Helium abundances and its radial gradient from the spectra of H II regions and ring nebulae of the Milky Way

Méndez-Delgado, J. E.; Esteban, C.; García-Rojas, J.; Arellano-Córdova, K. Z.; Valerdi, M.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society

Advertised on:
6
2020
Number of authors
5
IAC number of authors
4
Citations
15
Refereed citations
12
Description
We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 H II regions and ring nebulae surrounding massive O-type stars. We revise the Galactocentric distances of the objects considering Gaia DR2 parallaxes (Gaia Collaboration 2018) and determine the physical conditions and the ionic abundance of He+ in a homogeneous way, using between 3 and 10 He I recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ionization correction factor (ICF; He) schemes. The slope of the gradient is always negative and weakly dependent on the ICF(He) scheme, especially when only the objects with log(η) < 0.9 are considered. The slope values go from −0.0078 to −0.0044 dex kpc−1, consistent with the predictions of chemical evolution models of the Milky Way and chemodynamical simulations of disc galaxies. Finally, we estimate the abundance deviations of He, O, and N in a sample of ring nebulae around Galactic Wolf─Rayet stars, finding a quite similar He overabundance of about +0.24 ± 0.11 dex in three stellar ejecta ring nebulae.
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Jorge
García Rojas