CCD Windowing

Only the blue side can be windowed. The default spectral region is available. The red side can not be windowed.

Focusing the Spectrograph

The polarimeter may be focused in spectroscopic and imaging mode using the usual focus GUI.

Focusing the Telescope in Imaging Mode

The OA can focus the telescope using the MIRA script.


Optimal exposure times for imaging flat fields and spectroscopic wavelength calibrations may differ between normal LRIS observing and polarimetry mode. The following tables provide estimated exposure times for the RED side.

Estimated exposure times for spectroscopic-mode calibrations

Lamp Exposure Time
using 1.0" slit using 1.5" slit
Hg+Kr* 3 sec 2 sec
Neon 3 sec 2 sec
Argon 4 sec 3 sec
Internal Halogen lamp 18 sec 12 sec

*be sure to let this lamp warm up before taking the exposure!

Estimated exposure times for imaging-mode calibrations using dome lamps

Filter Exposure time
B 80 sec
V 20 sec
R 10 sec
I ?? sec

Calibration Stars

There are lists of polarized and unpolarized stars available in /kroot/starlists/0000_polarized and /kroot/starlists/0000_unpolarized, respectively. In these lists the HST standards are given first, sorted by R.A., followed by other standards used by previous polarimetry experts. Look at the text files for the polarization magnitude and angle (for polarized standards) or polarization and uncertainty (for unpolarized standards). The text files also contain the V magnitudes and spectral types.

These lists are derived from the following papers, which can be consulted for further details:

Another source of useful polarized standards can be found at:

You will also possibly need to take spectrophotometric flux standards and/or imaging photometric standards


Note on calibrations with polarizing elements in (the HNP'B UV/optical Polaroid and the IR800 IR polarizer); in some wave plate positions all of the light will be in one beam, so don't let yourself be fooled into doubling your exposure times and saturating the images at those angles!

See also: