Center for Stellar and Planetary AstrophysicsMonash University

Summary prepared by John Lattanzio, Dec 2003

Abundances in NGC6752

NGC6752: Everything you need to know!?

NGC6752: Back to Basics

[Fe/H] = -1.5 Age = Old… 13 Gyr or “more” Distance = 13,000 ly Log (M/M0) = 5.1 (DaCosta’s thesis,

1977) m-M = 13.13 C = 2.50 , core collapsed

NGC6752: HRD etc

V (HB) = 13.5 – 18 with a big gap!

V (TO) = 17 V (RGB tip) = 11 HB is very blue, with

a gap… Also a gap on Sub

Giant Branch…

Gaps on the sub-giant branch

NGC6752: the start

Da Costa and Cottrell 19801) 2 stars…on had CN up and one had

CN down Bell and Dickens 1980

1) 4 stars2) C down and N “probably” up

NGC6752: Norris et al 1981

69 Red Giants CN bimodal

NGC6752: Norris et al 1981

Also found Al up a bit AGB stars interesting..,

1) No AGB stars with enhanced N2) AGB stars are all low (normal?) C

NGC6752: Norris et al 1981 “model”

All gas forms with same [Fe/H] Half has normal CN, half has higher CN and hence higher Y by

~0.05 Thus two groups of stars

1) C and N normal, Y=0.252) C down, N up, Y=0.30

This gives two populations on HB! Given Z=0.001 and age = 13Gyr

1) MTO(Y=0.25) = 0.81M0

2) MTO(Y=0.30) = 0.74M0

Core mass same, so lower M = lower Menv

So lower mass is BLUER and leaves HB SOONER, not making it to the AGB

So AGB has the CN normal stars

Cottrell & Da Costa 1981

CN strong stars have 1) Na up by ~ 0.25 dex2) Al up by ~ 0.2 dex

Mg, Si, Ca, Fe, Ba are the same in all stars

Smith and Norris 1982

Tried to estimate the amount of N needed to match the observations

Hard to get C down and N up by enough!

They used old (Renzini and Voli 1981) yields. Do it more better??? Yeshe?

HB stars and their abunds

Heber et al 19861) He = 0.2% to 3% (by number)2) That is a factor of FIFTEEN!

Glaspey et al 19891) Fe in blue HB stars ~ 50 x Fe in RGB stars2) Believed due to gravitational settling and

high UV flux levitating light elements

Suntzeff and Smith 1991

12 red giants C12/C13 ~ 3-5 (ie

CN equilibrium) No dependence of

C12/C13 on CN!?

Suntzeff and Smith 1991

12 red giants Variation of C12

with B-V? The high C12 seem

to disappear There are low C12 at

all temperatures…

Smith and Norris 1993

AGB CN problem…. CN bands are weaker in AGB stars This is due to lower T and larger g BUT: there is still a smaller spread in

CN in the AGB stars than the RGB stars

Seen in other GC as well M4 and M5: AGB stars are CN-strong NGC6752: AGB stars are CN weak

INTERMISSION

Story So Far

Note: nothing as a function of L! Except C in Suntzeff and Smith But NGC6752 is bright/nearby So everyone went to look at the

TO… This they now do…© Python

(Monty)

Gratton et al 2001

Many TO and early RGB stars

Look at O, Na, Mg and Al

Gratton et al 2001

O-Na correlation exists at the TO

And at the bottom of RBG

Gratton et al 2001

Mg-Al correlation clear in subgiants

Less clear at the TO

They say that this is due to using different Al lines for the warmer TO stars

The AL correlates with Na (not shown) for TO stars

Grundahl et al 2002

21 red giants Many below RGB

bump Usual

correlations seen

Grundahl et al 2002

Li disappears once you get to the bump!

Yong et al 2003

20 bright RGB stars Look at Mg24:Mg25:Mg26 Solar value is 80:10:10 Mg24 made in supernova

Yong et al 2003

Mg24 down as Al up

Mg25 same for all Al

Mg26 up as Al up

Does not fit Mg-Al cycle (maybe at very high T?)

Yong et al 2003

No dependence of these on evolutionary state (thank God!)

Yong et al 2003

Highest Mg26 (dotted circles) has:

1) Lowest O2) Highest Na3) Highest Al

James et al 2003 (astro-ph)

9 TO stars and 9 SGB stars Sr, Y, Ba, Eu: little or no variation

1) [Sr/Fe] = 0.062) [Y/Fe] = -0.013) [Ba/Fe] = 0.184) [Eu/Fe] = 0.41

This gives [Ba/Eu] = -0.18 Pure r-process is –0.7 so there has been s-process active!

Fenner et al 2004 (MNRAS)

Initial burst of Z=0 stars Bimodal mass distribution Resulting yields used to mix to observed

[Fe/H] Resulting mixture evolved along AGB by

Simon

Fenner et al

O-Na and MG-Al correlations not reproduced

Red = individual stars from Simon

Blackline = evolution of ISM in NGC6752

Blue and Green = data…

Mg24 fits data!!!

Fenner et al No correlations with Mg isotopes match the

observations either!

Fenner et al

CN anti-correlation?

Not really…. Blue crosses are

averages of the CN weak and CN strong groups

Fenner et al

Total C+N+O Not very

constant!

Summary

Not much evidence for deep mixing on GB via the C and N variations

Very little data showing L variation… CN bimodal O-Na and Mg-Al anti-correlations seen at all

L Mg isotopes hard to understand:

1) Rich in high mass isotopes2) But how to keep Mg25 constant?

AGB models really don’t fit!

References

Norris et al, 1981, ApJ, 244, 205 Cottrell & DaCosta, 1981, ApJ, 245, L79 Smith & Norris, 1982, ApJ, 254, 594 Heber et al, 1986, A&A, 162, 171 Suntzeff & Smith, 1991, ApJ, 381, 160 Smith & Norris, 1993, ApJ, 105, 173 Gratton et al, 2001, A&A, 369, 87 Grundahl et al, 2002, A&A, 385, L14 Yong et al, 2003, A&A, 402, 985 Fenner et al, 2004, MNRAS, submitted