Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We report on the properties of halo coronal mass ejections (HCMEs) in solar cycles 23 and 24. We compare the HCME properties between the corresponding phases (rise, maximum, and declining) in cycles 23 and 24 and compare those between the whole cycles. Despite the significant decline in the sunspot number (SSN) in cycle 24, which dropped by 46% with respect to cycle 23, the abundance of HCMEs is similar in the two cycles. The HCME rate per SSN is 44% higher in cycle 24. In the maximum phase, cycle 24 rate normalized to SSN increased by 127%, while the SSN dropped by 43%. The source longitudes of cycle 24 HCMEs are more uniformly distributed than those in cycle 23. We found that the average sky-plane speed in cycle 23 is ∼16% higher than that in cycle 24. The size distributions of the associated flares between the two cycles and the corresponding phases are similar. The average speed at a central meridian distance (CMD) ≥ 60<jats:sup>0</jats:sup> for cycle 23 is ∼28% higher than that of cycle 24. We discuss the unusual bump in HCME activity in the declining phase of cycle 23 as being due to exceptional active regions that produced many CMEs during 2003 October–2005 October. The differing HCME properties in the two cycles can be attributed to the anomalous expansion of cycle 24 CMEs. Considering the HCMEs in the rise, maximum, and declining phases, we find that the maximum phase shows the highest contrast between the two cycles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an analysis of the radiation characteristics of kinetic shear boundary layers created by relativistic plasma jets. Using a model of electromagnetic field data based on particle-in-cell simulations of an electron–ion plasma, we solve the motion of individual test electrons and compute their instantaneous radiated power and peak frequency. By analyzing a large number of test electrons in this manner, we find two distinct electron populations present around the shear boundary layer. The most highly radiative electrons execute looping motion due to crossed electric and magnetic fields as they are accelerated along the bulk flow of the jet, and eventually cross the shear boundary interface at steep angles. Electrons that never cross the shear boundary interface radiate much less energy as a group. Summing over all of the highly radiative electrons, we compute the distribution of the total radiated energy as a function of the angle relative to the bulk flow. This result has important potential implications for the observed radiation output of short gamma-ray bursts viewed at large angles from the jet axis, such as the neutron star merger event GW170817/GRB 170817A.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We employ data from the 2019 Magnetospheric Multiscale (MMS) Solar Wind Turbulence Campaign to evaluate scaling and anisotropy of second-order magnetic field structure functions and scale-dependent kurtosis from a single data interval. Prior results have been based either on the Taylor approximation, which conflates time and space dependence, or on averaging many data sets, which introduces sample-to-sample variation of plasma parameters. The present results overcome these systematic effects. We find that for length scales between 57 and 201 km the fluctuations are anisotropic with a preferred orientation of 60°–70° to the magnetic field direction. The peak kurtosis also lies in this angular range. This confirms anisotropy of the spectrum and suggests that coherent structures such as current sheets are oriented nearly perpendicular to the magnetic field direction. Both the anisotropy and the kurtosis decrease approaching the ion inertial length, here ≈91 km.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on the second Gaia data release (DR2), combined with the LAMOST and APOGEE spectroscopic surveys, we study the kinematics and metallicity distribution of the high-velocity stars that have a relative speed of at least 220 <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{km}\ {{\rm{s}}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3dieqn1.gif" xlink:type="simple" /> </jats:inline-formula> with respect to the local standard of rest in the Galaxy. The rotational velocity distribution of the high-velocity stars with [Fe/H] <jats:inline-formula> <jats:tex-math> <?CDATA $\gt \ -1.0$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3dieqn2.gif" xlink:type="simple" /> </jats:inline-formula> dex can be well described by a two-Gaussian model, with peaks at <jats:inline-formula> <jats:tex-math> <?CDATA ${V}_{\phi }\sim +164.2\pm 0.7$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3dieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${V}_{\phi }\sim +3.0\pm 0.3$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3dieqn4.gif" xlink:type="simple" /> </jats:inline-formula> <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{km}\ {{\rm{s}}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3dieqn5.gif" xlink:type="simple" /> </jats:inline-formula>, associated with the thick disk and halo, respectively. This implies that there should exist a high-velocity thick disk (HVTD) and a metal-rich stellar halo (MRSH) in the Galaxy. The HVTD stars have the same position as the halo in the Toomre diagram but show the same rotational velocity and metallicity as the canonical thick disk. The MRSH stars have basically the same rotational velocity, orbital eccentricity, and position in the Lindblad and Toomre diagram as the canonical halo stars, but they are more metal-rich. Furthermore, the metallicity distribution function of our sample stars are well fitted by a four-Gaussian model, associated with the outer halo, inner halo, MRSH, and HVTD, respectively. Chemical and kinematic properties and age imply that the MRSH and HVTD stars may form in situ.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery and panchromatic follow-up observations of the young Type Ic supernova (SN Ic) SN 2020oi in M100, a grand-design spiral galaxy at a mere distance of 14 Mpc. We followed up with observations at radio, X-ray, and optical wavelengths from only a few days to several months after explosion. The optical behavior of the supernova is similar to those of other normal SNe Ic. The event was not detected in the X-ray band but our radio observations revealed a bright mJy source (<jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\nu }\approx 1.2\times {10}^{27}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{Hz}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>1.2</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>27</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:mi>erg</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:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>Hz</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="apjabbd38ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>). Given the relatively small number of stripped envelope SNe for which radio emission is detectable, we used this opportunity to perform a detailed analysis of the comprehensive radio data set we obtained. The radio-emitting electrons initially experience a phase of inverse Compton cooling, which leads to steepening of the spectral index of the radio emission. Our analysis of the cooling frequency points to a large deviation from equipartition at the level of <jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub>/<jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub>  ≳  200, similar to a few other cases of stripped envelope SNe. Our modeling of the radio data suggests that the shock wave driven by the SN ejecta into the circumstellar matter (CSM) is moving at <jats:inline-formula> <jats:tex-math> <?CDATA $\sim 3\times {10}^{4}\,\mathrm{km}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>3</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <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="apjabbd38ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Assuming a constant mass loss from the stellar progenitor, we find that the mass-loss rate is <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{M}\approx 1.4\times {10}^{-4}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>≈</mml:mo> <mml:mn>1.4</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>yr</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="apjabbd38ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> for an assumed wind velocity of <jats:inline-formula> <jats:tex-math> <?CDATA $1000\,\mathrm{km}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1000</mml:mn> <mml:mspace width="0.25em" /> <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="apjabbd38ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. The temporal evolution of the radio emission suggests a radial CSM density structure steeper than the standard <jats:italic>r</jats:italic> <jats:sup>−2</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We characterize the variability in nearly continuous optical observations of the bright radio-loud quasar 3C 273 and nine additional active galactic nuclei detected with the Fermi Gamma-ray Space Telescope Large Area Telescope (Fermi-LAT). Optical observations were obtained during the K2 mission with the Kepler spacecraft for periods of 49 to 83 days conducted with ≃1 minute (short) or ≃30 minutes (long) cadences in 2015–2017. 3C 273 was quiescent during the course of the observations, varying by only a factor of 1.02. Three objects, PKS 0047+023, PKS 1216-10, and PKS B2320-035, were active, varying by factors of 1.8–3.4. Six other objects were comparatively quiet, varying by factors of less than 1.4. Power spectral densities (PSDs) were calculated for each object. Overall, the slopes of most PSDs, as well as those we reported in an earlier paper, were in the range −2.0 to −2.7 and are consistent with those produced by turbulence in the relativistic jet, and not by “hot spots” in the disk emission. Mechanisms operating in the jet other than turbulence, such as “mini-jets” or “jet-in-jets”, may also produce the observed range of PSD slopes. Both accretion disk and jet models are plausible origins for the 3C 273 optical variability during the K2 observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the generation of turbulence during the prestellar gravitational contraction of a turbulent spherical core. We define the ratio <jats:italic>g</jats:italic> of the one-dimensional turbulent velocity dispersion <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{1{\rm{D}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn1.gif" xlink:type="simple" /> </jats:inline-formula> to the gravitational velocity <jats:inline-formula> <jats:tex-math> <?CDATA ${v}_{{\rm{g}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn2.gif" xlink:type="simple" /> </jats:inline-formula> to then analytically estimate <jats:italic>g</jats:italic> under the assumptions of (a) equipartition or virial equilibrium between the gravitational (<jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{{\rm{g}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn3.gif" xlink:type="simple" /> </jats:inline-formula>) and turbulent kinetic (<jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{\mathrm{turb}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn4.gif" xlink:type="simple" /> </jats:inline-formula>) energies and (b) stationarity of transfer from gravitational to turbulent energy (implying <jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{\mathrm{turb}}/{E}_{{\rm{g}}}\,=$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn5.gif" xlink:type="simple" /> </jats:inline-formula> cst). In the equipartition and virial cases, we find <jats:inline-formula> <jats:tex-math> <?CDATA $g=\sqrt{1/3}\approx 0.58$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn6.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA $g=\sqrt{1/6}\approx 0.41$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn7.gif" xlink:type="simple" /> </jats:inline-formula>, respectively; in the stationary case we find <jats:inline-formula> <jats:tex-math> <?CDATA $g=\langle {v}_{\mathrm{rad}}\rangle {{ \mathcal L }}_{{\rm{d}}}/(4\pi \sqrt{3}\eta {{Rv}}_{{\rm{g}}})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn8.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>η</jats:italic> is an efficiency factor, <jats:inline-formula> <jats:tex-math> <?CDATA ${{ \mathcal L }}_{{\rm{d}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn9.gif" xlink:type="simple" /> </jats:inline-formula> is the energy injection scale of the turbulence, and <jats:italic>R</jats:italic> is the core’s radius. Next, we perform AMR simulations of the prestellar collapse of an isothermal, transonic turbulent core at two different resolutions, and a nonturbulent control simulation. We find that the turbulent simulations collapse at the same rate as the nonturbulent one, so that the turbulence generation does not significantly slow down the collapse. We also find that (a) the simulations approach near balance between the rates of energy injection from the collapse and of turbulence dissipation; (b) <jats:inline-formula> <jats:tex-math> <?CDATA $g\approx 0.395\pm 0.035$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn10.gif" xlink:type="simple" /> </jats:inline-formula>, close to the “virial” value (turbulence is 30% ∼ 40% of nonthermal linewidth); (c) the injection scale is <jats:inline-formula> <jats:tex-math> <?CDATA ${{ \mathcal L }}_{{\rm{d}}}\lesssim R$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn11.gif" xlink:type="simple" /> </jats:inline-formula>, and (d) the “turbulent pressure” <jats:inline-formula> <jats:tex-math> <?CDATA $\rho {\sigma }_{1{\rm{D}}}^{2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn12.gif" xlink:type="simple" /> </jats:inline-formula> scales as <jats:inline-formula> <jats:tex-math> <?CDATA $\sim {\rho }^{1.64}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba1fieqn13.gif" xlink:type="simple" /> </jats:inline-formula>, an apparently nearly adiabatic scaling. We propose that this scaling and the nearly virial values of the turbulent velocity dispersion may be reconciled with the nondelayed collapse rate if the turbulence is dissipated as soon as it is generated.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper we present recent Low Frequency Array observations of the pulsar J1740+1000. We confirm that its spectrum has a turnover at 260 MHz, which is unusual for a typical pulsar. We argue that in this case interferometric imaging provides more accurate pulsar flux estimates than other, more traditional, means such as beamformed observations. We conclude that existing calibration and imaging techniques can be used for a more comprehensive study of the influence of the interstellar medium on the point-like sources at very low frequencies in the near future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In order to characterize giant exoplanets and better understand their origin, knowledge of how the planet’s composition depends on its mass and stellar environment is required. In this work, we simulate the thermal evolution of gaseous planets and explore how various common model assumptions such as different equations of state, opacities, and heavy-element distributions affect the inferred radius and metallicity. We examine how the theoretical uncertainties translate into uncertainties in the inferred planetary radius and bulk metallicity. While we confirm the mass–metallicity trend previously reported in the literature, this correlation disappears when removing a 20 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub> heavy-element core from all the planets. We also show that using an updated hydrogen–helium equation of state leads to more compact planets. As a result, we present six planets that should be classified as inflated warm Jupiters. We next demonstrate that including the opacity enhancement due to metal-rich envelopes of irradiated planets changes the planetary radius significantly, which can have large effects on the inferred metallicity. Even though there are other model assumptions that have not been considered in this work, we could show that the calculated theoretical uncertainties can already be comparable or even larger than the observational ones. Therefore, theoretical uncertainties are likely to be even larger. We therefore conclude that progress in theoretical models of giant planets is essential in order to take full advantage of current and future exoplanetary data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We show that the growth rate of dust grains in cold molecular clouds is enhanced by the high degree of compressibility of a turbulent, dilute gas. By means of high-resolution (1024<jats:sup>3</jats:sup>) numerical simulations, we confirm the theory that the spatial mean growth rate is proportional to the gas-density variance. This also results in broadening of the grain-size distribution (GSD) due to turbulence-induced variation of the grain-growth rate. We show, for the first time in a detailed numerical simulation of hydrodynamic turbulence, that the GSD evolves toward a shape that is a reflection of the gas-density distribution, regardless of the initial distribution. That is, in case of isothermal, rotationally forced turbulence, the GSD tends to be a lognormal distribution. We also show that in hypersonic turbulence, decoupling of gas and dust becomes important and that this leads to an even further accelerated grain growth.</jats:p>