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Insights into the Chemical Composition of M71: Stellar and Planetary Astrophysics

This summary presents a detailed analysis of the chemical abundances found in globular cluster M71. Through various studies, it highlights observations of red giants and horizontal branch stars, revealing significant variations in carbon and nitrogen (CN) content. The data indicate a consistent primordial enrichment pattern with minimal evidence of stellar pollution and deep mixing during stellar evolution. It also explores the relationships and trends of various elemental abundances, shedding light on the intricate history of this stellar cluster.

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Insights into the Chemical Composition of M71: Stellar and Planetary Astrophysics

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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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