Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Stars originate from the dense interstellar medium, which exhibits filamentary structure to scales of ∼1 kpc in galaxies like our Milky Way. We explore quantitatively how much resulting large-scale correlation there is among different stellar clusters and associations in orbit-phase space, characterized here by actions and angles. As a starting point, we identified 55 prominent stellar overdensities in the 6D space of orbit (actions) and orbit-phase (angles) among the ∼2.8 million stars with radial velocities from Gaia EDR3 and with <jats:italic>d</jats:italic> ≤ 800 pc. We then explored the orbit-phase distribution of all sample stars in the same orbit patch as any one of these 55 overdensities. We find that very commonly numerous other distinct orbit-phase overdensities exist along these same orbits, like pearls on a string. These “pearls” range from known stellar clusters to loose, unrecognized associations. Among orbit patches defined by one initial orbit-phase overdensity, 50% contain at least 8 additional orbit-phase pearls of 10 cataloged members; 20% of them contain 20 additional pearls. This is in contrast to matching orbit patches sampled from a smooth mock catalog, or offset nearby orbit patches, where there are only 2 (or 5, respectively) comparable pearls. Our findings quantify for the first time how common it is for star clusters and associations to form at distinct orbit-phases of nearly the same orbit. This may eventually offer a new way to probe the 6D orbit structure of the filamentary interstellar medium.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>White dwarfs (WDs) are useful across a wide range of astrophysical contexts. The appropriate interpretation of their spectra relies on the accuracy of WD atmosphere models. One essential ingredient of atmosphere models is the theory used for the broadening of spectral lines. To date, the models have relied on Vidal et al., known as the unified theory of line broadening (VCS). There have since been advancements in the theory; however, the calculations used in model atmosphere codes have only received minor updates. Meanwhile, advances in instrumentation and data have uncovered indications of inaccuracies: spectroscopic temperatures are roughly 10% higher and spectroscopic masses are roughly 0.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> higher than their photometric counterparts. The evidence suggests that VCS-based treatments of line profiles may be at least partly responsible. Gomez et al. developed a simulation-based line-profile code Xenomorph using an improved theoretical treatment that can be used to inform questions around the discrepancy. However, the code required revisions to sufficiently decrease noise for use in model spectra and to make it computationally tractable and physically realistic. In particular, we investigate three additional physical effects that are not captured in the VCS calculations: ion dynamics, higher-order multipole expansion, and an expanded basis set. We also implement a simulation-based approach to occupation probability. The present study limits the scope to the first three hydrogen Balmer transitions (H<jats:italic>α</jats:italic>, H<jats:italic>β</jats:italic>, and H<jats:italic>γ</jats:italic>). We find that screening effects and occupation probability have the largest effects on the line shapes and will likely have important consequences in stellar synthetic spectra.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do this, we focus on a sample of 11 galaxies with existing ground-based Balmer H<jats:italic>α</jats:italic> and H<jats:italic>β</jats:italic> measurements from slit spectra, plus space-based grism constraints on Paschen-<jats:italic>β</jats:italic>. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust-law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-<jats:italic>β</jats:italic>/H<jats:italic>α</jats:italic> ratios driving these results. We find that galaxies with high Paschen-<jats:italic>β</jats:italic>/H<jats:italic>α</jats:italic> ratios may be explained by slightly sub-unity covering fractions (&gt;97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that, while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies at <jats:italic>z</jats:italic> ≈ 0.3–2, enabling uniform constraints on the optical–infrared dust attenuation law and its intrinsic variation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A novel search technique for ultralight dark matter has been developed and carried out over a narrow range in the <jats:italic>L</jats:italic> band, utilizing the recent Breakthrough Listen public data release of three years of observation with the Green Bank Telescope. The search concept depends only on the assumption of decay or annihilation of virialized dark matter to a quasimonochromatic radio line, and additionally that the frequency and intensity of the line be consistent with most general properties expected of the phase space of our Milky Way halo. Specifically, the search selects for a line that exhibits a Doppler shift with position according to the solar motion through a static Galactic halo and similarly varies in intensity with the position with respect to the Galactic center. Over the frequency range 1.73–1.83 GHz, radiative annihilation of dark matter is excluded above 〈<jats:italic>σ</jats:italic> <jats:italic>v</jats:italic>〉 = 1.2 × 10<jats:sup>−47</jats:sup> cm<jats:sup>3</jats:sup> s<jats:sup>−1</jats:sup> and for decay above <jats:italic>λ</jats:italic> = 4.1 × 10<jats:sup>−35</jats:sup> s<jats:sup>−1</jats:sup>. The analysis of the full Breakthrough Listen GBT data set by this method (25,000 spectra, 1.1-11.6 GHz) is currently underway.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The short gamma-ray burst (SGRB) GRB 170817A was found to be related to a binary neutron star (BNS) merger. It is uncertain whether all SGRBs are caused by BNS mergers and also under what conditions a BNS merger can cause an SGRB. As BNS mergers can cause SGRBs, afterglow observations will also provide an alternative measurement of the BNS merger rate independent of gravitational-wave observations. In previous work by Feng et al., the feasibility of the detection of afterglows was considered using a variety of radio observatories and a simple flux threshold detection algorithm. Here, we consider a more sophisticated detection algorithm for SGRB afterglows and provide an estimate of the trials factors for a realistic search to obtain an updated estimate of the possibility of observing afterglows with the Canadian Hydrogen Intensity Mapping Experiment (CHIME). We estimate 893 and 312 afterglows per year can be detected using a 3<jats:italic>σ</jats:italic> confidence level threshold with two jet models, one with half-opening angle uniformly distributed in 6°–30° and the other uniformly distributed in 3°–8° with the median of 6°. We also find that 88% and 98%, respectively, of the detectable afterglows for each jet-opening distribution are off axis, which are candidates for orphan afterglows. Our result predicts fewer detectable sources per year than the earlier analysis but confirms the essential conclusion that using CHIME to search for afterglows will be effective in constraining the astrophysical merger rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The 3D exact analytical solutions of ideal two-fluid plasma, single-fluid plasma, and neutral fluid equations have been found using physically justifiable assumptions. Surprisingly these solutions satisfy all nonlinearities in the systems. It is pointed out that these solutions explain the fundamental mechanism behind the creation of a vast variety of ordered structures in plasmas and fluids. In the limiting case of 2D dependence of fields, the theoretical model for plasma is applied to explain the formation of spicules in the solar chromosphere. It is pointed out that the main contribution of electron (ion) baroclinic vectors is to produce vorticity in the plasma, and that magnetic field generation is coupled with the flow of both electrons and ions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the star formation rate (SFR) measurements based on the spectral energy distribution (SED) analysis with new submillimeter fluxes combined with archival multiwavelength data for a sample of 52 active galactic nucleus (AGN) host galaxies at <jats:italic>z</jats:italic> &lt; 0.2. We carried out submillimeter observations using the SCUBA-2 camera at the James Clerk Maxwell Telescope and obtained flux or an upper limit at 450 and 850 <jats:italic>μ</jats:italic>m for each target. By experimenting with the effect of the AGN dust component in the SED fit, we find that the dust luminosity can be overestimated if the AGN contribution is ignored. While the SFR based on the 4000 Å break shows a significant offset compared to the dust-luminosity-based SFR, the SFR obtained by the artificial neural network generally shows consistency, albeit with a large scatter. We find that SFR correlates with the AGN outflow strength manifested by the [O <jats:sc>iii</jats:sc>] <jats:italic>λ</jats:italic>5007 emission line, and that AGNs with higher Eddington ratios and stronger outflows are generally hosted by galaxies with a higher SFR, which is consistent with the correlation reported by Woo et al. This suggests no instantaneous quenching of star formation due to AGN feedback.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>During its exploration of the heliosheath, the region that lies between the termination shock of the solar wind and the heliopause that separates the solar wind from the local interstellar medium, the Voyager 1 spacecraft (V1) in 2012 encountered an apparent boundary where there was a precipitous decrease in energetic particles accelerated in the heliosheath, the so-called anomalous cosmic rays (ACRs), and from the occasional plasma density measurements on V1, a density comparable to the expected density in the interstellar medium. In 2013, the Voyager principal investigators announced that this apparent boundary was the heliopause and that V1 had entered the interstellar medium. In 2014, Fisk &amp; Gloeckler presented a detailed model that demonstrated that the apparent boundary was simply an internal surface within the heliosheath, across which compressed solar wind flows and will continue to flow until it encounters the actual heliopause. There is compelling observational evidence that the model of Fisk &amp; Gloeckler for the nose region of the heliosheath is correct: V1 did not cross the heliopause in 2012 and is not now in the interstellar medium. There is also compelling observational evidence that the ACRs are accelerated in the heliosheath by the pump acceleration mechanism of Fisk &amp; Gloeckler. The success of the models of Fisk &amp; Gloeckler confirms that the plasma in the nose region of the heliosheath consists of two separate components, the pickup ions and ACRs, and the thermal solar wind, and as a unique plasma is worthy of more study and, if possible, more exploration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The role of radiation pressure in dust migration and the opening of inner cavities in transitional disks is revisited in this paper. Dust dynamics including radiation pressure is often studied in axisymmetric models, but in this work, we show that highly non-axisymmetric features can arise from an instability at the inner disk edge. Dust grains clump into high density features there, allowing radiation to leak around them and penetrate deeper into the disk, changing the course of dust migration. Our proof-of-concept, two-dimensional, vertically averaged simulations show that the combination of radiation pressure, shadowing, and gas drag can produce a net outward migration, or recession, of the dust component of the disk. The recession speed of the inner disk edge is on the order of 10<jats:sup>−5</jats:sup> times Keplerian speed in our parameter space, which is faster than the background viscous flow, assuming a Shakura–Sunyaev viscosity <jats:italic>α</jats:italic> ≲ 10<jats:sup>−3</jats:sup>. This speed, if sustained over the lifetime of the disk, can result in a dust cavity as large as tens of astronomical units.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A tidal disruption event (TDE) involves the shredding of a star in the proximity of a supermassive black hole (SMBH). The nearby (≈230 Mpc) relatively radio-quiet, thermal-emission-dominated source AT2019dsg is the first TDE with a potential neutrino association. The origin of nonthermal emission remains inconclusive; possibilities include a relativistic jet or a subrelativistic outflow. Distinguishing between them can address neutrino production mechanisms. High-resolution very long baseline interferometry 5 GHz observations provide a proper motion of 0.94 ± 0.65 mas yr<jats:sup>−1</jats:sup> (3.2 ± 2.2 <jats:italic>c</jats:italic>; 1<jats:italic>σ</jats:italic>). Modeling the radio emission favors an origin from the interaction between a decelerating outflow (velocity ≈0.1 <jats:italic>c</jats:italic>) and a dense circumnuclear medium. The transition of the synchrotron self-absorption frequency through the observation band marks a peak flux density of 1.19 ± 0.18 mJy at 152.8 ± 16.2 days. An equipartition analysis indicates an emission-region distance of ≥ 4.7 × 10<jats:sup>16</jats:sup> cm, magnetic field strength ≥ 0.17 <jats:italic>G</jats:italic>, and number density ≥ 5.7 × 10<jats:sup>3</jats:sup> cm<jats:sup>−3</jats:sup>. The disruption involves a ≈2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> star with a penetration factor ≈1 and a total energy output of ≤ 1.5 × 10<jats:sup>52</jats:sup> erg. The outflow is radiatively driven by the accretion of stellar debris onto the SMBH. Neutrino production is likely related to the acceleration of protons to peta-electron-volt energies and the availability of a suitable cross section at the outflow base. The present study thus helps exclude jet-related origins for nonthermal emission and neutrino production, and constrains nonjetted scenarios.</jats:p>