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| This site collects information relevant to polarimetric observations at the IRAM 30m telescope. The observing method 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 [[attachment: |this presentation]]. |
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 [[attachment:xpolTutorial.pdf |this presentation]]. XPOL observations are possible in any any of the 4 EMIR bands. Instrumental effects have been best characterised in the 3mm band (see Technical document No.3). The least experience exists at 0.9mm, but a preliminary Technical document (No. 4) is available. Polarimetric observations of extended sources present the complex problem of contamination by the polarized sidelobes. Our current knbowledge of these sidelobes is collected in the section 'Beam Maps' below. A strategy to estimate the influence of the polarized sidelobes on slightly extended linearly polarized sources is described in the scientific document No.3. Their influence on the circular polarization of an extended source is demonstrated in Scientific documents No.4. |
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| An XPOL observation is made in the wobbler-switching observing mode. | An XPOL observation is made in the wobbler-switching observing mode. This [[attachment:setup|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. Obervers are advised to check the good performance of XPOL by observing a polarization angle calibrator, the Crab nebula or the steep spectrum quasar 3C286 (see Scientific publications No. 1 and 5 below). |
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| ---- /!\ '''Edit conflict - other version:''' ---- == Scientific publications == |
== Scientific publications (selected for illustrating specific technical aspects) == |
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| [[http://adsabs.harvard.edu/abs/2012A&A...541A.111A|Agudo et al.]] | |
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| ---- /!\ '''Edit conflict - other version:''' ---- 1.IAU convention concerning Stokes Parameters |
1. IAU convention concerning Stokes Parameters |
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---- /!\ '''Edit conflict - your version:''' ---- 1. IAU convention concerning Stokes Parameters Radioastronomy, including the 30m telescope, uses [[attachment:IAUdefs.pdf|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 [[attachment:bornWolf.pdf|Born & Wolf in "Classical Optics"]] * The sign of Stokes V in 30m observations with XPOL has been determined through several methods. They are described in [[attachment:stokesVweb.ps| 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. ---- /!\ '''End of edit conflict''' ---- |
Contents
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.
XPOL observations are possible in any any of the 4 EMIR bands. Instrumental effects have been best characterised in the 3mm band (see Technical document No.3). The least experience exists at 0.9mm, but a preliminary Technical document (No. 4) is available. Polarimetric observations of extended sources present the complex problem of contamination by the polarized sidelobes. Our current knbowledge of these sidelobes is collected in the section 'Beam Maps' below. A strategy to estimate the influence of the polarized sidelobes on slightly extended linearly polarized sources is described in the scientific document No.3. Their influence on the circular polarization of an extended source is demonstrated in Scientific documents No.4.
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. Obervers are advised to check the good performance of XPOL by observing a polarization angle calibrator, the Crab nebula or the steep spectrum quasar 3C286 (see Scientific publications No. 1 and 5 below).
Beam maps
Technical documents
- 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
- XPOL—the Correlation Polarimeter at the IRAM 30-m Telescope
Thum et al. 2008, PASP, 120, 777
- Polarimetry with EMIR/XPOL - commisioning report (August 2010)
== Scientific publications (selected for illustrating specific technical aspects) ==
- Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
- A sensitive upper limit to the circular polarization of the Crab nebula at λ3 mm
- 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
- A 3.5 mm Polarimetric Survey of Radio-loud Active Galactic Nuclei
- 3C 286: a bright, compact, stable, and highly polarized calibrator for millimeter-wavelength observations
Background material
- 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"
- 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.