Download Probing the first stars through the abundance of metal poor stars

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
Sun
Reid 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 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)
Metallicity distribution of the
early Halo stars
Komiya et al. 2007
Pair Instability SuperNovae
Heger & Woosley 2001
Carbon enhancement at low
metallcities
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)
[C/Fe]
~1000 EMP stars are
observed in the
Galactic halo.
12~25% of EMP
stars show carbon
enhancement (CEMP).
-5
-4
-3
-2
[Fe/H]
SDSS
Sample
SDSS calibration stars ~ 30,000
Z < 10 kpc
Kinematics
and
abundances were derived
[C/Fe]
Carollo et al (2012)
Sivarani, Carollo, Beers & Lai
2012
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
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
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 abundancesNH 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.
Pb enhancement
Signature of EMP AGB star
CS29497-030
[Fe/H] = -2.7
[Pb/Fe] = 2.9
Binary 342 days
S-process enhancement in the early Galaxy
Sivarani et al. 2004
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!
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:
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?
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
Critical metallicity
Population III
z~20-30 (Barakana &
Loeb 2001) Mass
~106M☉
EMP star
formation
Zcri~10^-4
Population II
Mgas~1011M☉
Talk by Komiya @first stars-III Santa Fe
Outer halo – UFD satellites?
Frebel & Bromm (2010)
Bootes dwarf galaxymore 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
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