Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.5831b&link_type=abstract
American Astronomical Society, AAS Meeting #211, #58.31; Bulletin of the American Astronomical Society, Vol. 39, p.839
Astronomy and Astrophysics
Astronomy
Scientific paper
Low resolution spectra have been obtained of giants (seven each) in the globular clusters Arp 2 and Terzan 7. These clusters are of interest as they are believed to have originated in the Sagittarius Dwarf Elliptical Galaxy, which is currently interacting with the Milky Way. In a hierarchical galaxy formation scenario, some (perhaps large) fraction of the Milky Way's globular clusters are expected to have originated in similar dwarf galaxies. The present day Galactic globulars exhibit very unique abundance signatures in various light elements (star-to-star scatter in N, C depletions with increasing luminosity, etc.). Thus, an examination of the C-N homogeneity of globular clusters associated with an extragalactic dwarf galaxy, such as the Sagittarius Dwarf Elliptical, will directly test whether such clusters are indeed consistent with the acquisition of the bulk of the Milky Way's globulars through this process.
Among the more metal-rich Terzan 7 ([Fe/H] = -0.6) stars, clear star-to-star variations in uv CN band strengths are seen, implying significant differences in N abundances. Variations in CH are also seen, although the correlation with CN is not clear (possibly due to our small sample). A similar situation appears to also exist in Arp 2, although the CN variations are masked by the considerably lower metallicity ([Fe/H] = -1.8). Modeling with synthetic spectra is currently underway as part of an analysis of the range of underlying abundances. Nonetheless, the similarities between these and the abundance patterns of the Galactic globulars cannot rule out an origin in the merger with Sagittarius Dwarf-like objects.
Any opinions, findings, conclusions, and recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
Briley Michael M.
Martell Sarah
Smith Graeme H.
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