| 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 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.