# Bolometric Magnitude and H-R diagram

I need to clarify something important, with the Hertzsprung-Russell diagram :

What actually is the Absolute Magnitude on the vertical axis ? **Rigorously**, is it the Visual Absolute Magnitude $$M_V$$ or is it the Bolometric Absolute Magnitude $$M_{bolo}$$ ?

Usually, we find "sloppy" H-R diagrams everywhere, which draws Luminosity (or Absolute Magn) on its vertical axis. But nowhere do they state clearly which one it is.

I'm now suspecting is should be the bolometric magnitude and Luminosity (i.e. total energy radiated away, and not just the visible part). Am I right ?

## Answers and Replies

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I think you can use both, because (if I'm not wrong) in stars $$M_V \simeq M_{bol}$$ ; from wikipedia:
"The bolometric magnitude can be computed from the visual magnitude plus a bolometric correction, $$M_{bol} = M_V + BC$$ . This correction is needed because very hot stars radiate mostly ultraviolet radiation, while very cool stars radiate mostly infrared radiation"
I think it's commonly used $$M_V$$.

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I need to clarify something important, with the Hertzsprung-Russell diagram :

What actually is the Absolute Magnitude on the vertical axis ? **Rigorously**, is it the Visual Absolute Magnitude $$M_V$$ or is it the Bolometric Absolute Magnitude $$M_{bolo}$$ ?

Usually, we find "sloppy" H-R diagrams everywhere, which draws Luminosity (or Absolute Magn) on its vertical axis. But nowhere do they state clearly which one it is.

I'm now suspecting is should be the bolometric magnitude and Luminosity (i.e. total energy radiated away, and not just the visible part). Am I right ?
The H-R diagram just uses Mv as the bolometric magnitude is difficult to measure and isn't accurately known for a lot of stars. Bolometric corrections can be computed, but they're estimates not exact. Stellar spectra are very complex.