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تسجيل مستخدم جديدThe Winds from HL Tau
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Outflowing motions, whether a wind launched from the disk, a jet launched from the protostar, or the entrained molecular outflow, appear to be an ubiquitous feature of star formation. These outwards motions have a number of root causes, and how they manifest is intricately linked to their environment as well as the process of star formation itself. Using the ALMA Science Verification data of HL Tau, we investigate the high velocity molecular gas being removed from the system as a result of the star formation process. We aim to place these motions in context with the optically detected jet, and the disk. With these high resolution ($sim 1$) ALMA observations of CO (J=1-0), we quantify the outwards motions of the molecular gas. We find evidence for a bipolar outwards flow, with an opening angle, as measured in the red-shifted lobe, starting off at 90$^circ$, and narrowing to 60$^circ$ further from the disk, likely because of magnetic collimation. Its outwards velocity, corrected for inclination angle is of order 2.4 km s$^{-1}$.
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The mechanism of angular momentum transport in protoplanetary disks is fundamental to understand the distributions of gas and dust in the disks. The unprecedented, high spatial resolution ALMA observations taken toward HL Tau and subsequent radiative
transfer modeling reveal that a high degree of dust settling is currently achieved at the outer part of the HL Tau disk. Previous observations however suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppress dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma $beta$ at the disk midplane is $beta_0 simeq 2 times 10^4$ under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.
Recent ALMA images of HL Tau show gaps in the dusty disk that may be caused by planetary bodies. Given the young age of this system, if confirmed, this finding would imply very short timescales for planet formation, probably in a gravitationally unst
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Dust polarization at (sub)millimeter wavelengths has been observed for many protoplanetary disks. Theoretically, multiple origins potentially contribute to the polarized emission but it is still uncertain what mechanism is dominant in disk millimeter
polarization. To quantitatively address the origin, we perform radiative transfer calculations of the mixture of alignment and self-scattering induced polarization to reproduce the 3.1 mm polarization of the HL Tau disk, which shows azimuthal pattern in polarization vectors. We find that a mixture of the grain alignment and self-scattering is essential to reproduce the HL Tau 3.1 mm polarization properties. Our model shows that the polarization of the HL Tau at 3.1 mm can be decomposed to be the combination of the self-scattering parallel to the minor axis and the alignment-induced polarization parallel to the major axis, with the orders of $sim 0.5%$ fraction for each component. This slightly eases the tight constraints on the grain size of $sim 70~{rm~mu m}$ to be $sim 130 {rm~mu m}$ in the previous studies but further modeling is needed. In addition, the grain alignment model requires effectively prolate grains but the physics to reproduce it in protoplanetary disks is still a mystery.
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We present archival high angular resolution ($sim$ 2$$) $^{12}$CO(3-2) line and continuum submillimeter observations of the young stellar object HL Tau made with the Submillimeter Array (SMA). The $^{12}$CO(3-2) line observations reveal the presence
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