Context.
GG Tauri A is the prototype of a young triple T Tauri star that is surrounded by a massive and extended Keplerian outer disk. The central cavity is not devoid of gas and dust and at least GG ...Tauri Aa exhibits its own disk of gas and dust emitting at millimeter wavelengths. Its observed properties make this source an ideal laboratory for investigating planet formation in young multiple solar-type stars.
Aims.
We used new ALMA
13
CO and C
18
O(3–2) observations obtained at high angular resolution (~0.2″) together with previous CO(3–2) and (6–5) ALMA data and continuum maps at 1.3 and 0.8 mm in order to determine the gas properties (temperature, density, and kinematics) in the cavity and to a lesser extent in the outer disk.
Methods.
By deprojecting, we studied the radial and azimuthal gas distribution and its kinematics. We also applied a new method to improve the deconvolution of the CO data and in particular better quantify the emission from gas inside the cavity. We perform local and nonlocal thermodynamic equilibrium studies in order to determine the excitation conditions and relevant physical parameters inside the ring and in the central cavity.
Results.
Residual emission after removing a smooth-disk model indicates unresolved structures at our angular resolution, probably in the form of irregular rings or spirals. The outer disk is cold, with a temperature <20 K beyond 250 au that drops quickly (∝
r
−1
). The kinematics of the gas inside the cavity reveals infall motions at about 10% of the Keplerian speed. We derive the amount of gas in the cavity, and find that the brightest clumps, which contain about 10% of this mass, have kinetic temperatures 40−80 K, CO column densities of a few 10
17
cm
−2
, and H
2
densities around 10
7
cm
−3
.
Conclusions.
Although the gas in the cavity is only a small fraction of the disk mass, the mass accretion rate throughout the cavity is comparable to or higher than the stellar accretion rate. It is accordingly sufficient to sustain the circumstellar disks on a long timescale.
Circumstellar disks are characteristic for star formation and vanish during the first few Myr of stellar evolution. During this time planets are believed to form in the dense midplane by growth, ...sedimentation and aggregation of dust. Indicators of disk evolution, such as holes and gaps, can be traced in the spectral energy distribution (SED) and spatially resolved images. We aim to construct a self-consistent model of HH 30 by fitting all available continuum observations simultaneously. New data sets not available in previous studies, such as high-resolution interferometric imaging with the Plateau de Bure Interferometer (PdBI) at lambda = 1.3 mm and SED measured with IRS on the Spitzer Space Telescope in the mid-infrared, put strong constraints on predictions and are likely to provide new insights into the evolutionary state of this object. A parameter study based on simulated annealing was performed to find unbiased best-fit models for independent observations made in the wavelength domain lambda ~ 1 micron ... 4 mm. The method essentially creates a Markov chain through parameter space by comparing predictions generated by our self-consistent continuum radiation transfer code MC3D with observations. We present models of the edge-on circumstellar disk of HH 30 based on observations from the near-infrared to mm-wavelengths that suggest the presence of an inner depletion zone with about 45 AU radius and a steep decline of mm opacity beyond 140 AU. Our modeling indicates that several modes of dust evolution such as growth, settling, and radial migration are taking place in this object. High-resolution observations of HH 30 at different wavelengths with next-generation observatories such as ALMA and JWST will enable the modeling of inhomogeneous dust properties and significantly expand our understanding of circumstellar disk evolution.
Context.
Molecular line surveys are among the main tools to probe the structure and physical conditions in protoplanetary disks (PPDs), the birthplace of planets. The large radial and vertical ...temperature as well as density gradients in these PPDs lead to a complex chemical composition, making chemistry an important step to understand the variety of planetary systems.
Aims.
We aimed to study the chemical content of the protoplanetary disk surrounding GG Tau A, a well-known triple T Tauri system.
Methods.
We used NOEMA with the new correlator PolyFix to observe rotational lines at ∼2.6 to 4 mm from a few dozen molecules. We analysed the data with a radiative transfer code to derive molecular densities and the abundance relative to
13
CO, which we compare to those of the TMC1 cloud and LkCa 15 disk.
Results.
We report the first detection of CCS in PPDs. We also marginally detect OCS and find 16 other molecules in the GG Tauri outer disk. Ten of them had been found previously, while seven others (
13
CN, N
2
H
+
, HNC, DNC, HC
3
N, CCS, and C
34
S) are new detections in this disk.
Conclusions.
The analysis confirms that sulphur chemistry is not yet properly understood. The D/H ratio, derived from DCO
+
/HCO
+
, DCN/HCN, and DNC/HNC ratios, points towards a low temperature chemistry. The detection of the rare species CCS confirms that GG Tau is a good laboratory to study the protoplanetary disk chemistry, thanks to its large disk size and mass.
The radio-quiet quasar BR1202–0725 (z = 4.695) is a remarkable source with a bright northwest (NW) companion detected at submillimeter and radio wavelengths but invisible in the optical. In the ...absence of amplification by gravitational lensing, BR1202−0725 would be the most luminous binary CO and far-infrared (far-IR) source in the Universe. In this paper, we report observations with the IRAM Plateau de Bure interferometer of BR1202–0725 in the redshifted emission of the CO(5–4) and (7–6) lines, the CI(3P2-3P1) line, a high angular resolution (0.3″ × 0.8″) 1.3 mm map of the rest-frame, far-IR dust continuum, and a search for the CO(11−10) line. We compare these results with recent ALMA data in the CII line. Both the quasar host galaxy and its NW companion are spatially resolved in the molecular line emission and the dust continuum. The CO profile of the NW companion is very broad with a full width at half maximum of ~1000 ± 130 km s-1, compared to ~360 ± 40 km s-1 for the quasar host galaxy to the southeast (SE). The difference in linewidths and center velocities, and the absence of any lens candidate or arc-like structure in the field, at any wavelength, show that the obscured NW galaxy and the SE quasar host galaxy cannot be lensed images of the same object. Instead, we find morphological and kinematic evidence for sub-structures in both the NW and SE sources. We interpret these results as strong indications that the BR1202–0725 complex is a group of young, interacting, and highly active starburst galaxies.
Context.
ALMA high angular resolution observations of the dust and CO emission have already revealed signatures of protoplanets embedded in protoplanetary disks. These detections are around single T ...Tauri stars, while exoplanet surveys reveal that planets can also form in binary (or multiple) systems, either in circumstellar or circumbinary orbits.
Aims.
We searched for indirect evidence for planet formation in the multiple system GG Tau A, which harbors the most massive circumbinary disk among T Tauri stars.
Methods.
We performed CO(2–1) ALMA Cycle 6 observations of GG Tau A at 0.3″ resolution. The images confirm the “hot spot” detected at higher frequencies, but also reveal prominent spiral-like features. We modeled these features using the analytic prescription for the linear perturbation regime induced by low-mass planets.
Results.
The brightest spiral is well reproduced by a density wave excited by a protoplanet (GG Tau Ac) at the hot-spot location (290 au), just outside the dust ring. The absence of a clear gap (in gas or dust) at the planet location implies that its mass is significantly lower than that of Jupiter, i.e., of about the mass of Neptune or lower. Furthermore, other prominent (trailing) spiral patterns can be represented by adding one (or more) planet(s) at larger orbital radii, with the most obvious candidate located near the 2:1 mean-motion resonance with GG Tau Ac.
Conclusions.
The (proto-)planet GG Tau Ac appears to externally confine the ring in a stable configuration, explaining its high mass. Our results also suggest that planets similar in mass to Neptune may form in dense circumbinary disks orbiting (wide) binary stars. In the GG Tau case, orbital resonances appear to play an important role in shaping this multiple circumbinary planet system.
Aims. We attempt to understand the presence of gas phase CO below its sublimation temperature in circumstellar disks. We study two promising mechanisms to explain this phenomenon: turbulent mixing ...and photodesorption. Methods: We compute the chemical evolution of circumstellar disks including grain surface reactions with and without turbulent mixing and CO photodesorption. Results: We show that photodesorption significantly enhances the gas phase CO abundance, by extracting CO from the grains when the visual extinction remains below about 5 mag. However, the resulting dependence of column density on radial distance is inconsistent with observations so far. We propose that this inconsistency could be the result of grain growth. On the other hand, the influence of turbulent mixing is not found to be straightforward. The efficiency of turbulent mixing depends upon a variety of parameters, including the disk structure. For the set of parameters we chose, turbulent mixing is not found to have any significant influence on the CO column density.
Context. Studying molecular species in protoplanetary disks is very useful to characterize the properties of these objects, which are the site of planet formation. Aims. We attempt to constrain the ...chemistry of S-bearing molecules in the cold parts of circumstellar disk of GG Tau A. Methods. We searched for H2S, CS, SO, and SO2 in the dense disk around GG Tau A with the NOrthem Extended Millimeter Array (NOEMA) interferometer. We analyzed our data using the radiative transfer code DiskFit and the three-phase chemical model Nautilus. Results. We detected H2S emission from the dense and cold ring orbiting around GG Tau A. This is the first detection of H2S in a protoplanetary disk. We also detected HCO+, H13CO+, and DCO+ in the disk. Upper limits for other molecules, CCS, SO2, SO, HC3N, and c-C3H2 are also obtained. The observed DCO+/HCO+ ratio is similar to those in other disks. The observed column densities, derived using our radiative transfer code DiskFit, are then compared with those from our chemical code Nautilus. The column densities are in reasonable agreement for DCO+, CS, CCS, and SO2. For H2S and SO, our predicted vertical integrated column densities are more than a factor of 10 higher than the measured values. Conclusions. Our results reinforce the hypothesis that only a strong sulfur depletion may explain the low observed H2S column density in the disk. The H2S detection in GG Tau A is most likely linked to the much larger mass of this disk compared to that in other T Tauri systems.
Aims.We constrain the dust distribution and its properties (temperature, emissivity) in inner proto-planetary disks Methods.We performed sub-arcsecond high-sensitivity interferometric observations of ...the thermal dust emission at 1.4 mm and 2.8 mm in the disks surrounding LkCa 15 and MWC 480, with the new 750 m baselines of the IRAM PdBI array. This provides a linear resolution of ~60 AU at the distance of Taurus. Results.We report the existence of a cavity of ~50 AU radius in the inner disk of LkCa 15. Whereas LkCa 15 emission is optically thin, the optically thick core of MWC 480 is resolved at 1.4 mm with a radius of ~35 AU, constraining the dust temperature. In MWC 480, the dust emission is coming from a colder layer than the CO emission, most likely the disk mid-plane. Conclusions.These observations provide direct evidence of an inner cavity around LkCa 15. Such a cavity most probably results from the tidal disturbance created by a low-mass companion or large planet at ~30 AU from the star. These results suggest that planetary system formation is already at work in LkCa 15. They also indicate that the classical steady-state viscous disk model is too simplistic a description of the inner 50 AU of “proto-planetary” disks and that the disk evolution is coupled to the planet formation process. The MWC 480 results indicate that a proper estimate of the dust temperature and size of the optically thick core are essential for determining the dust emissivity index β.
Investigating the dynamical evolution of dust grains in proto-planetary discs is a key issue to understand how planets should form. We identify under which conditions dust settling can be constrained ...by high angular resolution observations at mm wavelengths, and which observational strategies are suited for such studies. Exploring a large range of models, we generate synthetic images of discs with different degrees of dust settling, and simulate high angular resolution (∼0.05-0.3 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of these synthetic discs. The resulting data sets are then analysed blindly with homogeneous disc models (where dust and gas are totally mixed) and the derived disc parameters are used as tracers of the settling factor. Our dust discs are partially resolved by ALMA and present some specific behaviours on radial and mainly vertical directions, which can be used to quantify the level of settling. We find out that an angular resolution better than or equal to ∼0.1 arcsec (using 2.3 km baselines at 0.8mm) allows us to constrain the dust scale height and flaring index with sufficient precision to unambiguously distinguish between settled and non-settled discs, provided the inclination is close enough to edge-on (i ≥ 75°). Ignoring dust settling and assuming hydrostatic equilibrium when analysing such discs affect the derived dust temperature and the radial dependency of the dust emissivity index. The surface density distribution can also be severely biased at the highest inclinations. However, the derived dust properties remain largely unaffected if the disc scale height is fitted separately. ALMA has the potential to test some of the dust settling mechanisms, but for real discs, deviations from ideal geometry (warps, spiral waves) may provide an ultimate limit on the dust settling detection.
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