lithium patterns, globular clusters formation and the big bang lithium abundance

Lithium patterns, Globular Clusters formation

and the Big Bang Lithium abundance

Francesca D’AntonaINAF-OAR

Meeting in honour of Francesca Matteucci, Castiglione, Sept. 16-20 2013

Paolo VenturaRoberta Carini

INAF-OAR

plus my coworkers

Annibale D’ErcoleINAF-OABo

Enrico VesperiniIndiana State University

Francesca MatteucciUniversity of Trieste

Chemical evolution in the Universe: the next 30 years

and…

A short historical summary

• Fundamental discovery of the “Lithium plateau” by Spite & Spite (1982) at A(Li)~2.3 (mass fraction ~10-9)

• Is this the “Big Bang” Lithium abundance, or is it the solar system value, 10 times larger?

• (at that time, the problem was the difference between pop. II results -2.3- and the solar system value -3.3: no hint that WMAP would provide an “intermediate” Big Bang Lithium abundance)


0.0

already at that time, and in following years, three possibilities were listed:

2) BB Li = solar system Li = depletion of Li due to surface events in pop. II

1) BB Li = Spite’ Li production of Li during galactic chem. evol.

3) intermediate BB Li depletion of Li due to surface events in pop. II + production due to chem.ev.

A short historical summary• 1982: discovery of the “Lithium plateau” by Spite & Spite

(1982)


1990 data of Li chemical evolution

Modelling chemical evolution of Li

D ’Antona & Matteucci 1990

our best model included novae massive AGB strong production by Hot BottomBurning


my best collaborator…

Modelling chemical evolution of Li

… after D’Antona & Matteucci 1990…many models were published by others: all of them included “plausible” but “invented” and very large yields for the Lithium manifactured in the AGB phase


Romano, Matteucci, Ventura & D ’Antona (2001) take into account Ventura’s new Li-yields for AGBs, and show that AGBs are poor contributors!

Romano et al (2010) (unpublished) take into account Ventura’s new Li-yields including super-AGBs, and show that it might work!

The Cameron-Fowler (1971) model and HBB

◊ Li produced by the chain LieBeHe 773 ),(),(

in a convective hot region, so that 7Be is transported to cooler regions before it turns into Li. Convective mixing brings Li back to the hot region where it can be burned, but it temporarily survives in the envelope and in the atmosphere. Production of Li is linked to the 3He abundance in the region (remnant of incomplete p-p chain) and lasts until there is 3He ◊ Very luminous AGB starsVery luminous AGB stars a hydrostatic, slow process:the bottom of the convective envelope reaches the H-shell burning region and nuclear reaction products are transported to the surface by convection

Iben 1973, Sackman, Smith & Despain 1974, Scalo, Despain & Ulrich 1975 hot bottom convective envelopes Hot Bottom Burning (HBB)

THBB >4 x 107 K


Hot Bottom Burning : Li, C and O

3He + 4He -> 7Be -> 7Li(Cameron & Fowler 1971)

T>4 x 107 K

In these same envelopes, Carbon also burns, so that the Carbon star features disappear

12C -> 14N T>6.5 x 107 K

A third possible processing occurs at even larger T: H- burning through the ON cycle (this may occur in the low metallicity massive AGBs and is possibly at the basis of the self-enrichment process in GCs):

16O -> 14N T>8 x 107 K


HBB temperatures in pop. II

ON processing is at the basis of the O reduction in second generation stars in Globular Clusters!


The O-Na anticorrelation in

GCsExistence of “anomalous” stars well known from the ’80s

Carretta et al. 2009 A&A 450, 523

grand total of 1958 individual red giant stars in the 19 GCs of the project. [Na/Fe] and [O/Fe] ratios from GIRAFFE spectra are shown as open (red) circles; abundance ratios obtained from UVES spectra (Paper VIII) are superimposed as filled (blue) circles and show no offset from the GIRAFFE sample. Arrows indicate upper limits in oxygen abundances.

halo field stars

GC

halo stars should “never” be second generation

I

P

E


GC formation is in two steps

where is matter processed?

FRMS (Decressin et al. 2007…)AGB-SuperAGB stars (Ventura et al. 2001 &

following)

THE NEW PARADIGM OF GC FORMATION:after a first generation (FG) of stars is born, forming a globular cluster –or even something very different, like a dwarf galaxy-, a second star formation event, based (at least partly) on matter processed within FG stars (same Z!) gives origin to the chemically anomalous second generation (SG) stars. Loss of the ‘environmental’ dwarf galaxy, or of MOST of the FG stars from the former GC, leaves out a globular cluster as it is today


this is the range of abundances in low metallicity field stars

??

anticorrelation

models!!

Models provide O depletion, Na production, but…


Successful models: dilution

a “dilution” model is necessary in order to obtain the observed anticorrelation

AGB ejecta+

pristine gas

provide the mixture of composition that can explain the observations


“Strong” and “mild” O-Na anticorrelations

successful models should be able to reproduce different cases, as exemplified by NGC 2808 and M4


HST Treasury project GO13297 (Piotto)First data reduction of NGC2808 data

Chemical evolution modelsdata from Carretta et al. 2008 -2009

D ’Ercole et al. 2012, yields from Ventura& D’Antona 2011

NGC 2808

1) a ‘pure ejecta’ SG from super-AGBs, high Y

2) an intermediate SG formed by ejecta of massive AGBs plus pristine matter reaccreted

0) FG in place


Shortly: model for clusters with “strong” chemical anomalies

1: FG in place,standard C.C. Na-poor, O-rich

2: extreme SG first phases of cooling flow:C.C. of super-AGB ejecta: Na-rich, O-deprived

3: intermediate SG: mixture of massive AGB ejecta and pristine gas:C.C. moderately Na-rich andO-poor


Strong dilution in clusters with ‘mild’ O-Na

M4

data from Marino et al. 2008

1) the ‘pure ejecta ’ SG from super-AGBs, high Y, must be inhibited

2) mixing occurs with a larger % of pristine gas, SG formation provides small O-depletion and Y spread, some Na enhancement


Shortly: model for clusters with “mild” chemical anomalies

1: FG in place,standard C.C. Na-poor, O-rich

2: extreme SG first phases of cooling flow:C.C. of super-AGB ejecta: Na-rich, O-deprived

2: SG is born directly from pristine gas contaminated by massive AGB – superAGB ejecta:C.C. moderately Na-rich and scarcely deprived in O


Melendez & Ramirez Li plateau

for

-3<[Fe/H]<-1

(slope for Fe/H<-2.5 not included)

BUT GC dwarfs seem to have a

larger dispersion: is it due to the

presence of SG stars?

Lind et al. 2009Pasquini et al. 2007Bonifacio et al. 2007

What we expect for Lithium?


What we expect for Lithium?

65

4

e

1.5

5

higher M larger T_bottom stronger and faster Li production


Metallicity dependence at M=6Msun

higher Z smaller T_bottom smaller and slower Li production

0.0040.001

0.0006


But production does not mean yield!

two ingredients are important: how much Li is made,

and how long it lasts so that mass loss can recycle it in the

i.s.m.AND mass loss is another big unknown parameter (both absolute values and dependence on the luminosity)

Ventura et al. 2002 A&A 339,215


the yield depends dramatically on mass loss!

here we see the role of mass

loss at Z=10-3

Center: ‘standard’ Mdot

Upper models: Mdot*2

Lower: Mdot from Vassiliadis

& Wood


In VD models, mass loss rate calibrated on Li in the MC O-rich

luminous giants

A(Li) decreases with initial mass due to the faster He3 destruction in spite of larger abundances reached in the envelope

A(Li) re-increases due both to the stronger production and huge mass loss


Observational results in some clusters

M4D’Orazi & Marino 2010 giants shiftedMonaco et al. 2012 turnoff stars

Na-rich (SG) stars may have just 0.1 dex smaller Li than Na-poor (FG) stars!

Similar results in other clusters: NGC 6397, e.g.

Is there an influence of AGB Li production? Or not?


Observational results in some clusters

Use the D’Ercole et al. 2012 chemical evolution model

We have a further ambiguity: Which is the Lithium content of the diluting “pristine” matter? Is it the”observed” value A(Li)=2.2-2.3, or we have to make the hypothesis that the true value is the Big Bang abundance, now given at A(Li)=2.6-2.7 ??? In the latter case, we have also to assume that the same amount of Li surface depletion takes place in SG stars… THIS CHOICE MAKES A DIFFERENCE IN THE MODEL RESULTS


4: SG STARS:a) the Li at the surface is that resulting from the mixture above

b) Li observed is that resulting from the mixture, but REDUCED by the same mechanism which brings pop.II Li from 2.6-2.7 to 2.2-2.3

Possibilities (schematically)

1: OBSERVED:FG starsA(Li)=2.2-2.3

2: but in the gas forming the FG and diluting the SG:

a) A(Li)=2.2-2.3b) A(Li)=2.6-2.7

3: SG GAS:mixture of gas having either a) or b) plus Li of relevant AGB ejecta


model M4-3

A(Li)pristine=2.2 A(Li) pristine=2.7

A(Li)=2. in ejecta of 7.5 and 8Msun

A(Li)pristine=2.2 A(Li)pristine=2.7

result is OK also if we assume NO Li in the AGB ejecta, as done in the above figure…

Modelling M4


The super-AGB yields seem to be very overestimated to be consistent with M4 data for Li

If there is Li in the ejecta, or not, does not make any difference in the final result: We mainly need that the dilution of Na-rich gas with pristine gas is strong enough that the Lithium abundance is dominated by the primordial gas abundance

The choice a) vs. b) for the primordial Li is not discriminating (unless we take seriously the super-AGB yields)

Result to bring home, from modelling M4


The case of clusters with strong anomalies

A(Li)pristine=2.3

A(Li)pristine=2.6

FG

extreme SG

intermediate SG

IF the yields of super-AGBs by VD2011 are reliable, we should find a few very Li-rich stars (A(Li)=2.7-3) in the clusters having an extreme SG, born directly from super-AGB ejecta, e.g. in wCen, NGC 2808! (No evidence so far: these yields are too large?)


Role of intermediate SG

A(Li)pristine=2.3Slope=0.37

A(Li)pristine=2.6Slope = 0.6

FG

extreme SG

intermediate SG


The case of NGC 6752no extreme anomalies inthe O-Na anticorr.Y spread relatively small (from MS)

Shen et al. (2010) show that Li and O are correlated, with a slope much smaller than 1 (corresponding to dilution with matter devoid of both O and Li)


slope 1

The case of NGC 6752

A(Li)pristine=2.6 A(Li)pristine=2.3

A(LiO/Fe]=0.27±0.05A(LiO/Fe]=0.62±0.05

if we had 1) better oxygen – lithium data; 2) better confidence in the chemical evolution model we could use the data as a TEST for Big Bang Lithium!


Summary◊ Still we are not sure about how to interpret the observed abundance of Li in pop. II stars

◊ Galactic evolution of Lithium requires massive AGB – superAGB as source of Lithium

◊ The Hot Bottom Burning producing Lithium is also the source of further nucleosynthesis in AGB – superAGB, and the most plausible source of the processed matter forming second generation stars in Globular Clusters

◊ Modelling of GC abundance patterns (e.g. O – Na) can be successfully achieved. This allows to predict Li distribution among GC stars

◊ The result of simulations depend on the Big Bang Lithium abundance assumed to be available in the matter diluting the AGb ejecta. Observations of Li in GCs may in the end constrain the Original Li.


A MESSAGE FROM ITALO:Hi Francesca:

what can I say? I’m proud of you!But I’m proud of me as well, forI could help in pushing aheadsomebody who is BETTER,and not WORSE than I am!

So: to the next 30 yr of research …(my art. 10)!

Francesca, best wishes for your life,

and good work for the future 30yr (is this enough?)

from myself and Italo,thank you, you know why

M4D’Orazi & Marino 2010

lithium patterns, globular clusters formation and the big bang lithium abundance

Documents

honour of francesca

convective hot region

lithium plateau

production of li

hbb li

lithium patterns

spite spite

convective envelopes