1. The Hertzsprung-Russell diagram and the nature of stars

2. The Hertzsprung-Russell Diagram
Hertzsprung and Russell had the idea of plotting the luminosity of a star against its spectral type. This works best for a cluster, where you know the stars are all at the same distance. Then apparent brightness vs spectral type is basically the same as luminosity vs temperature. They found that stars only appear in certain parts of the diagram.

5. With information provided by spectroscopy, we can search for correlations between stellar properties

6. What the data show: the Hertzsprung-Russell Diagram
Highest quality data from the Hipparchus spacecraft

7. The Sun is generically related to most
The Sun is here
The Sun is generically related to most

8. Filling out the Hertzsprung-Russell diagram

9. The Hertzsprung-Russell Diagram and the Types of Stars
Types of stars, important terms
Main Sequence (luminosity class V)
Giants (luminosity class III)
Supergiants (luminosity class I)
White dwarfs
What does it all mean?

10. The Hertzsprung-Russell Diagram

11. Basics of the HR diagram
Size
Mass
Red dwarfs

12. Hertzsprung-Russell Diagram
Sizes scale
1 Rsun
10 Rsun
100 Rsun
1000 Rsun
Since there appears to be a strong correlation between luminosity and color (temperature), we put all the stars on a Luminosity – Temperature plot, and this is what it looks like:
Properties of Stars shown in the H-R Diagram:
Luminosity (log scale).
Temperature and spectral type
Size
Mass of the main sequence
Lifetime

13. Hertzsprung-Russell Diagram
Sizes scale
1 Rsun
10 Rsun
100 Rsun
1000 Rsun
Notice that…
Temperature scale decreases from left to right.
The scale of luminosity is in power of 10 (log scale).
Mass increases from lower right to upper left
Size increases from lower left to upper right.

14. Classification of Stars in H-R Diagram
Sizes scale
1 Rsun
10 Rsun
100 Rsun
1000 Rsun
The Main Sequence stars
healthy stars, fusing hydrogen in the core.
High-mass, high-luminosity, high-temperature, and short-lived stars on the upper-left-hand corner
Low-mass, low-luminosity, low-temperature, and long-lived stars on the lower-right-hand corner

15. Classification of Stars in H-R Diagram
Sizes scale
1 Rsun
10 Rsun
100 Rsun
1000 Rsun
2. The Supergiants,
3. The Giants,
Supergiants and giants are dying stars, fusing helium and heavier elements.
4. The White Dwarfs.
dead stars, exposed core of dead main-sequence stars.

16. The Mass-Luminosity Diagram
Main sequence stars
The payoff: we can decode the HR diagram and learn that the main sequence is a mass sequence (and that off the main sequence things are more complicated).

17. HR Diagram - Properties
Stars in different parts of the HR Diagram are in different phases of their life cycles. The Main Sequence is set by hydrogen fusion.
Masses on the Main Sequence Stellar Sizes

18. Size/Luminosity
Hot stars are very bright but very rare. They can affect the light, but not the mass of the Galaxy. Red giants are more common. Most common are red dwarfs. O5 B0 A0

19. The Hertzsprung-Russell diagram is a plotting board for the nature and evolution of stars

20. Wein’s Law
Ex. The light emitted by our sun is yellow light. It has a wavelength of 500nm. What is the surface temperature of the sun according to Wein’s Law?