Trends in Silicates in the β Pictoris Disk
Abstract
While β Pic is known to host silicates in ring-like structures, whether the properties of these silicate dust vary with stellocentric distance remains an open question. We re-analyze the β Pictoris debris disk spectrum from the Spitzer Infrared Spectrograph (IRS) and a new Infrared Telescope Facility Spectrograph and Imager 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 feature and recover a 23 μm forsterite emission feature with a substantially larger line-to-continuum ratio than previously reported. We find that these prominent spectral features are primarily produced by small submicron-sized grains, which are continuously generated and replenished from planetesimal collisions in the disk and can elucidate their parent bodies' composition. We discover three trends about these 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 trends 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 find a tentative 3-5 μm dust excess due to spatially unresolved hot dust emission close to the star. From our findings, we infer that the surfaces of large planetesimals are more Fe-rich and collisionally processed closer to the star but more Fe-poor and primordial farther from the star.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2022
- DOI:
- 10.3847/1538-4357/ac70d1
- arXiv:
- arXiv:2205.09138
- Bibcode:
- 2022ApJ...933...54L
- Keywords:
-
- Debris disks;
- Silicate grains;
- Planetary system formation;
- Exoplanet formation;
- Planetesimals;
- Exozodiacal dust;
- Spectroscopy;
- Infrared astronomy;
- 363;
- 1456;
- 1257;
- 492;
- 1259;
- 500;
- 1558;
- 786;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 19 pages, 12 figures, Accepted for Publication in ApJ