The physical and chemical fingerprint of planet- forming disks

One of the current major challenges in star- and planet-formation is to constrain the chemical composition of forming planets. To do so, chemical trends are assessed by studying the molecular composition of the disk at the time of planet formation, and how this composition changes with time. Thanks to the unique sensitivity offered by ALMA we can now finally start to observationally constrain the initial chemical conditions of disk formation and, thus, of planet formation. I will present an ALMA physico-chemical survey of 12 Class I sources in the Ophiuchus star- forming region. The covered molecular transitions were chosen specifically to trace the kinematics of disk formation (i.e., C17O, H13CO+, and C34S) and the warm chemistry in the inner envelope or disk (i.e., SO2 and CH3OH). The tracers reveal the chemistry and physics of the embedded disks, probing material with high temperatures and densities. A chemical differentiation is seen between C17O and SO2, where the former traces the disk mass and the latter traces accretion shocks. In addition, protostellar masses can now systematically be estimated through molecular line emission, which provides observational evidence that the mass accretion rate varies with time and that a typical protostar spends most of its lifetime in a quiescent state of accretion. These observations show the capacity of ALMA to study the physics at disk scales through molecular transitions, and how these physical processes may affect the chemistry and set the initial chemical conditions for planet formation.