Preliminary results on the instrumental polarization of NIKA2-Pol at the IRAM 30m telescope

¹ Laboratoire d’Astrophysique (AIM), CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
² Univ. Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 53, avenue des Martyrs, 38000 Grenoble, France
³ LLR (Laboratoire Leprince-Ringuet), CNRS, École Polytechnique, Institut Polytechnique de Paris, Palaiseau, France
⁴ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan, 1, planta 2, E-44001, Teruel, Spain
⁵ Astronomy Instrumentation Group, University of Cardiff, UK
⁶ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁷ Institut d’Astrophysique Spatiale (IAS), CNRS and Université Paris Sud, Orsay, France
⁸ Institut Néel, CNRS and Université Grenoble Alpes, France
⁹ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Roma, Italy
¹⁰ Institut de RadioAstronomie Millimétrique (IRAM), Grenoble, France
¹¹ Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, 28850 Madrid, Spain
¹² Instituto de Radioastronomía Milimétrica (IRAM), Granada, Spain
¹³ Aix Marseille Univ, CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille), Marseille, France
¹⁴ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, 75014 Paris, France
¹⁵ School of Earth and Space Exploration and Department of Physics, Arizona State University, Tempe, AZ 85287
¹⁶ Institut d’Astrophysique de Paris, CNRS (UMR7095), 98 bis boulevard Arago, 75014 Paris, France
¹⁷ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁸ National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
¹⁹ Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan

^* e-mail: hamza.ajeddig@cea.fr

Published online: 27 January 2020

Abstract

Clarifying the role of magnetic fields in the star formation process is crucial. Observations have already shown that magnetic fields play an important role in the early stages of star formation. The high spatial resolution (∼0.01 to 0.05 pc) provided by NIKA2-Pol 1.2 mm imaging polarimetry of nearby clouds will help us clarify the geometry of the B-field within dense cores and molecular filaments as part of the IRAM 30m large program B-FUN. There are numerous challenging issues in the validation of NIKA2-Pol such as the calibration of instrumental polarization. The commissioning phase of NIKA2-Pol is underway and is helping us characterize the intensity-to-polarization “leakage” pattern of the instrument. We present a preliminary analysis of the leakage pattern and its dependence with elevation. We also present the current leakage correction made possible by the NIKA2 pipeline in polarization mode based on the NIKA2-Pol commissioning data taken in December 2018. Based on reduced Stokes I, Q, U data we find that the leakage pattern of NIKA2-Pol depends on elevation and is sensitive to the focus of the telescope.