Long-slit spectroscopy

A new grism with a resolving power of $\sim$2000 covering the wavelength range 3550-5100Å, was received and commissioned. See

http://www.not.iac.es/instruments/alfosc/grisms/grism16.html

Michael Andersen has designed a medium-resolution VPH grism centered on H$\alpha$/LiI6708Å, covering the wavelength range 6400-6800Å, and giving a resolving power of R$\sim$7000 for a 1 arcsec slit. The peak efficiency of the grism is expected to be 90 percent, making the total efficiency of ALFOSC on the NOT better than that of the spectrograph ISIS on the WHT 4.2m telescope. This efficiency is also much better than that of ALFOSC in Echelle mode (with a R$\sim$4000 and a 0.5 arcsec slit).

It was noted by the instrument working group on low-resolution spectroscopy that it was difficult to do proper flat fielding in the blue. Tests were made that showed that it actually is possible to flat field in the blue to a level well below 1%. However, it has turned-out to be very difficult to find a spare for our current UV-bright lamp on the market, as UV light is seen as a health hazard and most lamps come with inbuilt UV shielding. We bought a Blue-bright lamp instead.