Neutron-Capture Elements in Low Metallicity Halo Giants

Details Neutron-Capture Elements in Low Metallicity Halo Giants Neutron-Capture Elements in Low Metallicity Halo Giants

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...195.4404s&link_type=abstract

American Astronomical Society, 195th AAS Meeting, #44.04; Bulletin of the American Astronomical Society, Vol. 31, p.1434

Astronomy and Astrophysics

Astronomy

Scientific paper

We are conducting a high resolution (R = 30,000) ultraviolet spectroscopic survey of 10 very metal-poor halo giants using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The general goal is to determine abundances of several key neutron-capture elements (Z > 30) that have no transitions accessible to ground-based spectroscopy. The stars chosen for STIS observations have -3.0 <= [Fe/H] <= --1.4, but they all have large relative overabundances of neutron-capture elements relative to iron. For example, all target stars have [Eu/Fe] > +0.5. We also have obtained STIS high resolution spectra of the well-studied halo giant HD 122563, whose substantial neutron-capture-element deficiency renders all transitions of these elements undetectably weak amid the forest of Fe-peak and OH lines in its UV spectrum. We develop synthetic spectrum line lists through iterative attempts to match the HD 122563 spectrum, and then use these in performing line-by-line differential abundance analyses of the neutron-capture-rich program stars. Detections of all possible neutron-capture elements are important, but for now we focus on Os, Ir, Pt, and Au because these are the heaviest of the stable elements (the so-called 3rd neutron-capture peak elements). With only half of the scheduled observations in hand, we have already detected at least six lines of Pt 1 in most targets, as well as lines of Os 1, Ge 1, Zr 2, Pb 1, and Ba 2. Additionally, we may have ``struck gold'' with the probable detection of the Au 1 resonance lines at 2428, 2676 Angstroms. The STIS spectra, derived with full model atmosphere, synthetic spectrum analyses, yield abundances that will shed light on star-to-star abundance variations of 3rd neutron-capture peak elements. Additionally, these abundances will be employed along with ground-based abundances of thorium to provide new estimates of the Galactic age. This research is supported by NASA STScI grant GO-08342 and NSF grants AST-9618364 to C.S. and AST-9618332 to J.J.C.

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