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Abundances in M92

This summary presents a detailed overview of M92, one of the oldest and most metal-poor globular clusters. With an age of approximately 16 billion years and a metallicity of [Fe/H] = -2.2, M92 serves as an essential reference for understanding stellar evolution. The document compiles findings from various studies, including significant observations of carbon and nitrogen variations among red giants. It highlights key parameters such as distance (27,000 light-years), mass (330,000 M☉), and the notable phenomena of ON cycling, deep mixing, and heterogeneous elemental abundances, revealing complexities in stellar evolution.

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Abundances in M92

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  1. Abundances in M92 Center for Stellar and Planetary Astrophysics Monash University Summary prepared by John Lattanzio, Oct 2003

  2. M92: Everything you need to know!

  3. M92: Everything you need to know! Lower HRD Upper HRD

  4. What’s special abut M92? • One of the most metal-poor: [Fe/H] = -2.2 • One of the oldest: 16Gyr (according to Grundahl et al 2000)

  5. Basic Parameters for M92 • [Fe/H] = -2.2 • Age = 16 Gyr • C = 1.81 • Distance = 27,000 ly • Mass = 330,000 Msun

  6. It all started with….Carbon et al 1982 • Observed 71 red giants (above HB) Solar

  7. It all started with….Carbon et al 1982 • Observed 71 red giants, above HB Variation in C+N too! Large variation in C and N

  8. Langer and Kraft 1984 • Looked at C, N and C+N in various populations • M3 and M13 (same [Fe/H]) • Field Giants • M92 and M15 (same [Fe/H])

  9. Langer and Kraft 1984: M3 and M13

  10. Langer and Kraft 1984: Field giants [Fe/H] < -2 [Fe/H] > -2

  11. Langer and Kraft 1984: M92 and M15

  12. Langer and Kraft 1984 • Average abundances

  13. Norris and Pilachowski 1985 • C+N may be bimodal • N correlates with Na (in all 4 giants studied!)

  14. Langer et al 1986 • Clear decrease of C with L • From as low as Mv=1.5

  15. Pilachowski 1988 • C, N and O in 6 giants • C+N+O is very constant…

  16. Sneden et al 1991 • 9 giants • No variations in [Fe/H] from star to star

  17. Sneden et al 1991 • Two groups: O-rich and O-poor? Low O not seen in field stars! ON cycling?

  18. Sneden et al 1991 • Definite evidence for ON cycling!

  19. Sneden et al 1991 • Possible variation of O with L? Not convincing!

  20. C, N, O, and Na • Clear decrease of C with L • Corresponding increase of N with L • C+N+O constant for some stars • Large spread in C & N at any given L • ON cycling has occurred in some giants • No O variation with L • No Na variation with L

  21. C variation • Clear decrease of C with L from Mv=1.5 Bellman et al 2001

  22. Mv=1.5 is fairly low L… Should we be worried??? • The bump in the LF is at Mv=-0.4 • Nearly 2 mag difference… Bellman et al 2001

  23. First Dredge-Up Start Finish D log L = 0.8 below bump Or 2 mag! LF Bump

  24. C variation with L • So I think they just forgot about FDU! • FDU changes C from base of GB • When L exceeds LF bump then deep mixing continues (mu gradient removed)

  25. But… • Smith and Martell 2003 • Measured values of d[C/Fe]/dMV • Get same value above and below LF bump… Whole of GB Upper GB

  26. C variation with L • Its not clear that FDU and deep mixing should change C at the same rate!!! • Needs work!

  27. Heavy elements: More on Fe • King et al 1998 looked at 3 subgiants in M92: [Fe/H] is 2 x lower than giants!? Checked their data with a standard of similar [Fe/H] (HD 140283) and got same as everyone else…

  28. Heavy elements: More on Fe • King et al 1998: 3 subgiants in M92 were not homogeneous: one was 0.15 dex different to the other two • Gravitational settling? Radiation effects? Richard et al 2002 expect factors of 2 or more in most metal poor systems • Later added data for 2 more subgiants: same average value of [Fe/H]

  29. Heavy elements: More on Fe • Langer et al 1998 • Used over 100 lines of various metals and looked at 3 bright giants • Two are identical • One differs by 0.18 dex from the other two…

  30. Heavy elements:Shetrone looked at Mg, Al, Eu in 6 giants • Intermediate [Fe/H] • High [Fe/H] • Low [Fe/H] Al up when Na up

  31. Heavy elements:Shetrone looked at Mg, Al, Eu in 6 giants • Intermediate [Fe/H] • High [Fe/H] • Low [Fe/H] Al up when Na up and O down

  32. Heavy elements:Shetrone looked at Mg, Al, Eu in 6 giants • Intermediate [Fe/H] • High [Fe/H] • Low [Fe/H] Mg down when Al up

  33. Heavy elements:Shetrone looked at Mg, Al, Eu in 6 giants • Intermediate [Fe/H] • High [Fe/H] • Low [Fe/H] No variation in Eu

  34. Heavy elements:Shetrone looked at Mg, Al, Eu in 6 giants No variation of Al with L

  35. Heavy elements: Neutron capture stuffAronsky et al 1994: 9 giants Elements as expected Ba constant

  36. Heavy elements: Neutron capture stuffAronsky et al 1994: 9 giants No variation with other elements No variation with Te

  37. Heavy elements: Neutron capture stuffAronsky et al 1994: 9 giants • No variation from star-to-star • No variation with evolutionary state • No variation with other elements • At last – something we understand 

  38. Heavy elements: 3 subgiants • King et al 1998 looked at 3 subgiants: Field star Mg depleted compared to field: just like giants in M92 Na enriched compared to field: just like giants in M92 Ba higher compared to field: just like giants in M92 Subgiants show same anomalies as giants!

  39. Heavy Elements: Sneden et al 2000 • 34 giants in M92 (and 31 in M15)

  40. Heavy Elements: Sneden et al 2000 • Ca: no variation • Na: • Large spread • No variation with L or Te • Correlates with N • Ba: no variation

  41. Heavy Elements: Sneden et al 2000 • Ba and Eu are useful… • Ba is lower in M92 than M15 (same [Fe/H]) • Just like M4 and M5 [Ba/Eu] = -0.4 for pure r-process [Ba/Eu] = -0.4 in M4 s-process active in M5 [Ba/Eu] = +0.2 in M5 (only 2 stars!) [Ba/Eu] = -0.4 in M92 [Ba/Eu] = -0.4 in M15 also pure r-process in M15 and M92

  42. Heavy Elements: Sneden et al 2000 • Si varies a lot from cluster to cluster [Si/Fe] = +0.59 M92 Si is primarily made in supernovae from stars With M=20-25 Msun [Si/Fe] = +0.23 NGC6752 NGC6723 [Si/Fe] = +0.68 M4 [Si/Fe] = +0.55 M5 [Si/Fe] = +0.60 Could we be seeing variations in the IMF?

  43. Constraints from Li abundances? • Deliyannis et al 1995 • 4 subgiants have A(Li) = 2 – 2.5 • Boesgaard et al 1998 • 7 subgiants have A(Li) = 2 – 2.6 • Bonifacio reanalized these stars: • Claims A(Li) = 2.3  0.1 ie little spread

  44. Constraints from Li abundances? • Subgiants now a problem • They show Na and Al enhancements • As expected from ON, NeNa and MgAl cycle • But Li not destroyed! • Wherever the hot H burning happened, the Li was added afterwards 

  45. Constraints from Li abundances? • Pilachowski et al 2000 • 60 giants in M92 • None have A(Li) > 0 (Te = 4500K) > 1 (Te = 5000K) Is this consistent with first dredge-up? Is it consistent with deep mixing? Should make some Li!

  46. Summary • Clear evidence for deep mixing on GB via the C and N variations • ON cycling has produced N and Na • Some Al made and Mg destroyed at the same time as the ON cycling and Na production • Na (etc?) variations seen in subgiants also • Some variation in Fe from star to star? From giant to subgiant? • Pure r-process in earlier life, no s-process • Need mixing and primordial variations • Is Li a problem? Or a useful constraint?

  47. Armosky et al, 1994, AJ, 108, 1364 Bellman, et al, 2001, PASP, 113, 326 Boesgaard et al, 1998, ApJ, 493, 206 Bonifacio, 2002, A&A, 395, 515 Buonanno et al, 1985, A&A, 145, 97 Carbon et al , 1982, ApJS, 49, 207 Deliyannis et al, 1995, ApJ, 452, L13 Grundahl et al, 2000, AJ, 120, 1884 King et al, 1998, AJ, 115, 666 Langer & Kraft, 1984, PASP, 96, 339 Langer et al, 1986, PASP, 98, 473 Langer et al, 1998, AJ, 115, 685 Norris & Pilachowski, 1985, ApJ, 299, 295 Pilachowski, 1988, ApJ, 326, L57 Pilachowski et al, 2000, AJ, 119, 2895 Richard et al, 2002, ApJ, 580, 1100 Shetrone, 1996, AJ, 112, 1517 Smith & Martell, 2003, PASP, 115, 1211 Sneden et al, 1991, AJ, 102, 2001 Sneden et al, 2000, AJ, 120, 1351 References

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