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Article overview
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Revisiting Spitzer transit observations with Independent Component Analysis: new results for the GJ436 system | | G. Morello
; I. P. Waldmann
; G. Tinetti
; I. D. Howarth
; G. Micela
; F. Allard
; | | Date: |
23 Jan 2015 | | Abstract: | We analyzed four Spitzer/IRAC observations at 3.6 and 4.5 {mu}m of the
primary transit of the exoplanet GJ436b, by using blind source separation
techniques. These observations are important to investigate the atmospheric
composition of the planet GJ436b. Previous analyses claimed strong inter-epoch
variations of the transit parameters due to stellar variability, casting doubts
on the possibility to extract conclusively 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. (2014) to
analyze 3.6 {mu}m transit light-curves of the hot Jupiter HD189733b; it
performes an Independent Component Analysis (ICA) 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 datasets we analyzed in this paper represent a more
challenging test compared to 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 10e-4 in the IR, and (3) the transit depth
measurements at the two wavelengths are consistent within 1{sigma}. We also
(4) detect a possible transit duration variation (TDV) of 80 s (2 {sigma}
significance level), that has not been pointed out in the literature, and (5)
confirm no transit timing variations (TTVs) >30 s. | | Source: | arXiv, 1501.5866 | | Services: | Forum | Review | PDF | Favorites | |
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