and spectral synthesis

Single Stellar Populations (SSP) are at the base of spectral synthesis galaxy models, as well as of studies of stellar clusters.

Our SSP spectral library is available for a wide range of metallicities, ages, and IMF (for more details see Silva et al 1998, ApJ, 509, 103; Bressan et al 1998, A&A, 332, 135; Silva 1999 PhD Thesis; Bressan, Silva, Granato 2002, A&A, 392, 377). If you want to download only this library, go to the  
DOWNLOAD page of GRASIL. There you have to download (or gslib.tar.gz) and/or SSP_radio.gz.


Gslib contains several inputs for GRASIL. Among these you can find the SSP files: Z*.sal, Z*.ken, Z*.msc, Z*.sca where:

        the * stands for the metallicity values (Z=0.0001, 0.0004, 0.004, 0.008, 0.02, 0.05, 0.1)

        sal, ken, msc, sca refer to the IMF, respectively Salpeter, Kennicutt, Miller&Scalo, and Scalo, with mass range 0.15-120 Mo

        each file contains the SEDs for a large range of ages (from ~ 105 yr to ~ 20 Gyr)

        when you use these SSPs with GRASIL, the radio emission is accounted for by GRASIL as described in Silva (1999)


SSP_radio contains SSP files for the Salpeter and Kennicutt IMF, with the SEDs extending to the radio (see Bressan et al 2002):

        gsrdk0bZ*.sal : SSP SEDs for different metallicities (Z) and ages for the Salpeter IMF, (slope=-1.35, mass range=0.15-120 Mo)

        gkn15rdZ*.ken: SSP SEDs for different metallicities (Z) and ages for the Kennicutt IMF, (slope=-0.4, mass range=0.15-1 Mo, slope=-1.5, mass range=1-120 Mo)

        gkn1rdZ*.ken : SSP SEDs for different metallicities (Z) and ages for a Kennicutt-type IMF, (slope=-0.4, mass range=0.15-1 Mo, slope=-1, mass range=1-120 Mo)


All these files are in a non readable ascii format. You can use them in several ways:

1.      You can read and rewrite them with readssp.f90 and sspfile.inp. The readssp.f90 program reads the ssp files you require in sspfile.inp, and rewrite each of them with the name Z*.*.col, writing wavelengths (in Ang) and luminosities (in 10^30 erg/s/A/M) in columns.

2.    You may need to have a SSP SED at a given age and metallicity: with per_SSP.f90 and per_SSP.dat you give in input the required age (in Gyr) and metallicity and have in output (written in file SED_SSP.out) the corresponding SED (wavelength in Ang, SED in 10^30 erg/s/A/Mo) interpolated among the SSPs read in per_SSP.dat.

3.    “STANDARD” SPECTRAL SYNTHESIS: Note that you can run GRASIL also if you are interested in performing simple stellar spectral synthesis, i.e. if you want to have the SED resulting from a given star formation law by considering only the integrated contribution by all stellar populations ever born without the interaction of stellar radiation with the ISM. In brief, it consists in solving the following integral for the spectral luminosity of a galaxy at age T:


where is the spectral luminosity of a SSP born at time t, i.e. of age T-t, with metallicity Z(t). The weight of each stellar generation depends then on the SFR at its birth. As you can see, the inputs needed to solve this integral are: the SEDs of SSP of different age and metallicity, the star formation history SFR(t), and the metallicity enrichment history Z(t). The gas and dust of the ISM do not enter here.



This computation is very fast with GRASIL. You have to do the following steps:


        Dowload CHE_EVO , our chemical evolution code that provides the input star formation history SFR(t) (che_evo allows to set either a Schidt type star formation law, i.e. SFR proportional to the mass of gas, or an analytical, exponential or constant, law or a combination of the two). The output of this code is a mod_name.sf file that is then read by GRASIL

        Download GRASIL (gslib, grasil and if you want also the additional SSPs in SSP_radio)

        In the mod_name.par file (i.e. the file where you set the input parameters to run GRASIL) just set mmolfraz = -1 (or any negative value), or, without changing the .par file, you can reset the parameter values directly from the command line: >grasil mod_name mmolfraz=-1.
In this way all the computation involving dust and therefore all the related parameters in the .par file are ignored. You only have to set mmolfraz=-1 and tgal, the age (in Gyr) of the galaxy model at which you want the SED, e.g. >grasil mod_name mmolfraz=-1 tgal=3.

        The galaxy model SED is output in a file mod_name.0 (of course for pure stellar synthesis there is no dependence on the inclination angle, so you need just the 0 degree angle).