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Aims. The outer atmosphere of K giants shows thermally inhomogeneous structures consisting of the hot chromospheric gas and the cool molecular gas. We present spectro-interferometric observations of the multicomponent outer atmosphere of the well-studied K1.5 giant Arcturus (α Boo) in the CO first overtone lines near 2.3 µm. Methods. We observed Arcturus with the AMBER instrument at the Very Large Telescope Interferometer (VLTI) at 2.28-2.31 µm with a spectral resolution of 12 000 and at projected baselines of 7.3, 14.6, and 21.8 m.Results. The high spectral resolution of the VLTI/AMBER instrument allowed us to spatially resolve Arcturus in the individual CO lines. Comparison of the observed interferometric data with the MARCS photospheric model shows that the star appears to be significantly larger than predicted by the model. It indicates the presence of an extended component that is not accounted for by the current photospheric models for this well-studied star. We found out that the observed AMBER data can be explained by a model with two additional CO layers above the photosphere. The inner CO layer is located just above the photosphere, at 1.04 ± 0.02 R ⋆ , with a temperature of 1600 ± 400 K and a CO column density of 10 20±0.3 cm −2 . On the other hand, the outer CO layer is found to be as extended as to 2.6 ± 0.2 R ⋆ with a temperature of 1800 ± 100 K and a CO column density of 10 19±0.15 cm −2 . Conclusions. The properties of the inner CO layer are in broad agreement with those previously inferred from the spatially unresolved spectroscopic analyses. However, our AMBER observations have revealed that the quasi-static cool molecular component extends out to 2-3 R ⋆ , within which region the chromospheric wind steeply accelerates.

Context. The open cluster (OC) NGC 2453 is of particular importance since it has been considered to host the planetary nebula (PN) NGC 2452, however their distances and radial velocities are strongly contested. Aims. In order to obtain a complete picture of the fundamental parameters of the OC NGC 2453, 11 potential members were studied. The results allowed us to resolve the PN NGC 2452 membership debate. Methods. Radial velocities for the 11 stars in NGC 2453 and the PN were measured and matched with Gaia data release 2 (DR2) to estimate the cluster distance. In addition, we used deep multi-band UBVRI photometry to get fundamental parameters of the cluster via isochrone fitting on the most likely cluster members, reducing inaccuracies due to field stars. Results. The distance of the OC NGC 2453 (4.7 ± 0.2 kpc) was obtained with an independent method solving the discrepancy reported in the literature. This result is in good agreement with an isochrone fitting of 40–50 Myr. On the other hand, the radial velocity of NGC 2453 (78 ± 3 km s−1) disagrees with the velocity of NGC 2452 (62 ± 2 km s−1). Our results show that the PN is a foreground object in the line of sight. Conclusions. Due to the discrepancies found in the parameters studied, we conclude that the PN NGC 2452 is not a member of the OC NGC 2453.

Seaweed exploitation in Chile has increased over the last decades, resulting in a reduction of seaweeds landings and the overharvesting of natural beds. In response, ecological baselines for their sustainable exploitation and the development of seaweed aquaculture have been implemented. In recent years, the culture of commercial red seaweed Chondracanthus chamissoi has been developed experimentally by spore and vegetative reproduction. These methods are facilitated by the formation of secondary attachment discs (SADs), generated to fasten the inoculated algae to substrates. In this study, the vegetative propagation was carried over an artificial substrate installed in a sea bottom culture system. The biomass yields, total amount of epiphytes, length of new thalli and number of SADs, per season and culture times (1, 2, 3 and 4 months) are reviewed in this work. Chondracanthus chamissoi showed growth under all treatments, with a maximum accumulated biomass of 60 g m−1, recorded in summer, and with no significant differences in biomass yield reported in autumn and spring seasons. A similar pattern was observed for epiphyte biomass, while the greatest SAD number and thalli lengths were recorded in winter.