Kavli Affiliate: Gregory J. Herczeg
| First 5 Authors: Chengyan Xie, Ilaria Pascucci, Feng Long, Klaus M. Pontoppidan, Andrea Banzatti
| Summary:
We present an analysis of the JWST/MIRI-MRS spectrum of Sz114, an accreting
M5 star surrounded by a large dust disk with a gap at ~39au. The spectrum is
molecular-rich: we report the detection of water, CO, CO2, HCN, C2H2, and H2.
The only identified atomic/ionic transition is from [NeII] at 12.81 micron. A
distinct feature of this spectrum is the forest of water lines with the 17.22
micron emission surpassing that of most late M-star disks by an order of
magnitude in flux and aligning instead with disks of earlier-type stars.
Moreover, flux rations of C2H2/H2O and HCN/H2O in Sz114 also resemble those of
earlier-type disks, with a slightly elevated CO2/H2O ratio. While accretion
heating can boost all infrared lines, the unusual properties of Sz114 could be
explained by the young age of the source, its formation under unusual initial
conditions (a large massive disk), and/or the presence of dust substructures.
The latter delay the inward drift of icy pebbles and thus preserve a lower C/O
ratio over an extended period. In contrast, late M-star disks-which are
typically faint, small in size, and likely lack significant substructures-may
have more quickly depleted the outer icy reservoir and already evolved out of a
water-rich inner disk phase. Our findings underscore the unexpected diversity
within mid-infrared spectra of late M-star disks, highlighting the need to
expand the observational sample for a comprehensive understanding of their
variations and thoroughly test pebble drift and planet formation models.
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