Probing the first stars with metal poor stars

T. Sivarani

Indian Institute of Astrophysics, Bangalore

Chemical abundances of metal poor stars

Probing the first stars – Stellar archeology

Looking for the fossil records of early star formation and Galaxy evolution In metal poor systems of Milky way and its satellite galaxies.

Complementary to high redshift observations (IGM, GRB, SNs) Nature of First stars Early IMF Formation of Milky way Connection between halo stars and satellite dwarf galaxies halo stars and globular clusters

Epoch of the first stars

Low Metallicites in Perspective

SunReid 2000

Definitions

[Fe/H] = log(N(Fe)/N(H)) –log(N(Fe)/N(H))ʘ

[Fe/H] = 0.0 Solar metallicity [Fe/H] = -1.5 Halo or (PopII) [Fe/H] ~ -2.5 Metal poor Globular clusters [Fe/H] < -2.5 Extreme metal poor (EMP) stars [Fe/H] < -5.0 Hyper metal poor (HMP) stars [C/Fe] > 0.7-1.0 Carbon enhance metal poor (CEMP) stars Metal poor DLA ~ -3.0 (Kobayashi et al. 2011) Metal poor LLS < -4.0 (Fumagali et al. 2011)

Chemical tagging as tool to probethe First stars

Fe-peak – SN Ia, core collapse SN, PISN (Massive and low mass stars)

Alpha elements (Mg, Ca) – Core collapse SN (massive stars)

s-process – AGB stars (0.8-3Msun), weak s-process in massive stars

r-process – Core collapse SN (10-25 Msun) carbon – primarily low mass AGBs, fast rotating massive star wind(only in low metallicities)

Nitrogen – RGB, AGB stars, massive star winds (solve the problem of primary nitrogen in IGM)

Metallicity distribution of the early Halo stars

Komiya et al. 2007

Pair Instability SuperNovae

Heger & Woosley 2001

Carbon enhancement at low metallcities

~1000 EMP stars are observed　 in the Galactic halo.12~25% of EMP stars show carbon enhancement (CEMP).

-5 -4 -3 -2 [Fe/H]

[C

/Fe]Aoki et al. (2000,2004, 2008) ,Sivarani et al (2003), (2006),Lucatello et al. (2004), Goswami et al.(2005),Cohen et al.(2006),Jonsell et al (2007)

SDSS calibration stars ~ 30,000

Z < 10 kpc

Kinematics and [C/Fe] abundances were derived

Carollo et al (2012)

Sivarani, Carollo, Beers & Lai 2012

SDSS Sample

Increasing carbon rich stars at low [Fe/H]

Z > 5kpc - to avoid contamination from milky way metal weak thick disk stars

CEMP frequency at different Galactic scale height

IMF depends on another parameter other than metallicity, Carollo et al (2012)

The CMB influence the IMF of EMP stars?

At low redshift, Z = Zmin = 10 K is set by metal and dust cooling. But at high z, the CMB itself is the minimum gas temperature!z = 5, 10, 20 T_CMB = 16, 30, 57 K M_c = 2, 6, 17 Msun

Thus stars formed early in MW history, at z>5,should be affected Enhanced AGB fraction at low metallicity and at larger distances from the Galactic plane

Tumlinson 2006

AGB yields at Z = 10^-4 (Lugaro et al 2004, Karakas & Lattanzio (2008)

HBB burning AGB stars in the Halo

Sivarani et al. (2007)

Carbon in the inner and outer halo of the Galaxy

CEMP fraction in ultra faint dwarf satellite galaxies

Lai et al. 2011

Zucker et al. 2006

Carbon at high redshifts DLA at z=2.3 [Fe/H] = -3.0, [C/Fe] = 1.53 AGBs can not contribute to IGM earlier than z=1.8 (Kobayashi et al. 2011)Faint SN (with fallback)? (Nomoto et al.)Massive star wind (Meynet et al.) - Nitrogen has to be high IGM abundances Primary nitrogen production at high redshifts

Globular cluster and Halo connectionGlobular clusters Lowest metallicity ~ -2.5 C-poor N-rich r-process similar to haloNa-O anticorrelation pollution of hydrogen burning products

Halo•Extended tail ~ -5.0 many stars < -2.5•C-normal/C-rich

Indo-SA collaboration• Search for metal poor stars with 1-2m facilities in India:

Target selection: GALEX, SDSS, 2MASS and WISEUVIT will be ideal with MgIIhk narrow band filter

Identifying milkway substructure with UVIT: Dwarf satellites, halo streams Combining the classification based on the broad band SEDs and narrow band filters to identify over densities in RV.Identification of High velocity stars.

Follow up metal poor stars: SALT RSS spectrograph -C,N, Fe-peak, alpha abundances- NH lines (3380A), CH 4350, MgH, CaII Triplet R=1000 s-process and r-process (R=10000)

Multi object capabilities will be ideal to study metal poor stars in the dwarf satellites and globular clusters and streams.

Indo-SA collaboration

HRS at SALT

• Origin of r-process – universality of r-process • U and Th abundances – cosmic chronometry• Primordial Lithium abundances - Lithium in inner and outer halo stars• Beryillum abundances in outer halo stars probing the pre-galactic magnetic fields• Oxygen, s-process and isotopic ratios

NIR spectroscopy: Flourine, 17O/18O ratios massive versus IM pollution in GCs.

S-process enhancement in the early Galaxy Sivarani et al. 2004

CS29497-030

[Fe/H] = -2.7

[Pb/Fe] = 2.9

Binary 342 days

Pb enhancementSignature of EMP AGB star

Summary

Stellar archeology is an ideal tool to study,

• The milestones of Early star formation First stars Transition of Top heavy to normal mode – CMB based IMF

•Chemical and kinematical origin of early galaxy.

•Primordial Lithium

•Cosmic ray spallation and magnetfields – Beryillium

1-2m telescopes in India and UVIT

Thank you!

CMB would have provided a temperature floor for the minimum gas temperature. Influenced the majority of stars formed at redshifts between z = 3-6, and probably even to higher redshift.

Five signatures of CMB-regulated star formation are:

1) Higher supernova rate than predicted at high redshift 2) Systematic discrepancy between direct and indirect measurements of the high redshift star formation rate 3)Lack of surviving globular clusters that formed at high metallicity and high redshift 4) More rapid rise in the metallicity of cosmic gas than is predicted by current simulations 5) Enhancement in the abundances of α elements such as O and Mg at metallicities −2 [Fe/H] −0.5.

Gradual change in the CMB-IMF evolution?

Conclusions

Metallicities in perspective

Fumagali et al (2011)

S-process enhancement at low metallicities

CEMP stars > -2.5 have 80% enhanced in s-process ==> AGB

CEMP < -2.5 – no s-process elements ==> massive stars

Further investications needed to confirm additional contribution of carbon below < -2.5

z~20-30 (Barakana & Loeb 2001) Mass ~106M ☉

Population III

Population II Mgas~1011M☉

EMP star formation Zcri~10^-4

Talk by Komiya @first stars-III Santa Fe

Critical metallicity

Outer halo – UFD satellites?

Frebel & Bromm (2010)

27/11/1141

Bootes dwarf galaxy- more metalPoor than the dsph, shows enhanced carbon and alphaElements similar to MW halo Lai et al. 2011

CEMP star in SEGUE-1 System Norris et al. 2011

Pols 2007

Pols 2007

Pols 2007

Pols 2007