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Extreme starlight polarization in a region with highly polarized dust emission

Panopoulou, Georgia V. and Hensley, Brandon S. and Skalidis, Raphael and Blinov, Dmitry and Tassis, Konstantinos (2019) Extreme starlight polarization in a region with highly polarized dust emission. Astronomy and Astrophysics, 624 . Art. No. L8. ISSN 0004-6361. doi:10.1051/0004-6361/201935266.

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Context. Galactic dust emission is polarized at unexpectedly high levels, as revealed by Planck. Aims. The origin of the observed ≃20% polarization fractions can be identified by characterizing the properties of optical starlight polarization in a region with maximally polarized dust emission. Methods. We measure the R-band linear polarization of 22 stars in a region with a submillimeter polarization fraction of ≃20%. A subset of 6 stars is also measured in the B, V, and I bands to investigate the wavelength dependence of polarization. Results. We find that starlight is polarized at correspondingly high levels. Through multiband polarimetry we find that the high polarization fractions are unlikely to arise from unusual dust properties, such as enhanced grain alignment. Instead, a favorable magnetic field geometry is the most likely explanation, and is supported by observational probes of the magnetic field morphology. The observed starlight polarization exceeds the classical upper limit of [pV/E(B−V)]_(max) = 9% mag^(−1) and is at least as high as 13% mag^(−1), as inferred from a joint analysis of Planck data, starlight polarization, and reddening measurements. Thus, we confirm that the intrinsic polarizing ability of dust grains at optical wavelengths has long been underestimated.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Panopoulou, Georgia V.0000-0001-7482-5759
Hensley, Brandon S.0000-0001-7449-4638
Tassis, Konstantinos0000-0002-8831-2038
Additional Information:© 2019 ESO. Article published by EDP Sciences. Received 13 February 2019; Accepted 23 March 2019; Published online 11 April 2019. We thank V. Guillet for his insightful review, V. Pelgrims, for helpful comments, and P. Martin, S. Clark and the ESA/Cosmos helpdesk for advice on using Planck data. G. V. P. acknowledges support from the National Science Foundation, under grant number AST-1611547. R. S., D. B. and K. T. acknowledge support from the European Research Council under the European Union’s Horizon 2020 research and innovation program, under grant agreement No 771282. Based on observations obtained with Planck (, a European Space Agency (ESA) science mission. This work has made use of data from the ESA mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Based on Galactic ALFA HI (GALFA HI) survey data obtained with the Arecibo L-band Feed Array (ALFA) on the Arecibo 305m telescope. The Arecibo Observatory is a facility of the National Science Foundation (NSF) operated by SRI International in alliance with the Universities Space Research Association (USRA) and UMET under a cooperative agreement. The GALFA HI surveys are funded by the NSF through grants to Columbia University, the University of Wisconsin, and the University of California.
Funding AgencyGrant Number
European Research Council (ERC)771282
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:polarization – ISM: magnetic fields – dust, extinction – submillimeter: ISM – local insterstellar matter
Record Number:CaltechAUTHORS:20190418-094724522
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Official Citation:Extreme starlight polarization in a region with highly polarized dust emission. Georgia V. Panopoulou, Brandon S. Hensley, Raphael Skalidis, Dmitry Blinov and Konstantinos Tassis. A&A, 624 (2019) L8. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94782
Deposited By: Tony Diaz
Deposited On:18 Apr 2019 18:24
Last Modified:16 Nov 2021 17:07

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