Large Interstellar Polarisation Survey (LIPS)

I. FORS2 spectropolarimetry in the Southern Hemisphere^⋆

¹ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Northern Ireland UK
e-mail: sba@arm.ac.uk
² Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
⁴ Sobolev Astronomical Institute, St. Petersburg University, Universitetskii prosp. 28, 198504 St. Petersburg, Russia
⁵ AAAS Science International, Clarendon House, Clarendon Road, Cambridge CB2 8FH, UK
⁶ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
⁷ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching b. München, Germany
⁸ Department of Physics and Astronomy and Centre for Planetary Science and Exploration (CPSX), The University of Western Ontario, London, ON N6A 3K7, Canada

Received: 28 June 2017
Accepted: 2 October 2017

Abstract

Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope. Our spectra cover the wavelength range 380–950 nm at a spectral resolving power of about 880. We have produced a publicly available catalogue of 127 linear polarisation spectra of 101 targets. We also provide the Serkowski-curve parameters, as well as the wavelength gradient of the polarisation position angle for the interstellar polarisation along 76 different lines of sight. In agreement with previous literature, we found that the best-fit parameters of the Serkowski-curve are not independent of each other. However, the relationships that we obtained are not always consistent with what has been found in previous studies.