RoboPol: a four-channel optical imaging polarimeter

Creators: Ramaprakash, A. N.; Panopoulou, G.; Kiehlmann, S.; King, O. G.; Mahabal, A.; Pearson, T. J.; Readhead, A. C. S.

Abstract

We present the design and performance of RoboPol, a four-channel optical polarimeter operating at the Skinakas Observatory in Crete, Greece. RoboPol is capable of measuring both relative linear Stokes parameters q and u (and the total intensity I) in one sky exposure. Though primarily used to measure the polarization of point sources in the R band, the instrument features additional filters (B, V, and I), enabling multiwavelength imaging polarimetry over a large field of view (13.6′ × 13.6′). We demonstrate the accuracy and stability of the instrument throughout its 5 yr of operation. Best performance is achieved within the central region of the field of view and in the R band. For such measurements the systematic uncertainty is below 0.1 per cent in fractional linear polarization, p (0.05 per cent maximum likelihood). Throughout all observing seasons the instrumental polarization varies within 0.1 per cent in p and within ∼1° in polarization angle.

Additional Information

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2019 February 21. Received 2019 February 20; in original form 2019 January 8. Published: 26 February 2019. We thank Anna Steiakaki for her invaluable contribution and technical support; John Kypriotakis for helping with edits in the paper; and the anonymous reviewer for their suggestions. The RoboPol project is a collaboration between Caltech in the USA, MPIfR in Germany, Toruń Centre for Astronomy in Poland, the University of Crete/FORTH in Greece, and IUCAA in India. The U. of Crete group acknowledges support by the 'RoboPol' project, which is implemented under the 'Aristeia' Action of the 'Operational Programme Education and Lifelong Learning' and is co-funded by the European Social Fund (ESF) and Greek National Resources, and by the European Comission Seventh Framework Programme (FP7) through grants PCIG10-GA-2011-304001 'JetPop', and PIRSES-GA-2012-31578 'EuroCal'. This research was supported in part by NASA grant NNX11A043G and NSF grant AST-1109911, and by the Polish National Science Centre, grant numbers 2011/01/B/ST9/04618 and 2017/25/B/ST9/02805. K. T. and G. P. acknowledge support by the European Commission Seventh Framework Programme (FP7) through the Marie Curie Career Integration Grant PCIG-GA-2011-293531 'SFOnset'. A.N.R., G.P., and A.C.S.R. acknowledge support from the National Science Foundation, under grant number AST-1611547. K. T. and D. B. acknowledge support from the European Research Counsil under the European Union's Horizon 2020 research and innovation programme, grant agreement No. 771282. M. B. acknowledges support from the International Fulbright Science and Technology Award. I.M. was funded by the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne. T. H. was supported by the Academy of Finland project number 317383. This research made use of Astropy, http://www.astropy.org, a community-developed core PYTHON package for Astronomy.

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