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We investigate the chemical abundances of NGC3603 in the Milky Way, of 30Doradus in the Large Magellanic Cloud, and of N66 in the Small Magellanic Cloud. Mid-infrared observations with the Infrared Spectrograph onboard the Spitzer Space Telescope allow us to probe the properties of distinct physical regions within each object: the central ionizing cluster, the surrounding ionized gas, photodissociation regions, and buried stellar clusters. We detect [SIII], [SIV], [ArIII], [NeII], [NeIII], [FeII], and [FeIII] lines and derive the ionic abundances. Based on the ionic abundance ratio (NeIII/H)/(SIII/H), we find that the gas observed in the MIR is characterized by a higher degree of ionization than the gas observed in the optical spectra. We compute the elemental abundances of Ne, S, Ar, and Fe. We find that the alpha-elements Ne, S, and Ar scale with each other. Our determinations agree well with the abundances derived from the optical. The Ne/S ratio is higher than the solar value in the three giant HII regions and points toward a moderate depletion of sulfur on dust grains. We find that the neon and sulfur abundances display a remarkably small dispersion (0.11dex in 15 positions in 30Doradus), suggesting a relatively homogeneous ISM, even though small-scale mixing cannot be ruled out.
We report the first results of a long term program aiming to provide accurate independent estimates of the Hubble constant (H0) using the L-sigma distance estimator for Giant extragalactic HII regions (GEHR) and HII galaxies. We have used VLT and S
(Abridged) We have obtained HST WFPC2 observations of three very luminous but morphologically different giant HII regions (GHRs) in M101, NGC5461, NGC5462, and NGC5471, in order to study cluster formation in GHRs. The measured (M_F547M - M_F675W) col
A study of star formation is carried out on 35 giant extragalactic HII regions (GEHRs) in seven galaxies using optical photometric data in BVR broad bands and in the emission line of H alpha. Interstellar extinction, metallicity and nebular contribut
We have combined observations of the Antennae galaxies from the radio interferometer ALMA (Atacama Large Millimeter/submillimeter Array) and from the optical interferometer GH$alpha$FaS (Galaxy H$alpha$ Fabry-Perot System). The two sets of observatio
We present C and O abundances in the Magellanic Clouds derived from deep spectra of HII regions. The data have been taken with the Ultraviolet-Visual Echelle Spectrograph at the 8.2-m VLT. The sample comprises 5 HII regions in the Large Magellanic Cl