The value of accurately knowing the absolute calibration of the polarizing elements in the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) becomes especially important when conducting studies which require measuring degrees of polarization of close to 1% in the near infrared. We present a comprehensive study of all previously observed polarimetric standards using the NIC2 camera on NICMOS. Considering both pre- and post-NICMOS Cooling System observations we find variations in the polarimetry consistent with the effects of sub-pixel mis-alignments and the point spread function. We also measure non-zero results from unpolarized standards indicating an instrumental polarization of p ~ 1.2%, theta ~ 88degrees. The lack of polarized and unpolarized standard stars with which to perform a comprehensive calibration study means we cannot be confident that the current calibration will be effective for a number of recent large NICMOS GO programs. Further observations of polarimetric standards are needed in order to fully characterize the behavior of NICMOS at around p=1%.
@article{arxiv.astro-ph/0601541,
title = {The NICMOS Polarimetric Calibration},
author = {D. Batcheldor and A. Robinson and D. Axon and D. C. Hines and W. Sparks and C. Tadhunter},
journal= {arXiv preprint arXiv:astro-ph/0601541},
year = {2009}
}