HRC-I/Chandra X-ray observations towards sigma Orionis

Aims: We investigated the X-ray emission from young stars and brown dwarfs in the sigma Orionis cluster (tau~3 Ma, d~385 pc) and its relation to mass, presence of circumstellar discs, and separation to the cluster centre by taking advantage of the superb spatial resolution of the Chandra X-ray Observatory. Methods: We used public HRC-I/Chandra data from a 97.6 ks pointing towards the cluster centre and complemented them with X-ray data from IPC/Einstein, HRI/ROSAT, EPIC/XMM-Newton, and ACIS-S/Chandra together with optical and infrared photometry and spectroscopy from the literature and public catalogues. On our HRC-I/Chandra data, we measured count rates, estimated X-ray fluxes, and searched for short-term variability. We also looked for long-term variability by comparing with previous X-ray observations. Results: Among the 107 detected X-ray sources, there were 70 cluster stars with known signposts of youth, two young brown dwarfs, 12 cluster member candidates, four field dwarfs, and two galaxies with optical-infrared counterpart. The remaining sources had extragalactic nature. Based on a robust Poisson-chi^2 analysis, nine cluster stars displayed flares or rotational modulation during the HRC-I observations, while other eight stars and one brown dwarf showed long-term X-ray flux variations. We constructed a cluster X-ray luminosity function from O9.5 (~18 Msol) to M6.5 (~0.06 Msol). We found: a tendency of early-type stars in multiple systems or with spectroscopic peculiarities to display X-ray emission, that the two detected brown dwarfs and the least-massive star are among the sigma Orionis objects with the highest L_X/L_J ratios, and that a large fraction of known classical T Tauri stars in the cluster are absent in this and other X-ray surveys. We concluded that dozens X-ray sigma Orionis stars and brown dwarfs are still to be detected [abridged].Comment: A&A, in pres

Deep XMM-Newton observation of the Eta Chamaleontis cluster

The members of the Eta Chamaleontis cluster are in an evolutionary stage in which disks are rapidly evolving. It also presents some peculiarities, such as the large fraction of binaries and accretion disks, probably related with the cluster formation process. Its proximity makes this stellar group an ideal target for studying the relation between X-ray emission and those stellar parameters. The main objective of this work is to determine general X-ray properties of the cluster members in terms of coronal temperature, column density, emission measure, X-ray luminosity and variability. We also aim to establish the relation between the X-ray luminosity of these stars and other stellar parameters, such as binarity and presence of accretion disks. A study of flare energies for each flare event and their relation with some stellar parameters is also performed. We used proprietary data from a deep XMM-Newton observation pointed at the core of the Eta Chamaleontis cluster. Specific software for the reduction of XMM-Newton data was used for the analysis of our observation. For the detection of sources, we used the wavelet-based code PWDetect. General coronal properties were derived from plasma model fitting. We also determined variability of the Eta Chamaleontis members in the EPIC field-of-view. A total of six flare-like events were clearly detected in five different stars. For them, we derived coronal properties during the flare events and pseudo-quiescent state separately. In our observations, stars that underwent a flare event have higher X-ray luminosities in the pseudo-quiescent state than cluster members with similar spectral type with no indications of flaring, independently whether they have an accretion disk or not. Observed flare energies are typical of both pre-main and main-sequence M stars. We detected no difference between flare energies of stars with and without an accretion disk.Comment: Accepted for publication in Astronomy and Astrophysics. 12 pages, 30 individual figure

The magnetically-active, low-mass, triple system WDS 19312+3607

Aims: We investigated in detail the system WDS 19312+3607, whose primary is an active M4.5Ve star previously thought to be young (tau ~ 300-500 Ma) based on high X-ray luminosity. Methods: We collected intermediate- and low-resolution optical spectra taken with 2 m-class telescopes, photometric data from the $B$ to 8 mum bands, and eleven astrometric epochs with a time baseline of over 56 years for the two components in the system, G 125-15 and G 125-14. Results: We derived M4.5V spectral types for both stars, confirmed their common proper motion, estimated the heliocentric distance and projected physical separation, determined the galactocentric space velocities, and deduced a most-probable age older than 600 Ma. We discovered that the primary, G 125-15, is in turn an inflated, double-lined, spectroscopic binary with a short period of photometric variability of P ~ 1.6 d, which we associated to orbital synchronisation. The observed X-ray and Halpha emissions, photometric variability, and abnormal radius and effective temperature of G 125-15 AB indicate strong magnetic activity, possibly due to fast rotation. Besides, the estimated projected physical separation between G 125-15 AB and G 125-14 of about 1200 AU makes WDS 19312+3607 to be one of the widest systems with intermediate M-type primaries. Conclusions: G 125-15 AB is a nearby (d ~ 26 pc), bright (J ~ 9.6 mag), active spectroscopic binary with a single proper-motion companion of the same spectral type at a wide separation. They are thus ideal targets for specific follow-ups to investigate wide and close multiplicity or stellar expansion and surface cooling due to reduced convective efficiency.Comment: A&A, in pres

Chemical abundances of late-type pre-main sequence stars in the σ\sigma-Orionis cluster

The young $\sigma$-Orionis cluster is an important location for understanding the formation and evolution of stars, brown dwarfs, and planetary-mass objects. Its metallicity, although being a fundamental parameter, has not been well determined yet. We present the first determination of the metallicity of nine young late-type stars in $\sigma$-Orionis. Using the optical and near-infrared broadband photometry available in the literature we derive the effective temperatures for these nine cluster stars, which lie in the interval 4300--6500 K (1--3 \Msuno). These parameters are employed to compute a grid of synthetic spectra based on the code MOOG and Kurucz model atmospheres. We employ a $\chi^2$-minimization procedure to derive the stellar surface gravity and atmospheric abundances of Al, Ca, Si, Fe, Ni and Li, using multi-object optical spectroscopy taken with WYFFOS+AF2 at at the William Herschel Telescope ($\lambda/\delta\lambda\sim7500$). The average metallicity of the $\sigma$-Orionis cluster is [Fe/H] $= -0.02\pm0.09\pm0.13$ (random and systematic errors). The abundances of the other elements, except lithium, seem to be consistent with solar values. Lithium abundances are in agreement with the "cosmic" $^7$Li abundance, except for two stars which show a $\log \epsilon(\mathrm{Li})$ in the range 3.6--3.7 (although almost consistent within the error bars). There are also other two stars with $\log \epsilon(\mathrm{Li})\sim 2.75$. We derived an average radial velocity of the $\sigma$-Orionis cluster of $28\pm4$km/s. The $\sigma$-Orionis metallicity is roughly solar.Comment: Accepted for publication in Astronomy and Astrophysic

Optimizing algorithms for thresholding segmentation applied to weed detection on UAV remote images.

En este trabajo se ha buscado la implementación de una alternativa al método de Otsu (1979) desarrollada por Hui-Fuang Ng (2006), el cual maximiza la diferencia entre varianzas espectrales y realiza una búsqueda multiumbral. En el estudio se emplearon imágenes procedentes de vehículos aéreos no tripulados (UAVs) tomadas en cultivos de maíz y girasol. Con una única ejecución del algoritmo en un entorno de análisis orientado a objetos, se discriminan aquellos objetos correspondientes a la fracción vegetal del suelo desnudo y se estima un umbral diferenciador entre cultivo y malas hierbas que contribuya a un subsiguiente proceso de clasificación. La técnica de Hui-Fuang detectó un mayor porcentaje de vegetación en todos los casos estudiados, oscilando el incremento entre un 3% y un 20%.This works aimed to implement an alternative to Otsu’s method (1979) developed by Hui- Fuang Ng (2006), which maximizes the difference between spectral variances and performs a multithreshold seeking. Unmanned aerial images taken in maize and sunflower crops were used in the research. In a single algorithm execution applied to an Object Based Image Analysis environment, the objects corresponding to both the vegetation fraction and bare soil are discriminated and a threshold to separate crop from weeds was also estimated, making easier a subsequent classification process. Fui-Huang’s technique provides a higher percentage of vegetation detection in all the cases, with an improvement which ranges from 3% to 20%

Insect Diversity of the Lower Montane Evergreen Forest of the Western Andes Mountain Range: Cascada Chilicay and Suncamal

Biological research in the low montane evergreen forests of Ecuador focuses on ecological and botanical aspects, while knowledge of the entomofauna of these areas is almost nil. In February 2022, sampling was carried out during the dry season for 15 days, using direct and indirect capture methods (tapping, sieving, and light traps) in two waterfalls of the low montane evergreen forest of the western Andean Cordillera: Chilicay and Suncamal waterfalls, with the objective of identifying the composition of the terrestrial insect fauna at the family level. Two orders and 21 families were recorded, among which the families Carabidae and Noctuidae represented the highest percentage of the total abundance. Although preliminary, this work constitutes the first contribution to the knowledge of the entomofauna of this ecosystem. Keywords: biodiversity, conservation, entomofauna, insects. Resumen Las investigaciones biológicas en los bosques siempreverdes montanos bajos de Ecuador, se centran en aspectos ecológicos y botánicos, mientras que el conocimiento de la entomofauna de estas zonas es escaso. En febrero de 2022, en la época seca y durante 15 días, utilizando métodos de captura directa e indirecta (golpeteo, tamizado y trampas de luz), se realizaron muestreos en dos cascadas del Bosque siempreverde montano bajo de la cordillera occidental de los Andes: Cascada Chilicay y Suncamal, con el objetivo de identificar la composición de la fauna de insectos terrestres a nivel de familia. Se registraron dos órdenes y 21 familias, entre las cuales, las familias Carabidae y Noctuidae representaron el mayor porcentaje de la abundancia total. Aunque en forma preliminar, este trabajo constituye el primer aporte al conocimiento de la entomofauna de este ecosistema. Palabras Clave: Biodiversidad, conservación, entomofauna, insectos

Towards an optimum design of wave energy converter arrays through an integrated approach of life cycle performance and operational capacity

Premio ETSI al mejor artículo científico del trimestre. 3a ed. Junio 2018 -Artículo subido a idUS con permiso de su primer autor (López-Ruiz, Alejandro), que proporciona las versiones preprint y postprint.Over the last few decades, several efforts have been made to develop an alternative and sustainable energy source from wind waves. To achieve financial sustainability of this technology, most of the research has focused on analyzing facilities composed of several wave energy converters (WECs) arrays instead of isolated ones. Although the interaction between devices and its implications on the performance of the facilities have been studied previously, these works considered only certain combinations of sea states, limiting the applicability of the results. This work applies a new methodology based on statistical methods to assess the performance of different WEC array distributions during their entire life-cycle in an efficient way, using downscaling techniques and advanced numerical modeling to propagate the wave climate. The results obtained during the hindcasting life-cycle are used to analyze the maintenance and operation capabilities of the different alternatives of arrays defined for the WEC facility. The interactions between devices and their efficiency considering the associated impact are also quantified. The assessment of these efficiencies during the complete life-cycle of the devices is highly valuable tool for promoters and coastal managers to evaluate different WEC array alternatives. The entire process was applied to a hypothetical array location in the Gulf of Cádiz (southwestern Spain), where three different array distributions were defined. The results show that the distance between WECs is a key parameter that controls the potential energy production, the efficiency of the facility and the interactions between several devices.Ministerio de Economía y Competitividad BES-2013-062617Universidad de Sevill

Towards an optimum design of wave energy converter arrays through an integrated approach of life cycle performance and operational capacity

Premio ETSI al mejor artículo científico del trimestre. 3a ed. Junio 2018 -Artículo subido a idUS con permiso de su primer autor (López-Ruiz, Alejandro), que proporciona las versiones preprint y postprint.Over the last few decades, several efforts have been made to develop an alternative and sustainable energy source from wind waves. To achieve financial sustainability of this technology, most of the research has focused on analyzing facilities composed of several wave energy converters (WECs) arrays instead of isolated ones. Although the interaction between devices and its implications on the performance of the facilities have been studied previously, these works considered only certain combinations of sea states, limiting the applicability of the results. This work applies a new methodology based on statistical methods to assess the performance of different WEC array distributions during their entire life-cycle in an efficient way, using downscaling techniques and advanced numerical modeling to propagate the wave climate. The results obtained during the hindcasting life-cycle are used to analyze the maintenance and operation capabilities of the different alternatives of arrays defined for the WEC facility. The interactions between devices and their efficiency considering the associated impact are also quantified. The assessment of these efficiencies during the complete life-cycle of the devices is highly valuable tool for promoters and coastal managers to evaluate different WEC array alternatives. The entire process was applied to a hypothetical array location in the Gulf of Cádiz (southwestern Spain), where three different array distributions were defined. The results show that the distance between WECs is a key parameter that controls the potential energy production, the efficiency of the facility and the interactions between several devices.Ministerio de Economía y Competitividad BES-2013-062617Universidad de Sevill

Stars and brown dwarfs in the sigma Orionis cluster: the Mayrit catalogue

The young sigma Orionis cluster is an indispensable basis for understanding the formation and evolution of stars, brown dwarfs and planetary-mass objects. Our knowledge of its stellar population is, however, incomplete. I present the Mayrit catalogue, that comprises most of the stars and high-mass brown dwarfs of the cluster. The basis of this work is an optical-near infrared correlation between the 2MASS and DENIS catalogues in a circular area of radius 30 arcmin centred on the OB-type binary sigma Ori AB. The analysis is supported on a bibliographic search of confirmed cluster members with features of youth and on additional X-ray, mid-infrared and astrometric data. I list 241 sigma Orionis stars and brown dwarfs with known features of youth, 97 candidate cluster members (40 are new) and 115 back- and foreground sources in the survey area. The 338 cluster members and member candidates constitute the Mayrit catalogue. This catalogue is a suitable input for studying the spatial ditribution, multiplicity, properties and frequency of discs and the complete mass function of sigma Orionis.Comment: accepted for publication in A&A, section 14. Online catalogs and dat