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<jats:title>Abstract</jats:title> <jats:p>The TESS lightcurves of the two cool Ap stars, 78 Vir and 52 Her, are used to derive new rotational periods for both stars. A frequency analysis of the light curve of 52 Her with the Generalized Lomb–Scargle periodogram reveals a periodic structure with three harmonics. The inverse of the fundamental frequency yields a rotational period of 3.840 ± 0.037 days for 52 Her. The same analysis for 78 Vir yields two harmonics with a rotation period of 3.718 ± 0.037 days, only slightly shorter than previous determinations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Convective motions extend beyond the nominal boundaries of a convection zone. These motions mix fluid through multiple mechanisms collectively called “convective boundary mixing.” In this note, we discuss three distinct fluid dynamical processes: convective overshoot, entrainment, and penetrative convection. We describe the structure of a convective boundary that these processes create. To resolve discrepancies between models and observations, the stellar astrophysics community should distinguish between these processes and parameterize each of them separately in 1D evolutionary models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A gravitational lens can imprint distinct features on the light curve of a gamma-ray burst (GRB). Most prominently, when creating multiple images, the light curves for all images should be identical, within a scale factor in amplitude. For GRB images that are bright enough to have significant counts in multiple time bins, the similarity of the light curves can be assessed with a straightforward <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> test. In response to a recent claim that the two pulses in GRB 200716C are lensed images of the same pulse, such a <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> test was computed. The test indicated that the likelihood that the two pulses are images of the same parent pulse is less than 0.218%, differing at about the 3.1<jats:italic>σ</jats:italic> confidence level. Therefore, under the given assumptions, GRB 200716C is not a compelling example of gravitational lensing.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Skye Equation of State (EOS) is built on top of automatic differentiation machinery. This makes it straightforward to modify, because all the requisite partial derivatives of the Helmholtz free energy are computed automatically via operator overloading. Here we demonstrate this advantage by implementing a new prescription for the anharmonic free energy of a crystalline one-component plasma. Apart from boilerplate and variable declarations, only 7 new lines of code were needed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>I show that the quadrupole of the Cosmic Microwave Background (CMB) evolves more rapidly than previously expected, as a result of the acceleration of the Sun toward the Galactic center. The acceleration, measured most recently by Gaia EDR3, implies a fractional change in the quadrupole of ∼10<jats:sup>−9</jats:sup> per year, an order of magnitude larger than expected from the evolution in the last scattering surface of the CMB.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Kuiper Belt contains a large number of minor bodies that collectively constrain the dynamical history of the solar system. These bodies are often classified into distinct populations. This note identifies a well-defined boundary (at <jats:italic>H</jats:italic>-magnitude = 5.65) that separates bright (large) objects from dimmer (smaller) objects. The probability that the two sub-samples are drawn from the same underlying distribution is <jats:italic>p</jats:italic> ∼ 10<jats:sup>−15</jats:sup>. The larger bodies (estimated radius <jats:italic>R</jats:italic> ≳ 125 km) are dynamically hot, as measured by their locations in the <jats:italic>e</jats:italic>-<jats:inline-formula> <jats:tex-math> <?CDATA $\sin i$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="rnaasac5b6cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> plane, and likely represent an implanted population. The smaller bodies (<jats:italic>R</jats:italic> ≲ 125 km) are dynamically colder and are likely to be primordial. The bright/large/hot population currently contains ∼200 members, including all ∼50 dwarf planet candidates in the Kuiper Belt.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We measured the parallax of the James Webb Space Telescope based on near simultaneous observations using the Lulin One-meter Telescope and the GROWTH India Telescope, separated at a distance of ∼4214 km. This serves a great demonstration for the concept of parallax commonly taught in introductory astronomy courses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Line variations are studied in the far-ultraviolet spectra of 78 Vir collected with International Ultraviolet Explorer at phases of far-UV maximum and <jats:italic>at phases of far-UV minimum</jats:italic>. The far-UV spectrum of 78 Vir is populated with low-excitation transitions of light elements and iron-peak elements. The low excitation C <jats:sc>i</jats:sc> and N <jats:sc>i</jats:sc> lines are stronger at <jats:italic>phases of far-UV minimum</jats:italic>. Carbon appears to be underabundant and aluminum very underabundant in the atmosphere of 78 Vir. The lines of Si <jats:sc>i</jats:sc> and Si <jats:sc>ii</jats:sc> are stronger at <jats:italic>phases of far-UV minimum</jats:italic>. Many lines which strengthen at <jats:italic>phases of far-UV minimum</jats:italic> are due to low-excitation lines of Fe <jats:sc>ii</jats:sc> and Cr <jats:sc>ii</jats:sc> which suggests that both iron and chromium are unevenly distributed over the surface of 78 Vir.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Quasi-periodic (1.5 days) dimming (by circumstellar dust) of the 135 Myr-old AB Doradus moving group member HD 240779 was detected in photometry by TESS in late 2018. Similar observations two years later show no such signal, and ground-based photometry indicate that the signal was absent in late 2019. This suggests that the source of the dust did not survive long after 2018, e.g., it was a disrupted planetesimal, or that dust production by the body is episodic, analogous to the “evaporating” planets detected by Kepler.</jats:p>