EUROPEAN SOUTHERN OBSERVATORY La Silla Science Operations: NTT
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16 February 2004

The system of the calibration lamps in EMMI has been completely renewed. All lamps work. The workaround below is not necessary anymore.

(It is kept for info).

22 September 2003

The Helium lamp in EMMI is dead. A spare has been put in place, but it's just a "less old" lamp, and it does not work (the new system for calibration lamps will be put in place soon). This might be very important for some programs interested by the blue part of the spectrum.

Workaround:

The Thorium lamp is not usable at low resolution (very narrow lines) although it has blue lines (the lines that Helium was providing).

To recover as much as possible the blue part of the wavelength calibration, the Neon (Ne) lamp should be used instead, in the OB. A minimum of 50 seconds is necessary (while Argon during 1 second is enough) to get good signal in the blue.

Here is the situation for the RILD grisms:

Grism ..........Exp.Time [s] ...Blue Limit [A]
-----------------------------------------------
Grism #1: ....NeAr 50+1 ....5870 instead of 4470
Grism #2: ....NeAr 50+1 ....5870 instead of 4470
Grism #3: ....NeAr 50+1 ....5870 instead of 4470
Grism #4: ....NeAr 50+1 ....unchanged.
Grism #5: ....Ar 300 ...........unchanged.
Grism #6: ....NeAr 50+1 ....unchanged.
Grism #7: ....NeAr 50+1 ....unchanged.

As you can see, the Neon lamp allows to recover blue lines down to 5870 A only. Without Neon lamp, the blue limit is around 6900 A!... So Grisms #1,2,3 have a reduced wavelength coverage, while the others not (they are not going that much in the blue).

Grism #5 is a bit special. It does not need Helium nor Neon. However, it uses Argon during 300 [s] with the filter BG38#643. In that configuration, Argon do provides blue lines down to 4000 A!, and the very intense red ones are weakened by the filter.

So Argon can be used to provide blue lines, but the transmission curve of BG38#643 falls down to 0 around 7100 A and the red lines will be absent. So, IF the visitor is more interested by the blue than the red, the configuration "Argon 300[s] + filter BG38#643" can be used.

The only way to recover for all grisms (except #5) the complete coverage would be to make 2 calibrations arcs spectra, one without the filter and using Neon, and the other with Argon300s + filter.

I have not checked in details the REMD, but the indications above should be sufficient to obtain the blue limit.

Note that a line list of Neon+Argon does not exists by itself, at least for people using IRAF. It must be built from the "henear.dat" and "ctiohear.dat" file.

22 Sep. 2003 (cf)