MedRes: a new MEDium RESolution integral field spectrograph for SPHERE

MedRes is a proposed MEDium RESolution integral field spectrograph for upgrading SPHERE, the high contrast instrument for the ESO VLT telescope. MedRes is actually thought of as a potential Visitor Instrument with the scope to provide high contrast diffraction limited medium-high resolution spectra (R ≥ 1000) over a reasonably large field of view (a square with a side of at least 0.4) and across the spectral region 1.2-1.65 microns. Two main science objectives are driving the proposition for such an instrument on SPHERE. First of all, MedRes shall improve the detection of previously unknown giant planets (contrast 10−5 , goal 10−6 ), in particular accreting planets, at small separation from the star (< 0.2", goal, 0.1"). And second, MedRes will boost the characterisation of known (faint) planets at a spectral resolution substantially higher than currently possible with SPHERE IFS (R ~ 35 − 50) and for contrasts much better than achievable with IRDIS Long Slit Spectroscopy (LSS) at small separations. The design will be optimised for SPHERE, fully exploiting the capabilities offered by a second stage Adaptive Optics (SAXO+) and complementing the niches of IRDIS, IFS and HiRise in the near IR channel. A preliminary optomechanical design and simulations of performance will be presented.