Computation of the Transmitted and Polarized Scattered Fluxes by the Exoplanet HD 189733b in X-Rays

Abstract

Thousands of exoplanets have been detected, but only one exoplanetary transit was potentially observed in X-rays from HD 189733A. What makes the detection of exoplanets so difficult in this band? To answer this question, we run Monte-Carlo radiative transfer simulations to estimate the amount of X-ray flux reprocessed by HD 189733b Despite its extended evaporating-atmosphere, we find that the X-ray absorption radius of HD 189733b at 0.7 keV, the mean energy of the photons detected in the 0.25-2 keV energy band by XMM-Newton, is ∼1.01 times the planetary radius for an atmosphere of atomic Hydrogen and Helium (including ions), and produces a maximum depth of ∼2.1% at ∼±46 min from the center of the planetary transit on the geometrically thick and optically thin corona. We compute numerically in the 0.25-2 keV energy band that this maximum depth is only of ∼1.6% at ∼±47 min from the transit center, and little sensitive to the metal abundance assuming that adding metals in the atmosphere would not dramatically change the density-temperature profile. Regarding a direct detection of HD 189733b in X-rays, we find that the amount of flux reprocessed by the exoplanetary atmosphere varies with the orbital phase, spanning between 3-5 orders of magnitude fainter than the flux of the primary star. Additionally, the degree of linear polarization emerging from HD 189733b is <0.003%, with maximums detected near planetary greatest elongations. This implies that both the modulation of the X-ray flux with the orbital phase and the scattered-induced continuum polarization cannot be observed with current X-ray facilities.

Unveiling the physics behind the spectral variations of changing-look quasars with optical polarimetry

“…This numerical tool was used to model, predict, fit and interpret the polarization signatures of large variety of sources, from exoplanets to AGN (see, e.g., Marin & Goosmann 2014;Marin & Grosso 2017). stokes works from the near-infrared to the hard X-ray bands and simulates the random and successive interactions of light with matter under a large number of possible geometries and scales.…”

“…To model the optical continuum polarization expected from a changing-look AGN, we use the Monte Carlo radiative transfer code stokes (Goosmann & Gaskell 2007;Marin et al 2012Marin et al , 2015a. This numerical tool was used to model, predict, fit and interpret the polarization signatures of large variety of sources, from exoplanets to AGN (see, e.g., Marin & Goosmann 2014;Marin & Grosso 2017). stokes works from the near-infrared to the hard X-ray bands and simulates the random and successive interactions of light with matter under a large number of possible geometries and scales.…”

Modeling the Lyαtransit absorption of the hot Jupiter HD 189733b

“…However, both in-and pre-transit absorption signatures were highly variable in time and strongly affected by stellar activity, making their interpretation difficult (Barnes et al 2016;Cauley et al 2017a;Kohl et al 2018). Furthermore, a 6-8% transit absorption in Xrays was reported by Poppenhaeger et al (2013), but more observations with higher sensitivity are needed to confirm this result (Marin & Grosso 2017).…”

M51-ULS-1b: The First Candidate for a Planet in an External Galaxy

“…The specific shape of the stellar-transit X-ray dip can be modeled by the interactions of X-rays from the stellar corona with the planetary atmosphere. (Marin & Grosso 2017).…”