2023ApJ...958...98F

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Class I source Oph IRS 63 in the context of the Early Planet Formation in Embedded Disks large program. Our ALMA observations of Oph IRS 63 show a myriad of protostellar features, such as a shell-like bipolar outflow (in ¹²CO), an extended rotating envelope structure (in ¹³CO), a streamer connecting the envelope to the disk (in C¹⁸O), and several small-scale spiral structures seen toward the edge of the dust continuum (in SO). By analyzing the velocity pattern of ¹³CO and C¹⁸O, we measure a protostellar mass of M_⋆ = 0.5 ± 0.2 M_⊙ and confirm the presence of a disk rotating at almost Keplerian velocity that extends up to ∼260 au. These calculations also show that the gaseous disk is about four times larger than the dust disk, which could indicate dust evolution and radial drift. Furthermore, we model the C¹⁸O streamer and SO spiral structures as features originating from an infalling rotating structure that continuously feeds the young protostellar disk. We compute an envelope-to-disk mass infall rate of ∼10^–6M_⊙ yr^–1 and compare it to the disk-to-star mass accretion rate of ∼10^–8M_⊙ yr^–1, from which we infer that the protostellar disk is in a mass buildup phase. At the current mass infall rate, we speculate that soon the disk will become too massive to be gravitationally stable.