Stellar Population Synthesis with BaSTI

1
Stellar Population Synthesis with BaSTI

• Susan Percival
• Maurizio Salaris
• ( Cassisi, Pietrinferni Castelli)

2
Overview

• Brief description of BaSTI database
• Stellar Population Synthesis programme for
  resolved populations
• Adding spectra to the SPS output
• Work in progress factors affecting line indices
  
• Where next?

3
http//www.te.astro.it/BASTI/index.php
4
BaSTI stellar models and isochrones

• 11 metallicities Z0.0001 to 0.04
• Scaled-solar a-enhanced
• Ages 30Myr to 19Gyr
• All evolutionary phases, including TP-AGB
• 2 values of mass-loss parameter (blue/red HB)
• With and without convective overshooting
• Magnitudes/colours for UBVRIJHKL and HST ACS
  filters
• Full details in Pietrinferni et al. (2004, 2006)

5
Ages metallicities from isochrone fitting to
CMDs
6
Cordier, Pietrinferni, Cassisi Salaris, 2007,
AJ, 133, 468
Program for resolved stellar populations.
7
(No Transcript)
8
Stellar population synthesis programSYNTHETIC
MAN
?
User input
Output

• Isochrone set
• SFH
• Mass range
• Binary fraction minimum mass ratio
• IMF
• Spatial depth
• E(B-V)
• Photometric error

• CMD file includes mags/colours for all stars in
  simulation
• Integrated properties
• Input parameters

9
Colour-colour plots using SPS output

Fe/H -1.79 -1.27 -0.66
0.06 0.4
14Gyr 10 6 3 1 0.6
Virgo ellipticals Field sample
Data from Michard (2005)
10
Creating integrated spectra with BaSTI
ESSENTIALS

• Working knowledge of stellar evolution
• Understanding of underlying stellar models
• Unwillingness to create a black box
• Healthy scepticism
• A thick skin

11
Note on use of the word models
I only use the term models to refer to
the stellar models (tracks or isochrones),
as produced by the BaSTI group (similarly e.g.
Padova or Geneva). I dont use the term to
describe the process of creating a synthetic
population whether CMDs, integrated
mags/colours, or spectra.
12
Creating integrated spectra with BaSTI
INGREDIENTS

• SPS output from BaSTI
• Fe/H, a-enhancement, mass, Teff, logg
  
• Spectra
• Theoretical, empirical, mixnmatch

13
Choice of spectra - considerations

• Coverage of chemical composition abundance
  ratios, Teff, logg (implications for late
  evolutionary stages)
• Wavelength range
• Resolution

14
Kurucz theoretical spectra Teff/logg coverage
-2.5 scaled solar a-enhanced
Low High Res (20Å 1Å/pix)
15
MILES empirical spectral library Teff/logg
coverage
3525-7500Å _at_ 2.3 Å res
Cenarro et al., 2007
16
Current choices low resolution

• Castelli/Kurucz for Teff 3500K (theoretical)
• Basel 3.1 for cooler RGB, and AGB 3200K
  (semi-empirical)
• Lançon/Mouhcine AGB for C-stars (empirical)
• Magnitudes/colours in any filters (broadband
  colours agree with SYNTHETIC MAN output)
• K-corrections
• Quantifying relative contribution of late
  evolutionary stages

17
(No Transcript)
18
(No Transcript)
19
Current choice high resolution

• Munari et al. 2005 (based on Kurucz)
• Wavelength coverage, 2500-10500 Å
• Uniform dispersion of 1Å/pixel
• Solar scaled and a-enhanced
• Teff 3500K only
• Line indices measured directly on integrated
  spectra (i.e. not using fitting functions or
  conversions to Lick system)

20
(No Transcript)
21
(No Transcript)
22
Playing with line indices
M67 47 Tuc indices measured on spectra from
Schiavon (2005, 2007)
23
What does it all mean?
24
Work in progress

• Effects of mixing scaled-solar/a-enhanced
  isochrones/spectra
• HB morphology blue/red or extended
• Effects of statistical fluctuations
• Relative contribution to fluxes/line strengths of
  various evolutionary stages
• What do observers need?

25
______________
SUE MAURIZIO