High-resolution spectroscopy of globular cluster post-Asymptotic Giant Branch stars

Francis Keenan, Philip Dufton, Jonathan Smoker, Robert Ryans, Carrie Trundle, C.J. Mooney, W.R.J. Rolleston, L.H. Aller

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Abstract

We present model atmosphere analyses of high resolution Keck and VLT optical spectra for three evolved stars in globular clusters, viz. ZNG-1 in M 10, ZNG-1 in M 15 and ZNG-1 in NGC 6712. The derived atmospheric parameters and chemical compositions confirm the programme stars to be in the post- Asymptotic Giant Branch (post-AGB) evolutionary phase. Differential abundance analyses reveal CNO abundance patterns in M 10 ZNG-1, and possibly M 15 ZNG-1, which Suggest that both objects may have evolved off the AGB before the third dredge-up occurred. The abundance pattern of these stars is similar to the third class of optically, bright post-AGB objects discussed by van Winckel (1997). Furthermore, M 10 ZNG-1 exhibits a large C underabundance (with Delta[C/O] similar to -1.6 dex), typical of other hot post-AGB objects. Differential Delta[alpha/Fe] abundance ratios in both M 10 ZNG-1 and NGC 6712 ZNG-1 are found to be approximately 0.0 dex, with the Fe abundance of the former being in disagreement with the cluster metallicity of M 10. Given that the Fe absorption features in both M 10 ZNG-1 and NGC6712 ZNG-1 are well observed and reliably modelled, we believe that these differential Fe abundance estimates to be secure. However, our Fe abundance is difficult to explain in terms of previous evolutionary processes that Occur oil both the Horizontal Branch and the AGB.
Original languageEnglish
Pages (from-to)1123-1132
Number of pages10
JournalAstronomy and Astrophysics
Volume419
Issue number3
Publication statusPublished - Jun 2004

ASJC Scopus subject areas

  • Space and Planetary Science

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    Keenan, F., Dufton, P., Smoker, J., Ryans, R., Trundle, C., Mooney, C. J., Rolleston, W. R. J., & Aller, L. H. (2004). High-resolution spectroscopy of globular cluster post-Asymptotic Giant Branch stars. Astronomy and Astrophysics, 419(3), 1123-1132.