Abundances for NGC6752
Gaps in the HRD
- Gaps are seen in the NGC6752 HRD at the base of the giant branch
- These are seen in other clusters too, such as NGC288 and maybe also in M92
- No explanation as far as I can tell...
HB abunds
- Heber et al 1986 A&A 162 171 found that He varied from 0.2% to 3% ((by number) in HB stars
- Glaspey et al 1989 found that Fe in blue HB stars was 50 x higher than in RGB stars
- These effects are believed to be due to UV flux levitating some light elements, and gravity causing heavy ones to sink.
- The conclusion is DO NOT TRUST ABUNS IN BLUE HB STARS!
Fe-peak elements
- [Fe/H] = -1.5
- There is as yet no evidence for any variation from star to star
- Estimates of [Fe/H] vary from -1.4 to -1.6, from one paper to another
- Other Fe-peak
- I found nothing in the literature...
n-capture elements
- Not much data!
- James et al 2003, astro-ph0311278 looked at Sr, Y, Ba and Eu in 9 TO stars and 9 SGB stars
- No variation from star to star
- <[Sr/Fe]> = 0.06
- <[Y/Fe]> = -0.01
- <[Ba/Fe]> = 0.18
- <[Eu/Fe]> = 0.41
- This gives <[Ba/Eu]> = -0.18 whereas pure r-rpocess is -0.7. This some s-process has been going on!
Alpha elements
- Ca, Si and Ti: I couldn't find any data
C and N
- Norris et al 1981, ApJ, 244, 205 looked at 69 giants
- CN clearly bimodal
- CN index vs colour here from Norris et al 1981, ApJ, 244, 205.
- Suntzeff and Smith 1991 ApJ, 381, 160 show the only graph I could find of C vs L
- Seems the high L has only low C whereas low L has all values of C. May be consistent with deep mixing of CN burnt material.
- No variation in C12/C13 with CN index, curiously.
O, Na, Mg and Al
- Gratton et al 2001 A&A 369, 87 looked on the MS and the SGB
- Clear O-Na anti-correlation exists on the MS and the SGB
- There is a not-so-clear Mg-Al anti-correlation on the MS and the SGB
- Gratton et al believe that the correlation, clear in the subgiants, is also present in the TO stars but is lost because they used a different Al line for these warmer stars. They say that Al correlates with Na? But not shown.
- Grundahl et al 2002 A&A, 385, L14 looked at 21 giants, many below the bump in the LF. They found the usual O-Na and Mg-Al corelations
- Grundahl et al 2002 also looked at Li, and found that once you get above the bump of the LF then the Li disappears. They don't convert their EQW to an abundance for stars below the GB, which would be very important!
- Cavallo et al (astro-ph/0403263) find no evidence for Al varying with luminosity
- Yong et al 2003, A&A, 402, 985 looked at 20 bright RGB stars