**Graduiertenkolleg 1351**

D. Mislis & R.Heller - Observatory
of Hamburg

J. Fernandez & U. Seemann - University of Göttingen

The Photometric Software for Transits (PhoS-T)^{1}
is a software for
data
reduction and analysis of transiting exoplanets. PhoS-T uses a
graphical
enviroment and is able to handle fits data for data reduction,
photometry and transit light curves correction, including all routines
for data reduction, data alignment, differential photometry and raw
light curves correction. PhoS-T also includes a Monte
Carlo routine that
can be applied to fit the light curve of transit candidates. The
software comes with functions for data reduction, transit search, and
model fitting of CoRoT data. PhoS-T is an open-source tool with a
focus
on follow-up photometric observations, light curve analysis and CoRoT
studies.

More that 10 years passed after the detection of the first transiting
exoplanet and many teams these days, restudy known exoplantes for
transit timing variation (TTV) ^{2} and
characteristic changes in these
systems. Also space missions like CoRoT and Kepler will provide
us with
thousands of objects for analysis. Transits offer
powerful
techniques for a complete study of exoplanets. Very few
teams are
searching for
transiting exoplanets but more and more are making follow up
observations in known systems. Although there are many tools for
data reduction and analysis (e.g. IRAF, DaoPhot,
Starlink,
Midas etc.), these codes and
sub-routines need
to be combined very often to yield a full analysis, starting with data
reduction and resulting in light curve modeling. The problem is
that some times we need
to combine
softwares, codes and sub-routines to complete a full analysis from data
reduction to light curve modeling. *PhoS-T
combines all techniques necessary for photometric follow-up
observations of transiting exoplanets*. PhOS is
an abbreviation for **Pho**tometric **S**oftware
for **T**ransits,
where 'phos' stems from the Greek word for 'light': ΦΩΣ.

Since December 2007, CoRoT data are public.
However, these data had some problems. PhoS-T includes sub-routines
for CoRoT light curve
reduction, detrending and analysis using CoRoT Detrend Algorithm (CDA)^{3}.
In principle we could say that PhoS-T has three kind of modes. The
first
is data reduction and photometry. The software can handle fits input
data in order to do the photometry and to extract the transit light
curve. The second mode is the analysis in transiting light curves
(model fitting, Monte Carlo simulations). The third mode is linked with
CoRoT data. PhoS-T reduces CoRoT data, and also applies standard
functions for transit detection and modeling. One of the advantages of
the software is the graphical environment.

The graphical environment of PhoS-T is set up with the programming languageGTK. For the majority of the sub-routines we have used Python but also AWK, Fortran and Bash-scripting in some parts of the code. PhoS-T' main screen is separated in two windows. The first one is the main window in which the user can select the functions and the routines (data reduction, align photometry etc). Moreover, information for data and the total procedure are given. The second window is the display window. The user there can check the output frames after the reduction, and all the output plots from align plot to the final light curve and transit model fit. Between functions, very often, there are dialog windows, which makes the procedure easier. For a package of 600 frames in total (1.2 Gb) - consisting of 30 bias frames, 70 flat frames, and 500 scientific frames - PhoS-T needs about 1 hour for the full procedure on a 4 GHz processor, from master frames creation until error calculation of the transit model.

PhoS-T is running under Linux Operating System and the first version is written for Ubuntu. A MAC version is planned. The software is free for the astronomical community. Here you can find the PhoS-T manual.

PhoS-T
requires GTK- dialog version 0.7.20 or higher, Python laguage version 2.6.2 or higher
(including PyFits sub-routine) and the Intel Fortran Compiler
(ifort). Also it needs AWK version higher than 3.1.6 and Gnuplot
version 4.2. Firefox browser is optional.

- Mislis et al. A&A, 2010 (Photometric Software for Transits)
- Kipping, D., Ribas, I., Font-Ribera, A., IAUS, 253, 490 2009
- Mislis et al. A&A, 2010 (CoRoT Detrend Algorithm)