Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Several massive (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub> &gt; 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), high-redshift (<jats:italic>z</jats:italic> = 8–10) galaxies have recently been discovered to contain stars with ages of several hundred million years, pushing the onset of star formation in these galaxies back to <jats:italic>z</jats:italic> ∼ 15. The very existence of stars formed so early may serve as a test for cosmological models with suppressed small-scale power (and, hence, late formation of cosmic structure). We explore the ages of the oldest stars in numerical simulations from the Cosmic Reionization On Computers project with cold dark matter (CDM) and two warm dark matter (WDM) cosmologies with 3 and 6 keV particles. There are statistically significant differences of ∼5 Myr between average stellar ages of massive galaxies in CDM and 3 keV WDM, while CDM and 6 keV WDM are statistically indistinguishable. Even this 5 Myr difference, however, is much less than current observational uncertainties on the stellar population properties of high-redshift galaxies. The age distributions of all galaxies in all cosmologies fail to produce a substantial Balmer break, although uncertainties in dust attenuation are a potentially significant factor. Finally, we assess the convergence of our simulation predictions and find that the systematic uncertainties on individual galaxy properties are comparable to the differences between cosmologies, suggesting these differences may not be numerically robust.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Global EUV waves remain a controversial phenomenon more than 20 yr after their discovery by SOHO/EIT. Although consensus is growing in the community that they are most likely large-amplitude waves or shocks, the wide variety of observations and techniques used to identify and analyze them have led to disagreements regarding their physical properties and interpretation. Here, we use a 3D magnetohydrodynamic (MHD) model of the solar corona to simulate an EUV wave event on 2009 February 13 to enable a detailed validation of the various commonly used detection and analysis techniques of global EUV waves. The simulated event exhibits comparable behavior to that of a real EUV wave event, with similar kinematic behavior and plasma parameter evolution. The kinematics of the wave are estimated via visual identification and profile analysis, with both approaches providing comparable results. We find that projection effects can affect the derived kinematics of the wave, due to the variation in fast-mode wave speed with height in the corona. Coronal seismology techniques typically used for estimates of the coronal magnetic field are also tested and found to estimate fast-mode speeds comparable to those of the model. Plasma density and temperature variations of the wave front are also derived using a regularized inversion approach and found to be consistent with observed wave events. These results indicate that global waves are best interpreted as large-amplitude waves and that they can be used to probe the coronal medium using well-defined analysis techniques.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Masses of classical Cepheids of 3–11 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> are predicted by theory but those measured clump between 3.6–5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. As a result, their mass–luminosity relation is poorly constrained, impeding our understanding of basic stellar physics and the Leavitt Law. All Cepheid masses come from the analysis of 11 binary systems, including only five that are double lined and well suited for accurate dynamical mass determination. We present a project to analyze a new, numerous group of Cepheids in double-lined binary (SB2) systems to provide mass determinations in a wide mass interval and study their evolution. We analyze a sample of 41 candidate binary LMC Cepheids spread along the <jats:italic>P</jats:italic>–<jats:italic>L</jats:italic> relation, which are likely accompanied by luminous red giants, and present indirect and direct indicators of their binarity. In a spectroscopic study of a subsample of 18 brightest candidates, for 16 we detected lines of two components in the spectra, already quadrupling the number of Cepheids in SB2 systems. Observations of the whole sample may thus lead to quadrupling all the Cepheid mass estimates available now. For the majority of our candidates, erratic intrinsic period changes dominate over the light-travel-time effect due to binarity. However, the latter may explain the periodic phase modulation for four Cepheids. Our project paves the way for future accurate dynamical mass determinations of Cepheids in the LMC, Milky Way, and other galaxies, which will potentially increase the number of known Cepheid masses even 10-fold, hugely improving our knowledge about these important stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To study acoustic wave propagation and the corresponding energy deposition in partially ionized plasmas, we use a two-fluid computational model that treats neutrals and charged particles (electrons and ions) as two separate fluids. This two-fluid model takes into account the ion–neutral collisions, ionization, and recombination, allowing us to investigate both the collisional and reactive interactions between uncoupled ions and neutrals in the plasmas. In the present numerical simulations, the initial density is specified to reach hydrostatic equilibrium, and as a comparison, chemical equilibrium is also taken into account to provide a density profile that differs from typical hydrostatic equilibrium profiles. External velocity drivers are then imposed to generate monochromatic acoustic waves. As is well known, the upward propagating acoustic waves steepen in gravitationally stratified plasmas due to the exponentially decreasing density, and they heat the plasmas in the nonlinear regimes where kinetic energy is dissipated by shock waves and collisional interactions. In particular, the lower ionization fraction resulting from the present initial chemical equilibrium significantly enhances the heating efficiency. Moreover, the ionization process absorbs a significant amount of energy, and the decoupling between ions and neutrals is also enhanced while considering ionization and recombination. Therefore, simulations without considering ionization and recombination may overestimate the overall heating effects but also underestimate the energy dissipation. The results also suggest that a more accurate ionization and recombination model could be essential for improving the modeling of partially ionized plasmas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>With an effective temperature of ≃200,000 K, KPD 0005+5106 is one of the hottest white dwarfs (WDs). ROSAT unexpectedly detected “hard” (∼1 keV) X-rays from this apparently single WD. We have obtained Chandra observations that confirm the spatial coincidence of this hard X-ray source with KPD 0005+5106. We have also obtained XMM-Newton observations of KPD 0005+5106, as well as PG 1159−035 and WD 0121−756, which are also apparently single and whose hard X-rays were detected by ROSAT at 3<jats:italic>σ</jats:italic>–4<jats:italic>σ</jats:italic> levels. The XMM-Newton spectra of the three WDs show remarkably similar shapes that can be fitted by models including a blackbody component for the stellar photospheric emission, a thermal plasma emission component, and a power-law component. Their X-ray luminosities in the 0.6–3.0 keV band range from 4 × 10<jats:sup>29</jats:sup> to 4 × 10<jats:sup>30</jats:sup> erg s<jats:sup>−1</jats:sup>. The XMM-Newton EPIC-pn soft-band (0.3–0.5 keV) light curve of KPD 0005+5106 is essentially constant, but the hard-band (0.6–3.0 keV) light curve shows periodic variations. An analysis of the generalized Lomb–Scargle periodograms for the XMM-Newton and Chandra hard-band light curves finds a convincing modulation (false-alarm probability of 0.41%) with a period of 4.7 ± 0.3 hr. Assuming that this period corresponds to a binary orbital period, the Roche radii of three viable types of companion have been calculated: M9V star, T brown dwarf, and Jupiter-like planet. Only the planet has a size larger than its Roche radius, although the M9V star and T brown dwarf may be heated by the WD and inflate past the Roche radius. Thus, all three types of companion may be donors to fuel accretion-powered hard X-ray emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present deep (265 ks) Chandra X-ray observations of PSO J352.4034−15.3373, a quasar at <jats:italic>z</jats:italic> = 5.831 that, with a radio-to-optical flux ratio of <jats:italic>R</jats:italic> &gt; 1000, is one of the radio-loudest quasars in the early universe and is the only quasar with observed extended radio jets of kiloparsec scale at <jats:italic>z</jats:italic> ≳ 6. Modeling the X-ray spectrum of the quasar with a power law, we find a best fit of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Gamma }}={1.99}_{-0.28}^{+0.29}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.99</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>0.29</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe710ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, leading to an X-ray luminosity of <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{2\mbox{--}10}={1.26}_{-0.33}^{+0.45}\times {10}^{45}\ \mathrm{erg}\ {{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>–</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.26</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.33</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.45</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>45</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em" /> <mml:mi>erg</mml:mi> <mml:mspace width="0.33em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe710ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and an X-ray to UV brightness ratio of <jats:italic>α</jats:italic> <jats:sub>OX</jats:sub> = −1.45 ± −0.11. We identify a diffuse structure 50 kpc (∼8″) to the NW of the quasar along the jet axis that corresponds to a 3<jats:italic>σ</jats:italic> enhancement in the angular density of emission and can be ruled out as a background fluctuation with a probability of <jats:italic>P</jats:italic> = 0.9985. While with few detected photons the spectral fit of the structure is uncertain, we find that it has a luminosity of <jats:italic>L</jats:italic> <jats:sub>2–10</jats:sub> ∼ 10<jats:sup>44</jats:sup> erg s<jats:sup>−1</jats:sup>. These observations therefore potentially represent the most distant quasar jet yet seen in X-rays. We find no evidence for excess X-ray emission where the previously reported radio jets are seen (which have an overall linear extent of 0.″28), and a bright X-ray point source located along the jet axis to the SE is revealed by optical and NIR imaging to not be associated with the quasar.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The unprecedented sky coverage and observing cadence of the All-Sky Automated Survey for SuperNovae (ASAS-SN) has resulted in the discovery and continued monitoring of a large sample of Galactic transients. The vast majority of these are accretion-powered dwarf nova outbursts in cataclysmic variable systems, but a small subset are thermonuclear-powered classical novae. Despite improved monitoring of the Galaxy for novae from ASAS-SN and other surveys, the observed Galactic nova rate is still lower than predictions. One way classical novae could be missed is if they are confused with the much larger population of dwarf novae. Here, we examine the properties of 1617 dwarf nova outbursts detected by ASAS-SN and compare them to classical novae. We find that the mean classical nova brightens by ∼11 mag during outburst, while the mean dwarf nova brightens by only ∼5 mag, with the outburst amplitude distributions overlapping by roughly 15%. For the first time, we show that the amplitude of an outburst and the time it takes to decline by two magnitudes from maximum are positively correlated for dwarf nova outbursts. For classical novae, we find that these quantities are negatively correlated, but only weakly, compared to the strong anticorrelation of these quantities found in some previous work. We show that, even if located at large distances, only a small number of putative dwarf novae could be misclassified as classical novae, suggesting that there is minimal confusion between these populations. Future spectroscopic follow-up of these candidates can show whether any are indeed classical novae.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery and timing of the young (age ∼28.6 kyr) pulsar PSR J0837–2454. Based on its high latitude (<jats:italic>b</jats:italic> = 98) and dispersion measure (DM = 143 pc cm<jats:sup>−3</jats:sup>), the pulsar appears to be at a <jats:italic>z</jats:italic>-height of &gt;1 kpc above the Galactic plane, but near the edge of our Galaxy. This is many times the observed scale height of the canonical pulsar population, which suggests this pulsar may have been born far out of the plane. If accurate, the young age and high <jats:italic>z</jats:italic>-height imply that this is the first pulsar known to be born from a runaway O/B star. In follow-up imaging with the Australia Telescope Compact Array (ATCA), we detect the pulsar with a flux density <jats:italic>S</jats:italic> <jats:sub>1400</jats:sub> = 0.18 ± 0.05 mJy. We do not detect an obvious supernova remnant around the pulsar in our ATCA data, but we detect a colocated, low-surface-brightness region of ∼15 extent in archival Galactic and Extragalactic All-sky MWA Survey data. We also detect colocated H<jats:italic>α</jats:italic> emission from the Southern H<jats:italic>α</jats:italic> Sky Survey Atlas. Distance estimates based on these two detections come out to ∼0.9 kpc and ∼0.2 kpc, respectively, both of which are much smaller than the distance predicted by the NE2001 model (6.3 kpc) and YMW model (&gt;25 kpc) and place the pulsar much closer to the plane of the Galaxy. If the pulsar/remnant association holds, this result also highlights the inherent difficulty in the classification of transients as “Galactic” (pulsar) or “extragalactic” (fast radio burst) toward the Galactic anticenter based solely on the modeled Galactic electron contribution to a detection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The zero point of the reddening toward the Large Magellanic Cloud (LMC) has been the subject of some dispute. Its uncertainty propagates as a systematic error for methods that measure the extragalactic distance scale through knowledge of the absolute extinction of LMC stars. In an effort to resolve this issue, we used three different methods to calibrate the most widely used metric to predict LMC extinction, the intrinsic color of the red clump, (<jats:italic>V</jats:italic> − <jats:italic>I</jats:italic>)<jats:sub> <jats:italic>RC</jats:italic>,0</jats:sub>, for the inner ∼3° of that galaxy. The first approach was to empirically calibrate the color zero points of the BaSTI isochrones over a wide metallicity range of Δ[Fe/H] ≈ 1.10 using measurements of red clump stars in 47 Tuc, the solar neighborhood, and NGC 6791. From these efforts, we also measure these properties of the solar neighborhood red clump, (<jats:italic>V</jats:italic> − <jats:italic>I</jats:italic>, <jats:italic>G</jats:italic> <jats:sub> <jats:italic>BP</jats:italic> </jats:sub> − <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>, <jats:italic>G</jats:italic> − <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>, <jats:italic>G</jats:italic> <jats:sub> <jats:italic>RP</jats:italic> </jats:sub> − <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>, <jats:italic>J</jats:italic> − <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>, <jats:italic>H</jats:italic> − <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>, <jats:italic>M</jats:italic> <jats:sub> <jats:italic>I</jats:italic> </jats:sub>, <jats:italic>M</jats:italic> <jats:sub> <jats:italic>Ks</jats:italic> </jats:sub>)<jats:sub> <jats:italic>RC</jats:italic>,0</jats:sub> = (1.02, 2.75, 2.18, 1.52, 0.64, 0.15, −0.23, −1.63). The second and third methods were to compare the observed colors of the red clump to those of Cepheids and RR Lyrae in the LMC. With these three methods, we estimated the intrinsic color of the red clump of the LMC to be (<jats:italic>V</jats:italic> − <jats:italic>I</jats:italic>)<jats:sub> <jats:italic>RC</jats:italic>,0,LMC</jats:sub> = {≈<jats:bold>0.93</jats:bold>, 0.91 ± 0.02, 0.89 ± 0.02}, respectively, and similarly, using the first and third methods, we estimated (<jats:italic>V</jats:italic> − <jats:italic>I</jats:italic>)<jats:sub> <jats:italic>RC</jats:italic>,0,SMC</jats:sub> = {≈<jats:bold>0.85</jats:bold>, 0.84 ± 0.02}, respectively, for the Small Magellanic Cloud. We estimate the luminosities to be <jats:italic>M</jats:italic> <jats:sub> <jats:italic>I</jats:italic>,<jats:italic>RC</jats:italic>,LMC</jats:sub> = −0.26 and <jats:italic>M</jats:italic> <jats:sub> <jats:italic>I</jats:italic>,<jats:italic>RC</jats:italic>,SMC</jats:sub> = −0.37. We show that this has important implications for recent calibrations of the tip of the red giant branch in the Magellanic Clouds used to measure <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using magnetospheric multiscale high-resolution measurements, we present the first comprehensive investigation of electron vorticity developing at earthward-propagating dipolarization fronts (DFs). Superposed epoch analysis reveals that electron vorticity increases at and behind the DFs, with its average magnitude slightly larger than lower hybrid frequency, indicating that vorticity is related to Hall dynamics at the DFs. Vorticity at the DFs exhibits clear anisotropy, <jats:italic>ω</jats:italic> <jats:sub>⊥</jats:sub> &gt; <jats:italic>ω</jats:italic> <jats:sub>∥</jats:sub>, where <jats:italic>ω</jats:italic> <jats:sub>⊥</jats:sub>, <jats:italic>ω</jats:italic> <jats:sub>∥</jats:sub> are the components perpendicular and parallel to local magnetic field, respectively. Parametric dependence analysis shows that electron vorticity is well anticorrelated with electron density. We find that in a statistical sense, vorticity-induced magnetic field perturbations are not significant, although in a few cases vorticity can generate intense magnetic field perturbations. This study can improve our current understanding of the DF dynamics.</jats:p>