We present Hα, [N ii] and [O iii] ground-based and HST archive images, VLA-A 3.6-cm continuum and H92α emission-line data and high-resolution long-slit [N ii] spectra of the planetary nebula Hu 2-1. A large number of structural components are identified in the nebula: an outer bipolar and an inner shell, two pairs of collimated bipolar structures at different directions, monopolar bow-shock-like structures, and an extended equatorial structure within a halo. The formation of Hu 2-1 appears to be dominated by anisotropic mass ejection during the late-AGB stage of the progenitor and by variable, ‘precessing’ collimated bipolar outflows during the protoplanetary nebula and/or early planetary nebula phases. Different observational results strongly support the existence of a binary central star in Hu 2-1, among them (1) the observed point-symmetry of the bipolar lobes and inner shell, and the departures from axial symmetry of the bipolar lobes, (2) the off-centre position of the central star, (3) the detection of mass ejection towards the equatorial plane, and (4) the presence of ‘precessing’ collimated outflows. In addition, (5) an analysis of the kinematics shows that the systemic velocity of the bipolar outflows does not coincide with the systemic velocity of the bipolar shell. We propose that this velocity difference is a direct evidence of orbital motion of the ejection source in a binary system. From a deduced orbital velocity of ∼10 km s⁻¹, a semimajor axis of ∼9–27 au and period of ∼25–80 yr are obtained, assuming a reasonable range of masses. These parameters are used to analyse the formation of Hu 2-1 within current scenarios of planetary nebulae with binary central stars.

We present Ha, [N II] j6583, [O III] j5007 ground-based images, Hubble Space T elescope (HST) (V band) archival images, VLA-A 3.6 cm continuum data, and high-resolution long-slit spectra of the planetary nebula NGC 6884. The VLA and HST images show an extremely knotty and Ðlamentary nebula with an elliptical central structure also recognizable in Ha and [O III]. The [N II] image is di †erent and is dominated by two bright arclike structures. The image ratio maps indicate a complex ionization structure within the nebula with low-excitation Ðlaments surrounded by high-excitation regions. The spectra make it possible to distinguish three basic structural components in NGC 6884 : (1) a compact P.A. ^32¡), high-excitation ([N II] j6583/Ha ¹ 0.15) ellipsoidal shell seen almost pole-on (3A .8 ] 2A .8, with polar and equatorial expansion velocities in the Ha line of ^25 and ^19 km s~1, respectively ; (2) two point-symmetric, low-excitation ([N II]/Ha ^0.6È1) spirals in which the distance to the central star and the radial velocity exhibit systematic variations ; (3) two compact, apparently isolated, low-excitation bipolar knots. All data agree that the spirals represent precessing bipolar jetlike outÑows. The observational properties of these precessing outÑows can satisfactorily be explained with an approximately constant ejection velocity (^55 km s~1) and a large precession angle (2/ ^120¡). The deduced precession period (^500 ] [D(kpc)/2] yr) is the shortest one measured so far in this kind of structure in planetary nebulae. The image ratio maps and the [N II]/Ha intensity ratio suggest shock excitation in the precessing jets. A general discussion of NGC 6884 is presented within the context of planetary nebulae with jetlike components.

The most massive AGB stars are expected to result in heavily obscured post-AGB stars, proto-PNe and PNe with highly axisymmetric morphologies. To investigate this evolutionary connection, we have selected a sample of 165 presumably obscured IRAS post-AGB star and PN candidates and obtained near-IR JHK images for 164 of them. These images, in conjunction with DSS, 2MASS, Spitzer GLIMPSE, MSX, AKARI, and IRAS archival data, have allowed us to identify the near-IR counterparts of 154 of these sources, providing reliable finding charts and coordinates. Near-IR narrow-band Brγ, H2, and K continuum images were acquired for 6 of these sources that were found to be resolved in near-IR JHK images. Among the extended post-AGB source and PN candidates, three are round and seven have bipolar morphologies. Five of the extended sources are ionized and may have thus entered the PN stage. We note that all extended sources with water maser emission have bipolar morphology. We have investigated the Galactic distribution of sources with the largest flux drop from the 9 μm AKARI band to the near-IR J band and found that the width of the distribution in Galactic latitude is consistent with those of bipolar PNe and DUPLEX (DUst-Prominent Longitudinally EXtended) sources.

K 3-35 is a planetary nebula (PN) where H2O maser emission has been detected, suggesting that it departed from the proto-PNe phase only some decades ago. Interferometric VLA observations of the OH 18 cm transitions in K 3-35 are presented. OH maser emission is detected in all four ground state lines (1612, 1665, 1667, and 1720 MHz). All the masers appear blueshifted with respect to the systemic velocity of the nebula and have different spatial and kinematic distributions. The OH 1665 and 1720 MHz masers appear spatially coincident with the core of the nebula, while the OH 1612 and 1667 MHz ones exhibit a more extended distribution. We suggest that the 1665 and 1720 masers arise from a region close to the central star, possibly in a torus, while the 1612 and 1667 lines originate mainly from the extended northern lobe of the outflow. It is worth noting that the location and velocity of the OH 1720 MHz maser emission are very similar to those of the H2O masers (coinciding within 0.'' 1 and similar to 2 km s(-1), respectively). We suggest that the pumping mechanism in the H2O masers could be produced by the same shock that is exciting the OH 1720 MHz transition. A high degree of circular polarization (> 50%) was found to be present in some features of the 1612, 1665, and 1720 MHz emission. For the 1665 MHz transition at similar to +18 km s(-1) the emission with left and right circular polarizations (LCP and RCP) coincide spatially within a region of similar to 0.'' 03 in diameter. Assuming that these RCP and LCP 1665 features come from a Zeeman pair, we estimate a magnetic field of similar to 0.9 mG within 150 AU from the 1.3 cm continuum peak. This value is in agreement with a solar-type magnetic field associated with evolved stars.

The planetary nebula (PN) NGC 6778 harbors a binary central star with a short orbital period and displays two systems of fast collimated outflows. To assess the influence of the evolution through a common-envelope phase of the binary system of NGC 6778 on its formation and shaping, we have used narrow-band images and high-dispersion long-slit spectra of the nebula to investigate its detailed morphology and kinematics. We find that the overall structure of NGC 6778 can be described as a bipolar PN. The equatorial ring is highly disrupted and many radial features (filamentary wisps and cometary knots) also show strong dynamical effects. There are clear connections between the bipolar lobes and the fast collimated outflows: the collimated outflows seem to arise from bright knots at the tips of the bipolar lobes, whereas the kinematics of the bipolar lobes is distorted. We suggest that the interaction of the fast collimated outflows of NGC 6778 with its nebular envelope has resulted in the disruption of the nebular shell and equatorial ring.