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SPIRAL integral field spectrograph

AAT Instrument. The original SPIRAL IFU and its "toy" spectrograph is a decommissioned instrument and is no longer offered or supported at the AAT. For current information regarding the use of the SPIRAL IFU, please refer to the AAOmega web pages. The following information is provided for historical completeness.

In Brief: SPIRAL is an integral field unit which feeds a dedicated spectrograph. The IFU has a field of view of 22.4 x 11.2 arc seconds squared with 0.7 arc second spatial sampling. There are 512 spatial sampling elements. The spectrograph is situated on the dome floor and is fed by 18m length of optical fibre.

SPIRAL operates from 4800-10000Å at a variety of wavelength resolutions. It is not recommended for use below 4800Å due to aberrations in the spectrograph optics.

SPIRAL was an "expert user" instrument and required full support from AAO staff. There are also operational limitations on its use, e.g., no grating changes during the night. Applicants granted more than one night of observing time by PATT or ATAC will be encouraged to go to the telescope for their run, to provide early feedback on the data quality, and gain experience in the use of the instrument. 

Instrument Scientist: No Instrument Scientist at present. Contact Head of Astronomy for information.
Manual: A Technical Manual is now available. This is aimed at those observing with Spiral, rather than those preparing proposals for Spiral.
The Data Reduction Manual is available
Other Info: Information on the diffraction gratings used with SPIRAL is available.

SPIRAL can be used in "nod and shuffle" observing mode which provides improved background subtraction at the expense of half the field of view (i.e. reducing the field from 22" by 11" arcsec to 11" by 11" arcsec). For compact objects it is also possible to improve the quality of the background subtraction by beam-switching within the field.

As SPIRAL is an expert user instrument, prospective users are encouraged to discuss their proposal with the Instrument Scientist prior to its submission so that any potential technical difficulties can be identified and addressed.

The SPIRAL commissioning report contains examples of images and information on performance. The AAO newsletter article contains a brief description of SPIRAL. Information is also available about the construction of SPIRAL.

Fact Sheet:


Detector: Spiral has been commissioned with MITLL-2A and EEV. The chips are binned by 2 in both directions giving a 1Kx2K image when read out and are orientated with the long axis in the spatial direction so as to fit the maximum number of fibres onto the chips. For MITLL-2A all 512 fibres will fit onto the detector giving the maximum field of view (22.4 x 11.2 arcseconds). The EEV chip is 10% smaller than the MITLL-2A chip and hence the field of view is only 22.4 x 9.8 arcsec.

MITLL-3 has yet to be commissioned with Spiral. It is the same physical size as MITLL-2A so the FoV will be 22.4 x 11.2 arcseconds. It cannot be binned before readout and thus the read-time will increase significantly (143s in normal mode compared with 50s for the binned MITLL-2A). Once the MITLL-3 data is binned 2x2 the read noise per pixel will be 4 e- (compared with 2.4 e- for the binned MITLL-2A data).

Focal Station: Mounted at the Cassegrain focus with F/8 top end. 
Image Scale: 0.7 arc seconds per microlens.
Spectral Resolution*: Due to aberrations in the spectrograph, SPIRAL is not recommended for use at wavelengths below 4800Å.

A range of gratings offer R=1186 (300R) to R= 7572 (1200V) at 5000Å. The 270R grating should NOT be used with SPIRAL.

Filters: A range of order sorting filters are available. See the AAO filter catalogue for a complete listing.
Sensitivities: We estimate R=17 per square arcsecond will give ~0.8 photons per second per microlens per pixel with the MITLL-2A CCD, and the 1200R grating. See the throughput and sensitivity page for more information.
*Spectral Resolution R measured as /, with = FWHM resolved line, usually = 2.7 pixels.