The intrinsic and interstellar broad-band linear polarization of nearby FGK dwarfs

Cotton, Daniel V. and Marshall, Jonathan P. and Bailey, Jeremy and Kedziora-Chudczer, Lucyna and Bott, Kimberly and Marsden, Stephen C. and Carter, Bradley D. (2017) The intrinsic and interstellar broad-band linear polarization of nearby FGK dwarfs. Monthly Notices of the Royal Astronomical Society, 467 (1). pp. 873-897. ISSN 0035-8711

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We present linear polarization measurements of nearby FGK dwarfs to parts-per-million (ppm) precision. Before making any allowance for interstellar polarization, we found that the active stars within the sample have a mean polarization of 28.5 ± 2.2 ppm, while the inactive stars have a mean of 9.6 ± 1.5 ppm. Amongst inactive stars, we initially found no difference between debris disc host stars (9.1 ± 2.5 ppm) and the other FGK dwarfs (9.9 ± 1.9 ppm). We develop a model for the magnitude and direction of interstellar polarization for nearby stars. When we correct the observations for the estimated interstellar polarization, we obtain 23.0 ± 2.2 ppm for the active stars, 7.8 ± 2.9 ppm for the inactive debris disc host stars and 2.9 ± 1.9 ppm for the other inactive stars. The data indicate that whilst some debris disc host stars are intrinsically polarized most inactive FGK dwarfs have negligible intrinsic polarization, but that active dwarfs have intrinsic polarization at levels ranging up to ∼45 ppm. We briefly consider a number of mechanisms, and suggest that differential saturation of spectral lines in the presence of magnetic fields is best able to explain the polarization seen in active dwarfs. The results have implications for current attempts to detect polarized reflected light from hot Jupiters by looking at the combined light of the star and planet.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to Published version in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 19 Jan 2018 06:06
Last Modified: 12 Mar 2019 05:46
Uncontrolled Keywords: polarimetric, stars, circumstellar matter, dust, extinction, magnetic fields
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1093/mnras/stx068

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