Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Circumbinary gas disks are often observed to be misaligned with the binary orbit, suggesting that planet formation may proceed in a misaligned disk. With <jats:italic>n</jats:italic>-body simulations, we consider the formation of circumbinary terrestrial planets from a particle disk that is initially misaligned. We find that if terrestrial planets form in this way, in the absence of gas, they can only form close to coplanar or close to polar to the binary orbit. Planets around a circular binary form coplanar while planets around an eccentric binary can form coplanar or polar depending on the initial disk misalignment and the binary eccentricity. The more massive a terrestrial planet is, the more aligned it is (to coplanar or polar) because it has undergone more mergers that lead on average to smaller misalignment angles. Nodal precession of particle disks with very large initial inclinations lead to high mutual inclinations between the particles. This produces high relative velocities between particles that lead to mass ejections that can completely inhibit planet formation. Misaligned terrestrial circumbinary planets may be able to form in the presence of a misaligned circumbinary gas disk that may help to nodally align the particle orbits and maintain the inclination of the planets during their formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We used New Horizons LORRI images to measure the optical-band (0.4 ≲ <jats:italic>λ</jats:italic> ≲ 0.9<jats:italic>μ</jats:italic>m) sky brightness within a high-galactic-latitude field selected to have reduced diffuse scattered light from the Milky Way galaxy (DGL), as inferred from the IRIS all-sky 100 <jats:italic>μ</jats:italic>m map. We also selected the field to significantly reduce the scattered light from bright stars (SSL) outside the LORRI field. Suppression of DGL and SSL reduced the large uncertainties in the background flux levels present in our earlier New Horizons cosmic optical background (COB) results. The raw total sky level, measured when New Horizons was 51.3 au from the Sun, is 24.22 ± 0.80 nW m<jats:sup>−2</jats:sup> sr<jats:sup>−1</jats:sup>. Isolating the COB contribution to the raw total required subtracting scattered light from bright stars and galaxies, faint stars below the photometric detection limit within the field, and the hydrogen plus ionized-helium two-photon continua. This yielded a highly significant detection of the COB at 16.37 ± 1.47 nW m<jats:sup>−2</jats:sup> sr<jats:sup>−1</jats:sup> at the LORRI pivot wavelength of 0.608 <jats:italic>μ</jats:italic>m. This result is in strong tension with the hypothesis that the COB only comprises the integrated light of external galaxies (IGL) presently known from deep HST counts. Subtraction of the estimated IGL flux from the total COB level leaves a flux component of unknown origin at 8.06 ± 1.92 nW m<jats:sup>−2</jats:sup> sr<jats:sup>−1</jats:sup>. Its amplitude is equal to the IGL.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gravitational waves from binary neutron star mergers can be used as alerts to enable prompt follow-up observations. In particular, capturing prompt electromagnetic and astroparticle emissions from the moment of a binary merger presents unique constraints on the timescale and sky localization for online gravitational-wave detection. Here we present the expected performance of the SPIIR online detection pipeline that is designed for this purpose in the upcoming international LIGO–Virgo’s 4th Science Run (O4). Using simulated Gaussian data for the two LIGO observatories with expected O4 sensitivity, we demonstrate that there is a nonnegligible opportunity to deliver premerger warnings at least 10 s before the final plunge. These alerts are expected to be issued at a nominal rate of one binary neutron star coalescence per year and localized within a median searched area of 300 deg<jats:sup>2</jats:sup>. We envision such detection to be extremely useful for follow-up observatories with a large field of view such as the Murchison Widefield Array radio facility in Western Australia.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observational data on the dust content of circumstellar disks show that the median dust content in disks around pre-main-sequence stars in nearby star-forming regions seems to increase from ∼1 to ∼2 Myr and then decline with time. This behavior challenges the models where the small dust grains steadily decline by accumulating into larger bodies and drifting inwards on a short timescale (≤1 Myr). In this Letter we explore the possibility to reconcile this discrepancy in the framework of a model where the early formation of planets dynamically stirs the nearby planetesimals and causes high-energy impacts between them, resulting in the production of second-generation dust. We show that the observed dust evolution can be naturally explained by this process within a suite of representative disk-planet architectures.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of pulsars in globular clusters (GCs) give evidence that more than &gt;10%–20% of neutron stars (NSs) that ever formed in GCs were retained there. However, the velocity distribution of field pulsars peaks at 5–10 times the escape velocities of GCs. Consequently, only a small fraction of GC NSs should have been retained, which is potentially difficult to explain even accounting for low-velocity NSs formed through electron-capture supernovae (SNe). Thus, too few low-velocity NSs should have been retained, giving rise to the NS retention problem in GCs. Here we suggest a novel solution, in which the progenitors of most GC NSs were ONe white dwarfs (WDs) that accreted ambient intracluster gas and formed low-velocity NSs through accretion-induced collapse (AIC). The existence of an early gas-enriched environment in GCs is supported by observations of multiple stellar populations in GCs. It is thought that 10–100s of megayears after the formation of the first generation of stars, and after ONe WDs were already formed, GCs were replenished with gas, which formed a second generation of stars. Accretion of such replenished gas onto the ONe WDs catalyzed the AIC processes. The number of AIC-formed NSs is then sufficient to explain the large number of NSs retained in GCs. Similar processes might also drive CO WDs to produce Type Ia SNe or to merge and form NSs and similarly drive NSs to AIC and mergers producing BHs. Moreover, the wide variety of gas-catalyzed binary mergers and explosive transients suggested to occur in the gas-rich environments of an active galactic nucleus disk could similarly, and even more efficiently, occur in second-generation gas in GCs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical spectroscopic and milliarcsecond-scale radio continuum observations of the quasar M1540–1453 (<jats:italic>z</jats:italic> <jats:sub>em</jats:sub> = 2.104 ± 0.002) that show associated H <jats:sc>i</jats:sc> 21 cm absorption at <jats:italic>z</jats:italic> <jats:sub>abs</jats:sub> = 2.1139. At subkiloparsec scales, the powerful radio source with 1.4 GHz luminosity of 5.9 × 10<jats:sup>27</jats:sup> W Hz<jats:sup>−1</jats:sup> shows Fanaroff–Riley class I morphology caused by the interaction with dense gas within 70 pc of the active galactic nucleus (AGN). Interestingly, while there are indications for the presence of absorption from low-ionization species like Fe <jats:sc>ii</jats:sc>, Si <jats:sc>ii,</jats:sc> and Si <jats:sc>iii</jats:sc> in the optical spectrum, the expected strong damped Ly<jats:italic>α</jats:italic> absorption is not detected at the redshift of the H <jats:sc>i</jats:sc> 21 cm absorber. In comparison to typical high-<jats:italic>z</jats:italic> quasars, the Ly<jats:italic>α</jats:italic> emission line is much narrower. The “ghostly” nature of the H <jats:sc>i</jats:sc> Ly<jats:italic>α</jats:italic> absorber partially covering the broad-line region of extent 0.05 pc and the detection of widespread H <jats:sc>i</jats:sc> 21 cm absorption covering the diffuse radio source (extent &gt;425 pc) imply the presence of a large clumpy H <jats:sc>i</jats:sc> halo, which may have been blown by the jet–interstellar medium (ISM) interaction. Further observations are needed to confirm the ghostly nature of the Ly<jats:italic>α</jats:italic> absorber and obtain a better understanding of the role played by the jet–ISM interaction in shaping the radio morphology of this powerful AGN. The study showcases how joint radio and optical analysis can shed light on the gaseous environment and origin of radio morphology in AGNs at high redshifts, when these are still the assembly sites of giant galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Tidal disruption events with tidal radius <jats:italic>r</jats:italic> <jats:sub>t</jats:sub> and pericenter distance <jats:italic>r</jats:italic> <jats:sub>p</jats:sub> are characterized by the quantity <jats:italic>β</jats:italic> = <jats:italic>r</jats:italic> <jats:sub>t</jats:sub>/<jats:italic>r</jats:italic> <jats:sub>p</jats:sub>, and “deep encounters” have <jats:italic>β</jats:italic> ≫ 1. It has been assumed that there is a critical <jats:italic>β</jats:italic> ≡ <jats:italic>β</jats:italic> <jats:sub>c</jats:sub> ∼ 1 that differentiates between partial and full disruption: for <jats:italic>β</jats:italic> &lt; <jats:italic>β</jats:italic> <jats:sub>c</jats:sub> a fraction of the star survives the tidal interaction with the black hole, while for <jats:italic>β</jats:italic> &gt; <jats:italic>β</jats:italic> <jats:sub>c</jats:sub> the star is completely destroyed, and hence all deep encounters should be full. Here we show that this assumption is incorrect by providing an example of a <jats:italic>β</jats:italic> = 16 encounter between a <jats:italic>γ</jats:italic> = 5/3, solar-like polytrope and a 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> black hole—for which previous investigations have found <jats:italic>β</jats:italic> <jats:sub>c</jats:sub> ≃ 0.9—that results in the reformation of a stellar core post-disruption that comprises approximately 25% of the original stellar mass. We propose that the core reforms under self-gravity, which remains important because of the compression of the gas both near pericenter, where the compression occurs out of the orbital plane, and substantially after pericenter, where compression is within the plane. We find that the core forms on a bound orbit about the black hole, and we discuss the corresponding implications of our findings in the context of recently observed, repeating nuclear transients.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We consider a hierarchical triple system consisting of an inner eccentric binary with an outer companion. A highly misaligned circumbinary disk around the inner binary is subject to two competing effects: (i) nodal precession about the inner binary eccentricity vector that leads to an increase in misalignment (polar alignment) and (ii) Kozai–Lidov (KL) oscillations of eccentricity and inclination driven by the outer companion that leads to a reduction in the misalignment. The outcome depends upon the ratio of the timescales of these effects. If the inner binary torque dominates, then the disk aligns to a polar orientation. If the outer companion torque dominates, then the disk undergoes KL oscillations. In that case, the highly eccentric and misaligned disk is disrupted and accreted by the inner binary, while some mass is transferred to the outer companion. However, when the torques are similar, the outer parts of the circumbinary disk can undergo large eccentricity oscillations while the inclination remains close to polar orientation. The range of initial disk inclinations that evolve to a polar orientation is smaller in the presence of the outer companion. Disk breaking is also more likely, at least temporarily, during the polar alignment process. The stellar orbits in HD 98800 have parameters such that polar alignment of the circumbinary disk is expected. In the absence of gas, solid particles are unstable at much smaller radii than the gas-disk inner tidal truncation radius because KL-driven eccentricity leads to close encounters with the binary.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Jets can facilitate the mass accretion onto the protostars in star formation. They are believed to be launched from accretion disks around the protostars by magnetocentrifugal force, as supported by the detections of rotation and magnetic fields in some of them. Here we report a radial flow of the textbook-case protostellar jet HH 212 at the base to further support this jet-launching scenario. This radial flow validates a central prediction of the magnetocentrifugal theory of jet formation and collimation, namely, the jet is the densest part of a wide-angle wind that flows radially outward at distances far from the (small, sub-au) launching region. Additional evidence for the radially flowing wide-angle component comes from its ability to reproduce the structure and kinematics of the shells detected around the HH 212 jet. This component, which can transport material from the inner to outer disk, could account for the chondrules and Ca–Al-rich inclusions detected in the solar system at large distances.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It has been shown that ultra-diffuse galaxies (UDGs) have higher specific frequencies of globular clusters, on average, than other dwarf galaxies with similar luminosities. The UDG NGC 5846-UDG1 is among the most extreme examples of globular cluster–rich galaxies found so far. Here we present new Hubble Space Telescope observations and analysis of this galaxy and its globular cluster system. We find that NGC 5846-UDG1 hosts 54 ± 9 globular clusters, three to four times more than any previously known galaxy with a similar luminosity and higher than reported in previous studies. With a galaxy luminosity of <jats:italic>L</jats:italic> <jats:sub> <jats:italic>V</jats:italic>,gal</jats:sub> ≈ 6 × 10<jats:sup>7</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub> (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> ≈ 1.2 × 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) and a total globular cluster luminosity of <jats:italic>L</jats:italic> <jats:sub> <jats:italic>V</jats:italic>,GCs</jats:sub> ≈ 7.6 × 10<jats:sup>6</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>, we find that the clusters currently comprise ∼13% of the total light. Taking into account the effects of mass loss from clusters during their formation and throughout their lifetime, we infer that most of the stars in the galaxy likely formed in globular clusters, and very little to no “normal” low-density star formation occurred. This result implies that the most extreme conditions during early galaxy formation promoted star formation in massive and dense clumps, in contrast to the dispersed star formation observed in galaxies today.</jats:p>