Using polarimetry to detect and characterize   
 Jupiter-like extrasolar planets

Stam, Daphné; Hovenier, J. W.; Waters, L. B. F. M.

doi:10.1051/0004-6361:20041578

Cited by 127 publications

(176 citation statements)

References 21 publications

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“…As mentioned above, the degree of polarisation P s is independent of r, d and πF 0 , and will thus not require any scaling. To calculate the planetary scattering matrix elements a 1 and b 1 of the reflected stellar light, we employ the algorithm described in Stam et al (2004), which consists of an efficient and accurate adding-doubling algorithm (de Haan et al 1987) in combination with a fast, numerical, disk integration algorithm, to calculate the radiative transfer in the locally plane-parallel planetary atmosphere, and to integrate the reflected light across the illuminated and visible part of the planetary disk. …”

Section: Description Of Starlight That Is Reflected By An Exoplanetmentioning

confidence: 99%

“…Polarimetry, i.e. measuring the direction and degree of polarisation of light, is considered to be a powerful tool for the direct detection of exoplanets (Keller 2006;Keller et al 2010;Stam et al 2004). The reason for this is that, when integrated over the stellar disk, starlight of solar type stars will be virtually unpolarised (Kemp et al 1987), while starlight that has been reflected by an exoplanet will generally be polarised, due to scattering and reflection processes in the planetary atmosphere and on the surface (if present).…”

Section: Introductionmentioning

confidence: 99%

“…Seager et al (2000); Saar & Seager (2003); Stam (2003); Stam et al (2004) and for terrestrial planets by Stam (2008). Note that in the first two papers, planets are considered that are too close to their star to be spatially resolved.…”

Section: Introductionmentioning

confidence: 99%

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Flux and polarisation spectra of water clouds on exoplanets

Karalidi

Stam

Hovenier

2011

A&A

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Context.A crucial factor for a planet's habitability is its climate. Clouds play an important role in planetary climates. Detecting and characterising clouds on an exoplanet is therefore crucial when addressing this planet's habitability. Aims. We present calculated flux and polarisation spectra of starlight that is reflected by planets covered by liquid water clouds with different optical thicknesses, altitudes, and particle sizes, as functions of the phase angle α. We discuss the retrieval of these cloud properties from observed flux and polarisation spectra. Methods. Our model planets have black surfaces and atmospheres with Earth-like temperature and pressure profiles. We calculate the spectra from 0.3 to 1.0 μm, using an adding-doubling radiative transfer code with integration over the planetary disk. The cloud particles' scattering properties are calculated using a Mie-algorithm. Results. Both flux and polarisation spectra are sensitive to the cloud optical thickness, altitude and particle sizes, depending on the wavelength and phase angle α. Conclusions. Reflected fluxes are sensitive to cloud optical thicknesses up to ∼40, and the polarisation to thicknesses up to ∼20. The shapes of polarisation features as functions of α are relatively independent of the cloud optical thickness. Instead, they depend strongly on the cloud particles' size and shape, and can thus be used for particle characterisation. In particular, a rainbow strongly indicates the presence of liquid water droplets. Single scattering features such as rainbows, which can be observed in polarisation, are virtually unobservable in reflected fluxes, and fluxes are thus less useful for cloud particle characterisation. Fluxes are sensitive to cloud top altitudes mostly for α < 60 • and wavelengths <0.4 μm, and the polarisation for α around 90 • and wavelengths between 0.4 and 0.6 μm.

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Section: Description Of Starlight That Is Reflected By An Exoplanetmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Flux and polarisation spectra of water clouds on exoplanets

Karalidi

Stam

Hovenier

2011

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“…Stam 2003;Stam et al 2004;Saar & Seager 2003;Seager et al 2000;Stam 2008;Karalidi et al 2011). Polarization provides us with a unique tool for the detection of liquid water on a planetary atmosphere and surface.…”

Section: Introductionmentioning

confidence: 99%

Looking for the rainbow on exoplanets covered by liquid and icy water clouds

Karalidi

Stam

Hovenier

2012

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Aims. Looking for the primary rainbow in starlight that is reflected by exoplanets appears to be a promising method to search for liquid water clouds in exoplanetary atmospheres. Ice water clouds, that consist of water crystals instead of water droplets, could potentially mask the rainbow feature in the planetary signal by covering liquid water clouds. Here, we investigate the strength of the rainbow feature for exoplanets that have liquid and icy water clouds in their atmosphere, and calculate the rainbow feature for a realistic cloud coverage of Earth. Methods. We calculate flux and polarization signals of starlight that is reflected by horizontally and vertically inhomogeneous Earth-like exoplanets, covered by patchy clouds consisting of liquid water droplets or water ice crystals. The planetary surfaces are black. Results. On a planet with a significant coverage of liquid water clouds only, the total flux signal shows a weak rainbow feature. Any coverage of the liquid water clouds by ice clouds, however, dampens the rainbow feature in the total flux, and thus the discovery of liquid water in the atmosphere. On the other hand, detecting the primary rainbow in the polarization signal of exoplanets appears to be a powerful tool for detecting liquid water in exoplanetary atmospheres, even when these clouds are partially covered by ice clouds. In particular, liquid water clouds covering as little as 10-20% of the planetary surface, with more than half of these covered by ice clouds, still create a polarized rainbow feature in the planetary signal. Indeed, calculations of flux and polarization signals of an exoplanet with a realistic Earth-like cloud coverage, show a strong polarized rainbow feature.

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“…Polarization signals of extrasolar planets have already been numerically simulated by several authors, who in particular investigated the influence of various scattering particles resulting from different atmospheric compositions. Seager et al (2000), Saar & Seager (2003), and Hough & Lucas (2003) have discussed close-in extrasolar giant planets with orbital radii smaller than 0.05 AU, which are thus unresolved and relatively hot, while Stam et al (2004) studied the flux and polarized spectra of resolved Jupiter-like planets in larger orbits. In contrast to others Sengupta & Maiti (2006) have considered elliptical rather than circular orbits to calculate the polarization in the R passband due to scattering by water and silicate condensates, taking the planetary oblateness also into account.…”

Section: Introductionmentioning

confidence: 99%

Orbital parameters of extrasolar planets derived from polarimetry

Fluri

Berdyugina

2010

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Context. Polarimetry of extrasolar planets becomes a new tool for their investigation, which requires the development of diagnostic techniques and parameter case studies. Aims. Our goal is to develop a theoretical model which can be applied to interpret polarimetric observations of extrasolar planets. Here we present a theoretical parameter study that shows the influence of the various involved parameters on the polarization curves. Furthermore, we investigate the robustness of the fitting procedure. We focus on the diagnostics of orbital parameters and the estimation of the scattering radius of the planet. Methods. We employ the physics of Rayleigh scattering to obtain polarization curves of an unresolved extrasolar planet. Calculations are made for two cases: (i) assuming an angular distribution for the intensity of the scattered light as from a Lambert sphere and for polarization as from a Rayleigh-type scatterer; and (ii) assuming that both the intensity and polarization of the scattered light are distributed according to the Rayleigh law. We show that the difference between these two cases is negligible for the shapes of the polarization curves. In addition, we take the size of the host star into account, which is relevant for hot Jupiters orbiting giant stars. Results. We discuss the influence of the inclination of the planetary orbit, the position angle of the ascending node, and the eccentricity on the linearly polarized light curves both in Stokes Q/I and U/I. We also analyze errors that arise from the assumption of a point-like star in numerical modeling of polarization as compared to consistent calculations accounting for the finite size of the host star. We find that errors due to the point-like star approximation are reduced with the size of the orbit, but still amount to about 5% for known hot Jupiters. Recovering orbital parameters from simulated data is shown to be very robust even for very noisy data because the polarization curves react sensitively to changes in the shape and orientation of the orbit.Conclusions. The proposed model successfully diagnoses orbital parameters of extrasolar planets and can also be applied to predict polarization curves of known exoplanets. Polarization curves of extrasolar planets thus provide an ideal tool to determine parameters that are difficult to obtain with other methods, namely inclination and position angle of the ascending node of orbits as well as true masses of extrasolar planets.

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Using polarimetry to detect and characterize Jupiter-like extrasolar planets

Cited by 127 publications

References 21 publications

Flux and polarisation spectra of water clouds on exoplanets

Flux and polarisation spectra of water clouds on exoplanets

Looking for the rainbow on exoplanets covered by liquid and icy water clouds

Orbital parameters of extrasolar planets derived from polarimetry

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