| 1. |
- Carrasco-Gonzalez, C., et al.
(författare)
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Observing the onset of outflow collimation in a massive protostar
- 2015
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 348:6230, s. 114-117
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Tidskriftsartikel (refereegranskat)abstract
- The current paradigm of star formation through accretion disks, and magnetohydrodynamically driven gas ejections, predicts the development of collimated outflows, rather than expansion without any preferential direction. We present radio continuum observations of the massive protostar W75N(B)-VLA 2, showing that it is a thermal, collimated ionized wind and that it has evolved in 18 years from a compact source into an elongated one. This is consistent with the evolution of the associated expanding water-vapor maser shell, which changed from a nearly circular morphology, tracing an almost isotropic outflow, to an elliptical one outlining collimated motions. We model this behavior in terms of an episodic, short-lived, originally isotropic ionized wind whose morphology evolves as it moves within a toroidal density stratification.
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| 2. |
- Sanna, A., et al.
(författare)
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Velocity and magnetic fields within 1000 AU of a massive YSO
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 583, s. L3-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: We study the velocity and magnetic field morphology in the vicinity ( 600 AU) of the molecular envelope, where the magnetic field orientation shows a smooth change with the maser cloudlets position (0.2° AU-1). Overall, the velocity field vectors accommodate the local magnetic field direction well, but still show an average misalignment of 30°. We interpret this finding as the contribution of a turbulent velocity field of about 3.5 km s-1, which would be responsible for breaking up the alignment between the velocity and magnetic field vectors. We do resolve different gas flows that develop both along the outflow axis and across the disk plane and that have an average speed of 7 km s-1. In the direction of the outflow axis, we establish a collimation of the gas flow at a distance of about 1000 AU from the disk plane. In the disk region, gas appears to stream outward along the disk plane for radii greater than 500-600 AU and inward for shorter radii.
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