Lecture 13: Stellar Evolution- Observations of Elderly Stars

"Shine on you Crazy Diamond"
Pink Floyd, Dark Side of the Moon

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Date: March 9, 1995
Reading Assignment: pp. 464-476

Description : observations of post-Main Sequence evolution

Objectives

be able to describe the formation of a Planetary Nebula and a white dwarf

be able to describe the size, temperature, and composition of a white dwarf

be able to describe what happens as a white dwarf cools

be able to describe what happens inside the cores of higher mass stars when they evolve of the main sequence

be able to discuss how star clusters can be used to test theories of stellar evolution

be able to discuss how mass transfer in binary stars can change the course of evolution for some stars

be able to sketch the evolutionary path of a one solar mass star from the Main Sequence until it becomes a white dwarf

Lecture Outline

Slide # 1: Stellar Evolution II

Observations of Elderly Stars

Slide # 2: Question 1

How long does it take a one solar mass star to evolve to the main sequence?

(starting from fragmentation of the gas cloud)

Slide # 3: Question 2

What is force causing star formation?

Slide # 4: The Steps

gas cloud

fragmentation

protostar

Helmholtz contraction

Hayashi track

ignition

adjustment to the Main Sequence

Slide # 5: The HR Diagram (GRAPHICS)

HR diagram

Slide # 6: The Story so Far

core runs out of hydrogen

no internal circulation of material

core contracts- hydrogen shell burning

red giant branch

core temperature reaches 100 million K

helium flash - degenerate helium core

helium core burning

core runs out of helium

no internal circulation

core contracts -helium shell burning

Slide # 7: Core Density Increases

Carbon core becomes degenerate

density > 107 gm per cubic cm

core temperature to low for carbon burning

T < 600 million degrees

Slide # 8: Helium Shell Flashes

the density of the Helium shells increase

contraction of the core increases the density

Helium burning becomes unstable

helium fusion rate depends strongly on temperature

Helium shell flashes begin

the star begins to pulse

Slide # 9: Stellar Envelope Separates

extra energy pushes stellar envelope away from the core

hydrogen rich material escapes

nuclear burning ends in and around core

no pressure from the envelope

planetary nebula forms

Slide # 10: Planetary Nebula (GRAPHICS)

M57 - the Ring Nebula

Slide # 11: Planetary Nebula (GRAPHICS)

cross section

Slide # 12: Planetary Nebula

not a ring, but a three dimensional shell

not a planet, but part of a dead star

becomes thin and dim in < 100,000 years

Slide # 13: The Core

no nuclear reactions

not enough surface pressure

no hydrogen gas

cools very slowly by emitting radiation

small size slows cooling

spends 1 billion years cooling

about 9% of a stars' lifetime is in the white dwarf stage

becomes a white dwarf

cools and becomes a black dwarf

Slide # 14: White Dwarfs

very high density

107 gm per cubic cm

1 ton = 1 teaspoon

composition mostly carbon

some oxygen from more massive stars

very common

9% of stars are white dwarfs

Slide # 15: Post Main Sequence- Internal Changes

core depletion of hydrogen

hydrogen shell burning

helium flash and helium core burning

helium depletion

helium shell burning

helium shell flashes

planetary nebula - white dwarf

Slide # 16: Post-Main Sequence Slide # 17: HR Diagram (GRAPHICS)

subgiant branch

giant branch

horizontal branch

asymptotic giant branch

planetary nebula

white dwarf

Slide # 18: The HR Diagram (GRAPHICS)

one solar mass star over 8 billion years

Slide # 19: The HR Diagram (GRAPHICS)

one solar mass star over 8 billion years

Slide # 20: The HR Diagram (GRAPHICS)

one solar mass star over 8 billion years

Slide # 21: The HR Diagram (GRAPHICS)

one solar mass star over 8 billion years

Slide # 22: The HR Diagram (GRAPHICS)

Why?

Slide # 23: The Proton-Proton Chain (GRAPHICS)

hydrogen into helium in 3 easy steps

Slide # 24: The Triple Alpha Process (GRAPHICS)

Helium into Carbon

Slide # 25: Internal Structure of the Star

the following are diagrams of the internal structure of the star

the diagrams are NOT to scale

Slide # 26: Stellar Composition (GRAPHICS)

helium fraction increase in the core

Slide # 27: Stellar Composition (GRAPHICS)

helium fraction increase in the core

Slide # 28: Hydrogen Shell Burning (GRAPHICS)

inert core- hydrogen burning shell

Slide # 29: The Helium Flash (GRAPHICS)

two energy sources!

Slide # 30: Core Helium Burning (GRAPHICS)

two energy sources!

Slide # 31: Helium Shell Burning (GRAPHICS)

4 layers in the star

Slide # 32: Planetary Nebula (GRAPHICS)

cross section

Slide # 33: Red Giant Size (GRAPHICS)

before and after

Slide # 34: Constellation Corner (GRAPHICS)

Constellation De Jour

Slide # 35: Winter Constellations

Fairfax - 8pm - S - 4.0 - March 5

Slide # 36: Winter Constellations

Fairfax - 8pm - S - 4.0 - March 5

Slide # 37: Looking North (GRAPHICS)

March 6 - 8pm - NW - 4.0 - Fairfax

Slide # 38: Looking North (GRAPHICS)

March 6 - 8pm - NW - 4.0 - Fairfax

Slide # 39: Abundance of Red Giants

90% stars are on the main sequence

8 billion years = 1 solar mass star

1% stars are red giants

80 million years (not including subgiants)

9% of stars are white dwarfs

Slide # 40: The HR Diagram (GRAPHICS)

one solar mass star over 8 billion years

Slide # 41: Evolution of Massive Stars

massive stars have the same types of internal changes as low mass stars

same types of compositional changes occur

massive stars evolve more rapidly

extra mass causes extra gravity

extra gravity causes extra core heating

extra core heating causes faster nuclear burning

more luminous, so they use fuel more rapidly

Slide # 42: Cluster Evolution

clusters are at uniform distances

relative apparent magnitude will indicate luminosity

clusters have the same age

most stars in clusters formed at the same time

ideal tests for stellar evolution

Slide # 43: Star Clusters (GRAPHICS)

the Pleiades - about 90 million years old

Slide # 44: Cluster HR Diagrams

the HR diagram of a cluster can be used to determine the cluster's age

massive stars evolve more rapidly than low mass stars

Slide # 45: The HR Diagram (GRAPHICS)

HR diagram

Slide # 46: The HR Diagram (GRAPHICS)

10 Million Years

Slide # 47: The HR Diagram (GRAPHICS)

10 Million Years

Slide # 48: The HR Diagram (GRAPHICS)

100 Million Years

Slide # 49: The HR Diagram (GRAPHICS)

100 Million Years

Slide # 50: The HR Diagram (GRAPHICS)

1 Billion Years

Slide # 51: The HR Diagram (GRAPHICS)

1 Billion Years

Slide # 52: The HR Diagram (GRAPHICS)

10 Billion Years

Slide # 53: The HR Diagram (GRAPHICS)

10 Billion Years

Slide # 54: The HR Diagram (GRAPHICS)