P52-006: Polarimetric monitoring of MAGIC blazars
P.I.: Stefano Covino
This ToO program has no override. Can only trigger during Tech and Nordic
Service nights. Max 4 hours per observation.
Allocated: 2 triggers and a total of 12 hours.
Overview
When this ToO is triggered it can spend a total of 6 hours per target over
period 52 doing imaging polarimetry with ALFOSC+FAPOL in either of the filters B or R,
or both.
The trigger email will contain information about the target, and the PI
will submit
pointing scripts with finding charts for
- the target,
- one zero polarisation standard, and
- one high polarisation standard.
Note that the standards are usually bright and may be taken during twilight.
Possible targets:
Instrument setup:
- The "Calcite" in the ALFOSC aperture wheel
- The lambda/2 retarder in FAPOL (for linear polarimetry)
- Standard B and R filters in ALFOSC (#74 and #76)
This is a setup that by default should be standard.
Afternoon Calibrations
In the afternoon, please take 10 biases with the polwin setup:
- Set remote path: alfosc.rempath /data/service/calib/
- and activate remote saving: alfosc.remsave_on
- Reset the CCD to default values: alfosc.resetxy
- Set the window to default for FAPOL imaging polarimetry: alfosc.polwin
- Set the object name: object bias-polwin
- Start taking 10 biases: mdark 0 10
- De-activate remote saving: alfosc.remsave_off
- Reset CCD window: alfosc.resetxy
Sky flats
The normal full-size skyflats in B and R (NOT filters #74 and #76) are
adequate, i.e. no need for special flats taken with the polarimetry setup.
These flats when taken with the script alfosc.easyflat will be
automatically copied to the ftp directory pub/service/calib/ for
external retrieval.
Observing instructions:
- If not already done, setup for ALFOSC: tcs.setup-tel-alfosc
Make sure the telescope has been focused for ALFOSC, and that this focus is set.
- In a sequencer window type cd ~/scripts/52-006/
- In this directory find the pointing scripts for the target and both standards as mentioned
in the trigger email from the PI. Run the script and make sure auto-guiding is ok.
- Find in the trigger email the filter(s) to be used (B or R or both). For each
object (target and standards) find also the given exposure times to use.
- Enter FAPOL lambda/2 plate into the beam with: alfosc.carriage IN
- Setup ALFOSC for R-band polarimetry with: alfosc.wheels -s Calcite -f 76 -forceFASU
or for B-band polarimetry with: alfosc.wheels -s Calcite -f 74 -forceFASU
- Make sure the focus is adjusted: alfosc.focus-offset
- Set the remote file storage path with: alfosc.rempath /data/service/52/006/
- Switch on remote saving: alfosc.remsave_on
- Set the window size to default for imaging polarimetry: alfosc.polwin
- Start the sequence of exposures at 4 angles of the lambda/2 plate with the script:
alfosc.linpolexpose 4 target-name exptime N
where you have to fill in target-name, exptime (in seconds) and the number of
cycles N according to instructions in the trigger email.
Note that you will see two horizontally displaced (by ~ 15'') images of the same field as that
shown in the finding chart. The field-of-view is approximately 140''.
- Follow the trigger instructions regarding how many cycles to do in each filter, before
changing the filter setup and the focus (see points 6 and 7 above).
- When finished with all observations, go back to default ALFOSC setup with the
commands alfosc.remsave_off, resetxy and alfosc.allopen.
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