Resolved molecular line observations reveal an inherited molecular layer in the young disk around TMC1A

Context. Physical processes that govern the star and planet formation sequence influence chemical composition evolution of protoplanetary disks. Recent studies allude to an early start already during a disk. To understand protoplanets, we need constrain structure disks from whence they are formed. Aims. We aim determine molecular abundance young disk around TMC1A protostar on au scales in order its any possible implications for formation. Methods. present spatially resolved Atacama Large Millimeter/submillimeter Array observations CO, HCO + , HCN, DCN, SO line emission, as well dust continuum vicinity TMC1A. Molecular column densities estimated both under assumption optically thin emission molecules local thermodynamical equilibrium (LTE) through more detailed non-LTE radiative transfer calculations. Results. Resolved is detected between 220 260 GHz. Rotational transitions also inner 100 region. further report upper limits vibrational HCN ? 2 = 1, N D lines. The appears trace Keplerian surrounding infalling rotating envelope. peaks toward outflow cavity region connected with CO wind red-shifted part From derived abundance, estimate ionization fraction surface, find values imply accretion process not driven by magneto-rotational instability. abundances averaged over similar protostellar envelope other, older Class II meanwhile discrepancy disk’s relative Solar System objects. Conclusions. Abundance comparisons several species reveal bulk planet-forming material enters unaltered. Differences H O TMC1A, disks, objects