESO2p2/WFI instrument
for the years 2008 to 2015. From these images, using the PRAIA
software (Platform for Reduction of Astronomical Images
Automatically) positions have been determined in the UCAC2
frame with errors of 50mas for
stars up to R = 19mag, and 25mas up to R=17mag.. 2252 predictions
of stellar occultations have been predicted for the Pluto system
for 2008 to 2015. New proper motions have been evaluated with
2MASS and USNO B1.0 catalog. Pluto's offset has been determined by
using the occultations of the years 2005 - 2008.
other TNO's however, no occultations are available yet, therefore
dedicated astrometric observations from other sources have been
used (M. Assafin wrote: " the offsets were derived from
dedicated astrometric observations with small to mid-sized
telescopes from collaborators, not from previous (inexistent)
occultations as in the case of Pluto.").
Otherwise, the procedure is similar to that of the Pluto system.
it is to believe, that the predictions are the best predictions,
we can get for the moment. As soon as better data are coming in,
they will be presented here.