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Focus on barycenter and other questions (Read 2107 times)
Caver
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Focus on barycenter and other questions
07/22/05 at 10:09:42
 
First, thanks for a very neat program! I spent way too long playing around with it today. Unfortunately, I have no clue what I am doing which is making things a little slow going. I have barely the faintest knowledge about orbital mechanics.   embarrassed
 
That said, I'm trying to simulate a fictional planetary system for some friends. They've somewhat written themselves into a corner. I'm trying to come up with a system that has:
 
A G2 V star (or thereabouts) and a sdB star (of roughly 0.48-0.50 solar masses) with about 1 AU separation. I need a planet of roughly 0.7 earth masses, hopefully not much further than 3 AU from the pair, and I need a few gas giants holding the whole thing together. They want to work an asteroid belt in there somehow, too, but... I'll worry about that later. Smiley
 
I can't seem to figure out how to focus on the barycenter of the two stars, for one thing. But my main problem is getting more than two objects in there without causing trouble. And I think it is almost as much me as it is the difficulty in what I am trying to accomplish.
 
Any hints, advice, or words of encouragement?
 
I also have a suggestion... it would be fun to be able to graphically represent the habitable zones of any particular star. The formula isn't too difficult, so long as you are only concerned with "will you have liquid water" and none of the other variables such as too much/too little UV, atmosphere of the planets, and so on.
 
Thanks for anything anyone is able to offer? I have a lot to learn about orbital dynamics!
 
-Caver
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Tony
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Re: Focus on barycenter and other questions
Reply #1 - 07/23/05 at 00:33:45
 
Hi Caver,
 
I'm glad you like the program.
 
To focus on a barycenter, press the F button on your keyboard to toggle between Absolute and Floating modes.  In order to focus on the barycenter, all objects that orbit your parent object must have the parent object as their Reference Object.  I'll explain more below.
 
To create the simulation you describe, follow these steps:
 
With Gravity Simulator running:
 
menu File > New
This creates a new simulation with one object.  This red object has 1 solar mass.  G2 stars have about 1 solar mass so you could keep that value or edit it.  To edit:
 
menu File > Save As...
Give your new simulation a name and save it.
 
menu Objects > Edit Objects
This opens a window that allows you to change many of its properties including mass.  At this point you may want to consider changing its Name, and Color as well to your preferences.  Don't touch the X,Y,&Z values.
 
To create your 2nd star of 0.5 solar masses:
 
menu Objects > Create Objects
 
An window will open that will enable you to create objects.  Choose the following values for the fields:
 
Number of Objects: 1
Size:  1113600 km (~80% of the Sun's size,or your preference)
 
Semi-major axis: 1 Astronomical Unit (or your preference)
This is the 2nd star's average distance from the 1st star.
 
Eccentricity: 0, +/- 0 %
This describes the shape of the orbit.  Do you want your stars to orbit their barycenter in perfect circles?  If so leave it at 0.  If not, choose a different value.  I'd keep it under 0.2 though.
 
Inclination: 0, +/- 0%
This defines the plane of your system.  Leave it at 0.
 
Reference Object: Object 1 (or if you renamed it, whatever you changed it to).  This is important if you want to focus on a barycenter.
 
Mass: 0.5 Sun Masses (or your preference), +/- 0%
 
Longitude of the ascending node: 180 +/- 100%
This is the point where your objects will cross the system plane.  Unless you entered a value other than 0 for inclination, this value is meaningless.  Just leave it at 180 and 100%.
 
Argument of perifocus: 180 +/- 100%
This is the point where your objects are at their closest approach to eachother.  Unless you entered a value other than 0 for eccentricity, this value is meaningless.  Just leave it at 180 and 100%.
 
Mean Anomoly: 180 +/- 100%
This is the point in its orbit where your object will be when the simulation begins.  Just leave it at 180 +/- 100%.
 
Name:  Your preference
 
Color: Your preference
 
Units: Degrees
 
Press Create.
 
File > Save  (Save your simulation to this point)
 
Your universe should now contain 2 objects.
 
If you do not have your user controls visible, press F8 or F9.  Or menu View > Dashboard Elements > Show All > Align ...
Use the F button on the Graphics Options window to focus the barycenter.
 
Now create the planet:
 
menu Objects > Create Objects
Fill in the following values:
 
Number of Objects: 1
Size:  10000 km (~80% of the Earth's size,or your preference)
 
Semi-major axis: 3 Astronomical Units (or your preference)
 
Eccentricity: 0, +/- 0 %
 
Inclination: 0, +/- 0%
 
Reference Object: Object 1, Barycenter  (or if you renamed it, whatever you changed it to).  Make sure your click the barycenter option.
 
Mass: 0.7 Earth Masses, +/- 0%
(or your preference)  
 
Longitude of the ascending node: 180 +/- 100%
 
Argument of perifocus: 180 +/- 100%
 
Mean Anomoly: 180 +/- 100%
 
Name:  Your preference
 
Color: Your preference
 
Units: Degrees
 
Press Create.
 
File > Save (Save your simulation to this point)
 
Your universe should now contain 3 objects.
 
You don't need gas giants to hold the system together.  In fact, they'd have the opposite effect.  They'd tend to want to eject things from the system.  If you want to include a few, just give them a good spacing of 6 AU or farther.  Follow the same steps as your first planet. .
 
To create an asteroid belt, first decide where it should be?  In this system, anything under 3 AU would likely be unstable.  Try centering the asteroid belt at about 6 AU.:
 
menu Objects > Create Objects  
 
Fill in the following values:
 
Number of Objects: 50 (or your preference.  If you have a fast computer you can increase this to a couple hundred)
 
Size:  0 km
 
Semi-major axis: 6 Astronomical Unit, +/- 50% (or your preference).  This will create a range of semi-major axes between 3 and 9 AUs.
 
Eccentricity: 0, +/- 0 %
 
Inclination: 0, +/- 0%
 
Reference Object: Object 1, Barycenter (or if you renamed it, whatever you changed it to).  Make sure your click the barycenter option.
 
Mass:0 Earth Masses, +/- 0% (mass isn't too important since the asteroids are unlikely to perturb each other, and the simulation will run much faster if you create massless particles)  
 
Longitude of the ascending node: 180 +/- 100%
 
Argument of perifocus: 180 +/- 100%
 
Mean Anomoly: 180 +/- 100%
 
Name:  Your preference
 
Color: Your preference
 
Units: Degrees
 
Press Create.
 
File > Save As...  (Give your simulation a new name.  That way, if your asteroid beld doesn't work out, you can resort back to your pre-asteroid belt version and try new numbers.)
 
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