Polarimetric Standard Stars

Topics

Status

Currently, ISAAC calibration plans do not support observations in SWP mode.  In case of service mode  SWI Polarimetric  observations the night support astronomer will only take care about executing normal twilight flats with no Wollaston prism and with the same filter as in the science OB.  No standard stars are observed in SWP mode by the night support astronomer! The user has to provide his/her own OBs for the standard star observation, should he/she need it. The user provided standard star must not be brighter than 10.5 mag in the case of broad band filters, and not brighter than 7.5 mag in the case of narrow band filters.

Given that there is only a Wollaston prism in ISAAC, there is no real need of polarized standard stars. It is recommended to observe (at least two)  unpolarized stars at different parallactic angles (e.g. alpha and alpha+45º) in order to be able to correct for the instrumental polarization and measure indipendently the polarization introduced by ISAAC and that introduced by M3.  We provide below a short list of both unpolarized and polarized standard that can be used.

Unpolarized Standard Stars

The following list of unpolarized standard stars is suitable for ISAAC SWP mode observations. They have been selected among the unpolarized standard stars used for FORS1 calibration plans. . They J H and K mags are from the 2MASS catalog.

OBJ Name RA DEC J H K
WD 2359-434 00:02:11 -43:09:55 12.597 12.427 12.445
WD 0310-688 03:10:31 -68:36:02 11.758 11.790 11.861
WD 0752-676 07:53:08 -67:47:33 12.726 12.476 12.362
WD 1344+106(*) 13:47:24 +10:21:38 14.407 14.139 14.235
WD 1615-154 16:17:55 -15:35:51 14.039 14.210 14.318
WD 1620-391(*) 16:23:36 -39:13:22 11.577 11.708 11.768
WD 2039-202 20:42:35 -20:04:36 12.825 12.921 13.004

Polarized Standard Stars

The two polarized standard stars have been selected from Whittet et al.  (1992).
OBJ Name RA DEC J H K p% (J) PAº (J) p% (H) PAº (H) p% (K) PAº (K)
R CrA 19:05:12.6 -37:29:16 11.409 11.085 10.911 2.28 96 1.44 100 - -
HD 188112 19:54:31.4 -28:20:20.7 10.667 10.777 10.841 - - - - - -