J/MNRAS/452/715 Optical polarization of the Polaris Flare (Panopoulou+, 2015)
Optical polarization map of the Polaris Flare with RoboPol.
Panopoulou G.V., Tassis K., Blinov D., Pavlidou V., King O.G.,
Paleologou E., Ramaprakash A., Angelakis E., Balokovic M., Das H.K.,
Feiler R., Hovatta T., Khodade P., Kiehlmann S., Kus A., Kylafis N.,
Liodakis I., Modi D., Myserlis I., Papadakis I., Papamastorakis I.,
Pazderska B., Pazderski E., Pearson T.J., Rajarshi C., Readhead A.C.S.,
Reig P., Zensus J.A.
<Mon. Not. R. Astron. Soc. 452, 715 (2015)>
=2015MNRAS.452..715P 2015MNRAS.452..715P
ADC_Keywords: Polarization ; Interstellar medium
Keywords: magnetic fields - polarization - stars: formation - ISM: clouds -
ISM: individual objects: Polaris Flare
Abstract:
The stages before the formation of stars in molecular clouds are
poorly understood. Insights can be gained by studying the properties
of quiescent clouds, such as their magnetic field structure. The
plane-of-the-sky orientation of the field can be traced by polarized
starlight. We present the first extended, wide-field (∼10deg2) map of
the Polaris Flare cloud in dust-absorption induced optical
polarization of background stars, using the Robotic Polarimeter
(RoboPol) polarimeter at the Skinakas Observatory. This is the first
application of the wide-field imaging capabilities of RoboPol. The
data were taken in the R band and analysed with the automated
reduction pipeline of the instrument. We present in detail
optimizations in the reduction pipeline specific to wide-field
observations. Our analysis resulted in reliable measurements of 641
stars with median fractional linear polarization 1.3%. The
projected magnetic field shows a large-scale ordered pattern. At high
longitudes it appears to align with faint striations seen in the
Herschel-Spectral and Photometric Imaging Receiver (SPIRE) map of dust
emission (250um), while in the central 4.5 deg2 it shows an eddy-like
feature. The overall polarization pattern we obtain is in good
agreement with large-scale measurements by Planck of the dust emission
polarization in the same area of the sky.
Description:
The RoboPol Optical Polarization data of the Polaris Flare were
obtained with the RoboPol polarimeter at the 1.3m telescope at the
Skinakas Observatory in Crete, Greece. Observations cover the area
l=[122.6deg, 126.0deg], b=[+24.7deg, +27.9deg] (almost 10 square
degrees). All observations were in the R band. Measurements presented
in the accompanying table have fractional linear polarization (p) to
error (σ_p) greater or equal to 2.5. Coordinates are those of
the corresponding source in the USNO-B1.0 star catalog.
Objects:
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RA (2000) DE Designation(s)
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11 00 14.8 +86 10 52 Polaris Flare = NAME Polaris flare
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 72 609 Optical polarization data of the Polaris Flare
(corrected version 20-Jun-2016)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension (J2000) (1)
13- 20 F8.5 deg DEdeg Declination (J2000) (1)
24- 32 F9.5 deg GLON Galactic longitude (1)
36- 43 F8.5 deg GLAT Galactic latitude (1)
47- 49 F3.1 % Pol [0.5/4.5] Polarization degree percentage (2)
53- 55 F3.1 % e_Pol [0.2/1.9] Error in polarization degree
59- 61 I3 deg EVPA [-90/90] Electric vector polarization angle (3)
65- 66 I2 deg e_EVPA [2/19] Error in EVPA
70- 72 I3 deg galPA [0/180] Galactic polarization angle (4)
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Note (1): Coordinates correspond to those in the USNO-B1.0 catalog
Monet et al. (2003AJ....125..984M 2003AJ....125..984M, Cat. I/284).
Note (2): The polarization degree is dimensionless because it is defined as
the polarized intensity divided by the total intensity. The values of this
column are percentages. These values have been debiased following equation
1 of the paper.
Note (3): The Electric Vector Polarization Angle (EVPA) is measured in the
celestial coordinate system starting from the North direction and increasing
towards the East and is given in the range [-90,90], as specified by the IAU.
Note (4): The Polarization Angle measured in the Galactic coordinate system
using the same convention for the EVPA. These values were transformed from
EVPA as in Stephens et al., 2011ApJ...728...99S 2011ApJ...728...99S.
They are in the range [0,180].
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Acknowledgements:
Georgia Virginia Panopoulou, panopg(at)physics.uoc.gr
History:
* 13-Jul-2015: First on-line version
* 20-Jun-2016: Corrected table2 (from author)
(End) Georgia Panopoulou [Univ. Crete], Patricia Vannier [CDS] 11-Jul-2015