Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Coronal holes are the observational manifestation of the solar magnetic field open to the heliosphere and are of pivotal importance for our understanding of the origin and acceleration of the solar wind. Observations from space missions such as the Solar Dynamics Observatory now allow us to study coronal holes in unprecedented detail. Instrumental effects and other factors, however, pose a challenge to automatically detect coronal holes in solar imagery. The science community addresses these challenges with different detection schemes. Until now, little attention has been paid to assessing the disagreement between these schemes. In this COSPAR ISWAT initiative, we present a comparison of nine automated detection schemes widely applied in solar and space science. We study, specifically, a prevailing coronal hole observed by the Atmospheric Imaging Assembly instrument on 2018 May 30. Our results indicate that the choice of detection scheme has a significant effect on the location of the coronal hole boundary. Physical properties in coronal holes such as the area, mean intensity, and mean magnetic field strength vary by a factor of up to 4.5 between the maximum and minimum values. We conclude that our findings are relevant for coronal hole research from the past decade, and are therefore of interest to the solar and space research community.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Parker Solar Probe (PSP) routinely observes magnetic field deflections in the solar wind at distances less than 0.3 au from the Sun. These deflections are related to structures commonly called “switchbacks” (SBs), whose origins and characteristic properties are currently debated. Here, we use a database of visually selected SB intervals—and regions of solar wind plasma measured just before and after each SB—to examine plasma parameters, turbulent spectra from inertial to dissipation scales, and intermittency effects in these intervals. We find that many features, such as perpendicular stochastic heating rates and turbulence spectral slopes are fairly similar inside and outside of SBs. However, important kinetic properties, such as the characteristic break scale between the inertial to dissipation ranges differ inside and outside these intervals, as does the level of intermittency, which is notably enhanced inside SBs and in their close proximity, most likely due to magnetic field and velocity shears observed at the edges. We conclude that the plasma inside and outside of an SB, in most of the observed cases, belongs to the same stream, and that the evolution of these structures is most likely regulated by kinetic processes, which dominate small-scale structures at the SB edges.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report 1.2 mm polarized continuum emission observations carried out with the Atacama Large Millimeter/submillimeter Array toward the high-mass star formation region G5.89–0.39. The observations show a prominent 0.2 pc north–south filamentary structure. The ultracompact H <jats:sc>ii</jats:sc> region in G5.89–0.39 breaks the filament into two pieces. Its millimeter emission shows a dusty belt with a mass of 55–115 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and 4500 au in radius, surrounding an inner part comprising mostly ionized gas, with dust emission only accounting for about 30% of the total millimeter emission. We also found a lattice of convex arches that may be produced by dragged dust and gas from the explosive dispersal event involving the O5 Feldt’s star. The north–south filament has a mass between 300 and 600 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and harbors a cluster of about 20 mm envelopes with a median size and mass of 1700 au and 1.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, respectively, some of which are already forming protostars. We interpret the polarized emission in the filament as mainly coming from magnetically aligned dust grains. The polarization fraction is ∼4.4% in the filaments and 2.1% at the shell. The magnetic fields are along the North Filament and perpendicular to the South Filament. In the Central Shell, the magnetic fields are roughly radial in a ring surrounding the dusty belt between 4500 and 7500 au, similar to the pattern recently found in the surroundings of Orion BN/KL. This may be an independent observational signpost of explosive dispersal outflows and should be further investigated in other regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Convection and turbulence in core-collapse supernovae (CCSNe) are inherently three-dimensional (3D) in nature. However, 3D simulations of CCSNe are computationally demanding. Thus, it is valuable to modify simulations in spherical symmetry to incorporate 3D effects using some parametric model. In this paper, we report on the formulation and implementation of general relativistic neutrino-driven turbulent convection in the spherically symmetric core-collapse supernova code <jats:monospace>GR1D</jats:monospace>. This is based upon the recently proposed method of Simulated Turbulence in Reduced Dimensionality (STIR) in Newtonian simulations from Couch et al. (2020). When the parameters of this model are calibrated to 3D simulations, we find that our general relativistic formulation of STIR requires larger turbulent eddies to achieve a shock evolution similar to the original STIR model. We also find that general relativity may alter the correspondence between progenitor mass and successful versus failed explosions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical spectroscopy for 18 halo white dwarfs identified using photometry from the Canada–France Imaging Survey and Pan-STARRS1 DR1 3<jats:italic>π</jats:italic> survey combined with astrometry from Gaia DR2. The sample contains 13 DA, 1 DZ, 2 DC, and 2 potentially exotic types of white dwarf. We fit both the spectrum and the spectral energy distribution in order to obtain the temperature and surface gravity, which we then convert into mass and then age using stellar isochrones and the initial-to-final mass relation. We find a large spread in ages that is not consistent with expected formation scenarios for the Galactic halo. We find a mean age of <jats:inline-formula> <jats:tex-math> <?CDATA ${9.03}_{-2.03}^{+2.13}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>9.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.13</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf2b2ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Gyr and a dispersion of <jats:inline-formula> <jats:tex-math> <?CDATA ${4.21}_{-1.58}^{+2.33}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>4.21</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.58</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.33</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf2b2ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> Gyr for the inner halo using a maximum-likelihood method. This result suggests an extended star formation history within the local halo population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical and near-infrared observations of SN 2019ehk, which was initially reported as a Type Ib supernova (SN). We show that it evolved to a Ca-rich transient according to its spectral properties and evolution in late phases. However, it shows a few properties distinct from those of the canonical Ca-rich transients: a short-duration first peak in the light curve, high peak luminosity, and association with a star-forming environment. Indeed, some of these features are shared with iPTF14gqr and iPTF16hgs, which are candidates for a special class of core-collapse SNe: the so-called ultra-stripped envelope SNe, i.e., a relatively low-mass He (or C+O) star explosion in a binary as a precursor of short-period double neutron star (NS) binaries. The estimated ejecta mass (0.4<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) and explosion energy (1.7 × 10<jats:sup>50</jats:sup> erg) are consistent with this scenario. The analysis of the first peak suggests the existence of dense circumstellar material in the vicinity of the progenitor, implying a CCSN origin. Based on this analysis, we suggest SN 2019ehk is another candidate for a low-mass He star explosion. It might create a double NS binary, but with a wide separation. These candidates for low-mass stripped envelope SNe, including ultra-stripped envelope SN candidates, seem to form a subpopulation among Ca-rich transients, associated with young population. We propose that the key to distinguishing this population is the early first peak in their light curves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Permanently deformed objects in binary systems can experience complex rotation evolution, arising from the extensively studied effect of spin–orbit coupling as well as more nuanced dynamics arising from spin–spin interactions. The ability of an object to sustain an aspheroidal shape largely determines whether or not it will exhibit nontrivial rotational behavior. In this work, we adopt a simplified model of a gravitationally interacting primary and satellite pair, where each body’s quadrupole moment is approximated by two diametrically opposed point masses. After calculating the net gravitational torque on the satellite from the primary, as well as the associated equations of motion, we employ a Hamiltonian formalism that allows for a perturbative treatment of the spin–orbit and retrograde and prograde spin–spin coupling states. By analyzing the resonances individually and collectively, we determine the criteria for resonance overlap and the onset of chaos, as a function of orbital and geometric properties of the binary. We extend the 2D planar geometry to calculate the obliquity evolution. This calculation indicates that satellites in spin–spin resonances undergo precession when inclined out of the plane, but they do not tumble. We apply our resonance overlap criteria to the contact binary system (216) Kleopatra, and find that its satellites, Cleoselene and Alexhelios, may plausibly be exhibiting chaotic rotational dynamics from the overlap of the spin–orbit and retrograde spin–spin resonances. While this model is, by construction, generalizable to any binary system, it will be particularly useful for studies of small bodies in the Solar System, whose irregular shapes make them ideal candidates for exotic rotational states.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Building on recent work by Chandar et al., we construct X-ray luminosity functions (XLFs) for different classes of X-ray binary (XRB) donors in the nearby star-forming galaxy M83 through a novel methodology. Rather than classifying low- versus high-mass XRBs based on the scaling of the number of X-ray sources with stellar mass and star formation rate, respectively, we utilize multiband Hubble Space Telescope imaging data to classify each Chandra-detected compact X-ray source as a low-mass (i.e., donor mass ≲3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), high-mass (donor mass ≳8<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), or intermediate-mass XRB based on either the location of its candidate counterpart on optical color–magnitude diagrams or the age of its host star cluster. In addition to the standard (single and/or truncated) power-law functional shape, we approximate the resulting XLFs with a Schechter function. We identify a marginally significant (at the 1<jats:italic>σ</jats:italic>-to-2<jats:italic>σ</jats:italic> level) exponential downturn for the high-mass XRB XLF, at <jats:inline-formula> <jats:tex-math> <?CDATA ${\ell }\simeq {38.48}_{-0.33}^{+0.52}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">ℓ</mml:mi> <mml:mo>≃</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>38.48</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.33</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.52</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe531ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (in log CGS units). In contrast, the low- and intermediate-mass XRB XLFs, as well as the total XLF of M83, are formally consistent with sampling statistics from a single power law. Our method suggests a non-negligible contribution from low- and possibly intermediate-mass XRBs to the total XRB XLF of M83, i.e., between 20% and 50%, in broad agreement with X-ray-based XLFs. More generally, we caution against considerable contamination from X-ray emitting supernova remnants to the published, X-ray-based XLFs of M83, and possibly all actively star-forming galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the coming years, next-generation space-based infrared observatories will significantly increase our samples of rare massive stars, representing a tremendous opportunity to leverage modern statistical tools and methods to test massive stellar evolution in entirely new environments. Such work is only possible if the observed objects can be reliably classified. Spectroscopic observations are infeasible with more distant targets, and so we wish to determine whether machine-learning methods can classify massive stars using broadband infrared photometry. We find that a Support Vector Machine classifier is capable of coarsely classifying massive stars with labels corresponding to hot, cool, and emission-line stars with high accuracy, while rejecting contaminating low-mass giants. Remarkably, 76% of emission-line stars can be recovered without the need for narrowband or spectroscopic observations. We classify a sample of ∼2500 objects with no existing labels and identify 14 candidate emission-line objects. Unfortunately, despite the high precision of the photometry in our sample, the heterogeneous origins of the labels for the stars in our sample severely inhibit our classifier from distinguishing classes of stars with more granularity. Ultimately, no large and homogeneously labeled sample of massive stars currently exists. Without significant efforts to robustly classify evolved massive stars—which is feasible given existing data from large all-sky spectroscopic surveys—shortcomings in the labeling of existing data sets will hinder efforts to leverage the next generation of space observatories.</jats:p>