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Bill Merline, at SwRI in Boulder, Colorado, has some thoughts about the occultation of Sirius discussed in his message below. He points out that small asteroids like Jurgenstock are more likely than larger ones to be binary, and that their satellites can be farther away, twice as far as my 10-diameter estimates, and he also recommends observing for a longer period of time, for +/-200s plus the prediction time uncertainty. This would still be smaller than the approximately 10-min. drift-through time for a mighty mini.   David
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You wrote:

David - I've been looking over your notes on this event to
see if I might be able to participate.

Recall that I have the 80 mm mighty-midi that you provided
This is really the only instrument I think I could use.

I have not talked to any of the others who have helped before,
but we have only this one instrument.

My house is about 180 km off your projected center-line, and
the drive to the center line may be so much that I might just
use my site to cover one chord, well to the west, especially
since the track is uncertain anyway. I could possibly
drive far to the southeast and hit something on your 1 sigma
limit north of Colo Springs. But that is still about a 2 hr
drive. It is possible that just staying at home might be
almost as useful, given the uncertainties. More on the range of
useful observations below.

But I have a few issues at first:

1) how can I get more of the camcorder tapes? [I answered that separately; the MiniDV tapes are available at Best Buy and other places].

2) aperture --- it seems like you told me the 5th mag star from last March (1997 UV14) would have saturated with the 80 mm scope. That means that for Sirius, we'd have to stop down the aperture to something like 4 mm just to avoid saturation. There is a lens cover with a smaller central removable cap, but that is still 45mm diameter.
I could easily make a 4 mm mask. But it would have to be put on after pre-point, hoping not to mess up the pointing. And even if you did that, it seems like there would be no other stars visible in the field from which to judge any brightness drops. How is that handled?

3) Thanks for promoting the wider range of observers for the (396) event. It looks like you are recommending to go out to 20 asteroid radii. Yes, it is true that most larger asteroids have satellites that do not exceed this. But in the case of small asteroids, such as (4388), the formation mechanism is different, and satellites can and
have been seen out to 200 primary-radii. For (4388), this means out to +/- 700 km. It also means that one should observe, even near- or on-track, for much longer than you are recommending. I think it translates to something like +/- 200 sec w/o uncertainties. Further, objects of this size have a higher chance of being binary than larger asteroids.

In this case, as I pointed out before, the combination of a bright star, and a very wide swath for possible satellites, means that there could be many more participants (most of whom would get misses of course) and contribute simply by sitting at home. We don't want to discourage those willing to travel and set up a nice grid. But we also don't want to lead people to believe that if they can't travel, then they can't contribute.

Now, one might say that a satellite of (4388) will be so small as to hardly have any noticeable signature. But here, the star is bright, as you point out, making the S/N better.  But, in particular, for binaries around this type of object, they tend to be more similar in size to the primary, and the event may not look that much different than what you describe for the primary. It could even be that the predicted position of the asteroid is to center-of-light, and if a binary, then there may be two tracks, possibly well separated. This object would not be a known binary if the separation is less than something like 1" (or wider).  If I have your numbers right, then a 1" separated binary would be separated by about 370 km on the ground (not accounting for the projection).

I could also bet that with probably few other stars visible in any device used, for judging brightness fluctuations, due to brightness of Sirius, that there could be many false positives that would be hard to track down.

Further, you may know that Sirius itself is a binary, with Sirius B currently near apoapsis, being separated by about 11" to the NE.
This approx 8.4 mag star would be occulted also, but I estimate that to be about 4000 km off from the shadow from Sirius A, and probably off the Earth. It seems to have mass of 1/2 that of Sirius, so I would think this would make quite a wobbly-track for Sirius A itself, and should contribute substantially to the uncertainty in its actual position, unless that is already built into the astrometry. The period is 50 years, but maybe such a bright star does not have astrometry even to the uncertainties you are expecting.

Anyway, let me know your thoughts.


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Thanks for your message. You have some useful points and information that Iíll include in an update to the page about the event that Iíll make either tomorrow or the next day. Iím afraid that Sirius is too bright to have any reference stars for photometry. I think using the cover with the center off, but partially taped over, is the best solution. Pre-point first without it, then gently put the cover back on for the observation.