European Southern Observatory New Technology Telescope

General :
Observations :

EMMI Echelle Spectroscopy (REMD-High-Res)

Generalities

Echelle spectroscopy is done in the REMD mode by combining the medium-dispersion slit, one of the echelle gratings, and one of the grisms as cross-disperser The echelle gratings can not be rotated. The following figure illustrate the light path (same as the REMD light path).

Echelle Gratings

Three echelle gratings (#9, #10 and #14) are presently offered. They can be used in combination with a cross-dispersing grism to obtain data in an echelle format, Grisms #3 and #4 are used with the echelle grating #9, grisms #3, #4, #5 and #6 with the echelle grating #10 and #14. The properties of the echelle spectra obtained using the different cross-dispersers are given in the table below.

For echelle spectroscopy, a mask can be mounted in order to reduce the inter-order scattered light by 30%. The presence of the mask limits the field of view to about 30'' in the slit direction. The mask can not be removed during the night. The echelle gratings can also be used without a cross disperser by using a filter to separate the order that you are interested in. See the filter page.

Echelle grating #14 is the grating which gives the highest resolution (up to 70 000 with a slit width of 0.8'', corresponding to a line width of 2.1-2.2 pixels at the blue end of the order) in combination with a wide wavelength range.

Order separations

The order separations for the echelle gratings are shown below, for all cross-dispersers.

Echelle Grating Throughputs

Measured count rates in echelle spectroscopy (in e-/s/nm) are shown below. Count rates are monitored during the technical time and scaled to an AB star with a 15th magnitude and unit airmass. The latest news of the performance will be updated soon in this page, as the Red CCD is better characterized. (23 Sep. 2002).

Send comments to: NTT Webmasters <nttweb@www.ls.eso.org> Last Update: 25 Sep. 2002 (cf)