Li abundance of to stars in globular clusters
This presentation is the property of its rightful owner.
Sponsored Links
1 / 41

Li Abundance of TO stars in globular clusters PowerPoint PPT Presentation

  • Uploaded on
  • Presentation posted in: General

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.

Download Presentation

Li Abundance of TO stars in globular clusters

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Li abundance of to stars in globular clusters

Li Abundance of TO stars in globular clusters

Zhixia Shen

Luca Pasquini

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



  • 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: Fe Group--compared to field stars

Gratton et al., 2004

Chemical anomaly of gcs fe group compared to field stars1

Chemical Anomaly of GCs: Fe Group--compared to field stars

Gratton et al., 2004

Chemical anomaly of gcs n capture elements

Chemical Anomaly of GCs: n-capture elements

Gratton et al., 2004

The c n c l anti correlation

Large spread in Carbon and Nitrogen in many GCs:

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

Gratton et al., 2004

O na anticorrelation1

O-Na Anticorrelation

  • 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 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…



  • 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)



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

  • Indicator of globular cluster chemical evolution history

    • The low temperature for Li depletion (2.5 MK)

    • CNO circle: ~30 MK

  • TO stars: unevolved

Li abundance of to stars in globular clusters

  • History

    • 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.

Li abundance of to stars in globular clusters

One of the most metal-poor:

[Fe/H] = -2.2

One of the oldest:


(according to Grundahl et al 2000)


Distance = 27,000 ly

M 92

Li abundance of to stars in globular clusters

Boesgaard et al. 1998

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

Age ~ 13-14 Gyr

Distance ~ 7,200 ly

One of the closest

m-M ~ 12.5


Bonifacio et al. 2002

NGC 6397

Something interesting

Something interesting…

  • 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] ~-1.43

Age ~ 13 Gyr

Distance ~13,000 ly

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

m-M ~ 13.13


Pasquini et al. 2005

NGC 6752

47 tuc

[Fe/H] ~ -0.7

Age ~ 10 Gyr

Distance ~ 13,400 ly

m-M ~ 13.5


Bonifacio et al. 2007

47 Tuc

Our data

TO stars:

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

With the same temperature and mass, at the same stage


For Li 6708Å, R~17,000, S/N ~ 80-100

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

Our data



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

Li abundance of to stars in globular clusters

  • Li variation: 1.7-2.5, 0.8 dex

    • 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



  • 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

  • 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

  • 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

  • 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

Li abundance of to stars in globular clusters

  • Weiss et al. (2000) 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

  • 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

  • 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

Li abundance of to stars in globular clusters


  • 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

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

  • 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

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



  • 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

Thank you

Thank you!

Invitation for Lunch

Time: 11:30 am today

Place: The third floor of NongYuan

Everyone is welcomed!

Shen Zhixia & Wang Lan

  • Login