Atomic processes in planetary nebulae

Liu, Xiaowei

doi:10.1017/s1743921312010836

Cited by 2 publications

(1 citation statement)

References 27 publications

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“…The 2 Ryd and the BB spectra have been multiplied by 10 2 and 10 5 for clarity. Many nebulae present complex geometries with observations often indicating that density fluctuations are present (Liu 2012;Peimbert & Peimbert 2013;Zhang & Liu 2002). Using different collisionally excited lines (CELs) to measure the density lead typically to a factor ∼2 uncertainty in the value of the density (Peimbert & Peimbert 2013;, 2011, although uncertainties can reach much higher values.…”

Section: Discussionmentioning

confidence: 99%

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

Guzmán

Badnell

Chatzikos

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abundances and recombination. There are now several competing theories for the treatment of this process, and it is not possible to test these experimentally. We show that the H I two-photon continuum produced by astrophysical nebulae is strongly affected by l-changing collisions. We perform an analysis of the different underlying atomic processes and simulate the recombination and two-photon spectrum of a nebula containing H and He. We provide an extended set of effective recombination coefficients and updated l-changing 2s − 2p transition rates using several competing theories. In principle, accurate astronomical observations could determine which theory is correct.Key words: cosmology: cosmic background radiation -cosmology: observations -atomic data -atomic processes -H ii regions -planetary nebulae: general MOTIVATIONOptical recombination lines (ORL) are produced from recombination of ions followed by cascades from highly excited recombined levels. Theoretical emissivities of these lines should be known with high accuracy, and observations of such lines in nebulae provide valuable and accurate information on their composition, temperature and density. This is summarized in the textbook of Osterbrock & Ferland (2006), while Schirmer (2016) applies this theory to spectral simulations.Although many processes contribute to the formation of these lines, recently attention has been brought to l-changing collisions. These act to redistribute the populations within an n-shell and so change the subsequent cascade to lower levels. Intra n-shell l-levels are energy degenerate for hydrogenic systems, so the orbiting electron changes its angular momentum with no energy change. This is caused by a long range Stark interaction with the electric field of the projectile. Due to this peculiarity, slow high-mass projectiles are favored over electrons.There are now several competing theories for how l-changing collisions occur, as summarized in our previous work (Guzmán et al. 2016(Guzmán et al. , 2017, hereafter P1 and P2, and in the next section. These have an important effect on recombination line intensities, as shown in P1 and P2. In addition, l-mixing collisions in relatively low n-shells play an important role in producing cosmological recombination radiation (CRR; Chluba et al. 2010). In fact, Lyα and two-photon emissivities are the two bottlenecks at different redshifts: Lyα at z > 1300, and two-photon at lower redshift during the recombination epoch. Chluba & Sunyaev (2006) show that an accurate treatment of l-mixing collisions, and the 2s and 2p populations is needed to predict the CMB to a precision of ∼ 0.1%. These processes have a similar effect on helium recombination lines, which introduces uncertainties in measurements of the primordial helium abundance (Porter et al. 2009).It is not possible to experimentally determine which of the l-changing theories is correct. Measurements of l-changing rates have been d...

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Section: Discussionmentioning

confidence: 99%

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

Guzmán

Badnell

Chatzikos

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Abundance discrepancy factors in high-density planetary nebulae

Ruiz-Escobedo

Peña

2022

Monthly Notices of the Royal Astronomical Society

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From high-resolution spectra, chemical abundances from collisionally excited lines (CELs) and optical recombination lines (ORLs) have been determined for planetary nebulae 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. Exception 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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Atomic processes in planetary nebulae

Cited by 2 publications

References 27 publications

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

Abundance discrepancy factors in high-density planetary nebulae

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