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We conduct three-dimensional hydrodynamical simulations of two opposite jets that interact with a spherical slow wind that includes a denser shell embedded within it, and obtain a bipolar nebula where each of the two lobes is composed of two connected bubbles and Rayleigh-Taylor instability tongues that protrude from the outer bubble and form the `columns crown'. The jets are launched for a short time of 17 years and inflate a bipolar nebula inside a slow wind. When the bipolar structure encounters the dense shell, the interaction causes each of the two lobes to split to two connected bubbles. The interaction is prone to Rayleigh-Taylor instabilities that form tongues that protrude as columns from the outer bubble. The bases of the columns form a ring on the surface of the outer bubble, and the structure resemble a crown that we term the columns crown. This structure resembles, but is not identical to, the many filaments that protrude from the lobes of the bipolar planetary nebula Menzel~3. We discuss our results in comparison to the structure of Menzel~3 and the ways by which the discrepancies can be reconciled, and possibly turn our failure to reproduce the exact structure of Menzel~3 to a success with jets-shell interaction simulations that include more ingredients., Accepted to MNRAS

The asymptotic giant branch (AGB) star HR3126, associated with the arcminute-scale bipolar Toby Jug Nebula, provides a rare opportunity to study the emergence of bipolar structures at the end of the AGB phase. We carried out long-baseline interferometric observations with AMBER and GRAVITY (2--2.45 micron) at the Very Large Telescope Interferometer, speckle interferometric observations with VLT/NACO (2.24 micron), and imaging with SPHERE-ZIMPOL (0.55 micron) and VISIR (7.9--19.5 micron). The images reconstructed in the continuum at 2.1--2.29 micron from the AMBER+GRAVITY data reveal the central star surrounded by an elliptical ring-like structure with a semimajor and semiminor axis of 5.3 and 3.5 mas, respectively. The ring is interpreted as the inner rim of an equatorial dust disk viewed from an inclination angle of ~50 degrees, and its axis is approximately aligned with the bipolar nebula. The disk is surprisingly compact, with an inner radius of a mere 3.5 Rstar (2 au). Our 2-D radiative transfer modeling shows that an optically thick flared disk with silicate grains as large as ~4 micron can reproduce the observed continuum images and the spectral energy distribution. The images obtained in the CO first overtone bands reveal elongated extended emission around the central star, suggesting the oblateness of the star's atmosphere or the presence of a CO gas disk inside the dust cavity. The object is unresolved with SPHERE-ZIMPOL, NACO, and VISIR. If the disk formed together with the bipolar nebula, the grain growth from sub-micron to a few microns should have taken place over the nebula's dynamical age of ~3900 yrs. The non-detection of a companion in the reconstructed images implies that either its 2.2 micron brightness is more than ~30 times lower than that of the red giant or it might have been shredded due to binary interaction., Comment: 24 pages, 14 figures, published in Astronomy and Astrophysics

OH231.8+4.2 is an archetypal pre-planetary nebulae (pPN). It is a binary system surrounded by bipolar nebula. Some years ago the authors extensively studied it and performed several VLBI observations from which they obtained mas-resolution maps of the SiO (7 mm) and H2O (1.3 cm) maser emissions. H2O masers were found to be distributed in two areas along the symmetry axis of the nebulae oriented nearly north-south delineating a bipolar outflow and their astrometric positions were accurately measured. SiO masers, indicating the position of the Mira component of the binary system, form a structure perpendicular to the axis of the nebulae. The general picture of the source looked satisfactory, except for the relative position of the two masers. Surprisingly, SiO masers, were tentatively placed 250 mas away (370 AU) from the apparent center of the outflow. Using the ALMA we observed the SiO maser emission at 86 GHz and accurately derived the position of the Mira component. Combining our previous VLBA data and our new ALMA observations we are now able to give a more complete and detailed description of the inner part of this amazing pPN., Accepted 6 pages, 2 figures 14th European VLBI Network Symposium & Users Meeting (EVN 2018)8-11 October 2018Granada, Spain - POS(EVN2018)-074

Two southern objects are studied. The first, the planetary nebula PK 349-01.1, is of interest because it has a chain of jets ejected from the central star. 12C(1-0) observations of the vicinity of this object reveal red- and blue-shifted molecular outflows. The second object is a star formation region consisting of two groups of IR stars. These groups have a trapezium-like configuration. Two stars in one of these groups are associated with a ring-shaped nebulae. This star formation region is associated with a new radial system of dark globules.

Observations of the ejecta from the final flash (FF) of helium shell burning in Sakurai’s Object (V4334 Sgr) are presented for 2015–2019, a period ∼20–24 yr after discovery. Adaptive optics images at K s trace the expanding debris. While most of the ejecta mass is in ∼200 K dust, a small fraction, ∼0.4%, of the dust mass is at ∼760 K. The 760 K continuum dominates the near-IR images. Spatial-spectral images in He i 10830 Å show an ∼16 diameter bipolar planetary nebula at position angle 21° ± 5° with the SW moving toward us and the NE moving away. Seen in integrated light, the nebula is nearly circular. Near-IR continuum images show ejecta moving radially away from a bright central point source. High-resolution mid-IR spectra reveal molecular hydrocarbon lines with an expansion velocity of 270 ± 5 km s−1 seen in absorption against the dust continuum. The hydrocarbons originate in material produced in the FF. The bipolar nebula and debris clouds are discussed in the context of a highly inclined disk model. The proper motion has been measured placing V4334 Sgr in the thick disk population. There is no evidence that a hot white dwarf Wolf–Rayet ([WR]) wind has emerged; no [WR] spectral features were detected. The possibility of a binary companion involved in the evolution is discussed.

33 pags., 21 figs., 4 tabs., 2 apps., We present continuum and molecular line emission ALMA observations of OH 231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star. The high-angular resolution (~0.¿¿2¿0.¿¿3) and sensitivity of our ALMA maps provide the most detailed and accurate description of the overall nebular structure and kinematics of this object to date. We have identified a number of outflow components previously unknown. Species studied in this work include 12CO, 13CO, CS, SO, SO2, OCS, SiO, SiS, H3O+, Na37Cl, and CH3OH. The molecules Na37Cl and CH3OH are first detections in OH 231.8+4.2, with CH3OH being also a first detection in an AGB star. Our ALMA maps bring to light the totally unexpected position of the mass-losing AGB star (QX Pup) relative to the large-scale outflow. QX Pup is enshrouded within a compact (¿60 AU) parcel of dust and gas (clump S) in expansion (Vexp ~ 5¿7 km s¿1) that is displaced by ~ 0.¿¿6 to the south of the dense equatorial region (or waist) where the bipolar lobes join. Our SiO maps disclose a compact bipolar outflow that emerges from QX Pup¿s vicinity. This outflow is oriented similarly to the large-scale nebula but the expansion velocities are about ten times lower (Vexp ¿ 35 km s¿1). We deduce short kinematical ages for the SiO outflow, ranging from ~50¿80 yr, in regions within ~150 AU, to ~400¿500 yr at the lobe tips (~3500 AU). Adjacent to the SiO outflow, we identify a small-scale hourglass-shaped structure (mini-hourglass) that is probably made of compressed ambient material formed as the SiO outflow penetrates the dense, central regions of the nebula. The lobes and the equatorial waist of the mini-hourglass are both radially expanding with a constant velocity gradient (Vexp ¿ r). The mini-waist is characterized by extremely low velocities, down to ~1 km s¿1 at ~150 AU, which tentatively suggest the presence of a stable structure. The spatio-kinematics of the large-scale, high-velocity lobes (HV lobes), and the dense equatorial waist (large waist) known from previous works are now precisely determined, indicating that both were shaped nearly simultaneously about ~800¿900 yr ago. We report the discovery of two large (~8¿¿ × 6¿¿), faint bubble-like structures (fish bowls) surrounding the central parts of the nebula. These are relatively old structures, although probably slightly (~100¿200 yr) younger than the large waist and the HV lobes. We discuss the series of events that may have resulted in the complex array of nebular components found in OH 231.8+4.2 as well as the properties and locus of the central binary system. The presence of ¿80 yr bipolar ejections indicate that the collimated fast wind engine is still active at the core of this outstanding object., This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.00256.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The data here presented have been reduced by CASA (ALMA default calibration software; https://casa.nrao.edu); data analysis was made using the GILDAS software (http://www.iram. fr/IRAMFR/GILDAS). This work has been partially supported by the Spanish MINECO through grants AYA2012-32032, AYA2016-75066-C2-1-P, and AYA2016-78994-P and by the European Research Council through ERC grant 610256: NANOCOSMOS. This research has made use of the The JPL Molecular Spectroscopy catalog, The Cologne Database for Molecular Spectroscopy, the SIMBAD database operated at CDS (Strasbourg, France), the NASA’s Astrophysics Data System and Aladin.

Aims. We aim to identify bipolar Galactic H II regions and to understand their parental cloud structures, morphologies, evolution, and impact on the formation of new generations of stars. Methods. We use the Spitzer-GLIMPSE, Spitzer-MIPSGAL, and Herschel-Hi-GAL surveys to identify bipolar H II regions and to examine their morphologies. We search for their exciting star(s) using NIR data from the 2MASS, UKIDSS, and VISTA surveys. Massive molecular clumps are detected near these bipolar nebulae, and we estimate their temperatures, column densities, masses, and densities. We locate Class 0/I young stellar objects (YSOs) in their vicinities using the Spitzer and Herschel-PACS emission. Results. Numerical simulations suggest bipolar H II regions form and evolve in a two-dimensional flat- or sheet-like molecular cloud. We identified 16 bipolar nebulae in a zone of the Galactic plane between ℓ ± 60° and |b| < 1°. This small number, when compared with the 1377 bubble H II regions in the same area, suggests that most H II regions form and evolve in a three-dimensional medium. We present the catalogue of the 16 bipolar nebulae and a detailed investigation for six of these. Our results suggest that these regions formed in dense and flat structures that contain filaments. We find that bipolar H II regions have massive clumps in their surroundings. The most compact and massive clumps are always located at the waist of the bipolar nebula, adjacent to the ionised gas. These massive clumps are dense, with a mean density in the range of 105 cm−3 to several 106 cm−3 in their centres. Luminous Class 0/I sources of several thousand solar luminosities, many of which have associated maser emission, are embedded inside these clumps. We suggest that most, if not all, massive 0/I YSO formation has probably been triggered by the expansion of the central bipolar nebula, but the processes involved are still unknown. Modelling of such nebula is needed to understand the star formation processes at play.

V4334 Sgr (Sakurai&rsquo, s object) is an enigmatic evolved star that underwent a very late thermal pulse a few years before its discovery in 1996. It ejected a new hydrogen-deficient nebula in the process. The source has been observed continuously since, at many wavelengths ranging from the optical to the radio regime. In this paper we evaluate these data and discuss the evolution of this object. We reach the conclusion that we have seen no evidence for photoionization of the nebula yet and that the spectral features we see are caused either by shocks or by dust. These shocks are an integral part of the hydrodynamic shaping that is now producing a new bipolar nebula inside the old planetary nebula (PN), implying that we have a detailed observational record of the very early stages of the shaping of a bipolar nebula.

The shaping of various morphological features of planetary nebulae (PNe) is increasingly linked to the role of binary central stars. Identifying a binary within a PN offers a powerful tool with which to directly investigate the formation mechanisms behind these features. The Etched Hourglass Nebula, MyCn 18, is the archetype for several binary-linked morphological features, yet it has no identified binary nucleus. It has the fastest jets seen in a PN of 630 km s$^{-1}$, a central star position offset from the nebula centre, and a bipolar nebula with a very narrow waist. Here we report on the Southern African Large Telescope (SALT) High Resolution Spectrograph (HRS) detection of radial velocity variability in the nucleus of MyCn 18 with an orbital period of $18.15\pm0.04$ days and a semi-amplitude of $11.0\pm0.3$ km s$^{-1}$. Adopting an orbital inclination of $38\pm5$ deg and a primary mass of $0.6\pm0.1$ $M_\odot$ yields a secondary mass of $0.19\pm0.05$ $M_\odot$ corresponding to an M5V companion. The detached nature of the binary rules out a classical nova (CN) as the origin of the jets or the offset central star as hypothesised in the literature. Furthermore, scenarios that produce the offset central star during the AGB and that form narrow waist bipolar nebulae result in orbital separations 80--800 times larger than observed in MyCn 18. The inner hourglass and jets may have formed from part of the common envelope ejecta that remained bound to the binary system in a circumbinary disk, whereas the offset central star position may best be explained by proper motion. Detailed simulations of MyCn 18 are encouraged that are compatible with the binary nucleus to further investigate its complex formation history., 13 pages, 5 figures, 2 tables. Accepted for publication in PASA

The central area (40"x40") of the bipolar nebula S106 was mapped in the OI line at 63.2 micron with high angular (6") and spectral resolution, using GREAT on board SOFIA. The OI emission distribution is compared to the CO 16-15, CII 158 micron, and CO 11-10 lines, mm-molecular lines, and continuum. It is composed of several velocity components in the range from -30 km/s to 25 km/s. The high-velocity blue- and redshifted emission can be explained as arising from accelerated photodissociated (PDR) gas associated with a dark lane close to the massive binary system S106 IR, and from shocks caused by the stellar wind and/or a disk--envelope interaction. At velocities from -9 to -4 km/s and 0.5 to 8 km/s line wings are observed that we attribute to cooling in PDRs created by the ionizing radiation impinging on the cavity walls. The bulk velocity range is dominated by PDR emission from the clumpy molecular cloud. Modelling the emission in the different velocity ranges with the KOSMA-tau code constrains a radiation field chi of a few times 10^4 and densities n of a few times 10^4 cm^-3. Considering self-absorption of the OI line results in higher densities (up to 10^6 cm^-3) only for the gas component seen at high blue- and red velocities. The dark lane has a mass of 275 Msun and shows a velocity difference of 1.4 km/s along its projected length of 1 pc, determined from H13CO+ 1-0 mapping. It can be interpreted as a massive accretion flow, or the remains of it, linked to S106 IR/FIR. The most likely explanation is that the binary system is at a stage of its evolution where gas accretion is counteracted by the stellar winds and radiation, leading to the very complex observed spatial and kinematic emission distribution of the various tracers., Comment: Final version as it will appear in Asronomy&Astrophysics, accepted 22.5.2018

The bipolar nebula Menzel 3 (Mz 3) was observed as part of the \textit{Herschel} Planetary Nebula Survey (\textit{HerPlaNS}), which used the PACS and SPIRE instruments aboard the \textit{Herschel Space Observatory} to study a sample of planetary nebulae (PNe). In this paper, one of the series describing \textit{HerPlaNS} results, we report the detection of H I recombination lines (HRLs) in the spectrum of Mz 3. Inspection of the spectrum reveals the presence of 12 HRLs in the 55 to 680 $\mu$m range covered by the PACS and SPIRE instruments (H11$\alpha$ to H21$\alpha$ and H14$\beta$). The presence of HRLs in this range is unusual for PNe and has not been reported in Mz 3 before. Our analysis indicates that the HRLs we observed are enhanced by laser effect occurring in the core of Mz 3. Our arguments for this are: (i) the available Mz 3 optical to submillimetre HRL $\alpha$ line intensity ratios are not well reproduced by the spontaneous emission of optically thin ionized gas, as would be typical for nebular gas in PNe; (ii) the compact core of Mz 3 is responsible for a large fraction of the Herschel HRLs emission; (iii) the line intensity ratios for Mz 3 are very similar to those in the core emission of the well known star MWC 349A, where laser effect is responsible for the enhancement of HRLs in the Herschel wavelength range; (iv) the physical characteristics relevant to cause laser effect in the core of MWC 349A are very similar to those in the core of Mz 3., Comment: Published in MNRAS. ESA Portal Story. 13 Pages, 7 figures

Our Cycle 0 ALMA observations confirmed that the Boomerang Nebula is the coldest known object in the Universe, with a massive high-speed outflow that has cooled significantly below the cosmic background temperature. Our new CO 1-0 data reveal heretofore unseen distant regions of this ultra-cold outflow, out to $\gtrsim120,000$ AU. We find that in the ultra-cold outflow, the mass-loss rate (dM/dt) increases with radius, similar to its expansion velocity ($V$) - taking $V\propto r$, we find $dM/dt \propto r^{0.9-2.2}$. The mass in the ultra-cold outflow is $\gtrsim3.3$ Msun, and the Boomerang's main-sequence progenitor mass is $\gtrsim4$ Msun. Our high angular resolution ($\sim$0".3) CO J=3-2 map shows the inner bipolar nebula's precise, highly-collimated shape, and a dense central waist of size (FWHM) $\sim$1740 AU$\times275$ AU. The molecular gas and the dust as seen in scattered light via optical HST imaging show a detailed correspondence. The waist shows a compact core in thermal dust emission at 0.87-3.3 mm, which harbors $(4-7)\times10^{-4}$ Msun~of very large ($\sim$mm-to-cm sized), cold ($\sim20-30$ K) grains. The central waist (assuming its outer regions to be expanding) and fast bipolar outflow have expansion ages of $\lesssim1925$ yr and $\le1050$ yr: the "jet-lag" (i.e., torus age minus the fast-outflow age) in the Boomerang supports models in which the primary star interacts directly with a binary companion. We argue that this interaction resulted in a common-envelope configuration while the Boomerang's primary was an RGB or early-AGB star, with the companion finally merging into the primary's core, and ejecting the primary's envelope that now forms the ultra-cold outflow., accepted ApJ, 12 Apr, 2017

[Aims] We aim to study the rotating and expanding gas in the Red Rectangle, which is a well known bipolar nebula surrounding a double stellar system whose primary is a post-asymptotic giant branch (post-AGB) star. We analyze the properties of both components and the relation between them. Rotating disks have been very elusive in post-AGB nebulae, in which gas is almost always found to be in expansion., [Methods] We present new high-quality ALMA observations of this source in C17O J = 6−5 and H13CN J = 4−3 line emission and results from a new reduction of already published 13CO J = 3−2 data. A detailed model fitting of all the molecular line data, also discussing previous maps and single-dish observations of lines of CO, CII, and CI, was performed using a sophisticated code that includes an accurate nonlocal treatment of radiative transfer in 2D (assuming axial symmetry). These observations (of low- and high-opacity lines requiring various degrees of excitation) and the corresponding modeling allowed us to deepen the analysis of the nebular properties. We also stress the uncertainties, particularly in the determination of the boundaries of the CO-rich gas and some properties of the outflow., [Results] We confirm the presence of a rotating equatorial disk and an outflow, which is mainly formed of gas leaving the disk. The mass of the disk is ~0.01 M⊙, and that of the CO-rich outflow is around ten times smaller. High temperatures of ≳100 K are derived for most components. From comparison of the mass values, we roughly estimate the lifetime of the rotating disk, which is found to be of about 10 000 yr. Taking data of a few other post-AGB composite nebulae into account, we find that the lifetimes of disks around post-AGB stars typically range between about 5000 and more than 20 000 yr. The angular momentum of the disk is found to be high, ~9 M⊙ AU km s-1, which is comparable to that of the stellar system at present. Our observations of H13CN show a particularly wide velocity dispersion and indicate that this molecule is only abundant in the inner Keplerian disk, at ≲60 AU from the stellar system. We suggest that HCN is formed in a dense photodissociation region (PDR) due to the UV excess known to be produced by the stellar system, following chemical mechanisms that are well established for interstellar medium PDRs and disks orbiting young stars. We further suggest that this UV excess could lead to an efficient formation and excitation of PAHs and other C-bearing macromolecules, whose emission is very intense in the optical counterpart., This work has been supported by the Spanish MICINN, program CONSOLIDER INGENIO 2010, grant “ASTROMOL> (CSD2009-00038), by the Spanish MINECO, grants AYA2012-32032 and FIS2012-32096, and by the European Research Council (ERC Grant 610256: NANOCOSMOS).

We show that a fast wind that expands into a bipolar nebula composed of two opposite jet-inflated bubbles can form a pair of bipolar rings around giant stars. Our model assumes three mass loss episodes: a spherical slow and dense shell, two opposite jets, and a spherical fast wind. We use the FLASH hydrodynamical code in three-dimensions to simulate the flow, and obtain the structure of the nebula. We assume that the jets are launched from an accretion disk around a stellar companion to the giant star. The accretion disk is assumed to be formed when the primary giant star and the secondary star suffer a strong interaction accompanied by a rapid mass transfer process from the primary to the secondary star, mainly a main sequence star. Later in the evolution the primary star is assumed to shrink and blow a fast tenuous wind that interacts with the dense gas on the surface of the bipolar structure. We assume that the dense mass loss episode before the jets are launched is spherically symmetric. Our results might be applicable to some planetary nebulae, and further emphasize the large variety of morphological features that can be formed by jets. But we could not reproduce some of the properties of the outer rings of SN1987A. It seems that some objects, like SN1987A, require a pre-jets mass loss episode with a mass concentration at mid-latitudes., Submitted

NGC 6751 is a highly structured multiple-shell planetary nebula (PN) with a bipolar outflow. In this work, we present a comprehensive set of spatially resolved, high spectral resolution, long-slit spectra and deep imaging from San Pedro Martir, Gemini, the Hα composite full sky survey and archive images from the Hubble Space Telescope and Spitzer. This material allows us to identify all the main morphological components and study their detailed kinematics. We find a thick equatorial structure fragmented into multiple knots that enclose a fast expanding bubble with a filamentary surface structure. The knotty ring is surrounded by faint emission from a disk-like envelope. Lobes with embedded filaments form a bipolar outflow. The equatorial ring is tilted with respect to the line of sight and with respect to the bipolar outflow. A spherical halo surrounds the PN and there is material further out identified as a fragmented outer halo. This information is used to derive a three-dimensional morpho-kinematic model using the code SHAPE that closely replicates the observed image and long-slit spectra of the nebula, providing a fair representation of its complex structure. NGC 6751 is located close to the galactic plane and its large-scale surrounding environment is shown to be a gas-rich region. We find indications that the PN is interacting with the interstellar medium. Emission components from an extended nebulosity located a couple of arcminutes away from the nebula have radial velocities that are inconsistent with the rest of NGC 6751 and are confirmed as originating from the ambient material, not related to the PN, in agreement with a previous suggestion.

The transition from spherically symmetric asymptotic giant branch mass loss to aspherical planetary nebulae is an intriguing problem of stellar astrophysics. On 12 μm maps of the Infrared Astronomical Satellite (IRAS), we detected a huge (2.6 pc) dust emission region around the evolved planetary nebula NGC 1514. On 100 and 60 μm IRAS maps, we additionally found two giant (2.1 and 0.9 pc) bipolar dust emission structures centred on NGC 1514; we suspect that each of these regions is physically connected to the planetary nebula. The bipolar structures are slightly tilted with respect to each other, possibly due to precession. The total mass (dust + gas) of all structures is 2.2 ± 1.4 M ⊙ . We argue that NGC 1514 and its dusty surroundings represent one of the very few known cases where the preserved history of all main mass-loss phases of a star of intermediate initial mass can be seen.

From near-infrared and molecular hydrogen imaging observations, we have discovered that the planetary nebula NGC 6072 has a multipolar structure with a prominent equatorial ring. We have modeled the object by a double bipolar system, each with an equatorial ring and a pair of bipolar lobes. The bipolar axes of the two systems are estimated to be separated by 47°. The existence of such a double bipolar system suggests that the object has undergone separate fast outflow episodes separated by several thousand years.

We examine a binary merger model for the formation of the mysterious triple-ring nebula surrounding Supernova 1987A, which still has not been convincingly explained in detailed hydrodynamical calculations. During the merger of 15 and 5 M⊙ binary systems, mass is ejected primarily at mid-latitudes for a sufficiently evolved primary, as demonstrated by Morris & Podsiadlowski. This material is swept up by the fast wind of the central star during its post-merger blue supergiant phase, leading to a density contrast of ∼150 in the outer rings at the time of the supernova. The equatorial ring probably formed later when the star contracted to become a blue supergiant. The asymmetry between the northern and southern outer rings can be explained by a 10 per cent asymmetry during the merger, perhaps due to a pulsational instability in the common envelope. We present a parameter study from which we determine a mass-loss rate in the blue supergiant wind in the range 1.5–3 × 10−7 M⊙ yr−1 in agreement with previous estimates. The morphology of the best model is consistent with the well-known Hubble Space Telescope image at better than 5 per cent and is also in broad agreement with light-echo observations. The circumstellar environment on larger scales (up to 3 pc) is also investigated. We conclude with a brief discussion of the bipolar nebulae surrounding the Galactic stars, Sheridan 25, HD 168625 and η Carinae.

Using images centered around the 2.12 μm line of molecular hydrogen obtained with the Wide Field Infrared Camera on the Canada-France-Hawaii Telescope, we show that in spite of the different apparent morphologies, the Dumbbell Nebula and the Ring Nebula share the same intrinsic three-dimensional triple biconic structure.

The bipolar planetary nebula NGC 650-1 has been imaged in Ha, Hβ, [N II ] λ6583 A and [S II ] λλ6717+6731 A. These results are used to map the variation of extinction over the interior regions of the shell, where we find evidence for a gradual increase in A v between the SW and NE limits of the central emission bar. It is argued that this is likely to arise from dust associated with the nebular envelope itself. We have also produced a map of electron densities over this region, and find evidence for marked variations in He over a scale of ∼5 arcsec, a variation which is probably related to the clumpy emission structure observed in low-excitation images. We finally present contour mapping of mid-infrared Spitzer images of the source at 3.6, 4.5, 5.8 and 8 μm. These show that the central bar has a more or less uniform emission structure, although with evidence for condensations which are similar to, and in most cases coincidental with, comparable low-excitation structures noted in [N II ]. There is also evidence for an increase in 8/4.5 μm and 5.8/4.5 μm emission ratios with distance from the nucleus, and for an extension of 8 and 5.8 μm emission beyond the ionized regime; a trend which is attributed to strong polycyclic aromatic hydrocarbon band emission within the nebular photodissociative regime.

We have undertaken echelle spectroscopy and narrow-band line imaging of the bipolar planetary nebula M 1-8. This has permitted us to map the outflow in [N II ] λλ 6548+6583 A, Ha, and in the v = 1-0 S(1) transition of H 2 at λ 2.122 μm. It has also permitted us to acquire high-resolution spectra for [N II ] λ 6583 A, Ha and He II λ 6560 A. Our observations support the results of a previous 2MASS analysis by two of the authors (J. P. Phillips and G. Ramos-Larios), and confirm that there is strong H 2 emission outside of the ionized zone, as well as along the major axis of the outflow. Finally, we have investigated the spatial structure of the outflow in low and high excitation lines, and noted evidence for strong ionization stratification within the envelope of the source. We also note that major axis spectra show asymmetries attributable to outflow along the lobes, oriented at an angle i ∼ 35°-40° to the line of sight. Asymmetries along the minor axis, by contrast, appear to be associated with the central collimating disc, and may be interpretable in terms of asymmetries in disc structure, or rotation at an angular velocity of Ω ∼ 1.4 10 -12 rad s -1 . If the disc arises due to common-envelope evolution, then it seems that angular momentum constraints must be relatively tight, and can only be satisfied given fairly extreme physical assumptions (such as low disc mass, high primary star mass, a low distance to the source and so forth).

Planetary nebulae are formed by an interacting winds process where the remnant of the AGB wind is compressed and accelerated by a later-developed fast wind from the central star. One-dimensional dynamical models have successfully explained the multi-shell (bubble, shell, crown, haloes) structures and the kinematics of planetary nebulae. However, the origin of the diverse asymmetric morphology of planetary nebulae is still not understood. Recent observations in the visible, infrared, and the submillimeter have suggested that the AGB mass loss becomes aspherical in the very late stages, forming an expanding torus around the star. A fast, highly collimated wind then emerges in the polar directions and carves out a cavity in the AGB envelope to form a bipolar nebula. Newly discovered structures such as concentric arcs, 2-D rings, multiple lobes, and point-symmetric structures suggest that both the slow and fast winds may have temporal and directional variations, and precession can play a role in the shaping of planetary nebulae. In this paper, we review the latest observations of planetary nebulae and proto-planetary nebulae and discuss the various physical mechanisms (rotation, binary, magnetic field, etc) that could lead to the observed morphologies.

We show that the inclination to the line of sight of bipolar planetary nebulae strongly affects some of their observed properties. We model these objects as having a dusty equatorial density enhancement that produces extinction that varies with the viewing angle. Our sample of 29 nebulae taken from the literature shows a clear correlation between the inclination angle and the near-infrared and optical photometric properties as well as the detected luminosity of the objects. As the inclination angle increases (the viewing angle is closer to the equatorial plane) the objects become redder, their apparent luminosity decreases, and their projected expansion velocity becomes smaller. We compute two-dimensional models of stars embedded in dusty disklike structures of various shapes and compositions and show that the observed data can be reproduced by disk-star combinations with reasonable parameters. To compare with the observational data, we generate sets of model data by randomly varying the star and disklike structure parameters within a physically meaningful range. We conclude that a only a smooth pole to equator density gradient agrees with the observed phenomena.

We report the detection of a molecular bipolar outflow in the CO J = 3–2 line in the optical multipolar planetary nebula NGC 2440. The observed CO J = 3–2 emission shows two major velocity components which are blue- and redshifted by 18 km s−1 relative to the systemic velocity of VLSR = 43 km s−1. Both components are detected only near the central region and have a size of about 24''. In addition to this bulk motion, weak CO emissions in the central region are detected at higher velocities of ±20 to ±40 km s−1. The presence of the fast CO components are in line with the picture that the neutral dense torus is being torn apart by very fast outflowing winds. The spatial distribution of CO emission shows two emission peaks at the systemic velocity that are located 30'' to the northeast and 30'' to the southwest from the center in point symmetry. The positions of the two CO emission peaks coincide well with the emission knots in the optical, suggesting that the CO outflow corresponds to one pair of the multiple optical bipolar lobes of the nebula. This particular pair of bipolar lobes seem distinctly rich in heavy molecules compared with the other optical bipolar lobes. The extent of CO emission in NGC 2440 is well constrained. The total amount of CO molecules in NGC 2440 is 3.5 × 1051 if the distance to NGC 2440 is 2.19 kpc and the excitation temperature is 25 K.

Abell 14 is a poorly studied object despite being considered a born again planetary nebula. We performed a detailed study of its 3D morphology and ionization structure using the SHAPE and MOCASSIN codes. We found that Abell 14 is a highly evolved, bipolar nebula with a kinematical age of $\sim$19,400 yr for a distance of 4 kpc. The high He abundance, and N/O ratio indicate a progenitor of 5 $M_{\odot}$ that has experienced the third dredge-up and hot bottom burning phases. The stellar parameters of the central source reveal a star at a highly evolved stage near to the white dwarf cooling track, being inconsistent with the born again scenario. The nebula shows unexpectedly strong [N I] $\lambda 5200$ and [O I] $\lambda 6300$ emission lines indicating possible shock interactions. Abell 14 appears to be a member of a small group of highly evolved, extreme Type-I PNe. The members of this group lie at the lower-left corner of the PNe regime on the [N II]/H$\alpha$ vs. [S II]/H$\alpha$ diagnostic diagram, where shock--excited regions/objects are also placed. The low luminosity of their central stars, in conjunction with the large physical size of the nebulae, result in a very low photo-ionization rate, which can make any contribution of shock interaction easily perceptible, even for small velocities., Comment: 12 pages, 9 figures and 4 tables, accepted for publication in MNRAS

10 pages, 6 figures, RWT 152 is one of the few known planetary nebulae with an sdO central star. We present subarcsecond red tunable filterHa imaging and intermediate-resolution, long-slit spectroscopy of RWT 152 obtained with OSIRIS/GTC (Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy/Gran Telescopio Canarias) with the goal of analysing its properties. The Ha image reveals a bipolar nebula with a bright equatorial region and multiple bubbles in the main lobes. A faint circular halo surrounds the main nebula. The nebular spectra reveal a very low excitation nebula with weak emission lines from H+, He+ and double-ionized metals, and absence of emission lines from neutral and single-ionized metals, except for an extremely faint [NII] lambda 6584 emission line. These spectra may be explained if RWT 152 is a density-bounded planetary nebula. Low nebular chemical abundances of S, O, Ar, N and Ne are obtained in RWT 152, which, together with the derived high peculiar velocity (similar to 92-131 km s(-1)), indicate that this object is a halo planetary nebula. The available data are consistent with RWT 152 evolving from a low-mass progenitor (similar to 1 M-circle dot) formed in a metal-poor environment., This paper has been partially supported by grant AYA 2011-24052 (AA, ES), AYA 2011-30228-C3-01 (LFM), ESP2014-55996-C2-2-R (AU) and AYA2014-57369-C3-3-P (LFM) of the Spanish MINECO (all them co-funded by FEDER funds). We also acknowledge support from grant IN-CITE09 312191PR (AU, LFM, AA) of Xunta de Galicia, partially funded by FEDER funds, from grant PRX15/00511 (AU) of the Spanish MECD, and from grant 12VI20 (AU, LFM, AA) of the University of Vigo. AA also acknowledges support from FONDECYT through postdoctoral grant 3160364. This research has made use of the SIMBAD data base, operated at the CDS, Strasbourg (France), Aladin, NASA's Astrophysics Data System Bibliographic Services and the Spanish Virtual Observatory supported from the Spanish MINECO through grant AYA2011-24052.

Mid-infrared imaging of two bipolar proto-planetary nebulae, IRAS 17150-3224 and IRAS 17441-2411, was obtained with the Gemini telescope. Dust emissions are detected in both the bipolar lobes and in the equatorial region of IRAS 17441-2411. In particular, the orientation of the axis of the infrared torus is found to be offset by 23° from the bipolar axis. If the torus is responsible for or related to the collimation of the bipolar outflow, this raises the possibility that the outflow has undergone precession over the last 100 years.

We have determined the gas kinematics, diagnostic and ionic radial profiles, spatial structure, and evolutionary phase of NGC 6720 (the Ring Nebula) by means of tomography and a three-dimensional recovery technique applied to long-slit high-resolution spectra. The main shell of the Ring Nebula is a triaxial ellipsoid (radii of 0.10, 0.13, and 0.20 pc) seen nearly pole-on and expanding in an approximately ballistic fashion (Vexp = 0.65 km s-1 arcsec-1). The central star characteristics [log(L*/L?) 2.3, T* 120,000 K], combined with the nebular age of 7000 yr, indicate that the M* 0.61-0.62 M? post-AGB star is approaching the white dwarf cooling sequence. The equator of the Ring Nebula is optically thick and much denser than the optically thin poles. The inner halo surrounding NGC 6720 represents the pole-on projection of the AGB wind at high latitudes (circumpolar) directly ionized by the central star, whereas the outer, fainter, and circular halo is the projection of the recombining AGB wind at mean to low latitudes, shadowed by the main nebula. The spatio-kinematical properties of the Ring Nebula and the origin of the dense knots commonly observed in late-stage planetary nebulae are critically compared with the predictions of radiation-hydrodynamic and wind interaction models.

A series of two-dimensional rings along a common axis aligned with the bipolar lobes is found in the planetary nebulaHb12.Theringshaveseparationsofabout0.3 00 ,whichcanbetranslatedintophysicalseparationsof � 1000AU, or time separations of the order of 50 yr. We suggest that the existence of the rings is a manifestation of the interactionbetweenat ime-variable,collimatedfastoutflowwiththe circumstellarenvelope createdbythestellarwind of an asymptotic giant branch star. Comparison of Hb 12 with other bipolar nebulae with hourglass structures such as Hen2-104,MyCn18,andSN1987Asuggeststhatthenebulaof Hb12mayrepresenttheinnernebulaofamuchlarger bipolar structures, and we propose to search for such outer structures with a wide-field infrared camera. Subject headingg binaries:symbiotic — planetarynebulae:general — planetarynebulae:individual(Hubble12) — stars: AGB and post-AGB

13 pags., 11 figs., 1 tab., Our imaging of the preplanetary nebula IRAS 19475+3119 (hereafter 119475) at 0.43 and 0.6 μm with HST reveals a quadrupolar nebula of size about 10.5″ × 4.7″, with two bipolar elongated lobes emanating from the center of the nebula. One of the bipolar lobes shows detailed point-symmetric structure with respect to the central star. A faint, surface brightness-limited, diffuse halo surrounds the lobes. Interferometric observations of the CO J = 1-0 line with OVRO at ∼8″ resolution show that the bulk of the emission comes from an unresolved molecular envelope expanding at 15 km s-1, resulting from the AGB progenitor's dense, slow wind. Weaker emission is seen from a fast bipolar outflow oriented along the longer and more tenuous pair of the sets of lobes. Optical spectroscopy reveals a complex Hα profile with a broad photospheric absorption feature and a narrow inverse P Cygni shaped core; comparison with previous data shows that the core profile shape varies dramatically with time. We find an unresolved source of millimeter-wave continuum emission in 119475, which together with previous submillimeter continuum measurements, implies a very substantial mass (roughly a few times 0.01 M⊙) of large (radius ≳1 mm), cold (∼30 K) dust grains in 119475. Combining our estimates of the circumstellar mass with the typical mass of a post-AGB star, we find that the main-sequence progenitor of 119475's central star had a mass ≳2.5 M⊙. We discuss the formation of 119475's quadrupolar nebula in the light of past and current ideas for the dramatic transformation of the morphology and kinematics of mass ejecta as AGB stars evolve into planetary nebulae. © 2007. The American Astronomical Society. All rights reserved., R. S. andM.M. thank NASA for partially funding this work by a NASA LTSA award (399-20-40-06); R. S. also received partial support for this work from NASA ADP award (399-20-00-08) and HST/GO awards (GO-09463.01-A and GO-09801.01-A) from the Space Telescope Science Institute, which is operated by theAURA, Inc., under NASA contract NAS5-26555). C. S. C. is partially funded for this work by National Science Foundation grant 9981546 to Owens Valley Radio Observatory, the Spanish MCyT under project AYA2003-2785, and the Astroscam project (Ref: S-0505 ESP-0237).

We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope. Using the optical spectrum obtained with the Southern African Large Telescope, we classify this star as B1 Ia. The evolved status of MN18 is supported by the detection of nitrogen overabundance in the nebula, which implies that it is composed of processed material ejected by the star. We analysed the spectrum of MN18 by using the code CMFGEN, obtaining a stellar effective temperature of \approx 21 kK. The star is highly reddened, E(B-V)\approx 2 mag. Adopting an absolute visual magnitude of M_V=-6.8\pm0.5 (typical of B1 supergiants), MN18 has a luminosity of log L/Lsun \approx 5.42\pm0.30, a mass-loss rate of \approx (2.8-4.5)\times10^{-7} Msun/yr, and resides at a distance of \approx 5.6^{+1.5} _{-1.2} kpc. We discuss the origin of the nebula around MN18 and compare it with similar nebulae produced by other blue supergiants in the Galaxy (Sher 25, HD 168625, [SBW2007] 1) and the Large Magellanic Cloud (Sk-69 202). The nitrogen abundances in these nebulae imply that blue supergiants can produce them from the main sequence stage up to the pre-supernova stage. We also present a K-band spectrum of the candidate luminous blue variable MN56 (encircled by a ring-like nebula) and report the discovery of an OB star at \approx 17 arcsec from MN18. The possible membership of MN18 and the OB star of the star cluster Lynga 3 is discussed., 21 pages, 14 figures, accepted for publication in MNRAS

NaSt1 (aka Wolf-Rayet 122) is a peculiar emission-line star embedded in an extended nebula of [N II] emission with a compact dusty core. This object was characterized by Crowther & Smith (1999) as a Wolf-Rayet (WR) star cloaked in an opaque nebula of CNO-processed material, perhaps analogous to Eta Car and its Homunculus nebula, albeit with a hotter central source. To discern the morphology of the [N II] nebula we performed narrowband imaging using the Hubble Space Telescope and Wide-field Camera 3. The images reveal that the nebula has a disk-like geometry tilted 12 degrees from edge-on, composed of a bright central ellipsoid surrounded by a larger clumpy ring. Ground-based spectroscopy reveals radial velocity structure (~10 km/s) near the outer portions of the nebula's major axis, which is likely to be the imprint of outflowing gas. Near-infrared adaptive-optics imaging with Magellan AO has resolved a compact ellipsoid of Ks-band emission aligned with the larger [N II] nebula, which we suspect is the result of scattered He I line emission (2.06 um). Observations with the Chandra X-ray Observatory have revealed an X-ray point source at the core of the nebula that is heavily absorbed at energies, Accepted to MNRAS on 2015 Feb 5; 14 pages, 9 figures (post-proof edit)

We have obtained X-ray observations of the bipolar planetary nebulae (PNe) NGC 2346 and NGC 7026 with XMM-Newton. These observations detected diffuse X-ray emission from NGC 7026 but not from NGC 2346. The X-ray emission from NGC 7026 appears to be confined within the bipolar lobes of the PN and has spectral properties suggesting a thermal plasma emitting at a temperature of 1.1 × 106 K. The X-ray spectrum of NGC 7026 is modeled using nebular and stellar abundances to assess whether a significant amount of nebular material has been mixed into the shocked wind, but the results of this comparison are not conclusive owing to the small number of counts detected. Observations of bipolar PNe indicate that diffuse X-ray emission is much less likely detected in open-lobed nebulae than closed-lobed nebulae, possibly because open-lobed nebulae do not have strong fast winds or are unable to retain hot gas.

In this paper, we compute theoretically the flux density and the spectral index of the free-free radiation at radio wavelengths produced by shocks in the inner bipolar emission nebula called the little Homunculus around the star η Carinae. The little Homunculus is believed to have formed as a result of the minor eruption suffered by the star in the 1890s. In our model, we consider a simplified interacting stellar wind scenario where the post-outburst η Carinae wind collides with the eruptive outflow (both assumed to be bipolar with conical symmetry). As a result of the interaction, shock-wave structures are formed and generate the development of two polar caps moving in opposite directions. After ∼100 yr (i.e. at present times), the polar caps are located ±2.3 arcsec on each side of the star, and remain embedded within the larger bipolar Homunculus that extends from -8 to +8 arcsec along its major axis. Using observational estimates of the characteristics of the eruptive event of the 1890s, and of the ambient wind powered by η Carinae in the decades after the eruption ended, we study the evolution of the polar caps formed as a result of a sudden increase in the wind velocity and an instantaneous drop in the mass-loss rate (just after the eruption) at the injection radius. We found that the little Homunculus emits continuum radiation that can be detected at radio frequencies and that indeed represents an important contribution to the total free-free emission detected from the η Carinae nebula.

We report long-slit spectroscopic observations of the Herbig Ae/Be star Elias 1 in the 3.2-3.6 mum region covering the C-H stretch emission features of hydrogen-terminated diamonds and PAHs. The data were recorded at UKIRT using UIST and yield information on the profiles and intensities of the bands as a function of offset along the N-S and E-W axes centred on the close binary. The diamond and nearby IR continuum emission arises from a symmetrical inner core region (< 0.34 arcsec or 48 AU). The 3.3 mum PAH emission is extended along the E-W axis up to ~ 100 AU each side of the star. This result supports a suggestion of Haas, Leinert & Richichi (1997) of an E-W oriented bipolar nebula in Elias 1.

We present AAO/UKST Hα+[N II] narrow-band imagery and low- and medium-resolution optical spectroscopy of RCW 24 and RCW 69. These nebulae were previously classified as H II regions, but we now show them to be two of the largest and nearest bipolar Type I PNe yet discovered. Distances were estimated using extinction-distance and kinematic methods, and via a new Ha surface brightness-radius relation. The adopted distances are 1.0 ± 0.3 kpc for RCW 24 and 1.3 ± 0.2 kpc for RCW 69. Both objects have enhanced nitrogen abundances, with log N/O ≃ +0.44 for RCW 24, and log N/O = +0.33 for RCW 69. Systemic velocities and |z| distances are V LSR = +5 km s -1 and |z| ∼ 23 pc for RCW 24, and V LSR = -33 km s -1 and only |z| ∼ 7 pc for RCW 69. Both PNe originated from massive progenitors (>2.0-2.5 M ⊙ ), as deduced from their chemical abundances, large ionized masses, small |z| distances, low peculiar velocities and relatively hot central stars. These two objects form an important addition to the small sample of evolved bipolar PNe in the solar neighbourhood.

H2 emission has been detected in the bipolar proto-planetary nebula IRAS 17150-3224 from the 1-0 S(1), 1-0 S(0), and 2-1 S(1) transitions in the 2 μm region. Line ratios suggest that this emission is due to collisional excitation. High-resolution imaging with NICMOS on HST shows that the emission comes from four regions: clumps near the ends of the lobes (the brightest region), the lobes in general, a particular region outside the northwest lobe, and a faint loop in the equatorial region. Spatially resolved high-resolution spectra at 2.12 μm reveal that the H2 1-0 S(1) line has a velocity width of about 35 km s-1 in the lobes, consistent with C-type shocks. The emission from the clumps in the lobes appears to arise from the impact of a fast wind with the slower moving material in the AGB wind.

We present a comprehensive study of a low-mass star-forming region,L1251B, at wavelengths from the near-infrared to the millimeter. L1251B, where only one protostar, IRAS 22376+7455, was known previously, is confirmed to be a small group of protostars based on observations with the Spitzer Space Telescope. The most luminous source of L1251B is located 5" north of the IRAS position. A near-infrared bipolar nebula, which is not associated with the brightest object and is located at the southeast corner of L1251B, has been detected in the IRAC bands. OVRO and SMA interferometric observations indicate that the brightest source and the bipolar nebula source in the IRAC bands are deeply embedded disk sources.Submillimeter continuum observations with single-dish telescopes and the SMA interferometric observations suggest two possible prestellar objects with very high column densities. Outside of the small group, many young stellar object candidates have been detected over a larger region of 12' x 12'. Extended emission to the east of L1251B has been detected at 850 micron; this "east core" may be a site for future star formation since no point source has been detected with IRAC or MIPS. This region is therefore a possible example of low-mass cluster formation, where a small group of pre- and protostellar objects (L1251B) is currently forming, alongside a large starless core (the east core)., Comment: 35 pages, 15 figures, accepted for publication in ApJ, for the full resolution paper, visit "http://peggysue.as.utexas.edu/SIRTF/PAPERS/pap27.pub.pdf"

We present high-resolution, nearly diffraction-limited narrow- and broadband mid-IR images of bipolar reflection nebula Hen 3-401. The deconvolved images yield a pixel-limited spatial resolution of 009, demonstrating the superior imaging quality of the Gemini telescope. The infrared image of Hen 3-401 consists of a prominent core region of size 1'' and extended emissions along the walls of the bipolar lobes. We find that the distribution of aromatic infrared band (AIB) emission is different from that of the continuum emission and that the star has undergone multiple ejection of the AIB emission feature carrier at the end stages of its evolution. From the observed temperature gradient in the core, we suggest that the core has a flared disk geometry.

ISO spectra of the bipolar planetary nebula Mz3 are used to determine the element abundances in the bright lobes of the nebula. The ISO spectra alone are sufficient to determine nitrogen, neon, argon, sulfur and iron abundances. These spectra are combined with spectra in the visual wavelength region (taken from the literature) to obtain an extinction corrected spectrum which is used to determine the abundance of oxygen and some other elements using a classical determination. We have tried abundance determination using photoionization modeling using cloudy, which is essential for determining the helium, silicon and chlorine abundances. It was found di.cult to model the entire spectrum. New information about the central star could be determined. The abundances determined are found to differ somewhat from earlier results using only visual spectra. The reasons for this difference are discussed. An elevated helium abundance is found, agreeing with the determination of Smith 2003. Taken together with the high nitrogen abundance found, it is concluded that the exciting star of Mz 3 had a high progenitor mass.

An observational study of the spatial variation of the electron temperature and density in 10 galactic planetary nebulae is presented. The data consist of long-slit spectra of high signal-to-noise ratio in the 3100 to 6900 A range. Electron temperatures were determined from the [Oiii](λ 4959 + λ 5007)/λ 4363 and [Nii](λ 6548 + λ 6583)/λ 5755 ratios and from the Balmer discontinuity. Electron densities were estimated from the [Sii]λ 6716/λ 6731, [Cliii]λ 5517/λ 5537, and [Ariv]λ 4711/λ 4740 ratios. Electron temperature variations of low amplitude were found across the nebular surface in the planetary nebulae studied. The temperature distribution across each nebula presents a variance relative to the mean corresponding to 0.0003 ≤ t 2 (Bal) ≤ 0.0078, 0.0003 ≤ t 2 (Nii) ≤ 0.0097, and 0.0011 ≤ t 2 (Oiii) ≤ 0.0050. A systematic spatial variation of electron density has been detected in most of objects (NGC 1535, NGC 2438, NGC 2440, NGC 3132, NGC 3242, NGC 6302, NGC 6563, and NGC 7009). The remaining objects (NGC 6781 and NGC 6853) have not shown any significant electron density dependence on position. NGC 2438, NGC 6563, NGC 6781, and NGC 6853 are in general the most diffuse and probably evolved objects studied here, with low mean densities in the range Ne(Sii) ≈ 95–158 cm −3 . An anti-correlation between temperature and density was found for NGC 2438 and NGC 3132, with the electron temperature increasing with the decrease of electron density and a correlation between temperature and density was found for NGC 2440, NGC 3242, NGC 6302, and NGC 7009, with the electron temperature increasing with the increase of electron density. These relationships seem to be associated with the structure of the nebula. The nebulae in which the correlation between temperature and density is present are ring shaped. The anti-correlation between temperature and density is found in bipolar planetary nebulae that are denser in the centre of the nebula.

We report the results of mapping observations of the bipolar nebula with SiO maser emission, IRAS 19312+1950, in the CO (J=1-0 and J=2-1), 13CO (J=1-0 and J=2-1), C18O (J=1-0), CS (J=2-1), SO (J_K=3_2-2_1) and HCO+ (J=3-2) lines with the Berkeley-Illinois-Maryland Association array. Evolutional status of this source has been evoking a controversy since its discovery, though SiO maser sources are usually identified as late-type stars with active mass loss. In line profiles, two kinematical components are found as reported in previous single-dish observations: a broad pedestal component and a narrow component. Spatio-kinetic properties of a broad component region traced by 12CO lines are roughly explained by a simple spherical outflow model with a typical expanding velocity of an AGB star, though some properties of the broad component region still conflict with properties of a typical AGB spherical outflow. A narrow component region apparently exhibits a bipolar flow. The angular size of the narrow component region is spatially larger than that of a broad component region. Intensity distribution of the CS emission avoids the central region of the source, and that of an SO broad component emission exhibits a small feature peaked exactly at the mapping center. According to the present results, if a broad component really originates in a spherical outflow, an oxygen-rich evolved stellar object seems to be a natural interpretation for the central star of IRAS 19312+1950., 27 pages, 11 figures; accepted for publication in ApJ

We present diffraction-limited images in the 11.3 micron PAH band and in the continuum at 11.9 microns of the S287B star forming region obtained with the newly commissioned mid-infrared imager/spectrometer VISIR at the VLT. In both filters five point-like sources are detected, of which at least one has a spectral energy distribution reminiscent of a Lada Class I source. We also report on the discovery of a new Herbig Ae star in this region. It is particularly striking that the brightest mid-infrared source in this region has not been detected at shorter wavelengths; it is a good candidate to be the driving source of the bipolar molecular outflow and optical reflection nebulosity previously reported in S287B., Comment: Accepted by A&A Letters

This paper reports on radiative transition rates and electron impact excitation rate coefficients for levels of the 3d 7 ground configuration of Ni IV. The radiative data were computed using the Thomas-Fermi-Dirac central potential method, which allows for configuration interactions (CI) and relativistic effects in the Breit-Pauli formalism. Collision strengths in LS-coupling were calculated in the close coupling approximation with the R-matrix method. Then, fine structure collision strengths were obtained by means of the intermediate-coupling frame transformation (ICFT) method that accounts for spin-orbit coupling effects. The collision strengths were integrated over a Maxwellian distribution of electron energies, and the resulting effective collision strengths are given for a wide range of temperatures. We build a multilevel model for the Ni IV system and use it to identify the most important lines in optical and infrared spectra and to compute line ratios as diagnostics of nebular conditions. Finally, we test these data against recent observations of the bipolar planetary nebula Mz 3.

We present JHK' imaging polarimetry for the massive star-forming region S87, and K-band spectrometry from 2.0 to 2.35 mum for several infrared sources in the region. The polarimetric patterns of S87E reveal a deeply embedded source (DES-S87) associated with reflection nebulosities. Exciting OH maser and 1.3 mm dust continuum emission, the DES-S87 is suggested to be the youngest star in S87 and the driving source of bipolar CO outflow in the region. A blue cavity is discovered in the [J-K'] color image, to the southwest of DES. Radial dependence of polarization degrees in the cavity could be fitted to the slab model of outflows at an inclination of similar to60degrees out of the plane of the sky (Minchin et al. 1991b). The nebular complex of S87E can be divided into three area. The North nebula, exhibiting a bipolar structure, may represent a bipolar outflow in the northwest-southeast direction. The southwest nebula traces the blueshifted CO outflow and corresponds to the cavity structure discovered in the [J-K'] color image. The nebular structure of S87E suggests a quadrupolar outflow driven by DES-S87. A well-defined centrosymmetric pattern is found in the nebula of S87W with high degrees of polarization, which indicates single scattering off small dust grains in the reflection nebula. The polarimetric vectors around NIRSA show a polarization disk feature oriented in the southeast-northwest direction. Strong Brgamma emission and H-2 emissions are found in the K-band spectra, indicating the presences of strong stellar wind, envelope/disk, shocked gas, and high-density PDRs in the circumstellar environment of S87E and S87W. According to the K-band spectrum, the mass of DES-S87E is estimated to be 20 M-circle dot.

e present Near Infrared imaging polarimetry of three regions of massive star formation, G$192.16 - 3.82$, Cepheus A, and W42. In W42 we have discovered a new bipolar nebula located at the far side of the HII region behind the visible cluster of exciting stars. The axis of this new nebula is aligned with the magnetic field threading the entire cluster region. Polarization in the bipolar outflow nebulosity associated with G192.16 is consistent with a single illuminating source, too faint to be detected at $2 \micron$. Polarization in the reflection nebulosity associated with Ceph A requires more than one illuminating source, although HW2 is clearly dominant. In all three objects, the magnetic field in the outflow at distances greater than $\sim 0.2$ pc is radial. In G192.16 the magnetic field geometry closer than $\sim 0.2$ pc to the embedded star appears chaotic. For G192.16 the outflow is not aligned with the surrounding magnetic field, which lies in the galactic plane. In Ceph A, the outflow axis could be interpreted as being aligned with the galactic plane, but the magnetic field threading the region is not. Only in the case of W42 is the magnetic field threading the HII region aligned with the mean field in the surrounding galactic plane.

We present the first high spatial resolution mid-IR and far-IR images of the planetary nebula NGC 2346 using the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. The morphology at 24 μm is strikingly similar to that seen in the optical image, with an additional unresolved hot dust component at the center. The 70 μm image reveals a torus-like structure near the narrow waist of the bipolar nebula, while the 160 μm image shows a very extended cold dust envelope around the nebula. Our new MIPS data provide direct evidence that the mass loss in the end of the asymptotic giant branch (AGB) phase diverts from spherical symmetry to axisymmetry and that the binary central star has played an important role in the bipolar nebular evolution.

Spatially resolved, long-slit spectra obtained with the Manchester echelle spectrometer of the planetary nebula J320 have been compared with Hubble Space Telescope and ground-based images. The morphology and kinematics of the nebular core have been convincingly modelled using the Xshape code. Two and possibly three bipolar lobes, expanding at ≈ 46 km s−1 but with different axial orientations, have been found to constitute the bright central nebula. These are found to be surrounded by two sets of point-symmetric, high-speed knots reminiscent of those that could be generated by a bipolar, rotating, episodic jet. Another isolated knot exists but without a counterpart. The sequence and nature of the periodic ejections that have given rise to this complex structure are considered in view of the most recent theories of the shaping and evolution of planetary nebulae.