Leon Kocharov¹, Silja Pohjolainen², Mike J. Reiner^3,4, Alexander Mishev⁵, Haimin Wang^6,7, Ilya Usoskin^1,5, and Rami Vainio⁸
Astrophysical Journal Letters 863, L27 Link to Article [DOI: 10.3847/2041-8213/aad86b]
¹National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
²Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan

The site of Zn production remains an elusive and challenging problem in astrophysics. A large enhancement of the [Zn/Fe] ratios of very metal-poor stars in the Galactic halo suggests the death of short-lived massive stars, i.e., core-collapse supernovae (CCSNe), as one major site for Zn production. Previous studies have claimed that some specific CCSNe can produce Zn in sufficient quantities. However, it remains unclear which models can withstand the critical test of observations. Using a Zn abundance feature similar to that of r-process elements in faint satellite galaxies, we find evidence that Zn production took place through events that are much rarer than canonical CCSNe. This finding can be unified with the implied decrease in the rate of Zn production with an increasing metallicity for Galactic halo stars, which narrows down the major site of Zn production in the early galaxy to magnetorotational SNe (MR-SNe). On the other hand, in the later phase of galactic evolution, we predict that the major Zn-production site switched from MR-SNe to thermonuclear SNe (SNe Ia). According to this scenario, an accumulation of the contributions from two types of SNe eventually led to the solar isotope composition of Zn, which mainly owes ^66,68Zn to MR-SNe and ⁶⁴Zn to SNe Ia triggered by He-detonation. The requirement of Zn production in SNe Ia sheds a new light on the debate concerning the scenario for SN Ia progenitors, suggesting that a He-detonation model might be one major channel for SNe Ia.

^1,4L.Nardi, ^1,2E.Palomba, ^1,3A.Longobardo, ^1,5A.Galiano, ¹F.Dirri
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.10.035]
¹INAF-IAPS, Via Fosso del Cavaliere 100, Roma 00133, Italy
²ASI-SSDC, via del Politecnico, Roma 00133, Italy
³Università Parthenope, Dist. Centro Direzionale Isola C4, 80143, Italy
⁴La Sapienza Università di Roma, Piazzale Aldo Moro 5, Roma 00185, Italy
⁵Università degli Studi di Roma Tor Vergata, Via Orazio Raimondo 18, Roma 00173, Italy
Copyright Elsevier

Olivine is one of the main abundant mineral in the Solar System, and the determination of its abundance on a surface may give fundamental information about its evolution. The study of surface distribution of olivine on asteroid (25143) Itokawa through near-Infrared reflectance spectroscopy is a difficult goal because olivine and pyroxene bands centred at 1 μm and 2 μm are not entirely included in Hayabusa/NIRS’ spectral range. In this work, the retrieval of olivine abundance has been performed by applying two different methods: the first one uses some spectral indices to retrieve olivine abundance, whilst the second one consists of the application of the Hapke’s theory in order to create synthetic spectra aimed at fitting a selection of NIRS’ spectra. The analysis performed with the first method brought to an approximately homogeneous distribution of olivine content (60  ±  15% on average) on Itokawa’s surface, with the exception of Sagamihara region, which has a slightly (up to 10%) lower olivine content. The second method brought to an average 60  ±  7.5% olivine content within 5 selected spectra, with the same reduction found in the spectrum from the Sagamihara region. All these values are in agreement with literature values on this topic, especially with the ones retrieved from particles sampled in Muses Sea by the Hayabusa probe.