Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We explore atmospheric escape from close-in exoplanets with the highest mass-loss rates. First, we locate the transition from stellar X-ray and UV-driven escape to rapid Roche lobe overflow, which occurs once the 10–100 nbar pressure level in the atmosphere reaches the Roche lobe. Planets enter this regime when the ratio of the substellar radius to the polar radius along the visible surface pressure level, which aligns with a surface of constant Roche potential, is X/Z ≳ 1.2 for Jovian planets (<jats:italic>M</jats:italic>p ≳ 100 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub>) and X/Z ≳ 1.02 for sub-Jovian planets (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub> ≈ 10–100 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub>). Around a Sun-like star, this regime applies to orbital periods of less than two days for planets with radii of about 3–14R<jats:sub>⊕</jats:sub>. Our results agree with the properties of known transiting planets and can explain parts of the sub-Jovian desert in the population of known exoplanets. Second, we present detailed numerical simulations of atmospheric escape from a planet like Uranus or Neptune orbiting close to a Sun-like star that support the results above and point to interesting qualitative differences between hot Jupiters and sub-Jovian planets. We find that hot Neptunes with solar-metallicity hydrogen and helium envelopes have relatively more extended upper atmospheres than typical hot Jupiters, with a lower ionization fraction and higher abundances of escaping molecules. This is consistent with existing ultraviolet transit observations of warm Neptunes, and it might provide a way to use future observations and models to distinguish solar-metallicity atmospheres from higher-metallicity atmospheres.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We characterize the average X-ray and radio properties of quiescent galaxies (QGs) with <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}({M}_{\star }/{M}_{\odot })\gt 10$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>&gt;</mml:mo> <mml:mn>10</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5aafieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at 0 &lt; <jats:italic>z</jats:italic> &lt; 5. QGs are photometrically selected from the latest COSMOS2020 catalog. We conduct the stacking analysis of X-ray images of the Chandra COSMOS Legacy Survey for individually undetected QGs. Thanks to the large sample and deep images, the stacked X-ray signal is significantly detected up to <jats:italic>z</jats:italic> ∼ 5. The average X-ray luminosity cannot be explained by the X-ray luminosity of X-ray binaries, suggesting that the low-luminosity active galactic nuclei (AGNs) ubiquitously exist in QGs. Moreover, the X-ray AGN luminosity of QGs at <jats:italic>z</jats:italic> &gt; 1.5 is higher than that of star-forming galaxies (SFGs), derived in the same manner as QGs. The stacking analysis of the VLA-COSMOS images is conducted for the identical sample, and the radio signal for QGs is also detected up to <jats:italic>z</jats:italic> ∼ 5. We find that the radio AGN luminosity of QGs at <jats:italic>z</jats:italic> &gt; 1.5 is also higher than SFGs, which is in good agreement with the X-ray analysis. The enhanced AGN activity in QGs suggested by the individual analysis in the X-ray and radio wavelength supports its important role for quenching at high redshift. Their enhanced AGN activity is less obvious at <jats:italic>z</jats:italic> &lt; 1.5, which can be interpreted as an increasing role of others at lower redshifts, such as environmental quenching.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>All stars produce explosive surface events such as flares and coronal mass ejections. These events are driven by the release of energy stored in coronal magnetic fields, generated by the stellar dynamo. However, it remains unclear if the energy deposition in the magnetic fields is driven by direct or alternating currents. Recently, we presented observational measurements of the flare intensity distributions for a sample of ∼10<jats:sup>5</jats:sup> stars across the main sequence observed by TESS, all of which exhibited power-law distributions similar to those observed in the Sun, albeit with varying slopes. Here we investigate the mechanisms required to produce such a distribution of flaring events via direct current energy deposition, in which coronal magnetic fields braid, reconnect, and produce flares. We adopt a topological model for this process, which produces a power-law distribution of energetic flaring events. We expand this model to include the Coriolis effect, which we demonstrate produces a shallower distribution of flare energies in stars that rotate more rapidly (corresponding to a weaker decline in occurrence rates toward increasing flare energies). We present tentative evidence for the predicted rotation-power-law index correlation in the observations. We advocate for future observations of stellar flares that would improve our measurements of the power-law exponents, and yield key insights into the underlying dynamo mechanisms that underpin the self-similar flare intensity distributions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An estimate of the expected photon flux above 10<jats:sup>17</jats:sup> eV from the interactions of ultra-high-energy cosmic rays with the matter in the Galactic disk is presented. Uncertainties arising from the distribution of the gas in the disk, the absolute level of the cosmic-ray flux, and the composition of the cosmic rays are taken into account. Within these uncertainties, the integrated photon flux above 10<jats:sup>17</jats:sup> eV is averaged out over Galactic latitude less than 5°, between ≃3.2 × 10<jats:sup>−2</jats:sup> km<jats:sup>−2</jats:sup> yr<jats:sup>−1</jats:sup> sr<jats:sup>−1</jats:sup> and ≃8.7 × 10<jats:sup>−2</jats:sup> km<jats:sup>−2</jats:sup> yr<jats:sup>−1</jats:sup> sr<jats:sup>−1</jats:sup>. The all-sky average value amounts to ≃1.1 ×10<jats:sup>−2</jats:sup> km<jats:sup>−2</jats:sup> yr<jats:sup>−1</jats:sup> sr<jats:sup>−1</jats:sup> above 10<jats:sup>17</jats:sup> eV and decreases roughly as <jats:italic>E</jats:italic> <jats:sup>−2</jats:sup>, making this diffuse flux the dominant one from cosmic-ray interactions for energy thresholds between 10<jats:sup>17</jats:sup> and 10<jats:sup>18</jats:sup> eV. Compared to the current sensitivities of detection techniques, a gain of between two and three orders of magnitude in exposure is required for a detection below ≃10<jats:sup>18</jats:sup> eV. The implications for searches for photon fluxes from the Galactic center that would be indicative of the decay of super-heavy dark matter particles are discussed, as the photon flux presented in this study can be considered as a floor below which other signals would be overwhelmed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We show that the gravitomagnetic interaction of a Kerr black hole (BH) with a surrounding magnetic field induces an electric field that accelerates charged particles to ultra-relativistic energies in the vicinity of the BH. Along the BH rotation axis, these electrons/protons can reach energies of even thousands of petaelectronvolts, so stellar-mass BHs in long gamma-ray bursts (GRBs) and supermassive BHs in active galactic nuclei can contribute to the ultrahigh-energy cosmic rays thorough this mechanism. At off-axis latitudes, the particles accelerate to energies of hundreds of gigaelectronvolts and emit synchrotron radiation at gigaelectronvolt energies. This process occurs within 60° around the BH rotation axis, and due to the equatorial symmetry, it forms a double-cone emission. We outline the theoretical framework describing these acceleration and radiation processes, how they extract the rotational energy of the Kerr BH and the consequences for the astrophysics of GRBs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on proper motion measurements of the forward- and reverse shock regions of the supernova remnant Cassiopeia A (Cas A), including deceleration/acceleration measurements of the forward shock. The measurements combine 19 yr of observations with the Chandra X-ray Observatory, using the 4.2–6 keV continuum band, preferentially targeting X-ray synchrotron radiation. The average expansion rate is 0.218 ± 0.029% yr<jats:sup>−1</jats:sup> for the forward shock, corresponding to a velocity of ≈5800 km s<jats:sup>−1</jats:sup>. The time derivative of the proper motions indicates deceleration in the east, and an acceleration up to 1.1 × 10<jats:sup>−4</jats:sup> yr<jats:sup>−2</jats:sup> in the western part. The reverse shock moves outward in the east, but in the west it moves toward the center with an expansion rate of −0.0225 ± 0.0007 % yr<jats:sup>−1</jats:sup>, corresponding to −1884 ± 17 km s<jats:sup>−1</jats:sup>. In the west, the reverse shock velocity in the ejecta frame is ≳3000 km s<jats:sup>−1</jats:sup>, peaking at ∼8000 km s<jats:sup>−1</jats:sup>, explaining the presence of X-ray synchrotron emitting filaments there. The backward motion of the reverse shock can be explained by either a scenario in which the forward shock encountered a partial, dense, wind shell, or one in which the shock transgressed initially through a lopsided cavity, created during a brief Wolf–Rayet star phase. Both scenarios are consistent with the local acceleration of the forward shock. Finally we report on the proper motion of the northeastern jet, using both the X-ray continuum band, and the Si <jats:sc>xiii</jats:sc> K-line emission band. We find expansion rates of, respectively, 0.21% and 0.24% yr<jats:sup>−1</jats:sup>, corresponding to velocities at the tip of the X-ray jet of 7830–9200 km s<jats:sup>−1</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present statistical analysis of 11,200 proton kinetic-scale current sheets (CS) observed by the Parker Solar Probe during 10 days around the first perihelion. The CS thickness <jats:italic>λ</jats:italic> is in the range from a few to 200 km with the typical value around 30 km, while current densities are in the range from 0.1 to 10 <jats:italic>μ</jats:italic>A m<jats:sup>−2</jats:sup> with the typical value around 0.7 <jats:italic>μ</jats:italic>A m<jats:sup>−2</jats:sup>. These CSs are resolved thanks to magnetic field measurements at 73–290 samples s<jats:sup>−1</jats:sup> resolution. In terms of proton inertial length <jats:italic>λ</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub>, the CS thickness <jats:italic>λ</jats:italic> is in the range from about 0.1 to 10<jats:italic>λ</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub> with the typical value around 2<jats:italic>λ</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub>. The magnetic field magnitude does not substantially vary across the CSs, and accordingly the current density is dominated by the magnetic-field-aligned component. The CSs are typically asymmetric with statistically different magnetic field magnitudes at the CS boundaries. The current density is larger for smaller-scale CSs, <jats:italic>J</jats:italic> <jats:sub>0</jats:sub> ≈ 0.15 × (<jats:italic>λ</jats:italic>/100 km)<jats:sup>−0.76</jats:sup> <jats:italic>μ</jats:italic>A m<jats:sup>−2</jats:sup>, but does not statistically exceed the Alfvén current density <jats:italic>J</jats:italic> <jats:sub> <jats:italic>A</jats:italic> </jats:sub> corresponding to the ion-electron drift of the local Alfvén speed. The CSs exhibit remarkable scale-dependent current density and magnetic shear angles, <jats:inline-formula> <jats:tex-math> <?CDATA ${J}_{0}/{J}_{A}\approx 0.17\times {(\lambda /{\lambda }_{p})}^{-0.67}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>J</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>J</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>A</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.17</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>λ</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.67</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5bd9ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}\theta \approx 21^\circ \times {(\lambda /{\lambda }_{p})}^{0.32}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>θ</mml:mi> <mml:mo>≈</mml:mo> <mml:mn>21</mml:mn> <mml:mo>°</mml:mo> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>λ</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>0.32</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5bd9ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Based on these observations and comparison to recent studies at 1 au, we conclude that proton kinetic-scale CSs in the near-Sun solar wind are produced by turbulence cascade, and they are automatically in the parameter range, where reconnection is not suppressed by the diamagnetic mechanism, due to their geometry dictated by turbulence cascade.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have observed the mass-losing carbon star V Hya that is apparently transitioning from an asymptotic giant branch star to a bipolar planetary nebula, at an unprecedented angular resolution of ∼0.″4–0.″6 with the Atacama Large Millimeter/submillimeter Array. Our <jats:sup>13</jats:sup>CO and <jats:sup>12</jats:sup>CO (<jats:italic>J </jats:italic>= 3–2 and <jats:italic>J</jats:italic> = 2–1) images have led to the discovery of a remarkable set of six expanding rings within a flared, warped disk structure undergoing dynamical expansion (DUDE) that lies in the system’s equatorial plane. We also find, for the first time, several bipolar, high-velocity outflows, some of which have parabolic morphologies, implying wide-opening angles, while one (found previously) is clumpy and highly collimated. The latter is likely associated with the high-velocity bullet-like ejections of ionized gas from V Hya; a possible molecular counterpart to the oldest of the four bullets can be seen in the <jats:sup>12</jats:sup>CO images. We find a bright, unresolved central source of continuum emission (FWHM size ≲165 au); about 40% of this emission can be produced in a standard radio photosphere, while the remaining 60% is likely due to thermal emission from very large (millimeter-sized) grains, having mass ≳10<jats:sup>−5 </jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We have used a radiative transfer model to fit the salient characteristics of the DUDE’s <jats:sup>13</jats:sup>CO and <jats:sup>12</jats:sup>CO emission out to a radius of 8″ (3200 au) with a flared disk of mass 1.7 × 10<jats:sup>−3</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, whose expansion velocity increases very rapidly with the radius inside a central region of size ∼200 au, and then more slowly outside it, from 9.5 to 11.5 km s<jats:sup>−1</jats:sup>. The DUDE’s underlying density decreases radially, interspersed with local increases that represent the observationally well-characterized innermost three rings.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observed changes in protostellar brightness can be complicated to interpret. In our James Clerk Maxwell Telescope (JCMT) Transient Monitoring Survey, we discovered that a young binary protostar, HOPS 373, is undergoing a modest 30% brightness increase at 850 <jats:italic>μ</jats:italic>m, caused by a factor of 1.8–3.3 enhancement in the accretion rate. The initial burst occurred over a few months, with a sharp rise and then a shallower decay. A second rise occurred soon after the decay, and the source is still bright one year later. The mid-IR emission, the small-scale CO outflow mapped with ALMA, and the location of variable maser emission indicate that the variability is associated with the SW component. The near-IR and NEOWISE W1 and W2 emission is located along the blueshifted CO outflow, spatially offset by ∼3 to 4″ from the SW component. The <jats:italic>K</jats:italic>-band emission imaged by UKIRT shows a compact H<jats:sub>2</jats:sub> emission source at the edge of the outflow, with a tail tracing the outflow back to the source. The W1 emission, likely dominated by scattered light, brightens by 0.7 mag, consistent with expectations based on the submillimeter light curve. The signal of continuum variability in <jats:italic>K</jats:italic> band and W2 is masked by stable H<jats:sub>2</jats:sub> emission, as seen in our Gemini/GNIRS spectrum, and perhaps by CO emission. These differences in emission sources complicate IR searches for variability of the youngest protostars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use surveys covering the redshift range 0.05 &lt; <jats:italic>z</jats:italic> &lt; 3.8 to explore quiescent galaxy scaling relations and the redshift evolution of the velocity dispersion, size, and dynamical mass at fixed stellar mass. For redshift <jats:italic>z</jats:italic> &lt; 0.6, we derive mass-limited samples and demonstrate that these large samples enhance constraints on the evolution of the quiescent population. The constraints include 2985 new velocity dispersions from the SHELS F2 survey. In contrast with the known substantial evolution of size with redshift, evolution in the velocity dispersion is negligible. The dynamical-to-stellar-mass ratio increases significantly as the universe ages, in agreement with recent results that combine high-redshift data with the Sloan Digital Sky Survey. Like other investigators, we interpret this result as an indication that the dark matter fraction within the effective radius increases as a result of the impact of the minor mergers that are responsible for size growth. We emphasize that dense redshift surveys covering the range 0.07 &lt; <jats:italic>z</jats:italic> &lt; 1 along with strong and weak lensing measurements could remove many ambiguities in evolutionary studies of the quiescent population.</jats:p>