Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We carry out a suite of simulations of the evolution of cosmic-ray (CR) driven, radiatively cooled cold clouds embedded in hot material, as found in galactic outflows. In such interactions, CRs stream toward the cloud at the Alfvén speed, which decreases dramatically at the cloud boundary, leading to a bottleneck in which pressure builds up in front of the cloud. At the same time, CRs stream along the sides of the cloud, forming a boundary layer where large filaments develop. Shear in this boundary layer is the primary mode of cloud destruction, which is relatively slow in all cases, but slowest in the cases with the lowest Alfvén speeds. Thus, the CR pressure in the bottleneck region has sufficient time to accelerate the cold clouds efficiently. Furthermore, radiative cooling has relatively little impact on these interactions. Our simulations are two-dimensional and limited by a simplified treatment of CR dynamics, the neglect of CR heating, and an idealized magnetic field geometry. Nevertheless, our results suggest that CRs, when acting as the primary source of momentum input, are capable of accelerating clouds to velocities comparable to those observed in galaxy outflows.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We observed the W51 high-mass star-forming complex with the Atacama Large Millimeter/submillimeter Array’s longest-baseline configurations, achieving an angular resolution of ∼20 mas, corresponding to a linear resolution of ∼100 au at <jats:italic>D</jats:italic> <jats:sub>W51</jats:sub> = 5.4 kpc. The observed region contains three high-mass protostars in which the dust continuum emission at 1.3 mm is optically thick up to a radius ≲1000 au and has brightness temperatures ≳200 K. The high luminosity (≳10<jats:sup>4</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>) in the absence of free–free emission suggests the presence of massive stars (<jats:italic>M</jats:italic> ≳ 20 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) at the earliest stages of their formation. Our continuum images reveal remarkably complex and filamentary structures arising from compact cores. Molecular emission shows no clear signs of rotation or infall on scales from 150 to 2000 au; we do not detect disks. The central sources drive young (<jats:italic>t</jats:italic> <jats:sub>dyn</jats:sub> ∼ 100 yr), fast (<jats:italic>v</jats:italic> ∼ 100 km s<jats:sup>−1</jats:sup>), powerful (<jats:inline-formula> <jats:tex-math> <?CDATA $\dot{M}\gt {10}^{-4}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc88eieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>), collimated outflows. These outflows provide indirect evidence of accretion disks on scales <jats:italic>r</jats:italic> ≲ 100–500 au (depending on the object). The active outflows are connected to fossil flows that have different orientations on larger spatial scales, implying that the orientations of these small disks change over time. These results together support a variant of an accretion model for high-mass star formation in which massive protostars do not form a large, stable Keplerian disk during their early stages but instead accrete material from multiple massive flows with different angular momentum vectors. This scenario therefore contrasts with the simplified classic paradigm of a stable disk+jet system, which is the standard model for low-mass star formation, and provides experimental confirmation of a multidirectional and unsteady accretion model for massive star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using photometry collected with the Zwicky Transient Facility, we are conducting an ongoing survey for binary systems with short orbital periods (<jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{{\rm{b}}}\lt 1\,\mathrm{hr})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc261ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> with the goal of identifying new gravitational-wave sources detectable by the upcoming Laser Interferometer Space Antenna (LISA). We present a sample of 15 binary systems discovered thus far, with orbital periods ranging from 6.91 to 56.35 minutes. Of the 15 systems, seven are eclipsing systems that do not show signs of significant mass transfer. Additionally, we have discovered two AM Canum Venaticorum systems and six systems exhibiting primarily ellipsoidal variations in their lightcurves. We present follow-up spectroscopy and high-speed photometry confirming the nature of these systems, estimates of their LISA signal-to-noise ratios, and a discussion of their physical characteristics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To understand how planetary spin evolves and traces planet formation processes, we measure rotational line broadening in eight planetary-mass objects (PMOs) of various ages (1–800 Myr) using near-infrared high-resolution spectra from NIRSPEC/Keck. Combining these with published rotation rates, we compile 27 PMO spin velocities, 16 of which derive from our NIRSPEC/Keck program. Our data are consistent with spin velocities <jats:italic>v</jats:italic> scaling with planetary radius <jats:italic>R</jats:italic> as <jats:italic>v</jats:italic> ∝ 1/<jats:italic>R</jats:italic>. We conclude that spin angular momentum is conserved as objects cool and contract over the sampled age range. The PMOs in our sample spin at rates that are approximately an order of magnitude below their break-up values, consistent with the hypothesis that they were spun down by magnetized circum-PMO disks (CPDs) during the formation era at ages ≲a few Myr. There is a factor of 4–5 variation in spin velocity that has yet to be understood theoretically. It also remains to be seen whether spin evolves on timescales ≳1 Gyr for PMOs, as it does for stars and high-mass brown dwarfs emitting magnetized winds.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Close white dwarf binaries consisting of a white dwarf and an A-, F-, G-, or K-type main-sequence star, henceforth close WD+AFGK binaries, are ideal systems to understand the nature of type Ia supernovae progenitors and to test binary evolution models. In this work we identify 775 WD+AFGK candidates from TGAS (The Tycho-Gaia Astrometric Solution) and Gaia Data Release 2 (DR2), a well-defined sample of stars with available parallaxes, and we measure radial velocities (RVs) for 275 of them with the aim of identifying close binaries. The RVs have been measured from high-resolution spectra obtained at the Xinglong 2.16 m Telescope and the San Pedro Mártir 2.12 m Telescope and/or from available LAMOST DR6 (low-resolution) and RAVE DR5 (medium-resolution) spectra. We identify 23 WD+AFGK systems displaying more than 3<jats:italic>σ</jats:italic> RV variation among 151 systems for which the measured values are obtained from different nights. Our WD+AFGK binary sample contains both AFGK dwarfs and giants, with a giant fraction ∼43%. The close binary fractions we determine for the WD+AFGK dwarf and giant samples are ≃24% and ≃15%, respectively. We also determine the stellar parameters (i.e., effective temperature, surface gravity, metallicity, mass, and radius) of the AFGK companions with available high-resolution spectra. The stellar parameter distributions of the AFGK companions that are members of close and wide binary candidates do not show statistically significant differences.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The aim of this paper is to investigate the impact of energy transfer on the evolution of contact binaries. Horizontal turbulence is triggered by the differential rotation induced by meridional circulation, which is a direct consequence of nonuniform heating at the inner critical Roche lobes because of strong rotational and tidal distortions. Thermal energy is transferred by the horizontal turbulence from the more massive star to the less massive one, and horizontal turbulence can be responsible for the redistribution of what is a significant fraction of the total core luminosity. The secondary becomes overluminous and oversized owing to energy transfer from the companion star, whereas the primary shifts toward smaller luminosity and is undersized. The convective regions for primaries are enlarged by the improved radiative temperature gradient. The main region for energy transport is located at the bottom of the common envelope because of a higher local density and enthalpy difference. One can find that thermal structure can be disturbed and display periodic thermal relaxation oscillations between the semidetached stage and the contact stage. W-type W UMa contact binaries acquire efficient energy transfer, which can cause the temperature of secondaries to exceed that of the primaries. However, angular momentum loss owing to nonconservative mass transfer can make the system maintain shallow contact and not evolve from overcontact to semidetached configurations, and the system may appear as an A-type W UMa contact binary.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>How massive early-type galaxies (ETGs) assembled their mass, on which timescales the star formation quenched, and when their supersolar metallicity has been established are still open and debated issues. Thanks to very deep spectroscopic observations carried out at the Large Binocular Telescope, we simultaneously measured stellar age, metallicity, and velocity dispersion for C1-23152, an ETG at redshift <jats:italic>z</jats:italic> = 3.352, corresponding to an epoch when the universe was ∼1.8 Gyr old. The analysis of its spectrum shows that this galaxy, hosting an active galactic nucleus (AGN), formed and assembled ∼2 × 10<jats:sup>11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, shaping its morphology within the ∼600 Myr preceding the observations, since <jats:italic>z</jats:italic> ∼ 4.6. The stellar population has a mean mass-weighted age of <jats:inline-formula> <jats:tex-math> <?CDATA ${400}_{-70}^{+30}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c4ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Myr, and it is formed between ∼600 and ∼150 Myr before the observed epoch, the latter being the time since quenching. Its high stellar velocity dispersion, <jats:italic>σ</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> = 409 ± 60 km s<jats:sup>−1</jats:sup>, confirms the high mass (<jats:italic>M</jats:italic> <jats:sub>dyn</jats:sub> = 2.2 (±0.4) × 10<jats:sup>11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) and the high mass density (<jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{e}^{{M}^{* }}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c4ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> = Σ<jats:sub>1kpc</jats:sub> = 3.2 (±0.7) × 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> kpc<jats:sup>−2</jats:sup>), suggesting a fast dissipative process at its origin. The analysis points toward a supersolar metallicity, [Z/H] = 0.25<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-0.10}^{+0.006}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c4ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, in agreement with the above picture, suggesting a star formation efficiency much higher than the replenishment time. However, subsolar-metallicity values cannot be firmly ruled out by our analysis. Quenching must have been extremely efficient to reduce the star formation to SFR &lt; 6.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> in less than 150 Myr. This could be explained by the presence of the AGN, even if a causal relation cannot be established from the data. C1-23152 has the same stellar and physical properties of the densest ETGs in the local universe of comparable mass, suggesting that they are C1-23152-like galaxies that evolved to <jats:italic>z</jats:italic> = 0 unperturbed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Broadband X-ray spectroscopy of the X-ray emission produced in the coronae of active galactic nuclei (AGNs) can provide important insights into the physical conditions very close to their central supermassive black holes. The temperature of the Comptonizing plasma that forms the corona is manifested through a high-energy cutoff that has been difficult to directly constrain even in the brightest AGN because it requires high-quality data at energies above 10 keV. In this paper we present a large collection of coronal cutoff constraints for obscured AGNs based on a sample of 130 AGNs selected in the hard X-ray band with Swift/BAT and observed nearly simultaneously with NuSTAR and Swift/XRT. We find that under a reasonable set of assumptions regarding partial constraints the median cutoff is well constrained to 290 ± 20 keV, where the uncertainty is statistical and given at the 68% confidence level. We investigate the sensitivity of this result to our assumptions and find that consideration of various known systematic uncertainties robustly places the median cutoff between 240 and 340 keV. The central 68% of the intrinsic cutoff distribution is found to be between about 140 and 500 keV, with estimated uncertainties of 20 and 100 keV, respectively. In comparison with the literature, we find no clear evidence that the cutoffs in obscured and unobscured AGNs are substantially different. Our analysis highlights the importance of carefully considering partial and potentially degenerate constraints on the coronal high-energy cutoff in AGNs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>How do active galactic nuclei with low optical luminosities produce powerful radio emission? Recent studies of active galactic nuclei with moderate radio and low optical luminosities (Fanaroff &amp; Riley class I, FR I) searching for broad nuclear emission lines in polarized light, as predicted by some active galactic nucleus unification models, have found heterogeneous results. These models typically consist of a central engine surrounded by a torus of discrete dusty clouds. These clouds would absorb and scatter optical emission, blocking broad nuclear emission lines, and reradiate in mid-infrared. Some scattered broad-line emission may be observable, depending on geometry, which would be polarized. We present a wide-band infrared spectroscopic analysis of 10 nearby FR I radio galaxies to determine whether there is significant emission from a dusty obscuring structure. We used Markov Chain Monte Carlo algorithms to decompose Spitzer/IRS spectra of our sample. We constrained the wide-band behavior of our models with photometry from the Two Micron All Sky Survey, Spitzer/IRAC, Spitzer/MIPS, and Herschel/SPIRE. We find that one galaxy is best fit by a clumpy torus and three others show some thermal mid-infrared component. This suggests that in those three there is likely some obscuring dust structure that is inconsistent with our torus models and there must be some source of photons heating the dust. We conclude that 40% of our FR I radio galaxies show evidence of obscuring dusty material, possibly some other form of hidden broad-line nucleus, but only 10% favor the clumpy torus model specifically.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at subsecond timescales. Imaging in narrow frequency bands has revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilize 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at ∼32 MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where <jats:italic>f</jats:italic> <jats:sub>pe</jats:sub> ≈ 32 MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wavevector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (∼32 MHz, but generated where <jats:italic>f</jats:italic> <jats:sub>pe</jats:sub> ≈ 16 MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at subsecond timescales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.</jats:p>