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Abundances in M71

Abundances in M71. Center for Stellar and Planetary Astrophysics Monash University. Summary prepared by John Lattanzio. 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).

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Abundances in M71

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  1. Abundances in M71 Center for Stellar and Planetary Astrophysics Monash University Summary prepared by John Lattanzio

  2. M71: Everything you need to know!

  3. M71: Everything you need to know!

  4. It all started with….Smith & Norris 82 • Observed 22 red giants, above HB

  5. Smith & Norris 82 (cont) • Large spread in CN at given MV

  6. 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

  7. 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

  8. Smith & Penny 1989 (cont) • No evidence for variation in ratio with evolutionary stage (there may be for 47 Tuc?)

  9. Penny, Smith, Churchill 1992 • Extend CN sample by looking at strong/weak • 22 stars on lower GB 0.8 • 17 stars on upper GB 0.3 • 15 red HB stars 0.7 • Why upper GB different? • Some evidence for lower CN occurrence on AGB? Maybe some contamination? • Is it statistically significant?

  10. Sneden et al 1994 • Choose 10 stars within 1 mag of GB tip • [Fe/H] = -0.78 • [a/Fe] = +0.39 • Age = 14-16 Gyr • m-M=13.0

  11. Sneden et al 1994 (cont) • <[Si/Fe]> = +0.31 with s=0.11 • <[Ca/Fe]> = +0.14 with s=0.10 • <[Ti/Fe]> = +0.48 with s=0.11 • <[O/Fe]> = +0.39 with s=0.02 • Very little variation in O! • But may be two groups: [O/Fe] = 0.39 and [O/Fe] = 0.19

  12. Sneden et al 1994 (cont)

  13. Sneden et al 1994 (cont) Large spread in Na but not much in O An anti-correlation???

  14. Briely, Smith & Lambert 1994 • Sample of 5 giants • Look at C12/C13 values C12/C13 [O/Fe] 3 CN strong5-6 +0.2 2 CN weak9 +0.4 Seems that N up means O down…ie ON cycling!

  15. Briely, Smith & Lambert 1994 (cont) • C+N+O = constant

  16. Briley Smith King Lambert 1997 • Add another 5 bright giants • Look again for C12/C13 • Same trend…

  17. Briley Smith Claver 2001 • Photometry for 75 giants down to MV=+2 • Use CN strength to estimate variation of C and N over GB

  18. Briley Smith Claver 2001 (cont) • Identical C and N values fit all stars!! • This means • No deep mixing on giant branch… • FDU has not altered CN, so pollution of an existing star is ruled out! • All of star is born with high or normal N • Hard to get enough N from AGB without screwing with the IMF…

  19. 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: • Little deep mixing • No pollution • Primoridal enrichment requires lots of N!

  20. Cohen Behr Briley 2001. Paper I. Sample. • Choose 25 stars • 10 on GB above HB • 3 on HB • 9 on GB below HB • 3 near turnoff

  21. 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!

  22. Ramirez & Cohen 2002. Paper III. Abundance Ratios • Iron Peak • Sc, V, Cr, Mn, Co and Ni measured • All follow Fe • No trend with L or Te

  23. Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) • n-capture • Y, Zr, Ba, La and Eu measured • No trend with L or Te • Very little scatter except for Zr • Believe this is due to observational errors and not evidence for variation from star to star

  24. Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) • a elements • Mg, Ca, Si and Ti measured • All over-abundant compared to Fe • No trend with L or Te • <[Ti/Fe]> = +0.20 ± 0.08 cf Sneden 0.48 • <[Si/Fe]> = +0.28 ± 0.14 cf Sneden 0.31 • <[Ca/Fe]> = +0.43 ± 0.05 cf Sneden 0.13 • <[Mg/Fe]> = +0.36 ± 0.09 • No sign of Mg variation…

  25. Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) • Na and O • O varies from star to star • By more than observational error • Na similar, but less variation

  26. Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) • There is an anti-correlation…. • Its just that O and Na do not vary much…

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

  28. Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) • Al • Only measured in a sub-sample • Correlates with Na (but lots of scatter)

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

  30. Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) • C • Best estimates of abunds come from molecular lines • These are consistent with a variation by only a factor of TWO! • “with a much larger anti-correlated variation in N” ??? • C + N + O =?

  31. Ramirez & Cohen 2002. Paper III. Abundance Ratios (cont) • C: factor of 2???

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

  33. 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

  34. 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

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