Population synthesis models and the VO RGB and AGB role in population synthesis models Maurizio Salaris ARI – Liverpool John Moores University Maurizio Salaris Astrophysics Research Institute Liverpool John Moores University “BaSTI for population synthesis” project in collaboration with: Susan Percival, Santi Cassisi, Adriano Pietrinferni BaSTI pop. synthesis project in collaboration with Susan Percival, Santi Cassisi, Adriano Pietrinferni

OUTLINE What/why population synthesis ? The role of RGB and AGB Some quantitative examples of the effect of uncertainties in RGB/AGB models Differences among population synthesis models with different RGB/AGB treatment Empirical calibrations from integrated light: possible ? Conclusions

WHAT Stellar population synthesis models are tools for interpreting the integrated light that we observe from unresolved stellar populations (galaxies, star clusters). A so-called ‘population synthesis model’ provides the integrated spectrum and magnitudes/colours (plus mass to light-ratios in various wavelength bands) of a stellar population with a given star formation history and IMF BaSTI, GALAXEV, Pegase, Starburst99, Buzzoni, GALEV, Vazdekis, SED@+ others

Population synthesis: Ingredients Library of stellar spectra Stellar model/isochrone library

isochrone is specified by (L, Teff, M, [Fe/H]) or also Isochrones. Each point along an isochrone is specified by (L, Teff, M, [Fe/H]) or also (Teff, g, [Fe/H]) Stellar spectra. Each spectrum is specified by (Teff, g [Fe/H]) Integrated spectrum Effect of dust IMF to give number of stars along isochrone for a fixed total mass of the population Nebular emission Line index strengths, integrated colours, magnitudes mass-to-light ratios K-correction

Use of pairs of integrated colours e.g. Hempel et al. (2003) Age-metallicity degeneracy ↓ James, Salaris et al. (2006)

Use of several photometric bands Technique described by, e.g. Anders et al. (2004)

Use of integrated spectra: line indices See, e.g. Worthey et al. (1994)

Use of integrated spectra: spectrum fitting GALAXEV models

The role of RGB and AGB stars Solar BaSTI

The role of RGB and AGB stars From Coelho et al. (2007)

Some quantitative tests of the sensitivity to RGB/AGB stars Mismatch between models and spectra for stars with Teff < 5000 K and log(g) < 3.0 3 Gyr 6 8 10 14 Red triangles  Teff + 100 K Blue circles  log(g) + 0.25 dex Asterisks  [Fe/H]±0.15 dex Open triangles  Teff + 100 K (whole isochrone) [Fe/H]= −0.7 −0.35 +0.06 +0.40

Number of RGB stars above the HB level reduced by a factor 2 6 Gyr 8 10 14 [Fe/H]= −1.3 −1.0 −0.7 −0.29 +0.05 [α/Fe]=+0.4

Mismatch between models and spectra of RGB stars Blue circles  Teff + 100 K Mismatches in g and [Fe/H] have negligible effect on these colours 14 Gyr 10 8 6 3 Blue circles  N/2 ‘Wrong’ RGB star counts above the ZAHB [Fe/H]=−0.7 −0.35 +0.06 +0.40

Varying the RGB mass loss η Reimers increased from 0.2 (reference) to 0.4 for the 14 Gyr old sequence ↓

Differences between different sets of models BaSTI Maraston (2005) bol V K

Different AGB contribution  different ages

Statistical fluctuations of integrated magnitudes !! Can we calibrate AGB/RGB modelling on the integrated colours of star clusters ? Statistical fluctuations of integrated magnitudes !! See also analytical work by Cervino & Luridiana

Fluctuation of  luminosity ratios

Co-add clusters with similar properties BaSTI (black) Mar05 (red) Padua 08 (blue) Co-added data from Gonzalez et al. (2004). Individual cluster data from Kyeong et al. (2003)

Different result from Mucciarelli et al. 2009 Maraston 2005 models

SBF and AGB calibration Definition of fluctuation luminosity BaSTI Data from Gonzalez et al. (2004)

Calibration on resolved star clusters INTEGRATED SPECTRA Index fluctuations in star clusters

CONCLUSIONS Inconsistent Teff and g scales between isochrones and spectra have a relatively small effect on the main Lick-type spectral indices, and a larger effect on colour-colour diagrams Star counts along the RGB and AGB have potentially a stronger effect on the ages derived from integrated colours and spectral indices Mass loss along the RGB has a very strong effect on ages derived from integrated colours and spectral indices. The overall modelling of the AGB phase has a strong influence on ages and metallicities derived from colour-colour diagrams. Empirical calibrations of the AGB contribution to the integrated fluxes (and spectral indices) are problematic and at present lead to some contradicting results.