J/A+A/698/A168 3D ISM structure challenges Serkowski relation (Mandarakas+ 2025)
3D interstellar medium structure challenges the Serkowski relation.
Mandarakas N., Tassis K., Skalidis R.
<Astron. Astrophys. 698, A168 (2025)>
=2025A&A...698A.168M 2025A&A...698A.168M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, distances
Keywords: polarization - techniques: polarimetric - ISM: clouds -
dust, extinction - ISM: magnetic fields - ISM: structure
Abstract:
The Serkowski relation is the cornerstone of studies of starlight
polarizations as a function of wavelength. Although empirical, its
extensive use since its inception in 1975 to describe polarization
induced by interstellar dust has elevated the relation to the status
of an indisputable "law": this is the benchmark against which models
of interstellar dust grains are validated.
We revisit the effects of the three - dimensional structure of the
interstellar medium (ISM) on the wavelength dependence of interstellar
polarization.
We use analytical models to show how the wavelength dependence of both
the polarization fraction and direction is affected by the presence of
multiple clouds along the line of sight (LOS). We account for recent
developments in dust distribution modelling and we utilize an expanded
archive of stellar polarization measurements to establish the effect
of multiple clouds along the LOS. We highlight concrete examples of
stars whose polarization profiles are severely affected by LOS
variations of the dust grain and magnetic field properties, and we
provide a recipe to accurately fit multiple cloud Serkowski models to
such cases.
We present, for the first time, compelling observational evidence that
the three - dimensional structure of the magnetized ISM often results
to the violation of the Serkowski relation. We show that three -
dimensional effects impact interstellar cloud parameters derived from
Serkowski fits. In particular, the dust size distribution in single -
cloud sightlines may differ from analyses that ignore 3D effects, with
important implications for dust modelling in the Galaxy.
Our results suggest that multiwavelength stellar polarization
measurements offer an independent probe of the LOS variations of the
magnetic field orientation, and thus constitute a potentially valuable
new tool for the 3D cartography of the interstellar medium. Finally,
we caution that, unless 3D effects are explicitly accounted for, a
poor fit to the Serkowski relation does not, by itself, constitute
conclusive evidence that a star is intrinsically polarized.
Description:
This table presents information about the statistical sample used in
Sect. 4.1 of the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 83 223 Information about the statistical sample
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia DR3 source_id
21- 29 F9.5 deg RAdeg Right Ascension (ICRS) at Ep=2016.0
31- 39 F9.5 deg DEdeg Declination (ICRS) at Ep=2016.0
41- 44 I4 pc Distance Distance of the source
46- 49 F4.2 mag Av Extinction of the source
51- 52 I2 --- Nbands Number of bands with measurements
54- 55 A2 --- NC Number of identified clouds
57- 61 F5.2 --- chi2nu chi2_nu for the q-u fitting
63- 66 F4.2 % Pmax Pmax retrieved from q-u fitting
68- 71 F4.2 --- K K retrieved from q-u fitting
73- 77 F5.3 um lambdamax lambdamax retrieved from q-u fitting
79- 83 F5.1 deg theta theta retrieved from q-u fitting
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Acknowledgements:
Nikos Mandarakas, nmandarakas(at)physics.uoc.gr
(End) Patricia Vannier [CDS] 28-Apr-2025