scholarly journals Atomic data and the density structures of planetary nebulae

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.

scholarly journals Flux Ratio [Ne v] 14.3/24.3 as a Test of Collision Strengths

2004 ◽  
Vol 217 ◽  
pp. 190-191
Author(s):  
R.H. Rubin
Keyword(s):  
Electron Density ◽  
Flux Ratio ◽  
Planetary Nebulae ◽  
Atomic Data ◽  
Line Flux ◽  
Astronomical Data ◽  
Data Collision

From ISO [Ne v] 14.3/24.3 μm line flux ratios, we find that 10 out of 20 planetary nebulae (PNs) have measured ratios below the low-electron density (Ne) theoretical predicted limit. Such astronomical data serve to provide important tests of atomic data, collision strengths in this case. In principle, well-calibrated measurements of the [Ne v] 14.3/24.3 flux ratio could improve upon the existing atomic data.

Measurement of Dysprosium Stark Width and the Electron Impact Width Parameter

2018 ◽  
Vol 73 (2) ◽  
pp. 203-213 ◽  
Author(s):  
Jhonatha R. dos Santos ◽  
Jonas Jakutis Neto ◽  
N. Rodrigues ◽  
M.G. Destro ◽  
José W. Neri ◽  
...  
Keyword(s):  
Electron Density ◽  
Impact Parameter ◽  
Plasma Temperature ◽  
Spectral Lines ◽  
Emission Lines ◽  
Spectroscopic Methods ◽  
Species Concentration ◽  
The Impact ◽  
Stark Width

In this work, we suggest a methodology to determine the impact parameter for neutral dysprosium emission lines from the characterization of the plasma generated by laser ablation in a sealed chamber filled with argon. The procedure is a combination of known consistent spectroscopic methods for plasma temperature determination, electron density, and species concentration. With an electron density of 3.1 × 1018 cm–3 and temperature close to 104 K, we estimated the impact electron parameter for nine spectral lines of the neutral dysprosium atom. The gaps in the impact parameter data in the literature, mainly for heavy elements, stress the importance of the proposed method.

scholarly journals A comparison of Galactic electron density models using PyGEDM

2021 ◽  
Vol 38 ◽  
Author(s):  
D. C. Price ◽  
C. Flynn ◽  
A. Deller
Keyword(s):  
Electron Density ◽  
Large Scale ◽  
Galactic Halo ◽  
Application Programming Interface ◽  
Dispersion Measure ◽  
Radio Pulsars ◽  
Distribution Models ◽  
Distance Measurements ◽  
Application Programming ◽  
The Impact

Abstract Galactic electron density distribution models are crucial tools for estimating the impact of the ionised interstellar medium on the impulsive signals from radio pulsars and fast radio bursts. The two prevailing Galactic electron density models (GEDMs) are YMW16 (Yao et al. 2017, ApJ, 835, 29) and NE2001 (Cordes & Lazio 2002, arXiv e-prints, pp astro–ph/0207156). Here, we introduce a software package PyGEDM which provides a unified application programming interface for these models and the YT20 (Yamasaki & Totani 2020, ApJ, 888, 105) model of the Galactic halo. We use PyGEDM to compute all-sky maps of Galactic dispersion measure (DM) for YMW16 and NE2001 and compare the large-scale differences between the two. In general, YMW16 predicts higher DM values towards the Galactic anticentre. YMW16 predicts higher DMs at low Galactic latitudes, but NE2001 predicts higher DMs in most other directions. We identify lines of sight for which the models are most discrepant, using pulsars with independent distance measurements. YMW16 performs better on average than NE2001, but both models show significant outliers. We suggest that future campaigns to determine pulsar distances should focus on targets where the models show large discrepancies, so future models can use those measurements to better estimate distances along those line of sight. We also suggest that the Galactic halo should be considered as a component in future GEDMs, to avoid overestimating the Galactic DM contribution for extragalactic sources such as FRBs.

scholarly journals Birthrate of PN

1983 ◽  
Vol 103 ◽  
pp. 424-425 ◽  
Author(s):  
D.C.V. Mallik
Keyword(s):  
Electron Density ◽  
Surface Density ◽  
Planetary Nebulae ◽  
Number Density ◽  
Continuum Radiation ◽  
Complete Catalogue

Recent observations of planetary nebulae have called into question the Shklovsky method of measuring distances. For those planetaries for which independent distance and electron density determinations are available, it is found that the ionized mass and the radius are linearly correlated (Maciel and Pottasch, 1980) and also that the ionized masses increase with decreasing electron density (Pottasch, 1981). These relations imply that the nebulae are optically thick in Ly continuum radiation and the distances based on the Shklovsky method are overestimates. Using an empirically determined mass-radius relationship Maciel and Pottasch have obtained new distances for the nebulae in the catalogue of Milne and Aller (1975). We have used the more complete catalogue of Cahn and Kaler (1971) to obtain distances corrected for possible variations in the ionized mass and have compiled a new list of local planetaries. We obtain a surface density of 15 ± 3 kpc−2 and a planar number density of 44 ± 4 kpc−3.

scholarly journals Factors Impacting σ- and π-Hole Regions as Revealed by the Electrostatic Potential and Its Source Function Reconstruction: The Case of 4,4′-Bipyridine Derivatives

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4409
Author(s):  
Carlo Gatti ◽  
Alessandro Dessì ◽  
Roberto Dallocchio ◽  
Victor Mamane ◽  
Sergio Cossu ◽  
...  
Keyword(s):  
Electron Density ◽  
Electrostatic Potential ◽  
Source Function ◽  
Noncovalent Interactions ◽  
Conformational Search ◽  
Atomic Group ◽  
Group Contributions ◽  
Conformational Freedom ◽  
Molecular Patterns ◽  
The Impact

Positive electrostatic potential (V) values are often associated with σ- and π-holes, regions of lower electron density which can interact with electron-rich sites to form noncovalent interactions. Factors impacting σ- and π-holes may thus be monitored in terms of the shape and values of the resulting V. Further precious insights into such factors are obtained through a rigorous decomposition of the V values in atomic or atomic group contributions, a task here achieved by extending the Bader–Gatti source function (SF) for the electron density to V. In this article, this general methodology is applied to a series of 4,4′-bipyridine derivatives containing atoms from Groups VI (S, Se) and VII (Cl, Br), and the pentafluorophenyl group acting as a π-hole. As these molecules are characterized by a certain degree of conformational freedom due to the possibility of rotation around the two C–Ch bonds, from two to four conformational motifs could be identified for each structure through conformational search. On this basis, the impact of chemical and conformational features on σ- and π-hole regions could be systematically evaluated by computing the V values on electron density isosurfaces (VS) and by comparing and dissecting in atomic/atomic group contributions the VS maxima (VS,max) values calculated for different molecular patterns. The results of this study confirm that both chemical and conformational features may seriously impact σ- and π-hole regions and provide a clear analysis and a rationale of why and how this influence is realized. Hence, the proposed methodology might offer precious clues for designing changes in the σ- and π-hole regions, aimed at affecting their potential involvement in noncovalent interactions in a desired way.

scholarly journals The impact of spectra quality on nebular abundances

2020 ◽  
Vol 495 (1) ◽  
pp. 1016-1034 ◽  
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.

scholarly journals MBPT Results for Δn=0 Electric Dipole Transitions

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.

scholarly journals Improved Neutron-Capture Element Abundances in Planetary Nebulae

2009 ◽  
Vol 26 (3) ◽  
pp. 339-344 ◽  
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.

Sign in / Sign up

Export Citation Format

Share Document