Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The IRAS Revised Bright Galaxy Sample (RBGS) comprises galaxies and unresolved mergers stronger than <jats:italic>S</jats:italic> = 5.24 Jy at <jats:italic>λ</jats:italic> = 60 <jats:italic>μ</jats:italic>m with Galactic latitudes ∣<jats:italic>b</jats:italic>∣ &gt; 5°. Nearly all are dusty star-forming galaxies whose radio continuum and far-infrared luminosities are proportional to their current rates of star formation. We used the MeerKAT array of 64 dishes to make 5 × 3 minutes snapshot observations at <jats:italic>ν</jats:italic> = 1.28 GHz covering all 298 southern (J2000 <jats:italic>δ</jats:italic> &lt; 0°) RBGS sources identified with external galaxies. The resulting images have <jats:italic>θ</jats:italic> ≈ 7.″5 FWHM resolution and rms fluctuations <jats:italic>σ</jats:italic> ≈ 20 <jats:italic>μ</jats:italic>Jy beam<jats:sup>−1</jats:sup> ≈ 0.26 K low enough to reveal even faint disk emission. The rms position uncertainties are <jats:italic>σ</jats:italic> <jats:sub> <jats:italic>α</jats:italic> </jats:sub> ≈ <jats:italic>σ</jats:italic> <jats:sub> <jats:italic>δ</jats:italic> </jats:sub> ≈ 1″ relative to accurate near-infrared positions, and the image dynamic ranges are DR ≳ 10<jats:sup>4</jats:sup>: 1. Cropped MeerKAT images of all 298 southern RBGS sources are available in FITS format from <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://doi.org/10.48479/dnt7-6q05" xlink:type="simple">10.48479/dnt7-6q05</jats:ext-link>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present far-infrared (FIR) spectroscopy of supernova remnants (SNRs) based on the archival data of the Infrared Space Observatory taken with the Long Wavelength Spectrometer (LWS). Our sample includes previously unpublished profiles of line and continuum spectra for 20 SNRs in the Galaxy and Magellanic Clouds. In several SNRs including G21.5–0.9, G29.7–0.3, the Crab Nebula, and G320.4–1.2, we find evidence for broad [O <jats:sc>i</jats:sc>], [O <jats:sc>iii</jats:sc>], [N <jats:sc>ii</jats:sc>], and [C <jats:sc>ii</jats:sc>] lines with velocity dispersions up to a few 10<jats:sup>3</jats:sup> km s<jats:sup>−1</jats:sup>, indicating that they are associated with high-velocity SN ejecta. Our detection of Doppler-broadened atomic emission lines and a bright FIR continuum hints at the presence of newly formed dust in SN ejecta. For G320.4–1.2, we present the first estimate of an ejecta-dust mass of 0.1–0.2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which spatially coincides with the broad-line emission, by applying a blackbody model fit with components of the SNR and background emission. Our sample includes raster maps of 63 <jats:italic>μ</jats:italic>m, 145 <jats:italic>μ</jats:italic>m [O <jats:sc>i</jats:sc>], and 158 <jats:italic>μ</jats:italic>m [C <jats:sc>ii</jats:sc>] lines toward SNRs Kes 79, CTB 109, and IC 443. Based on these line intensities, we suggest interacting shock types in these SNRs. Finally, we compare our LWS spectra of our sample SNRs with the spectra of several H <jats:sc>ii</jats:sc> regions, and discuss their FIR line intensity ratios and continuum properties. Follow-up observations with modern instruments (e.g., JWST and SOFIA) with higher spatial and spectral resolution are encouraged for an extensive study of the SN ejecta and the SN dust.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The origin of <jats:italic>γ</jats:italic>-ray flares observed from blazars is one of the major mysteries in jet physics. We have attempted to address this problem following a novel spectral energy distribution (SED) fitting technique that explored the flaring patterns identified in the broadband SEDs of two <jats:italic>γ</jats:italic>-ray bright blazars, 3C 279 (<jats:italic>z</jats:italic> = 0.54) and 3C 454.3 (<jats:italic>z</jats:italic> = 0.86), using near-simultaneous radio-to-<jats:italic>γ</jats:italic>-ray observations. For both sources, the <jats:italic>γ</jats:italic>-ray flux strongly correlates with the separation of the SED peaks and the Compton dominance. We propose that spectral hardening of the radiating electron population and/or enhancement of the Doppler factor can naturally explain these observations. In both cases, magnetic reconnection may play a pivotal role in powering the luminous <jats:italic>γ</jats:italic>-ray flares.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A solar active region is a source of disturbance for the Sun–terrestrial space environment and usually causes extreme space weather, such as geomagnetic storms. The main indicator of an active region is sunspots. Certain types of sunspots are related to extreme space weather caused by eruptive events such as coronal mass ejections or solar flares. Thus, the automatic classification of sunspot groups is helpful to predict solar activity quickly and accurately. This paper completed the automatic classification of a sunspot group data set based on the Mount Wilson classification scheme, which contains continuum and magnetogram images provided by the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager SHARP data from 2010 May 1 to 2017 December 12. After applying some data preprocessing steps such as image cropping and data standardization, the features of magnetic type in the data are more obvious, and the amount of data is increased. The processed data are spliced into two frames of single-channel data for the neural network to perform 3D convolution operations. This paper constructs a variety of convolutional neural networks with different structures and numbers of layers, selects 10 models as representatives, and chooses XGBoost, which is commonly used in ensemble-learning algorithms, to fuse the results of independent classification models. We found that XGBoost is an effective way to fuse models, which is proved by the relatively balanced high scores in the three magnetic types. The accuracy of the ensemble model is above 92%. The F1 scores of the magnetic types of Alpha, Beta, and Beta-x reached 0.95, 0.91, and 0.82 respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Our aim is to measure the interstellar <jats:sup>14</jats:sup>N/<jats:sup>15</jats:sup>N ratio across the Galaxy, to establish a standard data set on interstellar ammonia isotope ratios, and to provide new constraints on the Galactic chemical evolution. The (<jats:italic>J</jats:italic>, <jats:italic>K</jats:italic>) = (1, 1), (2, 2), and (3, 3) lines of <jats:sup>14</jats:sup>NH<jats:sub>3</jats:sub> and <jats:sup>15</jats:sup>NH<jats:sub>3</jats:sub> were observed with the Shanghai Tianma 65 m radio telescope (TMRT) and the Effelsberg 100 m telescope toward a large sample of 210 sources. One hundred fourty-one of these sources were detected by the TMRT in <jats:sup>14</jats:sup>NH<jats:sub>3</jats:sub>. Eight of them were also detected in <jats:sup>15</jats:sup>NH<jats:sub>3</jats:sub>. For 10 of the 36 sources with strong NH<jats:sub>3</jats:sub> emission, the Effelsberg 100 m telescope successfully detected their <jats:sup>15</jats:sup>NH<jats:sub>3</jats:sub>(1, 1) lines, including 3 sources (G081.7522, W51D, and Orion-KL) with detections by the TMRT telescope. Thus, a total of 15 sources are detected in both the <jats:sup>14</jats:sup>NH<jats:sub>3</jats:sub> and <jats:sup>15</jats:sup>NH<jats:sub>3</jats:sub> lines. Line and physical parameters for these 15 sources are derived, including optical depths, rotation and kinetic temperatures, and total column densities. <jats:sup>14</jats:sup>N/<jats:sup>15</jats:sup>N isotope ratios were determined from the <jats:sup>14</jats:sup>NH<jats:sub>3</jats:sub>/<jats:sup>15</jats:sup>NH<jats:sub>3</jats:sub> abundance ratios. The isotope ratios obtained from both telescopes agree for a given source within the uncertainties, and no dependence on heliocentric distance and kinetic temperature is seen. <jats:sup>14</jats:sup>N/<jats:sup>15</jats:sup>N ratios tend to increase with galactocentric distance, confirming a radial nitrogen isotope gradient. This is consistent with results from recent Galactic chemical model calculations, including the impact of superasymptotic giant branch stars and novae.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Research has analytically shown that the energy-conserving implicit nonsymplectic scheme of Bacchini, Ripperda, Chen, and Sironi provides a first-order accuracy to numerical solutions of a six-dimensional conservative Hamiltonian system. Because of this, a new second-order energy-conserving implicit scheme is proposed. Numerical simulations of a galactic model hosting a BL Lacertae object and magnetized rotating black hole background support these analytical results. The new method with appropriate time steps is used to explore the effects of varying the parameters on the presence of chaos in the two physical models. Chaos easily occurs in the galactic model as the mass of the nucleus, the internal perturbation parameter, and the anisotropy of the potential of the elliptical galaxy increase. The dynamics of charged particles around the magnetized Kerr spacetime is easily chaotic for larger energies of the particles, smaller initial angular momenta of the particles, and stronger magnetic fields. The chaotic properties are not necessarily weakened when the black-hole spin increases. The new method can be used for any six-dimensional Hamiltonian problems, including globally hyperbolic spacetimes with readily available (3 + 1) split coordinates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In an optical monitoring program to characterize the variability properties of blazars, we observed 10 sources from the Roma-BZCAT catalog for 26 nights in <jats:italic>V</jats:italic> and <jats:italic>R</jats:italic> bands during 2014 October to 2015 June with two telescopes located in India. The sample includes mainly newly discovered BL Lacertae objects (BL Lacs) for which the redshift of some sources is not yet known. We present the results of flux and color variations of the sample on intraday and short timescales obtained by using the power-enhanced F-test and the nested-ANOVA tests, along with their spectral behavior. We find significant intraday variability in the single flat-spectrum radio quasar in our sample, having an amplitude of variation ∼12%. Although a few of the BL Lacs showed probable variation in some nights, none of them passed the variability tests at 99.9% significance level. We find that 78% of the sample showed significant negative color–magnitude correlations, i.e., a redder-when-brighter spectral evolution. Those that do not show strong or clear chromatism predominantly exhibit a redder-when-brighter trend. Unlike on hourly timescales, the high-synchrotron-peaked blazars in the sample (BZGJ0656+4237, BZGJ0152+0147, and BZBJ1728+5013) show strong flux variation on timescales of days to months, where again we detect a decreasing trend of the spectral slope with brightness. We observe a global steepening of the optical spectrum with increasing flux on the intranight timescale for the entire blazar sample. The nonvariability in the BL Lacs in our sample might be caused by the distinct contribution from the disk as well as from other components in the studied energy range.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Breakthrough Listen’s Exotica Catalog as the centerpiece of our efforts to expand the diversity of targets surveyed in the Search for Extraterrestrial Intelligence (SETI). As motivation, we introduce the concept of survey breadth, the diversity of objects observed during a program. Several reasons for pursuing a broad program are given, including increasing the chance of a positive result in SETI, commensal astrophysics, and characterizing systematics. The Exotica Catalog is a 963 entry collection of 816 distinct targets intended to include “one of everything” in astronomy. It contains four samples: the Prototype sample, with an archetype of every known major type of nontransient celestial object; the Superlative sample of objects, with the most extreme properties; the Anomaly sample of enigmatic targets that are in some way unexplained; and the Control sample, with sources not expected to produce positive results. As far as we are aware, this is the first object list in recent times with the purpose of spanning the breadth of astrophysics. We share it with the community in hopes that it can guide treasury surveys and as a general reference work. Accompanying the catalog is an extensive discussion of the classification of objects and a new classification system for anomalies. Extensive notes on the objects in the catalog are available online. We discuss how we intend to proceed with observations in the catalog, contrast it with our extant Exotica efforts, and suggest how similar tactics may be applied to other programs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present PHANGS–ALMA, the first survey to map CO <jats:italic>J</jats:italic> = 2 → 1 line emission at ∼1″ ∼100 pc spatial resolution from a representative sample of 90 nearby (<jats:italic>d</jats:italic> ≲ 20 Mpc) galaxies that lie on or near the <jats:italic>z</jats:italic> = 0 “main sequence” of star-forming galaxies. CO line emission traces the bulk distribution of molecular gas, which is the cold, star-forming phase of the interstellar medium. At the resolution achieved by PHANGS–ALMA, each beam reaches the size of a typical individual giant molecular cloud, so that these data can be used to measure the demographics, life cycle, and physical state of molecular clouds across the population of galaxies where the majority of stars form at <jats:italic>z</jats:italic> = 0. This paper describes the scientific motivation and background for the survey, sample selection, global properties of the targets, Atacama Large Millimeter/submillimeter Array (ALMA) observations, and characteristics of the delivered data and derived data products. As the ALMA sample serves as the parent sample for parallel surveys with MUSE on the Very Large Telescope, the Hubble Space Telescope, AstroSat, the Very Large Array, and other facilities, we include a detailed discussion of the sample selection. We detail the estimation of galaxy mass, size, star formation rate, CO luminosity, and other properties, compare estimates using different systems and provide best-estimate integrated measurements for each target. We also report the design and execution of the ALMA observations, which combine a Cycle 5 Large Program, a series of smaller programs, and archival observations. Finally, we present the first 1″ resolution atlas of CO emission from nearby galaxies and describe the properties and contents of the first PHANGS–ALMA public data release.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The momentum diffusion of charged energetic particles is an important mechanism of the transport process in astrophysics, the physics of fusion devices, and laboratory plasmas. In addition to the momentum diffusion term for a uniform field, we obtain an additional momentum diffusion term due to the focusing effect of the large-scale magnetic field. After evaluating the coefficient of the additional momentum diffusion term, we find that it is determined by the sign of the focusing characteristic length and the cross helicity of the turbulent magnetic field. Furthermore, by deriving the mean momentum change rate contributed from the additional momentum diffusion term, we identify that the focused field provides an additional momentum loss or gain process.</jats:p>