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13 - THE PERFORMANCES

The following image shows a spectrum for Gamma Aql (spectral type K3 II). It is a mosaic of 4 elementary spectra obtained with our spectrograph @ R=3000. The spectrum's length is 2250 pixels, with a mean measured dispersion of 0.929 A/pixel. A few important spectral lines are shown: the magnesium triplet, the sodium doublet and the H-alpha line.

A spectrum for Gamma Aql. Processed using Iris and VisualSpec.

The spectral profile for Gamma Aql. This profile has not been radiometrically scaled (the CCD's sensitivity peak shows around 5800 A).

Detail of the spectral profile for Gamma Aql. Zone of the sodium doublet. The two lines, 6 A apart, are well separated.

Detail of the spectral profile for Gamma Aql. Zone of the magnesium triplet.

Detail of the spectral profile for Gamma Aql. Zone of the H-alpha line.

A spectrum for Vega obtained with a resolution of 3000 (dispersion is 0.929 A/mm). Grating with 1200 grooves/mm and Audine camera (click for enlarge).

Detail of the previous spectrum around the H-alpha line. The mottled aspect in the line's profile is indeed real and is caused by the presence of telluric spectral lines.

The same region in the spectrum for Vega, overlayed by the theoretical spectrum for the atmospheric H20 molecule as available in the LMD 's (Laboratoire de Météorologie Dynamique) GEISA databank. It should be noted that subtle modulations in the H-alpha spectral line are in fact due to telluric lines. By the way, water is responsible for most of the structures visible to the left of the H-alpha line.

Spectral resolution test. Now the zoomed region in the spectrum for Vega is centered on the wavelength of 6890 A. Again, this part of the spectrum is overwhelmed by telluric lines caused this time by the O2 molecule. In blue is an overlay of this molecule's spectrum from the GEISA databank . Those two spectra are in good agreement; above 6920 A the modulations in Vega's spectrum are due to H2O. The O2 tight doublet groups are separated by about 4 A. Those structures are clearly resolved. The spectrograph's separation power is in the range of 2 to 2.5 A, in good agreement with the calculations.