S-process Abundances in the M55 CH-Star L2406

Details S-process Abundances in the M55 CH-Star L2406 S-process Abundances in the M55 CH-Star L2406

Jan 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...19312401b&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #124.01; Bulletin of the American Astronomical Society, Vol. 31, p.667

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The CH-stars are a class of Pop II halo stars characterized by both strong CH and C2 features and enhanced abundances of s-process elements. Radial velocity studies indicate field CH-stars are binaries with an unseen white-dwarf companion, suggesting that the observed abundance anomalies are the result of mass transfer of C-rich, neutron exposed envelope material from the companion during its final stages of AGB evolution. Surprisingly few CH-stars have been identified within globular clusters. To date the list is confined to a handful of stars in ω Cen and M22 and one each in M2, M4, and M55. Moreover, some doubt remains as to the underlying nature of the cluster CH-stars and whether they are similar in origin to their field counterparts (versus the result of incomplete CN-processing and subsequent dredge-up during their own RGB ascent). We report the results of a high resolution spectroscopic analysis of the CH star L2406 in the Galactic globular cluster M55 as compared to the ''normal'' cluster member L2307. With regard to Fe and alpha capture elements, the stars appear indistinguishable within measurement errors as would be expected. [O/Fe] also is effectively solar in both stars, meaning that the CH nature of L2406 is due solely to a C excess. The abundances of s-process elements (e.g., Y, Zr, Mo, Ba, La, Ce, and Pr) are also clearly enhanced in L2406 by as much as a factor of 7 (relative to L2307). With this in mind, we suggest that L2406 is indeed analogous to the field CH-stars in its origin.

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