Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Solar flares have been linked to some of the most significant space weather hazards at Earth. These hazards, including radio blackouts and energetic particle events, can start just minutes after the flare onset. Therefore, it is of great importance to identify and predict flare events. In this paper we introduce the Detection and EUV Flare Tracking (DEFT) tool, which allows us to identify flare signatures and their precursors using high spatial and temporal resolution extreme-ultraviolet (EUV) solar observations. The unique advantage of DEFT is its ability to identify small but significant EUV intensity changes that may lead to solar eruptions. Furthermore, the tool can identify the location of the disturbances and distinguish events occurring at the same time in multiple locations. The algorithm analyzes high temporal cadence observations obtained from the Solar Ultraviolet Imager instrument aboard the GOES-R satellite. In a study of 61 flares of various magnitudes observed in 2017, the “main” EUV flare signatures (those closest in time to the X-ray start time) were identified on average 6 minutes early. The “precursor” EUV signatures (second-closest EUV signatures to the X-ray start time) appeared on average 14 minutes early. Our next goal is to develop an operational version of DEFT and to simulate and test its real-time use. A fully operational DEFT has the potential to significantly improve space weather forecast times.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Establishing the spatial extents and the nature of the outer stellar populations of dwarf galaxies is necessary for the determination of their total masses, current dynamical states, and past evolution. We here describe our investigation of the outer stellar content of the Boötes I ultra-faint dwarf galaxy, a satellite of the the Milky Way. We identify candidate member blue horizontal branch and blue straggler stars of Boötes I, both tracers of the underlying ancient stellar population, using a combination of multiband Pan-STARRS photometry and Gaia astrometry. We find a total of twenty-four candidate blue horizontal branch member stars with apparent magnitudes and proper motions consistent with membership of Boötes I, nine of which reside at projected distances beyond the nominal King profile tidal radius derived from earlier fits to photometry. We also identify four blue straggler stars of appropriate apparent magnitude to be at the distance of Boötes I, but all four are too faint to have high-quality astrometry from Gaia. The outer blue horizontal branch stars that we have identified confirm that the spatial distribution of the stellar population of Boötes I is quite extended. The morphology on the sky of these outer envelope candidate member stars is evocative of tidal interactions, a possibility that we explore further with simple dynamical models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Particle acceleration behind a shock wave due to interactions between magnetic islands in the heliosphere has attracted attention in recent years. The downstream acceleration may yield a continuous increase of particle flux downstream of the shock wave. Although it is not obvious how the downstream magnetic islands are produced, it has been suggested that current sheets are involved in the generation of magnetic islands due to their interaction with a shock wave. We perform 2D hybrid kinetic simulations to investigate the interaction between multiple current sheets and a shock wave. In the simulation, current sheets are compressed by the shock wave and a tearing instability develops at the compressed current sheets downstream of the shock. As the result of this instability, the electromagnetic fields become turbulent and magnetic islands form well downstream of the shock wave. We find a “post-cursor” region in which the downstream flow speed normal to the shock wave in the downstream rest frame is decelerated to ∼ 1<jats:italic>V</jats:italic> <jats:sub>A</jats:sub> immediately behind the shock wave, where <jats:italic>V</jats:italic> <jats:sub>A</jats:sub> is the upstream Alfvén speed. The flow speed then gradually decelerates to 0 accompanied by the development of the tearing instability. We also observe an efficient production of energetic particles above 100 <jats:italic>E</jats:italic> <jats:sub>0</jats:sub> during the development of the instability some distance downstream of the shock wave, where <jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{0}={m}_{p}{V}_{{\rm{A}}}^{2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msub> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> </mml:msub> <mml:msubsup> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">A</mml:mi> </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="apjac2e06ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:italic>m</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub> is the proton mass. This feature corresponds to Voyager observations showing that the anomalous cosmic-ray intensity increase begins some distance downstream of the heliospheric termination shock.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The astrophysical sites where <jats:italic>r</jats:italic>-process elements are synthesized remain mysterious: it is clear that neutron star mergers (kilonovae (KNe)) contribute, and some classes of core-collapse supernovae (SNe) are also possible sources of at least the lighter <jats:italic>r</jats:italic>-process species. The discovery of <jats:sup>60</jats:sup>Fe on the Earth and Moon implies that one or more astrophysical explosions have occurred near the Earth within the last few million years, probably SNe. Intriguingly, <jats:sup>244</jats:sup>Pu has now been detected, mostly overlapping with <jats:sup>60</jats:sup>Fe pulses. However, the <jats:sup>244</jats:sup>Pu flux may extend to before 12 Myr ago, pointing to a different origin. Motivated by these observations and difficulties for <jats:italic>r</jats:italic>-process nucleosynthesis in SN models, we propose that ejecta from a KN enriched the giant molecular cloud that gave rise to the Local Bubble, where the Sun resides. Accelerator mass spectrometry (AMS) measurements of <jats:sup>244</jats:sup>Pu and searches for other live isotopes could probe the origins of the <jats:italic>r</jats:italic>-process and the history of the solar neighborhood, including triggers for mass extinctions, e.g., that at the end of the Devonian epoch, motivating the calculations of the abundances of live <jats:italic>r</jats:italic>-process radioisotopes produced in SNe and KNe that we present here. Given the presence of <jats:sup>244</jats:sup>Pu, other <jats:italic>r</jats:italic>-process species such as <jats:sup>93</jats:sup>Zr, <jats:sup>107</jats:sup>Pd, <jats:sup>129</jats:sup>I, <jats:sup>135</jats:sup>Cs, <jats:sup>182</jats:sup>Hf, <jats:sup>236</jats:sup>U, <jats:sup>237</jats:sup>Np, and <jats:sup>247</jats:sup>Cm should be present. Their abundances and well-resolved time histories could distinguish between the SN and KN scenarios, and we discuss prospects for their detection in deep-ocean deposits and the lunar regolith. We show that AMS <jats:sup>129</jats:sup>I measurements in Fe–Mn crusts already constrain a possible nearby KN scenario.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of pulsations in the extremely low-mass (ELM), likely helium-core white dwarf GD 278 via ground- and space-based photometry. GD 278 was observed by the Transiting Exoplanet Survey Satellite (TESS) in Sector 18 at a 2 minute cadence for roughly 24 days. The TESS data reveal at least 19 significant periodicities between 2447 and 6729 s, one of which is the longest pulsation period ever detected in a white dwarf. Previous spectroscopy found that this white dwarf is in a 4.61 hr orbit with an unseen &gt;0.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> companion and has <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> = 9230 ± 100 K and <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}g=6.627\pm 0.056$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>g</mml:mi> <mml:mo>=</mml:mo> <mml:mn>6.627</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.056</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2d28ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, which corresponds to a mass of 0.191 ± 0.013 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Patterns in the TESS pulsation frequencies from rotational splittings appear to reveal a stellar rotation period of roughly 10 hr, making GD 278 the first ELM white dwarf with a measured rotation rate. The patterns inform our mode identification for asteroseismic fits, which, unfortunately, do not reveal a global best-fit solution. Asteroseismology reveals two main solutions roughly consistent with the spectroscopic parameters of this ELM white dwarf, but with vastly different hydrogen-layer masses; future seismic fits could be further improved by using the stellar parallax. GD 278 is now the tenth known pulsating ELM white dwarf; it is only the fifth known to be in a short-period binary, but is the first with extended, space-based photometry.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We determine radial velocities and mass flow rates in a sample of 54 local spiral galaxies by modeling high-resolution and high-sensitivity data of the atomic hydrogen emission line. We found that, although radial inflow motions seem to be slightly preferred over outflow motions, their magnitude is generally small. Most galaxies show radial flows of only a few km s<jats:sup>−1</jats:sup> throughout their H <jats:sc>i</jats:sc> disks, either inward or outward, without any clear increase in magnitude in the outermost regions, as we would expect for continuous radial accretion. Gas mass flow rates for most galaxies are less than 1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. Over the entire sample, we estimated an average inflow rate of 0.3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> outside the optical disk and of 0.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> in the outskirts of the H <jats:sc>i</jats:sc> disks. These inflow rates are about 5–10 times smaller than the average star formation rate of 1.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. Our study suggests that there is no clear evidence for systematic radial accretion inflows that alone could feed and sustain the star formation process in the inner regions of local spiral galaxies at its current rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recently, two photons from the Crab Nebula with energy of approximately 1 PeV were detected by the Large High Altitude Air Shower Observatory (LHAASO), opening an ultrahigh-energy window for studying pulsar wind nebulae (PWNe). Remarkably, the LHAASO spectrum at the highest-energy end shows a possible hardening, which could indicate the presence of a new component. A two-component scenario with a main electron component and a secondary proton component has been proposed to explain the whole spectrum of the Crab Nebula, requiring a proton energy of 10<jats:sup>46</jats:sup>–10<jats:sup>47 </jats:sup>erg remaining in the present Crab Nebula. In this paper, we study the energy content of relativistic protons in pulsar winds using the LHAASO data of the Crab Nebula, considering the effect of diffusive escape of relativistic protons. Depending on the extent of the escape of relativistic protons, the total energy of protons lost in the pulsar wind could be 10–100 times larger than that remaining in the nebula presently. We find that the current LHAASO data allow up to (10–50)% of the spindown energy of pulsars being converted into relativistic protons. The escaping protons from PWNe could make a considerable contribution to the cosmic-ray flux of 10–100 PeV. We also discuss the leptonic scenario for the possible spectral hardening at PeV energies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Orion Nebula Cluster (ONC) is the nearest dense star-forming region at ∼400 pc away, making it an ideal target to study the impact of high stellar density and proximity to massive stars (the Trapezium) on protoplanetary disk evolution. The OMC1 molecular cloud is a region of high extinction situated behind the Trapezium in which actively forming stars are shielded from the Trapezium’s strong radiation. In this work, we survey disks at high resolution with Atacama Large Millimeter/submillimeter Array at three wavelengths with resolutions of 0.″095 (3 mm; Band 3), 0.″048 (1.3 mm; Band 6), and 0.″030 (0.85 mm; Band 7) centered on radio Source I. We detect 127 sources, including 15 new sources that have not previously been detected at any wavelength. 72 sources are spatially resolved at 3 mm, with sizes from ∼8–100 au. We classify 76 infrared-detected sources as foreground ONC disks and the remainder as embedded OMC1 disks. The two samples have similar disk sizes, but the OMC1 sources have a dense and centrally concentrated spatial distribution, indicating they may constitute a spatially distinct subcluster. We find smaller disk sizes and a lack of large (&gt;75 au) disks in both our samples compared to other nearby star-forming regions, indicating that environmental disk truncation processes are significant. While photoevaporation from nearby massive Trapezium stars may account for the smaller disks in the ONC, the embedded sources in OMC1 are hidden from this radiation and thus must truncated by some other mechanism, possibly dynamical truncation or accretion-driven contraction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Blazar PG 1553+113 is thought to be a host of supermassive black hole binary system. A 2.2 yr quasi-periodicity in the <jats:italic>γ</jats:italic>-ray light curve was detected, possibly a result of jet precession. Motivated by the previous studies based on the <jats:italic>γ</jats:italic>-ray data, we analyzed the X-ray light curve and spectra observed during 2012–2020. The 2.2 yr quasi-periodicity might be consistent with the main-flare recurrence in the X-ray light curve. When a weak rebrightening in the <jats:italic>γ</jats:italic>-ray was observed, a corresponding relatively strong brightening in the X-ray light curve can be identified. The <jats:italic>harder-when-brighter</jats:italic> tendency in both X-ray main and weak flares was shown, as well as a weak <jats:italic>softer-when-brighter</jats:italic> behavior for the quiescent state. We explore the possibility that the variability in the X-ray band can be interpreted with two-jet precession scenario. Using the relation between jets and accretion disks, we derive the primary black hole mass ≃3.47 × 10<jats:sup>8</jats:sup> <jats:italic> M</jats:italic> <jats:sub>☉</jats:sub> and mass of the secondary one ≃1.40 × 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub>, and their mass ratio ∼0.41.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present and publicly release (<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.gclasshst.com" xlink:type="simple">www.gclasshst.com</jats:ext-link>) the first spatially resolved H<jats:italic>α</jats:italic> maps of star-forming cluster galaxies at <jats:italic>z</jats:italic> ∼ 1, made possible with the Wide Field Camera 3 (WFC3) G141 grism on the Hubble Space Telescope (HST). Using a similar but updated method to 3D-HST in the field environment, we stack the H<jats:italic>α</jats:italic> maps in bins of stellar mass, measure the half-light radius of the H<jats:italic>α</jats:italic> distribution, and compare it to the stellar continuum. The ratio of the H<jats:italic>α</jats:italic> to stellar continuum half-light radius, <jats:inline-formula> <jats:tex-math> <?CDATA $R[{\rm{H}}\alpha /{\rm{C}}]=\tfrac{{R}_{\mathrm{eff},{\rm{H}}\alpha }}{{R}_{\mathrm{eff},\mathrm{Cont}}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>R</mml:mi> <mml:mo stretchy="false">[</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo stretchy="false">]</mml:mo> <mml:mo>=</mml:mo> <mml:mstyle displaystyle="false"> <mml:mfrac> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> <mml:mo>,</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> <mml:mo>,</mml:mo> <mml:mi>Cont</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:mfrac> </mml:mstyle> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac26c3ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, is smaller in the clusters by (6 ± 9)%, but statistically consistent within 1<jats:italic>σ</jats:italic> uncertainties. A negligible difference in <jats:italic>R</jats:italic>[H<jats:italic>α</jats:italic>/C] with environment is surprising, given the higher quenched fractions in the clusters relative to the field. We postulate that the combination of high quenched fractions and no change in <jats:italic>R</jats:italic>[H<jats:italic>α</jats:italic>/C] with environment can be reconciled if environmental quenching proceeds rapidly. We investigate this hypothesis by performing similar analysis on the spectroscopically confirmed, recently quenched cluster galaxies. 87% have H<jats:italic>α</jats:italic> detections, with star formation rates 8 ± 1 times lower than star-forming cluster galaxies of similar stellar mass. Importantly, these galaxies have an <jats:italic>R</jats:italic>[H<jats:italic>α</jats:italic>/C] that is (81 ± 8)% smaller than coeval star-forming field galaxies at fixed stellar mass. This suggests the environmental quenching process occurred outside-in. We conclude that disk truncation due to ram pressure stripping is occurring in cluster galaxies at <jats:italic>z</jats:italic> ∼ 1, but more rapidly and/or efficiently than in <jats:italic>z</jats:italic> ≲ 0.5 clusters, such that the effects on <jats:italic>R</jats:italic>[H<jats:italic>α</jats:italic>/C] become observable just after the cluster galaxy has recently quenched.</jats:p>