On physical interpretations of the reference transit radius of gas-giant exoplanets

Heng, Kevin (2019). On physical interpretations of the reference transit radius of gas-giant exoplanets. Monthly notices of the Royal Astronomical Society, 490(3), pp. 3378-3383. Oxford University Press 10.1093/mnras/stz2746

Preview	Text 1909.12639.pdf - Submitted Version Available under License Publisher holds Copyright. Download (307kB) | Preview
Preview	Text stz2746.pdf - Published Version Available under License Publisher holds Copyright. Download (343kB) | Preview

Two theoretical quandaries involving transmission spectra of gas-giant exoplanets are elucidated. When computing the transit radius as a function of wavelength, one needs to specify a reference transit radius corresponding to a reference pressure. Mathematically, the reference transit radius is a constant of integration that originates from evaluating an integral for the transit depth. Physically, its interpretation has been debated in the literature. Jordan & Espinoza (2018) suggested that the optical depth is discontinuous across, and infinite below, the reference transit radius. Betremieux & Swain (2017, 2018) interpreted the spherical surface located at the reference transit radius to represent the boundary associated with an opaque cloud deck. It is demonstrated that continuous functions for the optical depth may be found. The optical depth below and at the reference transit radius need not take on special or divergent values. In the limit of a spatially uniform grey cloud with constant opacity, the transit chord with optical depth on the order of unity mimics the presence of a "cloud top". While the surface located at the reference pressure may mimic the presence of grey clouds, it is more natural to include the effects of these clouds as part of the opacity function because the cloud opacity may be computed from first principles. It is unclear how this mimicry extends to non-grey clouds comprising small particles.

Interest & Impact

Downloads

253 since deposited on 14 Apr 2020
39 in the past 12 months

Citations

5 Citations in Web of Science ®
6 Citations in Scopus

Search

in Google Scholar™

Services

Actions (login required)

Edit item

Actions (login required)

Edit item