Morello, G;
Waldmann, IP;
Tinetti, G;
Howarth, ID;
Micela, G;
Allard, F;
(2015)
Revisiting Spitzer transit observations with Independent Component Analysis: new results for the GJ436 system.
Astrophysical Journal
, 802
, Article 117. 10.1088/0004-637X/802/2/117.
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Abstract
We analyzed four Spitzer/IRAC observations at 3.6 and 4.5 μm of the primary transit of the exoplanet GJ436b, by using blind source separation techniques. These observations are impor- tant 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 dis- crepant results, hence the necessity of this reanalysis. The method we used has been proposed in Morello et al. (2014) to analyze 3.6 μm transit light-curves of the hot Jupiter HD189733b; it per- formes 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 de- tectable 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 1σ. We also (4) detect a possible transit duration variation (TDV) of ~80 s (2 σ significance level), that has not been pointed out in the literature, and (5) confirm no transit timing variations (TTVs) 30 s.
| Type: | Article |
|---|---|
| Title: | Revisiting Spitzer transit observations with Independent Component Analysis: new results for the GJ436 system |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1088/0004-637X/802/2/117 |
| Publisher version: | http://dx.doi.org/10.1088/0004-637X/802/2/117 |
| Language: | English |
| Additional information: | Copyright © 2016. The American Astronomical Society. All rights reserved. This is an author's manuscript version of an article accepted for publication in the Astrophysical Journal. |
| Keywords: | methods: data analysis; techniques: photometric; planets and satellites: atmospheres; planets and satellites: individual(GJ436b) |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/1474885 |
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