Evolution Of Central Stars Research Articles

NGC 6826- Integrated Study of the Planetary Nebula and Central Star Properties

This study provides a comprehensive analysis of NGC 6826, focusing on the structural, kinematic, and spectroscopic properties of its planetary nebula and the characteristics of its central star. By integrating multi- wavelength observational data, we examine the nebular morphology, ionization structure, and chemical composition, which reveal insights into the evolutionary processes shaping the nebula. Additionally, we analyze the central star’s luminosity, temperature, and spectral features to understand its role in driving the observed nebular dynamics. Our findings contribute to the broader understanding of planetary nebula formation, central star evolution, and the interaction mechanisms at play. This integrated approach underscores the importance of studying planetary nebulae in a holistic context to unravel the complexities of stellar evolution. Keywords: NGC 6826, planetary nebula, central star, kinematics, stellar evolution, spectroscopy

Planetary Nebulae Research: Past, Present, and Future

We review the evolution of our understanding of the planetary nebulae phenomenon and their place in the scheme of stellar evolution. The historical steps leading to our current understanding of central star evolution and nebular formation are discussed. Recent optical imaging, X-ray, ultraviolet, infrared, millimeter wave, and radio observations have led to a much more complex picture of the structure of planetary nebulae. The optically bright regions have multiple shell structures (rims, shells, crowns, and haloes), which can be understood within the interacting winds framework. However, the physical mechanism responsible for bipolar and multipolar structures that emerged during the proto-planetary nebulae phase is yet to be identified. Our morphological classifications of planetary nebulae are hampered by the effects of sensitivity, orientation, and field-of-view coverage, and the fraction of bipolar or multipolar nebulae may be much higher than commonly assumed. The optically bright bipolar lobes may represent low-density, ionization-bounded cavities carved out of a neutral envelope by collimated fast winds. Planetary nebulae are sites of active synthesis of complex organic compounds, suggesting that planetary nebulae play a major role in the chemical enrichment of the Galaxy. Possible avenues of future advancement are discussed.

Searching for central stars of planetary nebulae in Gaia DR2

Context. Accurate distance measurements are fundamental to the study of planetary nebulae (PNe) but they have long been elusive. The most accurate and model-independent distance measurements for galactic PNe come from the trigonometric parallaxes of their central stars, which were only available for a few tens of objects prior to the Gaia mission. Aims. The accurate identification of PN central stars in the Gaia source catalogues is a critical prerequisite for leveraging the unprecedented scope and precision of the trigonometric parallaxes measured by Gaia. Our aim is to build a complete sample of PN central star detections with minimal contamination. Methods. We developed and applied an automated technique based on the likelihood ratio method to match candidate central stars in Gaia Data Release 2 (DR2) to known PNe in the Hong Kong/AAO/Strasbourg Hα PN catalogue, taking into account the BP – RP colours of the Gaia sources as well as their positional offsets from the nebula centres. These parameter distributions for both true central stars and background sources were inferred directly from the data. Results. We present a catalogue of over 1000 Gaia sources that our method has automatically identified as likely PN central stars. We demonstrate how the best matches enable us to trace nebula and central star evolution and to validate existing statistical distance scales, and we discuss the prospects for further refinement of the matching based on additional data. We also compare the accuracy of our catalogue to that of previous works.

IFU spectroscopy of southern PNe – VII. Photoionization modelling of intermediate excitation class objects

We present integral field unit spectroscopic observations of southern Galactic planetary nebulae (PNe), IC 2501, Hen 2-7, and PB4. The goal of studying these objects together is that, although they have roughly similar intermediate excitation and evolution of central stars (CSs), they display very different evolution in their nebular structure which needs to be understood. The morphologies and ionisation structures of the objects are investigated using a set of emission-line maps representative of the different ionisation zones. We use those in order to construct two-zone self-consistent photoionisation models for each nebula to determine new model-dependent distances, progenitor luminosities, effective temperatures and CS masses. The physical conditions, chemical compositions, and expansion velocities and ages of these nebulae are derived. In Hen 2-7 we discover a strong poleward-directed jet from the presumed binary CS. Oxygen and nitrogen abundances derived from both collisionally excited and recombination lines reveal that PB4 displays an extreme abundance discrepancy factor, and we present evidence that this is caused by uorescent pumping of the OII ion by the EUV continuum of an interacting binary CS, rather than by recombination of the OIII ion. Both IC 2501 and PB4 were classified by others as Weak Emission Line Stars (WELS). However, our emission line maps show that their recombination lines are spatially extended in both objects, and are therefore of nebular rather than CS origin. Given that we have found this result in a number of other PNe, this result casts further doubt on the reliability, or even the reality, of the WELS classification.

Surveying Planetary Nebulae Central Stars for Close Binaries: Constraining Evolution of Central Stars Based on Binary Parameters

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 between the proto-planetary nebula and planetary nebula stages, demonstrating that the known proto-planetary nebulae are not the precursors of planetary nebulae with close binary central stars.

New models for the evolution of central stars of planetary nebulae: Faster and Brighter

AbstractThe post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The recent post-AGB evolutionary sequences computed by Miller Bertolami (2016) are at least three to ten times faster than those previously published by Vassiliadis & Wood (1994) and Blöcker (1995) which have been used in a large number of studies. This is true for the whole mass and metallicity range. The new models are also ~0.1–0.3 dex brighter than the previous models with similar remnant masses. In this short article we comment on the main reasons behind these differences, and discuss possible implications for other studies of post-AGB stars or planetary nebulae.

Evolution of the central stars of young planetary nebulae

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 observations. An increase of the [OIII] 5007 A line flux is frequently observed in young planetary nebulae hosting H-rich central stars. The increasing nebular excitation is the response to the increasing temperature and hardening radiation of the central stars. We did not observe any changes in the nebular fluxes in the planetary nebulae hosting late-type Wolf-Rayet (WR) central stars. This may indicate a slower temperature evolution (which may stem from a different evolutionary status) of late-[WR] stars. In young planetary nebulae with H-rich central stars, the evolution can be followed using optical spectra collected during a decade or longer. The observed evolution of H-rich central stars is consistent with the predictions of the evolutionary models provided in the literature. Late-[WR] stars possibly follow a different evolutionary path.

Chemical abundances in Galactic planetary nebulae withSpitzerspectra

We present new low-resolution (R~800) optical spectra of 22 Galactic PNe with Spitzer spectra. These data are combined with recent optical spectroscopic data available in the literature to construct representative samples of compact (and presumably young) Galactic disc and bulge PNe with Spitzer spectra. Attending to the nature of the dust features seen in their Spitzer spectra, Galactic disc and bulge PNe are classified according to four major dust types (oxygen chemistry or OC, carbon chemistry or CC, double chemistry or DC, featureless or F) and subtypes (amorphous and crystalline, and aliphatic and aromatic). Nebular gas abundances of He, N, O, Ne, S, Cl, and Ar, as well as plasma parameters (e.g. Ne, Te) are homogeneously derived and we study the median chemical abundances and nebular properties in Galactic disc and bulge PNe depending on their Spitzer dust types and subtypes. A comparison of the derived median abundance patterns with AGB nucleosynthesis predictions show mainly that i) DC PNe, both with amorphous and crystalline silicates, display high-metallicity (solar/supra-solar) and the highest He abundances and N/O ratios, suggesting relatively massive (~3-5 M_sun) hot bottom burning AGB stars as progenitors; ii) PNe with O-rich and C-rich unevolved dust (amorphous and aliphatic) seem to evolve from subsolar metallicity (z~0.008) and lower mass (<3 M_sun) AGB stars; iii) a few O-rich PNe and a significant fraction of C-rich PNe with more evolved dust (crystalline and aromatic, respectively) display chemical abundances similar to DC PNe, suggesting that they are related objects. A comparison of the derived nebular properties with predictions from models combining the theoretical central star evolution with a simple nebular model is also presented. Finally, a possible link between the Spitzer dust properties, chemical abundances, and evolutionary status is discussed.

The radio continuum from a planetary nebula as a mirror of the central star evolution

AbstractIn the frame of ISW model the rates of the evolutionary changes of the flux density and the critical frequency in radio continuum spectrum have been calculated in dependence on the kinematic age of a planetary nebula. The time changes of the instantaneous radio spectra of IC 418 and NGC 6369 do not contradict accounts.

The Evolution of Central Stars of Planetary Nebulae

The evolution of central stars of planetary nebulae can proceed in several distinct ways, either leading to H-deficiency or to H-normal surface composition. Several new simulations of the evolution channels that lead to H-deficiency are now available, mainly the born-again sce- narios that are triggered by a He-shell flash during the hot pre-white dwarf evolution phase. A realistic AGB progenitor evolution is important for correct HRD tracks, that allow mass de- terminations. New hydrodynamic simulations of He-shell flash convection including cases with H-ingestion are now performed, and allow a determination of the convective extra-mixing effi- ciency. This has direct consequences for the intershell abundance distribution of AGB stars that can be observed in the H-deficient CSPN.

H- and He-burning Central Stars and the Evolution to White Dwarfs

The structure and evolution of central stars of planetary nebulae (CSPNe) is reviewed. CSPNe represent the rapid transitional stage between the Asymptotic Giant Branch (AGB) and the white-dwarf domain. It is shown that the whole evolution off the AGB through the central-star regime depends on the evolutionary history. The detailed evolution into a white dwarf is controlled by the internal stellar structure which, in turn, is determined by the duration of the preceding AGB evolution and therefore by the AGB mass-loss history. The evolution of hydrogen-deficient central stars has been a matter of debate since many years. Convective overshoot appears to be a key ingredient to model these objects. Various thermal-pulse scenarios with inclusion of overshoot are discussed, leading to surface abundances in general agreement with those observed for Wolf-Rayet central stars.

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.

The radio continuum evolution in the planetary nebulae

The radio continuum variations from galactic planetary nebulae in the process of the central star evolution without helium flashes are considered. On the base of our distance scale we obtained empirical evolutionary dependences for the ionized mass and the hydrogen atom concentration. The parameters of a theoretical model of the interacting stellar winds (ISW) are determined to reach an agreement between empirical and theoretical dependences. In this model the time dependences are obtained for the intrinsic flux density at 15 v GHz and for the critical frequency. The flux density may increase with rate of several percents until the kinematic age does not exceed 1000 years.

Physics and Gas Dynamics of Wind-Blown Bubbles

We review the recent hydrodynamic modelling of wind-blown bubbles (WBB) which are result of interaction of a stellar wind with the circumstellar matter or the wind(s) emitted during the previous stages of the central star evolution. The much faster computers becoming available in the last decade allow a more complete picture of the physics of these objects to be built. Recent hydrodynamic models are capable of treating in detail different mechanisms as radiative plasma cooling, electron thermal conduction and the effects of magnetic fields. We discuss the various mechanisms proposed for shaping these objects and we emphasize on the problems related to the development of various instabilities and the X-ray emission from WBB.

Structure and evolution of central stars of Planetary Nebulae

In this review a critical examination of our present knowledge about the structure and evolution of central stars of planetary nebulae is presented. In particular, the still enigmatic origin of the Wolf-Rayet central stars is addressed, too. Some directions for future work are given at the end.

Observations of CSPN

It's a good thing that we're starting to meet every four years rather than every five. There has been tremendous progress in understanding the properties and evolution of central stars of planetary nebulae (CSPN) since the last meeting in Innsbruck in 1992. Much of the credit is due to new spectra and images obtained at observatories that weren't even in existence four years ago. Table 1 lists most of the space observatories used by astronomers reporting at this symposium. The ones marked with the asterisk are new to this conference. The double asterisks for the Hubble Space Telescope instruments remind us that the telescope was repaired in December 1993. The reference gives the identification of the poster paper given at this meeting. We can look forward to similar improvements in ground-based observatories to be reported at the next meeting.

Investigating the near-IR properties of PN: Deep imaging of molecular hydrogen emission

We present the first results of a deep near-infrared narrowband imaging study of several planetary nebulae. The data were acquired using the University of Hawaii 2.2m telescope on Mauna Kea and the “QUIRC” 1024 × 1024 array camera. With these sensitive high spatial resolution imaging data, we are able to explore in detail where H2 is found relative to the ionized region in planetary nebulae at various stages of evolution (See Figure 1, for an example). The objects were selected from previous studies to have evidence for extended emission from H2, and they are at several differing phases of central star evolution. The presence of molecules in the UV–flooded environment of a planetary nebula cannot be explained without highly non-spherical geometries and high densities, or clumping. Although there can be an ambiguity in the excitation mechanism (UV photons or shocks), the location of H2 emission identifies regions of the nebula with sufficient dust shielding and density for the survival of molecular species. The emission morphology also provides information that helps identify which excitation mechanism is most likely. When combined with data provided by other molecular studies, we can examine how the photodissociation region evolves through the circumstellar envelope as the planetary nebula tracks across the top of the HR diagram. We can also consider how morphological evolution of the nebula, through interacting winds and shocks, might provide the conditions necessary for molecular survival.

X-Ray Emission from the Wind-Blown Bubble in the Planetary Nebula BD +30°3639

An X-ray spectrum of a wind-blown bubble in the planetary nebula BD +30°3639, acquired by the Advanced Satellite for Cosmology and Astrophysics (ASCA), shows the presence of hot (T = 3 × 106 K) gas dominated by the Ne Kα line complex. There is circumstantial evidence for the enhanced abundances of other H- and He-burning products, although O is not as abundant as in the extremely C-rich stellar wind of the W-R central star. The temperature of the hot gas is several times lower than expected behind the shock from the 700 km s-1 stellar wind. This might be caused by variations in the stellar wind speed and its chemical abundances induced by the central star evolution, and possibly aided by mixing of the stellar wind gas with the nebular material. Mixing is hinted by the discovery of small (02) dusty clumps in the Hubble Space Telescope (HST) narrowband images of the nebula in [S III] λ9532 and [O II] λ3727 emission lines. These clumps are projected against an axisymmetric, nearly square nebular shell and are most likely associated with the neutral and molecular envelope surrounding the wind-blown bubble and the wind-swept shell.

Structure and evolution of central stars of planetary nebulae

We report on the present status of our knowledge concerning the structure and evolution of central stars of planetary nebulae. It is demonstrated how the whole evolution off the Asymptotic Giant Branch depends on the preceding mass-loss history. Mass loss determines not only the final mass but also the internal structure which controls the detailed evolution into a white dwarft configuration. However, since a theory of mass loss along the AGB is still lacking we have to rely on semi-empirical prescriptions, which do not allow to make precise predictions for the final evolution. In particular, the Wolf-Rayet central stars are still enigmatic objects and constitute a challenge for stellar evolution theory.

Further Models of Planetary Nebula Spectral Evolution

Four new calculations of planetary nebulae spectral evolution are presented, as in Volk (1992). These models use the 0.64 M⊙ central star evolution track of Schönberner (1983) but with the rate of evolution accelerated by a factor of 2, as the original models evolve to the planetary nebula phase too slowly to match the observations. Models were calculated for mass-loss rates of 2.1 × 10−5 and 5.2 × 10−5 MM⊙ yr−1 using solar composition and silicate dust, and using the average observed planetary nebula composition and graphite dust. An interacting winds shell was assumed to form. The model results were combined with an assumed Galactic distribution of 25000 planetary nebula to simulate a variety of observables including V magnitudes, Hβ fluxes, the IRAS colours, the 5 GHz radio flux densities, and the nebular radii.