Announcements• Exam 3 is scheduled for Wednesday April 8. Will be pushed back to Monday April 13 Tentatively will cover the rest of Chapter 4 and all of Chapters 5 & 6. Sample Questions will be posted tomorrow.

• 1st Quarter Observing Night Thursday night. Set-up starts at 6:30 if clear, 6:45 if cloudy.

Colored Card QuestionsClassAction website

ISM & Star Formation moduleStar Formation MassesEmission Nebula Energy Source

Stellar Properties II moduleStellar ParametersHR Groups

Life beyond the Main Sequence

What happens when a star runs out of hydrogen fuel in its core?

With no more hydrogen fusion occurring in the core, hydrogen fusion continues in a shell around the core

Energy imbalance from shell hydrogen fusion creates a Red Giant

Helium Fusion starts when core reaches 100,000,000°

The higher temperature is needed to overcome the stronger electric repulsion between the nuclei

Triple Alpha Helium Fusion

BeHeHe 844 CHeBe 1248

CHe 1243

Additional Fusion involving He

OHeC 16412

Ash from Helium Fusion:Carbon & Oxygen

Helium fusion begins differently for some stars

The determining factor is whether or not the core becomes degenerate

Normal versus degenerate

electron energy levels

Degeneracy• Electron energy levels crowded together

almost continuous

• All low energy levels are fullPauli Exclusion Principle

• Only place for additional electrons to go is

in high energy levels which meansthey must be moving at close to

thespeed of light

• Adding more mass decreases the volume

• Temperature is same everywhere

Evolution on an H – R DiagramHelium Flash

For low mass stars: a second red giant stage

The second red giant phase begins when the helium fuel in the core is exhausted and core fusion

once again stops

Internal Structure of AGB star

Convection in final stages dredges up products of

earlier fusion and ejects it into space

Thermal Pulses cause whole layers of a star to lift

off

Stars recycle most matter back out into the universe

Planetary Nebulae form from low mass stars

(<8Msun)

In the end, only the cooling core is left: a white dwarf star

Canis Major VisibleX-ray

Colored Card Questions

ClassAction website Stellar Evolution moduleHR Evolutionary TrackHR MovementCore Stages 1Core Stages 2

White dwarf stars are planetary size but stellar

mass

White Dwarf Stars are degenerate matter

Chandrasekhar Limit

1.4 Msun

The evolutionary path of white dwarf stars are cooling

curves

A white dwarf in a binary system can be revived to

become a cataclysmic variable

For stars with mass >8Msun Carbon fusion begins at

600,000,000°

Carbon fusion produces Oxygen, Neon and Magnesium

Higher fusion requires higher temperatures and takes less

time

Internal Structure becomes layered like an onion

Once iron starts to form energy is no longer produced

When the iron

core reaches 1.4 solar masses the end comes swiftly

The End: Photo-disintegration and Reverse Beta Decay

HeEnergyHighFe 4

npe

Type IIa Supernova

Watch Supernova videos