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We present chemical abundance determinations of two H  ii regions in the dwarf irregular (dIrr) galaxy Leo A from Gran Telescopio Canarias (GTC) Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) long-slit spectra. Both H  ii regions are of low excitation and seem to be ionized by stars later than O8V spectral type. In one of the H  ii regions we used the direct method: O+2 ionic abundance was calculated using an electronic temperature determined from the [O  iii ] λλ4363/5007 line ratio; ionic abundances of O+, N+, and S+ were calculated using a temperature derived from a parametrized formula. O, N, and S total abundances were calculated using ionization correction factors from the literature for each element. Chemical abundances using strong-line methods were also determined, with similar results. For the second H  ii region, no electron temperature was determined thus the direct method cannot be used. We computed photoionization structure models for both H  ii regions in order to determine their chemical composition from the best-fitting models. It is confirmed that Leo A in a very low metallicity galaxy, with 12 + log(O/H) = 7.4 ± 0.2, log(N/O) = −1.6, and log(S/O) = −1.1. Emission lines of the only planetary nebula (PN) detected in Leo A were re-analysed and a photoionization model was computed. This PN shows 12 + log(O/H) very similar to the ones of the H  ii regions and a low N abundance, although its log(N/O) ratio is much larger than the values of the H  ii regions. Its central star seems to have had an initial mass lower than 2 M⊙. [ABSTRACT FROM AUTHOR]

The kinematics of the plasma in 14 planetary nebulae (PNe) is analysed by measuring the expansion velocities (Vexp) of different ions as derived from their collisionally excited lines (CELs) and optical recombination lines (ORLs). Vexp is analysed as a function of the ionization potential of ions, which at a first approximation represents the distance of the ion from the central star. In most cases, the kinematics of ORLs is incompatible with the kinematics of CELs at the same ionization potential, especially if CELs and ORLs are considered for the same ion. In general, Vexp from ORLs is lower than Vexp from CELs, indicating that, if the gas is in ionization equilibrium, ORLs are emitted by a gas located closer to the central star. The velocity field derived from CELs shows a gradient accelerating outwards as predicted from hydrodynamic modelling of PNe ionization structures. The velocity field derived from ORLs is different. In many cases, the velocity gradient is flatter or non-existent and highly and lowly ionized species present nearly the same Vexp. In addition, the full width at half-maximum (FWHM) for ORLs is usually smaller than FWHM(CEL). Our interpretation is that ORLs are mainly emitted by a plasma that coexists with the plasma emitting CELs, but does not fit the ionization structures predicted by models. Such a plasma should have been ejected in a different event from the plasma emitting CELs. [ABSTRACT FROM AUTHOR]

Physical conditions and chemical abundances of two H II regions and a planetary nebula in the dIrr galaxy Leo A are presented. These determinations were performed using the direct method (T e measured) and the ONS method. We also constructed photoionization models for the three nebulae to determine the abundances and to analyse the ionizing stars. The O abundance was determined to be 12+log(O/H) = 7.4±0.2 in all cases. [ABSTRACT FROM AUTHOR]