EUROPEAN SOUTHERN OBSERVATORY La Silla Science Operations: NTT
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Generalities

Low-resolution long-slit spectroscopy is done in the RILD mode by combining one of the grisms with one of the fixed slits (starplates) and, if needed, an order-sorting filter. The grisms cannot be rotated: the achievable wavelength range is fixed for each grism. Due to the larger size of the new Red CCD, the wavelength coverage is larger than what it was with the old chip. As a consequence, many grisms show a second order contamination, hence the use of an order sorting filter is recommended.

There are six fixed slits available, with widths of 0.5'', 1.0'', 1.5'', 2'', 5'' and 10'', and each with a length of 8'. The 0.5'' slit will cause undersampling of your spectra, except when used in 1 x 1 binning mode, under exceptional seeing conditions.

The orientation of the slit can be adjusted by applying an offset to the rotation angle of EMMI.

Grisms and filters can also be combined to obtain slitless spectra imaged on the CCD. The use of filters in combination with a grism reduces the sky background intensity. It also selects the wavelength region of interest and limits the length of the spectrum, thus reducing crowding. The spectral coverage within this wavelength region depends on the position of the object in the field.

Grisms characteristics

The following table summarizes the Grisms available on EMMI and their characteristics.

[a] Efficiency at blaze.
[b] Resolution with 1'' slit at 600 nm (at central lambda for grisms 4,5 and 6) and for binning 2
[c] Second overlap occur beyond 800 nm if not using an order-sorting filter . See the manual for details.
[d] Dispersion with 1 x 1 binning

Grisms efficiencies

The efficiency curves for the grisms is shown below, and also available in PS format.

System efficiency

Here we show the total system efficiency (telescope+EMMI) in RILD mode

December 2003 (Ela)