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The quest for precision

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

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The quest for precision

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  1. 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.. The quest for precision

  2. Assuming an area of 900 m2 and a pixel size of 0.0125 A At 5000 A (R=100000 with a sampling of 4 pixels), neglecting RON, DK etc.. Using Eff=0.2: Nphot=0.0125*T*Eff*Area*5.7*1010*10(-0.4*Mn) /lambda(A) and SNR = Nphot/Sqrt(Nphot) We get in ½ hour: Mag. SN/pixel 10 2150 11 1355 12 855 13 540 14 340 15 215 16 138 17 86

  3. 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*106 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

  4. 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

  5. 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..

  6. Possible ‘concept’? Multi-fibre injection R~100000 4 Pixels 10 slices, R~200000 2 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..

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