Bipolar jets in planetary nebulae: An analytical model

The various and hitherto partially unsolved problems relative to the origin of bipolar jets or highly collimated fast outflows in planetary nebulae are reviewed within the framework of a stationary magnetohydrodynamic model. In order to explain the observations of high polar velocities and the presence of polar blobs or knots in planetary nebulae, theoretical models are proposed taking into account both a large scale azimuthal magnetic field and an anisotropic turbulent velocity field. The models predict equatorial-to-polar density ratios which are rather small, in the range 2 to 3. Conversely, the polar-to-equatorial velocity contrasts are higher, with typical values upto 10. Thus thead hoc hypothesis implicit in the literature that the density contrast is varying in inverse ratio to the velocity one, does not seem well adapted to the bipolar jet phenomenon in planetary nebulae. We point out, therefore, that the bipolar jets have to be considered as a transient aspect of a very complex phenomenon. The model can be applied to objects such as He 2–104 or Mz3, M2–9.     

Spectrophotometry of five planetary nebulae

The results of a spectroscopic investigation of five planetary nebulae are given. The relative intensities of emission lines observed in them were determined. The electron density and electron temperature of the central region of the nebula KjPn 8 were determined. It was shown that the gas in this region is very highly excited. Translated from Astrofizika, Vol. 41, No. 3, pp. 367–375, July–September, 1998.     

Searches for HH objects in star formation regions. VII. Herbig-Haro objects in the region of the nebula GM 2–41

Five new Herbig-Haro objects (HH 1036–1040) have been discovered in the neighborhood of the nebula GM 2–41 in a region with an area of 14′ × 14′, at the center of the HII region DR 15 located in the southern periphery of the Cyg OB2 association. Four of them have a complex structure typical of HH flows. Hydrogen molecular emission is detected in the object HH 1036 using archived images from the Spitzer telescope. Two new infrared nebulae illuminated by very red young stellar objects are also found.     

Planetary nebulae and ALMA

Our understanding of the late evolution of intermediate mass stars (∼1–8M_⊙) through the planetary nebula phase is undergoing major developments. Observations at infrared and millimeter wavelengths have revealed important components of neutral gas and dust in the nebulae that directly trace their formation from mass-loss on the Asymptotic Giant Branch. At the same time, high resolution imaging, especially with the Hubble Space Telescope, has revealed a surprising array of structures in the nebulae: multiple arcs, tori, jets, and myriads of small scale fragments. None of these are fully understood, and all involve the neutral gas component. This paper highlights recent observations of these structures and discusses the open questions, with an emphasis on those areas where observations with ALMA are likely to make important contributions.     

Further VLA observations of hydrogen deficient stars

VLA observations at 6 cm have been obtained for three hydrogen-deficient objects υ Sgr, V 348 Sgr, and A bell 58. A bell 58 was also observed at 2 cm. Only upper limits to the flux density could be set for these sources. A new radio source at 6 cm was found in the field of υ Sgr. The upper limit for 6 cm flux density of V348 Sgr sets an upper limit to its reddening asE(B–V) ≤ 0.65. The hydrogen deficient planetary nebula A 58 shows much lower radio flux than expected from the infrared-radio flux density relationship of planetary nebulae. National Radio Astronomy Observatory’s Very Large Array is operated by Associated Universities Inc. under contract with National Science Foundation, USA.     

Detecting planets in planetary nebulae

We examine the possibility of detecting signatures of surviving Uranus/Neptune-like planets inside planetary nebulae. Planets that are not too close to the stars (orbital separation larger than ∼5 au) are likely to survive the entire evolution of the star. As the star turns into a planetary nebula, it has a fast wind and strong ionizing radiation. The interaction of the radiation and wind with a planet may lead to the formation of a compact condensation or tail inside the planetary nebula, which emits strongly in H α , but not in [O  iii ]. The position of the condensation (or tail) will change over a time-scale of ∼10 yr. Such condensations might be detected with currently existing telescopes.     

Planetary nebulae in the Magellanic Clouds (I)

A classification scheme for planetary nebulae in the Magellanic Clouds using four key criteria is suggested. All nebulae can then be divided into three classes. The features of physical parameters and evolution of the Magellanic Cloud planetary nebulae and the way in which they differ from galactic planetary nebulae are investigated separately for each class of nebulae.     

Planetary nebulae in the Magellanic Clouds (II)

Using the classification scheme for planetary nebulae in the Magellanic Clouds using four criteria proposed in Paper I, all nebulae are divided into three classes on the basis of the mass of their central stars. The features of individual chemical abundances in the Magellanic Cloud planetary nebulae and the way in which these differ from the galactic planetary nebulae are investigated separately for each class of nebulae. The role of CN and ON cycling in intermediate mass star evolution is discussed.     

FLAIR observations of planetary nebulae in the Large Magellanic Cloud

This paper presents new observations of 97 planetary nebulae in the Large Magellanic Cloud (LMC) obtained using the FLAIR system on the UK 1.2-m Schmidt Telescope. These nebulae are mostly at the fainter end of the known population, and about 75 per cent have not been observed before in spectroscopic mode. Radial velocities have been measured using cross-correlation techniques, and represent an increase of 66 per cent in the sample of LMC planetary nebulae with known radial velocities. The major line ratios are given, and are analysed in conjunction with published data. One-quarter of the faint nebulae are Type I objects with very strong [N II ] and [S II ] lines; most of the other faint nebulae have low density, low excitation and relatively strong [S II ] lines.     

Planetary nebulae in the Galaxy

It is shown that the planetary nebulae can be divided into three types according to the values of the mass of shell and a central star. The criteria are given using which one can determine the mass type of the nebula. The distance scale of each mass-type planetary nebulae is given. The distribution of planetary nebulae in the Galaxy, their formation rate, scale-height and other physical and kinematic characteristics are investigated. A catalogue of planetary nebulae emitting in the radio range is given.     

Statistical and Physical Study of One-Sided Planetary Nebulae

We have investigated the spatial orientation of one-sided Planetary Nebulae. Most of them if not all are interacting with the interstellar medium. Seventy percent of the nebulae in our sample have inclination angles larger than 45^° to the galactic plane and 30% of the inclination angles are less than 45^°. Most of the selected objects are old, evolved planetary nebulae with large dimensions, and not far away from the galactic plane. Seventy-five percent of the objects are within 160 pc from the galactic plane. The enhanced concavity arc can be explained physically as a result of the `planetary nebulae – interstellar matter' interaction. We have discussed the possible effect of the interstellar magnetic field in the concavity regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

The dynamics of double-envelope planetary nebulae

A number of criteria are elaborated based on the careful analysis of nebulae images which confirm the version of the origin of double-envelope planetary nebulae by means of dynamical separation but not by multiple ejection. The importance of stellar winds in the origin of the gigantic halos around double envelope nebulae is outlined. The problem concerning the existence of two types of filamentary planetary nebulae (Figure 8) is raised: type A, filaments are the fragmentations of the Rayleigh-Taylor instability, the result of dynamical interaction of the envelope with the outer interstellar matter (NGC 6543), and type B, the origin of filaments is connected with the Magnetic field fluctuations (A 43, A 72).The possibility of the origin of three-envelope nebulae in the framework of the dynamic separation version is discussed (NGC 7293). Attention is paid to the impossibility of outbursts with low velocities (20–30 km s^–1) from hot stars, i.e., the nuclei of nebulae.     

Truncated Collimated Flows in Abell 30, Abell 78 and the Honeycomb Nebula

Localised collimated flows of ionized gas are found in two hydrogen deficient planetary nebulae, Abell 30 and Abell 78 as well as in the Honeycomb complex of interlocking shells in halo of 30 Dor in the Large Magellanic Cloud. One common feature of these flows, in seemingly disparate objects, is that they all terminate at around the same difference in radial velocity (with respect to that of the systemic radial velocity). A possible explanation involves high speed flows being decelerated by mass-loading. In Abell 30 and 78, mass is injected by clumps embedded in the fast wind. In the Honeycomb nebula, a supernova blast wave has pierced an old dense shell wall which adds mass to the post-shock flow via a boundary layer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pseudo-resonance absorption lines in planetary nebulae: Discovery?

The possibility of the formation of pseudo-resonance absorption lines in planetary nebulae is predicted only theoretically. However, this has not been confirmed by direct observations. In the present article an attempt has been made to show, as a result of careful analysis of IUE spectral recordings for a group of planetary nebulae, that the existence of one pseudo-resonance line 1300 SiIII is without doubt at least in spectra of three planetary nebulae: NGC 2610, NGC 3587, and NGC 6891. The presence of this line in the spectra of the other three planetary nebulae, NGC 6210, IC 3568, and IC 4776, seems to be probable. The role of the interstellar selective absorption, the blending effect by the resonance lines of SiII,Oi, andSi in the formation of the pseudo-resonance line 1300 SiIII as well as the possibility of formation of this line in the photosphere of central star of nebula were analysed.     

Dynamical and ionization structure of planetary nebulae in three dimensions. A simulation for NGC3132

Using a numerically accurate radiation-gas dynamical method we investigate the winds scenario for aspherical planetary nebulae (PNe). Our model includes the interaction of two winds: as low high mass-loss rate wind (a `super wind'); and a fast wind; low mass-loss rate wind. Our model also includes the evolution of the UV spectrum of the PNe centeral star. As stated in the section3 of Paper I (Ganbari and Khesali, 2001), we consider a three dimensional density distribution ρ(r,θφ for the super wind, in this way we enter the effects of cooling and heating mechanisms in our model. Taking into account the above assumptions, we introduce the code (DIS3D) and numerically we study the dynamical and ionization properties of the planetary nebula NGC3132. We show that it is possible by simulations to reproduce the shape of PNe in three dimensions, and calculating the physical quantities throughout the entire nebula. This revised version was published online in July 2006 with corrections to the Cover Date.     

[WR] nuclei of planetary nebulae: Inferences from statistical studies of the nebulae

There are about 50 galactic planetary nebulae know to have [WR] type nuclei. We have compared their nebular properties with those of the other planetary nebulae in the Galaxy. We have found that the nebular morphological types are similarly distributed in the two groups. Bipolar nebulae constitute only 20% of the total in each group. The distribution of the nebular electron densities and abundance ratios N/O, He/H and C/O are the same in the two groups. The only marked difference is that nebular expansion velocities are larger in the group of planetary nebulae with [WR] central stars. We argue that the WR phenomenon does not preferentially occur in more massive central stars of planetary nebulae, contrary to what has been suggested in some former studies. We demonstrate that, for most of the observed [WR] type objects, the WR phenomenon cannot be triggered by a late helium shell flash event.The results of our investigation are published inAstronomy & Astrophysics 303, 893 (1995) and in the proceedings of the 2nd International Colloquium on Hydrogen-deficient Stars, C.S. Jeffery & U. Heber (eds), Astronomical Society of the Pacific Conference Series, Vol. 96, p. 209 (1996).     

Search for HH objects and emission stars in star formation regions. IV. New Herbig-Haro flows and objects associated with cometary nebulae

As part of a project to search for new Herbig-Haro (HH) objects in star formation regions, observations are reported on the neighborhoods of five cometary nebulae: MacC H12, MacC sH15, GM 1-14, RNO 33, and Pars 17. We have been able to identify 9 previously unknown HH objects in those regions. Almost all of these objects belong to directed flows whose sources are, with high probability, the central stars of these nebulae. In the cases of MacC H12 and GM 1-14, the outflows have a distinct bipolar structure. The sources of the outflows are located on a J-H/H-K diagram in order to classify them. __________ Translated from Astrofizika, Vol. 51, No. 1, pp. 15–27 (February 2008).     

Photoionization modelling of planetary nebulae – II. Galactic bulge nebulae, a comparison with literature results

We have constructed photoionization models of five galactic bulge planetary nebulae using our automatic method, which enables a fully self-consistent determination of the physical parameters of a planetary nebula. The models are constrained using the spectrum, the IRAS and radio fluxes and the angular diameter of the nebula. We also conducted a literature search for physical parameters determined with classical methods for these nebulae. Comparison of the distance-independent physical parameters with published data shows that the stellar temperatures generally are in good agreement and can be considered reliable. The literature data for the electron temperature, electron density and also for the abundances show a large spread, indicating that the use of line diagnostics is not reliable and that the accuracy of these methods needs to be improved. Comparison of the various abundance determinations indicates that the uncertainty in the electron temperature is the main source of uncertainty in the abundance determination. The stellar magnitudes predicted by the photoionization models are in good agreement with observed values.     

Bubbles in planetary nebulae and clusters of galaxies: jet bending

We study the bending of jets in binary stellar systems. A compact companion accretes mass from the slow wind of the mass-losing primary star, forms an accretion disc and blows two opposite jets. These fast jets are bent by the slow wind. Disregarding the orbital motion, we find the dependence of the bending angle on the properties of the slow wind and the jets. Bending of jets is observed in planetary nebulae which are thought to be the descendants of interacting binary stars. For example, in some of these planetary nebulae, the two bubbles (lobes) which are inflated by the two opposite jets are displaced to the same side of the symmetry axis of the nebula. Similar displacements are observed in bubble pairs in the centre of some clusters and groups of galaxies. We compare the bending of jets in binary stellar systems with that in clusters of galaxies.     

Statistics of planetary nebulae with [WR] central stars

The status of planetary nebulae with Wolf-Rayet type central stars([WR] PN) remains one of the most important problems inthe investigation of planetary nebulae. We cannot claim to understand theevolution of low and intermediate-mass stars without answering the questionhow [WR] PN are created.Analyzing the statistical properties of the whole population of [WR] PNand comparing them to other planetary nebulae (non-[WR] PN) bringsimportant information on their origin and evolutionary status. In thisarticle I will summarize our results of this type of studies and show whatlimits they put on the possible evolutionary routes of [WR] PN creation.