Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosynthesis. Unfortunately, there is some question whether current theory can account for collisional contributions to He I. We present new observations of two planetary nebulae (PNs) in the range λ850-λ9650, which we use to assess the importance of collisonal effects in the He I spectrum. The first object, NGC 7027, is expected to show relatively strong collisional enhancement, while the second, NGC 7026, should display only small effects. We derive new collision-to-recombination correction factors, based on new collision strengths from the 29-state quantal calculation of He I extending to n = 5. Our results show that the correction factors base...
International audienceElastic collisions between neutral helium atoms from interstellar origin and p...
Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple proc...
Determinations of the primordial helium abundance are used in precision cosmological tests. These re...
Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosy...
Smits has recently calculated theoretical He I intensities for a large number of lines for condition...
This paper describes a new determination of the primordial helium abundance (Y_P), based on the abun...
Cosmological models can be constrained by determining primordial abundances. Accurate predictions of...
The theoretical calculations of helium triplet line strengths, including collisional enhancement, ar...
Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple proc...
Electron temperatures derived from the He I recombination line ratios, designated T e(He I), are pre...
Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abun...
Determinations of the primordial helium abundance are used in precision cosmological tests. These re...
International audienceWe determine the primordial helium mass fraction Yp using 93 spectra of 86 low...
Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abun...
We apply a recently developed theoretical model of helium emission to observations of both the Orion...
International audienceElastic collisions between neutral helium atoms from interstellar origin and p...
Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple proc...
Determinations of the primordial helium abundance are used in precision cosmological tests. These re...
Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosy...
Smits has recently calculated theoretical He I intensities for a large number of lines for condition...
This paper describes a new determination of the primordial helium abundance (Y_P), based on the abun...
Cosmological models can be constrained by determining primordial abundances. Accurate predictions of...
The theoretical calculations of helium triplet line strengths, including collisional enhancement, ar...
Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple proc...
Electron temperatures derived from the He I recombination line ratios, designated T e(He I), are pre...
Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abun...
Determinations of the primordial helium abundance are used in precision cosmological tests. These re...
International audienceWe determine the primordial helium mass fraction Yp using 93 spectra of 86 low...
Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abun...
We apply a recently developed theoretical model of helium emission to observations of both the Orion...
International audienceElastic collisions between neutral helium atoms from interstellar origin and p...
Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple proc...
Determinations of the primordial helium abundance are used in precision cosmological tests. These re...