Spatially resolved structures in protoplanetary disks hint at unseen planets. Previous imaging observations of the transitional disk around MWC 758 revealed an inner cavity, a ring-like outer disk, emission clumps, and spiral arms, all possibly generated by companions. We present ALMA dust continuum observations of MWC 758 at 0.87 millimeter (mm) wavelength with 43×39 mas angular resolution (6.9×6.2 AU) and 20 µJy beam −1 rms. The central sub-mm emission

Context. The disk-outflow connection is thought to play a key role in extracting excess angular momentum from a forming proto-star. Although jet rotation has been observed in a few objects, no rotation of molecular outflows has been unambiguously reported so far. Aims. We report new millimeter-interferometric observations of the edge-on T Tauri star -disk system in the isolated Bok globule CB 26. The aim of these observations was to study the disk-outflow relation in this 1 Myr old low-mass young stellar object. Methods. The IRAM PdBI array was used to observe 12 CO(2-1) at 1.3 mm in two configurations, resulting in spectral line maps with 1.5 resolution. We use an empirical parameterized steady-state outflow model combined with 2-D line radiative transfer calculations and χ 2 -minimization in parameter space to derive a best-fit model and constrain parameters of the outflow. Results. The data reveal a previously undiscovered collimated bipolar molecular outflow of total length ≈2000 AU, escaping perpendicular to the plane of the disk. We find peculiar kinematic signatures that suggest that the outflow is rotating with the same orientation as the disk. However, we could not ultimately exclude jet precession or two misaligned flows as possible origins of the observed peculiar velocity field. There is indirect indication that the embedded driving source is a binary system, which, together with the youth of the source, could provide a clue to the observed kinematic features of the outflow. Conclusions. CB 26 is so far the most promising source in which to study the rotation of a molecular outflow. Assuming that the outflow is rotating, we compute and compare masses, mass flux, angular momenta, and angular momentum flux of the disk and outflow and derive disk dispersal timescales of 0.5 . . . 1 Myr, comparable to the age of the system.

Aims. The long-term evolution of a circumstellar disk starting from its formation and ending in the T Tauri phase was simulated numerically with the purpose of studying the evolution of dust in the disk with distinct values of viscous α-parameter and dust fragmentation velocity v frag . Methods. We solved numerical hydrodynamics equations in the thin-disk limit, which are modified to include a dust component consisting of two parts: sub-micron-sized dust and grown dust with a maximum radius ar. The former is strictly coupled to the gas, while the latter interacts with the gas via friction. The conversion of small to grown dust, dust growth, and dust self-gravity are also considered. Results. We found that the process of dust growth known for the older protoplanetary phase also holds for the embedded phase of disk evolution. The dust growth efficiency depends on the radial distance from the star -ar is largest in the inner disk and gradually declines with radial distance. In the inner disk, ar is limited by the dust fragmentation barrier. The process of small-to-grown dust conversion is very fast once the disk is formed. The total mass of grown dust in the disk (beyond 1 AU) reaches tens or even hundreds of Earth masses already in the embedded phase of star formation and even a greater amount of grown dust drifts in the inner, unresolved 1 AU of the disk. Dust does not usually grow to radii greater than a few cm. A notable exception are models with α ≤ 10 −3 , in which case a zone with reduced mass transport develops in the inner disk and dust can grow to meter-sized boulders in the inner 10 AU. Grown dust drifts inward and accumulates in the inner disk regions. This effect is most pronounced in the α ≤ 10 −3 models where several hundreds of Earth masses can be accumulated in a narrow region of several AU from the star by the end of embedded phase. The efficiency of grown dust accumulation in spiral arms is stronger near corotation where the azimuthal velocity of dust grains is closest to the local velocity of the spiral pattern. In the framework of the adopted dust growth model, the efficiency of small-to-grown dust conversion was found to increase for lower values of α and v frag .

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Context. In the dense and cold interiors of starless molecular cloud cores, a number of chemical processes allow for the formation of complex molecules and the deposition of ice layers on dust grains. Dust density and temperature maps of starless cores derived from Herschel continuum observations constrain the physical structure of the cloud cores better than ever before. We use these to model the temporal chemical evolution of starless cores. Aims. We derive molecular abundance profiles for a sample of starless cores. We then analyze these using chemical modeling based on dust temperature and hydrogen density maps derived from Herschel continuum observations. Methods. We observed the 12 CO (2-1), 13 CO (2-1), C 18 O (2-1) and N 2 H + (1-0) transitions towards seven isolated, nearby low-mass starless molecular cloud cores. Using far infrared (FIR) and submillimeter (submm) dust emission maps from the Herschel key program Earliest Phases of Star formation (EPoS) and by applying a ray-tracing technique, we derived the physical structure (density, dust temperature) of these cores. Based on these results we applied time-dependent chemical modeling of the molecular abundances. We modeled the molecular emission profiles with a line-radiative transfer code and compared them to the observed emission profiles. Results. CO is frozen onto the grains in the center of all cores in our sample. The level of CO depletion increases with hydrogen density and ranges from 46% up to more than 95% in the core centers of the three cores with the highest hydrogen density. The average hydrogen density at which 50% of CO is frozen onto the grains is 1.1 ± 0.4 × 10 5 cm −3 . At about this density, the cores typically have the highest relative abundance of N 2 H + . The cores with higher central densities show depletion of N 2 H + at levels of 13% to 55%. The chemical ages for the individual species are on average (2 ± 1) × 10 5 yr for 13 CO, (6 ± 3) × 10 4 yr for C 18 O, and (9 ± 2) × 10 4 yr for N 2 H + . Chemical modeling indirectly suggests that the gas and dust temperatures decouple in the envelopes and that the dust grains are not yet significantly coagulated. Conclusions. We observationally confirm chemical models of CO-freezeout and nitrogen chemistry. We find clear correlations between the hydrogen density and CO depletion and the emergence of N 2 H + . The chemical ages indicate a core lifetime of less than 1 Myr.

The generation of infrared (IR) radiation and the observed IR intensity distribution at wavelengths of 8, 24, and 100 µm in the ionized hydrogen region around a young, massive star is investigated. The evolution of the HII region is treated

À2 M (with a factor of $7 uncertainty), and (5) that the disk is in Keplerian rotation. Furthermore, indirect evidence for a local inhomogeneity of the envelope at k600 AU is found. The single-dish spectra are synthesized for three different cases, namely, for the disk model, for the envelope model, and for their combination. An overall reasonable agreement between all modeled and acquired line intensities, widths, and profiles is achieved for the latter model, with the exception of the CS (5-4) data that require the presence of high-density clumpy structures in the model. This allows us to constrain the physical structure of the AB Aur inner envelope: (1) its mass-average temperature is about 35 AE 14 K; (2) the density goes inversely down with the radius, / r À1:0AE0:3 , starting from an initial value n 0 % 3:9 ; 10 5 cm À3 at 400 AU; and (3) the mass of the shielded region within 2200 AU is about 4 ; 10 À3 M (the latter two quantities are uncertain by a factor of $7). In addition, evolutionary nature and lifetime for dispersal of the AB Aur system and Herbig Ae/ Be systems in general are discussed.

We report on a sensitive search for mid-infrared molecular hydrogen emission from protoplanetary disks. We observed the Herbig Ae/Be stars UX Ori, HD 34282, HD 100453, HD 101412, HD 104237 and HD 142666, and the T Tauri star HD 319139, and searched for H 2 0−0 S (2) (J = 4−2) emission at 12.278 micron and H 2 0−0 S (1) (J = 3−1) emission at 17.035 micron with VISIR, ESO-VLT's high-resolution mid-infrared spectrograph. None of the sources present evidence for molecular hydrogen emission at the wavelengths observed. Stringent 3σ upper limits to the integrated line fluxes and the mass of optically thin warm gas (T = 150, 300 and 1000 K) in the disks are derived. The disks contain less than a few tenths of Jupiter mass of optically thin H 2 gas at 150 K, and less than a few Earth masses of optically thin H 2 gas at 300 K and higher temperatures. We compare our results to a Chiang & Goldreich (1997, ApJ, 490, 368, CG97) two-layer disk model of masses 0.02 M and 0.11 M . The upper limits to the disk's optically thin warm gas mass are smaller than the amount of warm gas in the interior layer of the disk, but they are much larger than the amount of molecular gas expected to be in the surface layer. If the two-layer approximation to the structure of the disk is correct, our non-detections are consistent with the low flux levels expected from the small amount of H 2 gas in the surface layer. We present a calculation of the expected thermal H 2 emission from optically thick disks, assuming a CG97 disk structure, a gas-to-dust ratio of 100 and T gas = T dust . We show that the expected H 2 thermal emission fluxes from typical disks around Herbig Ae/Be stars are of the order of 10 −16 to 10 −17 erg s −1 cm −2 for a distance of 140 pc. This is much lower than the detection limits of our observations (5 × 10 −15 erg s −1 cm −2 ). H 2 emission levels are very sensitive to departures from the thermal coupling between the molecular gas and dust in the surface layer. Additional sources of heating of gas in the disk's surface layer could have a major impact on the expected H 2 disk emission. Our results suggest that in the observed sources the molecular gas and dust in the surface layer have not significantly departed from thermal coupling (T gas /T dust < 2) and that the gas-to-dust ratio in the surface layer is very likely lower than 1000.