In spectroscopic mode UIST will only be used with the 0.12″/pixel plate scale.

The instrument has a 16-slot slit wheel which contains polarimetry masks, field stops and the slits for spectroscopy. The table below lists the slit wheel’s population.

25 July 2006 – Present

Posn	Slit	Description	Ref
1	Small field stop (long cam)	1arcmin x 1arcmin square	V
2	Long 4pixel slit with spacer*	0.48arcsec x 120arcsec	K
3	Long 2pixel slit with spacer*	0.24arcsec x 120arcsec	I
4	Coronographic Imaging pol mask**	Two slots 20arcsec x 120arcsec (170x1024pix) with occulting wires	S
5	Large field stop (short cam)	2arcmin x 2arcmin square	D
6	Long 4pixel slit	0.48arcsec x 120arcsec	K
7	Long 5pixel slit	0.60arcsec x 120arcsec	L
8	Long 2pixel slit	0.24arcsec x 120arcsec	I
9	Long 1pixel slit	0.12arcsec x 120arcsec	H
10	Long 7pixel slit	0.84arcsec x 120arcsec	Y
11	Pol mask imaging	Two slots 20arcsec x 120arcsec (170x1024pix)	F
12	Pol 2-pix spectroscopy	Two slots 0.24arcsec x 20arcsec	G
13	Pol 5-pix spectroscopy	Two slots 0.60arcsec x 20arcsec	X
14	2pixel pinhole	2pix x 2pix	B
15	large hole	—	N
16	IFU pick-off	5arcsec x 5arcsec square	—

Note: Datum switch region posns 5-10.

^*These two slits were to be used with the IJ and JH grisms (see below).
^**This is essentially the same as the Pol imaging mask in posn 11, but with two wires attached across the BOTTOM (western) aperture for coronographic imaging polarimetry. Can also be used for normal coronographic imaging, though the open aperture on sky will be the same.

History

1 February 2006: Cross-dispersed spectroscopy slits in posns 2,3 and 4 removed in January 2006. These were replaced with the coronographic pol mask, and new 2-pixel and 4-pixel slits with spacers. These were to be used with the IJ and JH grisms; the equivalent slits without spacers in posns. 6 and 8 give poor focus (as does the 1-pixel slit). However, the slits with spacers didn’t solve our problems, so at present these aren’t being used.

25 July 2006: Tried new spacers with the Long 2/4pix slits for IJ/JH grisms. Spacers not as big this time! Also, replaced the prototype coron mask with a proper mask (with two wires, 6pix and 11 pix).

Previous slit wheel arrangement (1 Feb 2006 – 1 Aug 2006) is available here.