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The first generations of stars
Elisabetta Caffau
GEPI 0.1
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The first generations stars
In collaboration with:
Norbert Christlieb, Hans-Gunter Ludwig, Simon Glover, Ralf Klessen, Andreas Koch ZAH, Heidelberg
- Germany
Matthias Steffen Leibniz-Institut fur Astrophysik Potsdam - Germany
Alessandro Chieffi, Marco Limongi, Paolo Molaro, Sofia Randich, Simone Zaggia INAF Italy
Piercarlo Bonifacio, Andy Gallagher, Roger Cayrel, Patrick Francois, Francois Hammer, Monique Spite,
Francois Spite GEPI, Observatoire de Paris - France
Bertrand Plez Universite de Montpellier - France
Vanessa Hill Universite de Nice Sophia Antipolis, CNRS, Observatoire de la Cote d’Azur - France
Lorenzo Monaco Universidad Andres Bello, Santiago - Chile
Luca Sbordone Pontificia Universidad Catolica de Chile, Santiago - Chile
Lyudmila Mashonkina Institute of Astronomy, Russian Academy of Sciences - Russia
MP stars . Bologna . 7.05.2015 1.1
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Main Questions
Understand formation of low mass stars in low metallicity gas
Do zero-metal low mass stars exist?If not: value of the “critical metallicity”Derive the fraction of C-enhanced extremely metal-poor(CEMP) stars/“normal” extremely metal-poor (EMP) stars
Lithium and the primordial nucleosynthesis predictions
Li abundance (Li destruction?) in EMP stars
First massive stars
Masses of Pop III massive stars from chemical composition ofa large sample of EMP stars
Questions . Bologna . 7.05.2015 2.1
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Only H, He, and traces of Li are present in the primordial gas
The Universe emerging from the Big Bang
First stars . Bologna . 7.05.2015 3.1
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Formation of the first stars
The first stars formed ~ 200 Myr after the Big Bang
The first stars were most likely
very massive (50-300 M☉)
The cooling of the contracting material was inefficient due to the lack of metals and dust.
First stars . Bologna . 7.05.2015 4.1
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The first massive stars evolved rapidly and synthetised metals
At the end of their lives (~10 Myr) they exploded as SN and polluted the ISM with the metals.
First stars . Bologna . 7.05.2015 5.1
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Second generation of stars
Low mass stars ?
High mass stars
lifetime ~13 Gyr
First stars . Bologna . 7.05.2015 6.1
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SN explosions
Sun and low mass stars
PN stage
First stars . Bologna . 7.05.2015 7.1
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10 Myr
13.8 Gyr ago NOW
massive stars
low mass stars
First stars . Bologna . 7.05.2015 8.1
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Formation of primordial mass stars shining today?
The cooling (by radiation) of the contracting material was inefficient, due to lackof metals and dust
Historically the first extremely iron-poor ([Fe/H]≤ −4.5) stars found are all C-, N-and O-enhanced, and others have been found
My recent founding of new C-rich extremely metal-poor stars reinforces the theory onlow-mass star formation with cooling through C ii and O i fine-structure transitionsradiate energy (collisional excitation and radiative de-excitation)
BUT . . .CEMP stars . Bologna . 7.05.2015 9.1
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According to the theory of Bromm & Loeb (2003) a minimal quantity of C and O is necessary to form low mass stars
Figure from Frebel et al. 2007
Forbidden zone
EMP stars . Bologna . 7.05.2015 10.1
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The star that should not exist
[Fe/H]=−4.9
[C/H]< −4.5
Z = 5 × 10−5Z�
EMP star non-enhanced in C,N =⇒over-abundance C not necessary to cool EMP gas
Caffau et al. (2011) Nature 2011, 477, 67
Leo-star . Bologna . 7.05.2015 11.1
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But we have found a star in the forbidden zone
Figure from Frebel et al. 2007
Forbidden zone
SDSS J102915+172927 Caffau et al. 2011
EMP stars . Bologna . 7.05.2015 12.1
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Formation of low mass stars
• Zero metallicity ⇒
FRAGMENTATION (Clarke et al. 2011, never observed)
• Metallicity > Zcr⇒
★ CII & OI fine structure cooling (Bromm & Loeb 2003, ex. HE 1327-2326, HE 0107-5240)
★ dust cooling + fragmentation (Schneder et al. 2011, ex. SDSS J102915+172927) From Greif et al (2011)
EMP stars . Bologna . 7.05.2015 13.1
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CEMP
Spite, Caffau, et al. 2013, A&A 552, 107
CEMP . Bologna . 7.05.2015 14.1
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CEMP
CEMP . Bologna . 7.05.2015 15.1
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CEMP . Bologna . 7.05.2015 16.1
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EMP . Bologna . 7.05.2015 17.1
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Working plan
Selection of EMP candidates
Follow-up observation at intermediate/highresolution
1D-LTE analysis
Computation of 3D corrections and NLTE effects
Calibration of the low-resolution data
Derivation metallicity distribution function (MDF)
Plan . Bologna . 7.05.2015 18.1
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Searching for and analysing EMP stars
Stars of extremely low metallicity (EMP)are exceedingly rare
To select them large amount of obser-vations is needed
Large databases available at low resolu-tion
Spectra of EMP stars show few lines andthese are weak
Follow-up at higher resolution is neces-sary
EMP stars . Bologna . 7.05.2015 19.1
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SDSS Telescope copyright SDSS 9853 deg2, photometry for 287 million unique objects. 218019 spectra of stars earlier than M
SDSS . Bologna . 7.05.2015 20.1
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Selection
Limited information derived from R=2 000 resolution spectra + photometry
Many such spectra available from several surveys, essential for searching for rare objects
Extremely metal-poor stars can be extracted from low resolution surveys
150 000 SDSS spectra (potentially TO stars) analysed automatically
final selection by visual inspection
Caffau et al. A&A 2011
Observed spectrum and over-imposed synthetic spectra [Fe/H]=-3.0 and [Fe/H]=-4.0
EMP star selection . Bologna . 7.05.2015 21.1
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Working plan
Selection of EMP candidates
Follow-up observation at intermediate/highresolution
1D-LTE analysis
Computation of 3D corrections and NLTE effects
Calibration of the low-resolution data
Derivation metallicity distribution function (MDF)
Plan . Bologna . 7.05.2015 22.1
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Follow-up observations facility: Paranal
European Southern Observatory - ESO
Follow-up . Bologna . 7.05.2015 23.1
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Metal-poor star selected from SDSS and observed with thespectrograph X-Shooter at VLT - February 2011
[Fe/H]=−3.71± 0.27
[Fe/H]=−3.22± 0.24
[Fe/H]=−3.24± 0.24
[Fe/H]=−3.52± 0.14
[Fe/H]=−3.49± 0.32
Caffau et al. 2011 A&A
X-Shooter . Bologna . 7.05.2015 24.1
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Other interesting stars from the GTO July 2012
[Fe/H]=–4.1
α low
CEMP, α low
CEMP, [Fe/H]=-4.8
Caffau et al. 2013 A&A
X-Shooter . Bologna . 7.05.2015 25.1
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Two more CEMP stars
SDSS J161956+1505396191/4.0/–3.57A(C)=7.1
SDSS J174259+2531356345/4.0/–5.00A(C)=7.4
CEMP . Bologna . 7.05.2015 26.1
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Observations: high resolution follow-up
Turn Off Primordial Stars
PI Elisabetta Caffau20 researchers10 laboratories5 countries
Large Programme Observations:
120 h X-Shooter (medium resolution)30 h UVES (high resolution)
Other observations:
82 h UVES3 night X-Shooter3 nights Subaru
Tragets: Turn-Off stars
Present/Future
CoI of the Gaia ESO Survey: 300 nights @FLAMES-VLT 2012-2016Gaia satellite observations (expected in 2015)High-resolution observations: UVES and X-Shooter @ESO, Subaru, LBT, . . .
High-res. observations . Bologna . 7.05.2015 27.1
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Working plan
Selection of EMP candidates
Follow-up observation at intermediate/highresolution
1D-LTE analysis
Computation of 3D corrections and NLTE effects
Calibration of the low-resolution data
Derivation metallicity distribution function (MDF)
Plan . Bologna . 7.05.2015 28.1
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Analysis of high resolution spectra:automatic code MyGIsFOS
Data analysis . Bologna . 7.05.2015 29.1
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Data quality: UVES
6422 K[Fe/H] -3.27
S/N~110
6452 K[Fe/H] -3.29
S/N~32
Data analysis . Bologna . 7.05.2015 30.1
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Data quality: X-Shooter
6392 K[Fe/H] -3.13
S/N~40
6332 K[Fe/H] -4.1
S/N~70
Data analysis . Bologna . 7.05.2015 31.1
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MgI linesfor [α/Fe] determination
Data analysis . Bologna . 7.05.2015 32.1
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[Mg/Fe] vs. [Fe/H]
Caffau et al. (2013)
[Mg/Fe] . Bologna . 7.05.2015 33.1
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StrontiumFlux vs. wavelegth
407.5 407.6 407.7 407.8 407.9 408.0 408.1 408.2wavelength (nm)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Res. In
tens.
EW 6.58 pmOEW 6.86 pmEW_N 0.85 pmS/N 61.0PROB 0.0827ABU -3.20
Flux vs. wavelegth
421.2 421.4 421.6 421.8 422.0 422.2wavelength (nm)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Res. In
tens.
EW 7.28 pmOEW 7.26 pmEW_N 0.82 pmS/N 65.3PROB 0.1251ABU -2.87
Sr . Bologna . 7.05.2015 34.1
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TOPoS: first results
105 TO stars selected
100 stars with [Fe/H] ≤ −3 (doubled known sample);28 stars with [Fe/H] ≤ −3.5;6 stars with [Fe/H] ≤ −4 (9 stars known before our program);4 stars with [Fe/H] ≤ −4.5 of which three CEMP.
. Bologna . 7.05.2015 35.1
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Working plan
Selection of EMP candidates
Follow-up observation at intermediate/highresolution
1D-LTE analysis
Computation of 3D corrections and NLTE effects
Calibration of the low-resolution data
Derivation metallicity distribution function (MDF)
Plan . Bologna . 7.05.2015 36.1
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The CIFIST
7000 6500 6000 5500 5000 4500 4000 3500Teff [K]
5
4
3
2
1
log 1
0 g
[cm
s−
2 ]
metallicity [M/H]
+05+00−05−20−15−10
−25−30−40
runningdone
M0K0G0F5
Data analysis . Bologna . 7.05.2015 37.1
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The G-band
From A. Gallagher
G-band . Bologna . 7.05.2015 38.1
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NLTE analysis: Li, C, N, O, Si;Na, Mg, Sr, Ba (Andrievsky); Fe (Mashonkina)
Data analysis . Bologna . 7.05.2015 39.1
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Spite plateau
Lithium . Bologna . 7.05.2015 40.1
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Working plan
Selection of EMP candidates
Follow-up observation at intermediate/highresolution
1D-LTE analysis
Computation of 3D corrections and NLTE effects
Calibration of the low-resolution data
Derivation metallicity distribution function (MDF)
Plan . Bologna . 7.05.2015 41.1
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Calibration
Calibration . Bologna . 7.05.2015 42.1
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Working plan
Selection of EMP candidates
Follow-up observation at intermediate/highresolution
1D-LTE analysis
Computation of 3D corrections and NLTE effects
Calibration of the low-resolution data
Derivation metallicity distribution function (MDF)
Plan . Bologna . 7.05.2015 43.1
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Metallicity Distribution Function
MDF from SDSS-DR9(182 807 TO stars)
MP-component of MDF SDSS-DR9TO stars with g < 19.5 and observablefrom Paranal compared with a sampleof 39 stars we analysed
MDF . Bologna . 7.05.2015 44.1
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★Do zero-metal low mass stars exist ? (yes/no)
★If not: value of the “critical metallicity”
★Fraction of CEMP/”normal” EMP stars
★Li abundances (Li destruction ?)
★Masses of Pop III massive stars from chemical composition of a large sample of EMP stars
“Leo” star
Expected Results
First stars . Bologna . 7.05.2015 45.1