Abstract
A double-peaked profile with a stronger blue peak in a molecular line spectrum is considered strong evidence for the infall motion in the gas envelope surrounding a protostar. Some past studies performed model calculations for reproducing observed spectral profiles using simplified dynamical models such as isothermal similarity solutions. However, validity of the similarity solutions for spectral line synthesis should be examined in comparison with more realistic dynamical models.
In this paper we carry out theoretical modeling of molecular line spectra, adopting a spherically symmetric radiation hydrodynamical model for protostar formation taken from a recent work by the authors. This study concentrates on how infall motions could account for the asymmetric line profiles observed toward protostellar sources. We do not explicitly consider the effects of rotation and outflows on the generation of line profiles. In our numerical code for the non-LTE line transfer, the level populations are fully consistent with the radiation field under an arbitrary physical structure in spherical symmetry, and hence, reliable spectral synthesis has been enabled and compared to the LTE, large velocity gradient (or Sobolev), and microturbulence approximations.
Contrary to the remarks by Zhou, we do not find an overestimation of line widths, although the dynamical evolution resembles the Larson-Penston solution rather than the expansion-wave solution. Furthermore, the infall motion produces wings extending to v = ±2 km s-1 in line spectra, in contrast to previous works where wings could not be produced by infall models. These results imply that simplified infall models, such as the isothermal similarity solutions adopted by previous authors, are not always suitable to the detailed modeling of line spectra.
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