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Title: REVISITING SPITZER TRANSIT OBSERVATIONS WITH INDEPENDENT COMPONENT ANALYSIS: NEW RESULTS FOR THE GJ 436 SYSTEM

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 levelmore » ∼10{sup −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.« less

Authors:
; ; ;  [1];  [2];  [3]
  1. Department of Physics and Astronomy, University College London, Gower Street, WC1E6BT (United Kingdom)
  2. INAF—Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 (Italy)
  3. Centre de Recherche Astrophysique de Lyon—École Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07 (France)
Publication Date:
OSTI Identifier:
22522006
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 802; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; COMPARATIVE EVALUATIONS; DATA ANALYSIS; DIAGRAMS; JUPITER PLANET; PHOTOMETRY; PLANETARY ATMOSPHERES; SATELLITE ATMOSPHERES; SATELLITES; STARS; VARIATIONS; VISIBLE RADIATION; WAVELENGTHS

Citation Formats

Morello, G., Waldmann, I. P., Tinetti, G., Howarth, I. D., Micela, G., and Allard, F., E-mail: giuseppe.morello.11@ucl.ac.uk. REVISITING SPITZER TRANSIT OBSERVATIONS WITH INDEPENDENT COMPONENT ANALYSIS: NEW RESULTS FOR THE GJ 436 SYSTEM. United States: N. p., 2015. Web. doi:10.1088/0004-637X/802/2/117.
Morello, G., Waldmann, I. P., Tinetti, G., Howarth, I. D., Micela, G., & Allard, F., E-mail: giuseppe.morello.11@ucl.ac.uk. REVISITING SPITZER TRANSIT OBSERVATIONS WITH INDEPENDENT COMPONENT ANALYSIS: NEW RESULTS FOR THE GJ 436 SYSTEM. United States. doi:10.1088/0004-637X/802/2/117.
Morello, G., Waldmann, I. P., Tinetti, G., Howarth, I. D., Micela, G., and Allard, F., E-mail: giuseppe.morello.11@ucl.ac.uk. Wed . "REVISITING SPITZER TRANSIT OBSERVATIONS WITH INDEPENDENT COMPONENT ANALYSIS: NEW RESULTS FOR THE GJ 436 SYSTEM". United States. doi:10.1088/0004-637X/802/2/117.
@article{osti_22522006,
title = {REVISITING SPITZER TRANSIT OBSERVATIONS WITH INDEPENDENT COMPONENT ANALYSIS: NEW RESULTS FOR THE GJ 436 SYSTEM},
author = {Morello, G. and Waldmann, I. P. and Tinetti, G. and Howarth, I. D. and Micela, G. and Allard, F., E-mail: giuseppe.morello.11@ucl.ac.uk},
abstractNote = {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{sup −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.},
doi = {10.1088/0004-637X/802/2/117},
journal = {Astrophysical Journal},
number = 2,
volume = 802,
place = {United States},
year = {Wed Apr 01 00:00:00 EDT 2015},
month = {Wed Apr 01 00:00:00 EDT 2015}
}