Probing the physical properties of directly imaged gas giant exoplanets through polarization

Marley, Mark S.; Sengupta, Sujan

doi:10.1111/j.1365-2966.2011.19448.x

Cited by 93 publications

(100 citation statements)

References 53 publications

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“…Dust is also present in the photospheres of dwarfs cooler than T eff = 2700 K (e.g., Tsuji et al 1996) as a result of the natural chemistry of low-temperature and high-gravity atmospheres that includes the condensation of refractory elements into liquid and solid particles. Based on a scenario of large rotation velocities (that induce oblate shapes) and/or inhomogeneous distributions of dusty clouds, Sengupta & Marley (2010) and Marley & Sengupta (2011) theoretically show that the net linear polarization of dusty dwarfs by single scattering processes can be as high as a few per cent at optical and near-infrared wavelengths. Miles-Páez et al (2013, and references therein) provided observational proof of linear polarization detections in ultracool dwarfs.…”

Section: Discussionmentioning

confidence: 99%

Rotational modulation of the linear polarimetric variability of the cool dwarf TVLM 513−46546

Miles-Páez

Osorio

Πάλλη

2015

A&A

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Aims. We aim to monitor the optical linear polarimetric signal of the magnetized, rapidly rotating M8.5 dwarf TVLM 513−46546. Methods. R-and I-band linear polarimetry images were collected with the Andalucía Faint Object Spectrograph and Camera (ALFOSC) instrument of the 2.56-m Nordic Optical Telescope (NOT) on two consecutive nights, covering about 0.5 and four rotation cycles in the R and I filters, respectively. We also obtained simultaneous intensity curves by means of differential photometry. The typical precision of the data is ±0.46% (R), ±0.35% (I) in the linear polarization degree and ±9 mmag (R), ±1.6 mmag (I) in the differential intensity curves. Results. Strong and variable linear polarization is detected in the R and I filters, with values of maximum polarization (p * = 1.30 ± 0.35 %), that are similar for both bands. The intensity and the polarimetric curves present a sinusoid-like pattern with a periodicity of ∼1.98 h, which we ascribe to structures in the surface of TVLM 513−46546 synchronized with its rotation. We found that the peaks of intensity and polarimetric curves occur with a phase difference of 0.18 ± 0.01 and that the maximum of the linear polarization occurs nearly half a period (0.59 ± 0.03) after the radio pulse. We discuss different scenarios to account for the observed properties of the light curves.

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Section: Discussionmentioning

confidence: 99%

Rotational modulation of the linear polarimetric variability of the cool dwarf TVLM 513−46546

Miles-Páez

Osorio

Πάλλη

2015

A&A

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“…Sengupta & Marley (2010) argued that the Iband degree of polarization of field L dwarfs can be explained by rotationally-induced oblateness and a uniform cloud layer, suggesting low surface gravity (see also Sengupta & Kwok 2005). The same authors have extended their work to gas giant exoplanets and pointed out the potential of infrared polarization measurements of directly imaged planets for the study of their surface gravity and cloud inhomogeneities (Marley & Sengupta 2011). The effect of horizontal inhomogeneities in exoplanet atmospheres was studied by de Kok et al (2011), including the dependence of the degree of polarization on a temperature gradient in the atmosphere.…”

Section: Introductionmentioning

confidence: 98%

“…Thermal radiation from a planetary atmosphere can also be polarized when it has been scattered. However, the disk-integrated polarization from the thermal photons will be negligible unless scattering occurs in an atmosphere that deviates from spherical symmetry (Sengupta & Marley 2010;Marley & Sengupta 2011;de Kok et al 2011). Therefore, a polarization measurement may provide information on the oblateness of an atmosphere or the presence of horizontal cloud variations (e.g., bands or patches).…”

Section: Introductionmentioning

confidence: 99%

Polarized scattered light from self-luminous exoplanets

Stolker

Min

Stam

et al. 2017

A&A

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Context. Direct imaging has paved the way for atmospheric characterization of young and self-luminous gas giants. Scattering in a horizontally-inhomogeneous atmosphere causes the disk-integrated polarization of the thermal radiation to be linearly polarized, possibly detectable with the newest generation of high-contrast imaging instruments. Aims. We aim to investigate the effect of latitudinal and longitudinal cloud variations, circumplanetary disks, atmospheric oblateness, and cloud particle properties on the integrated degree and direction of polarization in the near-infrared. We want to understand how 3D atmospheric asymmetries affect the polarization signal in order to assess the potential of infrared polarimetry for direct imaging observations of planetary-mass companions. Methods. We have developed a three-dimensional Monte Carlo radiative transfer code (ARTES) for scattered light simulations in (exo)planetary atmospheres. The code is applicable to calculations of reflected light and thermal radiation in a spherical grid with a parameterized distribution of gas, clouds, hazes, and circumplanetary material. A gray atmosphere approximation is used for the thermal structure. Results. The disk-integrated degree of polarization of a horizontally-inhomogeneous atmosphere is maximal when the planet is flattened, the optical thickness of the equatorial clouds is large compared to the polar clouds, and the clouds are located at high altitude. For a flattened planet, the integrated polarization can both increase or decrease with respect to a spherical planet which depends on the horizontal distribution and optical thickness of the clouds. The direction of polarization can be either parallel or perpendicular to the projected direction of the rotation axis when clouds are zonally distributed. Rayleigh scattering by submicronsized cloud particles will maximize the polarimetric signal whereas the integrated degree of polarization is significantly reduced with micron-sized cloud particles as a result of forward scattering. The presence of a cold or hot circumplanetary disk may also produce a detectable degree of polarization ( 1%) even with a uniform cloud layer in the atmosphere.

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“…Marley & Sengupta (2011, their Figure 2) more accurately derive a breakup velocity and show that for brown dwarfs or gas planets older than 0.1 Gyr the lower limit on rotation period is 5 hr or 1.8 hr for a 1 or a 10 M Jupiter object, respectively. For W1738 with mass ≈5 M Jupiter and age between 0.15 and 1.0 Gyr (Leggett et al 2016), the rotational period must be greater than about 3 hr.…”

Section: Interpretation Of the W1738 Variabilitymentioning

confidence: 99%

OBSERVED VARIABILITY AT 1 and 4 μm IN THE Y0 BROWN DWARF WISEP J173835.52+273258.9

Leggett

Cushing

Hardegree-Ullman

et al. 2016

ApJ

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We have monitored photometrically the Y0 brown dwarf WISEP J173835.52+273258.9 (W1738) at both nearand mid-infrared wavelengths. This 1 Gyr old 400 K dwarf is at a distance of 8pc and has a mass around 5 M Jupiter . We observed W1738 using two near-infrared filters at λ≈1 μm, Y and J, on Gemini Observatory and two mid-infrared filters at λ≈4 μm, [3.6] and [4.5], on the Spitzer observatory. Twenty-four hours were spent on the source by Spitzer on each of 2013 June 30 and October 30 UT. Between these observations, around 5 hr were spent on the source by Gemini on each of 2013 July 17 and August 23 UT. The mid-infrared light curves show significant evolution between the two observations separated by 4 months. We find that a double sinusoid can be fit to the [4.5] data, where one sinusoid has a period of 6.0±0.1 hr and the other a period of 3.0±0.1 hr. The nearinfrared observations suggest variability with a ∼3.0 hr period, although only at a 2σ confidence level. We interpret our results as showing that the Y dwarf has a 6.0±0.1 hr rotation period, with one or more large-scale surface features being the source of variability. The peak-to-peak amplitude of the light curve at [4.5] is 3%. The amplitude of the near-infrared variability, if real, may be as high as 5%-30%. Intriguingly, this size of variability and the wavelength dependence can be reproduced by atmospheric models that include patchy KCl and Na 2 S clouds and associated small changes in surface temperature. The small number of large features, as well as the timescale for evolution of the features, is very similar to what is seen in the atmospheres of the solar system gas giants.

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Probing the physical properties of directly imaged gas giant exoplanets through polarization

Cited by 93 publications

References 53 publications

Rotational modulation of the linear polarimetric variability of the cool dwarf TVLM 513−46546

Rotational modulation of the linear polarimetric variability of the cool dwarf TVLM 513−46546

Polarized scattered light from self-luminous exoplanets

OBSERVED VARIABILITY AT 1 and 4 μm IN THE Y0 BROWN DWARF WISEP J173835.52+273258.9

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