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Low Dispersion Survey Spectrograph (LDSS++)

AAT Instrument - IRIS is a decommissioned instrument and is no longer offered or supported at the AAT. The following information is provided for historical completeness.

In Brief: LDSS ++is not offered as a common user instrument. It is an expert instrument which means that the proposal must be thoroughly discussed with the Instrument Scientist to assess feasibility before submission and more work will be required of the applicants than usual to prepare for and carry out the observations. If a lot of work is required of the Instrument Scientist they may wish to collaborate on the project.

LDSS++ is a low resolution multi-object multi-slit spectrograph using slit masks. Imaging, long slit, and slit-less spectroscopy modes are also available. LDSS++ is an upgrade to our exisiting LDSS spectrograph. More details about this upgrade can be found on the LDSS++ home page.

Note LDSS++ observations require an observer to ride in the Cassegrain Cage during the course of the observations. Thus a minimum of two observers are normally required.

Instrument Scientist: No Instrument Scientist at present. Contact Head of Astronomy for information.
Manual: None. A general description of the optical system is available in: Wynne & Worsick, The Observatory, 108, 161 (1988). As this journal can be a bit hard to find we have scanned it in, with the journal's permission, and made this article available as a gzipped Postscript file (0.8 Mb). 
Other Info: There is an entry in the Observer's Guide

Fact Sheet:

Detector: Portable CCDs, usually MIT/LL CCD with 15 micron pixels.
Focal Station: Mounted at the Cassegrain focus with f/8 top end. 
Imaging Scale: 0.39 arcsec/pixel with MIT/LL CCD.
Spectral Resolution: FWHM of ~8A with 1.0 arcsec slit, 11A with 1.5 arcsec slit. Dispersion = 2.6 A/pixel.
Slit Modes: Multislit mode allows 40-60 targets over the 12 arcmin FOV with 40-60 targets.
Long Slit provides conventional spectra.
Slit-less provides spectra of all objects in the field. Overlap and sky contamination are problems.
Microslit mode allows up to 300 targets in a 9 arcmin FOV. Sky subtraction is acheived by CCD charge-shuffling + telescope nodding.
Sensitivities: Typical performance for S/N=3 per 10A bin in a 4 hour exposure in 1 arcsec seeing:

      B=24.3 with blue grism + MITLL CCD - details.

      V=24.1 with blue grism (or red VPH grism) + MITLL CCD - details.

      R=23.5 with red VPH + MITLL Deep Depletion CCD (MITLL3) - details.