Spectroscopy of planetary nebulae in the region of Canis Major

We present the results of a pilot project of spectroscopic observations for planetary nebulae (PNe) and PN candidates in Canis Major, a sky region where the remnant of a disrupted dwarf galaxy cannibalized by the Milky Way may be located. The spectra of seven objects were taken while testing the SALT spectrograph (South African Astronomical Observatory). All elemental abundances have been obtained by the T _e method, where the electron temperature is calculated directly using the measured weak auroral [OIII] ?? 4363 ? and/or [NII] ?? 5755 ? lines. We have measured the intensities of all the detected emission lines and determined the abundances of oxygen and several other elements (N, Ne, S, Cl, C, and He) in all PNe. The radial velocity for one PN has been measured for the first time and the velocities for all of the remaining PNe have been measured with a considerably better accuracy than that of the previously published ones. The elemental abundances for three PNe have been calculated for the first time and the accuracies of determining the abundances for three others have been improved. The measured heavy-element abundance ratios (S/O, Ne/O, Cl/O) are in good agreement with their typical values for HII regions. Among the PNe studied, ESO 428-05 is the first and so far the most likely candidate for belonging to the remnants of a possible dwarf galaxy disrupted by the tidal interaction with the Milky Way.     

Evolution of elemental abundances in planetary nebulae

We study the evolution of elemental abundances in an ensemble of Galactic planetary nebulae as a function of the masses of the central stars (M _cs) and their progenitors (M _ini). We derive the dependences of the C, N, Ne, Cl, Ar, and S abundances on M _cs and M _ini for a large sample of nebulae. We calculate the theoretical elemental abundances in nebulae under the assumption of complete mixing of the progenitor’s matter ejected at different stages of its evolution. The theoretical dependences of the C and N abundances on M _ini have been found to correspond to the observed ones. At the same time, the observed mean O abundance is approximately half its theoretical value. The Ne, Cl, Ar, and S abundances monotonically increase with increasing mass of the progenitor star, which reflects an increase in the mean abundances of heavy elements during the chemical evolution of the Galaxy. We have derived the relation between the abundances of the elements under consideration in planetary nebulae and the masses of their central stars. This relation is used to construct the mass function for the nuclei of planetary nebulae.     

Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution

Planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the Hubble Space Telescope Data Archive and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, and S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extragalactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe-specifically, that the genesis of PNe structure should relate strongly to the population type, and by inference the mass, of the progenitor star and less strongly on whether the central star is a member of a close binary system.     

Chemical Evolution of the System of Galactic Planetary Nebulae

The problem of the chemical evolution of the system of Galactic planetary nebulae, starting with the early stage of development of the Galaxy, is investigated. The radial and vertical gradients of C, N, O, Ne, Ar, Cl, and S abundances are determined for different ages of the precursor stars of the nebulae. A statistically significant age dependence of the gradients is derived.     

Planetary nebula chemical abundances: Z-distribution and connection with the central star masses

Dependencies of galactic planetary nebula chemical abundances and their central star masses on the distance from the galactic plane are discussed.Z-dependencies of He/H, N/H, N/O and Ar/H and dependencies of He/H, N/H, N/O, Ne/H and Ar/H on central star mass are found. Three galactic planetary nebula distance scale samples are used and it is shown that the distance scale system (where distances of each planetary nebula mass class are determined with the separate scale) is the most reliable. The correlations obtained for the Magellanic Cloud planetary nebulae are used for comparison.     

Chemical abundances of the WR-ring nebulae NGC 2359 and RCW 78

We report on extensive spectroscopic observations of the WR-ring nebulae NGC 2359 and RCW 78, respectively, excited by the WN5 stars HD 56925 and WN8 HD 117688. For the first object we have determined abundances for O/H, Ne/H, N/H, and He/H in many different positions, including the ionized gas in the bubble, inside the optical shell structure, and the outermost zones associated with the S 298 Hii region. We do not find any significant difference in the N/H and O/H abundances over the entire nebula. The O/H and N/H abundances expected are close to those for a normal Hii region located at similar distance. In the case of He/H we find indication of local enhancements which sum to the abundance of metal rich galactic Hii regions like M17. RCW 78 appears to show slight overabundances of He/H and N/H in the two observed positions.The ionising temperature for the WN central star (HD 56925) of NGC 2359 is determined from the observed Hii region spectrum giving a value of 50000 K, appropriate to its spectral type.     

Rapid photometric and spectroscopic evolution of the young planetary nebula Hen 3–1357 and its central star SAO 244567

We present the results of spectroscopic and photometric observations for the young compact planetary nebula Hen 3–1357 and its central star SAO 244567. High-resolution spectroscopy has allowed the expansion velocity of the nebula, V _exp = 8.4 ± 1.5 km s^?1, and the heliocentric velocity of the object, V _r = +12.6 ± 1.7 km s^?1, to be determined. The gas shell parameters (N _e , T _e ), the extinction in the Hβ line, and the O, N, Ne, Ar, S, Cl, He, and C abundances have been determined from low-resolution spectra taken in 1992 and 2011. We have found significant changes in the relative intensities of forbidden lines in the spectrum of Hen 3–1357 within the last 20 years: the low-excitation [O I], [O II], and [N II] lines became stronger relative to Hβ by a factor of ～2, while the [O III] lines weakened by a factor of ～ 2, suggesting a decrease in the excitation class of the nebula. The V-band photometry performed under the ASAS-3 program revealed a decline in the yearly mean brightness of SAO 244 567 from 2001 to 2009 by $0_.^m 5$ and rapid variability with an amplitude of a few tenths of a magnitude. Published observational data in a wide spectral range, from the near ultraviolet to the radio band, suggest an appreciable weakening of the flux from the star and the nebula.     

He,C, N,and O abundances in an ensemble of galactic planetary nebulae

The He, C, N, and O abundances in more than 120 planetary nebulae (PNe) of our Galaxy and the Magellanic Clouds have been redetermined by analyzing new PNe observations. The characteristics of PNe obtained by modeling their spectra have been used to compile a new catalog of parameters for Galactic and extragalactic PNe, which is accessible at http://www.astro.spbu.ru/staff/afk/GalChemEvol.html. The errors in the parameters of PNe and their elemental abundances related to inaccuracies in the observational data have been analyzed. The He abundance is determined with an accuracy of 0.06 dex, while the errors in the C, N, and O abundances are 0.1–0.2 dex. Taking into account the inaccuracies in the corrections for the ionization stages of the elements whose lines are absent in the PNe spectra increases the errors in the He abundance to 0.1 dex and in the C, N, and O abundances to 0.2–0.3 dex. The elemental abundances in PNe of various Galactic subsystems and the Magellanic Clouds have been analyzed. This analysis suggests that the Galactic bulge objects are similar to type II PNe in Peimbert’s classification, whose progenitor stars belong to the thin-disk population with ages of at least 4–6 Gyr. A similarity between the elemental abundances in PNe of the Magellanic Clouds and the Galactic halo has been established.     

Metal-poor planetary nebulae: Effects of winds

Some planetary nebulae in the galactic thick disk display extremely low abundances of heavy elements such as O, Ne, S, and Ar, compared with normal or type II nebulae. Their central stars are generally relatively cool and underluminous, indicating that the progenitor stars had very low masses. It is suggested that strong stellar winds have had an important role in the formation of these objects, which is supported by the large mass loss rates now observed.     

Chemical enrichment by massive stars

Heavy element abundances derived from high-quality ground-based and Hubble Space Telescope (HST) spectroscopic observations of low-metallicity blue compact galaxies (BCGs) with oxygen abundances 12+log O/H between 7.1 and 8.3 are discussed. None of the heavy element-to-oxygen abundance ratios studied here (C/O, N/O, Ne/O, Si/O, S/O, Ar/O, Fe/O) depend on oxygen abundance for BCGs with 12+log O/H≤7.6 (Z≤Z_⊙/20). This constancy implies that all these heavy elements have a primary origin and are produced by the same massive (M≥10 M_⊙) stars responsible for O production. The dispersion of the C/O and N/O ratios in these galaxies is found to be remarkably small, being only ±0.03 dex and ±0.02 dex respectively. This very small dispersion is strong evidence against any time-delayed production of C and primary N in the lowest-metallicity BCGs, and hence against production of these elements by intermediate-mass (3 M_⊙≤M≤9 M_⊙) stars at very low metallicities, as commonly thought.In higher metallicity BCGs (7.6<12+log O/H<8.2), the Ne/O, Si/O, S/O, Ar/O and Fe/O abundance ratios retain the same constant value they had at lower metallicities. By contrast, there is an increase of the C/O and N/O ratios along with their dispersions at a given O. We interpret this increase as due to the additional contribution of C and primary N production in intermediate-mass stars, on top of that by high-mass stars. BCGs show the same O/Fe overabundance with respect to the Sun (∼0.4 dex) as galactic halo stars, suggesting the same chemical enrichment history.     

Infrared photometry of eight planetary nebulae

We discuss the infrared (IR) (1.25–5 µm) photometry of eight planetary nebulae performed in 1999–2006. For all of the nebulae under study, we have firmly established IR brightness and color variations on time scales shorter than one year and up to 6–8 years. The greatest IR brightness variations were observed in IC 2149, IC 4997, and NGC 7662. Their J magnitudes varied within 0 _. ^m 2–0 _. ^m 25. In the remaining objects, the J magnitude variations did not exceed 0 _. ^m 15. All of the planetary nebulae under study exhibited IR color variations. Based on the IR photometry, we have classified the central regions of the planetary nebula NGC 1514 and of the northern part of NGC 7635 seen through a 12″ aperture as a B(3–7) main-sequence star (NGC 1514) and a ～O9.5 upper-main-sequence star (NGC 7635). The nebulae IC 4997 and NGC 7027 exhibited an excess emission (with respect to the emission from a hot source) at λ > 2.5 µm.     

Dust masses and abundances in planetary nebulae: likely strong elemental depletion in low-abundance sources

An analysis is undertaken of the relation between dust/gas mass ratios and elemental abundances within planetary nebulae (PNe). It is found that M _DUST/ M _GAS is broadly invariant with abundance, and similar to the values observed in asymptotic giant branch (AGB)-type stars. However, it is noted that the masses of dust observed in low-abundance PNe are similar to the masses of heavy elements observed in the gas phase. This is taken to imply that levels of elemental depletion must be particularly severe, and extend to many more species than have been identified so far. In particular, given that levels of C and O depletion are likely to be large, then this probably implies that species such as Fe, S, Si and Mg are depleted as well. There is already evidence for depletion of Fe, Si and Mg in individual PNe. It follows that whilst quoted abundances may accurately reflect gas-phase conditions, they are likely to be at variance with intrinsic abundances in low Z _N nebulae.
Finally, we note that there appears to be a variation in dust/gas mass ratios with galactocentric distance, with gradient similar to that observed for several elemental abundances. This may represent direct evidence for a correlation between dust/gas mass ratios and nebular abundances.     

Neon and argon optical emission lines in ionized gaseous nebulae: implications and applications

In this work, we present a study of the strong optical collisional emission lines of Ne and Ar in an heterogeneous sample of ionized gaseous nebulae for which it is possible to derive directly the electron temperature and hence the chemical abundances of Ne and Ar. We calculate using a grid of photoionization models new ionization correction factors for these two elements and we study the behaviour of Ne/O and Ar/O abundance ratios with metallicity. We find a constant value for Ne/O, while there seems to be some evidence for the existence of negative radial gradients of Ar/O over the discs of some nearby spirals. We study the relation between the intensities of the emission lines of [Ne  iii ] at 3869 Å and [O  iii ] at 4959 and 5007 Å. This relation can be used in empirical calibrations and diagnostic ratios extending their applicability to bluer wavelengths and therefore to samples of objects at higher redshifts. Finally, we propose a new diagnostic using [O  ii ], [Ne  iii ] and Hδ emission lines to derive metallicities for galaxies at high z .     

Self-consistent photoionization models of planetary nebulae luminescence: stellar ionizing continuum,nebular abundances,and evolution of the envelopes

The modern self-consistent photoionization model of planetary nebula luminescence is described. All of the processes which play an important role in the ionization and thermal equilibrium of the nebular gas are taken into consideration. The diffuse ionizing radiation is taken into account completely. The construction of the model is carried out for the radial distribution of gas density in the nebular envelope which is consistent with isophotal map of the nebula. The application of the model is illustrated on the example of the planetary nebulae BD+30°3639 and NGC 7293. It is shown that the continuum of the central star at 912 Å does not correspond to the blackbody spectrum but agrees with the spectrum of corresponding non-LTE model atmosphere. The radial distributions of electron density, electron temperature, and other parameters in the nebular envelopes are found.The evolution of the radial distribution of gas density in the planetary nebulae envelopes is investigated. Approximative analytical expression which describe both such distribution and its change with time is adjusted. It is shown that the nebular envelope is formed as a result of quiet evolution of the slow stellar wind of star-precursor, and the formation of the envelope begins from the decrease of star-precursor's mass loss rate. Obtained radial distributions of gas density in the envelopes of young nebulae rule out the idea that the planetary nebula is formed as a result of a rapid ejection of clear-cut envelope. So, there is no necessity for the superwind which is used for this purpose in theoretical calculations.A new method of the determination of planetary nebulae abundances is proposed. Unobserved ionization stages are taken into account with aid of the correlations between relative abundances of various ions which had been obtained from the grid of the photoionization models of planetary nebulae luminescence. Simple approximative expressions for the determination of He/H, C/H, N/H, O/H, Ne/H, Mg/H, Si/H, S/H, and Ar/H are found. The chemical composition of 130 Galactic planetary nebulae is revised. A comparative analysis of the abundances in the Galactic disk, bulge, and halo nebulae is carried out.     

Radio planetary nebulae in the Magellanic Clouds

We report the extragalactic radio-continuum detection of 15 planetary nebulae (PNe) in the Magellanic Clouds (MCs) from recent Australia Telescope Compact Array+Parkes mosaic surveys. These detections were supplemented by new and high-resolution radio, optical and infrared observations which helped to resolve the true nature of the objects. Four of the PNe are located in the Small Magellanic Cloud (SMC) and 11 are located in the Large Magellanic Cloud (LMC). Based on Galactic PNe the expected radio flux densities at the distance of the LMC/SMC are up to ∼2.5 and ∼2.0 mJy at 1.4 GHz, respectively. We find that one of our new radio PNe in the SMC has a flux density of 5.1 mJy at 1.4 GHz, several times higher than expected. We suggest that the most luminous radio PN in the SMC (N S68) may represent the upper limit to radio-peak luminosity because it is approximately three times more luminous than NGC 7027, the most luminous known Galactic PN. We note that the optical diameters of these 15 Magellanic Clouds (MCs) PNe vary from very small (∼0.08 pc or 0.32 arcsec; SMP L47) to very large (∼1 pc or 4 arcsec; SMP L83). Their flux densities peak at different frequencies, suggesting that they may be in different stages of evolution. We briefly discuss mechanisms that may explain their unusually high radio-continuum flux densities. We argue that these detections may help solve the 'missing mass problem' in PNe whose central stars were originally  1–8 M_⊙  . We explore the possible link between ionized haloes ejected by the central stars in their late evolution and extended radio emission. Because of their higher than expected flux densities, we tentatively call this PNe (sub)sample –'Super PNe'.     

The Gaia Data Release 1 parallaxes and the distance scale of Galactic planetary nebulae

In this paper we gauge the potentiality of Gaia in the distance scale calibration of planetary nebulae (PNe) by assessing the impact of DR1 parallaxes of central stars of Galactic PNe (CSPNe) against known physical relations. For selected PNe targets with state-of-the-art data on angular sizes and fluxes, we derive the distance-dependent parameters of the classical distance scales, i.e., physical radii and ionized masses, from DR1 parallaxes; we propagate the uncertainties in the estimated quantities and evaluate their statistical properties in the presence of large relative parallax errors; we populate the statistical distance scale diagrams with this sample and discuss its significance in light of existing data and current calibrations. We glean from DR1 parallaxes 8 CSPNe with S/N> 1. We show that this set of potential calibrators doubles the number of extant trigonometric parallaxes (from HST and ground-based), and increases by two orders of magnitude the domain of physical parameters probed previously. We then use the combined sample of suitable trigonometric parallaxes to fit the physical-radius-to-surface-brightness relation. This distance scale calibration, although preliminary, appears solid on statistical grounds, and suggestive of new PNe physics. With the tenfold improvement in PNe number statistics and astrometric accuracy expected from future Gaia releases the new distance scale, already very intriguing, will be definitively constrained.     

Integrated fluxes for emission lines in the ultraviolet spectra of several planetary nebulae

The IUE satellite observatory has been used to obtain absolutely-calibrated emission line fluxes for diagnostic lines of multiply-ionized C, N, O, Si, Ne, and Ar which occur in the ultraviolet spectral region of planetary nebulae. These data, when combined with data from the blue, visual, and near infrared, will provide improved estimates of ionic concentrations, plasma temperatures and densities, and elemental abundances.     

Low-ionization pairs of knots in planetary nebulae: physical properties and excitation

We obtained optical long-slit spectra of four planetary nebulae (PNe) with low-ionization pair of knots, namely He 1-1, IC 2149, KjPn 8 and NGC 7662.
These data allow us to derive the physical parameters and excitation of the pairs of knots, and those of higher ionization inner components of the nebulae, separately.
Our results are as follows. (1) The electron temperatures of the knots are within the range 9500–14 500 K, similar to the temperatures of the higher ionization rims/shells. (2) Typical knots' densities are 500–2000 cm⁻³. (3) Empirical densities of the inner rims/shells are higher than those of the pairs of knots, by up to a factor of 10. Theoretical predictions, at variance with the empirical results, suggest that knots should be denser than the inner regions, by at least a factor of 10. (4) Empirical and theoretical density contrasts can be reconciled if we assume that at least 90 per cent of the knots' gas is neutral (likely composed of dust and molecules). (5) By using the new Raga et al. shock modelling and diagnostic diagrams appropriated for spatially resolved PNe, we suggest that high-velocity shocked knots travelling in the photoionized outer regions of PNe can explain the emission of the pairs of knots analysed in this paper.     

Primordial noble gases in “phase Q” in carbonaceous and ordinary chondrites studied by closed‐system stepped etching

Abstract— The HF/HCI‐resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, CO3.4 Lancé, CO3.7 Isna, LL3.4 Chainpur, and H3.7 Dimmitt have been measured by closed‐system stepped etching (CSSE) in order to better characterise the noble gases in “phase Q”, a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for (²⁰Ne/²²Ne)_Q. As already suggested by precise earlier measurements (Schelhaas et al., 1990; Wieler et al., 1991, 1992), (²⁰Ne/²²Ne)_Q is the least uniform isotopic ratio of the Q noble gases. The data cluster ～10.1 for Cold Bokkeveld and Lancé and 10.7 for Chainpur, Grosnaja, and Dimmitt, respectively. No correlation of (²⁰Ne/²²Ne)_Q with the classification or the alteration history of the meteorites has been found. The Ar, Kr, and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar‐Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne‐Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases “Q1” and “Q2” with slightly distinct chemical properties. Ratios (Ar/Xe)_Q and (Kr/Xe)_Q reflect both thermal metamorphism and aqueous alteration. These parent‐body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar)_Q and (Ne/Ar)_Q ratios. This suggests that Q1 is less susceptible to aqueous alteration than Q₂. Both subphases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large, depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q₁ and Q₂ must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q₁ may be related to presolar graphite. Phases Q₁ and Q₂ might be related to the subphases that have been suggested by Gros and Anders (1977). The distribution of the ²⁰Ne/²²Ne ratios cannot be attributed to the carriers Q₁ and Q₂. The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne‐E(L), and the data confirm the suggestion of Huss (1997) that the ²²Ne‐E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.     

Chemical abundances in LMC and SMC planetary nebulae

Abundances of He, N, O, and Ne are calculated for 29 faint planetary nebulae in the LMC and SMC from spectrophotometry obtained by Boroson and Liebert. When the results are combined with abundances from Aller and Czyzak's galactic planetary sample, the following conclusions are drawn: (1) O and Ne in planetaries remains generally unchanged throughout the evolution of the progenitor; (2) O and Ne abundances are indicators of progenitor metallicity; (3) Significant amounts of N are produced during evolution of intermediate mass stars, and (4) H production in intermediate mass stars over time can explain the current interstellar abundance of N in the LMC but not in the SMC.