Delta Scuti (δ Sct) stars are opacity-driven pulsators with masses of 1.5-2.5M⊙, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, withno firm theoretical basis, models predict that the convective envelope in δ Sct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δ Sct star HD 187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted.
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When the Sun is observed in X-ray or extreme ultraviolet wavelengths, hundreds of bright and compact structures with a rounded shape and sizes similar to that of our planet Earth can be easily distinguished in the solar corona. These structures are known as Coronal Bright Points or CBPs and they consist of sets of magnetic loops that connect areas of opposite magnetic polarity on the solar surface. These loops confine the solar plasma and in them, by mechanisms that have been debated for many years among solar physicists, the gas remains with temperatures of several million degrees, emitting
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Active galactic nuclei (AGN) consist of a supermassive black hole fed by the circumnuclear material close to the galaxy center. Around 10% of the AGNs develop a pair of jets that are launched to the interstellar medium at speed close to velocity of light. Blazars are observed when one of the jets points very close to our line of sight, which produce an extraordinary boosting of the emission by relativistic effects. Jets produce electromagnetic emission that varies rapidly and covers from radio waves to gamma rays. The observed light is mostly random without an apparent pattern. The source BL
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In this work we discuss and confront recent results on metallicity variations in the local interstellar medium, obtained from observations of H II regions by our group and neutral clouds (from literature) of the Galactic thin disk, and compare them with recent high-quality metallicity determinations of other tracers of the chemical composition of the interstellar medium as B-type stars, classical Cepheids, and young clusters. We find that the metallicity variations obtained for these last kinds of objects are consistent with each other and with that obtained for H II regions but
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