0/I类YSO引力不稳定盘中的视盘质量减少和星子形成
Apparent disk-mass reduction and planetesimal formation in gravitationally unstable disks in Class 0/I YSOs
摘要：
我们研究了引力不稳定盘的尘埃结构，这些尘埃盘经历了从包层到0/I类年轻恒星天体（YSO）的质量吸积。我们发现，尘埃盘很快进入稳定状态，与具有星际介质（ISM）尘气质量比和微米级尘埃的盘相比，稳态时粉尘质量减少1/2 ~ 1/3，粉尘热辐射减少1/3 ~ 1/5。后者的减少是由于尘埃耗尽和不透明度下降，由于尘埃的增长。我们的研究结果表明，在0/I类YSO的引力不稳定磁盘的质量被低估了1/3至1/5的因素时，从尘埃热辐射计算假设ISM尘埃-气体质量比和微米大小的尘埃不透明度，并在0/I类YSO的磁盘的较大比例是引力不稳定比以前认为的。我们还调查了轨道半径$r_{\rm P}$内的微行星通过凝聚的多孔尘埃聚集体，并表明，$r_{\rm P}$成为$\sim 20$ AU的引力不稳定盘周围的太阳质量的恒星。由于$r_{\rm P}$随着气体表面密度的增加而增加，并且引力不稳定盘具有最大气体表面密度，因此$r_{\rm P}\sim 20$ AU是理论上的最大半径。我们认为，在0/I类阶段的星子形成是优选的，在II类阶段，因为大的气体表面密度预计和大量的尘埃是由盘吸积提供。
英文摘要：
We investigate the dust structure of gravitationally unstable disks undergoing mass accretion from the envelope envisioning the application to Class 0/I young stellar objects (YSOs) We find that the dust disk quickly settles into a steady state and that, compared to a disk with interstellar medium (ISM) dust-to-gas mass ratio and micron-sized dust, the dust mass in the steady-state decreases by a factor of 1/2 to 1/3, and the dust thermal emission decreases by a factor of 1/3 to 1/5. The latter decrease is caused by dust depletion and opacity decrease owing to dust growth. Our results suggest that the masses of gravitationally unstable disks in the Class 0/I YSOs are underestimated by a factor of 1/3 to 1/5 when calculated from the dust thermal emission assuming an ISM dust-to-gas mass ratio and micron-sized dust opacity, and that a larger fraction of disks in Class 0/I YSOs is gravitationally unstable than was previously believed. We also investigate the orbital radius $r_{\rm P}$ within which planetesimals form via coagulation of porous dust aggregates and show that $r_{\rm P}$ becomes $\sim 20$ AU for a gravitationally unstable disk around a solar mass star. Because $r_{\rm P}$ increases as the gas surface density increases and a gravitationally unstable disk has a maximum gas surface density, $r_{\rm P}\sim 20$ AU is the theoretical maximum radius. We suggest that planetesimals formation in the Class 0/I phase is preferable to that in the Class II phase because large gas surface density is expected and large amount of dust is supplied by envelope-to-disk accretion.
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