AGBstarsinGalacticGlobularClusters–AreTheyChemically.pptVIP

AGB stars in Galactic Globular Clusters – Are They Chemically Distinct to Their Fellow RGB and HB Stars? M5: SDSS Simon Campbell Collaborators RSAA, Mt Stromlo, Australia: David Yong Elizabeth Wylie de Boer Monash University, Australia: John Lattanzio Richard Stanciffe George Angelou University of Aarhus, Denmark: Frank Grundahl University of Texas, USA: Chris Sneden AGBs in Globular Clusters High quality photometry is now making the AGB accessible in GCs, we can now get good numbers of AGBs. M5 (SDSS) B-I I M5 (Sandquist Bolte 2004) 100 AGBs! Quantifying Cyanogen Abundance:The S(3839) CN Index So basically you see how much flux is missing in a wavelength region due to CN absorption by comparing to piece of continuum nearby. Only need fairly low (~2 Ang) resolution. CN Weak CN Strong Continuum Norris et al. (1981) Cyanogen (CN) is a molecule whose abundance is thought to track that of Nitrogen. It absorbs over a few regions in the spectrum. Here we consider the Blue CN bands. Blue CN Index: CN Bimodality in GC Giants Early observations of GC giants showed that the molecule Cyanogen (CN) has a bimodal distribution. This suggests that each population – “CN-weak” and “CN-strong” have different nitrogen abundances. CN Index NGC 6752, Norris et al 1981 Mag CN-Strong CN-Weak This is not observed in halo field stars! (see eg. Langer et al, 1992) References: eg. Bell Dickens 1974, Da Costa Cottrell 1980, Norris et al. 1981. Note trend with Temp. No. Stars Bimodal CN distribution on RGB More recent work has shown that the CN bimodality extends down to the Main Sequence, suggesting that the bimodal composition has primordial origens. Cannon et al, 1998 V B-V Cannon et al., 1998 CN Bimodality on MS/SGB 47 Tuc More GC Weirdness? – CN in AGBs Norris et al. 1981 noted that their sample of AGB stars in NGC 6752 were all CN-weak (triangles = AGBs). Could this be chance, due to the small sample size – or is something strange happening on the AGB?? CN Index NGC 675