StellarStellar PhysicsPhysics
Peter Woitke
St Andrews University
INSET, Kirkcaldy High School, November 13th, 2015 talktalk outlineoutline 1. the sun 2. basic stellar properties – Teff, Rstar, Lstar , apparent and absolute brightness 3. stellar atmospheres – why absorption lines? – spectral classification 4. stellar structure – nuclear burning reactions 5. Hertzsprung-Russel diagram – main sequence stars – why on a line? – dwarfs and giants 6. stellar evolution 7. cosmic cycle of matter – winds, bubbles, planetary nebulae, supernovae, ... 8. planets – habitability
talktalk outlineoutline 1. the sun 2. basic stellar properties – Teff, Rstar, Lstar , apparent and absolute brightness 3. stellar atmospheres – why absorption lines? W A R N I N G – spectral classification I will ask you some questions!
– to prevent you from falling asleep
4. stellar structure – you might want to ask those – nuclear burning reactions questions to your pupils ... 5. Hertzsprung-Russel diagram – main sequence stars – why on a line? – dwarfs and giants 6. stellar evolution 7. cosmic cycle of matter – winds, bubbles, planetary nebulae, supernovae, ... 8. planets – habitability
1.1. thethe sunsun
21.1 nm 9.4 nm extreme Soft X-ray ultraviolet 6.3 x 106 K 2.0 x 106 K
170 nm 450 nm far ultraviolet optical 5 x 103 K 5 x 103 K
The Dynamic Sun
credit: NASA solar flares & coronal mass ejections
credit: Solar Dynamics Observatory, NASA solar flares & coronal mass ejections
2.2. basicbasic stellarstellar propertiesproperties stellar radius Rstar: radius from which photons can freely escape into space
optical depth
on optical path to observer
( what is the problem with this definition? ) stellar luminosity Lstar: total energy production rate [W]
2 spectral flux Fλ: flux of photon energy in λ … λ+dλ through area per dλ [W/m /A]
effective temperature Teff: measure of total flux F [W/m2] at surface Rstar (analog to black-body radiation)
Stefan-Boltzman law:
– giants are luminous – observable flux ~ 1/r2 (r = distance d)
( is Teff the “surface temperature” T(Rstar)? ) 2.2. basicbasic stellarstellar propertiesproperties IIII magnitude mλ: (historic) log-measure of observed flux Fλ at wavelength λ
A B A B – example: Fλ = 10 Fλ => mλ = mλ 2.5
absolute magnitude Mλ: magnitude of star at standard distance 10 pc, zeropoint for the magnitude scale is Vega (all λ)
2 – use Fλ ~ 1/d to derive – mλ – Mλ is called distance module (why?)
3.3. stellarstellar atmospheresatmospheres
basic stellar atmosphere model
basic stellar atmosphere model
Why do stars have absorption lines?
Joseph von Fraunhofer 1787 – 1826
sodium absorption spectrum Fraunhofer lines of the sun
– what did Fraunhofer actually prove ? –
Why do stars have absorption lines? ← stellar atmosphere →
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λ λ
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Spectral Classification eff
Oh Be A Fine Girl Kiss Me Spectral Classification
Oh Be A Fine Girl Kiss Me L T Y 4.4. stellarstellar structurestructure
● Energy transport through convection and radiative transfer (as in stellar atmospheres)
● Additional energy production due to nuclear reactions → time-dependent problem → stellar evolution
5.5. Hertzsprung-RusselHertzsprung-Russel diagramdiagram
why does the main sequence form a line in the HR-diagram?
6.6. stellarstellar evolutionevolution
tracks for massive stars
7.7. cosmiccosmic cyclecycle ofof mattermatter
Red Giant Winds
AGB (carbon) star IRC+10216, brightest object at λ = 10 micro-meter on the sky (after the sun), mass loss rate K-band interferometric observations, evolution 1995-2001 (Weigelt et al. 2002, A&A 392, 131)
hydro-simulation (Woitke 2006, A&A 452, 537) including dust formation and radiation pressure on dust.
Movie shows the degree of condensation around the star.
Planetary Nebulae
Wind bubbles Sharpless 308, diameter = 3x full moon, central Wolf-Rayet star, M = 45 Msun, d = 3 pc
Crescent Nebula, surrounding the Wolf-Rayet star WR136
NGC 7635 “bubble nebular”, Casiopeia, central O-star, d = 4 kpc
Supernova remnants Crab nebula, 1054 discovered by chinese astronomers, 2R ~ 3pc, pulsar in centre SN 1987A, 30 yrs old d = 50 kpc (X-ray = blue, visible = green, mm = red) type II, but no neutron star found
Tycho Brahe's Supernova 1572, no central object, type Ia
Kepler's Supernova 1604, d = 6 kpc, peak brightness ~ Venus Supernova remnants
Cygnus loop (Veil nebula), 7500 years old, diameter ~ 5x full moon, d = 0.5 kpc, peak luminosity was ~ full moon 8.8. planetsplanets
8.8. planetsplanets
from stars to planets
What do you need to make a planet habitable?
What do you need to make a planet habitable?
Solar irradiation provides right amount of heat … and … non-equilibrium conditions
liquid water … and … an atmosphere
What do you need to make a planet habitable?
What do you need to make a planet habitable?
… and …
a magnetic field to keep its atmosphere What do you need to make a planet habitable?