More Like this

1. Resolved molecular line observations reveal an inherited molecular layer in the young disk around TMC1A

   https://doi.org/10.1051/0004-6361/202038697  

   Harsono, D. ; van der Wiel, M. H. ; Bjerkeli, P. ; Ramsey, J. P. ; Calcutt, H. ; Kristensen, L. E. ; Jørgensen, J. K. ( February 2021 , Astronomy & Astrophysics)

   Context. Physical processes that govern the star and planet formation sequence influence the chemical composition and evolution of protoplanetary disks. Recent studies allude to an early start to planet formation already during the formation of a disk. To understand the chemical composition of protoplanets, we need to constrain the composition and structure of the disks from whence they are formed. Aims. We aim to determine the molecular abundance structure of the young disk around the TMC1A protostar on au scales in order to understand its chemical structure and any possible implications for disk formation. Methods. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of CO, HCO + , HCN, DCN, and SO line emission, as well as dust continuum emission, in the vicinity of TMC1A. Molecular column densities are estimated both under the assumption of optically thin emission from molecules in local thermodynamical equilibrium (LTE) as well as through more detailed non-LTE radiative transfer calculations. Results. Resolved dust continuum emission from the disk is detected between 220 and 260 GHz. Rotational transitions from HCO + , HCN, and SO are also detected from the inner 100 au region. We further report on upper limits to vibrational HCN υ 2more »= 1, DCN, and N 2 D + lines. The HCO + emission appears to trace both the Keplerian disk and the surrounding infalling rotating envelope. HCN emission peaks toward the outflow cavity region connected with the CO disk wind and toward the red-shifted part of the Keplerian disk. From the derived HCO + abundance, we estimate the ionization fraction of the disk surface, and find values that imply that the accretion process is not driven by the magneto-rotational instability. The molecular abundances averaged over the TMC1A disk are similar to its protostellar envelope and other, older Class II disks. We meanwhile find a discrepancy between the young disk’s molecular abundances relative to Solar System objects. Conclusions. Abundance comparisons between the disk and its surrounding envelope for several molecular species reveal that the bulk of planet-forming material enters the disk unaltered. Differences in HCN and H 2 O molecular abundances between the disk around TMC1A, Class II disks, and Solar System objects trace the chemical evolution during disk and planet formation.« less
2. Early Planet Formation in Embedded Disks (eDisk). III. A First High-resolution View of Submillimeter Continuum and Molecular Line Emission toward the Class 0 Protostar L1527 IRS

   https://doi.org/10.3847/1538-4357/accf87  

   van ’t Hoff, Merel L. R. ; Tobin, John J. ; Li, Zhi-Yun ; Ohashi, Nagayoshi ; Jørgensen, Jes K. ; Lin, Zhe-Yu Daniel ; Aikawa, Yuri ; Aso, Yusuke ; de Gregorio-Monsalvo, Itziar ; Gavino, Sacha ; et al ( June 2023 , The Astrophysical Journal)

   Studying the physical and chemical conditions of young embedded disks is crucial to constrain the initial conditions for planet formation. Here we present Atacama Large Millimeter/submillimeter Array observations of dust continuum at ∼0.″06 (8 au) resolution and molecular line emission at ∼0.″17 (24 au) resolution toward the Class 0 protostar L1527 IRS from the Large Program eDisk (Early Planet Formation in Embedded Disks). The continuum emission is smooth without substructures but asymmetric along both the major and minor axes of the disk as previously observed. The detected lines of¹²CO,¹³CO, C¹⁸O, H₂CO, c-C₃H₂, SO, SiO, and DCN trace different components of the protostellar system, with a disk wind potentially visible in¹²CO. The¹³CO brightness temperature and the H₂CO line ratio confirm that the disk is too warm for CO freezeout, with the snowline located at ∼350 au in the envelope. Both molecules show potential evidence of a temperature increase around the disk–envelope interface. SO seems to originate predominantly in UV-irradiated regions such as the disk surface and the outflow cavity walls rather than at the disk–envelope interface as previously suggested. Finally, the continuum asymmetry along the minor axis is consistent with the inclination derived from the large-scale (100″ or 14,000 au)more »outflow, but opposite to that based on the molecular jet and envelope emission, suggesting a misalignment in the system. Overall, these results highlight the importance of observing multiple molecular species in multiple transitions to characterize the physical and chemical environment of young disks.

   « less
3. Protoplanetary disk masses in NGC 2024: Evidence for two populations

   https://doi.org/10.1051/0004-6361/201937403  

   van Terwisga, S. E. ; van Dishoeck, E. F. ; Mann, R. K. ; Di Francesco, J. ; van der Marel, N. ; Meyer, M. ; Andrews, S. M. ; Carpenter, J. ; Eisner, J. A. ; Manara, C. F. ; et al ( August 2020 , Astronomy & Astrophysics)

   Context. Protoplanetary disks in dense, massive star-forming regions are strongly affected by their environment. How this environmental impact changes over time is an important constraint on disk evolution and external photoevaporation models. Aims. We characterize the dust emission from 179 disks in the core of the young (0.5 Myr) NGC 2024 cluster. By studying how the disk mass varies within the cluster, and comparing these disks to those in other regions, we aim to determine how external photoevaporation influences disk properties over time. Methods. Using the Atacama Large Millimeter/submillimeter Array, a 2.9′× 2.9′ mosaic centered on NGC 2024 FIR 3 was observed at 225 GHz with a resolution of 0.25″, or ~100 AU. The imaged region contains 179 disks identified at IR wavelengths, seven new disk candidates, and several protostars. Results. The overall detection rate of disks is 32 ± 4%. Few of the disks are resolved, with the exception of a giant ( R = 300 AU) transition disk. Serendipitously, we observe a millimeter flare from an X-ray bright young stellar object (YSO), and resolve continuum emission from a Class 0 YSO in the FIR 3 core. Two distinct disk populations are present: a more massive one in themore »east, along the dense molecular ridge hosting the FIR 1-5 YSOs, with a detection rate of 45 ± 7%. In the western population, towards IRS 1, only 15 ± 4% of disks are detected. Conclusions. NGC 2024 hosts two distinct disk populations. Disks along the dense molecular ridge are young (0.2–0.5 Myr) and partly shielded from the far ultraviolet radiation of IRS 2b; their masses are similar to isolated 1–3 Myr old SFRs. The western population is older and at lower extinctions, and may be affected by external photoevaporation from both IRS 1 and IRS 2b. However, it is possible these disks had lower masses to begin with.« less
4. Kinematics around the B335 protostar down to au scales

   https://doi.org/10.1051/0004-6361/201935948  

   Bjerkeli, Per ; Ramsey, Jon P. ; Harsono, Daniel ; Calcutt, Hannah ; Kristensen, Lars E. ; van der Wiel, Matthijs H. ; Jørgensen, Jes K. ; Muller, Sébastien ; Persson, Magnus V. ( November 2019 , Astronomy & Astrophysics)

   Context. The relationship between outflow launching and the formation of accretion disks around young stellar objects is still not entirely understood, which is why spectrally and spatially resolved observations are needed. Recently, the Atacama Large Millimetre/sub-millimetre Array (ALMA) carried out long-baseline observations towards a handful of young sources, revealing connections between outflows and the inner regions of disks. Aims. Here we aim to determine the small-scale kinematical and morphological properties of the outflow from the isolated protostar B335 for which no Keplerian disk has, so far, been observed on scales down to 10 au. Methods. We used ALMA in its longest-baseline configuration to observe emission from CO isotopologues, SiO, SO 2 , and CH 3 OH. The proximity of B335 provides a resolution of ~3 au (0.03′′). We also combined our long-baseline data with archival observations to produce a high-fidelity image covering scales up to 700 au (7′′). Results. 12 CO has an X-shaped morphology with arms ~50 au in width that we associate with the walls of an outflow cavity, similar to what is observed on larger scales. Long-baseline continuum emission is confined to <7 au from the protostar, while short-baseline continuum emission follows the 12 CO outflow andmore »cavity walls. Methanol is detected within ~30 au of the protostar. SiO is also detected in the vicinity of the protostar, but extended along the outflow. Conclusions. The 12 CO outflow does not show any clear signs of rotation at distances ≳30 au from the protostar. SiO traces the protostellar jet on small scales, but without obvious rotation. CH 3 OH and SO 2 trace a region <16 au in diameter, centred on the continuum peak, which is clearly rotating. Using episodic, high-velocity, 12 CO features, we estimate the launching radius of the outflow to be <0.1 au and dynamical timescales of the order of a few years.« less
5. A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS: First polarimetric detections revealing disks around DH Tau B and GSC 6214-210 B

   https://doi.org/10.1051/0004-6361/202039290  

   van Holstein, R.G. ; Stolker, T. ; Jensen-Clem, R. ; Ginski, C. ; Milli, J. ; de Boer, J. ; Girard, J.H. ; Wahhaj, Z. ; Bohn, A.J. ; Millar-Blanchaer, M.A. ; et al ( March 2021 , Astronomy & Astrophysics)

   Context. Young giant planets and brown dwarf companions emit near-infrared radiation that can be linearly polarized up to several percent. This polarization can reveal the presence of an (unresolved) circumsubstellar accretion disk, rotation-induced oblateness of the atmosphere, or an inhomogeneous distribution of atmospheric dust clouds. Aims. We aim to measure the near-infrared linear polarization of 20 known directly imaged exoplanets and brown dwarf companions. Methods. We observed the companions with the high-contrast imaging polarimeter SPHERE-IRDIS at the Very Large Telescope. We reduced the data using the IRDAP pipeline to correct for the instrumental polarization and crosstalk of the optical system with an absolute polarimetric accuracy <0.1% in the degree of polarization. We employed aperture photometry, angular differential imaging, and point-spread-function fitting to retrieve the polarization of the companions. Results. We report the first detection of polarization originating from substellar companions, with a polarization of several tenths of a percent for DH Tau B and GSC 6214-210 B in H -band. By comparing the measured polarization with that of nearby stars, we find that the polarization is unlikely to be caused by interstellar dust. Because the companions have previously measured hydrogen emission lines and red colors, the polarization most likely originatesmore »from circumsubstellar disks. Through radiative transfer modeling, we constrain the position angles of the disks and find that the disks must have high inclinations. For the 18 other companions, we do not detect significant polarization and place subpercent upper limits on their degree of polarization. We also present images of the circumstellar disks of DH Tau, GQ Lup, PDS 70, β Pic, and HD 106906. We detect a highly asymmetric disk around GQ Lup and find evidence for multiple scattering in the disk of PDS 70. Both disks show spiral-like features that are potentially induced by GQ Lup B and PDS 70 b, respectively. Conclusions. The presence of the disks around DH Tau B and GSC 6214-210 B as well as the misalignment of the disk of DH Tau B with the disk around its primary star suggest in situ formation of the companions. The non-detections of polarization for the other companions may indicate the absence of circumsubstellar disks, a slow rotation rate of young companions, the upper atmospheres containing primarily submicron-sized dust grains, and/or limited cloud inhomogeneity.« less