Multi-wavelength aperture polarimetry of debris disc host stars

Marshall, Jonathan P.; Cotton, Daniel V.; Bott, Kimberly; Bailey, Jeremy; Kedziora-Chudczer, Lucyna; Brown, E L

doi:10.1093/mnras/stad979

Monthly Notices of the Royal Astronomical Society

2023

DOI: 10.1093/mnras/stad979

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Multi-wavelength aperture polarimetry of debris disc host stars

Jonathan P. Marshall

Daniel V. Cotton

Kimberly Bott

et al.

Abstract: Debris discs around main sequence stars have been extensively characterised from infrared to millimetre wavelengths through imaging, spectroscopic, and total intensity (scattered light and/or thermal emission) measurements. Polarimetric observations have only been used sparingly to interpret the composition, structure, and size of dust grains in these discs. Here we present new multi-wavelength aperture polarisation observations with parts-per-million sensitivity of a sample of twelve bright debris discs, span… Show more

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Cited by 4 publications

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Impact of hot exozodiacal dust on the polarimetric analysis of close-in exoplanets

Ollmann,

Wolf,

Lietzow

et al. 2023

A&A

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Context. Hot exozodiacal dust (HEZD) found around main-sequence stars through interferometric observations in the photometric bands H to L is located close to the dust sublimation radius, potentially at orbital radii comparable to those of close-in exoplanets. Consequently, HEZD has a potential influence on the analysis of the scattered-light polarization of close-in exoplanets and vice versa. Aims. We analyze the impact of HEZD on the polarimetric characterization of close-in exoplanets. This study is motivated in particular by the recently proven feasibility of exoplanet polarimetry. Methods. Applying the 3D Monte Carlo radiative transfer code POLARIS in an extended and optimized version for radiative transfer in exoplanetary atmospheres and an analytical tool for modeling the HEZD, we simulated and compared the polarization characteristics of the wavelength-dependent scattered-light polarization of HEZD and close-in exoplanets. As a starting point for our analysis, we defined a reference model consisting of a close-in exoplanet with a scattered-light polarization consistent with the upper limit determined for WASP-18b, and a HEZD consistent with the near-infrared excess detected for HD 22484 (10 Tau). Results. The varied parameters are the planetary phase angle (0°–180°), the dust grain radius (0.02 µm−10 µm), the HEZD mass (10−10 M⊙−10−8 M⊙), the orbital inclination (0°−90°), the composition of the planetary atmosphere (Mie and Rayleigh scattering atmosphere), the orbital radius of HEZD (0.02 au−0.4 au), and the planetary orbital radius (0.01 au−0.05 au). The dust grain radius has the strongest influence on the polarimetric analysis due to its significant impact on the wavelength-dependent polarization characteristics and the total order of magnitude of the scattered-light polarization. In certain scenarios, the scattered-light polarization of the HEZD even exceeds that of the close-in exoplanet, for example for a dust grain radius of 0.1 µm, a HEZD mass of 8 × 10−10 M⊙, an orbital radius of HEZD of 0.04 au and an orbital inclination of 90°. Conclusions. The presence of HEZD potentially has a significant impact on the polarimetric investigations of close-in exoplanets. Furthermore, interferometric observations are required to better constrain the parameter space for HEZD and thus the possible resulting scattered-light polarization.

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Impact of hot exozodiacal dust on the polarimetric analysis of close-in exoplanets

Ollmann,

Wolf,

Lietzow

et al. 2023

A&A

View full text Add to dashboard Cite

show abstract

Polarization position angle standard stars: a reassessment of θ and its variability for seventeen stars based on a decade of observations

Cotton,

Bailey,

Kedziora-Chudczer

et al. 2024

Monthly Notices of the Royal Astronomical Society

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Observations of polarization position angle (θ) standards made from 2014 to 2023 with the High Precision Polarimetric Instrument (HIPPI) and other HIPPI-class polarimeters in both hemispheres are used to investigate their variability. Multi-band data were first used to thoroughly recalibrate the instrument performance by bench-marking against carefully selected literature data. A novel Co-ordinate Difference Matrix (CDM) approach – which combines pairs of points – was then used to amalgamate monochromatic (g′ band) observations from many observing runs and re-determine θ for 17 standard stars. The CDM algorithm was then integrated into a fitting routine and used to establish the impact of stellar variability on the measured position angle scatter. The approach yields variability detections for stars on long time scales that appear stable over short runs. The best position angle standards are ℓ Car, o Sco, HD 154445, HD 161056 and ι1 Sco which are stable to ≤ 0.123○. Position angle variability of 0.27–0.82○, significant at the 3-σ level, is found for 5 standards, including the Luminous Blue Variable HD 160529 and all but one of the other B/A-type supergiants (HD 80558, HD 111613, HD 183143 and 55 Cyg), most of which also appear likely to be variable in polarization magnitude (p) – there is no preferred orientation for the polarization in these objects, which are all classified as α Cygni variables. Despite this we make six key recommendations for observers – relating to data acquisition, processing and reporting – that will allow them to use these standards to achieve < 0.1○ precision in the telescope position angle with similar instrumentation, and allow data sets to be combined more accurately.

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ϵ Sagittarii: An Extreme Rapid Rotator with a Decretion Disk

Bailey,

Lewis,

Howarth

et al. 2024

ApJ

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We report high-precision, multiwavelength linear-polarization observations of the bright B9 (or A0) star ϵ Sagittarii. The polarization shows the distinctive wavelength dependence expected for a rapidly rotating star. Analysis of the polarization data reveals an angular rotation rate ω (=Ω/Ωcrit) of 0.995 or greater, the highest yet measured for a star in our Galaxy. An additional wavelength-independent polarization component is attributed to electron scattering in a low-density, edge-on gas disk that also produces the narrow absorption components seen in the spectrum. Several properties of the star (polarization due to a disk, occasional weak Hα emission, and multiple periodicities seen in space photometry) resemble those of Be stars, but the level of activity in all cases is much lower than that of typical Be stars. The stellar properties are inconsistent with single-rotating-star evolutionary tracks, indicating that it is most likely a product of binary interaction. The star is an excellent candidate for observation by interferometry, optical spectropolarimetry to detect the Öhman effect, and ultraviolet polarimetry, any of which would allow its extreme rotation to be tested and its stellar properties to be refined.

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Multi-wavelength aperture polarimetry of debris disc host stars

Cited by 4 publications

References 128 publications

Impact of hot exozodiacal dust on the polarimetric analysis of close-in exoplanets

Impact of hot exozodiacal dust on the polarimetric analysis of close-in exoplanets

Polarization position angle standard stars: a reassessment of θ and its variability for seventeen stars based on a decade of observations

ϵ Sagittarii: An Extreme Rapid Rotator with a Decretion Disk

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