Clay weekly context brief for the Astro category (ISO week 2026-W33). Clay tracks publications from the Astro feed list. Below are recent items from this category, each with its source and a short description of what the publication covers when one is available in the source feed. Recent publications: 1. 3-form dark energy and cosmic birefringence Source: astro-ph.CO (Cosmology and Nongalactic Astrophysics) Link: https://arxiv.org/abs/2608.05296 3-forms are interesting fields to study in the cosmological context for numerous reasons, such as being candidates for explaining inflation and dark energy. 2. The Zero-Age Massive Stellar Population of W49A from VLA Observations Source: astro-ph.SR (Solar and Stellar Astrophysics) Link: https://arxiv.org/abs/2608.05453 We use all-configuration VLA data at 3.3 cm with a physical resolution of ~2000 AU to infer the embedded zero-age massive stellar population of the W49A protocluster, as traced by its compact, ultracompact (UC), and hypercompact (HC) H II regions. 3. Can the Efron-Petrosian Method Recover the Inverse-Square Distance Law for Simulated Radio Pulsar Fluxes? Source: astro-ph.HE (High Energy Astrophysical Phenomena) Link: https://arxiv.org/abs/2512.00784 We test whether the Efron-Petrosian (E-P) method can recover the inverse-square law dependence of the radio pulsar flux, using a synthetic catalog generated according to the specifications of the Parkes Multi-beam survey using the {\tt PsrPopPy} software. 4. The Dynamics of Planetary Ejection Source: astro-ph.EP (Earth and Planetary Astrophysics) Link: https://arxiv.org/abs/2608.00173 The ubiquity of free-floating planets inferred from microlensing and direct imaging surveys suggests that planetary ejection---a process in which planets initially born encircling a stellar host become gravitationally unbound---is common. 5. The Most Dangerous Seed: Nonlinear Optimal Perturbations in Rayleigh-Taylor Instability Source: astro-ph.GA (Astrophysics of Galaxies) Link: https://arxiv.org/abs/2608.04085 Long-term instabilities in astrophysical fluids are inherently nonlinear, where even small-amplitude perturbations can trigger dramatic instability. 6. Hard X-Ray Focal-Plane Compton Spectro-Polarimeter: Detector Development and Sensitivity Evaluation Source: astro-ph.IM (Instrumentation and Methods for Astrophysics) Link: https://arxiv.org/abs/2608.01529 The scientific potential of X-ray polarimetry has long been recognized, yet the challenges of measuring polarization have left it largely unexplored, mainly in the hard X-ray regime. 7. A Gaussian Covariance Matrix for Joint Pre- and Post-Reconstruction Full-Shape Power Spectrum Analysis Source: astro-ph.CO (Cosmology and Nongalactic Astrophysics) Link: https://arxiv.org/abs/2608.05504 We apply the Gaussian covariance formalism to develop a semi-analytical covariance model for the joint analysis of pre-reconstruction, post-reconstruction, and cross full-shape galaxy power spectra. 8. Decomposition of Solar Wind Velocity Distribution Functions with Orthogonal Polynomials Source: astro-ph.SR (Solar and Stellar Astrophysics) Link: https://arxiv.org/abs/2608.06324 We present a framework for decomposing solar-wind velocity distribution functions (VDFs) using orthogonal polynomial bases. 9. Vacuum birefringence and the polarized X-ray emission from a radio magnetar Source: astro-ph.HE (High Energy Astrophysical Phenomena) Link: https://arxiv.org/abs/2509.19446 Magnetars are isolated neutron stars with exceptionally strong surface fields exceeding $10^{14}$ G. 10. Two inner dust clumps in PDS 70. A third protoplanet traced by trojan material or a substructured inner disk? Source: astro-ph.EP (Earth and Planetary Astrophysics) Link: https://arxiv.org/abs/2606.26381 The PDS 70 cavity hosts two confirmed directly imaged protoplanets and a third inner planet candidate at 13au, labeled PDS 70 d. 11. Predicting the Kinematics of the Cold Circumgalactic Medium from its Morphology using Convolutional Neural Networks Source: astro-ph.GA (Astrophysics of Galaxies) Link: https://arxiv.org/abs/2608.04087 We present a novel approach to predicting plane-of-sky velocities of cold gas clouds in the circumgalactic medium (CGM) of galaxies. 12. In orbit background for hard X-ray CubeSat polarimeters: case study of the CUSP mission in low-earth orbit Source: astro-ph.IM (Instrumentation and Methods for Astrophysics) Link: https://arxiv.org/abs/2608.01524 The CUbesat Solar Polarimeter (CUSP) project aims to measure the linear polarization of solar flares in the 25 - 100 keV hard X-ray band using a Compton scattering polarimeter. 13. photo-3x2-pt: Cosmology from cosmic shear and galaxy clustering with a single photometric galaxy catalog Source: astro-ph.CO (Cosmology and Nongalactic Astrophysics) Link: https://arxiv.org/abs/2608.05530 We perform a joint cosmological analysis using angular power spectra of galaxy clustering, galaxy-shear cross correlation, and cosmic shear (hereafter referred to as photo-3x2-pt) measured from the Hyper Suprime-Cam year-3 (HSC-Y3) weak lensing shape catalog. 14. Strong Zeeman effects in the Fe I 5434.5 {\AA} line observed in a sunspot on August 17, 2024 Source: astro-ph.SR (Solar and Stellar Astrophysics) Link: https://arxiv.org/abs/2608.06316 The Fe I 5434.5 {\AA} line is widely used as a non-magnetic reference due to its small effective Land\'e factor of $-0.014$. 15. Large Gravitational Wave Phase Shifts from Strong 3-body Interactions in Dense Stellar Clusters Source: astro-ph.HE (High Energy Astrophysical Phenomena) Link: https://arxiv.org/abs/2411.08572 The phase evolution of gravitational waves (GWs) can be modulated by the astrophysical environment surrounding the source, which provides a probe for the origin of individual binary black holes (BBHs) using GWs alone. 16. Characterizing the bolometric-photoevaporative transition in young sub-Neptunes with radiation-hydrodynamic simulations Source: astro-ph.EP (Earth and Planetary Astrophysics) Link: https://arxiv.org/abs/2605.02766 Hydrodynamic atmospheric escape plays a central role in shaping the demographics of small, close-in exoplanets. 17. Column-Density Estimation from the Equivalent Widths of Absorption Doublets Source: astro-ph.GA (Astrophysics of Galaxies) Link: https://arxiv.org/abs/2608.04088 Na I D absorption is widely used to estimate the dust extinction toward Galactic and extragalactic sources, but the inferred column densities are unreliable once the lines saturate. 18. MiraSOL: a DMD-based spectrograph for resolved solar spectroscopy Source: astro-ph.IM (Instrumentation and Methods for Astrophysics) Link: https://arxiv.org/abs/2608.01493 We present the science motivation, preliminary design requirements, device laboratory testing and a prototype for an new experimental platform for solar observations, MiraSOL. 19. Reanalyzing Megamasers: a low value of $H_0$ from a local probe changes our view of the Hubble Tension Source: astro-ph.CO (Cosmology and Nongalactic Astrophysics) Link: https://arxiv.org/abs/2608.06247 Megamaser distances can be measured without using the traditional distance ladder. 20. On the degeneracy of solutions from stellar spectropolarimetric data Source: astro-ph.SR (Solar and Stellar Astrophysics) Link: https://arxiv.org/abs/2608.06306 In this work we investigate the inversion accuracy of stellar magnetic fields through the analysis of spectropolarimetric data. 21. A Neutron Star Hidden Inside a Black Hole Source: astro-ph.HE (High Energy Astrophysical Phenomena) Link: https://arxiv.org/abs/2608.06224 We investigate dark matter admixed neutron stars in which the neutron star coexists with an anisotropic dark matter halo described by the Einasto density profile, a model recently shown to produce regular, singularity-free black hole solutions~[Phys. 22. Magnetic Dynamo Driven by Inertial Waves Source: astro-ph.EP (Earth and Planetary Astrophysics) Link: https://arxiv.org/abs/2608.06086 We demonstrate, by studying precession-driven flows, that inertial wave hydrodynamic turbulence can drive a robust magnetic dynamo action. 23. Implications of Broad [O III] 4364 and UV Line Emission in Two Little Red Dots at z ~ 7 - 8 Source: astro-ph.GA (Astrophysics of Galaxies) Link: https://arxiv.org/abs/2608.04101 We present deep, NIRSpec G140M and G395M spectroscopy of Little Red Dots (LRDs) at z = 6.68 and z = 8.35. 24. Design and modeling of an oblique incidence dichroic mirror for a high contrast imaging system Source: astro-ph.IM (Instrumentation and Methods for Astrophysics) Link: https://arxiv.org/abs/2608.01394 The proposed Habitable Worlds Observatory (HWO) aims to detect and characterize Earth-like planets around Sun-like stars from the ultraviolet to the infrared using high-contrast imaging. 25. SPT-3G D1: Foreground-Robust Lensing Templates for Primordial Gravitational Wave Searches Source: astro-ph.CO (Cosmology and Nongalactic Astrophysics) Link: https://arxiv.org/abs/2608.06343 Gravitational lensing of the cosmic microwave background (CMB) generates B-mode polarization that acts as a source of contamination to searches for B modes generated by primordial gravitational waves (PGWs). 26. HI envelope around the carbon star V420 Vul Source: astro-ph.SR (Solar and Stellar Astrophysics) Link: https://arxiv.org/abs/2608.06245 We report the detection of an extended 21-cm parsec-scale \ion{H}{i} structure toward the Mira variable V420\,Vul using archival Galactic Arecibo L-band Feed Array survey data. 27. Emission line formation in scattering dominated media: implications for LRDs Source: astro-ph.HE (High Energy Astrophysical Phenomena) Link: https://arxiv.org/abs/2608.05283 Recent JWST observations of ``Little Red Dots'' (LRDs) reveal broad and prominent Balmer emission lines. 28. Inventories of Rich Carbon-Chain Chemistry in Prestellar and Starless Cores in the Perseus Molecular Cloud Source: astro-ph.EP (Earth and Planetary Astrophysics) Link: https://arxiv.org/abs/2608.05264 Carbon-chain molecules serve as an important reservoir of reactive organic matter that will eventually be incorporated into protoplanetary disks, planets, and cometary material. 29. Resolving dense photo-dissociation regions: the structure of photochemical fronts in three-dimensional gas distributions Source: astro-ph.GA (Astrophysics of Galaxies) Link: https://arxiv.org/abs/2608.04116 For decades, the Orion Bar has been the prototypical photo-dissociation region. 30. Towards optimal photometric calibration of digital astronomical plates with deep learning Source: astro-ph.IM (Instrumentation and Methods for Astrophysics) Link: https://arxiv.org/abs/2608.01391 Photometric calibration of digitized photographic plates is commonly modeled with separable magnitude-, color-, and position-dependent terms, but this separability can break down when image quality varies across the field in a magnitude-dependent way, leaving coupled spatial systematics in the residuals. 31. Equivalence of mapping gravitational wave background anisotropy across bases at equal information content Source: astro-ph.CO (Cosmology and Nongalactic Astrophysics) Link: https://arxiv.org/abs/2608.05200 Mapping anisotropies in the gravitational-wave background (GWB) requires choosing a basis to represent the sky intensity, such as pixel and spherical harmonic bases. Sources in this brief: astro-ph.CO (Cosmology and Nongalactic Astrophysics); astro-ph.EP (Earth and Planetary Astrophysics); astro-ph.GA (Astrophysics of Galaxies); astro-ph.HE (High Energy Astrophysical Phenomena); astro-ph.IM (Instrumentation and Methods for Astrophysics); astro-ph.SR (Solar and Stellar Astrophysics). Selected 31 of 389 available items for this weekly brief.