Analysing data in the Virtual Observatory: Spectra of stellar populations

Spectroscopy and the VO -- Philippe Prugniel -- ESAC 21-23 March 2007

Analysing data in the Virtual Observatory:

Spectra of stellar populations

Philippe Prugniel

Observatoire de Lyon & Observatoire de Paris


Context

• The VO is presented as a mean to facilitate astronomical research– By discovering and accessing data (observations and models)

– By extracting the information (statistics, fits to models …)


Context



• Responsibility of VO is to provide the standards and some infrastructure (like libraries to use the standards, validators…)– Standards for data exchanges, query protocols…

– Description of the data


Context



• Responsibility of VO is to provide the standards and some infrastructure (like libraries to use the standards, validators…)– Standards for data exchanges, query protocols…

– Description of the data

• It is a big task– Because the standards need to be general

– Need consensus in an heterogeneous community

– … need compromises


Guided by science cases

• Classify / identify stellar spectra

• …

• Analyse spectra of stellar populations


Fitting population spectra

Observed spectrum

Modelled spectrum

FitStar Formation History …

As good as possible

Better than the observations

Get as much as possible from the

observations



Observed spectrum

Modelled spectrum


As good as possible



observations

Approaches:Spectrophotometric indices

-> well calibrated, but uses only a fraction of the signalSED fitting (Shape of the spectrum)

-> sensitive to extinction & flux calibration uncertaintiesSpectrum fitting (Absorption lines)

-> importance of the spectral resolution



Observed spectrum

Modelled spectrum


As good as possible



observations

Approaches:Spectrum fitting: Absorption lines

-> importance of the spectral resolutionFits simultaneously the characteristics of the stellar

population and the internal kinematics



Observed spectrum

Modelled spectrum


As good as possible



observations

Approaches:Spectrum fitting: Absorption lines

-> importance of the spectral resolutionFits simultaneously the characteristics of the stellar

population and the internal kinematics

Chilingarian 2006, thesis


Why do we want the VO there?

1) More modularity in the spectral modelling to understand the discrepancies between the codes?

2) Give a simple access to a complex method


Discrepancies between the models

SSPs

Bruzual &Charlot ‘03



SSPs

Inversion byPegase.HR

Le Borgne + ,04



Is it due to the stellar libraries? To the way they are interpolated? To implementation aspects in the programs? To the physics of the model?




Easy…Just have to permute the librariesor the physical ingredients …





Aie…*

The synthesis programs have proprietary formats for the libraries and for the physical ingredients, they are not fully documented nor publicly available…

* Ouch





Aie…The synthesis programs have proprietary formats for the libraries, for the physical ingredients, they are not fully documented not publicly available…

Koleva et al. 2007





Aie…The synthesis programs have proprietary formats for the libraries, for the physical ingredients, they are not fully documented not publicly available…

To understand the differences between analyses performed with various methods and models, ones needs to check individually each ingredient, or each module.We are seeking for interoperable bricks…We need a VO workflow.


Simple access to a complex process

isochronesStellar librariesStellar libraries3D obs & cal

PEGASE.HR

Data reduction

Resolution matching

Adaptive filter (tessellation)

1D-extraction Inversion

Field reconstruction

Galactic extinction

interpolation


Simple access to a complex process

Stellar librariesStellar libraries

interpolation

Elodie interpolator,SSA in the VO(see poster session)

Other benefice of VO services:A function can have different usages than the one for which it was developed…Here: do stellar classification


How to fit?

Server:model

Client:GUIfitting enginevisu

Server:modelfitting engine

Client:GUIvisu

or


Spectra of stellar populations: summary

• Use the VO as a framework for the comparisons of the ingredients of complex models

• Extract individual functions of a wider interest, useful in different contexts

• Develop workflows in the VO

Analysing data in the Virtual Observatory: Spectra of stellar populations

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