Polarimetry Standard Stars - Observing Method and Star List

The following is a quick summary of the method of observation of polarimetric standards with Mimir and the list of standards recommended for Mimir use.

[updated as of 2007/09/27 - DPC] - especially note the coordinate fields containing multiple standards

[further updated 2009/01/13 - DPC] - note doubles ("- D") among the standards, detected by Mimir

1. Observation Method
2. Polarimetric Standard Star List - Coordinates, Finding Charts

Observation Method

The primary list of polarimetric standard stars is drawn from Whittet, Martin, Hough, Rouse, Bailey, & Axon (ApJ, 386, 562 - 1992). These stars span a brightness range at H-band of 6-9th mag so the observations take very little time to execute (about 10 minutes total per standard).

At least one standard should be observed each night polarimetry is performed, with at least 4-5 different standards observed at least once in an observing run.

The procedure to observe a polarimetric standard is:

1. Select a standard (or field) from the list below that can safely be observed
   • NOTE: the standards near rho Oph (those at RA=16h, Dec=-24) must NOT be observed east of the meridian or Mimir will impact the north pier!
2. Point the telescope to the standard star
   1. Guiding is not necessary, so the guider can be ignored
3. Determine the exposure time as per the Table below
   1. The brightest pixel should not exceed 2,000 counts - if it does, then reduce the exposure time
4. Click the "gpips_cal" button, with the exposure time filled in the box
   1. If LOIS complains that it can't find that script, then compile the tcl code ("cd ../tcl.mimir; source gpips.tcl; show user buttons")

In order to map the instrumental polarization across the field of view of Mimir, observations of globular clusters away from the galactic plane are recommended. This should be done once per observing run, but not nightly.

Polarimetric Standard Star List

The list below is a subset of the Whittet et al. 1992 list, and all polarimetric values are theirs. This list has been chosen based on Mimir observations, which revealed some binaries in the original Whittet list and so not ideal for use, and the desire to sample the range of percentage polarization and polarization position angle - these are needed to establish instrumental polarization, polarization efficiency, and HWP offset angle. Estimated integration times are approximate for F/5 observations.

DPC 20090113