WSO-UV Spectrographs Units (WUVS)

The WUVS spectrographs assembly consists of three channels:

  • Vacuum Ultraviolet Echelle Spectrograph, VUVES.
  • Ultraviolet Echelle Spectrograph, UVES
  • Long-Slit Spectrograph, LSS
The WSO-UV Spectrographs (WUVS)

VUVES and UVES optical design is based on a Rowland circle; as a result, if the slit is placed anywhere on the circumference of the circle, the spectral orders are exactly focused in the circumference around the circle. The LSS optical design is show in the figure below. It makes use of two toroidal gratings to produce the 102-300nm spectrum in the reduced space left for the third WUVS channel. The main optical characteristics of WUVES optical elements are summarized in the table below.

Optical design of WUVS/LSS. The letters in the figure stand for: S: entrance slit, G1,G2: gratings 1 and 2, respectively; FM: folding mirror, W: window of the CCD detector
Main characteristics of WUVES optical elements

The effective area of WUVS compared with the performance of similar instruments on board the Hubble Space Telescope (HST) is shown in the figure below. WSO-UV collecting surface is a factor of 2 smaller than Hubble however, the high efficiency of WUVS new generation detectors raises significantly its sensitivity, especially above 200 nm.

Effective area of the UVES and VUVES channels of the WUVS, compared with the COS/HST and STIS/HST instruments
Effective area of the LSS channel of the WUVS, compared with the COS/HST channels
WUVS Main features

WUVS Operational Modes

FUV echellé Spectroscopy.

The FUV high-resolution spectrograph (VUVES) provides echellé spectroscopy capabilities with high resolution (R∼50,000) in the 115-176 nm range.

NUV echellé Spectroscopy.

The NUV high-resolution spectrograph (UVES) provides echellé spectroscopy capabilities with R∼50,000 in the 174-310 nm range.

Long Slit Spectroscopy.

The Long-Slit Spectrograph (LSS) provides low resolution (R∼1,000), long slit spectroscopy in the 115-305 nm range. The spatialresolution is better than 0,5 arsec.