- 1Istituto Nazionale di Astrofisica (INAF-OAPa)
- 2Department of Physics, National Central University, Taiwan
- 3Università degli studi di Palermo
- 4Centro de AstroBiologia (CAB-INTA)
Young stars emit a large amount of X-rays that can penetrate deep into protoplanetary disks, reaching the inner and more shielded regions. In the interaction of X-ray photons with ices, it produces ionisation of core electrons of the atoms forming part of the molecules. The ionisation of an inner-shell electron is followed by Auger decays for light elements [1]. The decay of the Auger stimulates the emission of an electron. The injection of these electrons into the ice produces multiple ionisations that dominate the chemistry [2].
In this study, we investigate the role of the photon energy of X-rays on a realistic ice mixture H2O:CO:NH3 at 10 K. To elucidate the dependence of the X-ray energy photons on the induced chemistry, we irradiated the ice sample with X-rays at different energies, scanning from 250 up to 900 eV, increasing the photon energy by a few eV after each irradiation step.
The results indicate that variation of the column density of different components of the ice strongly depends on the X-ray absorption profile of the sample at each energy. We observe a sharp variation of the column densities at ~300, ~400, and ~550 eV corresponding to the C, N, and O X-ray absorption edges, respectively. Comparison of the experimental edges, measured during X-ray irradiation, with the literature values reveals discrepancies with the atomic values, giving information about the chemical environment of the absorber (e.g., if C is bonded with O).
Comparing the destruction/formation yields measured in our experiments indicates that the energy of the photons is not a determining factor in the chemical network but only the total energy deposited in the ice through ionisations produced by secondary electrons. In addition, these experiments also show clues about a possible contribution of the substrate to the ice chemistry through the electron emitted from the surface of the substrate to the ice.
[1] Y-J. Chen, A. Ciaravella, G. M. Muñoz Caro, C. Cecchi-Pestellini, A. Jimenez-Escobar, K.-J. Juang, and T.-S. Yih, 2013, ApJ, 778, 162
[2] A. Jiménez-Escobar, Y.-J. Chen, A. Ciaravella, C.-H. Huang, G. Micela, and C. Cecchi-Pestellini, 2016, ApJ, 820, 25.
How to cite: jimenez Escobar, A., Cecchi-Pestellini, C., Ciaravella, A., Chen, Y.-J., Lee, C.-Y., Chiu, Y.-H., Mangione, A., Piazzese, F., and Muñoz Caro, G. M.: Soft X-Ray Irradiation of realisticIce Analogs: The Role of Absorption Edges and Secondary Electrons, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-374, https://doi.org/10.5194/epsc2026-374, 2026.
