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Title: A CLOUDINESS INDEX FOR TRANSITING EXOPLANETS BASED ON THE SODIUM AND POTASSIUM LINES: TENTATIVE EVIDENCE FOR HOTTER ATMOSPHERES BEING LESS CLOUDY AT VISIBLE WAVELENGTHS

Abstract

We present a dimensionless index that quantifies the degree of cloudiness of the atmosphere of a transiting exoplanet. Our cloudiness index is based on measuring the transit radii associated with the line center and wing of the sodium or potassium line. In deriving this index, we revisited the algebraic formulae for inferring the isothermal pressure scale height from transit measurements. We demonstrate that the formulae of Lecavelier et al. and Benneke and Seager are identical: the former is inferring the temperature while assuming a value for the mean molecular mass and the latter is inferring the mean molecular mass while assuming a value for the temperature. More importantly, these formulae cannot be used to distinguish between cloudy and cloud-free atmospheres. We derive values of our cloudiness index for a small sample of seven hot Saturns/Jupiters taken from Sing et al. We show that WASP-17b, WASP-31b, and HAT-P-1b are nearly cloud-free at visible wavelengths. We find the tentative trend that more irradiated atmospheres tend to have fewer clouds consisting of sub-micron-sized particles. We also derive absolute sodium and/or potassium abundances ∼10{sup 2} cm{sup −3} for WASP-17b, WASP-31b, and HAT-P-1b (and upper limits for the other objects). Higher-resolution measurements of both themore » sodium and potassium lines, for a larger sample of exoplanetary atmospheres, are needed to confirm or refute this trend.« less

Authors:
 [1]
  1. University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012, Bern (Switzerland)
Publication Date:
OSTI Identifier:
22654501
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 826; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BORON 17; IRRADIATION; JUPITER PLANET; MASS; PARTICLES; POTASSIUM; RESOLUTION; SATELLITE ATMOSPHERES; SATELLITES; SATURN PLANET; SCALE HEIGHT; SODIUM; SPECTRA; WASPS; WAVELENGTHS

Citation Formats

Heng, Kevin, E-mail: kevin.heng@csh.unibe.ch. A CLOUDINESS INDEX FOR TRANSITING EXOPLANETS BASED ON THE SODIUM AND POTASSIUM LINES: TENTATIVE EVIDENCE FOR HOTTER ATMOSPHERES BEING LESS CLOUDY AT VISIBLE WAVELENGTHS. United States: N. p., 2016. Web. doi:10.3847/2041-8205/826/1/L16.
Heng, Kevin, E-mail: kevin.heng@csh.unibe.ch. A CLOUDINESS INDEX FOR TRANSITING EXOPLANETS BASED ON THE SODIUM AND POTASSIUM LINES: TENTATIVE EVIDENCE FOR HOTTER ATMOSPHERES BEING LESS CLOUDY AT VISIBLE WAVELENGTHS. United States. doi:10.3847/2041-8205/826/1/L16.
Heng, Kevin, E-mail: kevin.heng@csh.unibe.ch. 2016. "A CLOUDINESS INDEX FOR TRANSITING EXOPLANETS BASED ON THE SODIUM AND POTASSIUM LINES: TENTATIVE EVIDENCE FOR HOTTER ATMOSPHERES BEING LESS CLOUDY AT VISIBLE WAVELENGTHS". United States. doi:10.3847/2041-8205/826/1/L16.
@article{osti_22654501,
title = {A CLOUDINESS INDEX FOR TRANSITING EXOPLANETS BASED ON THE SODIUM AND POTASSIUM LINES: TENTATIVE EVIDENCE FOR HOTTER ATMOSPHERES BEING LESS CLOUDY AT VISIBLE WAVELENGTHS},
author = {Heng, Kevin, E-mail: kevin.heng@csh.unibe.ch},
abstractNote = {We present a dimensionless index that quantifies the degree of cloudiness of the atmosphere of a transiting exoplanet. Our cloudiness index is based on measuring the transit radii associated with the line center and wing of the sodium or potassium line. In deriving this index, we revisited the algebraic formulae for inferring the isothermal pressure scale height from transit measurements. We demonstrate that the formulae of Lecavelier et al. and Benneke and Seager are identical: the former is inferring the temperature while assuming a value for the mean molecular mass and the latter is inferring the mean molecular mass while assuming a value for the temperature. More importantly, these formulae cannot be used to distinguish between cloudy and cloud-free atmospheres. We derive values of our cloudiness index for a small sample of seven hot Saturns/Jupiters taken from Sing et al. We show that WASP-17b, WASP-31b, and HAT-P-1b are nearly cloud-free at visible wavelengths. We find the tentative trend that more irradiated atmospheres tend to have fewer clouds consisting of sub-micron-sized particles. We also derive absolute sodium and/or potassium abundances ∼10{sup 2} cm{sup −3} for WASP-17b, WASP-31b, and HAT-P-1b (and upper limits for the other objects). Higher-resolution measurements of both the sodium and potassium lines, for a larger sample of exoplanetary atmospheres, are needed to confirm or refute this trend.},
doi = {10.3847/2041-8205/826/1/L16},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 826,
place = {United States},
year = 2016,
month = 7
}
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