Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a spectral analysis of NuSTAR and NICER observations of the luminous, persistently accreting neutron star (NS) low-mass X-ray binary Cygnus X-2. The data were divided into different branches that the source traces out on the Z-track of the X-ray color–color diagram; namely, the horizontal branch, the normal branch, and the vertex between the two. The X-ray continuum spectrum was modeled in two different ways that produced comparable quality fits. The spectra showed clear evidence of a reflection component in the form of a broadened Fe K line, as well as a lower-energy emission feature near 1 keV likely due to an ionized plasma located far from the innermost accretion disk. We account for the reflection spectrum with two independent models (<jats:sc>relxillns</jats:sc> and <jats:sc>rdblur*rfxconv</jats:sc>). The inferred inclination is in agreement with earlier estimates from optical observations of ellipsoidal lightcurve modeling (<jats:sc>relxillns</jats:sc>: <jats:italic>i</jats:italic> = 67° ± 4°; <jats:sc>rdblur*rfxconv</jats:sc>: <jats:italic>i</jats:italic> = 60° ± 10°). The inner disk radius remains close to the NS (<jats:italic>R</jats:italic> <jats:sub>in</jats:sub> ≤ 1.15 <jats:italic>R</jats:italic> <jats:sub>ISCO</jats:sub>) regardless of the source position along the Z-track or how the 1 keV feature is modeled. Given the optically determined NS mass of 1.71 ± 0.21 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, this corresponds to a conservative upper limit of <jats:italic>R</jats:italic> <jats:sub>in</jats:sub> ≤ 19.5 km for <jats:italic>M</jats:italic> = 1.92 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> or <jats:italic>R</jats:italic> <jats:sub>in</jats:sub> ≤ 15.3 km for <jats:italic>M</jats:italic> = 1.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We compare these radius constraints to those obtained from NS gravitational wave merger events and recent NICER pulsar lightcurve modeling measurements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The third-order scaling law, Yaglom law, of Elsässer fluctuations in the solar wind is believed to reflect the inertial range energy cascade of the MHD turbulence and provides an approach to evaluate the cascade rate. However, the occurrence ratio with the Yaglom scaling law, the fraction of the intervals where the Yaglom linear scaling is observed, is reported to be low (0.05–0.30) in the high-latitude solar wind observed by the Ulysses spacecraft. Whether the occurrence ratio could be higher in other conditions remains unknown. Here, we analyze the occurrence of the third-order scaling in the inner heliosphere with the first 100 days of observation of the Helios 1 and Helios 2 spacecraft. We investigate 162 intervals in the leading edges and 323 intervals in the trailing edges of the high-speed streams, respectively. All of these intervals have a time duration of 9 hr. We find that in the inner heliosphere the occurrence ratio is relatively high in the leading edges (0.58) and moderate in the trailing edges (0.45). Among the data intervals with the Yaglom scaling in the leading edges, 94.7% of intervals give positive rates, while in the trailing edges 78.6% give negative rates. The variations of the occurrence ratio with various turbulence parameters are shown. The cascade rate is found to be higher than the proton heating rate calculated from the data, which have third-order scaling. These new results raise several questions related to the nature and origin of the third-order scaling law and may initiate new studies on solar wind turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>DI Herculis is an eclipsing binary famous for a longstanding disagreement between theory and observation of the apsidal precession rate, which was resolved when both stars were found to be severely misaligned with the orbit. We used data from the Transiting Exoplanet Survey Satellite (TESS) to refine our knowledge of the stellar obliquities and sharpen the comparison between the observed and theoretical precession rates. The TESS data show variations with a 1.07 day period, which we interpret as rotational modulation from starspots on the primary star. This interpretation is supported by the detection of photometric anomalies during primary eclipses consistent with starspot crossings. The secondary eclipse light curve shows a repeatable asymmetry that we interpret as an effect of gravity darkening. By combining the TESS data with previously obtained data, we determined the three-dimensional spin directions of both stars. Using this information, the updated value of the theoretical apsidal precession rate (including the effects of tides, rotation, and general relativity) is <jats:inline-formula> <jats:tex-math> <?CDATA ${1.35}_{-0.50}^{+0.58}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1.35</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.50</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.58</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4f65ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> arcsec cycle<jats:sup>−1</jats:sup>. The updated value of the observed rate (after including new TESS eclipse times) is <jats:inline-formula> <jats:tex-math> <?CDATA ${1.41}_{-0.28}^{+0.39}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1.41</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.28</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.39</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4f65ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> arcsec cycle<jats:sup>−1</jats:sup>. Given the agreement between the observed and theoretical values, we fitted all the relevant data simultaneously, assuming the theory is correct. This allowed us to place tighter constraints on the stellar obliquities, which are <jats:inline-formula> <jats:tex-math> <?CDATA ${75}_{-3}^{+3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>75</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4f65ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${80}_{-3}^{+3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>80</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4f65ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> degrees for the primary and secondary stars, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study stellar models for Betelgeuse using the HR diagram and surface abundances as observational constraints. Previous studies on Betelgeuse have not systematically investigated the surface abundances, but we believe they can be impacted by, and thus be used as an observational constraint for various parameters such as initial mass, rotation, and overshoot scheme. We investigate stellar models with varying initial mass as they evolve past the main sequence, and we examine the red supergiant (RSG) properties in detail. For each mass, we vary the initial rotation up to ∼300 km s<jats:sup>−1</jats:sup>, and test two different overshoot parameters. Overall, the acceptable initial mass range is 12–25 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, but for nonrotating models only, the range is decreased to 15–24 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Also for rotating models, we find that <jats:italic>v</jats:italic>/<jats:italic>v</jats:italic> <jats:sub>K</jats:sub> = 0.3 is the upper limit for initial rotation, as more rapidly rotating models are unable to fit to Betelgeuse’s surface abundances as an RSG. In addition, we report two possibilities for the current stage of evolution, core helium burning or core carbon burning and beyond. We find that certain 17 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> models could fit both stages. Finally, we discuss the implications of our results in the context of merger scenarios which have been suggested as a mechanism to attain the observed surface velocity of Betelgeuse.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The weak <jats:italic>r</jats:italic>-process offers an explanation of the formation of lighter heavy elements 36 ≤ <jats:italic>Z</jats:italic> ≤ 47 in ultra-metal-poor stars. Magnetohydrodynamically driven supernovae are thought to be a robust astronomical site of the weak <jats:italic>r</jats:italic>-process and recently gave a good description of the observational abundance pattern of an extremely metal-poor star. However, the characteristics of nuclear reactions in the MHD nucleosynthesis are not as clear as in another site, that of core-collapse supernovae. In this paper, the trajectories of the MHD model are implemented into <jats:monospace>SkyNet</jats:monospace> network calculations. By varying the reaction rates of each type, the (<jats:italic>α</jats:italic>,<jats:italic>n</jats:italic>) reactions are much more active than other types of reactions, such as (<jats:italic>n</jats:italic>,<jats:italic>γ</jats:italic>), (<jats:italic>p</jats:italic>,<jats:italic>γ</jats:italic>), (<jats:italic>n</jats:italic>,<jats:italic>p</jats:italic>), and (<jats:italic>α</jats:italic>,<jats:italic>p</jats:italic>). A further detailed sensitivity study investigates the (<jats:italic>α</jats:italic>,<jats:italic>n</jats:italic>) reactions and lists the most influential ones over the whole range, and the impactful reactions on each element from Sr to Ag are tabulated.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the <jats:italic>γ</jats:italic>-ray spectra of 30 globular clusters (GCs) thus far detected with the Fermi Gamma-ray Space Telescope. Presuming that <jats:italic>γ</jats:italic>-ray emission of a GC comes from millisecond pulsars (MSPs) contained within the GC, a model that generates spectra for the GCs is built based on the <jats:italic>γ</jats:italic>-ray properties of the detected MSP sample. We fit the GCs’ spectra with the model, and for 27 of them, their emission can be explained as arising from MSPs. The spectra of the other three, NGC 7078, 2MS-GC01, and Terzan 1, cannot be fit with our model, indicating that MSPs’ emission should not be the dominant one in the first two and the third one has a unique hard spectrum. We also investigate six nearby GCs that have relatively high encounter rates compared to the comparison cases. The candidate spectrum of NGC 6656 can be fit with that of one MSP, supporting its possible association with the <jats:italic>γ</jats:italic>-ray source at its position. The five others do not have detectable <jats:italic>γ</jats:italic>-ray emission. Their spectral upper limits set limits of ≤1 MSPs in them, consistent with the numbers of radio MSPs found in them. The estimated numbers of MSPs in the <jats:italic>γ</jats:italic>-ray GCs generally match well those reported for radio pulsars. Our studies of the <jats:italic>γ</jats:italic>-ray GCs and the comparison nearby GCs indicate that the encounter rate should not be the only factor determining the number of <jats:italic>γ</jats:italic>-ray MSPs a GC contains.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The surface abundances of the light elements lithium (Li) and beryllium (Be) reveal information about the physical processes taking place in stellar interiors. The investigation of the amount of these two elements in stars in open clusters shows the effect of age on those mechanisms. We have obtained spectra of both Li and Be in main-sequence stars in NGC 752 at high spectral resolution and high signal-to-noise ratios with HIRES on the Keck I telescope. In order to make meaningful comparisons with other clusters, we have determined the stellar parameters on a common scale. We have found abundances of Li and Be by spectral synthesis techniques. NGC 752 is twice the age of the well-studied Hyades. We find that (1) the Li dip centered near 6500 K is wider in NGC 752, having expanded toward cooler temperatures; (2) the Be dip is deeper in the older NGC 752; (3) the Li “peak” near 6200 K is lower by about 0.3 dex; (4) although there is little Be depletion in the cooler stars, it is possible that Be may be lower in NGC 752 than in the Hyades; and (5) the Li content in both clusters declines with decreasing temperature, but there is less Li in NGC 752 at a given temperature by ∼0.4 dex. These differences are consistent with the transport of the light-element nuclei below the surface convection zone as predicted by theory. That connection to rotational spin-down is indicated by the pattern of rotation with temperature in the two clusters.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using data from the Cluster mission and the First-Order Taylor Expansion method, we investigate the spiral magnetic nulls nested in the diffusion region of turbulent reconnection in the magnetotail. We particularly focus on the relation between the magnetic null topologies and currents, which can be decomposed into a component perpendicular to spine (<jats:italic>j</jats:italic> <jats:sub>⊥</jats:sub>) and a component parallel to spine (<jats:italic>j</jats:italic> <jats:sub>∥</jats:sub>). We find that (1) the currents surrounding the spiral nulls are mainly contributed by <jats:italic>j</jats:italic> <jats:sub>∥</jats:sub>; (2) the null with large (<jats:italic>j</jats:italic> <jats:sub>⊥</jats:sub>) and small spine-fan angle (<jats:italic>θ</jats:italic>), which are predicted by traditional linear theory, does not exist in the turbulent diffusion region; (3) the background current <jats:italic>j</jats:italic> <jats:sub> <jats:italic>b</jats:italic> </jats:sub> plays an important role in determining the direction of the currents around spiral nulls and consequently the orientation of the magnetic null structures; and (4) the spiral nulls with strong current (large magnitude <jats:inline-formula> <jats:tex-math> <?CDATA $\left|j\right|$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="∣" open="∣"> <mml:mrow> <mml:mi>j</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4eedieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) tend to degenerate into 2D configurations, whereas the nulls with weak currents retain the 3D features. Since the spiral magnetic nulls are crucial for the energy dissipation during the turbulent reconnection process, all of these results can provide important information for better understanding 3D turbulent reconnection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Simulating the irradiation of planetary atmospheres by cosmic ray particles requires, among others, the ability to understand and to quantify the interactions of charged particles with planetary magnetic fields. Here we present a process that is very often ignored in such studies: the dispersion and focusing of cosmic ray trajectories in magnetospheres. The calculations were performed using our new code CosmicTransmutation, which has been developed to study cosmogenic nuclide production in meteoroids and planetary atmospheres and which includes the computation of the irradiation spectrum on top of the atmosphere. Here we discuss effects caused by dispersion and focusing of cosmic ray particle trajectories.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present “Extending the Satellites Around Galactic Analogs Survey” (xSAGA), a method for identifying low-<jats:italic>z</jats:italic> galaxies on the basis of optical imaging and results on the spatial distributions of xSAGA satellites around host galaxies. Using spectroscopic redshift catalogs from the SAGA Survey as a training data set, we have optimized a convolutional neural network (CNN) to identify <jats:italic>z</jats:italic> &lt; 0.03 galaxies from more-distant objects using image cutouts from the DESI Legacy Imaging Surveys. From the sample of &gt;100,000 CNN-selected low-<jats:italic>z</jats:italic> galaxies, we identify &gt;20,000 probable satellites located between 36–300 projected kpc from NASA-Sloan Atlas central galaxies in the stellar-mass range <jats:inline-formula> <jats:tex-math> <?CDATA $9.5\lt \mathrm{log}({M}_{\star }/{M}_{\odot })\lt 11$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>9.5</mml:mn> <mml:mo>&lt;</mml:mo> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</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>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>&lt;</mml:mo> <mml:mn>11</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4eeaieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. We characterize the incompleteness and contamination for CNN-selected samples and apply corrections in order to estimate the true number of satellites as a function of projected radial distance from their hosts. Satellite richness depends strongly on host stellar mass, such that more-massive host galaxies have more satellites, and on host morphology, such that elliptical hosts have more satellites than disky hosts with comparable stellar masses. We also find a strong inverse correlation between satellite richness and the magnitude gap between a host and its brightest satellite. The normalized satellite radial distribution between 36–300 kpc does not depend on host stellar mass, morphology, or magnitude gap. The satellite abundances and radial distributions we measure are in reasonable agreement with predictions from hydrodynamic simulations. Our results deliver unprecedented statistical power for studying satellite galaxy populations and highlight the promise of using machine-learning for extending galaxy samples of wide-area surveys.</jats:p>