Instrument: Description

MEGARA is an optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) designed for the 10.4m GTC. MEGARA operates in two observing modes that cover different sky areas:

  1. The LCB mode covers the central area of 12.5 arcsec x 11.3 arcsec with a spaxel size of 0.62 arcsec and includes the fibers coming from 8 positioners located at the external perimeter of the MOS area, which are devoted to the simultaneous determination of the sky.

  2. The MOS mode allows observing 92 objects in a region of 3.5 arcmin x 3.5 arcmin around the LCB IFU bundle. Both the LCB IFU and MOS capabilities of MEGARA will provide intermediate-to-high spectral resolutions (R~6,000, 12,000 and 18,700; LR, MR, and HR spectral setups, respectively). The quoted resolving powers (which correspond to the FWHM of the extracted spectra) are the design requirements set by the MEGARA team and are, therefore, guaranteed.

The next table provides a summary of the characteristics of the two MEGARA modes and the corresponding spectral resolutions set as a requirement for each VPH.

Parameter LCB MOS
Spaxel size 0.62 arcsec 0.62 arcsec
Field of View 12.5 x 11.3 arcsec2 3.5 x 3.5 arcmin2

3.6 pix

3.6 pix
R = λ/Δλ LR R ∼ 6,000
R ∼ 6,000
MR R ∼ 12,000
R ∼ 12,000
HR R ∼ 18,700
R ∼ 18,700

Out of the total 18 VPHs to be built, a total of 11 of them can be simultaneously mounted on the MEGARA spectrograph VPH wheel. We anticipate the use of the instrument two different spectral configurations: (i) LR+HR, when the entire optical spectrum is simultaneously available at low resolution (all 6 LR VPHs), a significant fraction is covered at mid-spectral resolution (3 out of the 10 MR VPHs) plus two spectral windows at high resolution (all 2 HR VPHs) and (ii) MR+HR, when the entire optical window is available at either mid- or high-spectral resolution (9 MR VPHs and 2 HR VPHs).

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