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Séminaire du jeudi 23 novembre 2017

The impact of X-rays on dust in protoplanetary disks

Lisseth Gavilan (LATMOS)
Thursday November 23rd - 11am
IPAG Seminar Room - IPAG

Planets form in protoplanetary disks following a long process where icy dust grains collide and stick. The evolution of dust is integrated in the evolution of the star and disk, a complex system where radiative, dynamic and chemical processes intertwine. One of the critical drivers of disk evolution may be the vigorous X-ray emission of young stars, which irradiate their circumstellar disks. Chemical disk models have recently applied X-ray photochemical rates to the gas phase, but the impact of X-rays on disk solids is much less constrained.

To address this issue, we explore the effect of X-rays on protoplanetary dust via laboratory experiments. We begin by the synthesis of laboratory analogs of interstellar dust : silicate and organic nanomaterials. To simulate a classical T Tauri X-ray spectrum, we use synchrotron radiation.

We recently showed that hard X-rays lead to the amorphization of crystalline silicate nanograins, but only when these are admixed with organics1. Such effect signals that heterogeneous dust grains evolve in synergy under ionizing radiation. It also demonstrates that X-rays alone can modify the structure of dust grains. We then irradiated organic dust analogs with soft X-rays, and found out that the X-irradiated regions presented drastically enhanced D/H ratios2. Our experiments show that X-rays could impact the earliest stages of planet formation and leave radiative imprints in solids during the protoplanetary stage.

Figure. Top : Hard X-ray irradiation of crystalline silicates. Bottom : Evolving X-ray diffraction shows X-rays alone can modify the structure of heterogeneous dust1.

References
1 Gavilan et al. A&A 587, A144 (2016)
2 Gavilan et al. ApJ 840, 35 (2017)


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Sous la tutelle de:

CNRS Université Grenoble Alpes