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

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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.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Heng, Kevin

Subjects:

500 Science
500 Science > 520 Astronomy
500 Science > 530 Physics

ISSN:

0035-8711

Publisher:

Oxford University Press

Language:

English

Submitter:

Danielle Zemp

Date Deposited:

14 Apr 2020 11:49

Last Modified:

14 Apr 2020 11:57

Publisher DOI:

10.1093/mnras/stz2746

ArXiv ID:

1909.12639v1

BORIS DOI:

10.7892/boris.142643

URI:

https://boris.unibe.ch/id/eprint/142643

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