Amanda I. Karakas^1,2, Ashley J. Ruiter^1,3, and Melanie Hampel^1,4
1Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia
²Kavli IPMU (WPI), The University of Tokyo, Japan
³ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO), Australia
⁴Argelander-Institut für Astronomie, University of Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

We present a new theoretical estimate for the birthrate of R Coronae Borealis (RCB) stars that is in agreement with recent observational data. We find the current Galactic birthrate of RCB stars to be ≈25% of the Galactic rate of Type Ia supernovae, assuming that RCB stars are formed through the merger of carbon–oxygen and helium-rich white dwarfs. Our new RCB birthrate (1.8 × 10^-3 yr^-1) is a factor of 10 lower than previous theoretical estimates. This results in roughly 180–540 RCB stars in the Galaxy, depending on the RCB lifetime. From the theoretical and observational estimates, we calculate the total dust production from RCB stars and compare this rate to dust production from novae and born-again asymptotic giant branch (AGB) stars. We find that the amount of dust produced by RCB stars is comparable to the amounts produced by novae or born-again post-AGB stars, indicating that these merger objects are a viable source of carbonaceous pre-solar grains in the Galaxy. There are graphite grains with carbon and oxygen isotopic ratios consistent with the observed composition of RCB stars, adding weight to the suggestion that these rare objects are a source of stardust grains.

Reference
Karakas AI, Ruiter AJ and Hampel M (2015) R Coronae Borealis stars are viable factories of pre-solar grains. Astrophysical Journal 809:184.
Link to Article [doi:doi:10.1088/0004-637X/809/2/184]

Evan Groopman¹ et al. (>10)*
¹Laboratory for Space Sciences, Physics Department, Washington University, One Brookings Drive, Campus Box 1105, Saint Louis, MO 63130, USA

We performed an in-depth exploration of the Al–Mg system for presolar graphite, SiC, and Si₃N₄ grains found to contain large excesses of ²⁶Mg, indicative of the initial presence of live ²⁶Al. Ninety of the more than 450 presolar grains processed in this study contain well-correlated δ²⁶Mg/²⁴Mg and ²⁷Al/²⁴Mg ratios, derived from Nano-scale Secondary Ion Mass Spectrometer depth profiles, whose isochron-like regression lines yield inferred initial ²⁶Al/²⁷Al ratios that, on average, are ~1.5–2 times larger than the ratios previously reported for the grains. The majority of presolar graphite and SiC grains are heavily affected by Al contamination, resulting in large negative δ²⁶Mg/²⁴Mg intercepts of the isochron lines. Al contamination is potentially due to etching of the grains’ surfaces and subsequent capture of dissolved Al during the acid dissolution of their meteorite host rocks. From the isochron fits, the magnitude of Al contamination was quantified for each grain. The amount of Al contamination on each grain was found to be random and independent of grain size, following a uniform distribution with an upper bound at 59% contamination. The Al contamination causes conventional whole-grain estimates to underpredict the initial ²⁶Al/²⁷Al ratios. The presolar grains with the highest ²⁶Al/²⁷Al ratios are from Type II supernovae whose isochron-derived initial ²⁶Al/²⁷Alratios greatly exceed those predicted in the He/C and He/N zones of SN models.

Reference
Groopman et al. (2015) Inferred initial 26Al/27Al ratios in presolar stardust grains from supernovae are higher than previously estimated. Astrophysical Journal 809:31.
Link to Article [doi:10.1088/0004-637X/809/1/31]

R. E. Johnson^1,2, A. Oza^3,4, L. A. Young⁵, A. N. Volkov⁶, and C. Schmidt^1,3
1Engineering Physics, University of Virginia, Charlottesville, VA 22904, USA
²Physics, New York University, New York, NY 10003, USA
³Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁴CNRS, LATMOS/IPSL, Université Pierre et Marie Curie, Paris, France
⁵SwRI, 1050 Walnut Street, Boulder, CO 80302-5150, USA
⁶Department of Mechanical Engineering, University of Alabama, Tuscaloosa, AL 35487, USA

Observations indicate that some of the largest Kuiper Belt Objects (KBOs) have retained volatiles in the gas phase (e.g., Pluto), while others have surface volatiles that might support a seasonal atmosphere (e.g., Eris). Since the presence of an atmosphere can affect their reflectance spectra and thermal balance, Schaller & Brown examined the role of volatile escape driven by solar heating of the surface. Guided by recent simulations, we estimate the loss of primordial N2 for several large KBOs, accounting for escape driven by UV/EUV heating of the upper atmosphere as well as by solar heating of the surface. For the latter we present new simulations and for the former we scale recent detailed simulations of escape from Pluto using the energy limited escape model validated recently by molecular kinetic simulations. Unlike what has been assumed to date, we show that unless the N2 atmosphere is thin (<~10¹⁸ N2 cm^-2) and/or the radius small (<~200–300 km), escape is primarily driven by the UV/EUV radiation absorbed in the upper atmosphere. This affects the discussion of the relationship between atmospheric loss and the observed surface properties for a number of the KBOs examined. Our long-term goal is to connect detailed atmospheric loss simulations with a model for volatile transport for individual KBOs.

Reference
Johnson RE, Oza A, Young LA, Volkov AN and Schmidt C (2015) Volatile loss and classification of Kuiper belt objects. Astrophysical Journal 809:43.
Link to Article [doi:10.1088/0004-637X/809/1/43]

Ji Yeon Seok and Aigen Li
Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA

The debris disk around the Vega-type star HD 34700 is detected in dust thermal emission from the near-infrared (IR) to millimeter (mm) and submm wavelength range. Also detected is a distinct set of emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7µm, which are commonly attributed to polycyclic aromatic hydrocarbon (PAH) molecules. We model the observed dust IR spectral energy distribution (SED) and PAH emission features of the HD 34700 disk in terms of porous dust and astronomical-PAHs. Porous dust together with a mixture of neutral and ionized PAHs closely explains the dust IR SED and PAH emission features observed in the HD 34700 disk. Due to the stellar radiation pressure and Poynting–Robertson drag together with the photodissociation of PAHs, substantial removal of dust and PAHs has occurred in the disk, and continuous replenishment of these materials is required to maintain their current abundances. This implies that these materials are not primitive but secondary products probably originating from mutual collisions among planetesimals, asteroids, and comets.

Reference
Seok JY and Li A (2015)Dust and polycyclic aromatic hydrocarbon in the HD 34700 debris disk. Astrophysical Journal 809:22.
Link to Article [doi:10.1088/0004-637X/809/1/22]

Alyssa K. Cobb^1,2, Ralph E. Pudritz^1,2, and Ben K. D. Pearce^1,2
1Origins Institute, McMaster University, ABB 241, 1280 Main Street, Hamilton, ONL8S 4M1, Canada; alyssacobb107@gmail.com, pudritz@physics.mcmaster.ca, ben.pearce@alumni.ubc.ca
²Department of Physics and Astronomy, McMaster University, ABB 241, 1280 Main Street, Hamilton, ONL8S 4M1, Canada

Carbonaceous chondrite meteorites are known for having high water and organic material contents, including amino acids. Here we address the origin of amino acids in the warm interiors of their parent bodies (planetesimals) within a few million years of their formation, and we connect this with the astrochemistry of their natal protostellar disks. We compute both the total amino acid abundance pattern and the relative frequencies of amino acids within the CM2 (e.g., Murchison) and CR2 chondrite subclasses based on Strecker reactions within these bodies. We match the relative frequencies to well within an order of magnitude among both CM2 and CR2 meteorites for parent body temperatures <200°C. These temperatures agree with 3D models of young planetesimal interiors. We find theoretical abundances of approximately 7 × 105 parts per billion, which is in agreement with the average observed abundance in CR2 meteorites of (4 ± 7) × 105, but an order of magnitude higher than the average observed abundance in CM2 meteorites of (2 ± 2) × 104. We find that the production of hydroxy acids could be favored over the production of amino acids within certain meteorite parent bodies (e.g., CI1, CM2) but not others (e.g., CR2). This could be due to the relatively lower NH3 abundances within CI1 and CM2 meteorite parent bodies, which leads to less amino acid synthesis. We also find that the water content in planetesimals is likely to be the main cause of variance between carbonaceous chondrites of the same subclass. We propose that amino acid abundances are primarily dependent on the ammonia and water content of planetesimals that are formed in chemically distinct regions within their natal protostellar disks.

Reference
Cobb AK, Pudritz RE and Pearce BKD (2015) Nature’s starships. II. Simulating the synthesis of amino acids in meteorite parted bodies. Astrophysical Journal 809:6.
Link to Article [doi:10.1088/0004-637X/809/1/6]

^1,2Asmaa Boujibar, ²Denis Andrault, ²Nathalie Bolfan-Casanova, ²Mohamed Ali Bouhifd, ²Julien Monteux
¹Astromaterials Research and Exploration Science, NASA Johnson Space Center, 2101 Nasa Parkway, Houston, Texas 77058, USA.
²Laboratoire Magmas et Volcans, Université Blaise Pascal, CNRS UMR-6524, 5 rue Kessler, 63000 Clermont-Ferrand, France

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Boujibar A, Andrault D, Bolfan-Casanova N, Bouhifd MA, Monteux J (2015) Cosmochemical fractionation by collisional erosion during the Earth’s accretion. Nature Communications 6, 8295
Link to Article [doi:10.1038/ncomms9295]

^1,2A. E. Gleason et al. (>10)*
¹Shock and Detonation Physics, Los Alamos National Laboratory, PO Box 1663, Los Alamos, New Mexico 87545, USA Stanford Institute for Materials and Energy Sciences
²SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA

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Reference
A. E. Gleason et al. (2015) Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2. Nature Communications 6, 8191
Link to Article [doi:10.1038/ncomms9191]

^1,2Joanna Gurgurewicz, ^1,3Daniel Mège, ³Véronique Carrère, ³Anne Gaudin, ⁴Joanna Kostylew, ³Yann Morizet, ⁵Peter G. Purcell, ³Laetitia Le Deit
¹Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Wrocław, Podwale St. 75, PL-50449 Wrocław, Poland
²Space Research Centre, Polish Academy of Sciences, Bartycka St. 18A, PL-00716 Warsaw, Poland
³Laboratoire de Planétologie et Géodynamique, UMR CNRS 6112, Université de Nantes, 2 rue de la Houssiniere, 44322 Nantes, France
⁴Institute of Geological Sciences, University of Wrocław, Cybulskiego St. 30, PL-50205 Wrocław, Poland
⁵P&R Geological Consultants, 141 Hastings Street, Scarborough WA 6019, Australia

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Gurgurewicz J, Mège D, Carrère V, Gaudin A, Kostylew J, Morizet Y, Purcell PG, Le Deit(2015) Inferring alteration conditions on Mars: Insights from near-infrared spectra of terrestrial basalts altered in cold and hot arid Environments. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2015.09.002]

¹Stefanie Brachfeld, ¹Deepa Shah, ²Emily First, ²Julia Hammer, ³Julie Bowles
¹Department of Earth and Environmental Studies, Montclair State University, Montclair, New Jersey, USA
²Department of Geology and Geophysics, University of Hawai‘i, Honolulu, Hawai‘i, USA
³Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA

We evaluate the relationship between the intensity of remanent magnetization and fO2 in natural and synthetic Mars meteorites. The olivine-phyric shergottite meteorite Yamato 980459 (Y-980459) and a sulfur-free synthetic analog (Y-98*) of identical major element composition were analyzed to explore the rock magnetic and remanence properties of a basalt crystallized from a primitive melt, and to explore the role of magmatic and alteration environment fO2 on Mars crustal anomalies. The reducing conditions under which Y-980459 is estimated to have formed (QFM-2.5; Shearer et al. 2006) were replicated during the synthesis of Y-98*. Y-980459 contains pyrrhotite and chromite. Chromite is the only magnetic phase in Y-98*. The remanence-carrying capacity of Y-980459 is comparable to other shergottites that formed in the fO2 range of QFM-3 to QFM-1. The remanence-carrying capacity of these low fO2 basalts is 1–2 orders of magnitude too weak to account for the intense crustal anomalies observed in Mars’s southern cratered highlands. Moderately oxidizing conditions of >QFM-1, which are more commonly observed in nakhlites and Noachian breccias, are key to generating either a primary igneous assemblage or secondary alteration assemblage capable of acquiring an intense remanent magnetization, regardless of the basalt character or thermal history. This suggests that if igneous rocks are responsible for the intensely magnetized crust, these oxidizing conditions must have existed in the magmatic plumbing systems of early Mars or must have existed in the crust during secondary processes that led to acquisition of a chemical remanent magnetization.

Reference
Brachfeld S, Shah D, First E, Hammer J, Bowles J (2015) Influence of redox conditions on the intensity of Mars crustal magnetic anomalies. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12505]
Published by arrangement with John Wiley & Sons

¹Mehmet Yesiltas, ¹Robert E. Peale, ²Miriam Unger, ³Julia Sedlmair,²Carol J. Hirschmugl
¹Department of Physics, University of Central Florida, Orlando, Florida, USA
²Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
³Forest Products Laboratory, US Department of Agriculture Forest Service, Madison, Wisconsin, USA

Relationships between organic molecules and inorganic minerals are investigated in a single 34 μm diameter grain of the CR2 chondrite Northwest Africa 852 (NWA) 852 with submicron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for the various constituents are determined using statistical correlation analysis. The silicate band is found to be correlated with the hydration band, and the latter is highly correlated with stretching modes of aliphatic hydrocarbons. Spatial distribution maps show that water+organic combination, silicate, OH, and C-H distributions overlap, suggesting a possible catalytic role of phyllosilicates in the formation of organics. In contrast, the carbonate band is anticorrelated with water+organic combination, however uncorrelated with any other spectral feature. The average ratio of asymmetric CH2 and CH3 band strengths (CH2/CH3 = 2.53) for NWA 852 is similar to the average ratio of interplanetary dust particles (~2.40) and Wild 2 cometary dust particles (2.50), but it significantly exceeds that of interstellar medium objects (~1.00) and several aqueously altered carbonaceous chondrites (~1.40). This suggests organics of similar length/branching, and perhaps similar formation regions, for NWA 852, Wild 2 dust particles, and interplanetary dust particles. The heterogeneous spatial distribution of ratio values indicates the presence of a mixture of aliphatic organic material with different length/branching, and thus a wide range of parent body processes, which occurred before the considered grain was formed.

Reference
Yesiltas M, Peale RE, Unger M, Sedlmair J, Hirschmugl CJ (2015) Organic and inorganic correlations for Northwest Africa 852 by synchrotron-based Fourier transform infrared microspectroscopy. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12498]
Published by arrangement with John Wiley & Sons