pre-observations and models · precision and accuracy needed on the final parameters ? p? ......

Pre-observations and models

Carine BabusiauxObservatoire de Paris - GEPI

GREAT-ITN, IAC, September 2012

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 ?

Using models to define where your best constraints are

3

Minchev & Quillen 2007

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

Modelling the observations

Gaia simulation – a quite complete (and complex!) example

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X

simulated observations


Gaia simulation – a quite complete (and complex!) example

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X

X simulated catalogue


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Simple tools are often enough... http://iraf.noao.edu/

Instrument specific exposure time calculators & user manual

http://iraf.noao.edu/

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

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)

Observing Strategy

Goal is to optimize :

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Nfields x Nsetups x exptime(SNR,Vlim) = Nnights

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

The magnitude limit

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mλ=M 0+ 5 log10(d )−5+ Aλ

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 *

SNR

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σ (F )=√ F ¿

SNR

Exposure Time Calculator

http://www.eso.org/observing/etc/

15Mean SNR for a G2V star for GES set-ups

SNR

Exposure Time Calculator

16Mean SNR for a G2V star for GES set-ups

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

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 ?

Contents






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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

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

Astrometry Good precision needed for fibre positioning

23From FPOS User Manual

For FLAMES, accuracy≤ 0.3 arcsec is needed

Astrometry

High proper motion for nearby objects needs to be taken into account!

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White DwarfCopyright © Rochester Institute of Technology.

“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

Checking available data

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http://www.star.bris.ac.uk/~mbt/topcat/

Contents






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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

Object selection : test on empirical data

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Ex: magnitude/colour selection of G2V with Hipparcos / 2MASS

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

Checking total number of targets

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Target selection

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J

Which selection will increase your % of targets ?

Target selection

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What are your contaminants ?

Will they be easy to identify ? remove ? model ?

Target selection

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Easy to model

Enough margin (catalogues and models uncertainties)

Contents






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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

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

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

Presentation






– 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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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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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

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

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


Drimmel et al. 2003:

3D, full sky, model calibrated at ∞ to Schlegel

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Marshall et al. 2006:

3D, |l| ≤ 100° and |b| ≤ 10°, 15' resolution

Besançon model fitted on 2MASS data

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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

pre-observations and models · precision and accuracy needed on the final parameters ? p? ......

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