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Message started by frankuitaalst on 08/03/10 at 12:35:39

Title: Binary precession
Post by frankuitaalst on 08/03/10 at 12:35:39

Recently I've found this paper : http://www.mathpages.com/home/kmath280/kmath280.htm, dealing with the Newtonian precession .
It inspired me for making the following simulation , in which we have 2 stars each having Msun and are orbiting at 0.1 Au .
There's also a planet which has eccentricity 0.5 and is at 5AU .
The period of the planet is about 2 years .
After about 215 revolutions the aphelion has precessed over 360 as can be seen in this animation .
Quite fast !
The driving force for the precession is here the torque the planet experiences by the rotating binary .

Title: Binary precession - Kozai revisited
Post by frankuitaalst on 08/03/10 at 14:10:43

If , in the highy exceptional case,  the planet starts in a polar orbit we meet an old friend : Kozai .
The planet starts precessing in the polar orbit but gets disturbed very slowly first , then gets excited and tilts away from his polar orbit to finally get an inclination of about 66 , which is overshoot . The planet then tends to the original polar orbit and the cycle starts over again .

Title: Re: Binary precession
Post by Mal on 08/07/10 at 22:44:48

Interesting! Is the planet orbit otherwise stable?

I wonder what would happen if you had two planets in the (non-polar) system. Would precession of their orbits cause instability?

Title: Re: Binary precession
Post by frankuitaalst on 08/08/10 at 01:14:39

The precession itself causes no instability . I've run a sim for 20 periods of precession and find no signs of instability , even with a two planet system .
I can post the results . However , if orbits are crossing the planets may influence each other .
Planets which are further away precess slower than those which are closer

Title: Re: Binary precession
Post by frankuitaalst on 08/08/10 at 06:18:14

Here's an animation of two planets . The inner is the same as in the previous animation. The outer orbits at 25% more distance as the inner planet .

Title: Re: Binary precession
Post by Mal on 08/08/10 at 15:59:01

Interesting - is precession the only effect the binary has on the planets? (I'm presuming the orbits of the planets were coplanar?)
I would have thought that the planets get into some kind of resonance whereby they never come close to eachother despite the crossing orbits... do you see that happening at all?

Title: Re: Binary precession
Post by frankuitaalst on 08/12/10 at 09:31:59


Mal wrote:
Interesting - is precession the only effect the binary has on the planets? (I'm presuming the orbits of the planets were coplanar?)
I would have thought that the planets get into some kind of resonance whereby they never come close to eachother despite the crossing orbits... do you see that happening at all?


I'll ty to simulate a 2:1 resonance and see what happens

Title: Re: Binary precession
Post by Mal on 08/12/10 at 12:00:14

And also, does this precession happen at all if the planet's orbit a solo star instead of a binary? i.e. is the rate of precession already there but accelerated by the binary?

Title: Re: Binary precession
Post by frankuitaalst on 08/12/10 at 14:14:06


Mal wrote:
And also, does this precession happen at all if the planet's orbit a solo star instead of a binary? i.e. is the rate of precession already there but accelerated by the binary?


A single star with one planet does not  show precession .
Adding another planet will give precession of both planets . This precession is small , as is the case in our solar system .

If we start with a binary all the planets will experience a strong precession . This is what I tried to show in the animations .
The reason of this precession is that the planets are attracted by two strong central stars which rotate around a common barycenter .

Title: Re: Binary precession
Post by Mal on 08/12/10 at 17:25:06

Thanks... I suspected as much :)

Title: Re: Binary precession
Post by Mal on 08/23/10 at 17:04:53

http://www.universetoday.com/71934/tight-binaries-are-%E2%80%98death-stars%E2%80%99-for-planets/

Hmmm. I wonder if the extreme precession shown above has anything to with this. I'd imagine it'd make planetary collisions more likely?

Title: Re: Binary precession
Post by frankuitaalst on 08/23/10 at 22:41:05

I was thinking the same way when I read the article :)
AFAIR there's one known binary with planets : HW Virginis , may be a good idea to simulate this one

Title: Re: Binary precession
Post by frankuitaalst on 08/24/10 at 11:50:27

Question for Tony :
I tried to input the following system ( HW Virginis ) ( data available from exoplanets links)

M1=0.485Msun, M2=0.152 Msun at 2037500 km , ecc=0
c : 8.47Mj, 3.62Au , ecc 0.31 orbiting M1
b : 19.23Mj, 5.30 Au, ecc 0.46? , orbiting M1.
I think I once again have the "." problem when inputting because the planets fly away just after starting .
I first created M2 around M1 , no problem , then created c and b around M1.
Is it possible to give the system a try ?

Title: Re: Binary precession
Post by Tony on 08/25/10 at 10:52:55

You can't have c and b orbit M1 without also orbiting M2, as M2 is only 2 million km away from M1.  So you have to check the "barycenter" option under the "Reference Object" in the Create Objects interface when creating b and c.

I tried it and got it to work, but this system doesn't look very stable.  With b & c at 3.62 & 5.3 AU, and high eccentricities, their orbits intersect each other.

Title: Re: Binary precession
Post by frankuitaalst on 08/25/10 at 11:44:46

Thanks Tony , I also thought there must be intersection.
Is it possible to post your sim as a .gsim file ?
Then I can compare to the .gsim file I got after the input .  

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