Exploring the Early Universe with Extremely Metal …...Exploring the Early Universe with Extremely...

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Exploring the Early Universe with ExtremelyMetal-Poor Stars.

Terese HansenLandessternwarte, Heidelberg University

IAU General assembly, IAUS 317

September 14, 2015

Terese Hansen Landessternwarte, Heidelberg University IAU General assembly, IAUS 317

Exploring the Early Universe with Extremely Metal-Poor Stars.

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Metal-Poor Stars in the Halo

Sample of ∼ 200 homogeneously analysed stars, 1D LTE analysis(Yong+ 2013, Hansen+ 2015)

Number [Fe/H] < −4 [Fe/H] < −3 [Fe/H] < −2 [Fe/H] < −1

Total 12 102 208 213CEMP 8 25 66 70

Normal: 143 CEMP-no: 32 CEMP-s: 30 CEMP-r: 4 CEMP-r/s: 4[Fe/H] < −1 [Fe/H] < −1 [Fe/H] < −1 [Fe/H] < −1 [Fe/H] < −1

[C/Fe] > 0.7 [C/Fe] > 0.7 [C/Fe] > 0.7 [C/Fe] > 0.7[Ba/Fe] < 0.0 [Ba/Fe] > 1.0 [Eu/Fe] > 1.0 [Ba/Fe] > 0.0

[Ba/Eu] > 0.5 0.0 < [Ba/Eu] < 0.5



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Spectra

4074.8 4075.2 4075.6 4076.0 4076.4 4076.8 4077.2 4077.6 4078.0 4078.4 4078.8 4079.2 4079.6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

EMP

4074.8 4075.2 4075.6 4076.0 4076.4 4076.8 4077.2 4077.6 4078.0 4078.4 4078.8 4079.2 4079.6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

CEMP-no

4074.8 4075.2 4075.6 4076.0 4076.4 4076.8 4077.2 4077.6 4078.0 4078.4 4078.8 4079.2 4079.6Wavelength

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

CEMP-s



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Progenitors of CEMP Stars

CEMP-noSpinstars (Meynet+ 2006, Hirschi 2007, Chiappini+ 2008)Mixing and fallback Supernova (Umeda & Nomoto 2003, 2005)Mass transfer from AGB binary companion (Masseron+ 2010)

CEMP-sMass transfer from AGB binary companion (Lucatello+ 2005)

CEMP-r and CEMP-r/s



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Mixing in the Early Universe

Level of mixing and CN processing of the material in metal-poorstars:

C > N and 12C/13C high → low processing

N > C and 12C/13C low → high processing



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Carbon and Nitrogen Abundances

-1

0

1

2

3

4

5

[C/F

e]

-1

0

1

2

3

4

5

[N/F

e]

-6 -5 -4 -3 -2 -1[Fe/H]

-2

-1

0

1

2

[C/N

]

[C/N] > 0 | [C/N] < 0

0

5

10

15

20

Nu

mb

er

NMPCEMP-noCEMP-sCEMP-r/sCEMP-r

Dots: C > N , triangles: C < Nfilled: Hansen+ 2015, open: Yong+ 2013



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12C/13C Ratios

Star 12C/13C TypeHE 0010-3422 5 CEMP-rHE 0054-2542 16 CEMP-sHE 0100-1622 13 CEMP-noHE 0134-1519 >4 CEMP-noHE 0233-0343 >5 CEMP-noHE 0243-3044 10 CEMP-r/sHE 0440-3426 13 CEMP-sHE 0448-4806 10 CEMP-rHE 1029-0546 9 CEMP-sHE 1310-0536 3 CEMP-noHE 2208-1239 4 CEMP-r/sHE 2238-4131 16 CEMP-sHE 2331-7155 5 CEMP-no

4229.5 4230.0 4230.5Wavelength

0

1

No

rmalised

Flu

x

Hansen+ 2015



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Light Elements

Below [Fe/H] ∼ −3.4large over-abundances ofNa, Mg and Al are foundin some CEMP-no stars.

-1

0

1

2

3

[Na/F

e]

-1

0

1

2

[Mg

/Fe]

-6 -5 -4 -3 -2 -1[Fe/H]

-1

0

1

[Al/F

e]

Filled: Hansen+ 2015, Open: Yong+ 2013



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Alpha and Iron Peak Elements

-1

0

1

[Si/F

e]

-1

0

1

[Ca/F

e]

-6 -5 -4 -3 -2 -1[Fe/H]

-1

0

1

[Ti/F

e]

-2

-1

0

1

[Cr/

Fe]

-2

-1

0

1

[Co

/Fe]

-6 -5 -4 -3 -2 -1[Fe/H]

-2

-1

0

1

[Ni/F

e]

Moderate over-abundances of α elements and lowstar to star scatter for both iron and α elements(Filled: Hansen+ 2015, Open: Yong+ 2013)



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Carbon Bands

4

5

6

7

8

9

A(C

)

-6 -5 -4 -3 -2 -1[Fe/H]

3

4

5

6

7

8

9

A(C

)

Dots: Hansen+ 2015,Plusses: Yong+ 2013

Carbon bands of Spite+2013, intrinsic/extrinsicorigin of CThis sample confirm these.Broad transition rangeCEMP-no stars on both.Different origin for the Cfound in CEMP-no stars onthe low band vs. those foundon the high band.CEMP-r and r/s stars onboth



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Neutron-Capture Elements

-4

-3

-2

-1

0

1

2

3

A(S

r)

-6 -5 -4 -3 -2 -1[Fe/H]

-4

-3

-2

-1

0

1

2

3

A(B

a)

Dots: Hansen+ 2015,Plusses: Yong+ 2013

Different behavior of Srand Ba for the CEMP-no

Indication of a “floor” inthe Ba abundances ofCEMP-no stars at−3 > [Fe/H] > −4



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Binarity

Binary mass transfer → radial-velocity variation

See poster #39 IAUS317 and talk FM7.2.04 J. Andersen



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Summary

Large fraction of CEMP stars in the haloSigns of mixing happening at very early times (low Fe)Two bands found in the absolute carbon abundances of CEMPstarsDifferent behavior of Sr and Ba and hint of floor in the Baabundances of CEMP-no starsBinary nature see poster #39 IAUS317 and talk FM7.2.04 J.Andersen



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Thank You.

Collaborators: Camilla J. Hansen, Norbert Christlieb, Tim Beers,Vini Placco, David Yong, Mike Bessel, John Norris, JohannesAndersen, Birgitta Nordstrom.



Exploring the Early Universe with Extremely Metal …...Exploring the Early Universe with Extremely...

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