Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We use helioseismic data obtained over two solar cycles to determine whether there are changes in the near-surface shear layer (NSSL). We examine this by determining the radial gradient of the solar rotation rate. The radial gradient itself shows a solar-cycle dependence, and the changes are more pronounced in the active latitudes than at adjoining higher latitudes; results at the highest latitudes (≳70°) are unreliable. The pattern changes with depth, even within the NSSL. We find that the near-surface shear layer is deeper at lower latitudes than at high latitudes and that the extent of the layer also shows a small solar-cycle-related change.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Chandra X-Ray Observatory (CXO) imaged the high-mass <jats:italic>γ</jats:italic>-ray binary HESS J0632+057 with the Advanced CCD Imaging Spectrometer (ACIS). We analyzed the CXO data together with 967 ks of archival Swift-XRT observations. On arcsecond scales we find a hint of asymmetric extended emission. On arcminute scales, a region of extended emission (“the blob”), located <jats:inline-formula> <jats:tex-math> <?CDATA $\approx 5\buildrel{\,\prime}\over{.} 5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>≈</mml:mo> <mml:mn>5</mml:mn> <mml:mo>.′</mml:mo> <mml:mn>5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3822ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> east of the binary, is seen in both the CXO-ACIS and the Swift-XRT images. The blob does not have a counterpart in the radio, near-IR, IR, or optical images. The ACIS spectrum of the blob fits either an absorbed power-law model with Γ ≃ 2.6, or a thermal plasma model with <jats:italic>kT</jats:italic> ≃ 3 keV. Since the blob’s <jats:italic>N</jats:italic> <jats:sub>H</jats:sub> is significantly higher than that of the binary we conclude that the blob and binary are not directly related. The somewhat larger, very deep XRT image suggests that the binary may be located within a shell (or cavity). The four ACIS spectra taken within the ∼20 day interval near the light-curve minimum suggest that <jats:italic>N</jats:italic> <jats:sub>H</jats:sub> varies on timescales of days, possibly due to the inhomogeneous circumbinary environment. The XRT spectra extracted from wider orbital phase intervals support significant changes in <jats:italic>N</jats:italic> <jats:sub>H</jats:sub> near the light-curve maximum/minimum, which may be responsible for the substantial systematic residuals seen near 1 keV, and provide tentative evidence for an Fe line at 6.4 keV. We find no significant periodic signal in the ACIS data up to 0.156 Hz.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Eddington-inspired Born–Infeld gravity is an important modification of Einstein’s general relativity, which can give rise to nonsingular cosmologies at the classical level, and avoid the end-stage singularity in a gravitational collapse process. In the Newtonian limit, this theory gives rise to a modified Poisson’s equation, as a consequence of which stellar observables acquire model dependent corrections, compared to the ones computed in the low energy limit of general relativity. This can in turn be used to establish astrophysical constraints on the theory. Here, we obtain such a constraint using observational data from cataclysmic variable binaries. In particular, we consider the tidal disruption limit of the secondary star by a white dwarf primary. The Roche lobe filling condition of this secondary star is used to compute stellar observables in the modified gravity theory in a numerical scheme. These are then contrasted with the values obtained by using available data on these objects, via a Monte Carlo error progression method. This way, we are able to constrain the theory within the 5<jats:italic>σ</jats:italic> confidence level.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic fields and mass accretion processes create dark and bright spots on the surface of young stars. These spots manifest as surface thermal inhomogeneities, which alter the global temperature measured on the stars. To understand the effects and implications of these starspots, we conducted a large iSHELL high-resolution infrared spectroscopic survey of T Tauri stars in Taurus-Auriga and Ophiuchus star-forming regions. From the <jats:italic>K-</jats:italic>band spectra, we measured stellar temperatures and magnetic field strengths using a magnetic radiative transfer code. We compared our infrared-derived parameters against literature optical temperatures and found (a) a systematic temperature difference between optical and infrared observations, and (b) a positive correlation between the magnetic field strengths and the temperature differences. The discrepant temperature measurements imply significant differences in the inferred stellar masses from stellar evolutionary models. To discern which temperature better predicts the mass of the star, we compared our model-derived masses against dynamical masses measured from Atacama Large Millimeter/submillimeter Array and the Plateau de Bure Interferometer for a subsample of our sources. From this comparison we conclude that, in the range of stellar masses from 0.3 to 1.3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, neither infrared nor optical temperatures perfectly reproduce the stellar dynamical masses. But, on average, infrared temperatures produce more precise and accurate stellar masses than optical ones.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report a systematic study of all known methyl carbon chains toward TMC-1 using the second data release of the GOTHAM survey, as well as a search for larger species. Using Markov Chain Monte Carlo simulations and spectral line stacking of over 30 rotational transitions, we report statistically significant emission from methylcyanotriacetylene (CH<jats:sub>3</jats:sub>C<jats:sub>7</jats:sub>N) at a confidence level of 4.6<jats:italic>σ</jats:italic>, and use it to derive a column density of ∼10<jats:sup>11</jats:sup> cm<jats:sup>−2</jats:sup>. We also searched for the related species, methyltetraacetylene (CH<jats:sub>3</jats:sub>C<jats:sub>8</jats:sub>H), and place upper limits on the column density of this molecule. By carrying out the above statistical analyses for all other previously detected methyl-terminated carbon chains that have emission lines in our survey, we assess the abundances, excitation conditions, and formation chemistry of methylpolyynes (CH<jats:sub>3</jats:sub>C<jats:sub>2<jats:italic>n</jats:italic> </jats:sub>H) and methylcyanopolyynes (CH<jats:sub>3</jats:sub>C<jats:sub>2<jats:italic>n</jats:italic>-1</jats:sub>N) in TMC-1, and compare those with predictions from a chemical model. Based on our observed trends in column density and relative populations of the <jats:italic>A</jats:italic> and <jats:italic>E</jats:italic> nuclear spin isomers, we find that the methylpolyyne and methylcyanopolyyne families exhibit stark differences from one another, pointing to separate interstellar formation pathways, which is confirmed through gas–grain chemical modeling with <jats:monospace>nautilus</jats:monospace>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the production of very light elements (<jats:italic>Z</jats:italic> &lt; 20) in the dynamical and spiral-wave wind ejecta of binary neutron star mergers by combining detailed nucleosynthesis calculations with the outcome of numerical relativity merger simulations. All our models are targeted to GW170817 and include neutrino radiation. We explore different finite-temperature, composition-dependent nuclear equations of state, and binary mass ratios, and find that hydrogen and helium are the most abundant light elements. For both elements, the decay of free neutrons is the driving nuclear reaction. In particular, ∼0.5–2 × 10<jats:sup>−6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of hydrogen are produced in the fast expanding tail of the dynamical ejecta, while ∼1.5–11 × 10<jats:sup>−6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of helium are synthesized in the bulk of the dynamical ejecta, usually in association with heavy <jats:italic>r</jats:italic>-process elements. By computing synthetic spectra, we find that the possibility of detecting hydrogen and helium features in kilonova spectra is very unlikely for fiducial masses and luminosities, even when including nonlocal thermodynamic equilibrium effects. The latter could be crucial to observe helium lines a few days after merger for faint kilonovae or for luminous kilonovae ejecting large masses of helium. Finally, we compute the amount of strontium synthesized in the dynamical and spiral-wave wind ejecta, and find that it is consistent with (or even larger than, in the case of a long-lived remnant) the one required to explain early spectral features in the kilonova of GW170817.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We propose a model for interpreting highly variable ion composition ratios in solar energetic particle (SEP) events recently observed by the Parker Solar Probe (PSP) at 0.3–0.45 au. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scales down to the gyration scale of energetic particles. We show that when the source regions of different species are offset by a distance comparable to the size of the source regions, the observed energetic particle composition He/H can be strongly variable over more than two orders of magnitude, even if the source ratio is at the nominal value. Assuming a <jats:sup>3</jats:sup>He/<jats:sup>4</jats:sup>He source ratio of 10% in impulsive <jats:sup>3</jats:sup>He-rich events and the same spatial offset of the source regions, the <jats:sup>3</jats:sup>He/<jats:sup>4</jats:sup>He ratio at observation sites also vary considerably. The variability of the ion composition ratios depends on the radial distance, which can be tested by observations made at different radial locations. We discuss the implications of these results on the variability of ion composition of impulsive events and on further PSP and Solar Orbiter observations close to the Sun.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The 2 mm Mapping Obscuration to Reionization with ALMA (MORA) Survey was designed to detect high-redshift (<jats:italic>z</jats:italic> ≳ 4), massive, dusty star-forming galaxies (DSFGs). Here we present two likely high-redshift sources, identified in the survey, whose physical characteristics are consistent with a class of optical/near-infrared (OIR)-invisible DSFGs found elsewhere in the literature. We first perform a rigorous analysis of all available photometric data to fit spectral energy distributions and estimate redshifts before deriving physical properties based on our findings. Our results suggest the two galaxies, called MORA-5 and MORA-9, represent two extremes of the “OIR-dark” class of DSFGs. MORA-5 (<jats:inline-formula> <jats:tex-math> <?CDATA ${z}_{\mathrm{phot}}={4.3}_{-1.3}^{+1.5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>phot</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac366aieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) is a significantly more active starburst with a star formation rate (SFR) of <jats:inline-formula> <jats:tex-math> <?CDATA ${830}_{-190}^{+340}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>830</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>190</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>340</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac366aieqn2.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> compared to MORA-9 (<jats:inline-formula> <jats:tex-math> <?CDATA ${z}_{\mathrm{phot}}={4.3}_{-1.0}^{+1.3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>phot</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.3</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac366aieqn3.gif" xlink:type="simple" /> </jats:inline-formula>), whose SFR is a modest <jats:inline-formula> <jats:tex-math> <?CDATA ${200}_{-60}^{+250}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>200</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>60</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>250</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac366aieqn4.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. Based on the stellar masses (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> ≈ 10<jats:sup>10−11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), space density (<jats:italic>n</jats:italic> ∼ (5 ± 2) × 10<jats:sup>−6</jats:sup> Mpc<jats:sup>−3</jats:sup>, which incorporates two other spectroscopically confirmed OIR-dark DSFGs in the MORA sample at <jats:italic>z</jats:italic> = 4.6 and <jats:italic>z</jats:italic> = 5.9), and gas depletion timescales (&lt;1 Gyr) of these sources, we find evidence supporting the theory that OIR-dark DSFGs are the progenitors of recently discovered 3 &lt; <jats:italic>z</jats:italic> &lt; 4 massive quiescent galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore the contribution of the Gaia Sausage to the stellar halo of the Milky Way by making use of a Gaussian mixture model (GMM) and applying it to halo star samples of Large Sky Area Multi-Object Fiber Spectroscopic Telescope K giants, Sloan Extension for Galactic Understanding and Exploration K giants, and Sloan Digital Sky Survey blue horizontal branch stars. The GMM divides the stellar halo into two parts, of which one represents a more metal-rich and highly radially biased component associated with an ancient, head-on collision referred to as the Gaia Sausage, and the other one is a more metal-poor and isotropic halo. A symmetric bimodal Gaussian is used to describe the distribution of spherical velocity of the Gaia Sausage, and we find that the mean absolute radial velocity of the two lobes decreases with the Galactocentric radius. We find that the Gaia Sausage contributes about 41%–74% of the inner (Galactocentric radius <jats:italic>r</jats:italic> <jats:sub>gc</jats:sub> &lt; 30 kpc) stellar halo. The fraction of stars of the Gaia Sausage starts to decline beyond <jats:italic>r</jats:italic> <jats:sub>gc</jats:sub> ∼ 25–30 kpc, and the outer halo is found to be significantly less influenced by the Gaia Sausage than the inner halo. After the removal of halo substructures found by integrals of motion, the contribution of the Gaia Sausage falls slightly within <jats:italic>r</jats:italic> <jats:sub>gc</jats:sub> ∼ 25 kpc but is still as high as 30%–63%. Finally, we select several possible Sausage-related substructures consisting of stars on highly eccentric orbits. The GMM/Sausage component agrees well with the selected substructure stars in their chemodynamical properties, which increases our confidence in the reliability of the GMM fits.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The analytic Gibson–Low (GL) model, a time-dependent self-similar solution of the magnetohydrodynamics, is first used to directly reconstruct a coronal mass ejection (CME) through the method of forward modeling in this study. A systematic description of the GL model is presented at the beginning, and a set of parameters is introduced to define the model. Then a CME on 2011 March 7 is reconstructed by fitting of GL (FGL) of the multi-viewpoint and time series observations. The first step of FGL is the initialization of the location and orientation of the GL using the information of the CME source region. The second step is to fit the parameters of size, shape, velocity, and strength of the magnetic field of the GL to the observations of coronagraphs at 20:24 and 20:39. The GL at 20:54 and 3 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> is generated through the theory of self-similar expansion respectively. Comparisons between the synthetic images of the GL and the real observations of the CME prove the performance of FGL that the reconstructions well match the observations.</jats:p>