Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We report a new, plasmoid-fed scenario for the formation of an eruptive prominence (PF<jats:sup>2</jats:sup>), involving reconnection and condensation. We use grid-adaptive resistive two-and-a-half-dimensional magnetohydrodynamic simulations in a chromosphere-to-corona setup to resolve this plasmoid-fed scenario. We study a preexisting flux rope (FR) in the low corona that suddenly erupts due to catastrophe, which also drives a fast shock above the erupting FR. A current sheet (CS) forms underneath the erupting FR, with chromospheric matter squeezed into it. The plasmoid instability occurs and multiple magnetic islands appear in the CS once the Lundquist number reaches ∼3.5 × 10<jats:sup>4</jats:sup>. The remnant chromospheric matter in the CS is then transferred to the FR by these newly formed magnetic islands. The dense and cool mass transported by the islands accumulates in the bottom of the FR, thereby forming a prominence during the eruption phase. More coronal plasma continuously condenses into the prominence due to the thermal instability as the FR rises. Due to the fine structure brought in by the PF<jats:sup>2</jats:sup> process, the model naturally forms filament threads, aligned above the polarity inversion line. Synthetic views at our resolution of 15 km show many details that may be verified in future high-resolution observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present XMM-Newton X-ray observations of nine confirmed lensed quasars at 1 ≲ <jats:italic>z</jats:italic> ≲ 3 identified by the Gaia Gravitational Lens program. Eight systems are strongly detected, with 0.3–8.0 keV fluxes <jats:italic>F</jats:italic> <jats:sub>0.3−8.0</jats:sub> ≳ 5 ×10<jats:sup>−14</jats:sup> erg cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>. Modeling the X-ray spectra with an absorbed power law, we derive power-law photon indices and 2–10 keV luminosities for the eight detected quasars. In addition to presenting sample properties for larger quasar population studies and for use in planning for future caustic-crossing events, we also identify three quasars of interest: a quasar that shows evidence of flux variability from previous ROSAT observations, the most closely separated individual lensed sources resolved by XMM-Newton, and one of the X-ray brightest quasars known at <jats:italic>z</jats:italic> &gt; 3. These sources represent the tip of the discoveries that will be enabled by SRG/eROSITA.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Young stars are highly variable in the X-ray regime. In particular, bright X-ray flares can substantially enhance ionization in the surrounding protoplanetary disk. Since disk chemical evolution is impacted by ionization, X-ray flares have the potential to fundamentally alter the chemistry of planet-forming regions. We present two-dimensional disk chemical models that incorporate a stochastic X-ray flaring module, named XGEN, and examine the flares’ overall chemical impact compared to models that assume a constant X-ray flux. We examine the impact of 500 yr of flaring events and find global chemical changes on both short timescales (days) in response to discrete flaring events and long timescales (centuries) in response to the cumulative impact of many flares. Individual X-ray flares most strongly affect small gas-phase cations, where a single flare can temporarily enhance the abundance of species such as <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{3}^{+}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac549fieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, HCO<jats:sup>+</jats:sup>, CH<jats:sub>3</jats:sub> <jats:sup>+</jats:sup>, and C<jats:sup>+</jats:sup>. We find that flares can also drive chemistry out of “steady state” over longer time periods, where the disk-integrated abundance of some species, such as O and O<jats:sub>2</jats:sub>, changes by a few percent over the 500 yr model. We also explore whether the specific history of X-ray flaring events (randomly drawn but from the same energy distribution) impacts the chemical evolution and find that it does not. Finally, we examine the impact of X-ray flares on the electron fraction. While most molecules modeled are not highly sensitive to flares, certain species, including observable molecules, are very reactive to the dynamic environment of a young star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of HCN and HCO<jats:sup>+</jats:sup> have been carried out toward 13 planetary nebulae (PNe) using the facilities of the Arizona Radio Observatory (ARO). These nebulae represent a wide range of morphologies and ages (∼2000–28,000 yr). For both molecules, the <jats:italic>J</jats:italic> = 1 → 0 transitions at 88–89 GHz and the <jats:italic>J</jats:italic> = 3 → 2 lines at 265–267 GHz were measured, together with CO lines (<jats:italic>J</jats:italic> = 1 → 0, 2 → 1, and 3 → 2, depending on the source), using the ARO 12 m and Submillimeter Telescopes. HCN and HCO<jats:sup>+</jats:sup> were detected with at least one transition in 10 nebulae: He 2-459, Hu 1-1, K3-52, K3-65, M1-8, M1-40, M1-59, M2-53, M4-17, and NGC 6445. HCO<jats:sup>+</jats:sup> was additionally identified via two transitions in Na 2. Some observed line profiles were complex, with multiple velocity components tracing varied outflows. From radiative transfer modeling, column densities were established for HCN and HCO<jats:sup>+</jats:sup>: <jats:italic>N</jats:italic> <jats:sub>tot</jats:sub>(HCN) = 0.005–1.1 × 10<jats:sup>14</jats:sup> and <jats:italic>N</jats:italic> <jats:sub>tot</jats:sub>(HCO<jats:sup>+</jats:sup>) = 0.008–9.5 × 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup>. Gas densities of <jats:italic>n</jats:italic>(H<jats:sub>2</jats:sub>) ∼ 10<jats:sup>5</jats:sup>–10<jats:sup>7</jats:sup> cm<jats:sup>−3</jats:sup> were also determined for all PNe. Fractional abundances with respect to H<jats:sub>2</jats:sub>, calculated using CO as a proxy, are <jats:italic>f</jats:italic>(HCN) ∼ 0.2–1.5 × 10<jats:sup>−7</jats:sup> and <jats:italic>f</jats:italic>(HCO<jats:sup>+</jats:sup>) ∼ 0.3–5.1 × 10<jats:sup>−8</jats:sup>. The abundances of HCN and HCO<jats:sup>+</jats:sup> did not significantly vary with nebular age to 28,000 yr. Combined with previous observations, at least 30 PNe contain HCN and/or HCO<jats:sup>+</jats:sup>, indicating that polyatomic molecules are common constituents of these objects. The data strongly support a scenario where dense ejecta from PNe seed the interstellar medium with molecular material.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The level of central segregation of Blue Straggler stars has proved to be an excellent tracer of the dynamical evolution of old star clusters (the so-called “dynamical clock”), both in the Milky Way and in the Large Magellanic Cloud. The <jats:italic>A</jats:italic> <jats:sup>+</jats:sup> parameter, used to measure the Blue Stragglers degree of segregation, has in fact been found to strongly correlate with the parent cluster central relaxation time. Here, we have studied the Blue Straggler population of two young stellar systems in the Small Magellanic Cloud, namely NGC 339 (which is 6 Gyr old) and NGC 419 (with an age of only 1.5 Gyr), in order to study their dynamical state. Thanks to multi-epoch, high angular resolution Hubble Space Telescope observations available for both clusters, we took advantage of the stellar proper motions measured in the regions of the two systems and we selected a population of likely cluster members, removing the strong contamination from Small Magellanic Cloud stars. This enabled us to study, with unprecedented accuracy, the radial distribution of Blue Stragglers in these two extra-Galactic clusters and to measure their dynamical age. As expected for such young clusters, we found that both systems are poorly evolved from the dynamical point of view, also fully confirming that the <jats:italic>A</jats:italic> <jats:sup>+</jats:sup> parameter is a sensitive “clock hand” even in the dynamically young regime.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The gas-phase reaction of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{O}}+{{\rm{H}}}_{3}^{+}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">O</mml:mi> <mml:mo>+</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac41ceieqn1.gif" xlink:type="simple" /> </jats:inline-formula> has two exothermic product channels: OH<jats:sup>+</jats:sup> + H<jats:sub>2</jats:sub> and H<jats:sub>2</jats:sub>O<jats:sup>+</jats:sup> + H. In the present study, we analyze experimental data from a merged-beams measurement to derive thermal rate coefficients resolved by product channel for the temperature range from 10 to 1000 K. Published astrochemical models either ignore the second product channel or apply a temperature-independent branching ratio of 70% versus 30% for the formation of OH<jats:sup>+</jats:sup> + H<jats:sub>2</jats:sub> versus H<jats:sub>2</jats:sub>O<jats:sup>+</jats:sup> + H, respectively, which originates from a single experimental data point measured at 295 K. Our results are consistent with this data point, but show a branching ratio that varies with temperature reaching 58% versus 42% at 10 K. We provide recommended rate coefficients for the two product channels for two cases, one where the initial fine-structure population of the O(<jats:sup>3</jats:sup> <jats:italic>P</jats:italic> <jats:sub> <jats:italic>J</jats:italic> </jats:sub>) reactant is in its <jats:italic>J</jats:italic> = 2 ground state and the other one where it is in thermal equilibrium.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Methane is typically thought to be formed in the solid state on top of cold interstellar icy grain mantles via the successive atomic hydrogenation of a carbon atom. In the current work we investigate the role of molecular hydrogen in the CH<jats:sub>4</jats:sub> reaction network. We make use of an ultrahigh vacuum cryogenic setup combining an atomic carbon atom beam with atomic and/or molecular beams of hydrogen and deuterium on a water ice. These experiments lead to the formation of methane isotopologues detected in situ through reflection absorption infrared spectroscopy. Most notably, CH<jats:sub>4</jats:sub> is experimentally formed by combining C atoms with only H<jats:sub>2</jats:sub> on amorphous solid water, albeit more slowly than in experiments where H atoms are also present. Furthermore, CH<jats:sub>2</jats:sub>D<jats:sub>2</jats:sub> is detected in an experiment involving C atoms with H<jats:sub>2</jats:sub> and D<jats:sub>2</jats:sub> on H<jats:sub>2</jats:sub>O ice. CD<jats:sub>4</jats:sub>, however, is only formed when D atoms are present in the experiment. These findings have been rationalized by means of computational and theoretical chemical insights. This leads to the following conclusions: (a) the reaction C + H<jats:sub>2</jats:sub> → CH<jats:sub>2</jats:sub> takes place, although it is not barrierless for all binding sites on water, (b) the reaction CH + H<jats:sub>2</jats:sub> → CH<jats:sub>3</jats:sub> is barrierless, but has not yet been included in astrochemical models, (c) the reactions CH<jats:sub>2</jats:sub> + H<jats:sub>2</jats:sub> → CH<jats:sub>3</jats:sub> + H and CH<jats:sub>3</jats:sub> + H<jats:sub>2</jats:sub> → CH<jats:sub>4</jats:sub> + H can take place only via a tunneling mechanism, and (d) molecular hydrogen possibly plays a more important role in the solid-state formation of methane than assumed so far.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Deep rest-optical observations are required to accurately constrain the stellar populations of <jats:italic>z</jats:italic> ∼ 8 galaxies. Due to significant limitations in the availability of such data for statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. To revolutionize the present characterization of <jats:italic>z</jats:italic> ∼ 8 galaxies, we exploit the ultradeep (∼27 mag, 3<jats:italic>σ</jats:italic>) Spitzer/Infrared Array Camera (IRAC) 3.6 and 4.5 <jats:italic>μ</jats:italic>m data, probing the rest-frame optical at <jats:italic>z</jats:italic> ∼ 8, over ∼200 arcmin<jats:sup>2</jats:sup> of the GOODS fields from the recently completed GOODS Re-ionization Era wide-Area Treasury from Spitzer program (GREATS), combined with observations in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)/Ultra Deep Survey (UDS) and CANDELS/Cosmic Evolution Survey (COSMOS) fields. We stacked ≳100 <jats:italic>z</jats:italic> ∼ 8 Lyman-break galaxies in four bins of UV luminosity (<jats:italic>M</jats:italic> <jats:sub>UV</jats:sub> ∼ −20.7 to −18.4 mag) and study their <jats:italic>H</jats:italic> <jats:sub>160</jats:sub> − [3.6] and [3.6]–[4.5] colors. We find young ages (≲100 Myr) for the three faintest stacks, inferred from their blue <jats:italic>H</jats:italic> <jats:sub>160</jats:sub> − [3.6] ∼ 0 mag colors, consistent with a negative Balmer break. Meanwhile, the redder <jats:italic>H</jats:italic> <jats:sub>160</jats:sub> − [3.6] color seen in the brightest stack is suggestive of slightly older ages. We explored the existence of a correlation between the UV luminosity and age, and find either no trend or fainter galaxies being younger. The stacked SEDs also exhibit very red [3.6]–[4.5] ∼ 0.5 mag colors, indicative of intense [O <jats:sc>iii</jats:sc>]+H<jats:italic>β</jats:italic> nebular emission and star formation rate (SFR). The correspondingly high specific SFRs, sSFR ≳10 Gyr<jats:sup>−1</jats:sup>, are consistent with recent determinations at similar redshifts and higher luminosities, and support the coevolution between the sSFR and the specific halo mass accretion rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a high-resolution (2.5 au) multiband analysis of the protoplanetary disk around TW Hya using Atacama Large Millimeter/submillimeter Array (ALMA) long baseline data at Bands 3, 4, 6, and 7. We aim to reconstruct a high-sensitivity millimeter continuum image and revisit the spectral index distribution. The imaging is performed by combining new ALMA data at Bands 4 and 6 with available archive data. Two methods are employed to reconstruct the images: multifrequency synthesis (MFS) and the fiducial image-oriented method, where each band is imaged separately and the frequency dependence is fitted pixel by pixel. We find that MFS imaging with a second-order Taylor expansion can reproduce the frequency dependence of the continuum emission between Bands 3 and 7 in a manner consistent with previous studies, and that it is a reasonable method for reconstructing the spectral index map. The image-oriented method provides a spectral index map consistent with the MFS imaging, but with a two times lower resolution. Mock observations of an intensity model were conducted to validate the images from the two methods. We find that the MFS imaging provides a high-resolution spectral index distribution with an uncertainty of &lt;10%. Using the submillimeter spectrum reproduced from our MFS images, we directly calculate the optical depth, power-law index of the dust opacity coefficient (<jats:italic>β</jats:italic>), and dust temperature. The derived parameters are consistent with previous works, and the enhancement of <jats:italic>β</jats:italic> within the intensity gaps is also confirmed, supporting a deficit of millimeter-sized grains within the gaps.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Understanding how the Galactic magnetic field threads the multiphase interstellar medium (ISM) remains a considerable challenge, as different magnetic field tracers probe dissimilar phases and field components. We search for evidence of a common magnetic field shared between the ionized and neutral ISM by comparing 1.4 GHz radio continuum polarization and H <jats:sc>i</jats:sc> line emission from the Galactic Arecibo <jats:italic>L</jats:italic>-Band Feed Array Continuum Transit Survey (GALFACTS) and Galactic Arecibo <jats:italic>L</jats:italic>-Band Feed Array H <jats:sc>i</jats:sc> (GALFA-H <jats:sc>i</jats:sc>) survey, respectively. We compute the polarization gradient of the continuum emission and search for associations with diffuse/translucent H <jats:sc>i</jats:sc> structures. The polarization gradient is sensitive to changes in the integrated product of the thermal electron density and line-of-sight field strength (<jats:italic>B</jats:italic> <jats:sub>∥</jats:sub>) in warm ionized gas, while narrow H <jats:sc>i</jats:sc> structures highlight the plane-of-sky field orientation in cold neutral gas. We identified one region in the high Galactic latitude Arecibo sky, G216+26 centered on (<jats:italic>ℓ</jats:italic>, <jats:italic>b</jats:italic>) ∼ (216°, +26°), containing filaments in the polarization gradient that are aligned with narrow H <jats:sc>i</jats:sc> structures roughly parallel to the Galactic plane. We present a comparison of multiphase observations and magnetic field tracers of this region, demonstrating that the warm ionized and cold neutral media are connected likely via a common magnetic field. We quantify the physical properties of a polarization gradient filament associated with H<jats:italic>α</jats:italic> emission, measuring a line-of-sight field strength <jats:italic>B</jats:italic> <jats:sub>∥</jats:sub> = 6 ± 4 <jats:italic>μ</jats:italic>G and a plasma beta <jats:inline-formula> <jats:tex-math> <?CDATA $\beta ={2.1}_{-2.1}^{+3.1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>β</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3.1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac400dieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. We discuss the lack of widespread multiphase magnetic field alignments and consider whether this region is associated with a short-timescale or physically rare phenomenon. This work highlights the utility of multitracer analyses for understanding the magnetized ISM.</jats:p>