The First? Asteroid Occultation of 2016 - Rosalia

Jan 1, 2016

The question mark is - this "sure thing" event had a nasty little cloud that came out of nowhere and glommed on to the moon just for the fraction of a critical minute of the occultation, as seen at Cabrillo Observatory. I'll post the light curve and you can see what happens during varying cloud cover over a faint 11.8 magnitude star. It wasn't the only handicap this event had to overcome - my good friends the Delucchi's had their anniversary that night, with a big bash as they rented out the Food Lounge in downtown Santa Cruz. Lots of forbidden but delicious morsels as well as the comradship of the (mostly) Santa Cruz county running community. Little brownie'ette's, mini-chicken wings, "fireballs" (whisky and cinnamon)... you get the picture. Not conducive to a good night's sleep.

I'd thought, since I still had all the telescope and recording gear still packed in my RAV4, that I could just set up on the driveway for this 2am event... but, when I got back from the party, I realized new "anti-crime (not!!)" lights and a large hedge next door would ruin that plan. Also, I didn't have a printer at home for the finder charts. Since I had to pick up Dave D for the 10K race in the early morning anyway, and Cabrillo College is on the way, I'd just sleep at the observatory after doing it there. Here's the eyepiece chart, and the camcorder chart.

I arrived at the observatory around 1am, and noted a few rogue low stratus clouds. Still, it remained clear around the target star near the Canis Minor/Monoceros border. That stayed true right up until 1 minute before the predicted 4 second occultation... and then a band of cloud covered the target till 1 minute AFTER the event. The rank was high and I was near the centerline, so it was a high-probability event - bummer! Derek Breit over the hill in Morgan Hill had a 4 second positive event, so even more that pointed to my being inside the path.

A minute after the event, clear skies showed how dim the target was, vs the tracking star (just above the UT display), and the comparison star (middle left of screen).


LiMovie light curves. Target is blue, hugging zero. The Watec 910hx was at 4-frame integration (8x).

Zoom: The comparison star in pink, indicates fully 2.0 magnitudes of cloud extinction around the event time.

Closer look at the low counts of the target. I don't see anything but noise here. And that includes at the expected D and R between frames 1558 and frame 1686

Derek's D was very late; 10:01:27.0, which corresponds to my frame 1558. Central occultation UT would be virtually identical for both of us

And his R was 4.4 seconds later, at 10:01:31.4 UT corresponding to my frame 1686

In the end, thanks to Derek's sending his LiMovie analysis, I have to conclude that dimming the target star by 1.8 to 2.0 magnitudes (11.7 to 13.5-13.7) was fatal. I see no hint of an occultation in the blue curve at the time I know there should be one.

I packed up the gear, stowed it, and then to help send me to sleep, I had the observatory computer play me a short lecture on economics and carbon emissions. That sent me to sleep by 3am. I was jolted awake at 6:35am by Ferrell, a wake-up call so I could hammer down some breakfast, and get myself over to pick up Dave D then head to his place for carpooling to Carmel for the Rio Resolution 10K Run. But, that's another story...