Abstract
Time series photometry and spectroscopy of transiting exoplanets allow
us to study their atmospheres. Unfortunately, the required precision to
extract atmospheric information surpasses the design specifications of
most general purpose instrumentation, resulting in instrumental
systematics in the light curves that are typically larger than the
target precision. Systematics must therefore be modelled, leaving the
inference of light-curve parameters conditioned on the subjective choice
of systematics models and model selection criteria. This paper aims to
test the reliability of the most commonly used deterministic systematics
models and model selection criteria. As we are primarily interested in
recovering light-curve parameters rather than the favoured systematics
model, marginalization over systematics models is introduced as a more
robust alternative than simple model selection. This can incorporate
uncertainties in the choice of systematics model into the error budget
as well as the model parameters. Its use is demonstrated using a series
of simulated transit light curves. Stochastic models, specifically
Gaussian processes, are also discussed in the context of marginalization
over systematics models, and are found to reliably recover the transit
parameters for a wide range of systematics functions. None of the tested
model selection criteria - including the Bayesian information criterion
- routinely recovered the correct model. This means that commonly used
methods that are based on simple model selection may underestimate the
uncertainties when extracting transmission and eclipse spectra from real
data, and low significance claims using such techniques should be
treated with caution. In general, no systematics modelling techniques
are perfect; however, marginalization over many systematics models helps
to mitigate poor model selection, and stochastic processes provide an
even more flexible approach to modelling instrumental systematics.
Original language | English |
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Pages (from-to) | 3401-3414 |
Number of pages | 14 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 445 |
Issue number | 4 |
Early online date | 29 Oct 2014 |
DOIs | |
Publication status | Published - 21 Dec 2014 |
Externally published | Yes |
Keywords
- methods: data analysis
- methods: statistical
- techniques: photometric
- techniques: spectroscopic
- planetary systems