Context. The study of the radial variations of metallicity across the Galactic disc is a powerful method for understanding the history of star formation and chemical evolution of the Milky Way. Although several studies about gradients have been performed so far, the knowledge of the Galactic antincentre is still poor. Aims. This work aims to determine accurately the physical and chemical properties of a sample of H ii regions located at R G >11 kpc and to study the radial distribution of abundances in the outermost part of the Galaxy disc. Methods. We carried out new optical spectroscopic observations of nine H ii regions with the William Herschel Telescope covering the spectral range from 3500 Å to 10100Å. In addition, we increased the sample by searching the literature for optical observations of regions towards the Galactic anticentre, re-analysing them to obtain a single sample of 23 objects to be processed in a homogeneous and consistent manner. The total sample distribution covers the Galactocentric radius from 11 kpc to 18 kpc. Results. Emission line ratios were used to determine accurate electron densities and temperatures of several ionic species in 13 H ii regions. These physical parameters were applied to the spectra to determine direct total chemical abundances. For those regions without direct estimations of temperature, chemical abundances were derived by performing tailor-made photoionisation models and/or by using an empirical relation obtained from radio recombination and optical temperatures. We performed weighted least-squares fits to the distribution of the derived abundances along the Galactocentric distances to study the radial gradients of metallicity across the outermost part of the MW. The distributions O/H, N/H, S/H, and Ar/H towards the anticentre can be represented by decreasing linear radial gradients, while in the case of N/O abundances the radial distribution is better fitted with a two-zone model. The He/H radial gradient is presented here for the first time; we find a slope that is not significantly different from zero. The derived gradient for oxygen shows a clear decrease with distance with a slope of -0.053±0.009 dex kpc −1 . Although a shallower slope at large Galactocentric distances is suggested by our data, the flattening of the distribution cannot be confirmed and more objects towards the anticentre need to be studied in order to establish the true form of the metallicity gradient.

New integral field spectroscopy (IFS) has been obtained for the nearby metal-poor Wolf-Rayet (WR) galaxy Mrk 178 to examine the spatial correlation between its WR stars and the neighbouring ionized interstellar medium (ISM). The strength of the broad WR features and its low metallicity make Mrk 178 an intriguing object. We have detected the blue and red WR bumps in different locations across the field-of-view (∼ 300 pc × 230 pc) in Mrk 178. The study of the WR content has been extended, for the first time, beyond its brightest star-forming knot uncovering new WR star-clusters. Using SMC/LMC-template WR stars we empirically estimate a minimum of ∼ 20 WR stars within the region sampled. Maps of the spatial distribution of the emission-lines and of the physical-chemical properties of the ionized ISM have been created and analyzed. Here we refine the statistical methodology by Pérez-Montero et al. (2011) to probe the presence of variations in the ISM properties. An error-weighted mean of 12+log(O/H)=7.72 ± 0.01 is taken as the representative oxygen abundance for Mrk 178. A localized N and He enrichment, spatially correlated with WR stars, is suggested by this analysis. Nebular Heiiλ4686 emission is shown to be spatially extended reaching well beyond the location of the WR stars. This spatial offset between WRs and Heii emission can be explained based on the mechanical energy input into the ISM by the WR star winds, and does not rule out WR stars as the Heii ionisation source. We study systematic aperture effects on the detection and measurement of the WR features, using SDSS spectra combined with the power of IFS. In this regard, the importance of targeting low metallicity nearby systems is discussed.

Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.

Context. The study of nebulae around Wolf-Rayet (WR) stars gives us clues about the mass-loss history of massive stars, as well as about the chemical enrichment of the interstellar medium (ISM). Aims. This work aims to search for the observational footprints of the interactions between the ISM and stellar winds in the WR nebula NGC 6888 in order to understand its ionization structure, chemical composition, and kinematics. Methods. We have collected a set of integral field spectroscopy observations across NGC 6888, obtained with PPAK in the optical range performing both 2D and 1D analyses. Attending to the 2D analysis in the northeast part of NGC 6888, we have generated maps of the extinction structure and electron density. We produced statistical frequency distributions of the radial velocity and diagnostic diagrams. Furthermore, we performed a thorough study of integrated spectra in nine regions over the whole nebula. Results. The 2D study has revealed two main behaviours. We have found that the spectra of a localized region to the southwest of this pointing can be represented well by shock models assuming n = 1000 cm −3 , twice solar abundances, and shock velocities from 250 to 400 km s −1 . With the 1D analysis we derived electron densities ranging from <100 to 360 cm −3 . The electron temperature varies from ∼7700 K to ∼10 200 K. A strong variation of up to a factor 10 between different regions in the nitrogen abundance has been found: N/H appears lower than the solar abundance in those positions observed at the edges and very enhanced in the observed inner parts. Oxygen appears slightly underabundant with respect to solar value, whereas the helium abundance is found to be above it. We propose a scenario for the evolution of NGC 6888 to explain the features observed. This scheme consists of a structure of multiple shells: i) an inner and broken shell with material from the interaction between the supergiant and WR shells, presenting an overabundance in N/H and a slight underabundance in O/H; ii) an outer shell very intense in [OIII]λ5007 Å corresponding to the main sequence bubble broken up as a consequence of the collision between supergiant and WR shells. Nitrogen and oxygen do not appear enhanced here, but helium appears enriched; iii) and finally it includes an external and faint shell that surrounds the whole nebula like a thin skin representing the early interaction between the winds from the main sequence star with the ISM for which typical circumstellar abundances are derived.