A Laboratory-driven Multiscale Investigation of X-Ray Induced Mass Loss and Photochemical Evolution in Cosmic Carbon and Silicate Dust

1,2Lisseth Gavilan,3Phay J. Ho,1,4Uma Gorti,5Hirohito Ogasawara,6Cornelia Jäger, 1Farid Salama
The Astrophysical Journal 925, 86 Open Access Link to Article [DOI 10.3847/1538-4357/ac3dfd]
1NASA Ames Research Center, Space Science & Astrobiology Division, Moffett Field, CA 94035, USA
2Universities Space Research Association (USRA), Columbia, MD 21046, USA
3Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL 60439, USA
4SETI Institute, Carl Sagan Center, Mountain View, CA 94035, USA
5Stanford Synchrotron Radiation Laboratory, P.O. Box 20450, Stanford, CA 94309, USA
6Laboratory 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

We present the results of an integrated laboratory and modeling investigation into the impact of stellar X-rays on cosmic dust. Carbonaceous grains were prepared in a cooled (<200 K) supersonic expansion from aromatic molecular precursors, and were later irradiated with 970 eV X-rays. Silicate (enstatite) grains were prepared via laser ablation, thermally annealed, and later irradiated with 500 eV X-rays. Infrared spectra of the 3.4 μm band of the carbon sample prepared with benzene revealed 84% ± 5% band area loss for an X-ray dose of 5.2 ×1023 eV.cm−2. Infrared spectra of the 8–12 μm Si–O band of the silicate sample revealed band area loss up to 63% ± 5% for doses of 2.3 × 1023 eV.cm−2. A hybrid Monte Carlo particle trajectory approach was used to model the impact of X-rays and ensuing photoelectrons, Auger and collisionally ionized electrons through the bulk. As a result of X-ray ionization and ensuing Coulomb explosions on surface molecules, the calculated mass loss is 60% for the carbonaceous sample and 46% for the silicate sample, within a factor of 2 of the IR band loss, supporting an X-ray induced mass-loss mechanism. We apply the laboratory X-ray destruction rates to estimate the lifetimes of dust grains in protoplanetary disks surrounding 1 M and 0.1 M G and M stars. In both cases, X-ray destruction timescales are short (a few million years) at the disk surface, but are found to be much longer than typical disk lifetimes (≳10 Myr) over the disk bulk.

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