Measuring elemental abundance ratios in protoplanetary disks at millimeter wavelengths

D. Fedele; C. Favre

doi:10.1051/0004-6361/202037927

paper

Measuring elemental abundance ratios in protoplanetary disks at millimeter wavelengths

arXiv:2005.03891 · doi:10.1051/0004-6361/202037927

Abstract

During the million years of evolution, gas dust and ice in protoplanetary disks can be chemically reprocessed. There are evidences that the gas-phase carbon and oxygen abundances are sub-solar in disks belonging to nearby star forming regions. These findings have a major impact on the composition of the primary atmosphere of giant planets (but it may also be valid for super-Earths and sub-Neptunes) as they accrete their gaseous envelopes from the surrounding material in the disk. In this study, we performed a thermo-chemical modelling analysis with the aim at testing how reliable and robust are the estimates of elemental abundance ratios based on (sub-)millimeter observations of molecular lines. We created a grid of disk models for the following different elemental abundance ratios: C/O, N/O and S/O, and, we computed the line flux of a set of carbon-, nitrogen and sulphur-bearing species, namely CN, HCN, NO, C $_{2}$ H, c--C $_{3}$ H $_{2}$ , H $_{2}$ CO, HC $_{3}$ N, CH $_{3}$ CN, CS, SO, H $_{2}$ S and H $_{2}$ CS, that have been detected with present (sub-)millimeter facilities such as ALMA and NOEMA. We find that the line fluxes, once normalized to the flux of the $^{13}$ CO $J = 2 - 1$ line, are sensitive to the elemental abundance ratios. On the other hand, the stellar and disk physical parameters have only a minor effect of the line flux ratios. Our results demonstrate that a simultaneous analysis of multiple molecular transitions is a valid approach to constrain the elemental abundance ratio in protoplanetary disks.

Accepted for publication to A&A

Measuring elemental abundance ratios in protoplanetary disks at millimeter wavelengths

Abstract

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