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Casassus, S., Carcamo, M., Hales, A., Weber, P., & Dent, B. (2022). The Doppler Flip in HD 100546 as a Disk Eruption: The Elephant in the Room of Kinematic Protoplanet Searches. Astrophys. J. Lett., 933(1), L4.
Abstract: The interpretation of molecular-line data using hydrodynamical simulations of planet-disk interactions fosters new hope for the indirect detection of protoplanets. In a model-independent approach, embedded protoplanets should be found at the roots of abrupt Doppler flips in velocity centroid maps. However, the largest velocity perturbation known for an unwarped disk, in the disk of HD 100546, leads to a conspicuous Doppler flip that coincides with a thick dust ring, in contradiction with an interpretation in terms of a greater than or similar to 1 M-jup body. Here we present new ALMA observations of the (CO)-C-12(2-1) kinematics in HD 100546, with a factor of 2 finer angular resolutions. We find that the disk rotation curve is consistent with a central mass 2.1 < M-*/M-circle dot < 2.3 and that the blueshifted side of the Doppler flip is due to vertical motions, reminiscent of the disk wind proposed previously from blueshifted SO lines. We tentatively propose a qualitative interpretation in terms of a surface disturbance to the Keplerian flow, i.e., a disk eruption, driven by an embedded outflow launched by a similar to 10 M-earth body. Another interpretation involves a disk-mass-loading hot spot at the convergence of an envelope accretion streamer.
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Nogueira, P. H., Zurlo, A., Perez, S., Gonzalez-Ruilova, C.,, Cieza, L. A., Hales, A., et al. (2023). Resolving the binary components of the outbursting protostar HBC 494 with ALMA. Mon. Not. Roy. Astron. Soc., 523(4), 4970–4991.
Abstract: Episodic accretion is a low-mass pre-main sequence phenomenon characterized by sudden outbursts of enhanced accretion. These objects are classified into two: protostars with elevated levels of accretion that lasts for decades or more, called FUors, and protostars with shorter and repetitive bursts, called EXors. HBC 494 is a FUor object embedded in the Orion Molecular Cloud. Earlier Atacama Large (sub-)Millimeter Array (ALMA) continuum observations showed an asymmetry in the disc at 0.“2 resolution. Here, we present follow-up observations at similar to 0.”03, resolving the system into two components: HBC 494 N (primary) and HBC 494 S (secondary). No circumbinary disc was detected. Both discs are resolved with a projected separation of similar to 0."18 (75 au). Their projected dimensions are 84 +/- 1.8 x66.9 +/- 1.5 mas for HBC 494 N and 64.6 +/- 2.5 x46.0 +/- 1.9 mas for HBC 494 S. The discs are almost aligned and with similar inclinations. The observations show that the primary is similar to 5 times brighter/more massive and similar to 2 times bigger than the secondary. We notice that the northern component has a similar mass to the FUors, while the southern has to EXors. The HBC 494 discs show individual sizes that are smaller than single eruptive YSOs. In this work, we also report (CO)-C-12, (CO)-C-13, and (CO)-O-18 molecular line observations. At large scale, the (CO)-C-12 emission shows bipolar outflows, while the (CO)-C-13 and (CO)-O-18 maps show a rotating and infalling envelope around the system. At a smaller scale, the (CO)-C-12 and (CO)-C-13 moment zero maps show cavities within the continuum discs' area, which may indicate continuum over-subtraction or slow-moving jets and chemical destruction along the line of sight.
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Ruiz-Rodriguez, D. A., Cieza, L. A., Casassus, S., Almendros-Abad, V., Jofre, P., Muzic, K., et al. (2022). Discovery of a Brown Dwarf with Quasi-spherical Mass Loss. Astrophys. J., 938(1), 54.
Abstract: We report the serendipitous discovery of an elliptical shell of CO associated with the faint stellar object SSTc2d J163134.1-240060 as part of the “Ophiuchus Disk Survey Employing ALMA” (ODISEA), a project aiming to study the entire population of protoplanetary disks in the Ophiuchus Molecular Cloud from 230 GHz continuum emission and (CO)-C-12 (J = 2-1), (CO)-C-13 (J = 2-1) and (CCO)-C-18 (J = 2-1) lines readable in Band 6. Remarkably, we detect a bright (CO)-C-12 elliptical shape emission of similar to 3 '' x 4 '' toward SSTc2d J163134.1-240060 without a 230 GHz continuum detection. Based on the observed near-IR spectrum taken with the Very Large Telescope (KMOS), the brightness of the source, its three-dimensional motion, and Galactic dynamic arguments, we conclude that the source is not a giant star in the distant background (>5-10 kpc) and is most likely to be a young brown dwarf in the Ophiuchus cloud, at a distance of just similar to 139 pc. This is the first report of quasi-spherical mass loss in a young brown dwarf. We suggest that the observed shell could be associated with a thermal pulse produced by the fusion of deuterium, which is not yet well understood, but for a substellar object is expected to occur during a short period of time at an age of a few Myr, in agreement with the ages of the objects in the region. Other more exotic scenarios, such as a merger with planetary companions, cannot be ruled out from the current observations.
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