The Occultaton of a R=15.2 Star by Plutino KBO (55638) 2002 VE95

Feb 10, 2024 at 7:33:13pm PST

This is a rare, valuable Plutino KBO event. Plutino's are objects in a 3:2 resonance with Neptune. But it'll be tough; R=15.2 mag. It may take up to a 2s integration to get it. Be generous! It should last 13s and any detection of an occultation will improve the orbit by a big amount. Don't scrimp on timing accuracy. Make sure you can see the target. Odds only 10%, but that means glory if you hit jackpot. Wikipedia page. OWcloud page

This is a Plutino KBO. We know very little about these. We have only 2 KBO's with close up photos, from the New Horizons Mission (Pluto and Arreketh). Astronomers want to learn anything they can about them. Do they have moons more commonly? Are they spherical rubble piles? Are they rigid frozen Nitrogen objects? What are they made of (density, from moon discoveries). Occultations can tell us a lot, but first we need accurate orbits. So this event, while unlikely, is worth putting effort into. It did not show on my OW predictions, perhaps because the magnitude was too dim at R=15.2 and even dimmer in visual G=16.8. To put together the charts below, I went to the LuckyStar prediction page, clicked on our location and that pops up the box with the local predictions. The wide red dashed line suggested the event could be as much as a minute early or late. I chose to do 4 minutes on either side of the predicted time. The target does(?) show up on the UCAC4 chart I made, but I will have to look more closely if the star I clicked on for the C2A chart is the real target. In any case, the SDSS Aladin chart shows much deeper and shows the neighboring stars. I note the brightnesses of the stars is not entirely consistent with what my Finder image showed. Perhaps the SDSS photos are in V or G, not R, and the Watec is apparently closer to R than V or G.

The target star is very faint, so likely rather distant, and as it is in the middle of the plane of the Milky Way, interstellar dust reddening is likely. That's good. It may help us with our red-sensitive cameras.

The LuckyStar predicted duration is 13.4 s and the depth of the drop is 4.7 magnitudes.

The OWc map is below. There are two prediction orbits on the OWc page

Results:

Richard Nolthenius PyOTE log file

Despite being late home from my activities and the gym, I was able to get the planning page done and gear thrown into the RAV4 and drive quickly up to the site. I set up at the mtn bike crossing at the Upper Meadow of UCSC, on the asphalt just off the shoulder on the west side. I got there with only 19 minutes till the occultation. I got set up as absolutely rapidly as possible, and everything went perfectly. I was on target and ready to record with 10 minutes to spare. I chose the site in hopes of a darker sky so I could do a long integration. R=15.2 is fainter than any event I've tried on the 8SE scopes. However, conditions looked about as perfect as could be. No clouds, no wind, no moon, good 46 degree altitude. I thought 2 second integrations would reveal the star reasonably well, and 1sec if I was lucky At the scope. I tried 2 s (128x), but the sky was too bright, so backed off to 64x; a bit over 1s integration.

For analysis, I made a 444 frame Fourier Finder and used that finder to position the apertures. I used TME snap-to apertures (10px was the solution) on the two reference stars, brighter but not saturated, compared to the target. I tried using a TME aperture on the target, but then deleted that since it spilled onto the neighbors, and went instead with a static circular aperture and tightened the radius to only 3px to exclude the neighbors, although I'm not totally sure the faintest of the 3 star cluster that included the target, was totally excluded.

The light curves below look like a clear occultation, about 1.5 asteroid diameters later than the predicted time, and within 1/2 second duration of the predicted centerline duration. However, the light curve looks unusual, with a deep to zero integration at the end of the event, and a deep partial occcultation for most of it. There's also a suspicious complimentary shallower depth drop for about 6 seconds a few seconds after the primary, but not by itself convincing. I think a binary star might be involved? I'll let LuckyStar astronomers sort it out.

Long 122 04 46.29 W
Lat 37 01 03.39 N
Elev 1126 ft

magDrop report: percentDrop: 78.3 magDrop: 1.660 +/- 0.456 (0.95 ci)

DNR: 2.68

D time: [03:33:38.6027]
D: 0.6800 containment intervals: {+/- 0.4220} seconds
D: 0.9500 containment intervals: {+/- 1.1912} seconds
D: 0.9973 containment intervals: {+/- 3.0874} seconds

R time: [03:33:52.9122]
R: 0.6800 containment intervals: {+/- 0.4220} seconds
R: 0.9500 containment intervals: {+/- 1.1912} seconds
R: 0.9973 containment intervals: {+/- 3.0874} seconds

Duration (R - D): 14.3095 seconds
Duration: 0.6800 containment intervals: {+/- 0.6389} seconds
Duration: 0.9500 containment intervals: {+/- 1.5259} seconds
Duration: 0.9973 containment intervals: {+/- 3.3144} seconds

I've inserted full brightness and half brightness lines to help visually decide if a binary star might be involved.

False positive test satisfied rather well for such a faint target. I'm encouraged! Stars this faint are do-able with enough data points involved.

This is just to aid Kirk in ID'ing the target in his video capture.

It looks like we got lucky and got the occultation; 14s long, as was most likely given the available estimates on this object.

Kirk Bender