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

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

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. Bromm etal, 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) < [Fe/H]< UMP (ultra metal-poor) < [Fe/H]< HMP (hyper metal-poor) < [Fe/H]< 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

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 Ia SNe (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.

 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

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 The r-process crisis

2. Heavy elements in oldest Stars and Early Universe First example : the r-process rich star CS show some interesting results A similar case is CS (Hill et al. 2002) remarkable EMP: [Fe/H]=-3.1 n-capture elements with Z  56 in this meta-poor star match closely solar system r- process pattern 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 Sneden eta al: APJ, 591, 936 (2003) Weak r-process Main r=process

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 and HE Both are rich in CNO but very poor in n-capture elements. This is different from the previous cases (CS or CS ) 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

Heavy n-capture elements CS HD BD+17  3248 CS HD HE CS He Cs HE Figure indicate: All heavy n-capture elements (Ba and above) consistent with solar system r-process distribution (Sneden et al 2009) 10 r-process rich stars [ Fe/H]=-3.1

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= Their suggestion: LEPP may have been important in synthesizing the abundances in the r-process poor star HD (see next slide)

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

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

Comparison of the abundances in the stars BD and HD 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) Such comparison argue for a combination of processes: LEPP, -p process, ??? insight

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

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

Log n n =20-22 Log n n =20-24 Log n n =20-26 Log n n =20-28

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?

Timeline of light in the universe Galaxies formed more recently and can be seen at visible wavelength. 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. 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 3. Cosmological Motivation & Evolutionary Scenarios

AGB Planetary Nebula White Dwarf Iron core collapse Shock/neutrino driven Neutron stars Black holes Evolutionary Scenario: overview Massive C/O Cores: M Sun Explosive oxygen burning Pair Creation Supernovae Black holes

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

What is a Pair Instability Supernov a (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 10 9 K Example follows

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

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 Entropy per unit volume divided by baryon density  When this happens, the adiabatic index drops below 4/3 and not only at center as we have see on the previous slide s=10

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 Why does  <4/3 has a finite range? At high temperatures:  >4/3 because the particles become relativistic such that the energy gap for pair creation is no more important

Langer, N. Nature 462, 579 (2009) 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 Z Solar /3. While the common view is that these events may be associated to Pop Iii stars Here is a case

Gal-Yam et al (2009) 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 M Sun Another object is SN2006gy (Smith et al, Apj 666, 1116 (2007)) Light curves of super luminous SNe R-band light curve of SN2007bi. With a peak magnitude of mag If this light curve is radioactively driven, > 3 M sun of 56 Ni 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 M sun and very high explosion energy > erg

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 M sun ) 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.

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 M sun which undergo PCSNe, with different assumption of the exponent of a Salpeter-like IMF Heger & Woosley (2002)

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

Different mixture of odd an even Ba (Z=56) isotopes are produced by the r-process and s-process 134 Ba 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. Shielding of the Barium isotopes

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

Exotic n-capture scenario (1)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=25x10 6 K At T=15x10 6 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< As seen on next page, the hydrogen-burning shell remains convective all the time.

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

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

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

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

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

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

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

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

Elemental ratio La/Eu for large number of stars Filled circles for halo stars: Simmerer et al : APJ, 617, 1091 (2004) Filled diamonds (disk starts): Woolf et al, APJ, 453, 660 (1995) r-process only  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  Only the most metal- poor stars seem to have La/Eu ratio consistent with r-process-only ratio La: mainly s-process Eu: mainly r-process  Some s-processing below [Fe/H]=-2.0 s-process rich Total solar system r-process enhanced

References Cowan, J.J xiv: /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

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