Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Low-metallicity galaxies may provide key insights into the evolutionary history of galaxies. Galaxies with strong emission lines and high equivalent widths (rest-frame EW(H<jats:italic>β</jats:italic>) ≳ 30 Å) are ideal candidates for the lowest-metallicity galaxies to <jats:italic>z</jats:italic> ∼ 1. Using a Keck/DEIMOS spectral database of about 18,000 galaxies between <jats:italic>z</jats:italic> = 0.2 and <jats:italic>z</jats:italic> = 1, we search for such extreme emission-line galaxies with the goal of determining their metallicities. Using the robust direct <jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> method, we identify eight new extremely metal-poor galaxies (XMPGs) with <jats:inline-formula> <jats:tex-math> <?CDATA $12+\mathrm{log}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>12</mml:mn> <mml:mo>+</mml:mo> <mml:mi>log</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac81c7ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> O/H ≤7.65, including one at 6.949 ± 0.091, making it the lowest-metallicity galaxy reported to date at these redshifts. We also improve upon the metallicities for two other XMPGs from previous work. We investigate the evolution of H<jats:italic>β</jats:italic> using both instantaneous and continuous starburst models, finding that XMPGs are best characterized by continuous starburst models. Finally, we study the dependence on age of the buildup of metals and the emission-line strength.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A new, fast technique to measure the solar wind’s ambipolar <jats:italic>E</jats:italic> <jats:sub>∥</jats:sub> routinely with 10% precision and accuracy is demonstrated using 4 yr of 1 au electron data from the Wind 3DP experiment. The 3DP electron instrument duty cycle determines <jats:italic>E</jats:italic> <jats:sub>∥</jats:sub> ≃ 0.1 nV m<jats:sup>−1</jats:sup> from a single spectrum over much shorter time intervals than those requiring radial transits for pressure profiles. The measured weak electric field is invariably strong (in the dimensionless sense of Dreicer), with a modal value of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }=0.8$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="double-struck">E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">∥</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.8</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6871ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, and positively correlated with solar wind speed, while <jats:italic>E</jats:italic> <jats:sub>∥</jats:sub> decreases with increasing wind speed. These observations establish across all solar wind conditions the nearly equal accelerations provided by <jats:italic>E</jats:italic> <jats:sub>∥</jats:sub> and coulomb drags on thermal electrons, a central hypothesis of the Steady Electron Runaway Model (SERM) for the solar wind. Filtered <jats:italic>E</jats:italic> <jats:sub>∥</jats:sub> observations successfully recover previously reported 1 au bulk speed dependence of electron temperature gradients. The filter screens for unstructured spherically symmetric solar wind (USSSW) conditions of solar wind theory. Outside USSSW conditions much shorter scaled pressure gradients (of both signs) and stronger ∣<jats:italic>E</jats:italic> <jats:sub>∥</jats:sub>∣ are observed predominantly in corotating regimes. Consistent with modeling by Dreicer and SERM, the observed spectral hardness of electrons at suprathermal energies is positively correlated with increasing local values of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="double-struck">E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">∥</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6871ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> across the 4 yr data set. Virtually all <jats:italic>strahl</jats:italic> electrons, crucial to the electron heat flux, are shown to be confined <jats:italic>within</jats:italic> the local closed coulomb separatrix of each spectrum as determined using the locally measured value of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="double-struck">E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">∥</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6871ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Several redback and black widow millisecond pulsar binaries have episodes of flaring in X-rays and optical. We initially detected such behavior from the Fermi selected redback candidate 1FGL J0523.5–2529 during optical time-series monitoring. Triggered observations with the Neil Gehrels Swift Observatory over the next ≈100 days showed episodic flaring in X-rays with luminosity up to 8 × 10<jats:sup>33</jats:sup> erg s<jats:sup>−1</jats:sup> (∼100 times the minimum), and a comparable luminosity in the optical/UV, with similar power-law spectra of <jats:italic>f</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub> ∝ <jats:italic>ν</jats:italic> <jats:sup>−0.7</jats:sup>. These are the most luminous flares seen in any nonaccreting “spider” pulsar system, which may be related to the large size of the companion through the fraction of the pulsar wind that it or its ablated wind intercepts. Simultaneously with an optical flare, we see Balmer line and He <jats:sc>i</jats:sc> emission, not previously known in this object, which is evidence of a stellar wind that may also inhibit detection of radio pulsations. The quiescent optical light curves, while dominated by ellipsoidal modulation, show evidence of variable nonuniform temperature that could be due either to large starspots or asymmetric heating of the companion by the pulsar. This may explain a previous measurement of unusual nonzero orbital eccentricity as, alternatively, distortion of the radial-velocity curve by the surface temperature distribution of the large companion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Parker Solar Probe (PSP) has shown that the solar wind in the inner heliosphere is characterized by the quasi omnipresence of magnetic switchbacks (“switchback” hereinafter), local backward bends of magnetic field lines. Switchbacks also tend to come in patches, with a large-scale modulation that appears to have a spatial scale size comparable to supergranulation on the Sun. Here we inspect data from the first 10 encounters of PSP focusing on different time intervals when clear switchback patches were observed by PSP. We show that the switchbacks modulation, on a timescale of several hours, seems to be independent of whether PSP is near perihelion, when it rapidly traverses large swaths of longitude remaining at the same heliocentric distance, or near the radial-scan part of its orbit, when PSP hovers over the same longitude on the Sun while rapidly moving radially inwards or outwards. This implies that switchback patches must also have an intrinsically temporal modulation most probably originating at the Sun. Between two consecutive patches, the magnetic field is usually very quiescent with weak fluctuations. We compare various parameters between the quiescent intervals and the switchback intervals. The results show that the quiescent intervals are typically less Alfvénic than switchback intervals, and the magnetic power spectrum is usually shallower in quiescent intervals. We propose that the temporal modulation of switchback patches may be related to the “breathing” of emerging flux that appears in images as the formation of “bubbles” below prominences in the Hinode/SOT observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Synchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high-energy electrons accelerated at the shock front and the acceleration process. We performed a spatially resolved spectral analysis of NuSTAR and XMM-Newton observations of the young Kepler’s SNR, aiming to study in detail its nonthermal emission in hard X-rays. We selected a set of regions all around the rim of the shell and extracted the corresponding spectra. The spectra were analyzed by adopting a model of synchrotron radiation in the loss-limited regime, to constrain the dependence of the cutoff energy of the synchrotron radiation on the shock velocity. We identify two different regimes of particle acceleration, characterized by different Bohm factors. In the north, where the shock interacts with a dense circumstellar medium (CSM), we found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with the dense CSM. Our results suggest an enhanced efficiency of the acceleration process in regions where the shock–CSM interaction generates an amplified and turbulent magnetic field. By combining hard X-ray spectra with radio and <jats:italic>γ</jats:italic>-ray observations of Kepler’s SNR, we modeled the spectral energy distribution. In the light of our results we propose that the observed <jats:italic>γ</jats:italic>-ray emission is mainly hadronic and originates in the northern part of the shell.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Phosphorus is a necessary element for life on Earth, but at present, we have limited constraints on its chemistry in star- and planet-forming regions; to date, phosphorus carriers have only been detected toward a few low-mass protostars. Motivated by an apparent association between phosphorus molecule emission and outflow shocking, we used the IRAM 30 m telescope to target PN and PO lines toward seven solar-type protostars with well-characterized outflows and firmly detected phosphorus molecules in three new sources. This sample, combined with archival observations of three additional sources, enables the first exploration of the demographics of phosphorus chemistry in low-mass protostars. The sources with PN detections show evidence for strong outflow shocks based on their H<jats:sub>2</jats:sub>O 1<jats:sub>10</jats:sub>–1<jats:sub>01</jats:sub> fluxes. On the other hand, no protostellar properties or bulk outflow mechanical properties are found to correlate with the detection of PN. This implies that gas-phase phosphorus is specifically linked to shocked gas within the outflows. Still, the PN and PO line kinematics suggest an emission origin in postshocked gas rather than directly shocked material. Despite sampling a wide range of protostellar properties and outflow characteristics, we find a fairly narrow range of source-averaged PO/PN ratios (0.6–2.2) and volatile P abundances as traced by (PN+PO)/CH<jats:sub>3</jats:sub>OH (∼1%–3%). Spatially resolved observations are needed to further constrain the emission origins and environmental drivers of the phosphorus chemistry in these sources.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We observed the high-mass star-forming region G176.51+00.20 using the Five-hundred-meter Aperture Spherical radio Telescope with the 19 beam tracking observational mode. This is a pilot work of searching for neutral stellar winds traced by atomic hydrogen (i.e., H <jats:sc>i</jats:sc> winds) using the high-sensitivity H <jats:sc>i</jats:sc> line toward high-mass star-forming regions where bipolar molecular outflows have been detected with high sensitivity by Liu et al. H <jats:sc>i</jats:sc> wind was detected in this work only in Beam 1. We find here that, similar to low-mass star formation, no matter how large the inclination is, the H <jats:sc>i</jats:sc> wind is likely sufficiently strong to drive a molecular outflow. We also find that the abundance of H <jats:sc>i</jats:sc> in the H <jats:sc>i</jats:sc> wind is consistent with that of the H <jats:sc>i</jats:sc> narrow-line self-absorption (HINSA) in the same beam (i.e., Beam 1). This implies that there is probably an internal relationship between H <jats:sc>i</jats:sc> winds and HINSA. This result also reinforces the assertion that H <jats:sc>i</jats:sc> winds and detected molecular outflows are associated with each other.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the long-term evolution of two or more stellar black holes (BHs) on initially separated but unstable circular orbits around a supermassive BH (SMBH). Such a close-packed orbital configuration can naturally arise from BH migrations in the AGN disk. Dynamical instability of the orbits leads to recurring close encounters between two BHs, during which the BH separation <jats:italic>r</jats:italic> <jats:sub>p</jats:sub> becomes less than the Hill radius <jats:bold> <jats:italic>R</jats:italic> </jats:bold> <jats:sub>H</jats:sub>. In rare very close encounters, a tight merging BH binary can form with the help of gravitational wave emission. We use <jats:italic>N</jats:italic>-body simulations to study the time evolution of close encounters of various degrees of <jats:italic>closeness</jats:italic>. For a typical “SMBH+2BH” system, the averaged cumulative number of close encounters (with <jats:italic>r</jats:italic> <jats:sub>p</jats:sub> ≲ <jats:bold> <jats:italic>R</jats:italic> </jats:bold> <jats:sub>H</jats:sub>) scales approximately as ∝ <jats:italic>t</jats:italic> <jats:sup>0.5</jats:sup>. The minimum encounter separation <jats:italic>r</jats:italic> <jats:sub>p</jats:sub> follows a cumulative distribution <jats:italic>P</jats:italic>(&lt;<jats:italic>r</jats:italic> <jats:sub>p</jats:sub>) ∝ <jats:italic>r</jats:italic> <jats:sub>p</jats:sub> for <jats:italic>r</jats:italic> <jats:sub>p</jats:sub> ≪ <jats:bold> <jats:italic>R</jats:italic> </jats:bold> <jats:sub>H</jats:sub>. We obtain a semi-analytical expression for the averaged rate of binary captures that lead to BH mergers. Our results suggest that close-packed BHs in AGN disks may take a long time (≳10<jats:sup>7</jats:sup> orbits around the SMBH) to experience a sufficiently close encounter and form a bound binary. This time can be shorter if the initial BH orbits are highly aligned. The BH binary mergers produced in this scenario have high eccentricities when entering the LIGO band and broad distribution of orbital inclinations relative to the original AGN disk. We explore the effects of the gas disk and find that simple gas drags on the BHs do not necessarily lead to an enhanced BH binary capture rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the detection of 51 thermonuclear X-ray bursts observed from 4U 1636–536 by the Neutron Star Interior Composition Explorer (NICER) over the course of a 3 yr monitoring campaign. We perform time-resolved spectroscopy for 40 of these bursts and show the existence of a strong soft excess in all the burst spectra. The excess emission can be characterized by the use of a scaling factor (the <jats:italic>f</jats:italic> <jats:sub> <jats:italic>a</jats:italic> </jats:sub> method) to the persistent emission of the source, which is attributed to the increased mass accretion rate onto the neutron star due to Poynting–Robertson drag. The soft excess emission can also be characterized by the use of a model taking into account the reflection of the burst emission off the accretion disk. We also present time-resolved spectral analysis of five X-ray bursts simultaneously observed by NICER and AstroSat, which confirm the main results with even greater precision. Finally, we present evidence for Compton cooling using seven X-ray bursts observed contemporaneously with NuSTAR, by means of a correlated decrease in the hard X-ray lightcurve of 4U 1636–536 as the bursts start.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Diagnosing the solar atmospheric plasma remains one of the major challenges in solar physics. In recent years, new methods have been developed to apply the powerful concept of solar magneto-seismology (SMS) to obtain information about plasma parameters in solar structures guiding magnetohydrodynamic (MHD) waves that would otherwise be difficult to measure. This paper uses the Cartesian model of a magnetic slab placed in an asymmetric magnetic environment to generalize recently discovered SMS techniques. Utilizing the fact that the asymmetric environment changes the character of the classical kink and sausage eigenmodes, we describe two spatial seismology methods built upon this mixed character of quasi-sausage and quasi-kink modes. First, we present the amplitude ratio technique, which compares the oscillation amplitudes measured at the two boundaries of the slab, and we provide expressions to estimate the internal Alfvén speed in the thin slab and in the incompressible plasma approximations. The second main technique relies on the changed distribution of wave power throughout the slab under the effect of waveguide asymmetry. This minimum perturbation shift technique is then also utilized to provide Alfvén speed estimates that depend on the plasma and magnetic parameters of the environment, as well as the measured slab width and oscillation frequency. Finally, we perform a brief investigation of how the amplitude ratio and the minimum perturbation shift depend on the different sources of waveguide asymmetry, and illustrate our findings with numerical results.</jats:p>