The Occultation of a 12.3 by (11977) Leonrisoldi

July 18/19, 2023 at 10:59:50pm

 

This event is mediocre rank, but should otherwise be fairly easy. A 12.3 star 30 degrees up, Azimuth=170 almost due south. The drop is full, but - it only lasts 0.7 seconds, so keep integration to a minimum, maybe 4x , or even 2x if skies are very good. It's in a dense star cloud in Sagittarius, so I made a second eyepiece chart that's wider and shows only SAO stars. It's also very close to small NGC open star cluster; NGC 6573.

I'm worried about fog, and if I cannot observe from home due to fog, I'll try for upper UCSC meadow. Odds at home of a hit are 29%, and 27% from upper UCSC meadow. For Karl, the odds are only about 10% or less. The track is thin and only just grazes the West Cliff area of Santa Cruz, and the rank is not great. But, the time is convenient at 11pm, and it's worth a try. I'll try from home if I can, but migrate up out of the fog if necessary. Kirk's claimed a site at home.

 

   

 

Results:

Richard Nolthenius

I observed from the Upper Meadow UCSC bike crossing, west side. Good conditions, used 4x (maybe should have done 8x?). The light curve of the target shows an interesting long wave modulation of about 25% in brightness. The reference stars do not show this. The median correction used in PyMovie was for both horizontal and vertical noise and so on the ScreenCapture you don't see the column noise that's visible on the raw frames. I believe the modulation has to do with the sky subtraction difficulty in that there were many dim stars within a few pixels of the target. I picked reference stars which were brighter but not saturated, and which seemed to be in less crowded locations and this may be why they don't show the waviness. Kirk has sometimes seen this behavior as well. I used a 3.6px static circular aperture for all stars.

The astronomical conclusion is clear, however. A miss. An occultation would have given a full drop to zero and none happened, and nothing suspicious near the predicted event time.

begin 05:58:20
end 06:01:55 UT

PyMovie Screen capture showing the layout and apertures. The Pymovie option to median filter both horizontally and vertically was applied, which removed the artifacts..

There are several fainter stars rather close to the target which may have tainted the photometry and produced the wavy light curve at right

Ref1 star, looks fairly quiet

Target star has more waviness. Not relevant for answering the main question - occultation? It's clearly a miss. The waves in the light curve are probably also complicated by the thin cirrus in the area.

Another reference star, fairly quiet light curve

10mm fisheye lens pictures of my setup. This one was taken just a minute before the event.

The target star is in the Sagittarius star cloud, with thin cirrus nearby

 

This and the next picture were taken several minutes after the event.

PyOTE reduction, with vertical bar at the predicted time for the 0.7 second occultation. One red bar with a dropped frame, well before the predicted time of the event.

IOTA report sent in July 26, 2023.

 

Kirk Bender

Observed from "the berm" on Empire Grade just below Felton-Empire intersection. He had a miss under good conditions.

A bit of cloud, interfered for Kirk, but using the reference star showed there was a miss

PyMovie light curve for the target

The target star below, using the reference star (top, in green) to calibrate. Vertical bar at predicted event time. A miss.

Zoomed in on the predicted time. A miss.