Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a data set and properties of 18,785 proton kinetic-scale current sheets collected over 124 days in the solar wind using magnetic field measurements at 1/11 s resolution aboard the Wind spacecraft. We show that all of the current sheets are in the parameter range where reconnection is not suppressed by diamagnetic drift of the X-line. We argue this necessary condition for magnetic reconnection is automatically satisfied due to the geometry of current sheets dictated by their source, which is the local plasma turbulence. The current sheets are shown to be elongated along the background magnetic field and dependence of the current sheet geometry on local plasma beta is revealed. We conclude that reconnection in the solar wind is not likely to be suppressed or controlled by the diamagnetic suppression condition.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The promise by the LIGO/Virgo/Kagra (LVK) collaboration to detect black-hole–neutron-star (BH–NS) mergers via gravitational wave (GW) emission has recently been fulfilled with the detection of GW200105 and GW200115. Mergers of BH–NS binaries are particularly exciting for their multimessenger potential since GW detection can be followed by an electromagnetic (EM) counterpart (kilonova, gamma-ray burst, afterglow) that can reveal important information on the equation of state (EOS) of NSs and the nature of the BH spin. This can happen whenever the NS does not directly plunge into the BH, but rather is tidally disrupted, leaving behind debris to accrete. We carry out a statistical study of the binary stars that evolve to form a BH–NS binary and compute the rate of merger events that can be followed by an EM counterpart. We find that ≳50% of the mergers can lead to an EM counterpart only in the case where BHs are born highly spinning (<jats:italic>χ</jats:italic> <jats:sub>BH</jats:sub> ≳ 0.7), while this fraction does not exceed about 30% for stiff NS EOSs and a few percent for soft NS EOSs for low-spinning BHs (<jats:italic>χ</jats:italic> <jats:sub>BH</jats:sub> ≲ 0.2), suggesting that a high rate of EM counterparts of BH–NS would provide support for high natal BH spins. However, the possibilities that BHs are born with near-maximal spins and that NS internal structure is described by a stiff EOS are disfavored by current LVK constraints. Considering that these values only represent an upper limit to observe an EM counterpart due to current observational limitations, such as brightness sensitivity and sky localization, BH–NS mergers are unlikely multimessenger sources.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the detection of a chemically fresh inflow that is feeding high-mass young-stellar-object (HMYSO) growth in the nearby high-mass star-forming region G352.63 made with both the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array (SMA). High-quality images of the dust and molecular lines from both ALMA and SMA have consistently revealed a gravitationally controlled cold (∼10 K) gas inflow of chemically fresh molecules (e.g., CCH and HC<jats:sub>3</jats:sub>N) toward the central HMYSO and its surrounding dense gas structure, which has a possible torus- or disk-like morphology. The HMYSO is also observed to have an outflow, which is nearly perpendicular to the torus and its parental filament, and thus can be clearly separated from the inflows. These kinematic features provide observational evidence to support the conjecture that the infalling streamers in high-mass star-forming regions could proceed in a similar process to that observed in low-mass counterparts. The chemically fresh infalling streamers could also be involved in the disk or torus configuration, fragmentation, and accretion bursts that occur in both simulations and observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The absolute absorption cross section of dangling OH bonds in water ice, a free OH stretch mode by three-coordinated surface water molecules, is derived experimentally as 1.0 ± 0.2 × 10<jats:sup>−18</jats:sup> cm<jats:sup>2</jats:sup> at 3696 cm<jats:sup>−1</jats:sup> for amorphous water at 90 K using infrared multiple-angle incidence resolution spectrometry (IR–MAIRS). The integrated absorption cross section (band strength) of the dangling OH bond at 90 K (1.4 ± 0.3 × 10<jats:sup>−17</jats:sup> cm molecule<jats:sup>−1</jats:sup> at 3710–3680 cm<jats:sup>−1</jats:sup>) is found to be more than 1 order of magnitude smaller than those in bulk ice or liquid water. This indicates that a lack of hydrogen-bonding significantly decreases the band strength of dangling OH bonds. The present study also provides average molecular orientations of dangling OH bonds at 10 K and 90 K, because both the surface-parallel (in-plane) and surface-perpendicular (out-of-plane) vibration spectra of dangling OH bonds are quantitatively measured by IR–MAIRS. The intensity ratio of the dangling-OH peaks between in-plane to out-of-plane spectra shows the isotropic nature (random orientation) of the two- and three-coordinated dangling OH bonds in microporous amorphous water prepared at 10 K; however, the three-coordinated dangling OH bonds in nonporous amorphous water prepared at 90 K are dominantly located at the top ice surface and oriented perpendicular to it. These findings provide fundamental insights into the relationship between the structure and optical properties of ice surfaces, and aid quantitative understanding of the surface structure of interstellar ices and their laboratory analogs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Planets are known to grow out of a star-encircling disk of the gas and dust inherited from an interstellar cloud; their formation is thought to begin with coagulation of submicron dust grains into aggregates, the first foundational stage of planet formation. However, with nanoscale and submicron solids unobservable directly in the interstellar medium (ISM) and protoplanetary disks, how dust grains grow is unclear, as are the morphology and structure of interstellar grains and the whereabouts and form of “missing iron.” Here we show an elementary composite binary in 3D sub-10 nm detail—and the alignments of its two subunits and nanoinclusions and a population of elongated composite grains locked in a primitive cosmic dust particle—noninvasively uncovered with phase-contrast X-ray nanotomography. The binary comprises a pair of oblate, quasi-spheroidal grains whose alignment and shape meet the astrophysical constraints on polarizing interstellar grains. Each member of the pair contains a high-density core of octahedral nanocrystals whose twin relationship is consistent with the magnetite’s diagnostic property at low temperatures, with a mantle exhibiting nanoscale heterogeneities, rounded edges, and pitted surfaces. This elongated binary evidently formed from an axially aligned collision of the two similar composite grains whose core–mantle structure and density gradients are consistent with interstellar processes and astronomical evidence for differential depletion. Our findings suggest that the ISM is threaded with dust grains containing preferentially oriented iron-rich magnetic nanocrystals that hold answers to astronomical problems from dust evolution, grain alignment, and the structure of magnetic fields to planetesimal growth.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present unprecedented high-fidelity radio images of the M87 jet. We analyzed Jansky Very Large Array broadband full-polarization radio data from 4 to 18 GHz. The observations were taken with the most extended configuration (A configuration), which allows the study of the emission of the jet up to kiloparsec scales with a linear resolution of ∼10 pc. The high sensitivity and resolution of our data allow us to resolve the jet width. We confirm a double-helix morphology of the jet material between ∼300 pc and ∼1 kpc. We found a gradient of the polarization degree with a minimum at the projected axis and maxima at the jet edges and a gradient in the Faraday depth with opposite signs at the jet edges. We also found that the behavior of the polarization properties along the wide range of frequencies is consistent with internal Faraday depolarization. All of these characteristics strongly support the presence of a helical magnetic field in the M87 jet up to 1 kpc from the central black hole, although the jet is most likely particle-dominated at these large scales. Therefore, we propose a plausible scenario in which the helical configuration of the magnetic field has been maintained to large scales thanks to the presence of Kelvin–Helmholtz instabilities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of an isolated white dwarf with a spin period of 70 s. We obtained high-speed photometry of three ultramassive white dwarfs within 100 pc and discovered significant variability in one. SDSS J221141.80+113604.4 is a 1.27 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> (assuming a CO core) magnetic white dwarf that shows 2.9% brightness variations in the BG40 filter with a 70.32 ± 0.04 s period, becoming the fastest spinning isolated white dwarf currently known. A detailed model atmosphere analysis shows that it has a mixed hydrogen and helium atmosphere with a dipole field strength of <jats:italic>B</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub> = 15 MG. Given its large mass, fast rotation, strong magnetic field, unusual atmospheric composition, and relatively large tangential velocity for its cooling age, J2211+1136 displays all of the signatures of a double white dwarf merger remnant. Long-term monitoring of the spin evolution of J2211+1136 and other fast-spinning isolated white dwarfs opens a new discovery space for substellar and planetary mass companions around white dwarfs. In addition, the discovery of such fast rotators outside of the ZZ Ceti instability strip suggests that some should also exist within the strip. Hence, some of the monoperiodic variables found within the instability strip may be fast-spinning white dwarfs impersonating ZZ Ceti pulsators.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Line-intensity mapping is emerging as a novel method that can measure the collective intensity fluctuations of atomic/molecular line emission from distant galaxies. Several observational programs with various wavelengths are ongoing and planned, but there remains a critical problem of line confusion; emission lines originating from galaxies at different redshifts are confused at the same observed wavelength. We devise a generative adversarial network that extracts designated emission-line signals from noisy three-dimensional data. Our novel network architecture allows two input data, in which the same underlying large-scale structure is traced by two emission lines of H <jats:italic>α</jats:italic> and [O<jats:sc>iii</jats:sc>], so that the network learns the relative contributions at each wavelength and is trained to decompose the respective signals. After being trained with a large number of realistic mock catalogs, the network is able to reconstruct the three-dimensional distribution of emission-line galaxies at <jats:italic>z</jats:italic> = 1.3−2.4. Bright galaxies are identified with a precision of 84%, and the cross correlation coefficients between the true and reconstructed intensity maps are as high as 0.8. Our deep-learning method can be readily applied to data from planned spaceborne and ground-based experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this Letter we report a discovery of a prominent flash of a peculiar overluminous Type Ia supernova, SN 2020hvf, in about 5 hr of the supernova explosion by the first wide-field mosaic CMOS sensor imager, the Tomo-e Gozen Camera. The fast evolution of the early flash was captured by intensive intranight observations via the Tomo-e Gozen high-cadence survey. Numerical simulations show that such a prominent and fast early emission is most likely generated from an interaction between 0.01 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> circumstellar material (CSM) extending to a distance of ∼10<jats:sup>13</jats:sup> cm and supernova ejecta soon after the explosion, indicating a confined dense CSM formation at the final evolution stage of the progenitor of SN 2020hvf. Based on the CSM–ejecta interaction-induced early flash, the overluminous light curve, and the high ejecta velocity of SN 2020hvf, we suggest that the SN 2020hvf may originate from a thermonuclear explosion of a super-Chandrasekhar-mass white dwarf (“super-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub> WD”). Systematical investigations on explosion mechanisms and hydrodynamic simulations of the super-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub> WD explosion are required to further test the suggested scenario and understand the progenitor of this peculiar supernova.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the internal 3D magnetic structure of dense interstellar filaments within NGC 1333 using polarization data at 850 <jats:italic>μ</jats:italic>m from the <jats:italic>B</jats:italic>-fields In STar-forming Region Observations survey at the James Clerk Maxwell Telescope. Theoretical models predict that the magnetic field lines in a filament will tend to be dragged radially inward (i.e., pinched) toward the central axis due to the filament’s self-gravity. We study the cross-sectional profiles of the total intensity (<jats:italic>I</jats:italic>) and polarized intensity (PI) of dust emission in four segments of filaments unaffected by local star formation that are expected to retain a pristine magnetic field structure. We find that the filaments’ FWHMs in PI are not the same as those in <jats:italic>I</jats:italic>, with two segments being appreciably narrower in PI (FWHM ratio ≃0.7–0.8) and one segment being wider (FWHM ratio ≃1.3). The filament profiles of the polarization fraction (<jats:italic>P</jats:italic>) do not show a minimum at the spine of the filament, which is not in line with an anticorrelation between <jats:italic>P</jats:italic> and <jats:italic>I</jats:italic> normally seen in molecular clouds and protostellar cores. Dust grain alignment variation with density cannot reproduce the observed <jats:italic>P</jats:italic> distribution. We demonstrate numerically that the <jats:italic>I</jats:italic> and PI cross-sectional profiles of filaments in magnetohydrostatic equilibrium will have differing relative widths depending on the viewing angle. The observed variations of FWHM ratios in NGC 1333 are therefore consistent with models of pinched magnetic field structures inside filaments, especially if they are magnetically near-critical or supercritical.</jats:p>