Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Fabry–Pérot etalons illuminated with collimated beams have been analytically characterized in detail since their invention. Meanwhile, most of the features of etalons located in telecentric planes have been studied only numerically, despite the wide use of this configuration in astrophysical instrumentation for decades. In this work we present analytical expressions for the transmitted electric field and its derivatives that are valid for etalons placed in slow telecentric beams, like the ones commonly employed in solar instruments. We use the derivatives to infer the sensitivity of the electric field to variations in the optical thickness for different reflectivities and apertures of the incident beam, and we compare them to the collimated case. This allows us to estimate the wavefront degradation produced by roughness errors on the surfaces of the Fabry–Pérot etalons and to establish the maximum allowed rms value of the cavity irregularities across the footprint of the incident beam on the etalons that ensures diffraction-limited performance. We also evaluate the wavefront degradation intrinsic to these mounts, which is produced only by the finite aperture of the beam and that must be added to the one produced by defects. Finally, we discuss the differences in performance of telecentric and collimated etalon-based instruments and we generalize our formulation to anisotropic etalons.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this study, we extend the prior interstellar pickup ion (PUI) observations from the Solar Wind Around Pluto (SWAP) instrument on New Horizons out to nearly 47 au—essentially halfway to the termination shock in the upwind direction. We also provide significantly improved analyses of these and prior observations, including incorporating a cooling index, <jats:italic>α</jats:italic>, to characterize the nonadiabatic heating of PUI distributions. We find that the vast majority (93.6%) of all distributions show additional heating above adiabatic cooling. Speed jumps indicate compressional waves and shocks with associated enhancements in core solar wind and PUI densities and temperatures. Interestingly, additional heating of the PUIs as indicated by a peak in the cooling index follows the jumps by about a week. We characterize nearly continuous solar wind and H<jats:sup>+</jats:sup> PUI data over ∼22–47 au, producing radial gradients, “fiducial” values at 45 au—halfway to the nominal upstream termination shock—for direct comparison to models, and extrapolated values at the shock. These termination shock values are <jats:italic>n</jats:italic> <jats:sub>PUI</jats:sub> = (4.1 ± 0.6) × 10<jats:sup>−4</jats:sup> cm<jats:sup>−3</jats:sup>, <jats:italic>T</jats:italic> <jats:sub>PUI</jats:sub> = (5.0 ± 0.4) × 10<jats:sup>6</jats:sup> K, <jats:italic>P</jats:italic> <jats:sub>PUI</jats:sub> = 30 ± 4 fPa, <jats:italic>α</jats:italic> = 2.9 ± 0.2, <jats:italic>n</jats:italic> <jats:sub>PUI</jats:sub>/<jats:italic>n</jats:italic> <jats:sub>Total</jats:sub> = 0.24 ± 0.02, <jats:italic>T</jats:italic> <jats:sub>PUI</jats:sub>/<jats:italic>T</jats:italic> <jats:sub>SW</jats:sub> = 716 ± 124, <jats:italic>P</jats:italic> <jats:sub>PUI</jats:sub>/<jats:italic>P</jats:italic> <jats:sub>SW</jats:sub> = 173 ± 32, <jats:italic>P</jats:italic> <jats:sub>PUI</jats:sub>/<jats:italic>P</jats:italic> <jats:sub>SW − Dyn</jats:sub> = 0.14 ± 0.01. The PUI thermal pressure exceeds by more than an order of magnitude the thermal solar wind and magnetic pressures in the outer heliosphere. SWAP provides the first and only direct observations of interstellar PUIs in the outer heliosphere, which are critical for both inferring the plasma conditions at the termination shock and understanding PUI-mediated shocks in general. This study examines these observations and serves as the citable reference for these critical data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we present a systematic search for stellar groups in the Taurus field by applying the DBSCAN algorithm to the data from Gaia DR2. We find 22 groups, consisting of 8 young groups (Groups 1–8) at ages of 2–4 Myr and distances of ∼130–170 pc, and 14 old groups (Groups 9–22) at ages of 8–49 Myr and distances of ∼110–210 pc. We characterize the disk properties of group members and find 19 new disk-bearing stars, 8 of which are in the young groups with 11 others belonging to the comparatively old groups at the ages of 8–11 Myr. We characterize the accretion properties of the group members with H<jats:italic>α</jats:italic> emission lines in their Large Sky Area Multi-Object Fibre Spectroscopic Telescope spectra, and discover one source in Group 10 at an age of 10 Myr which still shows accretion activity. We investigate the kinematic relations among the old groups, find that Group 9 is kinematically related to the known Taurus members, and exclude any kinematic relations between Groups 10–22 and the known Taurus members.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report calculations of photoionization cross sections for hydrogen atoms in white-dwarf magnetic fields. The calculations were implemented using the adiabatic-basis-expansion method and the coupled-channel theory, which are valid for low and high magnetic fields, respectively. The magnetic fields span over a typical white-dwarf strength regime from 23.5 to 2350 MG. Lyman and Balmer continuum spectra for bound–free transitions in magnetic white-dwarf stars are presented with various field strengths. The current results are compared with those from the complex-rotation method. Excellent agreement is shown in the energy region away from Landau thresholds, but the pronounced discrepancies are found in the small vicinity below Landau thresholds. The agreement shown illustrates the reliability of these two theoretical approaches used, while the discrepancies should be attributed to the limitation of the complex-rotation method. The photoionization cross sections presented here should be applicable to the analyses of continuum spectra and their polarization properties observed in the atmospheres of hydrogen-dominated magnetic white dwarfs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Inference of the physical properties of stellar populations from observed photometry and spectroscopy is a key goal in the study of galaxy evolution. In recent years, the quality and quantity of the available data have increased, and there have been corresponding efforts to increase the realism of the stellar population models used to interpret these observations. Describing the observed galaxy spectral energy distributions in detail now requires physical models with a large number of highly correlated parameters. These models do not fit easily on grids and necessitate a full exploration of the available parameter space. We present <jats:sc>Prospector</jats:sc>, a flexible code for inferring stellar population parameters from photometry and spectroscopy spanning UV through IR wavelengths. This code is based on forward modeling the data and Monte Carlo sampling the posterior parameter distribution, enabling complex models and exploration of moderate dimensional parameter spaces. We describe the key ingredients of the code and discuss the general philosophy driving the design of these ingredients. We demonstrate some capabilities of the code on several data sets, including mock and real data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a case study of solar flare forecasting by means of metadata feature time series, by treating it as a prominent class-imbalance and temporally coherent problem. Taking full advantage of pre-flare time series in solar active regions is made possible via the Space Weather Analytics for Solar Flares (SWAN-SF) benchmark data set, a partitioned collection of multivariate time series of active region properties comprising 4075 regions and spanning over 9 yr of the Solar Dynamics Observatory period of operations. We showcase the general concept of temporal coherence triggered by the demand of continuity in time series forecasting and show that lack of proper understanding of this effect may spuriously enhance models’ performance. We further address another well-known challenge in rare-event prediction, namely, the class-imbalance issue. The SWAN-SF is an appropriate data set for this, with a 60:1 imbalance ratio for GOES M- and X-class flares and an 800:1 imbalance ratio for X-class flares against flare-quiet instances. We revisit the main remedies for these challenges and present several experiments to illustrate the exact impact that each of these remedies may have on performance. Moreover, we acknowledge that some basic data manipulation tasks such as data normalization and cross validation may also impact the performance; we discuss these problems as well. In this framework we also review the primary advantages and disadvantages of using true skill statistic and Heidke skill score, two widely used performance verification metrics for the flare-forecasting task. In conclusion, we show and advocate for the benefits of time series versus point-in-time forecasting, provided that the above challenges are measurably and quantitatively addressed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We describe the Dark Energy Survey (DES) photometric data set assembled from the first three years of science operations to support DES Year 3 cosmologic analyses, and provide usage notes aimed at the broad astrophysics community. <jats:monospace>Y3</jats:monospace> <jats:monospace>GOLD</jats:monospace> improves on previous releases from DES, <jats:monospace>Y1</jats:monospace> <jats:monospace>GOLD</jats:monospace>, and Data Release 1 (DES DR1), presenting an expanded and curated data set that incorporates algorithmic developments in image detrending and processing, photometric calibration, and object classification. <jats:monospace>Y3</jats:monospace> <jats:monospace>GOLD</jats:monospace> comprises nearly 5000 deg<jats:sup>2</jats:sup> of <jats:italic>grizY</jats:italic> imaging in the south Galactic cap, including nearly 390 million objects, with depth reaching a signal-to-noise ratio ∼10 for extended objects up to <jats:italic>i</jats:italic> <jats:sub>AB</jats:sub> ∼ 23.0, and top-of-the-atmosphere photometric uniformity &lt;3 mmag. Compared to DR1, photometric residuals with respect to Gaia are reduced by 50%, and per-object chromatic corrections are introduced. <jats:monospace>Y3</jats:monospace> <jats:monospace>GOLD</jats:monospace> augments DES DR1 with simultaneous fits to multi-epoch photometry for more robust galactic color measurements and corresponding photometric redshift estimates. <jats:monospace>Y3</jats:monospace> <jats:monospace>GOLD</jats:monospace> features improved morphological star–galaxy classification with efficiency &gt;98% and purity &gt;99% for galaxies with 19 &lt; <jats:italic>i</jats:italic> <jats:sub>AB</jats:sub> &lt; 22.5. Additionally, it includes per-object quality information, and accompanying maps of the footprint coverage, masked regions, imaging depth, survey conditions, and astrophysical foregrounds that are used to select the cosmologic analysis samples.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed analysis of the behavior of the triaxial Schwarzschild orbit superposition method near the axisymmetric limit. Orbit superposition modeling is the primary method used to determine dynamical masses of supermassive black holes (<jats:italic>M</jats:italic> <jats:sub>BH</jats:sub>) in nearby galaxies; however, prior studies have reported conflicting results when comparing the outcome from axisymmetric orbit codes with that from a triaxial orbit code in the axisymmetric limit. We show that in order to achieve (oblate) axisymmetry in a triaxial code, care needs to be taken to axisymmetrize the short-axis tube orbits and to exclude both the long-axis tube and box orbits from the orbit library. Using up to 12 Gauss–Hermite moments of the line-of-sight velocity distributions as constraints, we demonstrate the effects of orbit types on the best-fit <jats:italic>M</jats:italic> <jats:sub>BH</jats:sub> in orbit modeling of the massive elliptical galaxy NGC 1453 reported in Liepold et al. In addition, we verify the efficacy of our updated code on a mock galaxy data set. We identify a subset of slowly precessing quasi-planar orbits for which the typical integration times can be insufficient to fully capture the equilibrium orbital behavior in both axisymmetric and triaxial systems with central black holes. Further investigation is needed for a more reliable treatment of these orbits.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>As a follow-up to the optical spectroscopic campaign aimed at achieving completeness in the Third Catalog of Hard Fermi-LAT Sources (3FHL), we present here the results of a sample of 28 blazars of an uncertain type observed using the 4 m telescope at Cerro Tololo Inter-American Observatory in Chile. Out of these 28 sources, we find that 25 are BL Lacertae objects (BL Lacs) and 3 are flat-spectrum radio quasars (FSRQs). We measure redshifts or lower limits for 16 of these blazars, and it is observed that the 12 remaining blazars have featureless optical spectra. These results are part of a more extended optical spectroscopy follow-up campaign for 3FHL blazars, where, until now, 51 blazars of an uncertain type have been classified into BL Lac and FSRQ categories. Furthermore, this campaign has resulted in redshift measurements and lower limits for 15 of these sources. Our results contribute toward attaining a complete sample of blazars above 10 GeV, which then will be crucial in extending our knowledge on blazar emission mechanisms and the extragalactic background light.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>There have been many studies aiming to reveal the origins of the star–gas misalignment found in galaxies, but there still is a lack of understanding of the contribution from each formation channel candidate. We aim to answer the question by investigating the misaligned galaxies in the Horizon-AGN simulation. There are 27,903 galaxies of stellar mass <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> &gt; 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> in our sample, of which 5984 are in a group in the halo mass of <jats:italic>M</jats:italic> <jats:sub>200</jats:sub> &gt; 10<jats:sup>12</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We have identified four main formation channels of misalignment and quantified their levels of contribution: mergers (35%), interaction with nearby galaxies (23%), interaction with dense environments or their central galaxies (21%), and secular evolution, including smooth accretion from neighboring filaments (21%). We found in the simulation that the gas, rather than stars, is typically more vulnerable to dynamical disturbances; hence, misalignment formation is mainly due to the change in the rotational axis of the gas rather than stars, regardless of the origin. We have also inspected the lifetime (duration) of the misalignment. The decay timescale of the misalignment shows a strong anticorrelation with the kinematic morphology (<jats:italic>V</jats:italic>/<jats:italic>σ</jats:italic>) and the cold gas fraction of the galaxy. The misalignment has a longer lifetime in denser regions, which is linked with the environmental impact on the host galaxy. There is a substantial difference in the length of the misalignment lifetime depending on the origin, and it can be explained by the magnitude of the initial position angle offset and the physical properties of the galaxies.</jats:p>