ABSTRACT The recent ALMA observations of the disk surrounding HL Tau reveal a very complex dust spatial distribution. We present a radiative transfer model accounting for the observed gaps and bright ...rings as well as radial changes of the emissivity index. We find that the dust density is depleted by at least a factor of 10 in the main gaps compared to the surrounding rings. Ring masses range from 10-100 M⊕ in dust, and we find that each of the deepest gaps is consistent with the removal of up to 40 M⊕ of dust. If this material has accumulated into rocky bodies, these would be close to the point of runaway gas accretion. Our model indicates that the outermost ring is depleted in millimeter grains compared to the central rings. This suggests faster grain growth in the central regions and/or radial migration of the larger grains. The morphology of the gaps observed by ALMA-well separated and showing a high degree of contrast with the bright rings over all azimuths-indicates that the millimeter dust disk is geometrically thin (scale height 1 AU at 100 AU) and that a large amount of settling of large grains has already occurred. Assuming a standard dust settling model, we find that the observations are consistent with a turbulent viscosity coefficient of a few 10−4. We estimate the gas/dust ratio in this thin layer to be of the order of 5 if the initial ratio is 100. The HCO+ and CO emission is consistent with gas in Keplerian motion around a 1.7 M star at radii from ≤10-120 AU.
Disks of gas and dust surrounding young stars are the birthplace of planets. However, the direct detection of protoplanets forming within disks has proved elusive to date. We present the detection of ...a large, localized deviation from Keplerian velocity in the protoplanetary disk surrounding the young star HD 163296. The observed velocity pattern is consistent with the dynamical effect of a two-Jupiter-mass planet orbiting at a radius 260 au from the star.
ABSTRACT
We present ALMA images of the sub-mm continuum polarization and spectral index of the protoplanetary ringed disc HD163296. The polarization fraction at 870 µm is measured to be ∼0.9 per cent ...in the central core and generally increases with radius along the disc major axis. It peaks in the gaps between the dust rings, and the largest value (∼4 per cent) is found between rings 1 and 2. The polarization vectors are aligned with the disc minor axis in the central core, but become more azimuthal in the gaps, twisting by up to ±9° in the gap between rings 1 and 2. These general characteristics are consistent with a model of self-scattered radiation in the ringed structure, without requiring an additional dust alignment mechanism. The 870/1300 µm dust spectral index exhibits minima in the centre and the inner rings, suggesting these regions have high optical depths. However, further refinement of the dust or the disc model at higher resolution is needed to reproduce simultaneously the observed degree of polarization and the low spectral index.
Here we present deep (16 Jy beam−1), very high (40 mas) angular resolution 1.14 mm, polarimetric, Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protostar driving ...the HH 80-81 radio jet. The observations clearly resolve the disk oriented perpendicularly to the radio jet, with a radius of 0 171 (∼291 au at 1.7 kpc distance). The continuum brightness temperature, the intensity profile, and the polarization properties clearly indicate that the disk is optically thick for a radius of R 170 au. The linear polarization of the dust emission is detected almost all along the disk, and its properties suggest that dust polarization is produced mainly by self-scattering. However, the polarization pattern presents a clear differentiation between the inner (optically thick) part of the disk and the outer (optically thin) region of the disk, with a sharp transition that occurs at a radius of ∼0 1 (∼170 au). The polarization characteristics of the inner disk suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 m. The outer part of the disk has a clear azimuthal pattern but with a significantly higher polarization fraction compared to the inner disk. This pattern is broadly consistent with the self-scattering of a radiation field that is beamed radially outward, as expected in the optically thin outer region, although contribution from non-spherical grains aligned with respect to the radiative flux cannot be excluded.
Context.
Observations at millimeter wavelengths of bright protoplanetary disks have shown the ubiquitous presence of structures such as rings and spirals in the continuum emission. The derivation of ...the underlying properties of the emitting material is nontrivial because of the complex radiative processes involved.
Aims.
In this paper we analyze new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and the
Karl G. Jansky
Very Large Array (VLA) at high angular resolution corresponding to 5 – 8 au to determine the dust spatial distribution and grain properties in the ringed disk of HD 163296.
Methods.
We fit the spectral energy distribution as a function of the radius at five wavelengths from 0.9 to 9 mm, using a simple power law and a physical model based on an analytic description of radiative transfer that includes isothermal scattering. We considered eight dust populations and compared the models' performance using Bayesian evidence.
Results.
Our analysis shows that the moderately high optical depth (
τ
>1) at
λ ≤
1.3 mm in the dust rings artificially lower the millimeter spectral index, which should therefore not be considered as a reliable direct proxy of the dust properties and especially the grain size. We find that the outer disk is composed of small grains on the order of 200 µm with no significant difference between rings at 66 and 100 au and the adjacent gaps, while in the innermost ~30 au, larger grains (≥mm) could be present. We show that the assumptions on the dust composition have a strong impact on the derived surface densities and grain size. In particular, increasing the porosity of the grains to 80% results in a total dust mass about five times higher with respect to grains with 25% porosity. Finally, we find that the derived opacities as a function of frequency deviate from a simple power law and that grains with a lower porosity seem to better reproduce the observations of HD 163296.
Conclusions.
While we do not find evidence of differential trapping in the rings of HD 163296, our overall results are consistent with the postulated presence of giant planets affecting the dust temperature structure and surface density, and possibly originating a second-generation dust population of small grains.
We present Atacama Large Millimeter and Submillimeter Array observations of the protoplanetary disk around the Herbig Ae star HD 163296 that trace the spatial distribution of millimeter-sized ...particles and cold molecular gas on spatial scales as small as 25 astronomical units (A.U.). The image of the disk recorded in the 1.3 mm continuum emission reveals three dark concentric rings that indicate the presence of dust depleted gaps at about 60, 100, and 160 A.U. from the central star. The maps of the ^{12}CO, ^{13}CO, and C^{18}O J=2-1 emission do not show such structures but reveal a change in the slope of the radial intensity profile across the positions of the dark rings in the continuum image. By comparing the observations with theoretical models for the disk emission, we find that the density of CO molecules is reduced inside the middle and outer dust gaps. However, in the inner ring there is no evidence of CO depletion. From the measurements of the dust and gas densities, we deduce that the gas-to-dust ratio varies across the disk and, in particular, it increases by at least a factor 5 within the inner dust gap compared to adjacent regions of the disk. The depletion of both dust and gas suggests that the middle and outer rings could be due to the gravitational torque exerted by two Saturn-mass planets orbiting at 100 and 160 A.U. from the star. On the other hand, the inner dust gap could result from dust accumulation at the edge of a magnetorotational instability dead zone, or from dust opacity variations at the edge of the CO frost line. Observations of the dust emission at higher angular resolution and of molecules that probe dense gas are required to establish more precisely the origins of the dark rings observed in the HD 163296 disk.
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations at 0 3 resolution of EX Lup, the prototype of the EXor class of outbursting pre-main-sequence stars. The circumstellar disk ...of EX Lup is resolved for the first time in 1.3 mm continuum emission and in the J = 2-1 spectral line of three isotopologues of CO. At the spatial resolution and sensitivity achieved, the compact dust continuum disk shows no indications of clumps, fragments, or asymmetries above the 5 level. Radiative transfer modeling constrains the characteristic radius of the dust disk to 23 au and the total dust mass to 1.0 × 10−4 M (33 M⊕), similar to other EXor sources. The 13CO and C18O line emissions trace the disk rotation and are used to constrain the disk geometry, kinematics, and a total gas disk mass of 5.1 × 10−4 M . The 12CO emission extends out to a radius of 200 au and is asymmetric, with one side deviating from Keplerian rotation. We detect blueshifted, 12CO arc-like emission located 0 8 to the northwest and spatially disconnected from the disk emission. We interpret this extended structure as the brightened walls of a cavity excavated by an outflow, which are more commonly seen in FUor sources. Such outflows have also been seen in the borderline FU/EXor object V1647 Ori, but not toward EXor objects. Our detection provides evidence that the outflow phenomenon persists into the EXor phase, suggesting that FUor and EXor objects are a continuous population in which outflow activity declines with age, with transitional objects such as EX Lup and V1647 Ori.
Context.
The Lupus star-forming complex includes some of the closest low-mass star-forming regions, and together they house objects that span evolutionary stages from prestellar to premain sequence.
...Aims.
By studying seven objects in the Lupus clouds from prestellar to protostellar stages, we aim to test if a coherence exists between commonly used evolutionary tracers.
Methods.
We present Atacama Large Millimeter Array (ALMA) observations of the 1.3 mm continuum and molecular line emission that probe the dense gas and dust of cores (continuum, C
18
O, N
2
D
+
) and their associated molecular outflows (
12
CO). Our selection of sources in a common environment, with an identical observing strategy, allows for a consistent comparison across different evolutionary stages. We complement our study with continuum and line emission from the ALMA archive in different bands.
Results.
The quality of the ALMA molecular data allows us to reveal the nature of the molecular outflows in the sample by studying their morphology and kinematics, through interferometric mosaics covering their full extent. The interferometric images in IRAS 15398-3359 appear to show that it drives a precessing episodic jet-driven outflow with at least four ejections separated by periods of time between 50 and 80 yr, while data in IRAS 16059-3857 show similarities with a wide-angle wind model also showing signs of being episodic. The outflow of J160115-41523 could be better explained with the wide-angle wind model as well, but new observations are needed to further explore its nature. We find that the most common evolutionary tracers in the literature are useful for broad evolutionary classifications, but they are not consistent with each other to provide enough granularity to disentangle a different evolutionary stage of sources that belong to the same Class (0, I, II, or III). The evolutionary classification revealed by our analysis coincides with those determined by previous studies for all of our sources except J160115-41523. Outflow properties used as protostellar age tracers, such as mass, momentum, energy, and opening angle, may suffer from differences in the nature of each outflow and, therefore, detailed observations are needed to refine evolutionary classifications. We found both AzTEC-lup1-2 and AzTEC-lup3-5 to be in the prestellar stage, with the possibility that the latter is a more evolved source. IRAS 15398-3359, IRAS 16059-3857, and J160115-41523, which have clearly detected outflows, are Class 0 sources, although, we are not able to determine which is younger and which is older. Finally Sz 102 and Merin 28 are the most evolved sources in our sample and show signs of having associated outflows, which are not as well traced by CO as for the younger sources.
The asymptotic-giant-branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star underwent a brief period of increased ...mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse--parameters that determine the lifetime of the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3″. What was previously thought to be only a thin, spherical shell with a clumpy structure is revealed to also contain a spiral structure. Spiral structures associated with circumstellar envelopes have been previously seen, leading to the conclusion that the systems must be binaries. Combining the observational data with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse about 1,800 years ago, lasting approximately 200 years. About 3 × 10(-3) solar masses of material were ejected at a velocity of 14.3 km s(-1) and at a rate around 30 times higher than the pre-pulse mass-loss rate. This shows that about three times more mass was returned to the interstellar medium during and immediately after the pulse than previously thought.
We performed a comprehensive demographic study of the CO extent relative to dust of the disk population in the Lupus clouds in order to find indications of dust evolution and possible correlations ...with other disk properties. We increased the number of disks of the region with measured
R
CO
and
R
dust
from observations with the Atacama Large Millimeter/submillimeter Array to 42, based on the gas emission in the
12
CO
J
= 2−1 rotational transition and large dust grains emission at ~0.89 mm. The CO integrated emission map is modeled with an elliptical Gaussian or Nuker function, depending on the quantified residuals; the continuum is fit to a Nuker profile from interferometric modeling. The CO and dust sizes, namely the radii enclosing a certain fraction of the respective total flux (e.g.,
R
68%
), are inferred from the modeling. The CO emission is more extended than the dust continuum, with a
R
68%
CO
/
R
68%
dust
median value of 2.5, for the entire population and for a subsample with high completeness. Six disks, around 15% of the Lupus disk population, have a size ratio above 4. Based on thermo-chemical modeling, this value can only be explained if the disk has undergone grain growth and radial drift. These disks do not have unusual properties, and their properties spread across the population’s ranges of stellar mass (
M
⋆
), disk mass (
M
disk
), CO and dust sizes (
R
CO
,
R
dust
), and mass accretion of the entire population. We searched for correlations between the size ratio and
M
⋆
,
M
disk
,
R
CO
, and
R
dust
: only a weak monotonic anticorrelation with the
R
dust
is found, which would imply that dust evolution is more prominent in more compact dusty disks. The lack of strong correlations is remarkable: the sample covers a wide range of stellar and disk properties, and the majority of the disks have very similar size ratios. This result suggests that the bulk of the disk population may behave alike and be in a similar evolutionary stage, independent of the stellar and disk properties. These results should be further investigated, since the optical depth difference between CO and dust continuum might play a major role in the observed size ratios of the population. Lastly, we find a monotonic correlation between the CO flux and the CO size. The results for the majority of the disks are consistent with optically thick emission and an average CO temperature of around 30 K; however, the exact value of the temperature is difficult to constrain.
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