ABSTRACT The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887 m survey of ...the disk population around objects from ∼2 to 0.03 M in the nearby ∼2 Myr old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887 m flux densities into dust disk masses, hereafter Mdust. We find that the relation is steeper than linear and of the form Mdust ∝ (M*)1.3-1.9, where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1-3 Myr old regions of Taurus, Lupus, and Chamaeleon I share the same relation, while the 10 Myr old Upper Sco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.
We present Atacama Large Millimeter/Sub-Millimeter Array (ALMA) Band 6 observations of a complete sample of protoplanetary disks in the young (∼1-3 Myr) Lupus star-forming region, covering the 1.33 ...mm continuum and the 12CO, 13CO, and C18O J = 2-1 lines. The spatial resolution is ∼0 25 with a medium 3 continuum sensitivity of 0.30 mJy, corresponding to Mdust ∼ 0.2 M⊕. We apply Keplerian masking to enhance the signal-to-noise ratios of our 12CO zero-moment maps, enabling measurements of gas disk radii for 22 Lupus disks; we find that gas disks are universally larger than millimeter dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission and the growth and inward drift of the dust. Using the gas disk radii, we calculate the dimensionless viscosity parameter, visc, finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in Lupus disks. By combining our 1.33 mm continuum fluxes with our previous 890 m continuum observations, we also calculate the millimeter spectral index, mm, for 70 Lupus disks; we find an anticorrelation between mm and millimeter flux for low-mass disks (Mdust 5), followed by a flattening as disks approach mm 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. In sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased ALMA disk surveys.
Context. Analyzing the properties of dust and its evolution in the early phases of star formation is crucial to put constraints on the collapse and accretion processes as well as on the pristine ...properties of planet-forming seeds. Aims. In this paper, we aim to investigate the variations of the dust grain size in the envelopes of the youngest protostars. Methods. We analyzed Plateau de Bure interferometric observations at 1.3 and 3.2 mm for 12 Class 0 protostars obtained as part of the CALYPSO survey. We performed our analysis in the visibility domain and derived dust emissivity index (β1−3mm) profiles as a function of the envelope radius at 200–2000 au scales. Results. Most of the protostellar envelopes show low dust emissivity indices decreasing toward the central regions. The decreasing trend remains after correction of the (potentially optically thick) central region emission, with surprisingly low β1−3mm < 1 values across most of the envelope radii of NGC 1333-IRAS 4A, NGC 1333-IRAS 4B, SVS13B, and Serpens-SMM4. Conclusions. We discuss the various processes that could explain such low and varying dust emissivity indices at envelope radii 200–2000 au. Our observations of extremely low dust emissivity indices could trace the presence of large (millimeter-size) grains in Class 0 envelopes, in which case our results would point to a radial increase of the dust grain size toward the inner envelope regions. While it is expected that large grains in young protostellar envelopes could be built via grain growth and coagulation, we stress that the typical timescales required to build millimeter grains in current coagulation models are at odds with the youth of our Class 0 protostars. Additional variations in the dust composition could also partly contribute to the low β1−3mm we observe. We find that the steepness of the β1−3mm radial gradient depends strongly on the envelope mass, which might favor a scenario in which large grains are built in high-density protostellar disks and transported to the intermediate envelope radii, for example with the help of outflows and winds.
Aims. We attempt to explain grain growth to mm sized particles and their retention in the outer regions of protoplanetary disks, as observed at sub-mm and mm wavelengths, by investigating whether ...strong inhomogeneities in the gas density profiles can decelerate excessive radial drift and help the dust particles to grow. Methods. We use coagulation/fragmentation and disk-structure models, to simulate the evolution of dust in a bumpy surface density profile, which we mimic with a sinusoidal disturbance. For different values of the amplitude and length scale of the bumps, we investigate the ability of this model to produce and retain large particles on million-year timescales. In addition, we compare the pressure inhomogeneities considered in this work with the pressure profiles that come from magnetorotational instability. Using the Common Astronomy Software Applications ALMA simulator, we study whether there are observational signatures of these pressure inhomogeneities that can be seen with ALMA. Results. We present the conditions required to trap dust particles and the corresponding calculations predicting the spectral slope in the mm-wavelength range, to compare with current observations. Finally, we present simulated images using different antenna configurations of ALMA at different frequencies, to show that the ring structures will be detectable at the distances of either the Taurus Auriga or Ophiucus star-forming regions.
ABSTRACT We present the first high-resolution sub-millimeter survey of both dust and gas for a large population of protoplanetary disks. Characterizing fundamental properties of protoplanetary disks ...on a statistical level is critical to understanding how disks evolve into the diverse exoplanet population. We use the Atacama Large Millimeter/Submillimeter Array (ALMA) to survey 89 protoplanetary disks around stars with in the young (1-3 Myr), nearby (150-200 pc) Lupus complex. Our observations cover the 890 m continuum and the 13CO and C18O 3-2 lines. We use the sub-millimeter continuum to constrain to a few Martian masses (0.2-0.4 M⊕) and the CO isotopologue lines to constrain to roughly a Jupiter mass (assuming an interstellar medium (ISM)-like abundance). Of 89 sources, we detect 62 in continuum, 36 in 13CO, and 11 in C18O at significance. Stacking individually undetected sources limits their average dust mass to Lunar masses (0.03 M⊕), indicating rapid evolution once disk clearing begins. We find a positive correlation between and M*, and present the first evidence for a positive correlation between and M*, which may explain the dependence of giant planet frequency on host star mass. The mean dust mass in Lupus is 3× higher than in Upper Sco, while the dust mass distributions in Lupus and Taurus are statistically indistinguishable. Most detected disks have and gas-to-dust ratios , assuming an ISM-like abundance; unless CO is very depleted, the inferred gas depletion indicates that planet formation is well underway by a few Myr and may explain the unexpected prevalence of super-Earths in the exoplanet population.
ABSTRACT
We predict magnitudes for young planets embedded in transition discs, still affected by extinction due to material in the disc. We focus on Jupiter-sized planets at a late stage of their ...formation, when the planet has carved a deep gap in the gas and dust distributions and the disc starts to being transparent to the planet flux in the infrared (IR). Column densities are estimated by means of three-dimensional hydrodynamical models, performed for several planet masses. Expected magnitudes are obtained by using typical extinction properties of the disc material and evolutionary models of giant planets. For the simulated cases located at 5.2 au in a disc with a local unperturbed surface density of 127 $\mathrm{g} \, \mathrm{cm}^{-2}$, a 1MJ planet is highly extinct in the J, H, and Kbands, with predicted absolute magnitudes ≥ 50 mag. In the L and Mbands, extinction decreases, with planet magnitudes between 25 and 35 mag. In the Nband, due to the silicate feature on the dust opacities, the expected magnitude increases to ∼40 mag. For a 2MJ planet, the magnitudes in the J, H, and Kbands are above 22 mag, while for the L, M, and Nbands, the planet magnitudes are between 15 and 20 mag. For the 5MJ planet, extinction does not play a role in any IR band, due to its ability to open deep gaps. Contrast curves are derived for the transition discs in CQ Tau, PDS 70, HL Tau, TW Hya, and HD 163296. Planet mass upper limits are estimated for the known gaps in the last two systems.
Context.
Understanding the initial properties of star forming material and how they affect the star formation process is a key question. The infalling gas must redistribute most of its initial ...angular momentum inherited from prestellar cores before reaching the central stellar embryo. Disk formation has been naturally considered as a possible solution to this “angular momentum problem”. However, how the initial angular momentum of protostellar cores is distributed and evolves during the main accretion phase and the beginning of disk formation has largely remained unconstrained up to now.
Aims.
In the framework of the IRAM CALYPSO survey, we obtained observations of the dense gas kinematics that we used to quantify the amount and distribution of specific angular momentum at all scales in collapsing-rotating Class 0 protostellar envelopes.
Methods.
We used the high dynamic range C
18
O (2−1) and N
2
H
+
(1−0) datasets to produce centroid velocity maps and probe the rotational motions in the sample of 12 envelopes from scales ~50 to ~5000 au.
Results.
We identify differential rotation motions at scales ≲1600 au in 11 out of the 12 protostellar envelopes of our sample by measuring the velocity gradient along the equatorial axis, which we fit with a power-law model v ∝
r
α
. This suggests that coherent motions dominate the kinematics in the inner protostellar envelopes. The radial distributions of specific angular momentum in the CALYPSO sample suggest the following two distinct regimes within protostellar envelopes: the specific angular momentum decreases as
j
∝
r
1.6±0.2
down to ~1600 au and then tends to become relatively constant around ~6 × 10
−4
km s
−1
pc down to ~50 au.
Conclusions.
The values of specific angular momentum measured in the inner Class 0 envelopes suggest that material directly involved in the star formation process (<1600 au) has a specific angular momentum on the same order of magnitude as what is inferred in small T-Tauri disks. Thus, disk formation appears to be a direct consequence of angular momentum conservation during the collapse. Our analysis reveals a dispersion of the directions of velocity gradients at envelope scales >1600 au, suggesting that these gradients may not be directly related to rotational motions of the envelopes. We conclude that the specific angular momentum observed at these scales could find its origin in other mechanisms, such as core-forming motions (infall, turbulence), or trace an imprint of the initial conditions for the formation of protostellar cores.
Context. The formation of planets strongly depends on the total amount as well as on the spatial distribution of solids in protoplanetary disks. Thanks to the improvements in resolution and ...sensitivity provided by ALMA, measurements of the surface density of mm-sized grains are now possible on large samples of disks. Such measurements provide statistical constraints that can be used to inform our understanding of the initial conditions of planet formation. Aims. We aim to analyze spatially resolved observations of 36 protoplanetary disks in the Lupus star forming complex from our ALMA survey at 890 μm, aiming to determine physical properties such as the dust surface density, the disk mass and size, and to provide a constraint on the temperature profile. Methods. We fit the observations directly in the uv-plane using a two-layer disk model that computes the 890 μm emission by solving the energy balance at each disk radius. Results. For 22 out of 36 protoplanetary disks we derive robust estimates of their physical properties. The sample covers stellar masses between ~0.1 and ~ 2 M⊙, and we find no trend in the relationship between the average disk temperatures and the stellar parameters. We find, instead, a correlation between the integrated sub-mm flux (a proxy for the disk mass) and the exponential cut-off radii (a proxy of the disk size) of the Lupus disks. Comparing these results with observations at similar angular resolution of Taurus-Auriga and Ophiuchus disks found in literature and scaling them to the same distance, we observe that the Lupus disks are generally fainter and larger at a high level of statistical significance. Considering the 1–2 Myr age difference between these regions, it is possible to tentatively explain the offset in the disk mass-size relation with viscous spreading, however with the current measurements other mechanisms cannot be ruled out.
ABSTRACT Star formation is primarily controlled by the interplay between gravity, turbulence, and magnetic fields. However, the turbulence and magnetic fields in molecular clouds near the Galactic ...center may differ substantially compared to spiral-arm clouds. Here we determine the physical parameters of the central molecular zone (CMZ) cloud G0.253+0.016, its turbulence, magnetic field, and filamentary structure. Using column density maps based on dust-continuum emission observations with ALMA+Herschel, we identify filaments and show that at least one dense core is located along them. We measure the filament width and the sonic scale of the turbulence, and find . A strong velocity gradient is seen in the HNCO intensity-weighted velocity maps obtained with ALMA+Mopra. The gradient is likely caused by large-scale shearing of G0.253+0.016, producing a wide double-peaked velocity probability distribution function (PDF). After subtracting the gradient to isolate the turbulent motions, we find a nearly Gaussian velocity PDF typical for turbulence. We measure the total and turbulent velocity dispersion, and , respectively. Using magnetohydrodynamical turbulence simulations, we find that G0.253+0.016's turbulent magnetic field is only of the ordered field component. Combining these measurements, we reconstruct the dominant turbulence driving mode in G0.253+0.016 and find a driving parameter of , indicating solenoidal (divergence-free) driving. We compare this to spiral-arm clouds, which typically have a significant compressive (curl-free) driving component ( ). Motivated by previous reports of strong shearing motions in the CMZ, we speculate that shear causes the solenoidal driving in G0.253+0.016 and show that this reduces the star-formation rate by a factor of 6.9 compared to typical nearby clouds.
ABSTRACT
We present MUSE integral field data of two H ii region complexes in the Large Magellanic Cloud: N44 and N180. Both regions consist of a main superbubble and a number of smaller, more compact ...H ii regions that formed on the edge of the superbubble. For a total of 11 H ii regions, we systematically analyse the radiative and mechanical feedback from the massive O-type stars on the surrounding gas. We exploit the integral field property of the data and the coverage of the He ii λ5412 line to identify and classify the feedback-driving massive stars and from the estimated spectral types and luminosity classes we determine the stellar radiative output in terms of the ionizing photon flux Q0. We characterize the H ii regions in terms of their sizes, morphologies, ionization structure, luminosity and kinematics, and derive oxygen abundances via emission line ratios. We analyse the role of different stellar feedback mechanisms for each region by measuring the direct radiation pressure, the pressure of the ionized gas, and the pressure of the shock-heated winds. We find that stellar winds and ionized gas are the main drivers of H ii region expansion in our sample, while the direct radiation pressure is up to three orders of magnitude lower than the other terms. We relate the total pressure to the star formation rate per unit area, ΣSFR, for each region and find that stellar feedback has a negative effect on star formation, and sets an upper limit to ΣSFR as a function of increasing pressure.