This event is very high rank, and centrally through Santa Cruz. Karl, Kirk and I each would seem to have a "sure thing". However, it will be difficult and a challenge. The star is quite faint at 14.4, and worse, it's only about 12arc sec from a brighter star that will make it look like a close double. I would recommend not using the f/3.3 adapter, and also taking great pains to get a sharp focus. That'll better enable using a smaller aperture in PyMovie and still get the event, I hope. The drop is only 0.4 magnitudes. Fortunately, it's long - it lasts 8 seconds at max, and the altitude is nice at +40 degrees. Azimuth 95. That allows good integration. If clear, I'd recommend at least 8x setting, maybe even 16x (Karl).
Again, I recommend you NOT use the f/3.3 or f/6.3 reducer. That means you'll have to refocus to an unfamiliar place, so give yourself plenty of time. In my experience, you can use the f/3.3 reducer and focus it, then remove the f/3.3 reducer and then to achieve focus you turn the 8SE focus knob 20 cranks clockwise. A "crank" is what I call my normal hand movement when going through big focus changes. It's like a "quantum" of focus turn. It's about "noon" to "4:30pm" if a clock, or about 135 degrees of rotation per "crank". For the f/6.3 it's probably less. If instead you've got it focused using the 32mm Q70 eyepiece, then instead of 20 then crank it 15 "cranks".
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Karl set up for it too, but had power / data cable trouble to the Watec camera and got no data. My IOTA report sent in mid February 2023
Nolthenius: PyOTE Log File
I set up from home. Had a few delays: from a delivery guy trying to find a neighbor, a last minute battery charge, being surprised the target wouldn't (barely) be visible from the back of my parked RAV4, my usual deploy configuration, etc. I got a 2pt align with Castor and Sirius, only about 50 deg apart, not ideal. The GoTo was not perfect, and that slowed me again in ID'ing the star field, and there was some slow telescope drift. I did find the target with 15min to go, then first got it on the chip with the f/3.3 reducer, then swapped it out for no-reducer in order to get better separation from the 12" away 13th mag neighbor, and tried to re-focus but failed. Time getting short, and I decided to start again, fearing drift got me, so put in the eyepiece, and indeed I'd drifted about 1 eyepiece field. Got back on target, then swapped in the f/3.3+Watec and got it focused, moved again to the target, and started the recording with about 8 seconds to till predicted center of occultation(!). Taped for another 3 minutes.
My first look through the eyepiece at the target and neighbor, showed only the neighbor, no target or (apparently) the asteroidt, it was invisible next to the brighter star. I later realized that the asteroid came in from that direction and it was too merged with the neighboring bright star. When I got on target again with the f/3.3, now just before the event, the target+asteroid were much easier to see separated from the bright neighbor. I went with 16x to see things to my satisfaction in the driveway, with dew shield.
The "D" clearly happened just a moment after my recording began. About as close as it's possible to be and not lose it altogether. In PyMovie I made sure to back up the recording to the very first frame before beginning analysis.
My first set of apertures didn't work because telescope drift carried one of the tracking stars off the top of the chip. So I did a data-remove, return to mark, and set a new aperture for the target and a new tracking star. For some reason, the older target remained in memory, apparently now on empty sky and shows labelled as "target" but in fact is obsolete and should be ignored. The true target aperture is in red. |
The PyMovie screen capture, showing the aperture setting on the target, and the neighboring 13th mag star below/left of the target. The small 3 pixel aperture was adequate to capture the target star and exclude adequately the neighbor star, barely. |
The target star in PyMovie, at 16x setting. 8 fields per integration. 8 dots per integration on this plot. |
The false-positive test. The D point distribution is likely narrowed from the fact that I got only 1 integration completed before the occultation began. |
PyOTE Solution. I used a nearby star about 12th magnitude and therefore unsaturated, as my reference star, since early in the afternoon there was barely visible slight high altitude cirrus and at night before moonrise I could not tell if it was still there. The rank of the event was high, and I was near the predicted centerline, and my 7.5 sec occultation agrees well with the predicted 7.7 seconds on the centerline. |
Kirk Bender (PyOTE LOG file)
Kirk observed from that wide spot up the winding section of Empire Grade, where there is a lip separating the road from a large flat area now overgrown with weeds. Given that Karl got no data, that was a good choice for separation from my chord. His first reductions were quite noisy with slow pulsing light variations on all stars lasting around 10 seconds per period, which made his occultation barely detectable by PyOTE and failing the FP test. He tried again with a range of apertures and tracking on the target and got a very good reduction in the end. AppSum in PyOTE helped.
PyMovie screen capture. Kirk's sky background is dark, and the target star quite easily stands out and in good focus. The neighbor star is well separated at this f/10 focal length |
PyOTE light curve. |
Light curve zoomed in. |
This reduction passed the FP test very well. The timings agree pretty well with mine. The event was early by about 3 seconds from the OW predicted time. |
PyOTE D: 3:49:32.996 vs. 33.61 for RN. So RN's D was 0.6s later
PyOTE R: 3:49:40.47
vs. 41.09 for RN. So RN's R was 0.6s later
Kirk's first reductions gave a skew relative to mine. But for this second reduction he used the target also as tracking star and a range of apertures. It improved his results relative to mine. Both his raw PyOTE timings were 0.6s later than mine, which might be due to down-track time offset, or, in the noise. Timing accuracies alone for this faint target star make this small offset not unreasonable. I was very close to the centerline, Kirk was about 0.2 path radii north of the centerline.
For future reference, Kirk also took a 256x integration of a star field without f/3.3 reducer decently high in the sky, after this asteroid event. I'm surprised that the skylight from SiValley didn't inhibit taking such a deep shot. It shows some stars down to 16.3 magnitude, barely. I had relayed that there is a KBO with a moon whose path crosses southern California early Friday morning. But the target star is 16.0 magnitude (g band). The cloud predictions are not giving it any chance, though.
