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Probing the first stars with metal poor stars T. Sivarani Indian Institute of Astrophysics, Bangalore.

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Presentation on theme: "Probing the first stars with metal poor stars T. Sivarani Indian Institute of Astrophysics, Bangalore."— Presentation transcript:

1 Probing the first stars with metal poor stars T. Sivarani Indian Institute of Astrophysics, Bangalore

2 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

3 Epoch of the first stars

4 Low Metallicites in Perspective Sun Reid 2000

5 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] > Carbon enhance metal poor (CEMP) stars Metal poor DLA ~ -3.0 (Kobayashi et al. 2011) Metal poor LLS < -4.0 (Fumagali et al. 2011)

6 Chemical tagging as tool to probe the 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)

7 Metallicity distribution of the early Halo stars Komiya et al. 2007

8 Pair Instability SuperNovae Heger & Woosley 2001

9 Carbon enhancement at low metallcities ~1000 EMP stars are observed in the Galactic halo. 12~25% of EMP stars show carbon enhancement (CEMP) [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)‏

10 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


12 Increasing carbon rich stars at low [Fe/H] Z > 5kpc - to avoid contamination from milky way metal weak thick disk stars

13 CEMP frequency at different Galactic scale height IMF depends on another parameter other than metallicity, Carollo et al (2012)

14 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

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

16 HBB burning AGB stars in the Halo Sivarani et al. (2007)

17 Carbon in the inner and outer halo of the Galaxy

18 CEMP fraction in ultra faint dwarf satellite galaxies Lai et al Zucker et al. 2006

19 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

20 Globular cluster and Halo connection Globular clusters Lowest metallicity ~ -2.5 C-poor N-rich r-process similar to halo Na-O anticorrelation  pollution of hydrogen burning products Halo Extended tail ~ -5.0 many stars < -2.5 C-normal/C-rich



23 Indo-SA collaboration Search for metal poor stars with 1-2m facilities in India: Target selection: GALEX, SDSS, 2MASS and WISE UVIT 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.

24 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.

25 S-process enhancement in the early Galaxy Sivarani et al CS [Fe/H] = -2.7 [Pb/Fe] = 2.9 Binary 342 days Pb enhancement Signature of EMP AGB star

26 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

27 Thank you!


29 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? Gradual change in the CMB-IMF evolution? Conclusions

30 Metallicities in perspective Fumagali et al (2011)




34 S-process enhancement at low metallicities


36 CEMP stars > -2.5 have 80% enhanced in s-process ==> AGB CEMP massive stars Further investications needed to confirm additional contribution of carbon below < -2.5

37 z~20-30 (Barakana & Loeb 2001) Mass ~106M ☉ Population III Population II Mgas~1011M ☉ EMP star formation Zcri~10^-4 Talk by stars-III Santa Fe Critical metallicity

38 Outer halo – UFD satellites? Frebel & Bromm (2010)



41 27/11/11 41 Bootes dwarf galaxy- more metal Poor than the dsph, shows enhanced carbon and alpha Elements similar to MW halo Lai et al CEMP star in SEGUE-1 System Norris et al. 2011


43 Pols 2007




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