Design of TFOSC Compatible Polarimeter for Polarimetric Observations

This study proposes a design steps of a TFOSC focal plane instrument compatible optical polarimeter in order to investigate the physical parameters of targets (such as albedo, diameter, taxonomy of asteroids, porosity) based on the polarization properties of light. Images captured with Polarimeter will be reduced for the atmospheric efiect and device errors. The light impinging on WeDoWo prism is divided into four difierent images which is polarized at 0, 45, 90, 135 degrees and used to determine Stokes' parameters of electromagnetic waves. WeDoWo prism has been designed by using commercial optical design software named ZEMAX, it is 40mm in diameter and has a thickness of 20mm. Aim of this study is to design a TFOSC (TUBITAK National Observatory \TUG" Faint Object Spectrograph and Camera) focal plane instrument compatible polarimeter and investigate the phys- ical parameters of targeted asteroids (such as albedo, diameter, taxonomy of asteroids, porosity) based on the polarization properties of light by using this polarimeter which will be designed. Polarized light can provide additional information about the scene that cannot be obtained directly from the intensity or spectral images. Rather than treating the optical fleld as scalar, polarization images seek to obtain the vector nature of the optical fleld from the scene (1). Instrumental base of 1.5m Russian-Turkish telescope RTT150 makes it possible to carry out practically whole kind of astrophysical observations in the visible range. Until recently the obser- vational complex included light detectors for high positional and photometric CCD observations, fast photometry, and for obtaining low and high resolution spectra. During the last observation campaign of PHA Apophis close approach, we are faced with lack of spectroscopic observations to determine the taxonomy class of asteroids with visual magnitude fainter than 16m, due to the re- quirement of extremely long observational time. In addition to spectroscopic method for taxonomy determination, polarimetric method should also be employed. We present design of a polarimeter for RTT150 for simultaneous imaging of celestial sources on polarization planes on the base of WeDoWo (Wedge Double Wollaston) (2). The accuracy and magnitude limits are discussed. The designed polarimeter may be used for not only asteroid observations but also for astrophysical sources like SN (Super Nova), AGN (Active Galactic Nuclei) and so on. Thus, the polarimeter in- tegration to the RTT150 telescope increases its capabilities in ground-based observational support of present and future astrophysical space missions (GAIA \Global Astrometric Interferometer for Astrophysics", SRG \Spectrum-Rontgen-Gamma"). In this paper, we propose a Wollaston-based optical prism design principles, and images will be gathered by means of CCD. First measurement results will be presented in the conference.