Spectroscopic auxiliary data :
Empirical stellar spectra
Why we need real spectra for GAIA ?
What spectra are required ?
Do we need new observations ?
Caroline Soubiran
Observatoire de Bordeaux
Stellar parametrization from GAIA RVS and MBP-BBP :
Teff, logg, [Fe/H], Av, [X/Fe]…
Reference system : templates / calibration stars
Grids of synthetic spectra = provide templates all over
the parameter space with a regular sampling as dense as
desired
But synthetic spectra do not perfectly reproduce real stars
over the whole wavelength range and parameter range because of
simplifying assumptions, uncomplete line data….+ some class of stars
are not well understood and cannot be easily modelised
Spectra of real stars are necessary
¾ to see how different class of stars will appear in the GAIA data space
¾ to assess performances of parametrization algorithms with realistic conditions
¾ to improve grids of synthetic spectra (see POLLUX project)
¾ to study in detail calibration stars
™ « well known » atmospheric parameters and abundances
™ representative of whole parameter space (Teff, logg, [Fe/H], [α/Fe]..)
ƒ Empirical libraries of reference spectra
ƒ Compilations - catalogues
ƒ Observations (homogenity, completness)
What spectra are required ?
For the photometry :
• SEDs from 300 to 1100nm
• relative flux calibration better than 1%
• 1-3 nm resolution (FWHM C1M system from 7nm to 80nm)
• reddening free
For RVS :
• 845-875 nm
• resolution ≥ 11500
For the characterisation of reference stars :
• large optical range
• resolution ≥ 40000
high S/N for all + wide coverage of the parameter space
(ie large number of stars)
Are new observations necessary ?
Or are there enough on-line resources to build adequate libraires ?
- make a complete inventory of available spectrophotometric and HR
spectroscopic resources
- see with theoricians what observational material they need to validate their
models
- define the grid points (astrophysical parameters) for which we would like
to have spectra
- identify reference stars corresponding to these grid points
Critical inventory of available SED libraries in progress
(see http://www.obs.u-bordeaux1/m2a/soubiran/SEDs_inventory.html +
HFA = Hyperleda Fits Archive))
Also the Asiago Database of Spectroscopic Databases
(Sordo & Munari, Monte-Rosa conference, 2002) ?
•The Indo-U.S. Library of Coudé Feed Stellar Spectra (Valdes et al. 2004)
•The ELODIE library (Prugniel & Soubiran 2001, 2004)
•STELIB (Le Borgne et al 2003)
• A Stellar Spectral Flux Library 131 stars (Pickles 1998).
• Stellar spectroscopic atlas (Gunn & Stryker 1983)
•
…….
None of these libraries has the required properties !
MILES (Sanchez-Blazquez et al 2005, submitted)
• wavelength range: 350 - 750 nm
• resolution 0.23 nm (FWHM)
• 1003 stars with a good coverage of stellar properties
• S/N : high
• photometric precision (synthetic B-V) : 0.013 mag (internal), 0.011 (external)
submitted, spectra not yet available
ASTRA (Adelman et al, in project)
• wavelength range: 330 - 900 nm
• resolution 1.4 nm / 7 nm (FWHM)
• stars ??
• S/N ??
• photometric precision : ??
no information about the progress, observations were supposed to start in april 2004
We have 3 possibilities :
1 - Build a completely new library but
- it will take several years
- do we have the competence to make good spectrophotometry ?
- which excellent site and instrument can we use ?
2 - Wait for other projects : MILES and ASTRA
3 - Combine existing libraries (VO tools)
Empirical libraries in the RVS range
• Marrese et al 2003
• Cenaro et al 2003
• Munari & Tomasella 1999
• Montes et al 1999
• Montes et al 1998
• …..
1087 stars but
~250 stars with reliable (Teff, logg, [Fe/H])
~170 stars with measured [α/Fe]
A campaign to measure accurate atmospheric parameters and
abundances, in an homogenous way, is necessary
¾ focus on primary standards which are very well studied to define an initial grid
ex : ~100 stars have been submitted to more than 10 detailed spectroscopic analyses
in the last 20 yr, σ(Teff)=80K, σ(logg)=0.21, σ([Fe/H])=0.11
¾ define a denser grid with secondary standards
ex : what range of apparent magnitude will be optimal for GAIA observation of
these stars (external calibration)
¾ atmospheric parameters and abundances being model-dependant, spectra of
reference stars will have to be re-analysed as models and line data improve
(build a database of EW ?)
¾ a lot of high quality spectra of reference stars will be available in the POLLUX database
in Montpellier but new observations might be necessary for a sake of completness
¾ identify all stars which lack in spectral libraries : hot stars, cool dwarfs, peculiar abundances
emission lines,…
Observational facilities
¾ In France, 2 new echelle spectrographs will be available in 2006 :
SOPHIE@OHP and NARVAL@Pic_du_Midi
well adapted for abundance studies + NARVAL includes the RVS λ-range
¾ GAIA is a priority of the French programmes for stellar physics and galaxies
(PNPS and PNG) --> possible to define a key program
(ex : COROT obtained 12n /semester over 5 years on ELODIE@OHP)
¾ ESO : necessary to have reference stars in the Southern hemisphere
emmi@ntt, ces@3m6, harps@3m6, feros@2m2……
¾ OPTICON telescopes
To be done in the next months :
1 - discuss with theoricians and see what they need to validate their grids of
synthetic spectra
2 - draw up an inventory of useful available spectra and see how they can
be combined
3 - build a catalogue of primary and secondary reference stars
for atmospheric parameters
4 - define observing programs to fill the gaps
5 - find manpower to make the observations, reduce the spectra, measure EW,
determine atmospheric parameters and abundances….