Center for Stellar and Planetary Astrophysics Monash 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/M 0 ) = 5.1 (DaCosta’s thesis, 1977) m-M = 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 ) 2 stars…on had CN up and one had CN down Bell and Dickens ) 4 stars 2) C down and N “probably” up

NGC6752: Norris et al Red Giants CN bimodal

NGC6752: Norris et al 1981 Also found Al up a bit AGB stars interesting.., 1) No AGB stars with enhanced N 2) 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=0.25 2) C down, N up, Y=0.30 This gives two populations on HB! Given Z=0.001 and age = 13Gyr 1) M TO (Y=0.25) = 0.81M 0 2) M TO (Y=0.30) = 0.74M 0 Core mass same, so lower M = lower M env 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 dex 2) 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 ) He = 0.2% to 3% (by number) 2) That is a factor of FIFTEEN! Glaspey et al ) Fe in blue HB stars ~ 50 x Fe in RGB stars 2) Believed due to gravitational settling and high UV flux levitating light elements

Suntzeff and Smith red giants C12/C13 ~ 3-5 (ie CN equilibrium) No dependence of C12/C13 on CN!?

Suntzeff and Smith 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 red giants Many below RGB bump Usual correlations seen

Grundahl et al 2002 Li disappears once you get to the bump!

Yong et al 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 O 2) Highest Na 3) 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] = ) [Y/Fe] = ) [Ba/Fe] = ) [Eu/Fe] = 0.41 This gives [Ba/Eu] = 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 isotopes 2) 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