Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>With more than 4300 confirmed exoplanets and counting, the next milestone in exoplanet research is to determine which of these newly found worlds could harbor life. Coronal mass ejections (CMEs), spawned by magnetically active, superflare-triggering dwarf stars, pose a direct threat to the habitability of terrestrial exoplanets, as they can deprive them of their atmospheres. Here we develop a readily implementable atmosphere sustainability constraint for terrestrial exoplanets orbiting active dwarfs, relying on the magnetospheric compression caused by CME impacts. Our constraint focuses on an understanding of CMEs propagation in our own Sun–heliosphere system that, applied to a given exoplanet requires as key input the observed bolometric energy of flares emitted by its host star. Application of our constraint to six famous exoplanets, Kepler-438b, Proxima Centauri b, and Trappist-1d, -1e, -1f, and -1g, within or in the immediate proximity of their stellar host’s habitable zones showed that only for Kepler-438b might atmospheric sustainability against stellar CMEs be likely. This seems to align with some recent studies that, however, may require far more demanding computational resources and observational inputs. Our physically intuitive constraint can be readily and en masse applied, as is or generalized, to large-scale exoplanet surveys to detect planets that warrant further scrutiny for atmospheres and, perhaps, possible biosignatures at higher priority by current and future instrumentation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using high-resolution hydrodynamics simulations, we show that equal-mass binaries accreting from a circumbinary disk evolve toward an orbital eccentricity of <jats:italic>e</jats:italic> ≃ 0.45, unless they are initialized on a nearly circular orbit with <jats:italic>e</jats:italic> ≲ 0.08, in which case they further circularize. The implied bi-modal eccentricity distribution resembles that seen in post-AGB stellar binaries. Large accretion spikes around periapse impart a tell-tale, quasiperiodic, bursty signature on the light curves of eccentric binaries. We predict that intermediate-mass and massive black hole binaries at <jats:italic>z</jats:italic> ≲ 10 entering the LISA band will have measurable eccentricities in the range of <jats:italic>e</jats:italic> ≃ 10<jats:sup>−3</jats:sup> − 10<jats:sup>−2</jats:sup>, if they have experienced a gas-driven phase. On the other hand, GW190521 would have entered the LIGO/Virgo band with undetectable eccentricity ∼10<jats:sup>−6</jats:sup> if it had been driven into the gravitational-wave regime by a gas disk.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We apply our novel Markov Chain Monte Carlo (MCMC)–based algorithm for asteroid mass estimation to asteroid (16) Psyche, the target of NASA’s eponymous Psyche mission, based on close encounters with 10 different asteroids, and obtain a mass of (1.117 ± 0.039) × 10<jats:sup>−11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We ensure that our method works as expected by applying it to asteroids (1) Ceres and (4) Vesta, and find that the results are in agreement with the very accurate mass estimates for these bodies obtained by the Dawn mission. We then combine our mass estimate for Psyche with the most recent volume estimate to compute the corresponding bulk density as (3.88 ± 0.25) g cm<jats:sup>−3</jats:sup>. The estimated bulk density rules out the possibility of Psyche being an exposed, solid iron core of a protoplanet, but is fully consistent with the recent hypothesis that ferrovolcanism would have occurred on Psyche.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic reconnection is a natural energy converter that can have a significant impact on global processes in space, astrophysics, and fusion plasmas. Macroscopic modeling of reconnection is crucial in understanding the global responses to local kinetic processes. The key issue in developing the reconnection model is the description of the magnetic dissipation around the x-line to drive reconnection. In collisionless plasma, the dissipation can be generated by plasma turbulence through wave–particle interactions. However, the mechanisms to yield turbulence and dissipation in the reconnection current layer are currently poorly understood. In this study, we show, using three-dimensional particle-in-cell simulations, that the electron Kelvin–Helmholtz instability plays a primary role in driving intense electromagnetic turbulence leading to the dissipation and electron heating. We find that the ions hardly react to the turbulence, which indicates that the turbulence does not cause significant momentum exchange between electrons and ions resulting in electrical resistivity. It is demonstrated that the dissipation is mainly caused by viscosity associated with electron momentum transport across the current layer. The present results suggest a fundamental modification of the current magnetohydrodynamics models using the resistivity to generate the dissipation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The unexpectedly large radii of hot Jupiters are a longstanding mystery whose solution will provide important insights into their interior physics. Many potential solutions have been suggested, which make diverse predictions about the details of inflation. In particular, although any valid model must allow for maintaining large planetary radii, only some allow for radii to increase with time. This reinflation process would potentially occur when the incident flux on the planet is increased. In this work, we examine the observed population of hot Jupiters to see if they grow as their parent stars brighten along the main sequence. We consider the relation between radius and other observables, including mass, incident flux, age, and fractional age (age over main-sequence lifetime), and show that main-sequence brightening is often sufficient to produce detectable reinflation. We further argue that these provide strong evidence for the relatively rapid reinflation of giant planets, and discuss the implications for proposed heating mechanisms. In our population analysis we also find evidence for a “delayed cooling effect,” wherein planets cool and contract far more slowly than expected. While not capable of explaining the observed radii alone, it may represent an important component of the effect. Finally, we identify a weak negative relationship between stellar metallicity and planet radius that is presumably the result of enhanced planetary bulk metallicity around metal-rich stars and has important implications for planet formation theory.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Thousands of transiting exoplanets have already been detected orbiting a wide range of host stars, including the first planets that could potentially be similar to Earth. The upcoming Extremely Large Telescopes and the James Webb Space Telescope will enable the first searches for signatures of life in transiting exoplanet atmospheres. Here, we quantify the strength of spectral features in transit that could indicate a biosphere similar to the modern Earth on exoplanets orbiting a wide grid of host stars (F0 to M8) with effective temperatures between 2500 and 7000 K: transit depths vary between about 6000 ppm (M8 host) to 30 ppm (F0 host) due to the different sizes of the host stars. CO<jats:sub>2</jats:sub> possess the strongest spectral features in transit between 0.4 and 20 <jats:italic>μ</jats:italic>m. The atmospheric biosignature pairs O<jats:sub>2</jats:sub>+CH<jats:sub>4</jats:sub> and O<jats:sub>3</jats:sub>+CH<jats:sub>4</jats:sub>—which identify Earth as a living planet—are most prominent for Sun-like and cooler host stars in transit spectra of modern Earth analogs. Assessing biosignatures and water on such planets orbiting hotter stars than the Sun will be extremely challenging even for high-resolution observations. All high-resolution transit spectra and model profiles are available online: they provide a tool for observers to prioritize exoplanets for transmission spectroscopy, test atmospheric retrieval algorithms, and optimize observing strategies to find life in the cosmos. In the search for life in the cosmos, transiting planets provide the first opportunity to discover whether or not we are alone, with this database as one of the keys to optimize the search strategies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The jet composition and radiative efficiency of gamma-ray bursts (GRBs) are poorly constrained from the data. If the jet composition is matter-dominated (i.e., a fireball), the GRB prompt emission spectra would include a dominant thermal component originating from the fireball photosphere and a nonthermal component presumably originating from internal shocks whose radii are greater than the photosphere radius. We propose a method to directly dissect the GRB fireball energy budget into three components and measure their values by combining the prompt emission and early afterglow data. The measured parameters include the initial dimensionless specific enthalpy density (<jats:italic>η</jats:italic>), bulk Lorentz factors at the photosphere radius (Γ<jats:sub>ph</jats:sub>) and before fireball deceleration (Γ<jats:sub>0</jats:sub>), the amount of mass loading (<jats:italic>M</jats:italic>), and the GRB radiative efficiency (<jats:italic>η</jats:italic> <jats:sub> <jats:italic>γ</jats:italic> </jats:sub>). All the parameters can be derived from the data for a GRB with a dominant thermal spectral component, a deceleration bump feature in the early afterglow lightcurve, and a measured redshift. The results only weakly depend on the density <jats:italic>n</jats:italic> of the interstellar medium when the composition <jats:inline-formula> <jats:tex-math> <?CDATA ${ \mathcal Y }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabe6abieqn1.gif" xlink:type="simple" /> </jats:inline-formula> parameter (typically unity) is specified.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Arcades of flare loops form as a consequence of magnetic reconnection powering solar flares and eruptions. We analyze the morphology and evolution of flare arcades that formed during five well-known eruptive flares. We show that the arcades have a common saddle-like shape. The saddles occur despite the fact that the flares were of different classes (C to X), occurred in different magnetic environments, and were observed in various projections. The saddles are related to the presence of longer, relatively higher, and inclined flare loops, consistently observed at the ends of the arcades, which we term “cantles.” Our observations indicate that cantles typically join straight portions of flare ribbons with hooked extensions of the conjugate ribbons. The origin of the cantles is investigated in stereoscopic observations of the 2011 May 9 eruptive flare carried out by the Atmospheric Imaging Assembly and Extreme Ultraviolet Imager. The mutual separation of the instruments led to ideal observational conditions allowing for simultaneous analysis of the evolving cantle and the underlying ribbon hook. Based on our analysis we suggest that the formation of one of the cantles can be explained by magnetic reconnection between the erupting structure and its overlying arcades. We propose that the morphology of flare arcades can provide information about the reconnection geometries in which the individual flare loops originate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The latest study has reported that plasma emission can be generated by energetic electrons of Dory–Guest–Harris distribution via the electron cyclotron maser instability (ECMI) in plasmas characterized by a large ratio of plasma oscillation frequency to electron gyro-frequency (<jats:italic>ω</jats:italic> <jats:sub> <jats:italic>pe</jats:italic> </jats:sub>/Ω<jats:sub> <jats:italic>ce</jats:italic> </jats:sub>). In our study, on the basis of the ECMI-plasma emission mechanism, we examine the double plasma resonance (DPR) effect and the corresponding plasma emission at both harmonic (H) and fundamental (F) bands using particle-in-cell simulations with various <jats:italic>ω</jats:italic> <jats:sub> <jats:italic>pe</jats:italic> </jats:sub>/Ω<jats:sub> <jats:italic>ce</jats:italic> </jats:sub>. This allows us to directly simulate the feature of the zebra pattern (ZP) observed in solar radio bursts for the first time. We find that (1) the simulations reproduce the DPR effect nicely for the upper hybrid and Z modes, as seen from their variation of intensity and linear growth rate with <jats:italic>ω</jats:italic> <jats:sub> <jats:italic>pe</jats:italic> </jats:sub>/Ω<jats:sub> <jats:italic>ce</jats:italic> </jats:sub>, (2) the intensity of the H emission is stronger than that of the F emission by ∼2 orders of magnitude and varies periodically with increasing <jats:italic>ω</jats:italic> <jats:sub> <jats:italic>pe</jats:italic> </jats:sub>/Ω<jats:sub> <jats:italic>ce</jats:italic> </jats:sub>, while the F emission is too weak to be significant (therefore, we suggest that it is the H emission accounting for solar ZPs), (3) the peak-valley contrast of the total intensity of H is ∼4, and the peak lies around integer values of <jats:italic>ω</jats:italic> <jats:sub> <jats:italic>pe</jats:italic> </jats:sub>/Ω<jats:sub> <jats:italic>ce</jats:italic> </jats:sub> (=10 and 11) for the present parameter setup. We also evaluate the effect of energy of energetic electrons on the characteristics of ECMI-excited waves and plasma radiation. The study provides novel insight on the physical origin of ZPs of solar radio bursts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>As exoplanetary science matures into its third decade, we are increasingly offered the possibility of pre-existing, archival observations for newly detected candidates. This is particularly poignant for the TESS mission, whose survey spans bright, nearby dwarf stars in both hemispheres—precisely the types of sources targeted by previous radial velocity (RV) surveys. On this basis, we investigated whether any of the TESS Objects of Interest (TOIs) coincided with such observations, from which we find 18 single-planet candidate systems. Of these, one exhibits an RV signature that has the correct period and phase matching the transiting planetary candidates with a false-alarm probability of less than 1%. After further checks, we exploit this fact to validate HD 183579b (TOI-1055b). This planet is &lt;4 <jats:italic>R</jats:italic> <jats:sub>⊕</jats:sub> and has better than 33% planetary mass measurements, thus advancing TESS’ primary objective of finding 50 such worlds. We find that this planet is among the most accessible small transiting planets for atmospheric characterization. Our work highlights that the efforts to confirm and even precisely measure the masses of new transiting planet candidates need not always depend on acquiring new observations—in some instances, these tasks can be completed with existing data.</jats:p>