gaia and metal-poor stars

Gaia and Metal-Poor Stars Bengt Gustafsson, Dept of Astronomy and Space Physics

Friedrich G.W. Struve 1793-1864Parallax for Vega 1838; 26 light years, 4% error ?

Gaia: 4% for 108 stars, 103 times further away.

Radial Velocity Spectrometer Photometry5 broad, 11 intermediate bands

109 stars, compl. to V~20Parallaxes: Distances:V (), as # rel 10 4 2x106 1%

15 11 50x106 2%

20 160 110x106 5%

220x106 10%

Tang. vel.: # , 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

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

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 [/Fe] estim., also

with reddening.

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=GaiaClassification Working Group: www.mpia-hd.mpg.de/GAIA/Photometry Working Group: gaia.am.ub.se/PWG/index.htmlRadial Velocity Spectrometer Working Group: wwwhip.obspm.fr/gaia/rvs Wilkinson et al. (’05), MN 359

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)

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, ...

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!

EMP stars

Current [Fe/H] distribution from HK and HES =>

Gaia will give • 104 [Fe/H] <-3• 103 ? <-4• 102 ?? <-5

... but ...

N = 9669< -2 = 2756< -3 = 380

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??

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 SupernovaeSequences (SSSs)!

The remarkably small scatter in [X/Fe] for many X

Arnone et al (’05):

[/Fe] < 0.08

Cayrel, Spite et al (’05):

[Na, Al/Fe] ≈ 0.10

for dwarfs (TOP stars)

Why??

C rich

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 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)

QuickTime och enTIFF (okomprimerat)-dekomprimerare

krävs för att kunna se bilden.

About 200 mergers expected. Can Gaia trace them?

Tidal streams, perturbed by• background• errors• inhomogeneities in grav. potential.

Explore the E - Lz plane:

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

Chemical evidence?

• Thin disk stars• Thick disk• Halo stars• Retrograde halo

Open black squares:dSph

from Venn et al. (’04)

Challenges CDM?

No! ? argue Bullock, Font, Johnston in (’05)

SPH simulations with chemical evolution.

• Few massive dIrr with rapid SF and high [/Fe] contribute most Halo stars …

… in particular in Inner Halo.

Outer Halo should have lower [/Fe]. Remains to be seen.

• Predicted scatter in [/Fe] ~ 0.10,

observations => smaller scatter?

Will Gaia measure [/Fe]?

/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

Tracing dark sub-halos

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

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

Binaries:

• Fraction: 28 ± 2% (Carney et al. ’05) but

10 ± 2% for V < -300 km/s !

Cen-like dynamically and chemically!?

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, Y/Z

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 ?

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

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!

Unexpected discoveries

• ?

• ?

• ?

• ?

• Pop III stars in the Bulge?

• ?

• ?

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!

For developing the Gaia potential:

Follow-up spectroscopy of considerable samples of Halo stars: (1) R ~ 5000-10,000 (classification: CH, r, s, EMP; V> 17)

(2) R ~ 35,000 (, i)New telescopes: 3 automatic 8 meter telescopes with multi-object echelle

spectrometers 300 - 1,000 nm and large detectors.

GaiaUranos and Pontos

12 titans 3 cyclops 3 giants

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.