Why do Spectroscopic Binaries Have Short Periods?

[blumfeld0]

Why do spectroscopic binaries have short periods? I figure it is because they have small separation and p^2=A^3
but why small separations?
thanks

 

[Kurdt]

You are right to think that they have a small separation and this gives them a short orbital period. When binary stars are separated by small distances and are too close to be distinguished as visula binaries spectroscopy can tell us if it is a binary system or not. So the reason spectroscopic binaries have small separations is that otherwise they'd be visual binaries.

 

[selfAdjoint]

You are right to think that they have a small separation and this gives them a short orbital period. When binary stars are separated by small distances and are too close to be distinguished as visula binaries spectroscopy can tell us if it is a binary system or not. So the reason spectroscopic binaries have small separations is that otherwise they'd be visual binaries.

Hah! AN "anthropical" explanation!

 

[Kurdt]

What can I say? I have a deft touch with words

 

[SpaceTiger]

Why do spectroscopic binaries have short periods? I figure it is because they have small separation and p^2=A^3
but why small separations?

Despite the lack of theoretical underpinning, I think Kurdt's answer really is the best one. The definition of a spectroscopic binary is purely observational and depends not just on the physical characteristics of the system, but also the limitations of our instruments. A spectroscopic binary could become a visual binary if observed with an instrument of higher resolution or an astrometric binary if observed with an interferometer.

The question of how stars can end up close to one another in binary systems also has multiple answers. For example,

- Certainly some of them form that way.
- Three-body interactions in a dynamically cold system of stars can lead to the tightening of a binary.
- Stars that are already close can spiral towards one another if they both fill their Roche lobe.