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H II region age indicators

M. V. F. Copetti, M. G. Pastoriza, H. Dottori

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Abstract

The evolution of some properties of H II regions such as the relative volume R of the He⁺ and H⁺ zones, the equivalent width Wнβ of the Hβ emission line and the ratio [O III]/Hβ of the lines [O II] λλ4959, 5007 to Hβ, was studied through models which take into account: a single burst for the formation of the ionizing association with different initial mass function IMF (1 ≤ x ≤ 3) and upper stellar mass limits (30 ≤ Mu/Mѳ ≤ 120); different chemical composition models of stellar evolution with and without mass loss. It was found that Wнβ, R and [OIII]/Hβ decrease monotonically as a function of time and consequently they are good H II region age indicators.

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What this paper is about

The evolution of some properties of H II regions such as the relative volume R of the He⁺ and H⁺ zones, the equivalent width Wнβ of the Hβ emission line and the ratio [O III]/Hβ of the lines [O II] λλ4959, 5007 to Hβ, was studied through models which take into account: a single burst for the formation of the ionizing association with different initial mass function IMF (1 ≤ x ≤ 3) and upper stellar mass limits (30 ≤ Mu/Mѳ ≤ 120); different chemical composition models of stellar evolution with and without mass loss. It was found that Wнβ, R and [OIII]/Hβ decrease monotonically as a function of time and consequently they are good H II region age indicators.

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Available abstract

The evolution of some properties of H II regions such as the relative volume R of the He⁺ and H⁺ zones, the equivalent width Wнβ of the Hβ emission line and the ratio [O III]/Hβ of the lines [O II] λλ4959, 5007 to Hβ, was studied through models which take into account: a single burst for the formation of the ionizing association with different initial mass function IMF (1 ≤ x ≤ 3) and upper stellar mass limits (30 ≤ Mu/Mѳ ≤ 120); different chemical composition models of stellar evolution with and without mass loss. It was found that Wнβ, R and [OIII]/Hβ decrease monotonically as a function of time and consequently they are good H II region age indicators.

Key concepts: Physics, Astrophysics, Astronomy

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