Astrochemistry

The Characterisation of Water Ice in Debris Discs: Implications for JWST Scattered Light Observations

By Keith Cowing
Status Report
astro-ph.EP
August 13, 2024
Filed under , , , ,
The Characterisation of Water Ice in Debris Discs: Implications for JWST Scattered Light Observations
The relative SNR (i.e., the signal strength of the ice feature/combined noise from both channels) of debris discs harbouring amorphous ice-dust aggregate (top panels) and crystalline ice-dust aggregate (bottom panels) as a function of the ice fraction ℱice depending on the spectral type of central stars. A higher SNR value indicates better resolution and detection capability for the ice features around 3 𝜇m. See Sect. 3.2 for details. — astro-ph.EP

Water ice plays a crucial role throughout the different stages of planetary evolution and is abundant in the Universe. However, its presence and nature in debris discs of exoplanetary systems are not yet strongly established observationally.

In this study, we quantify and discuss the impact of ice parameters such as volume fraction ice, blow-out grain size, size distribution, and its phase on the observational appearance of debris discs, considering the diverse nature of these systems around stellar spectral types ranging from A to M.

Our findings reveal that the prominent ice features at approximately 2.7 and 3.3\,μm depend on both the water ice fraction ice and the scattering angle, with backscattering geometries yielding the most prominent signatures. When the phase function is considered and data are not background limited, strong forward and backward scattering (near edge-on discs) are expected to yield the strongest detections in images/spectra for A or F-type stars, while scattering angle matters less for later type stars. The Fresnel peak at 3.1\,μm serves as a viable discriminant for the transitional phase (crystalline/amorphous), while simultaneously constraining the water ice temperature.

For JWST imaging, we find that the F356W and F444W filter combination is most effective for constraining the grain size distribution, while the F356W and F277W filter combination provides better constraints on the ice fraction ice in debris discs. However, degeneracy between the grain size distribution and ice fraction when using photometric flux ratios means that obtaining robust constraints will likely require more than two filters, or spectroscopic data.

Minjae Kim, Grant M. Kennedy, Veronica Roccatagliata

Comments: 22 pages, 20 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2408.03278 [astro-ph.EP] (or arXiv:2408.03278v1 [astro-ph.EP] for this version)
Submission history
From: Minjae Kim
[v1] Tue, 6 Aug 2024 16:20:23 UTC (41,516 KB)
https://arxiv.org/abs/2408.03278
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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