Why do Spectroscopic Binaries Have Short Periods?

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Discussion Overview

The discussion revolves around the reasons why spectroscopic binaries tend to have short orbital periods. Participants explore the relationship between orbital separation and period, as well as the observational definitions that categorize these systems.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the short periods of spectroscopic binaries are due to their small separations, referencing Kepler's third law (p² = A³).
  • Others argue that spectroscopic binaries are defined by their observational characteristics, suggesting that they would be classified as visual binaries if they were further apart and observable with higher resolution instruments.
  • A later reply mentions that the formation of close binary systems can occur through various mechanisms, including initial formation, three-body interactions, or the spiraling of stars that fill their Roche lobes.
  • One participant humorously notes the anthropic nature of the explanation regarding the observational limits that define spectroscopic binaries.

Areas of Agreement / Disagreement

Participants generally agree that small separations lead to short periods, but there is no consensus on the underlying reasons for these separations or how stars end up in such configurations. Multiple competing views regarding the formation and classification of these binaries remain present.

Contextual Notes

The discussion highlights the observational nature of spectroscopic binaries and the potential influence of instrument limitations on their classification. There are also unresolved questions regarding the mechanisms that lead to close binary systems.

Who May Find This Useful

This discussion may be useful for those interested in binary star systems, observational astronomy, and the dynamics of stellar interactions.

blumfeld0
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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
 
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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.
 
Kurdt said:
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!:smile:
 
What can I say? I have a deft touch with words :wink:
 
blumfeld0 said:
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.
 

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