A deep narrowband survey for planetary nebulae at the outskirts of M33

Context: Planetary nebulae (PNe) are excellent tracers of stellar populations with low surface brightness, and therefore provide a powerful method to detect and explore the rich system of substructures discovered around the main spiral galaxies of the Local Group. Aims: We searched the outskirts of the Local Group spiral galaxy M33 (the Triangulum) for PNe to gain new insights into the extended stellar substructure on the northern side of the disc and to study the existence of a faint classical halo. Methods: The search is based on wide field imaging covering a 4.5 square degree area out to a maximum projected distance of about 40 kpc from the centre of the galaxy. The PN candidates are detected by the combination of images obtained in narrowband filters selecting the [OIII]$\lambda5007\AA$ and H$\alpha$ + [NII] nebular lines and in the continuum g' and r' broadband filters. Results:Inside the bright optical disc of M33, eight new PN candidates were identified, three of which were spectroscopically confirmed. No PN candidates were found outside the limits of the disc. Fourteen additional sources showing [OIII] excess were also discovered. Conclusions:The absence of bright PN candidates in the area outside the galaxy disc covered by this survey sets an upper limit to the luminosity of the underlying population of $\mathrm{\sim1.6\cdot10^{7}L_{\odot}}$, suggesting the lack of a massive classical halo, which is in agreement with the results obtained using the RGB population.Comment: 13 pages, 18 figure

A new key locality for the Pliocene vertebrate record of Europe : the Camp dels Ninots maar (NE Spain)

A new Pliocene Konservat-Lagerstätte in north-eastern Spain is described here for the first time. It is referred to as Camp dels Ninots. The particular geological conditions of the site, which correspond to lacustrine sedimentation in a maar, made it ideal for the preservation of fossils. At present, five large mammal skeletons in anatomical connection have been recovered: three individuals of Alephis tigneresi, one of Stephanorhinus jeanvireti and one of Tapirus arvernenis, as well as isolated remains. A minimum of five individuals of the chelonian Mauremys leprosa have been recovered, some of them in anatomical connection. The rodent Apodemus atavus, the amphibians cf. Pleurodeles sp., Lissotriton aff. helveticus and Pelophylax cf. perezi and freshwater fishes (Leuciscus ?) complete the vertebrate assemblage uncovered up to the present time. The coexistence of Stephanorhinus jeanvireti and Alephis tigneresi suggests an age of about 3.2Ma for the Camp dels Ninots, near the MN15-MN16 transition. The Camp del Ninots fossil record enables one to extend the biogeographic range of some vertebrate taxa, such as Stephanorhinus jeanvireti, Tapirus arvernensis or Mauremys leprosa to the Iberian Peninsula. Taphonomic evidences of the skeletal remains indicates minimal (if any) weathering. Deposition at the lake bottom seems to have taken place in oxygen depleted layers. In this way, Camp dels Ninots is comparable to other remarkable maar sites such as Messel, the Eocene site situated in Germany

High performance LATP thin film electrolytes for all-solid-state microbattery applications

The NASICON superionic solid electrolyte Li1+xAlxTi2-x(PO4)3 (LATP) with 0.3 = x = 0.5 remains one of the most promising solid electrolytes thanks to its good ionic conductivity and outstanding stability in ambient air. Despite the intensive research for bulk systems, there are only very few studies of LATP in a thin film form (thickness < 1 µm) and its implementation in all-solid-state batteries and microbatteries. The following study fills this gap by exploring the properties of high performance LATP thin films fabricated by large-area Pulsed Laser Deposition (PLD). The as-deposited thin films exhibit an ionic conductivity of around 0.5 µS cm-1 at room temperature (comparable to the state-of-the-art of LiPON) which increases to a remarkably high value of 0.1 mS cm-1 after an additional annealing at 800 °C. A possible cause for this significant enhancement in ionic conductivity by two orders of magnitude is the formation of a glassy, intergranular phase. The performance of both as-deposited and annealed LATP films makes them suitable as solid electrolytes, which opens the path to a new family of stable and high performance all-solid-state thin film batteries. This journal is © The Royal Society of Chemistry

Experimental and theoretical assessment of native oxide in the superconducting TaN

In this manuscript, we show through an experimental-computational proof of concept the native oxide formation into superconducting TaN films. First, TaN was synthesized at an ultra-high vacuum system by reactive pulsed laser deposition and characterized in situ by X-ray photoelectron spectroscopy. The material was also characterized ex situ by X-ray diffraction, transmission electron microscopy, and the four-point probe method. It was detected that TaN contained considerable oxygen impurities (up to 26 %O) even though it was grown in an ultra-high vacuum chamber. Furthermore, the impurified TaN evidence a face-centered cubic crystalline structure only and exhibits superconductivity at 2.99 K. To understand the feasibility of the native oxide in TaN, we study the effect of incorporating different amounts of O atoms in TaN using ab-initio calculations. A thermodynamic stability analysis shows that a TaOxN1-x model increases its stability as oxygen is added, demonstrating that oxygen may always be present in TaN, even when obtained at ultra-high vacuum conditions. All analyzed models exhibit metallic behavior. Charge density difference maps reveal that N and O atoms have a higher charge density redistribution than Ta atoms. The electron localization function maps and line profiles indicate that Ta-O and Ta-N bonds are mainly ionic. As expected, stronger ionic behavior is observed in the Ta-O bonds due to the electronegativity difference between O and N atoms. Recent evidence points to superconductivity in bulk TaO, confirming the asseverations of superconductivity in our samples. The results discussed here highlight the importance of considering native oxide when reporting superconductivity in TaN films since the TaO regions formed in the compound may be key to understanding the different critical temperatures reported in the literature.Comment: 23 pages, 7 figure

Direct measurement of stellar angular diameters by the VERITAS Cherenkov Telescopes

The angular size of a star is a critical factor in determining its basic properties. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for optical astronomy due to the modest optical quality of the mirror surface. However, their large mirror area makes them well suited for such high-time-resolution precision photometry measurements. Here we report two occultations of stars observed by the VERITAS Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars' angular diameter at the $\leq0.1$ milliarcsecond scale. This is a resolution never achieved before with optical measurements and represents an order of magnitude improvement over the equivalent lunar occultation method. We compare the resulting stellar radius with empirically derived estimates from temperature and brightness measurements, confirming the latter can be biased for stars with ambiguous stellar classifications.Comment: Accepted for publication in Nature Astronom

Evidence for proton acceleration up to TeV energies based on VERITAS and Fermi-LAT observations of the Cas A SNR

We present a study of $\gamma$-ray emission from the core-collapse supernova remnant Cas~A in the energy range from 0.1GeV to 10TeV. We used 65 hours of VERITAS data to cover 200 GeV - 10 TeV, and 10.8 years of \textit{Fermi}-LAT data to cover 0.1-500 GeV. The spectral analysis of \textit{Fermi}-LAT data shows a significant spectral curvature around $1.3 \pm 0.4_{stat}$ GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from \textit{Fermi}-LAT and VERITAS deviates significantly from a simple power-law, and is best described by a power-law with spectral index of $2.17\pm 0.02_{stat}$ with a cut-off energy of $2.3 \pm 0.5_{stat}$ TeV. These results, along with radio, X-ray and $\gamma$-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and conclude that proton acceleration up to at least 6 TeV is required to explain the observed $\gamma$-ray spectrum. From modeling of the entire multi-wavelength spectrum, a minimum magnetic field inside the remnant of $B_{\mathrm{min}}\approx150\,\mathrm{\mu G}$ is deduced.Comment: 33 pages, 9 Figures, 6 Table

Las acequias de careo de Sierra Nevada (sur de España), un sistema de recarga ancestral en acuíferos de alta montaña

En las partes altas de Sierra Nevada (sur de España) se realiza, desde época andalusí (Edad Media), un Sistema Integrado de Gestión del Agua Subterránea, en el que las acequias de careo constituyen un elemento clave. Estos canales excavados en el terreno están diseñados para recargar las aguas procedentes del deshielo, a lo largo de su recorrido y en distintas zonas concretas, donde hay una mayor permeabilidad del terreno. Una vez que el agua se infiltra en las partes altas de los valles, pasa a circular lentamente por los acuíferos superficiales y surge por ríos y manantiales situados a media ladera. En este trabajo se presentan los resultados conseguidos mediante el monitoreo e investigación hidrogeológica de una cuenca de 68 km2 (cuenca del río Bérchules), situada en Sierra Nevada, donde se aplica la técnica de careo. Los resultados conseguidos han permitido comprobar que el careo aplana el hidrograma de los ríos de alta montaña, reduciendo su componente nival y aumentando la subterránea. Además contribuye a mantener el caudal de los manantiales y los ecosistemas asociados a esta descarga. Su uso en otras zonas de alta montaña permitiría disponer de una excelente herramienta de adaptación al cambio climático.Instituto Geológico y Minero de España, EspañaUniversidad Politécnica de Cataluña, EspañaAgencia de Medio Ambiente y Agua de la Junta de Andalucía, EspañaUniversidad Pablo de Olavide, EspañaConsejería de Medio Ambiente y Ordenación del Territorio, Junta de Andalucía, EspañaPeer reviewe