DATA FROM P.O. REPORT 37
Fcoll = 1290.6 mm
Fcam = 286.9 mm
TNG is f/10.755
WHT is f/10.942
CCD
The design assumed 15 um pixels but detectors with
13.5 um pixel size were in fact used during commissioning
at the WHT. The following table assumes a 2048x4096 detector
with 13.5 um pixels, oriented with the short
axis along the dispersion direction.
INSTRUMENT
-
The PN.S is to be commissioned with two oppoitely oriented gratings
but the option of exchanging these for a single grating must be
kept available.
-
Operating Range: 4950-5070A (without retuning).
This affects coatings, optical design etc.
-
Grating(s) 600g/mm 8.5 degree blaze,
e.g. Jobin-Yvon 510-13-XXX or
Milton-Roy 35-53-*-260
-
I.A. (angle between collimator & camera) 35 degrees
-
Input angle 26.6 degrees, adjustable by adjusting the
gratings slightly.
Initially adjusted for +1200 km/s redshift
of the [OIII] line
- Imaging 90% EER < 18 micron
PARAMETERS AT THE TELESCOPE
- The Nominal field size is the projection, on the sky, of
a square detector of size 30.7 mm
(2k x 2k x 15um) as assumed in the design. The field is not
square as a result of the anamorphic effect of the gratings:
it is larger in the dispersion direction by a factor 1.11
(cos(8.4)/cos(26.6)).
- The PN.S was commissioned with EEV chips with an extent of
2150 x 13.5um (29.0 mm) in the dispersion direction, giving a
field (10.79 arcmin) slightly less than Nominal. In the
spatial direction the window was set at 2500 (33.75mm), giving
a field (11.35 arcmin) much larger
than Nominal with probably reduced image quality over the last
0.5 arcmin.
| | WHT | TNG
|
| Telescope diam: | 4200 mm | 3500 mm
|
| Focal station: | f/10.942 cass | f/10.755 nasmyth
|
| Collimated beam: | 117.9 mm | 120.0 mm
|
| Dispersion (pxl/A): | 1.29 | 1.29
|
| Scale (pxl/arcsec) | |
|
| in dispersed direction: | 3.32 | 2.72
|
| in spatial direction: | 3.67 | 3.01
|
| Nominal field size (dispersed x spatial) (arcmin):
| 11.43 x 10.34
| 13.95 x 12.59
|
| |
|
| As commissioned (2150 x 2500) (arcmin):
| 10.79 x 11.35
|
|
PERFORMANCE
- Efficiency:
With the included angle 35 deg we calculate an efficiency of 83%
(see the gratings page),
slightly better than for the 1200g/mm case. For comparison, in 1986 H.
Johnston and colleagues measured 76% for the 600V grating from the AAO
spectrograph (this result is interpolated from efficiencies at 25 and 40
deg included angle) - see AAO UM 19. I believe this is the same
grating.
Corresponding values
of instrument and total efficiencies.
- Resolution:
with the 1200g/mm gratings and 15um pixels the PN.S design
had a dispersion of 1.91 pxl/Angstrom. With the
600g/mm gratings
the value is reduced to 1.16 pxl/Angstrom (same sized pixels).
A velocity shift of
30km/s (0.5 angstrom) therefore produces a differential shift of
1.2 pixel. If the centroiding is good to 0.4 pixel (differential error
is then 0.57) the standard error in the velocity measurement is
0.57/1.2 * 30 = 14 km/s. Given that the intrinsic width of the PN line
is 25 km/s, this result is probably not significantly worse than we
would have had with the 1200g/mm gratings.
The PN.S was commissioned at the WHT (7/2001) with EEV detectors
with 13.5um pixels, which gives the larger value for the dispersion
listed above.
An earlier document lists the
old specs and gives the standard parameters for S/N calculations.
Document Date: Nov 29, 1999
Revised August 20, 2001