Near‐Ultraviolet Observations of HD 221170: New Insights into the Nature of r ‐Process–rich Stars

Abstract

Employing high-resolution spectra obtained with the near-UV-sensitive detector on the Keck I HIRES, supplemented by data obtained with the McDonald Observatory 2d-coudé, we have performed a comprehensive chemical composition analysis of the bright r -process-rich metal-poor red giant star HD 221170. Analysis of 57 individual neutral and ionized species yielded abundances for a total of 46 elements and significant upper limits for an additional five. Model stellar atmosphere parameters were derived with the aid of ~200 Fe peak transitions. From more than 350 transitions of 35 neutron-capture ( Z > 30) species, abundances for 30 neutron-capture elements and upper limits for three others were derived. Utilizing 36 transitions of La, 16 of Eu, and seven of Th, we derive ratios of log ##IMG## [http://ej.iop.org/icons/Entities/epsi.gif] {epsilon} (Th/La) = -0.73 (σ = 0.06) and log ##IMG## [http://ej.iop.org/icons/Entities/epsi.gif] {epsilon} (Th/Eu) = -0.60 (σ = 0.05), values in excellent agreement with those previously derived for other r -process-rich metal-poor stars such as CS 22892-052, BD +17 3248, and HD 115444. Based on the Th/Eu chronometer, the inferred age is 11.7 ± 2.8 Gyr. The abundance distribution of the heavier neutron-capture elements ( Z ��?56) is fitted well by the predicted scaled solar system r -process abundances, as also seen in other r -process-rich stars. Unlike other r -process-rich stars, however, we find that the abundances of the lighter neutron-capture elements (37 < Z < 56) in HD 221170 are also in agreement with the abundances predicted for the scaled solar r -process pattern.