The optical integral-field spectrograph OASIS is installed at one of the science ports of NAOMI, in the WHT's AO-dedicated Nasmyth enclosure. The instrument is optimised for use with adaptive optics, but may also be used without it.

Light from the sky is imaged onto OASIS's IFU, which contains ~1100 hexagonal lenslets in a rectangular array. Three different enlargers can currently be placed in front of the lenslet array in order to change the field of view and corresponding spatial sampling per lenslet.

The light from each lenslet is then dispersed using a grism (or prism) and imaged onto the 2k x 4k detector. 15 different spectroscopic configurations are available, giving a variety of spectral ranges and resolutions. The ~1100 spectra can then be extracted using a dedicated data reduction package to form a datacube.

As the spatial sampling and the spectroscopic configuration are independent of each other, this leads to a total of 45 possible configurations for spectroscopy. The available options are given on the OASIS Configurations page.

Information about applying for time, using adaptive optics with OASIS, data reduction and other technical details can be found on the FAQs page. Please note that all OASIS observations are performed in service mode by ING staff astronomers.