Subject: change in default center for DIS R300 grating, from Russet

From: Michael Strauss

Submitted: Fri, 12 Oct 2007 09:16:17 -0400

Message number: 1064 (previous: 1063, next: 1065 up: Index)

Hello all,

We plan to make a small change in the default wavelength center for
the DIS R300 grating, from 7600 Angstroms to 7500.  For the reddest
targets, the red-side spectrum just about fills the chip with not a
lot of room to spare; this change should ensure that we get better
coverage of the blue end around the dichroic cutoff, while still
allowing spectra to reach SIII 9530.

As always, any user may still request 7600 (or any other red
wavelength) as their center if preferred.  This change will only
affect users who request the default center.  If you have requested
the default center in the past and you care more about the red end of
the spectrum than the dichroic overlap, or if it's important to you
for future data to match past data as closely as possible, feel free
to explicitly request spectra centered on 7600 instead of the new
default.

For reference, the default center for the B400 grating, which is
usually used in tandem with the R300, is 4400 Angstroms -- this
should allow full coverage from the dichroic to the blue cutoff with
room to spare.  The R1200 and B1200 gratings do not offer full
spectral coverage, and so the choice of wavelength center is more
specific to the desired science; however, the defaults for those
gratings are 7300 and 4400 Angstroms, respectively.

			      Russet McMillan.



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