Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present an improved inverse-ray-shooting code based on graphics processing units (GPUs) to generate microlensing magnification maps. In addition to introducing GPUs to accelerate the calculations, we also invest effort into two aspects: (i) A standard circular lens plane is replaced by a rectangular one to reduce the number of unnecessary lenses as a result of an extremely prolate rectangular image plane. (ii) An interpolation method is applied in our implementation, achieving significant acceleration when dealing with the large number of lenses and light rays required by high-resolution maps. With these applications, we have greatly reduced the running time while maintaining high accuracy: The speed was increased by about 100 times compared with an ordinary GPU-based inverse-ray-shooting code and a GPU-D code when handling a large number of lenses. If a high-resolution situation with up to 10,000<jats:sup>2</jats:sup> pixels, resulting in almost 10<jats:sup>11</jats:sup> light rays, is encountered, the running time can also be reduced by two orders of magnitude.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore the use of observed polar coronal holes (CHs) to constrain the flux distribution within the polar regions of global solar magnetic field maps in the absence of reliable quality polar field observations. Global magnetic maps, generated by the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model, are modified to enforce field unipolarity thresholds both within and outside observed CH boundaries. The polar modified and unmodified maps are used to drive Wang–Sheeley–Arge (WSA) models of the corona and solar wind (SW). The WSA-predicted CHs are compared with the observations, and SW predictions at the WIND and Ulysses spacecraft are also used to provide context for the new polar modified maps. We find that modifications of the polar flux never worsen and typically improve both the CH and SW predictions. We also confirm the importance of the choice of the domain over which WSA generates the coronal magnetic field solution but find that solutions optimized for one location in the heliosphere can worsen predictions at other locations. Finally, we investigate the importance of low-latitude (i.e., active region) magnetic fields in setting the boundary of polar CHs, determining that they have at least as much impact as the polar fields themselves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hub-filament systems (HFSs) are potential sites of protocluster and massive star formation, and play a key role in mass accumulation. We report JCMT POL-2 850 <jats:italic>μ</jats:italic>m polarization observations toward the massive HFS SDC13. We detect an organized magnetic field near the hub center with a cloud-scale “U-shape” morphology following the western edge of the hub. Together with larger-scale APEX <jats:sup>13</jats:sup>CO and PLANCK polarization data, we find that SDC13 is located at the convergent point of three giant molecular clouds (GMCs) along a large-scale, partially spiral-like magnetic field. The smaller “U-shape” magnetic field is perpendicular to the large-scale magnetic field and the converging GMCs. We explain this as the result of a cloud–cloud collision. Within SDC13, we find that local gravity and velocity gradients point toward filament ridges and hub center. This suggests that gas can locally be pulled onto filaments and overall converges to the hub center. A virial analysis of the central hub shows that gravity dominates the magnetic and kinematic energy. Combining large- and small-scale analyses, we propose that SDC13 is initially formed from a collision of clouds moving along the large-scale magnetic field. In the post-shock regions, after the initial turbulent energy has dissipated, gravity takes over and starts to drive the gas accretion along the filaments toward the hub center.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of the extragalactic (<jats:italic>z</jats:italic> = 0.0141) transient AT 2018cow established a new class of energetic explosions shocking a dense medium, producing luminous emission at millimeter and submillimeter wavelengths. Here we present detailed millimeter- through centimeter-wave observations of a similar transient, ZTF 20acigmel (AT 2020xnd), at <jats:italic>z</jats:italic> = 0.2433. Using observations from the NOrthern Extended Millimeter Array and the Very Large Array, we model the unusual millimeter and radio emission from AT 2020xnd under several different assumptions and ultimately favor synchrotron radiation from a thermal electron population (relativistic Maxwellian). The thermal electron model implies a fast but subrelativistic (<jats:italic>v</jats:italic> ≈ 0.3<jats:italic>c</jats:italic>) shock and a high ambient density (<jats:italic>n</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> ≈ 4 × 10<jats:sup>3</jats:sup> cm<jats:sup>−3</jats:sup>) at Δ<jats:italic>t</jats:italic> ≈ 40 days. The X-ray luminosity of <jats:italic>L</jats:italic> <jats:sub> <jats:italic>X</jats:italic> </jats:sub> ≈ 10<jats:sup>43</jats:sup> erg s<jats:sup>−1</jats:sup> exceeds simple predictions from the radio and UVOIR luminosity and likely has a separate physical origin, such as a central engine. Using the fact that month-long luminous (<jats:italic>L</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub> ≈ 2 × 10<jats:sup>30</jats:sup> erg s<jats:sup>−1</jats:sup> Hz<jats:sup>−1</jats:sup> at 100 GHz) millimeter emission appears to be a generic feature of transients with fast (<jats:italic>t</jats:italic> <jats:sub>1/2</jats:sub> ≈ 3 days) and luminous (<jats:italic>M</jats:italic> <jats:sub>peak</jats:sub> ≈ −21 mag) optical light curves, we estimate the rate at which transients like AT 2018cow and AT 2020xnd will be detected by future wide-field millimeter transient surveys such as CMB-S4 and conclude that energetic explosions in dense environments may represent a significant population of extragalactic transients in the 100 GHz sky.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Most current models of low-mass red giant stars do not reproduce the observed position of the red giant branch luminosity bump, a diagnostic of the maximum extent of the convective envelope during the first dredge up. Global asteroseismic parameters, the large frequency separation and frequency of maximum oscillation power, measured for large samples of red giants, show that modeling convective overshoot below the convective envelope helps match the modeled luminosity bump positions to observations; however, these global parameters cannot be used to probe envelope overshoot in a star-by-star manner. Red giant mixed modes, which behave like acoustic modes at the surface and like gravity modes in the core, contain important information about the interior structure of the star, especially near the convective boundary. Therefore, these modes may be used to probe interior processes, such as overshoot. Using a grid of red giant models with varying mass, metallicity, surface gravity, overshoot treatment, and amount of envelope overshoot, we find that changing the overshoot amplitude (and prescription) of overshoot below the convection zone in red giant stellar models results in significant differences in the evolution of the models’ dipole mixed-mode oscillation frequencies, the average mixed-mode period spacing (〈Δ<jats:italic>P</jats:italic>〉), and gravity-mode phase offset term (<jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>g</jats:italic> </jats:sub>).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first direct measurement of the proper motion of pulsar J1124–5916 in the young, oxygen-rich supernova remnant G292.0+1.8. Using deep Chandra ACIS-I observations from 2006 to 2016, we measure a positional change of 0.″21 ± 0.″05 over the ∼10 yr baseline, or ∼0.″02 yr<jats:sup>−1</jats:sup>. At a distance of 6.2 ± 0.9 kpc, this corresponds to a kick velocity in the plane of the sky of 612 ± 152 km s<jats:sup>−1</jats:sup>. We compare this direct measurement against the velocity inferred from estimates based on the center of mass of the ejecta. Additionally, we use this new proper-motion measurement to compare the motion of the neutron star to the center of expansion of the optically emitting ejecta. We derive an age estimate for the supernova remnant of ≳2000 yr. The high measured kick velocity is in line with recent studies of high proper motion neutron stars in other Galactic supernova remnants and consistent with a hydrodynamic origin to the neutron star kick.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Rossby waves are found at several levels in the Sun, most recently in its supergranule layer. We show that Rossby waves in the supergranule layer can be excited by an inverse cascade of kinetic energy from the nearly horizontal motions in supergranules. We illustrate how this excitation occurs using a hydrodynamic shallow-water model for a 3D thin rotating spherical shell. We find that initial kinetic energy at small spatial scales inverse cascades quickly to global scales, exciting Rossby waves whose phase velocities are similar to linear Rossby waves on the sphere originally derived by Haurwitz. Modest departures from the Haurwitz formula originate from nonlinear finite amplitude effects and/or the presence of differential rotation. Like supergranules, the initial small-scale motions in our model contain very little vorticity compared to their horizontal divergence, but the resulting Rossby waves are almost all vortical motions. Supergranule kinetic energy could have mainly gone into gravity waves, but we find that most energy inverse cascades to global Rossby waves. Since kinetic energy in supergranules is three or four orders of magnitude larger than that of the observed Rossby waves in the supergranule layer, there is plenty of energy available to drive the inverse-cascade mechanism. Tachocline Rossby waves have previously been shown to play crucial roles in causing <jats:italic>seasons</jats:italic> of space weather through their nonlinear interactions with global flows and magnetic fields. We briefly discuss how various Rossby waves in the tachocline, convection zone, supergranule layer, and corona can be reconciled in a unified framework.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Periodic variables illuminate the physical processes of stars throughout their lifetime. Wide-field surveys continue to increase our discovery rates of periodic variable stars. Automated approaches are essential to identify interesting periodic variable stars for multiwavelength and spectroscopic follow-up. Here we present a novel unsupervised machine-learning approach to hunt for anomalous periodic variables using phase-folded light curves presented in the Zwicky Transient Facility Catalogue of Periodic Variable Stars by Chen et al. We use a convolutional variational autoencoder to learn a low-dimensional latent representation, and we search for anomalies within this latent dimension via an isolation forest. We identify anomalies with irregular variability. Most of the top anomalies are likely highly variable red giants or asymptotic giant branch stars concentrated in the Milky Way galactic disk; a fraction of the identified anomalies are more consistent with young stellar objects. Detailed spectroscopic follow-up observations are encouraged to reveal the nature of these anomalies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We develop and apply a bespoke fitting routine to a large volume of solar wind electron distribution data measured by Parker Solar Probe over its first five orbits, covering radial distances from 0.13 to 0.5 au. We characterize the radial evolution of the electron core, halo, and strahl populations in the slow solar wind during these orbits. The fractional densities of these three electron populations provide evidence for the growth of the combined suprathermal halo and strahl populations from 0.13 to 0.17 au. Moreover, the growth in the halo population is not matched by a decrease in the strahl population at these distances, as has been reported for previous observations at distances greater than 0.3 au. We also find that the halo is negligible at small heliocentric distances. The fractional strahl density remains relatively constant at ∼1% below 0.2 au, suggesting that the rise in the relative halo density is not solely due to the transfer of strahl electrons into the halo.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We propose a novel mechanism where primordial black hole (PBH) dark matter is formed much later in the history of the universe, between the epochs of Big Bang nucleosynthesis and cosmic microwave background photon decoupling. In our setup, one does not need to modify the scale-invariant inflationary power spectra; instead, a late-phase transition in a strongly interacting fermion–scalar fluid (which occurs naturally around redshift 10<jats:sup>6</jats:sup> ≤ <jats:italic>z</jats:italic> <jats:sub> <jats:italic>T</jats:italic> </jats:sub> ≤ 10<jats:sup>8</jats:sup>) creates an instability in the density perturbation as the sound speed turns imaginary. As a result, the dark matter perturbation grows exponentially in sub-Compton scales. This follows the immediate formation of an early dense dark matter halo, which finally evolves into PBHs due to cooling through scalar radiation. We calculate the variance of the density perturbations and the PBH fractional abundances <jats:italic>f</jats:italic>(<jats:italic>M</jats:italic>) by using a nonmonochromatic mass function. We find that the peak of our PBH mass function lies between 10<jats:sup>−16</jats:sup> and 10<jats:sup>−14</jats:sup> solar mass for <jats:italic>z</jats:italic> <jats:sub> <jats:italic>T</jats:italic> </jats:sub> ≃ 10<jats:sup>6</jats:sup>, and thus that it can constitute the entire dark matter of the universe. In PBH formation, one would expect a temporary phase where an attractive scalar balances the Fermi pressure. We numerically confirm that such a state indeed exists, and we find the radius and density profile of the temporary static structure of the dark matter halo, which finally evolves into PBHs due to cooling through scalar radiation.</jats:p>