Spectra of planetary nebulae (PNe) are characterised by strong forbidden emission lines and often also by an infrared (IR) excess. A few PNe show dust obscuration events and/or harbour long-period binaries. Some post-asymptotic giant branch stars, symbiotic stars, or B[e] stars may feature similar characteristics. Recently, dust clouds eclipsing white dwarfs were also detected. We report the discovery of an object with a very peculiar variability pattern that bears signatures compatible with the above-mentioned classes of objects. The object is ZTFJ201451.59+120353.4 and identifies with PM 1-322. The object was discovered in Zwicky Transient Facility archival data and investigated with historical and newly obtained photometric and spectroscopic observations. The ZTF r and g data show a one magnitude deep, eclipse-like event with a duration of about half a year that occurred in 2022. The variability pattern of the star is further characterised by several dimming events in the optical region that are accompanied by simultaneous brightenings in the red and IR regions. Apart from that, two fast eruption-like events were recorded in ZTF r data. Archival data from WISE indicate long-term variability with a possible period of 6 or 12 yr. Our follow-up time series photometry reveals a stochastic short-term variability with an amplitude of about 0.1 mag on a timescale of about one hour. The spectral energy distribution is dominated by IR radiation. Our high-resolution spectroscopy shows strong forbidden emission lines from highly ionised species and symmetric double-peaked emission in Halpha, which is very different from what is seen in earlier spectra obtained in 2007. Several explanatory scenarios are presented. Our most likely interpretation is that our target object involves a hot central star surrounded by gaseous and dusty disks, an extended nebula, and a possible companion star.
Close binary interactions perform a key role in the formation and shaping of planetary nebulae. However only a small fraction of Galactic planetary nebulae are known to host close binary systems. Many such systems are detectable through photometric variability. We searched recently published epoch photometry data from Gaia DR3 for planetary nebula central stars with periodic photometric variability indicative of binarity, uncovering four previously unknown close binaries.
Planetary Nebulae are the ionised ejected envelopes surrounding the remnant cores of dying stars. Theory predicts that main-sequence stars with one to about eight times the mass of our sun may eventually form planetary nebulae. Until now no example has been confirmed at the higher mass range. Here we report that planetary nebula BMP J1613-5406 is associated with Galactic star cluster NGC 6067. Stars evolving off the main sequence of this cluster have a mass around five solar masses. Confidence in the planetary nebula-cluster association comes from their tightly consistent radial velocities in …
We investigate Galactic bulge planetary nebulae without emission-line central stars for which peculiar infrared spectra have been obtained with the Spitzer Space Telescope, including the simultaneous signs of oxygen and carbon based dust. Three separate sub-groups can be defined characterized by the different chemical composition of the dust and the presence of crystalline and amorphous silicates. We find that the classification based on the dust properties is reflected in the more general properties of these planetary nebulae. However, some observed properties are difficult to relate to the c…
We present evidence that the nebular cocoon and bow-shock emission nebula putatively and recently reported as deriving from the 9th magnitude "runaway" star HD 185806 is the previously discovered but obscure planetary nebula WHTZ 1 (Ra 7). It has a Gaia DR3 G~16 blue ionizing star at its geometric centre. We present imagery, spectroscopy, other data and arguments to support that this emission source is a high excitation Planetary Nebula not a stellar wind bow shock.
The Stingray Nebula, aka Hen3-1357, appeared for the first time in 1990 when bright nebular lines and radio emission that had not been observed before were unexpectedly discovered (Parthasarathy et al. 1993). In the ensuing years the nebula faded precipitously. We report changes in shape and large decreases in its nebular emission-line fluxes based on well-calibrated images obtained by the Hubble Space Telescope in 1996 and 2016. Hen3-1357 is now a "recombination nebula".
Radio continuum observations trace thermal emission of ionized plasma in planetary nebulae and bring useful information on nebular geometries. A model of homogeneous sphere or shell cannot fit the nebular spectra and brightness temperatures. Two alternative models have been proposed in the literature: the first one consists of two homogeneous components, while the other one is a model of a shell with a significant radial density gradient. On the other side, prolate ellipsoidal shell model can successfully fit the surface brightness distribution of selected objects. We verify the existing model…
We present observations of planetary nebulae with the LOw Frequency ARray (LOFAR) between 120 and 168 MHz. The images show thermal free-free emission from the nebular shells. We have determined the electron temperatures for spatially resolved, optically thick nebulae. These temperatures are 20 to 60% lower than those estimated from collisionally excited optical emission lines. This strongly supports the existence of a cold plasma component, which co-exists with hot plasma in planetary nebulae. This cold plasma does not contribute to the collisionally excited lines, but does contribute to recom…
We report confirmation of a large, evolved, bipolar planetary nebula and its blue, white dwarf central star as a member of the ~500 Myr old Galactic open star cluster M37 (NGC 2099). This is only the third known example of a planetary nebula in a Galactic open cluster and was found via our on-going program of identifying and studying planetary nebulae - open cluster associations. High confidence in the association comes from the consistent radial velocities and proper motions for the confirmed central star and cluster stars from Gaia, reddening agreement and location of the planetary nebula we…
We study the line widths in the [\ion{O}{3}]$λ$5007 and H$α$ lines for two groups of planetary nebulae in the Milky Way bulge based upon spectroscopy obtained at the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir (OAN-SPM) using the Manchester Echelle Spectrograph. The first sample includes objects early in their evolution, having high H$β$ luminosities, but [\ion{O}{3}]$λ5007/\mathrm Hβ< 3$. The second sample comprises objects late in their evolution, with \ion{He}{2} $λ4686/\mathrm Hβ> 0.5$. These planetary nebulae represent evolutionary phases preceeding and following thos…
Planetary nebulae (PNe) were expected to be filled with hot pressurized gas driving their expansion. ROSAT hinted at the presence of diffuse X-ray emission from these hot bubbles and detected the first sources of hard X-ray emission from their central stars, but it was not until the advent of Chandra and XMM-Newton that we became able to study in detail their occurrence and physical properties. Here I review the progress in the X-ray observations of PNe since the first WORKshop for PLAnetary Nebulae observationS (WORKPLANS) and present the perspective for future X-ray missions with particular …
The likely membership of the planetary nebula Abell 8 (PN G167.0--00.9) in the open cluster Bica 6 is confirmed by CCD spectra, UBV(RI)c photometry, and radial velocities for luminous cluster stars. The reddening, estimated distance, and radial velocity of the planetary nebula agree with parameters derived for Bica 6 of E(B-V)=0.42, d=1.60+-0.11 kpc, and Vr=57+-1 km/s, with a cluster age of 1 Gyr, a diagnostic blue hook, and a few blue stragglers, including a peculiar B1 Vnn star (HDE 277593) that may be a post-AGB star. The results identify Bica 6 as a potential calibrator of the planetary ne…
We present kinematic data for 211 bright planetary nebulae in eleven Local Group galaxies: M31 (137 PNe), M32 (13), M33 (33), Fornax (1), Sagittarius (3), NGC 147 (2), NGC 185 (5), NGC 205 (9), NGC 6822 (5), Leo A (1), and Sextans A (1). The data were acquired at the Observatorio Astronómico Nacional in the Sierra de San Pedro Mártir using the 2.1m telescope and the Manchester Echelle Spectrometer in the light of [\ion{O}{3}]$λ$5007 at a resolution of 11 km/s. A few objects were observed in H$α$. The internal kinematics of bright planetary nebulae do not depend strongly upon the metallicity or…
The brightest planetary nebulae achieve similar maximum luminosities, have similar ratios of chemcial abundances, and apparently share similar kinematics in all galaxies. These similarities, however, are not necessarily expected theoretically and appear to hide important evolutionary differences. As predicted theoretically, metallicity appears to affect nebular kinematics, if subtly, and there is a clear variation with evolutionary stage. To the extent that it can be investigated, the internal kinematics for galactic and extragalactic planetary nebulae are similar. The extragalactic planetary …
We present a summary of current research on planetary nebulae and their central stars, and related subjects such as atomic processes in ionized nebulae, AGB and post-AGB evolution. Future advances are discussed that will be essential to substantial improvements in our knowledge in the field.
We present 2D hydrodynamical simulations of the transition of a proto-planetary nebula to a planetary nebula for central stars in binary systems that have undergone a common envelope event. After 1,000 yr of magnetically driven dynamics (proto-planetary nebula phase), a line-driven stellar wind is introduced into the computational domain and the expansion of the nebula is simulated for another 10,000 yr, including the effects of stellar photoionization. In this study we consider central stars with main sequence (final) masses of 1 (0.569) and 2.5 (0.677) \Mo, together with a 0.6 \Mo ma in sequ…
The increase in discovered close binary central stars of planetary nebulae is leading to a sufficiently large sample to begin to make broader conclusions about the effect of close binary stars on common envelope evolution and planetary nebula formation. Herein I review some of the recent results and conclusions specifically relating close binary central stars to nebular shaping, common envelope evolution off the red giant branch, and the total binary fraction and double degenerate fraction of central stars. Finally, I use parameters of known binary central stars to explore the relationship bet…
During the last years, many observational studies have revealed that binaries play an active role in the shaping of non spherical planetary nebulae. We review the different works that lead to the direct or indirect evidence for the presence of binary companions during the Asymptotic Giant Branch, proto-Planetary Nebula and Planetary Nebula phases. We also discuss how these binaries can influence the stellar evolution and possible future directions in the field.
Why 80% of planetary nebulae are not spherical is not yet understood. The Binary Hypothesis states that a companion to the progenitor of the central star of a planetary nebula is required to shape the nebula and even for a planetary nebula to be formed at all. A way to test this hypothesis is to estimate the binary fraction of central stars of planetary nebula and to compare it with the main sequence population. Preliminary results from photometric variability and infrared excess techniques indicate that the binary fraction of central stars of planetary nebulae is higher than that of the putat…
There is no quantitative theory to explain why a high 80% of all planetary nebulae are non-spherical. The Binary Hypothesis states that a companion to the progenitor of a central star of planetary nebula is required to shape the nebula and even for a planetary nebula to be formed at all. A way to test this hypothesis is to estimate the binary fraction of central stars of planetary nebulae and to compare it with that of the main sequence population. Preliminary results from photometric variability and the infrared excess techniques indicate that the binary fraction of central stars of planetary…
We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7$-$05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve modelling reveals the newly discovered binary system to comprise a highly-irradiated, M-type main-sequence star in a 5.9 hour orbit with a hot pre-white-dwarf. The nebular progenitor is found to have a particularly low mass of around 0.4 M$_\odot$, making…
It is now clear that a binary formation pathway is responsible for a significant fraction of planetary nebulae, and this increased sample of known binaries means that we are now in a position to begin to constrain their influence on the formation and evolution of their host nebulae. Here, we will review current understanding of how binarity influences the resulting nebulae, based on observations and modelling of both the central binary systems and the planetary nebulae themselves. We will also highlight the most important test-cases which have proved the most interesting in studying the evolut…
We present high resolution spectroscopy in the [\ion{O}{3}]$λ$5007 and H$α$ lines of bright planetary nebulae in the Milky Way bulge and the dwarf galaxies M32, Fornax, Sagittarius, and NGC 6822 obtained at the Observatorio Astronomico Nacional in the Sierra San Pedro Martir using the Manchester Echelle Spectrograph. We use the high signal-to-noise (S/N) observations of Milky Way bulge planetary nebulae to explore what kinematic information can be determined reliably when observing extragalactic planetary nebulae in the [\ion{O}{3}]$λ$5007 line at modest S/N. We find that the intrinsic line wi…
The question of what physical mechanisms shape planetary nebulae into their observed morphologies remains open. However, intensified efforts since the last meeting in this series, Asymmetrical Planetary Nebulae IV, in July 2007 have yielded some excellent results. In this review we concentrate on those developments that have taken place in the last three years, with emphasis on results obtained since the review by De Marco (2009).
We report the discovery of a planetary nebula centered on the poorly studied symbiotic binary star DT Ser. In a few other symbiotic stars spatially resolved nebulae have been discovered: however, only one of them might be a genuine planetary nebula, while the others are likely to originate in complex mass ejections episodes from the interacting binary central stars, possibly related to nova-like outbursts. The rim of the planetary nebula around DT Ser is severely distorted toward a brighter star, 5 arcsec away. In infrared WISE data, this star shows the presence of a detached cold dust shell s…
We report the first detection of buckminsterfullerene (C60) in a proto-planetary nebula (PPN). The vibrational transitions of C60 at 7.0, 17.4, and 18.9um are detected in the Spitzer/IRS spectrum of IRAS 01005+7910. This detection suggests that fullerenes are formed shortly after the asymptotic giant branch but before the planetary nebulae stage. A comparison with the observations of C60 in other sources is made and the implication on circumstellar chemistry is discussed.
One of the possible mechanisms responsible for the panoply of shapes in planetary nebulae is the presence of magnetic fields that drive the ejection of ionized material during the proto-planetary nebula phase. Therefore, detecting magnetic fields in such objects is of key importance for understanding their dynamics. Still, magnetic fields have not been detected using polarimetry in the central stars of planetary nebulae. Circularly polarized light spectra have been obtained with the Focal Reducer and Low Dispersion Spectrograph at the Very Large Telescope of the European Southern Observatory a…
The evolution of central stars of planetary nebulae was so far documented in just a few cases. However, spectra collected a few decades ago may provide a good reference for studying the evolution of central stars using the emission line fluxes of their nebulae. We investigated evolutionary changes of the [OIII] 5007 A line flux in the spectra of planetary nebulae. We compared nebular fluxes collected during a decade or longer. We used literature data and newly obtained spectra. A grid of Cloudy models was computed using existing evolutionary models, and the models were compared with the observ…
Planetary nebulae had a double anniversary in 2014, 250 year since their discovery and 150 year since the correct spectroscopic identification. This paper gives an overview of planetary nebula research published in 2014. Topics include surveys, central stars, abundances, morphologies, magnetic fields, stellar population and galactic dynamics. An important continuing controversy is the discrepancy between recombination-line and forbidden-line abundances. A new controversy is the relation between symbiotic stars and [WC] stars. PN of the year is undoubtedly CRL 618, with papers on its binary sym…
It is now clear that a binary pathway is responsible for a significant fraction of planetary nebulae, and the continually increasing sample of known central binaries means that we are now in a position to begin to use these systems to further our understanding of binary evolution. Binary central stars of planetary nebulae are key laboratories in understanding the formation processes of a wide-range of astrophysical phenomena - a point well-illustrated by the fact that the only known double-degenerate, super-Chandrasekhar mass binary which will merge in less than a Hubble time is found inside a…
RWT 152 is one of the few known planetary nebulae with an sdO central star. We present subarcsecond red tunable filter Halpha imaging and intermediate-resolution, long-slit spectroscopy of RWT 152 obtained with OSIRIS/GTC with the goal of analyzing its properties. The Halpha 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 s…
Planetary nebulae retain the signature of the nucleosynthesis and mixing events that occurred during the previous AGB phase. Observational signatures complement observations of AGB and post-AGB stars and their binary companions. The abundances of the elements heavier than iron such as Kr and Xe in planetary nebulae can be used to complement abundances of Sr/Y/Zr and Ba/La/Ce in AGB stars, respectively, to determine the operation of the slow neutron-capture process (the s process) in AGB stars. Additionally, observations of the Rb abundance in Type I planetary nebulae may allow us to infer the …
In this work, we present the first results of an ongoing survey to search for planetary nebulae (PNe) around hot subdwarf stars (sdOs). Deep images and intermediate-resolution long-slit spectra of RWT 152, the only confirmed PN+sdO system in the northern hemisphere, as well as preliminary results for other sdO+PN candidate are presented.
We present a comprehensive analysis of the compact planetary nebula M2-31 investigating its spectral properties, spatio-kinematical structure and chemical composition using GTC MEGARA integral field spectroscopic observations and NOT ALFOSC medium-resolution spectra and narrow-band images. The GTC MEGARA high-dispersion observations have remarkable tomographic capabilities, producing an unprecedented view of the morphology and kinematics of M2-31 that discloses a fast spectroscopic bipolar outflow along position angles 50$^\circ$ and 230$^\circ$, an extended shell and a toroidal structure or w…
The transition from Asymptotic Giant Branch star to Planetary Nebula is short-lived and mysterious. Though it lasts only a few thousand years, it is thought to be the time when the asymmetries observed in subsequent phases arise. During this epoch, the star is shrouded in thick clouds of dust and molecular gas; infrared observations are needed to reveal these objects at their most pivotal moment. I present preliminary results of a Spitzer study of targets spanning the range from post-AGB stars to Planetary Nebulae with the goal of determining the genesis of asymmetry in these objects.
We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula HaTr 4, one of few known to contain a post-common-envelope central star system. Common envelope evolution is believed to play an important role in the shaping of planetary nebulae, but the exact nature of this role is yet to be understood. High spatial- and spectral- resolution spectroscopy of the [OIII]5007 nebular line obtained with VLT-UVES are presented alongside deep narrowband Ha+[NII]6584 imagery obtained using EMMI-NTT, and together the two are used to derive the three-dimensional morphology…
We present Gemini-South observations of nine faint and extended planetary nebulae. Using direct images taken with the spectrograph GMOS, we built the $(u' - g')$ vs. $(g' - r')$ diagrams of the stars in the observed areas which allowed us, also considering their geometrical positions, to identify the probable central stars of the nebulae. Our stellar spectra of seven stars, also taken with GMOS, indicate that four (and probably two more) objects are white dwarfs of the DAO subtype. Moreover, the white dwarf status of the four stars is confirmed by the parameters $ T_{\mathrm{eff}}$ and $ \log …
While analysing the images of the IPHAS H$α$ survey, we noticed that the central star of the candidate planetary nebula IPHASXJ211420.0+434136 (also named Ou5) was clearly variable. This is generally considered as an indication of binarity. To confirm it, we performed a photometric monitoring of the central star, and obtained images and spectra of the nebula. The nebular spectrum confirms that IPHASXJ211420.0+434136 is a planetary nebula of moderately high excitation. It has a remarkable morphology with two nested pairs of bipolar lobes, and other unusual features. The light curve of the centr…
In this paper we will discuss the images of Planetary Nebulae that have recently been obtained with PACS and SPIRE on board the Herschel satellite. This comprises results for NGC 650 (the little Dumbbell nebula), NGC 6853 (the Dumbbell nebula), and NGC 7293 (the Helix nebula).
RWT 152 is one of the few planetary nebula with an sdO central star. We present subarcsecond red tunable filter imaging and intermediate-resolution, long-slit spectroscopy of RWT 152, obtained with OSIRIS/GTC, which allow us to describe in detail its morphology and to obtain its physical conditions and chemical abundances.
Most of the planetary nebulae (PN) have bipolar or other non-spherically symmetric shapes. The presence of a magnetic field in the central star may be the reason for this lack of symmetry, but observational works published in the literature have so far reported contradictory results. We try to correlate the presence of a magnetic field with the departures from the spherical geometry of the envelopes of planetary nebulae. We determine the magnetic field from spectropolarimetric observations of ten central stars of planetary nebulae. The results of the analysis of the observations of four stars …
We present deep, high-resolution (R~40000) UVES at VLT spectrophotometric data of the planetary nebula NGC 3918. This is one of the deepest spectra ever taken of a planetary nebula. We have identified and measured more than 700 emission lines and, in particular, we have detected very faint lines of several neutron-capture elements (s-process elements: Kr, Xe and Rb) that enable us to compute their chemical abundances with unprecedented accuracy, thus constraining the efficiency of the s-process and convective dredge-up.
Eight planetary nebulae have been identified as `born-again', a class of object typified by knotty secondary ejecta having low masses ($\sim$$10^{-4}$ M$_{\odot}$) with nearly no hydrogen. Abell 30, the archetype of the class, also belongs to a small subset of planetary nebulae that exhibit extreme abundance discrepancy factors (where Abell 30 is the most extreme), a phenomenon strongly linked to binary star interactions. We report the presence of light curve brightness variations having a period of 1.060 days that are highly suggestive of a binary central star in Abell 30. If confirmed, this …
We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Shapley 1 (Sp 1), which is known to contain a close-binary central star system. Close-binary central stars have been identified as a likely source of shaping in planetary nebulae, but with little observational support to date. Deep narrowband imaging in the light of [O III] λ5007A suggests the presence of a large bow-shock to the west of the nebula, indicating that it is undergoing the first stages of an interaction with the interstellar medium. Further narrowband imaging in the light of Hα+[NII] λ6…
We present the discovery of 6 nebular objects made by amateur astronomers. Four of these discoveries are clearly planetary nebulae (PNe), one is a possible PN, and another is a likely H II region. The bipolar nebula Ou4 presents the largest angular extent ever found : over one degree on the sky! We consider various scenarios that could explain such a nebula. Ou4 could be one of the nearest PNe known, though its possible PN nature will need confirmation.
