1. The origin of the elements heavier than iron
Maria Lugaro
Konkoly Observatory of the Hungarian Academy of Sciences
Budapest

2. Pb
H, He
Fe, Co, Ni
Au, Pt Eu Ba
C, N, O Z U
Sr, Y, Zr N

3. The Solar System abundances

4. Pb
H, He
Fe, Co, Ni
Au, Pt Eu Ba
C, N, O Z U
Sr, Y, Zr N
Because of their high number of protons (>26), elements heavier than Fe have a large Coulomb barrier and can be produced mostly by capturing neutrons.

5. Pb
H, He
Fe, Co, Ni
Au, Pt Eu Ba
C, N, O Z U
Sr, Y, Zr N
Because of their high number of protons (>26), elements heavier than Fe have a large Coulomb barrier and can be produced mostly by capturing neutrons.

6. Slow neutron captures Time scale (n,g) >> time scaleβdecay
Nn ~ 108 n/cm3

7. Rapid neutron captures
Aaa
Time scale (n,g) << time scaleβdecay
Nn > 1020 n/cm3
Aaa

8. Slow and Rapid neutron captures

9. r-only s-only p-only

10. Which of these statements is wrong?
Kr has one p-only isotope
Sr has one s-only isotope
Sr has one p-only isotope
Kr has one s-only isotope

11. Which of these statements is wrong?
Kr has one p-only isotope
Sr has one s-only isotope
Sr has one p-only isotope
Kr has one s-only isotope

12. Branching points on the s-process path, half lives roughly > a day

13. Which of these statements is correct?
81Se is a branching point
81Kr is a not branching point
85Kr is not a branching point
86Rb is a branching point

14. Which of these statements is correct?
Its half life is so long we can consider it as stable during the s process
81Se is a branching point
81Kr is a not branching point
85Kr is not a branching point
86Rb is a branching point

15. Which of these statements is wrong?
The branching point at 85Kr means that 86Kr is not really an r-only isotope
There is a branching point at 80Br
86Rb is a branching point
89Sr and 90Sr are both branching points

16. Which of these statements is wrong?
The branching point at 85Kr means that 86Kr is not really an r-only isotope
There is a branching point at 80Br
86Rb is a branching point
89Sr and 90Sr are both branching points
6-4 – 5-5 +
It can decay both beta+ and beta-

17. What do the s-process peaks correspond to?
The Solar System abundances
What do the s-process peaks correspond to?
s-process peaks

18. What happens at Ba that makes it a peak?
There are 5 stable isotopes in a row
There is a branching point at 134Cs
There are two s-only 134Ba and 136Ba
138Ba is neutron magic

19. What happens at Ba that makes it a peak?
There are 5 stable isotopes in a row
There is a branching point at 134Cs
There are two s-only 134Ba and 136Ba
138Ba is neutron magic

20. Stable magic nuclei act as bottlenecks on the s-process path and tend to accumulate
Go to kadonis
N=82

21. The Solar System abundances
The s-process peaks correspond to stable nuclei with Neutron Magic Numbers
N=50,82,126
s-process peaks

22. The Solar System abundances
The s-process peaks correspond to stable nuclei with Neutron Magic Numbers
N=50,82,126
r-process peaks
s-process peaks

23. What do the r-process peaks correspond to?
Isotopes with known mass and half-lives
Isotopes on (n,g)-(g,n) equilibrium
Unstable neutron magic nuclei
Isotopes on the neutron drip line
At high temperatures (T > 5 GK) nuclear reactions form nuclei and photons destroy them (photodissociation) at the same speed

24. What do the r-process peaks correspond to?
Isotopes with known mass and half-lives
Isotopes on (n,g)-(g,n) equilibrium
Unstable neutron magic nuclei
Isotopes on the neutron drip line

25. What do the r-process peaks correspond to?

26. The Solar System abundances
The s-process peaks correspond to stable nuclei with Neutron Magic Numbers
N=50,82,126
r-process peaks
s-process peaks
The r-process peaks correspond
to unstable nuclei with N=50,82,126
Anyone has questions?

27. How do we reproducethem?
The Solar System abundances
How do we reproducethem?
r-process peaks
s-process peaks

28. nuclides with known masses
The main nuclear physics inputs: neutron-capture cross sections, beta-decay rates, nuclear masses… are known much better for the s process than for the r process
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nuclides with known masses

29. First we find a s-process model that reproduces the s-only isotopes:
We can use a parametric model feeding a given neutron flux into a nuclear network
Kaeppeler et al. (1990)

30. Needs to be matched by r-process models.
“r-residuals” method
For each isotope of mass A:
solar r process = solar abundance – solar s process
Needs to be matched by r-process models.
The only one for a long time….
Kaeppeler et al. 1989
Arlandini et al. 1999
Sneden & Cowan 2003

31. Solar system r residuals
Observational hints from old stars [Fe/H] ~ -2; -3
Solar system r residuals
For the element with Z > 55 stars and solar r residuals are the same!
For elements with Z < 55 instead there is a scatter.
How many “r processes”?

32. The r process for Z > 55 is coupled to a-elements and Z < 55 production
The r process for Z > 55 is decoupled from a-elements and coupled to Z < 55 production
The r process for Z > 55 is decoupled from a-elements and Z < 55 production
The r process for Z > 55 is coupled from a-elements and decoupled to Z < 55 production

33. The r process for Z > 55 is coupled to a-elements and Z < 55 production
The r process for Z > 55 is decoupled from a-elements and coupled to Z < 55 production
The r process for Z > 55 is decoupled from a-elements and Z < 55 production
The r process for Z > 55 is coupled from a-elements and decoupled to Z < 55 production

34. Astrophysical sites: The r process
It needs a neutron-rich explosive environment:
core-collapse supernovae (SNII)
neutron star mergers

35. Astrophysical sites: The r process
The r process for Z > 55 is decoupled from a-elements and Z < 55 production
np process, charged-particle reactions in SNII, … (?)
SNII
The r process for Z > 55 does not happen in every SNII
Neutron star mergers, neutron-rich jets….

36. Astrophysical sites: The s process
Since the 1950s it has been observed to occur in asymptotic giant branch (AGB) stars
The AGB star TT Cygni: central emission from material blown off the red giant over a few hundred yr; thin ring is a shell of gas that has been expanding outward for 6,000 years (H. Olofsson).
Merrill 1952, Burbidge et al. 1957

37. All stars with masses <10 M go through the AGB phase
Post-AGB track
Core He exhaustion
Core H exhaustion

Planetary nebulae
Core He burning starts


AGB stars
Schematic evolutionary track of a star of 2 M

38. All stars with masses <10 M go through the AGB phase
Artist impression. Courtesy of Pedro Garcia-Lario, ESA and Anibal García-Hernandez, IAC

39. The core is hot and dense:
Extended convective envelope
Compact core
The core is hot and dense:
a perfect place for nuclear reactions to produce heavy elements!

40. 13C(a,n)16O (M < 4 Msun, the 13C pocket )
Extended convective envelope
13C(a,n)16O (M < 4 Msun, the 13C pocket )
22Ne(a,n)25Mg (M > 4 Msun)
Mixing between the core and the envelope carries the heavy elements to the surface.
Compact core
Ne22(a,n) uncertain

41. What is the effect of rotation?
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42. What is the effect of rotation?
mixing at the core-envelope boundary: carries 14N inside the 13C pocket,
14N + n is efficient: it steals neutrons from the s process
Rotation can dramatically change the number of free neutrons (Herwig, Langer, & Lugaro 2003, Siess & Goriely 2004, Piersanti, Cristallo & Straniero 2013)
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43. What is the effect of rotation?
mixing at the core-envelope boundary: carries 14N inside the 13C pocket,
14N + n is efficient: it steals neutrons from the s process
Rotation can dramatically change the number of free neutrons (Herwig, Langer, & Lugaro 2003, Siess & Goriely 2004, Piersanti, Cristallo & Straniero 2013)
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Coupling of envelope and core can slow down the core

44. Asteroseismology!
Cantiello et al. (2014): “…evolution of the star from the He burning clump to the cooling WD phase appears to be at nearly constant core angular momentum.”

45. Constraints for AGB s-process models
Spectroscopic observations:
MS, S, C(N) stars, post-AGB stars (Busso et al. 2001, Reyniers et al. 2004, De Smedt et al. 2012, 2014)
Massive OH/IR stars (van Raai et al. 2012, Karakas et al. 2012, Garcia-Hernandez et al.2013)
Planetary nebulae (Sterling & Dinerstein 2007, Karakas, et al. 2009)
Ba, CH, and carbon-enhanced metal-poor (CEMP, [Fe/H] ~ -2.3) stars, as the signature of mass transfer from an AGB binary companion (Bisterzo et al. 2011, 2012; Lugaro et al. 2012)
Laboratory analysis of meteoritic stardust silicon carbide (SiC) grains that originated from C-rich AGB stars (Lugaro et al. 2003).

46. Meteors and meteorites!
Inside a meteor there is always a meteorite
A meteorite is a rock that falls to Earth while a meteor is a rock that does not fall to Earth
A meteor “stays up”, a meteorite “falls down”
A meteor is a shooting star and a meteorite is an extraterrestrial rock

47. Meteors and meteorites

48. Is this a meteor or a meteorite?

49. Stardust grains are microscopic dust particles
Allende meteorite (Mexico, 1969)
Carbonaceous chondrite
Matrix: amalgam of amorphous material and crystals of very
small dimensions
size ~ 1 m
Chondrules
size ~ 1 mm
Stellar grains

50. …with extremely exotic isotopic compositions…
This SiC grain has 12C/13C=55, in the Sun =89

51. Types of stellar dust from meteorites

52. Types of stellar dust from meteorites
C > O
O > C
In the solar system C/O = 0.4 

53. Which Mo isotope is an s-only? 92, 94, 96, or 100?
SiC grain from a supernova
SiC grain from an AGB star

54. = dN/dt = - l N [ ln(N1) - ln(N0) ]/l = t0 – t1
Radioactivity as a cosmochronometer! =
dN/dt = - l N
N=abundance
l = constant decay rate
N1 ; N0 = abundances of a radioactive nucleus at times t1 ; t0
[ ln(N1) - ln(N0) ]/l = t0 – t1

55. N0 is available from meteoritic analysisaa t0
birth of the Sun
N0 is available from meteoritic analysis

56. N0 is available from meteoritic analysis
Detailed chronology of planetary growth from micrometer-sized dust to terrestrial planets aa t0
birth of the Sun
N0 is available from meteoritic analysis t1
chondrule formation ~ 1 Myr
Dauphas & Chaussidon 2011, Annual Reviews of Earth and Planetary Science

57. t0 t1 t1 birth of the Sun Isolation time? chondrule formation ~ 1 Myr
Detailed chronology of the events that predated the birth of the Sun?
Detailed chronology of planetary growth from micrometer-sized dust to terrestrial planets aa t1
Isolation time?
Last addition of material from a star? t0
birth of the Sun
N0 is available from meteoritic analysis t1
chondrule formation ~ 1 Myr
Dauphas & Chaussidon 2011, Annual Reviews of Earth and Planetary Science

58. ×
3 hours! (Takashi & Yokoi 1987)

59. 42.5 days! (Lugaro et al. 2014)

60. last r process last s process -100 Myr -30 Myr Isolation Period
Star birth a a
-100 Myr
A neutron star merger
or special supernova
adds 129I to the Solar System matter
(with the final ~1% of gold and silver).
-30 Myr
An AGB star adds 182Hf to the Solar System matter
(with the final ~1% of rare earth elements, tungsten, and lead).
Birth of the Sun
Isolation Period
Star forming
nebula:
no more additions!
Lugaro, Heger, Osrin, Goriely, Zuber, Karakas, Gibson, Doherty, Lattanzio, & Ott, Science, 345, 650 (8th August 2014)

61. last r process last s process -100 Myr -30 Myr Isolation Period
Star birth a a
-100 Myr
-30 Myr
Birth of the Sun
Isolation Period
Implications on the circumstances of the birth of the Sun:
Small star-forming clouds appear to live as short as 4-5 Myr (Hartmann et al. 2001).
More massive clouds (>104 solar masses) have longer lifetimes, up to 40 Myr (Murray 2011, Colin et al. 2013).
A protracted isolation timescales would imply that our Sun was born in a high-mass stellar nursery!