Morphology Of Planetary Nebulae Research Articles

Spectroscopic survey of faint planetary-nebula nuclei – II. The subdwarf O central star of Fr 2-30

ABSTRACT Fr 2-30 = PN? G126.8−15.5 is a faint emission nebula, hosting a 14th-mag central star that we identify here for the first time. Deep Hα and [O iii] images reveal a roughly elliptical nebula with dimensions of at least 22 arcmin × 14 arcmin, fading into a surrounding network of even fainter emission. Optical spectrograms of the central star show it to have a subdwarf O spectral type, with a Gaia parallax distance of 890 pc. A model-atmosphere analysis gives parameters of $T_{\rm eff}=60\, 000$ K, log g = 6.0, and a low helium content of nHe/nH = 0.0017. The location of the central star in the log g–Teff plane is inconsistent with a post-asymptotic-giant-branch evolutionary status. Two alternatives are that it is a helium-burning post-extreme-horizontal-branch object, or a hydrogen-burning post-red-giant-branch star. In either case, the evolutionary ages are so long that a detectable planetary nebula (PN) should not be present. We find evidence for a variable radial velocity (RV), suggesting that the star is a close binary. However, there are no photometric variations, and the spectral-energy distribution rules out a companion earlier than M2 V. The RVs of the star and surrounding nebula are discordant, and the nebula lacks typical PN morphology. We suggest that Fr 2-30 is a ‘PN mimic’ – the result of a chance encounter between the hot sdO star and an interstellar cloud. However, we note the puzzling fact that there are several nuclei of genuine PNe that are known to be in evolutionary states similar to that of the Fr 2-30 central star.

Discovery of SiO Masers in the “Water Fountain” Source IRAS 16552−3050

Abstract In this paper, we report new detections of SiO v = 1 and v = 2 J = 1 → 0 masers in the “water fountain” source IRAS 16552−3050, which was observed with the Nobeyama 45 m telescope during 2021 March–April. Water fountains are evolved stars whose H2O maser spectra trace high-velocity outflows of >100 km s−1. This is the second known case of SiO masers in a water fountain, after their prototypical source, W 43A. These SiO masers should shed light on the evolutionary status of this category of evolved stars, which are likely to be at the end of the asymptotic giant branch phase, when the star exhibits the most copious stellar mass loss, followed by development of the complicated morphologies of planetary nebulae. The origin of a large (up to 25 km s−1) velocity offset of the SiO masers with respect to the systemic velocity derived from the spectrum of CO J = 2 → 1 line is discussed here.

Detailed studies of IPHAS sources - I. The disrupted late bipolar IPHASX J193718.6+202102

Abstract We present a detailed analysis of the new planetary nebula (PN) IPHASX J193718.6+202102 using deep imaging and intermediate- and high resolution spectroscopy that are interpreted through morpho-kinematic and photoionisation modelling. The physical structure of the nebula consists of a fragmented torus and an extremely faint orthogonal bipolar outflow, contrary to the pinched waist PN morphology suggested by its optical image. Our kinematic analysis indicates that the torus is expanding at 25±5 km s−1 and is gradually breaking up. At an estimated distance of 7.1$_{-0.3}^{+0.8}$ kpc, the corresponding kinematic age of ∼26000 years is consistent with a faint and disintegrating PN. The intermediate-resolution spectra reveal an excited PN with chemical abundances typical of Type II PNe. Based on the latter we also estimate an initial mass for the progenitor in the range 2–3 M⊙ and a central star (CSPN) mass MCSPN ∼0.61 M⊙. The Spitzer MIPS 24 μm emission that closely follows the fragmented torus could be attributed to the emission of [O iv] at 25.9 μm rather than to dust emission. All the results coherently point towards an evolved moderately massive bipolar Type II PN on the brink of dissolving into the interstellar medium.

Common Envelope Shaping of Planetary Nebulae

Abstract The morphology of planetary nebulae emerging from the common envelope phase of binary star evolution is investigated. Using initial conditions based on the numerical results of hydrodynamical simulations of the common envelope phase, it was found that the shapes and sizes of the resulting nebula are very sensitive to the effective temperature of the remnant core, the mass-loss rate at the onset of the common envelope phase, and the mass ratio of the binary system. These parameters are related to the efficiency of the mass ejection after the spiral-in phase, the stellar evolutionary phase (i.e., RG, AGB, or TP-AGB), and the degree of departure from spherical symmetry in the stellar wind mass-loss process itself, respectively. It was also found that the shapes are mostly bipolar in the early phase of evolution, but that they can quickly transition to elliptical and barrel-type shapes. Solutions for nested lobes are found where the outer lobes are usually bipolar and the inner lobes are elliptical, bipolar, or barrel-type, a result due to the flow of the photo-evaporated gas from the equatorial region. Also, the lobes can be produced without the need for two distinct mass ejection events. In all the computations, the bulk of the mass is concentrated in the orbital or equatorial plane, in the form of a large toroid, which can be either neutral (early phases) or photoionized (late phases), depending of the evolutionary state of the system.

The imprints of the last jets in core collapse supernovae

We analyse the morphologies of three core collapse supernova remnants (CCSNRs) and the energy of jets in other CCSNRs and in Super Luminous Supernovae (SLSNe) of type Ib/Ic/IIb, and conclude that these properties are well explained by the last jets’ episode as expected in the jet feedback explosion mechanism of core collapse supernovae (CCSNe). The presence of two opposite protrusions, termed ears, and our comparison of the CCSNR morphologies with morphologies of planetary nebulae strengthen the claim that jets play a major role in the explosion mechanism of CCSNe. We crudely estimate the energy that was required to inflate the ears in two CCSNRs and assume that the ears were inflated by jets. We find that the energies of the jets which inflated ears in 11 CCSNRs span a range that is similar to that of jets in some energetic CCSNe (SLSNe) and that this energy, only of the last jets’ episode, is much less than the explosion energy. This finding is compatible with the jet feedback explosion mechanism of CCSNe, where only the last jets, which carry a small fraction of the total energy carried by earlier jets, are expected to influence the outer parts of the ejecta. We reiterate our call for a paradigm shift from neutrino-driven to jet-driven explosion models of CCSNe.

Gaia: mapping the dynamics and morphologies of Galactic Planetary Nebulae: First results from Gaia Data Release 1

AbstractThis paper comments on the use Gaia in studying the internal dynamics and morphologies of Planetary Nebulae (PN). It is noted that the second and subsequent releases of Gaia data, will have significant potential in unravelling PN morphologies.

A morpho-kinematic and spectroscopic study of the bipolar nebulae: M 2−9, Mz 3, and Hen 2−104

Context. Complex bipolar shapes can be generated either as a planetary nebula or a symbiotic system. The origin of the material ionised by the white dwarf is very different in these two scenarios, and it complicates the understanding of the morphologies of planetary nebulae.

A study of the effect of ionization and illumination on morphologies of planetary nebulae

AbstractWe carry out a modelling study of the effect of ionization and illumination on the morphologies of planetary nebulae (PNs), aiming to investigate the hypothesis of Kwok (2010) that the bipolar and multipolar lobes of PNs can be produced by leakage of UV photons into those directions. Using photoinization code, we construct a series of nebular models consisting of a dense envelope and cones of low density. The results show that the visible morphologies of PNs may be fundamentally different from their intrinsic structures.

Weak emission line central stars of planetary nebulae

AbstractTo understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.

Shape, structure, and morphology in planetary nebulae

AbstractA revival over the past two decades in planetary nebula (PN) morphological studies springs from a combination of factors, including the advent of wide-area, high dynamic range detectors; the growing archives of high resolution images from the X-ray to the sub-mm; and the advent of sophisticated models of the co-evolution of PNe and their central stars. Yet the story of PN formation from their immediate precursors, the AGB stars, is not yet fully written. PN morphology continues to inspire, provide context for physical interpretation, and serve as an ultimate standard of comparison for many investigations in this area of astrophysics. After a brief review of the remarkable successes of PN morphology, I summarize how this tool has been employed over the last half-decade to advance our understanding of PNe.

Estimating the binary fraction of planetary nebulae central stars

AbstractDuring the past 20 years, the idea that non-spherical planetary nebulae might need a binary or planetary interaction to be shaped was discussed by various authors. It is now generally agreed that the varied morphologies of planetary nebulae cannot be fully explained solely by single star evolution. Observationally, more binary central stars of planetary nebulae have been discovered, opening new possibilities to understand the connections between binarity and morphology. So far, ≃45 binary central stars of planetary nebulae have been detected, most being close systems detected via flux variability. In order to determine the PN binary fraction, one needs a method that can detect wider binaries. We present here recent results concentrating on binary infrared excess observations aimed at detecting binaries of any separation.

The Role of Planets in Shaping Planetary Nebulae

ABSTRACTIn 1997 Soker laid out a framework for understanding the formation and shaping of planetary nebulae (PN). Starting from the assumption that nonspherical PN cannot be formed by single stars, he linked PN morphologies to the binary mechanisms that may have formed them, basing these connections almost entirely on observational arguments. In light of the last decade of discovery in the field of PN, we revise this framework, which, although simplistic, can still serve as a benchmark against which to test theories of PN origin and shaping. Within the framework, we revisit the role of planets in shaping PN. Soker invoked a planetary role in shaping PN because there are not enough close binaries to shape the large fraction of nonspherical PN. In this article we adopt a model whereby only ∼20% of all 1–8 M⊙ stars make a PN. This reduces the need for planetary shaping. Through a propagation of percentages argument, and starting from the assumption that planets can only shape mildly elliptical PN, we conclude that ∼20% of all PN were shaped via planetary and other substellar interactions, but we add that this corresponds to only ∼5% of all 1–8 M⊙ stars. This may be in line with findings of planets around main-sequence stars. PN shaping by planets is made plausible by the recent discovery of planets that have survived interactions with red giant branch (RGB) stars. Finally, we conclude that of the ∼80% of 1–8 M⊙ stars that do not make a PN, about one-quarter do not even ascend the AGB due to interactions with stellar and substellar companions, while three-quarters ascend the AGB but do not make a PN. Once these stars leave the AGB they evolve normally and can be confused with post-RGB, extreme horizontal branch stars. We propose tests to identify them.

A three-dimensional magnetohydrodynamic model of planetary nebula jets, knots, and filaments

The morphologies of planetary nebulae are believed to be self-organized configurations. These configurations are modeled by three-dimensional temporally self-similar magnetohydrodynamic solutions with radial flow, under the gravitational field of a central star of mass $M$. These solutions reproduce basic features, such as jets, point-symmetric knots, and filaments, through plasma pressure, mass density, and magnetic field lines. The time evolution function of the radial velocity starts as a slow wind and terminates as a fast wind.

Stellar Evolution from AGB to Planetary Nebulae

AbstractPlanetary 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.

Dust Extinction in Compact Planetary Nebulae

The effects of dust extinction on the departure from axi-symmetry in the morphology of planetary nebulae (PNs) are investigated through a comparison of the radio free-free emission and hydrogen recombination line images. The dust exctinction maps of five compact PNs are derived using high-resolution (~ 0.1) H-alpha and radio images maps of the HST and VLA. These extinction maps are then analyzed by an ellipsoidal shell ionization model including the effects of dust extinction to infer the nebulae's intrinsic structure and orientation in the sky. This method provides a quantitative analysis of the morphological structure of PNs and represents a step beyond qualitative classification of morphological types of PNs.

Morphology of Planetary Nebulae—Possible Effects of Rotation on Stellar Ejecta

Planetary nebulae are formed as the result of the interaction between a slow stellar wind from the asymptotic giant branch progenitor and a later-developed fast outflow from the central star. Many of the morphological and kinematic properties of planetary nebulae have been successfully explained by this interacting stellar winds model. The observed diverse morphologies of planetary nebulae can also be understood if the slow wind is not spherically symmetric. However, new observational features such as collimated outflows and multi-polar lobes suggest that the fast wind may be non-isotropic and time variable. The possible roles of magnetic fields and rotation may play in the formation of these features are discussed.

The correlation between planetary nebula morphology and radio brightness temperatures

We have used model central star evolutionary tracks to evaluate the expected variation of 5 GHz brightness tempera- tures TB in planetary nebulae. Using these results, and previously derived central star mass functions, we find that there should be a correlation between TB and the mean central star massMCS� , and also between TB and nebular morphology. An analysis of the available observational results suggests that such a correlation between TB and nebular morphology does indeed exist. Bipolar nebulae appear to be concentrated towards high brightness temperatures, whilst circular sources tend to possess lower brightness temperature shells. Elliptical sources are present (and common) at all values of TB .T here are differences however between the observed and deduced morphological variations, and these enable us to place constraints upon the progenitor masses of the nebulae. In particular, it is clear that higher mass progenitors are likely to give rise to both bipolar and elliptical outflows; a result which is consistent with analyses of nebular abundances, Zanstra temperatures, and line excitations.

Space Telescope Imaging Spectrograph Slitless Observations of Small Magellanic Cloud Planetary Nebulae: A Study on Morphology, Emission‐Line Intensity, and Evolution

A sample of 27 planetary nebulae (PNs) in the Small Magellanic Cloud (SMC) have been observed with the Hubble Space Telescope Imaging Spectrograph (HST/STIS) to determine their morphology, size, and the spatial variation of the ratios of bright emission lines. The morphologies of SMC PNs are similar to those of LMC and Galactic PNs. However, only a third of the resolved SMC PNs are asymmetric, compared to half of those in the LMC. The low-metallicity environment of the SMC seems to discourage the onset of bipolarity in PNs. We measured the line intensity, average surface brightness, and photometric radius of each nebula in Hα, Hβ, [O III] λλ4959 and 5007, [N II] λλ6548 and 6584, [S II] λλ6716 and 6731, He I λ6678, and [O I] λλ6300 and 6363. We show that the surface brightness-to-radius relationship is the same as in LMC PNs, indicating its possible use as a distance scale indicator for Galactic PNs. We determine the electron densities and the ionized masses of the nebulae where the [S II] lines were measured accurately, and we find that the SMC PNs are denser than the LMC PNs by a factor of 1.5. The average ionized mass of the SMC PNs is 0.3 M☉. We also found that the median [O III]/Hβ intensity ratio in the SMC is about half that of the corresponding LMC median. We use CLOUDY to model the dependence of the [O III]/Hβ ratio on the oxygen abundance. Our models encompass very well the average observed physical quantities. We suggest that the SMC PNs are principally cooled by the carbon lines, making it hard to study their excitation based on the optical lines at our disposal.

The relation between elemental abundances and morphology in planetary nebulae

An investigation of the variation of elemental abundances with planetary nebula morphology is of considerable interest, since it has a bearing upon how such sources are formed, and from which progenitors they are ejected. Recent advances in morphological classification now enable us to assess such trends for a statistically significant number of sources. We find, as a result, that the distribution N[log(X/H)] of sources with respect to elemental abundance (X/H) varies between the differing morphologies. Circular sources tend to peak towards low abundance values, whilst bipolar nebulae (BPNe) peak towards somewhat higher values. This applies for most elemental species, although it is perhaps least apparent for oxygen. In contrast, elliptical sources appear to display much broader functions N[log(X/H)], which trespass upon the domains of both circular and elliptical planetary nebulae (PNe). We take these trends to imply that circular sources derive from lower-mass progenitors, bipolar sources from higher-mass stars, and that elliptical nebulae derive from all masses of progenitor, high and low. Whilst such trends are also evident in values of mean abundance (X/H), they are much less clear. Only in the cases of He/H, N/H, Ne/H and perhaps Ar/H is there evidence for significant abundance differences. Certain BPNe appear to possess low abundance ratios He/H and Ar/H, and this confirms that a few such outflows may arise from lower-mass progenitors. Similarly, we note that ratios (O/H) are quite modest in elliptical planetary nebulae, and not much different from those for circular and bipolar PNe; a result that conflicts with the expectations of at least one model of shell formation.

The Correlations between Planetary Nebula Morphology and Central Star Evolution: Analysis of the Northern Galactic Sample

Northern Galactic planetary nebulae (PNs) are studied to disclose possible correlations between the morphology of the nebulae and the evolution of the central stars (CSs). To this end, we have built the best database available to date, accounting for homogeneity and completeness. We use updated statistical distances and an updated morphological classification scheme, and we calculate Zanstra temperatures for a large sample of PNs. With our study we confirm that round, elliptical, and bipolar PNs have different spatial distributions within the Galaxy, with average absolute distances to the Galactic plane of 0.73, 0.38, and 0.21 kpc, respectively. We also find evidence that the distributions of the CS masses are different across these morphological groups, although we do not find that CSs hosted by bipolar PNs are hotter, on average, than CSs within round and elliptical PNs. Our results are in broad agreement with previous analyses, indicating that round, elliptical, and bipolar PNs evolve from progenitors in different mass ranges and might belong to different stellar populations, as also indicated by the helium and nitrogen abundances of PNs of different morphology.