The Occultation of an 11.5 Star by Trojan binary asteroid Hektor

Fri morning Feb 21, 2025 at 5:01:57am

OWc page , and LuckyStar page

 

This event is low probability. It's decently high probability if you drive to Nevada, but this event was advertised too late to try and plan for such an expedition. As it turns out, it looks to be clear and decent weather and might have been do-able as a van trip. But - too late.

However, it has a moon which is well within the possibility of seeing. Odds are still low, but we're only 1 asteroid diameter away and within the moonlet's orbit.

Alt=24, Az=272, so this is not visible from my carport. Will have to get up and drive somewhere.

Somewhere I saw something about the satellite, Skamandrios, being ~12 km dia. I think that came from https://en.wikipedia.org/wiki/624_Hektor#Satellite , which seems to have come from

[7] Marchis, F.; Durech, J.; Castillo-Rogez, J.; Vachier, F.; Cuk, M.; Berthier, J.; et al. (March 2014). "The Puzzling Mutual Orbit of the Binary Trojan Asteroid (624) Hektor". The Astrophysical Journal Letters. 783 (2): 6. arXiv:1402.7336. Bibcode:2014ApJ...783L..37M. doi:10.1088/2041-8205/783/2/L37. S2CID 19868908.

So, as usual, the size estimate seems like it’s most likely based on albedo assumptions, for which occultation observations would be especially valuable (single chords can only really put a lower bound on size), not to mention refining Skamandrios’ orbit, which will in turn constrain estimates of system total mass.

Looking at RECON’s updated listing at
https://www.boulder.swri.edu/~buie/recon/trojans/RECON_plan.html , and event details at
https://www.boulder.swri.edu/~buie/recon/trojans/624_Hektor_20250221130547.html
the list of RECON stations for Hektor itself have been reduced to fewer sites: (Chiloquin, Klamath Falls, Cedarville); Cedarville CA is near Alturas, in the NE corner of CA.

For additional reference for event planning, see also:
https://cloud.occultwatcher.net/event/1512-624-145362-649002-T01221-1
(Tom Heisey’s signed up, 1 sigma inside the south edge of the OWC path! The OWC path is a little south of the LuckyStar path. Good luck with the twilight, Tom!),
and
https://cloud.occultwatcher.net/event/1512-624-145362-649002-T01221-1/2172520

But those don’t speak to the path of Skamandrios, other than that we think (Wikipedia again) its orbit is
Semi-major axis 623.5±10 km
Eccentricity 0.31±0.03 based on [7].
As a rough comparison, it’s ~584 km from Klamath Falls to, say, Cabrillo Observatory, so it’s worth a shot. To the north, 623 km from Klamath Falls is north of Wenachee, WA (the actual normal to the path is somewhat more- I was just snapping a line in Google Earth).
The uncertainties for Skamandrios are so large that travel for it alone don’t pencil out (pending any updated information- I need to get into Occult and see if Miriade has any advice to offer. I couldn’t figure out how to query Miriade using the web interface, though I’m sure it’s simple).

Skamandrios event duration: If Hektor is ~181 km dia, Skamandrios is ~12 km dia, and Hektor’s max duration is 10.1 sec, a maximum duration for Skamandrios might be on the order of 0.67 sec. The event combined magnitude is 11.5 m, mag drop 2.0-2.69. If my scribblings are correct, a Skamandrios event should be “well within reach” of our usual 8” apertures.
-Ted

 

Results:

I did not try this one. Odds very low and at 5am, and given my chronic sleep deprivation, I skipped it. The Hektor path was definitely too far away. But Hektor has a moon but of unknown position. The moonlet was believed to be about 12km, leading to a 0.7 s duration, which should still be detectable. Clouded out at bed time. Heavy cirrus came in. Kirk tried anyway. The cirrus is evident in his reference star, largely calibrated out for the target star, but increased noise.

Kirk Bender

No apparent event.  Target star was relatively bright at 11.6m but because of clouds 32x integration was necessary. My location was out of the predicted path for Hektor, but observed to possibly detect its satellite, Skamandrios. Predicted duration for main body was 10.11s at 2.0m drop.  PyOTE detectability tool reported an event as short as 1.650s would likely be detectable. This was a Lucky Star event, I have uploaded my data to their occultation portal.