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NEW Images of Pluto and Target Star with DSI Imager by Dave Gault, Australia! Including Photometry!

Occultation of UCAC 25823784 by Pluto on the 18th of March 2007

A very rare event will take place for the USA and Mexico on the 18th of March 2007

Around 10h 56min UT Pluto will occult the star UCAC 25823784. The prediction is based on recent astrometric measurements of the star made by the swiss telescope of ESO/La Silla. It should be good to within 20 to 30 mas. Therefore the event is quite firmly confirmed for the southwestern USA and western parts of mexico. The following map shows the path of the occultation as predicted by Bruno Sicardy (Observatoire d' Paris/Meudon) based on images from Raoul Behrend.

Pluto 18032007

The map shows Pluto's shadow over the Earth, with light grey regions corresponding to astronomical twilight and dark grey corresponding to night time on Earth.

We call for all observers in the region to do whatever its possible, to make this an outstanding scientific campaign to achieve data about Pluto's atmosphere. The star is in the red about as bright as Pluto, as can be seen in the following table:

Star magnitudes: B= 16.4 V= 14.9 R= 14.1 I= 13.6 J=12.0 H= 11.2 K= 10.9
Pluto/Charon: B= 15.3 V= 14.4
I= 13.6 J= 13.0 H=12.8 K= 13.1

This occultation by Pluto is very special indeed. It is the first Pluto occultation over such a populated area (with regards to astronomers!) as the western USA. From our experiences with the recent Pluto occultation in Australia (2006) an instrument of 10 inch diameter equipped with a simple CCD imager, such as the DSI, will be sufficient, to gain valuable data.
A central flash, turbulence in Pluto's atmosphere and hypothetical haze distribution can be observed with an unprecedented dense mesh of observers.

IOTA-ES urgently calls to join the international campaign for this event!

More information about this event will be published here as soon as they come in.

On the webpage of Bruno Sicardy for this event you can find updates of the occultation track and other important information as well.

Images by Dave Gault:

Recently images from Dave Gault, Australia, who recorded successfully the Pluto event last year, have been analyzed and are presented here. They are recorded with a DSI imager with the black and white CCD chip (1/3 inch) and a 250mm Newtonian telescope. Because many observers in the USA have such a device, these images are of great importance for preparation of the event, which is now only two months ahead of us.

In order to analyze the images photometrically, they have been exposed for 4 seconds each. Here you can see the area of the target star, the target is the brighter one in the green circle:

And here is Pluto itself, recorded on the 13th of September 2006 around 11h30 min UTC.


Both images were taken at about 40 to 44deg elevation in the sky. The focal length of the  250mm Newtonian has been 1250mm (1/5).

The intensity ratio of Pluto was about 12000 intensity units, of the target star it was 5400 intensity units. This results in a ratio of (Pluto/(Pluto+Star)) of 0.69 .
If this result is compared with the photometry given above, you have to keep in mind, that no filter has been used. If you take into account the sensitivity curve of the DSI imager chip (Sony), it is like a B and V and R bandpass. The I intensity is only poorly recorded, compared to the other bands.

The intensity of Pluto may also vary of more than 0.2mag, which has not been taken into account. The results of 0.69 seems therefore to be pretty realistic, if compared with the other photometric data.

Using a telescope 30cm diameter of larger equipped with a DSI imager, it will be perfectly suited to get valuable data of this brilliant event.

Questions, remarks, contributions and other informations should be sent to

With best regards from Munich

Wolfgang Beisker

International Occultation Timing Association / European Section
Research and Development