Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a new 3D magnetohydrostatic (MHS) direct elliptic solver for extrapolating the coronal magnetic field from photospheric boundary conditions in a manner consistent with an assumed plasma distribution. We use it to study the uniqueness of the reconstructed magnetic field as a function of how significant the plasma forcing is on the force balance of the magnetic field. To this end, we consider an analytic MHS model as ground truth. The model uses two free parameters to decompose the current into two parts: a magnetic-field-aligned component and a cross-field component. We perform a comprehensive study of the 2D parameter space to understand under what conditions the ground truth can be reproduced uniquely. We find that current oriented perpendicular to the magnetic field has a smaller solution space than the same amount of current oriented parallel to the magnetic field, and so MHS regimes with larger proportions of plasma-related forcing may be a promising avenue toward finding unique magnetic field reconstructions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A newly calculated ab initio potential energy surface is used to compute collision-driven state-changing cross sections and rate coefficients over a range from 5 to 100 K for CN<jats:sup>−</jats:sup>(<jats:sup>1</jats:sup>Σ), the smallest anion detected in the interstellar medium, interacting with He, an abundant species in this environment. We compare our presently computed rate coefficients with those previously published for the similar and important systems CN–He, CN-H<jats:sub>2</jats:sub>, and CN<jats:sup>−</jats:sup>–H<jats:sub>2</jats:sub> to illustrate the broader network of inelastic, state-changing processes for these four systems. We also discuss the size-scaling effects that occur when changing partners from He to H<jats:sub>2</jats:sub>. We further analyze the differences in size between collision-driven rate coefficients when going from neutral CN to its anion. All the present results are discussed in detail, to provide accurate and realistic data for chemical networks that wish to include the CN<jats:sup>−</jats:sup> anion in their modeling of astrochemical environments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the properties of magnetic fields (<jats:italic>B</jats:italic> fields) in two clumps (clump 1 and clump 2), located at the waist of the bipolar H <jats:sc>ii</jats:sc> region Sh 2-201, based on James Clerk Maxwell Telescope SCUBA-2/POL-2 observations of 850 <jats:italic>μ</jats:italic>m polarized dust emission. We find that <jats:italic>B</jats:italic> fields in the direction of the clumps are bent and compressed, showing bow-like morphologies, which we attribute to the feedback effect of the H <jats:sc>ii</jats:sc> region on the surface of the clumps. Using the modified Davis–Chandrasekhar–Fermi method, we estimate <jats:italic>B</jats:italic>-field strengths of 266 and 65 <jats:italic>μ</jats:italic>G for clump 1 and clump 2, respectively. From virial analyses and critical mass ratio estimates, we argue that clump 1 is gravitationally bound and could be undergoing collapse, whereas clump 2 is unbound and stable. We hypothesize that the interplay of the thermal pressure imparted by the H <jats:sc>ii</jats:sc> region, the <jats:italic>B</jats:italic>-field morphologies, and the various internal pressures of the clumps (such as magnetic, turbulent, and gas thermal pressures) has the following consequences: (a) formation of clumps at the waist of the H <jats:sc>ii</jats:sc> region; (b) progressive compression and enhancement of the <jats:italic>B </jats:italic>fields in the clumps; (c) stronger <jats:italic>B</jats:italic> fields that will shield the clumps from erosion by the H <jats:sc>ii</jats:sc> region and cause pressure equilibrium between the clumps and the H <jats:sc>ii</jats:sc> region, thereby allowing expanding ionization fronts to blow away from the filament ridge, forming bipolar H <jats:sc>ii</jats:sc> regions; and (d) stronger <jats:italic>B</jats:italic> fields and turbulence that will be able to stabilize the clumps. A study of a larger sample of bipolar H <jats:sc>ii</jats:sc> regions would help to determine whether our hypotheses are widely applicable.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A statistical survey of spectral anisotropy of space plasma turbulence is performed using five years of measurements from the Magnetospheric Multiscale mission in the magnetosheath. By measuring the five-point second-order structure functions of the magnetic field, we have for the first time quantified the three-dimensional anisotropies and scalings at sub-ion scales (&lt;100 km). In the local reference frame <jats:inline-formula> <jats:tex-math> <?CDATA $({\hat{L}}_{\perp },{\hat{l}}_{\perp },{\hat{l}}_{\parallel })$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab99caieqn1.gif" xlink:type="simple" /> </jats:inline-formula> defined with respect to local mean magnetic field <jats:inline-formula> <jats:tex-math> <?CDATA ${{\boldsymbol{B}}}_{0}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab99caieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, the “statistical eddies” are found to be mostly elongated along <jats:inline-formula> <jats:tex-math> <?CDATA ${{\boldsymbol{B}}}_{0}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab99caieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and shortened in the direction perpendicular to both <jats:inline-formula> <jats:tex-math> <?CDATA ${{\boldsymbol{B}}}_{0}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab99caieqn4.gif" xlink:type="simple" /> </jats:inline-formula> and local field fluctuations. From several <jats:italic>d</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub> (ion inertial length) toward ∼0.05 <jats:italic>d</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub>, the ratio between eddies’ parallel and perpendicular lengths features a trend of rise then fall, whereas the anisotropy in the perpendicular plane appears scale-invariant. Specifically, the anisotropy relations for the total magnetic field at 0.1–1.0 <jats:italic>d</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub> are obtained as <jats:inline-formula> <jats:tex-math> <?CDATA ${l}_{\parallel }\simeq 2.44\cdot {l}_{\perp }^{0.71}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab99caieqn5.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\perp }\simeq 1.58\cdot {l}_{\perp }^{1.08}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab99caieqn6.gif" xlink:type="simple" /> </jats:inline-formula>, respectively. Our results provide new observational evidence to compare with phenomenological models and numerical simulations, which may help to better understand the nature of kinetic-scale turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on observations of a solar jet propagating along coronal loops taken by the Solar Dynamics Observatory, the Interface Region Imaging Spectrograph, and the 1 m New Vacuum Solar Telescope. The ejecta of the jet consist of multithermal components and propagate with a speed greater than 100 km s<jats:sup>−1</jats:sup>. Brightenings are found in the remote footpoints of the coronal loops having compact and round shape in the H<jats:italic>α</jats:italic> images. The emission peak of the remote brightening in the Atmospheric Imaging Assembly (AIA) 94 Å passband lags 60 s behind that in the jet base. The brightenings in the remote footpoints are believed to be consequences of heating by nonthermal electrons, MHD waves, and/or a conduction front generated by the magnetic reconnection processes of the jet. The heating in the remote footpoints leads to extension of the brightening along the loops toward the jet base, which is believed to be the chromospheric evaporation. This apparently acts as a brake on the ejecta, leading to a deceleration in the range from 1.5 to 3 km s<jats:sup>−2</jats:sup> with an error of ∼1.0 km s<jats:sup>−2</jats:sup> when the chromospheric evaporation and the ejecta meet at locations near the loop apexes. The dynamics of this jet allows for a unique opportunity to diagnose the chromospheric evaporation from the remote footpoints, from which we deduce a velocity in the range of 330–880 km s<jats:sup>−1</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>By combining LAMOST DR4 and Gaia DR2 common red clump stars with age and proper motion, we analyze the amplitude evolution of the stellar warp independently of any assumption with a simple model. The greatest height of the warp disk increases with galactocentric distance in different populations and is dependent on age: the younger stellar populations exhibit stronger warp features than the old ones, accompanied by the warp amplitude <jats:italic>γ</jats:italic> (age) decreasing with age, and its first derivative <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{\gamma }(\mathrm{age})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab93adieqn1.gif" xlink:type="simple" /> </jats:inline-formula> is different from zero. The azimuth of the line of nodes <jats:italic>ϕ</jats:italic> <jats:sub> <jats:italic>w</jats:italic> </jats:sub> is stable at −5° without clear time evolution, which perfectly confirms some previous works. All of this self-consistent evidence supports that our Galactic warp should most likely be a long-lived but nonsteady structure and not a transient one, which is supporting that the warp originated from gas infall onto the disk or other hypotheses that suppose that the warp mainly affects the gas, and consequently, younger populations tracing the gas are stronger than older ones. In other words, the Galactic warp is induced by the nongravitational interaction over the disk models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Large amplitude (up to 70 mV m<jats:sup>−1</jats:sup>) whistler-mode waves at frequencies of ∼0.2–0.4 <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub> (electron cyclotron frequency) are frequently observed in the solar wind. The waves are obliquely propagating at angles close to the resonance cone, resulting in significant electric fields parallel to the background magnetic field, enabling strong interactions with solar wind electrons. Very narrowband (sinusoidal waveforms) and less coherent waves (more irregular waveforms) occur, but do not have a bimodal distribution. Frequencies and/or propagation angles are distinctly different from whistler-mode waves usually observed in the solar wind, and amplitudes are 1–3 orders of magnitude larger. Waves occur most often in association with stream interaction regions, and are often “close-packed.” Wave occurrence as a function of normalized electron heat flux and beta is consistent with the whistler heat flux fan instability for both the narrowband coherent and the incoherent waves. The incoherent waves are associated with zero or near zero heat flux. This suggests that the less coherent waves may be more effective in regulating the electron heat flux, or that the scattering and energization of solar wind electrons by the narrowband waves results in broadening of the waves. The oblique propagation and large amplitudes of both the narrowband and less coherent whistlers enable resonant interactions with electrons over a broad energy range, and, unlike parallel whistlers, do not require that the electrons and waves counter-propagate. Therefore, they are much more effective in modifying solar wind electron distributions than parallel propagating waves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>With the distance sum rule in the Friedmann–Lemaître–Robertson–Walker metric, model-independent constraints on both the Hubble constant <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> and spatial curvature <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{K}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn1.gif" xlink:type="simple" /> </jats:inline-formula> can be obtained using strong lensing time-delay data and Type Ia supernovae (SNe Ia) luminosity distances. This method is limited by the relatively low redshifts of SNe Ia, however. Here, we propose using quasars as distance indicators, extending the coverage to encompass the redshift range of strong lensing systems. We provide a novel and improved method of determining <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{K}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn2.gif" xlink:type="simple" /> </jats:inline-formula> simultaneously. By applying this technique to the time-delay measurements of seven strong lensing systems and the known ultraviolet versus X-ray luminosity correlation of quasars, we constrain the possible values of both <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{K}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, and find that <jats:inline-formula> <jats:tex-math> <?CDATA ${H}_{0}={75.3}_{-2.9}^{+3.0}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn4.gif" xlink:type="simple" /> </jats:inline-formula> km <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn5.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{K}=-{0.01}_{-0.17}^{+0.18}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. The measured <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{K}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn7.gif" xlink:type="simple" /> </jats:inline-formula> is consistent with zero spatial curvature, indicating that there is no significant deviation from a flat universe. If we use flatness as a prior, we infer that <jats:inline-formula> <jats:tex-math> <?CDATA ${H}_{0}={75.3}_{-1.9}^{+1.9}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn8.gif" xlink:type="simple" /> </jats:inline-formula> km <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn9.gif" xlink:type="simple" /> </jats:inline-formula>, representing a precision of 2.5%. If we further combine these data with the 1048 current Pantheon SNe Ia, our model-independent constraints can be further improved to <jats:inline-formula> <jats:tex-math> <?CDATA ${H}_{0}={75.3}_{-2.9}^{+3.0}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn10.gif" xlink:type="simple" /> </jats:inline-formula> km <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn11.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{K}={0.05}_{-0.14}^{+0.16}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn12.gif" xlink:type="simple" /> </jats:inline-formula>. In every case, we find that the Hubble constant measured with this technique is strongly consistent with the value (∼74 km <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab959bieqn13.gif" xlink:type="simple" /> </jats:inline-formula>) measured using the local distance ladder, as opposed to the value optimized by Planck.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Event Horizon Telescope (EHT) provides the unprecedented ability to directly resolve the structure and dynamics of black hole emission regions on scales smaller than their horizons. This has the potential to critically probe the mechanisms by which black holes accrete and launch outflows, and the structure of supermassive black hole spacetimes. However, accessing this information is a formidable analysis challenge for two reasons. First, the EHT natively produces a variety of data types that encode information about the image structure in nontrivial ways; these are subject to a variety of systematic effects associated with very long baseline interferometry and are supplemented by a wide variety of auxiliary data on the primary EHT targets from decades of other observations. Second, models of the emission regions and their interaction with the black hole are complex, highly uncertain, and computationally expensive to construct. As a result, the scientific utilization of EHT observations requires a flexible, extensible, and powerful analysis framework. We present such a framework, <jats:sc>Themis</jats:sc>, which defines a set of interfaces between models, data, and sampling algorithms that facilitates future development. We describe the design and currently existing components of <jats:sc>Themis</jats:sc>, how <jats:sc>Themis</jats:sc> has been validated thus far, and present additional analyses made possible by <jats:sc>Themis</jats:sc> that illustrate its capabilities. Importantly, we demonstrate that <jats:sc>Themis</jats:sc> is able to reproduce prior EHT analyses, extend these, and do so in a computationally efficient manner that can efficiently exploit modern high-performance computing facilities. <jats:sc>Themis</jats:sc> has already been used extensively in the scientific analysis and interpretation of the first EHT observations of M87.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Very massive 140–260 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> stars can die as highly energetic pair-instability supernovae (PI SNe) with energies of up to 100 times those of core-collapse SNe that can completely destroy the star, leaving no compact remnant behind. These explosions can synthesize 0.1–30 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of radioactive <jats:sup>56</jats:sup>Ni, which can cause them to rebrighten at later times when photons due to <jats:sup>56</jats:sup>Ni decay diffuse out of the ejecta. However, heat from the decay of such large masses of <jats:sup>56</jats:sup>Ni could also drive important dynamical effects deep in the ejecta that are capable of mixing elements and affecting the observational signatures of these events. We have now investigated the dynamical effect of <jats:sup>56</jats:sup>Ni heating on PI SN ejecta with high-resolution two-dimensional hydrodynamic simulations performed with the <jats:monospace>CASTRO</jats:monospace> code. We find that expansion of the hot <jats:sup>56</jats:sup>Ni bubble forms a shell at the base of the silicon layer of the ejecta ∼200 days after the explosion but that no hydrodynamical instabilities develop that would mix <jats:sup>56</jats:sup>Ni with the <jats:sup>28</jats:sup>Si/<jats:sup>16</jats:sup>O-rich ejecta. However, while the dynamical effects of <jats:sup>56</jats:sup>Ni heating may be weak they could affect the observational signatures of some PI SNe by diverting decay energy into internal expansion of the ejecta at the expense of rebrightening at later times.</jats:p>