Helium line emissivities for nebular astrophysics

Abstract

We present the results of several collisional-radiative models describing optically-thin emissivities of the main lines in neutral helium formed by recombination, for a grid of electron temperatures and densities, typical of H II regions and Planetary Nebulae. Accurate emissivities are required for example to measure the helium abundance in nebulae and as a consequence its primordial value. We compare our results with those obtained by previous models, finding significant differences, well above the target accuracy of one percent. We discuss in some detail our chosen set of atomic rates and the differences with those adopted by previous models. The main differences lie in the treatment of electron and proton collision rates and we discuss which transitions are least sensitive to the choice of these rates and therefore best suited to high precision abundance determinations. We have focused our comparisons on the case B approximation where only He and He${}^{+}$ are considered, but also present results of full models including the bare nuclei, photo-excitation and photo-ionisation and either black-body or observed illuminating spectrum in the case of the Orion nebula, to indicate which spectral lines are affected by opacity. For those transitions, accurate radiative transfer calculations should be performed. We provide tables of emissivities for all transitions within $n\le 5$ and all those between the $n\le 5$ and $n^{\prime }\le 25$ states, in the log $T_{\mathrm{e}}$ [K]=10${}^{3.0(0.1)4.6}$ and log $N_{\mathrm{e}}$ [cm${}^{-3}$]=10${}^{2(0.5)6}$ ranges, and a FORTRAN code to interpolate to any $T_{\mathrm{e}},N_{\mathrm{e}}$ within these ranges.

arXiv commentAccepted for publication

References in corpus (18)

• A Grid of NLTE Line-Blanketed Model Atmospheres of O-type Stars
• PyNeb: a new tool for analyzing emission lines. I. Code description and validation of results
• The effects of He I 10830 on helium abundance determinations
• Improving Predictions for Helium Emission Lines
• A new determination of the primordial He abundance using the HeI 10830A emission line: cosmological implications
• Revised Primordial Helium Abundance Based on New Atomic Data
• CHIANTI - an atomic database for emission lines - Paper XV: Version 9, improvements for the X-ray satellite lines
• The primordial helium abundance from updated emissivities
• Improved He I Emissivities in the Case B Approximation
• Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
• Theoretical He I Emissivities in the Case B Approximation
• He~I Emission in the Orion Nebula and Implications for Primordial Helium Abundance
• Deviations from He I Case B Recombination Theory and Extinction Corrections in the Orion Nebula
• J-resolved He I emission predictions in the low-density limit
• Photoionized Herbig-Haro objects in the Orion Nebula through deep high-spectral resolution spectroscopy I: HH529II and III
• Helium line emissivities in the solar corona
• H, He-like recombination spectra II: $l$-changing collisions for He Rydberg states
• H, He-like recombination spectra IV; H, He-like recombination spectra IV: clarification and refinement of methodology for $l$-changing collisions

Cited by in corpus (7)

• GA-NIFS: A massive black hole in a low-metallicity AGN at $z\sim 5.55$ revealed by JWST/NIRSpec IFS
• PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar
• First Detection of Radio Recombination Lines of Ions Heavier than Helium
• Detection of Deuterated Hydrocarbon Nanoparticles in the Whirlpool Galaxy, M51
• Reduced atomic models for large-scale computations: Fe XIII near-infrared lines
• When Stars Mimic Monsters: Spectral Evidence for an $\eta$ Carinae-like Giant Eruption in SBS 0335$-$052 E
• H-, He-like recombination spectra -- V: On the dependence of the simulated line intensities on the number of electronic levels of the atoms