Call for Observations - Pluto and Charon Occultations
22nd June 2008 - 19:06 to 19:23 Universal Time (UT)
On the morning of the 23rd June 2008 (local time) Pluto and Charon will occult 2UCAC 25370733, a mag. 12.4 star in NW Sagittarius.
Observers from the Eastern Australian Coast and Indonesia to Madagascar and South Africa are encouraged to observe the events.
The goal is to measure the rate of dimming of the star as the planet and the atmosphere absorb the light. From this, the pressure and temperature can be calculated. This will contribute to ongoing studies undertaken by researchers at Observatorire de Paris and Southwest Research Institute and Lowell Observatory. These researchers will welcome all observations.
Typically an observer with a 8" scope or bigger would take intergrations as fast as your equipment will allow, ideally one or two per second or better. For the event in 2006 I used my 10"f5 and a Meade Deep Sky Imager (pro). For this event, I'm planning on using two scopes, an 8" SCT with the DSIpro and my 10" Newt with the Watec WAT-120N intergrating video camera.
Both Pluto and the Target Star will be in the FOV of this equipment from the 17th to the 27th so you will have plenty of opportunity to practice finding and observing. You will need images of the pair well separated anyway for accurate photometry, so start the observing project early.
Visual Observers should attempt the observation as well. When Pluto or Charon occult the star, there will be a 1.7 magnitude drop in brightness which should be easily detected. OK, you probably won't be able to detect the thermal layer in the atmosphere but your observation will aid in determining the actual path limits due to your geographic location and timing data. Besides, you can boast that you are among the first to visually observe an occultation of a Kuiper Belt Object.
Below are the latest path predictions for both events.
If you know of an observer near the path prediction for either event, please forward this message to them.
Any questions? I'm happy to help. Just ask here or direct an email to... (dave4gee "at" yahoo.com.au) "at" = @)
I would imagine then that my low light occultation video camera on the back of my 14" would be able to capture good video of the event! CheersDavid
Hi David,
I guess you are talking about the camera from RASNZ? If so then you might be able to detect mag. 13.9 Pluto as I can reach mag 12.5 stars using the same camera in my 10".
However I think you'd be better using your CCD camera (better S/N and greater bit depth) and binning 2x2 or 4x4 to get the frame rate up. We are not trying to get millisecond timing to plot the profile of pluto as we know it's spherical, rather we are after accurate photometry of the star's transition through the atmosphere during the disappearance and reappearance which could last 20 seconds each.
Remember DaveH got good data from the Pluto 07 event using identical equipment. IIRC you helped with the photometry then.
OK, then I could use my MX716 (the SBIG is parallel so the download time kills me). I'll have to experiment to see what the settings should be to get as high a frame rate as possible with as good a SNR as possible.
Below is an image of Pluto and target taken last night.
You should be observing from 19:00UT to 19:15UT 22nd June (5:00am to 5:15am MONDAY 23rd June)
Don't forget the pair are at Alt18.5 Az261 so keep clear of trees in
the west and it's a small slew from say Nunki in Sagittarius
AND don't forget the Pluto event is followed by the Charon event (about) 8 minutes later so if we miss Pluto (because of a southerly shift) we might catch Charon.
I forgot about it until late last night and so preparation was almost non-existent. As a result I was up until 11pm sorting out the automation script and then ended up with only about 2.64 images/minute and some images with slight trailing.
How does one come to an accurate decision on what exposure time to use for occultations??? I always wonder and never know. In this case I used 10 second exposures to get reasonable brightness (the star was at about 1500 ADU). But I think I could've & should've probably gone down to about 3 or 5 seconds? Unsure where the compromise between SNR and exposure time should be.
Anyone get this? I recorded it but not very well
Have no idea if my shots will be useful. Roger.
Good one Roger, Your observation will be very important to figure out where the path actually went. What is your location and what duration did you observe?
Observers on La Reunion and in South Africa also got positives but at this stage we are not sure if they got an atmospheric event from Pluto or they got Charon.
I got a nice light curve. See below.
I know of one other observer with a positive from Bankstown.
I have data for hours around it. Due to the problems in plate solving on pluto I ended up just setting it taking images with regular slew, plate solve & focus on a nearby starfield. So other than gaps of a minute or two every 30mins where the slew, plate-solve, focus, re-slew back to pluto occured, I have a couple of hours before and at least an hour afterwards.
I see you have a lot of dots in your graph! I'm guessing that equates to a lot of exposures? Do you know how many you were taking per min, and what brightness level Pluto was at ?
I see you have a lot of dots in your graph! I'm guessing that equates to a lot of exposures? Do you know how many you were taking per min, and what brightness level Pluto was at? Roger.
The camera is the Watec WAT-120N which is an integrating video camera. It takes images at 25 frames per second and can stack from 0 (no stack) to 256 frames in it's memory. To meet the requirement for TVs, VCRs and the like it outputs the stack at the rate of 25 (stacked) frames per second.
In this case I was stacking 32 frames, making and exposure of 1.28 seconds with almost instant download making for zero dead time.
The method I used to make the quick grab was to simply grab all the multiple stacked images. So my plot has 32x the amount of points.
Tonight I'll set up the software to grab 1 stacked image to PC for every 32 that comes off the VCR. This should give a cleaner result.
I'll also process the FITS from the 8"LX90/DSIpro.
Ahh, thanks for the extra info, helps my understanding. Very different way of recording the event, but certainly suggests I was doing much longer exposure times than I needed to - Pluto would be visible with 1 second exposures on my setup, but just barely. Yet I was doing 10 sec.
The compression plays havoc but you'll get the idea. The D and the R are unbelievably s-l-o-w and the star is gone for seemingly an eternity. It was a jaw dropper seeing it live.
Btw, I know this is a mine field of a question, but is there any easy answer to processing my FIT files into a graph? I have the reduced and aligned FIT files, never have tried going further with it. Am considering it, but fear it's a whole huge new learning curve. I might mess arround in CCDSoft tonight and see what it can do.
is there any easy answer to processing my FIT files into a graph?
I use AIP4Win.
You point it at your darks and flats, making a master dark and flat, then point it at your images. It loads the first image and you click on the V, C and K stars and hit GO. It opens each, measures the 3 stars, closes the image and repeats...
in the end you have a .txt file of measures that you open with Excel or similar and draw a graph.
