Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer ...disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in the H band, so that the shape and orientation of the shadows inform on the three-dimensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70degrees 5degrees. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions.
ABSTRACT Empirical evidence of planets in gas-rich circumstellar discs is required to constrain giant planet formation theories. Here we study the kinematic patterns which arise from planet–disc ...interactions and their observability in CO rotational emission lines. We perform 3D hydrodynamical simulations of single giant planets and predict the emergent intensity field with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes, and vortices bear strong kinematic counterparts. The isovelocity contours in the CO(2-1) line centroids $v$○ reveal large-scale perturbations, corresponding to abrupt transitions from below sub-Keplerian to super-Keplerian rotation along with radial and vertical flows. The increase in line optical depth at the edge of the gap also modulates $v$○, but this is a mild effect compared to the dynamical imprint of the planet–disc interaction. The large-scale deviations from the Keplerian rotation thus allow the planets to be indirectly detected via the first moment maps of molecular gas tracers, at Atacama Large Millimetre/submillimetre Array angular resolutions. The strength of these deviations depends on the mass of the perturber. This initial study paves the way to eventually determine the mass of the planet by comparison with more detailed models.
Context. Gaps, cavities, and rings in circumstellar disks are signposts of disk evolution and planet-disk interactions. We follow the recent suggestion that Herbig Ae/Be disks with a flared disk ...harbor a cavity, and investigate the disk around HD 97048. Aims. We aim to resolve the 34 ± 4 AU central cavity that has been predicted and to investigate the structure of the disk. Methods. We imaged the disk around HD 97048 using ALMA at 0.85 mm and 2.94 mm and ATCA (multiple frequency) observations. Our observations also include the 12CO J = 1−0, 12CO J = 3−2 and HCO+ J = 4−3 emission lines. Results. A central cavity in the disk around HD 97048 is resolved with a 40−46 AU radius. Additional radial structure present in the surface brightness profile can be accounted for either by an opacity gap at 90 AU or by an additional emitting ring at 150 AU. The continuum emission tracing the dust in the disk is detected out to 355 AU. The 12CO J = 3−2 disk is detected 2.4 times farther out. The 12CO emission can be traced down to ≈10 AU scales. Apparent non-Keplerian kinematics are detected inside the cavity on the HCO+ J = 4−3 velocity map. The mm spectral index measured from ATCA observations suggests that grain growth has occurred in the HD 97048 disk. Finally, we resolve a highly inclined disk out to 150 AU around the nearby 0.5 M⊙ binary ISO-ChaI 126. Conclusions. The data presented here reveal a cavity in the disk of HD 97048, and prominent radial structure in the surface brightness. The cavity size varies for different continuum frequencies and gas tracers. The gas inside the cavity follows non-Keplerian kinematics seen in HCO+ emission. The variable cavity size along with the kinematical signature suggests the presence of a substellar companion or a massive planet inside the cavity.
Exocometary Gas in the HD 181327 Debris Ring Marino, S.; Matra, L.; Stark, C. ...
Monthly notices of the Royal Astronomical Society,
08/2016, Letnik:
460, Številka:
3
Journal Article
Recenzirano
Odprti dostop
An increasing number of observations have shown that gaseous debris discs are not an exception. However, until now, we only knew of cases around A stars. Here we present the first detection of 12CO ...(2-1) disc emission around an F star, HD 181327, obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with radiative transfer calculations, we study the dust and CO mass distribution. We find the dust is distributed in a ring with a radius of 86.0 +/- 0.4 au and a radial width of 23.2 +/- 1.0 au. At this frequency, the ring radius is smaller than in the optical, revealing grain size segregation expected due to radiation pressure. We also report on the detection of low-level continuum emission beyond the main ring out to approximately 200 au. We model the CO emission in the non-local thermodynamic equilibrium regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging between 1.2 x 10(exp -6) solar mass and 2.9 x 10(exp -6) solar mass, depending on the gas kinetic temperature and collisional partners densities. The CO densities and location suggest a secondary origin, i.e. released from icy planetesimals in the ring. We derive a CO+CO2 cometary composition that is consistent with Solar system comets. Due to the low gas densities, it is unlikely that the gas is shaping the dust distribution.
Context. Large cavities in disks are important testing grounds for the mechanisms proposed to drive disk evolution and dispersion, such as dynamical clearing by planets and photoevaporation. Aims. We ...aim to resolve the large cavity in the disk around HD 34282, whose presence has been predicted by previous studies modeling the spectral energy distribution of the disk. Methods. Using ALMA band 7 observations we studied HD 34282 with a spatial resolution of 0.10″ × 0.17′′ at 345 GHz. Results. We resolve the disk around HD 34282 into a ring between 0.24′′ and 1.15′′ (78+7-11 and 374+33-54 au adopting a distance of 325+29-47 pc). The emission in this ring shows azimuthal asymmetry centered at a radial distance of 0.46′′ and a position angle of 135° and an azimuthal FWHM of 51°. We detect CO emission both inside the disk cavity and as far out as 2.7 times the radial extent of the dust emission. Conclusions. Both the large disk cavity and the azimuthal structure in the disk around HD 34282 can be explained by the presence of a 50 Mjup brown dwarf companion at a separation of ≈0.1′′.
ABSTRACT We present the results of ALMA band 7 observations of dust and CO gas in the disks around 7 objects with spectral types ranging between M5.5 and M7.5 in Upper Scorpius OB1, and one M3 star ...in Ophiuchus. We detect unresolved continuum emission in all but one source, and the 12CO J = 3 − 2 line in two sources. We constrain the dust and gas content of these systems using a grid of models calculated with the radiative transfer code MCFOST, and find disk dust masses between 0.1 and 1 M⊕, suggesting that the stellar mass/disk mass correlation can be extrapolated for brown dwarfs (BDs) with masses as low as 0.05 M . The one disk in Upper Sco in which we detect CO emission, 2MASS J15555600, is also the disk with the warmest inner disk, as traced by its H-4.5 photometric color. Using our radiative transfer grid, we extend the correlation between stellar luminosity and mass-averaged disk dust temperature, originally derived for stellar mass objects, to the BD regime to , applicable to spectral types of M5 and later. This is slightly shallower than the relation for earlier spectral type objects and yields warmer low-mass disks. The two prescriptions cross at 0.27 L , corresponding to masses between 0.1 and 0.2 M depending on age.
Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends ...up to 140 AU from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue observations of the gas-rich disk HD 142527, in the J = 2-1 line of super(12)CO, super(13)CO, and C super(18)O obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect emission coming from inside the dust-depleted cavity in all three isotopologues. Based on our analysis of the gas in the dust cavity, the super(12)CO emission is optically thick, while super(13)CO and C super(18)O emissions are both optically thin. The total mass of residual gas inside the cavity is ~1.5-2 M sub(Jup). We model the gas with an axisymmetric disk model. Our best-fit model shows that the cavity radius is much smaller in CO than it is in millimeter continuum and scattered light observations, with a gas cavity that does not extend beyond 105 AU (at 3sigma). The gap wall at its outer edge is diffuse and smooth in the gas distribution, while in dust continuum it is manifestly sharper. The inclination angle, as estimated from the high velocity channel maps, is 28 + or - 0.5 deg, higher than in previous estimates, assuming a fix central star mass of 2.2 M sub(middot in circle).
Context.
The mechanisms of planet formation are still under debate. We know little about how planets form, even if more than 4000 exoplanets have been detected to date. Recent investigations target ...the cot of newly born planets: the protoplanetary disk. At the first stages of their life, exoplanets still accrete material from the gas-rich disk in which they are embedded. Transitional disks are indeed disks that show peculiarities, such as gaps, spiral arms, and rings, which can be connected to the presence of substellar companions.
Aims.
To investigate what is responsible for these features, we selected all the known transitional disks in the solar neighborhood (<200 pc) that are visible from the southern hemisphere. We conducted a survey of 11 transitional disks with the SPHERE instrument at the Very Large Telescope. This is the largest H
α
survey that has been conducted so far to look for protoplanets. The observations were performed with the H
α
filter of ZIMPOL in order to target protoplanets that are still in the accretion stage. All the selected targets are very young stars, less than 20 Myr, and show low extinction in the visible.
Methods.
We reduced the ZIMPOL pupil stabilized data by applying the method of the angular spectral differential imaging (ASDI), which combines both techniques. The datacubes are composed of the Cnt_H
α
and the narrow band filter H
α
, which are taken simultaneously to permit the suppression of the speckle pattern. The principal component analysis method was employed for the reduction of the data. For each dataset, we derived the 5
σ
contrast limit and converted it in upper limits on the accretion luminosity.
Results.
We do not detect any new accreting substellar companions around the targeted transition disks down to an average contrast of 12 magnitudes at 0.′′2 from the central star. We have recovered the signal of the accreting M star companion around the star HD 142527. We have detected and resolved, for the first time in visible light, the quadruple system HD 98800. For every other system, we can exclude the presence of massive actively accreting companions, assuming that the accretion is not episodic and that the extinction is negligible. The mean accretion luminosity limit is 10
−6
L
⊙
at a separation of 0.′′2 from the host.
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