TNTCAM MARK II: a new mid-IR array imager/polarimeter

We present design considerations for a mid-IR imaging polarimeter, TNTCAM II. Using a 256 by 256 Si:As BIB array, the camera will be unparalleled as an polarimeter/imager by any instrument currently in use at these wavelengths. Thanks to NSF support, access by the general astronomical community will be arranged. In polarimetry mode, TNTCAM II will be sensitive to linear polarizations as small as 0.2 percent. Polarized emission from cosmic sources will be modulated at a frequency high enough to remove atmospheric and system noise fluctuations. Dewar design and the optical system are discussed, including CCD assisted digital shift and ad tip- tilt correction and use of a rotating entrance window assembly allowing on-the-fly f-ratio adjustment and optimal throughput across the entire 5-25 micrometers band. The camera can contribute to the understanding of YSOs and evolved stars, obtaining high resolution mid-IR observations of dusty environments immediately surrounding these objects. In imaging mode mosaics of extended objects can be made in 2' by 2' sub-fields. In polarimetry mode, B-fields in YSOs can be probed by dust emission from hot cores, incidentally constraining grain alignment scenarios in young stellar environments.