[P-CG20] Origin and evolution of materials in space

[PCG20-10] Understanding of the nature and the role of organic dust in space

★Invited Papers

*Itsuki Sakon¹, Izumi Endo¹, Riko Senoo¹, Takashi Onaka^1,8, Takashi Miyata¹, Yoko Kebukawa², Kensei Kobayashi², Hajime Yano³, Hajime Mita⁴, Yuki Kimura⁵, Masato Nakamura⁶, Masahiro Kobayashi⁷, Hiroaki Nakamura⁷ (1.University of Tokyo, 2.Yokohama National University, 3.JAXA, 4.Fukuoka Institute of Technology, 5.Hokkaido University, 6.Nihon University, 7.National Institute for Fusion Science, 8.Meisei University)

Keywords:interstellar organics, dust, infrared astronomical observations

The sites of dust formation in the stellar ejecta including nucleo syntehsized heavy elements during the late stages of evolution of low-mass and high-mass stars are important astrophysical events to understand the process of chemical evolution of the universe across the cosmic time. Particularly, understanding of the chemical properties of organic dust synthesized in the mass loss wind is crucial in identifying the composition of interstellar organics prevailing in the interstellar medium of galaxies and in discussing their possible evolutional relation with primitive organic materials of the solar system. While infrared astronomical observations work efficiently to demonstrate the formation process of organic dust and to exmaine their chemcical properties, attempts to synthesize organic dust that mimic the properties of those in real astrohysical environment and to carry out their denaturing experiments based on laboratory astrophysics are indespensable to attain more concrete chemical identification of the interstellar organics and to understand their chemical evolution.

We have synthesized a laboratory organic dust named quenched nitrogen-included carbonaceous composite (QNCC; Endo, Sakon, Onaka et al. 2021) through the quenched condensation of plasma gas generated from the nitrogen gas and aromatic and/or aliphatic hydrocarbon solids applying microwave discharge (2.45GHz, 300 W). The infrared properties of QNCC has a close resemblance to the UIR bands observed in the infrared spectra of dust forming novae and QNCC is regarded as thebest laboratory analogue of organic dust formed in the circumstellar medium of dusty classical novae. Moreover, we have noticed a close resemblance between the infrared properties of collected-back samples of QNCC after 1-year of space exposure experiment at the international space station (ISS) orbit and the insoluble organic matter (IOM) extracted from the carbonaceous meteorites. We have also introduced a plasma process monitoring system to characterize the properties of plasma and to investigate how the condensate attain chemical groups including nitrogen.

In this presentation, I will introduce our accumulated knowledge obtained from those experiments and discuss science that needs to be explored by future infrared observations.