NOTcam spectroscopy: slit shape monitoring

NOTcam currently can be equiped with 3 out of four available slits. The slits are made of copper/nickel laminate, and were originately mounted in aluminium holders. As of April 2004 the 128 micron and 64 micron slits are mounted in copper holders.

Although the slits look nice when warm, when cold the difference in thermal expansion of the metals leads to deformation. It appears that slits that are not tightly screwed to the holder suffer less deformation. Below some integrated slit images are presented (no grism in the beam). The light under the slit profile is integrated after local background subtraction. The slits were properly focussed on the detector.

128 micron slit, tight in holder, Jband, WFC. Average slitwidth: 2.1 pix.

44 micron slit, tight in holder, Jband, HRC. Average slitwidth: 2.8 pix.

64 micron slit, loose in holder, Hband, WFC. Average slitwidth: 1.6 pix.

Below with new holders:

64 micron slit, Hband, WFC. Average slitwidth: 1.5 pix.

128 micron slit, Hband, WFC. Average slitwidth: 2.6 pix.

Below after moving aperture wheel assembly:

128 (top) and 64 micron slit, Hband, WFC. Summed over slitwidth after flatfielding and badpix removal.
The Y-axis indicates the effective slit width in pixels.

44 micron slit, Hband, HRC. Summed over slitwidth after flatfielding and badpix removal.
The Y-axis indicates the effective slit width in pixels.

John Telting (jht)