Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The current work investigates the Venusian solar-wind-induced magnetosphere at a high spatial resolution using all Venus Express (VEX) magnetic observations through an unbiased statistical method. We first evaluate the predictability of the interplanetary magnetic field (IMF) during VEX’s Venusian magnetospheric transits and then map the induced field in a cylindrical coordinate system under different IMF conditions. Our mapping resolves structures on various scales, ranging from the ionopause to the classical IMF draping. We also resolve two recently reported structures, a low-ionosphere magnetization over the terminator, and a global “looping” structure in the near magnetotail. In contrast to the reported IMF-independent cylindrical magnetic field of both structures, our results illustrate their IMF dependence. In both structures, the cylindrical magnetic component is more intense in the hemisphere with an upward solar wind electric field (<jats:italic>E</jats:italic> <jats:sup>SW</jats:sup>) than in the opposite hemisphere. Under downward <jats:italic>E</jats:italic> <jats:sup>SW</jats:sup>, the looping structure even breaks, which is attributable to an additional draped magnetic field structure wrapping toward −<jats:italic>E</jats:italic> <jats:sup>SW</jats:sup>. In addition, our results suggest that these two structures are spatially separate. The low-ionosphere magnetization occurs in a very narrow region, at about 88°–95° solar zenith angle and 185–210 km altitude. A least-squares fit reveals that this structure is attributable to an antisunward line current with 191.1 A intensity at 179 ± 10 km altitude, developed potentially in a Cowling channel.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper, we present a multiwavelength analysis to mass draining and oscillations in a large quiescent filament prior to its successful eruption on 2015 April 28. The eruption of a smaller filament that was parallel and in close, ∼350″ proximity was observed to induce longitudinal oscillations and enhance mass draining within the filament of interest. The longitudinal oscillation with an amplitude of ∼25 Mm and ∼23 km s<jats:sup>−1</jats:sup> underwent no damping during its observable cycle. Subsequently the slightly enhanced draining may have excited a eruption behind the limb, leading to a feedback that further enhanced the draining and induced simultaneous oscillations within the filament of interest. We find significant damping for these simultaneous oscillations, where the transverse oscillations proceeded with the amplitudes of ∼15 Mm and ∼14 km s<jats:sup>−1</jats:sup>, while the longitudinal oscillations involved a larger displacement and velocity amplitude (∼57 Mm, ∼43 km s<jats:sup>−1</jats:sup>). The second grouping of oscillations lasted for ∼2 cycles and had a similar period of ∼2 hr. From this, the curvature radius and transverse magnetic field strength of the magnetic dips supporting the filaments can be estimated to be ∼355 Mm and ≥34 G. The mass draining within the filament of interest lasted for ∼14 hr. The apparent velocity grew from ∼35 to ∼85 km s<jats:sup>−1</jats:sup>, with the transition being coincident with the occurrence of the oscillations. We conclude that two filament eruptions are sympathetic, i.e., the eruption of the quiescent filament was triggered by the eruption of the nearby smaller filament.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Fermi-LAT unassociated sources represent some of the most enigmatic gamma-ray sources in the sky. Observations with the Swift-XRT and -UVOT telescopes have identified hundreds of likely X-ray and UV/optical counterparts in the uncertainty ellipses of the unassociated sources. In this work we present spectral fitting results for 205 possible X-ray/UV/optical counterparts to 4FGL unassociated targets. Assuming that the unassociated sources contain mostly pulsars and blazars, we develop a neural network classifier approach that applies gamma-ray, X-ray, and UV/optical spectral parameters to yield a descriptive classification of unassociated spectra into pulsars and blazars. From our primary sample of 174 Fermi sources with a single X-ray/UV/optical counterpart, we present 132 <jats:italic>P</jats:italic> <jats:sub>bzr</jats:sub> &gt; 0.99 likely blazars and 14 <jats:italic>P</jats:italic> <jats:sub>bzr</jats:sub> &lt; 0.01 likely pulsars, with 28 remaining ambiguous. These subsets of the unassociated sources suggest a systematic expansion to catalogs of gamma-ray pulsars and blazars. Compared to previous classification approaches our neural network classifier achieves significantly higher validation accuracy and returns more bifurcated <jats:italic>P</jats:italic> <jats:sub>bzr</jats:sub> values, suggesting that multiwavelength analysis is a valuable tool for confident classification of Fermi unassociated sources.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In recent years, the new physics of the Sun has been revealed using advanced data with high spatial and temporal resolutions. The Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory has accumulated abundant observation data for the study of solar activity with sufficient cadence, but their spatial resolution (about 1″) is not enough to analyze the subarcsecond structure of the Sun. On the other hand, high-resolution observation from large-aperture ground-based telescopes, such as the 1.6 m Goode Solar Telescope (GST) at the Big Bear Solar Observatory, can achieve a much higher resolution on the order of 0.″1 (about 70 km). However, these high-resolution data only became available in the past 10 yr, with a limited time period during the day and with a very limited field of view. The Generative Adversarial Network (GAN) has greatly improved the perceptual quality of images in image translation tasks, and the self-attention mechanism can retrieve rich information from images. This paper uses HMI and GST images to construct a precisely aligned data set based on the scale-invariant feature transform algorithm and t0 reconstruct the HMI continuum images with four times better resolution. Neural networks based on the conditional GAN and self-attention mechanism are trained to restore the details of solar active regions and to predict the reconstruction error. The experimental results show that the reconstructed images are in good agreement with GST images, demonstrating the success of resolution improvement using machine learning.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Fornax dwarf spheroidal galaxy has an anomalous number of globular clusters, five, for its stellar mass. There is a longstanding debate about a potential sixth globular cluster (Fornax 6) that has recently been “rediscovered” in DECam imaging. We present new Magellan/M2FS spectroscopy of the Fornax 6 cluster and Fornax dSph. Combined with literature data we identify ∼15–17 members of the Fornax 6 cluster, showing that this overdensity is indeed a star cluster and associated with the Fornax dSph. The cluster is significantly more metal-rich (mean metallicity of <jats:inline-formula> <jats:tex-math> <?CDATA $\overline{[\mathrm{Fe}/{\rm{H}}]}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mo stretchy="false">[</mml:mo> <mml:mi>Fe</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">]</mml:mo> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2cd2ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> = −0.71 ± 0.05) than the other five Fornax globular clusters (−2.5 &lt; [Fe/H] &lt; −1.4) and more metal-rich than the bulk of Fornax. We measure a velocity dispersion of <jats:inline-formula> <jats:tex-math> <?CDATA ${5.6}_{-1.6}^{+2.0}\mathrm{km}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>5.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi>km</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2cd2ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> corresponding to an anomalously high mass-to-light of 15 &lt; <jats:italic>M</jats:italic>/<jats:italic>L</jats:italic> &lt; 258 at 90% confidence when calculated assuming equilibrium. Two stars inflate this dispersion and may be either Fornax field stars or as yet unresolved binary stars. Alternatively, the Fornax 6 cluster may be undergoing tidal disruption. Based on its metal-rich nature, the Fornax 6 cluster is likely younger than the other Fornax clusters, with an estimated age of ∼2 Gyr when compared to stellar isochrones. The chemodynamics and star formation history of Fornax shows imprints of major events such as infall into the Milky Way, multiple pericenter passages, star formation bursts, and/or potential mergers or interactions. Any of these events may have triggered the formation of the Fornax 6 cluster.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We employ ionization-parameter mapping (IPM) to infer the optical depth of H <jats:sc>ii</jats:sc> regions in the northern half of M33. We construct [O <jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic>5007/[O <jats:sc>ii</jats:sc>]<jats:italic>λ</jats:italic>3727 and [O <jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic>5007/[S <jats:sc>ii</jats:sc>]<jats:italic>λ</jats:italic>6724 ratio maps from narrowband images continuum-subtracted in this way, from which we classify the H <jats:sc>ii</jats:sc> regions by optical depth to ionizing radiation, based on their ionization structure. This method works relatively well in the low-metallicity regime, <jats:inline-formula> <jats:tex-math> <?CDATA $12+\mathrm{log}({\rm{O}}/{\rm{H}})\leqslant 8.4$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>12</mml:mn> <mml:mo>+</mml:mo> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≤</mml:mo> <mml:mn>8.4</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2c85ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where [O <jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic> <jats:italic>λ</jats:italic>4959, 5007 is strong. However, at higher metallicities, the method breaks down due to the strong dependence of the [O <jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic> <jats:italic>λ</jats:italic>4959, 5007 emission lines on the nebular temperature. Thus, although O<jats:sup>++</jats:sup> may be present in metal-rich H <jats:sc>ii</jats:sc> regions, these commonly used emission lines do not serve as a useful indicator of its presence, and hence the O ionization state. In addition, IPM as a diagnostic of optical depth is limited by spatial resolution. We also report a region of highly excited [O <jats:sc>iii</jats:sc>] extending over an area ∼1 kpc across and [O <jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic>5007 luminosity of 4.9 ± 1.5 × 10<jats:sup>38</jats:sup> erg s<jats:sup>−1</jats:sup>, which is several times higher than the ionizing budget of any potential sources in this portion of the galaxy. Finally, this work introduces a new method for continuum subtraction of narrowband images based on the dispersion of pixels around the mode of the diffuse-light flux distribution. In addition to M33, we demonstrate the method on C <jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic>1909 imaging of Haro 11, ESO 338-IG004, and Mrk 71.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Partially ionized plasmas, such as the solar chromosphere, require a generalized Ohm’s law including the effects of ambipolar and Hall drift. While both describe transport processes that arise from the multifluid equations and are therefore of hyperbolic nature, they are often incorporated in models as a diffusive, i.e., parabolic process. While the formulation as such is easy to include in standard MHD models, the resulting diffusive time-step constraints do require often a computationally more expensive implicit treatment or super-time-stepping approaches. In this paper we discuss an implementation that retains the hyperbolic nature and allows for an explicit integration with small computational overhead. In the case of ambipolar drift, this formulation arises naturally by simply retaining a time derivative of the drift velocity that is typically omitted. This alone leads to time-step constraints that are comparable to the native MHD time-step constraint for a solar setup including the region from photosphere to lower solar corona. We discuss an accelerated treatment that can further reduce time-step constraints if necessary. In the case of Hall drift we propose a hyperbolic formulation that is numerically similar to that for the ambipolar drift and we show that the combination of both can be applied to simulations of the solar chromosphere at minimal computational expense.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Interplanetary coronal mass ejection (ICME) shocks are known to accelerate particles and contribute significantly to solar energetic particle events. We have performed magnetohydrodynamic-particle in cell simulations of ICME shocks to understand the acceleration mechanism. These shocks vary in Alfvénic Mach numbers as well as in magnetic field orientations (parallel and quasi-perpendicular). We find that diffusive shock acceleration plays a significant role in accelerating particles in a parallel ICME shock. In contrast, shock drift acceleration (SDA) plays a pivotal role in a quasi-perpendicular shock. High-Mach shocks are seen to accelerate particles more efficiently. Our simulations suggest that background turbulence and local particle velocity distribution around the shock can indirectly hint at the acceleration mechanism. Our results also point toward a few possible in situ observations that could validate our understanding of the topic.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Kepler transit survey with follow-up spectroscopic observations has discovered numerous super-Earth sized planets and revealed intriguing features of their sizes, orbital periods, and their relations between adjacent planets. For the first time, we investigate the size evolution of planets via both giant impacts and photoevaporation to compare with these observed features. We calculate the size of a protoplanet, which is the sum of its core and envelope sizes, by analytical models. <jats:italic>N</jats:italic>-body simulations are performed to evolve planet sizes during the giant impact phase with envelope stripping via impact shocks. We consider the initial radial profile of the core mass and the initial envelope mass fractions as parameters. Inner planets can lose their whole envelopes via giant impacts, while outer planets can keep their initial envelopes, because they do not experience giant impacts. Photoevaporation is simulated to evolve planet sizes afterward. Our results suggest that the period-radius distribution of the observed planets would be reproduced if we perform simulations in which the initial radial profile of the core mass follows a wide range of power-law distributions and the initial envelope mass fractions are ∼0.1. Moreover, our model shows that the adjacent planetary pairs have similar sizes and regular spacings, with slight differences from detailed observational results such as the radius gap.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Radio Arc is a system of organized nonthermal filaments (NTFs) located within the Galactic center (GC) region of the Milky Way. Recent observations of the Radio Arc NTFs revealed a magnetic field that alternates between being parallel and rotated with respect to the orientation of the filaments. This pattern is in stark contrast to the predominantly parallel magnetic field orientations observed in other GC NTFs. To help elucidate the origin of this pattern, we analyze spectro-polarimetric data of the Radio Arc NTFs using an Australian Telescope Compact Array data set covering the continuous frequency range from ∼4 to 11 GHz at a spectral resolution of 2 MHz. We fit depolarization models to the spectral polarization data to characterize Faraday effects along the line of sight. We assess whether structures local to the Radio Arc NTFs may contribute to the unusual magnetic field orientation. External Faraday effects are identified as the most likely origin of the rotation observed for the Radio Arc NTFs; however, internal Faraday effects are also found to be likely in regions of parallel magnetic field. The increased likelihood of internal Faraday effects in parallel magnetic field regions may be attributed to the effects of structures local to the GC. One such structure could be the Radio Shell local to the Radio Arc NTFs. Future studies are needed to determine whether this alternating magnetic field pattern is present in other multi-stranded NTFs, or is a unique property resulting from the complex interstellar region local to the Radio Arc NTFs.</jats:p>