Subject: DIS Medium Resolution Gratings

From: Gordon Richards

Submitted: Sun, 25 Jan 1998 00:31:02 -0600 (CST)

Message number: 40 (previous: 39, next: 41 up: Index)

Report on the installation and testing of the new medium resolution
gratings for DIS:
-------------------------------------------------------------------

The new medium resolution gratings for DIS have been fabricated and
Alan Uomoto brought them to the site last week for installation and
testing.  We have been doing some testing of the gratings and
potential users of the new gratings will find the following
information useful:

			Blue		Red
Lines/mm		600		300
Resolution		~3.18 A/pix	~3.53 A/pix
Coverage		1628 A		2824 A
Blaze			4000 A		?

 		        If the medium resolution gratings are in:

			Low res slots		High res slots
			-------------		--------------
			blue	red		blue	red	
			----	---		----	---
Step position		796	649		748	648
Angstroms per step	16.2	28.1		9.8	20.1
Central wavelength	~4763	~6826		4471.7	6825.8
Minimum wavelength	~3950	~5414		3960.3	5414.4
Maximum wavelength	~5576	~8237		5583.0	8237.1


For a single setting the wavelength coverage is: 3960 to 8237 Angstroms

The above wavelength coverage is for the medium resolution gratings in
the high resolution slots with a central wavelength of 4472 in the
blue and 6826 in the red, which yields a range of about 3960 to 5583
on the blue side and 5414 to 8237 on the red side.  I have found that
this gives sufficient overlap between the red and the blue sides and
minimizes the amount of spectral coverage with low S/N near the
dichroic.  If the medium resolution gratings are in the low resolution
slots, then the coverage is about 3650 - 5576 in the blue and the same
in the red.

Note that the Remark interface is set up to handle specific gratings,
so setting the grating tilts for the new gratings is not trivial.  In
theory, if the medium resolution gratings were in the low res slots
then one could simply multiply the central wavelength by 600/300 in
the blue and 300/150 in the red.  Similarly if the medium resolution
gratings were in the high resolution slots, then you would divide the
desired central wavelength by 1200/600 in the blue and 830/300 in the
red.

IMPORTANT:

The above formulas do NOT work.  However, we have empirically
determined the tilts.  If the medium resolution gratings are in the
high resolution slots, then to get a central wavelength of 4772 in the
blue, then set your grating tilt to 739 STEPS.  Similarly, to get a
central wavelength of 6826 in the red, then set your grating tilt to
649 STEPS.  If instead the medium resolution gratings are in the low
resolution slots, then for similar central wavelengths set the blue
side to 795 STEPS while the red side is still 649 STEPS.  Note the use
of steps here in concordance with the previous note regarding the
repeatability of DIS grating tilts.  For different central wavelengths
one can use the fact that there are about 9.8 Angstroms per step in
the blue and 20.05 Angstroms per step in the red if the new gratings
are in the high bays.  If the new gratings are in the low bays then it
is about 16.2 Angstroms per step in the blue and 28.1 Angstroms per
step in the red.

We hope to have throughput numbers sometime in the near future.

Gordon Richards
Alan Uomoto
APO APO APO APO APO  Apache Point Observatory 3.5m  APO APO APO
APO
APO  This is message 40 in the apo35-dis archive. You can find
APO  the archive on http://www.astro.princeton.edu/APO/apo35-dis/INDEX.html
APO  To join/leave the list, send mail to apo35-request@astro.princeton.edu
APO  To post a message, mail it to apo35-dis@astro.princeton.edu
APO
APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO