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Gaia and Metal-Poor Stars

Gaia and Metal-Poor Stars. Bengt Gustafsson, Dept of Astronomy and Space Physics Friedrich G.W. Struve 1793-1864 Parallax for Vega 1838; 26 light years, 4% error ? Gaia : 4% for 10 8 stars, 10 3 times further away.

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Gaia and Metal-Poor Stars

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  1. Gaia and Metal-Poor Stars Bengt Gustafsson, Dept of Astronomy and Space Physics Friedrich G.W. Struve 1793-1864 Parallax for Vega 1838; 26 light years, 4% error ? Gaia: 4% for 108 stars, 103 times further away.

  2. Radial Velocity SpectrometerPhotometry5 broad, 11 intermediate bands 109 stars, compl. to V~20 Parallaxes: Distances: V e(p), mas # rel e • 4 2x106 1% • 11 50x106 2% • 160 110x106 5% 220x106 10% Tang. vel.: # e, km/s Radial vel: 40x106 < 0.5 1-10 km/s 80x106 < 1 to V=16-17 200x106 < 3 i.e. ~ 108** 300x106 < 5 440x106 <10

  3. Radial Velocity Spectrometer • R=11,500 • 848-874 nm Ca II IR triplet Paschen lines 3 Mg I, 4 Si I, 2 Si, 7 Fe I Each source on average 93 times With S/N > 50 (V<13) Ca abundances will be measurable, not Fe etc for [Fe/H] < -1.5

  4. Photometry • 5 broad bands, intermediate/narrow bands, from 300 nm to 1000 nm => Goal: Teff to 5%, log g better than 0.1 dex, [Fe/H] to about 0.2 dex or better, some [a/Fe] estim., also with reddening.

  5. Further references: The Three-Dimensional Universe with Gaia”, Proc. of meeting in Paris-Meudon, Oct 2004, ESO SP-576 Presentations by P.E. Nissen, M. Spite ESA Gaia homepage: www.rssd.esa.int/index.php?project=Gaia Classification Working Group: www.mpia-hd.mpg.de/GAIA/ Photometry Working Group: gaia.am.ub.se/PWG/index.html Radial Velocity Spectrometer Working Group: wwwhip.obspm.fr/gaia/rvs Wilkinson et al. (’05), MN 359

  6. And what stars*? Population to G=17 G=20 mag. Thin disk 2x108 2x109 Thick disk 4x107 4x108 Bulge 1x107 2x108 Spheroid 2x106 2x107 Thus, accurate kinematic and physical parameters for millions of Pop II stars *) Data after Robin (2004)

  7. What will we get? • Distances => luminosities => masses for massive Pop I stars in anticentre direction, i.e. with somewhat varying metallicity => -- Better understanding of how physics changes with chemical composition. -- Better understanding of yields from AGB, PAGB, PNe, WR, ...

  8. What will we get for Pop II? • (EMP:s): ~ 104 new stars with [Fe/H] < -3.0, but .. • Structures in phase space -> tracing merging events, formation history … • Luminosity function for metal-poor stars • Ages • Binaries: frequency, masses … • Carbon-rich metal-poor stars • New discoveries!

  9. N = 9669 < -2 = 2756 < -3 = 380 EMP stars Current [Fe/H] distribution from HK and HES => Gaia will give • 104 [Fe/H] <-3 • 103 ? <-4 • 102 ?? <-5 ... but ...

  10. The most metal-poor stars, [Fe/H] < -5 • Christlieb et al. (’04), Frebel et al. (’05) • Origin? Fall-back SNe? Iwamoto et al. (’05) • Representativity??

  11. Effects of different yields in inhomogeneous modelKarlsson & Gustafsson (’05) Top: Woosley &Weaver (’95) Middle: Umeda &Nomote (’02) Bottom: Chieffi &Limongi (’04) Observations: Cayrel et al. (’04) NOTE: Single Supernovae Sequences (SSSs)!

  12. C rich The remarkably small scatter in [X/Fe] for many X Arnone et al (’05): s [a/Fe] < 0.08 Cayrel, Spite et al (’05): s [Na, Al/Fe] ≈ 0.10 for dwarfs (TOP stars) Why??

  13. Substructures in Phase Space, Streams, Mergers… • Sagittarius dSph system (Ibata ’94, …), M~109 Msun, [Fe/H]~ -1 ±0.5 • High lat Halo stream (Helmi et al. ’99, Fiorentin et al. ’05) 10% of halo outside solar orbit • Dwarf galaxy in CMa (Martin et al. ’04, 05), warp? (Momany et al’04) • Monoceros Ring (Newberg et al. ’02, Yanny et al. ’03, Ibata et al. ’03) 15-20 kpc, 2x108-109 Msun, [Fe/H]~ -1.6, part in CMa event (Conn et al. ’05)? • TriAnd cloud, 20 kpc away (Rocha-Pinto et al. ’04) • Arcturus group? (Navarro et al. ’04) • Debris from w Cen’s parent (Meza et al. ’05) External galaxies, proposed halo streams • M31 (Ibata et al. 01, Ferguson et al. 02) • NGC 5907 (Zheng et al ’99)

  14. About 200 mergers expected. Can Gaia trace them? Tidal streams, perturbed by • background • errors • inhomogeneities in grav. potential. Explore the E - Lz plane:

  15. Simulations by Brown et al. (2005), MNRAS 359: Quite a challenge! Physical parameters (e.g. photometric p) do simplify

  16. Chemical evidence? • Thin disk stars • Thick disk • Halo stars • Retrograde halo Open black squares:dSph from Venn et al. (’04)

  17. Challenges LCDM? No!? argue Bullock, Font, Johnston in (’05) SPH simulations with chemical evolution. • Few massive dIrr with rapid SF and high [a/Fe] contribute most Halo stars … … in particular in Inner Halo. Outer Halo should have lower [a/Fe]. Remains to be seen. • Predicted scatter in [a/Fe] ~ 0.10, observations => smaller scatter?

  18. Will Gaia measure [a/Fe]? e[a/Fe] ~ 0.1 dex for G= 15 mag, [Fe/H] indep. ~ 0.2 dex 16.5; Teff ≤ 5000K (Willemsen and Bailer-Jones ’05) Not enough to discriminate different sub-systems chemically in outer Halo. => Follow-up spectroscopy needed

  19. Tracing dark sub-halos • Effects on tidal streams from globular clusters -- heating expected by close encounters of sub-halos (Ibata et al. ’02)

  20. Luminosity function: IMF for Pop II? • Low mass end: Gould et al. (’98) • High M end: Indirect evidence for top-heavy (e.g. Lucatello et al. (’05), # C-rich stars

  21. Binaries: • Fraction: 28 ± 2% (Carney et al. ’05) but 10 ± 2% for V < -300 km/s ! w Cen-like dynamically and chemically!?

  22. Binaries, cont. • 104 eclipsing binaries of Pop II • 103-4 spectroscopic binaries of Pop II • >104 astrometric binaries of Pop II Masses to 2%, radii to 1-4%, mass ratios to 1% for 102-3 eclipsing binaries with V≤15. => ages, He-abundances, dY/dZ

  23. He abundances also from • Iben (’83) R = n/HB)/n(RGB) for field stars (cf. eg. Zoccali et al. ’00: cluster contamination by foreground stars, radial gradients) • MS in HR diagram • log g from spectrophotometry/evol. tracs ? No. Ages • from isochrones. • For subgiants to 5% for halo stars => age separation ?

  24. Single out C-rich Pop II stars? About 25% of EMP stars are CH strong (Christlieb et al. ’01). among those both stars with [Fe/H] < -5. Phenomenon not well understood. Can C-rich Pop II stars be distinguished by Gaia? No problem for Teff < 5500K with a proper G-band measure. Problematic for the hottest most Teff log g [Fe/H] metal-poor stars 6400 4.0 -2.7 5500 2.3 -2.1 late Pop II C star

  25. n-capture-element rich stars? • A considerable fraction of EMP stars s, s/r or r-I or r-II stars; e.g. ~5% of HERES sample CH normal stars are r-II stars (Barklem et al. ’05); ~10% of each s and r-I. • r-element profiles keys to r-processes? s/r stars not understood, s? • No measures from Gaia! Follow-up spectroscopy!

  26. Unexpected discoveries • ? • ? • ? • ? • Pop III stars in the Bulge? • ? • ?

  27. Gaia an extraordinary survey but … • Other spectrosocpic and photometric surveys running or to start before 2011: Sloan Extension for Galactic Understanding and Evolution (SEGUE) => 2000-5000 EMP stars SkyMapper (CEEC), Further spectroscopic surveys: RAVE, SSHS, LAMOST… Many raisins will be picked in advance!

  28. For developing the Gaia potential: Gaia Uranos and Pontos 12 titans 3 cyclops 3 giants Follow-up spectroscopy of considerable samples of Halo stars: • R ~ 5000-10,000 (classification: CH, r, s, EMP; V> 17) • R ~ 35,000 (a, ei) New telescopes: 3 automatic 8 meter telescopes with multi-object echelle spectrometers 300 - 1,000 nm and large detectors.

  29. The Cyclops:Arges, Brontes, Steropes The Cyclops by Euripides (408 BC, transl. E.P. Coleridge): Cyclops first entering: A light here! hold it up! What is this? …. Look up, not down. Leader: There! My head is bent back till I see Zeus himself: I behold the stars and Orion.

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