1,689 research outputs found
Chemical compositions of stars in two stellar streams from the Galactic thick disk
We present abundances for 20 elements for stars in two stellar streams
identified by Arifyanto & Fuchs (2006, A&A, 449, 533): 18 stars from the
Arcturus stream and 26 from a new stream, which we call AF06 stream, both from
the Galactic thick disk. Results show both streams are metal-poor and very old
(1014 Gyrs) with kinematics and abundances overlapping with the properties
of local field thick disk stars. Both streams exhibit a range in metallicity
but with relative elemental abundances that are identical to those of thick
disk stars of the same metallicity. These results show that neither stream can
result from dissolution of an open cluster. It is highly unlikely that either
stream represents tidal debris from an accreted satellite galaxy. Both streams
most probably owe their origin to dynamical perturbations within the Galaxy.Comment: 10 figures, Accepted for publication in MNRA
Missing Features Reconstruction Using a Wasserstein Generative Adversarial Imputation Network
Missing data is one of the most common preprocessing problems. In this paper,
we experimentally research the use of generative and non-generative models for
feature reconstruction. Variational Autoencoder with Arbitrary Conditioning
(VAEAC) and Generative Adversarial Imputation Network (GAIN) were researched as
representatives of generative models, while the denoising autoencoder (DAE)
represented non-generative models. Performance of the models is compared to
traditional methods k-nearest neighbors (k-NN) and Multiple Imputation by
Chained Equations (MICE). Moreover, we introduce WGAIN as the Wasserstein
modification of GAIN, which turns out to be the best imputation model when the
degree of missingness is less than or equal to 30%. Experiments were performed
on real-world and artificial datasets with continuous features where different
percentages of features, varying from 10% to 50%, were missing. Evaluation of
algorithms was done by measuring the accuracy of the classification model
previously trained on the uncorrupted dataset. The results show that GAIN and
especially WGAIN are the best imputers regardless of the conditions. In
general, they outperform or are comparative to MICE, k-NN, DAE, and VAEAC.Comment: Preprint of the conference paper (ICCS 2020), part of the Lecture
Notes in Computer Scienc
Planetary Candidates Observed by Kepler. VIII. A Fully Automated Catalog With Measured Completeness and Reliability Based on Data Release 25
We present the Kepler Object of Interest (KOI) catalog of transiting
exoplanets based on searching four years of Kepler time series photometry (Data
Release 25, Q1-Q17). The catalog contains 8054 KOIs of which 4034 are planet
candidates with periods between 0.25 and 632 days. Of these candidates, 219 are
new and include two in multi-planet systems (KOI-82.06 and KOI-2926.05), and
ten high-reliability, terrestrial-size, habitable zone candidates. This catalog
was created using a tool called the Robovetter which automatically vets the
DR25 Threshold Crossing Events (TCEs, Twicken et al. 2016). The Robovetter also
vetted simulated data sets and measured how well it was able to separate TCEs
caused by noise from those caused by low signal-to-noise transits. We discusses
the Robovetter and the metrics it uses to sort TCEs. For orbital periods less
than 100 days the Robovetter completeness (the fraction of simulated transits
that are determined to be planet candidates) across all observed stars is
greater than 85%. For the same period range, the catalog reliability (the
fraction of candidates that are not due to instrumental or stellar noise) is
greater than 98%. However, for low signal-to-noise candidates between 200 and
500 days around FGK dwarf stars, the Robovetter is 76.7% complete and the
catalog is 50.5% reliable. The KOI catalog, the transit fits and all of the
simulated data used to characterize this catalog are available at the NASA
Exoplanet Archive.Comment: 61 pages, 23 Figures, 9 Tables, Accepted to The Astrophysical Journal
Supplement Serie
Fox : a un año de la alternancia
Reflexiones crĂticas desde diversas disciplinas de las ciencias sociales acerca del primer año de gobierno de Vicente Fox Quesada. Entre los rubros que se analizan estĂĄn: la polĂtica cultural, el sector rural, los jĂłvenes, los derechos humanos, la cultura indĂgena y la seguridad pĂșblica.ITESO, A.C
The Gaia-ESO Survey::chemical signatures of rocky accretion in a young solar-type star
It is well known that newly formed planetary systems undergo processes of
orbital reconfiguration and planetary migration. As a result, planets or
protoplanetary objects may accrete onto the central star, being fused and mixed
into its external layers. If the accreted mass is sufficiently high and the
star has a sufficiently thin convective envelope, such events may result in a
modification of the chemical composition of the stellar photosphere in an
observable way, enhancing it with elements that were abundant in the accreted
mass. The recent Gaia-ESO Survey observations of the 10-20 Myr old Gamma
Velorum cluster have enabled identifying a star that is significantly enriched
in iron with respect to other cluster members. In this Letter we further
investigate the abundance pattern of this star, showing that its abundance
anomaly is not limited to iron, but is also present in the refractory elements,
whose overabundances are correlated with the condensation temperature. This
finding strongly supports the hypothesis of a recent accretion of rocky
material.Comment: Accepted for publicatio
Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
Recent progress in studies of globular clusters has shown that they are not
simple stellar populations, being rather made of multiple generations. Evidence
stems both from photometry and spectroscopy. A new paradigm is then arising for
the formation of massive star clusters, which includes several episodes of star
formation. While this provides an explanation for several features of globular
clusters, including the second parameter problem, it also opens new
perspectives about the relation between globular clusters and the halo of our
Galaxy, and by extension of all populations with a high specific frequency of
globular clusters, such as, e.g., giant elliptical galaxies. We review progress
in this area, focusing on the most recent studies. Several points remain to be
properly understood, in particular those concerning the nature of the polluters
producing the abundance pattern in the clusters and the typical timescale, the
range of cluster masses where this phenomenon is active, and the relation
between globular clusters and other satellites of our Galaxy.Comment: In press (The Astronomy and Astrophysics Review
Ayotzinapa y la crisis del estado neoliberal mexicano
ÂżQuĂ© pasĂł en Ayotzinapa? Es la pregunta que surgiĂł el 26 de septiembre de 2014, que no encuentra una respuesta satisfactoria pese a la intervenciĂłn de actores de distintas instancias, niveles y nacionalidades, y al esbozo de mĂșltiples hipĂłtesis sobre los enfrentamientos registrados en Iguala, Guerrero, que derivaron en la muerte de varias personas y la desapariciĂłn de 43 estudiantes de la Normal Rural âIsidro Burgosâ, en una tragedia que evidenciĂł la crisis que atraviesa el estado mexicano y que afecta a todo el paĂs.
A partir de lo acontecido en Ayotzinapa y con base en la teorĂa general de los campos de Pierre Bourdieu y su propuesta de anĂĄlisis teĂłrico metodolĂłgico sobre el estado, en esta obra se realiza un anĂĄlisis de la prĂĄctica sistemĂĄtica y generalizada de las desapariciones forzadas en MĂ©xico, con el fin de ofrecer otra manera de comprender el entretejido polĂticoâeconĂłmicoâsocial que hace posible este grave fenĂłmeno, que desgarra tanto a familias como a la comunidad.
La herida abierta por Ayotzinapa sangra y el objetivo Ășltimo de este libro es contribuir a evitar que se cierre en tanto no se responda la interrogante de quĂ© pasĂł ahĂ y que crĂmenes de lesa humanidad como este sigan aconteciendo en MĂ©xico.ITESO, A.C
âTourism, water, and genderââAn international review of an unexplored nexus
This international literature review of the tourismâwater nexus identifies a gender gap. Tourism development can affect water supply both quantitatively and qualitatively. Many regions will face considerable problems of water availability and quality, affecting their tourism sector and increasing competition with local residents, and other industries especially agriculture. This international review of literature explores the tourismâwater nexus, comparing and contrasting literature published in English, Chinese, and Spanish. Securing access to safe water for continued tourism development is a common theme and the vast majority of work has focused on hotels including water pricing, water-saving practices and innovative management methods. In all continents, struggles are apparent, and the unsustainability of tourism is having impacts on water quantity and quality. This article identifies significant gaps in the literature including climate change, the energy-water nexus, and the links with the Sustainable Development Goals. Furthermore, studies from a gendered perspective are minimal and the potential for areas of further gendered studies within the tourismâwater nexus are highlighted including intersectionality, water insecurity and sanitation, tourism and gender based violence, and additional unpaid care work
Fast demographic traits promote high diversification rates of Amazonian trees.
The Amazon rain forest sustains the world's highest tree diversity, but it remains unclear why some clades of trees are hyperdiverse, whereas others are not. Using dated phylogenies, estimates of current species richness and trait and demographic data from a large network of forest plots, we show that fast demographic traits ? short turnover times ? are associated with high diversification rates across 51 clades of canopy trees. This relationship is robust to assuming that diversification rates are either constant or decline over time, and occurs in a wide range of Neotropical tree lineages. This finding reveals the crucial role of intrinsic, ecological variation among clades for understanding the origin of the remarkable diversity of Amazonian trees and forests
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