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

Colored Card Questions ClassAction website ISM & Star Formation module Star Formation Masses Emission Nebula Energy Source Stellar Properties II module Stellar Parameters HR 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

Additional Fusion involving He 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 full Pauli Exclusion Principle Only place for additional electrons to go is in high energy levels which means they must be moving at close to the speed of light Adding more mass decreases the volume Temperature is same everywhere

Evolution on an H – R Diagram Helium 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 (<8M sun )

In the end, only the cooling core is left: a white dwarf star Canis Major Visible X-ray

Colored Card Questions ClassAction website Stellar Evolution module HR Evolutionary Track HR Movement Core Stages 1 Core Stages 2

White dwarf stars are planetary size but stellar mass

White Dwarf Stars are degenerate matter Chandrasekhar Limit 1.4 M sun

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 >8M sun 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

Type IIa Supernova Watch Supernova videos