^1,2Daohai Li,²Alexander J. Mustill,^2,3Melvyn B. Davies
The Astrophysical Journal 924, 61 Open Access Link to Article [DOI 10.3847/1538-4357/ac33a8]
¹Department of Astronomy Beijing Normal University, No.19, Xinjiekouwai Street, Haidian District, Beijing, 100875, People’s Republic of China; lidaohai@gmail.com, lidaohai@bnu.edu.cn
²Lund Observatory Department of Astronomy and Theoretical Physics Lund University, Box 43, SE-221 00 Lund, Sweden
³Centre for Mathematical Sciences Lund University, Box 118, SE-221 00 Lund, Sweden

White dwarfs (WDs) often show metal lines in their spectra, indicating accretion of asteroidal material. Our Sun is to become a WD in several gigayears. Here, we examine how the solar WD accretes from the three major small body populations: the main belt asteroids (MBAs), Jovian Trojan asteroids (JTAs), and trans-Neptunian objects (TNOs). Owing to the solar mass loss during the giant branch, 40% of the JTAs are lost but the vast majority of MBAs and TNOs survive. During the WD phase, objects from all three populations are sporadically scattered onto the WD, implying ongoing accretion. For young cooling ages ≲100 Myr, accretion of MBAs predominates; our predicted accretion rate ∼106 g s−1 falls short of observations by two orders of magnitude. On gigayear timescales, thanks to the consumption of the TNOs that kicks in ≳100 Myr, the rate oscillates around 106–107 g s−1 until several gigayears and drops to ∼105 g s−1 at 10 Gyr. Our solar WD accretion rate from 1 Gyr and beyond agrees well with those of the extrasolar WDs. We show that for the solar WD, the accretion source region evolves in an inside-out pattern. Moreover, in a realistic small body population with individual sizes covering a wide range as WD pollutants, the accretion is dictated by the largest objects. As a consequence, the accretion rate is lower by an order of magnitude than that from a population of bodies of a uniform size and the same total mass and shows greater scatter.

^1,2,8Thomas C. L. Trueman,^1,3,4,8Benoit Côté,^1,8Andrés Yagüe López,^1,8Jacqueline den Hartogh,^1,2,4,8Marco Pignatari,^1,5Benjámin Soós,^6,7Amanda I. Karakas,^1,5,6Maria Lugaro
The Astrophysical Journal 924, 10 Open Access Link to Article [DOI 10.3847/1538-4357/ac31b0]
¹Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Konkoly Thege Miklós út 15-17, H-1121 Budapest, Hungary; thomas.trueman@csfk.mta.hu
²E.A. Milne Centre for Astrophysics, Department of Physics & Mathematics, University of Hull, HU6 7RX, UK
³Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 2Y2, Canada
⁴Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, USA
⁵ELTE Eötvös Loránd University, Institute of Physics, Budapest 1117, Pázmány Péter sétány 1/A, Hungary
⁶School of Physics and Astronomy, Monash University, VIC 3800, Australia
⁷ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁸NuGrid Collaboration http://nugridstars.org.

Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives of 0.1–100 Myr existed in the early solar system (ESS). We investigate the ESS origin of ¹⁰⁷Pd, ¹³⁵Cs, and ¹⁸²Hf, which are produced by slow neutron captures (the s-process) in asymptotic giant branch (AGB) stars. We modeled the Galactic abundances of these SLRs using the OMEGA+ galactic chemical evolution (GCE) code and two sets of mass- and metallicity-dependent AGB nucleosynthesis yields (Monash and FRUITY). Depending on the ratio of the mean-life τ of the SLR to the average length of time between the formations of AGB progenitors γ, we calculate timescales relevant for the birth of the Sun. If τ/γ ≳ 2, we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted ¹⁰⁷Pd/¹⁰⁸Pd, ¹³⁵Cs/¹³³Cs, and ¹⁸²Hf/¹⁸⁰Hf ratios to their respective ESS ratios. The predicted ¹⁰⁷Pd/¹⁸²Hf ratio indicates that our GCE models are missing 9%–73% of ¹⁰⁷Pd and ¹⁰⁸Pd in the ESS. This missing component may have come from AGB stars of higher metallicity than those that contributed to the ESS in our GCE code. If τ/γ ≲ 0.3, we calculate instead the time (T_LE) from the last nucleosynthesis event that added the SLRs into the presolar matter to the formation of the oldest solids in the ESS. For the 2 M_⊙, Z = 0.01 Monash model we find a self-consistent solution of T_LE = 25.5 Myr.

^1,2Alan E. Rubin,¹Bidong Zhang
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13939]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, 90095-1567 USA
²Maine Mineral & Gem Museum, 99 Main Street, PO Box 500, Bethel, Maine, 04217 USA
Published by arrangement with John Wiley & Sons

Allan Hills A77255, Babb’s Mill (Blake’s Iron), Nordheim, and Chinga are ungrouped ataxitic iron meteorites that are similar to the IAB group of noncarbonaceous-type irons in their concentrations of common and refractory siderophile elements. Mo-isotopic data show that ALHA77255, Nordheim, and Chinga are carbonaceous-type (CC) irons. (The Mo-isotopic composition of Babb’s Mill [Blake’s Iron] has not yet been measured, but it also seems likely to be a CC iron.) Relative to mean IAB irons, these four ataxites are severely depleted in moderately volatile elements: Ga, >99%; Ge, >99%; Cu, 79%–97%; As, 70%–96%; P, 76%–90%. These samples were probably devolatilized by major collisions on separate parent asteroids (consistent with fractional crystallization modeling showing they are unlikely to be derived from the same metallic core). Collisionally induced devolatilization of ALHA77255 likely facilitated the formation of a 5-mm diameter silica–glass spheroid in this meteorite. The spheroid may have formed by a complex process involving impact-induced vaporization of mantle material in its parent asteroid, followed by fractional condensation.