Documentation
FISA v0.92 Documentation
By Alejandro Benítez-Llambay
1. What is FISA?
FISA is a code developed in the Observatorio Astronómico de Córdoba (OAC) by Alejandro Benítez-Llambay. It is written in Fortran and uses DISLIN (http://www.mps.mpg.de/dislin/) for the GUI. The code allows to estimate the age and reddening of open clusters.
The algorithm implemented by FISA can be found in Benítez-Llambay et al. (2012).
FISA is a FREE SOFTWARE and comes with no warranty.
2. Understanding FISA
FISA enables to determine the age and reddening of a small angular diameter OC by comparing its integrated spectrum to a set of template integrated spectra. The observed flux of an astronomical object is related to its intrinsic flux through:
,
This shows that to determine the reddening it is necessary to estimate the values of the interstellar extinction curve in the observed wavelengths.
2. Computing the extinction curve
As showin in Benítez-Llambay et al. (2011), it is necessary to compute the interstellar extinction curve as a function of the wavelength in order to obtain the reddening value of an OC.
Many measurements of the extinction curve are available in the literature. However, we decided to use Seaton's (1978) extinction law because it was used to construct the template spectrum library used by FISA. Because Seaton's extinction curve is analytically given only in the UV range, we carried out an interpolate for the visible range by using a few measured points. This was was performed with SPLINT and SPLINE cubic splines subroutines of Numerical Recipes.
If you take a look inside the /aux directory, you will find the extinctionlaw.ext file wich, by default, is written in two columns. The first one is 1/lambda, with lambda in micrometers, while the second one is the extinction value. We are giving only 91 values although it is possible add or remove some values as needed.
IMPORTANT: If you want to change the internal extinction curve used by FISA, you have to replace the aux/extinctionlaw.ext file. The size of the file is not important but its name and the format must be the same.
Once FISA loads the extintionlaw.ext file, it is possible to plot it by just clicking on the "Plot Extinction cuve" button.
3. The template spectra library
By default, FISA includes only the template spectrum libraries of Santos et al. 1995, Piatti et al. 2002 and Ahumada et al. 2007. Currently, there are only 27 available template spectra loaded in FISA. It is possible to select any of these template spectra from the list of FISA's main window:
If you want to use another one, you can choice two different ways to do it:
1) The easy way: You have to load another template spectra just by clicking on File menu --> Open another template.
2) The less easy way: You have to modify the template spectrum list file aux/template.lis. If you take a look inside this file, you will understand its structure. The file has only one column with the name of the template spectrum. The template spectra are stored on the templates directory. If you change any entry of this file, please make sure that the corresponding file is on the templates directory. The format of the template spectra consists in two different columns. The first one is the wavelength value while the second one is the flux value.
You can plot the selected template spectra by just clicking on the "Template Plot" button.
NOTE: I recommend the "less easy way" when you want to use the automate mode of FISA and when you need FISA takes into account your template spectra.
4. Observed spectrum
An observed spectrum can be loaded by clicking on File menu --> Open Spectrum. The default directory to begin the spectrum search will be your current directory. Once you load a spectrum, you can plot it by just clicking on "Spectrum Plot''. By default, all spectra are normalized at 5870 A. However, it is possible to change this value by clicking on "Change normalization point''.
When you do that, you have to enter the new normalization wavelength in the console. This will be the new default normalization point. If you change such point, FISA will tell you:
Normalization point changed
New normalization point : (e.g. 5000 A).
IMPORTANT: The normalization point is used only when you apply the E(B-V) correction manually.
5. Estimating the reddening
Given a template spectrum, you can estimate the reddening of an observed spectrum by clicking on the "Det E(B-V)" button.
This button will perform the reddening determination by using the average and chi^2 method described in Benítez-Llambay et al. 2011.
When you click on the " Det E(B-V)'', the output appears on the console by default as follows:
CHI SQUARE VALUE = 8.9786167
E(B-V)= 4.00016122E-02
in which "CHI SQUARE VALUE" is the miminum value reached by the chi^2 function for the chosen template spectrum and ''E(B-V)" is the reddening that produced it. Also, there is an output file named "average" that contains the E(B-V) measured distribution used to compute the initial E(B-V) in order carry out the minimum search. Would be a good idea to look this distribution.
Let me say that you can try to characterize each template spectrum of the library in order to find the global minimum of the chi^2 function. Then, the most probable combination of age and reddening for your observed spectrum will be the age of the template spectrum with the reddening that minimizes the chi^2 function globally. Although it is not hard to follow this procedure, it will take long. If you want to make the most of your time, FISA can work effectively for you. If you want to characterize each template spectrum with a chi^2 and E(B-V) values automatically, you should click on " Det E(B-V) Auto'' button.
The "Det E(B-V) Auto'' button do the same that "Det E(B-V)'' button but for all template spectra, characterizing each one with a chi^2 and redding value. The output appears on the console showing the 10 most probable template spectra that fit with the source spectrum.
Finally, if you want to do the things manually, FISA has the "E(B-V) Correction" button which allows to enter manually an E(B-V) correction. This is the only button for which the "user" normalization point applies.
With this button you are free to correct by reddening your spectrum as you need.
Since it is very useful to have the results in ascii format to make the plots, I decided to add a "Save" button and a "Output file" text box. In the text box you have to write the name of the output file. This name will be completed at the end with .fisa extension. The resulting ascii file will be written in four blocks, each one separated with two white lines. The header of the file will tell you what each block is:
#----------------------HEADER--------------------
# Spectrum analized with FISA v. 0.92
# Date 22/09/2011; time 12:10:43
# Reddening:
# Adopted Templated:
# Normalization Point:
# Format: Index 0 = Unreddened spectrum
# Index 1 = Template spectrum
# Index 2 = Observed spectrum
# Index 3 = Residual flux
#-------------------------------------------------
I decided to use this format to make easy plots with gnuplot by using the index command.
I think it is all you need to know to use FISA. If you have any question or comment, please contact me at alejandrobll@oac.uncor.edu.