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Metal Poor Stars Jeff Cummings Indiana University April 15, 2005.

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Presentation on theme: "Metal Poor Stars Jeff Cummings Indiana University April 15, 2005."— Presentation transcript:

1 Metal Poor Stars Jeff Cummings Indiana University April 15, 2005

2 Overview  Early (first) nucleosynthesis events in the universe (SN, BBN, hypernova?)  Primordial Lithium  Future Work Weiss et al. (2004)

3 CS  Characteristics (Depagne et al. 2002) - V=14.36, T eff =4900 K, log g=1.5 - V=14.36, T eff =4900 K, log g=1.5 - [Fe/H]=-3.9, [Mg/Fe]=+1.2, [Si/Fe]=+1.0, [Ca/Fe]=+0.45, [C/Fe]=+1.1, [N/Fe]=+2.7, [O/Fe]= [Fe/H]=-3.9, [Mg/Fe]=+1.2, [Si/Fe]=+1.0, [Ca/Fe]=+0.45, [C/Fe]=+1.1, [N/Fe]=+2.7, [O/Fe]=+1.97  How did this star get these abundances?  The super solar N is the most difficult - Rotationally induced mixing (Maeder 1997) - Rotationally induced mixing (Maeder 1997) - Convective overshoot or supermixing (Timmes et al. 1995) - Convective overshoot or supermixing (Timmes et al. 1995) - Zero heavy-element hypernovae (Woosley & Weaver 1982) - Zero heavy-element hypernovae (Woosley & Weaver 1982)

4 Msun zero metallicity SN output modeled by Woosley & Weaver (1995) Measurements by Depagne et al. (2002) with a 35 Msun zero metallicity SN output modeled by Woosley & Weaver (1995)

5 Zero Element Massive Stars  Fryer et al. (2001) look at the evolution of rotating zero heavy-element objects of mass 250 and 300 M sun  N is produced once traces of C and O from the He-burning core are mixed out into the H- burning shell by meridional circulation  This gives mass fractions in the envelope of a 250 M sun object of C=0.0026, N=0.078 and O=0.08 for; and 300 M sun object of C=00033, N=0.013, and O=0.057

6 Evolutionary Results  Their model for the 250 M sun object gives a He core of 130 M sun (133 M sun is needed to collapse to a black hole)  This results in a hypernova with a total kinetic energy of 9 x ergs (almost 100 times the energy of a normal SN), and the N enrichment is added to the ISM  Their model for the 300 M sun object gives a He core of 180 M sun resulting in collapse to a black hole  The N enrichment can only escape to the ISM from mass loss before the collapse, but mass loss is difficult for zero metallicity stars

7 Lithium in Metal Poor Stars  Spite & Spite (1982) found that halo dwarfs with T eff > 5700 K have ~constant lithium abundance independent of T and [Fe/H]  Either all of these stars were depleted uniformly, or they haven’t been depleted at all (primordial lithium)

8 Is It Really Flat?  More recent studies (Ryan et al. 1999; Zhang & Zhao 2003) have found that for metal poor stars with T eff > 5600 K: - dA(Li)/d[Fe/H]=0.118±0.023 (1σ) dex per dex - dA(Li)/d[Fe/H]=0.118±0.023 (1σ) dex per dex - dA(Li)/dT=0 (within the errors) - dA(Li)/dT=0 (within the errors) - A(Li) p ≈ 2.08 dex - A(Li) p ≈ 2.08 dex

9 Why Should We Care?  This new finding of dependence is very interesting for learning about how iron abundance and lithium abundance are related  Primordial lithium can set limits on η (the baryon-to-photon ratio) and Ω B (the universal baryon density)  Lithium is cool

10 Future Work  More metal poor stars need to be observed! - Get statistically significant and consistent abundances in similar metal poor stars - Get statistically significant and consistent abundances in similar metal poor stars - Larger samples of metal poor stars (especially [Fe/H]<-3]) are needed to accurately determine A(Li) p - Larger samples of metal poor stars (especially [Fe/H]<-3]) are needed to accurately determine A(Li) p

11 Conclusions  Modeling SN to match the observed element abundances in metal poor stars can yield information about the first generation of (massive?) stars  Primordial Li abundance measured from metal poor stars can constrain cosmological parameters

12 References  Depagne, E., Hill, V., Spite, M., Spite, F., Plez, B., Beers, T.C., Barbuy, B., Cayrel, R., Andersen, J., Bonifacio, P., Francois, P., Nordstrom, B., & Primas, F. 2002, A&A, 390, 187  Fryer, C.L. Woosley, S.E., & Heger, A. 2001, ApJ, 550, 372  Maeder, A. 1997, ASP Conf. Ser. 147  Ryan, S.G., Norris, J.E., Beers, T.C. 1999, ApJ, 523, 654  Spite, F., Spite, M. 1982, A&A, 115, 357  Timmes, F.X., Woosley, S.E., & Weaver, T.A. 1995, ApJS, 98, 617  Weiss, A., Schlattl, H., Salaris, M., & Cassisi, S. 2004, A&A, 422, 217  Woosley, S.E., & Weaver, T.A. 1982, Supernovae: A Survey of Current Research  Woosley, S.E., & Weaver, T.A. 1995, ApJS, 101, 181  Zhang, H., Zhao, G. 2003, CJAA, 5, 453


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