Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The recent discovery of nanojets by Antolin et al. represents magnetic reconnection in a braided field, thus clearly identifying reconnection-driven nanoflares. Due to their small scale (500 km in width, 1500 km in length) and short timescales (&lt;15 s), it is unclear how pervasive nanojets are in the solar corona. In this paper, we present Interface Region Imaging Spectrograph and Solar Dynamics Observatory observations of nanojets found in multiple coronal structures, namely, in a coronal loop powered by a blowout jet, and in two other coronal loops with coronal rain. In agreement with previous findings, we observe that nanojets are accompanied by small nanoflare-like intensity bursts in the (E)UV, have velocities of 150–250 km s<jats:sup>−1</jats:sup> and occur transversely to the field line of origin, which is sometimes observed to split. However, we find a variety of nanojet directions in the plane transverse to the loop axis. These nanojets are found to have kinetic and thermal energies within the nanoflare range, and often occur in clusters. In the blowout jet case study, the Kelvin–Helmholtz instability (KHI) is directly identified as the reconnection driver. For the other two loops, we find that both, KHI and Rayleigh–Taylor instability (RTI) are likely to be the drivers. However, we find that KHI and RTI are each more likely in one of the other two cases. These observations of nanojets in a variety of structures and environments support nanojets being a general result of reconnection that are driven here by dynamic instabilities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recently an improved nonlinear theory for the transport of energetic particles across a mean magnetic field has been developed. The latter theory is called the field line–particle decorrelation theory and is the first analytical theory that agrees with test-particle simulations without the need of a correction parameter, nor does the theory contain any other free parameter. In the current paper we derive analytical forms for the ratio of perpendicular and parallel spatial diffusion coefficients <jats:italic>κ</jats:italic> <jats:sub>⊥</jats:sub>/<jats:italic>κ</jats:italic> <jats:sub>∥</jats:sub> of low-energy particles. In the considered limit the latter ratio is constant meaning that it does not depend on particle energy or rigidity. It is shown that the ratio always has the form <jats:inline-formula> <jats:tex-math> <?CDATA ${\kappa }_{\perp }/{\kappa }_{\parallel }={a}^{2}\delta {B}_{x}^{2}/{B}_{0}^{2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>κ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊥</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>κ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">∥</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mi>δ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac85e4ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> if a two-dimensional turbulence model is employed. Furthermore, the parameter <jats:italic>a</jats:italic> <jats:sup>2</jats:sup> depends only on the shape of the turbulence spectrum but not on the magnetic fields. The obtained results can be important for a variety of applications such as studies of solar modulation and diffusive shock acceleration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The photometric transit method has been the most effective method to detect and characterize exoplanets as several ground based as well as space based survey missions have discovered thousands of exoplanets using this method. With the advent of the upcoming next generation large telescopes, the detection of exomoons in a few of these exoplanetary systems is very plausible. In this paper, we present a comprehensive analytical formalism in order to model the transit light curves for such moon-hosting exoplanets. In order to achieve analytical formalism, we have considered circular orbit of the exomoon around the host planet, which is indeed the case for tidally locked moons. The formalism uses the radius and orbital properties of both the host planet and its moon as model parameters. The coalignment or noncoalignment of the orbits of the planet and the moon are parameterized using two angular parameters and thus can be used to model all the possible orbital alignments for a star–planet–moon system. This formalism also provides unique and direct solutions to every possible star–planet–moon three circular body alignment. Using the formula derived, a few representative light curves are also presented.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the results of a broadband (0.5–78 keV) X-ray spectral study of the persistent Galactic black hole X-ray binary GRS 1758–258 observed simultaneously by Swift and NuSTAR. Fitting with an absorbed power-law model revealed a broad Fe line and reflection hump in the spectrum. We used different flavors of the relativistic reflection model for the spectral analysis. All models indicate the spin of the black hole in GRS 1758–258 is &gt;0.92. The source was in the low hard state during the observation, with the hot electron temperature of the corona estimated to be <jats:italic>kT</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> ∼ 140 keV. The black hole is found to be accreting at ∼1.5% of the Eddington limit during the observation, assuming the black hole mass of 10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and distance of 8 kpc.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the non-local thermodynamic equilibrium (non-LTE, hereafter NLTE) analysis for Cu <jats:sc>i</jats:sc> lines with the updated model atom that includes quantum-mechanical rate coefficients of Cu + H and Cu<jats:sup>+</jats:sup> + H<jats:sup>−</jats:sup> inelastic collisions from the recent study of Belyaev et al. The influence of these data on NLTE abundance determinations has been performed for six metal-poor stars in a metallicity range of −2.59 dex ≤ [Fe/H] ≤ −0.95 dex. For Cu <jats:sc>i</jats:sc> lines, the application of accurate atomic data leads to a decrease in the departure from LTE and lower copper abundances compared to that obtained with Drawin’s theoretical approximation. To verify our adopted copper atomic model, we also derived the LTE copper abundances of Cu <jats:sc>ii</jats:sc> lines for the sample stars. A consistent copper abundance from the Cu <jats:sc>i</jats:sc> (NLTE) and Cu <jats:sc>ii</jats:sc> (LTE) lines has been obtained, which indicates the reliability of our copper atomic model. It is noted that the [Cu/Fe] ratios increase with increasing metallicity when ∼−2.0 dex &lt; [Fe/H] &lt; ∼−1.0 dex, favoring a secondary (metallicity-dependent) copper production.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first results from our ongoing project to study extremely low-mass (ELM) white dwarfs (WDs) (<jats:italic>M</jats:italic> ≤ 0.3<jats:italic>M</jats:italic> <jats:sub>☉</jats:sub>) with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra. Based on the LAMOST DR8 spectral database, we analyzed 136 ELM WD candidates selected from Gaia DR2 data and 12 known objects previously identified by the ELM Survey. The atmospheric parameters and radial velocities of these stars were obtained by fitting the LAMOST low-resolution spectra. After comparing the atmospheric parameters of the 12 known objects from this work to the results reported by the ELM Survey, we demonstrated the potential of LAMOST spectra in probing into the nature of ELM WDs. Based on the atmospheric parameters and Gaia EDR3 data, we identified 21 new high-probability ELM WDs with masses <jats:italic>M</jats:italic> ≤ 0.3<jats:italic>M</jats:italic> <jats:sub>☉</jats:sub> and parallax estimates that agree to within a factor of 3. Two of them, J0338+4134 and J1129+4715, show significant radial velocity variability and are very likely to be binary systems containing at least one ELM WD.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Reacting astrophysical flows can be challenging to model, because of the difficulty in accurately coupling hydrodynamics and reactions. This can be particularly acute during explosive burning or at high temperatures where nuclear statistical equilibrium is established. We develop a new approach, based on the ideas of spectral deferred corrections (SDC) coupling of explicit hydrodynamics and stiff reaction sources as an alternative to operator splitting, that is simpler than the more comprehensive SDC approach we demonstrated previously. We apply the new method to a double-detonation problem with a moderately sized astrophysical nuclear reaction network and explore the time step size and reaction network tolerances, to show that the simplified-SDC approach provides improved coupling with decreased computational expense compared to traditional Strang operator splitting. This is all done in the framework of the <jats:sans-serif>Castro</jats:sans-serif> hydrodynamics code, and all algorithm implementations are freely available.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Wave emissions at frequencies near electron gyrofrequency harmonics are observed at small heliocentric distances below about 40 <jats:italic>R</jats:italic> <jats:sub>☉</jats:sub> and are known to occur in regions with quiescent magnetic fields. We show the close connection of these waves to the large-scale properties of the magnetic field. Near electron gyrofrequency harmonic emissions occur only when the ambient magnetic field points to a narrow range of directions bounded by polar and azimuthal angular ranges in the RTN coordinate system of correspondingly 80° ≲ <jats:italic>θ</jats:italic> <jats:sub> <jats:bold> <jats:italic>B</jats:italic> </jats:bold> </jats:sub> ≲ 100° and 10° ≲ <jats:italic>ϕ</jats:italic> <jats:sub> <jats:bold> <jats:italic>B</jats:italic> </jats:bold> </jats:sub> ≲ 30°. We show that the amplitudes of wave emissions are highest when both angles are close to the center of their respective angular interval favorable to wave emissions. The intensity of wave emissions correlates with the magnetic field angular changes at both large and small timescales. Wave emissions intervals correlate with intervals of decreases in the amplitudes of broadband magnetic fluctuations at low frequencies of 10–100 Hz. We discuss possible generation mechanisms of the waves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Dynamical models for 673 galaxies at <jats:italic>z</jats:italic> = 0.6–1.0 with spatially resolved (long-slit) stellar kinematic data from LEGA-C are used to calibrate virial mass estimates defined as <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\mathrm{vir}}=K\sigma {{\prime} }_{\star ,\mathrm{int}}^{2}R$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>vir</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mi>K</mml:mi> <mml:mi>σ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> <mml:mo>,</mml:mo> <mml:mi>int</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi>R</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac83c5ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, with <jats:italic>K</jats:italic> <jats:italic> </jats:italic>a scaling factor, <jats:inline-formula> <jats:tex-math> <?CDATA $\sigma {{\prime} }_{\star ,\mathrm{int}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>σ</mml:mi> <mml:msub> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> <mml:mo>,</mml:mo> <mml:mi>int</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac83c5ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> the spatially integrated stellar velocity second moment from the LEGA-C survey, and <jats:italic>R</jats:italic> the effective radius measured from a Sérsic profile fit to Hubble Space Telescope imaging. The sample is representative for <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> &gt; 3 × 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and includes all types of galaxies, irrespective of morphology and color. We demonstrate that using <jats:italic>R</jats:italic> = <jats:italic>R</jats:italic> <jats:sub>sma</jats:sub> (the semimajor axis length of the ellipse that encloses 50% of the light) in combination with an inclination correction on <jats:inline-formula> <jats:tex-math> <?CDATA $\sigma {{\prime} }_{\star ,\mathrm{int}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>σ</mml:mi> <mml:msub> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> <mml:mo>,</mml:mo> <mml:mi>int</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac83c5ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> produces an unbiased <jats:italic>M</jats:italic> <jats:sub>vir</jats:sub>. We confirm the importance of projection effects on <jats:inline-formula> <jats:tex-math> <?CDATA $\sigma {{\prime} }_{\star ,\mathrm{int}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>σ</mml:mi> <mml:msub> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> <mml:mo>,</mml:mo> <mml:mi>int</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac83c5ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> by showing the existence of a similar residual trend between virial mass estimates and inclination for the nearby early-type galaxies in the ATLAS<jats:sup>3D</jats:sup> survey. Also, as previously shown, when using a Sérsic profile-based <jats:italic>R</jats:italic> estimate, a Sérsic index-dependent correction to account for nonhomology in the radial profiles is required. With respect to analogous dynamical models for low-redshift galaxies from the ATLAS<jats:sup>3D</jats:sup> survey we find a systematic offset of 0.1 dex in the calibrated virial constant for LEGA-C, which may be due to physical differences between the galaxy samples or an unknown systematic error. Either way, with our work we establish a common mass scale for galaxies across 8 Gyr of cosmic time with a systematic uncertainty of at most 0.1 dex.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present multifrequency observations of the radio source 3CR 403.1, a nearby (<jats:italic>z</jats:italic> = 0.055), extended (∼0.5 Mpc) radio galaxy hosted in a small galaxy group. Using new high-frequency radio observations from the Sardinia Radio Telescope (SRT), augmented with archival low-frequency radio observations, we investigated radio spectral and polarimetric properties of 3CR 403.1. From the MHz-to-GHz spectral analysis, we computed the equipartition magnetic field in the lobes to be <jats:italic>B</jats:italic> <jats:sub>eq</jats:sub> = 2.4 <jats:italic>μ</jats:italic>G and the age of the source to be ∼100 Myr. From the spectral analysis of the diffuse X-ray emission we measured the temperature and density of the intracluster medium (ICM). From the SRT observations, we discovered two regions where the radio flux density is below the background value. We computed the Comptonization parameter both from the radio and from the X-ray observations to test whether the Sunyaev–Zel’dovich effect is occurring here and found a significant tension between the two estimates. If the negative signal is considered as real, then we speculate that the discrepancy between the two values could be partially caused by the presence of a nonthermal bath of mildly relativistic ghost electrons. From the polarimetric radio images, we find a net asymmetry of the Faraday rotation between the two prominent extended structures of 3CR 403.1 and constrain the magnetic field strength in the ICM to be 1.8–3.5 <jats:italic>μ</jats:italic>G. The position of 3CR 403.1 in the magnetic field–gas density plane is consistent with the trend reported in the literature between central magnetic field and central gas density.</jats:p>