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How to simulate the Gaia products Francesca Figueras Universidad de Barcelona (Spain)

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Presentation on theme: "How to simulate the Gaia products Francesca Figueras Universidad de Barcelona (Spain)"— Presentation transcript:

1 How to simulate the Gaia products Francesca Figueras Universidad de Barcelona (Spain)

2 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

3 Gaia focal plane Astrometry G band LR spectra GBP, GRP bands HR spectra GRVS band, Vr, Vsini Astrophysical parameters: Teff, logg, [Fe/H], Ao (interstellar absorption), [  /Fe]

4 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

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

6 Gaia Science Performances

7 A. Brown

8 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

9 A. Brown CRITICAL Halo K1III, 4kpc, G= 15  10 % error in parallax

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

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12 Example of the Gaia capabilities

13 HIP (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 parallax Was the star originated some ≈15 Myr ago, in the Crux-Scutum spiral arm? Irrgang, A., et al. 2010

14 The distance to LMC and SMC GUMS: Based on a real catalogue: 7.5·10 6 (LMC), (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

15 R136, the star cluster in the Tarantula (30 Doradus) Gaia (GIBIS) HST GIBIS: Gaia Basic Image Simulator Stellar density at G<20 ~ stars /sqdeg de Bruijne and de Marchi, 2011

16 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

17 Gaia error models Astrometry Photometry Spectra Radial Velocities Rotational velocities Astrophysical Parameters We describe here: 1)GOG approach 2)the receipts published in the Gaia Science Performance website

18 Gaia Science Performance web page

19 Astrometry

20 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)

21 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

22 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)

23 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-Star Sensitivity AL is proportional to sin ξ sin Γ ξ = Sun-spin axis angle = 45º for Gaia Γ = 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

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

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26 GOG: astrometric Epoch Data For 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 CCDs p r : relation between AC and AL pixel size (=3)   : line spread function centroiding error

27 GOG: astrometric epoch data Example of GOG products: Orbital motion for a binary system from GOG epoch data astrometry Units: mass

28 Astrometric end-of-mission g  = 0.787·g  g  = 0.699·g  g  = 0.556·g  g  = 0.496·g 

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

30 Photometry

31 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

32 Includes all known instrumental effects + 20% science margin This is the single-field-of-view transit, taking into account all CCDs along scan Photometric standard errors per transit Gaia Science Performance website

33 Includes all known instrumental effects + 20% science margin Photometric standard errors per transit Gaia Science Performance website

34 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

35 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

36 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)

37 BP/RP/RVS spectra

38 Low-resolution spectro-photometry obtained in the Blue and Red Photometers Spectral dispersion & wavelength range: BP: ~3 to ~27 nm pixel-1 ~ nm RP: ~7 to ~15 nm pixel-1 ~ nm 1 CCD along scan each RVS spectrometer: Resolving power ~11,500 wavelength range: nm. 3 CCDs (strips) along scan

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40 End-of-mission SNR per band

41 Radial Velocities

42 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)

43 From Sartoretti et al. (2007): -Monte Carlo simulations -Errors depending on Teff FeH logg vsini Vmag GOG: End-of-mission radial velocity error

44 Rotational Velocities (Vsini)

45 GOG: End-of-mission rotational velocity error

46 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

47 Gaia focal plane Astrometry G band LR spectra GBP, GRP bands HR spectra GRVS band, Vr, Vsini Astrophysical parameters: Teff, logg, [Fe/H], Ao (interstellar absorption), [  /Fe]

48 Astrophysical parameters are derived from (Liu et al., 2012): 1)BP/RP spectra (GOG) 2)the parallax 3)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

49 Aeneas-pq precision|estimated values from Aeneaspq – true| Teff Caution: different vertical scale!

50 Aeneas-pq precision|estimated values from Aeneaspq – true| Ao (absorption) Liu et al. (2012), Antiche et al. (2012, in preparation), see Bailer-Jones (2011) for the definition of Ao Caution: different vertical scale!

51 Aeneas-pq precision|estimated values from Aeneaspq – true| Log g Caution: different vertical scale!

52 Aeneas-pq precision |estimated values from Aeneaspq – true| [Fe/H] Caution: different vertical scale!

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

54 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)

55 Additional tools for Gaia errors computation: 1.Fortran code 2.Python code Application to a sample of Red Clump stars

56 The Red Clump Stars The Galactic Bar (s) and the Spirals M. Romero-Gómez et al. 2013

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

58 Galactic disk space distribution function Red clump surface density 1/  is a biased estimates of the true distance!!

59 Does our Galaxy have one/two bars? work in the space of the observables! distances parallaxes Romero-Gómez et al. 2013

60 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

61 Red Clump: accuracy in tangential velocities Gaia data Gaia + IR distances (10%) Mandatory to combine Gaia and IR data

62 Gaia and the distance scale

63 : Henrietta Leavitt discovered the key for the distance scale of the Universe Period-Luminosity relation (25 cepheids in the SMC)

64 The Cepheids Gaia will observe ~9000 Cepheids (extrapolated from Berdnikov et al. cat) Gaia: Metallicity dependence of the PL relation Windmark et al., 2011

65 Hipparcos suspected binarity in Cepheids ~ 50 % binaries, the companion star affect the brightness and motion Gaia 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)


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