The Polarization Signature of Extrasolar Planet Transiting Cool Dwarfs

Carciofi, A. C.; Magalhães, A. M.

doi:10.1086/497064

Cited by 55 publications

(49 citation statements)

References 17 publications

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“…Associated with maximum fluxes from HD 189733b that are not located at maximal planetary elongations, the net diluted polarization degree peaks at orbital phases +0.35 and +0.65. The highest degrees of P are of the order of 0.0025 ± 0.0002 % at 0.7 keV, similarly to the polarization found in the optical band (Carciofi & Magalhães 2005).…”

Section: Polarizationsupporting

confidence: 67%

“…These results can be achieved thanks to radial velocity measurements, orbital brightness modulations, gravitational microlensing, direct imaging, astrometry, and polarimetry. The later is probably one of the most delicate methods since the anticipated white light polarization degree (about 10 −5 , Carciofi & Magalhães 2005;Kostogryz et al 2014;Kopparla et al 2016) resulting from scattering of stellar photons onto the atmospheric layers of Hot frederic.marin@astro.unistra.fr 1 In December 2016, 2695 planets out of a total of 3547 have been discovered by transit techniques, see http://exoplanet.eu/ Jupiters is expected to be just about detectable given the current limits of current optical, broad-band, stellar polarimeters (Schmid et al 2005;Hough et al 2006;Wiktorowicz 2009). Berdyugina et al (2008Berdyugina et al ( , 2011 reported to have successfully achieved a B-band polarimetric detection of HD 189733b and found a peak polarization of 2×10 −4 (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Computation of the Transmitted and Polarized Scattered Fluxes by the Exoplanet HD 189733b in X-Rays

Marin

Grosso

2017

ApJ

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Thousands of exoplanets have been detected, but only one exoplanetary transit was potentially observed in X-rays from HD 189733A. What makes the detection of exoplanets so difficult in this band? To answer this question, we run Monte-Carlo radiative transfer simulations to estimate the amount of X-ray flux reprocessed by HD 189733b Despite its extended evaporating-atmosphere, we find that the X-ray absorption radius of HD 189733b at 0.7 keV, the mean energy of the photons detected in the 0.25-2 keV energy band by XMM-Newton, is ∼1.01 times the planetary radius for an atmosphere of atomic Hydrogen and Helium (including ions), and produces a maximum depth of ∼2.1% at ∼±46 min from the center of the planetary transit on the geometrically thick and optically thin corona. We compute numerically in the 0.25-2 keV energy band that this maximum depth is only of ∼1.6% at ∼±47 min from the transit center, and little sensitive to the metal abundance assuming that adding metals in the atmosphere would not dramatically change the density-temperature profile. Regarding a direct detection of HD 189733b in X-rays, we find that the amount of flux reprocessed by the exoplanetary atmosphere varies with the orbital phase, spanning between 3-5 orders of magnitude fainter than the flux of the primary star. Additionally, the degree of linear polarization emerging from HD 189733b is <0.003%, with maximums detected near planetary greatest elongations. This implies that both the modulation of the X-ray flux with the orbital phase and the scattered-induced continuum polarization cannot be observed with current X-ray facilities.

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Section: Polarizationsupporting

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Computation of the Transmitted and Polarized Scattered Fluxes by the Exoplanet HD 189733b in X-Rays

Marin

Grosso

2017

ApJ

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“…Stellar discs have a centrosymmetric polarization pattern due to light scattering (Leroy 2000), with maximum polarization very close to the limb of the star. In a uniform, spherically symmetric star the net polarization will be zero but star‐spots near the limb can produce a measurable polarization by breaking the symmetry, see Carciofi & Magalhães (2005).…”

Section: Resultsmentioning

confidence: 99%

Planetpol polarimetry of the exoplanet systems 55 Cnc and τ Boo

Lucas

Hough

Bailey

et al. 2009

Monthly Notices of the Royal Astronomical Society

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We present very sensitive polarimetry of 55 Cnc and τ Boo in an attempt to detect the partially polarized reflected light from the planets orbiting these two stars. 55 Cnc is orbited by a hot Neptune planet (55 Cnc e) at 0.038 au, a hot Jupiter planet (55 Cnc b) at 0.11 au and at least three more distant planets. The polarization of this system is very stable, showing no sign of the periodic variations that would be expected if a short‐period planet were detected. The measured standard deviation of the nightly averaged Stokes Q/I and U/I parameters is 2.2 × 10−6. We derive upper limits on the geometric albedo, AG, and planetary radius using Monte Carlo multiple scattering simulations of a simple model atmosphere. We assume Rayleigh‐like scattering and polarization behaviour (scaled by the maximum polarization, pm, at 90°) and pressure insensitive extinction. Atmospheres in which multiple scattering plays only a small role have an almost linear relation between polarization and AG. In this case, the 4σ upper limit is AG < 0.13(R/1.2RJup)−2p−1m for 55 Cnc e. This is most easily explained if 55 Cnc e is relatively small, like GJ 436b, and therefore not a pure H–He planet. The data do not provide a useful upper limit for 55 Cnc b. τ Boo is orbited by an unusually massive hot Jupiter planet. The data show a standard deviation in the night‐to‐night average Stokes Q/I and U/I polarization parameters of 5.1 × 10−6. The 4σ upper limit is AG < 0.37(R/1.2RJup)−2p−1m for τ Boo b, adopting the fairly well established orbital inclination i∼ 40°. This extends the similar upper limits reported previously for this planet to longer wavelengths. The fact that the τ Boo data show more scatter, despite the smaller photon noise for this bright star, may be due to the spot activity detected photometrically by the Microvariability & Oscillations of Stars (MOST) satellite. These results contrast markedly with the recent claim of a 3σ detection of a periodic polarization signal from HD 189733 with amplitude P= 2 × 10−4, attributed to the planet HD 189733 b.

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“…The value of this polarization is maximal when the planet is crossing the edge of the source (Carciofi & Magalhães 2005;Wiktorowicz & Laughlin 2014;Kostogryz et al 2015). However, the occultation happens for phase angles greater than 90…”

Section: Polarization Due To the Stellar Occultation By Planetmentioning

confidence: 97%

Polarimetry Microlensing of Close-in Planetary Systems

Sajadian

Hundertmark

2017

ApJ

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A close-in giant planetary (CGP) system has a net polarization signal whose value varies depending on the orbital phase of the planet. This polarization signal is either caused by the stellar occultation or by reflected starlight from the surface of the orbiting planet. When the CGP system is located in the Galactic bulge, its polarization signal becomes too weak to be measured directly. One method for detecting and characterizing these weak polarization signatures due to distant CGP systems is gravitational microlensing. In this work, we focus on potential polarimetric observations of highlymagnified microlensing events of CGP systems. When the lens is passing directly in front of the source star with its planetary companion, the polarimetric signature caused by the transiting planet is magnified. As a result some distinct features in the polarimetry and light curves are produced. In the same way microlensing amplifies the reflection-induced polarization signal. While the planetinduced perturbations are magnified, whenever these polarimetric or photometric deviations vanish for a moment the corresponding magnification factor or the polarization component(s) is equal to the related one due to the planet itself. Finding these exact times in the planet-induced perturbations helps us to characterize the planet. In order to evaluate the observability of such systems through polarimetric or photometric observations of high-magnification microlensing events, we simulate these events by considering confirmed CGP systems as their source stars and conclude that the efficiency for detecting the planet-induced signal with the state-of-the-art polarimetric instrument (FORS2/VLT) is less than 0.1%. Consequently, these planet-induced polarimetry perturbations can likely be detected under favorable conditions by high-resolution and short-cadence polarimeters of the next generation.

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The Polarization Signature of Extrasolar Planet Transiting Cool Dwarfs

Cited by 55 publications

References 17 publications

Computation of the Transmitted and Polarized Scattered Fluxes by the Exoplanet HD 189733b in X-Rays

Computation of the Transmitted and Polarized Scattered Fluxes by the Exoplanet HD 189733b in X-Rays

Planetpol polarimetry of the exoplanet systems 55 Cnc and τ Boo

Polarimetry Microlensing of Close-in Planetary Systems

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