Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>It has recently been shown that stellar clustering plays an important role in shaping the properties of planetary systems. We investigate how the multiplicity distributions and orbital periods of planetary systems depend on the 6D phase space density of stars surrounding planet host systems. We find that stars in high stellar phase space density environments (overdensities) have a factor of 1.6–2.0 excess in the number of single-planet systems compared to stars in low stellar phase space density environments (the field). The multiplicity distribution of planets around field stars is much flatter (i.e., there is a greater fraction of multiplanet systems) than in overdensities. This result is primarily driven by the combined facts that (i) “hot Jupiters” (HJs) are almost exclusively found in overdensities and (ii) HJs are predominantly observed to be single-planet systems. Nevertheless, we find that the difference in multiplicity is even more pronounced when only considering planets in the Kepler sample, which contains few HJs. This suggests that the Kepler dichotomy—an apparent excess of systems with a single transiting planet—plausibly arises from environmental perturbations. In overdensities, the orbital periods of single-planet systems are smaller than orbital periods of multiple-planet systems. As this difference is more pronounced in overdensities, the mechanism responsible for this effect may be enhanced by stellar clustering. Taken together, the pronounced dependence of planetary multiplicity and orbital period distributions on stellar clustering provides a potentially powerful tool to diagnose the impact of environment on the formation and evolution of planetary systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The field-aligned anisotropy of the solar wind turbulence, which is quantified by the ratio of the parallel to the perpendicular correlation (and Taylor) length scales, is determined by simultaneous two-point correlation measurements during the time period 2001–2017. Our results show that the correlation scale along the magnetic field is the largest, and the correlation scale in the field-perpendicular directions is the smallest, at both solar maximum and solar minimum. However, the Taylor scale reveals inconsistent results for different stages of the solar cycles. During the years 2001–2004, the Taylor scales are slightly larger in the field-parallel directions, while during the years 2004–2017, the Taylor scales are larger in the field-perpendicular directions. The correlation coefficient between the sunspot number and the anisotropy ratio is employed to describe the effects of solar activity on the anisotropy of solar wind turbulence. The results show that the correlation coefficient regarding the Taylor scale anisotropy (0.65) is larger than that regarding the correlation scale anisotropy (0.43), which indicates that the Taylor scale anisotropy is more sensitive to the solar activity. The Taylor scale and the correlation scale are used to calculate the effective magnetic Reynolds number, which is found to be systematically larger in the field-parallel directions than in the field-perpendicular directions. The correlation coefficient between the sunspot number and the magnetic Reynolds number anisotropy ratio is −0.75. Our results will be meaningful for understanding the solar wind turbulence anisotropy and its long-term variability in the context of solar activity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The object FRB 20180916B is a well-studied repeating fast radio burst source. Its proximity (∼150 Mpc), along with detailed studies of the bursts, has revealed many clues about its nature, including a 16.3 day periodicity in its activity. Here we report on the detection of 18 bursts using LOFAR at 110–188 MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are seen down to the lowest observed frequency of 110 MHz, suggesting that their spectra extend even lower. These observations provide an order-of-magnitude stronger constraint on the optical depth due to free–free absorption in the source’s local environment. The absence of circular polarization and nearly flat polarization angle curves are consistent with burst properties seen at 300–1700 MHz. Compared with higher frequencies, the larger burst widths (∼40–160 ms at 150 MHz) and lower linear polarization fractions are likely due to scattering. We find ∼2–3 rad m<jats:sup>−2</jats:sup> variations in the Faraday rotation measure that may be correlated with the activity cycle of the source. We compare the LOFAR burst arrival times to those of 38 previously published and 22 newly detected bursts from the uGMRT (200–450 MHz) and CHIME/FRB (400–800 MHz). Simultaneous observations show five CHIME/FRB bursts when no emission is detected by LOFAR. We find that the burst activity is systematically delayed toward lower frequencies by about 3 days from 600 to 150 MHz. We discuss these results in the context of a model in which FRB 20180916B is an interacting binary system featuring a neutron star and high-mass stellar companion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This letter capitalizes on a unique set of total solar eclipse observations acquired between 2006 and 2020 in white light, Fe <jats:sc>xi</jats:sc> 789.2 nm (<jats:italic>T</jats:italic> <jats:sub>fexi</jats:sub> = 1.2 ± 0.1 MK), and Fe <jats:sc>xiv</jats:sc> 530.3 nm (<jats:italic>T</jats:italic> <jats:sub>fexiv</jats:sub> = 1.8 ± 0.1 MK) emission complemented by in situ Fe charge state and proton speed measurements from Advanced Composition Explorer/SWEPAM-SWICS to identify the source regions of different solar wind streams. The eclipse observations reveal the ubiquity of open structures invariably associated with Fe <jats:sc>xi</jats:sc> emission from Fe<jats:sup>10+</jats:sup> and hence a constant electron temperature, <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> = <jats:italic>T</jats:italic> <jats:sub>fexi</jats:sub>, in the expanding corona. The in situ Fe charge states are found to cluster around Fe<jats:sup>10+</jats:sup>, independently of the 300–700 km s<jats:sup>−1</jats:sup> stream speeds, referred to as the continual solar wind. Thus, Fe<jats:sup>10+</jats:sup> yields the fiducial link between the continual solar wind and its <jats:italic>T</jats:italic> <jats:sub>fexi</jats:sub> sources at the Sun. While the spatial distribution of Fe <jats:sc>xiv</jats:sc> emission from Fe<jats:sup>13+</jats:sup> associated with streamers changes throughout the solar cycle, the sporadic appearance of charge states &gt;Fe<jats:sup>11+</jats:sup> in situ exhibits no cycle dependence regardless of speed. These latter streams are conjectured to be released from hot coronal plasmas at temperatures ≥<jats:italic>T</jats:italic> <jats:sub>fexiv</jats:sub> within the bulge of streamers and from active regions, driven by the dynamic behavior of prominences magnetically linked to them. The discovery of continual streams of slow, intermediate, and fast solar wind characterized by the same <jats:italic>T</jats:italic> <jats:sub>fexi</jats:sub> in the expanding corona places new constraints on the physical processes shaping the solar wind.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The precise astrometric measurements of the Gaia Data Release 2 have opened the door to detailed tests of the predictions of white dwarf cooling models. Significant discrepancies between theory and observations have been identified, the most striking affecting ultramassive white dwarfs. Cheng et al. found that a small fraction of white dwarfs on the so-called Q branch must experience an extra cooling delay of ∼8 Gyr not predicted by current models. <jats:sup>22</jats:sup>Ne phase separation in a crystallizing C/O white dwarf can lead to a distillation process that efficiently transports <jats:sup>22</jats:sup>Ne toward its center, thereby releasing a considerable amount of gravitational energy. Using state-of-the-art Monte Carlo simulations, we show that this mechanism can largely resolve the ultramassive cooling anomaly if the delayed population consists of white dwarfs with moderately above-average <jats:sup>22</jats:sup>Ne abundances. We also argue that <jats:sup>22</jats:sup>Ne phase separation can account for the smaller cooling delay currently missing for models of white dwarfs with more standard compositions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the 2020 reactivation of the energetic high magnetic field pulsar PSR J1846–0258 and its pulsar wind nebula (PWN) after 14 yr of quiescence with new Chandra and Green Bank Telescope observations. The emission of short-duration bursts from J1846–0258 was accompanied by an enhancement of X-ray persistent flux and significant spectral softening, similar to those observed during its first bursting episode in 2006. The 2020 pulsar spectrum is described by a power-law model with a photon index Γ = 1.7 ± 0.3 in comparison to a Γ = 1.2 ± 0.1 before outburst, and shows evidence of an emerging thermal component with blackbody temperature <jats:italic>kT</jats:italic> = 0.7 ± 0.1 keV. The 0.5–10 keV unabsorbed flux increased from <jats:inline-formula> <jats:tex-math> <?CDATA ${5.4}_{-0.5}^{+0.4}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabf11dieqn1.gif" xlink:type="simple" /> </jats:inline-formula> × 10<jats:sup>−12</jats:sup> erg cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> in quiescence to <jats:inline-formula> <jats:tex-math> <?CDATA ${1.3}_{-0.2}^{+0.3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabf11dieqn2.gif" xlink:type="simple" /> </jats:inline-formula> × 10<jats:sup>−11</jats:sup> erg cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> following the outburst. We did not detect any radio pulsations from the pulsar at 2 GHz, and we place an upper limit of 7.1 <jats:italic>μ</jats:italic>Jy and 55 mJy for the coherent pulsed emission and single pulses, respectively. The 2020 PWN spectrum, characterized by a photon index of 1.92 ± 0.04 and X-ray luminosity of (1.2 ± 0.1) × 10<jats:sup>35</jats:sup> erg s<jats:sup>−1</jats:sup> at a distance of 5.8 kpc, is consistent with those observed before the outburst. An analysis of regions closer to the pulsar shows small-scale time variabilities and brightness changes over the 20 yr period from 2000 to 2020, while the photon indices did not change. We conclude that the outburst in PSR J1846–0258 is a combination of crustal and magnetospheric effects, with no significant burst-induced variability in its PWN based on the current observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coronal extreme-ultraviolet (EUV) waves are large-scale disturbances propagating in the corona, whose physical nature and origin have been discussed for decades. We report the first three-dimensional (3D) radiative magnetohydrodynamic simulation of a coronal EUV wave and the accompanying quasi-periodic wave trains. The numerical experiment is conducted with the MURaM code and simulates the formation of solar active regions through magnetic flux emergence from the convection zone to the corona. The coronal EUV wave is driven by the eruption of a magnetic flux rope that also gives rise to a C-class flare. It propagates in a semicircular shape with an initial speed ranging from about 550 to 700 km s<jats:sup>−1</jats:sup>, which corresponds to an average Mach number (relative to fast magnetoacoustic waves) of about 1.2. Furthermore, the abrupt increase of the plasma density, pressure, and tangential magnetic field at the wave front confirms fast-mode shock nature of the coronal EUV wave. Quasi-periodic wave trains with a period of about 30 s are found as multiple secondary wavefronts propagating behind the leading wave front and ahead of the erupting magnetic flux rope. We also note that the true wave front in the 3D space can be very inhomogeneous; however, the line-of-sight integration of EUV emission significantly smoothes the sharp structures in 3D and leads to a more diffuse wave front.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Bubbles, the semi-circular voids below quiescent prominences (filaments), have been extensively investigated in the past decade. However, to this point the magnetic nature of bubbles has been unverifiable due to the lack of on-disk photospheric magnetic field observations. Here for the first time, we find and investigate an on-disk prominence bubble around a filament barb on 2019 March 18 based on stereoscopic observations from the New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory (SDO), and Spacecraft-A of the Solar TErrestrial RElations Observatory (STEREO-A). In high-resolution NVST H<jats:italic>α</jats:italic> images, this bubble has a sharp arch-like boundary and a projected width of ∼26 Mm. Combining SDO and STEREO-A images, we further reconstruct 3D structure of the bubble boundary, whose maximum height is ∼15.6 Mm. The squashing factor <jats:italic>Q</jats:italic> map deduced from extrapolated 3D magnetic fields around the bubble depicts a distinct arch-shaped interface with a height of ∼11 Mm, which agrees well with the reconstructed 3D structure of the observed bubble boundary. Under the interface lies a set of magnetic loops, which is rooted on a surrounding photospheric magnetic patch. To be more persuasive, another on-disk bubble on 2019 June 10 is presented as a supplement. According to these results obtained from on-disk bubble observations, we suggest that the bubble boundary corresponds to the interface between the prominence dips (barb) and the underlying magnetic loops rooted nearby. Therefore, it is reasonable to speculate that the bubble can form around a filament barb below which there is a photospheric magnetic patch.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>With a metallicity of 12 + Log(O/H) ≈ 7.1–7.2, I Zw 18 is a canonical low-metallicity blue compact dwarf (BCD) galaxy. A growing number of BCDs, including I Zw 18, have been found to host strong, narrow-lined, nebular He <jats:sc>ii</jats:sc> (<jats:italic>λ</jats:italic>4686) emission with enhanced intensities compared to H<jats:italic>β</jats:italic> (e.g., He <jats:sc>ii</jats:sc>(<jats:italic>λ</jats:italic>4686)/H<jats:italic>β</jats:italic> &gt; 1%). We present new observations of I Zw 18 using the Keck Cosmic Web Imager. These observations reveal two nebular He <jats:sc>ii</jats:sc> emission regions (or He <jats:sc>iii</jats:sc> regions) northwest and southeast of the He <jats:sc>iii</jats:sc> region in the galaxy’s main body investigated in previous studies. All regions exhibit He <jats:sc>ii</jats:sc>(<jats:italic>λ</jats:italic>4686)/H<jats:italic>β</jats:italic> greater than 2%. The two newly resolved He <jats:sc>iii</jats:sc> regions lie along an axis that intercepts the position of I Zw 18's ultraluminous X-ray (ULX) source. We explore whether the ULX could power the two He <jats:sc>iii</jats:sc> regions via shock activity and/or beamed X-ray emission. We find no evidence of shocks from the gas kinematics. If the ULX powers the two regions, the X-ray emission would need to be beamed. Another potential explanation is that a class of early-type nitrogen-rich Wolf–Rayet stars with low winds could power the two He <jats:sc>iii</jats:sc> regions, in which case the alignment with the ULX would be coincidental.</jats:p>