The quest for precision High Aperture implies lot of photons: High S/N, high precision Open this new parameter space LEGACY Precision: Fidelity, Doppler Velocity, Wavelength Accuracy… Stellar atmospheres, finest abundances, Exo - Earths, Physical Constants, Expansion.. 1

Assuming an area of 900 m 2 and a pixel size of A At 5000 A (R= with a sampling of 4 pixels), neglecting RON, DK etc.. Using Eff=0.2: N phot =0.0125*T*Eff*Area*5.7*10 10 *10 (-0.4*Mn) /lambda(A) and SNR = N phot /Sqrt(N phot ) We get in ½ hour: Mag. SN/pixel

Considering for Doppler shifts a rule of thumb of Doppler Precision ~ 100/(S/N) m/sec (Liske et al, for QSO, HARPS for stars)… Doppler Precision of 20/30 cm/sec for extragalactic sources/observation AT MOST can be reached. For stars, likely the limit will be given by detector saturation: S/N 2000 for exposure (4*10 6 e - ) is probably a reasonable limit, or 5 cm/s. Line center: using S=(0.69/SNR)*SQRT(Pixel*FWHM) we obtain 16 m/sec for FWHM=3Km/s and SNR=1000 3

Implications -Fibre fed, scrambling (efficiency); but is there a real alternative?? -Temperature and pressure controlled (costs, obvious for IR) -Calibration (Costs or observing time) -NO MOVING functions inside the spectrograph – full spectral range (loss of flexibility) - increasing in costs, and complexity. (but would you like to spend a 0.5 ME(TBD) worth night to re-observe the same object because range was not covered? -If you do everything you can hardly be the best for all applications 4

Comments/questions -Be more ambitious?! Open space, go beyond extensions.. -Modularity: Be ready for AO? -Modularity: Be ready for larger wavelength coverage? -Modularity: Use different spectrographs on the same field? (FLAMES,GMT?) -Slit ?? -Polarimetry ? How? -Any critical timescale (scientific ground) ? -What will be surely NOT done in the next 12 yrs? -Any spectrum you take, calibrate it well (MM)? -Neglecting GAIA impact?? (new QSOs, new objects ??) -When will be the time to go back to low Z to understand high Z, to stars to understand planets ? Etc.. 5

Possible ‘concept’? -Multi-fibre injection -R~ Pixels 10 slices, R~ Pixels, R=10000 without slicing and multi object (likely 7-8) or IFU -Upgradable to use the AO with VHR mode -Upgradable to use polarimetry when available -Upgradable in wavelength range: 3-4 spectrographs divided in Lambda, NOT necessarily all arriving at the same time. May be NOT all with the same resolution? -If we are serious about expansion, asap is important -If we want be ambitious we MUST invest.. Sky subtraction, stellar models.. Etc.. 6