^1,2Thomas Stephan, ^1,2Reto Trappitsch, ^1,2,3Andrew M. Davis, ^1,2,3,4Michael J. Pellin, ^1,2Detlef Rost, ^2,3Michael R. Savina, ^1,2Manavi Jadhav, ^1,2Christopher H. Kelly, ^1,5Frank Gyngard, ^1,6Peter Hoppe, ^1,2,3Nicolas Dauphas
Geochmica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.05.001]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
²Chicago Center for Cosmochemistry, Chicago, IL, USA
³The Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA
⁴Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
⁵Laboratory for Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130, USA
⁶Max Planck Institute for Chemistry, 55128 Mainz, Germany
Copyright Elsevier

We used CHILI, the Chicago Instrument for Laser Ionization, a new resonance ionization mass spectrometer developed for isotopic analysis of small samples, to analyze strontium, zirconium, and barium isotopes in 22 presolar silicon carbide grains. Twenty of the grains showed detectable strontium and barium, but none of the grains had enough zirconium to be detected with CHILI. Nine grains were excluded from further consideration since they showed very little signals (<1000 counts) for strontium as well as for barium. Among the 11 remaining grains, we found three X grains. The discovery of three supernova grains among only 22 grains was fortuitous, because only ∼1% of presolar silicon carbide grains are type X, but was confirmed by silicon isotopic measurements of grain residues with NanoSIMS. While one of the X grains showed strontium and barium isotope patterns expected for supernova grains, the two other supernova grains have ⁸⁷Sr/⁸⁶Sr < 0.5, values never observed in any natural sample before. From their silicon isotope ratios, the latter two grains can be classified as X2 grains, while the former grain belongs to the more common X1 group. The differences of these grains in strontium and barium isotopic composition constrain their individual formation conditions in Type II supernovae.

¹Lisseth Gavilan, ²Laurent Remusat, ²Mathieu Roskosz, ³Horia Popescu, ³Nicolas Jaouen, ⁴Christophe Sandt, ⁵Cornelia Jäger, ⁶Thomas Henning, ⁷Alexandre Simionovici, ⁸Jean Louis Lemaire
The Astrophysical Journal 840, 35 Link to Article [https://doi.org/10.3847/1538-4357/aa6bfc]
¹LATMOS, Université Versailles St Quentin, UPMC Université Paris 06, CNRS, 11 blvd d’Alembert, F-78280 Guyancourt, France
²IMPMC, CNRS UMR 7590; Sorbonne Universités, UPMC Université Paris 06; IRD, Muséum National d’Histoire Naturelle, CP 52, 57 rue Cuvier, Paris F-75231, France
³SEXTANTS beamline, SOLEIL synchrotron, L’Orme des Merisiers, F-91190 Saint-Aubin, France
⁴SMIS beamline, SOLEIL synchrotron, L’Orme des Merisiers, F-91190 Saint-Aubin, France
⁵Laboratory Astrophysics and Cluster Physics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University & Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
⁶Max-Planck Institute for Astronomy Königstuhl 17, D-69117 Heidelberg, Germany
⁷Institut des Sciences de la Terre, Observatoire des Sciences de l’Univers de Grenoble, BP 53, F-38041 Grenoble, France
⁸Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Sud, Université Paris-Saclay, F-91405 Orsay, France
⁹Institut Jean Lamour, CNRS, Université de Lorraine, F-54011 Nancy, France

The deuterium enrichment of organics in the interstellar medium, protoplanetary disks, and meteorites has been proposed to be the result of ionizing radiation. The goal of this study is to simulate and quantify the effects of soft X-rays (0.1–2 keV), an important component of stellar radiation fields illuminating protoplanetary disks, on the refractory organics present in the disks. We prepared tholins, nitrogen-rich organic analogs to solids found in several astrophysical environments, e.g., Titan’s atmosphere, cometary surfaces, and protoplanetary disks, via plasma deposition. Controlled irradiation experiments with soft X-rays at 0.5 and 1.3 keV were performed at the SEXTANTS beamline of the SOLEIL synchrotron, and were immediately followed by ex-situ infrared, Raman, and isotopic diagnostics. Infrared spectroscopy revealed the preferential loss of singly bonded groups (N–H, C–H, and R–N≡C) and the formation of sp3 carbon defects with signatures at ~1250–1300 cm−1. Raman analysis revealed that, while the length of polyaromatic units is only slightly modified, the introduction of defects leads to structural amorphization. Finally, tholins were measured via secondary ion mass spectrometry to quantify the D, H, and C elemental abundances in the irradiated versus non-irradiated areas. Isotopic analysis revealed that significant D-enrichment is induced by X-ray irradiation. Our results are compared to previous experimental studies involving the thermal degradation and electron irradiation of organics. The penetration depth of soft X-rays in μm-sized tholins leads to volume rather than surface modifications: lower-energy X-rays (0.5 keV) induce a larger D-enrichment than 1.3 keV X-rays, reaching a plateau for doses larger than 5 × 1027 eV cm−3. Synchrotron fluences fall within the expected soft X-ray fluences in protoplanetary disks, and thus provide evidence of a new non-thermal pathway to deuterium fractionation of organic matter.