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Capella system (Read 5952 times)
APODman
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Capella system
01/31/08 at 07:15:23
 
Iīm trying simulated the quadruple system of Capella, but i canīt make Capela Aa and Capela Ab orbit around one other. The stars ever escape or colide with the barycentre "object".
 
How I can do the stars orbit a comom barycentre ?
 
The data that I use is here:
 
- http://www.solstation.com/orbits/cap-absys.htm
 
 
Thanks in advance
 
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Tony
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Re: Capella system
Reply #1 - 01/31/08 at 10:16:48
 
From that link, it seems that Aa is a single star, Ab a single star.  Together they make up the primary pair.  Then the distant stars C and D at 11,000 AU.  Do C and D orbit each other?  I'll assume they do.
 
File > New
Objects > Edit Objects
  Edit Object1 to Capella Aa.  Change its color, size and mass
 
Objects > Create Objects
  DO NOT USE barycenter option
  Create Ab.  Make sure to give it its proper mass
 
Objects > Create Objects
  USE barycenter option
  Create star C at 11,000 AU, using star Aa as the reference object
 
Objects > Create Objects
  DO NOT USE barycenter option.
  Create star D using star C as the reference object.
 
Let me know if this helps
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APODman
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Re: Capella system
Reply #2 - 01/31/08 at 13:47:43
 
Thanks Tony,
 
I will try ( Iīm searching for stable orbits in this quadruple system ).
 
About Capella C and D, they donīt orbit each other, look:
 
- http://www.solstation.com/orbits/cap-cdsys.htm
 
I post the simulation of the complete system here later ( if I can do it  Tongue )
 
 
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Re: Capella system
Reply #3 - 01/31/08 at 21:52:48
 
That page does show them orbiting each other, or at least orbiting a common barycenter.
 
One problem you'll have with this simulation is that the period of the CD pair around the AB pair will be very long compared to the period of the AB system, or the CD system.  A time step slow enough to accomodate the AB pair and the CD pair will be painfully slow to watch the CD pair orbit the AB pair.
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Re: Capella system
Reply #4 - 02/01/08 at 05:35:42
 
Well Tony it works, Thanks !
 
The only difference of your sugestion is that Capella D needs to be configurate with Capella Aa like reference object otherwise it ever escape of the system.
 
 
 
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Re: Capella system
Reply #5 - 02/01/08 at 12:34:32
 
Great!  Make sure to upload the simulation so we can all play with Capella.
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Re: Capella system
Reply #6 - 02/03/08 at 10:52:47
 
Posted the simulation file of Capella quadruple system.
 
I will try to find stable regions for planets around the stars.
 
Latter I will post the results
 
 
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Re: Capella system
Reply #7 - 02/03/08 at 13:22:12
 
In your simulation, Capella D is orbiting 37 AU from the AB pair, and Capella C is orbiting 11 AU from the AB pair.  This is not correct.  Capella C orbits 11 AU from the barycenter of the CD pair, and Capella D orbits 37 AU from the barycenter of the CD pair.  The barycenter of the CD pair orbits 11,000 AU from the barycenter of the AB pair.
 
It's tricky to set this up in Gravity Simulator, since the interfaces are designed for systems with up to 2 massive objects, but not 4.  So to set this up requires doing some math, coming up with distances and velocities on your own, and editing the system using these cartesian coordinates.  I'll try to put together a more detailed explanation later.
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Re: Capella system
Reply #8 - 02/03/08 at 15:33:43
 
Thanks by the observation Tony,  
 
I will waiting your further explanations to correct the simulation.
 
 
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Re: Capella system
Reply #9 - 02/04/08 at 07:54:54
 
Herunder is a possible calculation to input the initial parameters .  
I haven't tried it yet in GravSim .  
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Re: Capella system
Reply #10 - 02/04/08 at 12:40:14
 
Your diagram looks like mine  Grin  But I input your numbers with no luck.  Mine is not perfect either.  I've got to tweak the barycenter velocities.  This is simply because I was going for round orbits.  If I'm happy with the CD system in an eccentric orbit with 11000 AU as a minimum distance, then my method works:
 
http://www.orbitsimulator.com/gravity/capella.doc
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Re: Capella system
Reply #11 - 02/04/08 at 13:36:43
 
Have you tried to input these values Tony ?  
Your derivation is fantastic , you also take the zero motion of the total mass center into account , what I didn't do .
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Re: Capella system
Reply #12 - 02/04/08 at 14:32:14
 
Quote from frankuitaalst on 02/04/08 at 13:36:43:
Your derivation is fantastic...

If only it worked  Wink.  I'll tweak it later.
 
Yes, I input both your numbers and my numbers.  In mine, Aa and Ab orbit each other in circular orbits.  C and D orbit each other in circular orbits.  CD orbits AaAb in an elliptical orbit with a periastron of 11000 AU.  But I was trying for circular.  Your numbers had Aa and Ab passing each other on a hyperbolic trajectory.  Same with C and D.
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Re: Capella system
Reply #13 - 02/05/08 at 08:40:44
 
You're right . I made a mistake in the formula . Should be fixed in annex .  
It's tricky : for the calculation of the velocity one should consider 2 "r"s : first the "r" meaning the distance to the other body in order to get F and second "r" in the formula : v=omega*r where "r" is the radius to the center of rotation .  
As F=GMm/rē and F=moēR and v=oR then v= sqr(GM/rēR)*R
Please note that in this calculation I leave the Mc AB at zero velocity.  
 
Addition : after inputting the values I got also an ellipse for the AB Pair  Sad
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« Last Edit: 02/05/08 at 14:13:23 by frankuitaalst »  
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Re: Capella system
Reply #14 - 02/05/08 at 16:15:37
 
http://www.box.net/shared/k0cw1haasc
 
Do I win now? Tongue
 
I couldn't find an inclination for the CD-AaAb orbit, so that's just 0, but can be changed pretty easily if someone knows the right value. All the orbits are, I think, circular.
 
(I did this with my own program, which has a crude [but functional!] system for setting up group orbits like this.)
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Re: Capella system
Reply #15 - 02/05/08 at 17:11:48
 
Quote from guyy on 02/05/08 at 16:15:37:

 
Indeed you do Wink  And you converted it to .gsim so we can see it too.  Your CD-AaAb doesn't seem to have an inclination of 0 though, but that was never a prerequisite.  I imagine the inclination is unknown.  The shape of the orbit is probably also unknown.  Probably the only known thing is that the current seperation is 11000 AU.   The only reason I don't declare myself the winner with my elliptical Cd-AaAb orbit with periastron 11000 AU is because I was going for circular orbits.
 
Yes, all your orbits: Aa, Ab; C,D; AaAb,CD are circular.  Nice job.  I'm anxious to see your program.
 
**edit
by inclination 0, you were probably referring to its inclination as viewed from Earth, rather than inclination from the ecliptic plane, which is what Gravity Simulator considers to be inclination 0.  Your CD-AaAb orbit does seem to be coplanar to Aa-Ab and C-D.
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Re: Capella system
Reply #16 - 02/06/08 at 22:17:09
 
Hm...it had an inclination of 0 in my program, but maybe it exported wrong or your program uses a different plane for the ecliptic. Either way, not really a big deal, for this simulation at least.
 
My orbit program's not really ready for release yet, mostly because it's still packed with bugs (I ran into several major ones just while making this simulation) but also because it's still stuck with a barely decent name and I don't even know what I plan to do with it at this point.
 
...But, I'll still email you the current version sometime soon, the "excuse" being that I still need your permission for the .gsim import/export options it has. Tongue I just don't want you to send it to anyone else for now.
 
Even after many optimizations, your program is still faster than mine by an unbelievable factor (which is especially weird since mine uses RK4, but yours I think still uses Euler), so it won't be that useful for actually running simulations. On the other hand, I think you'll find the editor to be a massive improvement for most purposes (anything relatively simple is mostly point-and-click, and the ability to drag-select, edit, copy, and paste large groups of planets is more useful than I can hope to describe), and its "real" 3D graphics make things look a bit better and let you do things like view from a planet's surface.
 
So, though it may look kinda like Gravity Simulator and does similar things, "Orbit 3D" (my program's temporary name) is only useful for completely different things...and that's why I put in the .gsim import/export tools. Tongue
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