how to simulate the gaia products francesca figueras universidad de barcelona (spain)

How to simulate the Gaia products

Francesca FiguerasUniversidad de Barcelona (Spain)

How to simulate the Gaia products

Generalities: • Brief description of what Gaia will provide• Gaia Science Performances• Few examples of Gaia Scientific Challenges

The Gaia error models Additional tools for Gaia errors computation:

• Fortran code• Python code

Application to a sample of Red Clump stars

Gaia focal plane

AstrometryG band

LR spectraGBP, GRP

bands

HR spectraGRVS band, Vr,

Vsini

Astrophysical parameters: Teff, logg, [Fe/H], Ao (interstellar absorption) , [/Fe]

GOG: epoch parameters (per transit)

Epoch data will be provided in the last Gaia releases and will be mostly used to determine properties of multiple systems and variable sources

GOG: combined parameters (end-of-mission data)

Gaia Science Performances

A. Brown

Equatorial coordinates, units: mas (Palmer, Luri et al., 2013, in prep)

Scanning law (large number of transits)

The Galactic Center (large number of faint

stars)

Sky map of the mean parallax error

A. Brown

CRITICAL

Halo K1III, 4kpc, G= 15 10 % error in parallax

Solar type star, 1kpc, G=15, 3% error in distance, tangential Vel. Error < 1 km/s

Example of the Gaia capabilities

HIP 60350 (Runaway, B-star, 3.5 kpc)At the moment, the quality of the observational data is insufficient to pinpoint the

precise origin of the star within the spiral arm (cluster birthplace?)Gaia parallax accuracy ~10 as (G~11), 3 % accuracy in the relative parallaxWas the star originated some ≈15 Myr ago, in the Crux-Scutum spiral arm?

Irrgang, A., et al. 2010

The distance to LMC and SMC

GUMS: Based on a real catalogue:7.5·106 (LMC), 1.5 106 (SMC) with G<20

Distance estimate from Gaia: Large error in individual distances (LMC ~ 20 as)

Maximum Likelihood techniques mandatory (Luri et al., 1996)Relative error in mean distance: 0.5% (LMC), 1.5% (SMC) No 3D map

SMC with OGLE (Haschke et al., 2012): Cepheids (2522 stars): 63.1 3.0 kpc , 4.7 % accuracy RR Lyrae (1494 stars): 61.5 3.4 kpc , 5.5 % accuracy

R136, the star cluster in the Tarantula (30 Doradus)

Gaia (GIBIS) HST

GIBIS: Gaia Basic Image Simulator Stellar density at G<20 ~1.4 106 stars /sqdeg

de Bruijne and de Marchi, 2011

GAIA’s view R136 (LMC)

Transverse velocities ~1-2 km/s accuracy

G=12-15 mag (~10 as/yr)

de Bruijne and de Marchi, 2011

Gaia error modelsAstrometryPhotometry

SpectraRadial Velocities

Rotational velocities Astrophysical Parameters

We describe here:1) GOG approach2) the receipts published in the Gaia Science Performance website

http://www.rssd.esa.int/index.php?page=Science_Performance&project=GAIA

Gaia Science Performance web page

http://www.rssd.esa.int/index.php?page=Science_Performance&project=GAIA

Astrometry

The mean end-of-mission standard error for parallax includes:• all known instrumental effects• an appropriate calibration error• 20 % margin (results from the on-ground data processing are not

included)

Astrometric standard errors Gaia Science Performance website

It depends sensitively on the adopted TDI-gate scheme (G < 12 mag) (The decrease of the CCD exposure time to avoid saturation of the pixels)

End-of-mission parallax standard error

For bright stars (G<12 mag) the standard error is dominated by calibration errors, not by the photon noise

Astrometric End-of-mission errors Gaia Science Performance website

The end-of-mission performance depends on the scanning law. A more accurate standard error can be computed by:

1)Multiplying the mean value by a geometrical scaling factor (g), different for each of the five parameters (see figure and table) 2)Taking into account the individual number of transits the star will have by multiplying the mean error value by

Both corrections depend on the mean ecliptic latitude β of the source (ecliptic-longitude-averaged)

Geometrical scaling factor: Each particular transit does not carry the same astrometric weight. The weight depends on the angle between the along-scan direction (where we make the measurement) and the circle from the star to the sun (the parallax shift is directed along this circle). Therefore, a large number of transits does not guarantee a small parallax error (Jos de Bruijne)

Obtained from differential along-scan measurements between the two FoV. The error depend on the Γ angle (0.5 μas accuracy)

Parallactic displacement along the great cicle Sun-StarSensitivity AL is proportional to sin ξ sin Γ

ξ = Sun-spin axis angle = 45º for GaiaΓ = basic angle = 106.5º for Gaia

Optimal values between astrometry requirements - that call for a large angle - and implementation constraints - such as payload shading and solar array efficiency

Absolute parallaxes

Geometric factor (g) to be applied to the sky-averaged astrometric errors for the five astrometric parameters as function of ecliptic latitude β.

GOG: astrometric Epoch DataFor each transit GOG provides: -Local plane coordinates (, z)-Observing time (t), that is mean time per transit-Angle from local plane coordinates to equatorial coordinates ()-Precision in the local plane coordinates (, z)

n : along scan AF number of CCDspr : relation between AC and AL pixel size (=3): line spread function centroiding error

GOG: astrometric epoch dataExample of GOG products: Orbital motion for a binary system from GOG epoch data astrometry

Units: mass

Astrometric end-of-mission

g = 0.787·g

g = 0.699·g

g = 0.556·g

g = 0.496·g

End-off-mission longitude-proper-motion standard error respect to the mean (G=20 mag, meand 175 as/yr)

Photometry

Photometry

Magnitudes: G : broad-band (white-light),

fluxes obtained in the astrometric instrument

GBp and GRp: integrated from low resolution spectra

GRVS: integrated from RVS spectrometer

Includes all known instrumental effects + 20% science marginThis is the single-field-of-view transit, taking into account all CCDs along scan

Photometric standard errors per transit Gaia Science Performance website

Includes all known instrumental effects + 20% science margin

Photometric standard errors per transit Gaia Science Performance website

Estimated precisions for G for one transit on the focal plane with respect to the G The shape for bright stars is due to the decrease of the exposure time

to avoid saturation of the pixels.

GOG: Photometric standard error per CCD-transit

End-of-mission photometric standard errors

Gaia Science Performance website

• division of the single-field-of-view-transit photometric standard errors by the square root of the number of observations (~70 in average).• With an assumed calibration error of 30 mmag at CCD-level

Units: mmag

DPG: factor that takes into account the detection probability. It gives the probability that a star is detected and selected on-board for observation (TB implemented in GOG)

GOG: End-off-mission Photometric standard error

Jordi et al. (2010)

BP/RP/RVS spectra

BP/RP/RVS spectra Low-resolution spectro-photometry obtained in the Blue and Red Photometers

Spectral dispersion & wavelength range: BP: ~3 to ~27 nm pixel-1 ~330-680 nm RP: ~7 to ~15 nm pixel-1 ~640-1050 nm1 CCD along scan each

RVS spectrometer: Resolving power ~11,500 wavelength range: 847-874 nm. 3 CCDs (strips) along scan

End-of-mission SNR per band

Radial Velocities

End-of-mission radial velocity error Gaia Science Performance website

Errors are magnitude (V= Johnson Visual) and colour dependent (V-I)

Receipts outlined by JdB-022 (2005) At the time of the Gaia Mission Critical Design Review (April 2011)

From Sartoretti et al. (2007):-Monte Carlo simulations-Errors depending on Teff FeH logg vsini Vmag

GOG: End-of-mission radial velocity error

Rotational Velocities (Vsini)

GOG: End-of-mission rotational velocity error

Astrophysical Parameters (AP)

Remember that one of the most important Gaia goals is to reveal the formation and evolution of our Galaxy through

chemo-dynamical analysis

Gaia focal plane

AstrometryG band

LR spectraGBP, GRP

bands

HR spectraGRVS band, Vr,

Vsini

Astrophysical parameters: Teff, logg, [Fe/H], Ao (interstellar absorption) , [/Fe]

Astrophysical parameters are derived from (Liu et al., 2012): 1)BP/RP spectra (GOG)2)the parallax3)apparent magnitude of the star

Outputs from this work are:

1) Specific uncertainty estimates provided by Aeneas

2) Residuals computed as |estimated –true| values

GOG: AP error model

Aeneas-pq precision |estimated values from Aeneaspq – true|

Teff

Caution: different vertical scale!


Ao (absorption)

Liu et al. (2012), Antiche et al. (2012, in preparation), see Bailer-Jones (2011) for the definition of Ao



Log g



[Fe/H]


The thin disk is metal-rich and covers a wide age rangeThe other stellar components are all relatively old(note similarity of [Fe/H] range for thick disk and globular clusters)

The red points are potential omega Cen debris candidates.Less -enriched than other halo stars : implies a longer history of chemical evolution, as observed in omega Cen itself

Element abundances[/Fe] vs [Fe/H]

(Meza et al 2006)

Additional tools for Gaia errors computation:

1.Fortran code2.Python code

Application to a sample of Red Clump stars

The Red Clump Stars The Galactic Bar (s) and the Spirals

M. Romero-Gómez et al. 2013

Red Clump Stars: helium burning in the nuclei at a well defined luminosity

Hipparcos distances

Galactic disk space distribution function

Red clump surface density

1/ is a biased estimates of the true distance!!

Does our Galaxy have one/two bars?work in the space of the observables!

distances parallaxes Romero-Gómez et al. 2013

Does our Galaxy have one/two bars?work in the space of the observables!

Extinction is critical: A new 3D new map using Gaia and IR

Red Clump: accuracy in tangential velocities

Gaia data Gaia + IR distances (10%) Mandatory to combine Gaia and IR data

Gaia and the distance scale

63

1912: Henrietta Leavitt discovered the key for the distance scale of the Universe

Period-Luminosity relation (25 cepheids in the SMC)

The Cepheids

Gaia will observe ~9000 Cepheids (extrapolated from Berdnikov et al. cat)Gaia: Metallicity dependence of the PL relation

Windmark et al., 2011

Hipparcos suspected binarity in Cepheids

~ 50 % binaries, the companion star affect the brightness and motionGaia will treat several of them as binaries (astrometric orbit)

Hipparcos vs. 'ground-based' parallax

Hipparcos: no allowance for binarity, thus the motion along the orbital arc could falsify the deduced parallax value.

It is remarkable that all negative parallax values plotted in the figure belong to known binaries (open clicles).

(Laszlo Szabados, 2010)

how to simulate the gaia products francesca figueras universidad de barcelona (spain)

Documents