Questionnaire on polarimetric standard targets used for past
(since 2000) and future polarimetric observing programs
This is a questionnaire on the use and quality of polarimetric standard targets in
preparation of the COST Workshop at ETH Zurich in January 2013 on “Calibration
targets for astronomical polarimetry for the 0.3 to 30 μm wavelength range”.
With this questionnaire we want to compile information from the scientific community
about the use of polarimetric standard targets and investigate the need for new, more, or
better calibration targets for astronomical polarimetry. In particular we want to identify
possible calibration target projects for improving polarimetric data from existing or future
instruments and if possible initiate corresponding observing programs which might
benefit from support provided by the network of COST action MP-1104.
Instructions:
 Give information in boxes with … by just using the Word editor.
 Use ( x ) in empty boxes where appropriate
 You may give comments or additional information everywhere in this form or in
the special boxes provided a some places
 Please use one form for each type of polarimetric observing project
 fill in as much as you can – boxes may be left empty, more than one box may be
crossed ( x ), etc.
A. Name and basic information about this polarimetric project
1. Your name and institution
Name
Institute
…
…
e-mail
…
2. Give keywords for the science topic for this polarimetric project
…
Examples:
 Scattering geometry of Seyfert Galaxies
 Interstellar grain properties in the Milky Way
3. Indicate the physical process producing the polarized signal
…
Examples
 Scattering by circumnuclear dust and electrons
 Dichroic interstellar absorption by aligned dust grains
4. Targets types, and target brightness
Target types
Typical target brightness in mag for point sources
and mag/arcsec for extended sources
…
…
Examples:
 Low Z (<0.1) Seyfert 1 galaxies | V=15 mag
 halo stars | R=10 mag
5. Basic info about polarimetric observing project
Year of observations (since 2000) or
Approx number of
expected year for future programs
observing nights
…
…
Approx number of
science targets
…
6. Publications about this project
…
B. Information about the used instrument
7. Telescope, diameter, focal station and instrument used for this program
Telescope name and diameter
Focal station
Instrument
…
…
…
Examples:
 VLT 8.2m | Cass. | FORS1
 Telescope xx 2.5m | Cass. | own multi-color polarimeter
 ESO 3.6m | fiber-fed | HARPS-POL
8. Basic type of polarimetry
Aperture
Imaging
polarimetry polarimetry
of point
sources
Imaging
polarimetry
of extended
sources
Spectro-pol.
of point
sources
Spectro-pol.
of extended
sources
(long slit)
other
…
Describe roughly aperture dimensions, field of view, and spatial resolution
…
9. Stokes parameter measured (more than one can be selected):
Priority I*
I/Iref *
Q
U
V
Q/I
U/I
V/I
st
1
2nd
*: I means the absolute intensity and I/Iref the intensity normalized to some reference
level (e.g. intensity spectrum normalized to continuum or intensity map normalized to
peak intensity of central source).
10. Approximate wavelength range of your data:
100-300nm 300-1000nm 1-2.5μm
2.5-8μm
11. Approximate Spectral resolution
10-30μm
Other
….
Broad band
polarimetry
R=5
Narrow
band pol
R = 20
Low resolution
Medium res.
High res.
spectropolarimetry spectropolarimetry spectropolarimetry
R< 300
300 < R < 10000
R > 10000
12. Describe briefly basic measuring principle of your instrument (only keywords if
standard instrument)
…
Examples:
 Low resolution linear polarization grism spectropolarimetry with rotatable half
wave plate and Wollaston prism beam splitter and CCD detector
 Multi-filter polarimetry using a fast acusto-optic modulator (PEM) and lock-in
detector (photomultiplier)
 High resolution circular spectropolarimetry with quarter wave plate, beam splitter
and CCD detectors
13. Space for any other useful information about the used instrument
…
C. Requirements and limitations for science target measurements
Definition of polarimetric measuring sensitivity and calibration accuracy:
 Measuring sensitivity: fractional polarization sensitivity s due to the science
target, e.g. Q/I(x1) – Q/I(x2) = δ(Q/I) ± s (e.g. 0.063 % ± 0.013) which can be
detected in the data relative to some reference signal Q/I(xref)
 Calibration accuracy: calibration accuracy Δ for the fractional polarization
signal Q/I(x1) ± Δ (e.g. 0.72 % ± 0.14 %) on an absolute scale relative to an
unpolarized source.
14. Required measuring sensitivity for science target in fract. pol. Q/I, U/I or V/I
Extreme Very high
high
Good
Intermediate Low
Very low
<0.01% 0.01-0.03% 0.03-0.1% 0.1-0.3% 0.3 – 1%
1 -3%
> 3%
15. Required calibration accuracy for science target in fract. pol. Q/I, U/I or V/I
Extreme Very high
high
Good
Intermediate Low
Very low
<0.01% 0.01-0.03% 0.03-0.1% 0.1-0.3% 0.3 – 1%
1 -3%
> 3%
16. If linear polarization is measured indicate required accuracy of the position angle
Very high
high
Intermediate
low
Very low
< 0.3 degr
0.3 – 1 degr
1-3 degr
3 – 10 degr
> 10 degr
17. Limiting effect for measuring sensitivity of polarimetric measurement
Photon statistics
Target variability
Instrument stability Other (specify)
…
18. Limiting effect for the calibration accuracy of the measured polarization
Photon
Target
Instrument
Instrument
Background Other
statistics
variability
stability
calibration
subtraction
(specify)
…
19. Space for more information or comments
…
D. Information about the used polarimetric standard targets
20. Type of calibration targets used for your program (you may use the letters A, B, C, or
D for the identification of the standard star type in following questions)
A. Zero polarization B. High linear
C. High circular
D. Other, please
standard star
polarization
polarization
specify
standard star
standard star
…
21. Does your data provide an intrinsic polarization reference point? If yes, of what type?
Stellar continuum in Zeeman spectropolarimetry
Central star/source for circumstellar / circumnuclear scattering
Center of a symmetric object (axis-symmetric point)
Other (please specify) ….
22. Required accuracy in fractional polarization Q/I, U/I or V/I for calibration target
Type of polarimetric
extreme Very high
high
moderate
Low
standard star (A,B,C or D) <0.01% 0.01-0.03% 0.03-0.1% 0.1-0.3%
> 0.3%
…
...
23. If linear polarization is measured indicate required accuracy of the position angle for
standard star
Type of polarimetric
Very high
High
intermediate Low
standard star (A,B,C or D)
< 0.3 degr
0.3 – 1 degr
1-3 degr
>3 degr
…
...
24. Use and importance (not used, check, calibration) of polarimetric calibration target
for your observing project
Type of standard Pol. parameter
Not used
used as a
used for quant.
(A,B,C, D)
calibrated
check
calibration
A: (zero pol.
Instrument polarization
standard star)
zero point
B: (High linear
Position angle zero
pol. standard)
point
B:
Polarization efficiency
B:
Pol. cross talk from
Q,U  V
C: (high circular
Sign (+/-) for Stokes V
pol. standard)
C:
Polarization efficiency
C:
Pol. cross talk from
VU,Q
…
…
25. Brightness of the used polarimetric standard stars
Type of polarimetric standard Brightness
Too faint
stars (A,B,C or D)
(mag)
…
…
O.K.
too bright
26. Sky distribution of polarimetric standard stars useful for your program
Type of polarimetric standard stars
good
O.K.
Poor
(A,B,C or D)
…
…
Specification for good, OK, and poor:
 High = good standard stars well distributed over the sky and available all the time
 O.K. = sufficient standard stars available if observations are prepared carefully
 poor = there are sky regions without good standards and this affects the science
program.
27. Specify quality of the used standard stars with respect to your science needs (see
explanation below box)
Type of polarimetric standard star
High quality
Sufficient
Poor quality
(A,B,C or D)
quality
…
…
Specification of high, sufficient, poor and bad:
 High = accuracy of polarimetric parameter is better than required
 Sufficient = accuracy of polarimetric parameter is sufficient
 poor = accuracy of polarimetric parameters is not good and this affects the results
28. Would higher quality standard targets improve your measurements or help to advance
your science field. What needs to be improved to make progress?
Not better standards targets required, because
Yes, better
standard targets
Instrumental effects
Photon noise
Other reasons
required (see 29)
dominate
dominates
x
…
29. Which characteristics of the standard targets should be improved?
Type of polarimetric More
less
More
Fainter Other (specify)
standard star
accurate
variable
standard standard
(A,B,C or D)
polarimetric standard stars
stars
parameters
targets
…
…
…
…
Other requirements?
30. Please indicate the source or references for the used polarimetric standard stars
Type of polarimetric standard stars Reference
(A,B,C, D)
…
…
…
…
31. Space for more information or comments
…
Thank you very much for your effort to fill this questionnaire.