Evolution Of Planetary Nebulae Research Articles

The Variability and Radial Velocity of Planetary Nebula Central Stars

The extremely accurate estimates of stellar variability and radial velocity in the Gaia Data Release 3 (Gaia DR3) have enabled us to examine the close binarity and radial velocity (RV) of central stars (CSs) of planetary nebulae (PNe). This study is twofold: (1) searching for new close binary CS candidates to better understand how binarity affects the formation and evolution of PNe; and (2) extending the sample size of known RVs of PNe in order to understand their kinematics and the dynamics of the Milky Way. As a target sample, we used all true, possible, and likely PNe available in the literature. Then, we looked for their matched Gaia DR3 sources that provide measurements of variability and RV. As a result, we detected the first large collection of trustworthy photometric variability of 26 symbiotic stars and 82 CSs. In this CS group, there are 24 sources already classified as true close binary CSs in the literature. Hence, we discovered 58 new close binary CS candidates. This close binary (CB) sample represents more than half of what is currently available in the literature. In addition, we identified the radial velocities for 51 PNe. To our knowledge, 24 of these were measured for the first time. The RV measurements predicted by Gaia, based on the Doppler shift of the CS absorption lines, and those derived from nebular emission lines, show satisfactory agreement except for a few extremely high-velocity PNe.

Panchromatic HST/WFC3 Imaging Studies of Young, Rapidly Evolving Planetary Nebulae. II. NGC 7027

The iconic planetary nebula (PN) NGC 7027 is bright, nearby (D ∼ 1 kpc), highly ionized, intricately structured, and well observed. This nebula is hence an ideal case study for understanding PN shaping and evolution processes. Accordingly, we have conducted a comprehensive imaging survey of NGC 7027 comprised of 12 HST Wide Field Camera 3 images in narrow-band and continuum filters spanning the wavelength range 0.243–1.67 μm. The resulting panchromatic image suite reveals the spatial distributions of emission lines covering low-ionization species such as singly ionized Fe, N, and Si, through H recombination lines, to more highly ionized O and Ne. These images, combined with available X-ray and radio data, provide the most extensive view of the structure of NGC 7027 obtained to date. Among other findings, we have traced the ionization structure and dust extinction within the nebula in subarcsecond detail; uncovered multipolar structures actively driven by collimated winds that protrude through and beyond the PN’s bright inner core; compared the ionization patterns in the WFC3 images to X-ray and radio images of its interior hot gas and to its molecular outflows; pinpointed the loci of thin, shocked interfaces deep inside the nebula; and more precisely characterized the central star. We use these results to describe the recent history of this young and rapidly evolving PN in terms of a series of shaping events. This evolutionary sequence involves both thermal and ram pressures, and is far more complex than predicted by extant models of UV photoionization or winds from a single central progenitor star, thereby highlighting the likely influence of an unseen binary companion.

Millimetre Observations of Maser-Emitting Planetary Nebulae

Observations in the millimetre bands of maser-emitting planetary nebulae (PNe) are crucial to study their circumstellar molecular gas at the beginning of the PN phase. Maser-emitting PNe are in the earliest phases of PN formation; therefore, these sources are key objects to study the molecular content during the early evolution of PNe. These circumstellar envelopes are active sites for the formation of molecules. We present preliminary results of millimetre observations with the IRAM 30 m telescope towards one PN (IRAS 17393−2727) of a sample of five maser-emitting PNe, where we detect 12CO and 13CO lines in both J=1→0 and J=2→1 transitions.

Planetary nebulae with UVIT: A progress report

The spectral region between 1250–3000 \(\AA \) contains important spectral lines to understand the morphological structures and evolution of planetary nebulae. This is the region sampled by UVIT through various filter bands both in the continuum and in emission lines (e.g.. [C iv], [He i], [Mg ii] etc.). We have mapped several planetary nebulae with different characteristics, ranging in morphology from bipolar to wide and diffuse, and in various states of ionization, comparing the UV with the X-ray morphologies wherever the X-ray images were also available. The major unanticipated discovery with UVIT has been the detection of previously undetected, cold, fluorescent, \(\hbox {H}_2\) gas surrounding some planetary nebulae. This may be a possible solution to the missing mass problem. Here we present a review of our studies so far done (both published and on going) with UVIT.

Wide binaries in planetary nebulae withGaiaDR2

Context.TheGaiaData Release 2 (DR2) was used to select a sample of 211 central stars of planetary nebulae (CSPNe) with good-quality astrometric measurements, which we refer to as Golden Astrometry Planetary Nebulae (GAPN).Gaiaastrometric and photometric measurements allowed us to derive accurate distances and radii and to calculate luminosities with the addition of self-consistent literature values. Such information was used to plot the position of these stars in a Hertzsprung-Russel diagram and to study their evolutionary status in comparison with the evolutionary tracks of CSPNe.Aims.The extremely precise measurement of parallaxes and proper motions inGaiaDR2 has allowed us to search for wide binary companions in a region close to each of the central stars in the GAPN sample. We are interested in establishing the presence of binary companions at large separations which could allow to contribute additional information on the influence of binarity on the formation and evolution of planetary nebulae. We aim to study the evolutive properties of the binary pairs to check the consistency of spectral types and masses in order to better constrain the ages and evolutionary stage of the CSPNe.Methods.We limited our search to a region around 20 000 AU of each CSPN to minimise accidental detections. We only considered stars with reasonably good parallax and proper motions data, that is, with errors below 30% in DR2. We determined that the hypothetical binary pairs should show a statistically significant agreement for the three astrometric quantities, that is, parallax and both components of the proper motions.Results.We found eight wide binary systems among our GAPN sample, including one in a triple system. We compiled the astrometric and photometric measurements of these binary systems and discussed them in relation to previously published searches for binaries in PNe. By analysing the position in the HR diagram of the companion stars usingGaiaphotometry, we are able to estimate their temperatures, luminosities, masses and, for one star, the evolutionary age. The derived quantities yield a consistent scenario when compared with the corresponding values as obtained for the central stars using stellar evolutionary models in the postAGB phase.

A Mysterious Ring in Dark Space?

Abstract We report the discovery of a low-surface-brightness (27.42 mag arcsec−2 in g band) nebula, which has a ring-like shape in the Beijing–Arizona Sky Survey (BASS). Positive detections have been found in multiband data from far-ultraviolet to far-infrared, except the z band from BASS and W1, W2 from the Wide-field Infrared Survey Explorer. The reddening of the nebula E(B − V) ∼ 0.02 mag is estimated from Infrared Astronomical Satellite (IRAS) 100 μm intensity and H i column density. With the help of the 3D reddening map from Pan-STARRS 1, the Two Micron All Sky Survey, and Gaia, the distance to the nebula of about 500 pc from Earth is derived. Such a low-surface-brightness nebula whose energy can be interpreted by the diffuse Galactic light could account for the optical counterpart of the infrared cirrus, which was detected by IRAS more than 30 yr ago. The ring-like structure might be the ultimate phase of an evolved planetary nebula, while the central white dwarf star has been ejected from the nebula for an unclear reason. On the other hand, the ring structure being a superposition of two close filaments might be another reasonable explanation. Considering the lack of spectroscopic data and uncertainty in the distance measurement, these interpretations need to be checked by future observations.

Stellar wind models of central stars of planetary nebulae

Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

The real time evolution of post-AGB stars

AbstractEvolution of post-AGB stars is extremely fast. They cross the HR diagram vertically on a timescale of hundreds to some ten thousands of years to reach maximum temperature in their lifetime. This is reflected in an increasing excitation of planetary nebulae on a timescale of years and decades. Since evolutionary timescale of post-AGB stars is very sensitive to their mass, observed changes can be used to determine model dependent central star masses. If an additional parameter is determined (e.g. luminosity or dynamic age), the observed evolution of planetary nebulae can be utilized for observational verification of theoretical models.

Confronting expansion distances of planetary nebulae with Gaia DR2 measurements

Context. Individual distances to planetary nebulae are of the utmost relevance for our understanding of post-asymptotic giant-branch evolution because they allow a precise determination of stellar and nebular properties. Also, objects with individual distances serve as calibrators for the so-called statistical distances based on secondary nebular properties. Aims. With independently known distances, it is possible to check empirically our understanding of the formation and evolution of planetary nebulae as suggested by existing hydrodynamical simulations. Methods. We compared the expansion parallaxes that have recently been determined for a number of planetary nebulae with the trigonometric parallaxes provided by the Gaia Data Release 2. Results. Except for two out of 11 nebulae, we found good agreement between the expansion and the Gaia trigonometric parallaxes without any systematic trend with distance. Therefore, the Gaia measurements also prove that the correction factors necessary to convert proper motions of shocks into Doppler velocities cannot be ignored. Rather, the size of these correction factors and their evolution with time as predicted by 1D hydrodynamical models of planetary nebulae is basically validated. These correction factors are generally greater than unity and are different for the outer shell and the inner bright rim of a planetary nebula. The Gaia measurements also confirm earlier findings that spectroscopic methods often lead to an overestimation of the distance. They also show that even modelling of the entire system of star and nebula by means of sophisticated photoionisation modelling may not always provide reliable results. Conclusions. The Gaia measurements confirm the basic correctness of the present radiation-hydrodynamics models, which predict that both the shell and the rim of a planetary nebula are two independently expanding entities, created and driven by different physical processes, namely thermal pressure (shell) or wind interaction (rim), both of which vary differently with time.

X-ray Shaping of Planetary Nebulae

The stellar winds of the central stars of planetary nebulae play an essential role in the shaping of planetary nebulae. In the interacting stellar winds model, the fast stellar wind injects energy and momentum, which are transferred to the nebular envelope through an X-ray-emitting hot bubble. Together with other physical processes, such as the ionization of the nebular envelope, the asymmetrical mass-loss in the asymptotic giant branch (AGB), and the action of collimated outflows and magnetic fields, the pressurized hot gas determines the expansion and evolution of planetary nebulae. Chandra and XMM-Newton have provided us with detailed information of this hot gas. Here in this talk I will review our current understanding of the effects of the fast stellar wind in the shaping and evolution of planetary nebulae and give some hints of the promising future of this research.

The long-period binary central stars of the planetary nebulae NGC 1514 and LoTr 5

The importance of long-period binaries on the formation and evolution of planetary nebulae is still rather poorly understood, in part due to the lack of central star systems known to comprise such long-period binaries. Here, we report on the latest results from the on-going Mercator-HERMES survey for variability in the central stars of planetary nebulae. We present a study of the central stars of NGC 1514, BD+30$^\circ$623, the spectrum of which shows features associated with a hot nebular progenitor as well as a possible A-type companion. Cross-correlation of high-resolution HERMES spectra against synthetic spectra shows the system to be a highly eccentric ($e\sim0.5$), double-lined binary with a period of $\sim$3300 days. Previous studies indicated that the cool component might be a Horizontal Branch star of mass $\sim$0.55 M$_\odot$ but the observed radial velocity amplitudes rule out such a low mass. Assuming the nebular symmetry axis and binary orbital plane are perpendicular, the data are more consistent with a post-main-sequence star ascending towards the Giant Branch. We also present the continued monitoring of the central star of LoTr 5, HD 112313, which has now completed one full cycle, allowing the orbital period (P$\sim$2700 days) and eccentricity ($e\sim0.3$) to be derived. To date, the orbital periods of BD+30$^\circ$623 and HD 112313 are the longest to have been measured spectroscopically in the central stars of planetary nebulae. Furthermore, these systems, along with BD+33$^\circ$2642, comprise the only spectroscopic wide-binary central stars currently known.

History of the mass ejection in K4-37: from the AGB to the evolved planetary nebula phase

We present narrow-, broad-band, and WISE archive images, and high- and intermediate-resolution long-slit spectra of K 4-37, a planetary nebula that has never been analyzed in detail. Although K 4-37 appears bipolar, the morphokinematical analysis discloses the existence of three distinct axes and additional particular directions in the object, indicating that K 4-37 is a multi-axis planetary nebula that has probably been shaped by several bipolar outflows at different directions. A 4-6 M$_{\odot}$ main-sequence progenitor is estimated from the derived high nebular He and N abundances, and very high N/O abundance ratio ($\sim$2.32). The general properties are compatible with K 4-37 being a highly evolved planetary nebula located at $\sim$14 kpc. The WISE image at 22 $\mu$m reveals K 4-37 to be surrounded by a large ($\sim$13$\times$8 pc$^2$) elliptical detached shell probably related to material ejected from the AGB progenitor. The observed elliptical morphology suggests deformation of an originally spherical AGB shell by the ISM magnetic field or by the influence of a companion. We compare K 4-37 and NGC 6309 and found remarkable similarities in their physical structure but noticeably different chemical abundances that indicate very different progenitor mass. This strongly suggests that, irrespective of the initial mass, their (presumably binary) central stars have shared a very similar mass ejection history.

X-ray Studies of Planetary Nebulae

AbstractX-ray emission from planetary nebulae (PNe) provides unique insight on the formation and evolution of PNe. Past observations and the ongoing Chandra Planetary Nebulae Survey (ChanPlaNS) provide a consensus on the two types of X-ray emission detected from PNe: extended and compact point-like sources. Extended X-ray emission arises from a shocked “hot bubble” plasma that resides within the nebular shell. Cooler than expected hot bubble plasma temperatures spurred a number of potential solutions with one emerging as the likely dominate process. The origin of X-ray emission from compact sources at the location of the central star is less clear. These sources might arise from one or combinations of the following processes: self-shocking stellar winds, spun-up binary companions, and/or accretion, perhaps from mass transfer, PN fallback, or debris disks. In the discovery phase, X-ray studies of PNe have mainly focused on the origin of the various emission processes. New directions incorporate multi-wavelength observations to study the influence of X-ray emission on the rest of the electromagnetic spectrum.

Expansion parallaxes and intrinsic stellar properties for 15 simple planetary nebulae

AbstractWe determined individual distances to a small number of rather round, quite regularly shaped planetary nebulae by combining their angular expansion in the plane of the sky with a spectroscopically measured expansion along the line of sight. For this goal, we combined up to three epochs of Hubble Space Telescope imaging data and determined the respective proper motions of rim and shell edges, and of other features as well. Ground-based radial velocities are assigned separately to the nebular rims and shells and used to determine individual distances, thereby assuming that the expansions in the line-of-sight and in the plane of sky are equal. We employed 1D radiation-hydrodynamics simulations of planetary nebulae evolution to correct for the difference between the spectroscopically measured expansion velocities of rim and shell and the expansion speeds of their respective shock fronts.

The dynamical evolution of planetary nebulae

Based on modern 1D-radiation-hydrodynamics simulations of formation and evolution of planetary nebulae, I discuss in detail the basic dynamical processes responsible for the “grand design” of most planetary nebulae, i.e. their double-shell morphology and their typical expansion properties. Special emphasis is given for a proper definition of a nebula's true expansion rate and its relation to spectroscopically measurable Doppler velocities of the expanding material. It is found that the typical nebular expansion is about twice as fast as hitherto assumed, viz. ≃45 kms-1.

Tribute to Sun Kwok

Sun Kwok was bom in Hong Kong in 1949. He did all his early schooling in Hong Kong and went to the same high school, Pui Ching Middle School, as I did but he was more than a decade later. There are two Education Systems in Hong Kong; the Chinese Language Schools and English Language School. Pui Ching was started by Christian missionaries in China and has a long history of providing quality education. Pui Ching is a Chinese Language School, and during colonial times, school entrance was difficult for students as we were not eligible to apply for admission to the University of Hong Kong, nor were we able to join the civil service. In spite of these handicaps, the school still managed to produce many excellent academics, including one Nobel Prize winner in physics and one Field's medalist in mathematics. Most of its graduates who sought further education went to the U.S. Or Canada as Sun Kwok did. Sun graduated from McMaster University and then went to the University of Minnesota for graduate studies.

3D pyCloudy modelling of bipolar planetary nebulae: Evidence for fast fading of the lobes

We apply an axially symmetric pseudo-3D photoionization model, pyCloudy, to derive the structures of 6 bipolar nebulae and 2 suggested post-bipolars in a quest to constrain the bipolar planetary nebulae evolution. HST images and VLT/UVES spectroscopy are used for the modelling. The targets are located in the direction of the Galactic bulge. A 3D model structure is used as input to the photoionization code, so as to fit the HST images. Line profiles of different ions constrain the velocity field. The model and associated velocity fields allow us to derive masses, velocities, and ages. The 3D models find much lower ionized masses than required in 1D models: ionized masses are reduced by factors of 2-7. The selected bi-lobed planetary nebulae show a narrow range of ages: the averaged radii and velocities result in values between 1300 and 2000 yr. The lobes are fitted well with velocities linearly increasing with radius. These Hubble-type flows have been found before, and suggest that the lobes form at a defined point in time. The lobes appear to be slightly younger than the main (host) nebulae, by ~500 yr, they seem to form at an early phase of PN evolution, and fade after 1-2 kyr. We find that 30-35% of bulge PNe pass through a bipolar phase.

Low-ionization structures in planetary nebulae – I. Physical, kinematic and excitation properties

Though the small-scale, low-ionization knots, filaments and jets (LISs) of planetary nebulae (PNe) are known for ~30yr, some of their observational properties are not well established. In consequence our ability to include them in the wider context of the formation and evolution of PNe is directly affected. Why most structures have lower densities than the PN shells hosting them? Is their intense emission in low-ionization lines the key to their main excitation mechanism? Therefore, if considered altogether, can LISs line ratios, chemical abundances and kinematics enlighten the interplay between the different excitation and formation processes? Here we present a spectroscopic analysis of five PNe that possess LISs confirming that all nebular components have comparable electron temperatures, whereas the electron density is systematically lower in LISs than in the surrounding nebula. Chemical abundances of LISs versus other PN components do not show significant differences as well. By using diagnostic diagrams from shock models, we demonstrate that LISs' main excitation is due to shocks, whereas the other components are mainly photo-ionized. We also propose new diagnostic diagrams involving a few emission lines ([NII], [OIII], [SII]) and $\rm{log}$(f$_{shocks}$/f$_{\star}$), where f$_{shocks}$ and f$_{\star}$ are the ionization photon fluxes due to the shocks and the central star ionizing continuum, respectively. A robust relation differentiating the structures is found, with the shock-excited clearly having $\rm{log}$(f$_{shocks}$/f$_{\star}$)$>$-1; while the photo-ionized show $\rm{log}$(f$_{shocks}$/f$_{\star}$)$<$-2. A transition zone, with -2$<\rm{log}$(f$_{shocks}$/f$_{\star}$)$<$-1 where both mechanisms are equally important, is also defined.

PHOTOMETRY OF THE STINGRAY NEBULA (V839 ARA) FROM 1889 TO 2015 ACROSS THE IONIZATION OF ITS PLANETARY NEBULA

Up until around 1980, the Stingray was an ordinary B1 post-AGB star, but then it suddenly sprouted bright emission lines like in a planetary nebula (PN), and soon after this the Hubble Space Telescope (HST) discovered a small PN around the star, so apparently we have caught a star in the act of ionizing a PN. We report here on a well-sampled light curve from 1889 to 2015, with unique coverage of the prior century plus the entire duration of the PN formation plus three decades of its aftermath. Surprisingly, the star anticipated the 1980's ionization event by declining from B=10.30 in 1889 to B=10.76 in 1980. Starting in 1980, the central star faded fast, at a rate of 0.20 mag/year, reaching B=14.64 in 1996. This fast fading is apparently caused by the central star shrinking in size. From 1994-2015, the V-band light curve is almost entirely from the flux of two bright [OIII] emission lines from the unresolved nebula, and it shows a consistent decline at a rate of 0.090 mag/year. This steady fading (also seen in the radio and infrared) has a time scale equal to that expected for ordinary recombination within the nebula, immediately after a short-duration ionizing event in the 1980s. We are providing the first direct measure of the rapidly changing luminosity of the central star on both sides of a presumed thermal pulse in 1980, with this providing a strong and critical set of constraints, and these are found to sharply disagree with theoretical models of PN evolution.

Evolution of Planetary Nebulae with WR-type Central Stars

Bibliography: pages 387-442.%%%%Chapter 1. Introduction – Part I. Planetary nebulae with [WC] stars – Chapter 2. Spatially resolved kinematics – Chapter 3. Physical conditions and chemical abundances – Chapter 4. Hb 4: a planetary nebula with FLIERs – Part II. Planetary nebulae with [WN] stars – Chapter 5. Abell 48 with a [WN]-type star – Chapter 6. PB 8 with a [WN/WC]-type star – Part III. Planetary nebulae with PG 1159-type stars – Chapter 7. SuWt 2 with a PG 1159-type star – Chapter 8. Conclusions and Future Work – References – Part IV. Appendices%%%%In this thesis I present a study of the kinematics, physical conditions and chemical abundances for a sample of Galactic planetary nebulae (PNe) with Wolf-Rayet (WR) and weak emission-line stars (wels), based on optical integralfield unit (IFU) spectroscopy obtained with the Wide Field Spectrograph (WiFeS) on the Australian National University 2.3 telescope at Siding Spring Observatory, and complemented by spectra from the literature. PNe surroundingWR-type stars constitute a particular study class for this study. A considerable fraction of currently well-identified central stars of PNe exhibit ‘hydrogendeficient’ fast expanding atmospheres characterized by a large mass-loss rate.Most of them were classified as the carbon-sequence and a few of them as the nitrogen-sequence of the WR-type stars. What is less clear are the physical mechanisms and evolutionary paths that remove the hydrogen-rich outerlayer from these degenerate cores, and transform it into a fast stellar wind. The aim of this thesis is to determine kinematic structure, density distribution, thermal structure and elemental abundances for a sample of PNe with differenthydrogen-deficient central stars, which might provide clues about the origin and formation of their hydrogen-deficient stellar atmospheres.%%%%The Hɑ and [N II] emission features were used to measure the nebular radial velocities. Based on the spatially resolved velocity distributions of these emission lines combined with archival Hubble Space Telescope imaging for compact PNe, the kinematic structures of these PNe were determined. Comparing the velocity maps observed by the IFU spectrograph with those predicted by morpho-kinematic models excluded the projection effect from the nebula’s appearanceand identified the morphology of most PNe, apart from the compact objects. The results indicate that these PNe have axisymmetric morphologies, either bipolar or elliptical. In many cases, the associated kinematic maps for PNe around hot WR-type stars also show the presence of so-called fast lowionization emission regions (FLIERs).%%%%The WiFeS observations, complemented with archival spectra from the literature, have been used to carry out plasma diagnostics and abundance analysis using both collisionally excited lines (CELs) and optical recombination lines(ORLs). ORL abundances for carbon, nitrogen and oxygen have been derived where adequate recombination lines were available. The weak temperature dependence of ORLs has also been used to…