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<jats:title>Abstract</jats:title> <jats:p>In this Letter, we give a detailed analysis of the M3.3 class flare that occurred on 2013 August 17 (SOL2013-08-17T18:16). It presents a clear picture of mutual magnetic interaction initially from the photosphere to the corona via the abrupt rapid shearing motion of a small sunspot before the flare, and then suddenly from the corona back to the photosphere via the sudden retraction motion of the same sunspot during the flare’s impulsive phase. About 10 hr before the flare, a small sunspot in the active region NOAA 11818 started to move northeast along a magnetic polarity inversion line (PIL), creating a shearing motion that changed the quasi-static state of the active region. A filament right above the PIL was activated following the movement of the sunspot and then got partially erupted. The eruption eventually led to the M3.3 flare. The sunspot was then suddenly pulled back to the opposite direction upon the flare onset. During the backward motion, the Lorentz force underwent a simultaneous impulsive change both in magnitude and direction. Its directional change is found to be conformable with the retraction motion. The observation provides direct evidence for the role of the shearing motion of the sunspot in powering and triggering the flare. It especially confirms that the abrupt motion of a sunspot during a solar flare is the result of a backreaction caused by the reconfiguration of the coronal magnetic field.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To explain observations of abundant circumstellar dust and high stellar wind velocity, most models simply postulate the efficient nucleation and growth of silicate dust particles. Here, we report measurement of the SiO–(SiO<jats:sub>x</jats:sub>)<jats:sub>n</jats:sub> grain sticking coefficient in a microgravity sounding rocket experiment, indicating very inefficient (0.005–0.016) grain formation from the vapor. Application of this measurement to radiative-driven winds in oxygen-rich asymptotic giant branch stars indicates that the initial grain condensate population should consist of very tiny dust particles in very large numbers. Aggregation of this dust population will produce low-dimension fractal aggregates that should couple well to the stellar radiation field and efficiently drive stellar mass loss.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>KH 15D contains a circumbinary disk that is tilted relative to the orbital plane of the central binary. The precession of the disk and the orbital motion of the binary together produce rich phenomena in the photometric light curve. In this work, we present the discovery and preliminary analysis of two objects that resemble the key features of KH 15D from the Zwicky Transient Facility. These new objects, Bernhard-1 and Bernhard-2, show large-amplitude ( &gt;1.5 mag), long-duration (more than tens of days), and periodic dimming events. A one-sided screen model is developed to model the photometric behavior of these objects, the physical interpretation of which is a tilted, warped circumbinary disk occulting the inner binary. Changes in the object light curves suggest potential precession periods over timescales longer than 10 yr. Additional photometric and spectroscopic observations are encouraged to better understand the nature of these interesting systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We test the hypothesis that an embedded giant planet in the IM Lupi protostellar disk can produce velocity kinks seen in CO line observations as well as the spiral arms seen in scattered light and continuum emission. We inject planets into 3D hydrodynamics simulations of IM Lupi, generating synthetic observations using Monte Carlo radiative transfer. We find that an embedded planet of 2–3 <jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub> can reproduce non-Keplerian velocity perturbations, or “kinks”, in the <jats:sup>12</jats:sup>CO <jats:italic>J</jats:italic> = 2–1 channel maps. Such a planet can also explain the spiral arms seen in 1.25 mm dust continuum emission and 1.6 <jats:italic>μ</jats:italic>m scattered-light images. We show that the wake of the planet can be traced in the observed peak velocity map, which appears to closely follow the morphology expected from our simulations and from analytic models of planet–disk interaction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is usually thought that long-duration gamma-ray bursts (GRBs) are associated with massive star core collapse, whereas short-duration GRBs are associated with mergers of compact stellar binaries. The discovery of a kilonova associated with a nearby (350 Mpc) long-duration GRB—GRB 211211A, however, indicates that the progenitor of this long-duration GRB is a compact object merger. Here we report the Fermi-LAT detection of gamma-ray (&gt;100 MeV) afterglow emission from GRB 211211A, which lasts ∼20,000 s after the burst, the longest event for conventional short-duration GRBs ever detected. We suggest that this gamma-ray emission results from afterglow synchrotron emission. The soft spectrum of GeV emission may arise from a limited maximum synchrotron energy of only a few hundreds of MeV at ∼20,000 s. The usually long duration of the GeV emission could be due to the proximity of this GRB and the long deceleration time of the GRB jet that is expanding in a low-density circumburst medium, consistent with the compact stellar merger scenario.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recently, a kilonova-associated gamma-ray burst (GRB 211211A), whose light curve consists of a precursor (∼0.2 s), a hard spiky emission (∼10 s), and a soft long extended emission (∼40 s), has attracted great attention. Kilonova association could prove its merger origin, while the detection of the precursor can be used to infer at least one highly magnetized neutron star (NS) being involved in the merger. In this case, a strong magnetic flux Φ is expected to surround the central engine of GRB 211211A. Here we suggest that when Φ is large enough, the accretion flow could be halted far from the innermost stable radius, which will significantly prolong the lifetime of the accretion process, and so the GRB duration. For example, we show that as long as the central black hole (BH) is surrounded by a strong magnetic flux Φ ∼ 10<jats:sup>29</jats:sup>cm<jats:sup>2</jats:sup> G, an accretion flow with <jats:inline-formula> <jats:tex-math> <?CDATA ${\dot{M}}_{\mathrm{ini}}\simeq 0.1{M}_{\odot }\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>ini</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≃</mml:mo> <mml:mn>0.1</mml:mn> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac80c7ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> could be halted at 40 times the gravitational radius and be slowly transferred into the black hole on the order of ∼10 s, which naturally explains the duration of hard spiky emission. After most of the disk mass has been accreted onto the BH, the inflow rate will be reduced, so a long and soft extended emission is expected when a new balance between the magnetic field and the accretion current is reconstructed at a larger radius. Our results further support that the special behavior of GRB 211211A is mainly due to the strong magnetic field of its progenitor stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the analysis of five black hole candidates identified from gravitational microlensing surveys. Hubble Space Telescope astrometric data and densely sampled light curves from ground-based microlensing surveys are fit with a single-source, single-lens microlensing model in order to measure the mass and luminosity of each lens and determine if it is a black hole. One of the five targets (OGLE-2011-BLG-0462/MOA-2011-BLG-191 or OB110462 for short) shows a significant &gt;1 mas coherent astrometric shift, little to no lens flux, and has an inferred lens mass of 1.6–4.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. This makes OB110462 the first definitive discovery of a compact object through astrometric microlensing and it is most likely either a neutron star or a low-mass black hole. This compact-object lens is relatively nearby (0.70–1.92 kpc) and has a slow transverse motion of &lt;30 km s<jats:sup>−1</jats:sup>. OB110462 shows significant tension between models well fit to photometry versus astrometry, making it currently difficult to distinguish between a neutron star and a black hole. Additional observations and modeling with more complex system geometries, such as binary sources, are needed to resolve the puzzling nature of this object. For the remaining four candidates, the lens masses are &lt;2<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and they are unlikely to be black holes; two of the four are likely white dwarfs or neutron stars. We compare the full sample of five candidates to theoretical expectations on the number of black holes in the Milky Way (∼10<jats:sup>8</jats:sup>) and find reasonable agreement given the small sample size.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Accreting protoplanets enable the direct characterization of planet formation. As part of a high-contrast imaging search for accreting planets with the Hubble Space Telescope (HST) Wide Field Camera 3, we present H<jats:italic>α</jats:italic> images of AB Aurigae (AB Aur), a Herbig Ae/Be star harboring a transition disk. The data were collected in two epochs of direct-imaging observations using the F656N narrowband filter. After subtracting the point-spread function of the primary star, we identify a pointlike source located at a position angle of 182.°5 ± 1.°4 and a separation of 600 ± 22 mas relative to the host star. The position is consistent with the recently identified protoplanet candidate AB Aur b. The source is visible in two individual epochs separated by ∼50 days, and the H<jats:italic>α</jats:italic> intensities in the two epochs agree. The H<jats:italic>α</jats:italic> flux density is <jats:italic>F</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub> = 1.5 ± 0.4 mJy, 3.2 ± 0.9 times the optical continuum determined by published HST/STIS photometry. In comparison to PDS 70 b and c, the H<jats:italic>α</jats:italic> excess emission is weak. The central star is accreting and the stellar H<jats:italic>α</jats:italic> emission has a similar line-to-continuum ratio as seen in AB Aur b. We conclude that both planetary accretion and scattered stellar light are possible sources of the H<jats:italic>α</jats:italic> emission, and the H<jats:italic>α</jats:italic> detection alone does not validate AB Aur b as an accreting protoplanet. Disentangling the origin of the emission will be crucial for probing planet formation in the AB Aur disk.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the analysis of Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía (MEGARA) high-dispersion integral field spectroscopic observations of the bipolar planetary nebula (PN) M 3–38. These observations unveil the presence of a fast outflow aligned with the symmetry axis of M 3–38 that expands with a velocity of up to ±225 km s<jats:sup>−1</jats:sup>. The deprojected space velocity of this feature can be estimated to be ≈320<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-60}^{+130}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>60</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>130</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac78dcieqn1.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup>, which together with its highly collimated morphology suggests that it is one of the fastest jets detected in a PN. We have also used Kepler observations of the central star of M 3–38 to unveil variability associated with a dominant period of 17.7 days. We attribute this to the presence of a low-mass star with an orbital separation of ≈0.12–0.16 au. The fast and collimated ejection and the close binary system point toward a common envelope formation scenario for M 3–38.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An understanding of abundance and distribution of water vapor in the innermost region of protoplanetary disks is key to understanding the origin of habitable worlds and planetary systems. Past observations have shown H<jats:sub>2</jats:sub>O to be abundant and a major carrier of elemental oxygen in disk surface layers that lie within the inner few astronomical units of the disk. The combination of high abundance and strong radiative transitions leads to emission lines that are optically thick across the infrared spectral range. Its rarer isotopologue <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e55ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> traces deeper into this layer and will trace the full content of the planet-forming zone. In this work, we explore the relative distribution of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{16}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>16</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e55ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e55ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> within a model that includes water self-shielding from the destructive effects of ultraviolet radiation. In this Letter we show that there is an enhancement in the relative <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e55ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> abundance high up in the warm molecular layer within 0.1–10 au due to self-shielding of CO, C<jats:sup>18</jats:sup>O, and H<jats:sub>2</jats:sub>O. Most transitions of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e55ieqn7.gif" xlink:type="simple" /> </jats:inline-formula> that can be observed with JWST will partially emit from this layer, making it essential to take into account how H<jats:sub>2</jats:sub>O self-shielding may effect the H<jats:sub>2</jats:sub>O to <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e55ieqn8.gif" xlink:type="simple" /> </jats:inline-formula> ratio. Additionally, this reservoir of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e55ieqn9.gif" xlink:type="simple" /> </jats:inline-formula>-enriched gas in combination with the vertical “cold finger” effect might provide a natural mechanism to account for oxygen isotopic anomalies found in meteoritic material in the solar system.</jats:p>