Modifications Needed to Make this a General User Mode

• The N&S mode requires a `Neat Stop' -- i.e., an interrupt command that enables the observation to stop after the current complete nod. In the case of a BRACKET mode observation, the last sky observation must have half the exposure time length.

• Related to the above, We need a way of redefining the number of nods in mid-exposure, either extending / curtailing the total number of nods.

• A new or modified slitmask design program that

  (1)

  packs the slits together,

  (2)

  maximizes the slit length to fill empty space on the masks,

  (3)

  extends the slits on the end to fill in the full decker length

• The FITS header keywords need to contain all of the data that is normally reported and also include the relevant information describing the N&S mode (i.e., the N&S mode (NODPAT), the exposure time per nod (NODT0001), the exposure time on sky if this is different from the object exposure time (NODT0002), the total number of nods (NODCOUNT), the total exposure time on target (SEXP0001), the total dark time (DARKTIME or TOTTIME?), the number of shuffle rows (NODPIX). Rob Seaman has already included the following keywords shown in table 

• The N&S observing strategy would benefit from a mode in which the off (sky) position is unguided. This will likely increase the observing efficiency.

• One of the potential problems we noted was that the slitmask position is not repeatable - i.e., once the slitmask is moved, it does not necessarily return to its original position. This suggests that the mask should not be moved after it has been aligned on source. This is a problem that needs to be addressed independent of the N&S implementation.

IRAF HEADER KEYWORDS ADDED TO FITS HEADER

DARKTIME	=	4425.689	/	CCD dark time (sec)
NSUBEXPS	=	2	/	Number of subexposures
OBJT0001	=	'object '	/	Pointing type
SEXPOOO1	=	1800.	/	Object exposure 30x60.0 (sec)
OBJT0002	=	'sky '	/	Pointing type
SEXPOOO2	=	1800.	/	Sky exposure 30x60.0 (sec)
NODPAT	=	'bracket '	/	Nod pattern for charge shuffling
NODPIX	=	700	/	Number of pixels to shuffle
NODCOUNT	=	30	/	Number of full nods per exposure
NODT0001	=	60.	/	Object exposure per nod (sec)
NODT0002	=	60.	/	Sky exposure per nod (sec)
INITTIME	=	1.593	/	software/hardware initialization (sec)
PREPTIME	=	7.127	/	CCD preparation time (sec)
READTIME	=	122.047	/	CCD readout time (sec)
TOTTIME	=	4556.456	/	total time spent in task (sec)

Things to do in the future:

• test with a long slit (wide long slit as well)
• test with a standard star on one of the slitlets (or on the long slit) for good relative spectrophotometry calibration
• test with about 80 microslits
• measure the CTE using a line lamp and a long slit. There is some indication that the CTE results in higher noise over many shuffles, although i am not sure of this yet.

Need a mode in which we do not guide in the off position. Main thing that has to be fixed then is the handshake between the telescope and ICE.