The Occultation of a W=15.4 mag combined Image by Trojan Asteroid (2241) Alcathous

Wed morning Aug 1, 2024 at 4:38:12 am PDT

OWc page

This is a high rank and high value event with path over Santa Cruz and also possibly over MIRA Observatory and the rest of Monterey Bay and the southern Santa Cruz Mtns. It's also at a good altitude of 69 degrees at event time, and 64 degrees 20 minutes earlier. Low enough to clear our tripod interference, but high enough to minimize aerosol extinction. The thin 10% waning crescent moon is only 7 degrees up low in the southeast and not a problem. We should have very dark skies to work with. But with the faintness, it may be good to try to reserve a night at MIRA Observatory with the 36" scope. However, most likely the path is north of MIRA, based on this month's latest predictions. The LS page has not been updated since last year.

Alt=69, Az=204.

Alt=69 is do-able with a level tripod with our 8SE scopes, but requires pushing the telescope ALL the way as far as it will go into the dove-tail mount, to maximize clearance above the tripod head. Don't learn that the hard way. You should be able to mount the Watec in the normal way for events as long as the altitude of the target is not higher than about 73 degrees.

J2000 coords
23h 30' 52.03s
+17 29 50"

J(Date) Position
23h 32 06.9
+17 37 53"

The duration is 12 seconds, allowing integration to get a good signal. The depth of the occultation is only 0.7 magnitude, however, so that will be a challenge and require good S/N. For our 8" scopes, I believe that will require at least 1 or 2s integrations to get this. That's still 6 or 12 data points within the occultation. The 12" at Cabrillo is fogged out, and the MIRA scope is not inside the path as updated in the OWc page. So, we're stuck with 8SE scopes. With more planning on my part, perhaps I could have gotten checked out and permission on the 30" at Fremont Peak Observatory, but alas.

OWc prediction

Event time 11:38:16UT (4:38am), path is north of the above LS path, favors Cabrillo Observatory and FPO, misses MIRA. Duration 11.9s. Alt=68 in Az=204, sun= -17. Mag drop =0.63 in R. Estimated integration on the 12" scope.... A W=13.6 star requires 8x to get a good signal on the 8SE. So W=15.6 mag would require 6.3x more time or 50x or 1s integrations. But on the 12" scope that we get 0.88 more magnitude depth, or 2.25x more light, so 50/2.25 = 22x so 32x should be good maybe even 16x. 32x is 0.6s time resolution, for a ~10 event should be good enough. But fog?? Then we drive to high ground... I guess MIRA is out of the path as the night of the event, as I write this, still has the old 2023 path.

Late night on event night. Fog covers Aptos. I will try with the 8SE scope from Sunlit lane and hope 1s integration will work. If not, I'll try 2s if the sky allows. The drop will not be to zero, but to 1/2, so you'll have to be able to see the star well enough to get that drop. 2s integration may be required for seeing it, but that's OK if it lasts 13s, it still gives 6 points inside the occultation if we're lucky.

Checking... The LS page above has not been updated, and the last update shown at the bottom of the page for this event is Sept 22, 2023. I'm guessing the OWc prediction shown below then is better, as it's only 1 week old.

Results:

The cloud forecast looked hopeless, and I was sleep exhausted. I bailed out, despite all the work I put into getting the prediction page and planned locations sorted out.

Kirk thought there might be a hole or two in the high clouds and so, drove above the fog and tried it at the Upper UCSC bike crossing, and got a recording...

Kirk Bender

Asteroid is a Trojan. This is a Lucky Star event. PyOTE could not find an event.  PyOTE’s detectability tool reported “An event of duration 8.750 seconds with magDrop: 0.5 is likely detectable.” Predicted maximum duration was 11.87 sec at magnitude 0.5. Light curve is noisy but there is a suspicious multi-point dip in the light curve around the predicted time for a possible positive. Kent Osaki reported a positive to Lucky Star on another chord near Los Banos, CA for this event. My recording has been uploaded to the Occultation Portal for the Lucky Star team.