Triton occulted UCAC4 410-143659, night of 2017 Oct 5th/6th
~ predicted by the Lucky-Star Project~

Observing considerations:

1) Do test runs to establish optimum settings to detect Triton. Test runs are best done on nights prior to that of the occultation, as well as during the run-up to the occultation itself. The star is brighter than Triton, so it is worth while to give the event a try !

2) The planet is 100x brighter, so Neptune will create unwanted light: CCDs often produce leakage along the pixel columns (and sometimes along the row direction), so it is sometimes beneficial to turn the camera to minimise overlap of stray light interfering with the image of Triton, rather than having it aligned in RA and DEC. The WinJupos plot (above) indicates Triton is at PA (about) 110 degrees.

3) Will Moonlight effect visibility ? The event happens just 5 hours after the Moon is full and quite close to perigee, and higher in the sky than Neptune. With an angular separation of 34 degrees, it may be worth observers erecting a temporary 'moon shade' to stop moonlight entering the telescope aperture. It might mean the difference between success or failure for observers using relatively small apertures.

4) A telescope with long focal length will produce best results. e.g. SCT: There are fewer diffraction effects, and contrast should improve, so a SCT would be a good system to use.

5) Is use of a Barlow lens is indicated ? The Neptune / Star separation is 10" arc so a Barlow will increase the image scale. Getting good focus on the star will also be important. It may not be easy in poorer seeing, but if the star is recorded then we may get a result. Use of a Barlow should be part of the test.

6) Take as many short exposures as possible. Subsecond exposures between 0.16 to 0.64 sec are desirable depending on sky conditions and the aperture used.

7) Aim for good sensitivity. i.e. Triton+Star are detected clearly. If necessary longer exposures should be used e.g. 1 to 2 sec in order to capture the star.

8) If possible, use a 12-16bit FITS, otherwise 8bit AVI: Part of the extended test. This observer will use 8bit analogue video to (AVI) to start with.

9) Use of a USB planetary web cam requires the clock be Sync 'ed with Dimension4 (Thinking Man Software) or similar for NTP. Correct computer time is important.

10) Suggested software is: FireCapture or SharpCap for time stamping (or use an established method): Planetary web cams are useful, but the user will need to establish their sensitivity using a trial run.

11) It's not thought that filters will improve detection for this event: Since the planet is blue/green, the option would be a red filter. But since the spectral type of the star is not given, filtration may not provide any benefit.

12) Addendum to filtration: Atmospheric Dispersion will also reduce the amount of focused light reaching the detector. There is a good description of the ADC here. I am tempted to try a light green W11 filter during the test phase. (Wratten Filters). The use of an Atmospheric Dispersion Corrector might improve the detection limit by sharpening the image.

---

1 - RESULTS FROM TEST VIDEO-ING ON 2017 JULY 21 @ 0227UT

Note to the above image:
This was a 30cm F4 and 5x Powermate, with WAT-910HX Setting x32, 39dB gain (=0.64s).
The camera was pre-focused with a Bahtinov mask using alpha And. Stability was Ant iii (not good, not bad either).
A single integrated frame (0.64s) was selected for this illustration using TANGRA ( H. Pavlov)

---

2 - RESULTS of TEST with a University KLEE 2.8 x Barlow
2017 July 26, 0200UT
compared to NO Barlow (Filtered with Wratten 11)

Below: No Barlow. Native focal length is 1200mm @ F/4

 

Notes to the above test-2 images
By comparison with the first test, the KLEE Barlow [1] gave about the same amplification as a 5 x Powermate [ FL 6m ]. This was explained by the fact the WATEC CCD with nose piece and filter was positioned 35 mm from the normal eyepiece focal plain. This increased the amplification to about 4.5 (or 5). From an approximate calculation [2] the focal length of the KLEE was 25mm (1 inch). Much shorter than most other Barlows. With this in mind I measured a Revelation Astro ED 2x Barlow (2" fit) and found this to have a focal length of 100mm.

[1] Loaned by Adrian Jones (Maidenhead AS)
[2] J. B. Sidgwick, Amateur Astronomer's Handbook. 2nd ed 1960

Tangra Light Curve from the avi using 16/50s, gain 34dB NO Barlow, W 11 filter, with "pixels in the background annulus" reduced from 350 to 100 (Tangra>settings>photometry).

---

3 - RESULTS of TEST with an 2x ED-Barlow on 2017 July 28, 0200UT
with Wratten 11 (pale yellow-green)

 

Notes to the above test-3 images
Smaller angular separation from Planet (10-12") due to orbit. Scale is 0.7 arcsec / pixel. Wider field of view ( 7' x 9' ) so periodic error is less obvious. A single field star of Mag 13.5 was available as a guide star for the photometric software. Seeing stability was poorer compared to previous test images

---

4 - RESULTS of TEST with a 1.25" KLEE x2.8 Barlow on
2017 Aug 12, 0030UT
with and without Wratten 11 (pale yellow-green).
In Moon light [89% 15d to East]

 

Report Form

Observing Report ( for successful observations ) http://lesia.obspm.fr/lucky-star/predictions/2017/Triton/html/observers_report.pdf

Please copy reports to the BAA Asteroids and Remote Planets Section.