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Martin Asplund

Galactic archeology & planet formation. Martin Asplund. Galactic archaeology. Inner/outer halos. Bulge. Thin/thick disks. Stellar abundances + kinematics to unravel the history of the Milky Way and its populations: Nucleosynthesis, IMF, SFR, infall/outflow, migration etc

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Martin Asplund

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  1. Galactic archeology & planet formation Martin Asplund

  2. Galactic archaeology Inner/outer halos Bulge Thin/thick disks • Stellar abundances + kinematics to unravel the history of the Milky Way and its populations: • Nucleosynthesis, IMF, SFR, infall/outflow, migration etc • Nature of the first stars • Evolution of the bulge • The disks and their substructure • Chemical enrichment of globular clusters • dSph/UFD and MW accretion history dSph Tolstoy et al. (2009)

  3. Substructure in Galactic disk Reddy et al. (2003, 2006) Thick disk Classical Galactic chemical evolution models: Merger origin for thick disk? IMF SFR Thin disk Schönrich & Binney (2009) Galactic chemical evolution models w/ radial migration: Thick disk natural consequence of old stars from inner disk migrated to solar neighborhood

  4. Near-field cosmology • HERMES @ AAT 4m • High-resolution (R=30k) spectra of 106 stars for “chemical tagging”: • Reconstruct chemical, dynamical and SF history of Milky Way • Identify solar siblings Is the Sun’s chemical composition unusual?

  5. Solar system abundances Meteorites Mass spectroscopy Very high accuracy Element depletion Solar atmosphere Solar spectroscopy Modelling-dependent Very little depletion

  6. Solar/stellar model atmospheres • Radiative-hydrodynamical • Time-dependent • 3-dimensional • Realistic microphysics • Simplified radiative transfer •  Essentially parameter free + Detailed 3D line formation (LTE and non-LTE) For the aficionados: Stagger-code (Nordlund et al.) MHD equation-of-state (Mihalas et al.) MARCS opacities (Gustafsson et al.) Opacity binning (Nordlund)

  7. Solar abundances revisited • Asplund, Grevesse, Sauval, Scott, • 2009, ARAA, 47, 481 + series of A&A papers • Realistic model for the solar atmosphere • Detailed spectrum formation calculations • Improved atomic and molecular input data • Careful selection of lines Note: logarithmic scale with H defined to have 12.00

  8. Different reasons for low O [OI]: blends OI: non-LTE OH: 3D effects

  9. Complete solar inventory Asplund et al. (2009, ARAA): 3D analysis of all elements Statistical and systematic errors included in total uncertainties Revising an astronomical yardstick Solar metallicity Z=0.014 (not 0.02!)

  10. Is the Sun unusual? Melendez, Asplund, Gustafsson, Yong, 2009, Science Nature ApJL

  11. Precision stellar spectroscopy Melendez, Asplund, Gustafsson, Yong (2009): 11 solar twins + Sun observed with Magellan/MIKE: R=65,000 S/N~450 Teff<75K logg<0.1 [Fe/H]<0.1 Extremely high precision achieved: 0.01 dex in [X/H], [X/Fe]

  12. Signatures of planet formation Correlation with condensation temperature highly significant (probability <10-6 to happen by chance) ≈0.08 dex≈20%

  13. The Sun is unusual Only a minority of our solar twins resemble the Sun

  14. Confirmation of trend Ramirez, Melendez & Asplund (2009): Observations of 22 solar twins with McDonald 2.7m R=60,000, S/N~200 ~0.02 dex accuracy in [X/Fe] Note: opposite definition!

  15. Re-analyzing previous studies • Ramirez et al. (2010): • Signature exists also in previous stellar samples but disappears at high [Fe/H] • Metallicity-dependence of planet formation Data from Neves et al. 2009 Solar analogs from literature

  16. Scenario Sun: planet formation locked up refractories but less of volatiles during accretion phase Solar twins: less planet formation and thus more refractories than Sun Iron gradient in the inner solar system

  17. Terrestrial or giant planets? How much dust-cleansed gas accretion is required? Assume gas accretion once solar convection zone reached ≈ present size (~0.02 Mo): Refractories ~2*1028 g ≈4 M Rocky planets: ~8*1027 g ≈1.3 M Cores of giant planets: ≈30 M? Characteristic temperature of ~1200 K only encountered at <1 AU in proto-planetary disks

  18. Stars with/without giant planets • Fraction of stars resembling the Sun: • With hot Jupiters: ~0% • Without hot Jupiters: ~70% • Stars in general: ~20% Close-in giant planets prevent formation of terrestrial planets? An ideal candidate for terrestrial planet searches

  19. Galactic archeology and planets Reddy et al. (2006) Disk substructure and chemical tagging (Thick-thin) ≈ 0.1 dex (Thin) ≈ 0.01 dex? Planet signature larger! Size of signature will depend on MCZ, i.e. spectral type ≈0.08 dex

  20. Galactic archeology w/ HERMES • Combine Galactic archeology with identifying likely planet hosts • ~10,000 FG dwarfs • R=50,000 (slitmasks) • S/N=200+ • Many elements (oxygen!) • Calibration of main survey • Issues: • Extreme accuracy • (3D, non-LTE, parameters) • Automated analysis of huge stellar samples

  21. Summary • Solar chemical composition • New abundances for all elements • Low C, N, O and Ne abundances • Precision stellar spectroscopy • Sun is unusual • Signatures of planet formation • Galactic archeology • Complicates finding solar siblings • Planet formation as a mask

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