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Pre-observations and models · Precision and accuracy needed on the final parameters ? P? ......
Transcript of Pre-observations and models · Precision and accuracy needed on the final parameters ? P? ......
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Pre-observations and models
Carine BabusiauxObservatoire de Paris - GEPI
GREAT-ITN, IAC, September 2012
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The questions
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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 ?
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Using models to define where your best constraints are
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Minchev & Quillen 2007
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Using models to define the precision needed
4Antoja et al. 2010
Sun
Vr (km/s)
μ β (m
as/y
r)
+ GAIA errors+ survey σ(Vr)=2 km/s
l = 305°dist = 7 kpc
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Modelling the observations
Gaia simulation – a quite complete (and complex!) example
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X
simulated observations
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Modelling the observations
Gaia simulation – a quite complete (and complex!) example
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X
X simulated catalogue
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Modelling the observations
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Simple tools are often enough... http://iraf.noao.edu/
Instrument specific exposure time calculators & user manual
http://iraf.noao.edu/
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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 models8
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Field observability from the telescope !
http://www.eso.org/sci/observing/tools/calendar/observability.html
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Sky accessibility for one of the VTL
Air mass ≈ 1/cos(ZA)
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Observing Strategy
Goal is to optimize :
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Nfields x Nsetups x exptime(SNR,Vlim) = Nnights
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Observing Strategy
Example for spectroscopy : trade-offs to analyse :
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Nfields x Nsetups x exptime(SNR,Vlim) = Nnights
1) Radial Velocities
2) Teff, logg, [M/H]
3) Individual abundances
Resolving power R = λ / ΔλSNR
Wavelength coverage
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The magnitude limit
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mλ=M 0+ 5 log10(d )−5+ Aλ
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SNR
Signal-to-noise ratio (S/N or SNR)
signal : total number of photons of the source (F*)
noise :
– photon noise [ Poisson distribution : ]
– background noise
– dark current
– read-out noise
For bright stars :
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σ (F *)=√ F *
SN
=F*
σ (F *)=√ F *
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SNR
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σ (F )=√ F ¿
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SNR
Exposure Time Calculator
http://www.eso.org/observing/etc/
15Mean SNR for a G2V star for GES set-ups
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SNR
Exposure Time Calculator
16Mean SNR for a G2V star for GES set-ups
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SNR
Check the wavelength of your main spectral features...
17 UVES 580 SNR for a G2V star with V=15, 4*45 min exposure time
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Which wavelengths ? Resolution ? SNR ? Tests using synthetic or observed standard spectra with different SNR
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Tests made by A. Recio-Blanco et al. for GES
→ which set-ups ?→ which SNR ?
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Contents
1. Observing strategy – the trade-offs
2. Supporting catalogues
3. Testing the target selection
4. Extra considerations
5. Modelling the observations
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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
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Current main photometric surveys
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Survey H Filters Mag Lim Area Dates
GALEX - FUV,NUV 20.5 4 π 2003
OGLE S V,I 20.5 1992-2014
SDSS N u,g,r,i,z 22.0 / 20.5 1.4 π 2000-2009
IPHAS / VPHAS+ N/S (u,g),r,i,Hα 20 / 21 0.4 π 2003-2006 / 2012
APASS N/S B,V,g,r,i 17 4 π 2010-2013
SkyMapper S u,v,g,r,i,z 22.9 / 21.5 2 π 2009-2014
Pan-STARRS N g,r,i,z,y 24 3 π 2012-2022
2MASS N/S J,H,Ks 15.8 / 14.3 4 π 1997-2001
UKIDSS N (Z,Y),J,H,K 19.4 / 17.8 0.7 π 2005
VISTA S (Z,Y),J,H,Ks 20 / 18 2 π 2010
GLIMPSE - IR 0.2 π 2004
WISE - IR 4 π 2010
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Current main all sky astrometric surveys
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Survey Accuracy Mag Lim Nb stars
USNO-B1 200 mas V=21 1 billion
Tycho-2 60 mas V=12 2.5 million
UCAC-4 20-70 mas R=16 40 million
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Astrometry Good precision needed for fibre positioning
23From FPOS User Manual
For FLAMES, accuracy≤ 0.3 arcsec is needed
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Astrometry
High proper motion for nearby objects needs to be taken into account!
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White DwarfCopyright © Rochester Institute of Technology.
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“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
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“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
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Checking available data
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http://vizier.u-strasbg.fr/viz-bin/VizieR
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Checking available data
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http://www.star.bris.ac.uk/~mbt/topcat/
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Contents
1. Observing strategy – the trade-offs
2. Supporting catalogues
3. Testing the target selection
4. Extra considerations
5. Modelling the observations
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Object selection : test on synthetic data
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Ex: MS turn-off colour with Padova isochrones
http://stev.oapd.inaf.it/cgi-bin/cmd
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Object selection : test on empirical data
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Ex: magnitude/colour selection of G2V with Hipparcos / 2MASS
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Object selection : test on empirical data
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Ex: giant branch shape using Globular Clusters
[Fe/H]=-0.9
J-K
K
Ferraro et al. 2000
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Checking total number of targets
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Target selection
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J
Which selection will increase your % of targets ?
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Target selection
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What are your contaminants ?
Will they be easy to identify ? remove ? model ?
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Target selection
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Easy to model
Enough margin (catalogues and models uncertainties)
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Contents
1. Observing strategy – the trade-offs
2. Supporting catalogues
3. Testing the target selection
4. Extra considerations
5. Modelling the observations
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Multi-epoch
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Variability detection as a goal (primary or secondary) of the survey
(variable stars, binaries, proper motion...)
Removing pollution
– Cosmic rays
– Variables, binaries... removal
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Multi-epoch
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Un-detected binaries
→ abundances determination bias1% flux contamination can produce a 0.1 dex bias (Erspamer & North 2003)
→ Vr dispersion biasExtra Vr dispersion due to un-detected binaries on solar type stars at V=18 mag is ~ 8 km/s
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Calibrators
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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
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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
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Stellar population synthesis model
The Besançon model http://model.obs-besancon.fr/
The TRILEGAL modelhttp://stev.oapd.inaf.it/cgi-bin/trilegal
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Stellar population synthesis model - ingredients
4 components: thin disc, thick disc, halo, bulge
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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
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Stellar population synthesis model - ingredients
Evolutionary tracks (Padova, Dartmouth, BaSTI,Y2...)
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Stellar population synthesis model - ingredients synthetic spectral libraries (Basel2, ATLAS, MARCS, Phoenix...)
→ photometry in the required filters
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Stellar population synthesis model - ingredients Extinction law
47Cardelli et al. 89 & Fitzpatrick 99
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Spectral features
Synthetic spectra (ATLAS, MARCS, PHOENIX...)http://pollux.graal.univ-montp2.fr/ Lines identification in spectral standard atlases (e.g. solar) http://spectra.freeshell.org/spectroweb.html Checking sky emission and telluric absorptionhttp://www.eso.org/observing/dfo/quality/UVES/uvessky/http://www.eso.org/sci/facilities/eelt/science/drm/tech_data/background/
ISM absorption lines + DIBShttp://leonid.arc.nasa.gov/DIBcatalog.html
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Spectral features
49From Battaglia et al. 2008
Sky emission example in FLAMES LR08 spectra
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Extinction model
How to chose an extinction model ?― 2D / 3D (map or model)― Sky coverage― Spatial resolution― Accuracy
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Extinction model : some famous examples
Schlegel et al. 1998:
2D, full sky, 6' resolution, 16% accuracy
from IR photometry of extragalactic objects
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NGPSGP
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Extinction model : some famous examples
Drimmel et al. 2003:
3D, full sky, model calibrated at ∞ to Schlegel
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Extinction model : some famous examples
Marshall et al. 2006:
3D, |l| ≤ 100° and |b| ≤ 10°, 15' resolution
Besançon model fitted on 2MASS data
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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)
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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
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Diapo 1Diapo 2Diapo 3Diapo 4Diapo 5Diapo 6Diapo 7Diapo 8Diapo 9Diapo 10Diapo 11Diapo 12Diapo 13Diapo 14Diapo 15Diapo 16Diapo 17Diapo 18Diapo 19Diapo 20Diapo 21Diapo 22Diapo 23Diapo 24Diapo 25Diapo 26Diapo 27Diapo 28Diapo 29Diapo 30Diapo 31Diapo 32Diapo 33Diapo 34Diapo 35Diapo 36Diapo 37Diapo 38Diapo 39Diapo 40Diapo 41Diapo 42Diapo 43Diapo 44Diapo 45Diapo 46Diapo 47Diapo 48Diapo 49Diapo 50Diapo 51Diapo 52Diapo 53Diapo 54Diapo 55Diapo 56