Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a Bayesian inference approach to estimating the cumulative mass profile and mean-squared velocity profile of a globular cluster (GC) given the spatial and kinematic information of its stars. Mock GCs with a range of sizes and concentrations are generated from lowered-isothermal dynamical models, from which we test the reliability of the Bayesian method to estimate model parameters through repeated statistical simulation. We find that given unbiased star samples, we are able to reconstruct the cluster parameters used to generate the mock cluster and the cluster’s cumulative mass and mean-squared velocity profiles with good accuracy. We further explore how strongly biased sampling, which could be the result of observing constraints, might affect this approach. Our tests indicate that if we instead have biased samples, then our estimates can be off in certain ways that are dependent on cluster morphology. Overall, our findings motivate obtaining samples of stars that are as unbiased as possible. This may be achieved by combining information from multiple telescopes (e.g., Hubble and Gaia), but will require careful modeling of the measurement uncertainties through a hierarchical model, which we plan to pursue in future work.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Massive stars play critical roles for the reionization of the universe. Individual massive stars at the reionization epoch (<jats:italic>z</jats:italic> &gt; 6) are too faint to observe and quantify their contributions to reionization. Some massive stars, however, explode as superluminous supernovae (SLSNe) or pair-instability supernovae (PISNe) that are luminous enough to observe even at <jats:italic>z</jats:italic> &gt; 6 and allow for the direct characterization of massive star properties at the reionization epoch. In addition, hypothetical long-sought-after PISNe are expected to be present preferentially at high redshifts, and their discovery will have a tremendous impact on our understanding of massive star evolution and the formation of stellar mass black holes. The near-infrared Wide Field Instrument on the Nancy Grace Roman Space Telescope will excel at discovering such rare high-redshift supernovae. In this work, we investigate the best survey strategy to discover and identify SLSNe and PISNe at <jats:italic>z</jats:italic> &gt; 6 with Roman. We show that the combination of the F158 and F213 filters can clearly separate both SLSNe and PISNe at <jats:italic>z</jats:italic> &gt; 6 from nearby supernovae through their colors and magnitudes. The limiting magnitudes are required to be 27.0 mag and 26.5 mag in the F158 and F213 filters, respectively, to identify supernovae at <jats:italic>z</jats:italic> &gt; 6. If we conduct a 10 deg<jats:sup>2</jats:sup> transient survey with these limiting magnitudes for five years with a cadence of one year, we expect to discover 22.5 ± 2.8 PISNe and 3.1 ± 0.3 SLSNe at <jats:italic>z</jats:italic> &gt; 6, depending on the cosmic star formation history. The same survey is estimated to discover 76.1 ± 8.2 PISNe and 9.1 ± 0.9 SLSNe at 5 &lt; <jats:italic>z</jats:italic> &lt; 6. Such a supernova survey requires the total observational time of approximately 525 hr in five years. The legacy data acquired with the survey will also be beneficial for many different science cases including the study of high-redshift galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>During a failed core-collapse supernova, the protoneutron star eventually collapses under its own gravitational field and forms a black hole. This collapse happens quickly, on the dynamical time of the protoneutron star, ≲0.5 ms. During this collapse, barring any excessive rotation, the entire protoneutron star is accreted into the newly formed black hole. The main source of neutrinos is now removed and the signal abruptly shuts off over this formation timescale. However, while the source of neutrinos is turned off, the arrival times at an Earth-based detector will depend on the neutrino path. We show here that a modest amount of neutrinos, emitted just prior to the black hole forming, scatter on the infalling material into our line of sight and arrive after the formation of the black hole, up to 15 ms in our model. This neutrino echo, which we characterize with Monte Carlo simulations and analytic models, has a significantly higher average energy (upwards of ∼50 MeV) compared to the main neutrino signal, and for the canonical failed supernova explored here, is likely detectable in <jats:inline-formula> <jats:tex-math> <?CDATA ${ \mathcal O }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4420ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>(10 kT) supernova neutrino detectors for Galactic failed supernovae. The presence of this signal is important to consider if using black hole formation as a time post for triangulation or the post black hole timing profile for neutrino mass measurements. On its own, it can also be used to characterize or constrain the structure and nature of the accretion flow.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper we examine a low-energy solar energetic particle (SEP) event observed by IS⊙IS’s Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 au on 2020 September 30. This small SEP event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity are observed mainly along the open radial magnetic field. The event shows velocity dispersion, and strong particle anisotropies are observed throughout the event, showing that more particles are streaming outward from the Sun. We do not see a shock in the in situ plasma or magnetic field data throughout the event. Heavy ions, such as O and Fe, were detected in addition to protons and 4He, but without significant enhancements in 3He or energetic electrons. Our analysis shows that this event is associated with a slow streamer blowout coronal mass ejection (SBO-CME), and the signatures of this small CME event are consistent with those typical of larger CME events. The time–intensity profile of this event shows that the Parker Solar Probe encountered the western flank of the SBO-CME. The anisotropic and dispersive nature of this event in a shockless local plasma gives indications that these particles are most likely accelerated remotely near the Sun by a weak shock or compression wave ahead of the SBO-CME. This event may represent direct observations of the source of the low-energy SEP seed particle population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Classical Be stars are possible products of close binary evolution, in which the mass donor becomes a hot, stripped O- or B-type subdwarf (sdO/sdB), and the mass gainer spins up and grows a disk to become a Be star. While several Be+sdO binaries have been identified, dynamical masses and other fundamental parameters are available only for a single Be+sdO system, limiting the confrontation with binary evolution models. In this work, we present direct interferometric detections of the sdO companions of three Be stars—28 Cyg, V2119 Cyg, and 60 Cyg—all of which were previously found in UV spectra. For two of the three Be+sdO systems, we present first orbits and preliminary dynamical masses of the components, revealing that one of them could be the first identified progenitor of a Be/X-ray binary with a neutron star companion. These results provide new sets of fundamental parameters that are crucially needed to establish the evolutionary status and origin of Be stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A major discovery of Parker Solar Probe (PSP) was the presence of large numbers of localized increases in the radial solar wind speed and associated sharp deflections of the magnetic field—switchbacks (SBs). A possible generation mechanism of SBs is through magnetic reconnection between open and closed magnetic flux near the solar surface, termed interchange reconnection, that leads to the ejection of flux ropes (FRs) into the solar wind. Observations also suggest that SBs undergo merging, consistent with an FR picture of these structures. The role of FR merging in controlling the structure of SBs in the solar wind is explored through direct observations, analytic analysis, and numerical simulations. Analytic analysis reveals key features of the structure of FRs and their scaling with heliocentric distance <jats:italic>R, </jats:italic>which are consistent with observations and demonstrate the critical role of merging in controlling the structure of SBs. FR merging is shown to energetically favor reductions in the strength of the wrapping magnetic field and the elongation of SBs. A further consequence is the resulting dominance of the axial magnetic field within SBs that leads to the observed characteristic sharp rotation of the magnetic field into the axial direction at the SB boundary. Finally, the radial scaling of the SB area in the FR model suggests that the observational probability of SB identification should be insensitive to <jats:italic>R</jats:italic>, which is consistent with the most recent statistical analysis of SB observations from PSP.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper, we aim to use the DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO), a future Japanese space gravitational-wave antenna sensitive to the frequency range between LISA and ground-based detectors, to provide gravitational-wave constraints on the cosmic curvature at <jats:italic>z</jats:italic> ∼ 5. In the framework of the well-known distance sum rule, the perfect redshift coverage of the standard sirens observed by DECIGO, compared with lensing observations including the source and lens from LSST, makes such cosmological-model-independent tests more natural and general. Focusing on three kinds of spherically symmetric mass distributions for the lensing galaxies, we find that the cosmic curvature is expected to be constrained with the precision of ΔΩ<jats:sub> <jats:italic>K</jats:italic> </jats:sub> ∼ 10<jats:sup>−2</jats:sup> in the early universe (<jats:italic>z</jats:italic> ∼ 5.0), improving the sensitivity of ET constraints by about a factor of 10. However, in order to investigate this further, the mass-density profiles of early-type galaxies should be properly taken into account. Specifically, our analysis demonstrates the strong degeneracy between the spatial curvature and the lens parameters, especially the redshift evolution of the power-law lens index parameter. When the extended power-law mass-density profile is assumed, the weakest constraint on the cosmic curvature can be obtained, whereas the addition of DECIGO to the combination of LSST+DECIGO does improve significantly the constraint on the luminosity–density slope and the anisotropy of the stellar velocity dispersion. Therefore, our paper highlights the benefits of synergies between DECIGO and LSST in constraining new physics beyond the standard model, which could manifest themselves through accurate determination of the cosmic curvature.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The most accurate current methods for determining the ages of open star clusters, stellar associations, and stellar streams are based on isochrone fitting or the lithium depletion boundary. We propose another method for dating these objects based on the morphology of their extended tidal tails, which have been recently discovered around several open star clusters. Assuming that the tidal tails originate from the stars released from the cluster during early gas expulsion, or that they form in the same star-forming region as the cluster (i.e., being coeval with the cluster), we derive the analytical formula for the tilt angle <jats:italic>β</jats:italic> between the long axis of the tidal tail and the orbital direction for clusters or streams on circular trajectories. Since at a given Galactocentric radius <jats:italic>β</jats:italic> is only a function of age <jats:italic>t</jats:italic> regardless of the initial properties of the cluster, we estimate the cluster age by inverting the analytical formula <jats:italic>β</jats:italic> = <jats:italic>β</jats:italic>(<jats:italic>t</jats:italic>). We illustrate the method on a sample of 12 objects, which we compiled from the literature, and we find a reasonable agreement with previous dating methods in ≈70% of the cases. This can probably be improved by taking into account the eccentricity of the orbits and by revisiting the dating methods based on stellar evolution. The proposed morphological method is suitable for relatively young clusters (age ≲300 Myr), where it provides a relative age error of the order of 10%−20% for an error in the observed tilt angle of 5°.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine the origin of dynamical friction using a nonperturbative, orbit-based approach. Unlike the standard perturbative approach, in which dynamical friction arises from the LBK torque due to pure resonances, this alternative, complementary view nicely illustrates how a massive perturber significantly changes the energies and angular momenta of field particles on near-resonant orbits, with friction arising from an imbalance between particles that gain energy and those that lose energy. We treat dynamical friction in a spherical host system as a restricted three-body problem. This treatment is applicable in the “slow” regime, in which the perturber sinks slowly and the standard perturbative framework fails due to the onset of nonlinearities. Hence, it is especially suited to investigate the origin of core-stalling: the cessation of dynamical friction in central constant-density cores. We identify three different families of near-corotation-resonant orbits that dominate the contribution to dynamical friction. Their relative contribution is governed by the Lagrange points (fixed points in the corotating frame). In particular, one of the three families, which we call Pac-Man orbits because of their appearance in the corotating frame, is unique to cored density distributions. When the perturber reaches a central core, a bifurcation of the Lagrange points drastically changes the orbital makeup, with Pac-Man orbits becoming dominant. In addition, due to relatively small gradients in the distribution function inside a core, the net torque from these Pac-Man orbits becomes positive (enhancing), thereby effectuating a dynamical buoyancy. We argue that core-stalling occurs where this buoyancy is balanced by friction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This study is focused on the observational measurement of the viewing angle of individual quasars by modeling the broadband quasar spectrum ranging from the IR to soft X-ray band. Sources are selected from various published catalogs, and their broadband quasi-simultaneous spectral data points were collected and used for modeling. We started with a COSMOS sample of Type-1 sources that have broadband photometric points. To include more data points, we cross-matched the COSMOS with the Sloan Digital Sky Survey Data Release 14 quasar catalog, and eventually we find 90 sources which have broadband data ranging from IR to soft X-ray. The broadband spectral energy distribution modeling is done in <jats:monospace>Xspec</jats:monospace> by using the <jats:monospace>optxagnf</jats:monospace> and the <jats:monospace>SKIRTOR</jats:monospace> models for the X-ray, UV, optical, and IR regimes for each source. The whole sample is divided into four bins with respect to redshift, black hole (BH) mass, and Eddington ratio with an equal number of sources in each bin. The viewing angle is estimated in each bin, and its evolution with respect to redshift, BH mass, and Eddington ratio is examined. In result, we did not find any significant evolution of viewing angle with those parameters within the 95% confidence interval. We conclude that the use of quasars in cosmology to determine the expansion rate of the universe is therefore justified, and biases are not expected.</jats:p>