Celestia Forums

Do we have much info on inclinations in systems containing 3 or more stars? By which I mean, is the third star in a trinary system always in the same plane (or close to it) as the other two stars? If no, how inclined can it be - can you get the third star in a very inclined orbit?

Anyone got any links to any datasets that describe this?

I guess I'm out of luck here?

Malenfant wrote:I guess I'm out of luck here?

Have you scanned through nearstars.stc? There are a few multiple star systems with completely determined orbital parameters.

--Chris

Not yet, I was hoping there'd be a proper multiple star catalog out there somewhere that had this data.

Malenfant wrote:Not yet, I was hoping there'd be a proper multiple star catalog out there somewhere that had this data.

I think Celestia's catalogs of multiple stars are as good as you'll get at the moment. If there is better stellar orbit data out there, we'll certainly want to use it.

--Chris

Malenfant,
I don't know if this link will provide what you need since, I didn't see any direct references to Inclinations but, it does provide a wealth of information about individual and multiple star systems. Maybe it'll help you with your calculations.
http://nstars.nau.edu/index.cfm?fuseaction=singleSearch.searchForm

Here's one data point: the Algol system.

http://en.wikipedia.org/wiki/Algol

It contains three stars. The inclination of the AB orbit is 98 degrees, and the inclination of C is 84 degrees (not sure what the reference plane is--the ecliptic, Earth equator, or something else.) AB are separated by 0.062AU, and C has a mean distance of 2.69AU from AB.

--Chris

The reference plane for any binary star orbit is always the 'plane of the sky at the star,' that is, the plane 90?° to your line of sight to the star.

You'll still need to know the position angles of ascending node, arguments of periastron and epochs to complete full 3D orbit knowledge, and this probably doesn't exist for any star of Algol, since it's usually only possible with astrometric multiples...

Spiff.

Spaceman Spiff wrote:The reference plane for any binary star orbit is always the 'plane of the sky at the star,' that is, the plane 90?° to your line of sight to the star.

That's what I thought, but since Algol is and eclipsing binary shouldn't the angle be closer to 90 degrees? Then again, actually doing the math shows that at 0.062 AU, even an orbital plane 8 degrees from edge on allows an eclipse to be visible for large stars like the Algol pair.

You'll still need to know the position angles of ascending node, arguments of periastron and epochs to complete full 3D orbit knowledge, and this probably doesn't exist for any star of Algol, since it's usually only possible with astrometric multiples...

True . . . thought I wonder if tidal forces would have circularized the orbits of A and B. It appears that there is a completely determined orbit for the third star.

--Chris

chris wrote:Then again, actually doing the math shows that at 0.062 AU, even an orbital plane 8 degrees from edge on allows an eclipse to be visible for large stars like the Algol pair.

Yes, the stars are rather large, and I think the light curve of Algol shows it's not a complete eclipse - only partial - because of this extra 8?° tilt.

chris wrote:True . . . thought I wonder if tidal forces would have circularized the orbits of A and B.

Indeed the Wiki data you pointed to shows that the inner pair do orbit with eccentricity zero, thus the argument of periastron is undefined, and 0?° will suffice. You'd still need to know what the ascending node is - I think that only polarimetry could reveal this.

chris wrote:It appears that there is a completely determined orbit for the third star.

Oh goody! Where is that?

Spiff.

Spaceman Spiff wrote:

chris wrote:It appears that there is a completely determined orbit for the third star.

Oh goody! Where is that?

Scroll to the bottom of this page:

http://www.alcyone.de/SIT/mainstars/SIT000666.htm

Two orbits determined from different techniques are given, and there's some disagreement between the two.

--Chris