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Metal Poor Stars

Metal Poor Stars. Jeff Cummings Indiana University April 15, 2005. Overview. Early (first) nucleosynthesis events in the universe (SN, BBN, hypernova?) Primordial Lithium Future Work. Weiss et al. (2004). CS 22949-037. Characteristics (Depagne et al. 2002)

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Metal Poor Stars

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  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 22949-037 • Characteristics (Depagne et al. 2002) - V=14.36, Teff=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]=+1.97 • How did this star get these abundances? • The super solar N is the most difficult - Rotationally induced mixing (Maeder 1997) - Convective overshoot or supermixing (Timmes et al. 1995) - Zero heavy-element hypernovae (Woosley & Weaver 1982)

  4. 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 Msun • 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 Msun object of C=0.0026, N=0.078 and O=0.08 for; and 300 Msun object of C=00033, N=0.013, and O=0.057

  6. Evolutionary Results • Their model for the 250 Msun object gives a He core of 130 Msun (133 Msun is needed to collapse to a black hole) • This results in a hypernova with a total kinetic energy of 9 x 1052 ergs (almost 100 times the energy of a normal SN), and the N enrichment is added to the ISM • Their model for the 300 Msun object gives a He core of 180 Msun 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 Teff > 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 Teff > 5600 K: - dA(Li)/d[Fe/H]=0.118±0.023 (1σ) dex per dex - dA(Li)/dT=0 (within the errors) - 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 ΩB (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 - 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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