Post-Trip Photos and Results - Pleiades Occultation, Electra Graze, Io/Europa Occultation

Chris Kitting (professor, CSU East Bay) and I ended up on Sunshine Circle in Danville for the Electra graze, as our primary site on Sherburne Hills Rd was stymied by NIMBY neighbors. No matter, our site was good. Although I had to haul the 10" LX200 and associated gear across a footbridge over a creek and into the fields to get the required horizons and spacing from Chris' location. Chris took some beautiful pictures, and will license higher resolution versions of them (proceeds to benefit the two colleges we are employed by). His contact info is on the slide below.

First event was the Jupiter's moon Io eclipsing AND occulting Europa on this, the night of opposition of Jupiter. A unique convolution of both an eclipse and occultation at the same time. video recording these events gives a precision measurement of the relative position of these moons, useful for orbital evolution studies of the Jovian system. Brad Timerson also got the event, and posted a light curve shortly after the event. Chris had some equipment issues, and also trouble with a diffraction grating as an experiment to help determine duplicity of Electra. His image of Electra was considerably dimmer than on my setup, but he still was able to get timings on the last half of the graze.

The Electra graze, on real-time review of my tape, suggested no step events. However, when looking at the light curves below, I see that the D's are mostly sharp, while all of the R's show a faint tail lasting a tenth or two of a second before a change of slope sharply upward to the unocculted brightness. It suggests to me that there may be a faint mag= 8 or 9 companion which leads the primary. The star hit 7 mountains, and each event is shown below, plotted by LiMovie using a large enough red radius to capture all of the star. I will solicit the opinion of others familiar with occultation light curves for their opinions on whether these events suggest a secondary star or are simply due to finite star diameter and diffraction on variable shallow lunar slope impact angles. My suspicion of a secondary is mainly based on the fact that ALL the reappearances show significantly more light at faint levels for longer than for the D's. If there's a secondary, I would estimate that it is slightly north and west of the primary, and around 9th magnitude. However, the spacing would be close enough that there isn't time for a tell-tale step to emerge beyond Fresnel diffraction fringes. I'm suspicious, but not convinced, of duplicity. Unfortunately, that was the state of affairs BEFORE the graze, so have we clarified things? It would be worth estimating the spacing in AU's and calculate a resulting of the orbital velocity to see whether it would obviously have shown up in Doppler data by now. If the companion is quite faint, it may not have much gravity and if slow enough, not affect Doppler measurements in so obvious a way that it has been noticed. Properly motivated, longer term monitoring with today's Doppler technology might show something.

The timings below refer to the 50% drop level from full brightness. Each of the events reached through this level, even the partials, and so have D, R instead of blink or flash designations.

Richard Nolthenius: 1.210 km South. Long=121 56' 51.11", Lat=+37 48' 13.25", Elev 510 ft. from Google Earth.

Chris Kitting: 1.245 km South. Long=121 56' 48.96", Lat=+37 48' 13.08", Elev 510 ft. from his kiwi GPS, elevation from GoogleEarth and topo.

Kitting coords from Google Earth: Long=121 56 48.98", Lat=+37 48' 13.17", which is in very close agreement with Kiwi GPS within error of my ability to spot his position on G.E.

Thoughts on duplicity... The velocity of the star was about 530 mas / sec of time. The extended tails on the R's are quite variable and may be due to topography, but at a minimum is 3 or maybe 4 frames = 0.10 sec or 50 mas separation along the direction of motion. This is ~5x bigger than that claimed in earlier occultations (10 mas) and 100x bigger than the Jarad claims for a separation to the spectroscopic companion of 0.5mas. So, on the whole, it is much larger than the separation of the supposed spectroscopic companion. It may just be coincidence that it is the R's that have shallower impact angles with the star and produce more gradual events in such as way that there is a very faint-appearing possible companion. Can't seem to make a consistent story here. But at these separations, the supposed companion star would move rapidly compared to the ~50 or so years over which obserations have been made.