Physical and Chemical Structure of the Disk and Envelope of the Class 0/I Protostar L1527

Abstract

Submillimeter spectral line and continuum emission from the protoplanetary disks and envelopes of protostars is a powerful probe of their structure, chemistry, and dynamics. Here we present a benchmark study of our modeling code, RadChemT, that for the first time uses a chemical model to reproduce ALMA C 18 O (2–1), and CARMA 12 CO (1–0) and N 2 H + (1–0) observations of L1527; this allows us to distinguish the disk, the infalling envelope, and outflow of this Class 0/I protostar. RadChemT combines dynamics, radiative transfer, gas chemistry, and gas–grain reactions to generate models that can be directly compared with observations for individual protostars. Rather than individually fit abundances to a large number of free parameters, we aim to best match the spectral line maps by (i) adopting a physical model based on density structure and luminosity derived primarily from previous work that fit spectral energy distribution and 2D imaging data, updating it to include a narrow jet detected in CARMA and ALMA data near (≤75 au) the protostar, and then (ii) computing the resulting astrochemical abundances for 292 chemical species. Our model reproduces the C 18 O and N 2 H + line strengths within a factor of 3.0; this is encouraging considering the pronounced abundance variation (factor >10 3 ) between the outflow shell and CO snowline region near the midplane. Further, our modeling confirms suggestions regarding the anticorrelation between N 2 H + and the CO snowline between 400 au and 2000 au from the central star. Our modeling tools represent a new and powerful capability with which to exploit the richness of spectral line imaging provided by modern submillimeter interferometers.