Multiple Rings and Asymmetric Structures in the Disk of SR 21

Crescent-like asymmetric dust structures discovered in protoplanetary disks indicate aggregations. Thus, the research on them helps us understand planet formation process. Here we analyze ALMA data of disk around T-Tauri star SR 21, which has detected previous sub-millimeter observations. Imaged at Band 6 (1.3 mm) with a spatial resolution about 0.$\arcsec$04, is found to consist two rings and three structures, being same ring. Compared image, 3 (2.7 image also shows but some clumps. The elongated outer ring could be due interactions growing planet. By fitting continuum data, branches solutions maximum size are suggested: one larger than 1 mm, other smaller 300 $\mu m$. High-resolution observations longer wavelengths as well polarization can help break degeneracy. We suggest that prominent spiral previously identified VLT/SPHERE south 0.$\arcsec$25 may scattered light counterpart Inner Arc, structure dust-trapping vortex nature. features 21 make it good target for studying evolution formation.