The Occultation of a R=11.6 Star by Asteroid Pori

Apr 11, 2024 at 1:09:06am

 

This is a high rank event, bright, long enough to get a good positive at 1.1s duration. The target is in Corvus, just below/left of Corvus' beak. It's almost due south at Az=186, Alt=34. The path is centrally across downtown Santa Cruz, but slopes in such a way that Karl's nominal odds from home are ~0.

 

     

 

Results:

Both Kirk and I observed from home, and got clear positives.

Richard Nolthenius

I observed from about 20ft N of the driveway/street intersection, on the street. I used 2x. I used the nearest star of reasonable brightness, just above the target, as my reference star. I used 4px circular snap-to apertures for all. In PyOTE, I set the metric interval as the unocculted remainder of the light curve. I did have trouble getting PyOTE to behave properly when I had bad data at the end of the recording. Not sure if that bad data was from a light aimed into the scope (I don't remember such an incident) but anyway the screen still had the time stamps but all the rest of the field was white. This seemed to cause an error in PyOTE with a division by zero. I had to open the PyMovie output file in Excel and manually delete those lines before it would behave. Merely trimming inside PyOTE didn't solve that problem. That division by zero problem may have plagued me for a good hour of struggling in PyMovie and PyOTE both, and no error pop-ups on the screen happened. Instead, I saw it on the cmd box later. Before I noticed the cmd box error message, I was seeing all kinds of strange failures; to show error bars, or plot histogram, or to halt freeze mid stream somewhere. Solution, again, was to open the PyMovie output file in Excel and remove the last ~100 rows of the file. Then it all processed normally and quickly, as usual.

magDrop report: percentDrop: 86.6 magDrop: 2.181 +/- 0.235 (0.95 ci)

DNR: 3.95

D time: [08:09:05.3566]
D: 0.6800 containment intervals: {+/- 0.0074} seconds
D: 0.9500 containment intervals: {+/- 0.0185} seconds
D: 0.9973 containment intervals: {+/- 0.0363} seconds

R time: [08:09:06.4366]
R: 0.6800 containment intervals: {+/- 0.0074} seconds
R: 0.9500 containment intervals: {+/- 0.0185} seconds
R: 0.9973 containment intervals: {+/- 0.0363} seconds

Duration (R - D): 1.0800 seconds
Duration: 0.6800 containment intervals: {+/- 0.0106} seconds
Duration: 0.9500 containment intervals: {+/- 0.0236} seconds
Duration: 0.9973 containment intervals: {+/- 0.0421} seconds

I put in a line for the average value of the empty sky, as new reference for "zero". The predicted mag drop was 3.42 in G and R, and that looks about right here, if you raise the 'zero' level as per the next graph.

The average sky subtracted value of the sky should be zero, but instead was about 20.

Sharp easy D and R moments.

Predicted event duration was 1.1s, and that's what I saw, here on the centerline.

         

 

Kirk Bender

Observed from home, with the NTSC Watec setup as always. Good conditions, used 2x setting. No reference stars used in extracting timings, under clear skies.

Got a 1 sec event for Pori, 2x at home.
The Fourier finder failed though, I just got a blank screen.
I guess at 2x my field was overall too dim for it to find points to lock
onto.
I made a finder using the old method of choosing a star to track and the
finder worked ok.
No-star again looks centered on about 30.

magDrop report: percentDrop: 80.4  magDrop: 1.772  +/- 0.487  (0.95 ci)


DNR: 2.27

D time: [08:09:05.4575]
D: 0.6800 containment intervals:  {+/- 0.0157} seconds
D: 0.9500 containment intervals:  {+/- 0.0514} seconds
D: 0.9973 containment intervals:  {+/- 0.1347} seconds

R time: [08:09:06.4918]
R: 0.6800 containment intervals:  {+/- 0.0157} seconds
R: 0.9500 containment intervals:  {+/- 0.0514} seconds
R: 0.9973 containment intervals:  {+/- 0.1347} seconds

Duration (R - D): 1.0343 seconds
Duration: 0.6800 containment intervals:  {+/- 0.0248} seconds
Duration: 0.9500 containment intervals:  {+/- 0.0686} seconds
Duration: 0.9973 containment intervals:  {+/- 0.1503} seconds

 

Target light curve, in PyMovie

"no-star" light curve. Note there is no clipping, the distribution of points looks vertically ~gaussian. And this is the "signal" version, so the sky should be subtracted and yield an average of zero, but no, it's about 20 vertical scale units. We don't know why.

The occultation looks almost like a quick double, as if there were a hole in the asteroid, or a contact binary? but I was only a mile away from Kirk, and my light curve does not have that mid-occultation rise. So perhaps just noise.