Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>In this study, we present a visual explanation of a deep learning solar flare forecast model and its relationship to physical parameters of solar active regions (ARs). For this, we use full-disk magnetograms at 00:00 UT from the Solar and Heliospheric Observatory/Michelson Doppler Imager and the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, physical parameters from the Space-weather HMI Active Region Patch (SHARP), and Geostationary Operational Environmental Satellite X-ray flare data. Our deep learning flare forecast model based on the Convolutional Neural Network (CNN) predicts “Yes” or “No” for the daily occurrence of C-, M-, and X-class flares. We interpret the model using two CNN attribution methods (guided backpropagation and Gradient-weighted Class Activation Mapping [Grad-CAM]) that provide quantitative information on explaining the model. We find that our deep learning flare forecasting model is intimately related to AR physical properties that have also been distinguished in previous studies as holding significant predictive ability. Major results of this study are as follows. First, we successfully apply our deep learning models to the forecast of daily solar flare occurrence with TSS = 0.65, without any preprocessing to extract features from data. Second, using the attribution methods, we find that the polarity inversion line is an important feature for the deep learning flare forecasting model. Third, the ARs with high Grad-CAM values produce more flares than those with low Grad-CAM values. Fourth, nine SHARP parameters such as total unsigned vertical current, total unsigned current helicity, total unsigned flux, and total photospheric magnetic free energy density are well correlated with Grad-CAM values.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Molybdenum isotopes measured in most individual presolar silicon carbide grains are dominated by <jats:italic>s</jats:italic>-process contributions from the helium intershells of asymptotic giant branch (AGB) stars. The much smaller isotopic variations in molybdenum in meteorites and their components are largely controlled by <jats:italic>s</jats:italic>-process enrichments or depletions relative to terrestrial composition but lie along two parallel <jats:italic>s</jats:italic>-process mixing lines separated by what has been suggested to be an <jats:italic>r</jats:italic>-process contribution. The two mixing lines are populated by carbonaceous-chondrite- and noncarbonaceous-chondrite-related meteorites (CC and NC groups, respectively). We have compared molybdenum isotopic data for presolar grains with those from meteorites and renormalized the meteorite data in a way that is consistent with <jats:italic>s</jats:italic>-, <jats:italic>r</jats:italic>-, and <jats:italic>p</jats:italic>-process contributions observed in presolar SiC grains. The results indicate that (1) there seems to be a fixed ratio between <jats:italic>p</jats:italic>- and <jats:italic>r</jats:italic>-process contributions in <jats:italic>all</jats:italic> data, (2) the dichotomy in molybdenum isotopes between the CC and NC groups can be explained by variations in the isotope makeup of the <jats:italic>s</jats:italic>-process contribution to the meteoritic samples, (3) this variability is similar to the variations in <jats:italic>s</jats:italic>-process molybdenum from different AGB stars deduced from presolar grain analyses, and (4) the larger range of isotopic compositions found in refractory inclusions is also consistent with <jats:italic>s</jats:italic>-process isotope variability.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We studied general advective accretion solutions around a Kerr black hole (BH) by investigating two types of inflow gases at the outer accretion boundary (AB). We classified these two types of gases as cold-mode and hot-mode inflow gas at the outer AB on the basis of their temperatures and solutions. We found that the hot-mode gas is more efficient for angular momentum transport around the outer AB than the cold-mode gas. The hot-mode gas can give multiple global (popular as a shock solution) or single sonic point solutions, and the cold-mode gas can give a smooth global solution (popularly known as advection-dominated accretion flow) or two sonic point solutions. These solutions are also presented on a plane in energy and angular momentum (<jats:italic>B</jats:italic> <jats:sub>ob</jats:sub>−<jats:italic>L</jats:italic> <jats:sub>0</jats:sub>) parameter space. For the first time, we explored theoretically the relation between the nature of accretion solutions and the nature of the initial accreting gas at the AB with a detailed computational and possible physical analysis. We also found that the surface density of the flow is highly affected by changes in the temperature at the AB, which can alter the radiative emissivities of the flow. The flow variables of various advective solutions are also compared. On the basis of those results, we plotted some inner disk structures around the BHs. By doing so, we conjecture on the persistent/transient nature of spectral states, soft excess, and timescales of variabilities around the BH X-ray binaries and active galactic nuclei.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The vegetation red edge (VRE) is a unique spectral fingerprint of light-harvesting vegetation on Earth and provides a robust remote detectable surface biosignature of exoplanets. To improve the detectability and sensitivity, we have studied the diurnal variability of VRE in the disk-integrated spectra of Earth and also Earth analogs in the case of different observing geometry conditions. Simulation results show that the VRE index varies from &lt;−0.4 to &gt;0.6 at a diurnal timescale for both present and also Late Triassic Earth, and the maximum variation of VRE in 1 day changes by &gt;3 times with different observing geometry conditions. This means that the extraterrestrial light-harvesting vegetation (even if it really exists) will not be efficiently detectable without proper observing geometry conditions and time, especially in the case of the exoplanets covered with thick clouds. The VRE temporal variation curve can also be used to retrieve the cloud cover fraction and continent distribution of exoplanets with relatively high precision. Several observational strategies are proposed to detect the light-harvesting vegetation and retrieve the planetary information from the planet’s VRE variation signals, and a mock observation is also demonstrated.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use a generic thermophysical model to study in detail the formation of water-ice frost in the near-surface layers of comet 67P/Churyumov-Gerasimenko. We show that nightly frost formation is a common phenomenon. In particular, while abrupt landscapes may be conducive to frost formation, they are not a requisite condition. We show that the process of subsurface frost formation is similar to that of the condensed ice layer, or crust, underneath. The sublimation of frost produces regular, enhanced outgassing early in the morning. In the case of 67P, this activity is subordinate to and precedes the daily peak sourced from the ice-rich layers located above the diurnal skin depth. In any case, frost activity should be a nominal component of comet water activity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Interchange reconnection has been proposed as a mechanism for the generation of the slow solar wind, and a key contributor to determining its characteristic qualities. In this paper we study the implications of interchange reconnection for the structure of the plasma and field in the heliosphere. We use the Adaptively Refined Magnetohydrodynamic Solver to simulate the coronal magnetic evolution in a coronal topology containing both a pseudostreamer and helmet streamer. We begin with a geometry containing a low-latitude coronal hole that is separated from the main polar coronal hole by a pseudostreamer. We drive the system by imposing rotating flows at the solar surface within and around the low-latitude coronal hole, which leads to a corrugation (at low altitudes) of the separatrix surfaces that separate open from closed magnetic flux. Interchange reconnection is induced both at the null points and separators of the pseudostreamer, and at the global helmet streamer. We demonstrate that a preferential occurrence of interchange reconnection in the “lanes” between our driving cells leads to a filamentary pattern of newly opened flux in the heliosphere. These flux bundles connect to but extend far from the separatrix-web (S-Web) arcs at the source surface. We propose that the pattern of granular and supergranular flows on the photosphere should leave an observable imprint in the heliosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have observed the very low-mass Class 0 protostar IRAS 15398−3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H<jats:sub>2</jats:sub>CO, SO, and C<jats:sup>18</jats:sup>O line emission, which extends from the source in a direction almost perpendicular to the known active outflow. Molecular line emission from H<jats:sub>2</jats:sub>CO, SO, SiO, and CH<jats:sub>3</jats:sub>OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398−3359, by 1200 au. The arc-like structure is blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s<jats:sup>−1</jats:sup> over 1200 au along the linear feature seen in the H<jats:sub>2</jats:sub>CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH<jats:sub>3</jats:sub>OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398−3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>HH 211 is a highly collimated jet with a chain of knots and a wiggle structure on both sides of a young Class 0 protostar. We used two epochs of Atacama Large Millimeter/submillimeter Array (ALMA) data to study its inner jet in the CO(<jats:italic>J</jats:italic> = 3–2), SiO(<jats:italic>J</jats:italic> = 8–7), and SO(<jats:italic>N</jats:italic> <jats:sub> <jats:italic>J</jats:italic> </jats:sub> = 8<jats:sub>9</jats:sub>–7<jats:sub>8</jats:sub>) lines at ∼25 au resolution. With these ALMA and previous 2008 Submillimeter Array data, the proper motion of 8 knots within ∼250 au of the central source is found to be ∼0068 per year (∼102 km s<jats:sup>−1</jats:sup>), consistent with previous measurements in the outer jet. At about four times higher resolution, the reflection-symmetric wiggle can be still fitted by a previously proposed orbiting jet source model. Previously detected continuous structures in the inner jet are now resolved, containing at least 5 subknots. These subknots are interpreted in terms of a variation in the ejection velocity of the jet with a period of ∼4.5 yr, shorter than that of the outer knots. In addition, backward and forward shocks are resolved in a fully formed knot, BK3, and signatures of internal working surface and sideways ejection are identified in position–velocity diagrams. In this knot, low-density SO and CO layers are surrounded by a high-density SiO layer.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a comprehensive study of three solar energetic electron events observed in the Earth’s cusp/lobe regions by the BeiDa Image Electron Spectrometer (BD-IES) on board a BeiDou satellite in an inclined (55°) geosynchronous orbit in 2015 October, 2015 November, and 2016 January, respectively. In all three events at energies above 50 keV, the electron omnidirectional differential fluxes from BD-IES show a strong (∼0.7–0.9) correlation with the simultaneous electron fluxes from the Wind 3DP instrument in the interplanetary medium, but generally with a smaller intensity. Compared to the Wind 3DP spectra of electron flux versus energy, the BD-IES electron spectra also fit well to a power-law function, <jats:inline-formula> <jats:tex-math> <?CDATA ${J}_{\mathrm{IES}}\propto {E}^{-{\gamma }_{\mathrm{IES}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabdb2bieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, but the power-law spectral index appears to be mostly smaller than the 3DP spectral index, for all three events. These measurements provide the first observational evidence that solar/interplanetary energetic electrons can directly and continuously enter the planet’s cusp/lobe regions and get trapped there, probably leading to a contribution to the energetic electrons and/or seed particles for acceleration in the planetary magnetosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, analogs to high-redshift galaxies, from the DYNAMO sample using new Atacama Large Millimeter/submillimeter Array and GMOS/Gemini observations. We combine our sample with 12 galaxies at <jats:italic>z</jats:italic> ∼ 0.5–2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor 2.45 ± 0.38 for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the coexistence of a thin molecular gas disk and a thick ionized one. This result has a direct impact on the Toomre <jats:italic>Q</jats:italic> and pressure derived in galaxies. We obtain pressures ∼0.22 dex lower on average when using the molecular gas velocity dispersion, <jats:italic>σ</jats:italic> <jats:sub>0,mol</jats:sub>. We find that <jats:italic>σ</jats:italic> <jats:sub>0,mol</jats:sub> increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimate <jats:italic>σ</jats:italic> <jats:sub>0,mol</jats:sub> at high redshift. Our results suggest that efforts to compare the kinematics of gas using ionized gas as a proxy for the total gas may overestimate the velocity dispersion by a significant amount in galaxies at the peak of cosmic star formation. When using the molecular gas as a tracer, our sample is not consistent with predictions from star formation models with constant efficiency, even when including transport as a source of turbulence. Feedback models with variable star formation efficiency, <jats:italic>ϵ</jats:italic> <jats:sub>ff</jats:sub>, and/or feedback efficiency, <jats:italic>p</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>m</jats:italic> <jats:sub>*</jats:sub>, better predict our observations.</jats:p>