Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We consider topological configurations of the magnetically coupled spinning stellar binaries (e.g., merging neutron stars or interacting star–planet systems). We discuss conditions when the stellar spins and the orbital motion nearly “compensate” each other, leading to very <jats:italic>slow</jats:italic> overall winding of the coupled magnetic fields; slowly winding configurations allow gradual accumulation of magnetic energy, which is eventually released in a flare when the instability threshold is reached. We find that this slow winding can be global and/or local. We describe the topology of the relevant space <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathbb{F}}={T}^{1}{S}^{2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="double-struck">F</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac29b8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> as the unit tangent bundle of the two-sphere and find conditions for slowly winding configurations in terms of magnetic moments, spins, and orbital momentum. These conditions become ambiguous near the topological bifurcation points; in certain cases, they also depend on the relative phases of the spin and orbital motions. In the case of merging magnetized neutron stars, if one of the stars is a millisecond pulsar, spinning at ∼10 ms, the global resonance <jats:italic>ω</jats:italic> <jats:sub>1</jats:sub> + <jats:italic>ω</jats:italic> <jats:sub>2</jats:sub> = 2Ω (spin-plus beat is two times the orbital period) occurs approximately one second before the merger; the total energy of the flare can be as large as 10% of the total magnetic energy, producing bursts of luminosity ∼10<jats:sup>44</jats:sup> erg s<jats:sup>−1</jats:sup>. Higher order local resonances may have similar powers, since the amount of involved magnetic flux tubes may be comparable to the total connected flux.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We search for signatures of gravitational lensing in the gravitational-wave signals from compact binary coalescences detected by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) and Advanced Virgo during O3a, the first half of their third observing run. We study: (1) the expected rate of lensing at current detector sensitivity and the implications of a non-observation of strong lensing or a stochastic gravitational-wave background on the merger-rate density at high redshift; (2) how the interpretation of individual high-mass events would change if they were found to be lensed; (3) the possibility of multiple images due to strong lensing by galaxies or galaxy clusters; and (4) possible wave-optics effects due to point-mass microlenses. Several pairs of signals in the multiple-image analysis show similar parameters and, in this sense, are nominally consistent with the strong lensing hypothesis. However, taking into account population priors, selection effects, and the prior odds against lensing, these events do not provide sufficient evidence for lensing. Overall, we find no compelling evidence for lensing in the observed gravitational-wave signals from any of these analyses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on CO and H <jats:sc>i</jats:sc> studies of the mixed-morphology supernova remnant (SNR) G346.6−0.2. We find a wind-blown bubble along the radio continuum shell with an expansion velocity of ∼10 km s<jats:sup>−1</jats:sup>, which was likely formed by strong stellar winds from the high-mass progenitor of the SNR. The radial velocities of the CO/H <jats:sc>i</jats:sc> bubbles at <jats:italic>V</jats:italic> <jats:sub>LSR</jats:sub> = −82 to −59 km s<jats:sup>−1</jats:sup> are also consistent with those of shock-excited 1720 MHz OH masers. The molecular cloud in the northeastern shell shows a high kinetic temperature of ∼60 K, suggesting that shock heating occurred. The H <jats:sc>i</jats:sc> absorption studies imply that G346.6−0.2 is located on the farside of the Galactic center from us, and the kinematic distance of the SNR is derived to be <jats:inline-formula> <jats:tex-math> <?CDATA ${11.1}_{-0.3}^{+0.5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>11.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac1c02ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> kpc. We find that the CO line intensity has no specific correlation with the electron temperature of recombining plasma, implying that the recombining plasma in G346.6−0.2 was likely produced by adiabatic cooling. With our estimates of the interstellar proton density of 280 cm<jats:sup>−3</jats:sup> and gamma-ray luminosity &lt;5.8 × 10<jats:sup>34</jats:sup> erg s<jats:sup>−1</jats:sup>, the total energy of accelerated cosmic rays of <jats:italic>W</jats:italic> <jats:sub>p</jats:sub> &lt; 9.3 × 10<jats:sup>47</jats:sup> erg is obtained. A comparison of the age–<jats:italic>W</jats:italic> <jats:sub>p</jats:sub> relation to other SNRs suggests that most of the accelerated cosmic rays in G346.6−0.2 have escaped from the SNR shell.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present 97 new high-quality strong lensing candidates found in the final ∼350 deg<jats:sup>2</jats:sup> that complete the full ∼1350 deg<jats:sup>2</jats:sup> area of the Kilo-Degree Survey (KiDS). Together with our previous findings, the final list of high-quality candidates from KiDS sums up to 268 systems. The new sample is assembled using a new convolutional neural network (CNN) classifier applied to <jats:italic>r</jats:italic>-band (best-seeing) and <jats:italic>g</jats:italic>, <jats:italic>r</jats:italic>, and <jats:italic>i</jats:italic> color-composited images separately. This optimizes the complementarity of the morphology and color information on the identification of strong lensing candidates. We apply the new classifiers to a sample of luminous red galaxies (LRGs) and a sample of bright galaxies (BGs) and select candidates that received a high probability to be a lens from the CNN (<jats:italic>P</jats:italic> <jats:sub>CNN</jats:sub>). In particular, setting <jats:italic>P</jats:italic> <jats:sub>CNN</jats:sub> &gt; 0.8 for the LRGs, the one-band CNN predicts 1213 candidates, while the three-band classifier yields 1299 candidates, with only ∼30% overlap. For the BGs, in order to minimize the false positives, we adopt a more conservative threshold, <jats:italic>P</jats:italic> <jats:sub>CNN</jats:sub> &gt; 0.9, for both CNN classifiers. This results in 3740 newly selected objects. The candidates from the two samples are visually inspected by seven coauthors to finally select 97 “high-quality” lens candidates which received mean scores larger than 6 (on a scale from 0 to 10). We finally discuss the effect of the seeing on the accuracy of CNN classification and possible avenues to increase the efficiency of multiband classifiers, in preparation of next-generation surveys from ground and space.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>HESS J0632+057 belongs to a rare subclass of binary systems that emit gamma rays above 100 GeV. It stands out for its distinctive high-energy light curve, which features a sharp “primary” peak and broader “secondary” peak. We present the results of contemporaneous observations by NuSTAR and VERITAS during the secondary peak between 2019 December and 2020 February, when the orbital phase (<jats:italic>ϕ</jats:italic>) is between 0.55 and 0.75. NuSTAR detected X-ray spectral evolution, while VERITAS detected TeV emission. We fit a leptonic wind-collision model to the multiwavelength spectra data obtained over the four NuSTAR and VERITAS observations, constraining the pulsar spin-down luminosity and the magnetization parameter at the shock. Despite long-term monitoring of the source from 2019 October to 2020 March, the MDM observatory did not detect significant variation in H<jats:italic>α</jats:italic> and H<jats:italic>β</jats:italic> line equivalent widths, an expected signature of Be-disk interaction with the pulsar. Furthermore, fitting folded Swift-XRT light-curve data with an intrabinary shock model constrained the orbital parameters, suggesting two orbital phases (at <jats:italic>ϕ</jats:italic> <jats:sub> <jats:italic>D</jats:italic> </jats:sub> = 0.13 and 0.37), where the pulsar crosses the Be-disk, as well as phases for the periastron (<jats:italic>ϕ</jats:italic> <jats:sub>0</jats:sub> = 0.30) and inferior conjunction (<jats:italic>ϕ</jats:italic> <jats:sub>IFC</jats:sub> = 0.75). The broadband X-ray spectra with Swift-XRT and NuSTAR allowed us to measure a higher neutral hydrogen column density at one of the predicted disk-passing phases.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using deep rest-frame optical spectroscopy from the Large Early Galaxy Astrophysical Census (LEGA-C) survey, conducted using VIMOS on the ESO Very Large Telescope, we search for low-ionization [O <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic> <jats:italic>λ</jats:italic> 3726,3729 emission in the spectra of a mass-complete sample of <jats:italic>z</jats:italic> ≈ 0.85 galaxies. We find that 59% of UVJ-quiescent (i.e., non-star-forming) galaxies in the sample have [O <jats:sc>ii</jats:sc>] emission detected above our completeness limit of 1.5 Å, and the median-stacked spectrum of the remaining sample also shows [O <jats:sc>ii</jats:sc>] emission. The overall fraction of sources with [O <jats:sc>ii</jats:sc>] above our equivalent width limit is comparable to what we find in the low-redshift universe from GAMA and MASSIVE, except perhaps at the highest stellar masses (&gt;10<jats:sup>11.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>). However, stacked spectra for the individual low-equivalent-width systems uniquely indicates ubiquitous [O <jats:sc>ii</jats:sc>] emission in the higher-<jats:italic>z</jats:italic> LEGA-C sample, with typical [O <jats:sc>ii</jats:sc>] luminosities per unit stellar mass that are a factor of ×3 larger than the lower-<jats:italic>z</jats:italic> GAMA sample. Star formation at higher-<jats:italic>z</jats:italic> could play a role in producing the [O <jats:sc>ii</jats:sc>] emission, although it is unlikely to provide the bulk of the ionizing photons. More work is required to fully quantify the contributions of evolved stellar populations or active galactic nuclei to the observed spectra.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first retrieval analysis of a substellar subdwarf, SDSS J125637.13−022452.4 (SDSS J1256−0224), using the <jats:italic>Brewster</jats:italic> retrieval code base. We find SDSS J1256−0224 is best fit by a cloud-free model with an ion (neutral H, H<jats:sup>−</jats:sup>, and electron) abundance corresponding to <jats:inline-formula> <jats:tex-math> <?CDATA ${\left[\mathrm{Fe}/{\rm{H}}\right]}_{\mathrm{ion}}=-1.5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi>Fe</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mi>ion</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac294eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. However, this model is indistinguishable from a cloud-free model with <jats:inline-formula> <jats:tex-math> <?CDATA ${\left[\mathrm{Fe}/{\rm{H}}\right]}_{\mathrm{ion}}=-2.0$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi>Fe</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mi>ion</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>2.0</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac294eieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and a cloud-free model with <jats:inline-formula> <jats:tex-math> <?CDATA ${\left[\mathrm{Fe}/{\rm{H}}\right]}_{\mathrm{ion}}=-1.5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi>Fe</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mi>ion</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac294eieqn3.gif" xlink:type="simple" /> </jats:inline-formula> assuming a subsolar carbon-to-oxygen ratio. We are able to constrain abundances for H<jats:sub>2</jats:sub>O, FeH, and CrH, with an inability to constrain any carbon-bearing species likely due to the low metallicity of SDSS J1256−0224. We also present an updated spectral energy distribution (SED) and semiempirical fundamental parameters. Our retrieval- and SED-based fundamental parameters agree with the Baraffe low-metallicity evolutionary models. From examining our “rejected” models (those with ΔBIC &gt; 45), we find that we are able to retrieve gas abundances consistent with those of our best fitting model. We find the cloud in these poorer fitting “cloudy” models is either pushed to the bottom of the atmosphere or made optically thin.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We identify hierarchical structures in the Vela OB2 complex and the cluster pair Collinder 135 and UBC 7 with Gaia EDR3 using the neural network machine-learning algorithm <jats:monospace>StarGO</jats:monospace>. Five second-level substructures are disentangled in Vela OB2, which are referred to as Huluwa 1 (Gamma Velorum), Huluwa 2, Huluwa 3, Huluwa 4, and Huluwa 5. For the first time, Collinder 135 and UBC 7 are simultaneously identified as constituent clusters of the pair with minimal manual intervention. We propose an alternative scenario in which Huluwa 1–5 have originated from sequential star formation. The older clusters Huluwa 1–3, with an age of 10–22 Myr, generated stellar feedback to cause turbulence that fostered the formation of the younger-generation Huluwa 4–5 (7–20 Myr). A supernova explosion located inside the Vela IRAS shell quenched star formation in Huluwa 4–5 and rapidly expelled the remaining gas from the clusters. This resulted in global mass stratification across the shell, which is confirmed by the regression discontinuity method. The stellar mass in the lower rim of the shell is 0.32 ± 0.14 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> higher than in the upper rim. Local, cluster-scale mass segregation is observed in the lowest-mass cluster Huluwa 5. Huluwa 1–5 (in Vela OB2) are experiencing significant expansion, while the cluster pair suffers from moderate expansion. The velocity dispersions suggest that all five groups (including Huluwa 1A and Huluwa 1B) in Vela OB2 and the cluster pair are supervirial and are undergoing disruption, and also that Huluwa 1A and Huluwa 1B may be a coeval young cluster pair. <jats:italic>N</jats:italic>-body simulations predict that Huluwa 1–5 in Vela OB2 and the cluster pair will continue to expand in the future 100 Myr and eventually dissolve.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work communicates the discovery of a binary open cluster within the Galaxy. NGC 1605 presents an unusual morphology with a sparse stellar distribution and a double core in close angular proximity. The 2MASS and Gaia-EDR3 field-star decontaminated color–magnitude diagrams (CMDs) show two distinct stellar populations located at the same heliocentric distance of ∼2.6 kpc, suggesting that there are two clusters in the region, NGC 1605a and NGC 1605b, with ages of 2 Gyr and 600 Myr, respectively. Both Gaia parallax and PM distributions are compact and very similar indicating that they are open clusters (OCs) and share the same kinematics. The large age difference, 1.4 Gyr, point to a formation by tidal capture during a close encounter and the close spatial proximity and similar kinematics suggest an ongoing merger event. There is some prominent tidal debris that appears to trace the cluster's orbits during the close encounter and, unexpectedly, some of them appear to be bound structures; this may suggest that in addition to the evaporation, the merging clusters are being broken apart into smaller structures by the combination of the Galactic disk, the Perseus arm, and mutual tidal interactions. In this sense, the newly found binary cluster may be a key object in the observational validation of theoretical studies on binary cluster pairs formation by tidal capture as well as in the formation of massive clusters by merging, and tidal disruption of stellar systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent work has revealed two classes of globular clusters (GCs), dubbed Type I and Type II. Type II GCs are characterized by both a blue and a red red giant branch composed of stars with different metallicities, often coupled with distinct abundances in the slow neutron-capture elements (s-elements). Here we continue the chemical tagging of Type II GCs by adding the two least massive clusters of this class, NGC 1261 and NGC 6934. Based on both spectroscopy and photometry, we find red stars in NGC 1261 to be slightly enhanced in [Fe/H] by ∼0.1 dex and confirm that red stars of NGC 6934 are enhanced in iron by ∼0.2 dex. Neither NGC 1261 nor NGC 6934 show internal variations in the s-elements, which suggests a GC mass threshold for the occurrence of <jats:italic>s</jats:italic>-process enrichment. We found a significant correlation between the additional Fe locked in the red stars of Type II GCs and the present-day mass of the cluster. Nevertheless, most Type II GCs retained a small fraction of Fe produced by SNe II, lower than the 2%; NGC 6273, M54, and <jats:italic>ω</jats:italic> Centauri are remarkable exceptions. In the Appendix, we infer for the first time chemical abundances of lanthanum, assumed as representative of the s-elements, in M54, the GC located in the nucleus of the Sagittarius dwarf galaxy. Red-sequence stars are marginally enhanced in [La/Fe] by 0.10 ± 0.06 dex, in contrast with the large [La/Fe] spread of most Type II GCs. We suggest that different processes are responsible for the enrichment in iron and <jats:italic>s</jats:italic>-elements in Type II GCs.</jats:p>