Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The study of the preflare environment is of great importance to understanding what drives solar flares. <jats:italic>k</jats:italic>-means clustering, an unsupervised machine-learning technique, has the ability to cluster large data set in a way that would be impractical or impossible for a human to do. In this paper we present a study using <jats:italic>k</jats:italic>-means clustering to identify possible preflare signatures in spectroscopic observations of the Mg <jats:sc>ii</jats:sc> h and k spectral lines made by NASA's Interface Region Imaging Spectrometer. Our analysis finds that spectral profiles showing single-peak Mg <jats:sc>ii</jats:sc> h and k and single-peaked emission in the Mg <jats:sc>ii</jats:sc> UV triplet lines are associated with preflare activity up to 40 minutes prior to flaring. Subsequent inversions of these spectral profiles reveal increased temperature and electron density in the chromosphere, which suggest that significant heating events in the chromosphere may be associated with precursor signals to flares.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>One prominent feature in the atmospheres of Jupiter and Saturn is the appearance of large-scale vortices (LSVs). However, the mechanism that sustains these LSVs remains unclear. One possible mechanism is that these LSVs are driven by rotating convection. Here, we present numerical simulation results on a rapidly rotating Rayleigh–Bénard convection at a small Prandtl number <jats:italic>Pr</jats:italic> = 0.1 (close to the turbulent Prandtl numbers of Jupiter and Saturn). We identified four flow regimes in our simulation: multiple small vortices, a coexisting large-scale cyclone and anticyclone, large-scale cyclone, and turbulence. The formation of LSVs requires that two conditions be satisfied: the vertical Reynolds number is large (<jats:inline-formula> <jats:tex-math> <?CDATA ${{Re}}_{z}\,\geqslant \,400$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">Re</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> </mml:msub> <mml:mspace width="0.50em" /> <mml:mo>≥</mml:mo> <mml:mspace width="0.50em" /> <mml:mn>400</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2c68ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), and the Rossby number is small (<jats:italic>Ro</jats:italic> ≤ 0.4). A large-scale cyclone first appears when <jats:italic>Ro</jats:italic> decreases to be smaller than 0.4. When <jats:italic>Ro</jats:italic> further decreases to be smaller than 0.1, a coexisting large-scale cyclone and anticyclone emerges. We have studied the heat transfer in rapidly rotating convection. The result reveals that the heat transfer is more efficient in the anticyclonic region than in the cyclonic region. Besides, we find that the 2D effect increases and the 3D effect decreases in transporting convective flux as the rotation rate increases. We find that aspect ratio has an effect on the critical Rossby number in the emergence of LSVs. Our results provide helpful insights into understanding the dynamics of LSVs in gas giants.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Asteroseismology is a powerful tool to infer the details of the inner chemical structure of white dwarfs. Using the nine observed frequencies of HS 0507+0434B, we explore the influence of the inner chemical profile on the pulsation periods. Based on the evolutionary C/O profile, we modify slightly the C/O core profile and make an asteroseismic analysis for HS 0507+0434B. We find that the trapped mode with the period of 445.3 s is mainly affected by the hydrogen and helium mass fraction. The inner C/O core profile has an influence on all modes extending into the inner core. When we use the iteration method with the optimal C/O core profile, the fit between the theoretical periods and observed ones is significantly improved. For the best-fitting model with the optimal parametric C/O core, there is a smaller C/O ratio and a smaller overshooting zone in the stellar interior. The fundamental parameters of the model with the optimal C/O core are <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ∼ 0.710 ± 0.005, <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> ∼ 12570 ± 106K, <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{{\rm{H}}}/{M}_{* }\sim -8.01\pm 0.08$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mo>−</mml:mo> <mml:mn>8.01</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.08</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac25f1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{\mathrm{He}}/{M}_{* }\sim -2.51\pm 0.08$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>He</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mo>−</mml:mo> <mml:mn>2.51</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.08</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac25f1ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the stellar binary black holes (BBHs) inspiraling/merging in galactic nuclei based on our numerical method <jats:monospace>GNC</jats:monospace>. We find that 3%–40% of all newborn BBHs will finally merge due to various dynamical effects. In a five-year mission, up to 10<jats:sup>4</jats:sup>, 10<jats:sup>5</jats:sup>, and ∼100 of BBHs inspiraling/merging in galactic nuclei can be detected with signal-to-noise ration &gt;8 in Advanced LIGO (aLIGO), Einstein<jats:bold>/</jats:bold>DECIGO, and TianQin/LISA/TaiJi, respectively. Roughly tens are detectable in both LISA/TaiJi/TianQin and aLIGO. These BBHs have two unique characteristics. (1) Significant eccentricities: 1%–3%, 2%–7%, or 30%–90% of them have <jats:italic>e</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub> &gt; 0.1 when they enter into aLIGO, Einstein, or space observatories, respectively. Such high eccentricities provide a possible explanation for that of GW190521. Most highly eccentric BBHs are not detectable in LISA/Tianqin/TaiJi before entering into aLIGO/Einstein, as their strain becomes significant only at <jats:italic>f</jats:italic> <jats:sub>GW</jats:sub> ≳ 0.1 Hz. DECIGO becomes an ideal observatory to detect those events, as it can fully cover the rising phase. (2) Up to 2% of BBHs can inspiral/merge at distances ≲10<jats:sup>3</jats:sup> <jats:italic>r</jats:italic> <jats:sub>SW</jats:sub> from the massive black hole, with significant accelerations, such that the Doppler phase drift of ∼10–10<jats:sup>5</jats:sup> of them can be detected with signal-to-noise ratio &gt;8 in space observatories. The energy density of the gravitational-wave backgrounds (GWBs) contributed by these BBHs deviates from the power-law slope of 2/3 at <jats:italic>f</jats:italic> <jats:sub>GW</jats:sub> ≲ 1 mHz. The high eccentricity, significant accelerations, and the different profile of the GWB of these sources make them distinguishable, and thus interesting for future gravitational-wave detections and tests of relativities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report observations of polarized line and continuum emission from the disk of TW Hya using the Atacama Large Millimeter/submillimeter Array. We target three emission lines, <jats:sup>12</jats:sup>CO (3–2), <jats:sup>13</jats:sup>CO (3–2), and CS (7–6), to search for linear polarization due to the Goldreich–Kylafis effect, while simultaneously tracing the continuum polarization morphology at 332 GHz (900 <jats:italic>μ</jats:italic>m), achieving a spatial resolution of 0.″5 (30 au). We detect linear polarization in the dust continuum emission; the polarization position angles show an azimuthal morphology, and the median polarization fraction is ∼0.2%, comparable to previous, lower frequency observations. Adopting a “shift-and-stack” technique to boost the sensitivity of the data, combined with a linear combination of the <jats:italic>Q</jats:italic> and <jats:italic>U</jats:italic> components to account for their azimuthal dependence, we detect weak linear polarization of <jats:sup>12</jats:sup>CO and <jats:sup>13</jats:sup>CO line emission at a ∼10<jats:italic>σ</jats:italic> and ∼5<jats:italic>σ</jats:italic> significance, respectively. The polarization was detected in the line wings, reaching a peak polarization fraction of ∼5% and ∼3% for the two molecules between disk radii of 0.″5 and 1″. The sign of the polarization was found to flip from the blueshifted side of the emission to the redshifted side, suggesting a complex, asymmetric polarization morphology. Polarization is not robustly detected for the CS emission; however, a tentative signal, comparable in morphology to that found for the <jats:sup>12</jats:sup>CO and <jats:sup>13</jats:sup>CO emission, is found at a ≲3<jats:italic>σ</jats:italic> significance. We are able to reconstruct a polarization morphology, consistent with the azimuthally averaged profiles, under the assumption that this is also azimuthally symmetric, which can be compared with future higher-sensitivity observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A significant fraction of Milky Way (MW) satellites exhibit phase-space properties consistent with a coherent orbital plane. Using tailored <jats:italic>N</jats:italic>-body simulations of a spherical MW halo that recently captured a massive (1.8 × 10<jats:sup>11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) LMC-like satellite, we identify the physical mechanisms that may enhance the clustering of orbital poles of objects orbiting the MW. The LMC deviates the orbital poles of MW dark matter particles from the present-day random distribution. Instead, the orbital poles of particles beyond <jats:italic>R</jats:italic> ≈ 50 kpc cluster near the present-day orbital pole of the LMC along a sinusoidal pattern across the sky. The density of orbital poles is enhanced near the LMC by a factor <jats:inline-formula> <jats:tex-math> <?CDATA $\delta {\rho }_{\max }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> <mml:msub> <mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2c05ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> = 30% (50%) with respect to underdense regions and <jats:italic>δ</jats:italic> <jats:italic>ρ</jats:italic> <jats:sub>iso</jats:sub> = 15% (30%) relative to the isolated MW simulation (no LMC) between 50 and 150 kpc (150–300 kpc). The clustering appears after the LMC’s pericenter (≈50 Myr ago, 49 kpc) and lasts for at least 1 Gyr. Clustering occurs because of three effects: (1) the LMC shifts the velocity and position of the central density of the MW’s halo and disk; (2) the dark matter dynamical friction wake and collective response induced by the LMC change the kinematics of particles; (3) observations of particles selected within spatial planes suffer from a bias, such that measuring orbital poles in a great circle in the sky enhances the probability of their orbital poles being clustered. This scenario should be ubiquitous in hosts that recently captured a massive satellite (at least ≈1:10 mass ratio), causing the clustering of orbital poles of halo tracers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on observations with the Chandra X-ray Observatory, we present the latest spectral evolution of the X-ray remnant of SN 1987A (SNR 1987A). We present a high-resolution spectroscopic analysis using our new deep (∼312 ks) Chandra HETG observation taken in 2018 March as well as archival Chandra grating spectroscopic data taken in 2004, 2007, and 2011 with similarly deep exposures (∼170–350 ks). We perform detailed spectral model fits to quantify changing plasma conditions over the last 14 yr. Recent changes in electron temperatures and volume-emission measures suggest that the shocks moving through the inner ring have started interacting with less dense circumstellar material, probably beyond the inner ring. We find significant changes in the X-ray line-flux ratios (among H- and He-like Si and Mg ions) in 2018, consistent with changes in the thermal conditions of the X-ray-emitting plasma that we infer based on the broadband spectral analysis. Post-shock electron temperatures suggested by line-flux ratios are in the range ∼0.8–2.5 keV as of 2018. We do not yet observe any evidence of substantial abundance enhancement, suggesting that the X-ray emission component from the reverse-shocked metal-rich ejecta is not yet significant in the observed X-ray spectrum.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Balmer-dominated shells in supernova remnants (SNRs) are produced by collisionless shocks advancing into a partially neutral medium and are most frequently associated with Type Ia supernovae. We have analyzed Hubble Space Telescope (HST) images and Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) or AAT/Wide Field Integral Spectrograph observations of five Type Ia SNRs containing Balmer-dominated shells in the LMC: 0509–67.5, 0519–69.0, N103B, DEM L71, and 0548–70.4. Contrary to expectations, we find bright forbidden-line emission from small dense knots embedded in four of these SNRs. The electron densities in some knots are higher than 10<jats:sup>4</jats:sup> cm<jats:sup>−3</jats:sup>. The size and density of these knots are not characteristic for interstellar medium—they most likely originate from a circumstellar medium ejected by the SN progenitor. Physical property variations of dense knots in the SNRs appear to reflect an evolutionary effect. The recombination timescales for high densities are short, and HST images of N103B taken 3.5 yr apart already show brightness changes in some knots. VLT/MUSE observations detect [Fe <jats:sc>xiv</jats:sc>] line emission from reverse shocks into SN ejecta as well as forward shocks into the dense knots. Faint [O <jats:sc>iii</jats:sc>] line emission is also detected from the Balmer shell in 0519–69.0, N103B, and DEM L71. We exclude the postshock origin because the [O <jats:sc>iii</jats:sc>] line is narrow. For the preshock origin, we considered three possibilities: photoionization precursor, cosmic-ray precursor, and neutral precursor. We conclude that the [O <jats:sc>iii</jats:sc>] emission arises from oxygen that has been photoionized by [He <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic>304 photons and is then collisionally excited in a shock precursor heated mainly by cosmic rays.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent works have indicated that the <jats:sup>56</jats:sup>Ni masses estimated for stripped envelope supernovae (SESNe) are systematically higher than those estimated for SNe II. Although this may suggest a distinct progenitor structure between these types of SNe, the possibility remains that this may be caused by observational bias. One important possible bias is that SESNe with low <jats:sup>56</jats:sup>Ni mass are dim, and therefore more likely to escape detection. By investigating the distributions of <jats:sup>56</jats:sup>Ni mass and distance of the samples collected from the literature, we find that the current literature SESN sample indeed suffers from a significant observational bias, i.e., objects with low <jats:sup>56</jats:sup>Ni mass—if they exist—will be missed, especially at larger distances. Note, however, that those distant objects in our sample are mostly SNe Ic-BL. We also conducted mock observations assuming that the <jats:sup>56</jats:sup>Ni mass distribution for SESNe is intrinsically the same as that of SNe II. We find that the <jats:sup>56</jats:sup>Ni mass distribution of the detected SESN samples moves toward higher mass than the assumed intrinsic distribution because of the difficulty in detecting the low-<jats:sup>56</jats:sup>Ni mass SESNe. These results could explain the general trend of the higher <jats:sup>56</jats:sup>Ni mass distribution (than SNe II) of SESNe found thus far in the literature. However, further finding clear examples of low-<jats:sup>56</jats:sup>Ni mass SESNe (≤ 0.01 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) is required to strengthen this hypothesis. Also, objects with high <jats:sup>56</jats:sup>Ni mass (≳ 0.2<jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>) are not explained by our model, which may require an additional explanation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the failed partial eruption of a filament system in NOAA AR 12104 on 2014 July 5, using multiwavelength EUV, magnetogram, and H<jats:italic>α</jats:italic> observations, as well as magnetic field modeling. The filament system consists of two almost co-spatial segments with different end points, both resembling a C shape. Following an ejection and a precursor flare related to flux cancellation, only the upper segment rises and then displays a prominent twisted structure, while rolling over toward its footpoints. The lower segment remains undisturbed, indicating that the system possesses a double-decker structure. The erupted segment ends up with a reverse-C shape, with material draining toward its footpoints, while losing its twist. Using the flux rope insertion method, we construct a model of the source region that qualitatively reproduces key elements of the observed evolution. At the eruption onset, the model consists of a flux rope atop a flux bundle with negligible twist, which is consistent with the observational interpretation that the filament possesses a double-decker structure. The flux rope reaches the critical height of the torus instability during its initial relaxation, while the lower flux bundle remains in stable equilibrium. The eruption terminates when the flux rope reaches a dome-shaped quasi-separatrix layer that is reminiscent of a magnetic fan surface, although no magnetic null is found. The flux rope is destroyed by reconnection with the confining overlying flux above the dome, transferring its twist in the process.</jats:p>