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1. The Comprehensive Archive of Substellar and Planetary Accretion Rates

   https://doi.org/10.3847/1538-3881/ad06b8  

   Betti, S K; Follette, K B; Ward-Duong, K; Peck, A E; Aoyama, Y; Bary, J; Dacus, B; Edwards, S; Marleau, G-D; Mohamed, K; et al (November 2023, The Astronomical Journal)

   Abstract Accretion rates ( $\dot{M}$) of young stars show a strong correlation with object mass (M); however, extension of the $\dot{M}–M$relation into the substellar regime is less certain. Here, we present the Comprehensive Archive of Substellar and Planetary Accretion Rates (CASPAR), the largest compilation to date of substellar accretion diagnostics. CASPAR includes: 658 stars, 130 brown dwarfs, and 10 bound planetary mass companions. In this work, we investigate the contribution of methodological systematics to scatter in the $\dot{M}–M$relation and compare brown dwarfs to stars. In our analysis, we rederive all quantities using self-consistent models, distances, and empirical line flux to accretion luminosity scaling relations to reduce methodological systematics. This treatment decreases the original 1σscatter in the $\log \dot{M}–\log M$relation by ∼17%, suggesting that it makes only a small contribution to the dispersion. The CASPAR rederived values are best fit by $\dot{M}\propto M^{2.02\pm 0.06}$from 10M_Jto 2M_⊙, confirming previous results. However, we argue that the brown-dwarf and stellar populations are better described separately and by accounting for both mass and age. Therefore, we derive separate age-dependent $\dot{M}–M$relations for these regions and find a steepening in the brown-dwarf $\dot{M}–M$slope with age. Within this mass regime, the scatter decreases from 1.36 dex to 0.94 dex, a change of ∼44%. This result highlights the significant role that evolution plays in the overall spread of accretion rates, and suggests that brown dwarfs evolve faster than stars, potentially as a result of different accretion mechanisms. 

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2. Fundamental Parameters for Central Stars of 103 Infrared Bow Shock Nebulae

   https://doi.org/10.3847/1538-4357/ade22f  

   Patten, Nikhil; Kobulnicky, Henry A; Povich, Matthew S; Whisnant, Angelica S; Andrews, Sydney; Boone, Alexandra; Dandu, Srujan; Jones, Naomi; Justice, S Nick; Hope, Dylan; et al (July 2025, The Astrophysical Journal)

   Abstract Stellar bow shock nebulae are arcuate shock fronts formed by the interaction of radiation-driven stellar winds and the relative motion of the ambient interstellar material. Stellar bow shock nebulae provide a promising means to measure wind-driven mass loss, independent of other established methods. In this work, we characterize the stellar sources at the center of bow shock nebulae drawn from all-sky catalogs of 24μm–selected nebulae. We obtain new, low-resolution blue optical spectra for 104 stars and measure stellar parameters temperatureT_eff, surface gravity $\log g$, and projected rotational broadening $v\sin i$. We perform additional photometric analysis to measure stellar radiusR_*, luminosityL_*, and visual-band extinctionA_V. All but one of our targets are O and early B stars, with temperatures ranging fromT= 16.5 to 46.8 kK, gravities from $\log g=$2.57 to 4.60, and $v\sin i$from <100 to 400 km s⁻¹. With the exception of rapid rotatorζOph, bow shock stars do not rotate at or near critical velocities. At least 60 of 103 (60%) OB bow shock stars are binaries, consistent with the multiplicity fraction of other OB samples. The sample shows a runaway fraction of 23%, with 19 stars havingv_2D≥ 25 km s⁻¹. Of the 19 runaways, at least 15 (≥79%) are binaries, favoring dynamical ejection over the binary supernova channel for producing runaways. We provide a comprehensive census of stellar parameters for bow shock stars, useful as a foundation for determining the mass-loss rates for OB-type stars—one of the single most critical factors in stellar evolution governing the production of neutron stars and black holes. 

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3. Mapping the Growth of Supermassive Black Holes as a Function of Galaxy Stellar Mass and Redshift

   https://doi.org/10.3847/1538-4357/ad27cc  

   Zou, Fan; Yu, Zhibo; Brandt, W N; Tak, Hyungsuk; Yang, Guang; Ni, Qingling (March 2024, The Astrophysical Journal)

   Abstract The growth of supermassive black holes is strongly linked to their galaxies. It has been shown that the population mean black hole accretion rate ( $\overline{\mathrm{BHAR}}$) primarily correlates with the galaxy stellar mass (M_⋆) and redshift for the general galaxy population. This work aims to provide the best measurements of $\overline{\mathrm{BHAR}}$as a function ofM_⋆and redshift over ranges of 10^9.5<M_⋆< 10¹²M_⊙andz< 4. We compile an unprecedentedly large sample with 8000 active galactic nuclei (AGNs) and 1.3 million normal galaxies from nine high-quality survey fields following a wedding cake design. We further develop a semiparametric Bayesian method that can reasonably estimate $\overline{\mathrm{BHAR}}$and the corresponding uncertainties, even for sparsely populated regions in the parameter space. $\overline{\mathrm{BHAR}}$is constrained by X-ray surveys sampling the AGN accretion power and UV-to-infrared multiwavelength surveys sampling the galaxy population. Our results can independently predict the X-ray luminosity function (XLF) from the galaxy stellar mass function (SMF), and the prediction is consistent with the observed XLF. We also try adding external constraints from the observed SMF and XLF. We further measure $\overline{\mathrm{BHAR}}$for star-forming and quiescent galaxies and show that star-forming $\overline{\mathrm{BHAR}}$is generally larger than or at least comparable to the quiescent $\overline{\mathrm{BHAR}}$. 

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4. Magnetogram-matching Biot–Savart Law and Decomposition of Vector Magnetograms

   https://doi.org/10.3847/1538-4357/add895  

   Titov, Viacheslav S; Downs, Cooper; Török, Tibor; Linker, Jon A; Prazak, Michael; Qiu, Jiong A (July 2025, The Astrophysical Journal)

   Abstract We generalize a magnetogram-matching Biot–Savart law (BSl) from planar to spherical geometry. For a given coronal current densityJ, this law determines the magnetic field $\tilde{\mathit{B}}$whose radial component vanishes at the surface. The superposition of $\tilde{\mathit{B}}$with a potential field defined by a given surface radial field,B_r, provides the entire configuration whereB_rremains unchanged by the currents. Using this approach, we (1) upgrade our regularized BSls for constructing coronal magnetic flux ropes (MFRs) and (2) propose a new method for decomposing a measured photospheric magnetic field as $\mathit{B}={\mathit{B}}_{\mathrm{pot}}+{\mathit{B}}_T+{\mathit{B}}_{\tilde{S}}$, where the potential,B_pot, toroidal,B_T, and poloidal, ${\mathit{B}}_{\tilde{S}}$, fields are determined byB_r,J_r, and the surface divergence ofB–B_pot, respectively, all derived from magnetic data. OurB_Tis identical to the one in the alternative Gaussian decomposition by P. W. Schuck et al., whileB_potand ${\mathit{B}}_{\tilde{S}}$are different from their poloidal fields ${\mathit{B}}_{\mathrm{P}}^{<}$and ${\mathit{B}}_{\mathrm{P}}^{>}$, which arepotentialin the infinitesimal proximity to the upper and lower side of the surface, respectively. In contrast, our ${\mathit{B}}_{\tilde{S}}$has no such constraints and, asB_potandB_T, refers to thesameupper side of the surface. In spite of these differences, for a continuousJdistribution across the surface,B_potand ${\mathit{B}}_{\tilde{S}}$are linear combinations of ${\mathit{B}}_{\mathrm{P}}^{<}$and ${\mathit{B}}_{\mathrm{P}}^{>}$. We demonstrate that, similar to the Gaussian method, our decomposition allows one to identify the footprints and projected surface-location of MFRs in the solar corona, as well as the direction and connectivity of their currents. 

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5. Microphysics of Relativistic Collisionless Electron-ion-positron Shocks

   https://doi.org/10.3847/1538-4357/ac713e  

   Grošelj, Daniel; Sironi, Lorenzo; Beloborodov, Andrei M. (July 2022, The Astrophysical Journal)

   Abstract We perform particle-in-cell simulations to elucidate the microphysics of relativistic weakly magnetized shocks loaded with electron-positron pairs. Various external magnetizationsσ≲ 10⁻⁴and pair-loading factorsZ_±≲ 10 are studied, whereZ_±is the number of loaded electrons and positrons per ion. We find the following: (1) The shock becomes mediated by the ion Larmor gyration in the mean field whenσexceeds a critical valueσ_Lthat decreases withZ_±. Atσ≲σ_Lthe shock is mediated by particle scattering in the self-generated microturbulent fields, the strength and scale of which decrease withZ_±, leading to lowerσ_L. (2) The energy fraction carried by the post-shock pairs is robustly in the range between 20% and 50% of the upstream ion energy. The mean energy per post-shock electron scales as ${\overline{E}}_{\mathrm{e}}\propto {\left(Z_{\pm }+1\right)}^{-1}$. (3) Pair loading suppresses nonthermal ion acceleration at magnetizations as low asσ≈ 5 × 10⁻⁶. The ions then become essentially thermal with mean energy ${\overline{E}}_{\mathrm{i}}$, while electrons form a nonthermal tail, extending from $E\sim {\left(Z_{\pm }+1\right)}^{-1}{\overline{E}}_{\mathrm{i}}$to ${\overline{E}}_{\mathrm{i}}$. Whenσ= 0, particle acceleration is enhanced by the formation of intense magnetic cavities that populate the precursor during the late stages of shock evolution. Here, the maximum energy of the nonthermal ions and electrons keeps growing over the duration of the simulation. Alongside the simulations, we develop theoretical estimates consistent with the numerical results. Our findings have important implications for models of early gamma-ray burst afterglows. 

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