A Search for Polarized Thermal Emission from Directly Imaged Exoplanets and Brown Dwarf Companions to Nearby Stars

Jensen-Clem, Rebecca; Millar‐Blanchaer, Maxwell A.; Holstein, R. van; Mawet, Dimitri; Graham, James R.; Sengupta, Sujan; Marley, Mark S.; Snik, Frans; Vigan, A.; Hinkley, Sasha; Boer, J. de; Girard, J.; Rosa, Robert J. De; Bowler, Brendan P.; Wiktorowicz, Sloane; Perrin, Marshall D.; Crepp, Justin R.; Macintosh, Bruce

doi:10.3847/1538-3881/abc33d

Cited by 15 publications

(24 citation statements)

References 93 publications

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“…Because interstellar dust creates the same polarization for the companion and the star, this contribution can often be determined from the measured stellar polarization (e.g., for 1RXS J1609, see Sect. 5.3, and ROXs 42B, see Jensen-Clem et al 2020). However, we cannot do that in this case because the star hosts a disk that we spatially resolve in our images (see Sect.…”

Section: Detection Of Intrinsic Polarization Of Dh Tau Bmentioning

confidence: 98%

A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS

Holstein

Stolker

Jensen-Clem

et al. 2021

A&A

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Context. Young giant planets and brown dwarf companions emit near-infrared radiation that can be linearly polarized up to several percent. This polarization can reveal the presence of an (unresolved) circumsubstellar accretion disk, rotation-induced oblateness of the atmosphere, or an inhomogeneous distribution of atmospheric dust clouds. Aims. We aim to measure the near-infrared linear polarization of 20 known directly imaged exoplanets and brown dwarf companions. Methods. We observed the companions with the high-contrast imaging polarimeter SPHERE-IRDIS at the Very Large Telescope. We reduced the data using the IRDAP pipeline to correct for the instrumental polarization and crosstalk of the optical system with an absolute polarimetric accuracy <0.1% in the degree of polarization. We employed aperture photometry, angular differential imaging, and point-spread-function fitting to retrieve the polarization of the companions. Results. We report the first detection of polarization originating from substellar companions, with a polarization of several tenths of a percent for DH Tau B and GSC 6214-210 B in H-band. By comparing the measured polarization with that of nearby stars, we find that the polarization is unlikely to be caused by interstellar dust. Because the companions have previously measured hydrogen emission lines and red colors, the polarization most likely originates from circumsubstellar disks. Through radiative transfer modeling, we constrain the position angles of the disks and find that the disks must have high inclinations. For the 18 other companions, we do not detect significant polarization and place subpercent upper limits on their degree of polarization. We also present images of the circumstellar disks of DH Tau, GQ Lup, PDS 70, β Pic, and HD 106906. We detect a highly asymmetric disk around GQ Lup and find evidence for multiple scattering in the disk of PDS 70. Both disks show spiral-like features that are potentially induced by GQ Lup B and PDS 70 b, respectively. Conclusions. The presence of the disks around DH Tau B and GSC 6214-210 B as well as the misalignment of the disk of DH Tau B with the disk around its primary star suggest in situ formation of the companions. The non-detections of polarization for the other companions may indicate the absence of circumsubstellar disks, a slow rotation rate of young companions, the upper atmospheres containing primarily submicron-sized dust grains, and/or limited cloud inhomogeneity.

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Section: Detection Of Intrinsic Polarization Of Dh Tau Bmentioning

confidence: 98%

A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS

Holstein

Stolker

Jensen-Clem

et al. 2021

A&A

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“…In our follow-up work we will expand to multiwavelength polarization predictions, both for Luhman 16 A and B, and for brown dwarfs generally over a larger parameter phase space, given the larger data sets being accumulated (Jensen-Clem et al 2020;van Holstein et al 2021). We will also explore a wider range of GCMs for Luhman 16 A and Luhman 16 B, to assess whether the observed broadband photometric variability in the visible and near infrared, as well as the polarization signal, can be interpreted in the framework of one model.…”

Section: Discussionmentioning

confidence: 99%

“…A number of observations of polarized emission from brown dwarfs have been published as well over the past two decades (Ménard et al 2002;Manjavacas et al 2017;Zapatero Osorio et al 2005Goldman et al 2009;Tata et al 2009;Miles-Páez et al 2013;Millar-Blanchaer et al 2020). Recently, upper limits on the polarized thermal emission have been determined for a large sample (23) of exoplanets and brown dwarf companions (Jensen-Clem et al 2016;van Holstein et al 2017;Jensen-Clem et al 2020;van Holstein et al 2021;Millar-Blanchaer et al 2015) using the Gemini Planet Imager (GPI, Macintosh et al (2014)) and Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE, Beuzit et al (2019)). van Holstein et al (2021) found that polarized thermal emission measurements from DH Tau B and GSC 6214-210 B hints towards the presence of circumsubstellar disks.…”

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confidence: 99%

Modeling Polarization Signals from Cloudy Brown Dwarfs: Luhman 16 A and B in Three Dimensions

Mukherjee,

Fortney,

Jensen-Clem

et al. 2021

Preprint

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The detection of disk-integrated polarization from Luhman 16A and B in H-band, and subsequent modeling, has been interpreted in the framework of zonal cloud bands on these bodies. Recently, Tan and Showman (2021) investigated three-dimensional atmospheric circulation and cloud structures of brown dwarfs with general circulation models (GCMs), and their simulations yield complex cloud distributions showing some aspects of zonal jets, but also complex vortices that cannot be captured by a simple model. Here we use these 3D GCMs specific to Luhman 16A and B, along with the three-dimensional Monte Carlo radiative transfer code ARTES, to calculate their polarization signals.We adopt the 3D temperature-pressure and cloud profiles from the GCMs as our input atmospheric structures. Our polarization calculations at 1.6 µm agree well with the measured degree of linear polarization from both Luhman 16 A and B. Our calculations reproduce the measured polarization for both the objects with cloud particle sizes between 0.5-1 µm for Luhman 16 A and 5 µm for Luhman 16 B. We find that the degree of linear polarization can vary on hour-long timescales over the course of a rotation period. We also show that models with azimuthally symmetric band-like cloud geometries, typically used for interpreting polarimetry observations of brown dwarfs, over-predict the polarization signal if the cloud patterns do not include complex vortices within these bands. This exploratory work shows that GCMs are promising for modeling and interpreting polarization signals of brown dwarfs.

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“…4 Using polarimetric differential imaging (PDI), the NIR polarimetric modes of the high-contrast imaging instruments SPHERE-IRDIS [7][8][9][10] at the Very Large Telescope, Germini Planetary Imager 5,11 at the Gemini South Telescope, and HiCIAO 12 at the Subaru telescope have been able to successfully image circumstellar disk of various ages. [13][14][15][16][17] SPHERE-IRDIS and the Gemini Planet imager have also been used to search for polarization signals from substellar and planetary objects, [18][19][20][21][22] leading to the polarimetric detections of two spatially unresolved circumsubstellar disks. 22 In 2017, the HiCIAO instrument at the Subaru telescope was decommissioned and replaced with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system.…”

Section: Introductionmentioning

confidence: 99%

Full characterization of the instrumental polarization effects of the spectropolarimetric mode of SCExAO/CHARIS

Hart

Holstein

Bos

et al. 2021

Polarization Science and Remote Sensing X

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A Search for Polarized Thermal Emission from Directly Imaged Exoplanets and Brown Dwarf Companions to Nearby Stars

Cited by 15 publications

References 93 publications

A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS

A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS

Modeling Polarization Signals from Cloudy Brown Dwarfs: Luhman 16 A and B in Three Dimensions

Full characterization of the instrumental polarization effects of the spectropolarimetric mode of SCExAO/CHARIS

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