Pre-observations and models

Transcription

1 Pre-observations and models Carine Babusiaux Observatoire de Paris - GEPI GREAT-ITN, IAC, September 2012

2 The questions 1) Can the observing program tackle the scientific problem? 2) What is the best configuration of the observing parameters to get the desired results? Which fields, which targets? Precision and accuracy needed on the final parameters? P? Wavelength coverage? Resolution? Minimum SNR? Target selection? Pollution expected in the sample? 2

3 Using models to define where your best constraints are Minchev & Quillen

4 Using models to define the precision needed l = 305 dist = 7 kpc + GAIA errors + survey σ(vr)=2 km/s μβ (mas/yr) Sun Vr (km/s) Antoja et al

5 Modelling the observations Gaia simulation a quite complete (and complex!) example X simulated observations 5

6 Modelling the observations Gaia simulation a quite complete (and complex!) example X X simulated catalogue 6

7 Modelling the observations Simple tools are often enough... Instrument specific exposure time calculators & user manual 7

8 Contents 1. Observing strategy the trade-offs 2. Supporting catalogues 3. Testing the target selection 4. Extra considerations 5. Modelling the observations Stellar population synthesis Photometry / Spectroscopy Extinction models 8

9 Field observability from the telescope! /observability.html Sky accessibility for one of the VTL Air mass 1/cos(ZA) 9

10 Observing Strategy Goal is to optimize : Nfields x Nsetups x exptime(snr,vlim) = Nnights 10

11 Observing Strategy Example for spectroscopy : trade-offs to analyse : Nfields x Nsetups x exptime(snr,vlim) = Nnights 1) Radial Velocities 2) Teff, logg, [M/H] 3) Individual abundances Resolving power R = λ / Δλ SNR Wavelength coverage 11

12 The magnitude limit mλ =M log 10 ( d ) 5+ Aλ 12

13 SNR Signal-to-noise ratio (S/N or SNR) signal : total number of photons of the source (F *) noise : photon noise [ Poisson distribution : σ ( F *)= F * ] background noise dark current read-out noise For bright stars : F* S = = F * N σ (F *) 13

14 SNR σ ( F )= F 14

15 SNR Exposure Time Calculator Mean SNR for a G2V star for GES set-ups 15

16 SNR Exposure Time Calculator Mean SNR for a G2V star for GES set-ups 16

17 SNR Check the wavelength of your main spectral features... UVES 580 SNR for a G2V star with V=15, 4*45 min exposure time 17

18 Which wavelengths? Resolution? SNR? Tests using synthetic or observed standard spectra with different SNR Tests made by A. Recio-Blanco et al. for GES which set-ups? which SNR? 18

19 Contents 1. Observing strategy the trade-offs 2. Supporting catalogues 3. Testing the target selection 4. Extra considerations 5. Modelling the observations 19

20 Supporting catalogues Target selection (incl. SNR estimation) Scientific analysis Stellar atmosphere parameters constrains Extinction estimates Proper motions Check that extra input do not bias your target selection 20

21 Current main photometric surveys Survey H Filters Mag Lim Area Dates GALEX - FUV,NUV π 2003 OGLE S V,I 20.5 SDSS N u,g,r,i,z 22.0 / π IPHAS / VPHAS+ N/S (u,g),r,i,hα 20 / π / 2012 APASS N/S B,V,g,r,i 17 4π SkyMapper S u,v,g,r,i,z 22.9 / π Pan-STARRS N g,r,i,z,y 24 3π MASS N/S J,H,Ks 15.8 / π UKIDSS N (Z,Y),J,H,K 19.4 / π 2005 VISTA S (Z,Y),J,H,Ks 20 / 18 2π 2010 GLIMPSE - IR 0.2 π 2004 WISE - IR 4π

22 Current main all sky astrometric surveys Survey Accuracy Mag Lim Nb stars USNO-B1 200 mas V=21 1 billion Tycho-2 60 mas V= million UCAC mas R=16 40 million 22

23 Astrometry Good precision needed for fibre positioning For FLAMES, accuracy 0.3 arcsec is needed From FPOS User Manual 23

24 Astrometry High proper motion for nearby objects needs to be taken into account! White Dwarf Copyright Rochester Institute of Technology. 24

25 Home-made pre-observations 1) Imaging ( photometry, astrometry) [+] multi-epoch (if variability or proper motion needed) [+] multi-wavelength (ex. Optical + NIR) 2) Low resolution spectroscopy ( tighter object selection) 3) High resolution spectroscopy 25

26 Home-made pre-observations Example: Metal poor stars in GES come from: HES (Hamburg/ESO objective-prism) survey pre-selection based on B-V, J-K and Ca II K line (Christlieb et al. 2008) Skymapper photometry + AAOmega LR spectroscopy 26

27 Checking available data 27

28 Checking available data 28

29 Contents 1. Observing strategy the trade-offs 2. Supporting catalogues 3. Testing the target selection 4. Extra considerations 5. Modelling the observations 29

30 Object selection : test on synthetic data Ex: MS turn-off colour with Padova isochrones 30

31 Object selection : test on empirical data Ex: magnitude/colour selection of G2V with Hipparcos / 2MASS 31

32 Object selection : test on empirical data Ex: giant branch shape using Globular Clusters [Fe/H]=-0.9 K J-K Ferraro et al

33 Checking total number of targets 33

34 Target selection Which selection will increase your % of targets? J 34

35 Target selection What are your contaminants? Will they be easy to identify? remove? model? 35

36 Target selection Easy to model Enough margin (catalogues and models uncertainties) 36

37 Contents 1. Observing strategy the trade-offs 2. Supporting catalogues 3. Testing the target selection 4. Extra considerations 5. Modelling the observations 37

38 Multi-epoch Variability detection as a goal (primary or secondary) of the survey (variable stars, binaries, proper motion...) Removing pollution Cosmic rays Variables, binaries... removal 38

39 Multi-epoch Un-detected binaries abundances determination bias 1% flux contamination can produce a 0.1 dex bias (Erspamer & North 2003) Vr dispersion bias Extra Vr dispersion due to un-detected binaries on solar type stars at V=18 mag is ~ 8 km/s 39

40 Calibrators Adding some objects for calibration (zero point) or objects in common with other programs (validation / scaling) checking for standard stars or clusters For GES, 10 nights have been allocated for calibration : standard stars, open and globular clusters, specific fields (e.g. Corot), outliers prototypes 40

41 Presentation 1. Observing strategy the trade-offs 2. Supporting catalogues 3. Testing the target selection 4. Extra considerations 5. Modelling the observations Stellar population synthesis Photometry / Spectroscopy Extinction model 41

42 Stellar population synthesis model The Besançon model The TRILEGAL model 42

43 Stellar population synthesis model - ingredients 4 components: thin disc, thick disc, halo, bulge 43

44 Stellar population synthesis model - ingredients SFH (Star Formation History) age IMF (Initial Mass Function) mass AMR (Age Metallicity Relation) [M/H] Density distributions X, Y, Z Velocity distributions Vx, Vy, Vz Evolutionary tracks Teff, logg + synthetic spectral libraries photometry 44

45 Stellar population synthesis model - ingredients Evolutionary tracks (Padova, Dartmouth, BaSTI,Y2...) 45

46 Stellar population synthesis model - ingredients synthetic spectral libraries (Basel2, ATLAS, MARCS, Phoenix...) photometry in the required filters 46

47 Stellar population synthesis model - ingredients Extinction law Cardelli et al. 89 & Fitzpatrick 99 47

48 Spectral features Synthetic spectra (ATLAS, MARCS, PHOENIX...) Lines identification in spectral standard atlases (e.g. solar) Checking sky emission and telluric absorption data/background/ ISM absorption lines + DIBS 48

49 Spectral features Sky emission example in FLAMES LR08 spectra From Battaglia et al

50 Extinction model How to chose an extinction model? 2D / 3D (map or model) Sky coverage Spatial resolution Accuracy 50

51 Extinction model : some famous examples Schlegel et al. 1998: 2D, full sky, 6' resolution, 16% accuracy from IR photometry of extragalactic objects SGP NGP 51

52 Extinction model : some famous examples Drimmel et al. 2003: 3D, full sky, model calibrated at to Schlegel 52

53 Extinction model : some famous examples Marshall et al. 2006: 3D, l 100 and b 10, 15' resolution Besançon model fitted on 2MASS data 53

54 Extinction model : some famous examples 2D bulge extinction maps based on the Red Clump colour Sumi et al. 2004, on OGLE-II (V,I) Gonzalez et al. 2012, on VVV (J,H,Ks) 54

55 Extinction models in GES 2D bulge (Gonzalez et al. 2012) for the bulge 2D (Schlegel et al. 1998) for the halo/thick disc 3D (Marshall et al. 2006) for the thin disc kinematics 55

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