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SPIRAL Web Pages


AAT Instrument.

In Brief: The SPIRAL Integral Field Unit (IFU) is a 512 element fibre feed for the AAOmega spectrograph.
SPIRAL provides 2D spectroscopy over a Field of View of 22.4 x 11.2 arcsec at a spatial resolution of 0.7 arcsec.
Instrument Scientist: AAOmega team - aaomega_instsci@aao.gov.au
Manual: There is no independent manual for the SPIRAL system.

SPIRAL uses the AAOmega spectrograph and so much of the information relevant to AAOmega MOS mode is also relevant for SPIRAL.

There is a separate IFU Exposure Time Calculator.

The user should note when selecting gratings that the smaller IFU fibres will give x1.5 increased spectral resolution (but with a less well-resolved PSF) than MOS.

SPIRAL is designed with Nod and Shuffle observations in mind but for many programs this will not be the optimal mode of operation due to overheads and increased (but systematic free subtraction) background noise for this mode.

The glass and fibres used in the SPIRAL IFU feed which is currently used with AAOmega have a poor UV performance (below ~4000A) and have a significant absorption band (due to water in the fibres used to construct SPIRAL) in the I band. U band observations are effectively impossible with SPIRAL. Concerned users should contact their support astronomer for more details.
Other Info:

AAOmega home page

Proposal preparation tools

How To prepare for a SPIRAL observing run

  • 2dfdr the data reduction tool

Support Astronomer Reference

Service observations:

A service program is available for projects requiring < 6 hrs.


2xE2V 2024x4096 CCDs (note that dispersion is along the 2k axis)

Focal Station:

Cass focus.

Note: since SPIRAL is mounted at Cass and uses the f/8 secondary, dual instrument runs using SPIRAL and 2dF observations cannot not made. It is possible to rapidly switch between SPIRAL and IRIS2 if the observational program justifies the overhead.

Spectral Resolution*:

R*= 1,500 to 10,000

Please read the notes on gratings at : http://local.aao.gov.au/AAO/2df/aaomega/aaomega_gratings.html

Also, due to the materials used in the construction of SPIRAL, the user should note that the system has very low U band response in comparison with the AAOmega MOS system.

Fibre diameter:

0.7 arcsec


See the AAOmega gratings page and the AAOmega Grating calculator for more information on the VPH gratings available


AAOmega SPIRAL (IFU) S/N Calculator

Note: The IFU S/N calculator assumes that the object presents a uniform surface brightness which will result in the given magnitude when integrated over an aperture of the radius selected by the user. The effect of this is that S/N will be lower, as presented by the calculator, for a constant magnitude and increasing aperture size. This is in contrast to the result that would be obtained if the input magnitude was a constant surface brightness per square arcsecond, which is a mode of operation often assumed by some users.
*Spectral Resolution, R, measured as lambda/delta_lambda, delta_lambda = Instrumental Resolution

Sarah Brough (sb@aao.gov.au)