First stars

Abstract

Context. A small fraction of extremely metal-poor (EMP) stars exhibit moderate to extreme excesses of heavy neutron-capture elements produced in the r-process. The production site(s) of these elements in the early Galaxy remain(s) unclear, as is the reason for their occasional enhancement in the otherwise regular pattern of abundances of elements up to the iron peak. The detailed abundance pattern of the heaviest elements in EMP stars provides insight into their origin and role in the chemical enrichment of the early Galaxy and in radioactive nucleochronology. Aims. The EMP giant star CS 31082-001 ([Fe/H] ∼ −2.9) exhibits an extreme enhancement of neutron-capture elements ([r/Fe] ∼ +1.7) with U and Th enhanced by a further ∼+0.7 dex, and a minimum of blending by molecular lines such as CH or CN. A rich inventory of r-process element abundances was established previously from optical spectra. Here we aim to supplement these data with abundances from near-UV spectroscopy of the third-peak neutron-capture elements, which are crucial for understanding the synthesis of the heaviest elements. Methods. Near-UV spectra from HST/STIS were analysed with LTE model atmospheres and spectrum synthesis calculations to derive new abundances of Os, Ir, Pt, Au, Bi and Pb in CS 31082-001. Results. Together with earlier data, the resulting abundance pattern for the r-process elements provides improved constraints on the nature of the r-process. The observed U and Th abundances and the initial production ratio place CS 31082-001 as one of the oldest stars in the Galaxy, consistent with its extreme metal deficiency. Comparison with the heaviest stable reference elements and with the daughter nuclides Pb and Bi provides a consistency check on this age determination. Finally, the existence of such r-element rich stars indicate that the early chemical evolution of the Galaxy was localised and inhomogeneous.

High-resolution abundance analysis of very metal-poor r-I stars

“…Figure 27 compares for each of our program stars the heavyelement abundances obtained in this work with the abundance pattern of the extremely metal-poor r-II uranium-rich star CS 31082-001, for which spectra from UVES and STIS/Hubble Space Telescope were used to derive accurate abundances (Barbuy et al 2011;Siqueira-Mello et al 2013). This star is taken to be representative of r-II stars, whose abundance patterns are almost identical, except for those beyond the third-peak region (Pb and Th).…”

“…Among the giants, six r-I stars and three r-II stars (CS 31082-001, CS 22953-003, and CS 22892-052) were studied in detail and were added to the present sample of r-I stars for the purpose of discussion. The relative abundances of the heavy elements for CS 31082-001 come from Hill et al (2002), Barbuy et al (2011), andSiqueira-Mello et al (2013), for CS 22953-003 they were taken from François et al (2007), and for CS 22892-052 from Sneden et al (1996Sneden et al ( , 2000Sneden et al ( , 2009. For the star CS 30315-029, we also used a spectrum obtained during the LP "First Stars," in the regions centered on 3960 Å and 5730 Å, to measure the Ba lines.…”

Precision Measurement Method for Branching Fractions of ExcitedP1/2States Applied toCa+40Ramm1, Pruttivarasin2, Kokish3 et al. 2013Phys. Rev. Lett.475650View full textAdd to dashboardCite

“…In Au, both theoretical [22] and experimental [1,2] studies on the atomic structure have been done and used to study the radiation spectrum from stars [5]. In Sc ++ and Sr + , experimental measurements have yet to be done to verify theoretical calculations [23][24][25].…”

“…Atomic properties such as excited state lifetimes and branching fractions of energy levels in various atomic species are of special interest because they can be readily measured both in atomic ensembles [1,2] and in single atoms [3,4]. Knowledge of these atomic properties is especially important for studying spectra of radiation from stars and other galactic objects [5,6]. Furthermore, precise measurement of atomic lifetimes and branching fractions can also be used to probe effects of weak interactions such as parity non-conservation of atomic levels [7][8][9][10].…”

Physical conditions for the r-process

“…The lowest metallicity stars ([Fe/H] ≈ −3) show deficient Pb abundances (factor of 2 smaller than the "solar" r-value) [27,28,29,30], although more metal-rich stars have higher values [31] (that could be affected from s-process contaminations). This indicates the Pb abundances in such stars being solely due to α-decay from Th and U with negligible production of α-decay progenitors of A = 210-230 [27].…”