Rare occultation by the moon Nereid 25 August

Hi everybody,

There is a rare occultation of a star by the moon Nereid

Occultations of stars by satellites of Neptune are extremely rare

When: night of Aug 25th (Monday)

What: Occultation of 13.6mag star by 18.7mag satellite of Neptune.

How: Just keep taking short exposures during the occultation period (23:20 - 23:30 BST).

The exposures should be just long enough to show a 14th mag star.

During the ~15sec occultation the star will completely disappear.

Dead time should be kept to a minimum (<< 10 sec). Use windowing or binning if you have to for those using CCD cameras.

By the way, if you find that the dead time is too long, you can do the following: Just take a very long exposure (say, 6 min) centered on the midtime of the event so in this case, covering the period 23:24 to 23:30 BST) and at least one other of the same duration either before or after the event (preferably both). That would not give you the timing but it will give you the duration +/- diameter size of Nereid.

Those more south of Ireland will have some advantage as the path of uncertainty improves more south. The more observers that image this event the chances of success. Any observer here with a 4 inch telescope and upwards plus a CCD camera can record these images.

If any body needs further help let me know.
If successful send the images to me and I'll process them into a light curve and determine the diameter of Nereid. A successful result of this event should determine a more accurate diameter than the present one.

Clear skies.

Eamonn A

www.kingslandobservatory.com

Hi Eamonn,

Great post!
And thanx for the instructions, they are absolutely helpfull!
I am also preparing for this event. Yesterday I followed the advice of Andrew Elliott and aquired some CCD images of Neptune in this beautiful semicircle of stars. I used a 5" ETX-125 (wow, what a telescope!) and ATIK 16-HR.
Location: my home in Athens.
It was easier than I had thought. Just 10 sec exp. and voila! a handfull of faint stars! Among them, Triton, just north of the planet and 2UCAC 26798093, the target star to be occulted by Nereid on 25 Aug.

Here is a frame (no image processing)


farm4.static.flickr.com/3147/2791900827_9f98a995d8_o.jpg

and another with star mag labels:
farm4.static.flickr.com/3185/2791911131_a00dc36cbd_o.jpg

I have also writen a post here on our greek forum, and a number of people are also going to try it, some visually, some with CCD.
As it is stated in IOTA site www.iota-es.de/nereid2008.html ALL European Occultation Observers should be on Alert!
It is a very important event, which will not only give Nereid's diameter, but also "its precise astrometric position of Nereid down to about 5km".

I have not yet decided how I am going to make this observation. I will either use the ATIK CCD on my 10" LX 50 SCT,
or use a 16" SCT to aquire live video with precise time stamp with WATEC 902H2 and GPS time inserter (my occultation equipment).

Good Luck & Clear Skies!

Thanks for all the information Eamonn and Vagelis. Vagelis your work will be very helpful in planning to make this information.

As Eamonn discussed, the key will be to minimise the 'Dead time' which occurs when the CCD is not integrating (i.e. downloading etc).

An idea which relates to Eamonn's might be to use a tracking rate which is NOT sidereal (Lunar would do nicely. Then a long exposure would make the target star look like a line on screen. Any successful detection of the occultation would be readily visibly as a dimming along the line. The timing of the occultation could be easily interpolated.

This is a real opportunity for anyone even with the most basic imaging equipment to make a really significant observation. I would also encourage anyone who has a scope big enough to see a mag 13.6 star to attempt this visually. An 8" scope under dark skies will be enough to make a visual observation. Basically if you can see Pluto in your scope then its big enough!

Hey Dave! How are you?

This is a great idea, using a lunar tracking speed. It is basically like the Drift Scan method, with the difference that it gives you shorter star trails, thus minimizing the need for large fields of view, right? Brilliant! Have you done it before?
The occultation of our star here, would show up as a very deep dimming in brightness, since the mag dif. between the star and Nereid is huge. I think it would rather dissappear, and we will have a black gap in the trail of 2UCAC 26798093.
(Well, I don't expect it to be a smooth dimming indicating atmosphere on Nereid!)

With Watec 902H camera on my 10" scope, I can have 12.3 mag stars twinkling at 30fps on my monitor. So I would rather expect 2UCAC 26798093 to be an easy target with a 16" scope. But I do have to try it first, and this will be done on the night of the event, I don't own the 16".

In case this doesn't work, I believe the best way to do it is Eamonn's suggestion about binning (2X2).
My CCD download time is 17 sec (1X1) and 7 sec (2X2).

PS: Greetings from Kyriakee!
PS2: BTW, another interesting event on that night is reappearance of Jupiter's moon Io out of the planet's shadow at 19:46 UT (I.Ec.R.).
I expect to have a nice video from that event, too.
(At least a guarenteed result, since Nereid occ. has a considerable uncertainty)

Vagelis

Excellent thread!
This is what it's all about.

As I have the same scope Vagelis,
I will try this too but...
I have is a Philips SPC900 webcam.
I'm not sure if this will be adequate.

Hm... practise makes perfect, Frank.
You won't know unless you try, a few nights before the expected event. Eamonn's and Dave's directions are very clear and right to the point!

BTW, here is the latest prediction track,from 8th August. Either you see it, or we see it, or the germans see it! I will be very happy if anybody sees it anywhere in Europe!

www.iota-es.de/images/2008_aug_25_star_nereid.jpg