Abundances of Rarely Detected s -process Elements Derived from the Ultraviolet Spectrum of the s -process-enhanced Metal-poor Star HD 196944 ∗

We present an analysis of the heavy-element abundances of HD 196944, a carbon-enhanced metal-poor (CEMP) star enriched with elements produced by the slow neutron-capture process ( s -process). We obtained a new high-resolution ultraviolet (UV) spectrum of this star, the UV-brightest known CEMP- s star, with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. This spectrum extends deeper into the UV (2029 ≤ λ ≤ 2303 Å) than previous studies of any CEMP- s star. When combined with previous UV and optical analysis, a total of 35 elements heavier than zinc ( Z = 30) can be detected in HD 196944, and upper limits are available for nine other heavy elements. The abundances can be well fit by models of s -process nucleosynthesis operating in a low-mass companion star that evolved through the asymptotic giant branch phase and transferred heavy elements to HD 196944. This s -process event did not contribute substantially to the Ga, Ge, or As abundances (31 ≤ Z ≤ 33). Our results demonstrate that UV spectroscopy can greatly expand the inventory of heavy elements detectable in CEMP- s stars.