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.

J. Escobar-Cerezo¹, A. Penttilä², T. Kohout^2,3, O. Muñoz¹, F. Moreno¹, and K. Muinonen^2,4
Astrophysical Journal 853, 71 Link to Article [DOI: 10.3847/1538-4357/aaa24d]
¹Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain
²Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland
³Institute of Geology, The Czech Academy of Sciences, Prague, Czech Republic
⁴National Land Survey of Finland, Finnish Geospatial Research Institute, P.O. Box 84, FI-00521 Helsinki, Finland

Lunar soil spectra differ from pulverized lunar rocks spectra by reddening and darkening effects, and shallower absorption bands. These effects have been described in the past as a consequence of space weathering. In this work, we focus on the effects of nanophase iron (npFe⁰) inclusions on the experimental reflectance spectra of lunar regolith particles. The reflectance spectra are computed using SIRIS3, a code that combines ray optics with radiative-transfer modeling to simulate light scattering by different types of scatterers. The imaginary part of the refractive index as a function of wavelength of immature lunar soil is derived by comparison with the measured spectra of the corresponding material. Furthermore, the effect of adding nanophase iron inclusions on the reflectance spectra is studied. The computed spectra qualitatively reproduce the observed effects of space weathered lunar regolith.

Alan M. Gersch, Lori M. Feaga, and Michael F. A’Hearn¹
Astrophysical Journal 854, 149 Link to Article [DOI: 10.3847/1538-4357/aa9795]
Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
¹Deceased.

We have adapted Coupled Escape Probability, a new exact method of solving radiative transfer problems, for use in asymmetrical spherical situations for use in modeling optically thick cometary comae. Here we present the extension of our model and corresponding results for two additional primary volatile species of interest, H₂O and CO₂, in purely theoretical comets. We also present detailed modeling and results for the specific examples of CO, H₂O, and CO₂ observations of C/2009 P1 Garradd by the Deep Impact flyby spacecraft.

Rainer Schräpler¹, Jürgen Blum¹, Sebastiaan Krijt^2,3, and Jan-Hendrik Raabe¹
Astrophysical Journal 853, 74 Link to Article [DOI: 10.3847/1538-4357/aaa0d2]
¹Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, D-38106 Braunschweig, Germany
²Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
³Hubble Fellow.

In a protoplanetary disk, dust aggregates in the μm to mm size range possess mean collision velocities of 10–60 m s⁻¹ with respect to dm- to m-sized bodies. We performed laboratory collision experiments to explore this parameter regime and found a size- and velocity-dependent threshold between erosion and growth. By using a local Monte Carlo coagulation calculation and along with a simple semi-analytical timescale approach, we show that erosion considerably limits particle growth in protoplanetary disks and leads to a steady-state dust-size distribution from μm- to dm-sized particles.

Erik Weaver, Andrea Isella, and Yann Boehler
Astrophysical Journal 853, 113 Link to Article [DOI: 10.3847/1538-4357/aaa481]
Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, TX 77005 USA

The accurate measurement of temperature in protoplanetary disks is critical to understanding many key features of disk evolution and planet formation, from disk chemistry and dynamics, to planetesimal formation. This paper explores the techniques available to determine temperatures from observations of single, optically thick molecular emission lines. Specific attention is given to issues such as the inclusion of optically thin emission, problems resulting from continuum subtraction, and complications of real observations. Effort is also made to detail the exact nature and morphology of the region emitting a given line. To properly study and quantify these effects, this paper considers a range of disk models, from simple pedagogical models to very detailed models including full radiative transfer. Finally, we show how the use of the wrong methods can lead to potentially severe misinterpretations of data, leading to incorrect measurements of disk temperature profiles. We show that the best way to estimate the temperature of emitting gas is to analyze the line peak emission map without subtracting continuum emission. Continuum subtraction, which is commonly applied to observations of line emission, systematically leads to underestimation of the gas temperature. We further show that once observational effects such as beam dilution and noise are accounted for, the line brightness temperature derived from the peak emission is reliably within 10%–15% of the physical temperature of the emitting region, assuming optically thick emission. The methodology described in this paper will be applied in future works to constrain the temperature, and related physical quantities, in protoplanetary disks observed with ALMA.