Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>In recent years, ALMA has been able to observe large-scale substructures within protoplanetary disks. Comparison with the predictions from models of planet–disk interactions has indicated that most of these disk substructures can be explained by the presence of planets with the mass of Neptune or larger at orbital radii of ≈5–100 au. Better resolution is needed to observe structures closer to the star, where terrestrial planets are expected to form, as well as structures opened by planets with masses lower than Neptune. We investigate the capabilities of a possible extension to ALMA that would double the longest baseline lengths in the array to detect and resolve disk substructures opened by Earth-mass and super-Earth planets at orbital radii of 1–5 au. By simulating observations of a family of disk models using this extended configuration in ALMA Bands 6 and 7, we show that an upgraded ALMA would detect gaps in disks formed by super-Earths as close as 1 au, as well as Earth-mass planets down to 2–3 au from the young host stars in nearby star-forming regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A scheme of Bayesian rotation inversion, which allows us to compute the probability of a model of a stellar rotational profile, is developed. The validation of the scheme with simple rotational profiles and the corresponding sets of artificially generated rotational shifts has been successfully carried out, and we can correctly distinguish the (right) rotational model, prepared beforehand for generating the artificial rotational shifts, from the other (wrong) rotational model. The Bayesian scheme is applied to a <jats:italic>γ</jats:italic> Dor–<jats:italic>δ</jats:italic> Sct-type hybrid star, KIC 11145123, leading to a result that the convective core of the star might be rotating much faster (∼10 times faster) than the other regions of the star. The result is consistent with that previously suggested by Hatta et al. based on a three-zone modeling, further strengthening their argument from a Bayesian point of view.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed study of very strong magnetic fields in the NOAA Active Region (AR) 12673, which was the most flare productive AR in solar cycle 24. It produced four X-class flares including the X9.3 flare on 2017 September 6 and the X8.2 limb event on September 10. Our analysis is based on direct measurements of full Zeeman splitting of the Fe <jats:sc>i</jats:sc> 1564.85 nm line using all Stokes I, Q, U, and V profiles. This approach allowed us to obtain reliable estimates of the magnitude of magnetic fields independent of the filling factor and atmosphere models. Thus, the strongest fields up to 5.5 kG were found in a light bridge (LB) of a spot, while in the dark umbra magnetic fields did not exceed 4 kG. In the case of the LB, the magnitude of the magnetic field is not related to the underlying continuum intensity, while in the case of umbral fields we observed a well-known anticorrelation between the continuum intensity and the field magnitude. In this study, the LB was cospatial with a polarity inversion line of <jats:italic>δ</jats:italic>-sunspot, and we speculate that the 5.5 kG strong horizontal fields may be associated with a compact twisted flux rope at or near the photosphere. A comparison of the depth of the Zeeman <jats:italic>π</jats:italic> and <jats:italic>σ</jats:italic> components showed that in the LB magnetic fields are, on average, more horizontal than those in the dark umbra.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stellar-mass BHs (sBHs) are predicted to be embedded in active galactic nucleus (AGN) disks owing to gravitational drag and in situ star formation. However, we find that, due to a high gas density in an AGN disk environment, compact objects may rapidly grow to intermediate-mass BHs and deplete matter from the AGN disk unless accretion is suppressed by some feedback process(es). These consequences are inconsistent with AGN observations and the dynamics of the Galactic center. Here we consider mechanical feedback mechanisms for the reduction of gas accretion. Rapidly accreting sBHs launch winds and/or jets via the Blandford–Znajek mechanism, which produce high-pressure shocks and cocoons. Such a shock and cocoon can spread laterally in the plane of the disk, eject the outer regions of a circum-sBH disk (CsBD), and puncture a hole in the AGN disk with horizontal size comparable to the disk scale height. Since the depletion timescale of the bound CsBD is much shorter than the resupply timescale of gas to the sBH, the time-averaged accretion rate onto sBHs is reduced by this process by a factor of ∼10–100. This feedback mechanism can therefore help alleviate the sBH overgrowth and AGN disk depletion problems. On the other hand, we find that cocoons of jets can unbind a large fraction of the gas accreting in the disks of less massive supermassive BHs (SMBHs), which may help explain the dearth of high-Eddington-ratio AGNs with SMBH mass ≲ 10<jats:sup>5</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Information on the rotation rate of the corona, and its variation over latitude and solar cycle, is valuable for making global connections between the corona and the Sun, for global estimates of reconnection rates and as a basic parameter for solar-wind modeling. Here, we use a time series of tomographical maps gained from coronagraph observations between 2007 and 2020 to directly measure the longitudinal drift of high-density streamers over time. The method reveals abrupt changes in rotation rates, revealing a complex relationship between the coronal rotation and the underlying photosphere. The majority of rates are between −1.°0 to +0.°5 day<jats:sup>−1</jats:sup> relative to the standard Carrington rate of 14.°18 day<jats:sup>−1</jats:sup>, although rates are measured as low as −2.°2 day<jats:sup>−1</jats:sup> and as high as 1.°6 day<jats:sup>−1</jats:sup>. Equatorial rotation rates during the 2008 solar minimum are slightly faster than the Carrington rate, with an abrupt switch to slow rotation in 2009, then a return to faster rates in 2017. Abrupt changes and large variations in rates are seen at all latitudes. Comparison with a magnetic model suggests that periods of equatorial fast rotation are associated with times when a large proportion of the magnetic footpoints of equatorial streamers are near the equator, and we interpret the abrupt changes in terms of the latitudinal distribution of the streamer photospheric footpoints. The coronal rotation rate is a key parameter for solar-wind models, and variations of up to a degree per day or more can lead to large systematic errors over forecasting periods of longer than a few days. The approach described in this paper gives corrected values that can form a part of future forecasting efforts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The corona is an integral component of active galactic nuclei (AGNs) which produces the bulk of the X-ray emission above 1–2 keV. However, many of its physical properties and the mechanisms powering this emission remain a mystery. In particular, the temperature of the coronal plasma has been difficult to constrain for large samples of AGNs, as constraints require high-quality broadband X-ray spectral coverage extending above 10 keV in order to measure the high-energy cutoff, which provides constraints on the combination of coronal optical depth and temperature. We present constraints on the coronal temperature for a large sample of Seyfert 1 AGNs selected from the Swift/BAT survey using high-quality hard X-ray data from the NuSTAR observatory combined with simultaneous soft X-ray data from Swift/XRT or XMM-Newton. When applying a physically motivated, nonrelativistic disk-reflection model to the X-ray spectra, we find a mean coronal temperature <jats:italic>kT</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> = 84 ± 9 keV. We find no significant correlation between the coronal cutoff energy and accretion parameters such as the Eddington ratio and black hole mass. We also do not find a statistically significant correlation between the X-ray photon index, Γ, and Eddington ratio. This calls into question the use of such relations to infer properties of supermassive black hole systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Evidence for cometary activity beyond Jupiter’s and Saturn’s orbits—such as that observed for Centaurs and long-period comets—suggests that the thermal processing of comet nuclei starts long before they enter the inner solar system, where they are typically observed and monitored. Such observations raise questions as to the depth of unprocessed material and whether the activity of Jupiter-family comets (JFCs) can be representative of any primitive material. Here we model the coupled thermal and dynamical evolution of JFCs, from the moment they leave their outer solar system reservoirs until their ejection into interstellar space. We apply a thermal evolution model to a sample of simulated JFCs obtained from dynamical simulations that successfully reproduce the orbital distribution of observed JFCs. We show that due to the stochastic nature of comet trajectories toward the inner solar system, all simulated JFCs undergo multiple heating episodes resulting in significant modifications of their initial volatile contents. A statistical analysis constrains the extent of such processing. We suggest that primordial condensed hypervolatile ices should be entirely lost from the layers that contribute to cometary activity observed today. Our results demonstrate that understanding the orbital (and thus, heating) history of JFCs is essential when putting observations in a broader context.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have examined Ulysses magnetic field measurements for the years 1993 through 1996 as the spacecraft moved sunward from 5 au at high southern latitudes, passing through perihelion during the first fast-latitude scan to achieve high northern latitudes, and finally returning to 5 au. These years represent near-solar-minimum activity, providing a clear measure of high-latitude solar-wind turbulence. We apply a series of tests to the data, examining both the magnetic variance anisotropy and the underlying wavevector anisotropy, finding them to be consistent with past 1 au observations. The variance anisotropy depends upon both the thermal proton temperature parameter and the amplitude of the magnetic power spectrum, while the underlying wavevector anisotropy is dominated by the component perpendicular to the mean magnetic field. We also examine the amplitude of the magnetic power spectrum as well as the associated turbulent transport of energy to small scales that results in the heating of the thermal plasma. The measured turbulence is found to be stronger than that seen at low latitudes by the Voyager spacecraft as it traverses the distance from 1 to 5 au during the years approaching solar maximum. If the high- and low-latitude sources are comparable, this would indicate that while the heating processes are active in both regions, the turbulence has had less decay time in the transport of energy to small scales. Alternatively, it may also be that the high-latitude source is stronger.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Many different studies have shown that a wealth of cosmological information resides on small, nonlinear scales. Unfortunately, there are two challenges to overcome to utilize that information. First, we do not know the optimal estimator that will allow us to retrieve the maximum information. Second, baryonic effects impact that regime significantly and in a poorly understood manner. Ideally, we would like to use an estimator that extracts the maximum cosmological information while marginalizing over baryonic effects. In this work we show that neural networks can achieve that when considering some simple scenarios. We made use of data where the maximum amount of cosmological information is known: power spectra and 2D Gaussian density fields. We also contaminate the data with simplified baryonic effects and train neural networks to predict the value of the cosmological parameters. For this data, we show that neural networks can (1) extract the maximum available cosmological information, (2) marginalize over baryonic effects, and (3) extract cosmological information that is buried in the regime dominated by baryonic physics. We also show that neural networks learn the priors of the data they are trained on, affecting their extrapolation properties. We conclude that a promising strategy to maximize the scientific return of cosmological experiments is to train neural networks on state-of-the-art numerical simulations with different strengths and implementations of baryonic effects.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the properties of the globular clusters (GCs) and nuclear star clusters (NSCs) of low-mass (10<jats:sup>5.5</jats:sup> &lt; <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> &lt; 10<jats:sup>8.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) early-type satellites of Milky Way–like and small group hosts in the Local Volume (LV) using deep, ground-based data from the ongoing Exploration of Local VolumE Satellites Survey. This sample of 177 dwarfs significantly increases the statistics for studying the star clusters of dwarfs in low-density environments, offering an important comparison to samples from nearby galaxy clusters. The LV dwarfs exhibit significantly lower nucleation fractions at fixed galaxy mass than dwarfs in nearby clusters. The masses of NSCs of LV dwarfs show a similar scaling of <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\star ,\mathrm{NSC}}\propto {M}_{\star ,\mathrm{gal}}^{0.4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> <mml:mo>,</mml:mo> <mml:mi>NSC</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> <mml:mo>,</mml:mo> <mml:mi>gal</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac457eieqn1.gif" xlink:type="simple" /> </jats:inline-formula> as that found in clusters but offset to lower NSC masses. To deal with foreground/background contamination in the GC analysis, we employ both a statistical subtraction and Bayesian approach to infer the average GC system properties from all dwarfs simultaneously. We find that the GC occupation fraction and average abundance are both increasing functions of galaxy stellar mass, and the LV dwarfs show significantly lower average GC abundance at fixed galaxy mass than a comparable sample of Virgo dwarfs analyzed in the same way, demonstrating that GC prevalence also shows an important secondary dependence on the dwarf’s environment. This result strengthens the connection between GCs and NSCs in low-mass galaxies. We discuss these observations in the context of modern theories of GC and NSC formation, finding that the environmental dependencies can be well explained by these models.</jats:p>