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ABUNDANCE VARIATIONS IN GLOBULAR CLUSTERS: from light to heavy elements

ABUNDANCE VARIATIONS IN GLOBULAR CLUSTERS: from light to heavy elements. Valentina D ’ Orazi Dept. of Physics and Astronomy, Macquarie University Monash Centre for Astrophysics, Monash University.

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ABUNDANCE VARIATIONS IN GLOBULAR CLUSTERS: from light to heavy elements

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  1. ABUNDANCE VARIATIONS IN GLOBULAR CLUSTERS: from light to heavy elements Valentina D’Orazi Dept. of Physics and Astronomy, Macquarie University Monash Centre for Astrophysics, Monash University Collaborators: RaffaeleGratton, Sara Lucatello (INAF Padova), Angela Bragaglia, Eugenio Carretta (INAF Bologna),Anna F. Marino (Max Planck Institute, Heidelberg), Chris Sneden (The University of Texas at Austin),Simon W. Campbell, Maria Lugaro, John Lattanzio, George Angelou (Monash University)Thomas Masseron (Universite de Brussels) IneseIvans (University of Utah) Marco Pignatari (University of Basel)

  2. “A Simple Stellar Population is defined as an assembly of coeval, initially chemically homogeneous, single stars.. Four main parameters are required to describe a SSP, namely its age, composition (Y,Z), and the initial mass function ..In nature the best example of SSPs are stellar clusters” (Renzini & Buzzoni 1986). Globular Clusters for many years considered as ideal benchmarks for studying stellar evolution & synthesis population models THIS TRADITIONAL PERSPECTIVE IS NOW PROVEN TO BE TOO SIMPLISTIC….

  3. Pancino et al. (2000) Bedin et al. (2004) Lee et al. (1999) Piotto et al. (2007) Milone et al. (2008) Globular Clusters ARE NOT Simple Stellar Populations Photometry ω Cen NGC 2808 NGC 1851

  4. M4 M22 Since ’70s anti-correlations between light elements (C, N, O, Na, Mg, Al) the abundances of C, O, Mg are depleted where those of N, Na, Al are enhanced Cohen (1978); Peterson (1980); Norris (1981) Spectroscopy Lick-Texas group (from Ivans et al. 2001) Marino et al.(2008, 2009)

  5. A PREVIOUS GENERATION of stars which synthesized in their interiors p-capture elements are RESPONSIBLE for these chemical signatures in GC stars HOT hydrogen burning, where the ON, NeNa, and MgAl chains are operating - the ON reduces O, the NeNa increases Na (T ~ 30 million K), while the MgAl produces Al (T~65 million K) Still debated…… • IM-AGB stars (4 – 8 M) experiencing Hot Bottom Burning (e.g. Ventura & D’Antona 2009) • Winds of Fast Rotating Massive Stars (e.g. Decressin et al. 2007)

  6. OUR SURVEY All the GCs show the Na-O anti-correlation  the second generation is always PRESENT The shape of Na-O distribution changes from cluster to cluster  POLLUTER’S MASS is varying: this change is driven by both Luminosity (~mass) & Metallicity Carretta et al. (2009a) P=primordial FG I=Intermediate SG E=Extreme SG • Na-O anticorrelation and HB in 19 GCs FLAMES@VLT (Giraffe+UVES),>100 hrs Fe-peak, Na, O, Mg, Al abundances derived for ~1200 stars

  7. The Mg-Al anticorrelation is not present in ALL the GCs ( POLLUTER’S MASS) Carretta et al. (2009b) The Mg-Al anticorrelation This can also be explained through high-temperature (T~ 65 million K) proton capture nucleosynthesis, via the MgAl chain (Mg depleted, Al enhanced). Kraft et al. 1997 Yong et al. 2003 (NGC 6752)

  8. Why Lithium ?? • Among the light elements Li has a special role. • Li is produced in Big Bang nucleosynthesis • It is enriched during the galaxy evolution,and • destroyed in the stellar interior • (Tburn starting @ 2.5 MK) • WMAP •  logn(Li)=2.72 ± 0.06 • (Cyburt et al. 2008) • Li-plateau •  logn(Li)=2.1 – 2.3 (halo stars) • ..solution still far…

  9. Lithium & p-capture elements (1) • Li has a fundamental role thanks to the fact that it is very easily destroyed in stellar interiors: • It is expected that at CNO/NeNa cycle temperatures NO Li is left •  Polluting material (ejected from the first generation stars) has Li ~ 0 • Na-poor, O/Li-rich stars are the FIRST POPULATION born in the cluster  share the same chemical composition of field stars • Na-rich, O/Li-poor stars, i.e. the SECOND GENERATION, formed from gas progressively enriched by the ejecta of first population IF PRISTINE AND POLLUTING MATERIAL ARE MIXED IN DIFFERENT PROPORTIONS THEN LITHIUM AND OXYGEN ARE EXPECTED TO BE CORRELATED, AND LITHIUM AND SODIUM ANTICORRELATED

  10. Lithium & p-capture elements (2) WHICH ARE THE POLLUTERS ?? • While Fast Rotating Massive Stars can only destroy Li, IM-AGB stars can also produce it THE CAMERON-FOWLER MECHANISM (“7Be transport” mechanism, Cameron & Fowler 1971) Any production of Lithium tends to erase the Li–O(Na) (anti–)correlation

  11. History (1): NGC 6752 Pasquini et al. (2005) [Fe/H] = –1.5 (Carretta et al. 2009c) (m-M)=13.13 Basing on 9 TO stars, Pasquini et al. found a Li depletion up to ~ 1 dex below the Spite plateau Li-Na anticorrelation  Li-O correlation  Li-N anticorrelation

  12. History (2): NGC 6397 Bonifacio et al. (2002) on only 4 stars: NO Li variation [Fe/H] = – 1.99 (Carretta et al. 2009c) (m-M) = 12.50 Lind et al. (2009)  the first large sample of Li, Na determinations in TO and early SGB stars, i.e. ~100 stars “a limited number of Na-enhanced and Li-deficient stars strongly contribute to forming a significant anti-correlation between the abundances of Na and Li.” (Lind et al. 2009)

  13. (1) Li, Na, O in GC dwarfs: the case of 47 Tuc (**) [X]=log[(1-dil) x10[XO] + dil x10[Xp]], where [XO] and [Xp] are logarithmic abundances of original and processed material Prantzos & Charbonnel (2006) D’Orazi et al. (2010a) ~100 TO stars FLAMES Giraffe spectra HR15n (Li I) HR19A (Na I @8183-8194 Å O I @7771-7775Å) The largest database of this kind available so far Red solid line  dilution model(**) • Na-O distributions in dwarfs and giants are identical  evolutionary effects acting during the RGB phase (D’Antona for M13) can be ruled out –at least for this cluster-

  14. Li-O are weakly positively • correlated within a • large scatter • Stars with low O have also low • Li content, but at higher oxygen, • Li can assume all values, • ranging from 1.54±0.06 to • 2.78±0.08 • Li-Na show NO anti-correlation • A simple dilution model fails in reproducing both Li-O and Li-Na distributions (maybe this model is just the upper envelope) • Different behaviour with respect to NGC 6397 ([Fe/H]=-1.99) • The scatter is reminiscent (a Pop. II analog?) of what found in the OC M67 (e.g. Randich et al. 2000) and in general in cool (Teff~5800K) disk stars (Ryan et al. 2001)

  15. (2) Li-Na anticorrelation in NGC 6121 (M 4) D’Orazi & Marino (2010) FLAMES UVES (R~50000, setup 580) spectra for ~90 giant stars from Marino et al. (2008) Stellar parameters + abundances for Fe, Na, O  Marino et al. (2008) Na-O anticorrelation Red stars: V > Vbump A depletion of Li of a factor of ~20 is predicted at 1 DUP (at the bump luminosity Li  0, thermohaline mixing, see Charbonnel & Zahn 2007)

  16. 1st generation 2nd generation • NO Li-Na anticorrelation • Na-rich and Na-poor stars have the SAME Li content, BUT the scatter is larger for the first group V > Vbump

  17. Low mass AGB polluters (~4M) moderate Li production • (≈Plateau value) • The “vertical” Na-O anti-correlation in M4 confirms very low • depletion of O • No Al variations (no MgAl cycle) Any Lithium production tends to erase the Li-Na anticorrelation WHICH ARE THE MODEL PREDICTIONS ? D’Antona & Ventura (2010) M 4

  18. From light to heavy elements Barium abundances in 15 Globular Clusters From Giraffe spectra INTERMEDIATE AGB STARS (4 – 8 M) AS CANDIDATE POLLUTERS • IS THERE ALSO THE CONTRIBUTION OF LOW MASS AGBs (s-process variation and CNO NOT constant) ??

  19. 1. Barium vs. [Na/Fe]/[O/Fe] D’Orazi et al. (2010b)

  20. Barium and Na-O anticorrelation • There is NO segregation along the NaO anticorrelation between Ba-rich and Ba-poor stars

  21. Barium stars Quite LARGE UNCERTAINTIES but STATISTICS 5 Ba stars on a total of 1205  ~0.4 % FIELD STARS  ~2 % [Fe/H] Mv 47 TUC -0.76 -9.42 NGC 288 -1.32 -6.74 NGC 6254 -1.57 -7.48 NGC 6397 -1.99 -6.63 NGC 6752 -1.55 -7.73 4 of 5 Ba-stars are P: between P stars, the fraction of Ba stars reaches ~2%  CLUSTER ENVIRONMENT

  22. What’s next?? (1) Run of Lithium with p-capture reaction elements in: NGC 6218, NGC 3201, NGC 5904 ESO P87 30 h with FLAMES@VLT (PI VD)  ~100 RGB stars per GC Preliminary results in NGC 6218 indicate an M4-like behaviour: Li is CONSTANT between First and Second Generation stars (D’Orazi+ 2012, in prep.)

  23. The chemical composition of nearby young clusters/associations Collaborators: SilvanoDesideraRaffaeleGratton (INAF Padova) Katia Biazzo , Elvira Covino (INAF Napoli), Sergei M. Andrievsky (Odessa National Observatory/GEPI Paris) Gayandhi De Silva (AAO) Claudio Melo (ESO Chile) Sofia Randich (INAF Arcetri) Carlos Torres (LaboratorioNacional/MCT, Brazil) ``

  24. Anticorrelation between [Ba/Fe] ratio and cluster age D’Orazi et al. (2009) Galactic chemical evolution model only assuming a higher Ba yield from low-mass AGB stars (i.e. 1-1.5 Msun) than that previously predicted (confirmed from other s-process elements, Maiorca + 2011)

  25. While a chemical evolution model with enhanced Ba production can account for the observed raising trend up to ~500 Myr, it dramatically fails in reproducing the young stellar clusters. Is the enhancement in the Ba content shared by the majority (totality?) of young clusters populating the solar neighbourhood? Are the nearby young clusters characterised by a unique [Ba/Fe] value? Do they show any intrinsic internal dispersion? Do the other s-process elements follow the enhancement in Ba?

  26. S-process elements in AB Doradus (~70 Myr), Carina-Near (~200 Myr) and Ursa Major (~500 Myr) D’Orazi et al. 2012 We find that while the s-process elements Y, Zr, La, and Ce exhibit solar ratios in all three associations, Ba is over-abundant by 0.2 dex.

  27. Run of s-process elements with OC ages

  28. None of the current models can account for such a trend in Ba, without bearing similar enhancement in other s-process elements Chromospheric effects???? • CaII H&K chromospheric emission, (logR_HK) • coronal emission (X-ray luminosity) • (iii) rotational velocity (vsini) Due to the presence of a hot chromosphere, one would expect a T(tau) function less steep compared to that of old stars (the outer atmosphere should be heated at a certain extent by the upper chromosphere levels). NLTE effects of the 5853 Å line Over-ionisation

  29. Although no correlation between [Ba/Fe] and several activity indicators seems to be present, we conclude that different effects could be at work which may (directly or indirectly) be related to the presence of hot stellar chromospheres. need for a large, homogeneous investigation of s-process abundances in clusters younger than the Hyades to draw final conclusions on this issue and provide observational constraints to new theoretical models. ..Stay tuned…

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