We present a method for estimating the heating rate of solar wind (SW) and pickup ion (PUI) protons from their respective energy equations. Here, we estimate the heating rate for SW protons along the New Horizons (NH), Voyager 2 (V2), and Pioneer 10 (P10) trajectories using plasma measurements, rather than the magnetic field measurements. We also compute the heating rate for PUI protons for the first time along the NH direction. We find that the SW proton heating rate in the V2 direction is higher than that along the NH direction between ∼26 and ∼52 au. Along the P10 direction, the proton heating rate exceeds that of V2 between 20 and 38 au, but is less beyond 38 au. The heating rate differs along the spacecraft trajectories in the upwind and downwind directions. The PUI proton heating rate is found to be more than 2 orders of magnitude larger than that of SW protons between ∼26 and ∼52 au. The SW/PUI heating rate correlates with SW speed and SW/PUI temperature. We present a comparison between the injection rate of turbulence energy in the energy-containing range and the intensity profile of energetic particles in the ∼50–110 keV range as a function of distance along the NH and V2 directions. It suggests that turbulence may play an important role in the modulation of energetic particles throughout the heliosphere.
Element abundances found in the solar corona and solar wind are often different from those measured in the solar photosphere, and the fractionation mechanisms are thought to be intimately tied to the physical processes leading to coronal heating and acceleration of the solar wind. The complexity of the data and the methods used to invert underconstrained problems and thus estimate abundances make it challenging to identify and study these mechanisms. In this work, we present an L1-norm inversion method to derive abundances from coronal spectral observations. We explored a variety of approaches, considering different sets of inverted variables (e.g., including the abundance of Si, S, and Fe, as separate independent variables), and we tested and validated them using synthetic data from numerical radiative MHD models. In addition, we investigated the effects of bound-free absorption from neutral hydrogen and helium on the method and Poisson noise. We discuss the advantages and limitations of the various inversion approaches presented.
The habitable zone (HZ) boundaries calculated with the Clima one-dimensional radiative–convective equilibrium (RCE) model have served as a standard reference for exoplanet target selection for three decades, but they have never been independently validated with a comparable model. We present ExoColumn , a new one-dimensional RCE model that couples an independently developed atmospheric column physics package to the ExoRT correlated- k radiative transfer core that is also used by the three-dimensional ExoCAM model. We calibrate ExoColumn to present-day conditions, which matches other RCE models to within a few kelvin through the troposphere. Line-by-line benchmarks show that the ExoRT and Clima radiation cores each reproduce the outgoing longwave flux to within a few percent, with the differences due to the spectral line databases used by each model. We follow the same inverse climate modeling method as previous studies have done to find inner edge moist- and runaway-greenhouse limits of 0.970 au and 0.966 au, and an outer-edge maximum-greenhouse limit of 1.611 au at a CO _2 partial pressure of 8.7 bar. We extend these calculations to 12 host stars spanning 2000–7200 K and to planets of 0.1, 1, and 5 Earth mass, and we provide updated HZ boundary coefficients for community use. The ExoColumn limits systematically fall closer to the host star than those of Clima but agree to within a few percent in orbital distance, which validates the robustness of the published Clima HZ boundaries.
Observations of H _2 CO and c-C _3 H _2 were conducted toward six planetary nebulae (PNs; M1-7, M1-8, M2-48, M4-9, NGC 6445, and NGC 6853) at 1, 2, and 3 mm using the Arizona Radio Observatory’s 12 m antenna and Submillimeter Telescope (SMT). H _2 CO was detected toward all six nebulae on the basis of multiple transitions: the J _Ka,Kc = 2 _1,2 → 1 _1,1 , 2 _0,2 → 1 _0,1 , and 2 _1,1 → 1 _1,0 lines at 2 mm and the J _Ka,Kc = 3 _0,3 → 2 _0,2 transition at 1 mm. The c-C _3 H _2 molecule was identified in three sources, M1-7, M4-9, and NGC 6445, from 2 and 3 mm transitions ( J _Ka,Kc = 2 _1,2 → 1 _0,1 , 3 _1,2 → 2 _2,1 , and 4 _1,4 → 3 _0,3 ). These detections increase the number of PNs known to contain H _2 CO from five to 11, and for c-C _3 H _2 from four to seven. From a radiative transfer analysis, column densities of N _tot (H _2 CO) ∼ 3.2 × 10 ^11 –1.2 × 10 ^13 cm ^−2 and N _tot (c-C _3 H _2 ) ∼ 6.7 × 10 ^11 –6.3 × 10 ^12 cm ^−2 were determined. These values correspond to fractional abundances of f (H _2 CO/H _2 ) ∼ (0.3–2.4) × 10 ^−8 and f (c-C _3 H _2 /H _2 ) ∼ (1.6–6.6) × 10 ^−9 . M4-9 exhibits the highest abundance of each molecule. Based on all known identifications in PNs, H _2 CO appears to be present in both carbon- and oxygen-rich nebulae, whereas c-C _3 H _2 is associated with only carbon-rich types. This result appears to reflect the chemistry of the previous asymptotic giant branch phase and is consistent with chemical continuity throughout PN evolution. Within the small sample, both species show fairly constant abundances across a nebular age range of 700–12,000 yr, with no statistically significant decrease. Both H _2 CO and c-C _3 H _2 are commonly observed in diffuse clouds. Therefore, their ongoing identifications in PNs suggest chemical continuity from the late phases of stellar evolution into the formation of the diffuse interstellar medium.
Well-modeled water megamaser disks offer a path to black hole shadow (BHS) tests of strong-field gravity beyond Sgr A* and M87*: their very long baseline interferometry (VLBI) angular dynamics precisely constrains M _• / D , the maser-disk orientation, and the dynamical center within the maser reference frame, thereby predicting the fiducial Schwarzschild BHS angular size without an externally adopted distance. We assess 21 megamaser galaxies as BHS targets using published maser measurements to calculate BHS angular sizes and baseline requirements. We combine new Submillimeter Array (SMA) continuum observations with archival Atacama Large Millimeter/submillimeter Array (ALMA) and Very Large Array (VLA) measurements to estimate arcsecond-scale 230 GHz flux densities and identify the strongest nuclear-region sources for higher-resolution follow-up. We also estimate the maximum dust and extended-jet contributions, examine limited variability measurements, and, for the leading candidate NGC 4258, evaluate the astrometry required to detect a spin-dependent offset between the BHS center and the maser dynamical center. Only NGC 4258 has an adopted BHS angular size resolvable with an Earth–L2 baseline; the other adopted sizes require longer baselines, while an Earth–L4/L5 separation would be sufficient for all. Five sources reach S _230 ≳ 10 mJy. However, whether the observed 230 GHz emission arises on BHS scales and is sufficiently optically thin to reveal a BHS remains unknown throughout the sample. NGC 4258’s submillimeter excess is consistent with a thin disk transitioning to an advection-dominated flow; its spin-offset test remains infeasible with present maser astrometry.
