Wierd transits, binary star, one planet.

[halfeye]

https://www.syfy.com/syfy-wire/bad-a...rs-in-a-binary

I like "Bad Astronomy" but this time I think Phil has forgotten a detail.

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Anyway, the point is that the orbital period of the planet (its "year") is much longer than the period of the stars, so the stars are going around each other much faster than the planet around them both. Since two transits were seen, this means they were due more to the stars moving more than the planet. That's a little funny to think about.

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So it might first transit star A and then B a few days later, but then next orbit it might transit B first and then A.

The thing is, the stars are orbiting far faster than the planet, so (assuming that the orbits are all in the same direction) they will be overtaking it (when they are at the "nearer us" ends of their orbits), and it might transit either or both of them multiple times in one orbit.

Thinking further about this, if the stars are as far apart as they get from our point of view when the planet comes past, it will pass in front of one fairly quickly, then the star it just transitted will overtake the planet, and that transit will be very slow, it seems possible that the star at the back will be transited by the other star while the planet is in front of that, so the planet may not transit the more distant star at all.

Thinking yet further, the fastest transit will be of the star at the far end of it's orbit, a star on the side of it's orbit will be transitted fairly fast, and a star at the nearest point in it's orbit to us will be transited very slowly indeed, as it overtakes the planet.

<edit> I no longer think either of the stars in this system can be transitted more than twice in one orbit, and I'm pretty sure that both can't be transitted twice in one orbit.

[DavidSh]

There is another complication, in that the Earth is not exactly in the plane of the orbits of the stars, and probably not in the plane of the orbit of the planet. So, for example, one of the stars on the far side of the orbit might pass too far north relative to the planet for there to be a transit.

[halfeye]

There is another complication, in that the Earth is not exactly in the plane of the orbits of the stars, and probably not in the plane of the orbit of the planet. So, for example, one of the stars on the far side of the orbit might pass too far north relative to the planet for there to be a transit.

The facts that the orbit of the stars is exremely eleptical and precessing makes things interesting too. At times the width of the stars' orbit would approximately halve as seen from Earth, while the planet's orbit being more or less circular would be more or less invariant. So sometimes the stars would catch the planet, and sometimes the planet would be faster (from the point of view of Earth).