SIMBAD references

We present a detailed photoionization model of the brightest knot of star formation in the blue compact dwarf galaxy Mrk 209. The model reproduces the intensities of main lines emitted by the ionized gas, resulting in a very good agreement between observed and predicted line temperatures and chemical abundances of the observed ionic species.

The model has been calculated using the spectral energy distribution of a massive cluster of recent formation as the ionizing source. The features of Wolf-Rayet (WR) stars observed in the spectrum of the object, along with its ionizing properties, lead to different solutions for the ages and characteristics of the ionizing stellar populations. The found solutions are compatible with either a composite population of two ionizing clusters or a continuous star formation. In the first case, a young cluster, with an age less than 3 Myr, would be responsible for most of the ionization properties while an older cluster, with either 3.2 or 4.2 Myr, would be responsible for the emission of the observed WR features in the spectrum of the knot. In the second case, the duration of the star formation episode is found to be 3.6 Myr.

The addition of a certain amount of dust was required in order to reproduce correctly the measured electron temperatures. This dust implies a gas/dust ratio of 6.13 x10^–3, identical to that in the Milky Way, and a fraction of absorbed photons of f = 0.58. The taking into account the dust grain physics combined with a thick-shell geometry solves the problem of the heating in this object and allows the fitting of the auroral lines, the line temperatures and the ionization structure of the nebula with a negligible presence of temperature fluctuations, in agreement with the most recent results found for this type of objects from the measurement of the Balmer jump temperature.

An analysis of the ionization structure of the gas as well as the calculation of the main ionization correction factors for the unseen ionic stages is presented.