We have mapped the 12 CO(3-2) line emission around the Mira AB system at 0. 5 resolution using the Atacama Large Millimeter/submillimeter Array (ALMA). The CO map shows amazing complexity. The circumstellar gas has been shaped by different dynamical actors during the evolution of the system, and several morphological components can be identified. The companion is marginally resolved in continuum emission and is currently at 0. 487 ± 0. 006 separation. In the main line component, centered on the stellar velocity, spiral arcs around Mira A are found. The spiral appears to be relatively flat and oriented in the orbital plane. An accretion wake behind the companion is clearly visible, and the projected arc separation is about 5 . In the blue wing of the line emission, offset from the main line, several large (∼5-10 ) opposing arcs are found. We tentatively suggest that this structure is created by the wind of Mira B blowing a bubble in the expanding envelope of Mira A.

Aims. Polarization observations of circumstellar dust and molecular (thermal and maser) lines provide unique information about dust properties and magnetic fields in circumstellar envelopes of evolved stars. Methods. We use Atacama Large Millimeter/submillimeter Array Band 5 science verification observations of the red supergiant VY CMa to study the polarization of SiO thermal/masers lines and dust continuum at ∼ 1.7 mm wavelength. We analyse both linear and circular polarization and derive the magnetic field strength and structure, assuming the polarization of the lines originates from the Zeeman effect, and that of the dust originates from aligned dust grains. We also discuss other effects that could give rise to the observed polarization. Results. We detect, for the first time, significant polarization (∼ 3%) of the circumstellar dust emission at millimeter wavelengths. The polarization is uniform with an electric vector position angle of ∼ 8• . Varying levels of linear polarization are detected for the J = 4−3 28 SiO v = 0, 1, 2, and 29 SiO v = 0, 1 lines, with the strongest polarization fraction of ∼ 30% found for the 29 SiO v = 1 maser. The linear polarization vectors rotate with velocity, consistent with earlier observations. We also find significant (up to ∼ 1%) circular polarization in several lines, consistent with previous measurements. We conclude that the detection is robust against calibration and regular instrumental errors, although we cannot yet fully rule out non-standard instrumental effects. Conclusions. Emission from magnetically aligned grains is the most likely origin of the observed continuum polarization. This implies that the dust is embedded in a magnetic field > 13 mG. The maser line polarization traces the magnetic field structure. The magnetic field in the gas and dust is consistent with an approximately toroidal field configuration, but only higher angular resolution observations will be able to reveal more detailed field structure. If the circular polarization is due to Zeeman splitting, it indicates a magnetic field strength of ∼ 1 − 3 Gauss, consistent with previous maser observations.

Context. Most disks observed at high angular resolution show signs of substructures, such as rings, gaps, arcs, and cavities, in both the gas and the dust. To understand the physical mechanisms responsible for these structures, knowledge about the gas surface density is essential. This, in turn, requires information on the gas temperature. Aims. The aim of this work is to constrain the gas temperature as well as the gas surface densities inside and outside the millimeter-dust cavities of two transition disks: LkCa15 and HD 169142, which have dust cavities of 68 AU and 25 AU, respectively. Methods. We use some of the few existing ALMA observations of the J = 6-5 transition of 13CO together with archival J = 2−1 data of 12CO, 13CO, and C18O. The ratio of the 13CO J = 6−5 to the J = 2−1 transition is used to constrain the temperature and is compared with that found from peak brightness temperatures of optically thick lines. The spectra are used to resolve the innermost disk regions to a spatial resolution better than that of the beam of the observations. Furthermore, we use the thermochemical code DALI to model the temperature and density structure of a typical transition disk as well as the emitting regions of the CO isotopologs. Results. The 13CO J = 6−5 and J = 2−1 transitions peak inside the dust cavity in both disks, indicating that gas is present in the dust cavities. The kinematically derived radial profiles show that the gas is detected down to 10 and 5-10 AU, much farther in than the dust cavities in the LkCa15 and HD 169142 disks, respectively. For LkCa15, the steep increase toward the star in the 13CO J = 6−5 transition, in contrast to the J = 2−1 line, shows that the gas is too warm to be traced by the J = 2−1 line and that molecular excitation is important for analyzing the line emission. Quantitatively, the 6−5/2−1 line ratio constrains the gas temperature in the emitting layers inside the dust cavity to be up to 65 K, warmer than in the outer disk, which is at 20-30 K. For HD 169142, the lines are optically thick, complicating a line ratio analysis. In this case, the peak brightness temperature constrains the gas in the dust cavity of HD 169142 to be 170 K, whereas that in the outer disk is only 100 K. The data indicate a vertical structure in which the 13CO 6-5 line emits from a higher layer than the 2-1 line in both disks, consistent with exploratory thermochemical DALI models. Such models also show that a more luminous central star, a lower abundance of polycyclic aromatic hydrocarbons, and the absence of a dusty inner disk increase the temperature of the emitting layers and hence the line ratio in the gas cavity. The gas column density in the LkCa15 dust cavity drops by a factor of >2 compared to the outer disk, with an additional drop of an order of magnitude inside the gas cavity at 10 AU. In the case of HD 169142, the gas column density drops by a factor of 200–500 inside the gas cavity. Conclusions. The gas temperatures inside the dust cavities steeply increase toward the star and reach temperatures of up to 65 K (LkCa15) and 170 K (HD 169142) on scales of ~15–30 AU, whereas the temperature gradients of the emitting layers in the outer disks are shallow, with typical temperatures of 20-30 and 100 K, respectively. The deep drop in gas column density inside the HD 169142 gas cavity at <10 AU could be due to a massive companion of several MJ, whereas the broad dust-depleted gas region from 10 to 68 AU for LkCa15 may imply several lower mass planets. This work demonstrates that knowledge of the gas temperature is important for determining the gas surface density and thus whether planets, and if so what kinds of planets, are most likely to be carving the dust cavities.

Context. Water fountain nebulae are AGB and post-AGB objects that exhibit high-velocity outflows traced by water maser emission. Their study is important to understand the interaction between collimated jets and the circumstellar material that leads to the formation of bipolar/multi-polar morphologies in evolved stars. Aims. To describe the three-dimensional morphology and kinematics of the molecular gas of the water-fountain nebula IRAS 16342−3814. Methods. Retrieving data from the ALMA archive to analyse it using a simple spatio-kinematical model. Using the software SHAPE to construct a three-dimensional spatio-kinematical model of the molecular gas in IRAS 16342−3814. Reproducing the intensity distribution and position-velocity diagram of the CO emission from the ALMA observations to derive the morphology and velocity field of the gas. Using CO(J=1→0) data to support the physical interpretation of the model. Results.A spatio-kinematical model that includes a high-velocity collimated outflow embedded within material expanding at relatively lower velocity reproduces the images and position-velocity diagrams from the observations. The derived morphology is in good agreement with previous results from IR and H 2 O maser emission observations. The high-velocity collimated outflow exhibits deceleration across its length, while the velocity of the surrounding component increases with distance. The morphology of the emitting region; the velocity field and the mass of the gas as function of velocity are in excellent agreement with the properties predicted for a molecular outflow driven by a jet. The timescale of the molecular outflow is estimated to be ∼70-100 years. The scalar momentum carried by the outflow is much larger than it can be provided by the radiation of the central star. An oscillating pattern was found associated to the high-velocity collimated outflow. The oscillation period of the pattern is T ≈60-90 years and its opening angle is θ op ≈2 • . Conclusions. The CO (J=3→2) emission in IRAS 16342−3814 is interpreted in terms of a jet-driven molecular outflow expanding along an elongated region. The position-velocity diagram and the mass spectrum reveal a feature due to entrained material that is associated to the driving jet. This feature is not seen in other more evolved objects that exhibit more developed bipolar morphologies. It is likely that the jet in those objects has already disappeared since it is expected to last only for a couple of hundred years. This strengthens the idea that water fountain nebulae are undergoing a very short transition during which they develop the collimated outflows that shape the CSE. The oscillating pattern seen in the CO high-velocity outflow is interpreted as due to precession with a relatively small opening angle. The precession period is compatible with the period of the corkscrew pattern seen at IR wavelengths. We propose that the high-velocity molecular outflow traces the underlying primary jet that produces such pattern.

The evolution of low-and intermediate-initial-mass stars beyond the asymptotic giant branch (AGB) remains poorly understood. High-velocity outflows launched shortly after the AGB phase are thought to be the primary shaping mechanism of bipolar and multipolar planetary nebulae (PNe). However, little is known about the launching and driving mechanism for these jets, whose momentum and energy often far exceed the energy that can be provided by radiation pressure alone. Here, we report direct evidence of a magnetically collimated jet shaping the bipolar morphology of the circumstellar envelope of a post-AGB star. We present radio continuum observations of the post-AGB star IRAS 15445−5449 (OH 326.5−0.4) which has water masers tracing a fast bipolar outflow. Our observations confirm the earlier observed steep negative spectral index of the spectral energy distribution (SED) above ∼ 3 GHz, and resolve, for the first time, the emission to originate from a radio jet, proving the existence of such jets around a post-AGB star. The SED is consistent with a synchrotron jet embedded in a sheath of thermal electrons. We find a close correspondence between the extent and direction of the synchrotron jet and the bipolar shape of the object observed at other wavelenghts, suggesting that the jet is responsible for the source morphology. The jet is collimated by a magnetic field of the order of mG at almost 7000 AU from the central star. We recover observations from the ATCA archive that indicate that the emission measure of the thermal component has increased by a factor of three between 1998 and 2005 after which it has remained constant. The short timescale evolution of the radio emission suggests a short lifetime for the jet. The observations of a synchrotron jet from a post-AGB star with characteristics similar to those from protostars and young stellar objects, for instance, suggest that magnetic launching and collimation is a common feature of astrophysical jets.