Edward R. D. Scott¹, Alexander N. Krot¹, and Ian S. Sanders²

Astrophysical Journal 854, 164 Link to Article [DOI: 10.3847/1538-4357/aaa5a5]
¹Hawai’i Institute of Geophysics and Planetology, University of Hawai’i, Honolulu, HI 96822, USA
²Department of Geology, Trinity College, Dublin 2, Ireland

Whole rock Δ¹⁷O and nucleosynthetic isotopic variations for chromium, titanium, nickel, and molybdenum in meteorites define two isotopically distinct populations: carbonaceous chondrites (CCs) and some achondrites, pallasites, and irons in one and all other chondrites and differentiated meteorites in the other. Since differentiated bodies accreted 1–3 Myr before the chondrites, the isotopic dichotomy cannot be attributed to temporal variations in the disk. Instead, the two populations were most likely separated in space, plausibly by proto-Jupiter. Formation of CCs outside Jupiter could account for their characteristic chemical and isotopic composition. The abundance of refractory inclusions in CCs can be explained if they were ejected by disk winds from near the Sun to the disk periphery where they spiraled inward due to gas drag. Once proto-Jupiter reached 10–20 M_⊕, its external pressure bump could have prevented millimeter- and centimeter-sized particles from reaching the inner disk. This scenario would account for the enrichment in CCs of refractory inclusions, refractory elements, and water. Chondrules in CCs show wide ranges in Δ¹⁷O as they formed in the presence of abundant ¹⁶O-rich refractory grains and ¹⁶O-poor ice particles. Chondrules in other chondrites (ordinary, E, R, and K groups) show relatively uniform, near-zero Δ¹⁷O values as refractory inclusions and ice were much less abundant in the inner solar system. The two populations were plausibly mixed together by the Grand Tack when Jupiter and Saturn migrated inward emptying and then repopulating the asteroid belt with roughly equal masses of planetesimals from inside and outside Jupiter’s orbit (S- and C-type asteroids).

Motohiko Kusakabe and Grant J. Mathews

Astrophysical Journal 854, 183 Link to Article [DOI: 10.3847/1538-4357/aaa125]
Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA

We investigate the cosmic-ray nucleosynthesis (CRN) of proton-rich stable nuclides (p-nuclides). We calculate the cosmic-ray (CR) energy spectra of heavy nuclides with mass number , taking into account the detailed nuclear spallation, decay, energy loss, and escape from the Galaxy during the CR propagation. We adopt the latest semiempirical formula SPACS for the spallation cross sections and the latest data on nuclear decay. Effective electron-capture decay rates are calculated using the proper cross sections for recombination and ionization in the whole CR energy region. Calculated CR spectral shapes vary for different nuclides. Abundances of proton-rich unstable nuclides increase in CRs with increasing energy relative to those of other nuclides. Yields of the primary and secondary spallation processes and differential yields from respective seed nuclides are calculated. We find that the CR energy region of MeV/nucleon predominantly contributes to the total yields. The atomic cross sections in the low-energy range adopted in this study are then necessary. Effects of CRN on the Galactic chemical evolution of p-nuclides are calculated. Important seed nuclides are identified for respective p-nuclides. The contribution of CRN is significant for ^180mTa, accounting for about 20% of the solar abundance. About 87% of the ^180m Ta CRN yield can be attributed to the primary process. The most important production routes are reactions of ¹⁸¹Ta, ¹⁸⁰Hf, and ¹⁸²W. CRN yields of other p-nuclides are typically about (10⁻⁴–10⁻²) of solar abundances.

Hongu Yang^1,2 and Masateru Ishiguro¹

Astrophysical Journal 854, 137 Link to Article [DOI: 10.3847/1538-4357/aaab59]
¹Department of Physics and Astronomy, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea
²Korea Astronomy and Space Science Institute (KASI), Republic of Korea

In this study, we numerically investigated the orbital evolution of cometary dust particles, with special consideration of the initial size–frequency distribution (SFD) and different evolutionary tracks according to the initial orbit and particle shape. We found that close encounters with planets (mostly Jupiter) are the dominating factor determining the orbital evolution of dust particles. Therefore, the lifetimes of cometary dust particles (~250,000 yr) are shorter than the Poynting–Robertson lifetime, and only a small fraction of large cometary dust particles can be transferred into orbits with small semimajor axes. The exceptions are dust particles from 2P/Encke and, potentially, active asteroids that have little interaction with Jupiter. We also found that the effects of dust shape, mass density, and SFD were not critical in the total mass supply rate to the interplanetary dust particle (IDP) cloud complex when these quantities are confined by observations of zodiacal light brightness and SFD around the Earth’s orbit. When we incorporate a population of fluffy aggregates discovered in the Earth’s stratosphere and the coma of 67P/Churyumov–Gerasimenko within the initial ejection, the initial SFD measured at the comae of comets (67P and 81P/Wild 2) can produce the observed SFD around the Earth’s orbit. Considering the above effects, we derived the probability of mutual collisions among dust particles within the IDP cloud for the first time in a direct manner via numerical simulation and concluded that mutual collisions can mostly be ignored.

Shinya Wanajo^1,2, Bernhard Müller^3,4, Hans-Thomas Janka⁵, and Alexander Heger^4,6,7

Astrophysical Journal 852, 40 Link to Article [DOI: 10.3847/1538-4357/aa9d97]
¹Department of Engineering and Applied Sciences, Sophia University, Chiyoda-ku, Tokyo 102-8554, Japan
²iTHES Research Group, RIKEN, Wako, Saitama 351-0198, Japan
³Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast, BT7 1NN, UK
⁴Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, VIC 3800, Australia
⁵Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching, Germany
⁶University of Minnesota, School of Physics and Astronomy, Minneapolis, MN 55455, USA
⁷Shanghai Jiao-Tong University, Department of Physics and Astronomy, Shanghai 200240, P. R. China

We examine nucleosynthesis in the innermost neutrino-processed ejecta (a few ) of self-consistent two-dimensional explosion models of core-collapse supernovae (CCSNe) for six progenitor stars with different initial masses. Three models have initial masses near the low-mass end of the SN range of (e8.8; electron-capture SN), (z9.6), and (u8.1), with initial metallicities of 1, 0, and 10⁻⁴ times the solar metallicity, respectively. The other three are solar-metallicity models with initial masses of (s11), (s15), and (s27). The low-mass models e8.8, z9.6, and u8.1 exhibit high production factors (nucleosynthetic abundances relative to the solar abundances) of 100–200 for light trans-Fe elements from Zn to Zr. This is associated with an appreciable ejection of neutron-rich matter in these models. Remarkably, the nucleosynthetic outcomes for the progenitors e8.8 and z9.6 are almost identical, including interesting productions of ⁴⁸Ca and ⁶⁰Fe, irrespective of their quite different (O–Ne–Mg and Fe) cores prior to collapse. In the more massive models s11, s15, and s27, several proton-rich isotopes of light trans-Fe elements including the p-isotope ⁹²Mo (for s27) are made, up to production factors of ~30. Both electron-capture SNe and CCSNe near the low-mass end can therefore be dominant contributors to the Galactic inventory of light trans-Fe elements from Zn to Zr and probably ⁴⁸Ca and live ⁶⁰Fe. The innermost ejecta of more massive SNe may have only subdominant contributions to the chemical enrichment of the Galaxy except for ⁹²Mo.

Benoit Côté^1,2,3,10, Pavel Denissenkov^1,3,10, Falk Herwig^1,3,10, Ashley J. Ruiter^4,5,6, Christian Ritter^1,3,7,10, Marco Pignatari^3,8,10, and Krzysztof Belczynski⁹

Astrophysical Journal 854, 131 Link to Article [DOI: 10.3847/1538-4357/aaaae8]
¹Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 2Y2, Canada
²Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary
³Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, USA
⁴Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 0200, Australia
⁵ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia
⁶School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Australian Defence Force Academy, Canberra, ACT 2600, Australia
⁷Keele University, Keele, Staffordshire ST5 5BG, UK
⁸E.A. Milne Centre for Astrophysics, Department of Physics & Mathematics, University of Hull, HU6 7RX, UK
⁹Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
¹⁰NuGrid Collaboration, http://nugridstars.org.

Rapidly accreting white dwarfs (RAWDs) have been proposed as contributors to the chemical evolution of heavy elements in the Galaxy. Here, we test this scenario for the first time and determine the contribution of RAWDs to the solar composition of first-peak neutron-capture elements. We add the metallicity-dependent contribution of RAWDs to the one-zone galactic chemical evolution code OMEGA according to RAWD rates from binary stellar population models combined with metallicity-dependent i-process stellar yields calculated following the models of Denissenkov et al. With this approach, we find that the contribution of RAWDs to the evolution of heavy elements in the Galaxy could be responsible for a significant fraction of the solar composition of Kr, Rb, Sr, Y, Zr, Nb, and Mo ranging from 2% to 45% depending on the element, the enrichment history of the Galactic gas, and the total mass ejected per RAWD. This contribution could explain the missing solar Lighter Element Primary Process for some elements (e.g., Sr, Y, and Zr). We do not overproduce any isotope relative to the solar composition, but ⁹⁶Zr is produced in a similar amount. The i process produces efficiently the Mo stable isotopes ⁹⁵Mo and ⁹⁷Mo. When nuclear reaction rate uncertainties are combined with our GCE uncertainties, the upper limits for the predicted RAWD contribution increase by a factor of 1.5–2 for Rb, Sr, Y, and Zr, and by 3.8 and 2.4 for Nb and Mo, respectively. We discuss the implication of the RAWD stellar evolution properties on the single-degenerate SN Ia scenario.

Francesco C. Pignatale¹, Sébastien Charnoz^1,2, Pascal Rosenblatt^3,4, Ryuki Hyodo⁵, Tomoki Nakamura⁶, and Hidenori Genda⁵

Astrophysical Journal 853, 118 Link to Article [DOI: 10.3847/1538-4357/aaa23e]
¹Institut de Physique du Globe de Paris (IPGP), 1 rue Jussieu, F-75005, Paris, France
²Institut de Physique du Globe/Universite Paris Diderot/CEA/CNRS, F-75005 Paris, France
³Royal Observatory of Belgium, Avenue circulaire 3, B-1180 Uccle, Belgium
⁴Now at ACRI-ST, 260 route du pin-montard-BP 234, F-06904 Sophia-Antipolis Cedex, France
⁵Earth-Life Science Institute/Tokyo Institute of Technology, 152-8550 Tokyo, Japan
⁶Tohoku University, 980-8578 Miyagi, Japan

The origin of Phobos and Deimos in a giant impact-generated disk is gaining larger attention. Although this scenario has been the subject of many studies, an evaluation of the chemical composition of the Mars’s moons in this framework is missing. The chemical composition of Phobos and Deimos is unconstrained. The large uncertainties about the origin of the mid-infrared features; the lack of absorption bands in the visible and near-infrared spectra; and the effects of secondary processes on the moons’ surfaces make the determination of their composition very difficult using remote sensing data. Simulations suggest a formation of a disk made of gas and melt with their composition linked to the nature of the impactor and Mars. Using thermodynamic equilibrium, we investigate the composition of dust (condensates from gas) and solids (from a cooling melt) that result from different types of Mars impactors (Mars-, CI-, CV-, EH-, and comet-like). Our calculations show a wide range of possible chemical compositions and noticeable differences between dust and solids, depending on the considered impactors. Assuming that Phobos and Deimos resulted from the accretion and mixing of dust and solids, we find that the derived assemblage (dust-rich in metallic iron, sulfides and/or carbon, and quenched solids rich in silicates) can be compatible with the observations. The JAXA’s Martian Moons eXploration (MMX) mission will investigate the physical and chemical properties of Phobos and Deimos, especially sampling from Phobos, before returning to Earth. Our results could be then used to disentangle the origin and chemical composition of the pristine body that hit Mars and suggest guidelines for helping in the analysis of the returned samples.

Cui Wenyuan^1,2, Jiang Xiaohua¹, Shi Jianrong^3,4, Zhao Gang^3,4, and Zhang Bo¹

Astrophysical Journal 854, 131 Link to Article [DOI: 10.3847/1538-4357/aaa75f]
¹Department of Physics, Hebei Normal University, Shijiazhuang 050024, People’s Republic of China
²School of Space Science and Physics, Shandong University at Weihai, Weihai 264209, People’s Republic of China
³Key Lab of Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, People’s Republic of China
⁴School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China

The origin of Phobos and Deimos in a giant impact-generated disk is gaining larger attention. Although this scenario has been the subject of many studies, an evaluation of the chemical composition of the Mars’s moons in this framework is missing. The chemical composition of Phobos and Deimos is unconstrained. The large uncertainties about the origin of the mid-infrared features; the lack of absorption bands in the visible and near-infrared spectra; and the effects of secondary processes on the moons’ surfaces make the determination of their composition very difficult using remote sensing data. Simulations suggest a formation of a disk made of gas and melt with their composition linked to the nature of the impactor and Mars. Using thermodynamic equilibrium, we investigate the composition of dust (condensates from gas) and solids (from a cooling melt) that result from different types of Mars impactors (Mars-, CI-, CV-, EH-, and comet-like). Our calculations show a wide range of possible chemical compositions and noticeable differences between dust and solids, depending on the considered impactors. Assuming that Phobos and Deimos resulted from the accretion and mixing of dust and solids, we find that the derived assemblage (dust-rich in metallic iron, sulfides and/or carbon, and quenched solids rich in silicates) can be compatible with the observations. The JAXA’s Martian Moons eXploration (MMX) mission will investigate the physical and chemical properties of Phobos and Deimos, especially sampling from Phobos, before returning to Earth. Our results could be then used to disentangle the origin and chemical composition of the pristine body that hit Mars and suggest guidelines for helping in the analysis of the returned samples.

Takashi Ishihara¹, Naoki Kobayashi², Kei Enohata², Masayuki Umemura³, and Kenji Shiraishi⁴

Astrophysical Journal 854, 81 Link to Article [DOI: 10.3847/1538-4357/aaa976]
¹Graduate School of Environmental and Life Science, Okayama University, Okayama 700-8530, Japan
²Department of Computational Science and Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
³Center for Computational Sciences, University of Tsukuba, Tsukuba 305-8577, Japan
⁴Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8601, Japan

The coagulation of dust particles is a key process in planetesimal formation. However, the radial drift and bouncing barriers are not completely resolved, especially for silicate dust. Since the collision velocities of dust particles are regulated by turbulence in a protoplanetary disk, turbulent clustering should be properly treated. To that end, direct numerical simulations (DNSs) of the Navier–Stokes equations are requisite. In a series of papers, Pan & Padoan used a DNS with Reynolds number Re ~ 1000. Here, we perform DNSs with up to Re = 16,100, which allow us to track the motion of particles with Stokes numbers of 0.01  St  0.2 in the inertial range. Through the DNSs, we confirm that the rms relative velocity of particle pairs is smaller by more than a factor of two, compared to that by Ormel & Cuzzi. The distributions of the radial relative velocities are highly non-Gaussian. The results are almost consistent with those by Pan & Padoan or Pan et al. at low Re. Also, we find that the sticking rates for equal-sized particles are much higher than those for different-sized particles. Even in the strong-turbulence case with α-viscosity of 10⁻², the sticking rates are as high as 50% and the bouncing probabilities are as low as ~10% for equal-sized particles of St  0.01. Thus, turbulent clustering plays a significant role in the growth of centimeter-sized compact aggregates (pebbles) and also enhances the solid abundance, which may lead to the streaming instability in a disk.

Lev Arzamasskiy¹ and Roman R. Rafikov^2,3

Astrophysical Journal 854, 84 Link to Article [DOI: 10.3847/1538-4357/aaa8e8]
¹Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540, USA
²Centre for Mathematical Sciences, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
³Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA

Spiral density waves are known to exist in many astrophysical disks, potentially affecting disk structure and evolution. We conduct a numerical study of the effects produced by a density wave, evolving into a shock, on the characteristics of the underlying disk. We measure the deposition of angular momentum in the disk by spiral shocks of different strengths and verify the analytical prediction of Rafikov for the behavior of this quantity, using shock amplitude (which is potentially observable) as the input variable. Good agreement between theory and numerics is found as we vary the shock amplitude (including highly nonlinear shocks), disk aspect ratio, equation of state, radial profiles of the background density and temperature, and pattern speed of the wave. We show that high numerical resolution is required to properly capture shock-driven transport, especially at small wave amplitudes. We also demonstrate that relating the local mass-accretion rate to shock dissipation in rapidly evolving disks requires accounting for the time-dependent contribution to the angular momentum budget caused by the time dependence of the radial pressure support. We provide a simple analytical prescription for the behavior of this contribution and demonstrate its excellent agreement with the simulation results. Using these findings, we formulate a theoretical framework for studying the one-dimensional (in radius) evolution of shock-mediated accretion disks, which can be applied to a variety of astrophysical systems.

Kunihiro Myojo¹, Tetsuya Yokoyama¹, Satoki Okabayashi¹, Shigeyuki Wakaki², Naoji Sugiura³, and Hikaru Iwamori^1,4
Astrophysical Journal 853, 48 Link to Article [DOI: 10.3847/1538-4357/aa9f2e]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
²Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe Otsu, Nankoku City, Kochi, Japan
³Emeritus professor, Department of Earth and Planetary Science, University of Tokyo, Japan
⁴Japan Agency for Marine-Earth Science and Technology, Japan

Nucleosynthetic isotope anomalies in meteorites are useful for investigating the origin of materials in the protoplanetary disk and dynamical processes of planetary formation. In particular, calcium and aluminum-rich inclusions (CAIs) found in chondrites are key minerals for decoding the initial conditions of the solar system before the accretion of small planetary bodies. In this study, we report isotopic analyses for three Allende CAIs, fluffy type A (FTA), type B, and fine-grained spinel rich (FS) inclusions, with a specific emphasis on the measurements of ⁸⁴Sr/⁸⁶Sr ratios. It was found that the average μ ⁸⁴Sr values (10⁶ relative deviations from a standard material) were 175, 129, and 56 ppm for the samples of FTA, type B, and FS inclusions, respectively. Additionally, the FTA samples exhibited heterogeneous μ ⁸⁴Sr values, while those for the type B and FS inclusions were homogeneous within individual inclusions. The elevated μ ⁸⁴Sr values were most likely explained by the relative enrichment of r-process nuclides in the CAI formation region. The variation of μ ⁸⁴Sr values between the FTA and type B inclusions, as well as within the FTA inclusion, suggests the presence of multiple CAI source reservoirs with distinct isotopic compositions, which is either inherited from isotopic heterogeneity in the molecular cloud or caused by the selective destruction of r-process-enriched supernova grains via nebular thermal processing. On the other hand, the reaction between a refractory precursor of the FS inclusion and a gaseous reservoir enriched in Mg, Si, and ¹⁶O resulted in the lowest μ ⁸⁴Sr values for the FS inclusion.