Li abundance of to stars in globular clusters
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Li Abundance of TO stars in globular clusters. Zhixia Shen Luca Pasquini. The Globular Cluster (GC). The same distance, the same age and [Fe/H]:GCs are good testbeds for stellar evolution Nucleosynthesis in old stars Galaxy chemical evolution The age of the universe. Outlines.

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The globular cluster gc
The Globular Cluster (GC)

  • The same distance, the same age and [Fe/H]:GCs are good testbeds for

    • stellar evolution

    • Nucleosynthesis in old stars

    • Galaxy chemical evolution

    • The age of the universe


Outlines
Outlines

  • Chemical inhomogeneity of GCs

  • Li variations of TO stars in GCs

    • History

    • Our work


Abundance anomalies in globular clusters
Abundance Anomalies in Globular clusters

  • Homogeneous Fe abundance

  • Homogeneous n-capture element abundances

  • Light element abundance anomalies

    • C-N

    • Na-O

    • Mg-Al

    • etc


Chemical anomaly of gcs fe group

Most globular clusters (GCs) have a very uniform distribution of Fe group elements - all the stars have the same [Fe/H].

Several years ago people believed that this indicated that the cluster was well-mixed when the stars formed

Now, no the 3rd dredge-up

Chemical Anomaly of GCs: Fe Group

Kraft, et al., 1992: M3, M13


Chemical anomaly of gcs fe group compared to field stars
Chemical Anomaly of GCs: distribution of Fe group elements - all the stars have the same [Fe/H].Fe Group--compared to field stars

Gratton et al., 2004


Chemical anomaly of gcs fe group compared to field stars1
Chemical Anomaly of GCs: distribution of Fe group elements - all the stars have the same [Fe/H].Fe Group--compared to field stars

Gratton et al., 2004


Chemical anomaly of gcs n capture elements
Chemical Anomaly of GCs: distribution of Fe group elements - all the stars have the same [Fe/H].n-capture elements

Gratton et al., 2004


The c n c l anti correlation

Large spread in Carbon and Nitrogen in many GCs: distribution of Fe group elements - all the stars have the same [Fe/H].

The first negative correlation (anticorrelation) : C is low when N is high.

The anticorrelation is explicable in terms of the CN cycle, where C is burnt to N14

The C abundance decreases with L on the RGB (and N increases). This isknown as the C-L anticorrelation

This is also observed in halo field stars.

M3, Smith 2002

The C-N & C-L anti-correlation

Cohen, Briley, & Stetson (2002)


O na anticorrelation
O-Na Anticorrelation distribution of Fe group elements - all the stars have the same [Fe/H].

Gratton et al., 2004


O na anticorrelation1
O-Na Anticorrelation distribution of Fe group elements - all the stars have the same [Fe/H].

  • This is readily explained by hot(ter) hydrogen burning, where the ON and NeNa chains are operating - the ON reduces O, while the NeNa increases Na (T ~ 30 million K)

  • Where this occurs is still debatable.

  • The amazing thing about this abundance trend is that it only occurs in Globulars - it is not seen in field halo stars


Mg al

Mg-Al anticorrelation distribution of Fe group elements - all the stars have the same [Fe/H]. in (some) GCs.

This can also be explained through high-temperature (T~ 65 million K) proton capture nucleosynthesis, via the MgAl chain (Mg depleted, Al enhanced).

It does not occur in field stars...

The light elements also show various correlations among themselves--->

(Kraft, et al, 1997. Giants)

Mg, Al…


Summary
Summary distribution of Fe group elements - all the stars have the same [Fe/H].

  • All these anticorellations point to hydrogen burning -- the CN, ON, MgAl, NeNa cycles/chains -- at various temperatures.

    • CN, ON, NeNa: T~20 MK-40 MK(?)

    • MgAl: T~40 MK-65 MK(?)

  • Previously, the most popular site* for this is at the base of the convective envelope in AGB stars - Hot Bottom Burning

  • And now, maybe winds from massive stars (WMS)


Summary1
Summary distribution of Fe group elements - all the stars have the same [Fe/H].

1) Heavy Elements are uniform throughout cluster

  • No the 3rd dredge-up

    2) C and N (only) have been shown (conclusively) to vary with evolution/luminosity.

  • Most likely ongoing deep mixing on RGB, but not very deep mixing.

    3) Light elements (C – Al) show spreads to varying degrees, and are linked through the (anti)correlations. Spreads are seen in non-evolved stars also.

  • Inhomogeneous light element pollution; could be

    • pre-formation: AGB? WMS?

    • intrinsic stellar pollution (i.e. deep mixing), Non-evolved star?

    • accretion (Bondi-Hoyle?, binaries?, planets?). Fe? Mass of accretion material (O depletion to 1/10, 9:1 accretion mass?)? Subgaints?


Li abundace in globular clusters

Among the light elements Li has a special role. Li is produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

WMAP: A(Li)=2.64

Li-plaue: 2.1-2.3 (halo stars, NGC 6397)

Diffusion or extra-mixing mechanism

Li abundace in globular clusters


Li abundance of to stars in gcs
Li abundance of TO stars in GCs produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • Indicator of globular cluster chemical evolution history

    • The low temperature for Li depletion (2.5 MK)

    • CNO circle: ~30 MK

  • TO stars: unevolved


  • History produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

    • M 92: can’t be trusted

    • NGC 6397: Li abundance is an constant

    • NGC 6752: Li-O correlation;Li-Na/N anti-correlation;

    • 47 Tuc: Li-Na anti-correlation, lack of correlation between Li and N.


One of the most metal-poor: produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

[Fe/H] = -2.2

One of the oldest:

16Gyr

(according to Grundahl et al 2000)

m-M=14.6

Distance = 27,000 ly

M 92


Boesgaard et al. 1998 produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

V ~ 18

Keck I

1.5-6.5 hr

R ~ 45,000

S/N: 20-40

Reanalysis of Bonifacio et al. (2002): a variation of only 0.18 dex

M 92


Ngc 6397

[Fe/H] ~ -2.0 produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

Age ~ 13-14 Gyr

Distance ~ 7,200 ly

One of the closest

m-M ~ 12.5

Li:

Bonifacio et al. 2002

NGC 6397


Something interesting
Something interesting… produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • For a long time, people believed that whereas NGC6752 shows much variation, NGC6397 does not (Gratton et al 2001)

    • [O/Fe] = 0.21

    • [Na/Fe] = 0.20

    • Star-to-star  0.14 dex

    • Can be explained by obs error and variance in atmospheric parameters

  • Carretta et al. (2004): Na, O variations in NGC 6397

    • Li?

    • Lack of Li-N correlation?


Ngc 6752

[Fe/H] produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior~-1.43

Age ~ 13 Gyr

Distance ~13,000 ly

Log (M/M0) = 5.1 (DaCosta’s thesis, 1977)

m-M ~ 13.13

Li:

Pasquini et al. 2005

NGC 6752


47 tuc

[Fe/H] ~ -0.7 produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

Age ~ 10 Gyr

Distance ~ 13,400 ly

m-M ~ 13.5

Li:

Bonifacio et al. 2007

47 Tuc


Our data

TO stars: produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

V = 17.0-17.3; (B-V)=0.4-0.51

With the same temperature and mass, at the same stage

VLT-FLAMES/GIRAFFE, medusa mode

For Li 6708Å, R~17,000, S/N ~ 80-100

For O 7771-7775Å, R~18,400, S/N ~ 40-50

Our data


Results
Results produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

Error:Li: 0.09-0.14 dexO: 0.17-0.26 dex


  • Li variation: 1.7-2.5, 0.8 dex produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

    • The upper bundary is consistent with the prediction of WMAP

    • Not all stars have Li

  • Li-O correlation:

    • Possibility > 99.9% (ASURV)

    • Can’t be made by TO star themselves

      • For CNO circle, Te > 30 MK

      • In the center of TO: 20 MK

      • Li depletion: 2.5 MK

  • Large dispersion in Li-O correlation


Explanation
Explanation produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • The Li/O-rich stars, which are also Na poor, have a composition close to the "pristine" one, while the Li/O-poor and Na-rich stars are progressively contaminated.

  • The contamination gas is from

    • the Hot bottom burning (HBB) of an AGB star or

    • Wind of massive stars.


The chemical component of pollution gas
The chemical component of pollution gas produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • If we assume a primordial Li abundance of 2.64, given the observed lower boundary of 1.8, more than 80% of the gas should be polluted for such stars.

  • If primordial [O/Fe] = 0.4, [O/Fe] of the most Li-poor stars are -0.3, then the pollution gas should have O/H~6.6

  • Pasquini et al. (2005) for pollution gas:

    • A(Li) ~2.0, Na/H > 5.4, O/H<7.0, N/H~7.4


Agb or wms production
AGB or WMS: production produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • The results of Pasquini et al. (2005) for NGC 6752 is qualitatively consistent with the AGB model of Venture et al. (2002)

  • The lack of N in 47 Tuc: WMS is more possible (Bonifacio et al. 2007)

    • For metal-poor AGB stars, the reaction from O to N is quite efficient (Denissenkov et al. 1997 etc)


Agb production problem
AGB: production problem produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • Quantatively, AGB can’t explain the abundance variation for most GCs (Fenner et al. 2004)

    • Too much or not enough Na while O is not depleted enough

    • When Mg needs to be burnt, it is produced

    • C+N+O can’t be constant as observed

  • AGB models depends on two uncertain factors:

    • Mass loss rate

    • Efficiency of convective transport


  • Weiss et al. (200 produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior0) for HBB production

    • When Al is produced, too much Na

  • Denissenkov et al. (2001): 23Na firstly produced then destroyed during interpulse phase --> accurate period for both O-depletion and 23Na production


Wms production
WMS: production produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • Decressin et al. (2007):

    • Fast rotate models of metal-poor ([Fe/H]=-1.5) massive stars from 20-120 solar mass

    • Surface chemical composition changes with mass loss

    • Based on Li abundances:

      • 30% primordial gas is added to the winds

      • The model could reproduce C,N,O and Li variation

      • But failed in Mg


Li pollution scenario prantzos charbonnel 2006 agb
Li: pollution scenario (Prantzos & Charbonnel 2006) - AGB produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • If IM-AGB (4-9 solar mass)

    • 20-150 Myr

    • Before that, M* > 9Msun --> SNe-->wind of 400km/s --> no Li-rich primordial gas left

      • Li-production? Hard to get A(Li)=2.5

    • After that, 2-4Msun stars eject almost the same amount of material as IM-AGB

      • Maybe no HBB, but the third dredge-up --> C and s-process elements variation


WMS produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • In 20 Myr, massive stars evolve and slowly release gas through winds. The gas is mixed with primordial material.

  • The shock wave of SNe induce the formation of the new stars

  • After 20 Myr, wind ejecta from low mass stars (<10 Msun) won’t form stars because of no trigger.


Li abundance variations and dynamics

AGB: the ejecta will concentrate to the center of the GC produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

In 47 Tuc, most CN-rich stars near the center

However, in NGC 6752:

Red: A(Li) < 2.0

Green: 2.0 < A(Li) < 2.3

Black: A(Li) > 2.3

Li abundance variations and dynamics


Different gcs different abundace variations
Different GCs, different abundace variations produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • Bekki et al. (2007): GCs come from dwarf galaxies in dark halo at early age. The pollution gas is from outside IM-AGB field stars

    • The difference of GCs

    • Can’t produce the abundance variation pattern

    • Supported by Gnedin & Prieto (2006): all GCs 10 kpc away from the Galaxy center are from satellite galaxies.


Primordial li abundance
Primordial Li abundance produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • Are field stars also polluted by the first generation stars?


Conclusions
Conclusions produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

  • Li variation is exist in GCs

  • Li abundance is correlated with Na and O

  • A mixing of contamination gas and primordial gas is needed

  • The contamination gas may comes from WMS

  • Next work:

    • The large scatter in Li-O correlation

    • New data of 47 Tuc


The scatter
The scatter produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior


Thank you
Thank you! produced in Big Bang nucleosynthesis,enriched during the galaxy evolution,and destroyed in the stellar interior

Invitation for Lunch

Time: 11:30 am today

Place: The third floor of NongYuan

Everyone is welcomed!

Shen Zhixia & Wang Lan


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