Fit acoustic glitches in the second differences of low-degree p-mode frequencies using the PIKAIA genetic algorithm.
This code was developed alongside sigs_freq, which fits acoustic glitches using the stellar oscillation frequencies directly.

A full description of the methods used and the development of the code can be found in Pereira, F. (2016).

Finds the signals corresponding to the acoustic glitches at the base of the convection zone and at the helium second ionization region.
Starts by removing a smooth component from the second differences of the oscillation frequencies and then fits the residuals to a parametric function.

The function adopted to describe the oscillatory signature of the glitches in the second differences follows the following form:

$$ \begin{align*} \delta \Delta_2 \nu \simeq & \ A_{bcz} \left( \frac{\nu_r}{\nu} \right)^2 \sin \left( 4 \pi \tau_{bcz} \nu + 2 \phi_{bcz} \right) \ + \\ + & \ A_{HeII} \left( \frac{\nu_r}{\nu} \right) \exp \left[ -\beta_{HeII} \frac{\nu_r}{\nu} \right]^2 \sin \left( 4 \pi \tau_{HeII} \nu + 2 \phi_{HeII} \right) \end{align*} $$

where $\tau_{bcz}$ and $\tau_{HeII}$ represent the acoustic depth of the base of the convective zone and of the helium second ionization zone, respectively.

More details regarding the adopted methods can be found in Sections 3 and 4 of Pereira, F. (2016).

This program requires the LAPACK and BLAS libraries and gfortran for the compilation.
It also needs gnuplot to use option -p that shows plots of the results.

In Linux these can be installed by running the command:

sudo apt-get install liblapack-dev
sudo apt-get install gfortran
sudo apt-get install gnuplot
# Install gnuplot-x11 if you are using an x11 server to show the plot windows

# Clone the repo
git clone https://github.com/Fill4/sigs_diff.git
# Move to repository folder
cd /path/to/repo/folder
# Compile
make

To use the code, a file with the same format as sun.freqs is required, containing stellar oscillation frequencies, with their respective angular degree and mode numbers.
The second differences are calculated from the frequencies.
Then run the command:

./sigs_diff -v -p -a

and when prompted, select the location of the frequencies file and click Enter.

The command -p shows the plots of the final fit and the final parameters will be printed to a file results_diff.
More commands and ways of running the code are available and can be consulted in Appendix A of Pereira, F. (2016).

To test the compilation go to the tests folder and run:

sigs_diff -v -p -a < freqs

The plots should appear at the end of execution and the file results_diff should have been created and contain the final parameters of the fitted function.

Pereira, F. (2016), Development of automatic tools for measuring acoustic glitches in seismic data of solar-type stars, MSc thesis
Faria, J. P. (2013), Asteroseismology of 16 cyg a and b, MSc thesis