Abundances for M92

Fe-peak elements

[Fe/H] = -2.2
- There is some evidence for some small variation from star to star
- Langer et al 1998, AJ, 115, 685
- Based on a sample of 3 stars, but over 100 lines per star
- Two of the stars showed no measurable difference
- The other was 0.18 dex higher, in Fe and other Fe-peak elements
Some evidence for a lower [Fe/H] in the subgiants!
- Average of 5 subgiants was [Fe/H] = -2.52
- King et al 1998, AJ, 115, 666
- This could be due to gravtitational settling
- See Richard et al, 2002, ApJ, 580, 1100
- They predict variatioins in Fe-peak stuff by factors of 2-10
- Should be most noticeable in metal-poor systems (like M92!)
- But predicted effect is larger than observed...
Other Fe-peak
- Data from Sneden et al 2000, AJ, 120, 1363, for 34 giants in M92
- Graph shows results for Ca, Na and Ba
- Ca shows no variation with Te or from star-to-star
- Na shows a large spread and it correlates with N
- No variation of Ba with Te or from star-to-star (See also below)

n-capture elements

Sneden et al showed no Ba variation in 34 giants
Armosky et al 1994 looked at 9 giants and showed no variation in Ba
The also showed no variation in Nd
They showed that average of various s-elements was constant with T_e as well as [O/Na].
Shetrone 1996 looked at various things (See below) including Eu, which showed no variation
Combining Shetraone's data with Sneden allowed estimates of [Ba/Eu] for precisely *two* stars! The value was -0.4, which indicates a pure r-process.
Armosky et al 1994, AJ, 108, 1364
Sneden et al 2000,AJ, 120, 1351
Shetrone 1996, AJ, 112, 1517

Alpha elements

Mg, Ca, Si and Ti: Not a lot of data!
- Shetrone 1996 showed that Mg decreased as Al increased
- Sneden et al 1991 claim that there is a high-O and a low-O population
- The low-O stars are not seen in the field! This is shown in the previous graph, where field stars are shown with squares.
- Note that there is a strong correlation with N which implicates ON cycling
- Is there a variation of O with L?
- Sneden et al also point out that there is a reasonably large3 spread in Si and Ti from one globular cluster to another. Since these elements are made by 20-25Msun supernovae, this could be telling us about variations in the IMF.
- For M92: <[Si/Fe]> = +0.59, but in others it caries from 0.2 to 0.6
- Sneden et al 1991, AJ, 102, 2001

C and N

Obvious variation with L and a large spread at a given L!

Langer and Kraft 1994 (PASP, 96, 339) looked at giants in many clusters and plotted C vs N, withlines of constant C+N.
- The plot for M3 shows that the variations here are consistent with a small spread in C+N and then processig of C into N
- Their plot for field giants with [Fe/H] > -2 shows little evidence for CN cylcing.
- Their plot for field giants with [Fe/H] < -2 shows stronger evidence for CN cylcing.
- Their plot for M92 shows evidence for CN cylcing as well as a very large spread in the intrinsic C+N!
- This is very similar to the case of M15 which has similar metallicity to M92.
Norris and Pilachowski (1985, APJ, 299, 295) show that the distribution of (C+N) may be bimodal. Note that this is based on one bin with very few stars :-) If the bin at 0.0 on x-axis was filled, we would have a nice Gaussian!
Langer et al 1986 (PASP, 98, 473) show a nice plot of C vs L which shows the clear burning of C and also the spread in C at a given L
At what L does this decrease start? Maybe at M_V = 2? Maybe lower??? M_V=1.5 (V=16.1 since m-M = 14.6) is about where the spread appears (is this due to lack of data at lower L?)
This is well below the bump in the luminosity function which is at M_V = -0.4 or V= 14.2(Bellman et al 2001, PASP, 113, 326). Note the HR diagrams for the upper and lower luminosities.
Recall that the bump in the LF is simply where the H shell burns through the innermost extent of the convective envelope, from the first dredge-up. This then removes the abundance discontinuity, which the deep-micing experts reckon then removes the mu-gradien which ahs been the barrier to deep-mixing prior to this event.
But the first dredge-up will change C and that occurs up to 2 magnitudes below the bump! See the movies on my home page. We should do this for the correct compositions though.
However, Snmith and Martel 2003 (PASP, 115, 1211) calculated the gradient d[C/Fe]/dt and found that it is remarkably constant from cluster to cluster, at a value about 0.22. However, it is the same above and below the bump. It seems to me that first dredge-up and deep-mixing should not give the same values. Maybe they are being muddied by the spread in C at a given L? Need to do some theoretical calculations using deep micing, to compare.
On another tack, Pilachowski (1988, ApJ, 326, L57) showed that C+N+O was very constant in a set of 6 giants, and that ON cycling was involved.

Na and Al

Shetrone 1996 showed that Na went up as Al went up as expected when NeNa and MgAl cycles operate
Similarly, Shetrone showed that O went down as Al went up , with the same explanation as the previous graph
Is there a variation of Al with L? Need more data!
These abundances also seem to be present in subgiants according to data for 5 subgiants (King et al, 1998, AJ, 115, 666). Comparing to a typical field star with similar [Fe/H], they conclude that the sbgiants are different to field stars, but similar to giants: increased Na and decreased Mg. Need more data!

Constraints from Li

Various people have looked at Li in subgiants in M92. It appears that they have A(Li) about 2.3 +- 0.2.
Pilachowski et al 2000 looked for Li in giants in M92, and found none. This is consistent wqith dilution once the convective envelope expands.
But how did the subgiants get an envelope which has NeNa and MgAl processed material, but still has A(Li)=2.3????
Pilachowski et al 2000, AJ, 119, 2895
Boesgaard et al 1998, ApJ, 493, 206
Deliyannis et al, 1995, ApJ, 452, L13
Bonifacio, 2002, A&A, 395, 515

Below the Giant Branch?

The only info I could find was for 5 subgiants (King et al 1998, AJ, 115, 666). Comparing to a typical field star with similar [Fe/H], they conclude that the subgiants are different to field stars, but similar to giants: increased Na and decreased Mg. Need more data!