Center for Stellar and Planetary AstrophysicsMonash University

Summary prepared by John Lattanzio

Abundances in M71

M71: Everything you need to know!

M71: Everything you need to know!

It all started with….Smith & Norris 82

Observed 22 red giants, above HB

Smith & Norris 82 (cont)

Large spread in CN at given MV

Smith & Norris 82 (cont)

No correlation with cluster mass or concentration parameter c

eg 47Tuc has same [Fe/H] but very different M and c

Smith & Penny 1989

Picked a sample of 16 HB stars Does CN vary in these also? Yes, and in same proportion

CN weak % CN strong %On RBG: 10/16 63 6/16 37 On HB: 13/18 72 5/18 28

Smith & Penny 1989 (cont)

No evidence for variation in ratio with evolutionary stage (there may be for 47 Tuc?)

Penny, Smith, Churchill 1992

Extend CN sample by looking at strong/weak

1) 22 stars on lower GB 0.82) 17 stars on upper GB 0.33) 15 red HB stars 0.7

Why upper GB different?1) Some evidence for lower CN occurrence

on AGB? Maybe some contamination?2) Is it statistically significant?

Sneden et al 1994

Choose 10 stars within 1 mag of GB tip

[Fe/H] = -0.78 [/Fe] = +0.39 Age = 14-16 Gyr m-M=13.0

Sneden et al 1994 (cont)

<[Si/Fe]> = +0.31 with =0.11 <[Ca/Fe]> = +0.14 with =0.10 <[Ti/Fe]> = +0.48 with =0.11 <[O/Fe]> = +0.39 with =0.02

1) Very little variation in O!2) But may be two groups: [O/Fe] =

0.39 and [O/Fe] = 0.19

Sneden et al 1994 (cont)

Sneden et al 1994 (cont)Large spread in Na but not much in O

An anti-correlation???

Briely, Smith & Lambert 1994

Sample of 5 giants Look at C12/C13 values C12/C13 [O/Fe]3 CN strong 5-6 +0.22 CN weak 9 +0.4

Seems that N up means O down…ie ON cycling!

Briely, Smith & Lambert 1994 (cont)

C+N+O = constant

Briley Smith King Lambert 1997

Add another 5 bright giants Look again for C12/C13 Same trend…

Briley Smith Claver 2001

Photometry for 75 giants down to MV=+2

Use CN strength to estimate variation of C and N over GB

Briley Smith Claver 2001 (cont)

Identical C and N values fit all stars!! This means

1) No deep mixing on giant branch…2) FDU has not altered CN, so pollution of

an existing star is ruled out!3) All of star is born with high or normal N4) Hard to get enough N from AGB without

screwing with the IMF…

Briley and Cohen 2001

Extend previous analysis to MS stars measured by Cohen in 1999

Same conclusion! C, N, O show essentially no

variation from MS to RGB tip…thus:1) Little deep mixing2) No pollution3) Primoridal enrichment requires lots of

N!

Cohen Behr Briley 2001. Paper I. Sample.

Choose 25 stars1) 10 on GB above

HB2) 3 on HB3) 9 on GB below HB4) 3 near turnoff

Ramirez et al 2001. Paper II. [Fe/H].

[Fe/H] = -0.71 ± 0.08 from FeI [Fe/H] = -0.84 ± 0.12 from FeII

And essentially NO spread!

Ramirez & Cohen 2002. Paper III. Abundance Ratios

Iron Peak1) Sc, V, Cr, Mn, Co and Ni measured2) All follow Fe3) No trend with L or Te

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

n-capture1) Y, Zr, Ba, La and Eu measured2) No trend with L or Te

3) Very little scatter except for Zr

4) Believe this is due to observational errors and not evidence for variation from star to star

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

elements1) Mg, Ca, Si and Ti measured

2) All over-abundant compared to Fe

3) No trend with L or Te

4) <[Ti/Fe]> = +0.20 ± 0.08 cf Sneden 0.48

5) <[Si/Fe]> = +0.28 ± 0.14 cf Sneden 0.31

6) <[Ca/Fe]> = +0.43 ± 0.05 cf Sneden 0.13

7) <[Mg/Fe]> = +0.36 ± 0.09 No sign of Mg variation…

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

Na and O1) O varies from star to

star2) By more than

observational error3) Na similar, but less

variation

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

There is an anti-correlation….

Its just that O and Na do not vary much…

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

Al1) Only measured in a sub-sample2) Correlates with Na (but lots of scatter)

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

C1) Best estimates of abunds come from

molecular lines2) These are consistent with a

variation by only a factor of TWO!3) “with a much larger anti-correlated

variation in N” ???4) C + N + O =?

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont)

C: factor of 2???

Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) Comparison with other clusters (later!)

Conclusion: M71 [Fe/H] =-0.8

CN varies, from RGB tip down to MS But not by much, apparently And this means it must be primordial

enrichment and not pollution of existing stars (as convective envelope depth changes a lot)

An O-Na anti-correlation exists (down to MS) but not much intrinsic variation in O or Na

ON cycle thus involved in some cases Nothing else seems to vary! Well, “no” variation of Mg but some slight

variation of Al

References

Smith & Norris, 1982, ApJ, 254, 159 Smith & Penny, 1989, AJ, 97, 1397 Penny, Smith & Churchill, 1992, MNRAS, 257, 89 Briley, Smith & Lambert, 1994, ApJ, 424, L119 Salaris & Weiss, 1998, A&A, 335, 943 Briley, Smith & Claver, 2001, AJ, 122, 2561 Briley & Cohen, 2001, AJ, 122, 242 Cohen, Behr & Briley, 2001, AJ, 122, 1420 Ramirez & Cohen, 2002, AJ, 123, 3277 Ramirez et al, 2001, AJ,122, 1429 Sneden et al, 1994, AJ, 107, 1773 Briley, Smith, King & Lambert, 1997, AJ, 113, 306