XPOL/EMIR Polarimetry at the 30m telescope

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 the VESPA. The method is described in the Technical Document No.2 (see below). The calibration of the instrumental phase is explained in detail in this presentation.

XPOL observations are possible in 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 upon request. Polarimetric observations of extended sources present the complex problem of contamination by the polarized sidelobes. Our current knowledge 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 document No.4.

The POLAMI monitoring projects use E0/E2.

The 1mm NIKA2 polarimetry mode is currently being commissioning with a lot of supporting XPOL observations. <6-Jul-2020 CK>

News

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 Table 4 of the VESPA user guide. Observers 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).

A separate note contains information on how to estimate the statistical error of an polarimetric observation. In addition, the note describes Zeeman observations and gives an estimate of the sensitivity for magnetic fields.

Beam maps

(under construction)

The following table lists the beam maps obtained with EMIR as of September 2012. The source name provides a link to the Stokes IQUV maps. The (x.y) cross on these maps indicates the horizontal and vertical directions in the Nasmyth cabin. Note that not all maps have been obtained under adequate weather conditions which can be judged from the appearance of non-gaussian features on the Stokes I maps. Copies of these maps are available in GILDAS format.

source

date

EMIR band

LST, h

HA

Dec, deg.

Freq, MHz

Elv, deg.

Eta, deg.

Chi0, deg.

size, "

Mars

18-JUN-2009

E0LI

1.01

-1.7

14.9

86243

58.4

-40.9

99.3

4.8

Mars

18-JUN-2009

E0LI

1.58

-1.1

14.9

86243

63.2

-31.3

94.5

Mars

19-JUN-2009

E0LI

23.28

20.5

15.1

86243

39.1

-54.2

93.3

Mars

19-JUN-2009

E0LI

23.79

21

15.2

86243

44.9

-52.3

97.2

Mars

19-JUN-2009

E0LI

0.46

-2.3

15.2

86243

52.4

-47.8

100.2

Mars

19-JUN-2009

E0LI

1.11

-1.7

15.2

86243

59

-40.5

99.5

Mars

19-JUN-2009

E0LI

1.11

-1.7

15.2

86243

59

-40.5

99.5

Mars

20-JUN-2009

E0LI

23.17

20.4

15.4

86243

37.4

-54.8

92.2

Mars

20-JUN-2009

E0LI

0.12

-2.7

15.4

86243

48.3

-50.9

99.2

Mercury

3-SEP-2009

E0LI

13.41

1.2

-5.6

86243

44.5

19.5

25

8.7

Mercury

11-FEB-2012

E0UO

22.08

0.3

-15.5

115271

37.3

4.7

32.7

4.9

Mercury

11-FEB-2012

E0UO

22.44

0.7

-15.5

115271

36.7

9.9

26.8

Mercury

11-FEB-2012

E0UO

22.89

1.1

-15.5

115271

35.2

16.2

19

Mercury

11-FEB-2012

E0UO

23.25

1.5

-15.5

115271

33.6

21.1

12.5

Mercury

11-FEB-2012

E0UO

23.76

2.0

-15.5

115271

30.6

27.3

3.3

Mercury

11-FEB-2012

E0UO

0.1

-21.7

-15.5

115271

28.2

31.0

-2.7

E1/MarsI4

15-OCT-2011

E1LI

5

-4.2

17.5

147047

31.7

-56.8

88.4

5.5

E1/MarsI5

15-OCT-2011

E1LI

5.36

-3.9

17.5

147047

35.9

-56.5

92.4

E1/MarsI6

15-OCT-2011

E1LI

5.7

-3.5

17.5

147047

39.9

-55.9

95.8

E2/Mars2009I10

21-JUN-2009

E2LI

23.15

20.3

15.6

220399

36.7

?

36.7

E2/Mars2009I11

21-JUN-2009

E2LI

23.75

20.9

15.6

220399

43.7

?

43.7

E2/Mercury2009I1

3-SEP-2009

E2LI

14.1

1.9

-5.6

228932

40.2

29.1

11.1

E2/Mercury2009I2

3-SEP-2009

E2LI

14.53

2.3

-5.6

228932

36.9

34

2.8

E2/Mercury2012I1

11-FEB-2012

E2UI

22.08

0.3

-15.5

230538

37.3

4.7

32.7

4.9

E2/Mercury2012I2

11-FEB-2012

E2UI

22.44

0.7

15.6

220399

36.7

?

36.7

E2/Mercury2012I3

11-FEB-2012

E2UI

22.89

1.1

-15.5

230538

35.2

16.2

19

E2/Mercury2012I4

11-FEB-2012

E2UI

23.25

1.5

-15.5

230538

33.6

21.1

12.5

E2/Mercury2012I5

11-FEB-2012

E2UI

23.76

2

-15.5

230538

30.6

27.3

3.3

E2/Mercury2012I6

11-FEB-2012

E2UI

0.1

-21.7

-15.5

230538

28.2

31

-2.7

E2/VenusI1

28-APR-2010

E2LI

0.96

-3.2

21.6

231901

46.4

-58.4

104.8

11.3

E2/VenusI2

28-APR-2010

E2LI

1.96

-2.2

21.6

231901

58

-53.9

112

E3/MarsI1

13-OCT-2011

E3LI

4.79

-4.4

17.8

316415

30.2

-56.9

87.1

5.4

E3/MarsI2

13-OCT-2011

E3LI

5.21

-3.9

17.8

316415

35.1

-56.8

91.9

E3/MarsI3

13-OCT-2011

E3LI

5.61

-3.5

17.8

316415

39.9

-56.2

96.1

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
  3. Polarimetry with EMIR/XPOL - commisioning report (August 2010)
  4. Polarimetry with EMIR/XPOL and the new optics - commissioning report (October 2015)
  5. Polarimetry with EMIR/XPOL: E090 with OMT - commissioning report (April 2016)

Scientific publications (selected for illustrating specific technical aspects)

  1. Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
  2. A sensitive upper limit to the circular polarization of the Crab nebula at λ3 mm
  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
  5. 3C 286: a bright, compact, stable, and highly polarized calibrator for millimeter-wavelength observations
  6. POLAMI: Polarimetric Monitoring of AGN at Millimetre Wavelengths - I. The programme, calibration and calibrator data products
  7. POLAMI: Polarimetric Monitoring of Active Galactic Nuclei at Millimetre Wavelengths - II. Widespread circular polarization
  8. POLAMI: Polarimetric Monitoring of Active Galactic Nuclei at Millimetre Wavelengths - III. Characterization of total flux density and polarization variability of relativistic jets

Background material

  1. IAU convention concerning Stokes Parameters
  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.

PolarimetryforAstronomers (last edited 2020-09-19 19:00:34 by CarstenKramer)