Astronomy 535 Stellar Structure Evolution. Course Philosophy “Crush them, crush them all!”...

Astronomy 535Stellar Structure Evolution

Course Philosophy

“Crush them, crush them all!”

-Professor John Feldmeier

Course Philosophy

Contextual stellar evolution– What we see stars doing– The stellar structure that makes stars look

that way– The physical processes determining the

stellar structure– How stars change with time– The impact of stars upon their environment

• Stars as ensembles– Clusters– Stellar populations– Starbursts

• Stellar yields and environment– Luminosity: Interstellar radiation field, heating,

photoionization– Kinetic Energy: Stellar winds, supernovae, feedback– Nucleosynthesis: Chemical evolution

• Evolution of ISM, IGM, gas fraction, composition, star formation, populations, galaxies, baryonic matter in general profoundly depends on stellar evolution

Motivation for studying stellar evolution

My god,it’s full of stars

• Stars as ensembles– Clusters– Stellar populations– Starbursts

• Stellar yields and environment– Luminosity: Interstellar radiation field, heating,

photoionization– Kinetic Energy: Stellar winds, supernovae, feedback– Nucleosynthesis: Chemical evolution




• Fits of models to observations by means of free parameters is standard procedure, but gives unreliable or downright bad results for most applications

• Must be able to predict evolution of a star as a function of mass and composition to high accuracy

• Also necessary to understand individual objects


Quantitative Uncertainties in Yields for Massive Stars

• Luminosity: – factors of 2 by 25 M

– Larger radii, lower Teff, fewer ionizing photons

– IMFs derived from observed luminosity functions

• Kinetic energy– Order of magnitude uncertainties in mass loss rates– complete uncertainty in composition of winds for a given star

• Nucleosynthetic– 2 orders of magnitude in Fe peak abundances from

progenitors, reaction calculations, supernova explosion calculations, etc.

How to study stars

• Too many stellar models are black boxes - tuning a free parameter (i.e. overshooting) to fit one particular observation allows you to predict nothing about other stars

How to study stars


• Stars are not black boxes - including complete physics in a stellar model should give you a correct model

How to study stars


• Stars are not black boxes - including complete physics in a stellar model should give you a correct model

• Stars are plasma physics problems - must account for B fields, ionization, multi-component EOS, & charge effects on reactions, radiation transport, hydrostatics, & dynamics

How to study stars• 3-pronged approach• Theory based on analytical work and simulations• Terrestrial High Energy Density experiments with

lasers and other facilities approximate stellar conditions

• Observational tests of theoretical models identify deficiencies in physics, not fits to free parameters

Syllabus1/11

Intro to classMotivation for studying starsSyllabusTimescales

1/13Equations of hydrodynamicsSound wavesHydrostatic equilibriumMass-Luminosity relations

1/16MLK Holiday

1/18ConvectionWaves

1/20WavesRotation

1/23 **Patrick Leaves for Santa Barbara**EOSOpacitiesAbundances

Syllabus1/25

Nuclear reactionsTYCHO

1/27 The HR diagramCMDsHigh mass vs. low massIntroduce project 1 (MS as f(z))

1/30Pre-MS

2/1Low mass objectsMain sequence startsHW: burning timescales

2/3pp vs. CNOConvection pp vs. CNO all the problems thereof

2/6Probably more convectionRotation

Syllabus2/8

Mass-Luminosity relation & lifetimesCluster agesComposition effectsFun opacity sources

2/10Misc & catch-up

2/13 **Patrick returns from Santa Barbara**Presentations

2/15Presentations

2/17Presentations

2/20Mass lossVery massive starsPop III

Syllabus2/22

Post-MS

H exhaustion

Shell burning

RGB

2/24

3alpha

degeneracy

Tip of RGB

He flash

2/27

Red clump/BHB

Stellar pulsations

Cepheids

kappa mechanism

Syllabus3/1

Double shell burningAGBRatio of BHB/AGB

3/3C stars, extreme pop IIThermal pulses-process

3/6Mass lossPN ejectionWhite dwarfs

3/8Massive starsMass lossWolf RayetsKinetic luminosity & feedback

3/10

3/13 - 3/17Spring Break

Syllabus3/20

Presentations3/22

Presentations3/24

Presentations3/27

Misc. & catch-up3/29

C ignitionneutrino coolingC burning

3/31Ne burningO burningweak interactions

Syllabus4/3

Dynamics of the shellURCAFlame fronts & wierd burning

4/5detailed balance & thermodynamic consistencyQSENSESi burning

4/7Core collapseNuclear reactions

4/10NeutrinosMechanisms

4/12AsymmetriesMixingExplosive nucleosynthesis

4/14alpha-rich freezeoutr-processuncertainties in nucleo

Syllabus4/17

Core collapse typesSpectraLightcurves87A

4/19Type 1aPair instabilityGRBs

4/21GRBscompact objectsCVs & XRBs

4/24 **Patrick leaves for Nepal**Population synthesisStellar pops (Christy?)

Syllabus

4/26

Misc. & catch-up

4/28

Presentations

5/1

Presentations

5/3

Presentations

TimescalesGravitational timescale

Hydrodynamic timescale

Note that in hydrostatic equilibrium

Hydrostatic adjustment timescale at 1M

White Dwarf: few s

Main sequence: 27 min (sun)

Red Giant: 18 days

For most phases HSE << evol

€

ff =R

g

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 2

=R3

GM

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 2

€

hyd =cs

R; cs

2 =∂P

∂ρS

€

−1

ρ

dP

dr= −

GM

r2

⇒P

ρ≈

GM

R

⇒ τ HSE ≈ τ hyd ≈ τ ff

Timescales

Kelvin-Helmholtz (Thermal)

For sun KH ~ 10 Myr

€

KH =Egrav

L

Egrav ≈Gm 2

r ≈

GM 2

2R; m =

M

2,r =

R

2

Egrav =Gm

rdm

0

M

∫

τ KH ≈GM 2

2RL

Timescales

Nuclear or Evolutionary Timescale

Quick ‘n’ dirty solar lifetime estimate

QHHe=6.3x1018erg g-1 (0.7% of rest mass energy)

assume 10% of H gets burned

Enuc = 2x1033g x 0.1 x 0.007 x c2 = 1.26x1051 erg

L = 4x1033 erg

3x1017 s = 10 Gyr

€

nuc =Enuc

L

Astronomy 535 Stellar Structure Evolution. Course Philosophy “Crush them, crush them all!”...

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