Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Active galactic nuclei (AGNs) can funnel stars and stellar remnants from the vicinity of the galactic center into the inner plane of the AGN disk. Stars reaching this inner region can be tidally disrupted by the stellar-mass black holes in the disk. Such micro tidal disruption events (micro-TDEs) could be a useful probe of stellar interaction with the AGN disk. We find that micro-TDEs in AGNs occur at a rate of ∼170 Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup>. Their cleanest observational probe may be the electromagnetic detection of tidal disruption in AGNs by heavy supermassive black holes (<jats:italic>M</jats:italic> <jats:sub>•</jats:sub> ≳ 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) that cannot tidally disrupt solar-type stars. The reconstructed rate of such events from observations, nonetheless, appears to be much lower than our estimated micro-TDE rate. We discuss two such micro-TDE candidates observed to date (ASASSN-15lh and ZTF19aailpwl).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is widely believed that magnetic flux ropes are the key structure of solar eruptions; however, their observable counterparts are not clear yet. We study a flare associated with flux rope eruption in a comprehensive radiative magnetohydrodynamic simulation of flare-productive active regions, especially focusing on the thermodynamic properties of the plasma involved in the eruption and their relation to the magnetic flux rope. The preexisting flux rope, which carries cold and dense plasma, rises quasi-statically before the onset of eruptions. During this stage, the flux rope does not show obvious signatures in extreme ultraviolet (EUV) emission. After the flare onset, a thin “current shell” is generated around the erupting flux rope. Moreover, a current sheet is formed under the flux rope, where two groups of magnetic arcades reconnect and create a group of postflare loops. The plasma within the “current shell,” current sheet, and postflare loops are heated to more than 10 MK. The postflare loops give rise to abundant soft X-ray emission. Meanwhile, a majority of the plasma hosted in the flux rope is heated to around 1 MK, and the main body of the flux rope is manifested as a bright arch in cooler EUV passbands such as the AIA 171 Å channel.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Of all the light elements, the evolution of lithium (Li) in the Milky Way is perhaps the most difficult to explain. Li is difficult to synthesize and is easily destroyed, making most stellar sites unsuitable for producing Li in sufficient quantities to account for the protosolar abundance. For decades, novae have been proposed as a potential explanation for this “Galactic Li problem,” and the recent detection of <jats:sup>7</jats:sup>Be in the ejecta of multiple nova eruptions has breathed new life into this theory. In this work, we assess the viability of novae as dominant producers of Li in the Milky Way. We present the most comprehensive treatment of novae in a galactic chemical evolution code to date, testing theoretically and observationally derived nova Li yields by integrating metallicity-dependent nova ejecta profiles computed using the binary population synthesis code <jats:monospace>binary</jats:monospace>_<jats:monospace>c</jats:monospace> with the galactic chemical evolution code <jats:monospace>OMEGA+</jats:monospace>. We find that our galactic chemical evolution models which use observationally derived Li yields account for the protosolar Li abundance very well, while models relying on theoretical nova yields cannot reproduce the protosolar observation. A brief exploration of physical uncertainties including single-stellar yields, the metallicity resolution of our nova treatment, common-envelope physics, and nova accretion efficiencies indicates that this result is robust to physical assumptions. Scatter within the observationally derived Li yields in novae is identified as the primary source of uncertainty, motivating further observations of <jats:sup>7</jats:sup>Be in nova ejecta.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Type Ia supernovae (SNe Ia) are securely understood to come from the thermonuclear explosion of a white dwarf as a result of binary interaction, but the nature of that binary interaction and the secondary object is uncertain. Recently, a double white dwarf model known as the dynamically driven double-degenerate double-detonation (D6) model has become a promising explanation for these events. One realization of this scenario predicts that the companion may survive the explosion and reside within the remnant as a fast moving (<jats:italic>V</jats:italic> <jats:sub>peculiar</jats:sub> &gt; 1000 km s<jats:sup>−1</jats:sup>), overluminous (<jats:italic>L</jats:italic> &gt; 0.1 <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>) white dwarf. Recently, three objects that appear to have these unusual properties have been discovered in the Gaia survey. We obtained photometric observations of the SN Ia remnant SN 1006 with the Dark Energy Camera over four years to attempt to discover a similar star. We present a deep, high-precision astrometric proper-motion survey of the interior stellar population of the remnant. We rule out the existence of a high-proper-motion object consistent with our tested realization of the D6 scenario (<jats:italic>V</jats:italic> <jats:sub>transverse</jats:sub> &gt; 600 km s<jats:sup>−1</jats:sup> with <jats:italic>m</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> &lt; 21 corresponding to an intrinsic luminosity of <jats:italic>L</jats:italic> &gt; 0.0176 <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>). We conclude that such a star does not exist within the remnant or is hidden from detection by either strong localized dust or the unlikely possibility of ejection from the binary system almost parallel to the line of sight.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Gaia mission recently revealed an excess population of equal-mass “twin” wide binaries, with mass ratio <jats:italic>q</jats:italic> ≳ 0.95, extending to separations of at least 1000 au. The origin of this population is an enigma: Twin binaries are thought to form via correlated accretion in circumbinary disks, but the typical observed protostellar disks have radii of ∼100 au, far smaller than the separations of the widest twins. Here, we infer the eccentricity distribution of wide twins from the distribution of their <jats:italic>v</jats:italic>–<jats:italic>r</jats:italic> angles, i.e., the angle between the components’ separation and relative velocity vectors. We find that wide twins must be on extremely eccentric orbits. For the excess-twin population at 400–1000 au, we infer a near-delta-function excess of high-eccentricity systems, with eccentricity 0.95 ≲ <jats:italic>e</jats:italic> ≤ 1. These high eccentricities for wide twins imply pericenter distances of order 10 au and suggest that their orbits were scattered via dynamical interactions in their birth environments, consistent with a scenario in which twins are born in circumbinary disks and subsequently widened. These results further establish twin wide binaries as a distinct population and imply that wide twins can be used as a probe of the dynamical history of stellar populations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first dynamical simulation that recreates the major properties of the archetypal nearby spiral galaxy M101. Our model describes a grazing but relatively close (∼14 kpc) passage of the companion galaxy NGC 5474 through M101's outer disk approximately 200 Myr ago. The passage is retrograde for both disks, yielding a relatively strong gravitational response while suppressing the formation of long tidal tails. The simulation reproduces M101's overall lopsidedness, as well as the extended NE Plume and the sharp western edge of the galaxy’s disk. The post-starburst populations observed in M101's NE Plume are likely a result of star formation triggered at the point of contact where the galaxies collided. Over time, this material will mix azimuthally, leaving behind diffuse, kinematically coherent stellar streams in M101's outer disk. At late times after the encounter, the density profile of M101's disk shows a broken “upbending” profile similar to those seen in spiral galaxies in denser environments, further demonstrating the connection between interactions and long-term structural changes in galaxy disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a follow-up study on the recent detection of two X-ray flaring events by MAXI/Gas Slit Camera observations in soft and hard X-rays from MAXI J0709–159 in the direction of HD 54786 (LY CMa), on 2022 January 25. The X-ray luminosity during the flare was around 10<jats:sup>37</jats:sup> erg s<jats:sup>−1</jats:sup> (MAXI), which got reduced to 10<jats:sup>32</jats:sup> erg s<jats:sup>−1</jats:sup> (NuSTAR) after the flare. We took low-resolution spectra of HD 54786 from the 2.01 m Himalayan Chandra Telescope and the 2.34 m Vainu Bappu Telescope (VBT) facilities in India, on 2022 February 1 and 2. In addition to H<jats:italic>α</jats:italic> emission, we found emission lines of He <jats:sc>i</jats:sc> in the optical spectrum of this star. By comparing our spectrum of the object with those from the literature we found that He <jats:sc>i</jats:sc> lines show variability. Using photometric studies we estimate that the star has an effective temperature of 20,000 K. Although HD 54786 is reported as a supergiant in previous studies, our analysis favors it to be evolving off the main sequence in the color–magnitude diagram. We could not detect any infrared excess, ruling out the possibility of IR emission from a dusty circumstellar disk. Our present study suggests that HD 54786 is a Be/X-ray binary system with a compact object companion, possibly a neutron star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present sensitive NH<jats:sub>3</jats:sub> (1,1)–(7,7) line images from the Karl G. Jansky Very Large Array toward successive shocks, which are associated with the blueshifted outflow lobe driven by the compact protobinary system L1157. Within a projection distance of 0.1 pc, our observations not only trace the quiescent and cold gas in the flattened envelope, but also illustrate the complex physical and chemical processes that take place where the high-velocity jet impinges on its surrounding medium. Specifically, the NH<jats:sub>3</jats:sub> ortho-to-para ratio is enhanced by a factor of 2–2.5 along the jet path, where the velocity offset between the line peak and the blueshifted wing reaches values as high as 10 km s<jats:sup>−1</jats:sup>; it also shows a strong spatial correlation with the NH<jats:sub>3</jats:sub> column density, which is enhanced to &gt;10<jats:sup>16</jats:sup> cm<jats:sup>−2</jats:sup> toward the shock cavities. At a linear resolution of 1500 au, our refined temperature map from the seven NH<jats:sub>3</jats:sub> lines shows a gradient from the warm B0 eastern cavity wall (&gt;120 K) to the cool cavity B1 and the earlier shock B2 (&lt;80 K), indicating shock heating.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this Letter, we report the discovery of an ultraluminous fast-evolving transient in rest-frame UV wavelengths, MUSSES2020J, soon after its occurrence by using the Hyper Suprime-Cam (HSC) mounted on the 8.2 m Subaru telescope. The rise time of about 5 days with an extremely high UV peak luminosity shares similarities to a handful of fast blue optical transients whose peak luminosities are comparable with the most luminous supernovae while their timescales are significantly shorter (hereafter “fast blue ultraluminous transient,” FBUT). In addition, MUSSES2020J is located near the center of a normal low-mass galaxy at a redshift of 1.063, suggesting a possible connection between the energy source of MUSSES2020J and the central part of the host galaxy. Possible physical mechanisms powering this extreme transient such as a wind-driven tidal disruption event and an interaction between supernova and circumstellar material are qualitatively discussed based on the first multiband early-phase light curve of FBUTs, although whether the scenarios can quantitatively explain the early photometric behavior of MUSSES2020J requires systematical theoretical investigations. Thanks to the ultrahigh luminosity in UV and blue optical wavelengths of these extreme transients, a promising number of FBUTs from the local to the high-<jats:italic>z</jats:italic> universe can be discovered through deep wide-field optical surveys in the near future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Pulsar radio emission may be generated in pair discharges that fill the pulsar magnetosphere with plasma as an accelerating electric field is screened by freshly created pairs. In this Letter, we develop a simplified analytic theory for the screening of the electric field in these pair discharges and use it to estimate total radio luminosity and spectrum. The discharge has three stages. First, the electric field is screened for the first time and starts to oscillate. Next, a nonlinear phase occurs. In this phase, the amplitude of the electric field experiences strong damping because the field dramatically changes the momenta of newly created pairs. This strong damping ceases, and the system enters a final linear phase, when the electric field can no longer dramatically change pair momenta. Applied to pulsars, this theory may explain several aspects of radio emission, including the observed luminosity, <jats:italic>L</jats:italic> <jats:sub>rad</jats:sub> ∼ 10<jats:sup>28</jats:sup> erg s<jats:sup>−1</jats:sup>, and the observed spectrum, <jats:italic>S</jats:italic> <jats:sub> <jats:italic>ω</jats:italic> </jats:sub> ∼ <jats:italic>ω</jats:italic> <jats:sup>−1.4±1.0</jats:sup>.</jats:p>