skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Statistical Analysis of Hubble /WFC3 Transit Spectroscopy of Extrasolar Planets

Abstract

Transmission spectroscopy provides a window to study exoplanetary atmospheres, but that window is fogged by clouds and hazes. Clouds and haze introduce a degeneracy between the strength of gaseous absorption features and planetary physical parameters such as abundances. One way to break that degeneracy is via statistical studies. We collect all published HST /WFC3 transit spectra for 1.1–1.65 μ m water vapor absorption and perform a statistical study on potential correlations between the water absorption feature and planetary parameters. We fit the observed spectra with a template calculated for each planet using the Exo-transmit code. We express the magnitude of the water absorption in scale heights, thereby removing the known dependence on temperature, surface gravity, and mean molecular weight. We find that the absorption in scale heights has a positive baseline correlation with planetary equilibrium temperature; our hypothesis is that decreasing cloud condensation with increasing temperature is responsible for this baseline slope. However, the observed sample is also intrinsically degenerate in the sense that equilibrium temperature correlates with planetary mass. We compile the distribution of absorption in scale heights, and we find that this distribution is closer to log-normal than Gaussian. However, we also find that the distribution of equilibriummore » temperatures for the observed planets is similarly log-normal. This indicates that the absorption values are affected by observational bias, whereby observers have not yet targeted a sufficient sample of the hottest planets.« less

Authors:
;  [1];  [2];  [3];  [4];  [5]
  1. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
  2. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States)
  3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  4. Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  5. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
Publication Date:
OSTI Identifier:
22654377
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 847; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABUNDANCE; CLOUDS; CORRELATIONS; DISTRIBUTION; EQUILIBRIUM; GRAVITATION; HYPOTHESIS; MASS; MOLECULAR WEIGHT; PLANETS; SATELLITE ATMOSPHERES; SATELLITES; SCALE HEIGHT; SPECTRA; SPECTROSCOPY; SURFACES; WATER VAPOR

Citation Formats

Fu, Guangwei, Deming, Drake, Knutson, Heather, Madhusudhan, Nikku, Mandell, Avi, and Fraine, Jonathan, E-mail: gfu@astro.umd.edu. Statistical Analysis of Hubble /WFC3 Transit Spectroscopy of Extrasolar Planets. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA8E40.
Fu, Guangwei, Deming, Drake, Knutson, Heather, Madhusudhan, Nikku, Mandell, Avi, & Fraine, Jonathan, E-mail: gfu@astro.umd.edu. Statistical Analysis of Hubble /WFC3 Transit Spectroscopy of Extrasolar Planets. United States. doi:10.3847/2041-8213/AA8E40.
Fu, Guangwei, Deming, Drake, Knutson, Heather, Madhusudhan, Nikku, Mandell, Avi, and Fraine, Jonathan, E-mail: gfu@astro.umd.edu. Sun . "Statistical Analysis of Hubble /WFC3 Transit Spectroscopy of Extrasolar Planets". United States. doi:10.3847/2041-8213/AA8E40.
@article{osti_22654377,
title = {Statistical Analysis of Hubble /WFC3 Transit Spectroscopy of Extrasolar Planets},
author = {Fu, Guangwei and Deming, Drake and Knutson, Heather and Madhusudhan, Nikku and Mandell, Avi and Fraine, Jonathan, E-mail: gfu@astro.umd.edu},
abstractNote = {Transmission spectroscopy provides a window to study exoplanetary atmospheres, but that window is fogged by clouds and hazes. Clouds and haze introduce a degeneracy between the strength of gaseous absorption features and planetary physical parameters such as abundances. One way to break that degeneracy is via statistical studies. We collect all published HST /WFC3 transit spectra for 1.1–1.65 μ m water vapor absorption and perform a statistical study on potential correlations between the water absorption feature and planetary parameters. We fit the observed spectra with a template calculated for each planet using the Exo-transmit code. We express the magnitude of the water absorption in scale heights, thereby removing the known dependence on temperature, surface gravity, and mean molecular weight. We find that the absorption in scale heights has a positive baseline correlation with planetary equilibrium temperature; our hypothesis is that decreasing cloud condensation with increasing temperature is responsible for this baseline slope. However, the observed sample is also intrinsically degenerate in the sense that equilibrium temperature correlates with planetary mass. We compile the distribution of absorption in scale heights, and we find that this distribution is closer to log-normal than Gaussian. However, we also find that the distribution of equilibrium temperatures for the observed planets is similarly log-normal. This indicates that the absorption values are affected by observational bias, whereby observers have not yet targeted a sufficient sample of the hottest planets.},
doi = {10.3847/2041-8213/AA8E40},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 847,
place = {United States},
year = {Sun Oct 01 00:00:00 EDT 2017},
month = {Sun Oct 01 00:00:00 EDT 2017}
}