Optical polarization map of the Polaris Flare with RoboPol
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 (∼10 deg^2) 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 per cent. 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 (250 μm), while in the central 4–5 deg^2 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.
Additional Information© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 June 9. Received 2015 June 9; in original form 2015 March 10. First published online July 8, 2015. We thank A. Kougentakis, G. Paterakis and A. Steiakaki, the technical team of the Skinakas Observatory. The University of Crete group acknowledges support by the 'RoboPol' project, implemented under the 'ARISTEIA' Action of the 'OPERATIONAL PROGRAMME EDUCATION AND LIFELONG LEARNING' and is cofunded by the European Social Fund (ESF) and Greek National Resources. The Nicolaus Copernicus University group acknowledges support from the Polish National Science Centre (PNSC), grant number 2011/01/B/ST9/04618. This research is supported in part by National Aeronautics and Space Administration (NASA) grants NNX11A043G and NSF grant AST-1109911. VP acknowledges support by the European Commission Seventh Framework Programme (FP7) through the Marie Curie Career Integration Grant PCIG10-GA-2011-304001 'JetPop'. KT acknowledges support by FP7 through the Marie Curie Career Integration Grant PCIG-GA-2011-293531 'SFOnset'. VP, EA, IM, KT and JAZ would like to acknowledge partial support from the EU FP7 Grant PIRSES-GA-2012-31578 'EuroCal'. IM is supported for this research through a stipend from the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne. MB acknowledges support from the International Fulbright Science and Technology Award. TH was supported by the Academy of Finland project number 267324. The RoboPol collaboration acknowledges observations support from the Skinakas Observatory, operated jointly by the University of Crete and the Foundation for Research and Technology – Hellas. Support from MPIfR, PNSC, the Caltech Optical Observatories and IUCAA for the design and construction of the RoboPol polarimeter is also acknowledged. This research has used data from the Herschel Gould Belt Survey (HGBS) project (http://gouldbelt-herschel.cea.fr). The HGBS is a Herschel Key Programme jointly carried out by SPIRE Specialist Astronomy Group 3 (SAG 3), scientists of several institutes in the PACS Consortium (CEA Saclay, INAF-IFSI Rome and INAF-Arcetri, KU Leuven, MPIA Heidelberg), and scientists of the Herschel Science Center (HSC). This research has used data from the NED which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the NASA. This research has made use of the SIMBAD data base, operated at CDS, Strasbourg, France as well as the VizieR catalogue access tool, CDS, Strasbourg, France. This work made use of APLPY, an open-source plotting package for PYTHON hosted at http://aplpy.github.com, ASTROPY, a community-developed core PYTHON package for Astronomy (Astropy Collaboration 2013), matplotlib, a PYTHON library for publication quality graphics (Hunter 2007) and the PYTHON library SCIPY (Jones, Oliphant & Peterson 2001). We would like to thank Malte Tewes for his help with the ALIPY package.
Published - MNRAS-2015-Panopoulou-715-26.pdf
Submitted - 1503.03054v3.pdf
Supplemental Material - Table2.zip
Erratum - MNRAS-2016-Panopoulou-2011-3.pdf