Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We find evidence for the first observation of the parametric decay instability (PDI) in the lower solar atmosphere. In particular, we find that the power spectrum of density fluctuations near the solar transition region resembles the power spectrum of the velocity fluctuations but with the frequency axis scaled up by about a factor of 2. These results are from an analysis of the Si <jats:sc>iv</jats:sc> lines observed by the Interface Region Imaging Spectrometer in the transition region of a polar coronal hole. We also find that the density fluctuations have radial velocity of about 75 km s<jats:sup>−1</jats:sup> and that the velocity fluctuations are much faster with an estimated speed of 250 km s<jats:sup>−1</jats:sup>, as is expected for sound waves and Alfvén waves, respectively, in the transition region. Theoretical calculations show that this frequency relationship is consistent with those expected from PDI for the plasma conditions of the observed region. These measurements suggest an interaction between sound waves and Alfvén waves in the transition region, which is evidence for the parametric decay instability.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the evolution of galactic bars using a suite of very high-resolution zoom-in cosmological simulations of galaxies at <jats:italic>z</jats:italic> ∼ 9–2. Our models were chosen to lie within similar-mass dark matter (DM) halos, log(<jats:italic>M</jats:italic> <jats:sub>vir</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) ∼ 11.65 ± 0.05, at <jats:italic>z</jats:italic> = 6, 4, and 2, in high- and low-overdensity environments. We apply two galactic wind feedback mechanisms for each model. All galaxies develop subkiloparsec stellar bars differing in their properties. We find that (1) the high-<jats:italic>z</jats:italic> bars form in response to various perturbations: mergers, close flybys, cold accretion inflows along the cosmological filaments, etc.; (2) these bars account for the large mass fraction of galaxies; (3) bars display large corotation-to-bar size ratios, are weaker compared to their low-redshift counterparts by measuring their Fourier amplitudes, and are very gas-rich; (4) their pattern speed does not exhibit monotonic decline with time owing to braking against DM, as at low <jats:italic>z</jats:italic>; (5) bar properties, including their stellar population (star formation rates and metal enrichment), depend sensitively on prevailing feedback; and (6) bars can weaken substantially during cosmological evolution, becoming weak oval distortions—hence bars are destroyed and reformed multiple times, unlike their low-<jats:italic>z</jats:italic> counterparts. In all cases, bars in our simulations have been triggered by interactions. In summary, not only do stellar bars appear to be a contemporary phenomenon, but based on increased frequency of mergers, flybys, and the strength of cold accretion flows at high <jats:italic>z</jats:italic>, we also expect them to be ubiquitous at redshifts ≳2—the epoch of rapid galaxy growth and larger stellar dispersion velocities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Thomson-scattered photospheric light is the dominant constituent of the lower solar corona’s spectral continuum viewed off-limb at optical wavelengths. Known as the K-corona, it is also linearly polarized. We investigate the possibility of using the a priori polarized characteristics of the K-corona, together with polarized emission lines, to measure and correct instrument-induced polarized crosstalk. First we derive the Stokes parameters of the Thomson scattering of unpolarized light in an irreducible spherical tensor formalism. This allows forward synthesis of the Thomson-scattered signal for the more complex scenario that includes symmetry-breaking features in the incident radiation field, which could limit the accuracy of our proposed technique. For this, we make use of an advanced 3D radiative magnetohydrodynamic coronal model. Together with synthesized polarized signals in the Fe <jats:sc>xiii</jats:sc> 10746 Å emission line, we find that an ad hoc correction of telescope- and instrument-induced polarization crosstalk is possible under the assumption of a nondepolarizing optical system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Here, we present our current updates to the gas-phase chemical reaction rates and molecular lines in the spectral synthesis code <jats:sc>cloudy</jats:sc>, and its implications in spectroscopic modeling of various astrophysical environments. We include energy levels, and radiative and collisional rates for HF, CF<jats:sup>+</jats:sup>, HC<jats:sub>3</jats:sub>N, ArH<jats:sup>+</jats:sup>, HCl, HCN, CN, CH, and CH<jats:sub>2</jats:sub>. Simultaneously, we expand our molecular network involving these molecules. For this purpose, we have added 561 new reactions and have updated the existing 165 molecular reaction rates involving these molecules. As a result, <jats:sc>cloudy</jats:sc> now predicts all the lines arising from these nine molecules. In addition, we also update H<jats:sub>2</jats:sub>–H<jats:sub>2</jats:sub> collisional data up to rotational levels <jats:italic>J</jats:italic> = 31 for <jats:italic>v</jats:italic> = 0. We demonstrate spectroscopic simulations of these molecules for a few astrophysical environments. Our existing model for globules in the Crab Nebula successfully predicts the observed column density of ArH<jats:sup>+</jats:sup>. Our model predicts a detectable amount of HeH<jats:sup>+</jats:sup>, OH<jats:sup>+</jats:sup>, and CH<jats:sup>+</jats:sup> for the Crab Nebula. We also model the interstellar medium toward HD185418, W31C, and NGC 253, and our predictions match with most of the observed column densities within the observed error bars. Very often molecular lines trace various physical conditions. Hence, this update will be very supportive for spectroscopic modeling of various astrophysical environments, particularly involving submillimeter and mid-infrared observations using the Atacama Large Millimeter/submillimeter Array and the James Webb Space Telescope, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>While <jats:italic>β</jats:italic> Pic is known to host silicates in ring-like structures, whether the properties of these silicate dust vary with stellocentric distance remains an open question. We re-analyze the <jats:italic>β</jats:italic> Pictoris debris disk spectrum from the Spitzer Infrared Spectrograph (IRS) and a new Infrared Telescope Facility Spectrograph and Imager spectrum to investigate trends in Fe/Mg ratio, shape, and crystallinity in grains as a function of wavelength, a proxy for stellocentric distance. By analyzing a re-calibrated and re-extracted spectrum, we identify a new 18 <jats:italic>μ</jats:italic>m forsterite emission feature and recover a 23 <jats:italic>μ</jats:italic>m forsterite emission feature with a substantially larger line-to-continuum ratio than previously reported. We find that these prominent spectral features are primarily produced by small submicron-sized grains, which are continuously generated and replenished from planetesimal collisions in the disk and can elucidate their parent bodies’ composition. We discover three trends about these small grains: as stellocentric distance increases, (1) small silicate grains become more crystalline (less amorphous), (2) they become more irregular in shape, and (3) for crystalline silicate grains, the Fe/Mg ratio decreases. Applying these trends to <jats:italic>β</jats:italic> Pic’s planetary architecture, we find that the dust population exterior to the orbits of <jats:italic>β</jats:italic> Pic b and c differs substantially in crystallinity and shape. We also find a tentative 3–5 <jats:italic>μ</jats:italic>m dust excess due to spatially unresolved hot dust emission close to the star. From our findings, we infer that the surfaces of large planetesimals are more Fe-rich and collisionally processed closer to the star but more Fe-poor and primordial farther from the star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Theoretical and observational studies suggest that stellar binaries exist in large numbers in galactic nuclei like our own Galactic Center. Neutron stars (NSs), and debatedly, black holes and white dwarfs, receive natal kicks at birth. In this work, we study the effect of two successive natal kicks on a population of stellar binaries orbiting the massive black hole (MBH) in our Galactic Center. These natal kicks can significantly alter the binary orbit in a variety of ways, and also the orbit of the binary around the MBH. We found a variety of dynamical outcomes resulting from these kicks, including a steeper cusp of single NSs relative to the initial binary distribution. Furthermore, hypervelocity star and binary candidates, including hypervelocity X-ray binaries, are a common outcome of natal kicks. In addition, we show that the population of X-ray binaries in the Galactic Center can be used as a diagnostic for the BH natal kick distribution. Finally, we estimate the rate of gravitational wave events triggered by natal kicks, including binary mergers and EMRIs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Episodic ejections of blobs (episodic jets) are widely observed in black hole sources and usually associated with flares. In this paper, by performing and analyzing three-dimensional general relativity magnetohydrodynamical numerical simulations of accretion flows, we investigate their physical mechanisms. We find that magnetic reconnection occurs in the accretion flow, likely due to the turbulent motion and differential rotation of the accretion flow, resulting in flares and formation of flux ropes. Flux ropes formed inside of 10–15 gravitational radii are found to mainly stay within the accretion flow, while flux ropes formed beyond this radius are ejected outward by magnetic forces and form the episodic jets. These results confirm the basic scenario proposed in Yuan et al. Moreover, our simulations find that the predicted velocity of the ejected blobs is in good consistency with observations of Sgr A*, M81, and M87. All of the processes were found to occur quasiperiodically, with the period being the orbital time at the radius where the flux rope is formed. The predicted period of the flares and ejections is consistent with those found from the light curves or image of Sgr A*, M87, and PKS 1510–089. The possible applications to protostellar accretion systems are discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An intense solar energetic particle (SEP) event was observed on 2021 October 9 by multiple spacecraft distributed near the ecliptic plane at heliocentric radial distances <jats:italic>R</jats:italic> ≲ 1 au and within a narrow range of heliolongitudes. A stream interaction region (SIR), sequentially observed by Parker Solar Probe (PSP) at <jats:italic>R</jats:italic> = 0.76 au and 48° east from Earth (<jats:italic>ϕ</jats:italic> = E48°), STEREO-A (at <jats:italic>R</jats:italic> = 0.96 au, <jats:italic>ϕ</jats:italic> = E39°), Solar Orbiter (SolO; at <jats:italic>R</jats:italic> = 0.68 au, <jats:italic>ϕ</jats:italic> = E15°), BepiColombo (at <jats:italic>R</jats:italic> = 0.33 au, <jats:italic>ϕ</jats:italic> = W02°), and near-Earth spacecraft, regulated the observed intensity-time profiles and the anisotropic character of the SEP event. PSP, STEREO-A, and SolO detected strong anisotropies at the onset of the SEP event, which resulted from the fact that PSP and STEREO-A were in the declining-speed region of the solar wind stream responsible for the SIR and from the passage of a steady magnetic field structure by SolO during the onset of the event. By contrast, the intensity-time profiles observed near Earth displayed a delayed onset at proton energies ≳13 MeV and an accumulation of ≲5 MeV protons between the SIR and the shock driven by the parent coronal mass ejection (CME). Even though BepiColombo, STEREO-A, and SolO were nominally connected to the same region of the Sun, the intensity-time profiles at BepiColombo resemble those observed near Earth, with the bulk of low-energy ions also confined between the SIR and the CME-driven shock. This event exemplifies the impact that intervening large-scale interplanetary structures, such as corotating SIRs, have in shaping the properties of SEP events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study anisotropic magnetohydrodynamic (MHD) turbulence in the slow solar wind measured by Parker Solar Probe (PSP) and Solar Orbiter (SolO) during its first orbit from the perspective of variance anisotropy and correlation anisotropy. We use the Belcher &amp; Davis approach (M1) and a new method (M2) that decomposes a fluctuating vector into parallel and perpendicular fluctuating vectors. M1 and M2 calculate the transverse and parallel turbulence components relative to the mean magnetic field direction. The parallel turbulence component is regarded as compressible turbulence, and the transverse turbulence component as incompressible turbulence, which can be either Alfvénic or 2D. The transverse turbulence energy is calculated from M1 and M2, and the transverse correlation length from M2. We obtain the 2D and slab turbulence energy and the corresponding correlation lengths from those transverse turbulence components that satisfy an angle between the mean solar wind flow speed and mean magnetic field <jats:italic>θ</jats:italic> <jats:sub>UB</jats:sub> of either (i) 65° &lt; <jats:italic>θ</jats:italic> <jats:sub>UB</jats:sub> &lt; 115° or (ii) 0° &lt; <jats:italic>θ</jats:italic> <jats:sub>UB</jats:sub> &lt; 25° (155° &lt; <jats:italic>θ</jats:italic> <jats:sub>UB</jats:sub> &lt; 180°), respectively. We find that the 2D turbulence component is not typically observed by PSP near perihelion, but the 2D component dominates turbulence in the inner heliosphere. We compare the detailed theoretical results of a nearly incompressible MHD turbulence transport model with the observed results of PSP and SolO measurements, finding good agreement between them.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present deep SCUBA-2 450 <jats:italic>μ</jats:italic>m imaging of the two GOODS fields, achieving a central rms of 1.14 mJy for the GOODS-N and 1.86 mJy for the GOODS-S. For each field, we give a catalog of &gt;4<jats:italic>σ</jats:italic> detections (79 and 16 sources, respectively). We construct the 450 <jats:italic>μ</jats:italic>m number counts, finding excellent agreement with others from the literature. We match the 450 <jats:italic>μ</jats:italic>m sources to 20 cm data (both fields) and ALMA 870 <jats:italic>μ</jats:italic>m data (GOODS-S) to gauge the accuracy of the 450 <jats:italic>μ</jats:italic>m positions. We use the extensive redshift information available on the fields to test how well redshift can be estimated from simple flux ratios (450 <jats:italic>μ</jats:italic>m /850 <jats:italic>μ</jats:italic>m and 20 cm/850 <jats:italic>μ</jats:italic>m), finding tight correlations. We provide a catalog of candidate high-redshift submillimeter galaxies. We look for evolution in dust temperature with redshift by fitting the spectral energy distributions of the sources, but we do not find any significant redshift evolution after accounting for the far-infrared luminosity. We do not find evidence for the 450 <jats:italic>μ</jats:italic>m selection picking out warmer sources than an 850 <jats:italic>μ</jats:italic>m selection. We find that a 450 <jats:italic>μ</jats:italic>m-selected sample only adds low-redshift (<jats:italic>z</jats:italic> &lt; 1.5) galaxies beyond an 850 <jats:italic>μ</jats:italic>m sample.</jats:p>