Problems modelling astrometric orbits

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Problems modelling astrometric orbits

Post by Sirius_Alpha on 27th January 2014, 11:26 pm

I've been working on a way to model astrometric orbits, essentially representing 3D orbits on a 2D plane for the purposes of this conversation. I've been having a hard time figuring out the math behind it. I've found what I thought was the proper formulation but it is producing results that are not particularly intuitive.

I will post some screenshots.

A simple, face-on configuration.


As expected, changing LongPeri for an inclined circular orbit does not produce a physical change.


But adding eccentricity seems to tilt the orbit.


Only changing e produces an unexpected result.


Here's my math.
Code:
//Theile-Innes constants.
double A = a * (Math.Cos(omega) * Math.Cos(Node) - Math.Sin(omega) * Math.Sin(Node) * Math.Cos(inc));
double B = a * (Math.Cos(omega) * Math.Sin(Node) + Math.Sin(omega) * Math.Cos(Node) * Math.Cos(inc));
double F = a * (-1 * Math.Sin(omega) * Math.Cos(Node) - Math.Cos(omega) * Math.Sin(Node) * Math.Cos(inc));
double G = a * (-1 * Math.Sin(omega) * Math.Sin(Node) + Math.Cos(omega) * Math.Cos(Node) * Math.Cos(inc));
Code:
double x_coord = A * (Math.Cos(E - ecc)) + F * Math.Sqrt(1 - (ecc * ecc)) * Math.Sin(E);
double y_coord = B * (Math.Cos(E - ecc)) + G * Math.Sqrt(1 - (ecc * ecc)) * Math.Sin(E);

I used my same formulation for the eccentric anomaly as used for these diagrams so I do not think it is a problem there.

Also, for eccentric orbits, the x and y coordinates of the orbit are not mapping them to positions that place the barycentre in the image centre.

I'll have to hack at it when I get home from work, but for now I can't figure out what's wrong. Any assistance would be appreciated.

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Re: Problems modelling astrometric orbits

Post by Sirius_Alpha on 28th January 2014, 6:19 pm

Follow-up. I've managed to get it working right. The orbit diagrams now match observations for known binary stars, etc.

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Re: Problems modelling astrometric orbits

Post by Lazarus on 4th June 2014, 5:54 pm

Checked out Upsilon Andromedae yet? When I tried to do this a few years back I was unable to match all the data/figures in McArthur et al. (2010) simultaneously.
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