Ministerio de Ciencia, Innovación y Universidades Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

Technological Development Projects

Microwave instrumentation

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CMB Polarimetry

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A Cosmic Microwave Background Polarimeter

Project website: External pages


The CMB group at the IAC ( ) , in collaboration with the University of Santa Barbara (UCSB), have developed a method of measuring microwave polarisation using a large number of low-cost radio-telescopes situated in several high quality observatories around the world. The resulting observations are of a high quality and, through the combination of simultaneous measurements, highly sensitive.

The main objective is to almost completely cover the entire sky,  allowing for highly sensitive measurements of B-modes at low multipoles, l . Given that the radiometers will be basically independent of each other (i.e. not in the same observatory) the ground-based systematic effects, like atmosphere, horizon, interference etc can be eliminated. This concept is different from other experiments, which have opted to place large ( >100) arrays of radiometers in the focal plane of one telescope. In this scenario systematic elimination and control is more difficult.

Each telescope in the IAC/UCSB design will sport a group of HEMT based radiometers. Each radiometer, as in the standard correlator design, is able to measure the Stokes parameters  - U and V - simultaneously. However, the new IAC/UCSB design differs from conventional microwave polarimeters in that the polar signal is derived from an optical polar modulator. This type of polarimeter is new to microwave polarimetry and is normally found at optical wavelengths (more commonly known as a (half-wave plate). The transfer to microwave frequencies brings limitations e.g bandwidth < 20% and loss 0.1dB. These limitations are not of so much concern at optical frequencies.

The scientific goals for the prototype are

  • Produce sensitive polarisation measurements of large angular scale (l>10) E-mode power spectra.
  • Characterise polar emissions from the CMB contaminants (Galactic synchrotron and dust  or extragalactic sources), to be subtracted from maps made by experiments observing  at low frequencies (< 100GHz).
  • Characterise the polar properties of the anomalous microwave emission in the Perseus region (Watson et al 2005) and in other regions of the galactic plane.
  • Quantify the systematics entering into the data taken by the new polarimeter design  and also the observing strategy previously used in intensity measurements of the CMB and the galactic emissions. That is, showing systematic error control in large polarisation maps.
  • Characterise the sky quality at the Teide Observatory for microwave polar measurements.

Principal Investigator: Rafael Rebolo

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