The Hertzsprung-Russell Diagram

Read:  Chapter 16
16-00





  Mr. Hertzsprung and Mr. Russell:


 
 

   





Properties of Stars 

 

SPECTRAL CLASS
Mass (solar masses)
Luminosity
(solar luminosities)

Temperature
degrees K

Radius
(solar radii)

O5
40
400,000
40,000
13
B0
15
13,000
28,000
4.9
A0
3.5
80
10,000
3.0
F0
1.7
6.4
7,500
1.5
G0
1.1
1.4
6,000
1.1
K0
0.08
0.46
5,000
0.9
M0
0.05
0.08
3,500
0.8


Also there are Giants, Supergiants and white dwarfs:  Same Temperature as stars in the table, but different luminosity and radii.



The H-R Diagram: 

Plot Luminosity versus Surface Temperature

(or equivalently, Luminosity versus spectral classification)




Main Sequence:  Stars fusing hydrogen to helium





Giants are more luminous than a main sequence star of the same temperature.
Giants tend to be relatively cool (T < 6000 Kelvin) but luminous (L = 100 to 1000 Lsun).

Supergiants are even more luminous than giants.
 Supergiants can have any temperature, but they are always VERY luminous, with L = 100,000 to 1,000,000 Lsun.

White Dwarfs are less luminous than a main sequence star of the same temperature.
They are called WHITE dwarfs because they are fairly hot; white-hot, in fact, with temperatures of T > 5000 Kelvin. The are low in luminosity, with L = 0.0001 to 0.01 Lsun.

In a sample of 1,000,000 stars from the Milky Way, on average you'd find:

ANIMATION



Stellar Lifetimes on the Main Sequence:

More Massive Stars are more luminous, and are burning hydrogen more efficiently.

They therefore have shorter lifetimes on the Main Sequence.

Mass

(Msun)

Lifetime

(years)

1
10 billion years
5
100 million
10
10 million


ANIMATION



Pulsating Variable Stars: Cepheid Variables, RR Lyrae







Period of pulsation is correlated with absolute magnitude.    Thus, given the apparent magnitude and period of pulsation, you can derive the DISTANCE to the star.





ANIMATION




STAR CLUSTERS

All the stars in a cluster are (1) at the same distance, and (2) were formed together, so are the same age.




Open Clusters:  Young (Less than a billion years old)

Globular Clusters:  Contain oldest stars in the Milky Way -- 12-13 billion years old



PLIEADES OPEN CLUSTER:





H & Chi Persei, a Double Cluster






GLOBULAR CLUSTER:






In Old clusters, some of the stars have "left" the Main Sequence -- and become Red Giants, white dwarfs, etc.

The age of the cluster = the lifetime of the stars at the "main sequence turnoff" in the H-R diagram.






ANIMATION
ANIMATION