Subject: DIS II.5 now in operation
From: Jeff Morgan
Submitted: Fri, 24 Jan 2003 16:34:35 -0800
Message number: 653
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My apologies if you receive this notice more than once. If you have =
already received a message with the subject line above, then you can =
ignore this one.
This is to inform the general population of DIS users that we have =
completed successful installation of the new BLUE camera optics. Details =
of initial measurements of the spectrograph are given below. We are =
currently planning to install the new RED camera optics sometime in =
February. At that time we will also make another effort to eliminate =
the pesky 120 Hz noise spikes that are present in the red camera =
electronics. Peter Doherty has made us a new preamp card which will be =
installed in the red dewar when it gets opened for the optics =
installation. With the installation of the red optics DIS will =
officially become DIS III and we will have completed all of the =
currently agreed upon upgrades. Note that discussions are still =
underway on whether or not we will attempt to fix the UV (i.e. below =
3800 A) throughput problems on DIS (and thus present you with a DIS IV =
sometime in the next 12 months). With this latest work on the =
spectrograph it is possible that some of the UV response has been =
improved, but we currently have no measurements to support this. It =
will be a high priority to obtain the appropriate on-sky measurements of =
the DIS UV throughput during the next scheduled engineering run.
Using the 0.9" slit and the high resolution blue grating, we have =
obtained slit images of about 2.3 pixels width. A dispersion of 0.62 =
A/pix was measured for this grating near 4400 A This line width is =
therefore equivalent to a spectral width of 1.43 A. Scaling suggests =
that the imaging scale is now 0.42"/pix. This parameter will not be =
measured directly until we have on-sky measurements from DIS. This =
should happen sometime this weekend.
These values are close to the expected values. Note that for a slit of =
0.9" width with perfect optics one might expect to see slit widths of =
2.14 pixels. We were in fact able to see slit width images of this =
size, but not simultaneously across the entire FOV. Some improvements =
in the focus might be made with a day or two of effort, but we didn't =
think it was worth that much fine tuning. It would be best to wait to =
see what the temperature variations do to us before spending this much =
effort on the focus.
We measured about a 2% variation of the dispersion from the center of =
the chip to the edge, with decreasing dispersions near the red end of =
the spectrum. We also measured a slight "bow" to the shape of the =
spectral lines, similar to that which was present in the old optics. =
From the center of the spectrum to the top or bottom there is about a 2 =
pixel difference in the column position of the slit image centroid. =
Users will note that there is a slight tilt in the spectrum which is the =
result of a comprimse between spatial and spectral purity. The top of =
the slit image on the left (blue side) of the spectrum is 5 pixels below =
the top of the slit image on the right side of the spectrum. This tilt =
is unaviodable if you wish to minimize the effect of the "bowing" of the =
spectral lines. We have chosen to align the spectrum in such a way as =
to maximize the spectra purity of each line rather than maximizing the =
spatial purity along the line. In any case, these are small effects, =
but we want the users to be aware of them.
Measurements of the low and medium resolution gratings have now been =
done through the efforts of John Barentine. He found dispersions of =
2.42 and 1.23 A/pix. These values are within 2.5% of what one would =
have expected based on scaling of the old DIS dispersions to match the =
new high resolution grating measurements. Plots of his dispersion =
measurements can be found at:
http://galileo.apo.nmsu.edu/~jcb/dis_blue_dispersion.gif
The spectrum is now nicely centered on the chip and the vignetting =
appears to be small. A few preliminary data points indicate that the =
vignetting is somewhere between 10% and 20% near the left and right =
edges of the chip. Vignetting along the spatial dimension should be =
much smaller than this. Further efforts are still needed to =
characterize the vignetting. =20
The chip is now nicely matched to the full 6x4 arcminute FOV of the
spectrograph. However, users should note that the current suite of =
slits
in use are only 5 arcminutes in length. I would highly encourage the =
site to quickly obtain a set of slits that make use of the complete FOV =
of the spectrograph. (Alan Uomoto, are you available to help us out =
here?)
In short, with the caveats that come with having only preliminary data,=20
the new blue camera does everything that we had hoped it would! My =
thanks once again go to Peter Doherty, Mark Klaene, Craig Loomis, Jon =
Davies, Dave Woods, and John Barentine for their dedicated and wonderful =
help with getting this work done. See you all in a month (except =
Peter...I'll see him in about 10 minutes)!
Jeff Morgan
UW Astronomy
Box 351580
Seattle, WA 98195 (206) 543-6182
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<DIV>My apologies if you receive this notice more than once. If =
you have=20
already received a message with the subject line above, then you can =
ignore this=20
one.</DIV>
<DIV> </DIV>
<DIV>
<DIV>This is to inform the general population of DIS users that we have=20
completed successful installation of the new BLUE camera optics. Details =
of=20
initial measurements of the spectrograph are given below. We are =
currently=20
planning to install the new RED camera optics sometime in =
February. At=20
that time we will also make another effort to eliminate the pesky 120 Hz =
noise=20
spikes that are present in the red camera electronics. Peter =
Doherty has=20
made us a new preamp card which will be installed in the red dewar =
when it=20
gets opened for the optics installation. With the installation of =
the red=20
optics DIS will officially become DIS III and we will have completed all =
of the=20
currently agreed upon upgrades. Note that discussions are still =
underway=20
on whether or not we will attempt to fix the UV (i.e. below 3800 A)=20
throughput problems on DIS (and thus present you with a DIS IV =
sometime in=20
the next 12 months). With this latest work on the spectrograph it =
is=20
possible that some of the UV response has been improved, but we =
currently have=20
no measurements to support this. It will be a high priority to =
obtain the=20
appropriate on-sky measurements of the DIS UV throughput during the next =
scheduled engineering run.</DIV>
<DIV> </DIV>
<DIV>Using the 0.9" slit and the high resolution blue grating, we =
have=20
obtained slit images of about 2.3 pixels width. A dispersion of =
0.62=20
A/pix was measured for this grating near 4400 A This =
line width=20
is therefore equivalent to a spectral width of 1.43 A. Scaling =
suggests=20
that the imaging scale is now 0.42"/pix. This parameter will not =
be=20
measured directly until we have on-sky measurements from DIS. This =
should=20
happen sometime this weekend.</DIV>
<DIV> </DIV>
<DIV>These values are close to the expected values. Note that for =
a slit=20
of 0.9" width with perfect optics one might expect to see slit widths of =
2.14=20
pixels. We were in fact able to see slit width images of this =
size, but=20
not simultaneously across the entire FOV. Some improvements in the =
focus=20
might be made with a day or two of effort, but we didn't think it was =
worth that=20
much fine tuning. It would be best to wait to see what the =
temperature=20
variations do to us before spending this much effort on the focus.</DIV>
<DIV><BR> We measured about a 2% variation of the dispersion from =
the=20
center of the chip to the edge, with decreasing dispersions near the red =
end of=20
the spectrum. We also measured a slight "bow" to the shape of the =
spectral=20
lines, similar to that which was present in the old optics. From =
the=20
center of the spectrum to the top or bottom there is about a 2=20
pixel difference in the column position of the slit image =
centroid. =20
Users will note that there is a slight tilt in the spectrum which is the =
result=20
of a comprimse between spatial and spectral purity. The =
top of=20
the slit image on the left (blue side) of the =
spectrum is 5=20
pixels below the top of the slit image on the right side of the =
spectrum. =20
This tilt is unaviodable if you wish to minimize the effect of the =
"bowing"=20
of the spectral lines. We have chosen to align the spectrum in =
such a way=20
as to maximize the spectra purity of each line rather than maximizing =
the=20
spatial purity along the line. In any case, these are small =
effects,=20
but we want the users to be aware of them.<BR><BR>Measurements of the =
low and=20
medium resolution gratings have now been done through the efforts of =
John=20
Barentine. He found dispersions of 2.42 and 1.23 =
A/pix. These=20
values are within 2.5% of what one would have expected based on scaling =
of the=20
old DIS dispersions to match the new high resolution grating =
measurements. =20
Plots of his dispersion measurements can be found at:</DIV>
<DIV><A=20
href=3D"http://galileo.apo.nmsu.edu/~jcb/dis_blue_dispersion.gif">http://=
galileo.apo.nmsu.edu/~jcb/dis_blue_dispersion.gif</A><BR><BR>The=20
spectrum is now nicely centered on the chip and the vignetting appears =
to be=20
small. A few preliminary data points indicate that the vignetting =
is=20
somewhere between 10% and 20% near the left and right edges of the =
chip. =20
Vignetting along the spatial dimension should be much smaller than=20
this. Further efforts are still needed to characterize the=20
vignetting. <BR><BR>The chip is now nicely matched to the full 6x4 =
arcminute FOV of the<BR>spectrograph. However, users should note =
that the=20
current suite of slits<BR>in use are only 5 arcminutes in length. =
I would=20
highly encourage the site to quickly obtain a set of slits that make use =
of the=20
complete FOV of the spectrograph. (Alan Uomoto, are you available to =
help us out=20
here?)<BR><BR>In short, with the caveats that come with having only =
preliminary=20
data, <BR>the new blue camera does everything that we had hoped it =
would! =20
My thanks once again go to Peter Doherty, Mark Klaene, Craig Loomis, Jon =
Davies,=20
Dave Woods, and John Barentine for their dedicated and wonderful =
help with=20
getting this work done. See you all in a month (except =
Peter...I'll see=20
him in about 10 minutes)!<BR></DIV></DIV>
<DIV> </DIV>
<DIV>Jeff Morgan<BR>UW Astronomy<BR>Box 351580<BR>Seattle, WA =
98195 (206)=20
543-6182</DIV></BODY></HTML>
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