PES 106        Spring 2003
Previous Lecture

General Astronomy II
Next Lecture

Lecture Notes:

Lives of Stars: Life Stories and Clusters of Stars

text: Chapter 13 (sections 13.1 and 13.9)

(If you have old National Geographics on your shelves: take a look at May 1988 page 618)

[Nice PC-based shareware software is Star Clock 2.0 which show the motion of stars during their lives on an HR diagram for various mass stars. You can see the relative duration of the H-burning, He-burning and other phases of different stars. Note: "My" = million years, type "R" to run the simulation and "Q" to quit. Download from ftp://ftp.seds.org/pub/software/pc/stars/ by clicking on sclock20.zip.]

Stars with less that 10 Solar Masses:

Number on HR diagram below

Stage

Approximate time period

1.

Hydrogen Burning (Main Sequence)

10 billion years

2.

Red Giant

500 million years - 1 billion years

3.
Helium Flash

minutes

4.

Yellow Giant (Helium burning)

100 million years

5.

Red Super Giant

10 million years

6.

Planetary Nebulae

10,000 years

7.

White Dwarf

5 - 20 billion years

8.

Black Dwarf

eternity
note: time periods will vary depending on details of the models being used.

 

HR diagram for low mass star

Figure 13.17 also shows an HR diagram and a timeline. [Link to Figure 13.17]

Stars with 10 - 20 Solar Masses

Number on HR diagram below

Stage

Approximate time period

1.

Hydrogen Burning (Main Sequence)

1 - 100 million years

2.

Yellow Giant (Supergiant)

<100,000 years

Red Giant (Supergiant)

3.
Helium Burning

< 1 million years

4.
Carbon Burning

500 - 1000 years

5.
Neon Burning

1 - 6 years

6.
Oxygen Burning

0.5 - 1 year

7.
Silicon Burning

1 - 4 days

8.

Collapse

100 seconds

9.

Supernova

2 hours

10.

Neutron Star

Hr diagram of 10-20 solar mass stars

Figure 13.21 also shows an HR diagram for high mass stars. [Link to Figure 13.21]

Stars with > 20 Solar Masses

Number on HR diagram below

Stage

Approximate time period

1.

Hydrogen Burning (Main Sequence)

2.

Yellow Giant (Supergiant)

Helium Burning

3.

Red Giant (Supergiant)

4.
Carbon Burning

5.
Neon Burning

6.
Oxygen Burning

7.
Silicon Burning

everything up to here in 100,000 - 1 million years

8.

Collapse

minutes

9.

Neutron Star

10.

Collapse Continues

seconds - days ?

11.

Black Hole

??

HR diagram of high mass stars

Clusters of Stars:

 groups of 10 - 1 million stars

located close to one another

Why important ?

1. Stars are all approximately the same distance away
we can compare them using brightness without knowing actual luminosities

2. They all probably formed at similar times (similar age stars)

3. They all probably formed from the same cloud (same composition)

=> only real difference is their MASS

We observe:

young clusters which have only Main Sequence stars (no giants)

older clusters with main sequence stars and red giants - but not hot, massive O-type stars

even older clusters with main sequence and red giants - but no O or B type stars.

 

Box Figure 13.2 in the text show the HR diagrams which correspond to different ages of clusters. [Link to Figure]

Previous Lecture Previous Lecture - - - INDEX OF LECTURES - - - Next Lecture Next lecture

RETURN to Lecture Notes Outline