SIMBAD references

2004ApJ...601..858M - Astrophys. J., 601, 858-863 (2004/February-1)

O star effective temperatures and H II region ionization parameter gradients in the Galaxy.


Abstract (from CDS):

Extensive photoionization model grids are computed for single-star H II regions using stellar atmosphere models from the WM-Basic code. Mid-IR emission-line intensities are predicted, and diagnostic diagrams of [Ne III/II] and [S IV/III] excitation ratios are built, taking into account the metallicities of both the star and the H II region. The diagrams are used in conjunction with Galactic H II region observations obtained with the Infrared Space Observatory to determine the effective temperature Teffof the exciting O stars and the mean ionization parameter U{d1}, where Teffand U{d1} are found to increase and decrease, respectively, with the metallicity of the H II region represented by the Ne/Neratio. No evidence is found for gradients of Teffor U{d1} with Galactocentric distance RGal. The observed excitation sequence with RGalis mainly due to the effect of the metallicity gradient on the spectral ionizing shape, upon which the effect of an increase in Teffwith Z is superposed. We show that not taking properly into account the effect of metallicity on the ionizing shape of the stellar atmosphere would lead to an apparent decrease of Teffwith Z and an increase of Teffwith RGal.

Abstract Copyright:

Journal keyword(s): Galaxy: Stellar Content - ISM: H II Regions - Infrared: ISM - Stars: Atmospheres - Stars: Fundamental Parameters - Stars: Supergiants

Simbad objects: 34

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