Combining angular differential imaging and accurate polarimetry with SPHERE/IRDIS to characterize young giant exoplanets

Rob van Holstein, Frans Snik, Julien N. Girard, Jozua de Boer, C. Ginski, CU Keller, Daphne Stam, Jean-Luc Beuzit, D. Mouillet, M Kasper, M. Langlois, Alice Zurlog, R.J. de Kok, A. Vigan

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

23 Citations (Scopus)


Young giant exoplanets emit infrared radiation that can be linearly polarized up to several percent. This linear polarization can trace: 1) the presence of atmospheric cloud and haze layers, 2) spatial structure, e.g. cloud bands
and rotational attening, 3) the spin axis orientation and 4) particle sizes and cloud top pressure. We introduce a novel high-contrast imaging scheme that combines angular dierential imaging (ADI) and accurate near-infrared
polarimetry to characterize self-luminous giant exoplanets. We implemented this technique at VLT/SPHEREIRDIS and developed the corresponding observing strategies, the polarization calibration and the data-reduction approaches. The combination of ADI and polarimetry is challenging, because the eld rotation required for ADI negatively aects the polarimetric performance. By combining ADI and polarimetry we can characterize planets that can be directly imaged with a very high signal-to-noise ratio. We use the IRDIS pupil-tracking mode and
combine ADI and principal component analysis to reduce speckle noise. We take advantage of IRDIS' dual-beam polarimetric mode to eliminate dierential eects that severely limit the polarimetric sensitivity (at-elding errors, dierential aberrations and seeing), and thus further suppress speckle noise. To correct for instrumental polarization eects, we apply a detailed Mueller matrix model that describes the telescope and instrument and that has an absolute polarimetric accuracy 0:1%. Using this technique we have observed the planets of HR 8799 and the (sub-stellar) companion PZ Tel B. Unfortunately, we do not detect a polarization signal in a rst analysis. We estimate preliminary 1 upper limits on the degree of linear polarization of 1% and 0:1% for the planets of HR 8799 and PZ Tel B, respectively. The achieved sub-percent sensitivity and accuracy show that our technique has great promise for characterizing exoplanets through direct-imaging polarimetry.
Original languageEnglish
Title of host publicationTechniques and Instrumentation for Detection of Exoplanets VIII
EditorsS. Shaklan
Number of pages17
Publication statusPublished - 2017
EventSPIE Optical Engineering 2017 + Applications - San Diego, United States
Duration: 6 Aug 201710 Aug 2017

Publication series

NameProceedings of SPIE
ISSN (Electronic)0277-786X


ConferenceSPIE Optical Engineering 2017 + Applications
CountryUnited States
CitySan Diego


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