Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Stellar magnetic activity, just like that of the Sun, manifests itself in the form of flares and spots on the surface of the star. In the solar case, the largest flares originate from large active regions. In this work, we present a study of the activity of the star Kepler-411, including spot modeling from planetary transits. Our goal was to search for a connection between the area of starspots with the energy of superflares produced by this star. Kepler-411 is a K2V-type star with an average rotation period of 10.52 days, radius of 0.79 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>, and a mass of 0.83 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which was observed by the Kepler satellite for about 600 days. Transit mapping allowed for the characterization of 198 starspots with estimates of their radius and temperature. Kepler-411 starspots had an average radius of (17 ± 7) × 10<jats:sup>3</jats:sup> km and a mean temperature of 3800 ± 700 K. Visual inspection of the light curves of Kepler-411 yields the identification of 65 superflares. The detected superflares lasted from 8 to 260 minutes and their energy varied from 10<jats:sup>33</jats:sup>–10<jats:sup>35</jats:sup> ergs. The power-law index of the flare frequency distribution as a function of energy is (−2.04 ± 0.13) for the flare on Kepler-411. A positive correlation between the area of starspots and the energy of superflares was found when considering the averages taken every 16–35 days, with the highest correlation occurring for averages every 21 days. This timing is probably related to the lifetime of the Kepler-411 spots.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The <jats:italic>z</jats:italic> = 6.327 quasar SDSS J010013.02+280225.8 (hereafter J0100+2802) is believed to be powered by a black hole more massive than 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, making it the most massive black hole known in the first billion years of the universe. However, recent high-resolution ALMA imaging shows four structures at the location of this quasar, potentially implying that it is lensed with a magnification of <jats:italic>μ</jats:italic> ∼ 450 and thus its black hole is significantly less massive. Furthermore, for the underlying distribution of magnifications of <jats:italic>z</jats:italic> ≳ 6 quasars to produce such an extreme value, theoretical models predict that a larger number of quasars in this epoch should be lensed, implying further overestimates of early black hole masses. To provide an independent constraint on the possibility that J0100+2802 is lensed, we reanalyzed archival XMM-Newton observations of the quasar and compared the expected ratios of X-ray luminosity to rest-frame UV and IR luminosities. For both cases, J0100+2802's X-ray flux is consistent with the no-lensing scenario; while this could be explained by J0100+2802 being X-ray faint, we find it does not have the X-ray or optical spectral features expected for an X-ray faint quasar. Finally, we compare the overall distribution of X-ray fluxes for known, typical <jats:italic>z</jats:italic> ≳ 6 quasars. We find a 3<jats:italic>σ</jats:italic> tension between the observed and predicted X-ray-to-UV flux ratios when adopting the magnification probability distribution required to produce a <jats:italic>μ</jats:italic> = 450 quasar.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Earth Trojans are coorbitals librating around the Lagrange points <jats:italic>L</jats:italic> <jats:sub>4</jats:sub> or <jats:italic>L</jats:italic> <jats:sub>5</jats:sub> of the Sun–Earth system. Although many numerical studies suggest that they can maintain their dynamical status and be stable on timescales up to a few tens of thousands of years or even longer, they remain an elusive population. Thus far only one transient member (2010 TK<jats:sub>7</jats:sub>) has been discovered serendipitously. Here, we present a dynamical study of asteroid 2020 XL<jats:sub>5</jats:sub>. With our meticulous follow-up astrometric observations of the object, we confirmed that it is a new Earth Trojan. However, its eccentric orbit brings it close encounters with Venus on a frequent basis. Based on our <jats:italic>N</jats:italic>-body integration, we found that the asteroid was captured into the current Earth Trojan status in the fifteenth century, and then it has a likelihood of 99.5% to leave the <jats:italic>L</jats:italic> <jats:sub>4</jats:sub> region within the next ∼10 kyr. Therefore, it is most likely that 2020 XL<jats:sub>5</jats:sub> is dynamically unstable over this timescale.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High-resolution and high-cadence observations have shown that Alfvén waves are ubiquitous in the solar atmosphere. Theoretical works suggest their ability to transfer large energy fluxes from the photosphere to the corona and solar wind. In this proof-of-concept Letter we show that torsional Alfvén waves can induce the formation of filamentary plasma structures in the solar corona. We perform high-resolution 3D ideal MHD simulations in an initially uniform coronal plasma permeated by a line-tied twisted magnetic field. We find that torsional Alfvén waves develop Kelvin–Helmholtz instabilities as a result of the phase mixing process. The Kelvin–Helmholtz instability drives plasma compression that breaks the uniformity of density, creating elongated overdense threads aligned with the direction of the magnetic field. With synthetic modeling of SDO/AIA imaging we show that the overdense filaments could be seen in observations as fine strands that illuminate the underlying magnetic structure.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Planets smaller than Neptune and larger than Earth make up the majority of the discovered exoplanets. Those with H<jats:sub>2</jats:sub>-rich atmospheres are prime targets for atmospheric characterization. The transition between the two main classes, super-Earths and sub-Neptunes, is not clearly understood as the rocky surface is likely not accessible to observations. Tracking several trace gases (specifically the loss of ammonia (NH<jats:sub>3</jats:sub>) and hydrogen cyanide (HCN)) has been proposed as a proxy for the presence of a shallow surface. In this work, we revisit the proposed mechanism of nitrogen conversion in detail and find its timescale on the order of a million years. NH<jats:sub>3</jats:sub> exhibits dual paths converting to N<jats:sub>2</jats:sub> or HCN, depending on the UV radiation of the star and the stage of the system. In addition, methanol (CH<jats:sub>3</jats:sub>OH) is identified as a robust and complementary proxy for a shallow surface. We follow the fiducial example of K2-18b with a 2D photochemical model on an equatorial plane. We find a fairly uniform composition distribution below 0.1 mbar controlled by the dayside, as a result of slow chemical evolution. NH<jats:sub>3</jats:sub> and CH<jats:sub>3</jats:sub>OH are concluded to be the most unambiguous proxies to infer surfaces on sub-Neptunes in the era of the James Webb Space Telescope.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report results from the first Earth-space VLBI observations of the Galactic Center supermassive black hole, Sgr A*. These observations used the space telescope Spektr-R of the RadioAstron project together with a global network of 20 ground telescopes, observing at a wavelength of 1.35 cm. Spektr-R provided baselines up to 3.9 times the diameter of the Earth, corresponding to an angular resolution of approximately 55 <jats:italic>μ</jats:italic>as and a spatial resolution of 5.5<jats:italic>R</jats:italic> <jats:sub>Sch</jats:sub> at the source, where <jats:italic>R</jats:italic> <jats:sub>Sch</jats:sub> ≡ 2<jats:italic>GM</jats:italic>/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> is the Schwarzschild radius of Sgr A*. Our short ground baseline measurements ( ≲ 80 M<jats:italic>λ</jats:italic>) are consistent with an anisotropic Gaussian image, while our intermediate ground baseline measurements (100–250 M<jats:italic>λ</jats:italic>) confirm the presence of persistent image substructure in Sgr A*. Both features are consistent with theoretical expectations for strong scattering in the ionized interstellar medium, which produces Gaussian scatter-broadening on short baselines and refractive substructure on long baselines. We do not detect interferometric fringes on any of the longer ground baselines or on any ground–space baselines. While space-VLBI offers a promising pathway to sharper angular resolution and the measurement of key gravitational signatures in black holes, such as their photon rings, our results demonstrate that space-VLBI studies of Sgr A* will require sensitive observations at submillimeter wavelengths.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The link between the circumgalactic medium (CGM) and the stellar growth of massive galaxies at high-<jats:italic>z</jats:italic> depends on the properties of the widespread cold molecular gas. As part of the SUPERCOLD-CGM survey (Survey of Protocluster ELANe Revealing CO/[C <jats:sc>i</jats:sc>] in the Ly<jats:italic>α</jats:italic>-Detected CGM), we present the radio-loud QSO Q1228+3128 at <jats:italic>z</jats:italic> = 2.2218, which is embedded in an enormous Ly<jats:italic>α</jats:italic> nebula. ALMA+ACA observations of CO(4–3) reveal both a massive molecular outflow, and a more extended molecular gas reservoir across ∼100 kpc in the CGM, each containing a mass of <jats:italic>M</jats:italic> <jats:sub>H2</jats:sub> ∼ 4–5 × 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The outflow and molecular CGM are aligned spatially, along the direction of an inner radio jet. After reanalysis of Ly<jats:italic>α</jats:italic> data of Q1228+3128 from the Keck Cosmic Web Imager, we found that the velocity of the extended CO agrees with the redshift derived from the Ly<jats:italic>α</jats:italic> nebula and the bulk velocity of the massive outflow. We propose a scenario where the radio source in Q1228+3128 is driving the molecular outflow and perhaps also enriching or cooling the CGM. In addition, we found that the extended CO emission is nearly perpendicular to the extended Ly<jats:italic>α</jats:italic> nebula spatially, indicating that the two gas phases are not well mixed, and possibly even represent different phenomena (e.g., outflow versus infall). Our results provide crucial evidence in support of predicted baryonic recycling processes that drive the early evolution of massive galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of cold molecular gas reservoirs are critical for understanding the shutdown of star formation in massive galaxies. While dust continuum is an efficient and affordable tracer, this method relies upon the assumption of a “normal” molecular-gas to dust mass ratio, <jats:italic>δ</jats:italic> <jats:sub>GDR</jats:sub>, typically of order 100. Recent null detections of quiescent galaxies in deep dust continuum observations support a picture where the cold gas and dust have been rapidly depleted or expelled. In this work, we present another viable explanation: a significant fraction of galaxies with low star formation per unit stellar mass are predicted to have extreme <jats:italic>δ</jats:italic> <jats:sub>GDR</jats:sub> ratios. We show that simulated massive quiescent galaxies at 0 &lt; <jats:italic>z</jats:italic> &lt; 3 in the <jats:sc>simba</jats:sc> cosmological simulations have <jats:italic>δ</jats:italic> <jats:sub>GDR</jats:sub> values that extend &gt;4 orders of magnitude. The dust in most simulated quiescent galaxies is destroyed significantly more rapidly than the molecular gas depletes, and cannot be replenished. The transition from star-forming to quiescent halts dust formation via star formation processes, with dust subsequently destroyed by supernova shocks and thermal sputtering of dust grains embedded in hot plasma. After this point, the dust growth rate in the models is not sufficient to overcome the loss of &gt;3 orders of magnitude in dust mass to return to normal values of <jats:italic>δ</jats:italic> <jats:sub>GDR</jats:sub> despite having high metallicity. Our results indicate that it is not straight forward to use a single observational indicator to robustly preselect exotic versus normal ratios. These simulations make strong predictions that can be tested with millimeter facilities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Extragalactic fast radio bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu &amp; Zhang, but no clear correlation hinting toward large-scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM &lt; 500 pc cm<jats:sup>−3</jats:sup>. A trend of nonconstant SF and nonzero correlation function (CF) at angular separations <jats:italic>θ</jats:italic> less than 10° is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at <jats:italic>θ</jats:italic> ≲ 10° can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of 100 Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the distribution of rest-frame <jats:italic>U</jats:italic> − <jats:italic>V</jats:italic> and <jats:italic>V</jats:italic> − <jats:italic>J</jats:italic> colors for star-forming galaxies at 0.5 &lt; <jats:italic>z</jats:italic> &lt; 2.5. Using stellar population synthesis, stochastic star formation histories, and a simple prescription for the dust attenuation that accounts for the shape and inclination of galaxies, we construct a model for the distribution of galaxy colors. With only two free parameters, this model is able to reproduce the observed galaxy colors as a function of redshift and stellar mass remarkably well. Our analysis suggests that the wide range of dust attenuation values measured for star-forming galaxies at a given redshift and stellar mass is almost entirely due to the effect of inclination; if all galaxies at a given stellar mass were observed edge-on, they would show very similar dust attenuation. This result has important implications for the interpretation of dust attenuation measurements, the treatment of UV and IR luminosity, and the comparison between numerical simulations and observations.</jats:p>