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内容記述 |
In the last two decades, the development of millimeters interferometers has enabled us to establish a standard scenario of sun-like (<i>M</i><sub>*</sub>～1 <i>M</i><small>Θ</small> ) star formation. However, details of formation and evolution of more massive stars (≥2 <i>M</i><small>Θ</small>, that is, intermediate- and high-mass protostars, remain poorly understood. Studies of the formation and evolution of intermediate-mass protostars will allow us to understand whether the established low-mass star-formation scenario is applicable to a wide range of protostar masses. However, there is no systematic observation toward interemediate-mass protostars. It is important to directly verify the accretion and dissipation (or destruction) processes of dense gas envelopes around intermediate-mass protostars. For these purpose, The author has performed multi-wavelength and multi-line survey observations toward intermediate-mass pre- and proto-stellar candidates in the Orion Molecular Cloud -2/3 region (OMC- 2/3）. The OMC- 2/3 region is one of the best targets to conduct asystematic survey of intermediate-mass protostars, because all of the sources are in the same distance and under the similar starforming environment.<br /><br /> Using the NMA, ASTE and SIRIUS / IRSF, The author observed the 3.3 mm dust continuum, H<sup>13</sup>CO<sup>＋</sup>(1-0), CO(1-0), CO(3-2) emissions, and near infrared (<i>JHK<small>s</small></i> band) continuum emissions toward the entire sample of intermediate-mass pre- and proto-stellar candidates in the Orion Molecular Cloud-2/3 region (OMC-2/3). Based on our H<sup>13</sup>CO<sup>＋</sup>(1-0), 3.3 mm continuum, CO(3-2) and <i>JHK<small>s</small></i> results, combined with the published VLA 3.6 cm and the archived 24 <i>mu</i>m data taken by Spitzer, The author unveiled the evolutionary changes, morphology and velocity structures of the dense envelopes and accompanied CO outflows around intermediate-mass protostars for the first time. The author classified these intermediate-mass pre- and proto-stellar candidates into three evolutionary phases as (i) pre-stellar phase, (ii) Class A phase, and (iii) Class B phase. Pre-stellar sources have no compact dusty emission taken with the NMA and 24 μm source, suggesting no any signature of dense (>10<sup>7</sup>cm<sup>-3</sup>) and hot (>100 K) envelopes. In this phase, there are no signature of jets/outflows. Class A sources are corresponding to the earlier evolutionary phase of the protosterllar cores, which are associated with compact dust emission and 24μm sources, suggesting the presence of the heating source. 0.1 pc scale CO outflows are also detected in this phase. Finally, Class B sources correspond to the later evolutionary phase of the protostellar cores, which are associated with the compact dust and 24 μm sources. 0.5-1.0 pc scale CO outflow and free-free jet are associated with these objects. In addition, our <i>JHK</i><small>s</small> images show a reflection nebula, suggesting the formation of the cavity along the CO outflows. In this phase, the author detected fan-shaped H<sup>13</sup>CO<sup>＋</sup> envelops with a size scale of 0.1 pc.<br /><br /> The author also found that the CO outflow momentum increases from the evolutionary sequence of Class A to Class B. The 24 μm peak flux also increases from the evolutionary sequence of Class A to Class B. The author suggests that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e., the CO outflow destroys the envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential role in the evolution of the intermediate-mass protostars. |
要旨・審査要旨 (295.2 kB)
