• 천문학회지
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• 제51권2호
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• pp.37-48
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• 2018

Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The amount of mechanical energy deposited in the interstellar medium by the wind from a massive star can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life. In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity due to all massive stars in the Galaxy is about ${\mathcal{L}}_w{\approx}1.1{\times}10^{41}erg\;s^{-1}$, which is about 1/4 of the power of supernova explosions, ${\mathcal{L}}_{SN}{\approx}4.8{\times}10^{41}erg\;s^{-1}$. If we assume that ~ 1 - 10 % of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds might be expected to make a significant contribution to GCR production, though lower than that of supernova remnants.

• 천문학회지
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• 제34권4호
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• pp.297-299
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• 2001

We have constructed the foundations to a series of theoretical diagnostic methods to probe the jet phenomenon in young stars as observed at various optical forbidden lines. We calculate and model in a self-consistent manner the physical and radiative processes which arise within an inner disk-wind driven magneto centrifugally from the circumstellar accretion disk of a young sun-like star. Comparing with real data taken at high angular resolution, our approach will provide the basis of systematic diagnostics for jets and their related young stellar objects, to attest the emission mechanisms of such phenomena. This work can help bring first-principle theoretical predictions to confront actual multi-wavelength observations, and will bridge the link between many very sophiscated numerical simulations and observational data. Analysis methods discussed here are immediately applicable to new high-resolution data obtained with HST and Adaptic Optics.

• 천문학회보
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• 제46권1호
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• pp.46.2-46.2
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• 2021

Presolar silicon carbide (SiC) grains form around in the envelopes of asymptotic giant branch (AGB) stars by satisfying C/O>1 which is an optimal condition for SiC grains to condense in the stellar outflows. Ruthenium (Ru) isotopes are locked into the SiC grains during the condensation of SiC grains. We investigate the isotopic compositions of Ru in the stellar winds by using the NuGrid data, which are obtained by nucleosynthesis calculations during the stellar evolution. We compare the isotopic compositions of Ru obtained from the NuGrid data with measurements and the predictions obtained from different codes. Our results present a piece of evidence that SiC grains in the presolar system came from low-mass and low-metallicity AGB stars, also confirming that they were not from massive stars. We also suggest a new scenario in which the total stellar yields are also considered because SiC grains can condense during the collapse of molecular clouds.

• 천문학회지
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• 제56권2호
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• pp.149-157
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• 2023

The propagation speed of a circumstellar pattern revealed in the plane of the sky is often assumed to represent the expansion speed of the wind matter ejected from a post-main-sequence star at the center. We point out that the often-adopted isotropic wind assumption and the binary hypothesis as the underlying origin for the circumstellar pattern in the shape of multilayered shells are, however, mutually incompatible. We revisit the hydrodynamic models for spiral-shell patterns induced by the orbital motion of a hypothesized binary, of which one star is losing mass at a high rate. The distributions of transverse wind velocities as a function of position angle in the plane of the sky are explored along viewing directions. The variation of the transverse wind velocity is as large as half the average wind velocity over the entire three dimensional domain in the simulated models investigated in this work. The directional dependence of the wind velocity is indicative of the overall morphology of the circumstellar material, implying that kinematic information is an important ingredient in modeling the snapshot monitoring (often in the optical and near-infrared) or the spectral imaging observations for molecular line emissions.

• 천문학회지
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• 제38권2호
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• pp.249-252
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• 2005

We present results of the velocity-resolved spectroscopy of the [Fe II] $\lambda$1.644${\mu}m$ emission toward outflow sources with the Subaru Telescope at the angular resolution of 0.apos;16 ${\~}$ 0.apos;5 arcseconds. The observed sources are L1551 IRS 5, DG Tau, HL Tau and RW Aur, which are located in the Taurus-Aurigae Molecular Cloud, one of the closest star forming regions (0.apos;1 = 14 AU). We were able to resolve outflow structure in the vicinity of the sources at a scale of a few tens of AU. The position-velocity diagram of each object shows two velocity components: the high velocity component (HVC: 200 - 400 km $s^{-l}$) and the low velocity component (LVC: 50 - 150 km $s^{-l}$), which are clearly distinct in space and velocity. The HVC may be a highly collimated jet presumed from its narrow velocity width and high velocity. The LVC, on the other hand, may be a widely opened disk wind inferred from its broad velocity width and low velocity. The spectrum taken perpendicular to the L1551 IRS 5 outflow at its base shows that the LVC has a spatially wide subcomponent, supporting the above interpretation. We demonstrated that the [Fe II] 1.644 $\mu$ spectroscopy is a very powerful tool for the studies of fast jets and winds that directly emanate from star-disk systems.