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.