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Trends in Silicates in the β Pictoris Disk

Presentation #102.111 in the session Poster Session.

Published onJun 20, 2022
Trends in Silicates in the β Pictoris Disk

We re-analyze the Spitzer Infrared Spectrograph (IRS) β Pictoris debris disk data and a new IRTF/SpeX spectrum to investigate trends in Fe/Mg ratio, shape, and crystallinity in grains as a function of wavelength, a proxy for stellocentric distance. By analyzing a re-calibrated and re-extracted spectrum, we identify a new 18 μm forsterite emission band and recover a 23 μm forsterite emission band with a substantially larger line-to-continuum ratio than previously reported. Small submicron-sized grains, continuously generated and replenished from planetesimal collisions in the disk, are responsible for these spectral features and can elucidate their parent bodies’ composition. We discover three trends about small grains: as stellocentric distance increases, (1) small silicate grains become more crystalline (less amorphous), (2) they become more irregular in shape, and (3) for crystalline silicate grains, the Fe/Mg ratio decreases. Applying these findings to β Pic’s planetary architecture, we find that the dust population exterior to the orbits of β Pic b and c differs substantially in crystallinity and shape. We also infer that the surfaces of planetesimal are more Fe-rich and collisionally-processed closer to the star but more Fe-poor and primordial farther from the star. Finally, we find a tentative 3–5 μm dust excess due to spatially-unresolved hot dust emission close to the star. Future JWST observations will constrain the spatial and temperature distributions of the cool forsterite grains and probe β Pic b’s atmospheric cloud compositions in MIR for comparison with dust properties in the planet’s vicinity.

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