Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAchromatizing a liquid-crystal spectropolarimeter: Retardance vs Stokes-based calibration of HiVIS
210
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Astronomical spectropolarimeters can be subject to many sources of systematic error which limit the precision and accuracy of the instrument. We present a calibration method for observing high-resolution polarized spectra using chromatic liquid-crystal variable retarders (LCVRs). These LCVRs allow for polarimetric modulation of the incident light without any moving optics at frequencies >10Hz. We demonstrate a calibration method using pure Stokes input states that enables an achromatization of the system. This Stokes-based deprojection method reproduces input polarization even though highly chromatic instrument effects exist. This process is first demonstrated in a laboratory spectropolarimeter where we characterize the LCVRs and show example deprojections. The process is then implemented the a newly upgraded HiVIS spectropolarimeter on the 3.67m AEOS telescope. The HiVIS spectropolarimeter has also been expanded to include broad-band full-Stokes spectropolarimetry using achromatic wave-plates in addition to the tunable full-Stokes polarimetric mode using LCVRs. These two new polarimetric modes in combination with a new polarimetric calibration unit provide a much more sensitive polarimetric package with greatly reduced systematic error.
rate research
Read More
We designed, built, and calibrated a new spectropolarimeter for the HiVIS spectrograph (R 12000-49000) on the AEOS telescope. We also did a polarization calibration of the telescope and instrument. We will introduce the design and use of the spectropolarimeter as well as a new data reduction package we have developed, then discuss the polarization calibration of the spectropolarimeter and the AEOS telescope. We used observations of unpolarized standard stars at many pointings to measure the telescope induced polarization and compare it with a Zemax model. The telescope induces polarization of 1-6% with a strong variation with wavelength and pointing, consistent with the altitude and azimuth variation expected. We then used scattered sunlight as a linearly polarized source to measure the telescopes spectropolarimetric response to linearly polarized light. We then made an all-sky map of the telescopes polarization response to calibrate future spectropolarimetry.
We present the design of a point-and-shoot non-imaging full-Stokes spectropolarimeter dedicated to detecting life on Earth from an orbiting platform like the ISS. We specifically aim to map circular polarization in the spectral features of chlorophyll and other biopigments for our planet as a whole. These non-zero circular polarization signatures are caused by homochirality of the molecular and supramolecular configurations of organic matter, and are considered the most unambiguous biomarker. To achieve a fully solid-state snapshot design, we implement a novel spatial modulation that completely separates the circular and linear polarization channels. The polarization modulator consists of a patterned liquid-crystal quarter-wave plate inside the spectrograph slit, which also constitutes the first optical element of the instrument. This configuration eliminates cross-talk between linear and circular polarization, which is crucial because linear polarization signals are generally much stronger than the circular polarization signals. This leads to a quite unorthodox optical concept for the spectrograph, in which the object and the pupil are switched. We discuss the general design requirements and trade-offs of LSDpol (Life Signature Detection polarimeter), a prototype instrument that is currently under development.
A new, inexpensive polarimetric unit has been constructed for the Dominion Astrophysical Observatory (DAO) 1.8-m Plaskett telescope. It is implemented as a plug-in module for the telescopes existing Cassegrain spectrograph, and enables medium resolution (R~10,000) circular spectropolarimetry of point sources. A dual-beam design together with fast switching of the wave plate at rates up to 100Hz, and synchronized with charge shuffling on the CCD, is used to significantly reduce instrumental effects and achieve high-precision spectropolarimetric measurements for a very low cost. The instrument is optimized to work in the wavelength range 4700 - 5300A to simultaneously detect polarization signals in the H beta line as well as nearby metallic lines. In this paper we describe the technical details of the instrument, our observing strategy and data reduction techniques, and present tests of its scientific performance.
SPIRou is a near-infrared (nIR) spectropolarimeter / velocimeter for the Canada-France-Hawaii Telescope (CFHT), that will focus on two forefront science topics, (i) the quest for habitable Earth-like planets around nearby M stars, and (ii) the study of low-mass star/planet formation in the presence of magnetic fields. SPIRou will also efficiently tackle many key programmes beyond these two main goals, from weather patterns on brown dwarfs to Solar-System planet and exoplanet atmospheres. SPIRou will cover a wide spectral domain in a single exposure (0.98-2.44um at a resolving power of 70K, yielding unpolarized and polarized spectra of low-mass stars with a 15% average throughput at a radial velocity (RV) precision of 1 m/s. It consists of a Cassegrain unit mounted at the Cassegrain focus of CFHT and featuring an achromatic polarimeter, coupled to a cryogenic spectrograph cooled down at 80K through a fluoride fiber link. SPIRou is currently integrated at IRAP/OMP and will be mounted at CFHT in 2017 Q4 for a first light scheduled in late 2017. Science operation is predicted to begin in 2018 S2, allowing many fruitful synergies with major ground and space instruments such as the JWST, TESS, ALMA and later-on PLATO and the ELT.
SPIRou is a near-infrared spectropolarimeter and high-precision radial-velocity instrument, to be mounted on the 3.6m Canada-France-Hawaii telescope ontop Maunakea and to be offered to the CFHT community from 2018. It focuses on two main scientific objectives : (i) the search and study of Earth-like planets around M dwarfs, especially in their habitable zone and (ii) the study of stellar and planetary formation in the presence of stellar magnetic field. The SPIRou characteristics (complete coverage of the near infrared wavelengths, high resolution, high stability and efficiency, polarimetry) also allow many other programs, e.g., magnetic fields and atmospheres of M dwarfs and brown dwarfs, star-planet interactions, formation and characterization of massive stars, dynamics and atmospheric chemistry of planets in the solar system.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
