Revisiting Spitzer Transit Observations with Independent Component Analysis: New Results for the GJ 436 System
Journal
Date Issued
2015
Author(s)
Description
G.M. is funded by UCL Perren/Impact scholarship (CJ4M/CJ0T). I.P.W. is funded by the European Research Council Grant “Exolights.” G.T. is funded by the Royal Society. G.M. is supported by “Progetto Premiale-A Way to Other Worlds”, funded by the Italian Minister for University and Scientific Research.
Abstract
We analyzed four Spitzer/IRAC observations at 3.6 and 4.5 μm of the primary transit of the exoplanet GJ 436b, by using blind source separation techniques. These observations are important for investigating the atmospheric composition of the planet GJ 436b. Previous analyses claimed strong inter-epoch variations of the transit parameters due to stellar variability, casting doubts on the possibility of conclusively extracting an atmospheric signal. Those analyses also reported discrepant results, hence the necessity of this reanalysis. The method we used has been proposed in Morello et al. to analyze 3.6 μm transit light curves of the hot Jupiter HD 189733b. It performes an Independent Component Analysis on a set of pixel light curves, i.e., time series read by individual pixels, from the same photometric observation. Our method only assumes the independence of instrumental and astrophysical signals, and therefore guarantees a higher degree of objectivity compared to parametric detrending techniques published in the literature. The data sets we analyzed in this paper represent a more challenging test than the previous ones. Contrary to previous results reported in the literature, our results (1) do not support any detectable inter-epoch variations of orbital and stellar parameters, (2) are photometrically stable at the level ̃10-4 in the IR, and (3) the transit depth measurements at the two wavelengths are consistent within 1σ. We also (4) detect a possible transit duration variation of ̃80 s (2σ significance level) that has not been pointed out in the literature, and (5) confirm no transit timing variations ≳30 s.
Volume
802
Issue
2
Start page
117
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...802..117M
Rights
open.access
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