Occultation of 13.0 star by 14.2 magnitude Pluto

Aug 14, 2018

This is one of the big events of 2018. 23 stations so far have signed up. The northern limit crosses the north Bay is the current best prediction. We have 84% odds of a "hit" at Fremont Peak Observatory, where I'm trying to get permission for us to try it on the 30" scope. Cresent moon will have just set in the west. Pluto is 31 degrees up. We should see enhanced atmospheric fading and variations due to temperature effects in Pluto's atmosphere. Exciting! Major planetary science papers with co-authorship should emerge from this, if we get good data and clear skies.

LuckyStar organization provides the predictions. Online page

Pluto Occultation page and science goals

Map of path and observer track claims

central occ= 10:32:32pm PDT

The LCD chip display on the ZR45mc camcorder, if mounted on the Celestron as per usual.

Q70 32mm eyepiece from the Celestron 8SE

Note, since Pluto is pretty much due south, then "up" is the same as "north" for charts. I am producing charts for the Celestron 8" SE with f/3.3 reducer as per usual. The view in the 30" scope will be different.

Results:

A successful occultation on the 30" at Fremont Peak! Good S/N. Thanks to Chris Angelos especially, and also Kirk Bender for their help to make it all possible. Will have photos and reductions sometime soon. OK, here's Kirk's photo page for the evening

Long: 121 29 55.31
Lat: 36 45 36.87
Elev. 2800 ft
Telescope: 30" f/4.8 Challenger Telescope at Fremont Peak Observatory
Camera: Watec 910hx, set gamma=1, 4x fields integration

LiMovie Photometry Analysis

The LiMovie light curves are below. After some experimenting, I decided that radii of 13/14/25 was best. The inner radius of 13 gave plenty of room beyond the 6-pixel radius of the de-focused stars. At first I had PSF tracking un-checked, but didn't like what I saw in the jumping around on the target especially. So I changed to PSF tracking (but not PSF photometry) and it seemed to settle down much better. I made sure when positioning at the telescope that both target and intended comparison (the star below, similar brightness) were far from any hot pixels. They remained so throughout the 14 minute full recording. I also recorded some twilight flat data, late in twilight, and not with the telescope focused. I saw horizontal banding and this could also be faintly seen in the video of the occultation. Probably some RF interference. We tried shutting off the mount motor tracking but it didn't change it. Perhaps due to the big big radio towers on top of Fremont Peak only 1/3 mile away? The frequency of the movement of the bands was very fast, and I think perhaps we'll get a much cleaner signal if we combine adjacent frames in software. I recorded at Watec 910hx setting =4x (fields) which is 2 frames per integration, or 1/15 second time resolution. By going up to 1/4 second I believe any slight banding would be averaged out, and certainly by 1/2 second.

In all the excitement of trying to get this 30" working, aimed, and ready, I forgot to record a dark frame video. But I can do that just as well once at home later, at a time when the temperature is the same as during the event, which was 62F.

Analysis by IOTA, LuckyStar, and the Southwest Research Institute
Below are images from the Pluto Occultation analysis. The IOTA reductions to get the sky plane Pluto outline gives the best agreement with the known diameter of Pluto if it is assumed that the 50% drop in light corresponds to the moment of occultation. That's an interesting number, because it's very close to the light drop that I saw, but for a full 43 seconds. However, color matters and so the net result is that it looks like Fremont Peak had a short occultation behind Pluto, despite the light level being much brighter than expected.

This page shows more IOTA tracks, again with 50% light level assumed for the limb of Pluto.

From the raw light curve, the gradual drop was about 25 sec long, and the flat bottom was 43 sec long. What's surprising is that the drop in brightness is only 50% of what I expected based on the magnitudes. From mag V=12.7 to Pluto's V=14.2 should have been 25% of full brightness at the bottom.

Aug 17 - dark frames and unocculted star instrumental calibration footage. Taken at home, on my deck, in identical sky conditions (dry, warm, same temperature of 62F, using 0.5x Highpoint focal reducer just as at FPO, but this time through the Cabrillo College 8" SE Celestron. FOV wider than event on 30" scope.

My IOTA Report

List of short comments reporting observations from each of the observers, in googleDocs

My local c:\ drive at AstOcc RawVids, as usual, has the event, and for this event also the dark, flat, and calibration footage. Took a long time to upload the files to the NextCloud repository set up by SWRI Institute. Days!

Report Procedure: Copied from post in IOTA group

1. For all successful IOTA observations:
1. Do a standard video analysis in Limovie or Tangra.  Save the light curve as a .csv file.
2. Submit the .csv file to Bruno Sicardy at:  Bruno.Sicardy@..., or, Josselin Desmars at:  josselin.desmars@...
3. Complete the Lucky Star report form page at:  https://docs.google.com/forms/d/e/1FAIpQLSd4r9Ka1o7kKILlwkQSWZloSPbS8bu6ikftNzSlhXE8IGuS8g/viewform?usp=sf_link, or, https://docs.google.com/forms/d/e/1FAIpQLSd4r9Ka1o7kKILlwkQSWZloSPbS8bu6ikftNzSlhXE8IGuS8g/viewform
4. Submit the .csv file to Brad Timerson at:  reports@... along with an IOTA Excel spreadsheet report documenting the camera used, settings, etc.
2. When Brad receives the report, he will send me all the .csv and Excel report files received and I will run the .csv file through ROTE and send the observer back analysis times for the Dend (end of the disappearance transition) and Rbegin (beginning of the reappearance transition) times that conform to the planetary body occultation.  The observer will then submit a revised IOTA report to Brad Timerson.  Brad will use the data to plot the diameter of Pluto, as if we were unaware of the official size, so that we can check to see how accurate our results would have been had New Horizons not flown to Pluto.
3. For observations where observers have difficulty getting a valid Limovie or Tangra light curve, you can submit the .avi video files for analysis by uploading to Google Drive or Dropbox.  However, these files are likely going to be long and take up a lot of memory on Dropbox, so we will have to be judicious about promoting this method of submitting observation(s).
   ---------- Tony George, Brad Timerson

My Reporting Chronology:
* 8/16/18 completed LuckyStar report form, which only had some preliminary information requested, not data.
* 8/17/18 late evening, got usable footage for dark and calibration images of field through Celestron 8SE, in clear skies at 62F temperature, same as a FPO during event. Altitude of Pluto = 30 degrees, only 1 degree lower than 31 degrees at event time. However, looking through city light glow and deeper atmosphere at 20 ft elevation instead of 3,000 ft elevation.
* 8/18/18 sent pluto occultation light curve from LiMovie .csv to Bruno, bcc to Tony, Brad, with short explanation and link to this page.
* 8/18/18 used Tony's ROTE analaysis to fill in IOTA report form, amended report with proper Pluto and Star designations and re-sent.
* 8/19/18 in morning, uploaded flat, dark, calib, and event avi files to SWRI NextCloud depository.
* 8/19/18 event .avi file won't upload, freezing after most is uploaded. Cancelled, then tried again, fails. Then when try to upload README.docx, gives message "not enough free space". Emailed Marc B at SWRI for help, still waiting for resolution and answer. Dunham says he had the same situation, then max size was raised and he got his files uploaded.
* 8/20/18 successfully uploaded README file. But event file gets from 1 hr down to about 18 minutes and then halts and freezes. Need yet ANOTHER bump in space on NextCloud by SWRI?
* 8/21/18 event .avi file successfully uploaded