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Numsgil

Multiple Star Systems and their Magnitude

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Numsgil    501
Okay, this is my last astronomy thread, I swear. My system for star creation has multiple star systems as quite common, where 60% of all stars occur in a multiple star system (just like in the real galaxy). I'm having trouble finding information on what this multiple star system's magnitude will be. In my tests, systems with 20+ planets is not unheard of (though very rare). Even if all 20 of these stars are red dwarfs, I'd expect their combined magnitude to be brighter than a K or maybe even G class star. Does anyone know of any links or equations which relate a systems absolute magnitude with the number and classification of its composite stars?

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Sandman    2210
I'm not sure why you want the composite magnitude, it's not really a very meaningful number, unless you want to be able to see what they look like at a great distance.

In any case, the composite magnitude depends on the orientation of the stars with respect to the viewer, and where the stars are in their respective orbits. If the viewer is on the orbital plane of the two stars, then the composite magnitude will be brightest when the stars are side by side, slightly less bright when the dimmer star passes behind the brighter one, and substantially dimmer when the dimmer star passes in front of the brighter one. If the viewer lies away from the plane, then you'll always see the compound brightness - assuming they are so close together that you can't resolve them as separate stars.

You could calculate the composite magnitude by calculating the flux of each star, adding them together, and calculating the magnitude representing that flux.

I think the equation you want is:

m = -2.5 log f + c

where m is the magnitude, f is the flux, and c is a constant which you can probably ignore for the purposes of this calculation, since you're only going to convert back to magnitudes afterwards.

You might also find this link interesting.

[Edited by - Sandman on August 5, 2004 3:44:44 PM]

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Numsgil    501
Quote:
Original post by Sandman
I'm not sure why you want the composite magnitude, it's not really a very meaningful number, unless you want to be able to see what they look like at a great distance.


Basically, when you reach new parts of the galaxy, new stars become visible which were too dull to see before (or smudged with other stars, like when we try to look towards the galactic core. The game treats them the same).

I need the composite magnitude to calculate wether the system is visible from a distance.

Quote:

If the viewer lies away from the plane, then you'll always see the compound brightness - assuming they are so close together that you can't resolve them as separate stars.


Yes, let's assume, for the sake of coding simplicity, that the game treats all multiple star systems as being viewed orthogonal to their plane. Do I just add their brightnesses together then? So I'd have to figure out how to add brightnesses from their logarithmic magnitudes?

Or is there some multiplying effect? Perhaps all those stars working together create some kind of constructive interference?

[edit - ah, I see Sandman has answerred my question in an edit. :P

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