This event is nice and long; 15 seconds, and decently good rank. Santa Cruz has a high probability of being well inside the path. Ted Swift and Jerry Bardecker are committed to getting it just inside the northern limit, and Kent Oaski and Y. Liu are on board in the Silicon Valley. So, we have the prospect of pinning down the position of this asteroid very well.
Caveats: Iit's in the AAVSO as a variable star. The IOTA predictions have the star at V=10.9 (10.7 combined magnitude) which would be very bright and make a deep 2.0 mag drop. But C2A has the star at 13.5 magnitude. The asteroid is 12.7 in the OW cloud, so if the star is indeed 13.5 magnitude, then it will drop from V=12.14 to 12.5 or about 0.43 magnitudes. That's still good enough to get good data with longer integration. Since the event lasts up to 15 seconds, that should be no problem. The star looks pretty red by the magnitudes.
Late update: Jerry Bardecker recorded the area with a 12" scope and the target star is indeed a bright 10th magnitude. That means this event is also going to be a good opportunity to hunt for a small so far undetected moon, if one exists. Be sure to record a full 3 minutes before and after the predicted time, and even a little longer if you want to be sure to comb the gravity well. The 15 sec duration and the bright star means that at 2x we should be able to detect a quite small moon if one exists. 2x should still give very good S/N in the clean dry skies of tonight.
|
|
|
I did a bike tour of possible locations I could try this event (impossible from home) in the afternoon, and settled on Mill Rd, which had a clear view of that direction and would not bother residents nearby. Clear, dry, calm. Very good conditions. I got stoped by the police on the way! Burned out license place light. That slowed me down, but I still was able to get up and running with a few minutes to spare. Got 9 minutes of taping, to see if any so far undetected satellite might cause a secondary event. None were seen. Very good data. The R was gradual, taking well over a second, suggesting the large'ish star (8 mas vs 106 mas for the asteroid) may have hit a slanted part of the asteroid. Kent and Liu got 10s events in the Campbell area, and Ted Swift in Davis and Jerry Bardecker in Carson City - nominally inside the northern limit - got misses.
Because of the very slow R, I decided to try the new capability of the new beta version of PyOTE could use a better model than the simple Square Wave model. I accepted the suggestion of the "disk on edge" model suggested. HOwever, the model does not have a "write report" or timing accuracies, so I'm waiting for clarification on how to use this.
Mill Rd near DeLaveaga, my site |
PyMovie screen, with target star shown below |
Pretty obvious which light curve is our target star - in blue |
No variance except frame to frame scatter obvious, so no ref star calibration was done, as in this case, it only adds noise. |
The target star's PyMovie light curve. |
And... the PyOTE reductions. The stellar diamater was a significant 8% of the diameter of the asteroid, as shown on the OWcloud page. The OWcloud page listed the target star as a variable listed in the AAVSO. I could not find the AAVSO listing for the star. But, the C2A chart showed the target star as 13th magnitude, while the actual star as shown the night before the occultation was at approximately the listed G=10.9 shown on the OWcloud. My guess is that it might be a long period variable star, to account for light variations that strong. We seemed to be getting the star closer to maximum brightness. Pulsating stars typically are brighter when they are smaller and hotter, since the luminosity goes as the temperature to the 4th power, while the area of the luminosity surface goes only as the square of the size. So, the star may have actually been smaller than the listed 8 mas. A star of 8 mas should have given D and R gradual events lasting about 8% of the duration. For a 12 second event, that's about a full second. The actual D and R were quite a bit faster, except for my R, which indeed lasted close to a second.
PyOTE will reduce the data under the assumption of not just the standard "square wave" model for the light curve, but for situations where Fresnel diffraction of stellar diameter are significant. However, I was not successful in getting this aspect of the software to work. For a significant stellar diameter, the D and R should be at the mid point of the gradual drop. When I used the squarewave model, the software in fact gave D and R times which matched that assumption pretty well. And, only the Squarewave model gives 1,2,3-sigma timining confidence limits. It was the square wave model which was used for this reduction
PyOTE light curve, with tracking star |
Recorded at 2x. One frame per integration. The D looks pretty sharp, without clear fading... |
But the R was gradual. Almost 1 second depending on how you correct for noise. The PyOTE determined R time however looks consistent with the mid point of the brightening, as would be expected for a large stellar diameter analysis. |
D and R. |
The large drop, long interval, and bright star combined to make a false-positive test that was a solid as I've seen. |
Observed from home on the north side of Santa Cruz. His data was just as good, and he too reduced using the square wave model. His D and R events both looked sharp.
 |
