The Occultation of a 14.8 Star (by magnitude 15.4 Helga
Sun eve 5:50:19pm Nov 30, 2025
This is a difficult event! But I might just try it from Cabrillo Observatory with the 12" dome scope purely as a test to see what other kinks need to get worked out before the 12" scope is suitable for occultations
The target star is only a little brighter than the asteroid, and the drop is predicted to be 1.0 magnitudes for 3.4s.
Alt=29, Az=205 in Capricorn. Sun=-12 so this is late twilight with little sun glow left. Altitude makes for about an extra 0.25 mag loss vs. overhead.
The OWc page says the drop is 0.75 in V and 0.9 in R. For our Watec, that means a drop of about 0.8 magnitudes, which means the target Helga is 14.9 magnitude. In V (?) OWc says Helga is 15.4 though. UCAC4 gives the magnitude (I correct to Watec mag) of 14.8. So, not totally consistent depending on source, but looks like a combined ~14.0 magnitude. But it drops for a good 3.4s and this is a low numbered asteroid with a good orbit and we're well inside the path for all of the Team Santa Cruz from home. We should get a solid 3s of drop and 14.0 should be detectable at 32x. Even 64x would give 3 points inside the occultation. From the 12", I will likely get it at 16x.
Charts for 8SE Alt/Az and 12" Cabrillo Observatory (as I estimate).
8SE eyepiece Q70 32mm view |
8SE Watec view |
|
CabObs 12" scope Orion ShortTube TV screen view, but cropped top and bottom to keep scale suitable for plotting UCAC4 stars
Sides of this image should be about 2 degrees and match the width of the new Orion ST view with the double 0.5x reducers. Field was rotated 180 deg as should be true for west-of-meridian scope orientation. |
Watec 910hx chip view from 12" scope at f/6.3. That should be 35% of the FOV on the 8SE at f/3.3, and both chip views are shown for comparison. Inner box is what I should see. Will have to get scope on target using SBIG camera and the swap in the Watec, if I have time. |
Results:
Clouds convinced me this event would be impossible, so I did not try. Kirk did, and so did Karl. Jerry B in NV did not. Kirk feels his data will be too noisy to be useable. Karl used 32x and sometimes saw the target star, from home. Neither Karl nor Kirk were able to get high enough S/N to make any conclusions.
Kirk Bender
My target curve does appear slightly higher than my no-star, but I don't see an event. An event would almost certainly be undetectable unless maybe it was much longer. The PyOTE detectability tool reports an event as long as 8.3 sec would likely be detectable, max predicted was 3.36 sec.
