An analytical theory for the resolution attainable using eclipse mapping of exoplanets
Monthly Notices of the Royal Astronomical Society 528:1 (2024) 596β607
Abstract:
We present an analytical theory for the resolution attainable via eclipse mapping of exoplanets, based on the Fourier components of the brightness distribution on the planetary disc. We find that the impact parameter determines which features can and cannot be seen, via the angle of the stellar edge relative to the axis of the orbit during the eclipse. We estimate the signal-to-noise ratio as a function of mapping resolution, and use this to determine the attainable resolution for a given starβplanet system. We test this theory against numerical simulations and find good agreement; in particular, our predictions for the resolution as a function of stellar edge angle are accurate to the simulated data to within 10 perβcent over a wide range of angles. Our prediction for the number of spatial modes that can be constrained given a light-curve error is similarly accurate. Finally, we give a list of exoplanets with the best expected resolution for observations with the NIRISS SOSS, NIRSpec G395H, and MIRI LRS instruments on JWST.
CoRoT 223992193: Investigating the variability in a low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk
Astronomy and Astrophysics Springer Verlag
Comparison of turbulent electron heat flux model predictions of the H-mode electron pedestal temperature profile across isotope mix and gas fuelling rate scans in JET with the Be/W wall
Journal of Plasma Physics. 2026;92(2):E47.
Abstract:
Predictions of the pedestal temperature profile calculated using a model for electron-temperature-gradient (ETG) turbulent electron heat transport Field et al. (2023 Philos. Trans. R. Soc. A, vol. 381, p. 20210228) are compared with the pedestal structure of H-mode plasmas in JET-Be/W (with Be wall and W divertor) over scans of the deuteriumβtritium (D:T) isotope mix and hydrogenic gas fuelling rate Frassinetti et al. (2023 Nucl. Fusion, vol. 63, p. 112009). Predictions for the electron temperature at the location of the density pedestal top ππβ‘(πππ,π‘β’πβ’π
π) (where ππ, is the normalised poloidal flux) are found to agree well with measured values over both scans across the full range of D:T ratio. However, the pedestal top temperature ππ,πβ’πβ’π, typically located somewhat inside the density pedestal top, is under-predicted by as much as a factor βΌ2. This implies that the ETG heat flux scaling appropriate for the steep-density gradient region, on which the model is based, is not applicable where the density gradient is weak. This difference might be attributed to a difference between the physics of the ETG turbulence in regimes where the density gradient is either strong or weak, which are thought to be dominated by either the βslabβ or βtoroidalβ branches of ETG turbulence. Other branches of turbulence might also play a role in the electron heat transport, particularly in regions of weak-density gradient. As in the experiment, the predicted ππ across the pedestal decreases with the ratio of separatrix to pedestal density ππ,π β’πβ’π/ππ,πβ’πβ’π, which increases with the gas fuelling rate. Results from three models combining the ETG heat flux model with the EPED1 pedestal (EPED) model (Snyder et al., Phys. Plasmas, 2009, vol. 16, p. 056118) are also presented, including one which also incorporates the density pedestal prediction mode of Saarelma et al. (Nucl. Fusion, 2023, vol. 63, p. 052002), this model providing a complete prediction of the pedestal profiles.
π) (where ππ, is the normalised poloidal flux) are found to agree well with measured values over both scans across the full range of D:T ratio. However, the pedestal top temperature ππ,πβ’πβ’π, typically located somewhat inside the density pedestal top, is under-predicted by as much as a factor βΌ2. This implies that the ETG heat flux scaling appropriate for the steep-density gradient region, on which the model is based, is not applicable where the density gradient is weak. This difference might be attributed to a difference between the physics of the ETG turbulence in regimes where the density gradient is either strong or weak, which are thought to be dominated by either the βslabβ or βtoroidalβ branches of ETG turbulence. Other branches of turbulence might also play a role in the electron heat transport, particularly in regions of weak-density gradient. As in the experiment, the predicted ππ across the pedestal decreases with the ratio of separatrix to pedestal density ππ,π β’πβ’π/ππ,πβ’πβ’π, which increases with the gas fuelling rate. Results from three models combining the ETG heat flux model with the EPED1 pedestal (EPED) model (Snyder et al., Phys. Plasmas, 2009, vol. 16, p. 056118) are also presented, including one which also incorporates the density pedestal prediction mode of Saarelma et al. (Nucl. Fusion, 2023, vol. 63, p. 052002), this model providing a complete prediction of the pedestal profiles.
Constraints on ion vs. electron heating by plasma turbulence at low beta
Abstract:
It is shown that in low-beta plasmas, such as the solar corona, some instances of the solar wind, the aurora, inner regions of accretion discs, their coronae, and some laboratory plasmas, Alfvenic fluctuations produce no ion heating within the gyrokinetic approximation, i.e., as long as their amplitudes (at the Larmor scale) are small and their frequencies stay below the ion Larmor frequency. Thus, all low-frequency ion heating in such plasmas is due to compressive fluctuations: density perturbations and non-Maxwellian perturbations of the ion distribution function. Because these fluctuations energetically decouple from the Alfvenic ones already in the inertial range, the above conclusion means that the energy partition between ions and electrons in low-beta plasmas is decided at the outer scale, where turbulence is launched, and can in principle be determined from MHD models of the relevant astrophysical systems. Any additional ion heating must come from non-gyrokinetic mechanisms such as cyclotron heating or the stochastic heating owing to distortions of ions' Larmor orbits. An exception to these conclusions occurs in the Hall limit, i.e., when the ratio of the ion to electron temperatures is as low as the ion beta (equivalently, the electron beta is order unity). In this regime, compressive fluctuations (slow waves) couple to Alfvenic ones above the Larmor scale (viz., at the ion inertial or ion sound scale), the Alfvenic and compressive cascades join and then separate again into cascades of fluctuations that linearly resemble kinetic Alfven and (oblique) ion cyclotron waves, with the former heating electrons and the latter ions. The two cascades are shown to decouple, scalings for them are derived, and it is argued physically that the two species will be heated by them at approximately equal rates.Gravitational radiation driven supermassive black hole binary inspirals as periodically variable electromagnetic sources
arXiv.org