Multiple scattering polarization – Application of Chandrasekhar’s formalisms to the atmosphere of brown dwarfs and extrasolar planets

Sengupta, Sujan; Marley, Mark S.

doi:10.1007/s12043-011-0125-0

Pramana - J Phys

2011

DOI: 10.1007/s12043-011-0125-0

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Multiple scattering polarization – Application of Chandrasekhar’s formalisms to the atmosphere of brown dwarfs and extrasolar planets

Sujan Sengupta

Mark S. Marley

Abstract: Chandrasekhar's formalisms for the transfer of polarized radiation are used to explain the observed dust scattering polarization of brown dwarfs in the optical band. Model polarization profiles for hot and young directly imaged extrasolar planets are presented with specific prediction of the degree of polarization in the infrared. The model invokes Chandrasekhar's formalism for the rotation-induced oblateness of the objects that gives rise to the necessary asymmetry for yielding net non-zero disk integrated li… Show more

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Cited by 2 publications

References 27 publications

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Linear polarization of rapidly rotating ultracool dwarfs

Miles-Páez

Osorio

Πάλλη

et al. 2013

A&A

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Aims. We aim to study the near-infrared linear polarization signal of rapidly rotating ultracool dwarfs with spectral types ranging from M7 through T2 and projected rotational velocities of v sin i 30 km s −1 . These dwarfs are believed to have dusty atmospheres and oblate shapes, which is an appropriate scenario to produce measurable linear polarization of the continuum light. Methods. Linear polarimetric images were collected in the J-band for a sample of 18 fast-rotating ultracool dwarfs, of which five were also observed in the Z-band using the Long-slit Intermediate Resolution Infrared Spectrograph (LIRIS) on the Cassegrain focus of the 4.2-m William Herschel Telescope. The measured median uncertainty in the linear polarization degree is ±0.13% for our sample, which allowed us to detect polarization signatures above ∼0.39% with a confidence interval of ≥3σ. Results. About 40 ± 15% of the sample is linearly polarized in the Z-and J-bands. All positive detections have linear polarization degrees ranging from 0.4% to 0.8% in both filters independent of spectral type and spectroscopic rotational velocity. However, simple statistics point at the fastest rotators (v sin i 60 km s −1 ) having a larger fraction of positive detections and a larger averaged linear polarization degree than the moderately rotating dwarfs (v sin i = 30-60 km s −1 ). Our data suggest little linear polarimetric variability on short timescales (i.e., observations separated by a few ten rotation periods), and significant variability on long timescales (i.e., hundred to thousand rotation cycles), supporting the presence of long-term weather in ultracool dwarf atmospheres.

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Linear polarization of rapidly rotating ultracool dwarfs

Miles-Páez

Osorio

Πάλλη

et al. 2013

A&A

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Effect of Multiple Scattering on the Transmission Spectra and the Polarization Phase Curves for Earth-like Exoplanets

Singla

Chakrabarty

Sengupta

2023

ApJ

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It is the most appropriate time to characterize the Earth-like exoplanets in order to detect biosignature beyond the Earth because such exoplanets will be the prime targets of big-budget missions like JWST, Roman Space Telescope, HabEx, LUVOIR, Thirty Meter Telescope, Extremely Large Telescope, etc. We provide models for the transmission spectra of Earth-like exoplanets by incorporating the effects of multiple scattering. For this purpose we numerically solve the full multiple-scattering radiative transfer equations instead of using Beer–Bouguer–Lambert’s law, which does not include the diffuse radiation due to scattering. Our models demonstrate that the effect of this diffuse transmission radiation can be observationally significant, especially in the presence of clouds. We also calculate the reflection spectra and polarization phase curves of Earth-like exoplanets by considering both cloud-free and cloudy atmospheres. We solve the 3D vector radiative transfer equations numerically and calculate the phase curves of albedo and disk-integrated polarization by using appropriate scattering phase matrices and integrating the local Stokes vectors over the illuminated part of the disks along the line of sight. We present the effects of the globally averaged surface albedo on the reflection spectra and phase curves as the surface features of such planets are known to significantly dictate the nature of these observational quantities. Synergic observations of the spectra and phase curves will certainly prove to be useful in extracting more information and reducing the degeneracy among the estimated parameters of terrestrial exoplanets. Thus, our models will play a pivotal role in driving future observations.

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Multiple scattering polarization – Application of Chandrasekhar’s formalisms to the atmosphere of brown dwarfs and extrasolar planets

Cited by 2 publications

References 27 publications

Linear polarization of rapidly rotating ultracool dwarfs

Linear polarization of rapidly rotating ultracool dwarfs

Effect of Multiple Scattering on the Transmission Spectra and the Polarization Phase Curves for Earth-like Exoplanets

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