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Marginalizing Instrument Systematics in HST WFC3 Transit Light CurvesHubble Space Telescope (HST) Wide Field Camera 3 (WFC3) infrared observations at 1.1-1.7 microns probe primarily the H2O absorption band at 1.4 microns, and have provided low-resolution transmission spectra for a wide range of exoplanets. We present the application of marginalization based on Gibson to analyze exoplanet transit light curves obtained from HST WFC3 to better determine important transit parameters such as "ramp" probability (R (sub p)) divided by "ramp" total (R (sub asterisk)), which are important for accurate detections of H2O. We approximate the evidence, often referred to as the marginal likelihood, for a grid of systematic models using the Akaike Information Criterion. We then calculate the evidence-based weight assigned to each systematic model and use the information from all tested models to calculate the final marginalized transit parameters for both the band-integrated and spectroscopic light curves to construct the transmission spectrum. We find that a majority of the highest weight models contain a correction for a linear trend in time as well as corrections related to HST orbital phase. We additionally test the dependence on the shift in spectral wavelength position over the course of the observations and find that spectroscopic wavelength shifts delta (sub lambda) times lambda) best describe the associated systematic in the spectroscopic light curves for most targets while fast scan rate observations of bright targets require an additional level of processing to produce a robust transmission spectrum. The use of marginalization allows for transparent interpretation and understanding of the instrument and the impact of each systematic evaluated statistically for each data set, expanding the ability to make true and comprehensive comparisons between exoplanet atmospheres.
Document ID
20170002458
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Wakeford, H. R.
(Universities Space Research Association Greenbelt, MD, United States)
Sing, D.K.
(Exeter Univ. United Kingdom)
Deming, D.
(Maryland Univ. College Park, MD, United States)
Mandell, A.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
March 23, 2017
Publication Date
February 23, 2016
Publication Information
Publication: The Astrophysical Journal
Publisher: IOP Publishing
Volume: 819
Issue: 1
ISSN: 0004-637X
e-ISSN: 1538-4357
Subject Category
Astronomy
Report/Patent Number
GSFC-E-DAA-TN40265
Funding Number(s)
CONTRACT_GRANT: ERC-336792
CONTRACT_GRANT: NNH15CO48B
Distribution Limits
Public
Copyright
Other

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