1. Midterm test and marks explored.
Visit Dr. English at Allen 514 on Monday at 3pm to take up your test.
Tests will be kept for 2 weeks.
Join the Star Fleet Academy to prepare for the exam – Tuesdays at noon starting Nov. 4th. Dr. English to express your interest.

2. massive star death (SNe): Chapt 21
Lecture 21 – Stellar Evolution
(Image unknown origin)
Chromosphere in H_alpha and prominences.
Read before class:
Star Birth Chapt 18 and 19
Stellar Evolution M ~1 Msun (PN & WD): Chapt 20
massive star death (SNe): Chapt 21
stellar populations Chapt 23 (p. 587)
Gamma-ray bursts & black holes Chapt 22 –
REVIEW GR model of gravity
ALL NOTES COPYRIGHT JAYANNE ENGLISH
The state of the affairs from the previous class is that we measure arcs on the sky.

3. HR Diagram and Stellar Characteristics.

4. Stars: Luminosity, Temperature and Radius on H-R diagram
position on the H-R diagram depends on mass, composition, and stage of evolution.
lifetime on the MS depends on mass.

5. The majority of stars are in pairs – binary systems.
Stars: Mass
The majority of stars are in pairs – binary systems.
Forbit = Finertia
(r = radius of of the orbit).
Recall we did this to find the mass of planets using their moons. 

6. v = circumference of ellipse/Period of orbit.
Stars: Mass
This can be done for any set of stars – they do not have to be on the main sequence.
Visual binary  r and v
v = distance/time
v = circumference of ellipse/Period of orbit.
Also Kepler’s III Law (book), Doppler shifts & light curves constrain masses.
Exercise

7. Example for mass of 2 stars:

8. Example for mass of 2 stars:

9. Example for mass of 2 stars:

10. Stars: Masses on Main Sequence
Determined from measurements:
M relates to r & L (low mass, low L).
Few percent are giants & supergiants.

11. Stars: Masses on Main Sequence
Empirical relationship for MS.
Relationship between L & M only on MS

12. On the MS, O stars are more massive than M stars
Application:
On the MS, O stars are more massive than M stars
Off the MS, K stars can be either more or less massive than M stars

13. Stars: MS Lifetimes Depend on Mass
Main sequence star:
H burning in core
Energy & radiation
Hydrostatic equilibrium
When the fuel in core is consumed
 no longer hydrostatic equilibrium
 evolves off MS
Most of its life is on MS – what is its MS lifetime?
Hydrostatic equilbrium is the balance between the outward pressure due to radiation and the inward pressure due to gravity.
Mass  amount of fuel available
L  rate at the fuel burns

14. Stars: MS Lifetimes Depend on Mass
Lifetime = tau
fuel & rate are determined by M.
massive star  core high density  higher temperature
 more nuclear reactions
 fuel burns faster.

15. Stars: MS Lifetimes Depend on Mass: Derive tau

16. Stars: MS Lifetimes Depend on Mass
Star P is ten times as massive as star Q. Compared to star Q, Star P has a shorter life time.
Massive stars live fast and die young!
 few massive stars and lots of dwarfs!
exercise!
Sun’s tau ~ 10 * 10**9 yrs & currently 4.5 * 10**9 yr old.

17. Stars: MS Lifetimes Depend on Mass
Star Q has a life time of 10 billion years. What is the life time of star P that has 10 times the mass of star Q.
Substitute in mass of P
and life time of Q
Star Q’s MS lifetime is like our own sun’s.
In (10 Mq) to the third power, each component has the power of 3 applied to it. That is, (10 to the power of 3) times (Mq to the power of 3). Therefore the (Mq to the power of 3) in the numerator and denominator cancel out.
Re-arrange the equation.
The MS life time of star P is only 10 million years!

18. Proxima Centauri with 0.1 solar masses
Exercises:
Practise for:
20 solar masses
Proxima Centauri with 0.1 solar masses
note age of universe is 13.5 * 10**9 yrs

19. Stars: Luminosity, Temperature and Radius on H-R diagram
position on H-R diagram depends on mass, composition, & stage of evolution.
lifetime on MS depends on mass.

20. How stars form:
At the end of this section you will describe to your neighbour the 6 main stages of evolution for a star like our sun, starting with star birth.

21. Star Formation in Galaxies:
HII regions: sites of star formation (SF) – gas converted into stars.
Young stars heat surrounding gas  HII

22. Star Formation: Examples in our Milky Way Galaxy
Interstellar medium (ISM).
HI gas & dust between stars.
dense H gas forms molecular clouds (MC) – traced by CO.

23. Blastwave of supernova. Spiral density wave.
Star Formation:
WRITEN NOTES
Pressure applied to dense, cold ISM clouds causes them to gravitationally collapse & form stars.
Blastwave of supernova.
Spiral density wave.

24. Classic HII region: Orion Nebula.
Star Formation:
Molecular Cloud: CO
& dust
Classic HII region: Orion Nebula.
Several hundred stars forming, + protoplanetary disks (propylds) around 1/3-1/2.

25. Proplyds
Finished here
protostars in centre