arXiv subjects

Soumya Sengupta

Publications and source records attributed to Soumya Sengupta.

5 recordsLinked to original sources

arXiv2025

Inflated hot Jupiters: Inferring average atmospheric velocity via Ohmic models coupled with internal dynamo evolution

The inflated radii observed in hundreds of hot Jupiters (HJ) represent a long-standing open issue. In this study, we quantitatively investigate this phenomenon within the framework of Ohmic dissipation arising from magnetic induction in the atmosphere, one of the most promising mechanisms for explaining the radius anomaly. We simulate the evolution of irradiated giant planets with MESA, spanning the observed range of masses and equilibrium temperatures, incorporating an internal source of Ohmic dissipation that extends to deep layers of the envelope. We infer average atmospheric wind intensities, averaged in the region $p < 10$ bar, in the range 0.01-1 km/s in order to reproduce the range of observed radii, decreasing roughly linearly with planetary mass, and much more steeply with equilibrium temperature. This is consistent with the expected effects of magnetic drag from the induced field, which is higher for more intense irradiation, via conductivity, and for larger masses, which have higher dynamo fields. Due to the evolution of the dynamo field and the proportionality of the induced currents on it, the Ohmic efficiency typically decreases by at least one order of magnitude from 0.1 to 10 Gyr, at contrast with the common assumption of a constant-in-time value. Notably, the extent of the main convective region, and the associated heat flux supporting the dynamo, is reduced in the presence of strong Ohmic dissipation, which in turn depends on the dynamo field strength, generating a non-trivial coupling of the latter with the atmospheric induction, potentially leading to an oscillatory behaviour of the field strength. These findings remain generally valid even when accounting for a long-term increase in the main-sequence host star luminosity, although this case can more readily lead to HJ re-inflation, consistent with previous studies.

astro-ph.EP↗

arXiv2025

Effect of Thermal Emission in Isotropic Scattering Atmospheres: An Invariant-Embedding Extension of Chandrasekhar's $H(\mu)$-Function

Chandrasekhar's H(mu)-function forms the foundation of radiative transfer theory for semi-infinite, isotropically scattering atmospheres under external illumination. However, the classical formulation does not account for thermal emission from internal heat sources, which is essential in many astrophysical environments, including hot Jupiters, brown dwarfs, and strongly irradiated exoplanets, where re-radiated stellar energy significantly alters the emergent intensity. To address this limitation, we extend Chandrasekhar's diffuse reflection framework by incorporating intrinsic thermal emission within the invariant-embedding formalism. In this approach, thermal emission enters as an embedded invariant contribution to the source function, leading to a generalized angular redistribution function M(mu). We derive the governing non-linear integral equations for M(mu) and express them in terms of the direction cosine mu, the thermal emission coefficient U(T)=B(T)/F, and the single-scattering albedo omega_0. High-precision numerical values of M(mu,U,omega_0) are computed for mu in [0,1], U<0.7, and omega_0<1 using a stable iterative scheme based on Gaussian quadrature. In the limit of vanishing thermal emission, the formulation reduces to Chandrasekhar's classical H(mu)-function, validating the approach. As an application, we consider the ultra-short-period exoplanet K2-137b and identify the wavelength range 0.85--2.5 micron where the model is most applicable, corresponding to the capabilities of JWST, HST, and ARIEL.

astro-ph.EP↗

arXiv2022

Atmospheric heat redistribution effect on Emission spectra of Hot-Jupiters

Hot Jupiters are the most studied and easily detectable exoplanets for transit observations.However, the correlation between the atmospheric flow and the emission spectra of such planets is still not understood. Due to huge day-night temperature contrast in hot Jupiter, the thermal redistribution through atmospheric circulation has a significant impact on the vertical temperature-pressure structure and on the emission spectra. In the present work, we aim to study the variation of the temperature-pressure profiles and the emission spectra of such planets due to different amounts of atmospheric heat redistribution. For this purpose, we first derive an analytical relation between the heat redistribution parameter f and the emitted flux from the uppermost atmospheric layers of hot Jupiter. We adopt the three possible values of f under isotropic approximation as 1/4, 1/2, and 2/3 for full-redistribution, semi-redistribution and no-redistribution cases respectively and calculate the corresponding temperature-pressure profiles and the emission spectra. Next, we model the emission spectra for different values of f by numerically solving the radiative transfer equations using the discrete space theory formalism. We demonstrate that the atmospheric temperature-pressure profiles and the emission spectra both are susceptible to the values of the heat redistribution function. A reduction in the heat redistribution yields a thermal inversion in the temperature-pressure profiles and hence increases the amount of emission flux. Finally, we revisits the hot Jupiter XO-1b temperature-pressure profile degeneracy case and show that a non-inversion temperature-pressure profile best explains this observed planetary dayside emission spectra.

astro-ph.EP↗

arXiv2022

Atmospheric Thermal Emission Effect on Chandrasekhar's Finite Atmosphere Problem

The solutions of the \textit{diffuse reflection finite atmosphere problem} are very useful in the astrophysical context. Chandrasekhar was the first to solve this problem analytically, by considering atmospheric scattering. These results have wide applications in the modeling of planetary atmospheres. However, they cannot be used to model an atmosphere with emission. We solved this problem by including \textit{thermal emission effect} along with scattering.Here, our aim is to provide a complete picture of generalized finite atmosphere problem in presence of scattering and thermal emission, and to give a physical account of the same. For that, we take an analytical approach using the invariance principle method to solve the diffuse reflection finite atmosphere problem in the presence of atmospheric thermal emission. We established the general integral equations of modified scattering function $S(τ; μ, ϕ; μ_0, ϕ_0)$, transmission function $T(τ; μ, ϕ; μ_0, ϕ_0)$ and their derivatives with respect to $τ$ for a thermally emitting atmosphere. We customize these equations for the case of isotropic scattering and introduce two new functions $V(μ)$ and $W(μ)$, analogous to Chandrasekhar $X(μ)$, and $Y(μ)$ functions respectively. We also derive a transformation relation between the modified S-T functions and give a physical account of $V(μ)$ and $W(μ)$ functions. Our final results are consistent with those of Chandrasekhar at low emission limit (i.e. only scattering). From the consistency of our results, we conclude that the consideration of thermal emission effect in diffuse reflection finite atmosphere problem gives more general and accurate results than considering only scattering.

astro-ph.EP↗

arXiv2021

Effects of thermal emission on Chandrasekhar's semi-infinite diffuse reflection problem

Context: The analytical results of Chandrasekhar's semi-infinite diffuse reflection problem is crucial in the context of stellar or planetary atmosphere. However, the atmospheric emission effect was not taken into account in this model, and the solutions are applicable only for diffusely scattering atmosphere in absence of emission. Aim: We extend the model of semi-infinite diffuse reflection problem by including the effects of thermal emission B(T ), and present how this affects Chandrasekhar's analytical end results. Hence, we aim to generalize Chandrasekhar's model to provide a complete picture of this problem. Method: We use Invariance Principle Method to find the radiative transfer equation accurate for diffuse reflection in presence of B(T ). Then we derive the modified scattering function S($μ,ϕ; μ_0 , ϕ_0$ ) for different kind of phase functions. Results: We find that, the scattering function S($μ, ϕ; μ_0 , ϕ_0$ ) as well as diffusely reflected specific intensity $I(0, μ; μ_0 )$ for different phase functions are modified due to the emission $B(T)$ from layer $τ = 0$. In both cases, B(T) is added to the results of only scattering case derived by Chandrasekhar, with some multiplicative factors. Thus the diffusely reflected spectra will be enriched and carries the temperature information of $τ = 0$ layer. As the effects are additive in nature, hence our model reduces to the sub-case of Chandrasekhar's scattering model in case of $B(T) = 0$. We conclude that our generalized model provides more accurate results due to the inclusion of the thermal emission effect in Chandrasekhar's semi-infinite atmosphere problem.

astro-ph.EP↗