**3.2 Abundances and Metallicities of young stars via Spectral Synthesis**

This subsection is based on the published work The use of Genetic Algorithms and Spectral Synthesis in the Calculation of Abundances and Metallicities of T Tauri stars (Hetem & Gregorio-Hetem 2009).

In the previous subsection, we presented a method that uses a calculation technique based on GA aiming to optimize the parameters estimation of protoplanetary disks of T Tauri stars. Inspired by the success of that application, which gives accurate and efficient calculations, we decided to develop a similar method to determine atomic stellar abundances.

#### **3.2.1 Artificial spectra as a measurement tool**

In astrophysics, the absorption spectra are obtained and employed as an analytical chemistry tool to determine the presence of atoms and ions in stellar atmospheres and, if possible, to quantify the amount of the atoms present. In stellar atmospheres, each element produces a number of spectrum absorption lines, at wavelengths which can be measured with extreme accuracy when compared to spectra emission tables provided by laboratory experiments.

The presence of a given element in the star atmosphere can be verified (and measured) by looking for its absorption lines at the correct wavelength. The hydrogen is present in all stars by its Balmer absorption lines, and is often used to calibrate the measurements. An example of a high-resolution spectrum is presented in figure 5.

The way astrophysics use to calculate the abundances of atoms in stars follows the steps:


The Search for Parameters and Solutions:

software ATLAS9 from Kurucz (1993).

spectral tool.

**3.2.3 Results** 

program (Kurucz 1993).

in a larger sample of T Tauri stars.

**4. Applications on Rocket Engine engineering** 

1 http://physics.nist.gov/PhysRefData/ASD/index.html

Applying Genetic Algorithms on Astronomy and Engineering 169

Establishing the abundances of each element as the parameters to be found, one individual in the GA terminology is the set of all elemental abundances added to some atmospheric parameters. The initial parameter set is used to build the first generation with 100 individuals. The evaluator routine creates a synthetic spectrum whose entries are the genetic data in each chromosome. This task is performed by calling the elected

There are a number of very efficient software tools that can be chosen. In our application, the abundances of chemical species are determined by using the spectral synthesis software SPECTRUM provided by Corbally (Gray & Corbally 1994) and the atmosphere model

In this section we present the results of the GA method for three stars, whose highresolution spectra were obtained at *European Southern Observatory* (ESO) in La Silla, Chile, with the *Fibber Extended Range Optical Spectrograph* (FEROS) at the 1.52m telescope. The stellar parameters (effective temperature and gravity) were calculated by excitation and ionization equilibrium of iron absorption lines (Rojas et al. 2008). The atomic and molecular line data were mainly from the National Institute of Standards and Technology1 and the Kurucz site2. The solar atomic abundances are from Grevesse & Sauval (1998), and the hyperfine structure constants were taken from Dembczyński et al. (1979) and Luc & Gerstenkorn (1972). The atmosphere models where obtained from the Kurucz library. Specific atmosphere models were calculated through a GNU-Linux porting of the ATLAS9

The method performs a multi-range fitting of specific regions of the observed spectrum, looking for best fit. The demands and commands to SPECTRUM are only those for generating the specific regions of interest, but the χ2 comparing index is evaluated over all wavelength ranges. Figures 7 and 8 present the results for some stars on chosen lines.

The metallicities and abundances found for the stars are compatible with those previously obtained for this particular sample. These preliminary results, achieved by using the GA technique, indicate the efficiency of the method. In the future, we intend to use the method

This section presents two solutions in applying GAs in the aerospace area, both concerning the fuel pumping in liquid propellant rocket engines. There are many choices to be done in

Two different types of pumps were modelled: the Harrington pumps and the turbo pumps. Both present a complex design methodology, which includes: tabled functions

the design of a high performance fuel pump, being one of them the type of pump.

interpolations, numerical integrals and constructive material choices.

2 http://kurucz.harvard.edu 4 and http://wwwuser.oat.ts.astro.it/castelli/
