Spectroscopy

The procedure for spectroscopic observations is similar to that of photometric observations. In both cases one needs to observe object, sky and PSF-reference. Instead of a photometric reference star, now a spectral reference star is necessary. In addition, to determine the line flux, one has to observe the continuum next to the line. Because of the variability of the transmission and emission, best calibration of the data is achieved by frequently observing the reference. Because narrow line observations result in wavelength dependent interference pattern (generated by the filter and entrance window of the camera), a separate flat field is necessary for every observed wavelength.

Special remarks on spectroscopy with SHARP II+:

• To minimize lost time between observations of different wavelengths and sky positions, several observing sequences are implemented in the software.
• The scale should not be used for spectroscopy. When observing with this pixel scale, there is additional vignetting at the northern edge of the field of view. Also the shift in passband across the filed of view has to be considered, when using the Fabry-Perot etalons.
• Only one of the two Fabry-Perot etalons should be used per night. The procedure for changing the Fabry-Perot etalon requires about half an hour and the support from ESO staff.
• The Fabry-Perot etalons have to be placed manually in the beam.