Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We use a numerical Galactic chemical evolution model and find that the common envelope jet supernova (CEJSN) <jats:italic>r</jats:italic>-process scenario can account for both the very early average ratio of europium to iron and its evolution at later times in the the Milky Way. In the CEJSN scenario a neutron star (NS) spirals in inside a red supergiant (RSG) star all the way to the core and destroys it. According to this scenario <jats:italic>r</jats:italic>-process isotopes are nucleosynthesized inside neutron-rich jets that the accretion disk around the NS launches inside the core. The merger of an NS with an RSG core already takes place in the very young Galaxy. We conclude that CEJSNe can be a major contributor to <jats:italic>r</jats:italic>-process nucleosynthesis.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the lower solar coronal regions where the magnetic field is dominant, the Alfvén speed is much higher than the wind speed. In contrast, the near-Earth solar wind is strongly super-Alfvénic, i.e., the wind speed greatly exceeds the Alfvén speed. The transition between these regimes is classically described as the “Alfvén point” but may in fact occur in a distributed Alfvén critical region. NASA’s Parker Solar Probe (PSP) mission has entered this region, as it follows a series of orbits that gradually approach more closely to the Sun. During its 8<jats:sup>th</jats:sup> and 9<jats:sup>th</jats:sup> solar encounters, at a distance of ≈16 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> from the Sun, PSP sampled four extended periods in which the solar wind speed was measured to be smaller than the local Alfvén speed. These are the first in situ detections of sub-Alfvénic solar wind in the inner heliosphere by PSP. Here we explore properties of these samples of sub-Alfvénic solar wind, which may provide important previews of the physical processes operating at lower altitude. Specifically, we characterize the turbulence, anisotropy, intermittency, and directional switchback properties of these sub-Alfvénic winds and contrast these with the neighboring super-Alfvénic periods.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Measuring the gas mass of protoplanetary disks, the reservoir available for giant planet formation, has proven to be difficult. We currently lack a far-infrared observatory capable of observing HD, and the most common gas mass tracer, CO, suffers from a poorly constrained CO-to-H<jats:sub>2</jats:sub> ratio. Expanding on previous work, we investigate if N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup>, a chemical tracer of CO-poor gas, can be used to observationally measure the CO-to-H<jats:sub>2</jats:sub> ratio and correct CO-based gas masses. Using disk structures obtained from the literature, we set up thermochemical models for three disks, TW Hya, DM Tau and GM Aur, to examine how well the CO-to-H<jats:sub>2</jats:sub> ratio and gas mass can be measured from N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> and C<jats:sup>18</jats:sup>O line fluxes. Furthermore, we compare these gas masses to gas masses independently measured from archival HD observations. The N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup>(3 − 2)/C<jats:sup>18</jats:sup>O(2 − 1) line ratio scales with the disk CO-to-H<jats:sub>2</jats:sub> ratio. Using these two lines, we measure 4.6 × 10<jats:sup>−3</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ≤ <jats:italic>M</jats:italic> <jats:sub>disk</jats:sub> ≤ 1.1 × 10<jats:sup>−1</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> for TW Hya, 1.5 × 10<jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ≤ <jats:italic>M</jats:italic> <jats:sub>disk</jats:sub> ≤ 9.6 × 10<jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> for GM Aur and 3.1 × 10<jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ≤ <jats:italic>M</jats:italic> <jats:sub>disk</jats:sub> ≤ 9.6 × 10<jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> for DM Tau. These gas masses agree with values obtained from HD within their respective uncertainties. The uncertainty on the N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> + C<jats:sup>18</jats:sup>O gas mass can be reduced by observationally constraining the cosmic-ray ionization rate in disks. These results demonstrate the potential of using the combination of N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> and C<jats:sup>18</jats:sup>O to measure gas masses of protoplanetary disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the Parker Solar Probe measurements, this Letter reports two new types of multiband electrostatic waves in and near the heliospheric current sheet. They are classified into the <jats:italic>f</jats:italic> &lt; <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub> and <jats:italic>f</jats:italic> &gt; <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub> multiband electrostatic waves, in which most (or all) of the bands in the former type are lower than <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub>, and all of the bands in the latter type are higher than <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub>, where <jats:italic>f</jats:italic> and <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub> denotes the wave frequency and the electron cyclotron frequency, respectively. This Letter also exhibits observational evidence of the existence of nonlinear wave–wave interactions of both types of electrostatic waves. In particular, the <jats:italic>f</jats:italic> &gt; <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub> multiband electrostatic waves are found to be modulated in the presence of low-frequency oblique ion-scale waves. According to the observed frequency distribution, this Letter proposes that the mode nature of the <jats:italic>f</jats:italic> &lt; <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub> multiband electrostatic waves could be the oblique ion acoustic wave or the lower-hybrid wave, and the <jats:italic>f</jats:italic> &gt; <jats:italic>f</jats:italic> <jats:sub>ce</jats:sub> multiband electrostatic waves are the electron Bernstein mode wave. These findings provide a challenge to understand the complex electron and ion dynamical processes in and near the heliospheric current sheet.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The dissipation effects of primordial magnetic fields on the primordial elemental abundances were investigated. When a magnetic field reconnects, its energy is converted to the kinetic energy of charged particles, as observed for solar energetic particles arriving on Earth. This accelerates the cosmic background nuclei and energetic nuclei induce nonthermal reactions. A constraint on the dissipation is derived from a theoretical calculation of the nonthermal reactions during Big Bang nucleosynthesis. We found that observations of the Li and D abundances can be explained if 0.01%–0.1% of the cosmic energy density was utilized for nuclear acceleration after the electron–positron annihilation epoch. Reconnections of such amplitudes of magnetic fields generate outgoing jets, the bulk velocity of which evolves to values appropriate for cosmic-ray (CR) nuclear energies of 0.1–1 MeV necessary for successful CR nucleosynthesis. Therefore, acceleration of cosmic background nuclei during the dissipation of primordial magnetic fields is a possible generation mechanism of soft CRs that has been suggested as a solution to the cosmic Li problem. Among the solutions suggested without exotic physics, only the dissipating magnetic field model suggested here explains observations of both low Li and high D abundances. Our results demonstrate that signatures of strong magnetic fields in the early universe have been observed in primordial elemental abundances.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Young solar-type stars are known to show frequent “superflares,” which may severely influence the habitable worlds on young planets via intense radiation and coronal mass ejections. Here we report an optical spectroscopic and photometric observation of a long-duration superflare on the young solar-type star EK Draconis (50–120 Myr age) with the Seimei telescope and Transiting Exoplanet Survey Satellite. The flare energy 2.6 × 10<jats:sup>34</jats:sup> erg and white-light flare duration 2.2 hr are much larger than those of the largest solar flares, and this is the largest superflare on a solar-type star ever detected by optical spectroscopy. The H<jats:italic>α</jats:italic> emission profile shows no significant line asymmetry, meaning no signature of a filament eruption, unlike the only previous detection of a superflare on this star. Also, it did not show significant line broadening, indicating that the nonthermal heating at the flare footpoints is not essential or that the footpoints are behind the limb. The time evolution and duration of the H<jats:italic>α</jats:italic> flare are surprisingly almost the same as those of the white-light flare, which is different from general M-dwarf (super-)flares and solar flares. This unexpected time evolution may suggest that different radiation mechanisms than general solar flares are predominant, such as: (1) radiation from (off-limb) flare loops and (2) re-radiation via radiative back-warming, in both of which the cooling timescales of flare loops could determine the timescales of H<jats:italic>α</jats:italic> and white light.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Star formation primarily occurs in filaments where magnetic fields are expected to be dynamically important. The largest and densest filaments trace the spiral structure within galaxies. Over a dozen of these dense (∼10<jats:sup>4</jats:sup> cm<jats:sup>−3</jats:sup>) and long (&gt;10 pc) filaments have been found within the Milky Way, and they are often referred to as “bones.” Until now, none of these bones has had its magnetic field resolved and mapped in its entirety. We introduce the SOFIA legacy project FIELDMAPS which has begun mapping ∼10 of these Milky Way bones using the HAWC+ instrument at 214 <jats:italic>μ</jats:italic>m and 18.″2 resolution. Here we present a first result from this survey on the ∼60 pc long bone G47. Contrary to some studies of dense filaments in the Galactic plane, we find that the magnetic field is often not perpendicular to the spine (i.e., the center line of the bone). Fields tend to be perpendicular in the densest areas of active star formation and more parallel or random in other areas. The average field is neither parallel nor perpendicular to the Galactic plane or the bone. The magnetic field strengths along the spine typically vary from ∼20 to ∼100 <jats:italic>μ</jats:italic>G. Magnetic fields tend to be strong enough to suppress collapse along much of the bone, but for areas that are most active in star formation, the fields are notably less able to resist gravitational collapse.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present 12 epochs of optical spectroscopy taken across the discovery outburst of the black hole (BH) candidate MAXI J1803−298 with the Gran Telescopio Canarias and Very Large Telescope. The source followed a standard outburst evolution with hard and soft states. The system displays a triangular shape in the hardness intensity diagram, consistent with that seen in high-inclination BH transients and the previously reported detection of X-ray dips. The two epochs observed during the initial hard state exhibited asymmetric emission-line profiles, including a P-Cygni profile simultaneously detected in H<jats:italic>α</jats:italic> and He <jats:sc>i</jats:sc> 6678, which indicates the presence of an optical wind in the system. The remaining spectra, obtained during the transition to the soft state and the subsequent decay, are instead characterized by narrower, double-peaked emission lines embedded into broad absorption components. One epoch (intermediate state) also includes near-infrared (NIR) coverage, revealing complex line profiles in the Paschen and Bracket series, which suggests that the outflow is still present during the outburst decay through the soft state. The growing list of low-mass X-ray binaries with optical and NIR outflow signatures indicates that these are common features. Furthermore, the lowest luminosity spectrum exhibits an H<jats:italic>α</jats:italic> FWHM of 1570 ± 100 km s<jats:sup>−1</jats:sup>. This, together with previous constraints on the binary parameters, allows us to favor a compact object mass of ∼3–10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, further supporting its BH nature.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ongoing large-scale optical time-domain surveys, such as the Zwicky Transient Facility (ZTF), are producing alerts at unprecedented rates. Analysis of transient sources has so far followed two distinct paths: archival analysis of data on transient sources at a time when they are no longer observable and real-time analysis at the time when the sources are first detected. The latter is the realm of alert brokers such as the Arizona-NOIRLab Temporal Analysis and Response to Events System (ANTARES). In this paper, we synthesize the two analysis paths and present a first systematic study of archival alert-broker data, focusing on extragalactic transients with multipeaked light curves identified in the ANTARES archive of ZTF alerts. Our analysis yields a sample of 37 such sources, including core-collapse supernovae (with two analogs of iPTF14hls), thermonuclear supernovae interacting with their surrounding circumstellar medium, tidal disruption events, luminous blue variables, and as yet unclassified objects. A large fraction of the identified sources is currently active, warranting allocation of follow-up resources in the immediate future to further constrain their nature and the physical processes at work.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>While stars are often found in binary systems, brown dwarf binaries are much rarer. Brown dwarf–brown dwarf pairs are typically difficult to resolve because they often have very small separations. Using brown dwarfs discovered with data from the Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, we inspected other, higher-resolution, sky surveys for overlooked cold companions. During this process, we discovered the brown dwarf binary system CWISE J0146−0508AB, which we find has a very small chance alignment probability based on the similar proper motions of the components of the system. Using follow-up near-infrared spectroscopy with Keck/NIRES, we determined component spectral types of L4 and L8 (blue), making CWISE J0146−0508AB one of only a few benchmark systems with a blue L dwarf. At an estimated distance of ∼40 pc, CWISE J0146−0508AB has a projected separation of ∼129 au, making it the widest-separation brown dwarf pair found to date. We find that such a wide separation for a brown dwarf binary may imply formation in a low-density star-forming region.</jats:p>