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Mounib El Eid American University of Beirut Department of Physics

Nucleosynthesis & Cosmology. Infrared light from first stars: Spitzer image ( z=11). You are back to about 400 million years after Big Bang. Mounib El Eid American University of Beirut Department of Physics. Santa Tecla : Sept. 18, 2011. program. 1. General comments.

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Mounib El Eid American University of Beirut Department of Physics

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  1. Nucleosynthesis & Cosmology Infrared light from first stars: Spitzer image ( z=11) You are back to about 400 million years after Big Bang Mounib El Eid American University of Beirut Department of Physics Santa Tecla: Sept. 18, 2011

  2. program 1. General comments 2. Heavy elements in oldest Stars and Early Universe 3. Cosmological Motivations and evolutionary scenarios. Just drawing a connection

  3. 1. General comments  First stars formed after Big Bang were quite different from those formed later, simply because they were composes of H, He and small fraction of Li  Classification of the first stars is not easy. Brommetal, Nature 459, 49 (2009) made the following classifications: pop III.1 stars formed under initial cosmological parameter pop III.2 stars formed from photo-ionized gas by earlier generation pop II stars: EMP (extreme metal-poor) 10-4 < [Fe/H]< 10-3 UMP (ultra metal-poor) 10-4 < [Fe/H]< 10-4 HMP (hyper metal-poor) 10-6 < [Fe/H]< 10-6 It seems that such a classification is related to nature of the first galaxies, where a galaxy is a system of stars, gas and a dark matter halo Within this picture: pop III.1 stars are assumed to be formed in isolation in minihalos (not in galaxies)  Many arguments exist (Bromm et al 2009 and references therein) that the first stars were massive and even very massive, mainly because of their formation in a medium devoted of heavy elements such that cooling and effective fragmentation were inhibited

  4. If so, the first stars represent extinct generations, because they ended in supernovae explosion, eventually not only as core collapse (later more)  Observing the chemical abundances in the oldest surviving stars is a way to learn about the nature of the first stars. But chemical abundances are related to nucleosynthesis processes occurring in stars, that is linked to stellar evolution. The heavy elements (neutron-capture elements beyond iron) in the universe were formed in very late evolutionary phases of stars by the s-process, like Barium (mainly in AGB stars) r-process, like platinum or gold (mainly supernovae) with a time scale of the order of millions to billions of years Early star formation not well understood .The iron abundance may tell about the history of star formation. Most of the iron comes from Type IaSNe (exploding white dwarf in binary systems). In other words, it comes from long-lived low-mass stars Thus the stars formed had little effect on the history of metallicity. In our Galaxy these metal-poor stars are found in the halo and the metal-rich in the galactic disk.

  5.  The metal-poor stars in the halo serve as “laboratory” for the study of the nucleosynthesis of neutron-capture elements. Their chemical compositions are linked to the types of synthesis processes that occurred early phase of the Galaxy. The presence of heavy elements in these stars indicate preceding extinct generation of massive stars (second generation?) which have synthesized all heavy elements But

  6. The r-process crisis I have also a crises after so many years of struggle with the r-process. But I am so strong to understand the weak r-process

  7. 2. Heavy elements in oldest Stars and Early Universe First example : the r-process rich star CS22892-52 show some interesting results A similar case is CS31082-001 (Hill et al. 2002) Sneden eta al: APJ, 591, 936 (2003) EMP: [Fe/H]=-3.1 remarkable n-capture elements with Z56 in this meta-poor star match closely solar system r-process pattern Main r=process Weak r-process Also remarkable Scaled solar r-process distribution does not extend to the lighter n-capture elements below Z=56 For example: Silver (Ag, Z=47) is deficient

  8. Conclusion from previous Figure: It seems that the r-process could be divided like the s-process into 2 components : weak r-process ( so far it is called LEPP=Light Element Primary Process) main r-process (classical r-process) Heavy elements have been also observed in extremely metal-poor stars with [Fe/H]=--5: HE 0107-5420 and HE1327-2326 Both are rich in CNO but very poor in n-capture elements. This is different from the previous cases (CS 22892-052 or CS31082-001) Learn effect Rapid change in nucleosynthesis in the early phase of the Galaxy. It seems: first stars were massive able to produce CNO elements but not the heavy n-capture elements

  9. Heavy n-capture elements 10 r-process rich stars [Fe/H]=-3.1 CS22892-052 HD115444 BD+173248 [Fe/H]=-3.1 CS310802-001 HD221170 HE13250901 CS22953-003 He2327-5642 Cs29491-069 HE1219-0312 Figure indicate: All heavy n-capture elements (Ba and above) consistent with solar system r-process distribution (Sneden et al 2009)

  10. Light n-capture Elements The lighter n-capture elements (Z<56) seem to fall below the solar system curve Observation of four metal-poor r-enriched stars (Grawford et al 1998) indicates: Ag (Z=47) produced in proportion of the heavier elements in stars with -2.2 <[Fe/H] <-1.2. Wasserburg et al (1996) proposed multiple processes of the heavy elements. Travaglio et al (2004) suggested: not all of the Sr-Zr solar system abundances can be explained by the classical r-process, or s-process (main and weak). The term LEPP has been invented to give such a process a name.(not really the best description). I would say: ENCP (early n-capture process) Montes et al (2007) extended the range of the LEPP up to Ba , Z=38- 56. Their suggestion: LEPP may have been important in synthesizing the abundances in the r-process poor star HD122563 (see next slide)

  11. r-process rich 32 elements Solar system normalized to Eu Relatively flat abundance distribution consistent with scaled solar system r-process for the heavies Farouqi et al (2009) HEW r-process poor [Eu/Fe]=-0.5 Solar system normalized to Sr Solar system normalized to Eu Here: sharp decrease with increasing atomic number ; looks like incomplete r-process (or weak r-process)

  12. Another comparison r-process rich: [Eu/Fe]=+1.6 r-process poor: [Eu/Fe]=-0.5

  13. Comparison of the abundances in the stars BD+173248 and HD122563 shows that the third peak of the r-process (Os, Ir, Pt: Z=76, 77, 78 ) is not formed High-entropy wind model in SNII: Farouqi et al (2009) Deviation starting Z=45: Ag (Z=46), Cd (Z=48) and also Pd (Z=46) insight Such comparison argue for a combination of processes: LEPP, -p process, ???

  14. r-process throughout the Galaxy 16 stars The difference between BD+173248 and HD122563 discussed above is found to be a general behavior as shown in the following Figure: r-process rich flat Nothing here r-process poor No heavy n-capture elements HD122563 References to this Figure: Cowan eta l (2011) preprint

  15. The abundances in HD122563 suggest an incomplete r-process, or let us say an n-capture process with a neutron density between 1020- 1024 cm-3, since the synthesis of the heavy n-capture elements needs 1024 – 1028 cm-3 \in the following some results by Kratz et al (2007):

  16. Log nn=20-22 Log nn=20-24 Log nn=20-26 Log nn=20-28

  17. Conclusions  clear presence of n-capture element in atmospheres of metal-poor stars and globular cluster stars The comparison between r-process rich ([Eu/Fe]> 1.0) and r-process poor ([Eu/Fe] < 1 indicates : abundances of the heavy elements (Ba and above, Z=56) consistent with solar system r-process distribution. This seems to be the main r-process. The distribution of the lighter (Z<56) n-capture elements is not conform to solar pattern. New detection of Pd, Ag, Cd (Z=46, 47,48) suggest a weak r-process not yet identied: LEEP -p process in core collapse SNe High Entropy Wind in core collapse SNe Exotic mixing in late phases of massive EMP stars Do different mass region (Ge, Sr-Zr Pd-Ag-Cd) require different processes?

  18. 3. Cosmological Motivation & Evolutionary Scenarios Timeline of light in the universe The oldest light we can see today is the cosmic background radiation . It came from the time 380,000 yrs after Big Bang when the universe became transparent. This light had a redshift of z=1100 and appears in the microwave WMAP data indicate: Some 400 million years later at z=11 the first stars appeared . They reionized the universe, and their light is now shifted to infrared wavelength . Galaxies formed more recently and can be seen at visible wavelength. Dark ages: era from recombination (at 380,00 yr) to the first stars at 400 million yr. This dark ages ended when the universe was filled for the first time with light from stars

  19. Evolutionary Scenario: overview Massive C/O Cores: 64- 133 MSun Explosive oxygen burning Iron core collapse Shock/neutrino driven AGB Planetary Nebula Pair Creation Supernovae Neutron stars Black holes Black holes White Dwarf

  20. The Central Evolution of Stars Iron Disintegration Core collapse supernova Electron-Positron –Creation. Pair Creation supernovae 25 Rapid Electron Capture Core collapse Supernva AGB stars WD Non-degenerate

  21. What is a Pair Instability Supernova (PCSNe)? PCSNe represents the final state evolution of a very massive stars which develops a very massive carbon-oxygen cores Such massive core composed mainly of oxygen and are largely supported by the radiation pressure. As seen in the Figures below, the central evolution of the core proceeds toward higher temperature and relatively low density such that electron-positron pairs are created in equilibrium by the radiation field according to Although the mean energy photons is about kT, there are enough photons in the tail of the Planck’s distribution that can create these pairs even at 109 K Example follows

  22. Example: several cores of different masses are shown. The core of mass 112 Msun corresponding to an initial mass of  200 Msun undergoes collapse and explosion induced by explosive oxygen burning leading to a very brilliant supernova. Central evolution About 25 Msun of oxygen needed to explode such a core with explosion energy > 1052 erg Temperature-density profile T- profile for a 112 Msun star at time reversal of the collapse. Note that significant part of the core is inside the instability region. Ober, El Eid & Fricke: A&A , 119, 61 (1983)

  23. More details on pair creation: What really happens is:  Radiation pressure and entropy decreases  Electron-positron pairs are created and their entropies increase along that of nuclei  When this happens, the adiabatic index s=10 drops below 4/3 and not only at center as we have see on the previous slide Entropy per unit volume divided by baryon density

  24. Why does <4/3 has a finite range? The decrease of  below 4/3 is a consequence of the new particles which do not immediately add their contribution to the total pressure.. At high densities: >4/3, because the electron becomes more degenerate At high temperatures: >4/3 because the particles become relativistic such that the energy gap for pair creation is no more important

  25. Here is a case This figure tells that the fate of a very massive stars depends on its mass and initial metallicity The lines are schematic and not well determined It may be interesting that the PCSN may be found in the local universe and at metallicity up to ZSolar/3. While the common view is that these events may be associated to Pop Iii stars Langer, N. Nature 462, 579 (2009)

  26. The PCSNe are usually associated with early stars, or Pop III stars Is there any evidence of this unusual supernova type? The observations of the SN 2007bi ( Gal-Yam et al, Nature ,462, 624, 2009) in a dwarf galaxy argue for this with an estimated core mass is about 100 MSun Another object is SN2006gy (Smith et al , Apj 666, 1116 (2007)) Light curves of super luminous SNe Gal-Yam et al (2009) R-band light curve of SN2007bi. With a peak magnitude of -21.3 mag If this light curve is radioactively driven, > 3 Msun of 56Ni are needed. The slow rise time (70 days) and photospheric velocity of 12,000 km/s indicate an exploding very massive object of about 100 Msunand very high explosion energy > 1052 erg

  27. Implication of the discovery of SN2007 bi  The estimated high core mass is in conflict with the commonly used mass loss rates as a function of metallicity • Regardless the correct description of mass loss, the data indicate that an extremely massive stars (>150 Msun ) are formed in the local universe in a dwarf galaxy with a metallicity • 12+log[O/H]=8.25 (less than 1/10 of the Sun’s metalicity • Can the dwarf galaxies serve as fossil laboratories for studying the earl universe? • Future missions like the • NASA’s James Webb Space telescope • will help to estimate the contribution of these events to the chemical evolution in the early universe.

  28. Nucleosynthesis in PCSNe Updated calculation by Heger & Woosley (2002) yield:  No heavier elements than Zinc, no r-process, no s-process  Mainly products of explosive oxygen burning. Even nuclear charges (Si, S, Ar, Ca,, ...) in almost solar distribution  Element of odd nuclear charges (Na, Al, P, V, Mn,...) are deficient. The explanation of this is because the massive C/O massive evolves almost directly to oxygen burning without creating a neutron excess Production factors of C/O cores of masses 64 to 130 Msun which undergo PCSNe, with different assumption of the exponent of a Salpeter-like IMF Heger & Woosley (2002)

  29. Interesting evolutionary scenario of extremely meta-poor massive stars Motivation: for example Barium Isotopes in the meta-poor subgiant HD 140283 : ( [Fe/H]=-2.6, [Ba/Eu]=-0.66 and [Eu/H]< -2.8 (r-poor) Author f odd Magain (1995) purleyS-process signature Ghallagher et al. (2010) Lambert et al (2002)

  30. Shielding of the Barium isotopes Different mixture of odd an even Ba (Z=56) isotopes are produced by the r-process and s-process 134Ba and 136 Ba are produced by the s-process only, since they are shielded by the Xenon (Z=54) isotopes made in the r-process.

  31. A challenging question (K.L. Kratz, private communication) : How can one get for a star like HD 140283: fodd = 0.1-0.2 (s-process) and [Ba/Eu}=-0.66 r-process

  32. Exotic n-capture scenario Zero-age mains sequence shifted to higher effective temperature as Z decreases. This is a consequence of reduced metallicity. Recall that the energy generation via the CN cycle: At T=25x106 K At T=15x106 K Lacking of heavy elements, the star has to contract and heats up to burn hydrogen at high temperature. (2) As consequence of the compactness of the star , it cannot evolve to become red giants. They remain confined to the blue part of the HR diagram, when Z<10-3 . As seen on next page, the hydrogen-burning shell remains convective all the time.

  33. Z=2x10-2 : Solar-like El Eid, The , Meyer Space Sci. Rev. , 147, 2009 Many references there Convective Envelope All this happen here red blue Z=10-3 No Convective Envelope

  34. Z=10-3 Possible mixing of protons into the helium shell. It works only at low metallicity. Here: [Fe/H]=-4.5

  35. Let’s believe it……… then What is the advantage of this game?

  36. If this would be true?, we make Primary Sr for example Result after one time step of proton mixing into the helium convective shell. Strong enhancement near Z=38 to more than 50

  37. Arnett, D. 1996: Supernovae and Nucleosynthesis, Princeton Univ. press, p. 244

  38. We need his optimism like this star From FC Barcelona (and FC Libya) to get an answer Does this game work? JJ with American muscles

  39. Final Words  Evolution of early stars linked to nucleosynthesis of heavy elements turns out to be a link to Near-field cosmology (understanding galaxy formation); It is a challenging topic and a revival of the importance of stellar evolution as a fundamental cornerstone of modern Astrophysics  The evolution of the neutron-capture elements traces back the chemical evolution of the galaxy and is bring us back to the dark ages where in order to become more enlightened and overcome our ignorance Thank you for your attention

  40. Imbriani et al (2001), ApJ 558, 903 Rate of 25 Msun star CF85 X 12=0.18 CF85 > CF88 No convective carbon-burning core X12 lower Remaining car bon mass fraction No convective core CF88 X12=0.42 But here

  41. La: mainly s-process Eu: mainly r-process  General increase in the ratio La/Eu ratio as the s-process contribution to La production rises with metallicity. That is after the low mass stars had time to evolve Elemental ratio La/Eu for large number of stars s-process rich  Only the most metal-poor stars seem to have La/Eu ratio consistent with r-process-only ratio Total solar system r-process enhanced  Some s-processing below [Fe/H]=-2.0 r-process only Filled circles for halo stars: Simmerer et al : APJ, 617, 1091 (2004) Filled diamonds (disk starts): Woolf et al , APJ, 453, 660 (1995)

  42. References Cowan, J.J xiv:1106.11091/1 Cowan, J.J, Sneden, C. heavy element synthesis in the old and the early universe. Nature, 440, 1151 (2006) Montes et al, APJ, 671, 1685 (2007) Heger, A, Woosle, S.E. 2002, ApJ 567, 532

  43. We need his optimism like this start From FC Barcelona To get the answer

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