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Abstract The physics of recombination lines in the Heisinglet system is expected to be relatively simple, supported by accurate atomic models. We examine the intensities of Heisingletsλ3614, λ3965, λ5016, λ6678, and λ7281 and the triplet Heiλ5876 in various types of ionized nebulae and compare them with theoretical predictions to test the validity of the “Case B” recombination scenario and the assumption of thermal homogeneity. Our analysis includes 85 spectra from Galactic and extragalactic Hiiregions, 90 from star-forming galaxies, and 218 from planetary nebulae, all compiled by the Deep Spectra of Ionized Regions Database Extended (DESIRED-E) project. By evaluating the ratios Heiλ7281/λ6678 and Heiλ7281/λ5876, we determineTe(Hei) and compare it with direct measurements ofTe([Oiii]λ4363/λ5007). We find thatTe(Hei) is systematically lower thanTe([Oiii]) across most objects and nebula types. Additionally, we identify a correlation between the abundance discrepancy factor (ADF(O2+)) and the differenceTe([Oiii]) –Te(Hei) for planetary nebulae. We explore two potential explanations: photon loss fromn1P → 11Stransitions and temperature inhomogeneities. Deviations from “Case B” may indicate photon absorption by Hirather than Heiand/or generalized ionizing photon escape, highlighting the need for detailed consideration of radiative transfer effects. If temperature inhomogeneities are widespread, identifying a common physical phenomenon affecting all ionized nebulae is crucial. Our results suggest that both scenarios can contribute to the observed discrepancies.
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This content will become publicly available on January 22, 2026
Theoretical insights into the vibrational spectra and chemical bonding of Ln( iii ) complexes with a tripodal N 4 O 3 ligand along the lanthanide series
This study provides new theoretical insights into the vibrational spectra of Ln(iii) complexes, along the lanthanide series by utilizing the LModeAGen protocol and integrating cutting-edge topological ideas.
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- Award ID(s):
- 2102461
- PAR ID:
- 10642479
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 27
- Issue:
- 4
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 1794 to 1803
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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