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GAIA: Derivation of Stellar Parameters
C. Jordi, J.M. Carrasco, F. Figueras, J. Torra, X. Luri, E. Masana
Universitat de Barcelona - IEEC, Avda. Diagonal 647, 08028 Barcelona, Spain
The GAIA mission, the next ESA Cornerstone 6 (launch 2010- 2012), will create a precise three dimensional map of about one billion stars throughout our Galaxy and beyond. To reach the scientific goals, that is to
quantify the dynamical, chemical and star formation evolution of the Milky Way, it is crucial to also accurately determine astrophysical parameters through the measured flux for the observed objects (effective
temperature, luminosities, global metallicity, ages, chemical anomalies,...). The spectrophotometric instrument on board GAIA, combined with the two astrometric instruments, will provide this information.
The medium and broad band photometric systems proposed for GAIA are presented. We discuss their capability to characterize the galactic populations than can be observed. The accuracy expected in the derivation of
astrophysical parameters using jointly astrometry and medium band GAIA photometry is also presented.
Scientific goals
Satellite & system (April 2002 design status)
Galactic Structure: origin and history of our Galaxy - tests of hierarchical
structure formation - inner bulge/bar dynamics - disk/halo interactions –
Star Formation and Evolution: dynamics of star forming regions - luminosity
function - complete and detailed local census down to single brown dwarfs
Distance Scale and Reference Frames: parallax calibration of all distance scale
indicators - definition of the local, kinematically non-rotating metric
Local Group and Beyond: rotational parallaxes for Local Group galaxies kinematical separation of stellar populations - internal dynamics of Local Group
dwarfs - detection of supernovae
Solar System: 105-106 new minor planets - taxonomy and evolution
Extra-Solar Planetary Systems: complete census of large planets out to 200-500
pc - orbital characteristics of several thousand planets
Fundamental Physics: determination of space curvature parameter g to 1 part in
5.10-7
ASTRO telescopes and focal plane
~ 750 mm
0.92 deg
• Launch: Proton
•Orbit: Sun-Earth L2 (Lissajous)
•Continuous scanning
600 mm
0.737 deg
• Two astrometric instruments
• Monolithic mirrors
• Non-deployable, 3-mirror, SiC optics
• Astro focal plane: TDI CCDs
• Radial velocity/photometry telescope
• Astrophysically driven payload:
• faint stars, to V=20 mag
• radial velocities
• broad-band photometry: chromaticity
• medium-band photometry: astrophysics
• Survey principles:
• revolving scanning
• on-board detection
• complete and unbiased sample
AF1-11
ASM1 ASM2
BBP
ASM: astrometric sky mappers
Astro field #1
AF1-11: astrometric field
Astro field #2
The scientific goals of GAIA require complementary
astrometry, photometry and radial velocity data
Main performances and capabilities
BBP: broad-band photometer
MBP: medium-band photometer
SPECTRO telescope and focal plane
Astrometric accuracy in as
RVS: radial velocity spectrometer
G (~V mag) 10 11 12 13 14 15 16 17 18 19
20
21
2 deg = 120 s = 74 mm
15%
Vignetted field
MBP #1 field height 1.6 deg
(60 mm)
0%
For more information please contact C. Jordi [email protected])
1.4 x 0.5 m2
> 0.86
10 x 30 μm2
44.2 x 133 mas2
1 x 10
11 x 10
5 x 10
3.3 s, 1.9 s
2 x 41
Entrance pupil
Optical transmission
Pixel size
Pixel size (angular)
Sample size (in pixels)
Number of CCDS in Astro
Number of CCDS in BBP
TDI integration time per chip
Average total obs/object
Entrance pupil
Optical transmission
Pixel size
Pixel size (angular)
Mission livetime: 5 years
m2
0.5 x 0.5
> 0.92
10 x 15 μm2
1 x 1.5 arcsec2
MBP
Mean number of observations per object during
mission:
RVS field height 1.6 deg
(60 mm)
RVSM
(located in telescope
focal plane, in vignetted field)
Astrometric field: 82 x 11 CCDs
Broad-band phot: 82 x 4 passbands
Medium-band phot: 204 x 11 passbands
MBP #2 field height 1.6 deg
(60 mm)
0%
Sample size (in pixels)
Number of CCDs
TDI integration time per chip
Average total obs./object 2 x 102
Spectral range
Spectral sampling
RVS
1x4
1x3
2 x (1+15) 1+6
5.5 s
16.8 s
102
849-874 nm
0.375 Å/pixel
Parallax
4
4
4
5
7 11 17 27 45 80 160 500
Position
3
3
3
4
6
9 15 23 39 70 140 440
Annual proper motion
3
3
3
4
5
8 13 20 34 60 120 380
Accuracies:
 4 as at V = 10 10 as at V = 15 0.2 mas at V = 20
 complete astrophysical sample: one billion stars
 1 km/s radial velocities complete to V = 17.5
 sky survey at ~ 0.25 arcsec spatial resolution to V = 20
 multi-colour multi-epoch photometry to V = 20
 dense quasar link to inertial reference frame
Capabilities:
 10 as  10% at 10 kpc  1 AU at 100 kpc
 10 as/yr at 20 kpc  1 km/s
 every star in the Galaxy and Local Group will be seen to move
 GAIA will quantify 6-D phase space for over 300 million stars
and 5-D phase-space for over 109 stars
Vignetted field
Radial velocity: 102 single observations
15%
The GAIA photometry
Broad band system
Goals
Correct chromatic aberrations in the astrometric focal
microarcsec accuracy level (BBP)
plane to achieve
Characterization of the observed objects in terms of astrophysical
parameters. (BBP+MBP)
Classification: star (single/multiple), solar system object, galaxy, QSO
Stellar astrophysics parameters: Teff, luminosity, chemical composition
([Fe/H], [α/Fe], C/O, ...), peculiarities, emssion,…
Solar system: taxanomy classification, variability, ...
QSO: photometric redshif
Galaxies: colours,…
Medium band system
The four (or five) broad band photometric filters will provide multicolour, multi-epoch photometric measurements for each object
observed in the astrometric field.
Considerable effort is being devoted to
the design of an optimum system for
GAIA, taking into account the spectral
energy distribution of the main
galactic stellar populations, as derived
from
model
atmosheres
and
spectrophotometric observations), as
well as the experience with existing
photometric systems.
Several filter transmision curves are being designed and tested to
optimize the BBP system for chromaticity calibration. Artificial
neural networks (among other techniques) are being used for this
purpouse.
Although somewhat redundant in terms of astrophysical
information content , BBP will supply higher S/N and angular
resolution than MBP, so useful for QSO and galaxy photometry
aplications.
The figures show some examples and the accuracy achivable
At present, 2F (shown in the figure) is
the base-line photometric system for
GAIA (final system by mid-2005).
G band in the astrometric fields
Very broad band: ~ 300-1050 nm
• Small bolometric correction
• 11 CCDs per passage (3.3s per CCD)
• 82 observations
• The best S/N for variability detection
•Glim~ 20
Vlim~ 20-25
• G-V is a function of SP and reddening
•
Example of a BBP colourcolour diagram for different
gravities and metallicities.
Arrow indicates reddening for
Av=1. Error bars indicate endof-mission errors for a source
with G=18.
Light curves: precision at V~20 as
Hipparcos at V~9
G magnitude accuracy (mag)
Photometric accuracy (in mag) in the spectro telescope in each of the relevant colour indices derived from the 11
medium photometric bands (2F system). The accuracy has been computed for an unreddened star. The abundance
of -elements is measured through the MgH reddening free index (QIMg) in the F and G stars and through the
QITiO reddening free index for later (K and early M) stars. QICN is used to measure the N abundance of red
stars with Teff < 4200 K.
Chemical composition determination
Temperature determination
Several passbands to
measure the continuum
Precision of 1-3% in Teff,
is achievable at G~19
K giant (Teff= 4500 K, log g=3.0)
M dwarf (Teff= 3500 K, log g=4.5)
(An error of 0.02 mag in E(b-y) is assumed)
Brown dwarfs: Chamaeleon #7 (M8 V)
Teff = 3500 K
(3 filter combinations)
V= 22.2 , (V-I) = 5.3, G = 18.8 mag
Δπ/π = 0.014
σM = 0.030
Av=0.26 mag, Teff ~ 2700 K, M= 0.05 Msun
0.2-0.3 dex precision is achievable at G~19
σTeff= 20-30K
Observed spectra of Chamaeleon #7 (provided by F.
Comerón). GAIA 75,78,83,89 filters are overploted
Expected accuracy of the location of Chamaeleon #7
in the HR diagram. Models from Baraffe et al. (1998).
Good
derivation of
Mass and age
Oxigen rich and Carbon rich
classification (variation with
phase)