Bipolar Planetary Nebulae Research Articles

XMM‐NewtonObservations of the Bipolar Planetary Nebulae NGC 2346 and NGC 7026

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.

Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way

This paper presents a homogeneous study of abundances in a sample of 79 northern Galactic planetary nebulae (PNe) whose morphological classes have been uniformly determined. Ionic abundances and plasma diagnostics were derived from selected optical line strengths in the literature, and elemental abundances were estimated with the ionization correction factor developed by Kingsbourgh & Barlow in 1994. We compare the elemental abundances to the final yields obtained from stellar evolution models of low- and intermediate-mass stars, and we confirm that most bipolar PNe have high nitrogen and helium abundance and are the likely progeny of stars with main-sequence mass greater than 3 M☉. We derive = 0.27 and discuss the implication of such a high ratio in connection with the solar neon abundance. We determine the Galactic gradients of oxygen and neon and found Δ log(O/H)/ΔR = -0.01 dex kpc-1 and Δ log(Ne/H)/ΔR = -0.01 dex kpc-1. These flat PN gradients are irreconcilable with Galactic metallicity gradients flattening with time.

SpitzerMIPS Imaging of NGC 650: Probing the History of Mass Loss on the Asymptotic Giant Branch

We present the far-infrared (IR) maps of a bipolar planetary nebula (PN), NGC 650, at 24, 70, and 160 μm, taken with the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. While the two-peak emission structure seen in all MIPS bands suggests the presence of a near edge-on dusty torus, the distinct emission structure between the 24 μm map and the 70/160 μm maps indicates the presence of two distinct emission components in the central torus. Based on the spatial correlation of these two far-IR emission components with respect to various optical line emission, we conclude that the 24 μm emission is largely due to the [O IV] line at 25.9 μm arising from highly ionized regions behind the ionization front, whereas the 70 and 160 μm emissions are due to dust continuum arising from low-temperature dust in the remnant asymptotic giant branch (AGB) wind shell. The far-IR nebula structure also suggests that the enhancement of mass loss at the end of the AGB phase has occurred isotropically, but has ensued only in the equatorial directions while ceasing in the polar directions. The present data also show evidence for the prolate spheroidal distribution of matter in this bipolar PN. The AGB mass-loss history reconstructed in this PN is thus consistent with what has been previously proposed based on the past optical and mid-IR imaging surveys of the post-AGB shells.

Two new evolved bipolar planetary nebulae in the solar neighbourhood

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 Hα 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 VLSR=+5 km s−1 and |z| ∼ 23 pc for RCW 24, and VLSR=−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.

Shaping Bipolar Planetary Nebulae: How Mass Loss Leads to Waistline Development

Asymptotic giant branch (AGB) stars generally have spherically symmetric envelopes, whereas most post-AGB stars and planetary nebulae (PNe) show axisymmetric circumstellar envelopes. While various mechanisms for axisymmetric circumstellar structures may explain the shapes of PNe, they do not address how the shape of the circumstellar shell evolves. Here we address the temporal changes in the axisymmetry of AGB star envelopes, and in particular the development of the torus required in the generalized interacting stellar winds (GISW) model. Assuming that (1) an AGB star rotates with sufficient angular speed at the start of the AGB phase, and (2) the rotational angular momentum of the AGB star is conserved, we demonstrate that some very important observational features of AGB star axisymmetry evolution can be reproduced. We find that, compared to the star's increasing luminosity and decreasing effective temperature, the decreasing mass of the star primarily affects the axisymmetry of the envelope. When a representative mass-loss history is adopted in which most of the mass is lost near the end of the AGB phase, the envelope's axisymmetry increases over time, with the strongest increase occurring near the end of the AGB phase. This may naturally explain why most AGB stars have spherically symmetric envelopes, while axisymmetry seems commonplace in the post-AGB/PNe phase. The degree of axisymmetry at the end of the AGB phase is found to increase with increasing main-sequence mass, and the onset of axisymmetry occurs only after the onset of the superwind phase, in good agreement with the observations.

Kinematical analysis of Bipolar Planetary Nebulae

Bipolar planetary nebulae (BPNe) offer a unique opportunity to test models that aim to reproduce the PNe morphologies. In particular, kinematic studies of BPNe allow a reconstruction of the 3D structure of the nebula, otherwise hidden in imaging studies. With this aim in mind we have obtained long-slit echelle spectra of a sample of PNe which cover the full range of observed bipolar morphologies, from elliptical to highly collimated. The analysis of our kinematical data reveals equatorial expansion velocities in the low to medium range (3 to 16 km s. We find that the kinematics of the PN K 3-46 can only be explained by a decrease in the expansion velocity with time. The kinematical ages, calculated by using distances estimated from Galactic rotation curves, when available, or by using statistical values, show that the BPNe in our sample – even those which show non-extreme collimation – appear to be young. We have compared our results with the latest theoretical models of BPN formation, and find good agreement between the observed expansion velocities and the numerical models that use magnetic fields coupled with stellar rotation as the collimation mechanism.

On the Origin of Bipolar Planetary Nebulae

We present a numerical simulation of the formation of a bipolar planetary nebula from a single star. At the late stage of AGB stars, surface convection and/or convection of shell burning would create differential rotation between the core and the envelope of such stars. If the core has a magnetic field threading the envelope, this differential rotation twists magnetic fields. Then like a cosmic jet model of accretion disks, such a twist of magnetic fields piles up a tower of magnetic fields atop the pole of the progenitor core and creates jets.

The Fe/Ni ratio in the Ant Nebula Mz 3

We have analyzed the [Fe II ] and [Ni II ] emission lines in the bipolar planetary nebula Mz 3. We find that the [Fe II ] and [Ni II ] lines arise exclusively from the central regions. Fluorescence excitation in the formation process of these lines is negligible for this low-excitation nebula. From the [Fe II ]/[Ni II ] ratio, we obtain a higher Fe/Ni abundance ratio than the solar value. The current result provides further supporting evidence for Mz 3 as a symbiotic Mira.

Formation of bipolar planetary nebula M 2-9 by confining toroidal magnetic field and surrounding high-ram pressure wind

Formation of bipolar planetary nebula M 2-9 by confining toroidal magnetic field and surrounding high-ram pressure wind

3D Photoionisation Modelling of NGC 6302

We present the first results from our 3D photoionisation modelling of NGC 6302, an extreme high-excitation bipolar planetary nebula with a dense dusty circumstellar disc. We are attempting to fully match the observed spectrum, including the high-ionization infrared coronal lines as well as the observed ISO spectrum. We use a bipolar model nebula with a dense circumstellar torus. Our initial results show that, considering the very high stellar temperature required to match the high ionization coronal lines, an extremely high density contrast between the bipolar lobes and the circumstellar disc is required to match the nebular line ratios.

Abundances in planetary nebulae: Mz 3

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.

Electron temperature fluctuations in planetary nebulae

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.

The symmetric dust shell and the central star of the bipolar planetary nebula NGC 6537

We present high-resolution images of the strongly bipolar planetary nebula NGC 6537, obtained with Hubble Space Telescope and with the infrared adaptive optics system on the Very Large Telescope. The central star is detected for the first time. Using the multi-band photometry and constraints from the dynamical age of the nebula, we derive a temperature in the range 1.5-2.5 10^5 K, a luminosity~10^3 L_sun and a core mass M_c~0.7-0.9 M_sun. The progenitor mass is probably in the range M_i = 3-7 M_sun. The extinction map shows a largely symmetric, and compact dust structure, which is most likely a shell, located at the neck of the bipolar flow, only 4 arcsec from the star. The dust shell traces a short-lived phase of very high mass loss at the end of the AGB. The dynamical age of the shell and bipolar lobes are very similar but the morphologies are very different. The data suggests that the mass loss during the ejection of the compact shell was largely spherically symmetric, and the pronounced bipolarity formed afterwards. The dynamical ages of the bipolar lobes and dust shell are similar, which is consistent with suggestions that bipolar structures form in a run-away event at the very last stages of the AGB mass loss. The inner edge of the dust shell is ionized, and PAH emission is seen just outside the ionized gas. We associate the PAH emission with the photo-dissociation region of the molecular shell.

Kinematic Structure of H2and [Feii] in the Bipolar Planetary Nebula M2-9

We present new high-dispersion, long-slit, infrared (IR) spectra of the double-shell bipolar planetary nebula M2-9 in the emission lines [Fe II] λ16435 and H2 v = 1–0 S(1) λ21218. H2 spectra reveal for the first time the kinematic structure of the shell in M2-9. Kinematics of the inner shell, traced by [Fe II], resemble those of optical forbidden lines like [N II] λ6583, although we note subtle differences. [Fe II] and H2 shells have expansion speeds roughly proportional to distance from the star (Hubble flows) and share the same dynamical age of 1200–2000 yr, depending on the distance to M2-9. Thus, the inner ionized lobes and molecular lobes, as well as the molecular torus and outer loops measured by other observers, were all formed around the same time. Consequently, their nested structure likely arises from an excitation gradient rather than independent ejections. H2 and [Fe II] emission is distributed more uniformly than [N II], and IR lines are not dominated by the moving ionization pattern like visual-wavelength lines. We suggest that this is because IR lines of [Fe II] and H2 are excited by relatively isotropic far-UV radiation (Balmer continuum), whereas optical lines respond to a directed rotating beam of Lyman continuum. Finally, we highlight intriguing similarities between M2-9 and the Homunculus of η Car, despite the different central engines powering the two nebulae.

Atomic data from the Iron project

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.

Space Telescope Imaging Spectrograph Ultraviolet Spectra of Large Magellanic Cloud Planetary Nebulae: A Study of Carbon Abundances and Stellar Evolution

We acquired spectra of 24 LMC planetary nebulae (PNs) in the 1150-3000 A range in order to determine carbon and other ionic abundances. The sample more than doubles the number of LMC PNs with high-quality UV spectra in this wavelength range and whose optical images are available in the Hubble Space Telescope archive. The Space Telescope Imaging Spectrograph was used with a very large aperture to obtain virtually slitless spectra; thus, the monochromatic images in the major nebula emission lines are also available. The analysis of the data shows extremely high quality spectra. This paper presents the emission lines identified and measured and the calculation of the ionic abundances of the emitting carbon and other ions, as well as total carbon abundance. P Cygni profiles have been found in a fraction of the nebulae, and the limiting velocities of the stellar winds estimated. The total carbon abundance can be inferred reliably in most nebulae. We found that the average carbon abundance in round and elliptical PNs is one order of magnitude larger than that of the bipolar PNs, while elliptical and round PNs with a bipolar core have a bimodal behavior. This results confirm that bipolarity in LMC PNs is tightly correlated with high-mass progenitors. When compared with predicted yields, we found that the observed abundance ratio shows a shift toward higher carbon abundances, which may be due to initial conditions assumed in the models not appropriate for LMC PNs.

Bipolar Symbiotic Planetary Nebulae in the Thermal Infrared: M2-9, Mz 3, and He 2-104

We present thermal-infrared images of three extreme bipolar objects, M2-9, Mz 3, and He 2-104. They are bipolar planetary nebulae with bright central stars and are thought to be powered by symbiotic binary systems. The mid-infrared images spatially resolve the spectral energy distributions of the central engines from the surrounding nebulae. A warm dust component of several hundred degrees can account for the core emission, while a cooler component of ~100 K produces the more extended emission from the bipolar lobes. In every case, the dust mass for the unresolved core region is orders of magnitude less than that in the extended lobes, raising doubts that the hypothetical disks in the core could have been responsible for pinching the waists of the nebulae. We find total masses of roughly 0.5–1 M⊙ in the nebulae of M2-9 and Mz 3, requiring that this material was donated by intermediate-mass progenitor stars. The mass of He 2-104's nebula is much lower, and any extended emission is too faint to detect in our images. Extended dust emission is detected around both M2-9 and Mz 3, in both cases resembling the distribution of ionized gas. Our images of Mz 3 have the highest signal-to-noise ratio in the extended polar lobes, and we show that the fairly uniform color temperature derived from our images can explain the 110 K dust component that dominates the far-infrared spectral energy distribution. In the case of Mz 3, most of the mass traced by dust is concentrated at high latitudes, and we note possible evidence for grain destruction in shocks indicated by an anticorrelation between [Fe II] and dust emission. Except for these regions with enhanced [Fe II] emission, the dust continuum closely resembles the distribution of ionized gas.

An X-Ray Jet from a White Dwarf: Detection of the Collimated Outflow from CH Cygni with Chandra

Most symbiotic stars consist of a white dwarf accreting material from the wind of a red giant. An increasing number of these objects have been found to produce jets. Analysis of archival Chandra data of the symbiotic system CH Cygni reveals faint extended emission to the south, aligned with the optical and radio jets seen in earlier Hubble Space Telescope and Very Large Array observations. CH Cygni thus contains only the second known white dwarf with an X-ray jet, after R Aquarii. The X-rays from symbiotic star jets appear to be produced when jet material is shock-heated following collision with the surrounding gas, as with the outflows from some protostellar objects and bipolar planetary nebulae.

Molecular Hydrogen in the Ionized Region of Planetary Nebulae

This paper presents an analysis of the concentration of the hydrogen molecule inside the ionized region of planetary nebulae. The equations corresponding to the ionization and chemical equilibria of H, H+, H-, H2, H2+, and H3+ are coupled with the equations of ionization and thermal balance for a photoionized atomic gas. Forty different reactions related to the formation or the destruction of these species are included. The presence of dust is taken into account, since grains act as catalysts for the production of H2, as well as shield the molecules against the stellar ionizing radiation. We analyze the effect of the stellar ionizing continuum, as well as of the gas and grain properties on the calculated H2 mass. It is shown that a significant concentration of H2 can survive inside the ionized region of planetary nebulae, mostly in the inner region of the recombination zone. The total H2 to total hydrogen mass ratio inside the ionized region increases with the central star temperature, and, depending on the PN physical conditions, it can be of the order of 10^-6 or even higher. The increase of the recombination zone with the stellar temperature can account for such correlation. This can explain why the H2 emission is more frequently observed in bipolar planetary nebulae (Gatley's rule), since this kind of object has typically hotter stars. Applying our results for the planetary nebula NGC 6720, we obtain an H2 to hydrogen mass ratio similar to the value obtained from the observed H2 line emission.

Spatial distribution of near-infrared and optical emission properties in the bipolar nebula Menzel 3

Ground-based optical spectra combined with near-infrared spectra and images of the young bipolar planetary nebula Menzel 3 (Mz 3) reveal positional variations in extinction, excitation, density and other characteristics. Interstellar extinction is probably less than A V = 2.65, while extinction toward the nucleus is approximately 4.6 mag. The lobes show stratified ionization, with high-excitation emission localized at high latitudes. Quantitative analysis using the CLOUDY spectral synthesis code suggests that the polar lobes 'see' an excitation source similar to a blackbody of roughly 36000 K and 10000 L O ., and chemical abundances reveal that the ejecta have He enhanced by a factor of ∼2, and N enhanced more strongly, with N/O∼1. The lobes are probably radiatively excited, but shocks may heat the 'blisters' at the polar axis. The bright, unresolved nucleus has a crowded emission spectrum distinct from the diffuse bipolar lobes, and it indicates high electron densities of 10 6 -10 7 cm - 3 . An equatorial disc-like geometry for dense gas in the nucleus is likely. The nucleus also shows a nearly power-law continuum; when corrected for reddening it may require two stars, one hot star and one cool giant, along with hot ∼900-K dust. A distance up to ∼2.5 kpc is possible. In general, the spectral characteristics of Mz 3 are similar to those of the well-studied nebula M 2-9, and the two objects may share a similar evolutionary history. However, an important difference between them is that Mz 3 appears to be mostly devoid of molecular hydrogen, while infrared H 2 lines are conspicuous in M 2-9.