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Creators/Authors contains: "Liu, Hauyu Baobab"

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  1. Abstract

    In this study, we reported the results of high-resolution (${0{^{\prime \prime}_{.}}14}$) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 225 GHz dust continuum and CO molecular emission lines from the transitional disk around SY Cha. Our high-resolution observations clearly revealed the inner cavity and the central point source for the first time. The radial profile of the ring can be approximated by a bright narrow ring superimposed on a fainter wide ring. Furthermore, we found that there is a weak azimuthal asymmetry in dust continuum emission. For gas emissions, we detected 12CO(2–1), 13CO(2–1), and C18O(2–1), from which we estimated the total gas mass of the disk to be 2.2 × 10−4 M ⊙ , assuming a CO/H2 ratio of 10−4. The observations showed that the gas is present inside the dust cavity. The analysis of the velocity structure of the 12CO(2–1) emission line revealed that the velocity is distorted at the location of the dust inner disk, which may be owing to a warping of the disk or radial gas flow within the cavity of the dust disk. High-resolution observations of SY Cha showed that this system is composed of a ring and a distorted inner disk, which may be common, as indicated by themore »survey of transitional disk systems at a resolution of ${\sim}{0{^{\prime \prime}_{.}}1}$.

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  2. Abstract

    We present Atacama Large Millimeter/submillimeter Array observations with a 800 au resolution and radiative-transfer modeling of the inner part (r≈ 6000 au) of the ionized accretion flow around a compact star cluster in formation at the center of the luminous ultracompact Hiiregion G10.6-0.4. We modeled the flow with an ionized Keplerian disk with and without radial motions in its outer part, or with an external Ulrich envelope. The Markov Chain Monte Carlo fits to the data give total stellar massesMfrom 120 to 200M, with much smaller ionized-gas massesMion-gas= 0.2–0.25M. The stellar mass is distributed within the gravitational radiusRg≈ 1000 to 1500 au, where the ionized gas is bound. The viewing inclination angle from the face-on orientation isi= 49°–56°. Radial motions at radiir>Rgconverge tovr,0≈ 8.7 km s−1, or about the speed of sound of ionized gas, indicating that this gas is marginally unbound at most. From additional constraints on the ionizing-photon rate and far-IR luminosity of the region, we conclude that the stellar cluster consists of a few massive stars withMstar= 32–60M, or one star in this range of masses accompanied by a population of lower-mass stars. Any active accretion of ionized gas onto the massive (proto)stars is residual. Themore »inferred cluster density is very large, comparable to that reported at similar scales in the Galactic center. Stellar interactions are likely to occur within the next million years.

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  3. Abstract

    Characterizing the physical conditions at disk scales in class 0 sources is crucial for constraining the protostellar accretion process and the initial conditions for planet formation. We use ALMA 1.3 and 3 mm observations to investigate the physical conditions of the dust around the class 0 binary IRAS 16293–2422 A down to ∼10 au scales. The circumbinary material’s spectral index,α, has a median of 3.1 and a dispersion of ∼0.2, providing no firm evidence of millimeter-sized grains therein. Continuum substructures with brightness temperature peaks ofTb∼ 60–80 K at 1.3 mm are observed near the disks at both wavelengths. These peaks do not overlap with strong variations ofα, indicating that they trace high-temperature spots instead of regions with significant optical depth variations. The lower limits to the inferred dust temperature in the hot spots are 122, 87, and 49 K. Depending on the assumed dust opacity index, these values can be several times higher. They overlap with high gas temperatures and enhanced complex organic molecular emission. This newly resolved dust temperature distribution is in better agreement with the expectations from mechanical instead of the most commonly assumed radiative heating. In particular, we find that the temperatures agree with shock heatingmore »predictions. This evidence and recent studies highlighting accretion heating in class 0 disks suggest that mechanical heating (shocks, dissipation powered by accretion, etc.) is important during the early stages and should be considered when modeling and measuring properties of deeply embedded protostars and disks.

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