Flux and polarization signals of spatially inhomogeneous gaseous exoplanets

Karalidi, Theodora; Stam, Daphné; Guirado, D.

doi:10.1051/0004-6361/201321492

Cited by 25 publications

(24 citation statements)

References 51 publications

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“…For an inhomogeneous planet, we must have negative α values between φ = [π, 2π] to en-sure that the correct scattering angles are used. Inhomogeneous atmospheres have been modeled by Karalidi & Stam (2012); Karalidi et al (2013), by calculating the brightness of homogeneous planets and creating an inhomogeneous planet from their area-weighted averages. One advantage of this method is that we do not need to repeat calculations for different homogeneous planets before arriving at the inhomogeneous case.…”

Section: Inhomogeneous Atmospheresmentioning

confidence: 99%

A MULTIPLE SCATTERING POLARIZED RADIATIVE TRANSFER MODEL: APPLICATION TO HD 189733b

Kopparla

Natraj

Zhang

et al. 2016

ApJ

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We present a multiple scattering vector radiative transfer model that produces disk integrated, full phase polarized light curves for reflected light from an exoplanetary atmosphere. We validate our model against results from published analytical and computational models and discuss a small number of cases relevant to the existing and possible near-future observations of the exoplanet HD 189733b. HD 189733b is arguably the most well observed exoplanet to date and the only exoplanet to be observed in polarized light, yet it is debated if the planet's atmosphere is cloudy or clear. We model reflected light from clear atmospheres with Rayleigh scattering, and cloudy or hazy atmospheres with Mie and fractal aggregate particles. We show that clear and cloudy atmospheres have large differences in polarized light as compared to simple flux measurements, though existing observations are insufficient to make this distinction. Futhermore, we show that atmospheres that are spatially inhomogeneous, such as being partially covered by clouds or hazes, exhibit larger contrasts in polarized light when compared to clear atmospheres. This effect can potentially be used to identify patchy clouds in exoplanets. Given a set of full phase polarimetric measurements, this model can constrain the geometric albedo, properties of scattering particles in the atmosphere, and the longitude of the ascending node of the orbit. The model is used to interpret new polarimetric observations of HD 189733b in a companion paper.

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Section: Inhomogeneous Atmospheresmentioning

confidence: 99%

A MULTIPLE SCATTERING POLARIZED RADIATIVE TRANSFER MODEL: APPLICATION TO HD 189733b

Kopparla

Natraj

Zhang

et al. 2016

ApJ

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“…Horizontal inhomogeneities are incorporated by dividing the signal from the planetary disk into a collection of independent pixels on the planet (e.g., de Kok et al 2011;Karalidi & Stam 2012;Karalidi et al 2013) because typically the differential transport of horizontally propagating radiation is negligible. However, there are scenarios in which horizontal radiation transport might affect the planet luminosity.…”

Section: Appendix C: Horizontal Radiation Transportmentioning

confidence: 99%

“…The power of polarization of reflected light as a diagnostic was first demonstrated by Hansen & Hovenier (1974) with their determination of the composition and size of the cloud particles in Venus' atmosphere (see also . The potential of this technique to detect and characterize exoplanets in reflected light has been widely recognized and several authors have provided numerical and analytical predictions (e.g., Seager et al 2000;Stam et al 2004;Buenzli & Schmid 2009;Madhusudhan & Burrows 2012;Karalidi et al 2013). A first detection of polarized reflected light from an exoplanet has been claimed for HD 189733b (Berdyugina et al 2008(Berdyugina et al , 2011, a hotJupiter that remains spatially unresolved from its star, but the measurements, which require the planet to have a very high degree of polarization, have not yet been confirmed by others (Wiktorowicz 2009;Wiktorowicz et al 2015;Bott et al 2016).…”

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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“…Sources: Cassini/ISS maps were obtained from http://ciclops.org. HST images in 2012 are from program GO-13067 (Karalidi et al 2013), and the HST composite image from 2017 is from the OPAL program GO-14756 (Simon et al 2015). IRTF maps from 2000 and 2013 are from co-author Orton.…”

Section: Observationsmentioning

confidence: 99%

The Gas Composition and Deep Cloud Structure of Jupiter's Great Red Spot

Bjoraker¹,

Wong

Pater

et al. 2018

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We have obtained high-resolution spectra of Jupiter's Great Red Spot (GRS) between 4.6 and 5.4 µm using telescopes on Mauna Kea in order to derive gas abundances and to constrain its cloud structure between 0.5 and 5 bars. We used line profiles of deuterated methane (CH 3 D) at 4.66 µm to infer the presence of an opaque cloud at 5±1 bars. From thermochemical models this is almost certainly a water cloud. We also used the strength of Fraunhofer lines in the GRS to obtain the ratio of reflected sunlight to thermal emission. The level of the reflecting layer was constrained to be at 570±30 mbars based on fitting strong NH 3 lines at 5.32 µm. We identify this layer as an ammonia cloud based on the temperature where gaseous NH 3 condenses. We found evidence for a strongly absorbing, but not totally opaque, cloud layer at pressures deeper than 1.3 bars by combining Cassini/CIRS spectra of the GRS at 7.18 µm with ground-based spectra at 5 µm. This is consistent with the predicted level of an NH 4 SH cloud. We also constrained the vertical profile of H 2 O and NH 3 . The GRS spectrum is matched by a saturated H 2 O profile above an opaque water cloud at 5 bars. The pressure of the water cloud constrains Jupiter's O/H ratio to be at least 1.1 times solar. The NH 3 mole fraction is 200±50 ppm for pressures between 0.7 and 5 bars. Its abundance is 40 ppm at the estimated pressure of the reflecting layer. We obtained 0.8±0.2 ppm for PH 3 , a factor of 2 higher than in the warm collar surrounding the GRS. We detected all 5 naturally occurring isotopes of germanium in GeH 4 in the Great Red Spot. We obtained an average value of 0.35±0.05 ppb for GeH 4 . Finally, we measured 0.8±0.2 ppb for CO in the deep atmosphere.

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Flux and polarization signals of spatially inhomogeneous gaseous exoplanets

Cited by 25 publications

References 51 publications

A MULTIPLE SCATTERING POLARIZED RADIATIVE TRANSFER MODEL: APPLICATION TO HD 189733b

A MULTIPLE SCATTERING POLARIZED RADIATIVE TRANSFER MODEL: APPLICATION TO HD 189733b

Polarized scattered light from self-luminous exoplanets

The Gas Composition and Deep Cloud Structure of Jupiter's Great Red Spot

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