Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We develop a physical framework for interpreting high-resolution images and kinematics of pre-planetary nebulae (“prePNe”). We use hydrodynamical models to infer the historical properties of fast collimated nuclear flows (“jet”) that successfully form hollow, candle-shaped lobes over ≈10<jats:sup>3</jats:sup> yr, including the density, momenta, and geometry of the jet and its environment. Next we vary the most influential parameters of this “baseline” model to investigate how changes in the flow parameters affect the model outcomes after 900 yr. Several generic conclusions emerge, such as the injected flows that create the hollow lobes must be light, “tapered,” and injected considerably faster than the lobe expansion speed. Multipolar and starfish prePNe probably evolve from wide-angle flows in which thin-shell instabilities corrugate their leading edges. We show how the common linear correlation of Doppler shift and position along the lobe is a robust outcome of the interaction of tapered diverging streamlines with the lobes’ curved walls. Finally, we probe how modest toroidal magnetic fields added to the fast flow affect the outcome of the baseline model. We conclude that the light, field-free, tapered baseline flow model is not only a successful and universal paradigm for unraveling the histories of lobe formation in prePNe, but also provides a comprehensive, inclusive framework for understanding the details of the shapes, sizes, and internal kinematics of their edges.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Polycyclic aromatic hydrocarbons (PAHs) and nanoparticles are expected to play an important role in many astrophysical processes due to their dominant surface area, including gas heating, chemistry, star formation, and anomalous microwave emission. In dense magnetized molecular clouds where C-shocks are present, PAHs and nanoparticles are widely believed to originate from grain shattering due to grain–grain collisions. The remaining question is whether these nanoparticles can survive in the dense and hot shocked regions, and how to constrain their size and abundance with observations. In this paper, we present a new mechanism to destroy nanoparticles in C-shocks based on centrifugal stress within rapidly spinning nanoparticles spun up by stochastic atomic bombardment, which is termed rotational disruption. We find that, due to supersonic neutral gas-charged grain drift in C-shocks, nanoparticles can be spun up to suprathermal rotation by stochastic torques exerted by supersonic neutral flow. The resulting centrifugal stress within suprathermally rotating nanoparticles can exceed the maximum tensile strength of grain material (<jats:italic>S</jats:italic> <jats:sub>max</jats:sub>), resulting in rapid disruption of nanoparticles smaller than <jats:italic>a</jats:italic> ∼ 1 nm for <jats:inline-formula> <jats:tex-math> <?CDATA ${S}_{\max }\sim {10}^{9}\,\mathrm{erg}\,{\mathrm{cm}}^{-3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab1845ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. The proposed disruption mechanism is shown to be more efficient than thermal sputtering in controlling the lower cutoff of grain size distribution in C-shocks. We model microwave emission from spinning nanoparticles in C-shocks subject to supersonic neutral drift and rotational disruption. We find that suprathermally rotating nanoparticles can emit strong microwave radiation, and both peak flux and peak frequency increase with increasing shock velocity. We suggest spinning dust as a new method to constrain nanoparticles and trace shock velocities in shocked dense regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We describe PSR J1926−0652, a pulsar recently discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using sensitive single-pulse detections from FAST and long-term timing observations from the Parkes 64 m radio telescope, we probed phenomena on both long and short timescales. The FAST observations covered a wide frequency range from 270 to 800 MHz, enabling individual pulses to be studied in detail. The pulsar exhibits at least four profile components, short-term nulling lasting from 4 to 450 pulses, complex subpulse drifting behaviors and intermittency on scales of tens of minutes. While the average band spacing <jats:italic>P</jats:italic> <jats:sub>3</jats:sub> is relatively constant across different bursts and components, significant variations in the separation of adjacent bands are seen, especially near the beginning and end of a burst. Band shapes and slopes are quite variable, especially for the trailing components and for the shorter bursts. We show that for each burst the last detectable pulse prior to emission ceasing has different properties compared to other pulses. These complexities pose challenges for the classic carousel-type models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper the unique data from the <jats:italic>Multi-Order Solar Extreme-Ultraviolet Spectrograph</jats:italic> (<jats:italic>MOSES</jats:italic>) are used to investigate transition region explosive events in the He <jats:sc>ii</jats:sc> <jats:italic>λ</jats:italic>304 spectral line. Particular attention is paid to two example events: one blueshifted jet and one bidirectional jet. Observations suggest that these events consist exclusively of high-velocity (∼100 km s<jats:sup>−1</jats:sup>) plasma. These two and other examples presented here exhibit a striking lack of emission in the line core. No acceleration phase is observed at the onset of either event. In total, 41 examples of explosive events are identified, including 5 blueshifted jets, 2 redshifted jets, and 10 bidirectional jets. The remaining 24 events resist simple classification, but observations indicate compact, highly Doppler-shifted emission. Event spatial scales and lifetimes are consistent with published explosive event characteristics. Data from the Michelson Doppler Imager provide magnetic context to the <jats:italic>MOSES</jats:italic> observations. Bidirectional jets lacking line core emission are interesting because they are predicted in models of Petschek reconnection in the transition region. </jats:p>