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] = Solar metallicity
[Fe/H] = Halo or (PopII)‏
[Fe/H] ~ Metal poor Globular clusters
[Fe/H] < Extreme metal poor (EMP) stars
[Fe/H] < Hyper metal poor (HMP) stars
[C/Fe] > Carbon enhance metal poor (CEMP) stars
Metal poor DLA ~ (Kobayashi et al. 2011)
Metal poor LLS < (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).
[C/Fe]
I talk about EMP star.
In this talk,
I call stars of metallicity [Fe/H] = -2.5 or less EMP stars (and distinguish them from Pop2 stars and zero metal pop3 stars. )‏
As you know, EMP star is a nearby probe into early universe.
However, we can observe only low mass EMP star still alive.
Large fraction of EMP stars show enhancement of the surface carbon abundance.
I focus on these CEMP stars.
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)‏
[Fe/H] 9

10. SDSS Sample SDSS calibration stars ~ 30,000 Z < 10 kpc
Kinematics and [C/Fe] abundances were derived
Carollo et al (2012)
Sivarani, Carollo, Beers & Lai 2012 10

11. 11

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, 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)‏15

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

17. Carbon in the inner and outer halo of the Galaxy

18. CEMP fraction in ultra faint dwarf satellite galaxies
Lai et al. 2011
Zucker et al. 2006 18

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

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. Signature of EMP AGB star
Pb enhancement
Signature of EMP AGB star CS
[Fe/H] = -2.7
[Pb/Fe] = 2.9
Binary 342 days
S-process enhancement in the early Galaxy
Sivarani et al. 2004 25

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. Gradual change in the CMB-IMF evolution?
Conclusions
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:
Higher supernova rate than predicted at high redshift
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?

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 < -2.5 – no s-process elements ==> massive stars
Further investications needed to confirm additional contribution of carbon below < -2.5

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

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

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

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