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Antilen, J., Casassus, S., Cieza, L. A., & Gonzalez-Ruilova, C. (2023). Gas distribution in ODISEA sources from ALMA long-baseline observations in (CO)-C-12(2-1). Mon. Not. Roy. Astron. Soc., 522(2), 2611–2627.
Abstract: The (CO)-C-12 rotational lines in protoplanetary discs are good tracers of the total spatial extension of the gas component, and potentially planet-disc interactions. We present ALMA long baseline observations of the (CO)-C-12(2-1) line of 10 protoplanetary discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project, aiming to set constraints on the gas distribution of these sources. The position angle of the gaseous disc can be inferred for five sources using high-velocity channels, which trace the gas in the inner part of the disc. We compare the high-velocity PAs to the orientations inferred from the continuum, representative of the orientation over similar to 53 to 256 au in these resolved discs. We find a significant difference in orientation for DoAr 44, which is evidence of a tilted inner disc. Eight discs show evidence of gas inside inner dust cavities or gaps, and the disc of ISO-Oph 196 is not detected in (CO)-C-12(2-1), except for the compact signal located inside its dust cavity. Our observations also point out a possible outflow in WLY 2-63.
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Casassus, S., & Carcamo, M. (2022). Variable structure in the PDS 70 disc and uncertainties in radio-interferometric image restoration. Mon. Not. Roy. Astron. Soc., 513(4), 5790–5798.
Abstract: The compact mm-wavelength signal in the central cavity of the PDS 70 disc, revealed by deep ALMA observations, is aligned with unresolved H alpha emission, and is thought to stem from a circumplanetary disc (CPD) around PDS 70c. We revisit the available ALMA data on PDS 70c with alternative imaging strategies, and with special attention to uncertainties and to the impact of the so-called 'JvM correction', which is thought to improve the dynamic range of restored images. We also propose a procedure for the alignment and joint imaging of multi-epoch visibility data. We find that the JvM correction exaggerates the peak signal-to-noise of the data, by up to a factor of 10. In the case of PDS 70, we recover the detection of PDS 70c from the 2019 July data, but only at 8 sigma. However, its non-detection in 2017 Dec. suggests that PDS 70c is variable by at least 42 per cent +/- 13 per cent over a 1.75 yr time-span, so similar to models of the H alpha variability. We also pick up fine structure in the inner disc, such that its peak is offset by similar to 0 ''.04 from the disc centre. The inner disc is variable too, which we tentatively ascribe to Keplerian rotation as well as intrinsic morphological changes.
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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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Casassus, S., Christiaens, V., Carcamo, M., Perez, S., Weber, P., Ercolano, B., et al. (2021). A dusty filament and turbulent CO spirals in HD 135344B-SAO 206462. Mon. Not. Roy. Astron. Soc., 507(3), 3789–3809.
Abstract: Planet-disc interactions build up local pressure maxima that may halt the radial drift of protoplanetary dust, and pile it up in rings and crescents. ALMA observations of the HD 135344B disc revealed two rings in the thermal continuum stemming from similar to mm-sized dust. At higher frequencies the inner ring is brighter relative to the outer ring, which is also shaped as a crescent rather than a full ring. In near-IR scattered light images, the disc is modulated by a two-armed grand-design spiral originating inside the ALMA inner ring. Such structures may be induced by a massive companion evacuating the central cavity, and by a giant planet in the gap separating both rings, that channels the accretion of small dust and gas through its filamentary wakes while stopping the larger dust from crossing the gap. Here we present ALMA observations in the J = (2 – 1) CO isotopologue lines and in the adjacent continuum, with up to 12 km baselines. Angular resolutions of similar to 0 ''.03 reveal the tentative detection of a filament connecting both rings, and which coincides with a local discontinuity in the pitch angle of the IR spiral, proposed previously as the location of the protoplanet driving this spiral. Line diagnostics suggests that turbulence, or superposed velocity components, is particularly strong in the spirals. The (CO)-C-12(2-1) 3D rotation curve points at stellocentric accretion at radii within the inner dust ring, with a radial velocity of up to similar to 5 per cent +/- 0.5 per cent Keplerian, which corresponds to an excessively large accretion rate of similar to 2 x 10(-6) M circle dot yr(-1) if all of the CO layer follows the (CO)-C-12(2-1) kinematics. This suggests that only the surface layers of the disc are undergoing accretion, and that the line broadening is due to superposed laminar flows.
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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.
Keywords: ASYMPTOTIC GIANT BRANCH; INFRARED-SPECTROSCOPY; STARS; EVOLUTION; CO; DEUTERIUM; ACCRETION; SPECTRA; CONSTRAINTS; OPHIUCHUS
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