Polarization in Exoplanetary Systems Caused by Transits, Grazing Transits, and Starspots

Костогрыз, Н. М.; Yakobchuk, T. M.; Berdyugina, S. V.

doi:10.1088/0004-637x/806/1/97

Cited by 25 publications

(25 citation statements)

References 35 publications

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“…This transit polarization effect has been investigated for planets transiting cool stars by Carciofi & Magalhaes (2005) and Kostogryz et al (2011). Kostogryz et al (2015) have calculated the transit polarization for a range of transiting planets, and shown that the size of the effect increases for lower stellar temperatures, lower gravities, and larger planet to star radius ratios, with the effect reaching up to 10 ppm or more at 400 nm in the most favourable cases. However, WASP-18 is outside the range of parameters considered in that study.…”

Section: Transit Polarimetrymentioning

confidence: 99%

The Polarization of the Planet-Hosting WASP-18 System

Bott¹,

Bailey²,

Cotton³

et al. 2018

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We report observations of the linear polarization of the WASP-18 system, which harbors a very massive (∼ 10 M J ) planet orbiting very close to its star with an orbital period of 0.94 days. We find the WASP-18 system is polarized at ∼200 parts-per-million (ppm), likely from the interstellar medium predominantly, with no strong evidence for phase dependent modulation from reflected light from the planet. We set an upper limit of 40 ppm (99% confidence level) on the amplitude of a reflected polarized light planetary signal. We compare the results with models for a number of processes that may produce polarized light in a planetary system to determine if we can rule out any phenomena with this limit. Models of reflected light from thick clouds can approach or exceed this limit, but such clouds are unlikely at the high temperature of the WASP-18b atmosphere. Additionally, we model the expected polarization resulting from the transit of the planet across the star and find this has an amplitude of ∼1.6 ppm, which is well below our detection limits. We also model the polarization due to the tidal distortion of the star by the massive planet and find this is also too small to be measured currently.

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Section: Transit Polarimetrymentioning

confidence: 99%

The Polarization of the Planet-Hosting WASP-18 System

Bott¹,

Bailey²,

Cotton³

et al. 2018

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“…Besides limb darkening, continuum radiation also carries some small degree of polarization; this depends on the wavelength and could be detected in exoplanet transit polarimetry (Kostogryz et al 2015(Kostogryz et al , 2016Wiktorowicz & Laughlin 2014).…”

Section: Exoplanet Detection Limitsmentioning

confidence: 99%

Spatially resolved spectroscopy across stellar surfaces

Dravins

Ludwig

Dahlén

et al. 2017

A&A

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Context. High-precision stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require stellar background spectra to be known along the transit path while detection of Earth analogs require stellar microvariability to be understood. Hydrodynamic 3D models can be computed for widely different stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-to-limb changes across stellar disks. Aims. We observe high-resolution spectral line profiles across spatially highly resolved stellar surfaces, which are free from the effects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic profiles from 3D models. Methods. During exoplanet transits, successive stellar surface portions become hidden and differential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than ∼1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identified through simulated observations of synthetic spectral lines. Results. In normal stars, line profile ratios between various transit phases may vary by ∼0.5%, requiring S /N 5000 for meaningful spectral reconstruction.While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters. Conclusions. For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches.

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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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Polarization in Exoplanetary Systems Caused by Transits, Grazing Transits, and Starspots

Cited by 25 publications

References 35 publications

The Polarization of the Planet-Hosting WASP-18 System

The Polarization of the Planet-Hosting WASP-18 System

Spatially resolved spectroscopy across stellar surfaces

Polarimetry Microlensing of Close-in Planetary Systems

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