Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>To reach a deeper understanding of the origin of elements in the periodic table, we construct Galactic chemical evolution (GCE) models for all stable elements from C (<jats:italic>A</jats:italic> = 12) to U (<jats:italic>A</jats:italic> = 238) from first principles, i.e., using theoretical nucleosynthesis yields and event rates of all chemical enrichment sources. This enables us to predict the origin of elements as a function of time and environment. In the solar neighborhood, we find that stars with initial masses of <jats:italic>M</jats:italic> &gt; 30<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> can become failed supernovae if there is a significant contribution from hypernovae (HNe) at <jats:italic>M</jats:italic> ∼ 20–50<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The contribution to GCE from super-asymptotic giant branch (AGB) stars (with <jats:italic>M</jats:italic> ∼ 8–10<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at solar metallicity) is negligible, unless hybrid white dwarfs from low-mass super-AGB stars explode as so-called Type Iax supernovae, or high-mass super-AGB stars explode as electron-capture supernovae (ECSNe). Among neutron-capture elements, the observed abundances of the second (Ba) and third (Pb) peak elements are well reproduced with our updated yields of the slow neutron-capture process (s-process) from AGB stars. The first peak elements (Sr, Y, Zr) are sufficiently produced by ECSNe together with AGB stars. Neutron star mergers can produce rapid neutron-capture process (r-process) elements up to Th and U, but the timescales are too long to explain observations at low metallicities. The observed evolutionary trends, such as for Eu, can well be explained if ∼3% of 25–50<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> HNe are magneto-rotational supernovae producing r-process elements. Along with the solar neighborhood, we also predict the evolutionary trends in the halo, bulge, and thick disk for future comparison with Galactic archeology surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Through the magnetic braking and the launching of protostellar outflows, magnetic fields play a major role in the regulation of angular momentum in star formation, which directly impacts the formation and evolution of protoplanetary disks and binary systems. The aim of this paper is to quantify those phenomena in the presence of nonideal magnetohydrodynamics effects, namely, the ohmic and ambipolar diffusion. We perform three-dimensional simulations of protostellar collapses varying the mass of the prestellar dense core, the thermal support (the <jats:italic>α</jats:italic> ratio), and the dust grain size distribution. The mass mostly influences the magnetic braking in the pseudo-disk, while the thermal support impacts the accretion rate and hence the properties of the disk. Removing the grains smaller than 0.1 <jats:italic>μ</jats:italic>m in the Mathis–Rumpl–Nordsieck distribution enhances the ambipolar diffusion coefficient. Similar to previous studies, we find that this change in the distribution reduces the magnetic braking with an impact on the disk. The outflow is also significantly weakened. In either case, the magnetic braking largely dominates the outflow as a process to remove the angular momentum from the disk. Finally, we report a large ionic precursor to the outflow with velocities of several km s<jats:sup>−1</jats:sup>, which may be observable.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present observations of linear polarization from dust thermal emission at 850 <jats:italic>μ</jats:italic>m toward the starless cloud L183. These data were obtained at the James Clerk Maxwell Telescope (JCMT) using the SCUBA-2 camera in conjunction with its polarimeter POL-2. Polarized dust emission traces the plane-of-sky magnetic field structure in the cloud, thus allowing us to investigate the role of magnetic fields in the formation and evolution of its starless core. To interpret these measurements, we first calculate the dust temperature and column density in L183 by fitting the spectral energy distribution obtained by combining data from the JCMT and the Herschel space observatory. We used the Davis–Chandrasekhar–Fermi technique to measure the magnetic field strength in five subregions of the cloud, and we find values ranging from ∼120 ± 18 <jats:italic>μ</jats:italic>G to ∼270 ± 64 <jats:italic>μ</jats:italic>G in agreement with previous studies. Combined with an average hydrogen column density (<jats:inline-formula> <jats:tex-math> <?CDATA ${N}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabad37ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) of ∼1.5 × 10<jats:sup>22</jats:sup> cm<jats:sup>−2</jats:sup> in the cloud, we also find that all five subregions are magnetically subcritical. These results indicate that the magnetic field in L183 is sufficiently strong to oppose the gravitational collapse of the cloud.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this multi-instrument paper, we search for evidence of sustained magnetic reconnection far beyond the impulsive phase of the X8.2-class solar flare on 2017 September 10. Using Hinode/EIS, CoMP, SDO/AIA, <jats:italic>K</jats:italic>-Cor, Hinode/XRT, RHESSI, and IRIS, we study the late-stage evolution of the flare dynamics and topology, comparing signatures of reconnection with those expected from the standard solar flare model. Examining previously unpublished EIS data, we present the evolution of nonthermal velocity and temperature within the famous plasma sheet structure, for the first four hours of the flare’s duration. On even longer timescales, we use differential emission measures and polarization data to study the longevity of the flare’s plasma sheet and cusp structure, discovering that the plasma sheet is still visible in observations of CoMP linear polarization on 2017 September 11, long after its last appearance in EUV. We deduce that magnetic reconnection of some form is still ongoing at this time—27 hr after flare onset.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a multifrequency study of eclipse properties of a transitional redback millisecond pulsar J1227−4853 discovered in 2014 with the GMRT. Emission from this pulsar is eclipsed at 607 MHz for about 37% of its orbit around the superior conjunction. We observe eclipse ingress and egress transitions that last for 12% and 15% of its orbit, respectively, resulting in only 36% of the orbit being unaffected by eclipsing material. We report an excess dispersion measure (DM) at eclipse boundaries of 0.079(3) pc cm<jats:sup>−3</jats:sup>, and the corresponding electron column density (<jats:italic>N</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub>) is 24.4(8) × 10<jats:sup>16</jats:sup> cm<jats:sup>−2</jats:sup>. Simultaneous timing and imaging studies suggest that the eclipses in J1227−4853 are not caused by temporal smearing due to excess dispersion and scattering but could be caused by removal of pulsar flux due to cyclotron absorption of the pulsed signal by intra-binary material constraining the companion’s magnetic field. Additionally, near the inferior conjunction at orbital phases 0.71 and 0.82 the pulsed emission is significantly delayed, which is associated with a fading of the pulsed and continuum flux densities. At orbital phase ∼0.82, we measure a change in DM of 0.035(3) pc cm<jats:sup>−3</jats:sup> and <jats:italic>N</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> of 10.8(8) × 10<jats:sup>16</jats:sup> cm<jats:sup>−2</jats:sup> associated with a dimming of up to ∼30% of the peak flux density. Such flux fading around a fixed orbital phase is not reported for other eclipsing binaries. Moreover, this event around the inferior conjunction could be caused by absorption of the pulsed signal by fragmented blobs of plasma generated from mass loss through the L2 Lagrangian point.</jats:p>