6 research outputs found
WALOP-South: A Four Camera One Shot Imaging Polarimeter for PASIPHAE Survey. Paper I -- Optical Design
The WALOP-South instrument will be mounted on the 1 m SAAO telescope in South
Africa as part of the PASIPHAE program to carry out a linear imaging
polarization survey of the Galactic polar regions in the optical band. Designed
to achieve polarimetric sensitivity of across a
arcminute field of view, it will be capable of measuring the Stokes parameters
I, q and u in a single exposure in the SDSS-r broadband and narrowband filters
between . For each measurement, four images of the
full field corresponding to linear polarization angles of 0 deg, 45 deg, 90 deg
and 135 deg in the instrument coordinate system will be created on four
detectors from which the Stokes parameters can be found using differential
photometry. In designing the optical system, major challenges included
correcting for the dispersion introduced by large split angle Wollaston Prisms
used as analysers as well as other aberrations from the entire field to obtain
imaging quality PSF at the detector. We present the optical design of the
WALOP-South instrument which overcomes these challenges and delivers near
seeing limited PSFs for the entire field of view.Comment: 31 pages, 18 Figures and 8 Tables. Accepted in the Journal of
Astronomical Telescopes, Instruments, and System
WALOP-South: A wide-field one-shot linear optical polarimeter for PASIPHAE survey
WALOP (Wide-Area Linear Optical Polarimeter)-South, to be mounted on the 1m SAAO telescope in South Africa, is first of the two WALOP instruments currently under development for carrying out the PASIPHAE survey. Scheduled for commissioning in the year 2021, the WALOP instruments will be used to measure the linear polarization of around 106 stars in the SDSS-r broadband with 0.1 % polarimetric accuracy, covering 4000 square degrees in the Galactic polar regions. The combined capabilities of one-shot linear polarimetry, high polarimetric accuracy (< 0.1 %) and polarimetric sensitivity (< 0.05 %), and a large field of view (FOV) of 35 35 arcminutes make WALOP-South a unique astronomical instrument. In a single exposure, it is designed to measure the Stokes parameters I, q and u in the SDSS-r broadband and narrowband filters between 500-700 nm. During each measurement, four images of the full field corresponding to the polarization angles of 0°, 45°, 90° and 135° will be imaged on four detectors and carrying out differential photometry on these images will yield the Stokes parameters. Major challenges in designing WALOP-South instrument include- (a) in the optical design, correcting for the spectral dispersion introduced by large split angle Wollaston Prisms used as polarization analyzers as well as aberrations from the wide field, and (b) making an optomechanical design adherent to the tolerances required to obtain good imaging and polarimetric performance under all temperature conditions as well as telescope pointing positions. We present the optical and optomechanical design for WALOP-South which overcomes these challenges