Shing-Chi Leung and Ken’ichi Nomoto
The Astrophysical Journal 861, 143 Link to Article [https://doi.org/10.3847/1538-4357/aac2df]
Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan

We present 2D hydrodynamics simulations of near-Chandrasekhar-mass white dwarf (WD) models for Type Ia supernovae (SNe Ia) using the turbulent deflagration model with a deflagration-to-detonation transition (DDT). We perform a parameter survey for 41 models to study the effects of the initial central density (i.e., WD mass), metallicity, flame shape, DDT criteria, and turbulent flame formula for a much wider parameter space than in earlier studies. The final isotopic abundances of ¹¹C to ⁹¹Tc in these simulations are obtained by post-process nucleosynthesis calculations. The survey includes SN Ia models with the central density from 5 × 10⁸ g cm⁻³ to 5 × 10⁹ g cm⁻³ (WD masses of 1.30–1.38 M _⊙), metallicity from 0 to 5 Z _⊙, C/O mass ratio from 0.3 to 1.0, and ignition kernels, including centered and off-centered ones. We present the yield tables of stable isotopes from ¹²Cl to ⁷⁰Zn, as well as the major radioactive isotopes for 33 models. Observational abundances of ⁵⁵Mn, ⁵⁶Fe, ⁵⁷Fe, and ⁵⁸Ni obtained from the solar-composition, well-observed SN Ia and SN Ia remnants are used to constrain the explosion models and the SN progenitor. The connection between the pure turbulent deflagration model and the subluminous SNe Iax is discussed. We find that dependencies of the nucleosynthesis yields on the metallicity and the central density (WD mass) are large. To fit these observational abundances, and also for the application of galactic chemical evolution modeling, these dependencies on the metallicity and WD mass should be taken into account.

Roman R. Rafikov^1,2
The Astrophysical Journal 861, 35 Link to Article [https://doi.org/10.3847/1538-4357/aac5ef]
¹Centre for Mathematical Sciences, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
²Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA

Discovery of the first interstellar asteroid (ISA)—1I/2017 ‘Oumuamua—raised natural questions regarding its origin, some related to its lack of cometary activity, suggesting refractory composition. Here we explore the possibility that ‘Oumuamua-like ISAs are produced in tidal disruption events (TDEs) of refractory planetoids (asteroids, terrestrial planets, etc.) by white dwarfs (WDs). This idea is supported by spectroscopic observations of metal-polluted WDs, indicating the predominantly volatile-poor composition of the accreted material. We show that such TDEs sourced by realistic planetary systems (including a population of 10³ km planetoids and massive perturbers—Neptune-to-Saturn mass planets) can eject up to 30% of planetary mass involved in TDEs to interstellar space. Collisional fragmentation, caused by vertical collapse of the disrupted planetoid’s debris inside the WD Roche sphere, channels most of its mass into 0.1–1 km fragments, similar to ‘Oumuamua. Such a size spectrum of ISAs (very different from the top-heavy distributions expected in other scenarios) implies that planetary TDEs can account for a significant fraction (up to ~30%) of ISAs. This figure is based on existing observations of WD metal pollution, which are de-biased using realistic models of circum-WD planetary systems. Such ISAs should exhibit kinematic characteristics of old, dynamically hot Galactic populations. ISA ejection in individual planetary TDEs is highly anisotropic, resulting in large fluctuations of their space density. We also show that other ISA production channels involving stellar remnants—direct ejection by massive planets around the WDs and supernova explosions—have difficulty explaining ‘Oumuamua-like ISAs.

Oliver Philcox^1,2, Jan Rybizki², and Thales A. Gutcke²
The Astrophysical Journal 861, 40 Link to Article [https://doi.org/10.3847/1538-4357/aac6e4]
¹Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
²Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

To fully harvest the rich library of stellar elemental abundance data available, we require reliable models that facilitate our interpretation of them. Galactic chemical evolution (GCE) models are one such set, a key part of which are the selection of chemical yields from different nucleosynthetic enrichment channels, predominantly asymptotic giant branch stars, Type Ia supernovae (SNe Ia), and core-collapse supernovae (CC-SNe). Here we present a scoring system for yield tables based on their ability to reproduce protosolar abundances within a simple parameterization of the GCE modeling software Chempy, which marginalizes over galactic parameters describing simple stellar populations (SSPs) and interstellar medium physics. Two statistical scoring methods are presented, based on Bayesian evidence and leave-one-out cross-validation, and are applied to five CC-SN tables, for (a) all mutually available elements and (b) a subset of the nine most abundant elements. We find that the yields of Prantzos et al. (P18, including stellar rotation) and Chieffi & Limongi (C04) best reproduce protosolar abundances for the two cases, respectively. The inferred best-fit SSP parameters for case (b) are for the initial mass function high-mass slope and for the SN Ia normalization, which are broadly consistent across tested yield tables. Additionally, we demonstrate how Chempy can be used to dramatically improve elemental abundance predictions of hydrodynamical simulations by plugging tailored best-fit SSP parameters into a Milky Way analog from Gutcke & Springel. Our code, including a comprehensive tutorial, is freely available and can additionally provide SSP enrichment tables for any combination of parameters and yield tables.

Andreas Schreiber¹ and Hubert Klahr
The Astrophysical Journal 861, 47 Link to Article [https://doi.org/10.3847/1538-4357/aac3d4]
¹Fellow of the International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg (IMPRS-HD).

The collapse of dust particle clouds directly to kilometer-sized planetesimals is a promising way to explain the formation of planetesimals, asteroids, and comets. In the past, this collapse has been studied in stratified shearing box simulations with super-solar dust-to-gas ratio , allowing for streaming instability (SI) and gravitational collapse. This paper studies the non-stratified SI under dust-to-gas ratios from up to without self-gravity. The study covers domain sizes of , , and in terms of the gas-disk scale height using the PencilCode. They are performed in radial-azimuthal (2D) and radial-vertical (2.5D) extents. The used particles of and 0.1 mark the upper end of the expected dust growth. SI activity is found up to very high dust-to-gas ratios, providing fluctuations in the local dust-to-gas ratios and turbulent particle diffusion δ. We find an SI-like instability that operates in r–, even when vertical modes are suppressed. This new azimuthal streaming instability (aSI) shows similar properties and appearance as the SI. Both, SI and aSI show diffusivity at only to be two orders of magnitude lower than at , suggesting a relation that is shallow around . The (a)SI ability to concentrate particles is found to be uncorrelated with its strength in particle turbulence. Finally, we performed a resolution study to test our findings of the aSI. This paper stresses the importance of properly resolving the (a)SI at high dust-to-gas ratios and planetesimal collapse simulations, leading otherwise to potentially incomplete results.

Christopher N. Shingledecker¹, Jessica Tennis¹, Romane Le Gal^1,2, and Eric Herbst^1,3
The Astrophysical Journal 861, 20 Link to Article [https://doi.org/10.3847/1538-4357/aac5ee]
¹Department of Chemistry, University of Virginia Charlottesville, VA 22904, USA
²Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
³Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA

In this paper, we present preliminary results illustrating the effect of cosmic rays on solid-phase chemistry in models of both TMC-1 and several sources with physical conditions identical to TMC-1 except for hypothetically enhanced ionization rates. Using a recent theory for the addition of cosmic-ray-induced reactions to astrochemical models, we calculated the radiochemical yields, called G values, for the primary dust grain ice-mantle constituents. We show that the inclusion of this nonthermal chemistry can lead to the formation of complex organic molecules from simpler ice-mantle constituents, even under cold core conditions. In addition to enriching ice mantles, we find that these new radiation-chemical processes can lead to increased gas-phase abundances as well, particularly for HOCO, NO₂, HC₂O, methyl formate (HCOOCH₃), and ethanol (CH₃CH₂OH). These model results imply that HOCO—and perhaps NO₂—might be observable in TMC-1. Future detections of either of these two species in cold interstellar environments could provide strong support for the importance of cosmic-ray-driven radiation chemistry. The increased gas-phase abundance of methyl formate can be compared with abundances achieved through other formation mechanisms such as pure gas-phase chemistry and surface reactions.