Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present the third and final data release of the K2 Galactic Archaeology Program (K2 GAP) for Campaigns C1–C8 and C10–C18. We provide asteroseismic radius and mass coefficients, <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>R</jats:italic> </jats:sub> and <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>M</jats:italic> </jats:sub>, for ∼19,000 red giant stars, which translate directly to radius and mass given a temperature. As such, K2 GAP DR3 represents the largest asteroseismic sample in the literature to date. K2 GAP DR3 stellar parameters are calibrated to be on an absolute parallactic scale based on Gaia DR2, with red giant branch and red clump evolutionary state classifications provided via a machine-learning approach. Combining these stellar parameters with GALAH DR3 spectroscopy, we determine asteroseismic ages with precisions of ∼20%–30% and compare age-abundance relations to Galactic chemical evolution models among both low- and high-<jats:italic>α</jats:italic> populations for <jats:italic>α</jats:italic>, light, iron-peak, and neutron-capture elements. We confirm recent indications in the literature of both increased Ba production at late Galactic times as well as significant contributions to <jats:italic>r</jats:italic>-process enrichment from prompt sources associated with, e.g., core-collapse supernovae. With an eye toward other Galactic archeology applications, we characterize K2 GAP DR3 uncertainties and completeness using injection tests, suggesting that K2 GAP DR3 is largely unbiased in mass/age, with uncertainties of 2.9% (stat.) ± 0.1% (syst.) and 6.7% (stat.) ± 0.3% (syst.) in <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>R</jats:italic> </jats:sub> and <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>M</jats:italic> </jats:sub> for red giant branch stars and 4.7% (stat.) ± 0.3% (syst.) and 11% (stat.) ± 0.9% (syst.) for red clump stars. We also identify percent-level asteroseismic systematics, which are likely related to the time baseline of the underlying data, and which therefore should be considered in TESS asteroseismic analysis.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a first-principles model of pitch-angle and energy distribution function evolution as particles are sequentially accelerated by multiple flare magnetic islands. Data from magnetohydrodynamic (MHD) simulations of an eruptive flare/coronal mass ejection provide ambient conditions for the evolving particle distributions. Magnetic islands, which are created by sporadic reconnection at the self-consistently formed flare current sheet, contract and accelerate the particles. The particle distributions are evolved using rules derived in our previous work. In this investigation, we assume that a prescribed fraction of particles sequentially “hops” to another accelerator and receives an additional boost in energy and anisotropy. This sequential process generates particle number spectra that obey an approximate power law at mid-range energies and presents low- and high-energy breaks. We analyze these spectral regions as functions of the model parameters. We also present a fully analytic method for forming and interpreting such spectra, independent of the sequential acceleration model. The method requires only a few constrained physical parameters, such as the percentage of particles transferred between accelerators, the energy gain in each accelerator, and the number of accelerators visited. Our investigation seeks to bridge the gap between MHD and kinetic regimes by combining global simulations and analytic kinetic theory. The model reproduces and explains key characteristics of observed flare hard X-ray spectra as well as the underlying properties of the accelerated particles. Our analytic model provides tools to interpret high-energy observations for missions and telescopes, such as RHESSI, FOXSI, NuSTAR, Solar Orbiter, EOVSA, and future high-energy missions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Thanks to ground-based infrared and submillimeter observations the study of the dusty torus of nearby active galactic nuclei has greatly advanced in the last years. With the aim of further investigating the nuclear mid-infrared emission of the archetypal Seyfert 2 galaxy NGC 1068, here we present a fitting to the <jats:italic>N</jats:italic>- and <jats:italic>Q</jats:italic>-band Michelle/Gemini spectra. We initially test several available spectral energy distribution (SED) libraries, including smooth, clumpy and two-phase torus models, and a clumpy disk+wind model. We find that the spectra of NGC 1068 cannot be reproduced with any of these models. Although, the smooth torus models describe the spectra of NGC 1068 if we allow variation of some model parameters among the two spectral bands. Motivated by this result, we produced new SEDs using the radiative transfer code <jats:sc>SKIRT</jats:sc>. We use two concentric tori that allow us to test a more complex geometry. We test different values for the inner and outer radii, half-opening angle, radial, and polar exponent of the power-law density profile, opacity, and viewing angle. Furthermore, we also test the dust grains’ size and different optical and calorimetric properties of silicate grains. The best-fitting model consists of two concentric components with outer radii of 1.8 and 28 pc, respectively. We find that the size and the optical and calorimetric properties of graphite and silicate grains in the dust structure are key to reproducing the spectra of NGC 1068. A maximum grain size of 1 <jats:italic>μ</jats:italic>m leads to a significant improvement in the fit. We conclude that the dust in NGC 1068 reaches different scales, where the highest contribution to the mid-infrared is given by a central and compact component. A less dense and extended component is present, which can be either part of the same torus (conforming a flared disk) or can represent the emission of a polar dust component, as already suggested from interferometric observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Hubble Space Telescope (HST) photometric results for NGC 6402, a highly reddened, very luminous Galactic globular cluster (GC). Recent spectroscopic observations of its red giant stars have shown a quite peculiar behavior in the chemistry of its multiple populations. These results have prompted UV and optical HST observations aimed at obtaining the cluster’s “chromosome map” (ChM), an efficient tool for classifying GCs and characterizing their multiple populations. We find that the discontinuity in the abundance distributions of O, Mg, Al, and Na inferred from spectroscopy is more nuanced in the ChM, which is mostly sensitive to nitrogen. Nevertheless, photometry in optical bands reveals a double main sequence, indicating a discontinuity in the helium content of the populations. The population with the largest chemical anomalies (extreme) peaks at a helium mass fraction <jats:italic>Y</jats:italic> ∼ 0.31. This helium content is consistent with results from the analysis of the distribution of horizontal branch stars and the spectrophotometry of the red giants. The ChM and the color–magnitude diagrams are compared with those of NGC 2808, a prototype GC with helium abundances up to <jats:italic>Y</jats:italic> ≳ 0.35, and both confirm that NGC 6402 does not host stellar populations with such extreme helium content. Further, the ChM reveals the presence of a group of stars with higher metallicity, thus indicating that NGC 6402 is a Type II cluster. The modalities of formation of the multiple populations in NGC 6402 are briefly surveyed, with main attention on the asymptotic giant branch and supermassive star models, and on possible cluster merging.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Identification of chemically similar stars using elemental abundances is core to many pursuits within Galactic archeology. However, measuring the chemical likeness of stars using abundances directly is limited by systematic imprints of imperfect synthetic spectra in abundance derivation. We present a novel data-driven model that is capable of identifying chemically similar stars from spectra alone. We call this relevant scaled component analysis (RSCA). RSCA finds a mapping from stellar spectra to a representation that optimizes recovery of known open clusters. By design, RSCA amplifies factors of chemical abundance variation and minimizes those of nonchemical parameters, such as instrument systematics. The resultant representation of stellar spectra can therefore be used for precise measurements of chemical similarity between stars. We validate RSCA using 185 cluster stars in 22 open clusters in the Apache Point Observatory Galactic Evolution Experiment survey. We quantify our performance in measuring chemical similarity using a reference set of 151,145 field stars. We find that our representation identifies known stellar siblings more effectively than stellar-abundance measurements. Using RSCA, 1.8% of pairs of field stars are as similar as birth siblings, compared to 2.3% when using stellar-abundance labels. We find that almost all of the information within spectra leveraged by RSCA fits into a two-dimensional basis, which we link to [Fe/H] and <jats:italic>α</jats:italic>-element abundances. We conclude that chemical tagging of stars to their birth clusters remains prohibitive. However, using the spectra has noticeable gain, and our approach is poised to benefit from larger data sets and improved algorithm designs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Supernova remnants (SNRs) are important objects in investigating the links among supernova (SN) explosion mechanism(s), progenitor stars, and cosmic-ray acceleration. Nonthermal emission from SNRs is an effective and promising tool for probing their surrounding circumstellar media (CSM) and, in turn, the stellar evolution and mass-loss mechanism(s) of massive stars. In this work, we calculate the time evolution of broadband nonthermal emissions from Type Ib/c SNRs, whose CSM structures are derived from the mass-loss history of their progenitors. Our results predict that Type Ib/c SNRs make a transition of brightness in radio and <jats:italic>γ</jats:italic>-ray bands from an undetectable dark for a certain period to a rebrightening phase. This transition originates from their inhomogeneous CSM structures in which the SNRs are embedded within a low-density wind cavity surrounded by a high-density wind shell and the ambient interstellar medium (ISM). The “resurrection” in nonthermal luminosity happens at an age of ∼1000 yr old for a Wolf-Rayet star progenitor evolved within a typical ISM density. Combining with the results of Type II SNR evolution recently reported by Yasuda et al., this result sheds light on a comprehensive understanding of nonthermal emissions from SNRs with different SN progenitor types and ages, which is made possible for the first time by the incorporation of realistic mass-loss histories of the progenitors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the next decade, deep galaxy surveys from telescopes such as the James Webb Space Telescope and Roman Space Telescope will provide transformational data sets that will greatly enhance the understanding of galaxy formation during the epoch of reionization (EoR). In this work, we present the Deep Realistic Extragalactic Model (DREaM) for creating synthetic galaxy catalogs. Our model combines dark matter simulations, subhalo abundance matching and empirical models, and includes galaxy positions, morphologies, and spectral energy distributions. The resulting synthetic catalog extends to redshifts <jats:italic>z</jats:italic> ∼ 12, and galaxy masses <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}(M/{M}_{\odot })=5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mi>M</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac46fbieqn1.gif" xlink:type="simple" /> </jats:inline-formula> covering an area of 1 deg<jats:sup>2</jats:sup> on the sky. We use DREaM to explore the science returns of a 1 deg<jats:sup>2</jats:sup> Roman ultra-deep field (UDF), and to provide a resource for optimizing ultra-deep survey designs. We find that a Roman UDF to ∼30 <jats:italic>m</jats:italic> <jats:sub>AB</jats:sub> will potentially detect more than 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>UV</jats:sub> &lt; − 17 galaxies, with more than 10<jats:sup>4</jats:sup> at redshifts <jats:italic>z</jats:italic> &gt; 7, offering an unparalleled data set for constraining galaxy properties during the EoR. Our synthetic catalogs and simulated images are made publicly available to provide the community with a tool to prepare for upcoming data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Accurately determining gas-phase metal abundances within galaxies is critical as metals strongly affect the physics of the interstellar medium. To date, the vast majority of widely used gas-phase abundance indicators rely on emission from bright optical lines, whose emissivities are highly sensitive to the electron temperature. Alternatively, direct-abundance methods exist that measure the temperature of the emitting gas directly, though these methods usually require challenging observations of highly excited auroral lines. Low-lying far-infrared (FIR) fine structure lines are largely insensitive to electron temperature and thus provide an attractive alternative to optically derived abundances. Here, we introduce the far-infrared abundance (FIRA) project, which employs these FIR transitions, together with both radio free–free emission and hydrogen recombination lines, to derive direct, absolute gas-phase oxygen abundances. Our first target is M101, a nearby spiral galaxy with a relatively steep abundance gradient. Our results are consistent with the O<jats:sup>++</jats:sup> electron temperatures and absolute oxygen abundances derived using optical direct-abundance methods by the CHemical Abundance Of Spirals (CHAOS) program, with a small difference (∼1.5<jats:italic>σ</jats:italic>) in the radial abundance gradients derived by the FIR/free–free-normalized versus CHAOS/direct-abundance techniques. This initial result demonstrates the validity of the FIRA methodology—with the promise of determining absolute metal abundances within dusty star-forming galaxies, both locally and at high redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Mergers of black holes (BHs) and neutron stars (NSs) result in the emission of gravitational waves that can be detected by LIGO. In this paper, we look at 2+2 and 3+1 quadruple-star systems, which are common among massive stars, the progenitors of BHs and NSs. We carry out a detailed population synthesis of quadruple systems using the Multiple Stellar Evolution code, which seamlessly takes into consideration stellar evolution, binary and tertiary interactions, <jats:italic>N</jats:italic>-body dynamics, and secular evolution. We find that, although secular evolution plays a role in compact object (BH and NS) mergers, (70–85)% (depending on the model assumptions) of the mergers are solely due to common envelope evolution. Significant eccentricities in the LIGO band (higher than 0.01) are only obtained with zero supernova (SN) kicks and are directly linked to the role of secular evolution. A similar outlier effect is seen in the <jats:italic>χ</jats:italic> <jats:sub>eff</jats:sub> distribution, with negative values obtained only with zero SN kicks. When kicks are taken into account, there are no systems that evolve into a quadruple consisting of four compact objects. For our fiducial model, we estimate the merger rates (in units of Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup>) in 2+2 quadruples (3+1 quadruples) to be 10.8 ± 0.9 (2.9 ± 0.5), 5.7 ± 0.6 (1.4 ± 0.4), and 0.6 ± 0.2 (0.7 ± 0.3) for BH–BH, BH–NS, and NS–NS mergers, respectively. The BH–BH merger rates represent a significant fraction of the current LIGO rates, whereas the other merger rates fall short of LIGO estimates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Oscillatory reconnection (a relaxation mechanism with periodic changes in connectivity) has been proposed as a potential physical mechanism underpinning several periodic phenomena in the solar atmosphere, including, but not limited to, quasi-periodic pulsations (QPPs). Despite its importance, however, the mechanism has never been studied within a hot, coronal plasma. We investigate oscillatory reconnection in a one million Kelvin plasma by solving the fully-compressive, resistive MHD equations for a 2D magnetic X-point under coronal conditions using the PLUTO code. We report on the resulting oscillatory reconnection including its periodicity and decay rate. We observe a more complicated oscillating profile for the current density compared to that found for a cold plasma, due to mode-conversion at the equipartition layer. We also consider, for the first time, the effect of adding anisotropic thermal conduction to the oscillatory reconnection mechanism, and we find this simplifies the spectrum of the oscillation profile and increases the decay rate. Crucially, the addition of thermal conduction does not prevent the oscillatory reconnection mechanism from manifesting. Finally, we reveal a relationship between the equilibrium magnetic field strength, decay rate, and period of oscillatory reconnection, which opens the tantalising possibility of utilizing oscillatory reconnection as a seismological tool.</jats:p>