Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Decayless kink oscillations of solar coronal loops (or decayless oscillations for short) have attracted great attention since their discovery. Coronal bright points (CBPs) are mini-active regions and consist of loops with a small size. However, decayless oscillations in CBPs have not been widely reported. In this study, we identified this kind of oscillations in some CBPs using 171 Å images taken by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. After using the motion magnification algorithm to increase oscillation amplitudes, we made time–distance maps to identify the oscillatory signals. We also estimated the loop lengths and velocity amplitudes. We analyzed 23 CBPs and found 31 oscillation events in 16 of them. The oscillation periods range from 1 to 8 minutes (on average about 5 minutes), and the displacement amplitudes have an average value of 0.07 Mm. The average loop length and velocity amplitude are 23 Mm and 1.57 km s<jats:sup>−1</jats:sup>, respectively. Relationships between different oscillation parameters are also examined. Additionally, we performed a simple model to illustrate how these subpixel oscillation amplitudes (less than 0.4 Mm) could be detected. Results of the model confirm the reliability of our data processing methods. Our study shows for the first time that decayless oscillations are common in small-scale loops of CBPs. These oscillations allow for seismological diagnostics of the Alfvén speed and magnetic field strength in the corona.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The origin(s) and mechanism(s) of fast radio bursts (FRBs), which are short radio pulses from cosmological distances, have remained a major puzzle since their discovery. We report a strong quasi-periodic oscillation (QPO) of ∼40 Hz in the X-ray burst from the magnetar SGR J1935+2154 and associated with FRB 200428, significantly detected with the Hard X-ray Modulation Telescope (Insight-HXMT) and also hinted at by the Konus–Wind data. QPOs from magnetar bursts have only been rarely detected; our 3.4<jats:italic>σ</jats:italic> (<jats:italic>p</jats:italic>-value is 2.9e–4) detection of the QPO reported here reveals the strongest QPO signal observed from magnetars (except in some very rare giant flares), making this X-ray burst unique among magnetar bursts. The two X-ray spikes coinciding with the two FRB pulses are also among the peaks of the QPO. Our results suggest that at least some FRBs are related to strong oscillation processes of neutron stars. We also show that we may overestimate the significance of the QPO signal and underestimate the errors of QPO parameters if QPO exists only in a fraction of the time series of an X-ray burst that we use to calculate the Leahy-normalized periodogram.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Compact protoplanetary disks with a radius of ≲50 au are common around young low-mass stars. We report high-resolution ALMA dust continuum observations toward a compact disk around CW Tau at Bands 4 (<jats:italic>λ</jats:italic> = 2.2 mm), 6 (1.3 mm), 7 (0.89 mm), and 8 (0.75 mm). The spectral energy distribution shows the spectral slope of 2.0 ± 0.24 between 0.75 and 1.3 mm, while it is 3.7 ± 0.29 between 2.17 and 3.56 mm. The steep slope between 2.17 and 3.56 mm is consistent with that of optically thin emission from small grains (≲350 <jats:italic>μ</jats:italic>m). We perform parametric fitting of the ALMA data to characterize the dust disk. Interestingly, if the dust-to-gas mass ratio is 0.01, the Toomre <jats:italic>Q</jats:italic> parameter reaches ∼1–3, suggesting that the CW Tau disk might be marginally gravitationally unstable. The total dust mass is estimated as ∼250 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub> for the maximum dust size of 140 <jats:italic>μ</jats:italic>m that is inferred from the previous Band 7 polarimetric observation and at least 80 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub> even for larger grain sizes. This result shows that the CW Tau disk is quite massive in spite of its smallness. Furthermore, we clearly identify a gap structure located at ∼20 au, which might be induced by a giant planet. In spite of these interesting characteristics, the CW Tau disk has <jats:italic>normal</jats:italic> disk luminosity, size, and spectral index at ALMA Band 6, which could be a clue to the mass budget problem in Class II disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>SN 2014C was originally classified as a Type Ib supernova, but at phase <jats:italic>ϕ</jats:italic> = 127 days, post-explosion strong H<jats:italic>α</jats:italic> emission was observed. SN 2014C has since been observed in radio, infrared, optical and X-ray bands. Here we present new optical spectroscopic and photometric data spanning <jats:italic>ϕ</jats:italic> = 947–2494 days post-explosion. We address the evolution of the broadened H<jats:italic>α</jats:italic> emission line, as well as broad [O <jats:sc>iii</jats:sc>] emission and other lines. We also conduct a parallel analysis of all publicly available multiwavelength data. From our spectra, we find a nearly constant H<jats:italic>α</jats:italic> FWHM velocity width of ∼2000 km s<jats:sup>−1</jats:sup> that is significantly lower than that of other broadened atomic transitions (∼3000–7000 km s<jats:sup>−1</jats:sup>) present in our spectra ([O <jats:sc>i</jats:sc>] <jats:italic>λ</jats:italic>6300; [O <jats:sc>iii</jats:sc>] <jats:italic>λ</jats:italic> <jats:italic>λ</jats:italic>4959, 5007; He <jats:sc>i</jats:sc> <jats:italic>λ</jats:italic>7065; [Ca <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic> <jats:italic>λ</jats:italic>7291, 7324). The late radio data demand a fast forward shock (∼10,000 km s<jats:sup>−1</jats:sup> at <jats:italic>ϕ</jats:italic> = 1700 days) in rarified matter that contrasts with the modest velocity of the H<jats:italic>α</jats:italic>. We propose that the infrared flux originates from a toroidal-like structure of hydrogen surrounding the progenitor system, while later emission at other wavelengths (radio, X-ray) likely originates predominantly from the reverse shock in the ejecta and the forward shock in the quasi-spherical progenitor He-wind. We propose that the H<jats:italic>α</jats:italic> emission arises in the boundary layer between the ejecta and torus. We also consider the possible roles of a pulsar and a binary companion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A universal stellar initial mass function (IMF) should not be expected from theoretical models of star formation, but little conclusive observational evidence for a variable IMF has been uncovered. In this paper, a parameterization of the IMF is introduced into photometric template fitting of the COSMOS2015 catalog. The resulting best-fit templates suggest systematic variations in the IMF, with most galaxies exhibiting top-heavier stellar populations than in the Milky Way. At fixed redshift, only a small range of IMFs are found, with the typical IMF becoming progressively top-heavier with increasing redshift. Additionally, subpopulations of ULIRGs, quiescent and star-forming galaxies are compared with predictions of stellar population feedback and show clear qualitative similarities to the evolution of dust temperatures.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Systems with ultra-short-period (USP) planets tend to possess larger mutual inclinations compared to those with planets located farther from their host stars. This could be explained due to precession caused by stellar oblateness at early times when the host star was rapidly spinning. However, stellar oblateness reduces over time due to the decrease in the stellar rotation rate, and this may further shape the planetary mutual inclinations. In this work, we investigate in detail how the final mutual inclination varies under the effect of a decreasing <jats:italic>J</jats:italic> <jats:sub>2</jats:sub>. We find that different initial parameters (e.g., the magnitude of <jats:italic>J</jats:italic> <jats:sub>2</jats:sub> and planetary inclinations) will contribute to different final mutual inclinations, providing a constraint on the formation mechanisms of USP planets. In general, if the inner planets start in the same plane as the stellar equator (or coplanar while misaligned with the stellar spin axis), the mutual inclination decreases (or increases then decreases) over time due to the decay of the <jats:italic>J</jats:italic> <jats:sub>2</jats:sub> moment. This is because the inner orbit typically possesses less orbital angular momentum than the outer ones. However, if the outer planet is initially aligned with the stellar spin while the inner one is misaligned, the mutual inclination nearly stays the same. Overall, our results suggest that either USP planets formed early and acquired significant inclinations (e.g., ≳30° with its companion or ≳10° with its host star spin axis for Kepler-653 c) or they formed late (≳Gyr) when their host stars rotated slower.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The stellar initial mass function (IMF) is predicted to depend upon the temperature of gas in star-forming molecular clouds. The introduction of an additional parameter, <jats:italic>T</jats:italic> <jats:sub>IMF</jats:sub>, into photometric template fitting, allows galaxies to be fit with a range of IMFs. Three surprising new features appear: (1) most star-forming galaxies are best fit with a bottom-lighter IMF than the Milky Way; (2) most star-forming galaxies at fixed redshift are fit with a very similar IMF; and (3) the most-massive star-forming galaxies at fixed redshift instead exhibit a less bottom-light IMF, similar to that measured in quiescent galaxies. Additionally, since stellar masses and star formation rates both depend on the IMF, these results slightly modify the resulting relationship, while yielding similar qualitative characteristics to previous studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We conduct three-dimensional hydrodynamical simulations of weak jets that we launch into a core collapse supernova (CCSN) ejecta half an hour after the explosion and find that the interaction of the fast jets with the CCSN ejecta creates high-pressure zones that induce a backflow that results in mass accretion onto the newly born neutron star. In cases of weak jets, with a total power of ≈10<jats:sup>45</jats:sup>–10<jats:sup>46</jats:sup> erg, the backflow mass accretion might power them up to more energetic jets by an order of magnitude. In total, the jets of the two postexplosion jet-launching episodes have enough energy to influence the morphology of the very inner ejecta, with a mass of ≈0.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Our results imply that in some, probably a minority of, CCSN remnants the very inner regions might display a bipolar structure that results from postexplosion weak jets. The regions outside this part might display the morphology of jittering jets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Both leptonic and hadronic emission processes may contribute to blazar jet emission; which dominates in blazars’ high-energy emission component remains an open question. Some intermediate synchrotron peaked blazars transition from their low- to high-energy emission components in the X-ray band making them excellent laboratories to probe both components simultaneously, and good targets for the newly launched Imaging X-ray Polarimetry Explorer (IXPE). We characterize the spectral energy distributions for three such blazars, CGRaBS J0211+1051, TXS 0506+056, and S5 0716+714, predicting their X-ray polarization behavior by fitting a multizone polarized leptonic jet model. We find that a significant detection of electron synchrotron dominated polarization is possible with a 300 ks observation for S5 0716+714 and CGRaBS J0211+1051 in their flaring states, while even 500 ks observations are unlikely to measure synchrotron self-Compton (SSC) polarization. Importantly, nonleptonic emission processes like proton synchrotron are marginally detectable for our brightest intermediate synchrotron peaked blazar (ISP), S5 0716+714, during a flaring state. Improved IXPE data reduction methods or next-generation telescopes like eXTP are needed to confidently measure SSC polarization.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the simulation methodology and results of our new data-driven global coronal magnetohydrodynamics (MHD) simulation model. In this model, the solar-surface electric field is first calculated such that the curl will satisfy both the induction equation and the given temporal variations of the solar-surface magnetic field. We use the synoptic maps of the Helioseismic and Magnetic Imager three-component vector-magnetic-field data to specify the solar-surface magnetic-field vector for a period from Carrington Rotations (CRs) 2106 to 2110. A set of whole-Sun three-component electric-field maps are obtained for each CR transition interval of about 27.3 days. Using the inverted electric field as the driving variable, our new global coronal MHD model, with the angular resolution of <jats:italic>π</jats:italic>/64, can trace the evolution of the three-dimensional coronal magnetic field that matches the specified time-dependent solar-surface magnetic-field maps and simultaneously satisfies the divergence-free condition. A set of additional boundary treatments are introduced to control the contribution of the horizontal components of the magnetic field at the weak-field regions. The strength of the solar-surface magnetic field is limited to 20 Gauss for the sake of computational stability in this study. With these numerical treatments, the nonpotential coronal features, such as twisted loop structures, and their eruptive outward motions are obtained. This present model, capable of introducing three-component solar-surface magnetic-field observation data to coronal MHD simulations, is our first step toward a better model framework for the solar corona and hence solar wind.</jats:p>