PG 1159-type Star Research Articles

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…

Modeling the optical radiation of the precataclysmic variable SDSS J212531-010745

Optical observations are analyzed to derive a set of basic parameters for the precataclysmic variable star SDSS J212531-010745, whose primary is a PG1159-type star. Spectroscopic and multiband photometric observations of the star were performed in 2008–2011 with the 6-m telescope and the Zeiss-1000 telescope of the Special Astrophysical Observatory. The shape of the binary’s orbital light curves is nearly sinusoidal, with the amplitude increasing with wavelength from Δm = 0.40m in the B band to Δm = 0.73m in the R band. The spectra contain absorption lines of HeII and neutral atoms, along with HI, HeI, CII, MgII, FeII emission lines, whose intensity increases synchronously with the brightness of the system. The optical radiation from SDSS J212531-010745 has a composite nature, corresponding to a model for a pre-cataclysmic variable with strong reflection effects. Cross-correlation techniques are used to measure the radial velocities and derive the component masses. Numerical modeling of the binary’s light curves, radial velocities, and spectra is performed, and a complete set of parameters determined. Considerable abundance anomalies (to 1 dex) were detected for the secondary. The primary’s characteristics correspond to the evolutionary predictions for DAO dwarfs with masses M ≈ 0.5 M⊙, and the secondary’s characteristics to low-mass, main-sequence stars with the solar metallicity.

A SPECTROSCOPIC AND PHOTOMETRIC STUDY OF THE PLANETARY NEBULAE Kn 61 AND Pa 5

We present the first morpho-kinematical analysis of the planetary nebulae Kn 61 and Pa 5 and explore the nature of their central stars. Our analysis is based on high resolution and medium resolution spectroscopic observations, deep narrow-band imaging, and integral photometry. This material allows us to identify the morphological components and study their kinematics. The direct images and spectra indicate an absence of the characteristic [N II] and [S II] emission lines in both nebulae. The nebular spectrum of Kn 61 suggests an hydrogen deficient planetary nebula and the stellar spectrum of the central star reveals a hydrogen deficient PG 1159-type star. The [O III] position velocity diagram reveals that Kn 61 is a closed, empty, spherical shell with a thin border and a filamentary surface expanding at 67.6 km s$^{-1}$, and the shell is currently not expanding isotropically. We derived a kinematic age of $\sim$ 1.6$\times$10$^4$ yrs for an assumed distance of 4 kpc. A photometric period of $\sim$ 5.7($\pm$0.4) days has been detected for Kn 61, indicating presence of a possible binary system at its core. A possible link between filamentary, spherical shells and PG 1159-type stars is noted. The morphology of Pa 5 is dominated by an equatorial toroid and faint polar extensions. The equatorial region of this planetary nebula is expanding at 45.2 kms$^{-1}$. The stellar spectrum corresponds to a very hot star and is dominated by a steep blue rising continuum and He II, Balmer and Ca II photospheric lines.

Observations and three-dimensional ionization structure of the planetary nebula SuWt 2★

The planetary nebula SuWt 2 (PN G311.0+02.4) is an unusual object with a prominent, inclined central emission ellipse and faint bipolar extensions. It has two A-type stars in a proven binary system at the centre. However, the radiation from these two central stars is too soft to ionize the surrounding material leading to a so far fruitless search for the responsible ionizing source. Such a source is clearly required and has already been inferred to exist via an observed temporal variation of the centre-of-mass velocity of the A-type stars. Moreover, the ejected nebula is nitrogen rich which raises question about the mass-loss process from a likely intermediate-mass progenitor. We use optical integral-field spectroscopy to study the emission lines of the inner nebula ring. This has enabled us to perform an empirical analysis of the optical collisionally excited lines, together with a fully three-dimensional photoionization modelling. Our empirical results are used to constrain the photoionization models, which determine the evolutionary stage of the responsible ionizing source and its likely progenitor. The time-scale for the evolutionary track of a hydrogen-rich model atmosphere is inconsistent with the dynamical age obtained for the ring. This suggests that the central star has undergone a very late thermal pulse. We conclude that the ionizing star could be hydrogen deficient and compatible with what is known as a PG 1159-type star. The evolutionary tracks for the very late thermal pulse models imply a central star mass of ∼0.64 M⊙, which originated from an ∼3 M⊙ progenitor. The evolutionary time-scales suggest that the central star left the asymptotic giant branch about 25 000 yr ago, which is consistent with the nebula's age.

The High‐Excitation Planetary Nebula NGC 246. II.FUSEandChandraObservations

This paper presents Far-Ultraviolet Spectroscopic Explorer (FUSE) medium-resolution slit and Chandra X-Ray Observatory ACIS-S observations of the high-excitation planetary nebula NGC 246. The Ne V λ1146 and [Ne V] λ3426 emission lines, the latter obtained in a previous investigation, indicate that the nebula is photoionized by the intense UV radiation of the central object and has a temperature of ~20,000 K. The O VI λ1032 and λ1037 emission lines are moderately optically thick and probably contain contributions from both collisional excitation and radiative scattering of the UV continuum of the central star. The Chandra observation did not detect any X-ray emission from the nebula, but did detect the central star. The absence of nebular X-ray emission and the photoionized nature of the nebula support the hypothesis that the nebula contains a biconical cavity, which extends to the edge of the nebula. In this geometry the stellar wind does not shock the nebular material, resulting only in a cool photoionized plasma. The X-ray spectrum of the central object is consistent with NLTE models for PG 1159-type stars.

Detection of non-radial g-mode pulsations in the newly discovered PG 1159 star HE 1429-1209

We performed time-series photometry of the PG 1159-type star HE 1429-1209, which was recently discovered in the ESO SPY survey. We show that the star is a low-amplitude (≈0.05 mag) non-radial g-mode pulsator with a period of 919 s. HE 1429-1209 is among the hottest known post-AGB stars ( K) and, together with the known pulsator RX J2117.1+3412, it defines empirically the blue edge of the GW Vir instability strip in the HRD at high luminosities.

Fe-Deficiency in H-Deficient Post-AGB Stars Due to n-Capture Nucleosynthesis

H-deficient post-AGB objects, e.g. PG1159 type star K1-16 and born-again AGB star Sakurai's object, have been reported to be significantly iron-deficient. We find that the iron deficiencies expected due to neutron-capture nucleosynthesis during either the progenitor AGB evolution and/or the neutron burst that occurs as a result of the rapid burning of protons during a post-AGB He-flash are generally in line with observations.

C IV and O VI Transitions in the Region lambda lambda 1100--2000 and Examples Found in IUE Spectra of Hot Stars

view Abstract Citations (18) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS C IV and O VI Transitions in the Region lambda lambda 1100--2000 and Examples Found in IUE Spectra of Hot Stars Feibelman, Walter A. ; Johansson, Sveneric Abstract We present Ritz wavelengths for more than 130 transitions of C IV and O VI in the range λλ1100-2000 and show examples of absorption features as seen in representative examples of high-dispersion IUE spectra of very hot (∼100,000 K) nuclei of planetary nebulae, white dwarfs, and PG 1159-type stars. The regions near He II λ640 and interstellar Si II λ1260 are of particular interest because they coincide with strong C IV and O VI transitions. O VI absorptions are detected in the lUE spectrum of the nucleus of the planetary nebula NGC 7293, which suggests that this object may be a "hybrid" star with an H-rich atmosphere. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1995 DOI: 10.1086/192226 Bibcode: 1995ApJS..100..405F Keywords: ISM: PLANETARY NEBULAE: GENERAL; LINE: IDENTIFICATION; STARS: EARLY-TYPE; STARS: WHITE DWARFS; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (15) MAST (1)