Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Gradual and large solar energetic particle (SEP) events (flux of ions with energy &gt;10 MeV above 10 pfu) are primarily produced in shocks driven by fast and wide coronal mass ejections (CMEs). Past research, both in theory and statistics, has found that the situation where a fast primary CME (priCME) is preceded by previous CMEs (preCMEs) is favorable to a more efficient particle acceleration. However, the physical causes of this association is still a matter of debate, including the association of the acceleration and release of SEPs with the interaction of successive CMEs. Taking advantage of the twin Solar TErrestrial RElations Observatory spacecraft, we study 41 large SEP events in solar cycle 24 by multi-viewpoint observations. Although 21 events (∼51%) have a preCME identifiable in the Large Angle and Spectrometric Coronagraph, we determine that the priCMEs overlap the preCMEs in three dimension (3D) for only 11 events (∼27%). We further investigate the acceleration (using type II radio bursts) and release (using velocity dispersion analysis) of the particles for all potential instances of CME–CME interaction in 3D. We find that, for six of 11 events, the priCME is far away from catching up with the preCME when the particles are released. However, for the limited samples, the SEP peak intensity is significantly higher in the events in which the priCME is closest to impacting the preCME, indicating the potential for the increased seed population or more enhanced turbulence levels occurring closer to the preCME.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We infer the density of hydrogen nuclei and optical depths associated with molecular gas in front of a star-forming region and in a quiescent region of the Galactic interstellar medium (ISM) using 18 cm OH and archival 3 mm <jats:sup>12</jats:sup>CO observations, together with a diffuse cloud model from the literature. The results indicate that the volume densities of hydrogen nuclei are greatest near the star-forming region, intermediate in the CO-bright portions of the quiescent region, and lowest in the CO-dark portions of the quiescent region. Low volume density and low column density appear to be correlated with the presence of CO-dark molecular gas, which is primarily located in the vast space outside of star-forming regions. Molecular gas containing CO may exist in similar quantities both outside of and in the vicinity of star-forming regions; however, the CO emission radiates more efficiently in regions where the ISM is locally compressed, leading to the observational phenomenon of CO-dark and CO-bright molecular gas. We suggest that processes occurring as a natural consequence of star formation such as shock waves and stellar winds lead to compression of the gas into smaller pockets of higher volume density, and such “clumpy” structures will naturally emit more efficiently in CO owing to higher rates of collisional excitation. In this picture, the apparent prominence of CO emission in and near star-forming regions is itself a by-product of the star formation process.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Sgr E is a massive star formation complex found toward the Galactic center that consists of numerous discrete, compact H <jats:sc>ii</jats:sc> regions. It is located at the intersection between the central molecular zone (CMZ) and the far dust lane of the Galactic bar, similar to “hot spots” seen in external galaxies. Compared with other Galactic star formation complexes, the Sgr E complex is unusual because its H <jats:sc>ii</jats:sc> regions all have similar radio luminosities and angular extents, and they are deficient in ∼10 <jats:italic>μ</jats:italic>m emission from their photodissociation regions (PDRs). Our Green Bank Telescope radio recombination line observations increase the known membership of Sgr E to 19 H <jats:sc>ii</jats:sc> regions. There are 43 additional H <jats:sc>ii</jats:sc> region candidates in the direction of Sgr E, 26 of which are detected for the first time here using MeerKAT 1.28 <jats:inline-formula> <jats:tex-math> <?CDATA $\,\mathrm{GHz}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabadf6ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> data. Therefore, the true H <jats:sc>ii</jats:sc> region population of Sgr E may number &gt;60. Using APEX SEDIGISM <jats:sup>13</jats:sup>CO <jats:inline-formula> <jats:tex-math> <?CDATA $2\to 1$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabadf6ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> data we discover a 3.0 × 10<jats:sup>5</jats:sup> <jats:inline-formula> <jats:tex-math> <?CDATA $\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabadf6ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> molecular cloud associated with Sgr E, but find few molecular or far-infrared concentrations at the locations of the Sgr E H <jats:sc>ii</jats:sc> regions. Comparison with simulations and an analysis of its radio continuum properties indicate that Sgr E formed upstream in the far dust lane of the Galactic bar a few million years ago and will overshoot the CMZ, crashing into the near dust lane. We propose that the unusual infrared properties of the Sgr E H <jats:sc>ii</jats:sc> regions are caused by their orbits about the Galactic center, which have possibly stripped their PDRs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The trans-Neptunian object 2014 MU69, named Arrokoth, is the most recent evidence that planetesimals did not form by successive collisions of smaller objects, but by the direct gravitational collapse of a pebble cloud. But what process sets the physical scales on which this collapse may occur? Star formation has the Jeans mass, that is, when gravity is stronger than thermal pressure, helping us to understand the mass of our Sun. But what controls mass and size in the case of planetesimal formation? Both asteroids and Kuiper Belt objects show a kink in their size distribution at 100 km. Here we derive a gravitational collapse criterion for a pebble cloud to fragment to planetesimals, showing that a critical mass is needed for the clump to overcome turbulent diffusion. We successfully tested the validity of this criterion in direct numerical simulations of planetesimal formation triggered by the streaming instability. Our result can therefore explain the sizes for planetesimals found forming in streaming instability simulations in the literature, while not addressing the detailed size distribution. We find that the observed characteristic diameter of ∼100 km corresponds to the critical mass of a pebble cloud set by the strength of turbulent diffusion stemming from streaming instability for a wide region of a solar nebula model from 2 to 60 au, with a tendency to allow for smaller objects at distances beyond and at late times, when the nebula gas gets depleted.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using 8.4 yr of photometry from the AllWISE/NEOWISE multi-epoch catalogs, we compare the mid-infrared variability properties of a sample of 2197 dwarf galaxies (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> &lt; 2 × 10<jats:sup>9</jats:sup> <jats:italic>h</jats:italic> <jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub>) to a sample of 6591 more massive galaxies (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> ≥ 10<jats:sup>10</jats:sup> <jats:italic>h</jats:italic> <jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub>) matched in mid-infrared apparent magnitude. We find only two dwarf galaxies with mid-infrared variability, a factor of ∼10 less frequent than the more massive galaxies (<jats:italic>p</jats:italic> = 6 × 10<jats:sup>−6</jats:sup>), consistent with previous findings of optical variability in low-mass and dwarf galaxies using data with a similar baseline and cadence. Within the more massive control galaxy population, we see no evidence for a stellar mass dependence of mid-infrared variability, suggesting that this apparent reduction in the frequency of variable objects occurs below a stellar mass of ∼10<jats:sup>10</jats:sup> <jats:italic>h</jats:italic> <jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub>. Compared to the more massive galaxies, active galactic nuclei (AGNs) selected in dwarf galaxies using either their mid-infrared color or optical emission-line classification are systematically missed by variability selection. Our results suggest, in agreement with previous optical studies at similar cadence, that variability selection of AGNs in dwarf galaxies is ineffective unless higher-cadence data are used.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We show that point sources of dark energy can explain accelerated late-time expansion and, simultaneously, satisfy observational constraints on massive compact objects. Population III stellar collapse into GEneric Objects of Dark Energy (GEODEs) between 8 ≲ <jats:italic>z</jats:italic> ≲ 20 mimics the observed Ω<jats:sub>Λ</jats:sub> within the typical concordance cosmology. We determine the appropriate dynamical model of aggregate GEODE flow within covariant linear perturbation theory. We find that all continuum fluid properties, at large scales, are determined by the internal properties and spin of individual GEODEs. For large spin, the spatial distribution of GEODEs becomes uniform on scales ≲200 Mpc. The power spectrum of cold dark matter is essentially unaltered. A Population III GEODE scenario provides an observationally consistent physical origin for accelerated late-time expansion while imposing no new constraints on structure formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Globular clusters host a variety of lower-luminosity (<jats:italic>L</jats:italic> <jats:sub>X</jats:sub> &lt; 10<jats:sup>35</jats:sup> erg s<jats:sup>−1</jats:sup>) X-ray sources, including accreting neutron stars (NSs) and  black holes (BHs), millisecond pulsars (MSPs), cataclysmic variables, and chromospherically active binaries. In this paper, we provide a comprehensive catalog of more than 1100 X-ray sources in 38 Galactic globular clusters (GCs) observed by the Chandra X-ray Observatory’s Chandra/ACIS detector. The targets are selected to complement the MAVERIC survey’s deep radio continuum maps of Galactic GCs. We perform photometry and spectral analysis for each source, determine a best-fit model, and assess the possibility of it being a foreground or background source based on its spectral properties and location in the cluster. We also provide basic assessments of variability. We discuss the distribution of X-ray binaries in GCs and their X-ray luminosity function, and we carefully analyze systems with <jats:italic>L</jats:italic> <jats:sub>X</jats:sub> &gt; 10<jats:sup>33</jats:sup> erg s<jats:sup>−1</jats:sup>. Among these moderately bright systems, we discover a new source in NGC 6539 that may be a candidate accreting stellar-mass BH or a transitional MSP. We show that quiescent NS low-mass X-ray binaries in GCs may spend ∼2% of their lifetimes as transitional MSPs in their active (<jats:italic>L</jats:italic> <jats:sub>X</jats:sub> &gt; 10<jats:sup>33</jats:sup> erg s<jats:sup>−1</jats:sup>) state. Finally, we identify a substantial underabundance of bright (<jats:italic>L</jats:italic> <jats:sub>X</jats:sub> &gt; 10<jats:sup>33</jats:sup> erg s<jats:sup>−1</jats:sup>) intermediate polars in GCs compared to the Galactic field, in contrast with the literature of the past two decades.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Comets provide unique information about the physical and chemical properties of the environment in which the solar system was formed. Understanding how cometary dust and ice evolve under the effect of sunlight is essential for constraining nuclear structure and triggering the mechanism of comet activity. In this paper, we first study the rotational disruption of dust grains lifted by outgassing from comet nuclei by radiative torques (RATs). We find that composite grains could be rapidly disrupted into small fragments by the RAT disruption mechanism. We then study rotational desorption of ice grains by RATs and find that icy grains could be desorbed from large heliocentric distances, beyond the sublimation radius of water at <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\mathrm{sub}}({{\rm{H}}}_{2}{\rm{O}})\sim 3\,\mathrm{au}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabafa5ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. We also calculate the production rate of water vapor versus the heliocentric distance of comets due to rotational desorption. Our results could explain the variation of dust properties and the presence of small grains frequently observed from cometary comae. Finally, we suggest that the activity of distant comets could be triggered by rotational disruption of grains and desorption of water-ice grains at large heliocentric distances.</jats:p>