:: Extra Credit ::

20% on HW 8

:: Submit ::

1) sketch & describe what’s observed with telescope

2) signature of TA

mitchell institute

star partyInterested in the night sky?

Always wanted to look through a telescope?

For more in format ion, contac t Dr . Jenni fer Marsha l l

marsha l l@phys ics . tamu.edu

Join the Texas A&M University Astronomy Group

for a star party!

Spring 2017 Star Party Dates:

Open to all: No need to RSVP in advance

Weather permitting—check website for updates:instrumentation.tamu.edu/starparty.html

In front of Sbisa Dining Hall

February 6, 7-9pmMarch 6, 7-9pm

April 10, 8-10pm

Simpson Drill Field Review StandJanuary 25, 7-9pmFebruary 21, 7-9pmMarch 28, 8-10pmApril 25, 8-10pm

Which of these stars is hotter ?

A. They are the same temperature

B. Star E is hotter

C. Star C is hotter

Poll Question:

Post Main Sequence: Solar Mass

How our Sun evolves off the Main Sequence to end up as a White Dwarf (degenerate Carbon-Oxygen core)

As a red giant, the outer envelopes of our Sun will be made of:

A. mostly Helium and a bit of Hydrogen with other trace nuclei

B. about half Helium and half Hydrogen with some trace nuclei

C. mostly Hydrogen and some Helium with other trace nuclei

Poll Question:

Helium Flash & BurningHelium Ignition:Once the He core reaches high enough density and temperature, He core burning starts.

Thermal pressure becomes dominate again.

Helium Burning StarSupported by thermal pressure so returns to stable equilibrium (Thermostat works again for ~100 million years)

Helium Burning Star

Horizontal Branch: He burning in the star’s core

No More Helium in Core ?

Asymptotic Giant Branch: Becoming a Red Giant again

When He in the Core Runs OutShell-burning = Hydrogen and Helium burning shells(Carbon-Oxygen ash core)

Pulsations due to double-shell burning eventually blow off the star’s outer layers to form a planetary nebula.

Helix NebulaPlanetary Nebula of Sun-like Star

Sun’s Evolution into White Dwarf

Low-Mass Star Maintains Gravitational EquilibriumWhat balances gravity? Electron Degeneracy!

Life as a High-Mass Star

• What are the life states of a high-mass star?• How do high-mass stars make the elements necessary for life?• How does a high-mass star die?

H-R Diagram Review

Post Main Sequence Tracks

5 solar mass star

Post Main Sequence

High mass:

Low mass:

Helium Capture

High-mass stars first make heavier elements by fusing with Helium:

Advanced Nuclear BurningAs temperature & density increase, fusing of heavier nuclei begins:

Nucleosynthesis

Nucleosynthesis

Hydrogen: 20 MyrHelium: 2 Myr

Carbon: 380 yearsNeon: 1.1 years

Oxygen: 8 monthsSilicon: 1 day

Creating heavy elements (stars of at least 8 Msun)

High-Mass StarsInternal changes have external consequences: 1) Hydrogen shell burning leads to expanded photosphere (red giant phase).2) Helium ignition in core leads to contraction of photosphere (horizontal branch)

3) Shell burning of multiple nuclei leads to an Iron core, but it’s not possible to release energy by fusing any nuclei heavier than Iron.

Question

Which of these elements cannot be made in the core of a star?

A. Uranium

B. Iron

C. Carbon

D. Oxygen

Crab Nebula

Close Binary Star Systems

Transferring Mass Between Close Stars

Close Binary Star Systems

What happens as both stars evolve?

Bigger

Smaller

Star 1 is more massive than Star 2, thus Star 1 evolves more quickly.

White Dwarf SupernovaeWhat happens to an accreting white dwarf once it reaches 1.4 solar masses?

Supernovae Lightcurves

Question

What is left behind after a white dwarf explodes in a Type I supernova?

A. a smaller white dwarf

B. a black hole

C. a pulsar

D. nothing

Tutorial: Star Formation

Get together in small groups of 2-3 people.

As a group, work through as much of the tutorial as you can. The tutorial is yours to keep as a study guide.

Ask us questions !

Example Problem

The Sun generates 3.83x1026 Joules per second.How much mass does the Sun lose per second ?