ASTR 400/700:
Stellar Astrophysics
Stephen Kane
A700 Oral Exam
●
Dec 6:
- Archana Dobaria
“Stellar Formation in Different Galaxies”
- Yuzo Ishikawa
“Understanding the Properties and Formation of
Black Holes”
●
Dec 8:
- Daniel McKeown
“Stellar Content in the Illustris Simulation”
- Heechan Yuk
“Structures and Mechanisms of Supernovae”
Upcoming schedule
●
Nov 3: Stellar evolution (Chapter 13)
●
Nov 8: Stellar pulsations (Chapter 14)
●
Nov 10: Stellar pulsations (Chapter 14)
●
Nov 15: Supernovae (Chapter 15)
●
Nov 17: Stellar remnants (Chapter 17)
●
Nov 29: Jonathan Fortney visit
●
Dec 1: Summary
Stellar Models:
The complete set of differential equations describing the interiors
of stars is therefore:
Equation of Continuity:
Hydrostatic Equilibrium:
Energy Generation:
Temperature Gradient:
dM ( r )
= 4π r 2 ρ
dr
dP − G M ( r ) ρ
=
dr
r2
dL
= 4π r 2 ρ ε
dr
− 3 κ ρ Lr
 dT 

 =
3
2
dr
4
ac
T
4
π
r

 rad
− 1 GM ( r )
 dT 

 =
2
dr
C
r

 ad
P
Stellar Evolution
Chapter 13.1, 13.2, 13.3
Width on the Main Sequence
•
Observed spread in H-R diagram
– Measurement error
– Differing Chemical compositions
– Different stages in evolution
Evolution on the Main Sequence
Development of an isothermal
core:
− 3 κ ρ Lr
 dT 

 =
3
2
 dr  rad 4ac T 4π r
Zero-Age
Main
Sequence
(ZAMS)
MS evolution
Lr = 0 => T = const.
The Schoenberg-Chandrasekhar
Limit
•
•
Isothermal core
No fusion…No energy
production
•
How much can it stand?
The Final Breaths of Sun-Like Stars:
Planetary Nebulae
Remnants of stars with ~ 1 – a few Msun
Radii: R ~ 0.2 - 3 light years
Expanding at ~10 – 20 km/s (← Doppler shifts)
Of order 10,000 years old
Have nothing to do with planets!
The Helix Nebula
Planetary Nebulae
The Helix Nebula
The Ring Nebula
The Dumbbell Nebula
Planetary Nebulae
Often asymmetric, possibly due to
• Stellar rotation
• Magnetic fields
• Interaction with ISM
Stellar Populations
Population I:
Young stars (< 2 Gyr);
metal rich (Z > 0.03);
located in open clusters in spiral arms
and disk
Population II:
Old stars (> 10 Gyr);
metal poor (Z < 0.03);
located in the halo (globular clusters) and
nuclear bulge
Evidence for Stellar Evolution:
HR Diagram of the Star Cluster M 55
High-mass stars
evolved onto the
giant branch
Turn-off point
Low-mass stars
still on the main
sequence
The Algol System
The binary star Algol consists of a 3.7MSun mainsequence star and a 0.8MSun subgiant star.
What’s strange about this pairing?
How did it come about?
Evolution of binary systems:
Gravitational field of the stars
combined with the rotation of the
system define the “Roche surface.”
Matter inside a star’s Roche
surface is gravitationally bound to
the star, but…
Two ways in which matter can be
transferred through L1;
1. Stellar wind (slow)
2. If the star expands past its
Roche surface (rapid)
Matter can be transferred from
one star to the other through the
inner Lagrangian point.
The “Algol paradox”
This would
correspond to the
Algol system
Q: How can we explain the Algol paradox?
Mass transfer explains this paradox!
The less massive star became a
giant while the more massive star
remained on the mainsequence!?! τ = 1
2.5
M