Are Brown Dwarfs Part of the Main Sequence on the H-R Diagram?

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Discussion Overview

The discussion centers on the classification of brown dwarfs in relation to the main sequence on the Hertzsprung-Russell (H-R) diagram. Participants explore whether brown dwarfs should be considered part of the main sequence or if they occupy a separate category, with references to their position on the diagram and their fusion capabilities.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions whether brown dwarfs appear on the lower right "tail" of the main sequence or if they are separate from it.
  • Another participant asserts that brown dwarfs are not main sequence stars since they do not perform hydrogen fusion, although they are shown in the lower right on a referenced diagram.
  • A participant seeks clarification on how to represent brown dwarfs on a sketch of the H-R diagram, considering their potential separation from the main sequence.
  • One response indicates that plotting brown dwarfs must adhere to the parameters of the graph, suggesting they would be placed in the lower right.
  • Another participant notes that additional spectral classes (L and T) were created for brown dwarfs, indicating their presence on the H-R diagram but emphasizing they are not considered main sequence stars. They mention the ability of some brown dwarfs to fuse deuterium under certain conditions.
  • A later reply reiterates that brown dwarfs are not on the main sequence, describing them as small and cool, located in the lower right corner of the H-R diagram.

Areas of Agreement / Disagreement

Participants generally agree that brown dwarfs are not classified as main sequence stars. However, there is disagreement regarding their representation on the H-R diagram and the implications of their position.

Contextual Notes

Some participants mention the accuracy of the referenced H-R diagram and the conditions under which brown dwarfs may fuse deuterium, indicating potential limitations in the discussion regarding definitions and classifications.

ZedCar
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Do Brown Dwarfs appear on the lower right hand "tail" of the main sequence of the H-R diagram?

Or are they separate from the main sequence?

The location here:
https://en.wikipedia.org/w/index.php?title=File:HR-diag-instability-strip.svg&page=1
appeared to show them in that location, but I wasn't sure if they are actually separate from the main sequence as the diagram isn't that clear on their location.

Thank you.
 
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Brown dwarfs are not main sequence stars, as they never perform hydrogen fusion, but they appear on your link at the bottom right. I don't know how accurate that particular graph is.
 
Thanks Drakkith.

So if I was drawing a sketch of the H-R diagram, and labelling the position of the brown dwarfs, would I just point out that they are on the lower right-hand tail of the main sequence.

Or should they be indicated as being completely separate from the main sequence in the way that white dwarfs are?
 
If you are going to plot them, you have to plot them according to the parameters of the graph. This necessarily puts them at the lower right I believe.
 
A couple extra spectral classes past M were invented for brown dwarfs - L and T, so they technically are on the HR diagram, but, not considered main sequence. They can fuse deuterium if they can achieve a core temperature of about 1 million degrees. The ones too small to fuse deuterium may as well be called orphan planets.
 
Brown dwarfs, as previously stated, are not on the main sequence. They are small and relatively cool and fall in the lower right hand corner of the HR diagram.
 

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