Search for: All records

Abstract Massive stars are a major source of chemical elements in the cosmos, ejecting freshly produced nuclei through winds and core-collapse supernova explosions into the interstellar medium. Among the material ejected, long-lived radioisotopes, such as⁶⁰Fe (iron) and²⁶Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed⁶⁰Fe/²⁶Al ratio by γ-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing⁶⁰Fe, and one reaction in particular, the neutron-capture on⁵⁹Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of⁶⁰Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted⁶⁰Fe/²⁶Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models. 

Using vessel-mounted acoustic Doppler current profiler data from four different routes between Scotland, Iceland and Greenland, we map out the mean flow of water in the top 400 m of the northeastern North Atlantic. The poleward transport east of the Reykjanes Ridge (RR) decreases from 8.5 to 10 Sv (1 Sverdrup 106 m3 s1) at 59.58N to 618N to 6 Sv crossing the IcelandFaroesScotland Ridge. The two longest 1200 km transport integrals have 1.40.94 Sv uncertainty, respectively. The overall decrease in transport can in large measure be accounted for by a 1.5 Sv flow across the RR into the Irminger Sea north of 59.58N and by a 0.5 Sv overflow of dense water along the IcelandFaroes Ridge. A remaining 0.5 Sv flux divergence is at the edge of detectability, but if real could be accounted for through wintertime convection to 400 m and densification of upper ocean water. The topography of the Iceland Basin and the banks west of Scotland play a fundamental role in controlling flow pathways towards and past Iceland, the Faroes and Scotland. Most water flows north unimpeded through the Iceland Basin, some in the centre of the basin along the Maury Channel, and some along Hatton Bank, turning east along the northern slopes of George Bligh Bank, Lousy Bank and Bill Bailey’s Bank, whereupon the flow splits with 3 Sv turning northwest towards the IcelandFaroes Ridge and the remainder continuing east towards and north of the Wyville-Thomson Ridge (WTR) to the Scotland slope thereby increasing the Slope Current transport from 1.5 Sv south of the WTR to 3.5 Sv in the FaroesShetland Channel