The recent rapid progress in observations of circumstellar disks and extrasolar planets has reinforced the importance of understanding an intimate coupling between star and planet formation. Under such a circumstance, it may be invaluable to attempt to specify when and how planet formation begins in star-forming regions and to identify what physical processes/quantities are the most significant to make a link between star and planet formation. To this end, we have recently developed a couple of projects. These include an observational project about dust growth in Class 0 YSOs and a theoretical modeling project of the HL Tauri disk. For the first project, we utilize the archive data of radio interferometric observations, and examine whether dust growth, a first step of planet formation, occurs in Class 0 YSOs. We find that while our observational results can be reproduced by the presence of large ($sim$ mm) dust grains for some of YSOs under the single-component modified blackbody formalism, an interpretation of no dust growth would be possible when a more detailed model is used. For the second project, we consider an origin of the disk configuration around HL Tauri, focusing on magnetic fields. We find that magnetically induced disk winds may play an important role in the HL Tauri disk. The combination of these attempts may enable us to move towards a comprehensive understanding of how star and planet formation are intimately coupled with each other.
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