Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The importance of the activation energy of surface diffusion (<jats:italic>E</jats:italic> <jats:sub>sd</jats:sub>) of adsorbed molecules on amorphous solid water (ASW) has been widely discussed in terms of chemical reactions on ASW at low temperatures. However, in previous work, <jats:italic>E</jats:italic> <jats:sub>sd</jats:sub> has not been measured directly but estimated from indirect experiments. It has been assumed in chemical network calculations that <jats:italic>E</jats:italic> <jats:sub>sd</jats:sub> is between 0.3 and 0.8 of the desorption energies of a molecule. It remains important to obtain direct measurements of <jats:italic>E</jats:italic> <jats:sub>sd</jats:sub>. We performed in situ observations of the deposition process of CO and CO<jats:sub>2</jats:sub> on ASW using transmission electron microscopy (TEM) and deduced the <jats:italic>E</jats:italic> <jats:sub>sd</jats:sub> of CO and CO<jats:sub>2</jats:sub> on ASW to be 350 ± 50 and 1500 ± 100 K, respectively. The value of <jats:italic>E</jats:italic> <jats:sub>sd</jats:sub> of CO is approximately 0.3 of the total adsorption energy of CO on ASW, i.e., much smaller than assumed in chemical network calculations, where the corresponding figure is 575 K, assuming approximately 0.5 of the desorption energy. We demonstrated that TEM is very useful not only for the observation of ices but also for the measurement of some physical properties that are relevant in astrochemistry and astrophysics. Using the <jats:italic>E</jats:italic> <jats:sub>sd</jats:sub> of CO measured in the present study (350 K), we have updated the chemical network model of Furuya et al., confirming that CO<jats:sub>2</jats:sub> could be efficiently formed by the reaction CO + OH → CO<jats:sub>2</jats:sub> + H in the initial stages of the evolution of molecular clouds.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational-wave data within the neutron star–black hole merger scenario. For the black hole, we yield a mass of <jats:inline-formula> <jats:tex-math> <?CDATA ${2.40}_{-0.32}^{+0.36}{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab745aieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and an aligned spin of <jats:inline-formula> <jats:tex-math> <?CDATA ${0.141}_{-0.064}^{+0.067}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab745aieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. As for the neutron star we find a mass of <jats:inline-formula> <jats:tex-math> <?CDATA ${1.15}_{-0.13}^{+0.15}{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab745aieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and the dimensionless tidal deformability of <jats:inline-formula> <jats:tex-math> <?CDATA ${1.4}_{-1.2}^{+3.8}\times {10}^{3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab745aieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. These parameter ranges are for 90% credibility. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star–black hole merger event. Benefitting from the continual enhancement of the sensitivities of the advanced gravitational detectors and the increase of the number of the observatories, similar events are anticipated to be much more precisely measured in the future and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest <jats:italic>r</jats:italic>-process elements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Exoplanets orbiting M-dwarfs present a valuable opportunity for their detection and atmospheric characterization. This is evident from recent inferences of H<jats:sub>2</jats:sub>O in such atmospheres, including that of the habitable-zone exoplanet K2-18b. With a bulk density between Earth and Neptune, K2-18b may be expected to possess a H/He envelope. However, the extent of such an envelope and the thermodynamic conditions of the interior remain unexplored. In the present work, we investigate the atmospheric and interior properties of K2-18b based on its bulk properties and its atmospheric transmission spectrum. We constrain the atmosphere to be H<jats:sub>2</jats:sub>-rich with a H<jats:sub>2</jats:sub>O volume mixing ratio of 0.02%–14.8%, consistent with previous studies, and find a depletion of CH<jats:sub>4</jats:sub> and NH<jats:sub>3</jats:sub>, indicating chemical disequilibrium. We do not conclusively detect clouds/hazes in the observable atmosphere. We use the bulk parameters and retrieved atmospheric properties to constrain the internal structure and thermodynamic conditions in the planet. The constraints on the interior allow multiple scenarios between rocky worlds with massive H/He envelopes and water worlds with thin envelopes. We constrain the mass fraction of the H/He envelope to be ≲6%; spanning ≲10<jats:sup>−5</jats:sup> for a predominantly water world to ∼6% for a pure iron interior. The thermodynamic conditions at the surface of the H<jats:sub>2</jats:sub>O layer range from the supercritical to liquid phases, with a range of solutions allowing for habitable conditions on K2-18b. Our results demonstrate that the potential for habitable conditions is not necessarily restricted to Earth-like rocky exoplanets.</jats:p>