OBSERVATIONAL RESEARCH OF ACCRETION IN PROTOPLANETARY DISKS

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In this research we investigated, through astronomical observations, dynamical collapse in star formation and formation of protoplanetary disks.Direct evidence of dynamical infall was found around two new protostars during the research in the fiscal year 1996. Both objects showed rotation as well as infall at the envelope radius of about 1000AU (=Astronomical Unit), suggesting the presence of 100 AU scale protoplanetary disks around the central objects, which were actually confirmed from other observations. Our results hence gave firm evidence of protoplanetary disks, which would be the site of planetary system formation, to be formed through dynamical accretion in protostellar envelopes.We then studied statistical characteristics of protostellar envelopes in the fiscal year 1997 based upon new observations, finding that, while the specific angular momentum of gas in envelopes is proportional to the 1.6-th power of the radius at radii larger than 0.03 parsec (pc), it is independent of radius and is constant at about 10^<-3> km s^<-1>pc at radii less than 0.03pc. This may mean that dynamical collapse in protostellar envelopes occurs inside radii of 0.03 pc and that, as a result, the gas keeps its specific angular momentum to form protoplanetary disks with their radii comparable to 100 AU.This new result naturally explains the 100 AU size scale of the solar system as well as that of protoplanetary disks.