Tuesday, November 13, 2012

A star or two of interest

kw: citizen science, stars

To date, I have classified about 7,000 stars in the Planet Hunters section of Zooniverse. Today I ran across a couple of interesting ones.

First we have a star whose temperature indicates it is a middling G star (~G5), just a bit cooler than the Sun. I could see two apparent transits, which I have marked here. After this screen, I had the chance to examine all the data from this star. There are no other transits apparent, and the star is usually flat-steady quiet. This particular period the instrument seems to have imposed a bit of gentle waviness to the data. These "transits" are pretty quick. #1 lasts 4 or 5 hours, and #2 about 3 hours. Those are consistent with orbits in the 30-60 day range in a star of this size. Since I saw no other transits in data from other periods, I have to instead suspect something else is going on.

Now this star definitely has a companion, but it is probably a small star, making this an eclipsing variable. The transits marked 1-4 show a dimming of about 10%, and thus indicate an object probably a third of the diameter of the main star. The transits marked 5-8 show that it is dim, but not nearly as dim as a planet would be. It is probably an M star, in a 4.5 day orbit, and the timing of the two kinds of transits shows that the orbit is quite eccentric. A short-period variable like this would not have been detected as a variable in the days of photographic photometry, because the variations are only about 4% of the main star's brightness. The Kepler spacecraft's instruments are truly marvels!

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