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  MAPCAT Observing Instructions    


  • Observations shall be performed once every ~1month within service time.


  • Every session, all observable pointlike blazars in Table 1 shall be measured in polarized light.


  • Observations shall be carried out at the 2.2m with CAFOS+polarizer through an R-filter.


  • Each object need to be measured with 4 position angles of the lambda/2 plate (0º, 22.5º, 45º and 67.5º).


  • The observer is requested to repeat any of these four measurement on which any problem is detected in the frame, but maintaining equal integration time for each polarizer position angle.


  • Please, window the CCD to a FOV of 7'x7' (1 kpixel x 1 kpixel) with no binning (1x1).


  • Indicative integration times (per position angle) for every source are listed in Table 1.


  • The observer is requested to increase such int. times, depending on observing conditions and source brightness, when the source peak counts (per position angle and individual image) gets <1500.


  • Figure 1 shows the time ranges of observability (airmass<2) from CA for every blazar in the sample.


  • Finding charts (FC) for the target sources are provided in Fig. 2.


  • There are no priorities, please, observe all visible sources in the night looking for optimum RA.


  • There are weak restrictions on the weather conditions (grey nights, weak clouds).


  • Please, always measure two of the following four polarized standard stars (see also FC in Fig. 3), by using the proposed reference integration times, but without defocussing the telescope:


-HD 19820 (R= 6.8) RA(J2000)= 03h 14m 05.4s; Dec(J2000)= +59º 33' 49'' (tint=0.1s)

-HD 25443 (R = 6.6) RA(J2000)= 04h 06m 08.1s; Dec(J2000)= +62º 06' 07'' (tint=0.1s)

-HD 154445 (R= 5.5) RA(J2000)= 17h 05m 32.3s; Dec(J2000)= -00º 53' 32'' (tint=0.1s)

-HD 161056 (R= 5.9) RA(J2000)= 17h 43m 47.2s; Dec(J2000)= -07º 04' 47'' (tint=0.1s)


  • Please, always measure 5 bias frames, as well as 5 dome flat fields per polarization angle.


  • However, at least one photometric night/semester would be valuable to double check the photometry.


  • When photometric conditions are present, please, measure photometric standards.


  • After the observations, please transfer the data to a directory accessible via ftp and notify.


  Table 1: Proposed integration times and source visibility period    


MAPCAT source list

* Observe 1622-297 whenever airmass>3 (Elv.>20º)


  Figure 1: Visibility (airmass<2 for more than 1h)period for Calar Alto.    


MAPCAT source visibility

* Observe 1622-297 whenever airmass>3 (Elv.>20º)


  Figure 2: Finding Charts from ESO-DSS-red archive for all MAPCAT target blazars    


MAPCAT blazar finding charts


MAPCAT blazar finding charts


MAPCAT blazar finding charts


MAPCAT blazar finding charts


MAPCAT blazar finding charts


MAPCAT blazar finding charts


MAPCAT blazar finding charts


MAPCAT blazar finding charts


MAPCAT blazar finding charts


  Figure 3: Finding Charts from the ESO-DSS-red archive for the 4 polarized stardad stars    


MAPCAT polarized standards



Glorieta de la Astronomía, s/n. E-18008 (España)
Tel:(+34) 958 230 637 / Fax:(+34) 958 814 530

Last updated on 2013-01-15