In the early stage of low-mass star formation, a rotationally-supported disk (Keplerian disk) is formed around a newly born protostar. To explore the disk formation in young stages, a protostellar source in an isolated environment can be an excellent testbed. The Class 0 protostar IRAS 18347+0727 in the Bok globule B335 (d=165 pc) stands for one of the best targets. Its physical structure of the disk/envelope system has extensively been studied with recent ALMA observations (e.g., Imai et al. 2019, Bjerkeli et al. 2019, Evans et al. 2022). However, a rotationally supported disk has not yet been discovered clearly.
We analyze the velocity structures of the CH3OH (Eu=447 K) and HCOOH (Eu=83 K) lines observed with ALMA at a high resolution of 0.”03 (~5 au). These lines have the extended (r~30 au) and compact (r~15 au) distributions, respectively, on a 10 au scale (Okoda et al. 2022). The CH3OH (Eu=447 K) line most likely traces an infalling-rotating envelope, whereas the HCOOH line is comparable to a Keplerian rotation with the protostellar mass of 0.04 M_?. As well, we detect the very high excitation line of CH3OH (Eu=1333 K). This line shows a compact distribution, and its velocity structure looks similar to that of HCOOH. We discuss the physical parameters, such as the protostellar mass, the centrifugal barrier, the outer and inner radius, and the inclination, based on the comparison with the results of FERIA (Flat Envelope model with Rotation and Infall under Angular momentum conservation) developed by Oya et al. (2022).