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Title: Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets

Abstract

We re-visit the principles of transmission spectroscopy for transiting extrasolar planets, focusing on the overlap between the planetary spectrum and the illuminating stellar spectrum. Virtually all current models of exoplanetary transmission spectra utilize an approximation that is inaccurate when the spectrum of the illuminating star has a complex line structure, such as molecular bands in M-dwarf spectra. In those cases, it is desirable to model the observations using a coupled stellar–planetary radiative transfer model calculated at high spectral resolving power, followed by convolution to the observed resolution. Not consistently accounting for overlap of stellar M-dwarf and planetary lines at high spectral resolution can bias the modeled amplitude of the exoplanetary transmission spectrum, producing modeled absorption that is too strong. We illustrate this bias using the exoplanet TRAPPIST-1b, as observed using Hubble Space Telescope /WFC3. The bias in this case is about 250 ppm, 12% of the modeled transit absorption. Transit spectroscopy using JWST will have access to longer wavelengths where the water bands are intrinsically stronger, and the observed signal-to-noise ratios will be higher than currently possible. We therefore expect that this resolution-linked bias will be especially important for future JWST observations of TESS-discovered super-Earths and mini-Neptunes transiting M-dwarfs.

Authors:
;  [1]
  1. Department of Astronomy, University of Maryland at College Park, College Park, MD 20742 (United States)
Publication Date:
OSTI Identifier:
22654477
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 841; 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; ABSORPTION; APPROXIMATIONS; NEPTUNE PLANET; NOISE; RADIANT HEAT TRANSFER; RESOLUTION; SATELLITE ATMOSPHERES; SATELLITES; SIGNAL-TO-NOISE RATIO; SPACE; SPECTRA; SPECTROSCOPY; STARS; TELESCOPES; WATER; WAVELENGTHS

Citation Formats

Deming, Drake, and Sheppard, Kyle. Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA706C.
Deming, Drake, & Sheppard, Kyle. Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets. United States. doi:10.3847/2041-8213/AA706C.
Deming, Drake, and Sheppard, Kyle. Sat . "Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets". United States. doi:10.3847/2041-8213/AA706C.
@article{osti_22654477,
title = {Spectral Resolution-linked Bias in Transit Spectroscopy of Extrasolar Planets},
author = {Deming, Drake and Sheppard, Kyle},
abstractNote = {We re-visit the principles of transmission spectroscopy for transiting extrasolar planets, focusing on the overlap between the planetary spectrum and the illuminating stellar spectrum. Virtually all current models of exoplanetary transmission spectra utilize an approximation that is inaccurate when the spectrum of the illuminating star has a complex line structure, such as molecular bands in M-dwarf spectra. In those cases, it is desirable to model the observations using a coupled stellar–planetary radiative transfer model calculated at high spectral resolving power, followed by convolution to the observed resolution. Not consistently accounting for overlap of stellar M-dwarf and planetary lines at high spectral resolution can bias the modeled amplitude of the exoplanetary transmission spectrum, producing modeled absorption that is too strong. We illustrate this bias using the exoplanet TRAPPIST-1b, as observed using Hubble Space Telescope /WFC3. The bias in this case is about 250 ppm, 12% of the modeled transit absorption. Transit spectroscopy using JWST will have access to longer wavelengths where the water bands are intrinsically stronger, and the observed signal-to-noise ratios will be higher than currently possible. We therefore expect that this resolution-linked bias will be especially important for future JWST observations of TESS-discovered super-Earths and mini-Neptunes transiting M-dwarfs.},
doi = {10.3847/2041-8213/AA706C},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 841,
place = {United States},
year = {Sat May 20 00:00:00 EDT 2017},
month = {Sat May 20 00:00:00 EDT 2017}
}