This event is rare and special - a relatively nearby (well, 1200 parsecs!) red giant pulsating star, and slow enough moving asteroid to give a very obvious gradual D and gradual R taking a large fraction of a second for each. This could be a good opportunity for accurate measurement of the diameter of this star, since the motion of the asteroid Montana is very accurately known, and with our 1/60 sec GPS timing resolution, we could get good data. I'd like to also use this data later in designing a lab for my Astro 8A students.
The star DF Leonis is a very red irregular M4 red giant, with a small range of only 6.7-6.9 in V. I have confirmed in photographs I've taken that the estimated visual magnitude is 6.8, not the 5.6 given in the Preston predictions. The parallax is only 2 milliarcseconds, distance 1200 pc. It would seem with good occultation data we could refine the diameter of the star, since the estimated duration of the D and R is a large fraction of a second. This event's gotten attention in the occultation astronomy community and has a good number of planned stations; however it will be very cloudy in Arizona, and in other parts of the U.S. that the 21km wide path crosses. Central California near Camp Roberts is unusual in that it is predicted to have clear skies, at least as of evening Sunday Jan 31.
It could provide an interesting light curve too, if it's irregular. Should try to get 1/60 sec time resolution and very definitely defocus in the extreme, to enable good photometry. This star more than others, the value will be in NOT just the timings but the shape of the D and R and that means to avoid saturation. That'll be hard given these red-sensitive camera and how bright the star is. But do-able if you defocus to a major extent. Fortunately, there are similar brightness comparison stars close by, so getting good photometry and tracking should be quite do-able. As of 24hr before, the skies look to be fairly clear during the event, and if the clouds are thin, and with no moon, the event should show through thin clouds well anyway.
The GoogleMaps app on my phone says 123 miles to the site, and on Sunday night, drive time is 1:54 minutes. On Monday night it will probably be slower. If I want to get there by 7:50pm, I should leave by 5pm. That should be do-able if I pack up before Astro 4 class meets. I'll make a last second decision at 5pm whether to go/no-go based on weather.
Predicted cloud map as of 24hr before
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Nolthenius:
I has a miss! There was a 10km south shift. I'd thought perhaps I'd already moved myself south of where I thought I'd chosen, after I passed the "Bradley" sign, and set up at Camp Roberts. Too busy to make sure of that, but in fact, I set up just a few hundred yards south of where I'd selected in O.W. Inside the northern limit well enough that if the predictions are as solid as the error bar line showed, it would have been almost a "sure thing". But alas, no. Also, my ZR85 camcorder recorded a test short segment just fine, before the event, but for the real thing - no recording. Argh! I did get it on the Nikon D7000 video, and it was definitely a clean miss. Why the failure?
Testing all my camcorder units after I got home and the next day, I discovered that all the ZR85's and ZR90's showed the battery icon on the flip screen would go on and off irregularly as I rattled the battery on the end of the camcorder. While on the ZR45mc (my old camcorder I'd lost faith in), the connection was solid and this was not an issue. Strange that if the battery was failing contact, it didn't shut down all power and shut off the machine in an obvious way. Instead, the most power-sensitive (I am assuming) aspect - the actual recording - is what loses power enough to shut it down, while the power to the LCD screen remains. So, I looked more closely at my old machine, tried recording on it, and it said "dirty tape heads", so I cleaned them with alcohol and Q-tip swap, let them dry, and now it seems to record fine. When looking at the recording head I see what I thought might be a "wear spot", but I now think is just the action place where the recording happens, as I see it on the other ZR85 and ZR90 camcorders as well. I tested recording on the ZR45mc several times and it always recorded. Then I put it outside in the early morning and at noon brought it back in, still cool but not really that cold, and it recorded fine. Then I took it outside and left it out for a few hours that night, when it got down into the high 40's air temperature, brought it inside and immediately tried to record for about 20 seconds and it recorded just fine. I'm hopeful that the alcohol and Q-tips I'm now keeping in the car will solve trouble, and I'll bring just that camcorder and the Nikon for the time being. The Win10 + StarTech solution still is not so clearly trouble-free. I did get a grant from Cabrillo to buy another HP computer just like the one I got the grant for the Planetarium, and a StarTech unit I can buy with Dept. funds, and try it out if it comes to that. But I still prefer not to bring laptops on these things.
My setup shortly after the event |
...With Nikon D7000 tripod mounted and aimed with zoom at the LCD screen. |
My "warm box" to keep the camcorder above minimum spec's temperature. |
The El Taco at King City, fav spot before the old Wildflower Triathlon, but, not tonight. |
Kirk Bender
Was about 10 miles south of me, 3 km south of the nominal centerline, on Wellsona Rd. He got a 2sec occultation and good data on the slow D and R. We're currently analyzing his tape to see how to fine tune parameters. Preliminary results, assuming a 63 degree impact angle and circular asteroid, give a stellar diameter of 2.7 mas. That's very close to the Gaia data according to David Herald of 2.6 milliarcsec. We can probably get a final best estimate with a little more testing. Tony thinks that Kirk's data looks clipped at the bottom as it's too flat and not enough noise. For such a bright star, I'm skeptical of Tony's conclusion; not sure how much noise you'd see, given how bright and out of focus the star was. I'm waiting for Kirk to answer whether he used a fixed mask on PyMovie or let it "on-the-fly" decide a mask, which I believe is a mistake for deliberately out of focus stars that disappear almost completely. I think if he did let it determine a mask, it would very likely miss all the very faint pixels since the light drop was predicted to be about 8 magnitudes or a factor of 2000x in brightness. The distance from Hipparcos early data was 369 pc, and 481 pc from the 2007 data release.
Below light curve from PyOTE " D fixed at 63.3 degrees, the best fit I could get without making metrics worse was R at 52 degrees and star at 2.7 mas". Visually fits the points pretty well.
Kirk posted a YouTube video of his event. and his PyOTE log file, and his original PyMovie CSV file
Kirk's PyOTE light curve assuming best parameters, after testing different stellar diameters, settling on 2.7 mas. |
John Moore - in Okhlahoma
Got a partial occultation of 0.62mag depth, and 0.4 sec duration, and looks very much like a partial occultation. He was between Kirk and I and got the northern limit. He was still several km south of me, so adds confidence that there was no bit of partial occultation at my station. I can't do photometry on my very out-of-focus image on the D7000 video anyway.
