The search for exo-planets is currently one of the most exiting and active topics in astronomy. Small and rocky planets are particularly the subject of intense research, since if they are suitably located from their host star, they may be warm and potentially habitable worlds. On the other hand, the discovery of giant planets in
short-period orbits provides important constraints on models that describe planet formation and orbital migration theories. Several
projects are dedicated to discover and characterize planets outside of our solar system. Among them, the Wide-Field Camera Transit Survey
(WTS) is a pioneer program aimed to search for extra-solar planets, that stands out for its particular aims and methodology. The WTS has
been in operation since August 2007 with observations from the United Kingdom Infrared Telescope, and represents the first survey that
searches for transiting planets in the near-infrared wavelengths; hence the WTS is designed to discover planets around M-dwarfs. The
survey was originally assigned about 200 nights, observing four fields that were selected seasonally (RA = 03, 07, 17 and 19h) during a year. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. For the most complete field (19h-1145 epochs) in the
survey, we produce an alternative set of light curves by using the method of difference imaging, which is a photometric technique that has
shown important advantages when used in crowded fields. A quantitative comparison between the photometric precision achieved with both methods is carried out in this work. We remove systematic
effects using the sysrem algorithm, scale the error bars on the light curves, and perform a comparison of the corrected light curves. The results show that the aperture photometry light curves provide slightly better precision for objects with J < 16. However, difference photometry light curves present a significant improvement for fainter stars. In order to detect transits in the WTS light curves, we use a modified version of the box-fitting algorithm. The implementation on the detection algorithm performs a trapezoid-fit to the folded light curve. We show that the new fit is able to produce more accurate results than the box-fit model. We describe a set of selection criteria to search for transit candidates that include a parameter calculated by our detection
algorithm: the V-shape parameter, which has proven to be useful to automatically identify and remove eclipsing binaries from the survey. The criteria are optimized using Monte-Carlo simulations of artificial transit signals that are injected into the real WTS light curves and subsequently analyzed by our detection algorithm. We separately optimize the selection criteria for two different sets of light curves, one for F-G-K stars, and another for M-dwarfs. In order
to search for transiting planet candidates, the optimized selection criteria are applied to the aperture photometry and difference imaging
light curves. In this way, the best 200 transit candidates from a sample of ~ 475 000 sources are automatically selected. A visual
inspection of the folded light curves of these detections is carried out to eliminate clear false-positives or false-detections. Subsequently, several analysis steps are performed
on the 18 best detections, which allow us to classify these objects as transiting planet and eclipsing binary candidates. We report one
planet candidate orbiting a late G-type star, which is proposed for photometric follow-up. The independent analysis on the M-dwarf sample
provides no planet candidates around these stars. Therefore, the null detection hypothesis and upper limits on the occurrence rate of giant
planets around M-dwarfs with J < 17 mag presented in a prior study are confirmed. In this work, we extended the search for transiting planets to stars with J < 18 mag, which enables
us to impose a more strict upper limit of 1.1 % on the occurrence rate of short-period giant planets around M-dwarfs, which is significantly
lower than other limit published so far.
The lack of Hot Jupiters around M-dwarfs play an important role in the existing theories of planet formation and orbital migration of exo-planets around low-mass stars. The dearth of gas-giant planets in short-period orbit detections around M stars indicates that it is not necessary to invoke the disk instability formation mechanism, coupled with an orbital migration process to explain the presence of such planets around low-mass stars. The much reduced efficiency of the
core-accretion model to form Jupiters around cool stars seems to be in agreement with the current null result. However, our upper limit
value, the lowest reported sofar, is still higher than the detection rates of short-period gas-giant planets around hotter stars. Therefore, we cannot yet reach any firm conclusion about Jovian
planet formation models around low-mass and cool main-sequence stars, since there are currently not sufficient observational evidences to support the argument that Hot Jupiters are less common around M-dwarfs than around Sun-like stars. The way to improve this situation is to monitor larger samples of M-stars. For example, an extended analysis of the remaining three WTS fields and currently running M-dwarf
transit surveys (like Pan-Planets and PTF/M-dwarfs projects, which are monitoring up to 100 000 objects) may reduce this upper limit. Current and future space missions like Kepler and GAIA could also help to either set stricter upper limits or finally detect Hot Jupiters around low-mass stars. In the last part of this thesis, we present other applications of the difference imaging light curves. We report the detection of five faint extremely-short-period eclipsing binary systems with periods shorter than 0.23 d, as well as two candidates and one confirmed
M-dwarf/M-dwarf eclipsing binaries. The etections and results presented in this work demonstrate the benefits of using the difference imaging light curves, especially when going to fainter magnitudes.