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How Evolutionary Synthesis models Works?

For simplicity we will focus in a integrated luminosity. So, for a given age, t the mean luminosity in a given band (L) results from the weigthed sum of the number of stars with initial mass mi, wi, given by the IMF, and the individual luminosities li(mi,t), given by the isochrone.
If the sum of the wi values is normalized to 1 Mo transformed into stars (as usual), the resulting luminosity will be also normalized. In the following we will use (L) = Lssp for refer to normalized quantities.

So, when the result is compared with a real cluster it is needed to know the initial mass transformed into stars .

Lclus = Lssp x .

It is not the case of ratios of luminosities like colors, or equivalent widths, where the dependence with cancels out. However, there will be an statistical dispersion around the mean values that depends on as we will see bellow.



Important Note

It is quite important to keep in mind that does not correspond to the total mass in the sistem, but only the initialmass into stars.

It is also important to know the mass limits used in the IMF when are infered from synthesis models. The following table shows some conversion factors for different mass ranges and for a Salpeter IMF:

  IMF mass range
  [0.1-120] [1-120] [2-120] [8-120] [25-120] [40-120]
Mass into stars 1 0.3962 0.2912 0.1442 0.0668 0.0428
Number of stars 2.8290 0.1262 0.0494 0.0074 0.0014 0.0007



Some synthesis codes


Here there is some links to others WWW address with synthesis models, However, let me suggest you to visit the following server developed by Joachim Koppen:
http://astro.u-strasbg.fr/~koppen/apindex.html

It is a quite interesting place with Java applest for Teaching (and learn) Physics and Astrophysics. It is really great!

And bellow some links realted with evolutive synthesis models. Mainly they use simillar input and the results are more or less consistent each other. The list is not complete, I have only put here the codes whose results are public in a WWW server and that they are making updates of their results.
  1. GALEV: by Uta Fritze - v. Alvensleben and co.
  2. PEGASE.2 (Projet d'Etude des GAlaxies par Synthese Evolutive) by Fioc & Rocca-Volmerange (with a link to the AAS CDROM paper by Leitherer et al. 1996, PASP 108, 996 with a database of synthesis models).
  3. STARBURST99: synthesis code devleoped at Space Telescope Science Institute by Claus Leitherer and co-workers.
  4. SED@: synthesis code devleoped by Daniel Kunth, Philipe Arnault, J.Miguel Mas-Hesse and Miguel Cerviño


    Old stellar populations
  5. Alberto Buzzoni synthesis models.
  6. Guy Worthey synthesis models
  7. Padova stellar evolutionary tracks, isochrones and Simple Stellar Populations results


And once the complete squeme of how the models works has been reviewed, lets go to a more carefull view of the problems related with the models in general. I want to stress that most of the questions I am going to adress here as been not solved by any group (as far as I know). Let's began from simple stars to the final model result step by step.

 
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