The AAO owns a set of 22 diffraction gratings which are used with 2dF,
the RGO spectrograph and SPIRAL on the AAT and with FLAIR on the UKST.
Current List of Gratings
A current list of gratings is
below.
Grating numbers have been assigned in order of acquisition. Three
gratings (150ECH, 600H and a second 600U) have been unmounted and are
not
available.
| Name |
Number |
Blaze (A) |
Status |
| 300B |
14 |
4200 |
Current |
| 300B |
19 |
4200 |
Current |
| 250B |
4 |
4300 |
Current, but 300B has higher efficiency |
| 270R |
3 |
7600 |
Current |
| 316R |
22 |
7500 |
Current, but frequently in use by 6dF* |
| 600U |
18 |
3500 |
Current, but not recommended lambda > 3500A |
| 600V |
8 |
5000 |
Current |
| 600V |
17 |
5000 |
Current |
| 600V |
21 |
5000 |
Available for 6dF only |
| 600R |
9 |
7500 |
Current |
| 1200B |
6 |
4300 |
Current |
| 1200B |
20 |
4300 |
Current |
| 1200V |
1 |
5000 |
Available for 6dF only |
| 1200V |
11 |
5000 |
Current |
| 1200V |
15 |
5000 |
Current |
| 1200R |
2 |
7500 |
Current |
| 1200R |
16 |
7500 |
Current |
| 1200I |
12 |
10000 |
Current, but recommended for order II only |
| 1200J |
10 |
12000 |
Not available - on loan to the UK** |
NB Blaze angles given are the
nominal Littrow values.
* The 316R is
being used for the 6dF Galaxy Survey, and is
usually at the Schmidt. Please contact Paul Cass
(cpc@aaocbn.aao.gov.au)
before use (ideally 1 week) to avoid grating conflicts.
**Contact your AAO
Support astronomer if you have any concerns.
For most purposes the 1200I will perform as well as the 1200J.
|
Wavelength Parameters
Calculators to estimate wavelength
centre, coverage and dispersion for
a given grating angle are available for 2dF
and the RGO
spectrograph.
Note that slightly different parameters are used for the RGO at the
telescope,
but the differences are within the estimate error. For exact values,
arc
frames should be used.
Grating Efficiencies
The efficiency curves of the older
gratings were measured in 1986 (AAO
Manual 19). New measurements in the V band were taken in 1999. They
showed
little change, with ~5% loss in V for most older gratings. The data
from
the old measurements are presented here, with new measurements of the
300B
grating (14) and the 316R (22).
Low
Dispersion Grating Efficiencies
 |
Postscript
version of comparison plot
Detailed plots showing 2dF /
RGO
25cm and RGO 82cm measurements and
higher orders:
|
Medium
Dispersion Grating Efficiencies
|
|
Postscript
version of comparison plot
Detailed plots showing 2dF /
RGO
25cm and RGO 82cm measurements and
higher orders:
|
High
Dispersion Grating Efficiencies
|
|
Postscript
version of comparison plot
Comparison of Order II
measurements: gif,
postscript
Detailed plots showing 2dF /
RGO
25cm and RGO 82cm measurements and
higher orders:
1200B: gif,
postscript,
data: 25cm,
82cm
1200V: gif,
postscript,
data: 25cm,
82cm
1200R: gif,
postscript,
data: 25cm,
82cm,
Order II 25cm,
82cm
1200I: gif,
postscript,
data: 25cm,
82cm,
Order II 25cm,
82cm,
Order III 82cm
1200J: gif,
postscript,
data: 25cm,
82cm,
Order II 25cm,
82cm,
Order III 82cm
Note that the 1200J is not currently
available. |
Appendix - Details
of Measurement Procedure
1985/86 Measurements
A laboratory experiment was setup
by R. Robinson and P. Gray in 1985. Measurements
were undertaken by H. Johnston and R. Stathakis. Results were presented
in AAO UM 19.
The angle between the incoming
light and the detector position was set
at 45o to simulate the 25cm RGO camera and 20o
for
the 82cm camera (this should have been 15o but was
restricted
by the physical limitations of the setup). 2dF has a similar angle to
the
25cm RGO camera (40o).
The light source was a 12V quartz
halogen lamp. Light passed through
an order sorting filter and a double monochromator system composed of
two
125 mm focal length Oriel 7240 grating monochromators. The second
monochromator
was necessary to avoid problems of scattered light. For wavelengths
above
4000A an exit slit of 0.35 mm was used, giving a bandwidth of 30A.
Because
of the low light levels below 4000A, the exit slit was widened to 1 mm.
An iris diaphram restricted light
to a 1 cm diameter beam which passed
through a 40 mm diamter 100 mm focal length fused silicon double convex
collimator lens. The light passed through a polaroid filter, was
reflected
by an aluminium flat mirror or the grating mounted on a turntable, and
refocused using a 50 mm diameter 75 mm focal length fused silicon
double
convex lens onto a 1 cm diameter EG & G silicon photo diode (type
UV-44B).
The wavelength range was divided
into three regions (U: 3600 - 4600A;
V: 4600 - 7000A; I: 7000A - 11400A). Polaroids used were HNP'B in U, HN
32 in V and HR for I. In overlap regions measurements usually agreed to
1-2% but occasionally disagreed by up to 4%. Observations were made at
steps of at most 200A, starting near the nominal blaze wavelength and
progressing
in both directions until an efficiency of 30% or less was attained or
the
measurement range was exceeded. At each position the reference mirror
was
measured, then the grating and finally the mirror again. Mirror
measurements
normally agreed to within 1-2%. Grating measurements were normalised by
the mirror measurements. The absolute reflectivity of the mirror flat
was
measured and grating curves were corrected to an absolute scale.
New measurements of 300B (14) and
316R (22).
Two spectrophotometric standards
were observed through the 300B grating
and then the 250B grating on the RGO 25cm camera in 1995. The weather
was
stable but not photometric, and absolute efficiencies of the other
components
of the spectrograph are not well known, so this test measured only the
relative efficiencies of the 250B and 300B gratings. The absolute curve
for the 300B grating was estimated by scaling by the 1985/6
measurements
of the 250B grating. Spot measurements in FLAIR and with the RGO in
photometric
weather are consistent with the efficiency curve.
Observations were taken by Ian
Lewis and Karl Glazebrook with the 300B,
316R and 270R gratings on 2dF in 1999 covering 4400A to 8000A. The
relative
efficiencies were reported in the AAO Newsletter 90, August 1999. After
scaling by the 1985/6 measurements of the 270R grating, the 300B
observations
agreed well with the 1997 figures for wavelengths redward of 5200A. The
316R figures agree well with test laboratory measurements.
The final 300B measurements are
combined from the 1995 and 1999 observations.
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