THE ABUNDANCES OF LIGHT NEUTRON-CAPTURE ELEMENTS IN PLANETARY NEBULAE. III. THE IMPACT OF NEW ATOMIC DATA ON NEBULAR SELENIUM AND KRYPTON ABUNDANCE DETERMINATIONS

AbstractNeutron(n)-capture elements are produced by s-process nucleosynthesis in low- and intermediate-mass AGB stars, and therefore can be enriched in planetary nebulae (PNe). In the last ten years, n-capture elements have been detected in more than 100 PNe in the Milky Way and nearby galaxies. In some objects, several different n-capture elements have been detected, providing valuable constraints to models of AGB nucleosynthesis and evolution. These detections have motivated theoretical and experimental investigations of the atomic data needed to derive accurate n-capture element abundances. In this review, I discuss the methods and results of these atomic data studies, and their application to abundance determinations in PNe.

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Atomic data and the density structures of planetary nebulae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2488 ◽

2021 ◽

Author(s):

Leticia Juan de Dios ◽

Mónica Rodríguez

Keyword(s):

Electron Density ◽

Planetary Nebulae ◽

Atomic Data ◽

The Impact

Abstract We study the density structures of planetary nebulae implied by four diagnostics that sample different regions within the nebulae: [S ii] λ6716/λ6731, [O ii] λ3726/λ3729, [Cl iii] λ5518/λ5538, and [Ar iv] λ4711/λ4740. We use a sample of 46 objects with deep spectra that allow the calculation of the electron density from these four diagnostics, and explore the impact that different atomic data have on the results. We compare the observational results with those obtained from photoionization models characterized by three different density structures. We conclude that the atomic data used in the calculations of electron density fully determine the density structures that are derived for the objects. We illustrate this by selecting three combinations of atomic data that lead to observational results that are compatible with each of the three different density structures explored with the models.

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Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834241 ◽

2019 ◽

Vol 622 ◽

pp. A159 ◽

Cited By ~ 3

Author(s):

Andreas Koch ◽

Moritz Reichert ◽

Camilla Juul Hansen ◽

Melanie Hampel ◽

Richard J. Stancliffe ◽

...

Keyword(s):

Neutron Capture ◽

Galactic Halo ◽

Asymptotic Giant Branch ◽

Galactic Bulge ◽

Element Abundances ◽

Intermediate Neutron ◽

Low Mass ◽

Process Component ◽

Process Elements ◽

The Impact

Metal-poor stars in the Galactic halo often show strong enhancements in carbon and/or neutron-capture elements. However, the Galactic bulge is notable for its paucity of these carbon-enhanced metal-poor (CEMP) and/or CH-stars, with only two such objects known to date. This begs the question whether the processes that produced their abundance distribution were governed by a comparable nucleosynthesis in similar stellar sites as for their more numerous counterparts in the halo. Recently, two contenders of these classes of stars were discovered in the bulge, at [Fe/H] = −1.5 and −2.5 dex, both of which show enhancements in [C/Fe] of 0.4 and 1.4 dex (respectively), [Ba/Fe] in excess of 1.3 dex, and also elevated nitrogen. The more metal-poor of the stars can be well matched by standard s-process nucleosynthesis in low-mass asymptotic giant branch (AGB) polluters. The other star shows an abnormally high [Rb/Fe] ratio. Here, we further investigate the origin of the abundance peculiarities in the Rb-rich star by new, detailed measurements of heavy element abundances and by comparing the chemical element ratios of 36 species to several models of neutron-capture nucleosynthesis. The i-process with intermediate neutron densities between those of the slow (s-) and rapid (r)-neutron-capture processes has been previously found to provide good matches of CEMP stars with enhancements in both r- and s-process elements (class CEMP-r/s), rather than invoking a superposition of yields from the respective individual processes. However, the peculiar bulge star is incompatible with a pure i-process from a single ingestion event. Instead, it can, statistically, be better reproduced by more convoluted models accounting for two proton ingestion events, or by an i-process component in combination with s-process nucleosynthesis in low-to-intermediate mass (2–3 M⊙) AGB stars, indicating multiple polluters. Finally, we discuss the impact of mixing during stellar evolution on the observed abundance peculiarities.

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Neutron-capture Elements in Planetary Nebulae: First Detections of Near-infrared [Te iii] and [Br v] Emission Lines

The Astrophysical Journal ◽

10.3847/2041-8213/aaccef ◽

2018 ◽

Vol 861 (1) ◽

pp. L8 ◽

Cited By ~ 7

Author(s):

Simone Madonna ◽

Manuel Bautista ◽

Harriet L. Dinerstein ◽

N. C. Sterling ◽

Jorge García-Rojas ◽

...

Keyword(s):

Neutron Capture ◽

Near Infrared ◽

Planetary Nebulae ◽

Emission Lines

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The impact of spectra quality on nebular abundances

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1286 ◽

2020 ◽

Vol 495 (1) ◽

pp. 1016-1034 ◽

Cited By ~ 1

Author(s):

Mónica Rodríguez

Keyword(s):

Planetary Nebulae ◽

The Other ◽

Statistical Equilibrium ◽

Emission Lines ◽

Reference Spectrum ◽

Equilibrium Equations ◽

Chemical Abundances ◽

Physical Conditions ◽

Observational Errors ◽

The Impact

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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MBPT Results for Δn=0 Electric Dipole Transitions

Symposium - International Astronomical Union ◽

10.1017/s0074180900170263 ◽

1993 ◽

Vol 155 ◽

pp. 96-96

Author(s):

G. Gaigalas ◽

R. Kisielius ◽

G. Merkelis ◽

Z. Rudzikas ◽

M. Vilkas

Keyword(s):

Electric Dipole ◽

Planetary Nebulae ◽

Atomic Data ◽

Atomic Lines

To identify spectra of Planetary Nebulae which usually have many atomic lines one needs very accurate theoretical atomic data.

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Heavy elements in planetary nebulae: A theorist's gold mine

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312010824 ◽

2011 ◽

Vol 7 (S283) ◽

pp. 127-130

Author(s):

Amanda I. Karakas ◽

Maria Lugaro

Keyword(s):

Neutron Capture ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Heavy Elements ◽

Gold Mine ◽

Agb Stars ◽

Capture Process ◽

Wide Range ◽

Model Predictions

AbstractObservations of planetary nebulae have revealed a wealth of information about the composition of heavy elements synthesized by the slow neutron capture process (the s process). In some of these nebulae the abundances of neutron-capture elements are enriched by factors of 10 to 30 times the solar value, indicating that these elements were produced in the progenitor star while it was on the asymptotic giant branch (AGB). In this proceedings we summarize results of our recent full s-process network predictions covering a wide range of progenitor masses and metallicities. We compare our model predictions to observations and show how this can provide important insights into nucleosynthesis processes occurring deep within AGB stars.

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Improved Neutron-Capture Element Abundances in Planetary Nebulae

Publications of the Astronomical Society of Australia ◽

10.1071/as08067 ◽

2009 ◽

Vol 26 (3) ◽

pp. 339-344 ◽

Cited By ~ 19

Author(s):

N. C. Sterling ◽

H. L. Dinerstein ◽

S. Hwang ◽

S. Redfield ◽

A. Aguilar ◽

...

Keyword(s):

Cross Sections ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Rate Coefficients ◽

Atomic Data ◽

Agb Stars ◽

Iron Species ◽

Element Abundances ◽

Ionization Balance ◽

Initial Results

AbstractSpectroscopy of planetary nebulae (PNe) provides the means to investigate s-process enrichments of neutron(n)-capture elements that cannot be detected in Asymptotic Giant Branch (AGB) stars. However, accurate abundance determinations of these elements present a challenge. Corrections for unobserved ions can be large and uncertain, since in many PNe only one ion of a given n-capture element has been detected. Furthermore, the atomic data governing the ionization balance of these species are not well-determined, inhibiting the derivation of accurate ionization corrections. We present initial results of a program that addresses these challenges. Deep high-resolution optical spectroscopy of ∼20 PNe has been performed to detect emission lines from trans-iron species including Se, Br, Kr, Rb and Xe. The optical spectral region provides access to multiple ions of these elements, which reduces the magnitude and importance of uncertainties in the ionization corrections. In addition, experimental and theoretical efforts are providing determinations of the photoionization cross sections and recombination rate coefficients of Se, Kr and Xe ions. These new atomic data will make it possible to derive robust ionization corrections for these elements. Together, our observational and atomic data results will enable n-capture element abundances to be determined with unprecedented accuracy in ionized nebulae.

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Atomic data for neutron-capture elements

Astronomy and Astrophysics ◽

10.1051/0004-6361/201116718 ◽

2011 ◽

Vol 529 ◽

pp. A147 ◽

Cited By ~ 15

Author(s):

N. C. Sterling ◽

M. C. Witthoeft

Keyword(s):

Neutron Capture ◽

Atomic Data

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R-matrix electron-impact excitation data for the N-like iso-electronic sequence

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039195 ◽

2020 ◽

Vol 643 ◽

pp. A95

Author(s):

Junjie Mao ◽

N. R. Badnell ◽

G. Del Zanna

Keyword(s):

Electron Impact ◽

Plasma Diagnostics ◽

Spectral Lines ◽

Impact Excitation ◽

Electron Impact Excitation ◽

Atomic Data ◽

Astrophysical Plasma ◽

Wide Range ◽

The Impact ◽

Effective Collision

Context. Spectral lines from N-like ions can be used to measure the temperature and density of various types of astrophysical plasmas. The atomic databases of astrophysical plasma modelling codes still have room for improvement in their electron-impact excitation data sets for N-like ions, especially for R-matrix data. This is particularly relevant for future observatories (e.g. Arcus), which will host high-resolution spectrometers. Aims. We aim to obtain level-resolved effective collision strengths for all transitions up to nl = 5d over a wide range of temperatures for N-like ions from O II to Zn XXIV (i.e. O+ to Zn23+) and to assess the accuracy of the present work. We also examine the impact of our new data on plasma diagnostics by modelling solar observations with CHIANTI. Methods. We carried out systematic R-matrix calculations for N-like ions, which included 725 fine-structure target levels in both the configuration interaction target and close-coupling collision expansions. The R-matrix intermediate coupling frame transformation method was used to calculate the collision strengths, while the AUTOSTRUCTURE code was used for the atomic structures. Results. We compare the present results for selected ions with those in archival databases and the literature. The comparison covers energy levels, oscillator strengths, and effective collision strengths. We show examples of improved plasma diagnostics when compared to CHIANTI models, which use only distorted wave data as well as some using previous R-matrix data. The electron-impact excitation data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf04 and will be available in OPEN-ADAS. The data can be used to improve the atomic databases for astrophysical plasma diagnostics.

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