Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The analysis of the photospheric velocity field is essential for understanding plasma turbulence in the solar surface, which may be responsible for driving processes such as magnetic reconnection, flares, wave propagation, particle acceleration, and coronal heating. Currently, the only available methods to estimate velocities at the solar photosphere transverse to an observer’s line of sight infer flows from differences in image structure in successive observations. Due to data noise, algorithms such as local correlation tracking may lead to a vector field with wide gaps where no velocity vectors are provided. In this paper, a novel method for image inpainting of highly corrupted data is proposed and applied to the restoration of horizontal velocity fields in the solar photosphere. The restored velocity field preserves all the vector field components present in the original field. The method shows robustness when applied to both simulated and observational data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To understand the formation process of massive stars, we present a multiscale and multiwavelength study of the W31 complex hosting two extended H <jats:sc>ii</jats:sc> regions (i.e., G10.30-0.15 (hereafter, W31-N) and G10.15-0.34 (hereafter, W31-S)) powered by a cluster of O-type stars. Several Class <jats:sc>i</jats:sc> protostars and a total of 49 ATLASGAL 870 <jats:italic>μ</jats:italic>m dust clumps (at <jats:italic>d</jats:italic> = 3.55 kpc) are found toward the H <jats:sc>ii</jats:sc> regions where some of the clumps are associated with the molecular outflow activity. These results confirm the existence of a single physical system hosting the early phases of star formation. The Herschel 250 <jats:italic>μ</jats:italic>m continuum map shows the presence of a hub-filament system (HFS) toward both W31-N and W31-S. The central hubs harbor H <jats:sc>ii</jats:sc> regions and they are depicted with extended structures (with <jats:italic>T</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub> ∼ 25–32 K) in the Herschel temperature map. In the direction of W31-S, an analysis of the NANTEN2 <jats:sup>12</jats:sup>CO(<jats:italic>J</jats:italic> = 1−0) and SEDIGISM <jats:sup>13</jats:sup>CO(<jats:italic>J</jats:italic> = 2−1) line data supports the presence of two cloud components around 8 and 16 km s<jats:sup>−1</jats:sup>, and their connection in velocity space. A spatial complementary distribution between the two cloud components is also investigated toward W31-S, where the signposts of star formation, including massive O-type stars, are concentrated. These findings favor the applicability of cloud–cloud collision (CCC) around ∼2 Myr ago in W31-S. Overall, our observational findings support the theoretical scenario of CCC in W31, which explains the formation of massive stars and the existence of HFSs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The effects of spontaneous fission on <jats:italic>r</jats:italic>-process nucleosynthesis are investigated in the hot wind <jats:italic>r</jats:italic>-process scenario. We perform network calculations using three sets of spontaneous fission rates to study how the abundance pattern is shaped when different sets of fissioning nuclei are encountered by the <jats:italic>r</jats:italic>-process nuclear flow. The relative contributions from spontaneous fission, neutron-induced fission, and <jats:italic>β</jats:italic>-delayed fission to the nucleosynthesis process are studied by calculating the corresponding fission flow. We show that the relative contributions of various fission channels in <jats:italic>r</jats:italic>-process nucleosynthesis depend on the astrophysical conditions and fission models used. By using the spontaneous fission rates from a modified Swiatecki’s formula with isospin and blocking effects, the spontaneous fission and neutron-induced fission play an equally important role in <jats:italic>r</jats:italic>-process nucleosynthesis under an extreme neutron-rich astrophysical scenario with <jats:italic>Y</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> = 0.1. The fissioning nuclei are located in different regions of the nuclear chart when different spontaneous fission models are used. The fission fragment distributions of fissioning nuclei in different regions have apparent diversity, which affects the mass regions where fission products are deposited, leading to the difference of the final abundance around the second <jats:italic>r</jats:italic>-process peak and rare-earth subpeak.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report our search for quasiperiodic signals in long-term optical and <jats:italic>γ</jats:italic>-ray data for the blazar PKS 1222+216, where the data are from the Steward Observatory blazar monitoring program and the all-sky survey with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope, respectively. A quasiperiodic signal, with a period of ≃420 days and a significance of &gt;5<jats:italic>σ</jats:italic>, is found in the measurements of the optical linear polarization degree for the source, while no similar signals are found in the optical and <jats:italic>γ</jats:italic>-ray light curves covering approximately the same time period of ∼10 yr. We study the quasiperiodic variations by applying a helical jet model and find that the model can provide a good explanation. This work shows that polarimetry can be a powerful tool for revealing the physical properties, in particular the configuration of the magnetic fields of jets from galactic supermassive black holes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the Five-hundred-meter Aperture Spherical radio Telescope in Guizhou, China, we detect the 21 cm neutral atomic hydrogen absorption in the young planetary nebula IC 4997. The absorption arises from a shell that is also associated with Na <jats:sc>i</jats:sc> D lines. The H <jats:sc>i</jats:sc> shell has a mass of 1.46 × 10<jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and a dynamic age of 990 yr. The column density of H <jats:sc>i</jats:sc> is estimated to be 7.1 × 10<jats:sup>20</jats:sup> cm<jats:sup>−2</jats:sup>, which can be well explained in terms of a photodissociation region around the ionized nebula, limited by the self-shielding of H<jats:sub>2</jats:sub>. We find that the atomic-to-ionized hydrogen ratio is 0.6, suggesting that H <jats:sc>i</jats:sc> substantially contributes to the overall nebular mass.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a new analysis of NuSTAR and Suzaku observations of the black hole Cygnus X-1 in the intermediate state. The analysis is performed using <jats:monospace>kerrC</jats:monospace>, a new model for analyzing spectral and spectropolarimetric X-ray observations of black holes. <jats:monospace>kerrC</jats:monospace> builds on a large library of simulated black holes in X-ray binaries. The model accounts for the X-ray emission from a geometrically thin, optically thick accretion disk, the propagation of the X-rays through the curved black hole spacetime, the reflection off the accretion disk, and the Comptonization of photons in coronae of different 3D shapes and physical properties before and after the reflection. We present the results from using <jats:monospace>kerrC</jats:monospace> for the analysis of archival NuSTAR and Suzaku observations taken on 2015 May 27–28. The best wedge-shaped corona gives a better fit than the cone-shaped corona. Although we included cone-shaped coronae in the funnel regions above and below the black hole to resemble to some degree the common assumption of a compact lamppost corona hovering above and/or below the black hole, the fit chooses a very large version of this corona that makes it possible to Comptonize a sufficiently large fraction of the accretion disk photons to explain the observed power-law emission. The analysis indicates a black hole spin parameter <jats:italic>a</jats:italic> (−1 ≤ <jats:italic>a</jats:italic> ≤ 1) between 0.861 and 0.921. The <jats:monospace>kerrC</jats:monospace> model provides new insights into the radial distribution of the energy flux of returning and coronal emission irradiating the accretion disk. <jats:monospace>kerrC</jats:monospace> furthermore predicts small polarization fractions around 1% in the 2–8 keV energy range of the recently launched Imaging X-ray Polarimetry Explorer.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Massive-star binaries are critical laboratories for measuring masses and stellar wind mass-loss rates. A major challenge is inferring viewing inclination and extracting information about the colliding-wind interaction (CWI) region. Polarimetric variability from electron scattering in the highly ionized winds provides important diagnostic information about system geometry. We combine for the first time the well-known generalized treatment of Brown et al. for variable polarization from binaries with the semianalytic solution for the geometry and surface density CWI shock interface between the winds based on Cantó et al. Our calculations include some simplifications in the form of inverse-square law wind densities and the assumption of axisymmetry, but in so doing they arrive at several robust conclusions. One is that when the winds are nearly equal (e.g., O+O binaries) the polarization has a relatively mild decline with binary separation. Another is that despite Thomson scattering being a gray opacity, the continuum polarization can show chromatic effects at ultraviolet wavelengths but will be mostly constant at longer wavelengths. Finally, when one wind dominates the other, as, for example, in WR+OB binaries, the polarization is expected to be larger at wavelengths where the OB component is more luminous and generally smaller at wavelengths where the WR component is more luminous. This behavior arises because, from the perspective of the WR star, the distortion of the scattering envelope from spherical is a minor perturbation situated far from the WR star. By contrast, the polarization contribution from the OB star is dominated by the geometry of the CWI shock.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work utilizes established models of synchrotron-powered light curves for core-collapse supernovae in dense circumstellar environments, namely, type IIn and Ibn, to demonstrate the potential for detecting millimeter emission from these events. The progenitor types of these supernovae are still an open question, but using the synchrotron light curves as probes for the circumstellar environments could shed light on the mass-loss histories of the progenitors and discern between different theories. Observations in millimeter bands are particularly fruitful, as they probe regions at smaller radii and higher ambient densities, where centimeter emission tends to be self-absorbed. In our application of these light curves, we explore a diversity of progenitor types and mass-loss profiles to understand their effects on the light-curve shapes. Additionally, we fit model parameters to the 8 GHz light curve of type IIn supernova 2006jd and then create millimeter light curves using these parameters to show the possibility of detecting an early millimeter peak from such an event. We predict that next generation millimeter surveys will possess the capability to detect nearby and extreme events. However, there is a pressing need for millimeter follow-up of optically discovered interacting supernovae to more completely sample the true population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Biosignature gas research has been growing in recent years thanks to next-generation space- and ground-based telescopes. Methanol (CH<jats:sub>3</jats:sub>OH) has many advantages as a biosignature gas candidate. First, CH<jats:sub>3</jats:sub>OH’s hydroxyl group (OH) has a unique spectral feature not present in other anticipated gases in the atmospheres of rocky exoplanets. Second, there are no significant known abiotic CH<jats:sub>3</jats:sub>OH sources on terrestrial planets in the solar system. Third, life on Earth produces CH<jats:sub>3</jats:sub>OH in large quantities. However, despite CH<jats:sub>3</jats:sub>OH’s advantages, we consider it a poor biosignature gas in the atmospheres of terrestrial exoplanets due to the enormous production flux required to reach its detection limit. CH<jats:sub>3</jats:sub>OH’s high water solubility makes it very difficult to accumulate in the atmosphere. For the highly favorable planetary scenario of an exoplanet with an H<jats:sub>2</jats:sub>-dominated atmosphere orbiting an M5V dwarf star, we find that only when the column-averaged mixing ratio of CH<jats:sub>3</jats:sub>OH reaches at least 10 ppm can we detect it with the James Webb Space Telescope (JWST). The CH<jats:sub>3</jats:sub>OH bioproduction flux required to reach the JWST detection threshold of 10 ppm must be of the order of 10<jats:sup>14</jats:sup> molecules cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, which is roughly three times the annual O<jats:sub>2</jats:sub> production on Earth. Considering that such an enormous flux of CH<jats:sub>3</jats:sub>OH is essentially a massive waste of organic carbon—a major building block of life, we think this flux, while mathematically possible, is likely biologically unattainable. Although CH<jats:sub>3</jats:sub>OH can theoretically accumulate on exoplanets with CO<jats:sub>2</jats:sub>- or N<jats:sub>2</jats:sub>-dominated atmospheres, such planets’ small atmospheric scale heights and weak atmospheric signals put them out of reach for near-term observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This paper investigates a new methodology to search for periods in light curves of high-energy gamma-ray sources such as active galactic nuclei (AGNs). High-energy light curves have significant stochastic components, making period detection somewhat challenging. In our model, periodic terms, drifts of the light curves, and random walk with a correlation between flux points due to colored noise are taken into account independently. The parameters of the model are obtained directly from a Markov Chain Monte Carlo minimization. The time periods found are compared to the output of the publicly available Agatha program. The search method is applied to high-energy periodic AGN candidates from the Fermi-LAT catalog. The significance of periodic models over pure noise models is discussed. Finally, the variability of the period and amplitude of oscillating terms is studied on the most significant candidates.</jats:p>