The Present and Future Sun & the s-Process
Brian Fields U. of Illinois TALENT School, MSU, May 2014 The pp-II, pp-III Chains
Other main pp chains: different 3He fate 7Be branching key: e capture rate ∼ 1000× p capture rate • 7Be: 15% of ν production • 8B ∼ 0.02% of ν production The CNOThe Cycle CNO Cycle
pre-existing C, N, O act as 4p→4He catalyst + 12 (p,γ) 13 e νe 13 C → N → C (p, α) ↑↓(p, γ) + 15 e νe 15 (p,γ) 14 N ← O ← N
Coulomb barriers high (Z =6, 7, 8): need high T to go
13 c ⇒ CNO cycle minor in Sun (CNO →1.6% L() > but main H-burner for M ∼ 1.5M( Testing the Nuclear-Powered Sun: Solar Neutrinos StandardSolar Solar Neutrino Neutrino Production Production Total SSM Flux 10 −2 −1 Rxn Eν,max = Q !Eν" Φν (10 ν cm s ) pp→deν 0.420 MeV 0.265 MeV 6.0 gs 7Be e→7Li ν lines: 7Li =0.861MeV;7Li∗ =0.383MeV 0.47 8B→8Be e ν 17.98 MeV 9.63 MeV 5.8 × 10−4
Q: Why are the 7Be neutrinos monoenergetic?
www: Bahcall neutrino spectrum
pp neutrinos largest flux, but low energies 7 8 Be neutrinos monoenergetic, strong ∼ Tc dependence 8 20 B neutrinos continuum, ultrastrong ∼ Tc dep 2 What should this mean for production vs radius? www: Bahcall fig of production vs R StandardSolar Solar Neutrino Neutrino Production Production Total SSM Flux 10 −2 −1 Rxn Eν,max = Q !Eν" Φν (10 ν cm s ) pp→deν 0.420 MeV 0.265 MeV 6.0 gs 7Be e→7Li ν lines: 7Li =0.861MeV;7Li∗ =0.383MeV 0.47 8B→8Be e ν 17.98 MeV 9.63 MeV 5.8 × 10−4
Q: Why are the 7Be neutrinos monoenergetic?
www: Bahcall neutrino spectrum
pp neutrinos largest flux, but low energies 7 8 Be neutrinos monoenergetic, strong ∼ Tc dependence 8 20 B neutrinos continuum, ultrastrong ∼ Tc dep 2 What should this mean for production vs radius? www: Bahcall fig of production vs R Standard Solar Neutrino Production Total SSM Flux 10 −2 −1 Rxn Eν,max = Q !Eν" Φν (10 ν cm s ) pp→deν Solar0.420 MeV Neutrino 0.265 MeV Production 6.0 Standardgs Solar Neutrino Production 7Be e→7Li ν lines: 7Li =0.861MeV;7Li∗ =0.383MeV 0.47 8B→8Be e ν 17.98 MeV 9.63 MeVTotal 5.8 × SSM10−4 Flux 10 −2 −1 Rxn Eν,max = Q !Eν" Φν (10 ν cm s ) pp→deν 0.420 MeV 0.265 MeV 6.0 gs Q: Why7Be e→ are7Li theν lines:7Be 7neutrinosLi =0.861MeV; monoenergetic?7Li∗ =0.383MeV 0.47 8B→8Be e ν 17.98 MeV 9.63 MeV 5.8 × 10−4 www: Bahcall neutrino spectrum Q: Why are the 7Be neutrinos monoenergetic?
pp neutrinos largest flux, but low energies www: Bahcall neutrino spectrum 7 8 Be neutrinos monoenergetic, strong ∼ Tc dependence 8 20 B ppneutrinosneutrinoscontinuum,largest flux, ultrastrong but low energies∼ Tc dep 7 8 2 Be neutrinos monoenergetic, strong ∼ Tc dependence What8 should this mean for production vs radius?20 B neutrinos continuum, ultrastrong ∼ Tc dep www: Bahcall fig of production vs R 2 What should this mean for production vs radius? www: Bahcall fig of production vs R Standard Solar Neutrino Production Total SSM Flux 10 −2 −1 Rxn Eν,max = Q !Eν" Φν (10 ν cm s ) pp→deν Solar0.420 MeV Neutrino 0.265 MeV Production 6.0 Standardgs Solar Neutrino Production 7Be e→7Li ν lines: 7Li =0.861MeV;7Li∗ =0.383MeV 0.47 8B→8Be e ν 17.98 MeV 9.63 MeVTotal 5.8 × SSM10−4 Flux 10 −2 −1 Rxn Eν,max = Q !Eν" Φν (10 ν cm s ) pp→deν 0.420 MeV 0.265 MeV 6.0 gs Q: Why7Be e→ are7Li theν lines:7Be 7neutrinosLi =0.861MeV; monoenergetic?7Li∗ =0.383MeV 0.47 8B→8Be e ν 17.98 MeV 9.63 MeV 5.8 × 10−4 www: Bahcall neutrino spectrum Q: Why are the 7Be neutrinos monoenergetic?
pp neutrinos largest flux, but low energies www: Bahcall neutrino spectrum 7 8 Be neutrinos monoenergetic, strong ∼ Tc dependence 8 20 B ppneutrinosneutrinoscontinuum,largest flux, ultrastrong but low energies∼ Tc dep 7 8 2 Be neutrinos monoenergetic, strong ∼ Tc dependence What8 should this mean for production vs radius?20 B neutrinos continuum, ultrastrong ∼ Tc dep www: Bahcall fig of production vs R 2 What should this mean for production vs radius? www: Bahcall fig of production vs R StandardStandard Solar Solar Model Model PredictionsPredictions
What are key SSM ν ingredients, predictions?
• time variations: at source? in detectors?
• L! fixes what?
7 8 • what connection between Φν( Be) andΦν( B)?
• ν spectra: determined by what? 3 Solar NeutrinoSSM Predictions Predictions
SSM Key Predictions:
• at source: steady νe flux from Sun
• elliptical Earth orbit → annual flux variation ∆Φν/Φν " 2δr⊕/r⊕ ∼ 4e⊕ ∼ 7%
• pp flux ∼ fixed by L%
7 8 7 8 • Be, BfluxT -dep, but Φν( Be) > Φν( B)
4 • neutrino spectra fixed by β decay indep of solar model (since Tc,% ∼ 1keV & Qnuke) SolarSolar Neutrino Neutrino Experiments Experiments
Original motivation (Davis, Bahcall): • confirm nuke energy generation • measure T!,c
Facts of life: 1. ν →small σ < 2. Eν ∼ few MeV → large natural background e.g., radioactivity, cosmic ray muons
Q: what is needed for neutrino observatory? 5 NeutrinoNeutrino Observatories: Observatories: Design Design Requirements Requirements
1. Large detector. −44 2 ν-nucleus absorption σνA ∼ 10 cm −36 −1 ⇒ event rate per target Γν(A)=ΦνσνA ∼ 10 s Solar Neutrino Unit:1SNU=10−36 event s−1 target−1 > −1 −5 −1 Want net rate R = NtargΓ ∼ 1day ∼ 10 s 31 ⇒ Need Ntarg = R/Γ ∼ 10
9 A A M = AmuN ∼ 10 g ∼ kiloton targ targ !50" !50" big!
2. Go underground.
6 “Clean” lab, low-background material RadiochemicalRadiochemical Experiments: Experiments: Chlorine Chlorine
HomestakeHomestake Mine Mine:Lead, SD, USA: 1967-1995 www:– Lead, Homestake, SD 1967-1995 note Ray Davis Ray Davis target: chlorine (cleaning fluid!, 0.61 kton) 37 37 & John Bahcall process: Cl + νe→ Ar + e (endothermic) threshold: ν must supply |Q| =0.814 MeV ⇒ only measure 7Be, 8B νs procedure: cycle fluid → filter, collect 37Ar atoms: ∼ few/week!
Measure:
Γobs =2.56 ± 0.16 ± 0.16 SNU (1) Compare to SSM prediction: Γ obs =0.33 ± 0.03 ± 0.05 $ 1! (2) Γ 7 SSM Only see ∼ 1/3 of predicted flux! ⇒original Solar ν problem WaterWater CerenkovCerenkovˇ Experiments Experiements
target: water process: electron scattering νe→νe > Infor praiseEν ∼ of0.5MeV,recoilelectron Water Cerenkovˇ ve ∼ c In praise of Water Cerenkovˇ •Indetect praise neutrinos of Water inCerenkovˇ “real time” • detect neutrinos in “real time” but in water, refactive index n =1.34 ⇒ ve > c/n • Edetecte → ν neutrinosenergyenergy →spectrumspectrum in “real time” emit• Ee “sonic→ ν boom”→ photons: Cerenkovˇ radiation • •coneEcone→ orientation orientationν energy→→→ν directionspectrumν direction info! info! “opticale shock wave,” cone of light cone orientation direction info! •cone opening angle depends→ ν on ve → Ee Super-KamiokandeSuper-Kamiokande.KamiokaMine,Japan:1996-.KamiokaMine,Japan:1996- www: Super-K image www:www: Super-K Super-K events image Super-KamiokandeSuper-K fortune cookie .KamiokaMine,Japan:1996- Super-K fortune cookie www:direction: Super-KνspointbacktoSun(check) image 9 Q: advantages of water Cerenkovˇ vs radiochemical? direction:Super-Kwww: Neutrino fortuneνspointbacktoSun(check) image cookie of the Sun www:eν elastic Neutrino scattering image in pure of the water Sun direction: νspointbacktoSun(check) eνEnergyelastic threshold: scattering 5 MeV in pure⇒ see water only 8B νs www: Neutrino image of the Sun Energyspectrum: threshold: shape matches 5 MeV SSM⇒ see only 8B νs ...but Φ(8B) /Φ(8B) ∼ 50%! 10 spectrum:eν elastic scattering shapeSK matchesSSM in pure SSM water Solar ν problem #3 8 ...butEnergyΦ( threshold:8B) /Φ(8B) 5 MeV∼⇒50%see! only B νs
10 SK SSM Solarspectrum:ν problem shape #3 matches SSM ...but Φ(8B) /Φ(8B) ∼ 50%!
10 SK SSM Solar ν problem #3 SudburySudbury Neutrino Neutrino Observatory Observatory (SNO) (SNO)
Sudbury, Ontario, Canada: 1999- ultrapure heavy water: D2O
Rxns: − νe + d→e + p + p Feynman diagram Charged current: νe only Threshold: 1.4 MeV → 8Bonly
# νx + d→νx + p + n Feynman diagram ν# flavor = ν flavor Neutral current: all flavors Threshold: 2.2 MeV → 8Bonly 11 also: Salt phase – dissolve NaCl in SNO tank big σ for 35Cl(n, γ)36Cl → improved NC SNOSNO Results Results
Charged-current (νe flux): SNO +0.08 +0.06 6 −2 −1 ΦCC = 1.59−0.07 (stat)−0.08 (sys) × 10 ν cm s (6) ! " Neutral-current (all-ν flux):
SNO 6 −2 −1 ΦNC = [5.21 ± 0.27(stat) ± 0.38(sys)] × 10 ν cm s (7)
Thus we have SNO ΦCC νe flux SNO = = 0.306 ± 0.026(stat) ± 0.024(sys) (8) ΦNC all ν flux
12 Which means... Implications:Implications: New New Neutrino Neutrino Physics!Physics
The Sun makes only νe Q: why? e.g., why not νµ? → if no new ν physics, only νe at Earth → predict ΦCC(νe)=ΦNC(νx)
SNO measures ΦCC(νe) > ΦNC(νx)! with very high confidence! non-νe flux arriving in detector!
Abigdeal: • demands new neutrino physics
13 • indep. of detailed solar model Nobel Prize 2002
Ray Davis Jr., USA
Masatoshi Koshiba, Japan
“for the detection of cosmic neutrinos”
UofI Astro Society, March 13 2007 The Future Sun Beyond the Main Sequence
Main seqeunce: hydrogen burning ‣ M<1.1 Msun: pp chain Evolution of Massive Stars ‣ M>1.1 Msun: CNO in our context, massive core-collapse: M > 8 10M → ∼ − $ Main sequence: Q: what happens when Hshort exhausted MS lifetime in (< core?30 Myr) • 7 ∼ Tc 3 10 K • ∼ × burn p 4He via CNO cycle when core is all He “ash”:• → ‣ no source of thermonuclearwhen energy H exhausted: = heat homologous contraction ‣ loss of pressure support • Hshellburningbegins red giant heat core ignite... ‣ core contracts • → • → 12
‣ compression heats core10 untilHe burning burn He:via 3α C → a3-bodyreactionQ: how might this work The Red Giant Phase: 6 Billion Years The Red Giant Phase: 6 Billion Years
When the hydrogen is gone in the core, fusion stops The Red Giant Phase: 6 Billion Years
When the hydrogen is gone in the core, fusion stops Equilibrium is shot. The Red Giant Phase: 6 Billion Years
When the hydrogen is gone in the core, fusion stops Equilibrium is shot. Core starts to contract under its own gravity The Red Giant Phase: 6 Billion Years
When the hydrogen is gone in the core, fusion stops Equilibrium is shot. Core starts to contract under its own gravity This contracting heats the core, and hydrogen fusion starts in a shell around the core The Red Giant Phase: 6 Billion Years The Red Giant Phase: 6 Billion Years
Energy is released, expands envelope ⇒ Lum. increases! The Red Giant Phase: 6 Billion Years
Energy is released, expands envelope ⇒ Lum. increases! As the envelope expands, it cools – so it becomes a red giant. The Red Giant Phase: 6 Billion Years
Energy is released, expands envelope ⇒ Lum. increases! As the envelope expands, it cools – so it becomes a red giant. This process takes 50-100 million years.
Cartoon version (way too fast) http://www.youtube.com/watch?v=fOM7DMxOiAk&feature=related Contraction Junction
• In core, contraction increases density • Hotter, and hotter, and hotter until… Contraction Junction
• 100 million degrees • Core heats ⇒ He fusion ignites • He ⇒ C & O The Horizontal Branch The Horizontal Branch
• Stars in helium burning phase: – “horizontal branch” The Horizontal Branch
• Stars in helium burning phase: – “horizontal branch” • Helium burning stabilizes the core – but destabilizes outer layers! The Horizontal Branch
• Stars in helium burning phase: – “horizontal branch” • Helium burning stabilizes the core – but destabilizes outer layers! • The outer envelope shrinks, heats up, and dims slightly The Horizontal Branch
• Stars in helium burning phase: – “horizontal branch” • Helium burning stabilizes the core – but destabilizes outer layers! • The outer envelope shrinks, heats up, and dims slightly • But helium doesn’t last very long as a fuel – Horizontal branch lifetime is only about 10% that of a star’s main sequence lifetime – Our Sun will burn helium for about a billion years When helium runs out…
Star expands and cools again into a red giant, now with two fusion shells! When Helium Runs Out… 7.8 Billion Years from Now When Helium Runs Out… 7.8 Billion Years from Now
• Fusion in the core stops – the helium has been converted to carbon and oxygen When Helium Runs Out… 7.8 Billion Years from Now
• Fusion in the core stops – the helium has been converted to carbon and oxygen • Stellar core collapses under its own gravity again When Helium Runs Out… 7.8 Billion Years from Now
• Fusion in the core stops – the helium has been converted to carbon and oxygen • Stellar core collapses under its own gravity again • Inner shell develops, starts fusing helium to carbon When Helium Runs Out… 7.8 Billion Years from Now
• Fusion in the core stops – the helium has been converted to carbon and oxygen • Stellar core collapses under its own gravity again • Inner shell develops, starts fusing helium to carbon • outer hydrogen burning shell remains When Helium Runs Out… 7.8 Billion Years from Now
• Fusion in the core stops – the helium has been converted to carbon and oxygen • Stellar core collapses under its own gravity again • Inner shell develops, starts fusing helium to carbon • outer hydrogen burning shell remains • Star starts to grow and cool again: asymptotic giant branch End Game
• At these last stages, the Sun will likely oscillate in size and temperature. • The two burning shells are unstable and their oscillations lead to a “Superwind” • Outer layers of the red giant star are cast off – Up to 80% (at least 50%) of the star’s original mass NGC 2440 – carries away all but the innermost material of the star – including all of the new elements created there: helium, carbon End Game
• The core remains, made of carbon/oxygen “ash” from helium fusion T > 200,000 K – The core is very hot, above 200,000 K – laid bare, and seen as “white hot” • Ultraviolet radiation from the core ionizes the cast off outer layers – Becomes a planetary nebula NGC 2440 – Unfortunate name (nothing to do with planets), but some of the most beautiful objects in the sky. Planetary Nebulae Solar System Abundances Progress Report Solar System Abundances Progress Report
Q: what do we now understand Solar System Abundances Rosetta Stone of Nuclear Astrophysics sums cumulative nucleosynthesis up to birth of solar system progress so far: Solar System Abundances Rosetta Stone of Nuclear Astrophysics sums cumulative nucleosynthesis up to birth of solar system progress so far: ‣ zig-zag: odd-even effect in nulcear binding Solar System Abundances Rosetta Stone of Nuclear Astrophysics sums cumulative nucleosynthesis up to birth of solar system progress so far: ‣ zig-zag: odd-even effect in nulcear binding ‣ 4He, 12C, 14N: contributions from H and He burning in low/ intermediate mass stars Solar System Abundances Rosetta Stone of Nuclear Astrophysics sums cumulative nucleosynthesis up to birth of solar system progress so far: ‣ zig-zag: odd-even effect in nulcear binding ‣ 4He, 12C, 14N: contributions from H and He burning in low/ intermediate mass stars so far so good, but much more to understand! Nucleosynthesis Beyond Iron: The s-Process ~l "'r $7 ~ L.
Vot.UME 29, NUMnaa 4 OcToaaR, 1957
' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California
"It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3)
"The fault, dear Brutus, is not in our stars, But in ourselves, " (Julius Caesar, Act I, Scene 2) TABLE OF CONTENTS IQge I. Introduction...... 548 A. Element Abundances and Nuclear Structure. . . . . , ...... 548 B. Four Theories of the Origin of the Elements...... 550 C. General Features of Stellar Synthesis...... 550 II. Physical Processes Involved in Stellar Synthesis, Their Place of Occurrence, and the Time-Scales Associated with Them 551 A. Modes of Element Synthesis...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong PI'ocesses (i) to (vill) ...... 553 C. Abundances and Synthesis Assignments Given in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis...... 556
III. Hydrogen Burning, Helium Burning, the e Process, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 0 ~ ~ & r 559 A. Cross-Section Factor and Reaction Rates...... , ...... 559
B. PuI'e HydI'ogen Burning. . . . ,...... ; ...... 562 C. Pure Helium Burning...... ~...... 565
D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567
E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 F. Burning of Hydrogen and Helium with Mixtures of Other Elements; Stellar Neutron Sources . . . . 569 IV. e Process . . 577
V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. C. General Dynamics of the s and r Processes...... 583
VI. Details of the s Process...... , ...... , ...... 583 Supported in part by the joint program of the ofBce of Naval Research and the U. S. Atomic Energy Commission. 547 Copyright O 1957 by the American Physical Society ~l "'r $7 ~ L.
Vot.UME 29, NUMnaa 4 OcToaaR, 1957
' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California
"It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3) SYNTHESIS OF ELEMENTS I N STARS
"The fault, dear Brutus, is not in our stars, But in ourselves, " TABLE XII,(Julius1. Caesar, Act I, Scene 2) TABLE OF CONTENTS Total massIofQgeall I. Introduction. . . . material. . . . .ejected. 548 Total mass in over lifetime of A. Element Abundances and Nuclear Structure. . . . . , ...... Mode of galaxy (M Oas galaxy. .(Mo. . 548as Required Elements productionB. Four Theories of theunit)Origin of the Elements. .Astrophysical...... origin unit). . . . . 550 efficiency C. General Features of Stellar Synthesis...... 550 He H burningII. Physical Processes8.Involved1X10' in Stellar Synthesis,EmissionTheirfromPlaceredof Occurrence,giants and the Time-Scales2X10" 0.4 Associated with Them and supergiants 551 D x process'A. Modes of Element7.5X10'PSynthesis...... Stellar...... atmospheres?...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong Supernovae?PI'ocesses (i) to (vill) ...... 553 Li, Be, B x processC. Abundances and8.5XSynthesis10' Assignments StellarGiven in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis. . . .atmospheres...... 556 C, O, Ne He burning 4.3X10' Red giants and supergiants 2X 10' 2X10 ' Silicon group a processIII. Hydrogen Burning,4.Helium0X10'.Burning, the ePre-SupernovaeProcess, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 2X0 ~ ~ & 1psr 559 0.2 Silicon group s processA. Cross-Section Factor8.5X10'and Reaction Rates.Red. . . .giants. . . . . , . .and. . . . .supergiants...... 2X. . .10&0. 559 4X10 4 Iron group e processB. PuI'e HydI'ogen 2.Burning.4X 107. . . ,...... Sup. . . . ;ernovae. . 2X1ps. . . . 562 0.1 A)63 s processC. Pure Helium Burning.4.5X 104...... ~...... Red. giants and supergiants 2X10". . . . 565 2X10 ' D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567 A &75 r process 5X104 Supernovae Type II 1.7X 10' 3X10 4 E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 A 104 3X10' 4 &75 r processF. Burning of Hydrogen and Helium with SupernovaeMixtures of OtherTypeElements;I Stellar Neutron Sources . . . . 569 3X10— A 1. 102 10s 6 p63 p processIV. e Process 3X Supernovae Type II 1.7X. . 577 10
V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. rate of star formation and deathC. General duringDynamics theof the slifetimeand r Processes.istence)...... make...... up 55% of the total. . . . 583mass. Stars which of the Galaxy, are given inVI. theDetails6fthof the scolumnProcess. . . .of. . . Table...... formed, ...... with...... magnitudes...... , .brighter...... 583than +3.5 (the XII,1 and were made in theSupportedfollowingin part by theway.joint program of the ofBce of NavalmajorityResearch and theofU. S.whichAtomic EnergyhaveCommission.gone through their whole 547 The rates of supernovae were taken to be 1 perCopyright300O 1957 by evolutionarythe American Physical Society path) make up the remaining 45%. years for Type I and 1 per 50 years for Type II, as We 6nd from his mass function that the average mass estimated by Baade and Minkowski (Ba57a), and of the stars brighter than +3.5 was 4 Ão. Since the the age of the Galaxy was taken as 6)&10' years. The upper limit to the mass of a white dwarf is about 1.4 average mass emission per supernova is not easy to Mo, we find that, of the remaining 45%, 16% may lie estimate (see Sec. XII,C), but we have taken it to be in white dwarfs and 29% in the form of ejected gas. 1.4 ufo. The exponential-decay light curve is char- Thus the division of mass between stars which have acteristic of Type I and not of Type II supernovae; not evolved, white dwarfs, and material which has this has been taken to indicate that the rapid production been processed by stars is approximately 4:1:2. and capture of neutrons, leading to synthesis of the Extrapolating these results to the Galaxy as a whole, heaviest r-process elements, occurs only in Type I we find that 2)&10"Mo has been processed by stars. supernovae. The lighter r-process elements are prob- Some of this is included in the estimate of matter ably made in Type II supernovae, while the products ejected by supernovae, but the majority will have of the n and e processes may perhaps be made in either been processed at temperatures &10' degrees, and type. ejected by red giants and supergiants. The estimate for the ejection of mass by red giants The eSciency of production of each group of ele- and supergiants was based on the assumption that ments in the total ejected material that is necessary such stars shed most of their material into space during to explain the abundances in column 3 of Table XII,1 the' giant phases of their evolution. Thus Deutsch is obtained by dividing column 3 by column 5, and is (De56) has shown that matter is streaming rapidly given in the last column. It must be emphasized here outwards from the surface of an M-type supergiant, that the estimates given in Table XII,1 are very and he considers from the spectroscopic data that preliminary. Even on an optimistic view they might probably all late-type supergiants are also ejecting well prove incorrect by as much as a factor 3. It is material at a comparab1y rapid rate. There is also noteworthy, however, that the emission seems adequate some evidence that normal giant stars are ejecting to explain the synthesis requirements, except possibly matter, although probably on a smaller scale. Hoyle in the case of deuterium, and helium, which is the (Ho56b) has indicated that mass loss may have. a more only element needing an eKciency near to unity for important effect on the evolution of giants and super- its production. It will be clear from the foregoing that giants of very low surface gravity than have nuclear our estimates are not accurate enough to establish processes. With these considerations in mind, it is whether or not it is necessary to assume some helium necessary to estimate the fraction of the mass of the in the original matter of the Galaxy. Galaxy that has been condensed into stars which have The eKciency necessary to produce the r-process gone through their whole evolutionary path. elements is considerably smaller than that required The luminosity and mass functions for solar-neigh- to give the observed supernova light curves (see Sec. borhood stars have been studied by Salpeter (Sa55a). XII,C). It should, in addition, be reiterated that we He has shown that stars which~lie on the main sequence have no evidence at all concerning the abundances of now with absolute visual magnitudes. fainter than the r. -only and p-process isotopes outside the, ".solar +3.5 (which form the bulk of stars at present in ex- system, as we pointed out in Sec. XI. ~l "'r $7 ~ L.
Vot.UME 29, NUMnaa 4 OcToaaR, 1957
' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California
"It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3) SYNTHESIS OF ELEMENTS I N STARS
"The fault, dear Brutus, is not in our stars, But in ourselves, " TABLE XII,(Julius1. Caesar, Act I, Scene 2) TABLE OF CONTENTS Total massIofQgeall I. Introduction. . . . material. . . . .ejected. 548 Total mass in over lifetime of A. Element Abundances and Nuclear Structure. . . . . , ...... Mode of galaxy (M Oas galaxy. .(Mo. . 548as Required Elements productionB. Four Theories of theunit)Origin of the Elements. .Astrophysical...... origin unit). . . . . 550 efficiency C. General Features of Stellar Synthesis...... 550 He H burningII. Physical Processes8.Involved1X10' in Stellar Synthesis,EmissionTheirfromPlaceredof Occurrence,giants and the Time-Scales2X10" 0.4 Associated with Them and supergiants 551 D x process'A. Modes of Element7.5X10'PSynthesis...... Stellar...... atmospheres?...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong Supernovae?PI'ocesses (i) to (vill) ...... 553 Li, Be, B x processC. Abundances and8.5XSynthesis10' Assignments StellarGiven in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis. . . .atmospheres...... 556 C, O, Ne He burning 4.3X10' Red giants and supergiants 2X 10' 2X10 ' Silicon group a processIII. Hydrogen Burning,4.Helium0X10'.Burning, the ePre-SupernovaeProcess, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 2X0 ~ ~ & 1psr 559 0.2 Silicon group s processA. Cross-Section Factor8.5X10'and Reaction Rates.Red. . . .giants. . . . . , . .and. . . . .supergiants...... 2X. . .10&0. 559 4X10 4 Iron group e processB. PuI'e HydI'ogen 2.Burning.4X 107. . . ,...... Sup. . . . ;ernovae. . 2X1ps. . . . 562 0.1 A)63 s processC. Pure Helium Burning.4.5X 104...... ~...... Red. giants and supergiants 2X10". . . . 565 2X10 ' D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567 A &75 r process 5X104 Supernovae Type II 1.7X 10' 3X10 4 E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 A 104 3X10' 4 &75 r processF. Burning of Hydrogen and Helium with SupernovaeMixtures of OtherTypeElements;I Stellar Neutron Sources . . . . 569 3X10— A 1. 102 10s 6 p63 p processIV. e Process 3X Supernovae Type II 1.7X. . 577 10
V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. rate of star formation and deathC. General duringDynamics theof the slifetimeand r Processes.istence)...... make...... up 55% of the total. . . . 583mass. Stars which of the Galaxy, are given inVI. theDetails6fthof the scolumnProcess. . . .of. . . Table...... formed, ...... with...... magnitudes...... , .brighter...... 583than +3.5 (the XII,1 and were made in theSupportedfollowingin part by theway.joint program of the ofBce of NavalmajorityResearch and theofU. S.whichAtomic EnergyhaveCommission.gone through their whole 547 The rates of supernovae were taken to be 1 perCopyright300O 1957 by evolutionarythe American Physical Society path) make up the remaining 45%. years for Type I and 1 per 50 years for Type II, as We 6nd from his mass function that the average mass estimated by Baade and Minkowski (Ba57a), and of the stars brighter than +3.5 was 4 Ão. Since the the age of the Galaxy was taken as 6)&10' years. The upper limit to the mass of a white dwarf is about 1.4 average mass emission per supernova is not easy to Mo, we find that, of the remaining 45%, 16% may lie estimate (see Sec. XII,C), but we have taken it to be in white dwarfs and 29% in the form of ejected gas. 1.4 ufo. The exponential-decay light curve is char- Thus the division of mass between stars which have acteristic of Type I and not of Type II supernovae; not evolved, white dwarfs, and material which has this has been taken to indicate that the rapid production been processed by stars is approximately 4:1:2. and capture of neutrons, leading to synthesis of the Extrapolating these results to the Galaxy as a whole, heaviest r-process elements, occurs only in Type I we find that 2)&10"Mo has been processed by stars. supernovae. The lighter r-process elements are prob- Some of this is included in the estimate of matter ably made in Type II supernovae, while the products ejected by supernovae, but the majority will have of the n and e processes may perhaps be made in either been processed at temperatures &10' degrees, and type. ejected by red giants and supergiants. The estimate for the ejection of mass by red giants The eSciency of production of each group of ele- and supergiants was based on the assumption that ments in the total ejected material that is necessary such stars shed most of their material into space during to explain the abundances in column 3 of Table XII,1 the' giant phases of their evolution. Thus Deutsch is obtained by dividing column 3 by column 5, and is (De56) has shown that matter is streaming rapidly given in the last column. It must be emphasized here outwards from the surface of an M-type supergiant, that the estimates given in Table XII,1 are very and he considers from the spectroscopic data that preliminary. Even on an optimistic view they might probably all late-type supergiants are also ejecting well prove incorrect by as much as a factor 3. It is material at a comparab1y rapid rate. There is also noteworthy, however, that the emission seems adequate some evidence that normal giant stars are ejecting to explain the synthesis requirements, except possibly matter, although probably on a smaller scale. Hoyle in the case of deuterium, and helium, which is the (Ho56b) has indicated that mass loss may have. a more only element needing an eKciency near to unity for important effect on the evolution of giants and super- its production. It will be clear from the foregoing that giants of very low surface gravity than have nuclear our estimates are not accurate enough to establish processes. With these considerations in mind, it is whether or not it is necessary to assume some helium necessary to estimate the fraction of the mass of the in the original matter of the Galaxy. Galaxy that has been condensed into stars which have The eKciency necessary to produce the r-process gone through their whole evolutionary path. elements is considerably smaller than that required The luminosity and mass functions for solar-neigh- to give the observed supernova light curves (see Sec. borhood stars have been studied by Salpeter (Sa55a). XII,C). It should, in addition, be reiterated that we He has shown that stars which~lie on the main sequence have no evidence at all concerning the abundances of now with absolute visual magnitudes. fainter than the r. -only and p-process isotopes outside the, ".solar +3.5 (which form the bulk of stars at present in ex- system, as we pointed out in Sec. XI. ~l "'r $7 ~ L.
Vot.UME 29, NUMnaa 4 OcToaaR, 1957
' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California
"It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3) SYNTHESIS OF ELEMENTS I N STARS
"The fault, dear Brutus, is not in our stars, But in ourselves, " TABLE XII,(Julius1. Caesar, Act I, Scene 2) TABLE OF CONTENTS Total massIofQgeall I. Introduction. . . . material. . . . .ejected. 548 Total mass in over lifetime of A. Element Abundances and Nuclear Structure. . . . . , ...... Mode of galaxy (M Oas galaxy. .(Mo. . 548as Required Elements productionB. Four Theories of theunit)Origin of the Elements. .Astrophysical...... origin unit). . . . . 550 efficiency C. General Features of Stellar Synthesis...... 550 He H burningII. Physical Processes8.Involved1X10' in Stellar Synthesis,EmissionTheirfromPlaceredof Occurrence,giants and the Time-Scales2X10" 0.4 Associated with Them and supergiants 551 D x process'A. Modes of Element7.5X10'PSynthesis...... Stellar...... atmospheres?...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong Supernovae?PI'ocesses (i) to (vill) ...... 553 Li, Be, B x processC. Abundances and8.5XSynthesis10' Assignments StellarGiven in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis. . . .atmospheres...... 556 C, O, Ne He burning 4.3X10' Red giants and supergiants 2X 10' 2X10 ' Silicon group a processIII. Hydrogen Burning,4.Helium0X10'.Burning, the ePre-SupernovaeProcess, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 2X0 ~ ~ & 1psr 559 0.2 Silicon group s processA. Cross-Section Factor8.5X10'and Reaction Rates.Red. . . .giants. . . . . , . .and. . . . .supergiants...... 2X. . .10&0. 559 4X10 4 Iron group e processB. PuI'e HydI'ogen 2.Burning.4X 107. . . ,...... Sup. . . . ;ernovae. . 2X1ps. . . . 562 0.1 A)63 s processC. Pure Helium Burning.4.5X 104...... ~...... Red. giants and supergiants 2X10". . . . 565 2X10 ' D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567 A &75 r process 5X104 Supernovae Type II 1.7X 10' 3X10 4 E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 A 104 3X10' 4 &75 r processF. Burning of Hydrogen and Helium with SupernovaeMixtures of OtherTypeElements;I Stellar Neutron Sources . . . . 569 3X10— A 1. 102 10s 6 p63 p processIV. e Process 3X Supernovae Type II 1.7X. . 577 10
V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. rate of star formation and deathC. General duringDynamics theof the slifetimeand r Processes.istence)...... make...... up 55% of the total. . . . 583mass. Stars which of the Galaxy, are given inVI. theDetails6fthof the scolumnProcess. . . .of. . . Table...... formed, ...... with...... magnitudes...... , .brighter...... 583than +3.5 (the XII,1 and were made in theSupportedfollowingin part by theway.joint program of the ofBce of NavalmajorityResearch and theofU. S.whichAtomic EnergyhaveCommission.gone through their whole 547 The rates of supernovae were taken to be 1 perCopyright300O 1957 by evolutionarythe American Physical Society path) make up the remaining 45%. years for Type I and 1 per 50 years for Type II, as We 6nd from his mass function that the average mass estimated by Baade and Minkowski (Ba57a), and of the stars brighter than +3.5 was 4 Ão. Since the the age of the Galaxy was taken as 6)&10' years. The upper limit to the mass of a white dwarf is about 1.4 average mass emission per supernova is not easy to Mo, we find that, of the remaining 45%, 16% may lie estimate (see Sec. XII,C), but we have taken it to be in white dwarfs and 29% in the form of ejected gas. 1.4 ufo. The exponential-decay light curve is char- Thus the division of mass between stars which have acteristic of Type I and not of Type II supernovae; not evolved, white dwarfs, and material which has this has been taken to indicate that the rapid production been processed by stars is approximately 4:1:2. and capture of neutrons, leading to synthesis of the Extrapolating these results to the Galaxy as a whole, heaviest r-process elements, occurs only in Type I we find that 2)&10"Mo has been processed by stars. supernovae. The lighter r-process elements are prob- Some of this is included in the estimate of matter ably made in Type II supernovae, while the products ejected by supernovae, but the majority will have of the n and e processes may perhaps be made in either been processed at temperatures &10' degrees, and type. ejected by red giants and supergiants. The estimate for the ejection of mass by red giants The eSciency of production of each group of ele- and supergiants was based on the assumption that ments in the total ejected material that is necessary such stars shed most of their material into space during to explain the abundances in column 3 of Table XII,1 the' giant phases of their evolution. Thus Deutsch is obtained by dividing column 3 by column 5, and is (De56) has shown that matter is streaming rapidly given in the last column. It must be emphasized here outwards from the surface of an M-type supergiant, that the estimates given in Table XII,1 are very and he considers from the spectroscopic data that preliminary. Even on an optimistic view they might probably all late-type supergiants are also ejecting well prove incorrect by as much as a factor 3. It is material at a comparab1y rapid rate. There is also noteworthy, however, that the emission seems adequate some evidence that normal giant stars are ejecting to explain the synthesis requirements, except possibly matter, although probably on a smaller scale. Hoyle in the case of deuterium, and helium, which is the (Ho56b) has indicated that mass loss may have. a more only element needing an eKciency near to unity for important effect on the evolution of giants and super- its production. It will be clear from the foregoing that giants of very low surface gravity than have nuclear our estimates are not accurate enough to establish processes. With these considerations in mind, it is whether or not it is necessary to assume some helium necessary to estimate the fraction of the mass of the in the original matter of the Galaxy. Galaxy that has been condensed into stars which have The eKciency necessary to produce the r-process gone through their whole evolutionary path. elements is considerably smaller than that required The luminosity and mass functions for solar-neigh- to give the observed supernova light curves (see Sec. borhood stars have been studied by Salpeter (Sa55a). XII,C). It should, in addition, be reiterated that we He has shown that stars which~lie on the main sequence have no evidence at all concerning the abundances of now with absolute visual magnitudes. fainter than the r. -only and p-process isotopes outside the, ".solar +3.5 (which form the bulk of stars at present in ex- system, as we pointed out in Sec. XI. Beyond the Iron Peak if all heavy elements made only in burning to nuclear statistical equilibrium – then should follow Fe peak, fall dramatically at high A – would have much less of the very heavy elements
How to synthesize nuclei beyond iron peak? – Coulomb barrier prohibitive – fusion reaction not exothermic
Yet silver, gold, lead, uranium, ... all exist! – nature has found a way
Q: Suggestions? Beyond the Iron Peak if all heavy elements made only in burning to nuclear statistical equilibrium – then should follow Fe peak, fall dramatically at high A – would have much less of the very heavy elements
How to synthesize nuclei beyond iron peak? – Coulomb barrier prohibitive – fusion reaction not exothermic
Yet silver, gold, lead, uranium, ... all exist! – nature has found a way
Q: Suggestions? Beyond the Iron Peak if all heavy elements made only in burning to nuclear statistical equilibrium – then should follow Fe peak, fall dramatically at high A Who ordered that? – would have much less of the very heavy elements
How to synthesize nuclei beyond iron peak? – Coulomb barrier prohibitive – fusion reaction not exothermic
Yet silver, gold, lead, uranium, ... all exist! – nature has found a way
Q: Suggestions? Neutron Capture Processes Solution: neutrons – no Coulomb barrier – capture reactions occur even at small thermal speeds
Microscopic approach: identify the needed physics (1) “let there be neutrons” (2) assume a heavy “seed” nucleus (e.g., 56Fe) (3) ignore charged particle rxns (Coulomb suppressed)
Q: what can happen when adding n seeds? A Tale of Two Limits
Neutron capture physics set by competition • neutron capture n +(A, Z)→(A +1,Z)+γ − • β decay (A, Z)→(A, Z +1)+e +¯νe
Two regimes (BBFH 1957; Cameron 1957): capture rate # decay rate ⇒ rapid capture: r-process decay rate # capture rate → slow capture: s-process
Detective story: • do these limiting cases occur? (Yes!) • what are astrophysical sites? 12 Neutron Capturen Capture Rates Rates
n-capture cross sections: typically, σ ∝ 1/v • enhanced at low energies! • σv = "σv# = const → T -indep! • fails for magic nuclei: tightly bound → small σ
Implications? 13 Neutron Capturen Capture Rates Rates
n-capture cross sections: typically, σ ∝ 1/v • enhanced at low energies! • σv = "σv# = const → T -indep! • fails for magic nuclei: tightly bound → small σ
Implications? Difficulty adding more neutrons to magic nuclei:
13 – abundance pileup at magic N Solar System Abundances Magic Neutron Numbers Solar System Abundances Magic Neutron Numbers
N=50 Solar System Abundances Magic Neutron Numbers
N=50 N=82 Solar System Abundances Magic Neutron Numbers
N=50 N=82 N=128 s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? Q: lessons? 59Co 60Co
56Fe 57Fe 58Fe 59Fe s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
60Ni 61Ni 62Ni Q: what happens? The s-Process: Basic Physics Q: lessons? 59Co 60Co
slow n capture: Γnγ ! Γβ ⇒ path in chart of nuclides: 56Fe 57Fe 58Fe 59Fe follow n-rich edge of β-stability www: s-process path
for isobar A dnA = −$σv% nnn + $σv% 1nnn 1 (1) dt A A A− A− except for seed (e.g., 56Fe)
dnseed/dt = −$σv%Annnseed (2) 2 Q: what behavior expected for nA? s-Process: Basic Physics add neutrons to seeds slowly: – capture time >> decay
The s-Process: Basic Physics 60Ni 61Ni 62Ni Q: what happens? The s-Process: Basic Physics Q:slow lessons?n capture: Γnγ ! Γβ 59Co 60Co ⇒ path in chart of nuclides: slow n capture: Γ ! Γ follow n-rich edgen ofγ β-stabilityβ ⇒ path in chart of nuclides: 56Fe 57Fe 58Fe 59Fe www: s-process path follow n-rich edge of β-stability www: s-process path for isobar A dnA = −$σv% nnn + $σv% 1nnn 1 (1) for isobar A dt A A A− A− except for seeddn(e.g.,A 56Fe) = −$σv% nnn + $σv% 1nnn 1 (1) dt A A A− A− dn /dt = −$σv% n n (2) except for seed (e.g.,seed56Fe) A n seed 2 dnseed/dt = −$σv%Annnseed (2) Q: what behavior expected for nA? 2 Q: what behavior expected for nA?
The Local Approximation dn A −n v σ n − σ n dt = n T ( A A A−1 A−1)
= −nnvV σA (nA − neq)
σA−1 where neq = nA−1 σA The Local Approximation dn A −n v σ n − σ n dt = n T ( A A A−1 A−1)
= −nnvV σA (nA − neq)
σA−1 where neq = nA−1 σA
Q: what if nA>neq? for adjacent nuclides, local approximation excellent between magic N:good but globally, fails ⇒ need distribution of τ Roughly: exponential distribution of τ needed i.e., imagine series of bursts of different intensities 4 n Q: how does nature do this? SolarSolar Abundances Abundances and and the s-Process the s_process For elements beyond Fe peak: plot NAσA vs A if s-process reaches equilibrium, predict flat curve Transp: NAσA plot for adjacent nuclides, local approximation excellent between magic N:good but globally, fails ⇒ need distribution of τ Roughly: exponential distribution of τ needed i.e., imagine series of bursts of different intensities 4 n Q: how does nature do this? SolarSolar Abundances Abundances and and the s-Process the s_process For elements beyond Fe peak: plot NAσA vs A if s-process reaches equilibrium, predict flat curve Transp: NAσA plot for adjacent nuclides, local approximation excellent between magic N:good Lessons? but globally, fails ⇒ need distribution of τ Roughly: exponential distribution of τ needed i.e., imagine series of bursts of different intensities 4 n Q: how does nature do this? SolarSolar Abundances Abundances and and the s-Process the s_process For elements beyond Fe peak: plot NAσA vs A if s-process reaches equilibrium, predict flat curve Transp: NAσA plot for adjacent nuclides, local approximation excellent betweenSolar magic N Abundances:good and theLessons? s-Process but globally, fails ⇒Forneed elementsdistribution beyond of Feτ peak: plot NAσA vs A if s-process reaches equilibrium, predict flat curve Roughly: exponential distribution of τ needed Transp: N σ plot i.e., imagineA seriesA of bursts of different intensities 4 n Q: how does nature do this? for adjacent nuclides, local approximation excellent between magic N:good but globally, fails ⇒ need distribution of τ Roughly: exponential distribution of τ needed i.e., imagine series of bursts of different intensities 4 n Q: how does nature do this? s-Process:s-Process: Astrophysical Astrophysical Site Site Intermediate mass stars: ∼ 3 − 8 M# recall–after main seq: 1. H shell burn → RGB 2. He ignition → core He burn 3Heshellburn→ asymptotically approach RGB again “asymptotic giant branch” = AGB HR diagram sketch On AGB: two burning shells: H, He instability → thermal pulses (TP) TP-AGB stars observed to have 6 • C/O > 1–“carbonstars” • high s-process! – “S-stars” s-Process: Crown Jewel technetium seen in AGB stars (Merrill 1952) s-Process: Crown Jewel technetium seen in AGB stars (Merrill 1952) Q: why is this amazing? s-Process: Crown Jewel technetium seen in AGB stars (Merrill 1952) Q: why is this amazing? Tc: no stable isotopes! – longest-lived τ(98Tc) = 6 Myr – 1st direct evidence for ongoing nucleosynthesis in stars! – direct “real-time” evidence of s-process activity! s-Process: Crown Jewel technetium seen in AGB stars (Merrill 1952) Q: why is this amazing? Tc: no stable isotopes! – longest-lived τ(98Tc) = 6 Myr – 1st direct evidence for ongoing nucleosynthesis in stars! – direct “real-time” evidence of s-process activity! s-process occurs in pulsing AGB stars s-Process: Crown Jewel technetium seen in AGB stars (Merrill 1952) Q: why is this amazing? Tc: no stable isotopes! – longest-lived τ(98Tc) = 6 Myr – 1st direct evidence for ongoing nucleosynthesis in stars! – direct “real-time” evidence of s-process activity! s-process occurs in pulsing AGB stars Q: where did the stars get the neutrons? the seeds? AGB neutron sources: • 13C from CNO cycle: 13C(α, n)16O • 14N from CNO cycle burnt to 14N(α, γ)18F(β)18O(α, γ)22Ne then 22Ne(α, n)25Mg occurs in intershell region n created during, between pulses ⇒ repeated n exposure of different intensities ⇒ can fit observed exposure distribution ...but now can make detailed, realistic models in context of stellar evolution 8 ~l "'r $7 ~ L. Vot.UME 29, NUMnaa 4 OcToaaR, 1957 ' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California "It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3) "The fault, dear Brutus, is not in our stars, But in ourselves, " (Julius Caesar, Act I, Scene 2) TABLE OF CONTENTS IQge I. Introduction...... 548 A. Element Abundances and Nuclear Structure. . . . . , ...... 548 B. Four Theories of the Origin of the Elements...... 550 C. General Features of Stellar Synthesis...... 550 II. Physical Processes Involved in Stellar Synthesis, Their Place of Occurrence, and the Time-Scales Associated with Them 551 A. Modes of Element Synthesis...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong PI'ocesses (i) to (vill) ...... 553 C. Abundances and Synthesis Assignments Given in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis...... 556 III. Hydrogen Burning, Helium Burning, the e Process, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 0 ~ ~ & r 559 A. Cross-Section Factor and Reaction Rates...... , ...... 559 B. PuI'e HydI'ogen Burning. . . . ,...... ; ...... 562 C. Pure Helium Burning...... ~...... 565 D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567 E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 F. Burning of Hydrogen and Helium with Mixtures of Other Elements; Stellar Neutron Sources . . . . 569 IV. e Process . . 577 V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. C. General Dynamics of the s and r Processes...... 583 VI. Details of the s Process...... , ...... , ...... 583 Supported in part by the joint program of the ofBce of Naval Research and the U. S. Atomic Energy Commission. 547 Copyright O 1957 by the American Physical Society ~l "'r $7 ~ L. Vot.UME 29, NUMnaa 4 OcToaaR, 1957 ' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California "It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3) SYNTHESIS OF ELEMENTS I N STARS "The fault, dear Brutus, is not in our stars, But in ourselves, " TABLE XII,(Julius1. Caesar, Act I, Scene 2) TABLE OF CONTENTS Total massIofQgeall I. Introduction. . . . material. . . . .ejected. 548 Total mass in over lifetime of A. Element Abundances and Nuclear Structure. . . . . , ...... Mode of galaxy (M Oas galaxy. .(Mo. . 548as Required Elements productionB. Four Theories of theunit)Origin of the Elements. .Astrophysical...... origin unit). . . . . 550 efficiency C. General Features of Stellar Synthesis...... 550 He H burningII. Physical Processes8.Involved1X10' in Stellar Synthesis,EmissionTheirfromPlaceredof Occurrence,giants and the Time-Scales2X10" 0.4 Associated with Them and supergiants 551 D x process'A. Modes of Element7.5X10'PSynthesis...... Stellar...... atmospheres?...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong Supernovae?PI'ocesses (i) to (vill) ...... 553 Li, Be, B x processC. Abundances and8.5XSynthesis10' Assignments StellarGiven in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis. . . .atmospheres...... 556 C, O, Ne He burning 4.3X10' Red giants and supergiants 2X 10' 2X10 ' Silicon group a processIII. Hydrogen Burning,4.Helium0X10'.Burning, the ePre-SupernovaeProcess, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 2X0 ~ ~ & 1psr 559 0.2 Silicon group s processA. Cross-Section Factor8.5X10'and Reaction Rates.Red. . . .giants. . . . . , . .and. . . . .supergiants...... 2X. . .10&0. 559 4X10 4 Iron group e processB. PuI'e HydI'ogen 2.Burning.4X 107. . . ,...... Sup. . . . ;ernovae. . 2X1ps. . . . 562 0.1 A)63 s processC. Pure Helium Burning.4.5X 104...... ~...... Red. giants and supergiants 2X10". . . . 565 2X10 ' D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567 A &75 r process 5X104 Supernovae Type II 1.7X 10' 3X10 4 E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 A 104 3X10' 4 &75 r processF. Burning of Hydrogen and Helium with SupernovaeMixtures of OtherTypeElements;I Stellar Neutron Sources . . . . 569 3X10— A 1. 102 10s 6 p63 p processIV. e Process 3X Supernovae Type II 1.7X. . 577 10 V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. rate of star formation and deathC. General duringDynamics theof the slifetimeand r Processes.istence)...... make...... up 55% of the total. . . . 583mass. Stars which of the Galaxy, are given inVI. theDetails6fthof the scolumnProcess. . . .of. . . Table...... formed, ...... with...... magnitudes...... , .brighter...... 583than +3.5 (the XII,1 and were made in theSupportedfollowingin part by theway.joint program of the ofBce of NavalmajorityResearch and theofU. S.whichAtomic EnergyhaveCommission.gone through their whole 547 The rates of supernovae were taken to be 1 perCopyright300O 1957 by evolutionarythe American Physical Society path) make up the remaining 45%. years for Type I and 1 per 50 years for Type II, as We 6nd from his mass function that the average mass estimated by Baade and Minkowski (Ba57a), and of the stars brighter than +3.5 was 4 Ão. Since the the age of the Galaxy was taken as 6)&10' years. The upper limit to the mass of a white dwarf is about 1.4 average mass emission per supernova is not easy to Mo, we find that, of the remaining 45%, 16% may lie estimate (see Sec. XII,C), but we have taken it to be in white dwarfs and 29% in the form of ejected gas. 1.4 ufo. The exponential-decay light curve is char- Thus the division of mass between stars which have acteristic of Type I and not of Type II supernovae; not evolved, white dwarfs, and material which has this has been taken to indicate that the rapid production been processed by stars is approximately 4:1:2. and capture of neutrons, leading to synthesis of the Extrapolating these results to the Galaxy as a whole, heaviest r-process elements, occurs only in Type I we find that 2)&10"Mo has been processed by stars. supernovae. The lighter r-process elements are prob- Some of this is included in the estimate of matter ably made in Type II supernovae, while the products ejected by supernovae, but the majority will have of the n and e processes may perhaps be made in either been processed at temperatures &10' degrees, and type. ejected by red giants and supergiants. The estimate for the ejection of mass by red giants The eSciency of production of each group of ele- and supergiants was based on the assumption that ments in the total ejected material that is necessary such stars shed most of their material into space during to explain the abundances in column 3 of Table XII,1 the' giant phases of their evolution. Thus Deutsch is obtained by dividing column 3 by column 5, and is (De56) has shown that matter is streaming rapidly given in the last column. It must be emphasized here outwards from the surface of an M-type supergiant, that the estimates given in Table XII,1 are very and he considers from the spectroscopic data that preliminary. Even on an optimistic view they might probably all late-type supergiants are also ejecting well prove incorrect by as much as a factor 3. It is material at a comparab1y rapid rate. There is also noteworthy, however, that the emission seems adequate some evidence that normal giant stars are ejecting to explain the synthesis requirements, except possibly matter, although probably on a smaller scale. Hoyle in the case of deuterium, and helium, which is the (Ho56b) has indicated that mass loss may have. a more only element needing an eKciency near to unity for important effect on the evolution of giants and super- its production. It will be clear from the foregoing that giants of very low surface gravity than have nuclear our estimates are not accurate enough to establish processes. With these considerations in mind, it is whether or not it is necessary to assume some helium necessary to estimate the fraction of the mass of the in the original matter of the Galaxy. Galaxy that has been condensed into stars which have The eKciency necessary to produce the r-process gone through their whole evolutionary path. elements is considerably smaller than that required The luminosity and mass functions for solar-neigh- to give the observed supernova light curves (see Sec. borhood stars have been studied by Salpeter (Sa55a). XII,C). It should, in addition, be reiterated that we He has shown that stars which~lie on the main sequence have no evidence at all concerning the abundances of now with absolute visual magnitudes. fainter than the r. -only and p-process isotopes outside the, ".solar +3.5 (which form the bulk of stars at present in ex- system, as we pointed out in Sec. XI. ~l "'r $7 ~ L. Vot.UME 29, NUMnaa 4 OcToaaR, 1957 ' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California "It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3) SYNTHESIS OF ELEMENTS I N STARS "The fault, dear Brutus, is not in our stars, But in ourselves, " TABLE XII,(Julius1. Caesar, Act I, Scene 2) TABLE OF CONTENTS Total massIofQgeall I. Introduction. . . . material. . . . .ejected. 548 Total mass in over lifetime of A. Element Abundances and Nuclear Structure. . . . . , ...... Mode of galaxy (M Oas galaxy. .(Mo. . 548as Required Elements productionB. Four Theories of theunit)Origin of the Elements. .Astrophysical...... origin unit). . . . . 550 efficiency C. General Features of Stellar Synthesis...... 550 He H burningII. Physical Processes8.Involved1X10' in Stellar Synthesis,EmissionTheirfromPlaceredof Occurrence,giants and the Time-Scales2X10" 0.4 Associated with Them and supergiants 551 D x process'A. Modes of Element7.5X10'PSynthesis...... Stellar...... atmospheres?...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong Supernovae?PI'ocesses (i) to (vill) ...... 553 Li, Be, B x processC. Abundances and8.5XSynthesis10' Assignments StellarGiven in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis. . . .atmospheres...... 556 C, O, Ne He burning 4.3X10' Red giants and supergiants 2X 10' 2X10 ' Silicon group a processIII. Hydrogen Burning,4.Helium0X10'.Burning, the ePre-SupernovaeProcess, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 2X0 ~ ~ & 1psr 559 0.2 Silicon group s processA. Cross-Section Factor8.5X10'and Reaction Rates.Red. . . .giants. . . . . , . .and. . . . .supergiants...... 2X. . .10&0. 559 4X10 4 Iron group e processB. PuI'e HydI'ogen 2.Burning.4X 107. . . ,...... Sup. . . . ;ernovae. . 2X1ps. . . . 562 0.1 A)63 s processC. Pure Helium Burning.4.5X 104...... ~...... Red. giants and supergiants 2X10". . . . 565 2X10 ' D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567 A &75 r process 5X104 Supernovae Type II 1.7X 10' 3X10 4 E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 A 104 3X10' 4 &75 r processF. Burning of Hydrogen and Helium with SupernovaeMixtures of OtherTypeElements;I Stellar Neutron Sources . . . . 569 3X10— A 1. 102 10s 6 p63 p processIV. e Process 3X Supernovae Type II 1.7X. . 577 10 V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. rate of star formation and deathC. General duringDynamics theof the slifetimeand r Processes.istence)...... make...... up 55% of the total. . . . 583mass. Stars which of the Galaxy, are given inVI. theDetails6fthof the scolumnProcess. . . .of. . . Table...... formed, ...... with...... magnitudes...... , .brighter...... 583than +3.5 (the XII,1 and were made in theSupportedfollowingin part by theway.joint program of the ofBce of NavalmajorityResearch and theofU. S.whichAtomic EnergyhaveCommission.gone through their whole 547 The rates of supernovae were taken to be 1 perCopyright300O 1957 by evolutionarythe American Physical Society path) make up the remaining 45%. years for Type I and 1 per 50 years for Type II, as We 6nd from his mass function that the average mass estimated by Baade and Minkowski (Ba57a), and of the stars brighter than +3.5 was 4 Ão. Since the the age of the Galaxy was taken as 6)&10' years. The upper limit to the mass of a white dwarf is about 1.4 average mass emission per supernova is not easy to Mo, we find that, of the remaining 45%, 16% may lie estimate (see Sec. XII,C), but we have taken it to be in white dwarfs and 29% in the form of ejected gas. 1.4 ufo. The exponential-decay light curve is char- Thus the division of mass between stars which have acteristic of Type I and not of Type II supernovae; not evolved, white dwarfs, and material which has this has been taken to indicate that the rapid production been processed by stars is approximately 4:1:2. and capture of neutrons, leading to synthesis of the Extrapolating these results to the Galaxy as a whole, heaviest r-process elements, occurs only in Type I we find that 2)&10"Mo has been processed by stars. supernovae. The lighter r-process elements are prob- Some of this is included in the estimate of matter ably made in Type II supernovae, while the products ejected by supernovae, but the majority will have of the n and e processes may perhaps be made in either been processed at temperatures &10' degrees, and type. ejected by red giants and supergiants. The estimate for the ejection of mass by red giants The eSciency of production of each group of ele- and supergiants was based on the assumption that ments in the total ejected material that is necessary such stars shed most of their material into space during to explain the abundances in column 3 of Table XII,1 the' giant phases of their evolution. Thus Deutsch is obtained by dividing column 3 by column 5, and is (De56) has shown that matter is streaming rapidly given in the last column. It must be emphasized here outwards from the surface of an M-type supergiant, that the estimates given in Table XII,1 are very and he considers from the spectroscopic data that preliminary. Even on an optimistic view they might probably all late-type supergiants are also ejecting well prove incorrect by as much as a factor 3. It is material at a comparab1y rapid rate. There is also noteworthy, however, that the emission seems adequate some evidence that normal giant stars are ejecting to explain the synthesis requirements, except possibly matter, although probably on a smaller scale. Hoyle in the case of deuterium, and helium, which is the (Ho56b) has indicated that mass loss may have. a more only element needing an eKciency near to unity for important effect on the evolution of giants and super- its production. It will be clear from the foregoing that giants of very low surface gravity than have nuclear our estimates are not accurate enough to establish processes. With these considerations in mind, it is whether or not it is necessary to assume some helium necessary to estimate the fraction of the mass of the in the original matter of the Galaxy. Galaxy that has been condensed into stars which have The eKciency necessary to produce the r-process gone through their whole evolutionary path. elements is considerably smaller than that required The luminosity and mass functions for solar-neigh- to give the observed supernova light curves (see Sec. borhood stars have been studied by Salpeter (Sa55a). XII,C). It should, in addition, be reiterated that we He has shown that stars which~lie on the main sequence have no evidence at all concerning the abundances of now with absolute visual magnitudes. fainter than the r. -only and p-process isotopes outside the, ".solar +3.5 (which form the bulk of stars at present in ex- system, as we pointed out in Sec. XI. ~l "'r $7 ~ L. Vot.UME 29, NUMnaa 4 OcToaaR, 1957 ' '~ Synt iesis oI. t.~e . . .ements in Stars K. MARGARET BURBIDGE) G. R. BURMDGE) %ILIIAM: A. Fowl, ER) AND F. HQYLK Margaret & Geoffrey Burbidge, Eellogg EadiatzonlLaboratory, California Instztute of Technology, and Mount Wilson and Palonzar Observatories, Carnegie Institution of Washington, Al Cameron Willy Fowler, Fred Hoyle Calzfornia Instztute of Technology, Pasadena, California "It is the stars, The stars above us, govern our conditions"; (Eing Lear, Act IV, Scene 3) SYNTHESIS OF ELEMENTS I N STARS "The fault, dear Brutus, is not in our stars, But in ourselves, " TABLE XII,(Julius1. Caesar, Act I, Scene 2) TABLE OF CONTENTS Total massIofQgeall I. Introduction. . . . material. . . . .ejected. 548 Total mass in over lifetime of A. Element Abundances and Nuclear Structure. . . . . , ...... Mode of galaxy (M Oas galaxy. .(Mo. . 548as Required Elements productionB. Four Theories of theunit)Origin of the Elements. .Astrophysical...... origin unit). . . . . 550 efficiency C. General Features of Stellar Synthesis...... 550 He H burningII. Physical Processes8.Involved1X10' in Stellar Synthesis,EmissionTheirfromPlaceredof Occurrence,giants and the Time-Scales2X10" 0.4 Associated with Them and supergiants 551 D x process'A. Modes of Element7.5X10'PSynthesis...... Stellar...... atmospheres?...... , ...... 55j. B. Method of AsslgnIIlent of IBotopes atnong Supernovae?PI'ocesses (i) to (vill) ...... 553 Li, Be, B x processC. Abundances and8.5XSynthesis10' Assignments StellarGiven in the Appendix ...... 555 D. Time-Scales for Different Modes of Synthesis. . . .atmospheres...... 556 C, O, Ne He burning 4.3X10' Red giants and supergiants 2X 10' 2X10 ' Silicon group a processIII. Hydrogen Burning,4.Helium0X10'.Burning, the ePre-SupernovaeProcess, and Neutron Production . . ~ ~ ~ ~ t ~ ~ ~ o ~ o ~ ~ ~ 2X0 ~ ~ & 1psr 559 0.2 Silicon group s processA. Cross-Section Factor8.5X10'and Reaction Rates.Red. . . .giants. . . . . , . .and. . . . .supergiants...... 2X. . .10&0. 559 4X10 4 Iron group e processB. PuI'e HydI'ogen 2.Burning.4X 107. . . ,...... Sup. . . . ;ernovae. . 2X1ps. . . . 562 0.1 A)63 s processC. Pure Helium Burning.4.5X 104...... ~...... Red. giants and supergiants 2X10". . . . 565 2X10 ' D ~ 6 Process t ~ o + ~ ~ ~ ~ ~ + ~ o o s e ~ + ~ ~ ~ e s ~ 4 ~ ~ ~ ~ ~ ~ ~ l ~ ~ ~ ~ ~ I ~ ~ ~ ~ i ~ 567 A &75 r process 5X104 Supernovae Type II 1.7X 10' 3X10 4 E. Succession of NU. clear Fuels in an Evolving Star...... ~ \ J ~ ~ 1 ~ ~ ~ ~ ~ ~ , . . . 568 A 104 3X10' 4 &75 r processF. Burning of Hydrogen and Helium with SupernovaeMixtures of OtherTypeElements;I Stellar Neutron Sources . . . . 569 3X10— A 1. 102 10s 6 p63 p processIV. e Process 3X Supernovae Type II 1.7X. . 577 10 V. s and r Processes: General Considerations...... , ...... , ...... 580 A. "Shielded" and "Shielding" Isohars and the s, r, p Processes...... 580 B. Neutron-Capture Cross Sections...... 58j. rate of star formation and deathC. General duringDynamics theof the slifetimeand r Processes.istence)...... make...... up 55% of the total. . . . 583mass. Stars which of the Galaxy, are given inVI. theDetails6fthof the scolumnProcess. . . .of. . . Table...... formed, ...... with...... magnitudes...... , .brighter...... 583than +3.5 (the XII,1 and were made in theSupportedfollowingin part by theway.joint program of the ofBce of NavalmajorityResearch and theofU. S.whichAtomic EnergyhaveCommission.gone through their whole 547 The rates of supernovae were taken to be 1 perCopyright300O 1957 by evolutionarythe American Physical Society path) make up the remaining 45%. years for Type I and 1 per 50 years for Type II, as We 6nd from his mass function that the average mass estimated by Baade and Minkowski (Ba57a), and of the stars brighter than +3.5 was 4 Ão. Since the the age of the Galaxy was taken as 6)&10' years. The upper limit to the mass of a white dwarf is about 1.4 average mass emission per supernova is not easy to Mo, we find that, of the remaining 45%, 16% may lie estimate (see Sec. XII,C), but we have taken it to be in white dwarfs and 29% in the form of ejected gas. 1.4 ufo. The exponential-decay light curve is char- Thus the division of mass between stars which have acteristic of Type I and not of Type II supernovae; not evolved, white dwarfs, and material which has this has been taken to indicate that the rapid production been processed by stars is approximately 4:1:2. and capture of neutrons, leading to synthesis of the Extrapolating these results to the Galaxy as a whole, heaviest r-process elements, occurs only in Type I we find that 2)&10"Mo has been processed by stars. supernovae. The lighter r-process elements are prob- Some of this is included in the estimate of matter ably made in Type II supernovae, while the products ejected by supernovae, but the majority will have of the n and e processes may perhaps be made in either been processed at temperatures &10' degrees, and type. ejected by red giants and supergiants. The estimate for the ejection of mass by red giants The eSciency of production of each group of ele- and supergiants was based on the assumption that ments in the total ejected material that is necessary such stars shed most of their material into space during to explain the abundances in column 3 of Table XII,1 the' giant phases of their evolution. Thus Deutsch is obtained by dividing column 3 by column 5, and is (De56) has shown that matter is streaming rapidly given in the last column. It must be emphasized here outwards from the surface of an M-type supergiant, that the estimates given in Table XII,1 are very and he considers from the spectroscopic data that preliminary. Even on an optimistic view they might probably all late-type supergiants are also ejecting well prove incorrect by as much as a factor 3. It is material at a comparab1y rapid rate. There is also noteworthy, however, that the emission seems adequate some evidence that normal giant stars are ejecting to explain the synthesis requirements, except possibly matter, although probably on a smaller scale. Hoyle in the case of deuterium, and helium, which is the (Ho56b) has indicated that mass loss may have. a more only element needing an eKciency near to unity for important effect on the evolution of giants and super- its production. It will be clear from the foregoing that giants of very low surface gravity than have nuclear our estimates are not accurate enough to establish processes. With these considerations in mind, it is whether or not it is necessary to assume some helium necessary to estimate the fraction of the mass of the in the original matter of the Galaxy. Galaxy that has been condensed into stars which have The eKciency necessary to produce the r-process gone through their whole evolutionary path. elements is considerably smaller than that required The luminosity and mass functions for solar-neigh- to give the observed supernova light curves (see Sec. borhood stars have been studied by Salpeter (Sa55a). XII,C). It should, in addition, be reiterated that we He has shown that stars which~lie on the main sequence have no evidence at all concerning the abundances of now with absolute visual magnitudes. fainter than the r. -only and p-process isotopes outside the, ".solar +3.5 (which form the bulk of stars at present in ex- system, as we pointed out in Sec. XI.