Lecture 1: Introduction. Literature: Onno Pols chapter 1, Prialnik chapter 1

Transcription

1 Lecture 1: Introduction Literature: Onno Pols chapter 1, Prialnik chapter 1!"

2 Goals of the Course! Understand the global characteristics of stars! Relate relevant microphysics to the global stellar characteristics! Understand stellar evolution and the factors driving it! Link stellar zoo to stellar evolutionary phases! Understand the role of stars in the elemental composition of the Universe

3 Primer! Go back to introduction to astronomy & read the literature for this chapter, focusing on:! What is a star?! What can we learn from observations?! How can we measure stellar parameters?! Distance, mass, radius, surface temperature, luminosity, composition, surface gravity, rotaiton velocity, surface magnetic field! Mass-Luminosity relationship! Hertzsprung-Russell diagram! Young open clusters, old globular clusters, field stars (magnitude limited samples, distance limited samples)

4 ! Sun 1. Some facts about stars a) Mass, luminosity, radius, & effective temperature! M! = g! R! = cm! L! = erg/sec ρ O! = g/cm 3! Stars! Apparent magnitudes & colors! Spectroscopy & Stellar atmosphere models: L, T eff, R! Certain binaries, M 10 L L O M M R R 1500 O O L = 4π R 2 4 σ T eff eff ρ ρ O T K T eff,o = 5780 K

5 b) Hertzsprung-Russell diagrams for star clusters

6 Gaia s 1st HR Diagram

7 Nomenclature H-R diagram AGB stars HB Giants Extreme HB Blue stragglers Turnoff point Subgiants MS WDs

8 Composite H-R Diagram for Star Clusters Aim is to understand: # Position of stars in this diagram # Evolution of stars in this diagram # Differences between cluster HRD s

9 c) Mass-luminosity relation Measure individual masses for double-lined eclipsing variables Popper 1980 ARA&A Martin & Mignard 1998 AA 330, 585 Recent measurements: L L O = 0.66( M M O ) M O M 0.5M O 0.92( M M O ) M O M 40M O 300( M M O ) 2 40M O M 130M O

10 d) Stellar Evolutionary Tracks! What causes evolution & what does it depend on?! How does the internal structure change?

11 e) Pulsational variables! What can pulsational variables tell us about stellar structure and evolution?! Dynamical time scales! Radial and non-radial modes! Instability strip

12 f) Astroseismology: Internal Structure Astroseismology # Study of oscillations of stellar surface # What can astroseismology tell us about the internal structure and evolution of stars

13 g) The Stellar Zoo! Low mass stars! Dwarfs! Sub-giants! Symbiotic stars! Supernova type Ia! Nova! Giants! Asymptotic Giant Branch stars! Horizontal Branch & red clump stars! Blue stragglers! Carbon stars & S-stars! White dwarfs! Planetary nebulae! Brown dwarfs! Cataclysmic variables! Massive stars! Luminous Blue variables! Supergiants! Hypergiants! Wolf-Rayet stars (WN, WC)! B[e] stars! Supernovae! Neutron stars! Stellar black holes

14 What causes the stellar zoo?! Stellar evolution! Mass loss! Diffusion & radiative levitation! Pulsations! Mixing! Magnetic fields! Binary evolution & mass transfer! Coalescence! Rotation

15 h) Nucleosynthesis Cosmic abundances of most of the elements produced by nucleosynthesis in stars (except H, He, and Li, Be, B) Mass number of element

16 i) Some questions! What generates different classes of stars in HR Diagram?! What causes the mass-luminosity relation?! What is the internal structure of stars?! What sets the range of stellar masses?! What are the final stages of stellar evolution?! How do stars produce heavy elements?! Why do some stars pulsate?

17 j) Course Requirements! This is a demanding course! Interdisciplinary: astronomy, thermodynamics, statistical physics, nuclear physics, radiative transfer, & atomic physics! Participate in lectures. Take notes and work them out immediately. Read the book. Ask questions!! Work out the exercises on the web & book! Assignment: Calculate simple stellar model and write a short and coherent (!) report! Have to pass the assignment to take the exam but get bonus point!! Lectures every week, Wednesdays 3:45-5:30pm! Office hours: Xander: Friday 11:00-12:00; Ann-Sofie: Tuesday 3-5pm! Written exam, May 27, 2015, 10am 1pm

18 k) Summary of characteristics! Star is spherically symmetric! Physical quantities are function of r only! Ignore effects of rotation and magnetic fields! Star is in hydrostatic equlibrium! Energy sources:! Gravitational energy, nuclear energy, thermal energy! Energy transport by! Radiation, convection, conduction! Chemical composition! Initially homogeneous but changes in the core/shells due to nucleosynthesis & envelope due to convection

19 l ) Outline of course # Derivation of four equations of stellar structure - Mass continuity ( 2) & Hydrostatic equilibrium ( 2) - Thermal equilibrium ( 3) - Energy transport by radiation ( 3.1) or convection ( 3.3) # Required physics - Thermodynamics ( 3.2) - Equation of state including degeneracy, and internal energy ( 3.2) - Opacity of stellar material ( 3.4) - Nuclear energy generation ( 4.1) & burning stages ( 4.2) # Eqns. Of SS ( 5.1), solution methods (5.4), polytropes ( 5.2) and simple models ( 5.3) # Overview of stellar evolution ( 6) # Pulsations ( 7.1) & Astroseismology ( 7.2)