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Abundances in M92
Summary prepared by John Lattanzio, Oct 2003
Center for Stellar and Planetary Astrophysics
Monash University
M92: Everything you need to know!
M92: Everything you need to know!
What’s special abut M92?
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One of the most
metal-poor:
[Fe/H] = -2.2
One of the oldest:
16Gyr
(according to Grundahl et al
2000)
Basic Parameters for M92
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[Fe/H] = -2.2
Age = 16 Gyr
C = 1.81
Distance = 27,000 ly
Mass = 330,000 Msun
It all started with….Carbon et al 1982
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Observed 71 red giants (above HB)
Solar
It all started with….Carbon et al 1982
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Observed 71 red giants, above HB
Langer and Kraft 1984
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Looked at C, N and C+N in various
populations
M3 and M13 (same [Fe/H])
Field Giants
M92 and M15 (same [Fe/H])
Langer and Kraft 1984: M3 and M13
Langer and Kraft 1984: Field giants
Langer and Kraft 1984: M92 and M15
Langer and Kraft 1984
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Average abundances
Norris and Pilachowski 1985
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C+N may be
bimodal
N correlates
with Na (in all 4
giants studied!)
Langer et al 1986
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Clear decrease of C with L
From as low as Mv=1.5
Pilachowski 1988
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C, N and O in 6 giants
C+N+O is very constant…
Sneden et al 1991
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9 giants
No variations in [Fe/H] from star to star
Sneden et al 1991
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Two groups: O-rich and O-poor?
Sneden et al 1991
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Definite evidence for ON cycling!
Sneden et al 1991
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Possible variation of O with L?
C, N, O, and Na
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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
C variation
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Clear decrease of C with L from Mv=1.5
Bellman et al 2001
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Bellman et al 2001
Mv=1.5 is fairly
low L…
The bump in
the LF is at
Mv=-0.4
Nearly 2 mag
difference…
First Dredge-Up
Start
Finish
LF Bump
D log L = 0.8 below bump
Or 2 mag!
C variation with L
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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)
But…
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Smith and Martell 2003
Measured values of d[C/Fe]/dMV
Get same value above and below LF bump…
C variation with L
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Its not clear that FDU and deep
mixing should change C at the same
rate!!!
Needs work!
Heavy elements: More on Fe
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King et al 1998 looked at 3 subgiants
in M92:
Checked their data with a standard of similar [Fe/H]
(HD 140283) and got same as everyone else…
Heavy elements: More on Fe
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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]
Heavy elements: More on Fe
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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…
Heavy elements:
Shetrone looked at Mg, Al, Eu in 6 giants
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High [Fe/H]
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Intermediate [Fe/H]
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Low [Fe/H]
Heavy elements:
Shetrone looked at Mg, Al, Eu in 6 giants
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High [Fe/H]
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Intermediate [Fe/H]
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Low [Fe/H]
Heavy elements:
Shetrone looked at Mg, Al, Eu in 6 giants
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High [Fe/H]
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Intermediate [Fe/H]
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Low [Fe/H]
Heavy elements:
Shetrone looked at Mg, Al, Eu in 6 giants
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High [Fe/H]
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Intermediate [Fe/H]
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Low [Fe/H]
Heavy elements:
Shetrone looked at Mg, Al, Eu in 6 giants
Heavy elements: Neutron capture stuff
Aronsky et al 1994: 9 giants
Heavy elements: Neutron capture stuff
Aronsky et al 1994: 9 giants
Heavy elements: Neutron capture stuff
Aronsky et al 1994: 9 giants
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No variation from star-to-star
No variation with evolutionary state
No variation with other elements
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At last – something we understand 
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Heavy elements: 3 subgiants
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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
Heavy Elements: Sneden et al 2000
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34 giants in M92 (and 31 in M15)
Heavy Elements: Sneden et al 2000
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Ca: no variation
Na:
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Large spread
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No variation with L or
Te
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Correlates with N
Ba: no variation
Heavy Elements: Sneden et al 2000
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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
[Ba/Eu] = +0.2 in M5
[Ba/Eu] = -0.4 in M92 (only 2 stars!)
[Ba/Eu] = -0.4 in M15 also
Heavy Elements: Sneden et al 2000
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Si varies a lot from cluster to cluster
M92
NGC6752
NGC6723
M4
M5
[Si/Fe] = +0.59
[Si/Fe] = +0.23
[Si/Fe] = +0.68
[Si/Fe] = +0.55
[Si/Fe] = +0.60
Si is primarily made in
supernovae from stars
With M=20-25 Msun
Constraints from Li abundances?
Deliyannis et al 1995
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4 subgiants have A(Li) = 2 – 2.5
1)
Boesgaard et al 1998
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7 subgiants have A(Li) = 2 – 2.6
Bonifacio reanalized these stars:
1)
2)
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Claims A(Li) = 2.3  0.1 ie little spread
Constraints from Li abundances?
Subgiants now a problem
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1)
2)
3)
4)
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 
Constraints from Li abundances?
Pilachowski et al 2000
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60 giants in M92
2)
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!
1)
Summary
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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?
References
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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
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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