Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>NASA’s Psyche spacecraft will carry a magnetometer to main-belt asteroid (16) Psyche to search for remanent magnetic fields, and to attempt electromagnetic sounding of the interior. However, the Psyche spacecraft does not carry an instrument to measure solar wind plasmas. We thus combine data from five missions that have measured the solar wind at the orbit of asteroid (16) Psyche. We characterize these upstream conditions for future modeling and reference. We consider the implications of these ambient conditions for the interaction between (16) Psyche and the solar wind, outlining four possible resulting magnetospheres. Any magnetosphere would be dominated by ion-scale (Hall) physics and exotic electron-scale physics, requiring sophisticated physical modeling to describe. Under these different regimes, plasma generates additional electromagnetic fields, resulting in complex magnetism which may complicate the magnetic environment near asteroid (16) Psyche. Future missions to asteroids would benefit from combined magnetic field and plasma measurements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the publicly available open-source code UCLCHEMCMC, designed to estimate physical parameters of an observed cloud of gas by combining Markov chain Monte Carlo (MCMC) sampling with chemical and radiative transfer modeling. When given the observed values of different emission lines, UCLCHEMCMC runs a Bayesian parameter inference, using an MCMC algorithm to sample the likelihood and produce an estimate of the posterior probability distribution of the parameters. UCLCHEMCMC takes a full forward-modeling approach, generating model observables from the physical parameters via chemical and radiative transfer modeling. While running UCLCHEMCMC, the created chemical models and radiative transfer code results are stored in an SQL database, preventing redundant model calculations in future inferences. This means that the more UCLCHEMCMC is used, the more efficient it becomes. Using UCLCHEM and RADEX, the increase oin efficiency is nearly two orders of magnitude, going from 5185.33 ± 1041.96 s for 10 walkers to take 1000 steps when the database is empty, to 68.89 ± 45.39 s when nearly all models requested are in the database. In order to demonstrate its usefulness, we provide an example inference of UCLCHEMCMC to estimate the physical parameters of mock data, and perform two inferences on the well-studied prestellar core, L1544, one of which shows that it is important to consider the substructures of an object when determining which emission lines to use.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The star formation rate density (SFRD) history of the universe is well constrained up to redshift <jats:italic>z</jats:italic> ∼ 2. At earlier cosmic epochs, the picture has been largely inferred from UV-selected galaxies (e.g., Lyman-break galaxies; LBGs). However, the inferred star formation rates of LBGs strongly depend on the assumed dust extinction correction, which is not well constrained at high <jats:italic>z</jats:italic>, while observations in the radio domain are not affected by this issue. In this work we measure the SFRD from a 1.4 GHz selected sample of ∼600 galaxies in the GOODS-N field up to redshift ∼3.5. We take into account the contribution of active galactic nuclei from the infrared-radio correlation. We measure the radio luminosity function, fitted with a modified Schechter function, and derive the SFRD. The cosmic SFRD shows an increase up to <jats:italic>z</jats:italic> ∼ 2 and then an almost flat plateau up to <jats:italic>z</jats:italic> ∼ 3.5. Our SFRD is in agreement with those from other far-IR/radio surveys and a factor 2 higher than those from LBG samples. We also estimate that galaxies lacking a counterpart in the HST/WFC3 <jats:italic>H</jats:italic>-band (<jats:italic>H-</jats:italic>dark) make up ∼25% of the <jats:italic>ϕ</jats:italic>-integrated SFRD relative to the full sample at <jats:italic>z</jats:italic> ∼ 3.2, and up to 58% relative to LBG samples.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Various exact laws governing compressible magnetohydrodynamic (MHD) and compressible Hall-MHD (CHMHD) turbulence have been derived in recent years. Other than their fundamental theoretical interest, these laws are generally used to estimate the energy dissipation rate from spacecraft observations in order to address diverse problems related, e.g., to heating of the solar wind and magnetospheric plasmas. Here we use various 1024<jats:sup>3</jats:sup> direct numerical simulation data of free-decay isothermal CHMHD turbulence obtained with the GHOST code (Geophysical High-Order Suite for Turbulence) to analyze two of the recently derived exact laws. The simulations reflect different intensities of the initial Mach number and the background magnetic field. The analysis demonstrates the equivalence of the two laws in the inertial range and relates the strength of the Hall effect to the amplitude of the cascade rate at sub-ion scales. When taken in their general form (i.e., not limited to the inertial range), some subtleties regarding the validity of the stationarity assumption or the absence of the forcing in the simulations are discussed. We show that the free-decay nature of the turbulence induces a shift from a large-scale forcing toward the presence of a scale-dependent reservoir of energy fueling the cascade or dissipation. The reduced form of the exact laws (valid in the inertial range) ultimately holds even if the stationarity assumption is not fully verified.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of protoplanetary disks have revealed them to be complex and dynamic, with vertical and radial transport of gas and dust occurring simultaneously with chemistry and planet formation. Previous models of protoplanetary disks focused primarily on chemical evolution of gas and dust in a static disk, or dynamical evolution of solids in a chemically passive disk. In this paper, we present a new 1D method for modeling pebble growth and chemistry simultaneously. Gas and small dust particles are allowed to diffuse vertically, connecting chemistry at all elevations of the disk. Pebbles are assumed to form from the dust present around the midplane, inheriting the composition of ices at this location. We present the results of this model after 1 Myr of disk evolution around a 1<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> star at various locations both inside and outside the CO snowline. We find that for a turbulent disk (<jats:italic>α</jats:italic> = 10<jats:sup>−3</jats:sup>), CO is depleted from the surface layers of the disk by roughly 1–2 orders of magnitude, consistent with observations of protoplanetary disks. This is achieved by a combination of ice sequestration and decreasing UV opacity, both driven by pebble growth. Further, we find the selective removal of ice species via pebble growth and sequestration can increase gas phase C/O ratios to values of approximately unity. However, our model is unable to produce C/O values of ∼1.5–2.0 inferred from protoplanetary disk observations, implying selective sequestration of ice is not sufficient to explain C/O ratios &gt;1.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent work has shown that near-infrared (NIR) Hubble Space Telescope (HST) photometry allows us to disentangle multiple populations (MPs) among M dwarfs of globular clusters (GCs) and to investigate this phenomenon in very-low-mass (VLM) stars. Here, we present the color–magnitude diagrams of nine GCs and the open cluster NGC 6791 in the F110W and F160W bands of HST, showing that the main sequences (MSs) below the knee are either broadened or split, thus providing evidence of MPs among VLM stars. In contrast, the MS of NGC 6791 is consistent with a single population. The color distribution of M dwarfs dramatically changes between different GCs, and the color width correlates with the cluster mass. We conclude that the MP ubiquity, variety, and dependence on GC mass are properties common to VLM and more-massive stars. We combined UV, optical, and NIR observations of NGC 2808 and NGC 6121 (M4) to identify MPs along with a wide range of stellar masses (∼0.2–0.8 <jats:inline-formula> <jats:tex-math> <?CDATA ${{ \mathcal M }}_{\odot }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic"></mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5046ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), from the MS turnoff to the VLM regime, and measured, for the first time, their mass functions (MFs). We find that the fraction of MPs does not depend on the stellar mass and that their MFs have similar slopes. These findings indicate that the properties of MPs do not depend on stellar mass. In a scenario where the second generations formed in higher-density environments than the first generations, the possibility that the MPs formed with the same initial MF would suggest that it does not depend on the environment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The pulsar profile is characterized by two distinct emission components, the core and the cone. The standard model of a pulsar radio emission beam originating from dipolar magnetic fields places the core at the center surrounded by concentric layers of inner and outer conal components. The core emission is expected to have steeper spectra compared to the cones. We present a detailed analysis of the relative differences between the spectra of the core and conal emission from a large sample of 53 pulsars over a wide frequency range between 100 MHz and 10 GHz. The core spectra were seen to be much steeper than those of the cones, particularly between 100 MHz and 1 GHz, with a relative difference between the spectral index of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}{\alpha }_{\mathrm{core}/\mathrm{cone}}\,\sim \,$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>core</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi>cone</mml:mi> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:mo>∼</mml:mo> <mml:mspace width="0.25em" /> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5039ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>−1.0. In addition we found the spectra of the outer conal components to be steeper than those of the inner cone with a relative difference in the spectral index of Δ<jats:italic>α</jats:italic> <jats:sub>in/out</jats:sub> ∼ +0.5. The flattening of the spectra from the magnetic axis toward the edge of the open field line region with increasing curvature of the field lines is a natural outcome of the coherent curvature radiation from charged soliton bunches and explains the difference in spectra between the core and the cones. In addition, due to the relativistic beaming effect, the radiation is only visible when it is directed toward the observer over a narrow angle <jats:italic>θ</jats:italic> ≤ 1/<jats:italic>γ</jats:italic>, where <jats:italic>γ</jats:italic> is the Lorentz factor of the outflowing plasma clouds. This restricts the emission particularly from outer cones that are associated with field lines with larger curvature, thereby making their spectra steeper than those of the inner cones.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Some studies of stars’ multielement abundance distributions suggest at least 5–7 significant dimensions, but others show that many elemental abundances can be predicted to high accuracy from [Fe/H] and [Mg/Fe] (or [Fe/H] and age) alone. We show that both propositions can be, and are, simultaneously true. We adopt a machine-learning technique known as normalizing flow to reconstruct the probability distribution of Milky Way disk stars in the space of 15 elemental abundances measured by APOGEE. Conditioning on <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> and <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}\,g$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mspace width="0.25em" /> <mml:mi>g</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5023ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> minimizes the differential systematics. After further conditioning on [Fe/H] and [Mg/Fe], the residual scatter for most abundances is <jats:italic>σ</jats:italic> <jats:sub>[<jats:italic>X</jats:italic>/H]</jats:sub> ≲ 0.02 dex, consistent with APOGEE’s reported statistical uncertainties of ∼0.01–0.015 dex and intrinsic scatter of 0.01–0.02 dex. Despite the small scatter, residual abundances display clear correlations between elements, which we show are too large to be explained by measurement uncertainties or by the finite sampling noise. We must condition on at least seven elements to reduce the correlations to a level consistent with the observational uncertainties. Our results demonstrate that cross-element correlations are a much more sensitive probe of a hidden structure than dispersion, and they can be measured precisely in a large sample even if the star-by-star measurement noise is comparable to the intrinsic scatter. We conclude that many elements have an independent story to tell, even for the <jats:italic>mundane</jats:italic> disk stars and elements produced by the core-collapse and Type Ia supernovae. The only way to learn these lessons is to measure the abundances directly, and not merely infer them.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a spectral study of the black hole candidate MAXI J1348−630 during its 2019 outburst, based on monitoring observations with Insight-HXMT and Swift. Throughout the outburst, the spectra are well fitted with power-law plus disk-blackbody components. In the soft-intermediate and soft states, we observed the canonical relation <jats:inline-formula> <jats:tex-math> <?CDATA $L\propto {T}_{\mathrm{in}}^{4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>L</mml:mi> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>in</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4fcaieqn1.gif" xlink:type="simple" /> </jats:inline-formula> between disk luminosity <jats:italic>L</jats:italic> and peak color temperature <jats:italic>T</jats:italic> <jats:sub>in</jats:sub>, with a constant inner radius <jats:italic>R</jats:italic> <jats:sub>in</jats:sub> (traditionally identified with the innermost stable circular orbit). At other stages of the outburst cycle, the behavior is more unusual, inconsistent with the canonical outburst evolution of black hole transients. In particular, during the hard rise, the apparent inner radius is smaller than in the soft state (and increasing), and the peak color temperature is higher (and decreasing). This anomalous behavior is found even when we model the spectra with self-consistent Comptonization models, which take into account the upscattering of photons from the disk component into the power-law component. To explain both anomalous trends at the same time, we suggest that the hardening factor for the inner-disk emission was larger than the canonical value of ≈1.7 at the beginning of the outburst. A more physical trend of radii and temperature evolution requires a hardening factor evolving from ≈3.5 at the beginning of the hard state to ≈1.7 in the hard-intermediate state. This could be evidence that the inner disk was in the process of condensing from the hot, optically thin medium and had not yet reached a sufficiently high optical depth for its emission spectrum to be described by the standard optically thick disk solution.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It was proposed that a remnant stable magnetar could be formed in a binary neutron-star merger, leading to a fast X-ray transient (FXT) that can last for thousands of seconds. Recently, Xue et al. suggested that CDF-S XT2 was exactly such a kind of source. If confirmed, such emission can be used to search for electromagnetic counterparts to gravitational wave events from binary neutron-star mergers that have short gamma-ray bursts and the corresponding afterglows seen off-axis and thus too weak to be detected. Here we report the discovery of three new FXTs, XRT 170901, XRT 030511, and XRT 110919, from a preliminary search over Chandra archival data. Similar to CDF-S XT2, these new FXTs had a very fast rise (less than a few tens of seconds) and a plateau of X-ray flux of ∼1.0 × 10<jats:sup>−12</jats:sup> erg s<jats:sup>−1</jats:sup> cm<jats:sup>−2</jats:sup> lasting for 1–2 ks, followed by a steep decay. Their optical/IR counterparts, if present, are very weak, arguing against a stellar flare origin for these FXTs. For XRT 170901, we identified a faint host galaxy with the source at the outskirts, very similar to CDF-S XT2. Therefore, our newly discovered FXTs are also strong candidates for magnetar-powered X-ray transients resulting from binary neutron star mergers.</jats:p>