Binary system

[Angry Space Goat]

I'm trying to set up a binary system where a white dwarf orbits a larger host star. I know how to do this if I'm creating the system from scratch, but the host star is already existant. I don't know how to put a star in orbit around an already existing star.

Any help?

[Tleilax]

I had this same question not too long ago... It's really simple...

For example, lets say that you want to add a companion star to the star Castor; in your extras folder, make a folder called Castor and in that, add a text document containing the information of the secondary star and simply use the original star as your barycenter.

This is an exerpt from my Castor addon which will have the complete Castor system of 6 stars...

"Castor Ab"
{
OrbitBarycenter "Castor"
SpectralType "M5V"
AppMag 6.33
Radius 348000

EllipticalOrbit { # fully specified orientation
Period 9.21
SemiMajorAxis 1.1306 # mass ratio 2.25:0.65
Eccentricity 0.499
Inclination 114.5
AscendingNode 298.1
ArgOfPericenter 187.9
MeanAnomaly 133.8
}
}

To be 100% accurate, you can "modify" the parent star itself in order for it to orbit around a common center of gravity with its companion - a barycenter.

[Angry Space Goat]

How would I go about doing that, then?

(That is, modifying the central star to orbit a barycenter.)

[Tleilax]

In order to have a default star orbit a barycenter you simply add the new information about the star to the .stc file and preceed with, "Modify." The only dificult thing is, you must know/find the Right Acention-Declination of the barycenter and then have your Binary System orbit that. I am trying to simply use Castor's coordinates for the barycenter and hoping celestia simply implaments the orbital paramiters of Castor, so it is no longer a fixed star. I'm still trying to get the bugs out of this one. Maybe you could figure it out? Good Luck.

Modify "Castor"
{
OrbitBarycenter "Castor Barycenter"

EllipticalOrbit { # fully specified orientation
Period 9.21
SemiMajorAxis 1.1306 # mass ratio 2.25:0.65
Eccentricity 0.499
Inclination 114.5
AscendingNode 298.1
ArgOfPericenter 187.9
MeanAnomaly 133.8

}

[Tleilax]

Oh, when modifying anything, do not put it in the default star database (in this case). Put your modified default star in the same text document as your new companion star.

[elioe]

I would like to create a planet to Lagrangian point 5 of two stars orbiting each other... but how do i do it?

[selden]

Unfortunately, the stable lagrangian points only exist when the masses of the two primary objects are not equal. In particular, the mass of one of the two large objects must be more than ~25x the mass of the other one.

See http://en.wikipedia.org/wiki/Libration_point

In other words, it's easiest to construct them in systems where the smaller (M1) of the two large objects is shown as orbiting around the larger (M2) one. Then the tiny body that's in L5 can be defined to have the same orbit as M1, but lagging by 60 degrees: specify a MeanAnomaly for L5 that's 60 degrees less than the MeanAnomaly of M1.

Does this help?

[elioe]

Yes, that helped very much... i had read only facts in http://www.cix.co.uk/~morven/worldkit/index.html#astro-sun

But fortunately and funnily I don't have to agree with laws of physics... Celestia helps me to disagree... Like when I made a moon to orbit inside a planet.

[elioe]

And I guess that it isn't possible to use horseshoe orbit either?

[selden]

Not as a permanent orbit.

Arbitrary xyz trajectories can be created that last for a specific interval of time.

Or you could modify Celestia's source code...

[Malenfant]

Isn't a horseshoe orbit just a specific type of ordinary orbit around a body that is seen from within a rotating reference frame?

[selden]

My understanding is that a horseshoe orbit involves a change of major axis value when one body approaches another one that's in a similar orbit.
See http://www.astro.uwo.ca/~wiegert/3753/3753.html

Celestia cannot directly represent that except as a special, short-term orbit represented by an xyz trajectory.

[buggs_moran]

My understanding is that a horseshoe orbit involves a change of major axis value when one body approaches another one that's in a similar orbit.
See http://www.astro.uwo.ca/~wiegert/3753/3753.html

Celestia cannot directly represent that except as a special, short-term orbit represented by an xyz trajectory.

Which could be fixed with cyclical (user defined) xyz trajectories.