Polarimetry at the 30m telescope (under construction)

This site collects information relevant to polarimetric observations at the IRAM 30m telescope. The observing method XPOL makes use of the dual-polarization feature of EMIR and the cross-correlation capability of VESPA. The method is described in the Technical Document No.2. The calibration of the instrumental phase is explained in detail in this presentation.

Observing

An XPOL observation is made in the wobbler-switching observing mode. This PaKo script sets up a simple XPOL observation at 3mm. More complex setups where two EMIR bands or two VESPA subbands are recorded are possible. The VESPA polarimetric capabilities are concisely described in the preliminary VESPA user guide.

Beam maps

Technical documents

1. Versatile IF polarimeter at the IRAM 30m telescope

   • Thum et al. 2003 including the first mm observation of the polarization of the moon's limb

2. XPOL—the Correlation Polarimeter at the IRAM 30-m Telescope

   • Thum et al. 2008, PASP, 120, 777

3. Polarimetry with EMIR/XPOL - commisioning report (August 2010)

   • Wiesemeyer & Thum 2010, IRAM Report

== Scientific publications (selected for illustrating specific technical aspects) ==

1. Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments

   • Aumont et al. 2010

2. A sensitive upper limit to the circular polarization of the Crab nebula at λ3 mm

   • Wiesemeyer et al. 2011

3. Observations of the Goldreich-Kylafis effect in star-forming regions with XPOL at the IRAM 30 m telescope

   • Forbrich et al. 2008 This publication includes examples for assessing the magnitude of instrumental polarization due to sidelobes

4. A 3.5 mm Polarimetric Survey of Radio-loud Active Galactic Nuclei

   • Agudo et al. 2010

5. 3C 286: a bright, compact, stable, and highly polarized calibrator for millimeter-wavelength observations

   • Agudo et al.

Background material

1. IAU convention concerning Stokes Parameters

   • Radioastronomy, including the 30m telescope, uses these IAU conventions. Note however that according to this convention the sign of Stokes V is opposite to the usage in traditional physics as described by Born & Wolf in "Classical Optics"

2. The sign of Stokes V in 30m observations

   • with XPOL has been determined through several methods. They are described in a short note. It was verified that Stokes V spectra generated by the 30m data acquisition program have the correct sign according to the IAU convention.