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The quest for precision The quest for precision

The quest for precision - PowerPoint Presentation

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Uploaded On 2017-01-25

The quest for precision - PPT Presentation

High Aperture implies lot of photons High SN high precision Open this new parameter space LEGACY Precision Fidelity Doppler V elocity Wavelength Accuracy Stellar atmospheres finest abundances ID: 513959

high doppler stars time doppler high time stars modularity snr nphot pixels wavelength sec precision range costs pixel polarimetry

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Slide1

The quest for precision

High Aperture implies lot of photons: High S/N , high precisionOpen this new parameter spaceLEGACYPrecision: Fidelity, Doppler Velocity, Wavelength Accuracy…Stellar atmospheres, finest abundances, Exo - Earths, Physical Constants, Expansion..

1Slide2

Assuming an area of 900 m2 and a pixel size of 0.0125 AAt 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 =

N

phot

/Sqrt(Nphot)We get in ½ hour: Mag. SN/pixel10 2150 11 1355 12 85513 54014 34015 21516 13817 86

2Slide3

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

3Slide4

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

4Slide5

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..

5Slide6

Possible ‘concept’?

Multi-fibre injectionR~100000 4 Pixels 10 slices, R~200000 2 Pixels, R=10000 without slicing and multi object (likely 7-8) or IFUUpgradable

to use the AO with VHR modeUpgradable 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 importantIf we want be ambitious we MUST invest.. Sky subtraction, stellar models.. Etc..

6