The Occultation of a R=12.2 Combined by Asteroid Doris

Mar 14, 2024 at 12:54:47am

 

Doris is a large asteroid and we're in the center of the path so this one's a "sure thing". But the drop is only 0.35 mag and the target + asteroid is 12.25 magnitude, dropping to 12.6 for 14 seconds. It'll be hard to get any separation from Kirk Bender w/o large travel which is not justified. I will plan to try it from UCSC. The Alt=20, Az=276 in the west.

 

     

 

Results

Richard Nolthenius

I recorded the occultation, saw the the fade as it happened, looked about the predicted length of time. The seeing was excellent and steady. I observed from just off the bike path crossing behind the Arboretum, which turned out to be a great spot for future events and photography. No troubles with private property, and the sky to the west has an excellent horizon. Only the SE has a big tree which would interfere with observing. The recording was successful and on transferring to my external HDD, the occultation was clearly visible visually.

I used 16x setting (about 1/3s integrations), and TME apertures (size=10), on the target, on the very similar nearby neighbor (ref1) and a more distant ref2, using both ref1 and ref2 as tracking apertures as well. Video was quite steady, and to my eye, no clouds. I had a remarkable experience with the reductions. The video showed more scatter to my mind than seemed visible on Kirk's video at a higher cadence. What was remarkable was that using a very low smoothing=6, which showed a lot of short term wiggle in the reference star, was the one which very clearly minimized the scatter in the target star and brought out the occultation much more clearly. I don't know if there was some sort of ~2s period noise picked up by both ref1 and the target in resonance, or whether it's an artifact of the TME aperture. Reductions appear pretty solid, for only a 0.25 magnitude drop.

magDrop report: percentDrop: 20.4 magDrop: 0.247 +/- 0.034 (0.95 ci)

DNR: 2.24

D time: [07:54:38.0388]
D: 0.6800 containment intervals: {+/- 0.2096} seconds
D: 0.9500 containment intervals: {+/- 0.9043} seconds
D: 0.9973 containment intervals: {+/- 2.3469} seconds

R time: [07:54:56.5987]
R: 0.6800 containment intervals: {+/- 0.2096} seconds
R: 0.9500 containment intervals: {+/- 0.9043} seconds
R: 0.9973 containment intervals: {+/- 2.3469} seconds

Duration (R - D): 18.5599 seconds
Duration: 0.6800 containment intervals: {+/- 0.3880} seconds
Duration: 0.9500 containment intervals: {+/- 1.2729} seconds
Duration: 0.9973 containment intervals: {+/- 2.8322} seconds

The raw PyMovie light curve has noise or thin cloud over time scales of many seconds. The occultation still stands out, at center, but there are correlated changes as if thin cloud was present.

The composite curve shows the same changes for each star. The ref1 star was quite close to the target, and was used as the reference for reductions.

The metric interval minimum scatter was reached at a smoothing length of only 6 points or about 2 seconds, showing the oscillations in the light curves were real changes in opacity common to both stars. The change in the metric flatness was quite clearly minimized at 6, and much worse at longer intervals.

The calibrated light curve is much flatter, and the occultation clearer.

Zoomed in. There's a hint of a 2-step occultaton, but not on the PyMovie raw plot. Real? Hard to say.

     

 

Kirk Bender

Observed from "the Berm" on Empire Grade just below Felton-Empire junction. This is about 3 or 4 miles north of the main UCSC campus. Good conditions, clear skies. I got a 17.75 sec event for Doris at 8x. I tried both TME and static circular apertures, I got slightly better DNR and containment intervals for static circular, that's what I'll report.

Static circular:

magDrop report: percentDrop: 21.3  magDrop: 0.260  +/- 0.035  (0.95 ci)

DNR: 1.34

D time: [07:54:38.2674]
D: 0.6800 containment intervals:  {+/- 0.2028} seconds
D: 0.9500 containment intervals:  {+/- 0.7877} seconds
D: 0.9973 containment intervals:  {+/- 2.0528} seconds

R time: [07:54:56.0182]
R: 0.6800 containment intervals:  {+/- 0.2028} seconds
R: 0.9500 containment intervals:  {+/- 0.7877} seconds
R: 0.9973 containment intervals:  {+/- 2.0528} seconds

Duration (R - D): 17.7508 seconds
Duration: 0.6800 containment intervals:  {+/- 0.3741} seconds
Duration: 0.9500 containment intervals:  {+/- 1.1049} seconds
Duration: 0.9973 containment intervals:  {+/- 2.4044} seconds

Kirk's points are denser, at 8x setting, 2.1x as many points as mine.

Unlike my data, Kirk's does not show the fine scale correlated changes apparently due to thin cirrus not apparent by eye to me, but is in my data. Kirk's optimum smoothing length is much longer. Clearer skies?