Статті в журналах: "Nebular abundances"

1

Pollacco, D. L., and S. A. Bell. "Imaging and spectroscopy of ejected common envelopes." Symposium - International Astronomical Union 180 (1997): 271. http://dx.doi.org/10.1017/s007418090013089x.

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Imaging and spectroscopy are presented for four planetary nebulae known to contain close binary central stars resulting from a recent phase of common envelope evolution. These objects are Abell 41, Abell 46, Abell 63 and Abell 65. Determinations of the nebula abundances show that He is significantly enhanced in all of the objects. These results are in agreement with theoretical expectations. Uncertainties in the nebular electron temperature constrain other abundances less well. The line fluxes indicate that N is unexpectedly under-abundant. This effect is probably not real and may be an artifact of electron temperature fluctuations within the nebulae.

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2

Peña, Miriam, Grazyna Stasińska, César Esteban, Lars Koesterke, Selene Medina, and Robin Kingsburgh. "Spectroscopy of planetary nebulae with [WR] nuclei." Symposium - International Astronomical Union 193 (1999): 382–83. http://dx.doi.org/10.1017/s0074180900205846.

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We have started an extensive program of systematic observations of planetary nebulae excited by [WR] nuclei with the aim of understanding the evolutionary status of the central stars. Detailed analysis of the nebular and stellar properties might reveal the presence of abundance variations across the nebulae, and allows to detect possible interactions between the massive stellar wind and the nebula. Such an analysis requires spatially resolved spectra, together with a reliable procedure to derive chemical abundances. This is best achieved by constructing individual photo-ionization models that reproduce the main observed properties. Here we present the spectroscopic analysis made for different knots of PB6, NGC2452, NGC2867, NGC6905 and He2–55. All these nebulae are ionized by [WC 2–3] stars and present very high ionization degrees.

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3

Walton, N. A., M. J. Barlow, D. J. Monk, and R. E. S. Clegg. "Abundances and nebular and central star masses for Magellanic Cloud planetary nebulae." Symposium - International Astronomical Union 148 (1991): 334–36. http://dx.doi.org/10.1017/s0074180900200727.

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We present the results of a spectroscopic study of planetary nebulae (PN) in the Magellanic Clouds. The optical survey of He, N, O, and Ne abundances by Monk et al. (1988) has been updated by higher S/N AAT optical data. In addition, carbon and other elemental abundances have been derived from the IUE spectra of 38 PN. Ionized nebular masses have been derived for 80 PN. The ionised mass versus nebular electron density plot shows that planetary nebulae become optically thin when their electron densities drop below 4500 cm--3. Below this density, the mean nebular hydrogen mass found for non-Type I PN is 0.22±0.08 M⊙. Using Zanstra and energy-balance methods, the mean central star mass found for 14 SMC and LMC PN is 0.59±0.02 M⊙.

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4

Pagomenos, G. J. S., J. Bernard-Salas, and S. R. Pottasch. "Neon, sulphur, and argon abundances of planetary nebulae in the sub-solar metallicity Galactic anti-centre." Astronomy & Astrophysics 615 (July 2018): A29. http://dx.doi.org/10.1051/0004-6361/201730861.

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Context. Spectra of planetary nebulae show numerous fine structure emission lines from ionic species, enabling us to study the overall abundances of the nebular material that is ejected into the interstellar medium. The abundances derived from planetary nebula emission show the presence of a metallicity gradient within the disk of the Milky Way up to Galactocentric distances of ~10 kpc, which are consistent with findings from studies of different types of sources, including H II regions and young B-type stars. The radial dependence of these abundances further from the Galactic centre is in dispute. Aims. We aim to derive the abundances of neon, sulphur and argon from a sample of planetary nebulae towards the Galactic anti-centre, which represent the abundances of the clouds from which they were formed, as they remain unchanged throughout the course of stellar evolution. We then aim to compare these values with similarly analysed data from elsewhere in the Milky Way in order to observe whether the abundance gradient continues in the outskirts of our Galaxy. Methods. We have observed 23 planetary nebulae at Galactocentric distances of 8–21 kpc with Spitzer IRS. The abundances were calculated from infrared emission lines, for which we observed the main ionisation states of neon, sulphur, and argon, which are little affected by extinction and uncertainties in temperature measurements or fluctuations within the planetary nebula. We have complemented these observations with others from optical studies in the literature, in order to reduce or avoid the need for ionisation correction factors in abundance calculations. Results. The overall abundances of our sample of planetary nebulae in the Galactic anti-centre are lower than those in the solar neighbourhood. The abundances of neon, sulphur, and argon from these stars are consistent with a metallicity gradient from the solar neighbourhood up to Galactocentric distances of ~20 kpc, albeit with varying degrees of dispersion within the data.

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5

Flynn, G. J., S. Bajt, S. R. Sutton, M. E. Zolensky, K. L. Thomas, and L. P. Keller. "The Abundance Pattern of Elements Having Low Nebular Condensation Temperatures in Interplanetary Dust Particles: Evidence for a New Chemical Type of Chondritic Material." International Astronomical Union Colloquium 150 (1996): 291–94. http://dx.doi.org/10.1017/s0252921100501717.

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AbstractThe abundances of Ni, Fe, Cr, Mn, P, Cu, K, Na, Ga, Ge, Se, Zn, S, Br, and C were measured in interplanetary dust particles (IDPs) collected from the Earth's stratosphere. All elements with nebular condensation temperatures lower than Mn, except S, were enriched relative to the most volatile-rich type of meteorite while the refractory elements Cr and Ni were present at chondritic abundances. This element abundance pattern is consistent with nebular condensation, suggesting the IDPs condensed at either a different location or time in the evolving solar nebula than do the meteorites. The enrichments of the major elements C, Na, P, and K exclude the possibility that the volatile enrichment in IDPs results from a minor amount of contamination.

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6

Monk, D. J., M. J. Barlow, and R. E. S. Clegg. "Chemical Abundances in Magellanic Cloud Planetary Nebulae." Symposium - International Astronomical Union 131 (1989): 354. http://dx.doi.org/10.1017/s0074180900138732.

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Optical spectroscopic data for 71 Planetary Nebulae (PN) in the Large and Small Magellanic Clouds have been analysed. The line fluxes have been used to determine nebular temperatures, densities, and the abundances of He, N, O, Ne and Ar, relative to H. In our sample there are 12 nebulae with N/O ≥ 0.5, resembling Peimbert's Type I PN; 6 low excitation (LE) objects (1 ≤ I(5007)/I(Hβ) ≤ 4); and 4 very-low-excitation (VLE) nebulae (I(Hβ) > I(5007), similar to the Galactic VLE class. Mean abundances have been calculated for the nebulae not in these special groups.

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7

Zhang, C. Y., and S. Kwok. "Chemical abundances and metallicity of Planetary Nebulae." Symposium - International Astronomical Union 180 (1997): 291. http://dx.doi.org/10.1017/s0074180900131080.

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Confrontations of the dredge-up theory with observed patterns of chemical abundances of planetary nebulae (PNs) have been carried out by many authors (see, e.g., Kaler & Jacoby 1990, 1991; Stasińska & Tylenda 1990). Although these studies suggest that the observational abundance ratios of PNs can qualitatively be explained by the current dredge-up theory, scatters around the theoretical predictions in their diagrams are always large. This has led Ratag (1991) to conclude that there is no correlation at all between the nebular abundances and the core mass of CSPNs (see also Pottasch 1993).

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8

Conlon, E. S., P. L. Dufton, F. P. Keenan, and R. J. H. McCausland. "LSIV −12° 111 – A Newly Emerging Halo Planetary Nebula." Symposium - International Astronomical Union 155 (1993): 356. http://dx.doi.org/10.1017/s0074180900171451.

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We report on multi-wavelength observations of a young halo planetary nebula, LSIV −12° 111. This object was previously classified as an emission-line young B-type star but a model atmosphere abundance analysis of high resolution optical spectra revealed it to be an evolved object, probably in the post-asymptotic giant branch (post-AGB) evolutionary phase. The presence of an infrared excess and low excitation nebular emission lines implies that the central star may have just started to photoionize the remnant (AGB) circumstellar material. Here we discuss the nebular and dust properties of LSIV −12° 111 and re-determine some metal abundances for the central star. These results are used to constrain the evolutionary status of this unique halo planetary nebula.

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9

Skillman, Evan D. "Uncertainties in nebular helium abundances." Proceedings of the International Astronomical Union 5, S268 (November 2009): 113–18. http://dx.doi.org/10.1017/s1743921310003947.

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AbstractEfforts to determine the primordial helium abundance via observations of metal poor HII regions have been limited by significant uncertainties. Because of a degeneracy between the solutions for density and temperature, the precision of the helium abundance determinations is limited. Spectra from the literature are used to show the effects of new atomic data and to demonstrate the challenges of determining precise He abundances. Several suggestions are made for meeting these challenges.

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10

Stasińska, Grażyna. "Nebular abundances in galaxies: Beware of biases." Proceedings of the International Astronomical Union 5, S262 (August 2009): 93–96. http://dx.doi.org/10.1017/s1743921310002590.

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AbstractThe derivation of nebular abundances in galaxies using strong line methods is simple and quick. Various indices have been designed and calibrated for this purpose, and they are widely used. However, abundances derived with such methods may be significantly biased, if the objects under study have different structural properties (hardness of the ionizing radiation field, morphology of the nebulae) than those used to calibrate the methods. Special caution is required when comparing the metallicities of different samples, like, for example, blue compact galaxies and other emission line dwarf galaxies, or samples at different redshifts.

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11

Clegg, R. E. S. "Stellar Mixing from Galactic and Magellanic Cloud Planetary Nebulae Abundances." Symposium - International Astronomical Union 145 (1991): 387–97. http://dx.doi.org/10.1017/s0074180900227526.

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The mixing and nucleosynthetic processes which occur in the main-sequence and red giant stages of evolution and which can affect measured PN abundances are discussed. It is suggested that samples of planetary nebulae contain a sufficient range of progenitor stars' initial metallicities, angular momenta, binarity, etc. so as to explain the large scatter always seen in abundance diagrams for PN samples. CNO abundances in the Galactic disk and in the Magellanic Clouds are reviewed. New results for nebular abundances and central star properties in the Clouds are given. The current red giant population in the Clouds mix out more 12C per star than their Galactic disk counterparts.

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12

Escalante, V., and J. A. Toalá. "A New Model of NGC 6210 to Solve its Abundance Discrepancy Problem." Proceedings of the International Astronomical Union 12, S323 (October 2016): 337–38. http://dx.doi.org/10.1017/s1743921317002113.

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AbstractWe present a model that solves the abundance discrepancy problem for NGC 6210. The model proposes a high abundance of CNONe elements that lowers the temperature of the central parts of the nebula. The colder gas model reproduces the observed intensity of the strong [N ii] and [O iii] emission lines, and increases the predicted weak recombination lines towards their observed values. We examine how the usual nebular diagnostic line ratios depend on model abundances.

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13

Dopita, M. A. "Planetary nebulae in the Magellanic Clouds." Symposium - International Astronomical Union 148 (1991): 299–306. http://dx.doi.org/10.1017/s0074180900200624.

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We present a simple two-wind model for the evolution of the Magellanic Cloud planetary nebulae (PN) which reproduces the observed density / radius / ionised mass relationships, and serves to define the geometrical relationship between the ionised nebula and the star. From self-consistent photoionisation modelling of 78 Magellanic Cloud PN, we have constructed the H-R Diagram for the central stars, and have derived both the chemical abundances and the nebular parameters. We find that the central stars have masses generally between 0.55 and 0.7 M⊙. Type I PN have more massive precursors, and show clear evidence for the Third dredge-up episode and for the dredge-up of ON processed material. The expansion velocity of the nebula is closely correlated with the position of the central star on the H-R Diagram, proving that the nebula undergoes continuous acceleration. Excluding Type I PN, the mean abundances derived for the LMC and the SMC agree with those derived from H II regions and evolved, radiative SNR.

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14

García-Hernández, D. A., P. Ventura, G. Delgado-Inglada, F. Dell'Agli, M. Di Criscienzo, and A. Yagüe. "Understanding Galactic planetary nebulae with precise/reliable nebular abundances." Proceedings of the International Astronomical Union 12, S323 (October 2016): 95–98. http://dx.doi.org/10.1017/s174392131700059x.

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AbstractWe compare recent precise/reliable nebular abundances - as derived from high-quality optical spectra and the most recent ICFs - in a sample of Galactic planetary nebulae (PNe) with nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch (AGB) ATON models in the metallicity range Z⊙/4 < Z < 2Z⊙. According to the infrared dust features, the sample is divided among carbon-, oxygen-, and double-dust chemistry (CC, OC, and DC, respectively), providing an independent proxy for the nature of the PNe progenitors. Our AGB models, with diffusive overshooting from all the convective borders, nicely reproduce the O overabundances observed in CC PNe, indicating that they evolve from low-Z low-mass (∼1 −3 M⊙) AGB stars. This indicates that O is not always a good indicator of the original ISM metallicity and that the O production by low-mass stars should be considered in galactic-evolution models. The lowest metallicity OC PNe evolve from low-mass (∼1 M⊙) O-rich AGBs, while the higher metallicity ones (all with uncertain dust classifications) display a chemical pattern similar to the DC PNe. In agreement with the recent literature, the DC PNe mostly descend from high-mass (M > 3.5 M⊙) solar/supersolar metallicity AGBs that experience hot bottom burning (HBB), but other formation channels in low-mass AGBs like extra mixing, stellar rotation, binary interaction, or He pre-enrichment cannot be disregarded until more accurate C/O ratios can be obtained. Two DC PNe show the imprint of advanced CNO processing and deep second dredge-up, suggesting progenitors masses close to the limit to evolve as core collapse supernovae (above 6 M⊙). Their actual C/O ratios, if confirmed, indicate contamination from the third dredge-up, rejecting the hypothesis that the chemical composition of such high-metallicity massive AGBs is modified exclusively by HBB.

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15

Ruiz-Escobedo, Francisco, and Miriam Peña. "Abundance discrepancy factors in high-density planetary nebulae." Monthly Notices of the Royal Astronomical Society 510, no. 4 (January 7, 2022): 5984–6000. http://dx.doi.org/10.1093/mnras/stac003.

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ABSTRACT From high-resolution spectra, chemical abundances from collisionally excited lines (CELs) and optical recombination lines (ORLs) have been determined for planetary nebulae (PNe) Cn 3-1, Vy 2-2, Hu 2-1, Vy 1-2 and IC 4997, which are young and dense objects. The main aim of this work is to derive their O+2/H+ abundance discrepancy factors (ADFs) between CELs and ORLs. He, O, N, Ne, Ar, S, and Cl abundances were obtained and our values are in agreement with those previously reported. We found that Cn 3-1, Hu 2-1, and Vy 1-2 have O abundances typical of disc PNe, while Vy 2-2 and IC 4997 are low O abundance objects ($\rm {12+log(O/H) \sim 8.2}$), which can be attributed to possible O depletion into dust grains. ADFs(O+2) of $4.30^{+1.00}_{-1.16}$, 1.85 ± 1.05, $5.34^{+1.27}_{-1.08}$ and $4.87^{+4.34}_{-2.71}$ were determined for Vy 2-2, Hu 2-1, Vy 1-2, and IC 4997, respectively. The kinematics of CELs and ORLs was analysed for each case to study the possibility that different coexisting plasmas in the nebula emit them. Expansion velocities of [O iii] and O ii are equal within uncertainties in three PNe, providing no evidence for these lines being emitted in different zones. Exceptions are Hu 2-1 and Vy 2-2, where ORLs might be emitted in different zones than CELs. For Vy 2-2 and IC 4997, we found that nebular and auroral lines of the same ion (S+, N+, Ar+2, Ar+3, O+2) might present different expansion velocities. Auroral lines show lower $\rm {V_{exp}}$, which might indicate that they are emitted in a denser and inner zone than the nebular ones.

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16

Tylenda, Romuald. "Photoionization Models of Chemically Inhomogeneous Planetary Nebulae." Symposium - International Astronomical Union 209 (2003): 389–90. http://dx.doi.org/10.1017/s0074180900209145.

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We have constructed photoionization models of NGC 6153, M 2–36, and M1–42. These planetary nebulae show large differences, both, in the CNO and Ne abundances as derived from recombination lines and collisionally excited lines, as well as, in the electron temperature determined from Balmer jump and [OIII] lines. The model nebulae have low mass (about 1% of the total nebular mass) inclusions where the CNO and Ne abundances are enhanced by a factor of 200 or so.

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17

Henry, Richard B. C., Angela Speck, Amanda I. Karakas, and Gary J. Ferland. "The curious conundrum regarding sulfur and oxygen abundances in planetary nebulae." Proceedings of the International Astronomical Union 7, S283 (July 2011): 384–85. http://dx.doi.org/10.1017/s1743921312011544.

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AbstractWe carefully consider numerous explanations for the sulfur abundance anomaly in planetary nebulae. No one rationale appears to be satisfactory, and we suggest that the ultimate explanation is likely to be a heretofore unidentified feature of the nebular gas which significantly impacts the sulfur ionization correction factor.

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18

Sterling, N. C., M. C. Witthoeft, D. A. Esteves, R. C. Bilodeau, A. L. D. Kilcoyne, E. C. Red, R. A. Phaneuf, G. Alna’Washi, and A. Aguilar. "New atomic data for trans-iron elements and their application to abundance determinations in planetary nebulae1This review is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas." Canadian Journal of Physics 89, no. 4 (April 2011): 379–85. http://dx.doi.org/10.1139/p10-105.

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Investigations of neutron(n)-capture element nucleosynthesis and chemical evolution have largely been based on stellar spectroscopy. However, the recent detection of these elements in several planetary nebulae (PNe) indicates that nebular spectroscopy is a promising new tool for such studies. In PNe, n-capture element abundance determinations reveal details of s-process nucleosynthesis and convective mixing in evolved low-mass stars, as well as the chemical evolution of elements that cannot be detected in stellar spectra. Only one or two ions of a given trans-iron element can typically be detected in individual nebulae. Elemental abundance determinations thus require corrections for the abundances of unobserved ions. Such corrections rely on the availability of atomic data for processes that control the ionization equilibrium of nebulae (e.g., photoionization cross sections and rate coefficients for various recombination processes). Until recently, these data were unknown for virtually all n-capture element ions. For the first six ions of Se, Kr, and Xe — the three most widely detected n-capture elements in PNe — we are calculating photoionization cross sections and radiative and dielectronic recombination rate coefficients using the multi-configuration Breit–Pauli atomic structure code AUTOSTRUCTURE. Charge transfer rate coefficients are being determined with a multichannel Landau–Zener code. To calibrate these calculations, we have measured absolute photoionization cross sections of Se and Xe ions at the Advanced Light Source synchrotron radiation facility. These atomic data can be incorporated into photoionization codes, which we will use to derive ionization corrections (hence abundances) for Se, Kr, and Xe in ionized nebulae. Using Monte Carlo simulations, we will investigate the effects of atomic data uncertainties on the derived abundances, illuminating the systems and atomic processes that require further analysis. These results are critical for honing nebular spectroscopy into a more effective tool for investigating the production and chemical evolution of trans-iron elements in the Universe.

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19

Walton, N. A., J. R. Walsh, G. Jacoby, and R. F. Peletier. "The chemical abundances of Planetary Nebulae in Centaurus-A (NGC 5128)." Symposium - International Astronomical Union 180 (1997): 478. http://dx.doi.org/10.1017/s0074180900131808.

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Abundances in early-type galaxies are measured from the analysis of stellar spectra (e.g. colour indices, Peletier et al, 1990). The presence of many planetary nebulae (PN) in early-type galaxies provides an independent measure of abundances for the old stellar population and allows the spread in abundances to be sampled at a range of galacto-centric distances. PN are feasible for this project since the nebular O, Ne and S abundances in most PN reflect that of the progenitor star.

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20

Golovaty, V. V., and Yu F. Malkov. "Abundances for a large sample of galactic Planetary Nebulae." Symposium - International Astronomical Union 180 (1997): 408. http://dx.doi.org/10.1017/s0074180900131602.

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We present a database on the chemical composition of 200 planetary nebulae (PNe) in our Galaxy. Abundances of He, C, N, O, Ne, Mg, Si, S, and Ar are found for 175, 64, 190, 200, 170, 13, 40, 173, and 187 PNe respectively. The abundances for all PNe are obtained with the same atomic data and by the same method of abundance determination, so the database is highly homogeneous. The method of the determination of nebular abundances based on a photoionization model grid is described by Golovaty et al. (1993). Observational data have been compiled from 105 papers published in 1976–1994. For most of PNe in our sample, the distances and central star masses are determined as well (Malkov, this volume).

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21

Liu, Xiaowei. "Atomic processes in planetary nebulae." Proceedings of the International Astronomical Union 7, S283 (July 2011): 131–38. http://dx.doi.org/10.1017/s1743921312010836.

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AbstractProgress in the study of the atomic processes in planetary nebulae (PNe) is reviewed, focusing on the literature published since the last IAU symposium on PNe five years ago. High quality photoionization cross sections and recombination coefficients are now available for the first six ions of the trans-iron elements selenium and krypton, enabling robust modeling of their ionization structure and consequently converting the measured ionic abundances to elemental abundances. Major progress has been achieved in utilizing the recombination spectra of helium and heavy element ions to probe the nebular physical conditions. New ab initio, density-dependent effective recombination coefficients have been calculated for the recombination spectra of O ii and N ii, down to very low temperatures (~ 100–300 K). Plasma diagnostics based entirely on those heavy element recombination lines are developed and applied to the observations. It is shown that these heavy element recombination lines originate predominately from cold plasmas of temperatures ~ 1,000 K, in agreement with the predictions of the bi-abundance model that has been proposed to explain the dichotomy of nebular plasma diagnostics and abundance determinations using collisional excited lines (CELs) on the one hand and optical recombination lines (ORLs) on the other.

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22

Clegg, R. E. S., and J. P. Harrington. "Helium Abundances in Gaseous Nebulae." Symposium - International Astronomical Union 131 (1989): 211. http://dx.doi.org/10.1017/s0074180900138227.

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New collision strengths, from a 19-state quantum calculation for He I, are used to derive revised He/H ratios in planetary nebulae (PN). Empirical formulae are given, for the correction of He I recombination line fluxes for collisional effects, and for the calculation of the population of metastable helium (He I 23S) in gaseous nebulae. The revised He abundances for PN, for four samples of published line fluxes, show a mean ratio He/H = 0.100 ±0.007 if nebulae with neutral He and Type I PN are excluded. The mean reduction due to collisional effects is only 10% for Galactic PN. It is shown that the hypothesis, that He/H should be independent of nebular temperature and density, is better satisfied when collisional effects are allowed for. The new He abundances indicate that there is very little He enrichment in Galactic PN of Types II, III, and IV, and that the enhancement of Type I PN in He over H II regions is reduced from earlier values by one third.

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23

Schmid, H. M., and H. Nussbaumer. "Elemental Abundances in Symbiotic Stars." Symposium - International Astronomical Union 155 (1993): 402. http://dx.doi.org/10.1017/s0074180900171918.

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Symbiotic objects are related to planetary nebulae in that they represent late stages of stellar evolution. They are interacting binary systems where a hot companion star ionizes the stellar wind of a red giant. This configuration offers the unique possibility for deriving elemental abundances for cool giants from a nebular spectrum with the diagnostic tools employed for HII regions. The analysis can be applied to different types of symbiotic systems having a G, K or M giant, a Mira variable or a carbon star as cool component. The great advantage of this technique is, that it does not depend on stellar parameters or molecular data, and that it can therefore be used as a test or an alternative for the traditional photospheric abundance determinations.

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24

Ratag, Mezak A. "The Sulphur Abundance in Planetary Nebulae." Symposium - International Astronomical Union 209 (2003): 385–86. http://dx.doi.org/10.1017/s0074180900209121.

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Ratag et al (1997) determined the chemical abundances of He, O, N, Ne, S, Ar, and Cl in ~110 planetary nebulae which are likely to be in the Galactic Bulge. The abundances are derived by employing theoretical nebular models as interpolation devices in establishing the ICFs. The overall agreement between the abundances obtained by employing the model-ICFs and those derived from the theoretical models is reasonably good. Based on this, it is of interest to study the reliability of various ICFs as well as to derive some alternative ICFs. The focus of the present study is sulphur.

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25

Gallardo Cava, Iván, Valentín Bujarrabal, Javier Alcolea, Miguel Gómez-Garrido, Arancha Castro-Carrizo, Hans Van Winckel, and Miguel Santander-García. "Rotating and Expanding Gas in Binary Post-AGB Stars." Astronomy 1, no. 2 (August 2, 2022): 84–92. http://dx.doi.org/10.3390/astronomy1020008.

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There is a class of binary post-AGB stars (binary system including a post-AGB star) that are surrounded by Keplerian disks and outflows resulting from gas escaping from the disk. To date, there are seven sources that have been studied in detail through interferometric millimeter-wave maps of CO lines (ALMA/NOEMA). For the cases of the Red Rectangle, IW Carinae, IRAS 08544-4431, and AC Herculis, it is found that around ≥85% of the total nebular mass is located in the disk with Keplerian dynamics. The remainder of the nebular mass is located in an expanding component. This outflow is probably a disk wind consisting of material escaping from the rotating disk. These sources are the disk-dominated nebulae. On the contrary, our maps and modeling of 89 Herculis, IRAS 19125+0343, and R Scuti, which allowed us to study their morphology, kinematics, and mass distribution, suggest that, in these sources, the outflow clearly is the dominant component of the nebula (∼75% of the total nebular mass), resulting in a new subclass of nebulae around binary post-AGB stars: the outflow-dominated sources.Besides CO, the chemistry of this type of source has been practically unknown thus far. We also present a very deep single-dish radio molecular survey in the 1.3, 2, 3, 7, and 13 mm bands (∼600 h of telescope time). Our results and detections allow us to classify our sources as O- or /C-rich. We also conclude that the calculated abundances of the detected molecular species other than CO are particularly low, compared with AGB stars. This fact is very significant in those sources where the rotating disk is the dominant component of the nebula.

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26

Luna, G. J. M., and R. D. D. Costa. "Nebular abundances of southern symbiotic stars." Astronomy & Astrophysics 435, no. 3 (May 13, 2005): 1087–97. http://dx.doi.org/10.1051/0004-6361:20041994.

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27

Moustakas, John, and Robert C. Kennicutt, Jr. "Integrated Nebular Abundances of Disk Galaxies." Astrophysical Journal 651, no. 1 (November 2006): 155–66. http://dx.doi.org/10.1086/507570.

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28

Sterling, Nicholas C., Michael C. Witthoeft, David A. Esteves, Phillip C. Stancil, A. L. David Kilcoyne, Rene C. Bilodeau, and Alejandro Aguilar. "Advances in atomic data for neutron-capture elements." Proceedings of the International Astronomical Union 7, S283 (July 2011): 504–5. http://dx.doi.org/10.1017/s1743921312012148.

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AbstractNeutron(n)-capture elements (atomic number Z > 30), which can be produced in planetary nebula (PN) progenitor stars via s-process nucleosynthesis, have been detected in nearly 100 PNe. This demonstrates that nebular spectroscopy is a potentially powerful tool for studying the production and chemical evolution of trans-iron elements. However, significant challenges must be addressed before this goal can be achieved. One of the most substantial hurdles is the lack of atomic data for n-capture elements, particularly that needed to solve for their ionization equilibrium (and hence to convert ionic abundances to elemental abundances). To address this need, we have computed photoionization cross sections and radiative and dielectronic recombination rate coefficients for the first six ions of Se and Kr. The calculations were benchmarked against experimental photoionization cross section measurements. In addition, we computed charge transfer (CT) rate coefficients for ions of six n-capture elements. These efforts will enable the accurate determination of nebular Se and Kr abundances, allowing robust investigations of s-process enrichments in PNe.

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29

Sterling, N. C. "Neutron-Capture Element Abundances in Planetary Nebulae." Galaxies 8, no. 2 (June 17, 2020): 50. http://dx.doi.org/10.3390/galaxies8020050.

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Nebular spectroscopy is a valuable tool for assessing the production of heavy elements by slow neutron(n)-capture nucleosynthesis (the s-process). Several transitions of n-capture elements have been identified in planetary nebulae (PNe) in the last few years, with the aid of sensitive, high-resolution, near-infrared spectrometers. Combined with optical spectroscopy, the newly discovered near-infrared lines enable more accurate abundance determinations than previously possible, and provide access to elements that had not previously been studied in PNe or their progenitors. Neutron-capture elements have also been detected in PNe in the Sagittarius Dwarf galaxy and in the Magellanic Clouds. In this brief review, I discuss developments in observational studies of s-process enrichments in PNe, with an emphasis on the last five years, and note some open questions and preliminary trends.

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30

Volk, Kevin, Harriet Dinerstein, and Chris Sneden. "Ca and dust in Planetary Nebulae." Symposium - International Astronomical Union 180 (1997): 284. http://dx.doi.org/10.1017/s0074180900131018.

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Under nebular conditions it is expected that the [CaII] lines at 7291.470 and 7323.880 Å should be among the strongest emission lines in the red part of the optical spectrum unless the nebula is matter bounded. The lines are observed in novae, supernovae and some symbiotic systems but the only observation of these lines in planetary nebulae (PN) is for AFGL 618 where the lines are thought to be shock-excited. While higher ionization states of Ca do produce some lines observed in a few high-excitation PN, from which gas-phase Ca abundances averaging to about 5% of solar are found, the CaII lines are not observed even in PN with massive neutral envelopes such as NGC 7027. If the Ca is depleted onto dust grains it would explain the absence of the CaII lines. However it is thought that the dust is destroyed with time in the ionized region. Any observation of the CaII lines would produce better abundance estimates and would test the extent of dust destruction that is taking place in the outer parts of the PN.

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31

Bresolin, Fabio. "Stellar vs. Hii region chemical abundances in nearby galaxies." Proceedings of the International Astronomical Union 5, S265 (August 2009): 233–36. http://dx.doi.org/10.1017/s1743921310000621.

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AbstractWe have obtained new spectrophotometric data for 28 Hii regions in the spiral galaxy NGC 300, a member of the nearby Sculptor Group. The detection of several auroral lines has allowed us to measure electron temperatures and direct chemical abundances for the whole sample. We determine for the first time in this galaxy a radial gas-phase oxygen abundance gradient based solely on auroral lines. The gradient corresponds to −0.077±0.006 dex kpc−1, which agrees very well with the galactocentric trend in metallicity obtained for 29 B and A supergiants in the same galaxy. The intercept of the regression for the nebular data virtually coincides with the intercept obtained from the stellar data. This result provides increased confidence on the direct method to determine extragalactic nebular abundances.

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32

Rodríguez, Mónica. "The impact of spectra quality on nebular abundances." Monthly Notices of the Royal Astronomical Society 495, no. 1 (May 15, 2020): 1016–34. http://dx.doi.org/10.1093/mnras/staa1286.

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ABSTRACT I explore the effects of observational errors on nebular chemical abundances using a sample of 179 optical spectra of 42 planetary nebulae (PNe) observed by different authors. The spectra are analysed in a homogeneous way to derive physical conditions and ionic and total abundances. The effects of recombination on the [O ii] and [N ii] emission lines are estimated by including the effective recombination coefficients in the statistical equilibrium equations that are solved for O+ and N+. The results are shown to be significantly different than those derived using previous approaches. The O+ abundances derived with the blue and red lines of [O ii] differ by up to a factor of 6, indicating that the relative intensities of lines widely separated in wavelength can be highly uncertain. In fact, the He ii lines in the range 4000–6800 Å imply that most of the spectra are bluer than expected. Scores are assigned to the spectra using different criteria and the spectrum with the highest score for each PN is taken as the reference spectrum. The differences between the abundances derived with the reference spectrum and those derived with the other spectra available for each object are used to estimate the 1σ observational uncertainties in the final abundances: 0.11 dex for O/H and Ar/H, 0.14 dex for N/H, Ne/H, and Cl/H, and 0.16 dex for S/H.

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33

Krawchuk, Curtis A. P., Marshall L. McCall, Michael Komljenovic, Robin Kingsburgh, Michael Richer, and Christopher Stevenson. "SNAP: Spreadsheet nebular analysis package." Symposium - International Astronomical Union 180 (1997): 116. http://dx.doi.org/10.1017/s0074180900130025.

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A flexible and extensible software package for analyzing two-dimensional and multi-object spectra of nebulae has been implemented within Microsoft Excel (version 5). From lists of calibrated fluxes (and errors) for lines in a series of spectra, the program first identifies transitions by referring to wavelengths generated from atomic data. Colour excesses can be computed from a reddening law and ratio of total to selective extinction of the user's choice. Line fluxes can be corrected for stellar absorption and reddening and reported in a format suitable for publication. Temperatures, densities, ionic abundances, ionization correction factors, and total abundances can be computed. (The interface for the temperture/density calculation is shown below.) Emission coefficients for forbidden transitions are calculated using an adaptation of the FIVEL five-level atom routine (DeRobertis, 1987). As well, emission coefficients are supplied for an extensive set of recombination lines. The user has complete control over which spectral lines are used in an analysis – there are no pre-ordained methods. Abundance analyses can be performed using the physical conditions either measured or specified for each spectrum. Uncertainties are propagated throughout. The atomic data used in all of the calculations are easily updated or augmented by the user. Since the software is embedded in Microsoft Excel, graphical representations of the data are easily created, and extended analyses using the full functionality of the spreadsheet are easily implemented.

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34

Kholtygin, A. F. "Density and temperature inhomogeneities in Planetary Nebulae." Symposium - International Astronomical Union 180 (1997): 247. http://dx.doi.org/10.1017/s0074180900130669.

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The carbon, nitrogen and oxygen abundances in the Planetary Nebulae (PN) derived from the optical recombination lines are usually much larger than those determined from collisional excited UV, IR and optical lines. This discordance is the bright evidence for PN to be strongly inhomogeneous. Starting with consideration by Peimbert (1967) we have been working out the code for calculation the nebular line intensities taking into account both temperature and density fluctuations.

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35

Aller, L. H., and C. D. Keyes. "Some Statistics of Nebular Chemical Compositions." Symposium - International Astronomical Union 131 (1989): 219. http://dx.doi.org/10.1017/s0074180900138318.

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Data from a survey of 51 planetary nebulae (PN) observed with the image tube scanner on Shane Telescope at Lick Observatory are combined with those for a comparable number of objects previously reported. For nearly all of the PN included in the later program, it was possible to obtain adequately accurate plasma diagnostics and line intensities to derive ionic concentrations for He, N, O, Ne, S, Cl, and Ar. To get ionization correction factors we calculated theoretical nebular models to fit the excitation level and the intensities of individual important lines. Final model parameters include the stellar radius, emergent flux, Fv(*), from Husfeld et al. (1984, Astron. Astrophys., 134, 139), nebular size, the optical depth at the hydrogenic Lyman limit, and chemical abundances. Many PN do not appear to be optically very thick in the Lyman continuum.

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36

Patrick, Lee R., Chris J. Evans, Ben Davies, Rolf-Peter Kudritzki, Maria Bergemann, and Annette N. M. Ferguson. "Red Supergiants as Chemical Abundance Probes: The Local Group dwarf NGC6822." Proceedings of the International Astronomical Union 14, S344 (August 2018): 213–16. http://dx.doi.org/10.1017/s174392131800649x.

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AbstractRed Supergiant Stars (RSGs) are important probes of stellar and chemical evolution in star-forming environments. They represent the brightest near-IR stellar components of external galaxies and probe the most recent stellar population to provide robust, independent abundance estimates. The Local Group dwarf irregular galaxy, NGC6822, is a reasonably isolated galaxy with an interesting structure and turbulent history. Using RSGs as chemical abundance probes, we estimate metallicities in the central region of NGC6822, finding a suggestion of a metallicity gradient (in broad agreement with nebular tracers), however, this requires further study for confirmation. With intermediate resolution Multi-object spectroscopy (from e.g. KMOS, EMIR, MOSFIRE) combined with state-of-the-art stellar model atmospheres, we demonstrate how RSGs can be used to estimate stellar abundances in external galaxies. In this context, we compare stellar and nebular abundance tracers in NGC 6822 and by combining stellar and nebular tracers we estimate an abundance gradient of −0.18 ± 0.05 dex/kpc.

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37

Liu, X. W. "Probing the Dark Secrets of PNe with ORLs." Symposium - International Astronomical Union 209 (2003): 339–46. http://dx.doi.org/10.1017/s0074180900208978.

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There are two long-standing problems in nebular astrophysics: a) The dichotomy of abundance determinations whereby heavy element abundances relative to hydrogen from collisionally excited lines (CELs) are systematically lower than those from (much fainter) optical recombination lines (ORLs), a discrepancy that can be traced back to Wyse (1942) and Aller & Menzel (1945) who pioneered the ORL method; and b) The dichotomy of temperature determinations whereby Te derived from the collisionally excited [O III] forbidden line ratio is systematically higher than that derived from Balmer jump of the H I recombination spectrum, a discrepancy first discovered by Peimbert (1971) and attributed to temperature fluctuations in the nebula (Peimbert 1967). Thanks to the rapid progress in detector technology and recombination theory for multi-electron systems, significant progress has been made in recent years in our understanding of these two fundamental problems, which could potentially affect the derivation of abundances for a wide range of photoionized nebulae, both galactic and extragalactic. Both types of dichotomy are found to be real and are most likely caused by astrophysical effects rather than uncertainties in observations or in the basic atomic physics. The two problems are shown to be related and can be explained by assuming that PNe contain a small mass of extremely cold (Te ~ 103 K) inclusions, highly enriched in helium and heavy elements, embedded in diffuse material of “normal” abundances (~ solar) and temperature (Te ~ 104 K). The existence and nature of such H-deficient inclusions in PNe remains a mystery. A recent review on this subject is given by Liu (2002).

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38

Lee, Henry, E. K. Grebel, and P. W. Hodge. "Nebular abundances of nearby southern dwarf galaxies." Astronomy & Astrophysics 401, no. 1 (March 17, 2003): 141–59. http://dx.doi.org/10.1051/0004-6361:20030101.

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39

Barlow, M. J., X. W. Liu, D. Péquignot, P. J. Storey, Y. G. Tsamis, and C. Morisset. "Recombination-line Abundances for the Third-Row Element, Magnesium." Symposium - International Astronomical Union 209 (2003): 373–74. http://dx.doi.org/10.1017/s0074180900209054.

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We have obtained optical recombination-line abundances for the third-row element magnesium in ten planetary nebulae. The nebulae in our sample include four (NGC 7009, NGC 6153, M 2–36 and M 1–42) for which we have previously found very large enhancements, relative to solar, in the recombination line abundances of the second-row elements carbon, nitrogen, oxygen and neon (Liu et al. 1995, Liu et al. 2000, Liu et al. 2001). Nebular temperature fluctuations appear unable to account for these effects. However, models that invoke high-density clumps, particularly clumps which are hydrogen-deficient, appear more viable as an explanation for the high recombination line abundances that are observed (see Liu et al. 2000 for more details). While it may be possible to appeal to astrophysical nucleosynthetic processes to enhance the CNONe second-row elements in AGB stars, such effects are not expected to modify the abundances of third-row elements such as magnesium. We have therefore measured and dereddened the intensities of the 4481 Å 4f-3d line of Mg II, relative to Hβ, in order to investigate whether magnesium recombination line abundances are enhanced or not.

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40

Bergerud, Brandon M., Steven R. Spangler, and Kara M. Beauchamp. "Realistic models for filling and abundance discrepancy factors in photoionized nebulae." Monthly Notices of the Royal Astronomical Society 492, no. 1 (December 16, 2019): 1142–53. http://dx.doi.org/10.1093/mnras/stz3515.

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ABSTRACT When comparing nebular electron densities derived from collisionally excited lines (CELs) to those estimated using the emission measure, significant discrepancies are common. The standard solution is to view nebulae as aggregates of dense regions of constant density in an otherwise empty void. This porosity is parametrized by a filling factor f < 1. Similarly, abundance and temperature discrepancies between optical recombination lines (ORLs) and CELs are often explained by invoking a dual delta distribution of a dense, cool, metal-rich component immersed in a diffuse, warm, metal-poor plasma. In this paper, we examine the possibility that the observational diagnostics that lead to such discrepancies can be produced by a realistic distribution of density and temperature fluctuations, such as might arise in plasma turbulence. We produce simulated nebulae with density and temperature fluctuations described by various probability distribution functions (pdfs). Standard astronomical diagnostics are applied to these simulated observations to derive estimates of nebular densities, temperatures, and abundances. Our results show that for plausible density pdfs, the simulated observations lead to filling factors in the observed range. None of our simulations satisfactorily reproduce the abundance discrepancy factors (ADFs) in planetary nebulae, although there is possible consistency with H ii regions. Compared to the case of density-only and temperature-only fluctuations, a positive correlation between density and temperature reduces the filling factor and ADF (from optical CELs), whereas a negative correlation increases both, eventually causing the filling factor to exceed unity. This result suggests that real observations can provide constraints on the thermodynamics of small-scale fluctuations.

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41

Arellano-Córdova, Karla Z., Danielle A. Berg, John Chisholm, Pablo Arrabal Haro, Mark Dickinson, Steven L. Finkelstein, Floriane Leclercq, et al. "A First Look at the Abundance Pattern—O/H, C/O, and Ne/O—in z > 7 Galaxies with JWST/NIRSpec." Astrophysical Journal Letters 940, no. 1 (November 1, 2022): L23. http://dx.doi.org/10.3847/2041-8213/ac9ab2.

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Abstract We analyze the rest-frame near-UV and optical nebular spectra of three z > 7 galaxies from the Early Release Observations taken with the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST). These three high-z galaxies show the detection of several strong emission nebular lines, including the temperature-sensitive [O iii] λ4363 line, allowing us to directly determine the nebular conditions and abundances for O/H, C/O, and Ne/O. We derive O/H abundances and ionization parameters that are generally consistent with other recent analyses. We analyze the mass–metallicity relationship (i.e., slope) and its redshift evolution by comparing between the three z > 7 galaxies and local star-forming galaxies. We also detect the C iii] λλ1907, 1909 emission in a z > 8 galaxy from which we determine the most distant C/O abundance to date. This valuable detection of log(C/O) = −0.83 ± 0.38 provides the first test of C/O redshift evolution out to high redshift. For neon, we use the high-ionization [Ne iii] λ3869 line to measure the first Ne/O abundances at z > 7, finding no evolution in this α-element ratio. We explore the tentative detection of [Fe ii] and [Fe iii] lines in a z > 8 galaxy, which would indicate a rapid buildup of metals. Importantly, we demonstrate that properly flux-calibrated and higher-S/N spectra are crucial to robustly determine the abundance pattern in z > 7 galaxies with NIRSpec/JWST.

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42

Richer, Michael G. "Planetary nebula populations and kinematics." Proceedings of the International Astronomical Union 7, S283 (July 2011): 243–50. http://dx.doi.org/10.1017/s1743921312011039.

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AbstractThe brightest planetary nebulae achieve similar maximum luminosities, have similar ratios of chemcial abundances, and apparently share similar kinematics in all galaxies. These similarities, however, are not necessarily expected theoretically and appear to hide important evolutionary differences. As predicted theoretically, metallicity appears to affect nebular kinematics, if subtly, and there is a clear variation with evolutionary stage. To the extent that it can be investigated, the internal kinematics for galactic and extragalactic planetary nebulae are similar. The extragalactic planetary nebulae for which kinematic data exist, though, probably pertain to a small range of progenitor masses, so there may still be much left to learn, particularly concerning the kinematics of planetary nebulae that descend from the more massive progenitors.

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43

Gallardo Cava, I., V. Bujarrabal, J. Alcolea, M. Gómez-Garrido, and M. Santander-García. "Chemistry of nebulae around binary post-AGB stars: A molecular survey of mm-wave lines,." Astronomy & Astrophysics 659 (March 2022): A134. http://dx.doi.org/10.1051/0004-6361/202142339.

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Context. There is a class of binary post-asymptotic giant branch (post-AGB) stars that exhibit remarkable near-infrared excess. Such stars are surrounded by Keplerian or quasi-Keplerian disks, as well as extended outflows composed of gas escaping from the disk. This class can be subdivided into disk- and outflow-dominated sources, depending on whether it is the disk or the outflow that represents most of the nebular mass, respectively. The chemistry of this type of source has been practically unknown thus far. Aims. Our objective is to study the molecular content of nebulae around binary post-AGB stars that show disks with Keplerian dynamics, including molecular line intensities, chemistry, and abundances. Methods. We focused our observations on the 1.3, 2, 3 mm bands of the 30mIRAM telescope and on the 7 and 13 mm bands of the 40 m Yebes telescope. Our observations add up ~600 h of telescope time. We investigated the integrated intensities of pairs of molecular transitions for CO, other molecular species, and IRAS fluxes at 12, 25, and 60 μm. Additionally, we studied isotopic ratios, in particular 17O/18O, to analyze the initial stellar mass, as well as 12CO/13CO, to study the line and abundance ratios. Results. We present the first single-dish molecular survey of mm-wave lines in nebulae around binary post-AGB stars. We conclude that the molecular content is relatively low in nebulae around binary post-AGB stars, as their molecular lines and abundances are especially weaker compared with AGB stars. This fact is very significant in those sources where the Keplerian disk is the dominant component of the nebula. The study of their chemistry allows us to classify nebulae around AC Her, the Red Rectangle, AI CMi, R Sct, and IRAS 20056+1834 as O-rich, while that of 89 Her is probably C-rich. The calculated abundances of the detected species other than CO are particularly low compared with AGB stars. The initial stellar mass derived from the 17O/18O ratio for the Red Rectangle and 89 Her is compatible with the central total stellar mass derived from previous mm-wave interferometric maps. The very low 12CO/13CO ratios found in binary post-AGB stars reveal a high 13CO abundance compared to AGB and other post-AGB stars.

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44

García-Rojas, J., S. Simón-Díaz, and C. Esteban. "The Cocoon nebula and its ionizing star: do stellar and nebular abundances agree?" Astronomy & Astrophysics 571 (November 2014): A93. http://dx.doi.org/10.1051/0004-6361/201424660.

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45

Oey, M. S., and J. C. Shields. "Calibration of Nebular Emission‐Line Diagnostics. II. Abundances." Astrophysical Journal 539, no. 2 (August 20, 2000): 687–705. http://dx.doi.org/10.1086/309276.

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46

Maness, H., and S. D. Vrtilek. "Nebular versus Stellar Wind Abundances in NGC 6543." Publications of the Astronomical Society of the Pacific 115, no. 810 (August 2003): 1002–5. http://dx.doi.org/10.1086/376573.

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47

Fernández-Ontiveros, J. A., E. Pérez-Montero, J. M. Vílchez, R. Amorín, and L. Spinoglio. "Measuring chemical abundances with infrared nebular lines: HII-CHI-MISTRY-IR." Astronomy & Astrophysics 652 (August 2021): A23. http://dx.doi.org/10.1051/0004-6361/202039716.

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We provide a new method for deriving heavy element abundances taking advantage of the unique suite of fine-structure lines in the mid- to far-infrared (IR) range. Using grids of photo-ionisation models that cover a wide range in O/H and N/O abundances and ionisation parameter, our code HII-CHI-MISTRY-IR (HCM-IR) provides model-based abundances based on extinction-free and temperature-insensitive tracers. These are two significant advantages over optical diagnostics when they are applied to dust-obscured regions or unresolved (stratified) nebulae, typical conditions found in high-z galaxies. The performance of the code is probed using three different samples of galaxies that extend over a wide range in metallicity, 7.2 ≲ 12 + log(O/H) ≲ 8.9, with available mid- to far-IR spectroscopic observations from Spitzer and Herschel, respectively. The samples correspond to 28 low-metallicity dwarf galaxies, 19 nearby starbursts, and 9 luminous IR galaxies. The IR model-based metallicities obtained are robust within a scatter of 0.03 dex when the hydrogen recombination lines, which are typically faint transitions in the IR range, are not available. When compared to the optical abundances obtained with the direct method, model-based methods, and strong-line calibrations, HCM-IR estimates show a typical dispersion of ∼ 0.2 dex. This is in line with previous studies comparing IR and optical abundances and does not introduce a noticeable systematic above 12 + log(O/H) ≳ 7.6. This accuracy can be achieved by measuring the sulphur ([S IV]10.5 μm and [S III]18.7, 33.5 μm) and the neon lines ([Ne III]15.6 μm and [Ne II]12.8 μm). Additionally, HCM-IR provides an independent N/O measurement when the oxygen ([O III]52, 88 μm) and nitrogen ([N III]57 μm) transitions are measured. The derived abundances in this case do not rely on particular assumptions on the N/O ratio. Large uncertainties (∼ 0.4 dex) may affect the abundance determinations of galaxies at sub- or over-solar metallicities when a solar-like N/O ratio is adopted. Finally, the code has been applied to 8 galaxies located at 1.8 < z < 7.5 with ground-based detections of far-IR lines redshifted in the submillimetre range, revealing solar-like N/O and O/H abundances in agreement with recent studies. A script to derive chemical abundances with HCM-IR has been made publicly available online.

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48

Schmidt, D. R., and L. M. Ziurys. "The Remarkable Molecular Content of Planetary Nebulae." Proceedings of the International Astronomical Union 13, S332 (March 2017): 218–24. http://dx.doi.org/10.1017/s1743921317011589.

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AbstractIn order to further define the molecular content of planetary nebulae (PNe), we have conducted searches for HCN, HCO+, HNC, and CCH at millimeter wavelengths in a sample of seventeen PNe using the new 12 m and Sub-Millimeter Telescopes of the Arizona Radio Observatory (ARO). HCN and HCO+ were identified in 75% of the PNe, with corresponding fractional abundances of f(HCN/H2) ~ 0.1-9.1 × 10−7 and f(HCO+/H2) ~ 0.04-7.4 × 10−7. HNC was subsequently identified in twelve PNe with f(HNC/H2) ~ 0.02-2.2 × 10−7. The [HCN]/[HNC] ratio was found to be ~1-8 in nebulae observed. CCH was also detected in eight PNe. The abundances for all molecules were found to remain relatively constant with nebular age across 10,000 years, in contrast to model predictions. They are also 10-100 greater than those observed in diffuse clouds, and suggest that molecular material from PNe seed the diffuse ISM.

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49

Zhang, C. Y. "Chemical Enrichment and Central Star Properties." Symposium - International Astronomical Union 155 (1993): 572. http://dx.doi.org/10.1017/s0074180900172468.

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We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.

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50

Vale Asari, N., G. Stasińska, R. Cid Fernandes, J. M. Gomes, M. Schlickmann, A. Mateus, and W. Schoenell. "The Evolution of the Mass–Metallicity Relation in Seyferts." Proceedings of the International Astronomical Union 5, S267 (August 2009): 144. http://dx.doi.org/10.1017/s1743921310006058.

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Various studies have shown that there is an empirical relation between the nebular metallicity of a galaxy and its stellar mass. Until now, most studies of the mass-metallicity relation (M–Z) have focused on the abundances of the interstellar medium as measured by emission-line features. This technique thus excludes galaxies with AGN from the working samples, due to the difficulty to measure the nebular abundances when emission-lines are powered both by stars and AGN. With our synthesis code starlight, we are able to recover the stellar metallicities of galaxies from the Sloan Digital Sky Survey (SDSS). Therefore, although we still cannot measure the nebular metallicity in AGN hosts, we know their present-day stellar metallicities. Moreover, because we measure the metallicity of stellar populations of different ages in a galaxy, we are also able also recover the history of its chemical enrichment.

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